INTEGRATED PROCESSES AND SYSTEMS FOR REFORMING AND ISOMERIZING HYDROCARBONS

Abstract

Processes and systems are provided for reforming and isomerizing hydrocarbons to produce octane upgraded hydrocarbons. The process involves providing a reforming feedstream to a reforming zone containing a reforming catalyst and operating the reforming zone at reforming conditions including reforming pressure in a range of from about 1 to about 18 atmospheres to generate a reforming zone effluent. The reforming zone effluent is separated to form a net gas stream comprising primarily hydrogen and a liquid reforming product stream, and then providing the net gas stream and an isomerization feedstream to an isomerization zone containing an isomerization catalyst. The isomerization zone is operated at an isomerization pressure that is greater than the reforming pressure, to produce an isomerization zone effluent. The system for reforming and isomerizing hydrocarbons includes a reforming zone containing a reforming catalyst, a reforming separator, an isomerization zone containing an isomerization catalyst, and an isomerization separator.

Description

TECHNICAL FIELD

The present disclosure generally relates to processes and systems for conversion of hydrocarbons and, more particularly, relates to integrated processes and systems for reforming and isomerizing hydrocarbons to produce aromatic and branched hydrocarbons.

BACKGROUND

Catalytic reforming and catalytic isomerization are two widely used processes for “upgrading” hydrocarbons, i.e., rearranging the structure of the hydrocarbons so they are useful for blending and formulation of high octane gasoline products. The traditional gasoline blending pool normally includes C₄ and heavier hydrocarbons having boiling points of less than 205° C. (401° F.) at atmospheric pressure. Preferably, high octane gasoline products have an octane rating, more specifically a Research Octane Number (RON), of from about 90 to about 101.

Mixtures of hydrocarbons comprising primarily C₇ and heavier hydrocarbons may be octane upgraded by reforming, which means converting paraffin and naphthene hydrocarbons to aromatic hydrocarbons. On the other hand, C₅ hydrocarbons (i.e., pentane) are not readily converted into aromatics and, therefore, normal C₅ hydrocarbons are typically octane upgraded by converting them to branched-chain C₅ hydrocarbons. Furthermore, while normal C₆ hydrocarbons (i.e., hexane) may be reformed to C₆ aromatic hydrocarbons, i.e., benzene, the health concerns related to benzene make isomerization of C₆ hydrocarbons to branched-chain C₆ hydrocarbons preferable to reforming. Accordingly, in industry practice, the octane number of C₅-C₆ hydrocarbons (i.e., C₅-C₆ paraffins) is generally upgraded by isomerizing the straight chain hydrocarbons thereof to form branched-chain C₅-C₆ hydrocarbons (i.e., branched C₅-C₆ paraffins) such as isopentane, dimethylbutane and methylpentane.

Combination processes involving reforming and isomerization of naphtha range feedstocks have been developed. In some such processes, such feedstocks are first subjected to reforming, followed by separation of a C₅-C₆ paraffin fraction from the reformate product, then isomerizing the C₅-C₆ paraffins fraction to upgrade the octane number of these components and recovering a C₅-C₆ isomerate liquid which may be blended with the reformate product. Other combination processes first subject the naphtha range feedstock to distillation to produce separate fractions, including a lighter fraction which is fed to the isomerization zone and a heavier fraction that is provided to the reforming zone. Sometimes the reformate product of such combined processes is subjected to further separation and conversion, which produces additional C₅-C₆ paraffins for recycling to the isomerization zone.

Various aspects inherent in each of the reforming and isomerization reactions have been the basis of modifications to combined processes that enhance their integration and reduce the amount and/or size of required apparatus. For example, since the reforming reaction is a hydrogen-producing reaction, the effluent from a reforming zone contains hydrogen, which, after separation, may be provided to the isomerization zone thereby reducing the amount of fresh hydrogen feed required. Accordingly, in some modified combination processes the reforming and isomerization effluents are combined and then a hydrogen-containing stream is separated from the combined effluent stream and recycled to the isomerization zone. Since existing combination processes still require significant quantities of raw materials and energy, as well as a myriad of equipment and devices that, in turn, require substantially sized areas for installation and operation, improvements that further increase efficiency would be welcomed by industry. For example, further reduction of raw material and energy consumption through additional reuse and recycle of material streams among process units in the system, or providing material streams and energy to other processes and systems that might otherwise be discarded as by-product or waste may further increase efficiency. Also, by reducing the number and size of apparatus required to generate products of equivalent quality through eliminating unnecessary separation, recycle or purification steps, capital costs as well as the size of the required footprint of the overall system may be reduced.

Accordingly, it is desirable to provide integrated processes and systems for reforming and isomerizing hydrocarbons to more efficiently produce octane upgraded aromatic and branched hydrocarbons. In addition, it is desirable to provide integrated processes and systems that require fewer process steps and fewer system apparatus while still producing hydrocarbons having improved octane numbers. Furthermore, other desirable features and characteristics of the integrated processes and systems contemplated herein will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings.

BRIEF SUMMARY

Processes and systems for reforming and isomerizing hydrocarbons are provided. In an exemplary embodiment, a process includes the steps of: providing a reforming feedstream to a reforming zone containing a reforming catalyst; operating the reforming zone at reforming conditions that comprise a reforming pressure in a range of from about 1 to about 18 atmospheres to generate a reforming zone effluent; separating the reforming zone effluent to form a net gas stream comprising primarily hydrogen and a liquid reforming product stream; providing the net gas stream and an isomerization feedstream to an isomerization zone containing an isomerization catalyst; and operating the isomerization zone at isomerization conditions that comprise an isomerization pressure that is greater than the reforming pressure, to produce an isomerization zone effluent.

