SLURRY HYDROCONVERSION WITH PITCH RECYCLE
Systems and methods are provided for performing slurry hydroconversion of feeds that include substantial amounts of 1050° F+ (566° C+) components. The productivity of the slurry hydroconversion reaction is improved by recycling slurry hydroconversion pitch or bottoms back to the slurry hydroprocessing reaction system. The mass flow rate of the recycle stream can correspond to 50% or more of the mass flow rate of the fresh feed to the reaction system, and the recycle stream can include more than 50 wt % of 566° C+ components. It has been discovered that using a substantial recycle stream composed of a majority of unconverted 566° C+ bottoms can increase the productivity of the slurry hydroprocessing reaction system when operating at a net conversion relative to 524° C (975° F) of less than 90 wt %. Additionally, by using a recycle stream composed of a majority of 566° C+ components, the amount of lower boiling components (in the heavy hydrocarbon feed and/or in the recycle stream) that are exposed multiple times to the slurry hydroprocessing environment is reduced or minimized This can allow for formation of slurry hydroconversion products with increased amounts of vacuum gas oil boiling range components.
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Systems and methods are provided for performing slurry hydroconversion of heavy oil feeds with recycle of the pitch or hydroconversion bottoms.
BACKGROUND OF THE INVENTIONDeveloping effective methods for processing and/or disposition of feeds including substantial amounts of 1050° F+ (566° C+) components is an ongoing challenge. Such heavy hydrocarbon feeds can have a relatively low value without processing, as the value of such feeds for use in asphalt or fuel oil is limited. Unfortunately, such heavy hydrocarbon feeds also have a tendency to cause fouling or other degradation in processing equipment. As a result, attempting to process such heavy hydrocarbon feeds can require substantial equipment investment in addition to resource investments for reagents and solvents used to process the feeds.
Various types of coking are examples of common methods for processing of heavy hydrocarbon feeds. Coking can be effective for processing of a wide variety of types of heavy hydrocarbon feeds without requiring excessive equipment costs and/or excessive use of additional resources. However, as the boiling range of a feed increases, the hydrogen content of heavy hydrocarbon feed tends to be reduced, leading to increasing amounts of coke production for heavier feeds. Such coke production limits total liquid yields and can further constrain the types of liquid products generated. For example, for feeds including substantial amounts of 566° C+ components, the coke yields can correspond to 30 wt % or more of the feedstock. When coking is used at remote geographic location, this substantial coke production can pose additional difficulties, as outlets for sale and/or disposal of the coke may be limited.
Coke production also contributes to the difficulties when attempting to hydroprocess feedstocks with substantial contents of 566° C+ components. Although hydroprocessing typically results in lower coke formation than coking, such coke formation can still lead to rapid fouling and/or degradation of hydroprocessing equipment, including hydroprocessing catalyst. As a result, mitigation of coke formation is a primary concern when attempting to hydroprocess a feed with a substantial content of 566° C+ components.
Some conventional methods for hydroprocessing of heavy feeds have focused on strategies related to using a solvent and/or recycle stream to reduce the relative amount of 566° C+ components present in the reaction environment. Conventionally, it is believed that reducing the amount of 566° C+ components in the reaction environment can reduce or minimize coke formation. Thus, in such strategies, the solvent or recycle stream includes a majority of components that boil below 566° C. This assists with maintaining a lower relative content of 566° C+ components in the reaction environment. However, this also leads to additional conversion of the recycle stream to lower boiling, lower value products. Additionally, for slurry hydroprocessing reactors, it is conventionally believed that bottoms recycle leads to reduced reactor productivity.
U.S. Pat. No. 5,972,202 describes an example of this strategy for reducing the relative amount of high boiling components in the reaction environment. In U.S. Pat. No. 5,972,202, slurry hydrocracking is performed using a recycle stream corresponding to 65 wt % or less of the fresh feed to the slurry hydrocracking stage. The recycle stream includes a small amount of 524° C+ material as part of a pitch fraction, while the majority of the recycle stream corresponds to vacuum gas oil boiling range stream described as an aromatic oil. The recycle of the aromatic oil is described as preventing the accumulation of asphaltenes on additive particles in the slurry hydroprocessing environment.
U.S. Pat. No. 6,004,453 describes a similar strategy for performing slurry hydrocracking with a recycle stream comprising a majority of vacuum gas oil boiling range components. It is noted that having a majority of the recycle stream correspond to vacuum gas oil boiling range components is described as being necessary for inclusion of pitch in the recycle stream, in order to prevent coke formation.
U.S. Pat. No. 4,252,634 describes slurry hydroprocessing of a full range bitumen where the volume of the recycle stream is at least twice the volume of the fresh feed delivered to the reactor. The amount of distillate and/or gas oil in the recycle stream is greater than 50 wt %, with the pitch in the recycle stream being defined based on cut point of 524° C. Thus, the portion of 566° C+ components in the recycle is substantially below 50 wt %. The substantial recycle is described as being useful for preventing coke formation.
U.S. Pat. No. 8,435,400 provides an example of why conventional recycle methods have focused on recycle of lower boiling range portions. In U.S. Pat. No. 8,435,400 slurry hydroprocessing of vacuum resid boiling range feeds is performed in a multi-stage reaction system. Some examples describe performing slurry hydroprocessing with recycle of a bottoms or resid stream from the final stage to an earlier stage, as opposed to having a recycle stream including a majority of lower boiling components. The recycle stream corresponded to roughly 15 wt % of the fresh feed into the reaction system. In the examples, it was reported that operating with recycle required a significantly higher catalyst concentration than once-through operation in order to maintain the same level of feed conversion at a given temperature. Operating with recycle at this increased catalyst concentration appeared to provide no benefit or improvement for the productivity of the reaction system.
U.S. Pat. No. 5,374,348 describes another example of conventional recycle during slurry hydrocracking of feed. A feed including a 524° C+ portion is processed in a slurry hydrocracking environment in the presence of additive (catalyst) particles. The hydrocracked effluent is fractionated to form a 450° C+ fraction that also includes a substantial portion of the additive particles. Up to 40 wt % of the 450° C+ fraction (relative to the weight of fresh feed) is recycled to the slurry hydroconversion reactor. The recycle stream allowed for a reduction in the amount of additive particles required for performing the slurry hydrocracking. Based on the examples, it appears that the reactor productivity after addition of the recycle stream was similar or slightly decreased relative to operating without the recycle stream.
In other types of hydroprocessing environments, use of bottoms recycle would be expected to either reduce reactor productivity or have no impact. U.S. Pat. No. 4,983,273 describes a fixed bed hydrocracking process for use with various feeds. The reaction system includes a hydrotreatment stage and a hydrocracking stage. A series of examples of hydrocracking of a vacuum gas oil boiling range feed are provided. In examples where bottoms recycle is used to return unconverted feed to the hydrotreatment stage, a decrease in reactor productivity for the hydrotreatment stage was observed. In examples where bottoms recycle was used to return unconverted feed to the hydrocracking stage, reactor productivity was substantially not changed, but the yield of distillate boiling range products was increased at the expense of naphtha products and light ends products. An improvement in denitrogenation with recycle to the hydrocracking reactor was also reported.
The other conventional strategy for mitigating coke formation is related to removal of asphaltenes from a recycle stream prior to introducing the recycle stream back into a reactor. Conventionally, it is believed that one of the sources of coke formation is due to loss of ability to maintain asphaltenes in solution in a heavy feedstock. By removing asphaltenes from the processing environment, this incompatibility issue is removed, and therefore coke formation in the reaction environment can be reduced or minimized While removal of asphaltenes can be effective, the asphaltene content can correspond to 15 wt % or more of the 566° C+ portion of a feed. Thus, removal of asphaltenes from a recycle stream represents a substantial loss of carbon to low (or possible zero) value products before considering any other losses due to hydroprocessing.
