Hydrocracking process and system including separation of heavy poly nuclear aromatics from recycle by ionic liquids and solid adsorbents

A process for the treatment of a hydrocracking unit bottoms recycle stream, and preferably the fresh hydrocracker feed to remove heavy poly-nuclear aromatic (HPNA) compounds and HPNA precursors employs, in the alternative, an adsorption step which removes most of the HPNA compounds followed by an ionic liquid extraction step to remove the remaining HPNA compounds, or a first ionic liquid extraction step which removes most of the HPNA compounds followed by an adsorption step to remove the remaining HPNA compounds. Ionic liquids of the general formula Q+A− are identified for use in the process; organic polar solvents are identified for removal of the HPNA compounds in solution. Suitable adsorbents are identified for use in packed bed or slurry bed columns that operate within specified temperature and pressure ranges.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to hydrocracking processes, and in particular to hydrocracking processes including separation of heavy poly nuclear aromatics from recycle streams using ionic liquids and solid adsorbents.

Description of Related Art

Hydrocracking processes are used commercially in a large number of petroleum refineries. They are used to process a variety of feeds boiling in the range of about 370 to 520° C. in conventional hydrocracking units and boiling at 520° C. and above in the residue hydrocracking units. In general, hydrocracking processes split the molecules of the feed into smaller, i.e., lighter, molecules having higher average volatility and economic value. Additionally, hydrocracking processes typically improve the quality of the hydrocarbon feedstock by increasing the hydrogen to carbon ratio and by removing organosulfur and organonitrogen compounds. The significant economic benefit derived from hydrocracking processes has resulted in substantial development of process improvements and more active catalysts.

In addition to sulfur-containing and nitrogen-containing compounds, a typical hydrocracking feedstream, such as vacuum gas oil (VGO), contains small amount of poly nuclear aromatic (PNA) compounds, i.e., those containing less than seven fused benzene rings. As the feedstream is subjected to hydroprocessing at elevated temperature and pressure, heavy poly nuclear aromatic (HPNA) compounds, i.e., those containing seven or more fused benzene rings, tend to form and are present in high concentration in the unconverted hydrocracker bottoms. For this reason, PNA compounds are defined as the precursors of the HPNAs, and the amount and type of the precursors is generally related to the type of feed stock and its boiling range. The HPNAs foul process equipment and shorten catalyst life.

Heavy feedstreams such as demetalized oil (DMO) or deasphalted oil (DAO) have much higher concentrations of nitrogen, sulfur and PNA compounds than VGO feedstreams. These impurities can lower the overall efficiency of the hydrocracking unit by requiring higher operating temperatures, higher hydrogen partial pressure or additional reactor/catalyst volume. In addition, high concentrations of impurities can accelerate catalyst deactivation.

Three major hydrocracking process schemes include single-stage once through hydrocracking, series-flow hydrocracking with or without recycle, and two-stage recycle hydrocracking. Single-stage once through hydrocracking is the simplest of the hydrocracker configuration and typically occurs at operating conditions that are more severe than hydrotreating processes, and less severe than conventional full pressure hydrocracking processes. It uses one or more reactors for both treating steps and cracking reaction, so the catalyst must be capable of both hydrotreating and hydrocracking. This configuration is cost effective, but typically results in relatively low product yields (for example, a maximum conversion rate of about 60%). Single stage hydrocracking is often designed to maximize mid-distillate yield over a single or dual catalyst systems. Dual catalyst systems can be used in a stacked-bed configuration or in two different reactors. The effluents are passed to a fractionator column to separate the H2S, NH3, light gases (C1-C4), naphtha and diesel products boiling in the temperature range of 36-370° C. The hydrocarbons boiling above 370° C. are typically unconverted bottoms that, in single stage systems, are passed to other refinery operations, for example fluid catalytic cracking units.

Series-flow hydrocracking with or without recycle is one of the most commonly used configuration. It uses one reactor (containing both treating and cracking catalysts) or two or more reactors for both treating and cracking reaction steps. In a series-flow configuration the entire hydrocracked product stream from the first reaction zone, including light gases (typically C1-C4, H2S, NH3) and all remaining hydrocarbons, are sent to the second reaction zone. Unconverted bottoms from the fractionator column are recycled back into the first reactor for further cracking. This configuration converts heavy crude oil fractions, i.e., vacuum gas oil, into light products and has the potential to maximize the yield of naphtha, jet fuel, or diesel, depending on the recycle cut point used in the distillation section.

Two-stage recycle hydrocracking uses two reactors and unconverted bottoms from the fractionation column are passed to the second reactor for further cracking. Since the first reactor accomplishes both hydrotreating and hydrocracking, the feed to second reactor is virtually free of ammonia and hydrogen sulfide. This permits the use of high performance zeolite catalysts which are susceptible to poisoning by sulfur or nitrogen compounds.

A typical hydrocracking feedstock is a vacuum gas oil stream having a nominal boiling range of 370 to 565° C. DMO or DAO, alone or blended with vacuum gas oil, is processed in a hydrocracking unit. For instance, a typical hydrocracking unit processes vacuum gas oils that contain from 10V % to 25V % of DMO or DAO for optimum operation. Undiluted 100% DMO or DAO can also be processed, but typically under more severe conditions, since the DMO or DAO stream contains a greater percentage of nitrogen compounds, e.g., 2,000 ppmw vs. 1,000 ppmw, and a higher micro carbon residue (MCR) content than the VGO stream (10 W % vs. <1 W %).

DMO or DAO content in blended feedstocks to a hydrocracking unit can lower the overall efficiency of the unit by increasing the operating temperature or reactor/catalyst volume for existing units, or by increasing hydrogen partial pressure requirements or reactor/catalyst volume for grass-roots units. These impurities can also reduce the quality of the desired intermediate hydrocarbon products in the hydrocracked effluent. When DMO or DAO are processed in a hydrocracker, further processing of hydrocracking reactor effluents may be required to meet the refinery fuel specifications, depending upon the refinery configuration. When the hydrocracking unit is operating in its desired mode, that is to say, discharging a high quality effluent product stream, its effluent can be utilized in blending and to produce gasoline, kerosene and diesel fuel to meet established fuel specifications.

Formation of HPNA compounds is an undesirable side reaction that occurs in recycle hydrocrackers. The HPNA molecules form by dehydrogenation of larger hydro-aromatic molecules or cyclization of side chains onto existing HPNA molecules followed by dehydrogenation, which is favored as the reaction temperature increases. HPNA formation depends on many known factors including the type of feedstock, catalyst selection, process configuration, and operating conditions. Since HPNA molecules accumulate in the recycle system and then cause equipment fouling, HPNA formation must be controlled in the hydrocracking process.

The rate of formation of the various HPNA compounds increases with higher inversion and heavier feed stocks. The fouling of equipment may not be apparent until large amounts of HPNA accumulate in the recycle liquid loop. The problem of HPNA formation is of universal concern to refiners and various removal methods have been developed by refinery operators to reduce its impact.

