PROCESS FOR MAKING STYRENE USING MIRCOHANNEL PROCESS TECHNOLOGY
The disclosed invention relates to a process for converting ethylbenzene to styrene, comprising: flowing a feed composition comprising ethylbenzene in at least one process microchannel in contact with at least one catalyst to dehydrogenate the ethylbenzene and form a product comprising styrene; exchanging heat between the process microchannel and at least one heat exchange channel in thermal contact with the process microchannel; and removing product from the process microchannel. Also disclosed is an apparatus comprising a process microchannel, a heat exchange channel, and a heat transfer wall positioned between the process microchannel and heat exchange channel wherein the heat transfer wall comprises a thermal resistance layer.
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/785,131 filed Mar. 23, 2006. The disclosure in this provisional application is incorporated herein by reference.
TECHNICAL FIELDThis invention relates to a process for making styrene using microchannel process technology.
BACKGROUNDStyrene is typically produced commercially by dehydrogenating ethylbenzene in the presence of an iron-based catalyst. This reaction is endothermic and equilibrium limited. The process is usually operated at temperatures between about 600-850° C. and at atmospheric or sub-atmospheric pressure. Steam is often co-fed to the reactor with the ethylbenzene. A problem with the process is that it consumes a high level of energy. The conversion of ethylbenzene is typically below 65% to maintain selectivity to styrene in excess of 95%. As a result, reactant recycles are often needed. However, the separation of unreacted ethylbenzene from styrene is costly due to the close boiling points of ethylbenzene (136° C.) and styrene (145° C.).
The use of oxidative dehydrogenation of ethylbenzene has been suggested as a substitute for the dehydrogenation of ethylbenzene. Thus far this process has not been commercialized. This reaction is exothermic. Although high styrene selectivities may be achieved, ethylbenzene conversions less than 60% are typically obtained in order to provide for such high selectivities. An increase in the reaction temperature may increase the ethylbenzene conversion, but styrene selectivity tends to decrease significantly due to combustion of styrene and ethylbenzene. The presence of hot spots in the catalyst bed tends to sinter the catalyst resulting in catalyst deactivation.
This invention, in at least one embodiment, provides a solution to these problems.
SUMMARYThis invention relates to a process for converting ethylbenzene to styrene, comprising: flowing a feed composition comprising ethylbenzene in at least one process microchannel in contact with at least one catalyst to dehydrogenate the ethylbenzene and form a product comprising styrene; exchanging heat between the process microchannel and at least one heat exchange channel in thermal contact with the process microchannel; and removing product from the process microchannel.
In one embodiment, the gas hourly space velocity for the flow of the feed composition in the process microchannel may be at least about 1000 normal liters of feed per hour per liter of volume. The conversion of ethylbenzene may be at least about 50% per cycle or per pass through the process microchannel. The selectivity to styrene may be at least about 70%.
In one embodiment, the catalyst may comprise at least one dehydrogenation catalyst.
In one embodiment, the feed composition may be combined with oxygen and the catalyst may comprise at least one oxidative dehydrogenation catalyst.
In one embodiment, a staged addition feed stream comprising the oxygen may flow in a staged addition channel, the staged addition channel being adjacent to the process microchannel, the process microchannel having an entrance for the feed composition, the feed composition entering the process microchannel through the entrance for the feed composition, the staged addition feed stream flowing from the staged addition channel into the process microchannel, the staged addition feed stream entering the process microchannel downstream of the entrance for the feed composition and contacting the feed composition in the process microchannel.
In one embodiment, the process may be conducted in a microchannel reactor comprising a plurality of the process microchannels and a plurality of the heat exchange channels.
In one embodiment, the invention relates to a process for converting ethylbenzene to styrene, comprising: flowing a feed composition comprising ethylbenzene in at least one process microchannel in contact with at least one catalyst to dehydrogenate the ethylbenzene and form a product comprising styrene; exchanging heat between the process microchannel and at least one heat exchange channel in thermal contact with the process microchannel; and removing product from the process microchannel; wherein the catalyst comprises at least one dehydrogenation catalyst; the catalyst being supported on a support, the support comprising a microgrooved support strip with a support strip having a length with a center axis extending along the length, a first surface, a first side edge, a second side edge, a front edge extending from the first side edge to the second side edge, a back edge extending from the first side edge to the second side edge, a plurality of parallel microgrooves in the first surface extending between the first side edge and the second side edge at an angle relative to the center axis sufficient to permit fluid flowing in the microgrooves to flow in a direction from the front edge to the back edge of the microgrooved strip. In one embodiment, the microgrooves project part way through the support strip from the first surface to the second surface. In one embodiment, the microgrooves project all the way through the support strip thereby providing open microgrooves that may be suitable for permitting fluid to flow through the support strip. In one embodiment, process fluids may flow over or by the microgrooves in a flow-by manner. In one embodiment, the microgrooves may extend across the entire width of the process microchannel, and in one embodiment they may extend over only part of the width of the process microchannel.
In one embodiment, the invention relates to a process for converting ethylbenzene to styrene, comprising: flowing a feed composition comprising ethylbenzene in at least one process microchannel in contact with at least one catalyst to dehydrogenate the ethylbenzene and form a product comprising styrene; exchanging heat between the process microchannel and at least one heat exchange channel in thermal contact with the process microchannel; and removing product from the process microchannel; wherein the catalyst comprises at least one dehydrogenation catalyst; the catalyst being supported by a composite support structure, the composite support structure being a flow through structure, the feed composition contacting the catalyst in the composite support structure and reacting to form the product, the composite support structure comprising: at least one first support strip comprising a first surface, a second surface, a length with a center axis extending along the length, a front edge, a back edge, a first side edge, a second side edge, the front edge and the back edge extending from the first side edge and to the second side edge, a plurality of parallel microgrooves in the first surface extending from the front edge to the second side edge, and a plurality of parallel microgrooves in the first surface extending from first side edge to the back edge; at least one second support strip comprising a first surface, a second surface, a length with a center axis extending along the length, a front edge, a back edge, a first side edge, a second side edge, the front edge and the back edge extending from the first side edge to the second side edge, a plurality of parallel microgrooves in the first surface extending from the front edge to the first side edge, and a plurality of parallel microgrooves in the first surface extending from second side edge to the back edge; the first support strip being adjacent to the second support strip with the second surface of the first support strip contacting the first surface of the second support strip; the front and back edges of each of the support strips being open to permit fluid to flow through the front and back edges; the side edges of each of the support strips being closed to prevent fluid from flowing through the side edges; each of the microgrooves penetrating through the support strips sufficiently to permit fluid to flow through the support strips from one support strip to another; the microgrooves in the first surface of the first support strip being oriented toward the front edge and the first side edge of the first support strip and forming an angle with the center axis of more than about 0° and less than 90°; and the microgrooves in the first surface of the second support strip being oriented toward the front edge and the first side edge of the second support strip and forming an angle with the center axis of more than 90° and less than about 180°.
In one embodiment, the invention relates to a process for converting ethylbenzene to styrene, comprising: flowing a feed composition comprising ethylbenzene in at least one process microchannel in contact with at least one catalyst to dehydrogenate the ethylbenzene and form a product comprising styrene; exchanging heat between the process microchannel and at least one heat exchange channel in thermal contact with the process microchannel; and removing product from the process microchannel; wherein the feed composition is combined with oxygen and the catalyst comprises at least one oxidative dehydrogenation catalyst; wherein the catalyst is supported on a support, the support comprising a microgrooved support strip with a support strip having a length with a center axis extending along the length, a first surface, a first side edge, a second side edge, a front edge extending from the first side edge to the second side edge, a back edge extending from the first side edge to the second side edge, a plurality of parallel microgrooves in the first surface extending between the first side edge and the second side edge at an angle relative to the center axis sufficient to permit fluid flowing in the microgrooves to flow in a direction from the front edge to the back edge of the microgrooved support strip.
In one embodiment, the invention relates to a process for converting ethylbenzene to styrene, comprising: flowing a feed composition comprising ethylbenzene in at least one process microchannel in contact with at least one catalyst to dehydrogenate the ethylbenzene and form a product comprising styrene; exchanging heat between the process microchannel and at least one heat exchange channel in thermal contact with the process microchannel; and removing product from the process microchannel; wherein the feed composition is combined with oxygen and the catalyst comprises at least one oxidative dehydrogenation catalyst; and wherein the catalyst is supported by a composite support structure, the composite support structure being a flow through structure, the feed composition and oxygen contacting the catalyst in the composite support structure and reacting to form the product, the composite support structure comprising: at least one first support strip comprising a first surface, a second surface, a length with a center axis extending along the length, a front edge, a back edge, a first side edge, a second side edge, the front edge and the back edge extending from the first side edge and to the second side edge, a plurality of parallel microgrooves in the first surface extending from the front edge to the second side edge, and a plurality of parallel microgrooves in the first surface extending from first side edge to the back edge; at least one second support strip comprising a first surface, a second surface, a length with a center axis extending along the length, a front edge, a back edge, a first side edge, a second side edge, the front edge and the back edge extending from the first side edge to the second side edge, a plurality of parallel microgrooves in the first surface extending from the front edge to the first side edge, and a plurality of parallel microgrooves in the first surface extending from second side edge to the back edge; the first support strip being adjacent to the second support strip with the second surface of the first support strip contacting the first surface of the second support strip; the front and back edges of each of the support strips being open to permit fluid to flow through the front and back edges; the side edges of each of the support strips being closed to prevent fluid from flowing through the side edges; each of the microgrooves penetrating through the support strips sufficiently to permit fluid to flow through the support strips from one support strip to another; the microgrooves in the first surface of the first support strip being oriented toward the front edge and the first side edge of the first support strip and forming an angle with the center axis of more than about 0° and less than 90°; and the microgrooves in the first surface of the second support strip being oriented toward the front edge and the first side edge of the second support strip and forming an angle with the center axis of more than 90° and less than about 180°.
In one embodiment, the invention relates to a process for converting ethylbenzene to styrene, comprising: flowing a feed composition comprising ethylbenzene in at least one process microchannel in contact with at least one catalyst to dehydrogenate the ethylbenzene and form a product comprising styrene; exchanging heat between the process microchannel and at least one heat exchange channel in thermal contact with the process microchannel; and removing product from the process microchannel; wherein the feed composition is combined with oxygen and the catalyst comprises at least one oxidative dehydrogenation catalyst; wherein a staged addition feed stream comprising the oxygen flows in a staged addition channel, the staged addition channel being adjacent to the process microchannel, the process microchannel having an entrance for the feed composition, the feed composition entering the process microchannel through the entrance for the feed composition, the staged addition feed stream flowing from the staged addition channel into the process microchannel, the staged addition feed stream entering the process microchannel downstream of the entrance for the feed composition and contacting the feed composition in the process microchannel.
In one embodiment, the invention relates to an apparatus, comprising: a process microchannel; a heat exchange channel; and a heat transfer wall positioned between the process microchannel and the heat exchange channel, the heat transfer wall comprising at least one thermal resistance layer. This apparatus may be used as a repeating unit in a microchannel reactor.
In one embodiment, the invention relates to a microchannel reactor comprising the foregoing apparatus.
In one embodiment, the invention relates to an apparatus, comprising: a plurality of the foregoing microchannel reactors positioned in a vessel, each microchannel reactor comprises a plurality of process microchannels, a plurality of heat exchange channels, and optionally a plurality of staged addition channels; the vessel being equipped with a manifold for flowing a feed to the process microchannels, a manifold for flowing product from the process microchannels, a manifold for flowing heat exchange fluid to the heat exchange channels, optionally a manifold for flowing oxygen or a source of oxygen to the staged addition channels, and a manifold for flowing heat exchange fluid from the heat exchange channels. In one embodiment, each microchannel reactor may comprise from about 1 to about 50,000 process microchannels, and the vessel may comprise from 1 to about 1000 microchannel reactors.
This invention, in at least one embodiment, provides the advantage of increasing product yield and energy efficiency by improving heat and mass transfer performance. With this invention it is possible to reduce capital costs by reducing the size of processing equipment and the number of downstream separation units. Catalyst productivity may be enhanced by allowing the catalyst to operate in its peak performance window and by avoiding hot spots. With this invention it is possible to provide cost-effective plant expansion by adding incremental capacity with favorable economics.
In the annexed drawings, like parts and features have like designations. A number of the annexed drawings are schematic illustrations which are not necessarily proportioned accurately or drawn to scale.
All ranges and ratio limits disclosed in the specification may be combined. It is to be understood that unless specifically stated otherwise, references to “a,” “an,” and/or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural.
The term “microchannel” may refer to a channel having at least one internal dimension of height or width of up to about 10 millimeters (mm), and in one embodiment up to about 5 mm, and in one embodiment up to about 2 mm, and in one embodiment up to about 1 mm. The microchannel may comprise at least one inlet and at least one outlet wherein the at least one inlet is distinct from the at least one outlet. The microchannel may not be merely an orifice. The microchannel may not be merely a channel through a zeolite or a mesoporous material. An example of a microchannel that may be used with the inventive process as a process microchannel and/or a heat exchange microchannel is illustrated in
The term “process microchannel” may refer to a microchannel wherein a process is conducted. The process may relate to converting ethylbenzene (EB) to styrene. The process microchannel may contain one or more catalysts.
The term “microchannel reactor” may refer to an apparatus comprising at least one process microchannel for conducting a reaction. The reactor may be used for converting ethylbenzene to styrene. The microchannel reactor may comprise a plurality of the process microchannels that may be operated in parallel, a header or manifold assembly for providing for the flow of fluid into the process microchannels, and a footer or manifold assembly providing for the flow of fluid out of the process microchannels. The microchannel reactor may comprise one or more heat exchange channels, for example heat exchange microchannels, adjacent to and/or in thermal contact with the process microchannels for cooling and/or heating the contents of the process microchannels.
The term “structured wall” or “SW” may refer to an interior channel wall, for example, a microchannel wall, with one or more strips or shims positioned or mounted on its surface. The strips or shims may contain one or more void spaces, openings or through holes. Two or more layers of the strips or shims may be stacked one above another or positioned side by side to provide a porous structure positioned or mounted on the channel wall. A catalyst may be supported by the structured wall. An open bulk flow region or gap may be positioned in the process microchannel adjacent the structured wall.
The term “structured wall reactor” may refer to a microchannel reactor comprising at least one process microchannel wherein the process microchannel contains one or more structured walls. A catalyst may be supported by the one or more structured walls. An open bulk flow region or gap may be positioned in the process microchannel adjacent the structured wall.
The term “volume” with respect to volume within a process microchannel may include all volume in the process microchannel a process fluid may flow through or flow by. This volume may include the volume within the void spaces, openings or holes in a structured wall within the process microchannel. This volume may include volume within surface features that may be positioned in the process microchannel and adapted for the flow of fluid in a flow-through manner or in a flow-by manner.
The term “shim” may refer to a planar or substantially planar sheet or plate. The thickness of the shim may be the smallest dimension of the shim and may be up to about 2 mm, and in one embodiment in the range from about 0.05 to about 2 mm, and in one embodiment in the range of about 0.05 to about 1 mm, and in one embodiment in the range from about 0.05 to about 0.5 mm. The shim may have any length and width.