U.S. Pat. No. 9,982,203 provides an example of this type of strategy, where an ebullating bed reactor is used to hydroconvert an atmospheric resid or vacuum resid feed. In some configurations, a recycle stream is returned to the reactor that is formed by deasphalting the hydroconversion bottoms to form deasphalted oil. By definition, a deasphalted oil recycle stream contains a minimized amount of asphaltenes. It is noted that this type of configuration would present additional challenges when attempting to use slurry hydroprocessing, as any catalyst in the hydroconversion bottoms would preferentially be separated into the deasphalter rock, and not the deasphalted oil.
U.S. Pat. No. 4,411,768 describes another example of asphaltene removal. In U.S. Pat. No. 4,411,768, removal of coke precursors is described as enabling higher conversion rates while avoiding reactor fouling. An ebullating bed reactor with a bottoms recycle loop is used for hydroconversion of a heavy feed. Prior to recycle of the hydroconversion bottoms, the bottoms are chilled to a temperature that causes precipitation and/or separation of all toluene insolubles and n-heptane insolubles (i.e., asphaltenes) in the recycle stream. As noted above, this represents a substantial rejection of material, as the n-heptane insolubles can correspond to 15 wt % or more of the 566° C+ portion of a feed, and the toluene insolubles can correspond to an additional 5 wt % or more of the 566° C+ portion of a feed.
U.S. Pat. No. 4,808,289 is directed to a method for performing hydroconversion in an ebullating bed unit while avoiding the need to remove coke precursors (such as asphaltenes) from any recycle streams. The solution provided in U.S. Pat. No. 4,808,289 is to perform a limited amount of recycle of flash drum bottoms, where the recycle stream includes at least 50 vol % gas oil boiling range components. In other words, the need to remove asphaltenes is avoided by using the first strategy described above, so that the recycle stream includes 50 vol % or more of lower boiling components.
What is needed are systems and methods that can allow for hydroconversion of heavy feeds that can mitigate reactor fouling while minimizing loss of reactor productivity and also minimizing losses of portions of a feed to lower value products, including reducing or minimizing overcracking.
SUMMARYIn various aspects, a method for performing slurry hydroconversion is provided. The method includes exposing a heavy hydrocarbon feed and a pitch recycle stream to a slurry hydroprocessing catalyst under slurry hydroconversion conditions in a reaction zone to form a slurry hydroprocessing effluent. The slurry hydroconversion conditions can include a net conversion of 60 wt % to 89 wt % relative to 524° C. The heavy hydrocarbon feed can include 50 wt % or more of 566° C+ components. Optionally, the heavy hydrocarbon feed and the pitch recycle stream can have a combined feed ratio of 1.5 to 3.5. The method can further include separating the pitch recycle stream from the slurry hydroconversion effluent. The pitch recycle stream can include more than 50 wt % of 566° C+ components.
All numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.
OverviewIn various aspects, systems and methods are provided for performing slurry hydroconversion of feeds that include substantial amounts of 1050° F+ (566° C+) components. The productivity of the slurry hydroconversion reaction is improved by recycling slurry hydroconversion pitch or bottoms back to the slurry hydroprocessing reaction system. The mass flow rate of the recycle stream can correspond to 50% or more of the mass flow rate of the fresh feed to the reaction system, and the recycle stream can include more than 50 wt % of 566° C+ components. It has been discovered that using a substantial recycle stream composed of a majority of unconverted 566° C+ bottoms can increase the productivity of the slurry hydroprocessing reaction system when operating at a net conversion relative to 524° C (975° F) of less than 90 wt %. For example, the net conversion can be 50 wt % to 89 wt % relative to 524° C, or 60 wt % to 89 wt %, or 70 wt % to 89 wt %. Additionally, by using a recycle stream composed of a majority of 566° C+ components, the amount of lower boiling components (in the heavy hydrocarbon feed and/or in the recycle stream) that are exposed multiple times to the slurry hydroprocessing environment is reduced or minimized This can allow for formation of slurry hydroconversion products with increased amounts of vacuum gas oil boiling range components.
Slurry hydroconversion is a hydroprocessing method that can achieve high conversion of heavy hydrocarbon feeds to liquid hydrocarbons without rejecting carbon. Conventionally, slurry hydroconversion has had only limited use, due in part to difficulties in balancing the high pressure and/or high liquid residence time required to achieve high conversion while avoiding reaction conditions that result in either foaming or fouling in the reactor.
A slurry hydroprocessing reactor operates as a bubble column, so that both gas and liquid are present within the reactor volume during operation. This creates a tension during operation when managing the gas superficial velocity and the liquid superficial velocity in the reactor. If the gas superficial velocity becomes too high relative to the liquid superficial velocity, the liquid phase in the reactor can begin to foam, which quickly leads to an inability to operate effectively. Unfortunately, reducing the gas superficial velocity by reducing the rate of introduction of hydrogen treat gas leads to lower partial pressures of hydrogen, which can result in increased coke formation. Additionally, increasing the liquid superficial velocity by increasing the fresh feed rate, at constant temperature, typically results in reduced conversion.
One option for increasing the liquid superficial velocity without requiring an increase in the fresh feed rate is to recirculate a portion of the total liquid effluent back to the reactor. This can be accomplished using a pump-around recirculation loop. In this discussion, recirculation of liquid effluent portion to a reactor is defined as returning to the reactor a portion of liquid effluent that has substantially the same composition as the liquid within the reactor. In other words, the liquid effluent is not fractionated and/or chemically modified prior to returning the liquid effluent to the reactor. Recirculation of liquid effluent can improve the hydrodynamics of operation within a slurry hydroprocessing reactor. Such recirculation can reduce or minimize the potential for “foaming” in the slurry hydroconversion environment. When determining “per pass” conversion within the reactor, the reactor is defined to include any recirculation loops. Thus, liquid within a recirculation loop, by definition, is liquid that remains in the reactor. Any conversion performed on liquid that has traveled through a recirculation loop is therefore considered part of the “per pass” conversion.
In contrast to recirculation, recycle of liquid to the slurry hydroconversion reactor corresponds to recycle of a liquid fraction that has a different composition than the liquid phase in the reactor. Conventionally, however, recycle of the bottoms from a hydroconversion reaction is believed to not be beneficial when processing a heavy feedstock in a slurry hydroprocessing reaction environment. This is due in part to lowering of reactor productivity when using recycle streams that are small relative to the rate of fresh feed in the reactor. When using these relatively small recycle amounts, incorporation of a substantial amount of bottoms in the recycle can lead to increased coking. In order to avoid this coking, the temperature needs to be lowered to avoid reactor fouling, but this also requires a corresponding decrease in fresh feed rate in order to maintain a constant level of feed conversion. In order to avoid this choice between increased reactor fouling and decreased reactor productivity, conventional recycle streams for slurry hydrocracking units have focused on use of streams where 50 wt % or more of the recycle stream corresponds to vacuum gas oil boiling components (and/or other lower boiling range components).
In contrast to the above, it has been discovered that when performing conversion of a sufficiently heavy feedstock, such as a heavy hydrocarbon feedstock including more than 50 wt % of 566° C+ components, or more than 50 wt % of 593° C+ components, an unexpected productivity increase can be achieved by operating a slurry hydroprocessing reactor (or reaction system) with a substantial recycle of pitch or unconverted bottoms, so long as the recycle stream is also sufficiently heavy. The substantial recycle can correspond to a recycle stream having a mass flow rate corresponding to 50% or more of the mass flow rate of fresh feed delivered to the reaction system, such as 50% to 250% of the amount of fresh feed, or 50% to 200%, or 60% to 250%, or 60% to 200%. Such recycle rates correspond to a combined feed ratio of 1.5 to 3.5, or 1.5 to 3.0, or 1.6 to 3.5, or 1.6 to 3.0. Additionally, the substantial recycle can correspond to a pitch or unconverted bottoms stream that includes more than 50 wt % of 566° C+ components, or 60 wt % or more. Optionally, the substantial recycle can correspond to a pitch or unconverted bottoms stream that includes 50 wt % or more of 593° C+ components, or 60 wt % or more.