The prior art methods to separate or treat heavy poly-nuclear aromatics formed in the hydrocracking process include adsorption, hydrogenation, extraction, solvent deasphalting and purging, or “bleeding” a portion of the recycle stream from the system to reduce the build-up of HPNA compounds and cracking or utilizing the bleed stream elsewhere in the refinery. The hydrocracker bottoms are treated in separate units to eliminate the HPNA's and recycle HPNA-free bottoms back to the hydrocracking reactor.

As noted above, one alternative when operating the hydrocracking unit in the recycle mode is to purge a certain amount of the recycle liquid to reduce the concentration of HPNA compounds introduced with the fresh feed, although purging reduces the conversion rate to below 100%. Another solution to the build-up problem is to eliminate the HPNAs by passing them to a special purpose vacuum column which effectively fractionates 98-99% of the recycle stream leaving most of the HPNAs at the bottom of the column for rejection from the system as fractionator bottoms. This alternative incurs the additional capital cost and operating expenses of a dedicated fractionation column.

As used herein, the term hydrocracking unit recycle stream is synonymous with the terms hydrocracker recycle stream, hydrocracker bottoms, hydrocracker unconverted material and fractionator bottoms. As used herein, the shorthand expressions “HPNAs” means “Heavy Polynuclear Aromatics” and “HPNAs/HPNA precursors” and “HPNAs and HPNA precursors” means “HPNA compounds and HPNA precursors”. “HPNAs” and “HPNA compounds” are used interchangeably. For convenience in the description that follows, it will be understood that a reference to HPNA compounds also includes HPNA precursors.

The problem therefore exists of providing a process for removing HPNA compounds from the bottoms recycle stream of a hydrocracking unit that is more efficient and cost effective than processes of the prior art.

SUMMARY OF THE INVENTION

In accordance with the process of the present invention, hydroprocessed bottoms fractions are treated to convert and separate HPNA compounds and produce a reduced-HPNA hydroprocessed bottoms stream effective for recycle, for instance, in a configuration of a single hydrocracking reactor, series flow once through hydrocracking unit operation, or two-stage hydrocracking unit operations.

The hydrocracking unit bottoms recycle stream, and preferably the fresh hydrocracking unit feed are treated in one of two alternative processes that employ both adsorption and extraction to remove HPNA compounds in two discrete steps. In one embodiment of the process, a first adsorption step removes most of the HPNA compounds and a second ionic liquid extraction step removes the remaining HPNA compounds from the hydrocracker bottoms recycle stream. In a second embodiment of the process, a first ionic liquid extraction step removes most of the HPNA compounds and a second adsorption step removes the remaining HPNA compounds from the bottoms recycle stream.

Embodiment 1: Adsorption Followed by Ionic Liquid Extraction

In this embodiment, the recycle stream is preferably combined with the fresh feed and the combined feedstream is sent to an adsorption column to remove HPNA compounds and HPNA precursors. The effluent from the adsorption column is then sent to an extractor to extract the remaining HPNA compounds and HPNA precursors with one or more ionic liquids. The extracted HPNAs and HPNA precursors together with ionic liquids are sent to a separator to separate the HPNAs and precursors using an organic polar solvent, and to recover the ionic liquids. The solvent is then recovered in a solvent recovery unit and recycled to the extractor. The treated stream having substantially no free HPNA compounds is then sent to a liquid-liquid separator to separate any remaining ionic liquids and HPNA compounds and to recover the HPNA-free stream.

Embodiment 2: Ionic Liquid Extraction Followed by Adsorption

In this embodiment, the recycle stream is preferably combined with the feedstream and sent to an extractor and mixed with one or more ionic liquids. The extracted HPNAs and HPNA precursors together with ionic liquids are sent to a separator to separate the HPNAs and precursors using an organic polar solvent, and to recover the ionic liquids. The solvent is then recovered in a solvent recovery unit and recycled to the extractor. The treated stream of reduced HPNA content is then sent to a liquid-liquid separator to separate any remaining ionic liquids and HPNA compounds and to recover the stream of reduced HPNA content. After separation of the ionic liquids and solvent, the treated hydrocarbon stream is sent to an adsorption column to remove the remaining HPNA compounds and HPNA precursors.

The above method for separation of HPNA compounds from a bottoms fraction can be integrated in a hydroprocessing operation using a single reactor or plural reactors in a “once through” configuration.

In addition, the above methods for separation of HPNAs from a bottoms fraction can be integrated in a two-stage hydroprocessing configuration.

Although the process has been described in connection with the treatment of the recycle stream of a hydrocracking unit, the treated stream containing no or a low concentration of HPNA compounds and/or HPNA precursors can alternatively be sent to an FCC unit.

The HPNA compounds recovered by the combination of either of the extraction/adsorption steps described above can be further processed in a delayed coker to produce high quality coke, and/or can be gasified to produce hydrogen, steam and electricity, and/or can be sent to the fuel oil pool as blending components, and/or can be sent to a fluid catalytic cracking (FCC) unit to form a small portion of the FCC feedstream and eventually be deposited as coke on the catalyst, which coke will be burned to produce heat in the catalyst regeneration step, and/or can be sent to the asphalt pool.

In the practice of the alternative adsorption/extraction processes described above, it is preferred that metals in the feedstock be removed by pre-treatment in a hydrodemetallization (HDM) bed containing HDM catalyst that is of large pore volume and size. It will also be understood that sulfur and nitrogen compounds in the feed are removed in the first stage of the hydrocracking unit.

The ionic liquid can be a non-aqueous ionic liquid of the general formula Q+A−. The A−ion is selected from the group consisting of halide anions, nitrate, sulfate, phosphate, acetate, haloacetates, tetrafluoroborate, tetrachloroborate, hexafluorophosphate, hexafluoroantimonate, fluorosulfonate, alkyl sulfonates, perfluoroalkyl sulfonates, bis(perfluoroalkylsulfonyl)amides, tris-trifluoromethanesulfononyl methylide of the formula C(CF3SO2)3—, unsubstituted arenesulfonates, arenesulfonates substituted by halogen or haloalkyl groups, the tetraphenylborate anion and the tetraphenylborate anions having substituted aromatic cores.

The Q+ion can be any suitable ammonium cation, a phosphonium cation or a sulfonium cation. The quaternary ammonium and/or phosphonium Q+ion can be of the general formula NR1R2R3R4+ in which R1, R2, R3and R4are the same or different and are selected from hydrogen and hydrocarbon radicals having from 1 to 30 carbon atoms, with the exception of an NH4+cation, and PR1R2R3R4+ in which R1, R2, R3and R4are the same or different and are selected from hydrogen and hydrocarbon radicals having from 1 to 30 carbon atoms.

The Q+ion can have the general formula R1R2N═CR3R4+, wherein R1, R2, R3and R4are the same or different and are selected from hydrogen and hydrocarbon radicals having from 1 to 30 carbon atoms.

The Q+ion can have the general formula R1R2P═CR3R4+, wherein R1, R2, R3and R4are the same or different and are selected from hydrogen and hydrocarbon radicals having from 1 to 30 carbon atoms.

The Q+ion can be a nitrogen-containing heterocyclic compound that includes 1, 2 or 3 nitrogen and atoms having cyclic compounds containing 4 to 10 atoms.

The Q+ion can have the general structural formula selected from the group consisting of the following structure, wherein R1, R2, R3, R4and R5are the same or different and represent hydrogen or hydrocarbonyl radicals that have 1 to 30 carbon atoms.