The term “surface feature” may refer to a depression in a microchannel wall and/or a projection from a microchannel wall that modifies flow and/or mixing within the microchannel. The surface features may be in the form of circles, spheres, frustrums, oblongs, squares, rectangles, angled rectangles, checks, chevrons, vanes, air foils, wavy shapes, and the like. The surface features may contain subfeatures where the major walls of the surface features further contain smaller surface features that may take the form of notches, waves, indents, holes, burrs, checks, scallops, and the like. The surface features may have a depth, a width, and for non-circular surface features a length. Examples are illustrated in
The term “microgroove” may refer to a groove in a substrate having a depth of up to about 1000 microns, and in one embodiment in the range from about 1 to about 1000 microns, and in one embodiment in the range from about 1 to about 500 microns, and in one embodiment from about 1 to about 100 microns. The substrate may be a strip or shim used as a support structure for a catalyst and/or to form a structured wall. The microgrooves may penetrate all the way through the substrate over part or all of the length of the microgrooves. The microgrooves may penetrate only partially through the substrate. The depth of the microgrooves may be measured at the deepest point of penetration into the substrate. The microgrooves may have a width up to about 1000 microns, and in one embodiment in the range from about 0.1 to about 1000 microns, and in one embodiment in the range from about 1 to about 500 microns. The width may be the width measured at the widest point of the microgroove. The microgroove may have any length, for example, up to about 100 cm, and in one embodiment from about 0.1 to about 100 cm, and in one embodiment from about 0.1 to about 10 cm. The microgroove may have a cross section of any shape. Examples include square, rectangle, vee, semi-circle, dovetail, trapezoid, and the like. The shape and/or size of the cross section of the microgroove may vary over the length of the microgroove.
The term “heat exchange channel” may refer to a channel having a heat exchange fluid in it that may give off heat and/or absorb heat. The heat exchange channel may be a microchannel.
The term “heat transfer wall” may refer to a common wall between a process microchannel and an adjacent heat exchange channel where heat transfers from one channel to the other through the common wall.
The term “thermal resistance layer” may refer to a layer on either or both sides of a heat transfer wall or embedded within a heat transfer wall that reduces the flow of heat through the heat transfer wall. In one embodiment, the thermal resistance layer is embedded within the heat transfer wall and may not directly contact the interior of the process microchannel and/or the interior of the heat exchange channel. The thermal resistance layer may comprise a vacuum, a gaseous material (e.g., air or an inert gas), a liquid material (e.g., a high boiling liquid) and/or a solid material. The solid material may contain void spaces, openings or through holes. The thermal resistance layer may be made of the same or substantially the same material as the heat transfer wall except that it may have a lower density than the heat transfer wall. The thermal resistance layer and/or heat transfer wall may comprise one or more sub-assemblies of a thermal resistant construction. Each sub-assembly may comprise two or more shims stacked one above another with one or more void spaces positioned between the shims. The void spaces may comprise a vacuum or a gas such as air or an inert gas. The thermal resistance layer may comprise any desired number of these sub-assemblies stacked one above another, for example, from 1 to about 100 sub-assemblies. The thermal resistance layer may comprise one or more strips or shims containing void spaces, openings and/or through holes. The strips or shims may contain grooves (e.g., microgrooves) in either or both sides of the strips or shims. The thermal resistance layer may comprise a plurality of strips or shims containing void spaces, openings and/or through holes, the strips or shims being stacked one above another resulting in the formation of a porous structure. The thermal resistance layer may be constructed of any suitable material that provides desired properties of thermal resistance (e.g., metal, metal alloy, ceramics, glass, quartz, silicon, polymer, or combinations of two or more thereof, etc.). The thermal resistance layer may have a void volume in the range from about 1% to about 99%, and in one embodiment from about 10% to about 90%. Alternatively, the thermal resistance layer may have a non-solid volume in the range from about 1% to about 99%, and in one embodiment from about 10% to about 90%. The thermal resistance layer may have a varying solid to void ratio or solid to non-solid ratio over the length and/or width of the heat transfer wall. The thermal resistance layer may have physical properties and/or a form that varies as a function of distance over the length of the heat transfer wall. For example, the thermal resistance layer may exhibit heat transfer characteristics that are relatively low at the entrance to a process microchannel and increase gradually or abruptly to a higher level near the exit of the process microchannel, or vice versa. The thermal resistance layer may change in composition gradually or abruptly as a function of distance from one location to another along the length of the heat transfer wall. The thickness of the thermal resistance layer may comprise from about 1 to about 99% of the thickness of the heat transfer wall, and in one embodiment from about 10 to about 90%.
The term “heat exchange fluid” may refer to a fluid that may give off heat and/or absorb heat.
The term “adjacent” when referring to the position of one channel relative to the position of another channel may mean directly adjacent such that a wall separates the two channels. This wall may vary in thickness. However, “adjacent” channels may not be separated by an intervening channel that would interfere with heat transfer between the channels.
The term “thermal contact” may refer to two bodies, for example channels, that are not necessarily in contact with each other or adjacent to each other but still may exchange heat with each other. Thus, for example, one body in thermal contact with another body may heat or cool the other body.
The term “fluid” may refer to a gas, a liquid, or a gas or a liquid containing dispersed solids, or a mixture thereof. The fluid may be in the form of a gas containing dispersed liquid droplets.
The term “bulk flow region” may refer to open areas within a process microchannel. A contiguous bulk flow region may allow rapid fluid flow through a process microchannel without significant pressure drops. In one embodiment there may be laminar flow in the bulk flow region. A bulk flow region may comprise at least about 5%, and in one embodiment from about 30 to about 80% of the internal volume of a process microchannel or the cross-sectional area of the process microchannel.
The term “residence time,” which may also be referred to as the “average residence time,” may be the internal volume of a channel occupied by a fluid flowing through the channel divided by the average volumetric flowrate for the fluid flowing through the channel at the temperature and pressure being used.
The terms “upstream” and “downstream” may refer to positions within a channel (e.g., a process microchannel) that is relative to the direction of flow of a fluid stream in the channel. For example, a position within the channel not yet reached by a portion of a fluid stream flowing toward that position would be downstream of that portion of the fluid stream. A position within the channel already passed by a portion of a fluid stream flowing away from that position would be upstream of that portion of the fluid stream. The terms “upstream” and “downstream” do not necessarily refer to a vertical position since the channels used herein may be oriented horizontally, vertically or at an inclined angle.
The terms “standard cubic feet” or “standard cubic meters” refer to volumes measured at a temperature of 20° C. and atmospheric pressure.
The term “normal liters” refers to volumes measured at a temperature of 20° C. and atmospheric pressure.
The term “gauge pressure” refers to absolute pressure, less atmospheric pressure. For example, a gauge pressure of zero atmospheres corresponds to atmospheric pressure. However, throughout the text and in the appended claims, unless otherwise indicated, all pressures are absolute pressures.
The term “graded catalyst” may refer to a catalyst with one or more gradients of catalytic activity. The graded catalyst may have a varying concentration or surface area of a catalytically active metal. The graded catalyst may have a varying turnover rate of catalytically active sites. The graded catalyst may have physical properties and/or a form that varies as a function of distance. For example, the graded catalyst may have an active metal concentration that is relatively low at the entrance to a process microchannel and increases to a higher concentration near the exit of the process microchannel, or vice versa; or a lower concentration of catalytically active metal nearer the center (i.e., midpoint) of a process microchannel and a higher concentration nearer a process microchannel wall, or vice versa, etc. The thermal conductivity of a graded catalyst may vary from one location to another within a process microchannel. The surface area of a graded catalyst may be varied by varying size of catalytically active metal sites on a constant surface area support, or by varying the surface area of the support such as by varying support type or particle size. A graded catalyst may have a porous support where the surface area to volume ratio of the support is higher or lower in different parts of the process microchannel followed by the application of the same catalyst coating everywhere. A combination of two or more of the preceding embodiments may be used. The graded catalyst may have a single catalytic component or multiple catalytic components (for example, a bimetallic or trimetallic catalyst). The graded catalyst may change its properties and/or composition gradually as a function of distance from one location to another within a process microchannel. The graded catalyst may comprise rimmed particles that have “eggshell” distributions of catalytically active metal within each particle. The graded catalyst may be graded in the axial direction along the length of a process microchannel or in the lateral direction. The graded catalyst may have different catalyst compositions, different loadings and/or numbers of active catalytic sites that may vary from one position to another position within a process microchannel. The number of catalytically active sites may be changed by altering the porosity of the catalyst structure. This may be accomplished using a washcoating process that deposits varying amounts of catalytic material. An example may be the use of different porous catalyst thicknesses along the process microchannel length, whereby a thicker porous structure may be left where more activity is required. A change in porosity for a fixed or variable porous catalyst thickness may also be used. A first pore size may be used adjacent to an open area or gap for flow and at least one second pore size may be used adjacent to the process microchannel wall.
The term “conversion of oxygen” refers to the oxygen mole change between reactant (including all oxygen added using staged addition) and product divided by the moles of oxygen in the reactant.
The term “conversion of ethylbenzene” refers to the ethylbenzene mole change between reactant and product divided by the moles of ethylbenzene in the reactant.
The term “selectivity to styrene” refers to the moles of styrene produced divided by the moles of styrene produced plus moles of ethylbenzene in the product.
The term “cycle” refers to a single pass of the reactants through the process microchannels.
The term “ml (milliliter) per gram of catalyst per hour” refers to a volume (ml) of product produced per gram of catalyst per hour wherein the gram of catalyst refers to catalytic material in the catalyst but not any support that may be present.
The term “yield” refers to moles of reactant converted to a specific product (for example, styrene) divided by the number of moles of reactant converted. The yield may be calculated by
The term “mm” may refer to millimeter. The term “nm” may refer to nanometer. The term “ms” may refer to millisecond. The term “μm” may refer to micron or micrometer. The terms “micron” and “micrometer” have the same meaning and may be used interchangeably.
The inventive process for converting ethylbenzene (EB) to styrene may be a dehydrogenation (DH) process or an oxidative dehydrogenation (ODH) process. The dehydrogenation reaction is an endothermic reaction, while the oxidative dehydrogenation reaction is an exothermic reaction. Although both processes may be conducted in a microchannel reactor in accordance with the invention, heat management with the oxidative dehydrogenation process may be easier and therefore advantageous. The inventive process for making styrene may be employed in a process where ethylene is formed in a microchannel reactor upstream of the styrene forming microchannel reactor. Also, the ethylbenzene may be formed upstream of the styrene forming microchannel reactor in an alkylation reactor. The alkylation reactor may be a microchannel reactor or a conventional alkylation reactor. When the process is an oxidative dehydrogenation process, oxygen or a source of oxygen may be used. The source of oxygen may be air or oxygen enriched air. The ethylbenzene may be mixed with air and/or steam. Flow sheets illustrating a number of these processes are provided in
Referring to
In the process illustrated in
In the process illustrated in
In the process illustrated in
The following description of the microchannel reactor used to make styrene in accordance with the inventive process is also applicable to the microchannel reactors used upstream for making ethylene and ethylbenzene. In one embodiment, the microchannel reactor may be in the form illustrated in
The microchannel reactor core 110 may be positioned adjacent to or in thermal contact with a preheat section and/or upstream from a cool down section. The preheat section may be positioned adjacent to or in thermal contact with the cool down section. The preheat section and cool down section may each comprise a plurality of process microchannels that are the same as or similar to the process microchannels in the microchannel core 110 except that the process microchannels in the preheat and cool down sections do not contain catalyst. This is illustrated in
The process illustrated in
In one embodiment, the microchannel reactor core 110 may contain layers 200 of process microchannels and layers 250 of heat exchange channels (e.g., microchannels) aligned side by side as illustrated in
The process microchannels 210 in process microchannel layer 200 may be aligned in parallel. Each process microchannel 210 may extend along the length of microchannel layer 200 from end 212 to end 214. The process microchannels 210 may extend along the width of the process microchannel layer 200 from end 216 to end 218. The catalyst may be positioned in the process microchannels 210. The flow of process fluid through the process microchannels 210 may be in the direction indicated by arrows 220 and 222. The staged addition channels, when used, may be configured in the same way as the process microchannels 210 except that the staged addition channels do not contain a catalyst. For each process microchannel 210, one or more adjacent staged addition channels may be used. The process microchannels and staged addition channels may have at least one common wall with an opening to permit flow of fluid from the staged addition channel into the process microchannel at various or numerous points along the length of the process microchannel.
The heat exchange microchannels 260 may be aligned in parallel in heat exchange microchannel layer 250. Each heat exchange microchannel 260 may extend along the width of microchannel layer 250 from end 266 to end 268. The heat exchange microchannels 260 may extend along the length of microchannel layer 250 from end 262 to end 264 of microchannel layer 250. The heat exchange fluid may flow through the heat exchange microchannels 260 in the direction indicated by arrows 270 and 272. The flow of heat exchange fluid in the direction indicated by arrows 270 and 272 may be cross-current to the flow of process fluid flowing through process microchannels 210, as indicated by arrows 220 and 222. Alternatively, the heat exchange microchannels 260 may be oriented to provide for flow of the heat exchange fluid along the length of the microchannel layer 250 from end 262 to end 264 or from end 264 to end 262. This would result in the flow of heat exchange fluid in a direction that would be cocurrent or counter-current to the flow of process fluid through the process microchannels 210.
The number of microchannels 210 and 260 in each of the microchannel layers 200 and 250, as well as the number of channels in the optional staged addition layers, may be any desired number, for example, one, two, three, four, five, six, eight, ten, hundreds, thousands, tens of thousands, hundreds of thousands, millions, etc. The number of repeating units containing process microchannel layers, heat exchange channel layers and optionally staged addition channel layers that may be used in the microchannel reactor core 110 may be any number, for example, one, two, three, four, five, six, eight, ten, hundreds, thousands, etc.
A number of repeating units that may be used in the microchannel reactor core 110 are illustrated in
The repeating unit 202 illustrated in
Repeating unit 202A, which may be used in the microchannel reactor core 110, is illustrated in
In an alternate embodiment of the repeating unit 202 illustrated in
The repeating unit 202B illustrated in
The repeating unit 202C illustrated in
The apertures 293 and 293A may be of sufficient size to permit the flow of the staged addition feed stream through the apertured sections 290 and 290A, respectively. The apertures may be referred to as pores. The apertured sections 290 and 290A containing the foregoing apertures may have thicknesses in the range from about 0.01 to about 50 mm, and in one embodiment about 0.05 to about 10 mm, and in one embodiment about 0.1 to about 2 mm. The apertures may have average diameters in the range up to about 250 microns, and in one embodiment up to about 100 microns, and in one embodiment up to about 50 microns, and in one embodiment in the range from about 0.001 to about 50 microns, and in one embodiment from about 0.05 to about 50 microns, and in one embodiment from about 0.1 to about 50 microns. In one embodiment, the apertures may have average diameters in the range from about 0.5 to about 10 nanometers (nm), and in one embodiment about 1 to about 10 nm, and in one embodiment about 5 to about 10 nm. The number of apertures in the apertured sections may be in the range from about 1 to about 5×108 apertures per square centimeter, and in one embodiment about 1 to about 1×106 apertures per square centimeter. The apertures may or may not be isolated from each other. A portion or all of the apertures may be in fluid communication with other apertures within the apertured section. That is, a fluid may flow from one aperture to another aperture. The ratio of the thickness of the apertured sections 290 and 290A to the length of the apertured sections along the flow path of the fluids flowing through the process microchannels 210 may be in the range from about 0.001 to about 1, and in one embodiment about 0.01 to about 1, and in one embodiment about 0.03 to about 1, and in one embodiment about 0.05 to about 1, and in one embodiment about 0.08 to about 1, and in one embodiment about 0.1 to about 1.