Another embodiment of the process provides a process for reforming and isomerizing hydrocarbons, comprising the steps of: providing a reforming feedstream to a reforming zone containing a reforming catalyst; operating the reforming zone at reforming conditions that comprise a reforming pressure in a range of from about 1 to about 18 atmospheres to generate a reforming zone effluent; and separating the reforming zone effluent to form a net gas stream comprising primarily hydrogen and a liquid reforming product stream. In this embodiment, the process further includes compressing the net gas stream; providing the net gas stream and an isomerization feedstream to an isomerization zone containing an isomerization catalyst; operating the isomerization zone with a single pass through of the net gas stream and at isomerization conditions that comprise an isomerization pressure that is greater than the reforming pressure and is in a range of from greater than about 18 to about 70 atm, to produce an isomerization zone effluent; and separating the isomerization zone effluent to form a total net gas stream and a liquid isomerization product stream. Additionally, at least a portion of the total net gas stream is compressed to form compressed total net gas, the steps of compressing the net gas stream and compressing at least a portion of the total net gas stream are performed using a single power source to operate independent compressors to compress each of the net gas and total net gas streams.

In still another embodiment, a system is provided for reforming and isomerizing hydrocarbons that includes: a reforming zone configured for containing a reforming catalyst and having a reforming feedstream inlet and a reforming zone effluent outlet; a reforming separator having an inlet in fluid communication with the reforming zone effluent outlet of the reforming zone and having at least a net gas outlet and a liquid reforming product outlet; an isomerization zone configured for containing an isomerization catalyst and having an isomerization feedstream inlet, a net gas inlet in fluid communication with the net gas outlet of the reforming separator, and an isomerization zone effluent outlet; an isomerization separator having an inlet in communication with the isomerization zone effluent outlet of the isomerization zone and having a total net gas outlet and a liquid isomerization product outlet.

BRIEF DESCRIPTION OF THE DRAWINGS

The processes and systems contemplated herein will hereinafter be described in conjunction with the following FIGURE which is a schematic diagram of an exemplary embodiment of the integrated processes and systems described herein for reforming and isomerizing hydrocarbons.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the processes and systems disclosed herein or the application and uses of the processes and systems. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

Generally, the processes and systems contemplated herein and described in further detail below are integrated processes and systems for concurrently reforming and isomerizing hydrocarbons to efficiently produce hydrocarbons having improved octane numbers. The presently described processes and systems for concurrently reforming and isomerizing hydrocarbons are integrated in various ways relating to streamlining the process streams and reducing the amount of system apparatus required to convert hydrocarbons to higher octane hydrocarbons.

Exemplary embodiments of the integrated processes and systems for reforming and isomerizing hydrocarbons will now be described with reference to the FIGURE. The FIGURE is a schematic diagram of an exemplary embodiment of a system 10 for reforming and isomerizing hydrocarbons. More particularly, in one exemplary embodiment, a reforming feedstream 12 is provided to a reforming zone 14 containing a reforming catalyst (not shown per se). The reforming and isomerization zones 14, 18 are generally operated concurrently. Furthermore, as shown in the FIGURE, the reforming zone 14 typically includes a reforming reactor 20 configured for containing a reforming catalyst and having a reforming feedstream inlet 22 and a reforming zone effluent outlet 24.

It should be understood that, although not shown in the FIGURE or described in great detail herein, the reforming zone 14, as well as other process zones to be described hereinafter, are not limited to a single reaction or other process vessel, but rather, each zone includes any and all typical apparatus required for, and ancillary to, performing the desired process. Such apparatus includes for example, but without limitation: reaction vessels, conduits, heat exchangers, mass exchange vessels, separation vessels, reboilers, recycle conduits, valves, temperature measurement and control apparatus, safety devices, condensers, compressors, etc. Furthermore, the process zones are not limited to one of any type of apparatus. Although not shown per se in the FIGURE, the reforming zone 14, for example, may comprise a plurality of reforming vessels or reactors (see, e.g., reforming reactor 20), each containing a reforming catalyst, as well as one or more heaters, conduits, valves, etc. Furthermore, although not shown, in some embodiments of the processes and apparatus described herein, the reforming zone 14 may also include a heat exchanger for heating the reforming feedstream 12 prior to entry into the reforming zone 14.

Furthermore, a wide variety of reforming zone feedstreams 12 may be used. In general, the reforming zone feedstream 12 contains primarily from about C₇ to about C₁₂ hydrocarbons with a boiling point range from about 82 to about 240° C. As with most mixtures of hydrocarbons, refining and other processes tend to concentrate the desired species of hydrocarbon in the mixture based on its intended use or anticipated further processing, but these mixtures quite often contain some small amount of hydrocarbon species in addition to those desired. This is one reason why hydrocarbon mixtures are often characterized by boiling ranges instead of or in addition to a range of hydrocarbon species contained therein. Accordingly, it should be understood that, as used herein, a mixture of hydrocarbons or a hydrocarbon stream described as containing or comprising “primarily” a specified hydrocarbon or range of carbon-numbered hydrocarbons means that the mixture or stream of hydrocarbons being described may also contain very small amounts of hydrocarbons besides the specified hydrocarbon or outside the stated carbon number range, without altering the general characteristics (e.g., boiling point) of the mixture or stream of hydrocarbons being described.