The Q+ion can be a phosphorous-containing compound.

The Q+ion can have the general structural formula selected from a group having the following structure.

The Q+quaternary ammonium or phosphonium cations can also correspond to one of the following general structural formula:
R1R2+N═CR3—R5—R3C═N+R1R2, and
R1R2+P3═CR3—R5—R3C═P+R1R2
in which R1, R2and R3are the same or different, and represent hydrogen or hydrocarbonyl radicals that have 1 to 30 carbon atoms and R5represents an alkylene radical or a phenylene radical.

The sulfonium cations can have the general formula:
SR1R2R3+
where R1, R2and R3, are the same or different hydrocarbonyl radicals having 1 to 12 carbon atoms.

The ionic liquid extraction process can be performed at a temperature in the range of 20° to 200° C. and at a pressure in the range of from 1 to 30 bars, and with a mole ratio of ionic liquid-to-HPNAs of from 1:1 to 10:1. The LHSV range can be from is 0.5-10 h−1.

Analogous processes are known for the treatment of the hydrocarbon effluents of hydrocracking units using ionic liquids to extract a variety of organosulfur and organonitrogen benzothiophene compounds based on their 6-member ring structures. Such processes are disclosed in U.S. Pat. No. 8,758,600 entitled “Ionic Liquid Desulfurization Process Incorporated in a Low Pressure Separator” and U.S. Pat. No. 8,992,767 entitled “Ionic Liquid Desulfurization Process Incorporated in a Contact Vessel”, the disclosures of which are incorporated by reference herein in their entirety.

Suitable extractors include centrifugal contactors and contacting columns such as tray columns, spray columns, packed towers, rotating disc contactors and pulse columns.

Adsorption columns suitable for use in the process can be packed bed or slurry bed columns. The adsorption bed can operate in the temperature range of from 20°−200° C. and at a pressure in the range of from 1 to 30 bars.

Suitable adsorbents include natural clays and preferably attapulgus clay, alumina, silica, activated carbon, natural and synthetic zeolites, spent catalysts, silica-titania and titania,

Suitable organic polar solvents for use in the process can be selected based on their Hildebrand solubility factors or on the basis of their two-dimensional solubility factors. The overall Hildebrand solubility parameter is a well-known measure of polarity and has been calculated for numerous compounds. SeeJournal of Paint Technology, Vol. 39, No. 505 (February 1967). The solvents can also be selected based on their two-dimensional solubility parameter comprising the complexing solubility parameter and the field force solubility parameter. See, for example, I. A. Wiehe,Ind. &Eng. Res.,34(1995), 661. The complexing solubility parameter component, which describes the hydrogen bonding and electron donor-acceptor interactions, measures the interaction energy that requires a specific orientation between an atom of one molecule and a second atom of a different molecule. The field force solubility parameter, which describes the van der Waals and dipole interactions, measures the interaction energy of the liquid that is not destroyed by changes in the orientation of the molecules. The polar solvents are further defined as having an overall solubility parameter greater than about 8.5 or a complexing solubility parameter of greater than 1 and field force parameter of greater than 8. Examples of polar solvents meeting the desired minimum solubility parameter are toluene (8.91), benzene (9.15), xylenes (8.85), and tetrahydrofuran (9.52). The preferred polar solvents used in the examples that follow are toluene and tetrahydrofuran.

DETAILED DESCRIPTION OF THE INVENTION

Integrated processes and systems are provided to improve efficiency of hydrocracking operations. The processes and systems described below are effective for treating a wide range of initial feedstocks obtained from various sources, such as one or more of straight run vacuum gas oil, treated vacuum gas oil, demetalized oil from a solvent demetalizing operations, deasphalted oil from a solvent deasphalting operations, coker gas oils from coker operations, cycle oils from fluid catalytic cracking operations including heavy cycle oil, and visbroken oils from visbreaking operations. The feedstream generally has a boiling point of from about 350 to 800° C., 350 to 700° C., 350 to 600° C., or 350 to 565° C.

As used herein, “HPNA compounds” refers to fused polycyclic aromatic compounds having seven or more rings, for example, including but not limited to coronenes (C24H12), benzocoronenes (C28H14), dibenzocorone (C32H16) and ovalenes (C32H14). The seven ring aromatic molecule, coronene, is shown below. The aromatic structure may have alkyl groups or naphthenic rings attached to it. Coronene has 24 carbon atoms and 12 hydrogen atoms. Its double bond equivalency (DBE) is 19. DBE is calculated based on the sum of the number double bonds and number of rings. For example, the DBE value for coronene is 19, e.g., 7 rings+12 double bonds. HPNA compounds generally have DBE values of 17 and above.

Single Reactor with Recycle

FIG. 1is a process flow diagram of an embodiment of an integrated hydroprocessing system100that includes a reaction zone106, a fractionating zone110, and an HPNA separation zone120.

Reaction zone106generally includes one or more inlets in fluid communication with a source of initial feedstock102, a source of hydrogen gas104, and the HPNA separation zone120to receive a recycle stream comprising all or a portion of a bottoms stream116. One or more outlets of reaction zone106that discharge effluent stream108is in fluid communication with one or more inlets of the fractionating zone110, optionally having one or more high pressure and low pressure separation stages (not shown) for recovery of recycle hydrogen.

Fractionating zone110includes one or more outlets for discharging gases112, typically H2, H2S, NH3, and light hydrocarbons (C1-C4); one or more outlets for recovering product114, such as naphtha and diesel products boiling in the temperature range of 36-370° C.; and one or more outlets for discharging bottoms116including hydrocarbons boiling above about 370° C. In certain embodiments, the temperature cut point for bottoms116and, correspondingly, the end point for the products114is a range corresponding to the upper temperature limit of the desired gasoline, kerosene and/or diesel product boiling point ranges for downstream operations.

The fractionator bottoms outlet116is in fluid communication with the HPNA separation zone120described herein, which generally includes an outlet for discharging HPNA-reduced fractionator bottoms122and an outlet for discharging a HPNAs/HPNA precursors stream124containing HPNA compounds. The outlet discharging HPNA-reduced fractionator bottoms122is in fluid communication with one or more inlets of reaction zone106for recycle of all or a portion of the stream. In certain embodiments, a bleed stream118is drawn from bottoms116upstream of the HPNA separation zone120. In additional embodiments, a bleed stream126is drawn from HPNA-reduced fractionator bottoms122downstream of the HPNA separation zone120, in addition to or instead of bleed stream118. Either or both of these bleed streams are hydrogen-rich and therefore can be effectively integrated with certain fuel oil pools, or serve as feed to fluidized catalytic cracking or steam cracking processes (not shown).

In operation of the system100, a feedstock stream102and a hydrogen stream104are charged to the reaction zone106. Hydrogen stream104provides a quantity of hydrogen that is effective to support the requisite degree of hydrocracking, feed type, and other factors, and can be any combination including make-up hydrogen, recycle hydrogen from optional gas separation subsystems (not shown) between reaction zone106and fractionating zone110, and/or derived from fractionator gas stream112. Reaction effluent stream108, after one or more optional high pressure and low pressure separation stages to recover recycle hydrogen, contains converted, partially converted and unconverted hydrocarbons, which includes HPNA compounds formed in the reaction zone106.