In one embodiment, the apertured sections 290 and 290A may comprise an interior portion that forms part of one or more of the interior walls of each process microchannel 210. A surface feature sheet may overlie this interior portion of the apertured section. Surface features may be formed in and/or on the surface feature sheet. The staged addition feed stream may flow through the apertured section and the surface feature sheet into the process microchannel. Part of the staged addition feed stream may be detached from the surface of the surface feature sheet while part may flow within the surface features of the surface feature sheet. The surface feature sheet may contain angled surface features that have relatively small widths or spans relative to the overall flow length. The surface feature sheet may provide mechanical support for the apertured section. The surface features may impart a vortical flow pattern to the staged addition feed stream. The vortical flow pattern may impart shear to the staged addition feed stream flowing through the apertured section and thus reduce the size of the staged addition feed stream bubbles or droplets in the bulk flow path.
The apertured sections 290 and 290A may be constructed of any material that provides sufficient strength and dimensional stability to permit the operation of the inventive process. These materials include: steel (e.g., stainless steel, carbon steel, and the like); monel; inconel; aluminum; titanium; nickel; platinum; rhodium; copper; chromium; brass; alloys of any of the foregoing metals; polymers (e.g., thermoset resins); ceramics; glass; composites comprising one or more polymers (e.g., thermoset resins) and fiberglass; quartz; silicon; microporous carbon, including carbon nanotubes or carbon molecular sieves; zeolites; or a combination of two or more thereof. The apertures may be formed using known techniques such as laser drilling, microelectro machining system (MEMS), lithography electrodeposition and molding (LIGA), electrical sparkling, photochemical machining (PCM), electrochemical machining (ECM), electrochemical etching, and the like. The apertures may be formed using techniques used for making structured plastics, such as extrusion, or membranes, such as aligned carbon nanotube (CNT) membranes. The apertures may be formed using techniques such as sintering or compressing metallic powder or particles to form tortuous interconnected capillary channels and the techniques of membrane fabrication. The apertures may be reduced in size from the size provided by any of these methods by the application of coatings over the apertures internal side walls to partially fill the apertures. The selective coatings may also form a thin layer exterior to the porous body that provides the smallest pore size adjacent to the continuous flow path. The smallest average pore opening may be in the range from about one nanometer to about several hundred microns depending upon the desired droplet size for the emulsion. The apertures may be reduced in size by heat treating as well as by methods that form an oxide scale or coating on the internal side walls of the apertures. These techniques may be used to partially occlude the apertures to reduce the size of the openings for flow.
The apertured sections 290 and 290A may be made from a metallic or nonmetallic porous material having interconnected channels or pores of an average pore size in the range from about 0.01 to about 1000 microns, and in one embodiment in the range from about 0.01 to about 200 microns. These pores may function as the apertures 293 and 293A. The porous material may be made from powder or particulates so that the average inter-pore distance is similar to the average pore size. The porous material may be tailored by oxidization at a high temperature in the range from about 300° C. to about 1000° C. for a duration of about 1 hour to about 20 days, or by coating a thin layer of another material such as alumina by sol coating or nickel using chemical vapor deposition over the surface and the inside of pores to block the smaller pores, decrease pore size of larger pores, and in turn increase the inter-pore distance. An SEM image of a tailored substrate or apertured section is shown in
The making of substrates for use as apertured sections 290 and 290A with sufficiently small micro-scale apertures or pores 293 and 293A to provide a staged addition feed stream having bubble or droplet sizes smaller than about one micron can be problematic. One of the reasons for this lies in the fact that relatively high surface roughness occurs with untreated regular porous materials such as a metallic porous substrates made from powder/particles by compression and/or sintering. These metallic porous substrates typically do not have the required pore size in the surface region when a given nominal pore size is lower than a certain value. While the bulk of the porous material may have the specified nominal pore size, the surface region is often characterized by merged pores and cavities of much larger sizes. This problem can be overcome by tailoring these substrates to provide for the desired pore size and inter-pore distance in the surface region. This may be done by removing a surface layer from the porous substrate and adding a smooth new surface with smaller openings. The droplet size or bubble size of staged addition feed stream that may be formed using these tailored substrates may be reduced without increasing the pressure drop across the substrate. Since direct grinding or machining of the porous surface may cause smearing of the surface structure and blockage of the pores, the porous structure may be filled with a liquid filler, followed by solidification and mechanical grinding/polishing. The filler is then removed to regain the porous structure of the material. The filler may be a metal with a low melting point such as zinc or tin or the precursor of a polymer such as an epoxy. The liquid filling and removing steps may be assisted by the use of a vacuum. Grinding/polishing may be effected using a grinding machine and a grinding powder. Metal filler removal may be effected by melting and vacuum suction, or by acid etching. Epoxies or other polymers may be removed by solvent dissolution or by burn-off in air.
Referring to
In the embodiment illustrated in
In the embodiment illustrated in
In one embodiment, the apertured sections 290 and 290A may be formed from an asymmetric porous material, for example, a porous material having multiple layers of sintered particles. The number of layers may be two, three, or more. An advantage of these multilayered substrates is that they provide enhanced durability and adhesion. Examples include sintered ceramics that have relatively large pores on one side and relatively small pores on the other side. The relatively small pores may have diameters in the range of about 2 to about 10 nm. The relatively small pores may be positioned in a relatively thin layer of the multilayered substrate. The relatively thin layer may have a thickness in the range of about 1 to about 10 microns. The side with the relatively small pores may be placed facing the interior of the process microchannel 210 to take advantage of relatively high shear forces to remove the relatively small droplets of reactant and/or liquid catalyst as they are formed.
During the inventive process the staged addition feed stream may flow through the apertured sections 290 and 290A into the process microchannel 210. In one embodiment, the apertured section may extend along at least about 5% of the axial length of the process microchannel, and in one embodiment at least about 20% of the axial length of the process microchannel, and in one embodiment at least about 35% of the axial length of the process microchannel, and in one embodiment at least about 50% of the axial length of the process microchannel, and in one embodiment at least about 65% of the axial length of the process microchannel, and in one embodiment at least about 80% of the axial length of the process microchannel, and in one embodiment at least about 95% of the axial length of the process microchannel, and in one embodiment from about 5% to about 100% of the axial length of the process microchannel, and in one embodiment from about 10% to about 95% of the axial length of the process microchannel, and in one embodiment from about 25% to about 75% of the axial length of the process microchannel, and in one embodiment from about 40% to about 60% of the axial length of the process microchannel.
The dehydrogenation catalyst may comprise at least one oxide of iron, chromium or a combination thereof. In one embodiment, the catalyst may comprise iron oxide and one or more of potassium oxide, molybdenum oxide, cerium oxide, and calcium carbonate. In one embodiment, the catalyst may comprise one or more Group VII nobel metals (e.g., platinum, iridium, rhodium, palladium). The catalytic metals may be combined with a carrier such as a refractory inorganic oxide. Alumina may be used as the carrier.
The oxidative dehydrogenation catalyst may comprise any vanadium-containing, molybdenum-containing or tungsten-containing oxidative dehydrogenation catalyst. Catalysts containing combinations of two or more of V, Mo and W may be used. The catalyst may comprise one or more of V2O5, MoO3 or WO3 catalysts. The catalyst may be supported. The support may comprise Al2O3, MgO, MgAl2O4, CaO, TiO2, ZrO2, SiO2, Ga2O3, rare earth oxide, active carbon, carbon fibers, molecular sieves, or a combination of two or more thereof. The catalyst may comprise any vanadate, molybdate, tungstate, or a combination of two or more thereof. Examples may include FeVO4, CrVO4, NaVO3, BiVO4, AlVO4, CeVO4, VOPO4, LaVO4, SmVO4, NiMoO4, MgMoO4, CaMoO4, FeMoO4, Fe2(MoO4)3, MgWO4, CaWO4, NiWO4, FeWO4, or a combination of two or more thereof. The catalyst may be promoted by alkali, alkaline earth, rare earth, transition metal oxides, Group VB elements (P, As, Sb and Bi), or a combination of two or more thereof. The catalyst may be prepared by impregnation, sol-gel, co-precipitation, ion-exchange, solution evaporation or deposition-precipitation. The catalyst may be coated on a substrate. The substrate may have a flat surface or a structured surface. Examples of the substrates may include flat coupons, shims, honeycombs, gauze, foams, fins, felts, and/or surface-featured coupons. The materials of the substrates may be made of a material comprising metal, alloys, super alloys, ceramics, or a combination of two or more thereof. The metallic substrates may be heat treated prior to catalyst coating. The catalyst coating may be performed by slurry-coating, sol-coating or solution-coating.
The catalyst may have any size and geometric configuration that fits within the process microchannels. The catalyst may be in the form of particulate solids (e.g., pellets, powder, fibers, and the like) having a median particle diameter of about 1 to about 1000 microns, and in one embodiment about 10 to about 500 microns, and in one embodiment about 25 to about 250 microns.
The catalyst may comprise a graded catalyst.
The catalyst may be in the form of a mesoporous material wherein the average pore size may be at or above about 1 nanometer (nm), for example, in the range from about 1 to about 100 nm, and in one embodiment from about 1 to about 20 nm. In one embodiment, mesoporous catalysts may be surprisingly active and selective for forming styrene.
The catalyst may be in the form of a fixed bed of particulate solids such as illustrated in
The catalyst may be supported on a porous support structure such as a foam, felt, wad or a combination thereof. The term “foam” is used herein to refer to a structure with continuous walls defining pores throughout the structure. The term “felt” is used herein to refer to a structure of fibers with interstitial spaces therebetween. The term “wad” is used herein to refer to a support having a structure of tangled strands, like steel wool. The catalyst may be supported on a support having a honeycomb structure or a serpentine configuration.
The catalyst may be supported on a flow-by support structure such as a felt with an adjacent gap, a foam with an adjacent gap, a fin structure with gaps, a washcoat on any inserted substrate, or a gauze that is parallel to the flow direction with a corresponding gap for flow. An example of a flow-by structure is illustrated in
The catalyst may be supported on a flow-through support structure such as a foam, wad, pellet, powder, or gauze. An example of a flow-through structure is illustrated in
The support may be formed from a material comprising silica gel, foamed copper, sintered stainless steel fiber, steel wool, alumina, poly(methyl methacrylate), polysulfonate, poly(tetrafluoroethylene), iron, nickel sponge, nylon, polyvinylidene difluoride, polypropylene, polyethylene, polyethylene ethylketone, polyvinyl alcohol, polyvinyl acetate, polyacrylate, polymethylmethacrylate, polystyrene, polyphenylene sulfide, polysulfone, polybutylene, or a combination of two or more thereof. In one embodiment, the support structure may be made of a heat conducting material, such as a metal, to enhance the transfer of heat away from the catalyst.
The catalyst may be directly washcoated on the interior walls of the process microchannels, grown on the walls from solution, or coated in situ on a fin structure. The catalyst may be in the form of a single piece of porous contiguous material, or many pieces in physical contact. In one embodiment, the catalyst may comprise a contiguous material and have a contiguous porosity such that molecules can diffuse through the catalyst. In this embodiment, the fluids may flow through the catalyst rather than around it. In one embodiment, the cross-sectional area of the catalyst may occupy from about 1 to about 99%, and in one embodiment from about 10 to about 95% of the cross-sectional area of the process microchannels. The catalyst may have a surface area, as measured by BET, of greater than about 0.5 m2/g, and in one embodiment greater than about 2 m2/g, and in one embodiment greater than about 5 m2/g, and in one embodiment greater than about 10 m2/g, and in one embodiment greater than about 25 m2/g, and in one embodiment greater than about 50 m2/g.
The catalyst may comprise a porous support, an interfacial layer overlying the porous support, and a catalyst material dispersed or deposited on the interfacial layer. The interfacial layer may be solution deposited on the support or it may be deposited by chemical vapor deposition or physical vapor deposition. In one embodiment the catalyst comprises a porous support, optionally a buffer layer overlying the support, an interfacial layer overlying the support or the optional buffer layer, and a catalyst material dispersed or deposited on the interfacial layer. Any of the foregoing layers may be continuous or discontinuous as in the form of spots or dots, or in the form of a layer with gaps or holes.
The porous support may have a porosity of at least about 5% as measured by mercury porosimetry and an average pore size (sum of pore diameters divided by number of pores) of about 1 to about 1000 microns. The porous support may be made of any of the above indicated materials identified as being useful in making a support structure. The porous support may comprise a porous ceramic support or a metal foam. Other porous supports that may be used include carbides, nitrides, and composite materials. The porous support may have a porosity of about 30% to about 99%, and in one embodiment about 60% to about 98%. The porous support may be in the form of a foam, felt, wad, or a combination thereof. The open cells of the metal foam may range from about 20 pores per inch (ppi) to about 3000 ppi, and in one embodiment about 20 to about 1000 ppi, and in one embodiment about 40 to about 120 ppi. The term “ppi” refers to the largest number of pores per inch (in isotropic materials the direction of the measurement is irrelevant; however, in anisotropic materials, the measurement is done in the direction that maximizes pore number).
The buffer layer, when present, may have a different composition and/or density than both the porous support and the interfacial layers, and in one embodiment has a coefficient of thermal expansion that is intermediate the thermal expansion coefficients of the porous support and the interfacial layer. The buffer layer may be a metal oxide or metal carbide. The buffer layer may be comprised of Al2O3, TiO2, SiO2, ZrO2, or combination thereof. The Al2O3 may be α-Al2O3, γ-Al2O3 or a combination thereof. α-Al2O3 provides the advantage of excellent resistance to oxygen diffusion. The buffer layer may be formed of two or more compositionally different sublayers. For example, when the porous support is metal, for example a stainless steel foam, a buffer layer formed of two compositionally different sub-layers may be used. The first sublayer (in contact with the porous support) may be TiO2. The second sublayer may be α-Al2O3 which is placed upon the TiO2. In one embodiment, the α-Al2O3 sublayer is a dense layer that provides protection of the underlying metal surface. A less dense, high surface area interfacial layer such as alumina may then be deposited as support for a catalytically active layer.
The porous support may have a thermal coefficient of expansion different from that of the interfacial layer. In such a case a buffer layer may be needed to transition between the two coefficients of thermal expansion. The thermal expansion coefficient of the buffer layer can be tailored by controlling its composition to obtain an expansion coefficient that is compatible with the expansion coefficients of the porous support and interfacial layers. The buffer layer should be free of openings and pin holes to provide superior protection of the underlying support. The buffer layer may be nonporous. The buffer layer may have a thickness that is less than one half of the average pore size of the porous support. The buffer layer may have a thickness of about 0.05 to about 10 μm, and in one embodiment about 0.05 to about 5 μm.
In one embodiment of the invention, adequate adhesion and chemical stability may be obtained without a buffer layer. In this embodiment the buffer layer may be omitted.