For example, the description that the reforming zone feedstream 12 contains “primarily” from about C₇ to about C₁₂ hydrocarbons with a boiling point range from about 82 to about 240° C. means that the reforming zone feedstream 12 contains at least 70 weight percent of hydrocarbon molecules each having from about 7 to about 12 carbon atoms with, possibly, very small amounts of hydrocarbon molecules each having less than about 7 carbon atoms, as well as very small amounts of hydrocarbon molecules each having more than 12 carbon atoms, such that the boiling point remains in the range of from about 82 to about 240° C. Similarly, the description that a net gas stream comprises primarily hydrogen means that the net gas stream contains at least 70 weight percent of hydrogen with, possibly, very small amounts of hydrocarbon molecules each having one or two, or more, carbon atoms.

Generally, suitable reforming zone feedstreams may be generated from various hydrocarbon sources using various separation techniques such as are known now, or in the future. As understood by persons of ordinary skill in the relevant art, there are many possible hydrocarbon sources including, without limitation, crude oil from oil and gas extraction activities, hydrocarbon fractions produced during crude oil refining activities, condensate streams generated by hydraulic fracturing activities, recycled hydrocarbons derived from recovery and processing of used hydrocarbon products, as well as the many intermediate hydrocarbon products and streams that are produced during processing of the aforesaid hydrocarbon sources. Hydrocarbon mixtures containing primarily C₇-C₁₂ hydrocarbons with a boiling point range from about 82 to about 240° C. that are suitable for use as reforming zone feedstreams 12 often result from processing the aforesaid hydrocarbon sources, as well as those which may be discovered or developed in the future.

One example of a hydrocarbon stream suitable for use as a reforming zone feedstream 12 may be derived from a full range naphtha feedstream that has been produced by processing any of the hydrocarbon sources described above. Such a full range naphtha feedstream may contain primarily C₅-C₁₂ hydrocarbons and have a boiling point from about 80 to about 240° C., and is typically further separated into two or more refined fractions such as, without limitation: a light naphtha fraction, a heart-cut naphtha fraction, and a heavy naphtha fraction. The light naphtha fraction may contain primarily C₅ and C₆ hydrocarbons (i.e., pentane and hexane) and have a boiling point of from about 80 to about 140° C. The heart-cut naphtha may contain primarily C₇-C₈ hydrocarbons and have a boiling point from about 130 to about 175° C., and preferably from about 145 to 165° C. Finally, the higher-boiling heavy naphtha fraction may contain primarily C₁₀ hydrocarbons, with significant quantities of C₉ and C₁₁-C₁₂ hydrocarbons depending primarily on a petroleum refiner's overall product balance. The boiling point of this heavy naphtha may be from about 160 to about 240° C., and preferably from about 170 to about 240° C.

With reference now back to the FIGURE, and as already stated, the reforming feedstream 12 suitable for use in connection with the system 10 described herein comprise primarily C₇-C₁₂ hydrocarbons and have a boiling point range from about 82 to about 240° C. Such a reforming feedstream 12 may, for example, comprise the heart-cut and heavy naphtha fractions generated as described above.

The reforming zone 14 is operated at reforming conditions that typically comprise a reforming pressure in a range of from about 1 atmosphere to about 18 atmospheres (absolute) (“atm”). For instance, without limitation, the reforming pressure may be in a range of from about 1 to about 15 atm, or from about 1 to about 10 atm, or from about 4 to about 18 atm, or even from about 4 to about 12 atm, to generate a reforming zone effluent 26. Suitable operating temperatures for the reforming zone 14 are generally in the range of from about 260 to about 560° C. A variety of reactions occur in the reforming zone 14 including naphthene dehydrogenation and paraffin dehydrocyclization and isomerization, whereby the resulting reforming zone effluent 26 has an upgraded octane number. Hydrogen is generated within the reforming zone 14, but additional hydrogen may be directed, if necessary, to the reforming zone 14 in an amount sufficient to correspond to a ratio of from about 0.1 to about 10 moles of hydrogen, total generated and added, per mole of reforming feedstream 12.

The reforming feedstream 12 may be contacted with the reforming catalyst (not shown) in the reforming zone 14 in upflow, downflow, or radial-flow mode. The volume of the contained reforming catalyst corresponds to a liquid hourly space velocity of from about 1 to about 40 hr⁻¹. The catalyst is typically contained in a fixed-bed reactor or in a moving-bed reactor whereby catalyst may be continuously withdrawn and added. Such configuration is associated with catalyst-regeneration options known to those of ordinary skill in the art, such as: (1) a semi-regenerative unit containing fixed-bed reactors that maintain operating severity by increasing temperature, eventually shutting the unit down for catalyst regeneration and reactivation; (2) a swing-reactor unit, in which individual fixed-bed reactors are serially isolated by manifold arrangements as the catalyst become deactivated and the catalyst in the isolated reactor is regenerated and reactivated while the other reactors remain on-stream; (3) continuous regeneration of catalyst withdrawn from a moving-bed reactor, with reactivation and substitution of the reactivated catalyst, permitting higher operating severity by maintaining high catalyst activity through regeneration cycles of a few days; or: (4) a hybrid system with semi-regenerative and continuous-regeneration provisions in the same unit. A preferred embodiment includes a semi-regenerative fixed- bed reactor with catalyst operating at relatively low pressures to realize high yields of desired C₅₊ hydrocarbon product associated with more moderate catalyst deactivation. As used herein, the term “C₅₊ hydrocarbon” includes linear, branched and aromatic hydrocarbons having 5 or more carbon atoms in each molecule. In some embodiments, the total reforming effluent 26 may be provided to a heat exchanger (not shown, but already mentioned above) to exchange heat with the reforming feedstream 12.