It has been discovered that recycling pitch (unconverted slurry hydroconversion product) can significantly improve the economics of the slurry hydroconversion process when performing hydroconversion at net conversion levels of less than 90 wt % relative to 524° C. In particular, recycling pitch can unexpectedly improve reactor productivity, allowing an increase in the unit capacity at constant 524° C net conversion. This is in contrast to conventional recycle methods, where using recycle streams containing 50 wt % or more of lower boiling components results in loss of reactor productivity (i.e., the fresh feed rate is reduced at constant net conversion at constant temperature). For example, when operating slurry hydroconversion with pitch recycle, the amount of net conversion relative to 524° C can be 60 wt % to 89 wt %, or 70 wt % to 89 wt %, or 60 wt % to 85 wt %, or 70 wt % to 85 wt %, or 75 wt % to 89 wt %. It is noted that the conversion at 566° C will be higher than the conversion at 524° C. The per-pass conversion can be lower, corresponding to 60 wt % or less conversion relative to 524° C.
Without being bound by any particular theory, it is believed that using a sufficiently high amount of a sufficiently heavy recycle can reduce the formation of incompatible compounds in the reactor environment. It is believed that the formation of incompatible compounds is reduced or minimized in part by reducing exposure of lower boiling components to the reaction environment multiple times, and in part by reducing the severity (i.e., reducing the per-pass conversion) of the reaction environment.
Under conventional conditions for slurry hydroconversion of 60 wt % or more of a feedstock relative to 524° C, the fresh feed into the reaction environment can often contain a substantial portion of lower boiling compounds, such as vacuum gas oil boiling range components (343° C-566° C components). It is believed that additional (secondary) cracking of such vacuum gas oil boiling range compounds increases the likelihood of resid (566° C+) components becoming incompatible with the liquid phase in the reaction environment. It is further believed that the amount of incompatible compounds generated due to overcracking of vacuum gas oil boiling range compounds within the slurry hydroprocessing reaction environment increases with increasing conversion relative to 524° C. It is believed that by increasing the amount of 566° C+ compounds in the reaction environment, and operating at moderate per-pass conversion, the problems due to incompatibility can be reduced or minimized This allows the reactor to be operated at increased productivity while maintaining reduced or minimized coke formation.
Due to the above combination of factors, using small recycle streams (regardless of composition) can tend to reduce the productivity of a slurry hydroprocessing reactor, or at best lead to no change in reactivity. When using a small recycle stream containing less than 40 wt % of the amount of fresh feed, at constant net conversion, the change in single-pass conversion in the reactor can be relatively small. As a result, introducing a small recycle stream does not provide a substantial reduction in the severity of the reaction environment. However, such small recycle streams typically also include previously processed vacuum gas oil boiling range components, which are then introduced into the reaction environment. It is believed that these previously processed vacuum gas oil boiling range components have an increased tendency to form incompatible compounds at a given level of conversion (or reaction condition severity). As a result, at constant fresh feed rate, the introduction of a small recycle stream is believed to result in either no impact on formation of incompatible compounds or an increase in formation of incompatible compounds. Thus, in order to avoid fouling, when using small recycle streams, the flow of fresh feed is reduced and/or large excesses of lower boiling components are included in the recycle stream.
By contrast, it has been discovered that using a substantially larger recycle stream, with a sufficiently large content of 566° C+ components, can provide increased reactor productivity when operating at net conversions of 60 wt % to less than 90 wt % for slurry hydroconversion of a heavy hydrocarbon feed. Without being bound by any particular theory, it is believed that the productivity benefits are based on a combination of factors that allow for operation of a slurry hydroprocessing reactor in an unexpected region of the reaction condition phase space for slurry hydroconversion. First, using a sufficiently high boiling initial feed, such as a heavy hydrocarbon feed containing 50 wt % or more of 566° C+ components, reduces or minimizes the amount of fresh feed that is susceptible to formation of incompatible compounds during a single pass through the slurry hydroconversion reactor. Second, using a recycle stream corresponding to 50 wt % or more of the fresh feed provides a sufficient amount of recycle so that the per-pass conversion can be substantially reduced. For example, by using a sufficient amount of recycle, the per-pass conversion relative to 524° C can be lower than the net conversion relative to 524° C by 15% or more, or 25% or more, or 30% or more, such as having a per-pass conversion that is lower than the net conversion by up to 50% or possibly still higher. By reducing the per-pass conversion (i.e., reducing the severity in the reactor), the amount of incompatible compounds generated in the reaction environment can be reduced. Third, by using a recycle stream containing more than 50 wt % of 1050° F+ (566° C+) components, the amount of previously processed lower boiling components introduced into the slurry hydroprocessing reaction environment can be reduced. This can further reduce or minimize generation of incompatible compounds within the reaction environment.
Based on the above factors, performing substantial recycle using a sufficiently heavy recycle stream allows for reduced formation of incompatible compounds. This reduction in formation of incompatible compounds allows the reaction system to process an unexpectedly heavy combination of feed and recycle streams while avoiding fouling and/or shutdown of the reactor due to substantial coke formation. By enabling operation in an unexpected region of the slurry hydroconversion phase space, additional benefits are also achieved. For example, by operating with a recycle stream containing a sufficiently high content of 566° C+ components, reactor productivity is increased, as an increased percentage of the reactions within the reaction environment correspond to primary cracking of 566° C+ compounds, as opposed to secondary cracking of 566° C− compounds. Such secondary cracking of 566° C− compounds is further reduced or minimized based on the lower single-pass conversion.
It is noted that the absence of any one of the multiple factors described above can inhibit or prevent the ability to access the unexpectedly desirable region of the reaction condition phase space for slurry hydroconversion. For example, if the size of the recycle stream is not sufficiently large, the reduction in per-pass conversion will not be sufficient to realize the benefits of the recycle, and instead a decrease in productivity will be observed. If the initial feedstock and/or the recycle stream does not contain a sufficiently high content of 566° C+ material, the feed itself will contain an undesirable amount of vacuum gas oil boiling range compounds that are susceptible to overcracking to form incompatible compounds.
In addition to improving reactor productivity, operating a slurry hydroprocessing reactor with pitch recycle can potentially provide various additional benefits. For example, bottoms or pitch recycle can increase the catalyst concentration in the reactor, permitting a reduction in the catalyst make-up rate and/or higher severity operation.
Still other potential benefits can include, but are not limited to: reducing or minimizing the amount of secondary cracking of primary VGO products into incompatible paraffin side chains and aromatic cores; improving VGO quality to facilitate processing in downstream units; and/or reducing hydrogen consumption and light ends production.
DefinitionsIn this discussion, unless otherwise specified, “conversion” of a feedstock or other input stream is defined as conversion relative to a conversion temperature of 524° C (975° F). Per-pass conversion refers to the amount of conversion that occurs during a single pass through a reactor/stage/reaction system. It is noted that recirculation streams (i.e., streams having substantially the same composition as the liquid in the reactor) are considered as part of the reactor, and therefore are included in the calculation of per-pass conversion. Net or overall conversion refers to the net products from the reactor/stage/reaction system, so that any recycle streams are included in the calculation of the net or overall conversion. It is noted that in all aspects described herein, the amount of conversion at 524° C is lower than the corresponding conversion at 566° C.