The interfacial layer may comprise nitrides, carbides, sulfides, halides, metal oxides, carbon, or a combination thereof. The interfacial layer provides high surface area and/or provides a desirable catalyst-support interaction for supported catalysts. The interfacial layer may be comprised of any material that is conventionally used as a catalyst support. The interfacial layer may be comprised of a metal oxide. Examples of metal oxides that may be used include γ-Al2O3, SiO2, ZrO2, TiO2, tungsten oxide, magnesium oxide, vanadium oxide, chromium oxide, manganese oxide, iron oxide, nickel oxide, cobalt oxide, copper oxide, zinc oxide, molybdenum oxide, tin oxide, calcium oxide, aluminum oxide, lanthanum series oxide(s), zeolite(s) and combinations thereof. The interfacial layer may serve as a catalytically active layer without any further catalytically active material deposited thereon. Usually, however, the interfacial layer is used in combination with a catalytically active layer. The interfacial layer may also be formed of two or more compositionally different sublayers. The interfacial layer may have a thickness that is less than one half of the average pore size of the porous support. The interfacial layer thickness may range from about 0.5 to about 100 μm, and in one embodiment from about 1 to about 50 μm. The interfacial layer may be either crystalline or amorphous. The interfacial layer may have a BET surface area of at least about 1 m2/g.
The catalyst may be deposited on the interfacial layer. Alternatively, the catalyst material may be simultaneously deposited with the interfacial layer. The catalyst layer may be intimately dispersed on the interfacial layer. That the catalyst layer is“dispersed on” or “deposited on” the interfacial layer includes the conventional understanding that microscopic catalyst particles are dispersed: on the support layer (i.e., interfacial layer) surface, in crevices in the support layer, and in open pores in the support layer.
The catalyst may be supported on an assembly of one or more fins positioned within the process microchannels. Examples are illustrated in
The catalyst may be supported by the microgrooved support strip illustrated in
The microgrooves 430 illustrated in
The support strip 410 may have a thickness (t) in the range from about 0.1 to about 5000 microns, and in one embodiment from about 1 to about 1000 microns. The support strip 410 may have any width (w) and any length (l), the width and length depending upon the dimensions of the microchannel for which the support strip 410 is to be used. The support strip 410 may have a width (w) in the range from about 0.01 to about 100 cm, and in one embodiment from about 0.1 to about 10 cm. The length (l) of the support strip 110 may be in the range of about 0.01 to about 100 cm, and in one embodiment from about 0.1 to about 10 cm. The support strip 410 as illustrated in
The support strip 410 may be made of any material that provides sufficient strength, dimensional stability and heat transfer characteristics to permit the use of the microgrooved support strip 400 in a microchannel for supporting a catalyst. The support strip 410 may be made of metal, silicon carbide, graphite or a combination of two or more thereof. The metal may comprise steel, aluminum, titanium, nickel, platinum, rhodium, copper, chromium, brass, or an alloy of any of the foregoing metals. The support structure 410 may be made of stainless steel or an alloy comprising iron, chromium, aluminum and yttrium.
The microgrooved support strip 400A illustrated in
The microgrooved support strip 400A is also shown in
The microgrooved support strip 400B illustrated in
The microgrooves 430 may be aligned at an angle of about 90° or a right angle with the center axis 424, and in one embodiment extend from the first side edge 416 to the second side edge 418.
The microgrooves 430 may be aligned parallel to the center axis 424, and in one embodiment extend from the front edge 420 to the back edge 422.
The microgrooved support strips 400 and 400B may be used as flow-through and/or flow-by support structures in a microchannel. Microgrooved support strip 400A may be used as a flow by support structure in a microchannel.
In one embodiment, a plurality of the microgrooved support strips may be stacked one above another or positioned side by side to form a composite support structure which may be used to support a catalyst for use in the inventive process. The composite support structure, in one embodiment, is illustrated in
The composite support structure 402 illustrated in
The catalyst may be supported by a composite support structure, comprising: at least one first support strip comprising a first surface, a second surface, a length with a center axis extending along the length, a front edge, a back edge, a first side edge, a second side edge, the front edge and the back edge extending from the first side edge and to the second side edge, a plurality of parallel microgrooves in the first surface aligned at an angle of about 90° with the center axis; and at least one second support strip comprising a first surface, a second surface, a length with a center axis extending along the length, a front edge, a back edge, a first side edge, a second side edge, the front edge and the back edge extending from the first side edge to the second side edge, a plurality of parallel microgrooves in the first surface aligned parallel with the center axis; the first support strip being adjacent to the second support strip with the second surface of the first support strip contacting the first surface of the second support strip; the microgrooves penetrating through the support strips sufficiently to permit fluid to flow through the support strips from one support strip to another support strip.
The catalyst may be supported by a composite support structure, comprising: at least one first support strip comprising a first surface, a second surface, a length with a center axis extending along the length, a front edge, a back edge, a first side edge, a second side edge, the front edge and the back edge extending from the first side edge and to the second side edge, and a plurality of parallel microgrooves in the first surface; at least one second support strip comprising a first surface, a second surface, a length with a center axis extending along the length, a front edge, a back edge, a first side edge, a second side edge, the front edge and the back edge extending from the first side edge to the second side edge, and a plurality of parallel microgrooves in the first surface; the first support strip being adjacent to the second support strip with the second surface of the first support strip contacting the first surface of the second support strip; the microgrooves penetrating through the support strips sufficiently to permit fluid to flow through the support strips from one support strip to another; microgrooves in the first surface of the first support strip intersecting microgrooves in the first surface of the second support strip to provide through holes extending through the first support strip and through the second support strip. In one embodiment, the through holes may be of sufficient dimension to permit reactants and/or product to flow from the first surface of the first support strip to the first surface of the second support strip and/or from the first surface of the second support strip to the first surface of the first support strip. In one embodiment, the first support strip and the second support strip are made of thermally conductive materials and the contacting between the second surface of the first support strip and the first surface of the second support strip is sufficient to permit heat to be conducted between the first support strip and the second support strip.
An advantage of the microgrooved support strips and composite structures relates to the fact that microsized particles of catalyst may be positioned in and anchored to the microgrooves thus reducing the tendency of the particulates being swept away by the flow of process fluids through the microchannels.
The support strips 400, 400A or 400B, or the composite support structure 402 may be positioned or mounted on one or more walls within a microchannel to form one or more structured walls within the microchannel.
The catalyst may be supported by one or more structured walls within the process microchannels wherein the one or more structured walls may be formed from one or more shims. One or more of the shims may contain one or more void spaces, openings or through holes. The shims may contain grooves or microgrooves that are formed in one surface of the shims or in both the front or first surface and the back or second surface of the shims. The grooves or microgrooves from the first surface may intersect the grooves or microgrooves from the second surface to form a plurality of voids, through holes or openings in the shim. Examples are illustrated in
The grooves or microgrooves 530 in the front or first surface 512 intersect the grooves or microgrooves in the back or second surface 514 at right angles in the illustrated embodiment, however, it is to be understood that the angles of intersection may be of any value (e.g., from about 30° to about 120°) and are therefore not limited to being only right angles.
The catalyst may be deposited on the support strips 400, 400A, 400B, 400C or 400D, or shims 510, using conventional techniques. These may include washcoating the catalyst on the support strips or shims, growing the catalyst on the support strips or shims, or depositing the catalyst on the support strips or shims using vapor deposition. The vapor deposition may be chemical vapor deposition or physical vapor deposition. The catalyst may be deposited by slurry-coating, sol-coating or solution-coating. In one embodiment, the catalyst may be in the form of microsized particulates deposited in and adhered to the grooves or microgrooves of the support strips or shims. The catalyst loading may be in the range from about 0.1 to about 100 milligrams (mg) per square centimeter of support strip or shim, and in one embodiment in the range from about 1 to about 10 mg of catalyst per square centimeter of support strip or shim. The microsized particulates may have average particle sizes in the range from about 0.01 to about 100 microns, and in one embodiment in the range from about 0.1 to about 50 microns, and in one embodiment in the range from about 0.1 to about 10 microns, and in one embodiment from about 0.1 to about 7 microns, and in one embodiment from about 0.1 to about 5 microns, and in one embodiment from about 0.1 to about 3 microns, and in one embodiment from about 0.1 to about 2 microns, and in one embodiment from about 0.1 to about 1 micron, and in one embodiment from about 0.1 to about 0.5 micron.
Repeating units for use in microchannel reactor core 110 employing support strip 400A for supporting a catalyst are illustrated in
The repeating unit 201B illustrated in
The repeating unit 201C illustrated in
The repeating unit 201D illustrated in
The repeating unit 201E illustrated in
The repeating unit 201F illustrated in
The interior wall 232 of process microchannel 210 is illustrated in
Surface features 235 of various designs are illustrated in
The repeating unit 201G illustrated in
The microchannel reactor core 110 including the process microchannels, optional staged addition channels, and heat exchange channels, as well as any process headers, process footers, heat exchange headers or heat exchange footers, and structured wall strips or shims, may be made of any material that provides sufficient strength, dimensional stability and heat transfer characteristics to permit operation of the inventive process. These materials include steel; aluminum, titanium; nickel, platinum; rhodium; copper; chromium; brass; alloys of any of the foregoing metals; polymers (e.g., thermoset resins); ceramics; glass; composites comprising one or more polymers (e.g., thermoset resins) and fiberglass; quartz; silicon; or a combination of two or more thereof.
The microchannel reactor core 110 may be fabricated using known techniques including wire electrodischarge machining, conventional machining, laser cutting, photochemical machining, electrochemical machining, molding, water jet, stamping, etching (for example, chemical, photochemical or plasma etching) and combinations thereof.
The microchannel reactor core 110 may be constructed by forming layers or sheets with portions removed that allow flow passage. A stack of sheets may be assembled via diffusion bonding, laser welding, diffusion brazing, and similar methods to form an integrated device. The microchannel reactor core 110 may be assembled using a combination of sheets or laminae and partial sheets or strips. In this method, the channels or void areas may be formed by assembling strips or partial sheets to reduce the amount of material required.
In one embodiment, subsections or modular units of the microchannel reactor core 110 may be fabricated using the following components: a substrate piece with a hermetically sealed perimeter and open top/bottom for process flow; and a heat exchange piece. The substrate piece and heat exchange piece may be joined (welded, glued, soldered, etc.) to form a leak-free operating unit. The heat exchange piece may be extruded. The substrate piece and the heat exchange piece may be made from plastic, metal, or other materials as discussed above.
In one embodiment, the microchannel reactor core 110 may be made by a process that comprises laminating or diffusion bonding shims made of any of the above-indicated materials (e.g., metal, plastic or ceramic) so that each layer has a defined geometry of channels and openings through which to convey fluids. After the individual layers have been created, the microgrooved support strips and/or composite support structures may be inserted and the desired catalyst or sorption medium may be applied to the microgrooved support strips and/or composite support structures. The catalyst or sorption medium may be applied to the microgrooved support strips and/or composite support structures prior to inserting the support strips into the desired process microchannels. The layers may then be stacked in a prescribed order to build up the lamination. The layers may be stacked side-by-side or one above the other. The completed stack may then be diffusion bonded to prevent fluids from leaking into or out of the microchannel reactor or microchannel separator. After bonding, the device may be trimmed to its final size and prepared for attachment of pipes and manifolds.
Feature creation methods include photochemical etching, milling, drilling, electrical discharge machining, laser cutting, and stamping. A useful method for mass manufacturing is stamping. In stamping, care should be taken to minimize distortion of the material and maintain tight tolerances of channel geometries. Preventing distortion, maintaining shim alignment and ensuring that layers are stacked in the proper order are factors that should be controlled during the stacking process.
The stack may be bonded through a diffusion process. In this process, the stack may be subjected to elevated temperatures and pressures for a precise time period to achieve the desired bond quality. Selection of these parameters may require modeling and experimental validation to find bonding conditions that enable sufficient grain growth between metal layers.
The next step, after bonding, may be to machine the device. A number of processes may be used, including conventional milling with high-speed cutters, as well as highly modified electrical discharge machining techniques. A full-sized bonded microchannel reactor or microchannel separator unit or sub-unit that has undergone post-bonding machining operations may comprise, for example, tens, hundreds or thousands of shims.
The microchannel reactor 100 may have appropriate manifolds, valves, conduit lines, etc. to control flow of the process fluid, and the flow of the heat exchange fluid. These are not shown in the drawings, but can be readily provided by those skilled in the art.
The staged addition channels 280 and 280A may be microchannels or they may have larger dimensions. The process microchannels 210 and the staged addition channels 280 and 280A may have cross sections with any shape, for example, a square, rectangle, circle, semi-circle, etc. Each process microchannel 210 and staged addition channel 280 and 280A may have an internal height or gap of up to about 10 mm, and in one embodiment up to about 6 mm, and in one embodiment up to about 4 mm, and in one embodiment up to about 2 mm. In one embodiment, the height or gap may be in the range of about 0.05 to about 10 mm, and in one embodiment about 0.05 to about 6 mm, and in one embodiment about 0.05 to about 4 mm, and in one embodiment about 0.05 to about 2 mm. The width of each process microchannel 210 and staged addition channel 280 and 280A may be of any dimension, for example, up to about 3 meters, and in one embodiment about 0.01 to about 3 meters, and in one embodiment about 0.1 to about 3 meters. The length of each process microchannel 210 and staged addition channel 280 and 280A may be of any dimension, for example, up to about 10 meters, and in one embodiment from about 0.1 to about 10 meters, and in one embodiment from about 0.2 to about 10 meters, and in one embodiment from about 0.2 to about 6 meters, and in one embodiment from 0.2 to about 3 meters.
The heat exchange channels 260, 295 and 296 may be microchannels or they may have larger dimensions. Each of the heat exchange channels 260, 295 and 296 may have a cross section having any shape, for example, a square, rectangle, circle, semi-circle, etc. Each of the heat exchange channels 260, 295 and 296 may have an internal height or gap of up to about 10 mm, and in one embodiment in the range of about 0.05 to about 10 mm, and in one embodiment from about 0.05 to about 5 mm, and in one embodiment from about 0.05 to about 2 mm. The width of each of these channels may be of any dimension, for example, up to about 3 meters, and in one embodiment from about 0.01 to about 3 meters, and in one embodiment about 0.1 to about 3 meters. The length of each of the heat exchange channels 260, 295 and 296 may be of any dimension, for example, up to about 10 meters, and in one embodiment from about 0.1 to about 10 meters, and in one embodiment from about 0.2 to about 6 meters, and in one embodiment from 0.2 to about 3 meters.
In one embodiment, the process microchannels and heat exchange channels used in the microchannel reactor core 110 may have rectangular cross sections and be aligned in side-by-side vertically oriented planes or horizontally oriented stacked planes. These planes may be tilted at an inclined angle from the horizontal. These configurations may be referred to as parallel plate configurations. Various combinations of two or more process microchannels with a single heat exchange channel, or two or more heat exchange channels in combination with a single process microchannel may be employed. An array of these rectangular channels may be arranged in a modularized compact unit for scale-up.
The cross-sectioned shape and size of the process microchannels may vary along their axial length to accommodate changing hydrodynamics of the reaction. For example, if the reaction is an oxidative dehydrogenation reaction and one of the reactants is in excess, the fluidic properties of the reaction mixture may change over the course of the reaction. Surface features may be used to provide a different geometry, pattern, angle, depth, or ratio of size relative to the cross-section of the microchannel along its axial length to accommodate these hydrodynamic changes.