The reaction effluent stream108is passed to fractionating zone110, to recover gas and liquid products and by-products112,114, and to separate a bottoms fraction116containing HPNA compounds. Gas stream112, typically containing H2, H2S, NH3, and light hydrocarbons (C1-C4), is discharged and recovered and can be further processed as is known in the art, including for recovery of recycle hydrogen. One or more cracked product streams114are discharged from appropriate outlets of the fractionator and can be further processed and/or blended in downstream refinery operations to produce gasoline, kerosene and/or diesel fuel, or other petrochemical products. In certain embodiments (not shown), fractionating zone110can operate as a flash vessel to separate heavy components at a suitable cut point, for example, a range corresponding to the upper temperature range of the desired gasoline, kerosene and/or diesel products for downstream operations. In certain embodiments, a suitable cut point is in the range of 350 to 450° C., 360 to 450° C., 370 to 450° C., 350 to 400° C., 360 to 400° C., 370 to 400° C., 350 to 380° C., or 360 to 380° C.

All or a portion of the fractionator bottoms stream116derived from the reaction effluent, including HPNA compounds formed in the reaction zone106, is passed to the HPNA separation zone120for treatment. In certain embodiments, a portion of the fractionator bottoms from the reaction effluent is removed as bleed stream118. Bleed stream118can be about 0-10 V %, 1-10 V %, 1-5 V % or 1-3 V % of the fractionator bottoms116. The concentration of HPNA compounds in the hydroprocessed effluent fractionator bottoms is reduced in the HPNA separation zone120to produce the HPNA-reduced fractionator bottoms stream122that is recycled to the reaction zone106. In certain embodiments, instead of, or in conjunction with bleed stream118, a portion of the HPNA-reduced fractionator bottoms stream122is removed from the recycle loop as bleed stream126. Bleed stream126can be about 0-10 V %, 1-10 V %, 1-5 V % or 1-3 V % of the HPNA-reduced fractionator bottoms stream122. A discharge stream124containing HPNA compounds is removed from the HPNA separation zone120.

Reaction zone106can contain one or more fixed-bed, ebullated-bed, slurry-bed, moving bed, continuous stirred tank (CSTR), or tubular reactors, in series and/or parallel arrangement. The reactor(s) are generally operated under conditions effective for the desired degree of conversion, particular type of reactor, the feed characteristics, and the desired product slate. For instance, these conditions can include a reaction temperature in the range of from about 300 to 500° C., 330 to 500° C., 300 to 475° C., 330 to 475° C., 300 to 475° C. or 330 to 450° C.; a reaction pressure in the range of from about 60 to 300 bar, 60 to 200 bar, 60 to 180 bar, 100 to 300 bar, 100 to 200 bar, 100 to 180 bar, 130 to 300 bar, 130 to 200 bar, or 130 to 180 bar; a hydrogen feed rate up to about 2500 standard liters per liter of hydrocarbon feed (SLt/Lt), in certain embodiments from about 800 to 2000 SLt/Lt, 800 to 1500 SLt/Lt, 1000 to 2000 SLt/Lt, or 1000 to 1500 SLt/Lt; and a feed rate in the range of from about 0.1 to 10 h−1, 0.1 to 5 h−1, 0.1 to 2 h−1, 0.25 to 10 h−1, 0.25 to 5 h−1, 0.25 to 2 h−1, 0.5 to 10 h−1, 0.5 to 5 h−1, or 0.5 to 2 h−1.

In systems using relatively lower hydrogen partial pressure values, HPNA compounds have relatively greater tendency accumulate due to the unavailability of hydrogen for cracking reactions. The operator typically must balance the accumulation of HPNA compounds against the higher cost of increased hydrogen consumption. However, when HPNA compounds in the recycle are removed as in the present process, the catalyst lifecycle can be increased.

The catalyst used in the reaction zone106contains one or more active metal components selected from IUPAC Groups 6-10 of the Periodic Table of the Elements. In certain embodiments the active metal component is one or more of cobalt, nickel, tungsten and molybdenum. The active metal component(s) are typically deposited or otherwise incorporated on a support, which can be amorphous and/or structured, such as alumina, silica-alumina, silica, titania, titania-silica, titania-silicates or zeolites. In embodiments using zeolite-based catalysts, HPNA compounds have relatively greater tendency to accumulate in the recycle stream due to the inability for these larger molecules to diffuse into the catalyst pore structure, particularly at relatively lower hydrogen partial pressure levels in the reactor. However, according to the process herein, by removing HPNA compounds from the recycle stream, the lifecycle of such zeolite catalyst is increased.

Series-Flow with Recycle

FIG. 2is a process flow diagram of another embodiment of an integrated hydrocracking unit operation, system200, which operates as series-flow hydrocracking system with recycle to the first reaction zone, the second reaction zone, or both the first and second reaction zones. In general, system200includes a first reaction zone228, a second reaction zone232, a fractionating zone210, and an HPNA separation zone220.

First reaction zone228generally includes one or more inlets in fluid communication with a source of initial feedstock202, a source of hydrogen gas204, and optionally the HPNA separation zone220to receive a recycle stream comprising all or a portion of the HPNA-reduced reaction zone bottoms stream222. One or more outlets of the first reaction zone228that discharge effluent stream230is in fluid communication with one or more inlets of the second reaction zone232. In certain embodiments, the effluents230are passed to the second reaction zone232without separation of any excess hydrogen and light gases. In optional embodiments, one or more high pressure and low pressure separation stages are provided between the first and second reaction zones228,232for recovery of recycle hydrogen (not shown).

The second reaction zone232generally includes one or more inlets in fluid communication with one or more outlets of the first reaction zone228, optionally a source of additional hydrogen gas205and optionally the HPNA separation zone220to receive a recycle stream comprising all or a portion of the HPNA-reduced reaction zone bottoms stream222. One or more outlets of the second reaction zone232that discharge effluent stream234is in fluid communication with one or more inlets of the fractionating zone210(optionally having one or more high pressure and low pressure separation stages therebetween for recovery of recycle hydrogen, not shown).

Fractionating zone210includes one or more outlets for discharging gases212, typically H2S, NH3, and light hydrocarbons (C1-C4); one or more outlets for recovering product214, such as naphtha and diesel products boiling in the temperature range of 36-370° C.; and one or more outlets for discharging bottoms216including hydrocarbons boiling above about 370° C. In certain embodiments, the temperature cut point for bottoms216(and correspondingly the end point for the products214) is in the range of 350 to 400° C. or 360 to 400° C.

The fractionating zone210bottoms outlet is in fluid communication with the HPNA separation zone220described herein, which generally includes an outlet for discharging HPNA-reduced fractionator bottoms222and an outlet for discharging a stream224containing HPNA compounds. The outlet discharging HPNA-reduced fractionator bottoms222is in fluid communication with one or more inlets of reaction zone228and/or232for recycle of all or a portion of the stream. In certain embodiments, a bleed stream218is drawn from bottoms216upstream of the HPNA separation zone220. In additional embodiments, a bleed stream226is drawn from HPNA-reduced fractionator bottoms222downstream of the HPNA separation zone220, in addition to or instead of bleed stream218. Either or both of these bleed streams are hydrogen-rich and therefore can be effectively integrated with certain fuel oil pools, or serve as feed to fluidized catalytic cracking or steam cracking processes (not shown).