In this discussion, the productivity of a reactor/reaction system is defined based on the feed rate of fresh feed to the reactor/reaction system that is required in order to maintain a target level of net conversion relative to 524° C at constant temperature. An increase in fresh feed rate while maintaining net conversion at constant temperature corresponds to an increase in productivity for a reactor/reaction system.
In this discussion, primary cracking is defined as cracking of 566° C+ components in the feed. Secondary cracking refers to any cracking of 566° C− components.
In this discussion, gas holdup refers to the amount of gas present within the reactor at a given moment in time.
In this discussion, the “combined feed ratio” (or CFR) is defined as a ratio corresponding to (mass flow rate of fresh feed+mass flow rate of recycle stream)/(mass flow rate of fresh feed). Based on this definition, the combined feed ratio when no recycle is used is 1.0. When recycle is present, the relative mass flow rate of the recycle stream as a percentage of the fresh feed can be added to 1.0 to provide the combined feed ratio. Thus, when the mass flow rate of the recycle stream is 10% of the mass flow rate of the fresh feed, the CFR is 1.1. When the mass flow rate of the recycle stream is 50% of the mass flow rate of the fresh feed, the CFR is 1.5. When the mass flow rate of the recycle stream is 100% of the mass flow rate of the fresh feed, the CFR is 2.0.
In this discussion, when describing the amount of a fresh feed stream, recirculation stream, recycle stream, or other stream, the mass flow rate of the stream may also be referred to as a “weight” of the stream.
In this discussion, the Liquid Hourly Space Velocity (LHSV) for a feed or a portion of a feed to a slurry hydrocracking reactor is defined as the volume of feed per hour relative to the volume of the reactor.
In this discussion, a “Cx” hydrocarbon refers to a hydrocarbon compound that includes “x” number of carbons in the compound. A stream containing “Cx—Cy” hydrocarbons refers to a stream composed of one or more hydrocarbon compounds that includes at least “x” carbons and no more than “y” carbons in the compound. It is noted that a stream comprising Cx—Cy hydrocarbons may also include other types of hydrocarbons, unless otherwise specified.
In this discussion, “Tx” refers to the temperature at which a weight fraction “x” of a sample can be boiled or distilled. For example, if 40 wt % of a sample has a boiling point of 343° C or less, the sample can be described as having a T40 distillation point of 343° C. In this discussion, boiling points can be determined by a convenient method based on the boiling range of the sample. This can correspond to ASTM D2887, or for heavier samples ASTM D7169.
In this discussion, references to “fresh feed” to a hydroconversion stage correspond to feedstock that has not been previously passed through the hydroconversion stage. This is in contrast to recycled feed portions that are formed by fractionation and/or other separation of the products from the hydroconversion stage.
In various aspects of the invention, reference may be made to one or more types of fractions generated during distillation of a petroleum feedstock, intermediate product, and/or product. Such fractions may include naphtha fractions, distillate fuel fractions, and vacuum gas oil fractions. Each of these types of fractions can be defined based on a boiling range, such as a boiling range that includes at least 90 wt % of the fraction, or at least 95 wt % of the fraction. For example, for naphtha fractions, at least 90 wt % of the fraction, or at least 95 wt %, can have a boiling point in the range of 85° F (29° C) to 350° F (177° C). It is noted that 29° C roughly corresponds to the boiling point of isopentane, a C5 hydrocarbon. For a distillate fuel fraction, at least 90 wt % of the fraction, or at least 95 wt %, can have a boiling point in the range of 350° F (177° C) to 650° F (343° C). For a vacuum gas oil fraction, at least 90 wt % of the fraction, or at least 95 wt %, can have a boiling point in the range of 650° F (343° C) to 1050° F (566° C.). Fractions boiling below the naphtha range can sometimes be referred to as light ends. Fractions boiling above the vacuum gas oil range can be referred to as vacuum resid fractions or pitch fractions.
Another option for specifying various types of boiling ranges can be based on a combination of T5 (or T10) and T95 (or T90) distillation points. For example, in some aspects, having at least 90 wt % of a fraction boil in the naphtha boiling range can correspond to having a T5 distillation point of 29° C or more and a T95 distillation point of 177° C or less. In some aspects, having at least 90 wt % of a fraction boil in the distillate boiling range can correspond to having a T5 distillation point of 177° C or more and a T95 distillation point of 343° C or less. In some aspects, having at least 90 wt % of a fraction boil in the vacuum gas oil range can correspond to having a T5 distillation point of 343° C or more and a T95 distillation point of 566° C or less.
In this discussion, the boiling range of components in a feed, intermediate product, and/or final product may alternatively be described based on describing a weight percentage of components that boil within a defined range. The defined range can correspond to a range with an upper bound, such as components that boil at less than 177° C (referred to as 177° C−); a range with a lower bound, such as components that boil at greater than 566° C (referred to as 566° C+); or a range with both an upper bound and a lower bound, such as 343° C-566° C.
FeedstocksIn various aspects, the initial feed corresponds to a heavy hydrocarbon feed. Examples of heavy hydrocarbon feeds include, but are not limited to, heavy crude oils, distillation residues, oils (such as bitumen) from oil sands, and heavy oils derived from coal. In this discussion, a heavy hydrocarbon feed corresponds to a feed where a substantial portion of the feed has a boiling point of 1050° F (566° C) or more, or 1100° F (593° C) or more. In some aspects, 50 wt % or more of a heavy hydrocarbon feed can have a boiling point of 566° C or more, or 60 wt % or more, or 70 wt % or more, or 80 wt % or more, such as up to substantially all of the heavy hydrocarbon feed corresponding to components with a boiling point of 566° C or more. In some aspects, 50 wt % or more of a heavy hydrocarbon feed can have a boiling point of 593° C or more, or 60 wt % or more, or 70 wt % or more, or 80 wt % or more, such as up to substantially all of the heavy hydrocarbon feed corresponding to components with a boiling point of 593° C or more. In this discussion, boiling points can be determined by a convenient method, such as ASTM D2887, ASTM D7169, or another suitable standard method.
Density, or weight per volume, of the heavy hydrocarbon feed can be determined according to ASTM D287-92 (2006) Standard Test Method for API Gravity of Crude Petroleum and Petroleum Products (Hydrometer Method), and is provided in terms of API gravity. In general, the higher the API gravity, the less dense the oil. API gravity can be 15° or less, or 10° or less, or 5° or less.
Heavy hydrocarbon feeds can be high in metals. For example, the heavy hydrocarbon feed can be high in total nickel, vanadium and iron contents. In one embodiment, the heavy oil will contain at least 0.00005 grams of Ni/V/Fe (50 ppm) or at least 0.0002 grams of Ni/V/Fe (200 ppm) per gram of heavy oil, on a total elemental basis of nickel, vanadium and iron. In other aspects, the heavy hydrocarbon feed can contain at least about 500 wppm of nickel, vanadium, and iron, such as at least about 1000 wppm.
Heteroatoms such as nitrogen and sulfur are typically found in heavy hydrocarbon feeds, often in organically-bound form. Nitrogen content can range from about 0.1 wt % to about 3.0 wt % elemental nitrogen, or 1.0 wt % to 3.0 wt %, or 0.1 wt % to 1.0 wt %, based on total weight of the heavy hydrocarbon feed. The nitrogen containing compounds can be present as basic or non-basic nitrogen species. Examples of basic nitrogen species include quinolines and substituted quinolines. Examples of non-basic nitrogen species include carbazoles and substituted carbazoles.