The separation between each process microchannel or staged addition channel and the next adjacent heat exchange channel may be in the range from about 0.05 mm to about 50 mm, and in one embodiment about 0.1 to about 10 mm, and in one embodiment about 0.2 mm to about 2 mm.
The invention may relate to an apparatus, comprising: a process microchannel; a heat exchange channel; and a heat transfer wall positioned between the process microchannel and the heat exchange channel, the heat transfer wall comprising at least one thermal resistance layer. The thermal resistance layer may be positioned on either or both sides of the heat transfer wall and/or embedded in the heat transfer wall. The apparatus, which is illustrated in
The heat exchange channel 604 may be a microchannel or it may have a larger dimension. The process microchannel 602 and the heat exchange channel 604 may each have an internal height or gap of up to about 10 mm, and in one embodiment in the range of about 0.05 to about 10 mm, and in one embodiment from about 0.05 to about 5 mm, and in one embodiment from about 0.05 to about 2 mm. The width of each of these channels may be of any dimension, for example, up to about 3 meters, and in one embodiment from about 0.01 to about 3 meters, and in one embodiment about 0.1 to about 3 meters. The length of each of the these channels may be of any dimension, for example, up to about 10 meters, and in one embodiment from about 0.1 to about 10 meters, and in one embodiment from about 0.2 to about 6 meters, and in one embodiment from 0.2 to about 3 meters. The heat transfer wall may have a thickness in the range from about 0.05 to about 5 mm, and in one embodiment from about 0.05 to about 4 mm, and in one embodiment from about 0.05 to about 3 mm, and in one embodiment from about 0.05 to about 2 mm, and in one embodiment from about 0.05 to about 1.5 mm, and in one embodiment from about 0 to about 1 mm. The thermal resistance layer 608 may have a thickness in the range from about 1 to about 99% of the thickness of the heat transfer wall 605, and in one embodiment from about 1 to about 80%, and in one embodiment from about 1 to about 50%, and in one embodiment from about 1 to about 30%, and in one embodiment from about 1 to about 20%, and in one embodiment from about 1 to about 10%.
The process microchannel 602, heat exchange channel 604, heat transfer wall 605, and thermal resistance layer 608 may independently be made of a material comprising: steel; monel; inconel; aluminum; titanium; nickel; copper; brass; an alloy of any of the foregoing metals; ceramics; glass; quartz; silicon; or a combination of two or more thereof.
The construction and/or material of construction of the thermal resistance layer 608 may comprise any construction and/or material of construction having a different thermal conductivity than the thermal conductivity of the heat transfer wall 605. The thermal resistance layer 608 may comprise a vacuum, a gaseous material, a liquid and/or a solid material embedded in the heat transfer wall 605. The solid material may contain void spaces, openings and/or through holes. The thermal resistance layer may comprise one or more strips or shims which may contain void spaces, openings and/or through holes. The thermal resistance layer may comprise one or more strips with grooves or microgrooves formed in the strip. The thermal resistance layer may comprise one or more shims, each of the shims having a first surface and a second surface, and grooves or microgrooves formed in the first surface and/or the second surface.
The thermal resistance layer 608 and/or heat transfer wall 605 may comprise one or more sub-assemblies of a thermal resistant construction. Each sub-assembly may comprise two or more shims stacked one above another with one or more void spaces positioned between the shims. The void spaces may comprise a vacuum, air or an inert gas. The thermal resistance layer 608 and/or heat transfer wall 605 may comprise any desired number of these sub-assemblies stacked one above another, for example, from 1 to about 100 sub-assemblies, and in one embodiment from 1 to about 50 sub-assemblies, and in one embodiment from 1 to about 20 sub-assemblies, and in one embodiment from 1 to about 10 sub-assemblies, and in one embodiment from 1 to about 5 sub-assemblies, and in one embodiment from 1 to about 3 sub-assemblies, and in one embodiment 1 or 2 sub-assemblies.
The structured wall 606 and the thermal resistance layer 608 may be constructed by stacking a plurality of the shims illustrated in
The mass of reactants may diffuse and to some extent flow within the open porous structure of the structured wall 606. The catalyst may coat part of or the entire surface area of the structured wall 606.
The bulk flow region 603 in the process microchannel may reduce the impediment to flow resistance and allow the reactants to diffuse into the open structured walls 606 to access the catalyst.
In one embodiment, the heat transfer wall 605 may form an interior wall of the process microchannel 602 and one or more shims may be positioned on said interior wall to form structured wall 606, the one or more shims containing void spaces, openings or through holes. A catalyst may be supported by the one or more shims.
The microchannel reactor 100 may comprise one or more of the repeating units 600. In one embodiment, the microchannel reactor may comprise from 1 to about 50,000 of the repeating units 600, and in one embodiment from about 10 to about 50,000 of the repeating units 600, and in one embodiment from about 10 to about 30,000 repeating units, and in one embodiment from about 10 to about 10,000 of the repeating units 600, and in one embodiment from about 10 to about 5000 repeating units 600, and in one embodiment from about 10 to about 2000 repeating units 600, and in one embodiment from about 10 to about 1000 repeating units 600, and in one embodiment from about 10 to about 500 repeating units 600, and in one embodiment from about 10 to about 100 repeating units 600.
A plurality of the microchannel reactors 100 may be housed in vessel 700 which is illustrated in
The vessel 700 may be constructed from any suitable material sufficient for operating under the pressures and temperatures required for operating the microchannel reactors. For example, the shell and heads of the vessels 700 may be constructed of cast steel. The flanges, couplings and pipes may be constructed of stainless steel or other suitable alloys. The vessel 700 may have any desired diameter, for example, from about 30 to about 500 cm, and in one embodiment from about 100 to about 300 cm. The axial length of the vessel 700 may be of any desired value, for example, from about 0.5 to about 50 meters, and in one embodiment from about 0.5 to about 15 meters, and in one embodiment from about 1 to about 10 meters.
As indicated above, the microchannel reactors 100 may comprise a plurality of process microchannels, heat exchange channels and optionally staged addition channels stacked one above the other or positioned side-by-side. The microchannel reactors 100 may be in the form of cubic blocks as illustrated in
In one embodiment, the reaction zone 212 in the process microchannel 210 may be characterized by having a bulk flow path. The term “bulk flow path” refers to an open path (contiguous bulk flow region) within the process microchannels. A contiguous bulk flow region allows rapid fluid flow through the microchannels without large pressure drops. In one embodiment, the flow of fluid in the bulk flow region is laminar. Bulk flow regions within each process microchannel 210 may have a cross-sectional area of about 0.05 to about 10,000 mm2, and in one embodiment about 0.05 to about 5000 mm2, and in one embodiment about 0.1 to about 2500 mm2. The bulk flow regions may comprise from about 5% to about 95%, and in one embodiment about 30% to about 80% of the cross-section of the process microchannels.
In one embodiment of the invention relatively short contact times, high selectivity to the desired product and relatively low rates of deactivation of the catalyst may be achieved by limiting the diffusion path required for the catalyst. For example, this may be achieved when the catalyst is in the form of a thin layer on an engineered support such as a metallic foam or on the wall of the process microchannel. This allows for increased space velocities. In one embodiment, the thin layer of catalyst can be produced using chemical vapor deposition. This thin layer may have a thickness in the range up to about 1 micron, and in one embodiment from about 0.1 to about 1 micron, and in one embodiment about 0.25 micron. These thin layers may reduce the time the reactants are within the active catalyst structure by reducing the diffusional path. This decreases the time the reactants spend in the active portion of the catalyst. The result may be increased selectivity to the product and reduced unwanted by-products. An advantage of this mode of catalyst deployment is that, unlike conventional catalysts in which the active portion of the catalyst may be bound up in an inert low thermal conductivity binder, the active catalyst film is in intimate contact with either the engineered structure or the wall of the process microchannel. This may leverage high heat transfer rates attainable in the microchannel reactor and allows for close control of temperature. The result is the ability to operate at increased temperature (faster kinetics) without promoting the formation of undesired by-products, thus producing higher productivity and yield and prolonging catalyst life.
In one embodiment, the catalyst may be regenerated. This may be done by flowing a regenerating fluid through the process microchannels in contact with the catalyst. The regenerating fluid may comprise hydrogen or a diluted hydrogen stream. The diluent may comprise nitrogen, argon, steam, methane, carbon dioxide, or a mixture of two or more thereof. The concentration of H2 in the regenerating fluid may range up to about 100% by volume, and in one embodiment from about 1 to about 100% by volume, and in one embodiment about 1 to about 50% volume. The regenerating fluid may flow from the header through the process microchannels to the footer, or in the opposite direction from the footer through the process microchannels to the header. The temperature of the regenerating fluid may be from about 20 to about 600° C., and in one embodiment about 20 to about 400° C., and in one embodiment about 80 to about 200° C. The pressure within the process microchannels during this regeneration step may range from about 1 to about 100 atmospheres absolute pressure, and in one embodiment about 1 to about 10 atmospheres. The residence time for the regenerating fluid in the process microchannels may range from about 0.001 to about 10 seconds, and in one embodiment about 0.01 second to about 1 second.
The contact time of the process fluids with the catalyst within the process microchannels may be in the range up to about 100 seconds, and in one embodiment in the range from about 1 millisecond (ms) to about 100 seconds, and in one embodiment in the range from about 1 ms to about 50 seconds, and in one embodiment in the range from about 1 ms to about 25 seconds, and in one embodiment in the range from about 1 ms to about 10 seconds, and in one embodiment from about 1 ms to about 1 second, and in one embodiment from about 1 ms to about 500 ms, and in one embodiment about 1 ms to about 200 ms, and in one embodiment about 1 ms to about 100 ms, and in one embodiment about 1 ms to about 50 ms, and in one embodiment about 1 ms to about 20 ms, and in one embodiment about 1 ms to about 10 ms. In one embodiment, the reactants may be combined with up to about 50% by volume diluent (e.g., nitrogen gas) and the contact time may be up to about 25 seconds, and in one embodiment up to about 10 seconds, and in one embodiment up to about 1 second. In one embodiment, the reactants may be combined with up to about 25% by volume diluent and the contact time may be up to about 50 seconds, and in one embodiment up to about 25 seconds, and in one embodiment up to about 5 seconds. In one embodiment, the reactants may be combined with up to about 10% by volume diluent and the contact time may be up to about 100 seconds, and in one embodiment up to about 50 seconds, and in one embodiment up to about 10 seconds.
The flow rate of process fluid flowing in the process microchannels may be in the range from about 0.001 to about 500 lpm, and in one embodiment about 0.001 to about 250 lpm, and in one embodiment about 0.001 to about 100 lpm, and in one embodiment about 0.001 to about 50 lpm, and in one embodiment about 0.001 to about 25 lpm, and in one embodiment about 0.01 to about 10 lpm. The velocity of fluid flowing in the process microchannels may be in the range from about 0.01 to about 200 m/s, and in one embodiment about 0.01 to about 75 m/s, and in one embodiment about 0.01 to about 50 m/s, and in one embodiment about 0.01 to about 30 m/s, and in one embodiment about 0.02 to about 20 m/s. The Reynolds Number for the fluid flowing in the process microchannels may be in the range from about 0.0001 to about 100000, and in one embodiment about 0.001 to about 10000.
The space velocity (or gas hourly space velocity (GHSV)) for the flow of the process fluids in the process microchannels may be at least about 1000 hr−1 (normal liters of feed per hour per liter of volume within the process microchannels), and in one embodiment at least about 2000 hr−1, and in one embodiment at least about 4000 hr−1, and in one embodiment at least about 7000 hr−1, and in one embodiment at least about 10000 hr−1. The space velocity may be in the range from about 1000 to about 500000 hr−1, and in one embodiment in the range from about 4000 to about 40000 hr−1. The volume within the process microchannels may include all volume in the process microchannels in which a process fluid may flow in a flow-through manner or a flow-by manner. The volume may include the volume within any microgrooved supports positioned in the microchannels as well as the volume within any surface features that may be present in the process microchannels.
The management of heat exchange with the inventive process may provide advantageous control of the conversion of ethylbenzene and the selectivity to styrene. The heat exchange channels may be adapted for heat exchange fluid to flow in the heat exchange channels in a direction that is co-current with the flow of fluid in process microchannels and/or staged addition channels that are adjacent to or in thermal contact with the heat exchange channels. Alternatively, the heat exchange fluid may flow through the heat exchange channels in a direction that is countercurrent to the flow of fluid through the process microchannels and/or staged addition channels. Alternatively, the heat exchange channels may be oriented relative to the process microchannels and/or staged addition channels to provide for the flow of heat exchange fluid in a direction that is cross-current relative to the flow of fluid through the process microchannels and/or staged addition channels. The heat exchange channels may have a serpentine configuration to provide a combination of cross-flow and co-current or counter-current flow.
The heat exchange fluid may be any fluid. These include air, steam, liquid water, gaseous nitrogen, liquid nitrogen, other gases including inert gases, carbon monoxide, carbon dioxide, oils such as mineral oil, gaseous hydrocarbons, liquid hydrocarbons, and heat exchange fluids such as Dowtherm A and Therminol which are available from Dow-Union Carbide. The heat exchange fluid may comprise one or more organic compounds containing 1 to about 5 carbon atoms per molecule such as methylenechloride, fluorochloromethanes (e.g., dichlordifluoromethane), hydrocarbons containing 1 to about 5 carbon atoms per molecule (e.g., methane, ethane, ethylene, propanes, butanes, pentanes, etc.), or a mixture of two or more thereof.
The heat exchange fluid may comprise the feed composition, staged addition feed stream and/or product. This can provide process pre-heat, cool-down and/or an increase in overall thermal efficiency of the process.
In one embodiment, the heat exchange channels may comprise process channels wherein an endothermic or exothermic process is conducted. These heat exchange process channels may be microchannels. Examples of endothermic processes that may be conducted in the heat exchange channels include steam reforming and dehydrogenation reactions. Examples of exothermic processes that may be conducted in the heat exchange channels include water-gas shift reactions, methanol synthesis reactions and ammonia synthesis reactions.
In one embodiment, the heat exchange fluid undergoes a phase change in the heat exchange channels. This phase change provides additional heat addition to or removal from the process microchannels and/or second reactant stream channels beyond that provided by convective heating or cooling. An example of such a phase change would be an oil or water that undergoes boiling. In one embodiment, the vapor mass fraction quantity of the boiling of the phase change fluid may be up to about 100%, and in one embodiment up to about 75%, and in one embodiment up to about 50%, and in one embodiment in the range from about of 1% to about 50%.
The pressure within each individual heat exchange channel may be controlled using passive structures (e.g., obstructions), orifices and/or mechanisms upstream of the heat exchange channels or in the channels. By controlling the pressure within each heat exchange channel, the temperature within each heat exchange channel can be controlled. A higher inlet pressure for each heat exchange fluid may be used where the passive structures, orifices and/or mechanisms let down the pressure to the desired heat exchange microchannel pressure. By controlling the temperature within each heat exchange channel, the temperature in the process microchannels in thermal contact with the heat exchange microchannel can be controlled. Thus, for example, each process microchannel may be operated at a desired temperature by employing a specific pressure in the heat exchange channel in thermal contact with the process microchannel. This may provide the advantage of precisely controlled temperatures for each process microchannel. The use of precisely controlled temperatures for each process microchannel may provide the advantage of a tailored temperature profile and an overall reduction in the energy requirements for the reaction process.