In operation of the system200, a feedstock stream202and a hydrogen stream204are charged to the first reaction zone228. Hydrogen stream204includes an effective quantity of hydrogen to support the requisite degree of hydrocracking, feed type, and other factors, and can be any combination including make-up hydrogen, recycle hydrogen from optional gas separation subsystems (not shown) between reaction zones228and232, recycle hydrogen from optional gas separation subsystems (not shown) between reaction zone232and fractionator210, and/or derived from fractionator gas stream212. First reaction zone228operates under effective conditions for production of reaction effluent stream230(optionally after one or more high pressure and low pressure separation stages to recover recycle hydrogen) which is passed to the second reaction zone232, optionally along with an additional hydrogen stream205. Second reaction zone232operates under conditions effective for production of the reaction effluent stream234, which contains converted, partially converted and unconverted hydrocarbons. The reaction effluent stream further includes HPNA compounds that were formed in the reaction zones228and/or232.

The reaction effluent stream234is passed to fractionation zone210, generally to recover gas and liquid products and by-products, and separate a bottoms fraction containing HPNA compounds. Gas stream212, typically containing H2, H2S, NH3, and light hydrocarbons (C1-C4), is discharged and recovered and can be further processed as is known in the art, including for recovery of recycle hydrogen. One or more cracked product streams214are discharged appropriate outlets of the fractionator and can be further processed and/or blended in downstream refinery operations to produce gasoline, kerosene and/or diesel fuel, or other petrochemical products. In certain embodiments (not shown), fractionating zone210can operate as a flash vessel to separate heavy components at a suitable cut point, for example, a range corresponding to the upper temperature range of the desired gasoline, kerosene and/or diesel products for downstream operations. In certain embodiments, a suitable cut point is in the range of 350 to 450° C., 360 to 450° C., 370 to 450° C., 350 to 400° C., 360 to 400° C., 370 to 400° C., 350 to 380° C., or 360 to 380° C.

All or a portion of the fractionator bottoms stream216from the reaction effluent, including HPNA compounds formed in the reaction zones228and/or232, is passed to the HPNA separation zone220for treatment. In certain embodiments, a portion of the fractionator bottoms from the reaction effluent is removed as bleed stream218. Bleed stream218can be about 0-10 V %, 1-10 V %, 1-5 V % or 1-3 V % of the fractionator bottoms216. The concentration of HPNA compounds in the fractionator bottoms is reduced in the HPNA separation zone220to produce the HPNA-reduced fractionator bottoms stream222. A discharge stream224containing HPNA compounds is removed from the HPNA separation zone220. In certain embodiments, instead of or in conjunction with bleed stream218, a portion of the HPNA-reduced fractionator bottoms stream222is removed from the recycle loop as bleed stream226. Bleed stream226can be about 0-10 V %, 1-10 V %, 1-5 V % or 1-3 V % of the HPNA-reduced fractionator bottoms stream222.

Accordingly, all or a portion of the HPNA-reduced fractionator bottoms stream222is recycled to the second reaction zone232as stream222a, the first reaction zone228as stream222b, or both the first and second reaction zones228and232. For instance, stream222bcomprises 0 to 100 V %, in certain embodiments 0 to about 80 V %, and in further embodiments 0 to about 50 V % of stream222which is recycled to zone228, and stream222acomprises 0 to 100 V %, in certain embodiments 0 to about 80 V %, and in further embodiments 0 to about 50 V % of stream222is recycled to zone232.

First reaction zone228can contain one or more fixed-bed, ebullated-bed, slurry-bed, moving bed, continuous stirred tank (CSTR), or tubular reactors, in series and/or parallel arrangement. The reactor(s) are generally operated under conditions effective for the desired degree of conversion in the first reaction zone228, the particular type of reactor, the feed characteristics, and the desired product slate. For instance, these conditions can include a reaction temperature in the range of from about 300 to 500° C., 330 to 500° C., 300 to 475° C., 330 to 475° C., 300 to 475° C. or 330 to 450° C.; a reaction pressure in the range of from about 60 to 300 bar, 60 to 200 bar, 60 to 180 bar, 100 to 300 bar, 100 to 200 bar, 100 to 180 bar, 130 to 300 bar, 130 to 200 bar, or 130 to 180 bar; a hydrogen feed rate up to about 2500 SLt/Lt, in certain embodiments from about 800 to 2000 SLt/Lt, 800 to 1500 SLt/Lt, 1000 to 2000 SLt/Lt, or 1000 to 1500 SLt/Lt; and a feed rate in the range of from about 0.1 to 10 h−1, 0.1 to 5 h−1, 0.1 to 2 h−1, 0.25 to 10 h−1, 0.25 to 5 h−1, 0.25 to 2 h−1, 0.5 to 10 h−1, 0.5 to 5 h−1, or 0.5 to 2 h−1.

The catalyst used in the first reaction zone228contains one or more active metal components selected from the Periodic Table of the Elements IUPAC Groups 6-10. In certain embodiments, the active metal component is one or more of cobalt, nickel, tungsten and molybdenum. The active metal component(s) are typically deposited or otherwise incorporated on a support, which can be amorphous and/or structured, such as alumina, silica alumina, silica, titania, titania-silica, titania-silicate or zeolites. In embodiments using zeolite-based catalysts, HPNA compounds have relatively greater tendency to accumulate in the recycle stream due to the inability for these larger molecules to diffuse into the catalyst pore structure, particularly at relatively lower hydrogen partial pressure levels in the reactor. However, according to the process herein, by removing HPNA compounds from the recycle stream in embodiments where HPNA-reduced bottoms are recycled to the first reaction zone228, the lifecycle of such zeolite catalyst is increased.

Second reaction zone232can contain one or more fixed-bed, ebullated-bed, slurry-bed, moving bed, continuous stirred tank (CSTR), or tubular reactors, in series and/or parallel arrangement. The reactor(s) are generally operated under conditions effective for the particular type of reactor, the feed characteristics, and the desired product slate. For instance, these conditions can include a reaction temperature in the range of from about 300 to 500° C., 330 to 500° C., 300 to 475° C., 330 to 475° C., 300 to 475° C. or 330 to 450° C.; a reaction pressure in the range of from about 60 to 300 bar, 60 to 200 bar, 60 to 180 bar, 100 to 300 bar, 100 to 200 bar, 100 to 180 bar, 130 to 300 bar, 130 to 200 bar, or 130 to 180 bar; a hydrogen feed rate up to about 2500 SLt/Lt, in certain embodiments from about 800 to 2000 SLt/Lt, 800 to 1500 SLt/Lt, 1000 to 2000 SLt/Lt, or 1000 to 1500 SLt/Lt; and a feed rate in the range of from about 0.1 to 10 h−1, 0.1 to 5 h−1, 0.1 to 2 h−1, 0.25 to 10 h−1, 0.25 to 5 h−1, 0.25 to 2 h−1, 0.5 to 10 h−1, 0.5 to 5 h−1, or 0.5 to 2 h−1.