The reforming catalyst (not shown per se in the FIGURE) is not particularly limited and may be any catalyst capable of catalyzing the conversion of linear and branched C₇ and heavier hydrocarbons to aromatic C₇ and heavier hydrocarbons. As used herein, the term “C₇ and heavier hydrocarbons” includes linear, branched and aromatic hydrocarbons having 7 or more carbon atoms in each molecule. For example, the reforming catalyst may comprise a supported platinum-group metal component. This component comprises one or more platinum-group metals, with a platinum component being preferred. The platinum may exist within the catalyst as a compound such as an oxide, sulfide, halide, or oxyhalide, in chemical combination with one or more other ingredients of the catalytic composite, or as an elemental metal. Best results are obtained when substantially all of the platinum exists in the catalytic composite in a reduced state. The preferred platinum component generally comprises from about 0.01 to about 2 mass % of the catalytic composite, preferably about 0.05 to about 1 mass %, calculated on an elemental basis.

The catalyst may contain other metal components known to modify the effect of the preferred platinum component. Such metal modifiers may include Group IVA (14) metals, other Group VII (8-10) metals, rhenium, indium, gallium, zinc, uranium, dysprosium, thallium and mixtures thereof. In one embodiment, the metal modifier is a tin component. Catalytically effective amounts of such metal modifiers may be incorporated into the catalyst by any means known in the art.

In some embodiments, the reforming catalyst may be a dual-function composite containing a metallic hydrogenation-dehydrogenation component on a refractory support that provides acid sites for cracking and isomerization. The refractory support of such a reforming catalyst should be a porous, adsorptive, high-surface-area material which is uniform in composition without composition gradients of the species inherent to its composition. In an embodiment, refractory supports contain one or more of: (1) refractory inorganic oxides such as alumina, silica, titania, magnesia, zirconia, chromia, thoria, boria or mixtures thereof; (2) synthetically prepared or naturally occurring clays and silicates, which may be acid-treated; (3) crystalline zeolitic aluminosilicates, either naturally occurring or synthetically prepared such as FAU, MEL, MFI, MOR, MTW (IUPAC Commission on Zeolite Nomenclature), in hydrogen form or in a form which has been exchanged with metal cations; (4) non-zeolitic molecular sieves,; (5) spinels such as MgAl₂O₄, FeAl₂O₄, ZnAl₂O₄, CaAl₂O₄; and (6) combinations of materials from one or more of these groups.

The reforming catalyst optimally contains a halogen component. The halogen component may be fluorine, chlorine, bromine, iodine or mixtures thereof. Chlorine is the preferred halogen component. The halogen component is generally present in a combined state with the inorganic-oxide support. The halogen component is preferably well dispersed throughout the catalyst and may comprise from more than about 0.2 to about 15 mass %, calculated on an elemental basis, of the final catalyst.

In some alternative embodiments, the reforming catalyst may comprise a large-pore molecular sieve, which is defined as a molecular sieve having an effective pore diameter of about 7 angstroms or larger. Examples of large-pore molecular sieves which might be incorporated into the present catalyst include LTL, FAU, AFI and MAZ (IUPAC Commission on Zeolite Nomenclature) and zeolite-beta. In such embodiments, the reforming catalyst contains a nonacidic L-zeolite (LTL) and an alkali-metal component as well as a platinum-group metal component. In order to be “nonacidic,” the zeolite will have substantially all of its cationic exchange sites occupied by non-hydrogen species. Preferably the cations occupying the exchangeable cation sites will comprise one or more of the alkali metals including lithium, sodium, potassium, rubidium, cesium and mixtures thereof, with potassium being preferred, although other cationic species may be present. The L-zeolite should also be composited with a binder to provide a convenient form for use as a suitable reforming catalyst. Suitable binders include any refractory inorganic oxide binder such as one or more of silica, alumina or magnesia, for example, without limitation.

Returning now to the FIGURE, the reforming zone 14 of the exemplary embodiment of the system 10 now being described includes a separation zone 28. The reforming zone effluent 26 is separated in the separation zone 28 to form a net gas stream 30 comprising primarily hydrogen and a liquid reforming product stream 32. Upon leaving the separation zone 28, the liquid reforming product stream 32 comprises a gasoline fraction having an Research Octane Number (RON) in a range of from about 90 to about 101 that can be separated out further downstream. As shown in the FIGURE, the separation zone 28 may comprise a reforming separator 28 having an inlet 34 in fluid communication with the reforming zone effluent outlet 24 of the reforming reactor 20 and having at least a net gas outlet 36 and a liquid reforming product outlet 38.

As shown in the FIGURE, an isomerization feedstream 16 is provided to an isomerization zone 18 containing an isomerization catalyst (not shown per se). Furthermore, as shown in the FIGURE, the isomerization zone 18 comprises an isomerization reactor 40 configured for containing an isomerization catalyst and having an isomerization feedstream inlet 42, a net gas inlet 44 in fluid communication with the net gas outlet 36 of the reforming separator 28, and an isomerization zone effluent outlet 46.