The heat flux for heat exchange in the microchannel reactor may be in the range from about 0.01 to about 500 watts per square centimeter (W/cm2) of the surface area of the heat transfer walls in the microchannel reactor, and in one embodiment from about 0.01 to about 250 W/cm2. The heat flux may be in the range from about 0.01 to about 125 W/cm2, and in one embodiment about 0.1 to about 50 W/cm2, and in one embodiment from about 0.1 to about 10 W/cm2. The heat flux may be in the range from about 1 to about 500 W/cm2, and in one embodiment from about 1 to about 250 W/cm2, and in one embodiment, from about 1 to about 100 W/cm2, and in one embodiment from about 1 to about 50 W/cm2, and in one embodiment from about 1 to about 25 W/cm2, and in one embodiment from about 1 to about 10 W/cm2.
In one embodiment, the temperature of the reactant streams entering the microchannel reactor may be within about 200° C., and in one embodiment within about 100° C., and in one embodiment within about 50° C., and in one embodiment within about 20° C., of the temperature of the product exiting the microchannel reactor.
The use of controlled heat exchange between heat exchange channels in thermal contact with or adjacent to the process microchannels and/or staged addition channels may allow for uniform temperature profiles for the process microchannels and/or staged addition channels. This provides for the possibility of a more uniform heat exchange at more rapid rates than can be obtained with conventional processing equipment such as mixing tanks. For a microchannel reactor employing multiple process microchannels and staged addition channels, the temperature difference between the process microchannels and/or staged addition channels at least one common position along the lengths of the process microchannels may be less than about 5° C., and in one embodiment less than about 2° C., and in one embodiment less than about 1° C.
The heat exchange channels in thermal contact with or adjacent to either the process microchannels and/or staged addition channels may employ separate temperature zones along the length of such channels. For example, in one embodiment, the temperature in a first zone near the entrance to the process microchannel may be maintained at a temperature above or below a second temperature in a second zone near the end of the process microchannel. A cool down or quench zone may be incorporated into the process microchannels to cool the product. Numerous combinations of thermal profiles are possible, allowing for a tailored thermal profile along the length of the process microchannels and/or staged addition channels, including the possibility of heating or cooling zones before and/or after the reaction zone in the process microchannels to heat or cool the reactants and/or product.
The heat exchange fluid entering the heat exchange channels may be at a temperature in the range from about 50° C. to about 650° C., and in one embodiment in the range from about 150° C. to about 600° C., and in one embodiment in the range from about 250° C. to about 500° C. The heat exchange fluid exiting the heat exchange channels may be at a temperature in the range from about 100° C. to about 700° C., and in one embodiment in the range from about 200° C. to about 650° C., and in one embodiment in the range from about 300° C. to about 550° C. The residence time of the heat exchange fluid in the heat exchange channels may be in the range from about 5 ms to about 1 minute, and in one embodiment from about 20 ms to about 1 minute, and in one embodiment from about 50 ms to about 1 minute, and in one embodiment about 100 ms to about 1 minute. The pressure drop for the heat exchange fluid as it flows through the heat exchange channels may be in the range up to about 1 atm/m, and in one embodiment up to about 0.5 atm/m, and in one embodiment up to about 0.1 atm/m, and in one embodiment from about 0.01 to about 1 atm/m. The heat exchange fluid may be in the form of a vapor, a liquid, or a mixture of vapor and liquid. The Reynolds Number for the flow of vapor through the heat exchange channels may be in the range from about 10 to about 5000, and in one embodiment about 100 to about 3000. The Reynolds Number for the flow of liquid through heat exchange channels may be in the range from about 10 to about 10000, and in one embodiment about 100 to about 5000.
The temperature of the reactants entering the microchannel reactor reactor core 110 may be in the range up to about 600° C., and in one embodiment in the range from about 150° C. to about 600° C., and in one embodiment from about 250° C. to about 550° C.
The temperature within the process microchannels for a dehydrogenation reaction process may be in the range from about 650° C. to about 900° C., and in one embodiment from about 700° C. to about 850° C. The temperature within the process microchannels for an oxidative dehydrogenation reaction process may be in the range from about 250° C. to about 650° C., and in one embodiment from about 350° C. to about 550° C., and in one embodiment from about 400° C. to about 500° C.
The temperature of the product exiting the microchannel reactor core 110 may be in the range up to about 650° C., and in one embodiment in the range from about 150° C. to about 650° C., and in one embodiment from about 200° C. to about 600° C., and in one embodiment from about 250° C. to about 550° C.
The pressure within the process microchannels may be in the range up to about 50 atmospheres absolute pressure, and in one embodiment up to about 40 atmospheres, and in one embodiment up to about 30 atmospheres. In one embodiment the pressure may be in the range from about 1 to about 50 atmospheres absolute pressure, and in one embodiment from about 10 to about 40 atmospheres, and in one embodiment from about 20 to about 30 atmospheres.
The pressure drop of the process fluids as they flow in the process microchannels may be in the range up to about 5 atmospheres per meter of length of the process microchannel (atm/m), and in one embodiment up to about 1 atm/m, and in one embodiment up to about 0.1 atm/m.
The pressure drop for the stage addition feed stream flowing through the apertured sections may be in the range up to about 0.1 atm, and in one embodiment from about 0.001 to about 0.1 atm, and in one embodiment from about 0.001 to about 0.05 atm, and in one embodiment about 0.001 to about 0.005 atm. The reactants and products flowing through the process microchannels may be in the form of a vapor, a liquid, or a mixture of vapor and liquid. The Reynolds Number for the flow of vapor through the process microchannels may be in the range from about 10 to about 10000, and in one embodiment about 100 to about 3000. The Reynolds Number for the flow of liquid through the process microchannels may be about 10 to about 10000, and in one embodiment about 100 to about 3000.
The conversion of the ethylbenzene may be in the range from about 25% or higher per cycle, and in one embodiment about 50% or higher per cycle, and in one embodiment from about 25 to about 100%, and in one embodiment from about 50% to about 100% per cycle. In one embodiment, the conversion may be at least about 70%.
The conversion of the oxygen, when used, may be in the range from about 40% or higher per cycle, and in one embodiment from about 40% to about 100% per cycle.
The yield of styrene may be in the range from about 20% or higher, and in one embodiment about 50% or higher, and in one embodiment from about 50% to about 99%.
The selectivity to styrene may be at least about 50%, and in one embodiment at least about 80%, and in one embodiment at least about 90%, and in one embodiment at least about 95%, and in one embodiment in the range from about 50% to about 99%, and in one embodiment in the range from about 80% to about 99%, and in one embodiment from about 95% to about 99%.
It may be possible to achieve a yield of styrene that is at least about 20% with less than about 20% change in the yield of styrene for a period of at least about 24 hours with a contact time of less than about 10 seconds and a feed composition containing less than about 50% by volume diluent (e.g., nitrogen gas). It may be possible to achieve a yield of styrene that is at least about 35%, and in one embodiment at least about 50%, and in one embodiment at least about 75% with less than about 20% change in the yield of styrene for at least about 24 hours with a contact time of less than about 10 seconds and a feed composition containing less than about 50% by volume diluent (e.g., nitrogen gas). In one of these embodiments, the contact time may be less than about 5 seconds, and in one embodiment less than about 2 seconds, and in one embodiment less than about 1 second. In one of these embodiments, the feed composition may contain less than about 25% by volume diluent, and in one embodiment less than about 10% by volume diluent.
It may be possible to produce styrene at a rate of at least about 500 ml per gram of catalyst per hour using the inventive process, and in one embodiment at least about 750 ml per gram of catalyst per hour, and in one embodiment at least about 900 ml per gram of catalyst per hour, and in one embodiment at least about 1000 ml per gram of catalyst per hour.
It may be possible to achieve a styrene yield that is at least about 20% with less than about 20% change in the styrene yield for at least about 24 hours wherein the styrene is produced at a rate of at least about 500 ml per gram of catalyst per hour. In one of these embodiments, the styrene yield may be at least about 35%, and in one embodiment at least about 50%, and in one embodiment at least about 75%. In one of these embodiments, the styrene may be produced at a rate of at least about 750 ml per gram of catalyst per hour, and in one embodiment at least about 900 ml per gram of catalyst per hour, and in one embodiment at least about 1000 ml per gram of catalyst per hour.
Example 10.7% K2O-15% MoO3/SiO2—TiO2 catalyst is prepared by the sol-gel method. 20.0 g tetraethylorthosilicate and 27.29 g titanium isopropoxide are dissolved in 200 ml isopropyl alcohol solution with stirring. In another beaker, 2.93 g ammonium paramolybdate are dissolved in 13.65 g H2O and then 0.30 g 45% KOH solution are added. The aqueous solution is added dropwise to the alcohol solution (1 ml/min). After all of the aqueous solution is added, the resulting gel is stirred for additional 15 min. The gel is dried at 110° C. overnight and calcined at 550° C. for 5 hours. The catalyst is crushed and sieved to 60-100 mesh.
The catalyst (0.4 g) is loaded in a quartz tube reactor having a 0.2 inch O.D. (0.635 cm). The reactor volume is 0.3 ml. A feed gas composition containing 9.9% by volume ethylbenzene, 5% by volume O2 and 85.1% by volume N2 flows into the reactor. The feed gas flow rate is 180 ml/min. The contact time based on reactor volume is 0.1 second. The process operates for 3 hours with no evidence of catalyst deactivation. The process is operated at atmospheric pressure. The GHSV based on reactor volume is 36000 hr−1. The GHSV based on the catalyst is 27000 ml/g-cat/hour. The GHSV for ethylbenzene based on catalyst is 2670 ml/g-cat/hour. The products are analyzed by GC. At 500° C., 43% ethylbenzene conversion and 91% styrene selectivity are achieved. The styrene yield is 39%. The styrene yield is 1041 ml/g-cat/hour. O2 conversion is 98%.
Example 20.7% K2O-18% V2O5/SiO2—ZrO2 catalyst is prepared by the sol-gel method. 7.05 g vanadium (III) 2,4-pentanedionate are dissolved in 200 ml iso-butanol with stirring at 60° C. After cooling, 19.97 g zirconium n-butoxide are added at room temperature with stirring, followed by 15.0 g n-butoxysilane. In another beaker, 0.19 g 45% KOH solution are mixed with 6.63 g H2O. The aqueous solution is added dropwise to the alcohol solution (1 ml./min). After all of the aqueous solution is added, the resulting mixture is stirred for an additional 15 min. The gel is then dried at 110° C. overnight and calcined at 550° C. for 5 hours. The catalyst is crushed and sieved to 60-100 mesh.
The catalyst (0.5 g) is loaded in the quartz tube reactor identified in Example 1. The feed gas composition contains 9.9% by volume ethylbenzene, 5% by volume O2 and 85.1% by volume N2. The contact time is 0.1 second. The process operates for 3 hours with no evidence of catalyst deactivation. The process is operated at atmospheric pressure. The products are analyzed by GC. At 450° C., 36% ethylbenzene conversion and 89% styrene selectivity are achieved. The styrene yield is 32%. O2 conversion is 96%.
Example 3Mg0.99MoO3.99 catalyst is prepared by the sol-gel method. 16.00 g molybdenum (VI) oxide bis(2,4-pentanedionate) is dissolved in 200 ml methoxyethanol. 5.56 g magnesium ethoxide are then added with stirring.
Subsequently, 14.13 g 2.5 mol/L NH4OH solution are added dropwise to the mixture. The resulting gel is dried at 110° C. for 5 hours and then calcined at 550° C. for 12 hours. The catalyst is crushed and sieved to 60-100 mesh.
The catalyst (0.3 g) is loaded in the quartz tube reactor identified in Example 1. The feed gas composition contains 9.9% by volume ethylbenzene, 5% by volume O2 and 85.1% by volume N2. The contact time is 0.1 second. The process operates for 4 hours with no evidence of catalyst deactivation. The process is conducted at atmospheric pressure. The products are analyzed by GC. At 500° C., 29% ethylbenzene conversion and 88% styrene selectivity are achieved. The styrene yield is 26%. O2 conversion is 78%.
Example 4Mesoporous V—Mg—Ox (18% V2O5) catalyst is prepared by the co-precipitation method. 6.97 g vanadium (III) 2,4-pentanedionate are dissolved in 200 ml ethanol solution with stirring at 70° C. In another beaker, 19.59 g MgCl2 and 9.03 g hexadecyltrimethylammonium chloride are dissolved in 200 ml H2O. The vanadium solution is added into the MgCl2 solution. The mixture is heated to 92-95° C. The pH is adjusted to 9 by 5 mol/L NH3.H2O and then to 10 by 45 wt % KOH solution. The temperature is kept at 92-95° C. for 2 h. Subsequently, the slurry is cooled to room temperature and aged overnight. The mixture is filtered and the solid is washed with H2O three times. After drying at 110° C. overnight, the sample is calcined at 550° C. for 4 hours. The catalyst is crushed and sieved to 60-100 mesh.
The catalyst (0.2 g) is loaded in the quartz tube reactor identified in Example 1. The feed gas composition contains 9.9% by volume ethylbenzene, 5% by volume O2 and 85.1% by volume N2. The contact time is 0.1 second. The process operates for 4 hours with no evidence of catalyst deactivation. The process is conducted at atmospheric pressure. The products are analyzed by GC. At 550° C., 36% ethylbenzene conversion and 89% styrene selectivity are achieved. The styrene yield is 32%. O2 conversion is 98%.
Example 5V2Mo6O26/MgO catalyst is prepared by the ion-exchange method. 1.66 g KVO3 and 8.57 g K2MoO4 are dissolved in 300 ml H2O. The pH of the solution is adjusted to 5.5 by HCl solution. After storing for 5 days, 1.45 g MgO powder are added into the solution and stirred for one day at room temperature. The mixture is filtered and the solid is washed with H2O three times. After drying at 110° C. overnight, the sample is calcined at 500° C. for 5 hours. The catalyst is sieved to 60-100 mesh.
The catalyst (0.16 g) is loaded in the quartz tube reactor identified in Example 1. The feed gas composition contains 9.9% by volume ethylbenzene, 5% by volume O2 and 85.1% by volume N2. The contact time is 0.1 second. The process operates for 5 hours with no evidence of catalyst deactivation. The process is conducted at atmospheric pressure. The products are analyzed by GC. At 550° C., 25% ethylbenzene conversion and 82% styrene selectivity are achieved. The styrene yield is 21%. O2 conversion is 97%.
Example 60.7% K2O-15% MoO3/SiO2—TiO2 catalyst is prepared by the sol-gel method. 20.0 g tetraethylorthosilicate and 27.29 g titanium isopropoxide are dissolved in 200 ml isopropyl alcohol solution with stirring. In another beaker, 2.93 g ammonium paramolybdate are dissolved in 13.65 g H2O and then 0.30 g 45% KOH solution are added. The aqueous solution is dropped slowly into the alcohol solution (1 ml/min). After all of the aqueous solution is added, the resulting gel is stirred for additional 15 min. The gel is dried at 110° C. overnight and calcined at 550° C. for 5 hours. The catalyst is crushed and sieved to 60-100 mesh.