The catalyst used in the second reaction zone232contains one or more active metal components selected from the Periodic Table of the Elements IUPAC Group 6-10. In certain embodiments, the active metal component is one or more of cobalt, nickel, tungsten and molybdenum. In embodiments in which the first reaction zone reduces contaminants such as sulfur and nitrogen, so that hydrogen sulfide and ammonia are minimized in the second reaction zone, active metal components effective as hydrogenation catalysts can include one or more noble metals such as platinum or palladium, alone or in combination with other active metals. The active metal component(s) are typically deposited or otherwise incorporated on a support, which can be amorphous and/or structured, such as alumina, silica alumina, silica, titania, titania-silica, titania-silicates or zeolites.

In embodiments using zeolite-based catalysts, HPNA compounds have relatively greater tendency to accumulate in the recycle stream due to the inability for these larger molecules to diffuse into the catalyst pore structure, particularly at relatively lower hydrogen partial pressure levels in the reactor. However, according to the process herein, by removing HPNA compounds from the recycle stream in embodiments where HPNA-reduced bottoms are recycled to the second reaction zone232, the lifecycle of such zeolite catalyst is increased.

Two-Stage with Recycle

FIG. 3is a process flow diagram of another embodiment of an integrated hydrocracking unit operation, system300, which operates as two-stage hydrocracking system with recycle. In general, system300includes a first reaction zone336, a second reaction zone340, a fractionating zone310, and an HPNA separation zone320.

First reaction zone336generally includes one or more inlets in fluid communication with a source of initial feedstock302and a source of hydrogen gas304. One or more outlets of the first reaction zone336that discharge effluent stream338is in fluid communication with one or more inlets of the fractionating zone310(optionally having one or more high pressure and low pressure separation stages therebetween for recovery of recycle hydrogen, not shown).

Fractionating zone310includes one or more outlets for discharging gases312, typically H2S, NH3, and light hydrocarbons (C1-C4); one or more outlets for recovering product314, such as naphtha and diesel products boiling in the temperature range of 36-370° C.; and one or more outlets for discharging bottoms316including hydrocarbons boiling above about 370° C. In certain embodiments, the temperature cut point for bottoms316(and correspondingly the end point for the products314) is a range corresponding to the upper temperature limit of the desired gasoline, kerosene and/or diesel product boiling point ranges for downstream operations.

The fractionating zone310bottoms outlet is in fluid communication with the HPNA separation zone320described herein, which generally includes an outlet for discharging HPNA-reduced fractionator bottoms322and an outlet for discharging a stream324containing HPNA compounds. The outlet discharging HPNA-reduced fractionator bottoms322is in fluid communication with one or more inlets of the second reaction zone340for recycle of all or a portion322aof the recycle stream322. In certain optional embodiments (as indicated by dashed lines inFIG. 3), a portion322bis in fluid communication with one or more inlets of the first reaction zone336. In certain embodiments, a bleed stream318is drawn from bottoms316upstream of the HPNA separation zone320. In additional embodiments, a bleed stream326is drawn from HPNA-reduced fractionator bottoms322downstream of the HPNA separation zone320, in addition to or instead of bleed stream318. Either or both of these bleed streams are hydrogen-rich and therefore can be effectively integrated with certain fuel oil pools, or serve as feed to fluidized catalytic cracking or steam cracking processes (not shown).

Second reaction zone340generally includes one or more inlets in fluid communication with one or more outlets of the HPNA separation zone320for receiving HPNA-reduced fractionator bottoms322and a source of hydrogen gas306. One or more outlets of the second reaction zone340that discharge effluent stream342are in fluid communication with one or more inlets of the fractionating zone310(optionally having one or more high pressure and low pressure separation stages therebetween for recovery of recycle hydrogen, not shown).

In operation of the system300, a feedstock stream302and a hydrogen stream304are charged to the first reaction zone336. Hydrogen stream304includes an effective quantity of hydrogen to support the requisite degree of hydrocracking, feed type, and other factors, and can be any combination including make-up hydrogen, recycle hydrogen from optional gas separation subsystems (not shown) between first reaction zone336and fractionating zone310, recycle hydrogen from optional gas separation subsystems (not shown) between second reaction zone340and fractionating zone310, and/or derived from fractionator gas stream312. First reaction zone336operates under effective conditions for production of reaction effluent stream338(optionally after one or more high pressure and low pressure separation stages to recover recycle hydrogen) which is passed to the fractionating zone310.

The reaction effluent stream338is passed to fractionation zone310, generally to recover gas and liquid products and byproducts, and separate a bottoms fraction containing HPNA compounds. Gas stream312, typically containing H2, H2S, NH3, and light hydrocarbons (C1-C4), is discharged and recovered and can be further processed as is known in the art, including for recovery of recycle hydrogen. One or more cracked product streams314are discharged appropriate outlets of the fractionator and can be further processed and/or blended in downstream refinery operations to produce gasoline, kerosene and/or diesel fuel, or other petrochemical products. In certain embodiments (not shown), fractionating zone310can operate as a flash vessel to separate heavy components at a suitable cut point, for example, a range corresponding to the upper temperature range of the desired gasoline, kerosene and/or diesel products for downstream operations. In certain embodiments, a suitable cut point is in the range of 350 to 450° C., 360 to 450° C., 370 to 450° C., 350 to 400° C., 360 to 400° C., 370 to 400° C., 350 to 380° C., or 360 to 380° C.

All or a portion of the fractionator bottoms stream316from the reaction effluent, including HPNA compounds formed in the first reaction zone336, is passed to the HPNA separation zone320for treatment. In certain embodiments, a portion of the fractionator bottoms from the reaction effluent is removed as bleed stream318. Bleed stream318can be about 0-10 V %, 1-10 V %, 1-5 V % or 1-3 V % of the fractionator bottoms316. The concentration of HPNA compounds in the fractionator bottoms is reduced in the HPNA separation zone320to produce the HPNA-reduced fractionator bottoms stream322. A discharge stream324containing HPNA compounds is removed from the HPNA separation zone320. In certain embodiments, instead of or in conjunction with bleed stream318, a portion of the HPNA-reduced fractionator bottoms stream322is removed from the recycle loop as bleed stream326. Bleed stream326can be about 0-10 V %, 1-10 V %, 1-5 V % or 1-3 V % of the HPNA-reduced fractionator bottoms stream322.

Accordingly, all or a portion of the HPNA-reduced fractionator bottoms stream322is passed to the second reaction zone340as stream322a. In certain embodiments, all or a portion of the HPNA-reduced fractionator bottoms stream322is recycled to the second reaction zone340as stream322a, the first reaction zone336as stream322b, or both the first and second reaction zones336and340. For instance, stream322bwhich is recycled to zone336comprises 0 to 100 V %, 0 to about 80 V %, or 0 to about 50 V % of stream322, and stream322awhich is recycled to zone340comprises 0 to 100 V %, 0 to about 80 V %, or 0 to about 50 V % of stream322is recycled to zone340.