The isomerization zone 18 also requires hydrogen. Since the net gas stream 30 derived from separation of the reforming effluent 26 comprises hydrogen, in accordance with the integrated processes and system 10 described herein, the net gas stream 30 is provided to the isomerization zone 18. The isomerization zone 18 is operated at isomerization conditions to produce an isomerization zone effluent 48. The isomerization zone effluent 48 typically comprises a mixture of primarily normal pentane, normal hexane, isopentane, dimethylbutane and methylpentane and hydrogen, with smaller amounts of C₄ and lighter hydrocarbons, as well as small amounts of C₇ and heavier hydrocarbons. As used herein, the term “C₄ and lighter hydrocarbons” includes linear and branched hydrocarbons having 4 or fewer carbon atoms in each molecule.

The net gas stream 30 contains hydrogen derived at least in part from reactions in the reforming zone 14, as well as smaller amounts of C₄ and lighter hydrocarbons and, therefore may advantageously be used to supplement or replace an independent hydrogen source to the isomerization zone 18. Since the reforming zone 14 is operated at a relatively low pressure and the net gas stream 30 is not subjected to recontact with the liquid reforming product stream 32 as in some existing processes, the net gas stream will also contain small amounts of C₅-C₇ and heavier hydrocarbons, The net gas stream 30 may be provided to the isomerization zone 18, either separately from the isomerization feedstream 16 (as shown), or by first mixing with the isomerization feedstream 16 and then providing the mixed stream to the isomerization zone 18.

As explained previously, and while not shown specifically in the Figure, the isomerization zone 18 may include not only one or more isomerization reactors 40, each containing isomerization catalyst, but also other apparatus such as heaters, heat exchangers, conduits, valves, temperature measurement and control apparatus, safety devices, etc., as required for, and ancillary to, performing the desired isomerization reaction. In the embodiment shown in the FIGURE, the isomerization zone 18 also includes a separation zone 50 that receives the isomerization zone effluent 48 and produces a total net gas stream 52 and a liquid isomerization product stream 54. More particularly, as shown in the FIGURE, the separation zone 50 may include an isomerization separator 50 having an inlet 56 in communication with the isomerization zone effluent outlet 46 of the isomerization reactor 40 and having a total net gas outlet 58 and a liquid isomerization product outlet 60.

The total net gas stream 52 derived from the isomerization zone effluent 48 comprises primarily hydrogen from the reforming zone effluent 26 and not consumed in the isomerization zone 18. The liquid isomerization product stream 54 also derived from the isomerization zone effluent 48 typically comprises a mixture of primarily normal pentane, normal hexane, isopentane, dimethylbutane and methylpentane.

As another example of ancillary apparatus that is typically included in the isomerization zone 18, while not shown in the FIGURE, a control valve may be included to meter the addition of hydrogen to the isomerization zone 18 directly, or to the isomerization feedstream 16 prior to entry into the isomerization zone 18. The hydrogen concentration in the isomerization zone effluent 48 or one of the outlet stream fractions derived therefrom is monitored by a hydrogen monitor (also not shown) and the control valve setting position is adjusted to maintain the desired hydrogen concentration. The hydrogen concentration at the effluent is calculated on the basis of total effluent flow rates. The molar ratio of hydrogen to hydrocarbon in the isomerization zone effluent 48 should be from about 0.05 to about 5.0. Hydrogen will be consumed in the isomerization zone 18, the net total of which is often referred to as the stoichiometric hydrogen requirement associated with a number of side reactions that occur. An amount of hydrogen in excess of the stoichiometric amounts for the side reactions may be maintained in the isomerization zone 18 to provide good stability and conversion by compensating for variations in feed stream compositions that alter the stoichiometric hydrogen requirements.

It is noted that other combined processes and systems for reforming and isomerizing hydrocarbons may generate a net gas stream for use as a hydrogen-containing feedstream by first combining a reforming zone effluent with an isomerization zone effluent and then separating that combined effluent stream to form a net gas stream comprising primarily hydrogen and a combined liquid product stream. In such other combined processes and systems, the resulting net gas stream may be provided to the isomerization zone; however, the resulting net gas stream is often first purified to remove the non-hydrogen components therefrom and increase the hydrogen concentration thereof. Such purification is typically accomplished by “recontacting” the combined effluent net gas stream with the combined liquid product stream one or more times prior to being provided to the isomerization zone. As is easily recognized, recontacting the net gas stream for purification requires additional apparatus such as a cooler, a vessel and associated regeneration equipment for each stage of recontact. In contrast, the integrated processes and system 10 contemplated and described herein do not require combining the reforming and isomerization effluents 26, 48 prior to separating and generating the net gas stream 30 comprising hydrogen and, furthermore, no recontacting of the net gas stream 30 is performed prior to providing the net gas stream to the isomerization zone 18. Without wishing to be bound in any way by theory, it is believed that some purification of the net gas stream occurs in the present integrated processes and system 10 in the separation zone 50 that separates the liquid isomerization product stream 54 from the isomerization zone effluent 48. This means that some apparatus (cooler, vessel and associated compression equipment) typically included in other combined processes and systems are not necessary and do not need to be included in the present integrated processes and systems.

Additionally, it is noted that the integrated processes and systems contemplated and described herein operate the isomerization zone 18 with a single pass-through of the hydrogen/net gas stream 30. A single pass-through of the hydrogen/net gas stream 30 means that there is no separate recycle compressor required in the isomerization zone 18 to recycle hydrogen from the isomerization separator 50 to the isomerization reaction reactor 40. In other combined processes and systems, the isomerization zone often includes separation of the isomerization zone effluent to form another net gas stream, at least a portion of which is recycled to the isomerization zone using additional apparatus such as a recycle gas cooler, a recycle gas drier, conduits and valves, none of which are necessary in the present integrated processes and systems.