The invention is particularly suited to treating heavy oil feedstocks containing at least 0.1 wt % sulfur, based on total weight of the heavy hydrocarbon feed. Generally, the sulfur content can range from 0.1 wt % to 10 wt % elemental sulfur, or 1.0 wt % to 10 wt %, or 0.1 wt % to 5.0 wt %, based on total weight of the heavy hydrocarbon feed. Sulfur will usually be present as organically bound sulfur. Examples of such sulfur compounds include the class of heterocyclic sulfur compounds such as thiophenes, tetrahydrothiophenes, benzothiophenes and their higher homologs and analogs. Other organically bound sulfur compounds include aliphatic, naphthenic, and aromatic mercaptans, sulfides, and di- and polysulfides.
Heavy hydrocarbon feeds can be high in n-heptane asphaltenes. In some aspects, the heavy hydrocarbon feed can contain 1 wt % to 80 wt % of n-heptane asphaltenes, or 5 wt % to 80 wt % of n-heptane asphaltenes, or 5 wt % to 60 wt %, or 5 wt % to 50 wt %, or 20 wt % to 80 wt %, or 10 wt % to 50 wt %, or 20 wt % to 60 wt %. In aspects where the heavy hydrocarbon feed includes a portion of a bitumen formed by conventional paraffinic froth treatment of oil sands, the heavy hydrocarbon feed can contain 10 wt % to 30 wt % of asphaltenes.
Still another method for characterizing a heavy hydrocarbon feed is based on the Conradson carbon residue of the feedstock, or alternatively the micro carbon residue content. The Conradson carbon residue/micro carbon residue content of the feedstock can be 5.0 wt % to 50 wt %, or 5.0 wt % to 30 wt %, or 10 wt % to 40 wt %, or 20 wt % to 50 wt %.
Slurry Hydroconversion Reaction ConditionsIn various aspects, a slurry hydroprocessing reactor (or other slurry hydroprocessing reaction system) can be operated using pitch recycle to provide improved reactor productivity while achieving conversion of less than 90 wt % (relative to 524° C) of a heavy hydrocarbon feed, such as 60 wt % to 89 wt % conversion, or 70 wt % conversion to 89 wt % conversion. The pitch recycle can correspond to 50 wt % or more of the amount of fresh feed entering the reactor (or reaction system). For example, the pitch recycle stream can correspond to 50 wt % to 250 wt % of the amount of fresh feed, or 50 wt % to 200 wt %, or 60 wt % to 250 wt %, or 60 wt % to 200 wt %, or 100 wt % to 250 wt %, or 75 wt % to 200 wt %. Such amounts for the pitch recycle stream correspond to a combined feed ratio of 1.5 to 3.5, or 1.5 to 3.0, or 1.6 to 3.5, or 1.6 to 3.0, or 2.0 to 3.5, or 1.75 to 3.0. The pitch recycle stream can include more than 50 wt % of 566° C+ components, or 60 wt % or more, such as including substantially only 566° C+ components. Optionally, the pitch recycle stream can include 50 wt % or more of 593° C+ components, or 60 wt % or more, such as including substantially only 566° C+ components.
It has been discovered that operating with substantial pitch recycle can provide a variety of unexpected advantages when performing slurry hydroconversion on a heavy hydrocarbon feed. Such advantages can include, but are not limited to, increased reactor productivity and reducing or minimizing reactor fouling. Conventionally, it is believed that avoiding coke formation and/or fouling required reducing the concentration of 566° C+ components when using recycle streams; removing asphaltenes from any recycle streams; or a combination thereof.
In particular, recycling pitch can unexpectedly improve reactor productivity, allowing an increase in the unit capacity at constant 524° C net conversion. This is in contrast to conventional recycle methods, where using recycle streams containing 50 wt % or more of lower boiling components results in loss of reactor productivity (i.e., the fresh feed rate is reduced at constant temperature). For example, when operating slurry hydroconversion with pitch recycle, the amount of net conversion relative to 524° C can be 60 wt % to 89 wt %, or 70 wt % to 89 wt %, or 60 wt % to 85 wt %, or 70 wt % to 85 wt %, or 75 wt % to 89 wt %. It is noted that the conversion at 566° C. will be higher than the conversion at 524° C. The per-pass conversion can be lower, corresponding to 60 wt % or less conversion relative to 524° C.
A goal of processing a feed under slurry hydroconversion conditions can be to convert the refractory 1050° F+ (566° C+) material which cannot be readily converted in other types of refinery processing units. In such aspects, it is therefore desirable to maximize the residence time of 566° C+ material in the reactor. To increase the 566° C+ residence time, one option can be to first distill the feed to a slurry hydroprocessing reactor to remove 566° C− material. However, even after removal of 566° C− material from the feed, a significant portion of the reactor volume is occupied by gas and/or conversion products during once-through operation. Specifically, a substantial amount of conversion of vacuum gas oil boiling range components can occur during operation at a per-pass conversion of 60 wt % or more relative to 524° C. Secondary cracking (conversion of VGO into distillate, naphtha, and gas range molecules) is undesirable since this material could be more economically processed in other refinery units such as a fixed-bed hydrocracker or fluid catalytic cracker. Such secondary cracking is particularly undesirable when partially upgrading heavy hydrocarbons, such as bitumen, into synthetic crude oils which are intended to be further processed in conventional refinery units elsewhere. Additionally, the secondary cracking results in an increased amount of gas phase material within the slurry hydroconversion reaction environment. Secondary cracking also results in increased light-ends make, with a corresponding undesirable increase in hydrogen consumption.
One alternative for reducing secondary cracking can be to increase the treat gas rate to strip more 566° C− material from the reactor liquid. Unfortunately, increasing the gas superficial velocity will also increase gas holdup at a fixed liquid superficial velocity, reducing liquid residence time and increasing the potential for foaming However, for a variety of reasons (such as limitations on reactor size or desire to avoid replacing existing equipment), increasing the treat gas rate is typically not a viable method to economically reduce secondary cracking in a slurry hydroconversion system.
High pitch recycle provides an alternative and economical method to decrease secondary cracking. Without being bound by any particular theory, pitch recycle increases the concentration of 566° C+ material in the reactor and allows a substantial portion of the pitch molecules to make multiple passes while conversion products are typically removed after a single pass. Moreover, per-pass liquid residence time is reduced, further reducing secondary cracking. As a result, the effective residence time of 566° C+ material in the reactor is increased and the effective residence time of 566° C− material is decreased. It has been discovered that his combination of increasing 566° C+ material residence time while decreasing 566° C− material residence time results in an increase in primary cracking while suppressing secondary cracking. The increase in primary cracking enables increased 566° C+ conversion at fixed reactor volume and fresh feed rate, increased fresh feed rate at fixed conversion and reactor volume, or decreased reactor volume at a fixed conversion and fresh feed rate.
Based on the above, from a reactor productivity perspective, it is desirable to increase or maximize the pitch recycle rate. As the combined feed rate (defined as mass ratio of fresh feed+recycle divided by fresh feed) increases, the reactor efficiency increases. The optimal pitch recycle rate can be determined by balancing the benefits of higher reactor efficiency against cost, product yield/quality, hydrodynamic, and reactor stability considerations.
The relative effectiveness of pitch recycle is also a function of the 566° C+ content in the recycle stream. At a constant total recycle rate, it has been discovered increasing the concentration of 566° C+ material in the recycle stream further increases reactor efficiency. Conversely, it has been discovered that if the recycle stream contains too little 566° C+ material, pitch recycle will decrease reactor efficiency, as this reduces the effective residence time of the 566° C+ material. In order to achieve improved reactor efficiency, the 566° C+ components in a recycle stream can correspond to more than 50 wt % of the recycle stream, or 60 wt % or more, or 75 wt % or more, such as up to having substantially all of the recycle stream correspond to 566° C+ material. Optionally, 50 wt % or more of the recycle stream can correspond to 593 ° C+ components, or 60 wt % or more, or 75 wt % or more, such as up to having substantially all of the recycle stream correspond to 593° C+ material.