Second reaction zone340operates under conditions effective for production of the reaction effluent stream342, which contains converted, partially converted and unconverted hydrocarbons. The second stage the reaction effluent stream342is passed to the fractionating zone310, optionally through one or more gas separators to recovery recycle hydrogen and remove certain light gases

First reaction zone336can contain one or more fixed-bed, ebullated-bed, slurry-bed, moving bed, continuous stirred tank (CSTR), or tubular reactors, in series and/or parallel arrangement. The reactor(s) are generally operated under conditions effective for the degree of conversion in the first reaction zone336, the particular type of reactor, the feed characteristics, and the desired product slate. For instance, these conditions can include a reaction temperature in the range of from about 300 to 500° C., 330 to 500° C., 300 to 475° C., 330 to 475° C., 300 to 475° C. or 330 to 450° C.; a reaction pressure in the range of from about 60 to 300 bar, 60 to 200 bar, 60 to 180 bar, 100 to 300 bar, 100 to 200 bar, 100 to 180 bar, 130 to 300 bar, 130 to 200 bar, or 130 to 180 bar; a hydrogen feed rate up to about 2500 SLt/Lt, in certain embodiments from about 800 to 2000 SLt/Lt, 800 to 1500 SLt/Lt, 1000 to 2000 SLt/Lt, or 1000 to 1500 SLt/Lt; and a feed rate in the range of from about 0.1 to 10 h−1, 0.1 to 5 h−1, 0.1 to 2 h−1, 0.25 to 10 h−1, 0.25 to 5 h−1, 0.25 to 2 h−1, 0.5 to 10 h−1, 0.5 to 5 h−1, or 0.5 to 2 h−1.

The catalyst used in the first reaction zone336contains one or more active metal components selected from the Periodic Table of the Elements IUPAC Groups 6-10. In certain embodiments the active metal component is one or more of cobalt, nickel, tungsten and molybdenum, typically deposited or otherwise incorporated on a support, which can be amorphous and/or structured, such as alumina, silica-alumina, silica, titania, titania-silica, titania-silicates, or zeolites. In embodiments using zeolite-based catalysts, HPNA compounds have relatively greater tendency to accumulate in the recycle stream due to the inability for these larger molecules to diffuse into the catalyst pore structure, particularly at relatively lower hydrogen partial pressure levels in the reactor. However, according to the process herein, by removing HPNA compounds from the recycle stream in embodiments where HPNA-reduced bottoms are recycled to the first reaction zone336, the lifecycle of such zeolite catalyst is increased.

Second reaction zone340can contain one or more fixed-bed, ebullated-bed, slurry-bed, moving bed, continuous stirred tank (CSTR), or tubular reactors in a series and/or parallel arrangement. The reactor(s) are operated under conditions effective for the particular type of reactor, the feed characteristics, and the desired product slate. For instance, these conditions can include a reaction temperature in the range of from about 300 to 500° C., 330 to 500° C., 300 to 475° C., 330 to 475° C., 300 to 475° C. or 330 to 450° C.; a reaction pressure in the range of from about 60 to 300 bar, 60 to 200 bar, 60 to 180 bar, 100 to 300 bar, 100 to 200 bar, 100 to 180 bar, 130 to 300 bar, 130 to 200 bar, or 130 to 180 bar; a hydrogen feed rate up to about 2500 SLt/Lt, in certain embodiments from about 800 to 2000 SLt/Lt, 800 to 1500 SLt/Lt, 1000 to 2000 SLt/Lt, or 1000 to 1500 SLt/Lt; and a feed rate in the range of from about 0.1 to 10 h−1, 0.1 to 5 h−1, 0.1 to 2 h−1, 0.25 to 10 h−1, 0.25 to 5 h−1, 0.25 to 2 h−1, 0.5 to 10 h−1, 0.5 to 5 h−1, or 0.5 to 2 h−1.

The catalyst used in the second reaction zone340contains one or more active metal components selected from IUPAC Groups 6-10 of the Periodic Table of the Elements. In certain embodiments, the active metal component is one or more of cobalt, nickel, tungsten and molybdenum. In embodiments in which the first reaction zone reduces contaminants such as sulfur and nitrogen so that hydrogen sulfide and ammonia are minimized in the second reaction zone, active metal components effective as hydrogenation catalysts can include one or more noble metals such as platinum or palladium alone or in combination with other active metals. The active metal component(s) are typically deposited or otherwise incorporated on a support, which can be amorphous and/or structured, such as alumina, silica-alumina, silica, titania, titania-silica, titania-silicates, or zeolites.

In embodiments using zeolite-based catalysts, HPNA compounds have relatively greater tendency to accumulate in the recycle stream due to the inability of these larger molecules to diffuse into the catalyst pore structure, particularly at relatively lower hydrogen partial pressure levels in the reactor. However, according to the present process, by removing HPNA compounds from the recycle stream in embodiments where HPNA-reduced bottoms are recycled to the second reaction zone340, the lifecycle of such zeolite catalyst is increased.

As noted above, heavy poly-nuclear aromatic compound formation is a major concern for hydrocracking unit operators. All known hydrocracking processes and catalysts are subject to undesirable side reactions leading to the formation of heavy poly-nuclear aromatic (HPNA) compounds, which accumulate in the unconverted oil recycle stream. These compounds are virtually impossible to convert by hydrocracking reactions and show a strong tendency to build up to high concentration levels in the recycle oil stream. As the concentration builds up, the performance of the reactor system is continuously degraded leading to inefficient and uneconomic conditions. These problems are addressed by the current process by the removal of HPNA molecules from the recycle stream by adsorption and ionic liquid extraction. The treated recycle stream that is substantially HPNA-free or HPNA-reduced will extend the efficient performance of the hydrocracking unit, catalyst activity, stability, and increase product yields and quality.

The process and system of the invention can advantageously be installed in an existing refinery as an integrated adsorption and extraction operation downstream of the hydrocracking systems, such as the ones described above in reference toFIGS. 1, 2 and/or 3, to remove HPNA compounds from the recycle stream to provide flexibility to refinery hydrocracking unit operations for removal of HPNA compounds from the recycle streams and avoid the need to purge a portion of the recycle stream, thereby improving the overall efficiency of the unit operation.

The HPNA separation zone120,220and320integrated in hydrocracking systems100,200and300described herein, and variations thereto which will be apparent to a person having ordinary skill in the art, is effective for removal of HPNA compounds from a bottoms recycle stream. These bottoms fractions contain HPNA compounds that were formed in the reaction zones, and are treated in the HPNA separation zone to separate HPNA compounds and produce the reduced-HPNA hydrocracked bottoms stream.

In accordance with the various embodiments herein, hydrocracked bottoms fractions containing HPNA compounds are subjected to ionic liquid extraction and adsorption, in either order, i.e., consistent with Embodiment 1 or Embodiment 2, under reaction conditions suitable to remove HPNA and form an HPNA-reduced hydrocracked bottoms fraction. The bottoms fraction is mostly naphthenic and paraffinic.

Referring toFIG. 5, a process and system500for the removal of HPNA from a hydrocracker recycle stream and feed is schematically illustrated that includes an adsorption zone, an ionic liquid extractor zone, and separation zones. It will be understood that process and system500can be any of120,220, or320that were described above.