Suitable isomerization feedstreams 16 comprise primarily C₅-C₆ hydrocarbons, and more specifically, primarily C₅-C₆ normal paraffins. Some common hydrocarbon processing product streams useful as such isomerization feedstreams 16 include, without limitation, light natural gasoline, light straight run naphtha, gas oil condensate, light raffinates, light reformate, light hydrocarbons, and straight run distillates having a boiling point of less than about 100° C. and containing substantial quantities of C₄-C₆ paraffins. The light naphtha fraction described earlier as derived from separation of a full range naphtha feedstream and containing primarily C₅-C₆ hydrocarbons (i.e., pentane and hexane) and having a boiling point of from about 80 to about 140° C. would, for example, serve advantageously as a suitable isomerization feedstream 16 for the integrated processes and systems described herein. These hydrocarbon processing product streams may be derived from any number of hydrocarbon sources, such as those described earlier in connection with suitable reforming feedstreams 12.

The isomerization zone 18 is generally operated at isomerization conditions that maximize the production of C₅-C₆ isoalkane products from the isomerization feedstream 16. In accordance with the integrated processes and systems contemplated and described herein, such isomerization conditions comprise an isomerization pressure that is greater than the reforming pressure in the reforming zone 14. In addition, suitable isomerization pressures are in a range of from greater than about 18 to about 70 atm (absolute). For instance, without limitation, the isomerization pressure may be in a range of from greater than about 18 to about 50 atm, or from greater than about 18 to about 45 atm, or from about 20 to about 50 atm, or even from about 20 to about 30 atm, to generate the isomerization zone effluent 48.

Suitable operating temperatures for the isomerization zone 18 are generally in the range of from about 40 to about 235° C. Lower reaction temperatures are generally preferred since they usually favor equilibrium mixtures of isoalkanes versus normal alkanes. Lower temperatures are particularly useful in processing feeds composed of C₅ and C₆ paraffin hydrocarbons where the lower temperatures favor equilibrium mixtures having the highest concentration of the most branched isoalkanes. When the isomerization feedstream 16 is primarily C₅ and C₆ paraffin hydrocarbons, isomerization temperatures in the range of from about 60 to about 160° C. are preferred. The feed rate to the isomerization zone 18 may vary over a wide range. These conditions include liquid hourly space velocities ranging from about 0.5 to about 12 hr⁻¹, such as, for example, from about 1 and about 6 hr⁻¹.

The isomerization catalyst (not shown per se in the FIGURE) is not particularly limited and may be any catalyst that is capable of catalyzing the conversion of linear C₅-C₆ hydrocarbons to branched C₅-C₆ hydrocarbon isomers. For example, various catalysts comprising platinum and aluminum, with or without an additional halogen component, have been known to catalyze the isomerization of C₄-C₇ hydrocarbons. A highly active isomerization catalyst comprising alumina with from about 0.01 to about 25 weight percent (wt %) platinum and from about 2 to about 10 wt % of a chloride component is capable of isomerizing C₄-C₇ hydrocarbons in the presence of very little hydrogen. Another exemplary embodiment includes a high chloride catalyst on an aluminum base containing platinum. The aluminum is an anhydrous gamma-alumina with a high degree of purity. The catalyst may also contain other platinum group metals, i.e., noble metals, excluding silver and gold, and selected from the group consisting of platinum, palladium, germanium, ruthenium, rhodium, osmium, and iridium. These metals demonstrate differences in activity and selectivity such that platinum has now been found to be the most suitable for this process. The platinum component may exist within the final catalytic composite as an oxide or halide or as an elemental metal. The presence of the platinum component in its reduced state has been found most advantageous.

Additionally, suitable isomerization catalysts include a type of catalyst that comprises a sulfated support of an oxide or hydroxide of a Group IVB (IUPAC 4) metal, such as zirconium oxide, titanium oxide or hydroxide, at least a first component which is a lanthanide element or yttrium component, and at least a second component being a platinum-group metal component. It is believed that these isomerization catalysts are more tolerant of the presence of sulfur and water in the isomerization zone 18. In particularly advantageous embodiments, the first component of such isomerization catalyst contains at least ytterbium and the second component is platinum. The lanthanide element or yttrium component can be incorporated into the catalyst in any amount that is catalytically effective, suitably from about 0.01 to about 10 mass % lanthanide, or yttrium, or mixtures thereof, in the catalyst on an elemental basis. In one embodiment, about 0.5 to about 5 mass % lanthanide or yttrium is used, calculated on an elemental basis. The second component, a platinum-group metal, may exist within the final catalytic composite as a compound such as an oxide, sulfide, halide, oxyhalide, etc., in chemical combination with one or more of the other ingredients of the composite or as the metal. Suitable amounts of the platinum-group metal are in a range of from about 0.01 to about 2 wt % platinum-group metal component, on an elemental basis. It is particularly advantageous when substantially all of the platinum- group metal is present in the elemental state. This isomerization catalyst optionally contains an inorganic-oxide binder, such as alumina. The support, sulfate, metal components and optional binder may be composited in any order effective to prepare a suitable isomerization catalyst.