The catalyst (5 g) is mixed with 45 g H2O and 95 g 6-mm ZrO2 beads in a jar. The mixture is ball-milled for three days. The resulting slurry (10 wt %) is then diluted to 2.5 wt % by H2O. The average particle size in the slurry is about 1 micron. The slurry is dropped onto the microgrooved support strip illustrated in
The catalyst coated microgrooved support strip is welded in the microchannel device shown in
A feed gas composition, which contains 18.8% ethylbenzene and 81.2% air, flows into the microchannel device. The feed gas flow rate is 2.93 ml/min. The ethylbenzene to oxygen molar ratio is 1.1. The contact time based on reactor volume is 0.8 second. The process is operated for 96 hours with no evidence of catalyst deactivation. The process is conducted at atmospheric pressure. The GHSV based on reactor volume is 4508 hr−1. The GHSV based on the catalyst is 6104 ml/g-cat/hour. The GHSV for the ethylbenzene is 1148 ml/g-cat/hour. The products are analyzed by GC. At an average temperature of 412° C., 86% ethylbenzene conversion and 94% styrene selectivity are achieved. The styrene yield is 81%. The styrene yield is 930 ml/g-cat/hour. O2 conversion is 98%.
The results of Examples 1-6 are summarized in Table I. For each of Examples 1-5, the feed stream contains 9.9% by volume ethylbenzene, 5% by volume oxygen, and 85.1% by volume nitrogen. For Example 6, the feed stream contains 18.8% by volume ethylbenzene, 17.1% by volume oxygen, and 64.1% by volume nitrogen.
A comparison between the results for Examples 1 and 6 is provided in Table II:
Examples 1 and 6 suggest that at a lower temperature (412° C. versus 450-500° C.) higher conversions of ethylbenzene may be achieved. A comparison between Examples 1 and 6 suggests that a higher single pass yield of styrene (81% versus 39%) may be achieved when the catalyst supported microgrooved support strip of Example 6 is used.
Example 7Microgrooved Test Reactors #1 and #2 are fabricated. The reactors contain inlet and outlet tubing, headers and footers, a body cover plate, a body backing plate and a microgrooved assembly. The inlet and outlet tubing is welded to the header and footer of each device. Each is a 3 inch (7.62 cm) length of ⅛ inch (0.318 cm) OD SS316 tube with a tubular wall thickness of 0.035 inch (0.089 cm). The headers and footers are fabricated from SS316 bar stock via conventional machining and have outer dimensions of 0.820 inch×0.375 inch×0.375 inch (2.08×0.953×0.953 cm). One of the 0.375 inch×0.820 inch (0.953×2.08 cm) faces is given a 45° 0.020 inch (0.0508 cm) chamfer on each of the 0.375 inch (0.953 cm) long edges. This face is the “top” of the piece. A 0.180 inch (0.457 cm) deep by 0.520 inch (1.32 cm) long by 0.069 inch (0.175 cm) wide slot is cut in one of the 0.820 inch×0.375 inch (2.08×0.953 cm) faces (orthogonal to the top face) such that the long axis of the slot is located 0.227 inch (0.577 cm) from the bottom face of the piece and the short axis of the slot is located 0.410 inch (1.04 cm) from the 0.375 inch (0.953 cm) long edge of the face. The slot is flat bottomed and terminated in a full round. On the face opposite the slot is drilled a 0.069 inch (0.175 cm) through hole with a 0.125 inch (0.318) counter bore to a depth of 0.125 inch (0.318 cm). The through hole is centered on the location of the slot.
The process microchannel is in the form depicted in
The tenon is formed by removing material 0.124 inch (0.315 cm) from either side of the tenon to a depth of 0.074 inch (0.188 cm). The lip of the step so formed is given a 0.030 inch (0.076 cm) 45° chamfer on either side as shown in the lower left of
The microgrooved support strips are fabricated via photochemical machining from 0.002 inch (50.8 microns) thick stainless steel 304. Each strip is 2.500 inches (6.35 cm) long and 0.500 inch (1.27 cm) wide. The microgrooves are parallel to each other, 0.007 inch (178 microns) wide and separated from adjacent grooves by 0.007 inch (178 microns) of the base material. The microgrooves form a 20° angle from the center line (long axis of the microgrooved support strip). The microgrooves start approximately 0.030 inch (0.076 cm) from the edge of the strip measuring 0.500 inch (1.27 cm) and each individual microgroove stops approximately 0.007 inch (178 microns) from the long (2.5 inches, 6.35 cm) edge of the strip (see
The microgrooved assembly and the body cover plates are cleaned first in an ultrasonic bath containing isopropanol, then a 20% nitric acid solution, and then deionized water. Each cleaning step has a duration of 30 minutes at 90% power output. The bath temperature is 25° C. The cleaned parts are then heated in stagnant air while increasing the temperature at a rate of 3.5° C. per minute to 650° C. and held at that temperature for 10 hours.
The catalyst described in Example 6 is prepared and washcoated on the microgrooved assembly using the procedure described in Example 6. The resulting microchannel reactor is designated as Microgroove Test Reactor #2.
The body cover plate is placed on the body backing plate and a seam weld is applied to close the device forming the microchannel reactor body assembly. The header and footer, after having their respective inlet and outlet tubing welded to them are also welded to the body assembly such that the slot on the header or footer is aligned with the channel formed by the body assembly which is shown in
Referring to
The mixed feed stream of ethylbenzene and oxygen flows through a 200 mesh screen before reaching the orifice and split section. All of the lines and the orifice are heated with and electrical heating tape holding the outside surface of the tubing at 200° C. An orifice with a diameter of 0.0007 inch (17.8 microns) is placed immediately upstream of the reactor. The orifice has a pressure drop that is significantly larger than the pressure drop across the reactor. The feed rate to the reactor is controlled by varying the back pressure of the split stream. The pressures upstream and downstream of the orifice are controlled in order to maintain the total flow to the reactor from 2 to 6 SCCM. The split stream is condensed via a microchannel heat exchanger and collected in two chilled product collection drums. The gasses exit through the back pressure regulator, septa sampling point, and bubble flow meter, before going to a vent. Samples of this exit gas stream are collected by a gas tight syringe and the liquid is collected and analyzed.
The microchannel reactor is installed inside an electrically powered ceramic heating element. This heater provides a temperature ranging from 350° C. to 500° C.
The product of the reactor is mixed with room temperature nitrogen flow of 15 SCCM from a second mass flow controller to help increase the total flow rate through the downstream components. The diluted product is condensed in a chilled, 2 mm glass bead packed sample collection drum. The product is collected in a chilled, open volume knock-out drum before the gas stream is sent through a bubble flow meter and to the on-line GC system. The flow rates of both the split and product gas streams are recorded.
There are two GCs that provide the analysis for the system. The product gas stream is analyzed by an Agilent 5890 GC equipped with two TCD detectors, three sample valves, and a sample pump. H2, O2, N2, CH4, CO, CO2, ethane and ethylene are quantified in the 5890GC with an analysis time of approximately 20 min. The liquid feed, liquid collected from the split stream knockout drum, split stream gas, liquid product and product stream gas are analyzed by an Agilent 6890GC with a FID detector. Benzene, toluene, ethylbenzene and styrene are quantified in approximately 20 min.
The system is started-up as follows. N2 flow at 200 SCCM purges the system as the devices begin to heat. The back pressure is increased on the split stream in order to push flow through the reactor. The reactor flow is established at 5 SCCM. The vaporizer is heated to 200° C. while the heat tracing is heated to 200° C. The reactor is heated to an average temperature of 380° C. at a rate of 3° C./min in the ceramic heater (clam shell furnace). Once the temperatures are steady ethylbenzene and air flows are stepped in, while the N2 flow is stepped out until an ethylbenzene:oxygen mole ratio of 2:1 and reactor inlet flow 4 SCCM is reached. The system is left until steady state and a full sample is recorded. The temperature is then increased at a rate of 2° C./min in 10° C. increments while taking product GC samples. The temperature ramp stops once full oxygen conversion has been reached. The temperature is held constant and a sample is taken at 412° C. average temperature. Next the ethylbenzene:oxygen mole ratio is decreased to 1.8:1, 1.5:1, and 1.1:1 consecutively. This increases conversion of the ethylbenzene and selectivity to styrene.
Conversion of the ethylbenzene and selectivity to styrene is determined using a methodology based on oxygen balance. This method involves determining the conversion of ethylbenzene based on performing an oxygen balance and assumes the following stoichiometry to dominate.
C8H10+0.5O2→C8H8+H2O Equation 1
C8H10+6.5O2→8CO+5H2O Equation 2
C8H10+10.5O2+5H2O Equation 3
The conversion of ethylbenzene is approximated as shown in the equations below:
where nCO,out, nCO2,out, and nST,out are calculated as follows:
In the above equations, ndry gas,out is the measured molar outlet dry flow rate, fi,out,dry is the mole fraction of component i (CO, CO2, or O2) in the dry outlet flow as measured by gas chromatograph, 5/8 is the assumed stoichiometric ratio of H2O to CO or CO2 formed during combustion, and
nO,in=2·nO
nO,out=ndry gas,out·(fCO,out,dry+2·fCO
where ni,in is the inlet molar flow rate of component i (O2 or air). The above calculations assume a perfect oxygen balance wherein the molar flow rate of water out of the system is equal to the molar flow rate of missing oxygen atoms. It is further assumed that one mole of water is formed for every mole of styrene produced, and five moles of water are formed for every eight moles of CO or CO2 produced.
The weight selectivity to styrene is calculated as follows:
Furthermore, the carbon selectivity to CO, and CO2 is calculated as shown below.
The selectivity to non-COx (taken to approximate the carbon selectivity to styrene) is calculated by subtracting the sum of the selectivity to CO and the selectivity to CO2 from 100%.
The results of testing the device are summarized in Table III where comparison is given between similar catalysts tested in a powdered state using a quartz tube reactor (inner diameter 4 mm). The catalyst is online under reactive conditions for 96.5 hours in the Microgroove Test Reactor #2 (see, Table IV).
The yield increases are achieved at lower WHSV in the Microgroove Test Reactor #2 but also at significantly reduced temperatures thus productivity may be increased markedly by increasing temperature. As the selectivity is not dramatically reduced by operation at 495° C. (condition 2 in Table III) it is anticipated that the WHSV may be increased in the microchannel reactor employing the microgrooved catalyst support.
Example 8Microgroove Test Reactor #1 is prepared in a manner similar to that described in Example 7 using the catalyst described in Examples 1, 6 and 7. Testing is conducted in a manner analogous to that described in Example 7 with several exceptions. One of these is that the flow of nitrogen used to aid in the down stream purge is 25 SCCM for conditions 3 through 7 and 0 SCCM for conditions 8 through 13. In addition the microgroove test device described in Example 7 is placed in a clam shell furnace such that the bottom (outlet of the microchannel) of the body assembly even with the bottom of the 3 inches long heating zone of the clam shell furnace thus approximately 0.9 inch (2.29 cm) sticks out above the heated zone. In this example the device is placed in the clam shell furnace such that the top (inlet of the microchannel) is even with the top of the heating zone thus approximately 0.9 inch (2.29 cm) sticks out below the heated zone. This leads to a more pronounced temperature profile (15° C. from inlet to outlet for Example 7 vs. 50° C. for Example 8) as can be seen by comparing Tables VII and V.
In Example 8 the advantages of the microgrooved support structure are apparent when the same catalyst is run in both a packed bed in a quartz tube (4 mm inner diameter) and the microgrooved reactor. In this case when condition 2 and condition 7 in Table VI are compared the microgrooved reactor allows for improve conversion and selectivity at a similar weight hourly space velocity (WHSV) and lower temperature. The term WHSV is used herein to refer to the mass of reactant (for example, ethylbenzene) per unit of time contacting a given mass of catalyst. The enhanced productivity of Microgroove Test Reactor #1 vs. Microgroove Test Reactor #2, where Microgroove Test Reactor #1 has a higher conversion at greater WHSV, may be due to the larger pressure drop experienced by Microgroove Test Reactor #1, a on possible outcome of which may be that part of the bulk flow is diverted from the flow by channel into the microgrooved structure.
The results for two microgrooved test reactors (Examples 7 and 8) are compared to results collected for the catalysts reported in Examples 1 through 5. The comparison is shown in
A computational fluid dynamics (CFD) study on thermal management for the formation of styrene via oxidative dehydrogenation of ethylbenzene is conducted. The production of styrene in a microchannel reactor may be particularly advantaged by the incorporation of a structured wall to increase the surface area for coating a highly active and selective ethylbenzene oxidative dehydrogenation (ODH) catalyst. The reactor may be further advantaged by incorporating a thermal resistance layer in the heat transfer wall between the heat exchange transfer channel and the process microchannel to create a controlled temperature gradient such that a lower temperature heat exchange fluid, such as an oil, may be used to remove heat for higher temperature oxidation reactions. Typical hot oils may be rated to a maximum of about 400° C. A desirable operating temperature window for styrene production via oxidative dehydrogenation of ethylbenzene may be in the range from about 300° to about 500° C., and in one embodiment from about 400° to about 450°. In one embodiment, the oxidant may be added by staged into the process microchannel to reduce the local partial pressure of oxygen and enhance the resulting reaction selectivity to styrene.
A microchannel reactor may be designed to maintain a heat exchange fluid temperature at 380° while running the process microchannel at 420° C. by positioning a thermal resistance layer between the process microchannel and heat exchange channel. The thermal resistance layer may not be open to flow of heat exchange fluid or process reactants. The thermal resistance layer may be formed using techniques and constructions similar to those used for making structured walls. The pattern selected for the thermal resistance layer may be the same as or different than the structured wall in the process microchannel for supporting the catalyst.
The temperature rise in the catalyst may be controlled by varying the thermal resistance in thermal resistance layer. The thermal resistance may be varied along the length of the process microchannel. It may be desirable to have a higher thermal lag at one end of the process microchannel or a varying function down the process microchannel length either digitally or in an analog fashion.
The structured walls that support the catalyst may vary along the length of the process microchannel to reduce or enhance the heat release such that isothermal or an axially varying temperature profile may be obtained.
Transient simulation shows that the thermal resistance layer may not create an unpredictable thermal response or thermal lag to the change of flow variables. Temperature overshoot may not occur at high temperature locations. This may be an important consideration to keep the catalyst temperature under control to avoid hot spots, sintering, deactivation, or otherwise unwanted thermal excursions.
Microchannel apparatus 600 illustrated in
The shims have alternating patterns such that a porous structure having a thickness of 1.5 mm is created when 30 shims are stacked together to form the structured wall 606. The openings in the alternating shims are arranged to create solid metal connections through the stack of 30 shims along with completely open large pores through the stack to facilitate rapid diffusion. There are cross members that extend from the solid metal connections through some of the open porous area to further increase the internal surface area. The mass of reactants diffuse and to some extent slightly flow within the open porous structure. The openings of the structured wall vary from about 25 microns to about 500 microns. The ODH catalyst may coat the entire surface area of the structured wall 606.