In general, pitch recycle results in a heavier product yield slate as 650° F− (343° C−) yields are reduced compared to operation without substantial pitch recycle. Thus, pitch recycle provides a means to increase the vacuum gas oil yield from processing of a heavy hydrocarbon feed. Increasing the yield of vacuum gas oil is desirable, since it is more economical to convert vacuum gas oil material in an alternative process unit such as a fixed-bed hydrocracker or fluid catalytic cracker. Moreover, the naphtha and distillate produced by slurry hydroconversion is typically high in heteroatoms and aromatics compared to virgin material. As a result, hydroconverted naphtha and hydroconverted distillate fractions from slurry hydroconversion typically require additional processing to meet finished product specifications. Therefore, it can be desirable to reduce the yields of these products to lower levels such that they can be blended into the refinery mogas/distillate pools without additional processing. Pitch recycle also reduces the yield of low-value light ends and correspondingly lowers hydrogen consumption, further improving process economics. As the pitch recycle rate increases, the yield slate will become heavier at constant conversion.
The yields at a given recycle rate can also be shifted by adjusting the amount of 1050° F+ (566° C+) material in the recycle stream. In general, increasing the 566° C+ content of the recycle stream will result in a heavier yield slate, while decreasing the 566° C+ content of the recycle stream will result in a lighter yield slate.
The choice of recycle cut point can also impact the quality of the VGO. Recycle operation with deep vacuum distillation shifts the T50 boiling point of the VGO product higher, and pulls a significant quantity of 566° C+ molecules into the liquid product that includes the VGO. These include very low hydrogen content polynuclear aromatics. In some aspects, the net result from the above combination of factors is a liquid product from slurry hydroconversion where the 343° C-454° C boiling range fraction is higher quality and the 454° C+ boiling range fraction is lower quality (due to the presence of 566° C+ components).
In some aspects, one of the operating challenges for slurry hydroconversion is reducing or minimizing the formation of incompatible material in the reactor. Such incompatible material can deposit in the reactor, reducing the effective reactor volume, or can cause plugging in the separation/fractionation train, resulting in a unit shutdown. Some incompatible material (coke) is formed during normal operation but is controlled by operating at an appropriate hydrogen partial pressure and catalyst make-up rate.
Operation of a slurry hydroprocessing reactor with pitch recycle returns incompatible material to the reactor which could result in fouling. However, without being bound by any particular theory, it is believed that when pitch recycle is performed as described herein, the pitch recycle can unexpectedly improve the stability of slurry hydrocracking reactors by increasing the solvency (aromaticity) of the circulating feedstocks in the reactor and the distillate products. Additionally or alternately, secondary cracking of primary VGO products into incompatible paraffin side chains and aromatic cores can be reduced or minimized. Additionally, it has been discovered that the composition of recycle pitch has a surprisingly low average molecular weight and that the viscosity of the recycle pitch drops unusually quickly as temperature rises. Pitch recycle surprisingly enables high severity slurry hydrocracking without fouling. High temperature operation of slurry hydroconversion at 800° F to 875° F (427° C to 468° C), or preferably at 840° F to 860° F (449° C to 460° C) produces a low viscosity, high aromatic content, high nitrogen recycle fluid that prevents reactor coking and fouling.
Tailoring the cut point and composition of the recycle stream can also be beneficial for remaining within the solubility limit of the reactor liquid. In some aspects, operability of the slurry hydrocracker with pitch recycle is improved by removing low solvency material from the feed. This can be achieved by, for example, deasphalting atmospheric or vacuum residue to produce a high solvency asphaltene fraction and/or by deep distillation of atmospheric residue to yield a high solvency vacuum residue, such as distillation at a cut point of 1050° F (566° C) or more, or 1080° F (582° C) or more, or 1100° F (593° C) or more.
The slurry hydroconversion process uses a dispersed catalyst which is continuously doped into the feed. This catalyst helps to suppress coke formation by capping free radicals formed by thermal conversion. Measurements of reactor liquid catalyst concentrations indicate the catalyst tracks the liquid phase. Therefore, when the slurry hydroconversion unit is operated once-through, the catalyst lifetime is equal to the liquid residence time. This is economical because a very low concentration of catalyst is used and the catalyst cost is low. However, it is desirable to increase the lifetime of the catalyst in order to reduce catalyst usage. Since it is difficult to isolate the catalyst from the product, this is most easily accomplished by bottoms recycle. Bottoms recycle increases the average catalyst lifetime. As a result, at constant make-up, the concentration of catalyst in the reactor liquid increases as bottoms recycle increases, even after accounting for reduced vaporization in the reactor. This allows the catalyst make-up rate to be reduced while maintaining equivalent coke suppression activity or, alternatively, the reactor severity can be increased while maintaining constant coke make. It is noted that in aspects where the heavy hydrocarbon feedstock corresponds to a bitumen derived from a froth treatment, clay particles remaining in the bitumen after the froth treatment can also contribute catalytic effect. Such clay particles can also be concentrated by the pitch recycle.
In a reaction system, slurry hydroprocessing can be performed by processing a feed in one or more slurry hydroprocessing reactors. In some aspects, the slurry hydroprocessing can be performed in a single reactor, or in a group of parallel single reactors. The reaction conditions in a slurry hydroconversion reactor can vary based on the nature of the catalyst, the nature of the feed, the desired products, and/or the desired amount of conversion.
With regard to catalyst, several options are available. In some aspects, the catalyst can correspond to one or more catalytically active metals in particulate form and/or supported on particles. In other aspects, the catalyst can correspond to particulates that are retained within the heavy hydrocarbon feed after using a froth treatment to form the feed. In still other aspects, a mixture of catalytically active metals and particulates retained in the heavy hydrocarbon feed can be used.
In aspects where a catalytically active metal is used as the catalyst, suitable catalyst concentrations can range from about 50 wppm to about 50,000 wppm (or roughly 5.0 wt %), depending on the nature of the catalyst. Catalyst can be incorporated into a hydrocarbon feedstock directly, or the catalyst can be incorporated into a side or slip stream of feed and then combined with the main flow of feedstock. Still another option is to form catalyst in-situ by introducing a catalyst precursor into a feed (or a side/slip stream of feed) and forming catalyst by a subsequent reaction.
Catalytically active metals for use in slurry hydroprocessing/hydroconversion can include those from Groups 4-10 of the IUPAC Periodic Table. Examples of suitable metals include iron, nickel, molybdenum, vanadium, tungsten, cobalt, ruthenium, and mixtures thereof. The catalytically active metal may be present as a solid particulate in elemental form or as an organic compound or an inorganic compound such as a sulfide or other ionic compound. Metal or metal compound nanoaggregates may also be used to form the solid particulates.
A catalyst in the form of a solid particulate is generally a compound of a catalytically active metal, or a metal in elemental form, either alone or supported on a refractory material such as an inorganic metal oxide (e.g., alumina, silica, titania, zirconia, and mixtures thereof). Other suitable refractory materials can include carbon, coal, and clays. Zeolites and non-zeolitic molecular sieves are also useful as solid supports. One advantage of using a support is its ability to act as a “coke getter” or adsorbent of asphaltene precursors that might otherwise lead to fouling of process equipment.
In some aspects, it can be desirable to form catalyst for slurry hydroprocessing in situ, such as forming catalyst from a metal sulfate catalyst precursor or another type of catalyst precursor that decomposes or reacts in the hydroconversion reaction zone environment, or in a pretreatment step, to form a desired, well-dispersed and catalytically active solid particulate. Precursors also include oil-soluble organometallic compounds containing the catalytically active metal of interest that thermally decompose to form the solid particulate having catalytic activity. Other suitable precursors include metal oxides that may be converted to catalytically active (or more catalytically active) compounds such as metal sulfides.