Returning now to the FIGURE, in some embodiments of the system 10 described herein, both the liquid reforming product stream 32 and the liquid isomerization product stream 54 are provided to a product separation zone 62, such as a debutanizer. The liquid reforming product stream 32 and the liquid isomerization product stream 54 may be provided separately to the product separation zone 62, or they may be first combined together and then provided to the product separation zone 62 as a single combined feedstream. The product separation zone 62 is operated to generate a product stream 66 enriched in C₅ and heavier hydrocarbons and an overhead stream 68 enriched in hydrogen, C₄ and lighter hydrocarbons. Conditions for the operation of the product separation zone 62 include pressures ranging from about 6 to about 40 atmospheres. Some embodiments utilize pressures from about 13 to about 34 atmospheres. Suitable designs for rectification columns and separator vessels suitable for the product separation zone 62 are well known to those skilled in the art. As shown schematically in the Figure, the product separation zone 62 typically includes at least one combined product separator 62 having an inlet 64 in fluid communication with both the liquid reforming product outlet 38 of the reforming separator 28 and the liquid isomerization product outlet 60 of the isomerization separator 50, and also having a product stream outlet 70 and an overhead stream outlet 100. As with other process zones, the product separation zone 62 may include one or more such separation columns or devices, as well as a reboiler and various conduits, valves and control devices (not shown per se). The product stream 66 enriched in C₅ and heavier hydrocarbons may be subjected to further processing, such as separations or gasoline blending.

In some exemplary embodiments, after the isomerization zone effluent 48 has been separated to produce the total net gas stream 52 which comprises primarily hydrogen, at least a portion of the total net gas stream 52 is compressed to form compressed total net gas 72. As shown in the FIGURE, the system 10 also includes a post-isomerization compressor 74 for compressing the total net gas stream 52. The post-isomerization compressor 74 has a total net gas inlet 76 in fluid communication with the total net gas outlet 58 of the isomerization separator 50 and a compressed total net gas outlet 78.

Prior to providing the total net gas stream 52 to the post-isomerization compressor 74, a portion 80 of total net gas stream 52 may be recycled by combining the portion 80 with the net gas stream 30 prior to the post-reforming compressor 86. The compressed net gas (in stream 30) leaving the post-reforming compressor 86 is provided to the isomerization zone 18. It is noted that the recycled portion 80 of total net gas 52 is not purified by any separate process steps prior to being recycled to the isomerization zone 18. The remaining portion of the total net gas stream 52 (i.e., the portion not recycled) is provided to the post-isomerization compressor 74 as already described. This partial total net gas recycle scheme may be useful, for example, when the net gas stream 30 derived from the reforming zone effluent 26 contains too little hydrogen to effectively operate the isomerization zone 18.

In another exemplary embodiment, at least another portion 102 of the compressed total net gas 72 derived from the isomerization zone effluent 48 is provided to a hydrogen-consuming process that is not already part of the integrated processes and systems contemplated and described above. While there are no particular limitations on the type of hydrogen-consuming process that would benefit from receiving at least a portion 102 of the compressed total net gas stream, such hydrogen-consuming processes may, for example, be a diesel hydrotreating process 82, or a naphtha hydrotreating process 84, or both, as shown in phantom in the FIGURE.

In some embodiments, the net gas stream 30 derived from the reforming zone effluent 26 is compressed and then provided to the isomerization zone 18. As shown in the FIGURE, the system 10 includes a post-reforming compressor 86 having a net gas inlet 88 in fluid communication with the net gas outlet 36 of the reforming separator 28 and a compressed net gas outlet 90 in fluid communication with the net gas inlet 44 of the isomerization reactor 40. Furthermore, in some such embodiments, as shown in the FIGURE, the integrated system 10 has a single power source 92 capable of operating the independent post-isomerization and post-reforming compressors 74, 86, respectively, to separately compress the total net gas stream 52 and the net gas stream 30 , respectively. The single power source 92, such as a single motor, and the post-isomerization and post-reforming compressors 74, 86 may all be mounted on a multi-compressor apparatus, such as a frame or platform 94 as shown schematically in the FIGURE. In this manner, a single power source 92 is used to compress each of the net gas stream 30 and total net gas stream 52, thereby decreasing the amount of required apparatus from two power sources to one.

Additionally, in some embodiments, operating the diesel hydrotreating process 82 generates a DHT recycle gas stream 96, which may be compressed and returned to the diesel hydrotreating process 82. In such embodiments, a diesel recycle compressor 98 for compressing the DHT recycle gas stream 96 may also be included on the multi-compressor apparatus 94, along with the other compressors 74, 86 and the single power source 92. In such an arrangement of apparatus, the single power source 92 would be in communication with each of the compressors 74, 86, 98 and capable of operating each separately and concurrently to compress the respective streams 30, 52, 96, respectively. In this manner, a single power source 92 would be used to compress each of the net gas stream 30, the total net gas stream 52, and the DHT recycle gas stream 96, thereby decreasing the amount of required apparatus from three power sources to one. As will be easily recognized by persons of ordinary skill, further embodiments of the integrated system contemplated and described herein could include more than two or three independent compressors mounted on the frame or platform 94 and operated by the single power source 92, thereby providing further capital cost and operational savings.

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the methods and apparatus described herein in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the methods and apparatus. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the methods and apparatus as set forth in the appended claims.

Claims

1. A process comprising the steps of:

providing a reforming feedstream to a reforming zone containing a reforming catalyst;

operating the reforming zone at reforming conditions that comprise a reforming pressure in a range of from about 1 to about 18 atmospheres to generate a reforming zone effluent;

separating the reforming zone effluent to form a net gas stream comprising primarily hydrogen and a liquid reforming product stream;

providing the net gas stream and an isomerization feedstream to an isomerization zone containing an isomerization catalyst; and

operating the isomerization zone at isomerization conditions that comprise an isomerization pressure that is greater than the reforming pressure, to produce an isomerization zone effluent.