The bulk flow region 603 in the process microchannel 602 has a height of 0.75 mm. The bulk flow region 603 reduces the impediment to flow resistance and allows the reactants to diffuse into the open structured walls 606 to access the catalyst. The length of the process microchannel 602 is 56 inches (142.2 cm). The channel width is 0.25 inches (0.64 cm).
The thermal resistance layer 608 has the same construction as the structured wall 606 (except that no catalyst is present). The thermal resistance layer 608 has a thickness of is 0.5 mm thick and is separated by wall 609 from the structured wall 606 and by wall 610 from the heat exchange channel 604.
The following chemical reactions are conducted:
1. C6H5CH2CH3+0.5O2→C6H5CH═CH2+H2O
2. C6H5CH═CH2+6O2→8CO+4H2O
3. C6H5CH═CH2+10O2→8CO2+4H2O
Reaction 1 is the main reaction.
The catalyst kinetics are shown below:
The parameters are given in the following Table.
The reaction rates are in kmol/mg-cat. The catalyst loading in the structured wall 606 is 1.365E+05 g-cat/m3 as experimentally demonstrated.
Simulations to evaluate the impact of the thermal resistance layer 608 are based on the following assumptions:
The reaction contact time is based on the volume defined by the total internal reactor volume inclusive of the structured walls 606 and bulk flow region 603 for process flow.
-
- Wall temperature 380° C.—as maintained by the boiling of a hot oil such as Therminol or Dowtherm, or the convective heat transfer of a fluid
- Reaction nominal temperature of 420° C.
- Ethylbenzene (EB) to O2 ratio=1.8 (O2 fed as air)
- Outlet pressure set to 1 atm
The concentration of the feed is given in the table below:
The heat removal rate is first estimated using a two-dimensional model of the process microchannel only. The structured wall catalyst has an effective thermal conductivity of 4 W/m-K. The wall temperature is maintained at a constant 420° C. and the feed inlet is also 420° C. The channel geometry is shown in
The heat flux profile for the flow of heat through the heat transfer wall wherein the catalyst structure is for a catalyst with 1× kinetics and a contact time of 200 ms is shown in
In the next step of the design, the thermal resistance or heat resistance layer 608 is added between the process microchannel 602 and the heat exchange channel 604. This is shown in
The required features of the heat resistance layer are estimated by one-dimensional heat conduction calculations. It is assumed that the effective thermal conductivity of the heat resistance layer 608 is constant k. The actual value may be calculated if the structure of the layer is known. The thickness of heat resistance layer 608 is assigned as H. The heat flux is determined from the temperature difference using the equation in
If the required heat flux Q is known, the value of the effective thermal conductivity of the heat resistance layer 608 can be determined given the thickness of the thermal resistance layer 608. The range of the heat flux may be from about 1.0E5 to about 1.0E6 W/m2. The thickness of the heat resistance layer 608 may be in the range from about 0.02 to about 0.08 inches (about 0.508 to about 2.032 mm). The effective thermal conductivities of the thermal resistance layer are reported in the following table. This table shows that if higher level of heat removal is desired, the thermal resistance layer should be either more conductive or fabricated using a material with a higher thermal conductivity. This may be accomplished by creating fewer voids in the strips or shims that may be used to form the thermal resistance layer 608. If the desired heat removal rate is 1.0E5 W/m2, the thermal conductivity may be from 1.27 to 5.08 W/m-K for a thermal resistance layer having a thickness from about 0.02 to about 0.08 inch (about 0.508 to about 2.032 mm). If the openness of the shim is 0.5 (that is 50% metal and 50% void), the effective thermal conductivity of the thermal resistance layer may be about one-fourth of that of the base material, which in this case is steel. The effective thermal conductivity may be about 4 W/m-K.
The table below shows reactor performance at four contact times. The catalyst activity in these models is 50% (or 0.5×) of the reported level. The thermal resistance layer is 0.02 inch (0.508 mm) thick and the thermal conductivity is 2.23 W/m-K.
Trends identified from these results may include:
-
- There exists a range of flow rates within which the reactor performance is stable.
- The maximum temperate increases as the contact time gets shorter.
- The location of maximum temperature shifts downstream as the contact time gets shorter.
- Ethylene conversion is low at short contact time, but the maximum temperature remains high. This trend shows the importance of further increases to the effective thermal conductivity of the structured wall 606 for supporting the catalyst.
The temperature predictions for a 2000 ms contact time are plotted in
The heat flux through the heat transfer wall at a contact time of 2000 ms is shown in
Even at modest levels of ethylbenzene conversion, the temperature in catalyst structure is significant. The temperature rises with more active catalysts. As such it may be advantageous to tailor the catalyst loading density along the reactor length to reduce the temperature rise. This may be achieved by using different patterns of the structured walls at different axial positions so that the surface area to volume is lower in the front of the reactor and higher near the end of the reactor. Another way to boost the ethylbenzene conversion while controlling temperature rise may be to tailor the thermal resistance of the thermal resistance layer along the reactor length. Based on the temperature profile for the 1000 ms contact time case, the reaction temperature in most of the reactor may be lower than the target level. As such, the thermal resistance in the second half of the reactor may be lowered in order to raise the reaction temperature to a temperature near the desired level.
Example 10This example shows that reactor performance may be improved by varying thermal resistance along the length of the process microchannel. The catalyst structure is divided into several sections along the process microchannel. The thermal resistance layer is also divided into the same number of sections. The details of catalyst activity and thermal resistance in each section are given in the following table.
The results show improvement in reactor performance by grading both the catalyst to reduce the activity near the front and by increasing the amount of thermal resistance (i.e., reducing the thermal conductivity of the thermal resistance layer) in the thermal resistance layer near the end of the reactor. The conversion increases with only a modest reduction to selectivity and minor increase in the maximum temperature. The temperature profiles are shown in
The catalyst structure is divided into several sections along the length of the process microchannel. The thermal resistance layer is also divided into the same number of sections. The details of catalyst activity and thermal resistance in each section are given in the following table.
The modest change in the catalyst loading in the first section shifts the maximum hot spot downstream. The temperature profiles for the contact time of 200 ms are shown in
CFD simulations are carried out to examine how reactor temperature responds to changes of operating parameters. The operating parameter reviewed for this study is the feed temperature. At time zero, the reactor is at steady state with the process feed stream temperature at 410° C. Then, the feed temperature is raised to 420° C. This temperature change leads to subsequent changes in reactor performance, temperature and other variables until a new steady state, if any, is reached. In order to obtain details of how the reactor responds to this change, catalyst temperature is monitored at five locations as illustrated in the following
Other conditions include:
-
- Catalyst activity is 50% of the original
- Contact time: 1000 ms
- Heat resistance layer thickness: 0.02 inch (0.508 mm)
- Effective thermal conductivity of heat resistance layer: 1 W/m-K
- Uniform catalyst activity and thermal resistance of the heat resistance layer along the reactor length
The temperatures at the five locations on the catalyst are plotted in
The table below compares the performance of three CFD cases. First case is steady state model with feed temperature at 410° C., and the second case is also steady state case with feed temperature at 420° C. The third case is transient simulation wherein the feed temperature is changed from 410° C. to 420° C. at time zero at 95 seconds after the temperature change of the process feed stream. The reactor almost reaches steady state after 95 seconds. The maximum temperature overshoots one degree and the oxygen conversion is a few percent higher. The reactor operation is robust to the perturbation with the use of the thermal resistance layer to create a lower coolant temperature (380° C. for the reported simulations) and a warmer and stable reaction operating temperature.
While the invention has been explained in relation to various embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.
Claims
1-148. (canceled)
149. An apparatus, comprising:
- a process microchannel, the process microchannel containing a catalyst;
- a heat exchange channel; and
- a heat transfer wall positioned between the process microchannel and the heat exchange channel, the heat transfer wall comprising at least one thermal resistance layer.
150. The apparatus of claim 149 wherein the thermal resistance layer is positioned on the heat transfer wall and/or embedded within the heat transfer wall.
151. The apparatus of claim 149 wherein the thermal resistance layer comprises a vacuum, a gaseous material, a liquid and/or a solid material.
152. The apparatus of claim 149 wherein the thermal resistance layer comprises a solid material which contains void spaces, openings and/or through holes.
153. The apparatus of claim 149 wherein the thermal resistance layer comprises one or more strips or shims which contain void spaces, openings and/or through holes.
154. The apparatus of claim 149 wherein the thermal resistance layer comprises one or more strips or shims with grooves formed in the strip.
155. The apparatus of claim 149 wherein the thermal resistance layer comprises one or more strips or shims, each of the shims having a first surface and a second surface, and grooves formed in the first surface and/or the second surface.
156. The apparatus of claim 149 wherein the process microchannel comprises at least one structured wall.
157. The apparatus of claim 149 wherein the heat transfer wall forms an interior wall of the process microchannel and one or more shims are positioned on said interior wall, the one or more shims containing void spaces, openings and/or through holes.
158. The apparatus of claim 157 wherein a the catalyst is supported by the one or more shims.
159. The apparatus of claim 149 wherein the process microchannel has an internal dimension of width or height of up to about 10 mm.
160. The apparatus of claim 149 wherein the process microchannel has a length in the range up to about 10 meters.
161. The apparatus of claim 149 wherein the process microchannel is made of a material comprising: steel; monel; inconel; aluminum; titanium; nickel; copper; brass; an alloy of any of the foregoing metals; ceramics; glass; quartz; silicon; or a combination of two or more thereof.
162. The apparatus of claim 149 wherein the process microchannel and/or heat exchange channel contain internal surface features for imparting a disruptive flow to fluid flowing in the process microchannels and/or heat exchange channels.
163. The apparatus of claim 149 wherein the heat exchange channel is a microchannel.
164. The apparatus of claim 149 wherein the heat exchange channel is made of a material comprising: steel; monel; inconel; aluminum; titanium; nickel; copper; brass; an alloy of any of the foregoing metals; ceramics; glass; quartz; silicon; or a combination of two or more thereof.
165. The apparatus of claim 149 wherein the heat transfer wall is made of a material comprising: steel; monel; inconel; aluminum; titanium; nickel; copper; brass; an alloy of any of the foregoing metals; ceramics; glass; quartz; silicon; or a combination of two or more thereof.
166. The apparatus of claim 149 wherein the heat transfer wall and/or thermal resistance layer comprise one or more sub-assemblies, each sub-assembly comprising two or more shims stacked one above another with one or more void spaces positioned between the shims.
167. The apparatus of claim 149 wherein one or more staged addition channels are adjacent the process microchannel.
168. A microchannel reactor comprising the apparatus of claim 149.
169. An apparatus, comprising:
- a plurality of the microchannel reactors of claim 168 positioned in a vessel, each microchannel reactor comprises a plurality of process microchannels, a plurality of heat exchange channels, and optionally a plurality of staged addition channels,
- the vessel being equipped with a manifold for flowing a feed to the process microchannels, a manifold for flowing product from the process microchannels, a manifold for flowing heat exchange fluid to the heat exchange channels, optionally a manifold for flowing oxygen or a source of oxygen to the staged addition channels, and a manifold for flowing heat exchange fluid from the heat exchange channels.
170. The apparatus of claim 169 wherein each microchannel reactor comprises from about 1 to about 50,000 process microchannels, and the vessel comprises from 1 to about 1000 microchannel reactors.
171. The apparatus of claim 169 wherein the process microchannels have internal dimensions of width or height of up to about 10 mm.
172. The apparatus of claim 169 wherein the process microchannels have lengths in the range up to about 10 meters.
173. The apparatus of claim 169 wherein the process microchannels are made of a material comprising: steel; monel; inconel; aluminum; titanium; nickel; copper; brass; an alloy of any of the foregoing metals; ceramics; glass; quartz; silicon; or a combination of two or more thereof.
174. The apparatus of claim 169 wherein the process microchannels and/or heat exchange channels contain internal surface features for imparting a disruptive flow to fluid flowing in the process microchannels and/or heat exchange channels.
175. The apparatus of claim 169 wherein the heat exchange channels are microchannels.
176. The apparatus of claim 169 wherein the heat exchange channels are made of a material comprising: steel; monel; inconel; aluminum; titanium; nickel; copper; brass; an alloy of any of the foregoing metals; ceramics; glass; quartz; silicon; or a combination of two or more thereof.
177. The apparatus of claim 169 wherein the staged addition channels are microchannels.
178. The apparatus of claim 169 wherein the staged addition channels are made of a material comprising: steel; monel; inconel; aluminum; titanium; nickel; copper; brass; an alloy of any of the foregoing metals; ceramics; glass; quartz; silicon; or a combination of two or more thereof.
179. A process for converting ethylbenzene to styrene in the apparatus of claim 149, the process comprising:
- flowing a feed composition comprising ethylbenzene in the process microchannel in contact with the catalyst to dehydrogenate the ethylbenzene and form a product comprising styrene;
- exchanging heat between the process microchannel and the heat exchange channel; and
- removing product from the process microchannel.
180. The process of claim 179 wherein the catalyst is a dehydrogenation catalyst and the process is a dehydrogenation process, the process microchannel being heated by heat being transferred from the heat exchange channel through the heat transfer wall to the process microchannel.
181. The process of claim 179 wherein the catalyst is an oxidative dehydrogenation catalyst and the process is an oxidative dehydrogenation process, the process microchannel being cooled by heat being transferred from the process microchannel through the heat transfer wall to the process microchannel.
182. The process of claim 180 wherein the temperature in the heat exchange channel is higher than the temperature in the process microchannel.
183. The process of claim 181 wherein the temperature in the heat exchange channel is lower than the temperature in the process microchannel.
184. The process of claim 179 wherein a tailored thermal profile is established along the length of the process microchannel.
185. A process for converting ethane to ethylene in the apparatus of claim 149, the process comprising:
- flowing a feed composition comprising ethane in the process microchannel in contact with the catalyst to dehydrogenate the ethane and form a product comprising ethylene;
- exchanging heat between the process microchannel and the heat exchange channel; and
- removing product from the process microchannel.
186. The process of claim 185 wherein the catalyst is a dehydrogenation catalyst and the process is a dehydrogenation process, the process microchannel being heated by heat being transferred from the heat exchange channel through the heat transfer wall to the process microchannel.
187. The process of claim 185 wherein the catalyst is an oxidative dehydrogenation catalyst and the process is an oxidative dehydrogenation process, the process microchannel being cooled by heat being transferred from the process microchannel through the heat transfer wall to the process microchannel.
188. The process of claim 186 wherein the temperature in the heat exchange channel is higher than the temperature in the process microchannel.
189. The process of claim 187 wherein the temperature in the heat exchange channel is lower than the temperature in the process microchannel.
190. The process of 185 wherein a tailored thermal profile is established along the length of the process microchannel.
Type: Application
Filed: Dec 2, 2010
Publication Date: May 12, 2011
Inventors: Anna Lee Tonkovich (Dublin, OH), Kai Tod Paul Jarosch (Bexley, OH), Bin Yang (Columbus, OH), Francis P. Daly (Delaware, OH), Thomas P. Hickey (Dublin, OH), Jeffrey Marco (South Charleston, OH), Timothy J. LaPlante (Columbus, OH), Richard Q. Long (New Albany, OH)
Application Number: 12/958,461
International Classification: C07C 5/367 (20060101); B01J 19/00 (20060101); C07C 5/333 (20060101);