The slurry hydroprocessing stage can be operated at a net conversion of 60 wt % to 89 wt %, relative to a conversion temperature of 524° C, or 70 wt % to 89 wt %, or 60 wt % to 85 wt %, or 70 wt % to 85 wt %, or 75 wt % to 89 wt %. Optionally but preferably, the slurry hydroprocessing stage can correspond to a single slurry hydroprocessing reactor, as opposed to having a plurality of reactors arranged in series. In some aspects, a portion of the pitch or unconverted bottoms from the slurry hydroprocessing reactor can be recycled. In such aspects, the per-pass conversion can be significantly lower, such as having a per-pass conversion of 60 wt % or less, or 50 wt % or less, or 40 wt % or less, relative to 524° C or alternatively relative to 566° C.
In addition to operating at reduced conversion, the slurry hydroprocessing reactor can also perform a relatively low level of hydrodesulfurization and/or hydrodenitrogenation. In various aspects, the amount of nitrogen removal (conversion to NH3 or other light end nitrogen compounds) can correspond to 35 wt % or less of the organic nitrogen in the feed to the slurry hydroprocessing reactor, or 30 wt % or less, or 25 wt % or less, such as down to 10 wt % or possibly still lower. Additionally or alternately, the amount of sulfur removal (conversion to H2S or other light end sulfur compounds) can correspond to 90 wt % or less of the sulfur in the feed to the slurry hydroprocessing reactor, or 85 wt % or less, or 80 wt % or less, such as down to 60 wt % or possibly still lower. For example, the amount of sulfur removal can correspond to 60 wt % to 90 wt %, or 70 wt % to 85 wt %.
The reaction conditions within a slurry hydroprocessing reactor that correspond to a target conversion level can include a temperature of 400° C to 480° C, such as 425° C or more, or 450° C or more. Some types of slurry hydroprocessing reactors are operated under high hydrogen partial pressure conditions, such as having a hydrogen partial pressure of 1000 psig (6.39 MPag) to 3400 psig (23.4 MPag), for example at least 1200 psig (8.3 MPag), or at least about 1500 psig (10.3 MPag). Examples of hydrogen partial pressures can be 1000 psig (6.9 MPag) to 3000 psig (20.7 MPag), or 1000 psig (8.3 MPag) to 2500 psig (17.2 MPag), or 1500 psig (10.3 MPag) to 3400 psig (23.4 MPag), or 1000 psig (6.9 MPag) to 2000 psig (13.8 MPag), or 1200 psig (8.3 MPag) to 2500 psig (17.2 MPag). Since the catalyst is in slurry form within the feedstock, the space velocity for a slurry hydroconversion reaction conditions can be characterized based on the volume of feed processed relative to the volume of the reactor used for processing the feed. Suitable liquid hourly space velocities (LHSV) for slurry hydroconversion can range, for example, from about 0.05 v/v/hr−1 to about 5 v/v/hr−1, such as about 0.1 v/v/hr−1 to about 2 v/v/hr−1.
In some aspects, the quality of the hydrogen stream used for slurry hydroprocessing can be relatively low. For example, in aspects where the catalyst is concentrated into the pitch and removed from the system as part of a product from a partial oxidation reactor, catalyst lifetime can be of minimal concern. This is due to the constant addition of fresh catalyst, whether in the form of particulates from the heavy hydrocarbon feed or in the form of a separately added catalyst. As a result, reaction conditions that conventionally are considered undesirable for hydroprocessing due to catalyst deactivation can potentially be used. This can potentially provide unexpected synergies when a partial oxidation reactor is used to provide at least a portion of the hydrogen for the hydroconversion process.
One example of a reaction condition that is avoided in conventional hydroprocessing is use of hydrogen streams that have relatively high concentrations of known catalyst poisons. Some catalyst poisons can correspond to catalyst poisons commonly found in recycled hydrogen treat gas streams, such as H2S, NH3, CO, and other contaminants. Other catalyst poisons can correspond to contaminants that may be present in hydrogen derived from processing of pitch in a partial oxidation reactor, such as nitrogen oxides (NOx), sulfur oxides (SOx), arsenic compounds, and/or boron compounds. In order to use hydrogen generated by partial oxidation of pitch in a conventional hydroprocessing reactor, various cleanup processes would be needed to reduce or minimize the content of various contaminants in the hydrogen treat gas. However, using a partial oxidation reactor to provide hydrogen for a slurry hydroprocessing reactor can provide the unexpected synergy of allowing at least some cleanup steps to be avoided, due to the tolerance of the slurry hydroprocessing reaction conditions for the presence of various contaminants.
In some aspects, the H2 content of the hydrogen-containing stream introduced into the slurry hydroprocessing reactor can be 90 vol % or less, or 80 vol % or less, or 60 vol % or less, such as down to 40 vol % or possibly still lower. In other aspects, the H2 content of the hydrogen-containing stream can be 80 vol % or more, or 90 vol % or more. For example, the hydrogen-containing stream can contain 80 vol % to 100 vol % H2, or 90 vol % to 100 vol %, or 80 vol % to 98 vol %, or 90 vol % to 98 vol %, or 80 vol % to 96 vol %, or 90 vol % to 96 vol %. Additionally or alternately, the combined content of H2S, CO, and NH3 in the hydrogen-containing stream can be 1.0 vol % or more, or 3.0 vol % or more, or 5.0 vol % or more, such as up to 15 vol % or possibly still higher. Further additionally or alternately, the combined content of H2, H2O, and N2 in the hydrogen-containing stream introduced into the slurry hydroprocessing reactor can be 95 vol % or less, or 90 vol % or less, or 85 vol % or less, such as down to 75 vol % or possibly still lower. For example, the combined content of H2, H2O, and N2 in the hydrogen-containing stream introduced into the slurry hydroprocessing reactor can be 75 vol % to 95 vol %.
Example of Slurry Hydroprocessing Reaction SystemAfter exposing the feed to slurry hydroconversion conditions in slurry hydroprocessing reactor 410, the resulting slurry hydroprocessing effluent 415 can be passed into one or more separation stages. In the example shown in
Both vapor fraction 422 and second product fraction 432 can optionally undergo further separations and/or additional processing, as desired. For example, as shown in
In the configuration shown in
A vaccum resid fraction was hydroprocessed in a fixed bed reactor to determine the impact of recycle on reactor productivity.
As shown in
A pilot scale configuration similar to the configuration in
The heavy hydrocarbon feedstock was a 975° F+ (524° C+) vacuum residue. The heavy hydrocarbon feedstock included more than 75 wt % of 566° C+ components. The pilot plant included a pump-around loop that was operated with sufficient recirculation to reduce or minimize foaming In the first reaction condition, a recycle stream was used that corresponded to 10 wt % of the fresh feed amount. In the second reaction condition, a recycle stream was used that corresponded to 50 wt % of the fresh feed amount. In the third reaction condition, the recycle stream corresponded to 100 wt % of the fresh feed amount (i.e., the mass flow rate of the recycle stream was substantially the same as the mass flow rate of the fresh feed). Table 1 provides additional details for each reaction condition, including the fresh feed rate that was needed to maintain conversion at roughly 90 wt % relative to 1050° F (566° C) based on the selected reaction temperature, pressure, and H2 treat gas rate. Table 1 also provides the relative reactor productivity for each condition, as well as a 566° C+ conversion rate constant.