2. The process according to claim 1, wherein the step of separating the reforming zone effluent to form a liquid reforming product stream comprises forming a liquid reforming product stream with a Research Octane Number (RON) in a range of from about 90 to about 101.

3. The process according claim 1, wherein the isomerization pressure is in a range of from greater than about 18 to about 70 atm.

4. The process according to claim 1, wherein the step of operating the isomerization zone is performed with a single pass-through of the net gas stream.

5. The process of claim 1, further comprising the step of separating the isomerization zone effluent to form a total net gas stream and a liquid isomerization product stream.

6. The process according to claim 5, further comprising the steps of:

providing both the liquid reforming product stream and the liquid isomerization product stream to a separation zone; and

operating the separation zone to generate a product stream enriched in C5 and heavier hydrocarbons and an overhead stream enriched in C4 and lighter hydrocarbons.

7. The process according to claim 5, further comprising the step of recycling at least a portion of the total net gas to the net gas stream prior to the step of providing the net gas stream to the isomerization zone.

8. The process according to claim 5, further comprising: wherein the steps of compressing the net gas stream and compressing at least a portion of the total net gas stream are performed using a single power source to operate independent compressors to compress each of said streams.

compressing the net gas stream prior to the step of providing the net gas stream to the isomerization zone; and

compressing at least a portion of the total net gas stream to form compressed total net gas;

9. The process according to claim 8, further comprising the step of providing at least a portion of the compressed total net gas to a hydrogen-consuming process.

10. The process according to claim 9, wherein the hydrogen-consuming process comprises a naphtha hydrotreating process, a diesel hydrotreating process, or both.

11. The process according to claim 9, wherein the hydrogen-consuming process comprises a diesel hydrotreating process, and wherein the steps of compressing the net gas stream, compressing at least a portion of the total net gas stream, and compressing the recycle gas stream from the diesel hydrotreating process are all performed using a single power source to operate independent compressors to compress each of said streams.

the process further comprises the steps of:

operating the diesel hydrotreating process to generate a recycle gas stream;

compressing the recycle gas stream; and

recycling the recycle gas stream back to the diesel hydrotreating process;

12. An integrated process for reforming and isomerizing hydrocarbons comprising the steps of:

providing a reforming feedstream to a reforming zone containing a reforming catalyst;

operating the reforming zone at reforming conditions that comprise a reforming pressure in a range of from about 1 to about 18 atmospheres to generate a reforming zone effluent;

separating the reforming zone effluent to form a net gas stream, comprising primarily hydrogen, and a liquid reforming product stream;

compressing the net gas stream;

providing the net gas stream and an isomerization feedstream to an isomerization zone containing an isomerization catalyst;

operating the isomerization zone with a single pass-through of the net gas stream and at isomerization conditions that comprise an isomerization pressure that is greater than the reforming pressure and is in a range of from greater than about 18 to about 70 atm to produce an isomerization zone effluent;

separating the isomerization zone effluent to form a total net gas stream and a liquid isomerization product stream; and

compressing at least a portion of the total net gas stream to form compressed total net gas,

wherein the steps of compressing the net gas stream and compressing at least a portion of the total net gas stream are performed using a single power source to operate independent compressors to compress each of the net gas and total net gas streams.

13. A system for reforming and isomerizing hydrocarbons, the system comprising:

a reforming reactor configured for containing a reforming catalyst and having a reforming feedstream inlet and a reforming zone effluent outlet;

a reforming separator having an inlet in fluid communication with the reforming zone effluent outlet of the reforming zone and having at least a net gas outlet and a liquid reforming product outlet;

an isomerization reactor configured for containing an isomerization catalyst and having an isomerization feedstream inlet, a net gas inlet in fluid communication with the net gas outlet of the reforming separator, and an isomerization zone effluent outlet;

an isomerization separator having an inlet in communication with the isomerization zone effluent outlet of the isomerization zone and having a total net gas outlet and a liquid isomerization product outlet.

14. The system according to claim 13, wherein the isomerization reactor comprises two or more isomerization reactors, each capable of withstanding isomerization pressures of from greater than about 18 to about 70 atmospheres.

15. The system according to claim 13, further comprising a post-reforming compressor having a net gas inlet in fluid communication with the net gas outlet of the reforming separator and a compressed net gas outlet in fluid communication with the net gas inlet of the isomerization reactor.

16. The system according to claim 15, further comprising a post-isomerization compressor having a total net gas inlet in fluid communication with the total net gas outlet of the isomerization separator, and a compressed total net gas outlet.

17. The system according to claim 16, further comprising a single power source which provides power for operating each of the post-reforming and post-isomerization compressors.

18. The system according to claim 17, further comprising a multi-compressor apparatus on which the single power source and each of the post-reforming and post-isomerization compressors are mounted and wherein each of the post-reforming and post-isomerization compressors is in communication with the power source.

19. The system according to claim 18, wherein the multi-compressor apparatus further comprises a diesel recycle compressor mounted thereon and also in communication with the power source, for compressing a gaseous stream derived either from operation of the system or operation of a another separate system.

20. The system according to claim 13, further comprising a combined product separator having an inlet in fluid communication with both the liquid reforming product outlet of the reforming separator and the liquid isomerization product outlet of the isomerization separator, and having a product stream outlet and an overhead stream outlet.