The adsorption zone510includes an inlet for receiving a hydrocracker residuals feed116,216or316that is rich in HPNAs/HPNA precursors, and hydrocracker bottoms recycle stream503. An effluent512from the adsorption column510, that has had most of the HPNAs and HPNA precursors removed, is sent to the inlet of an extractor560. Extractor560also has an inlet for receiving ionic liquid stream542consisting of one or more ionic liquids. Extractor560extracts the remaining HPNAs/HPNA precursors from the hydrocarbon oil with ionic liquids.

The extracted HPNAs/HPNA precursors from extractor560are sent with the ionic liquids via stream524to an inlet in solvent extractor540. Extractor540uses an organic polar solvent, introduced via solvent stream562, to separate the HPNAs/HPNA precursors from the ionic liquids. The ionic liquids recovered are recycled via stream542to the extractor560. Remaining solvent and HPNAs/HPNA precursors are sent from solvent extractor540via stream544to solvent recovery unit550, where the solvent is recovered and recycled via stream554back to the solvent extractor540. The remaining HPNAs/HPNA precursors are recovered via stream124,224, or324from the solvent recovery unit.

The treated stream522, that has substantially no free HPNAs/HPNA precursors or ionic liquids, is sent from extractor560to a liquid-liquid separator530. Any remaining ionic liquids and HPNAs/HPNA precursors are separated from the rest of the hydrocarbon stream and are discharged via stream534from the liquid-liquid separator530. HPNA compounds and HPNA precursors and ionic liquid stream534is mixed with HPNAs/HPNA precursors and ionic liquid stream524before being sent to solvent extractor540. A HPNA-reduced fractionator bottoms122,222, or322is then substantially free of HPNAs/HPNA precursors and can be recovered as the feed to the hydrocracking unit (not shown).

Referring toFIG. 6, a process and system600for the removal of HPNA compounds and HPNA precursors from a hydrocracker feed is schematically illustrated. The system includes an ionic liquid extraction zone, an adsorption zone, and separation zones. It will be understood that process and system600can be any of120,220, or320that were described above.

The ionic liquid extraction zone includes extractor660that has an inlet for receiving a hydrocracker residuals feed116,216, or316that is rich in HPNA compounds and HPNA precursors, ionic liquid stream642, and hydrocracker bottoms recycle stream603. Extractor660extracts most of the HPNA compounds and HPNA precursors with ionic liquids.

The extracted HPNAs/HPNA precursors from extractor660are sent with the ionic liquids via stream624to an inlet of a solvent extractor640. Extractor640uses a polar organic solvent, introduced via solvent stream662, to separate the HPNAs/HPNA precursors from the ionic liquids. The ionic liquids recovered are recycled via stream642to the extractor660. Remaining solvent and HPNAs/HPNA precursors are sent from solvent extractor640via stream644to solvent recovery unit650, where the solvent is recovered and recycled via stream654back to the solvent extractor640. The remaining HPNAs/HPNA precursors are recovered via stream124,224, or324from the solvent recovery unit.

The treated stream622that has had most of the HPNAs/HPNA precursors and ionic liquids removed is sent from extractor660to a liquid-liquid separator630. Remaining ionic liquids and HPNAs/HPNA precursors are separated from the hydrocarbon stream and are discharged via stream334from the liquid-liquid separator630. HPNAs/HPNA precursors and ionic liquid stream334is mixed with HPNAs/HPNA precursors and ionic liquid stream624before being sent to solvent extractor340.

Stream632, having a substantially reduced content of HPNAs/HPNA precursors, is sent to adsorption column610to remove any remaining HPNAs/HPNA precursors or ionic liquids. A fractionator bottoms stream122,222, or322from the adsorption column610that is substantially free of HPNAs/HPNA precursors is recovered for use as the feed to the hydrocracking unit.

EXAMPLES

The following laboratory examples demonstrate the effectiveness of the process in separating HPNA compounds and precursors from hydrocracker bottoms.

Ionic Liquid Extraction

A mixture of 80 grams of hydrocracking unit bottoms and 20 grams of the ionic liquid, 1-butyl-3-methylimidazolium-hexafluoro phosphate was heated to 50° C. and continuously stirred for 30 minutes at 50° C. Thereafter, 100 cc of pentane was added to the mixture with stirring to assure thorough contact of the constituents. The mixture was transferred to a separatory funnel to separate the ionic liquid and oil-pentane mixture. The pentane was evaporated from the oil-pentane mixture in a rotary evaporator and the treated hydrocracking unit bottom stream was recovered. The material balance for the example is shown in Table 1.

Ionic Liquid Extraction Followed by Adsorption

A mixture of 80 grams of hydrocracking unit bottoms and 20 grams of the ionic liquid, 1-butyl-3-methylimidazolium-hexafluoro phosphate was heated to 50° C. and continuously stirred for 30 minutes at 50° C. Thereafter, 100 cc of pentane was added to the mixture with stirring to assure thorough contact of the constituents. The mixture was transferred to a separatory funnel to separate the ionic liquid and the oil-pentane mixture. The oil-pentane mixture was passed thru a column containing 60 grams of attapulgus clay. The column effluents are collected and more pentane was added until a colorless effluent was obtained from the column. The pentane was evaporated in a rotary vaporator and a treated hydrocracker bottom stream was obtained. The material balance for this example is shown in Table 1.

Example 3 Adsorption Followed by Ionic Liquid Extraction

A mixture of 80 grams of hydrocracking unit bottoms and 100 cc of pentane was stirred to dissolve the oil. The solution was passed thru a column containing 60 grams of attapulgus clay. The column effluents were collected and more pentane was added until a colorless effluent was obtained from the column all of which were collected and mixed with 20 grams of the ionic liquid, 1-butyl-3-methylimidazolium-hexafluoro phosphate. The mixture was heated and maintained at 50° C. with continuous stirring for 30 minutes. The mixture was transferred to a separatory funnel for separation of the ionic liquid from the oil phase. The pentane was evaporated in a rotary vaporator and the treated hydrocracker bottom stream was recovered. The material balance for this example is shown in Table 1.

As noted above, the ionic liquid employed was 1-butyl-3-methylimidazolium-hexaflouro phosphate.

The products from Examples 1 and 2 were analyzed for HPNA molecules using high pressure liquid chromatography (HPLC) methods. The results are summarized in Tables 2, 3 and 4. The structure of these molecules are shown inFIG. 4.

The most difficult HPNA compounds to process in the hydrocracking unit are the molecules formed from 10 or more condensed aromatic rings. As shown in Table 2, the 10-ring ovalene removal rate is only 12 W % following ionic liquid extraction. However, when the adsorption step is added to the ionic liquid extraction step in the two-stage treatment, as much as 92 W % of the ovalenes were removed from the hydrocracking bottoms stream.

The combined adsorption followed by extraction steps and the extraction followed by adsorption steps of the processes described above are both highly efficient and effective in removing substantially all of the HPNA compounds and HPNA precursors without significant loss of the feed and/or hydrocracker bottom recycle stream.

The method and system of the present invention have been described above and in the attached drawings; however, modifications will be apparent to those of skill in the art and the scope of protection for the invention is to be determined by the claims that follow.