As shown in Table 1, Condition 1 corresponded to a conventional recycle, where a small recycle stream (˜10% of the fresh feed mass flow rate) containing less than 50 wt % 566° C+ components was used for recycle. It is believed that the reactor productivity for Condition 1 is similar to what the reactor productivity would be without recycle. Conditions 2 and 3 corresponded to pitch recycle as described herein, where the amount of the recycle was 50% or more of the mass flow rate of the fresh feed, and the recycle stream included greater than 60 wt % 566° C+ components. As shown in Table 1, operating with a substantial pitch recycle in Conditions 2 and 3 allowed for an increase in the fresh feed flow rate from 0.26 hr−1 (for 10% recycle) to either 0.36 hr−1 (for 50% recycle) or 0.41 hr−1 (for 100% recycle) while maintaining substantially constant conversion within the slurry hydroprocessing reactor. Thus, operating with substantial pitch recycle provided an unexpected productivity increase. This is in contrast to use of bottoms recycle when performing conversion in a fixed bed environment, where the bottoms recycle had substantially no impact on reactor productivity.
Table 2 shows the product yields from processing the heavy hydrocarbon feed at each condition. As shown in Table 2, even though Conditions 2 and 3 provided an unexpected productivity increase at constant conversion, the amount of hydrogen consumed unexpectedly decreased. This unexpected decrease appears to be due in part to reduced production of light ends and naphtha, with a corresponding increase in vacuum gas oil in the products. The reduction in light ends production also resulted in a net increase in liquid products (C5-566° C) at Conditions 2 and 3. For the product fraction weight percentages in Table 2, the weight percentages are relative to the weight (i.e., mass flow rate) of the fresh feed.
It is noted that pitch recycle also improved the quality of the resulting vacuum gas oil (343° C-566° C), based on an increase in API gravity and a reduction in nitrogen content. Table 3 provides information similar to Table 2, but on a volume basis.
Embodiment 1. A method for performing slurry hydroconversion, comprising: exposing a heavy hydrocarbon feed and a pitch recycle stream to a slurry hydroprocessing catalyst under slurry hydroconversion conditions in a reaction zone to form a slurry hydroprocessing effluent, the slurry hydroconversion conditions comprising a net conversion of 60 wt % to 89 wt % relative to 524° C, the heavy hydrocarbon feed comprising 50 wt % or more of 566° C+ components, the heavy hydrocarbon feed and the pitch recycle stream comprising a combined feed ratio of 1.5 to 3.5; and separating the pitch recycle stream from the slurry hydroconversion effluent, the pitch recycle stream comprising more than 50 wt % of 566° C+ components.
Embodiment 2. The method of Embodiment 1, wherein the pitch recycle stream comprises 60 wt % or more of 566° C+ components, or wherein the pitch recycle stream comprises 50 wt % or more of 593° C+ components, or a combination thereof.
Embodiment 3. The method of any of the above embodiments, wherein the heavy hydrocarbon feed comprises 60 wt % or more of 566° C+ components, or wherein the heavy hydrocarbon feed comprises 50 wt % or more of 593° C+ components, or a combination thereof.
Embodiment 4. The method of any of the above embodiments, wherein the heavy hydrocarbon feed comprises 5 wt % to 80 wt % n-heptane asphaltenes, or wherein the heavy hydrocarbon feed comprises 5 wt % to 50 wt % micro carbon residue, or a combination thereof.
Embodiment 5. The method of any of the above embodiments, wherein the combined feed ratio is 1.6 to 3.0.
Embodiment 6. The method of any of the above embodiments, wherein the slurry hydroconversion conditions comprise 70 wt % to 89 wt % net conversion relative to 524° C.
Embodiment 7. The method of any of the above embodiments, wherein the per-pass conversion at 524° C is lower than the net conversion at 524° C by 25 wt % or more, or wherein the per-pass conversion at 524° C is 60 wt % or less, or a combination thereof.
Embodiment 8. The method of any of the above embodiments, wherein the slurry hydroconversion conditions comprise a temperature of 400° C to 480° C, a pressure of 1000 psig (˜6.4 MPa-g) to 3400 psig (˜23.4 MPa-g), and a LHSV of 0.05 hr−1 to 5 hr−1.
Embodiment 9. The method of any of the above embodiments, wherein at least a portion of the slurry hydroconversion catalyst comprises a catalyst formed in-situ.
Embodiment 10. A slurry hydroconversion effluent made according to any of Embodiments 1-9.
When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated. While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those skilled in the art to which the invention pertains.
The present invention has been described above with reference to numerous embodiments and specific examples. Many variations will suggest themselves to those skilled in this art in light of the above detailed description. All such obvious variations are within the full intended scope of the appended claims.
Claims
1. A method for performing slurry hydroconversion, comprising:
- exposing a heavy hydrocarbon feed and a pitch recycle stream to a slurry hydroprocessing catalyst under slurry hydroconversion conditions in a reaction zone to form a slurry hydroprocessing effluent, the slurry hydroconversion conditions comprising a net conversion of 60 wt % to 89 wt % relative to 524° C, the heavy hydrocarbon feed comprising 50 wt % or more of 566° C+ components, the heavy hydrocarbon feed and the pitch recycle stream comprising a combined feed ratio of 1.5 to 3.5; and
- separating the pitch recycle stream from the slurry hydroconversion effluent, the pitch recycle stream comprising more than 50 wt % of 566° C+ components.
2. The method of claim 1, wherein the pitch recycle stream comprises 60 wt % or more of 566° C+ components, or wherein the pitch recycle stream comprises 50 wt % or more of 593° C+ components, or a combination thereof.
3. The method of claim 1, wherein the heavy hydrocarbon feed comprises 60 wt % or more of 566° C+ components, or wherein the heavy hydrocarbon feed comprises 50 wt % or more of 593 ° C+ components, or a combination thereof.
4. The method of claim 1, wherein the heavy hydrocarbon feed comprises 5 wt % to 80 wt % n-heptane asphaltenes, or wherein the heavy hydrocarbon feed comprises 5 wt % to 50 wt % micro carbon residue, or a combination thereof.
5. The method of claim 1, wherein the combined feed ratio is 1.6 to 3.0.
6. The method of claim 1, wherein the slurry hydroconversion conditions comprise 70 wt % to 89 wt % net conversion relative to 524° C.
7. The method of claim 1, wherein the per-pass conversion at 524° C is lower than the net conversion at 524° C by 25 wt % or more, or wherein the per-pass conversion at 524 ° C is 60 wt % or less, or a combination thereof.
8. The method of claim 1, wherein the slurry hydroconversion conditions comprise a temperature of 400° C to 480° C, a pressure of 1000 psig (˜6.4 MPa-g) to 3400 psig (−23.4 MPa-g), and a LHSV of 0.05 hr1 to 5 hr1.
9. The method of claim 1, wherein at least a portion of the slurry hydroconversion catalyst comprises a catalyst formed in-situ.
10. A slurry hydroconversion effluent made by the method comprising:
- exposing a heavy hydrocarbon feed and a pitch recycle stream to a slurry hydroprocessing catalyst under slurry hydroconversion conditions in a reaction zone to form a slurry hydroprocessing effluent, the slurry hydroconversion conditions comprising a net conversion of 60 wt % to 89 wt % relative to 524° C, the heavy hydrocarbon feed comprising 50 wt % or more of 566° C+ components, the heavy hydrocarbon feed and the pitch recycle stream comprising a combined feed ratio of 1.5 to 3.5; and
- separating the pitch recycle stream from the slurry hydroconversion effluent, the pitch recycle stream comprising more than 50 wt % of 566° C+ components.
Type: Application
Filed: Aug 14, 2020
Publication Date: Oct 6, 2022
Applicant: EXXONMOBIL TECHNOLOGY AND ENGINEERING COMPANY (Annandale, NJ)
Inventors: Samuel J. CADY (Morristown, NJ), Stephen H. BROWN (Lebanon, NJ), Eric B. SHEN (Basking Ridge, NJ)
Application Number: 17/640,105
