RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 62/983,652, filed on February 29, 2020, the disclosure of which is hereby incorporated by reference in its entirety.

FIELD

[0002] The present disclosure relates generally to processes and apparatuses for separating p-xylene from a liquid feed stream.

TECHNICAL BACKGROUND

[0003] In processes in the chemical, food, and pharmaceutical industries, various separation techniques are used to isolate one material from another. Common techniques for separating solid materials from a liquid include vacuum or pressure filtration, drying, centrifugation, sedimentation and clarification. In many chemical processes, these solid- liquid separation methods can play a critical role in the manufacture and isolation of particular chemical intermediates. For example, p-xylene is a chemical intermediate that, in a highly purified form, can be used to produce terephthalic acid.

[0004] Typically, p-xylene is crystallized and then separated from mother liquor in a centrifuge to provide a product sufficiently pure for industrial applications. Centrifugation is a common solid-liquid separation technique, in which rapid rotation causes denser materials to move outward from the axis of rotation, while less-dense materials are displaced and move inward. Centrifuges are necessarily complex, involving moving parts that rotate at high speeds for extended periods of time. Accordingly, centrifuges can be costly to install and difficult to maintain.

[0005] But previous efforts to utilize more robust techniques such as filtration for p- xylene recovery have been unsuccessful. With a large effective pore size, filtration can be robust, but the purity of the filtered product is too low. And with an effective pore size sufficiently small to provide a high-purity product, filtration can be slow and unreliable (e.g., at later, low-temperature crystallization stages), necessitating costly redundancy in plant design.

[0006] There accordingly remains a need for a p-xylene separation process having improved efficiency, throughput, and/or reliability.

SUMMARY

[0007] The scope of the present disclosure is not affected to any degree by the statements within the summary.

[0008] In one aspect, the disclosure provides a method for recovering p-xylene, comprising in a crystallizer of a first crystallization zone, cooling a liquid feed stream comprising p-xylene to form a first solid/liquid mixture comprising solid p-xylene and mother liquor; transferring an effluent of the first crystallization zone to a second crystallization zone; in a crystallizer of the second crystallization zone, cooling at least a portion of the effluent to form a second solid/liquid mixture comprising solid p-xylene and mother liquor; transferring an effluent of the second crystallization zone to a third crystallization zone; in a crystallizer of the third crystallization zone, cooling at least a portion of the effluent to form a third solid/liquid mixture comprising solid p-xylene and mother liquor; transferring an effluent of the third crystallization zone to a recovery zone; in the recovery zone, filtering at least a portion of the effluent through at least one filter of a filter column of the recovery zone, the filter having a fourth effective pore size, to form a fourth filtrate comprising mother liquor and a fourth product stream comprising solid p-xylene, and then slurrying the fourth product stream in a reslurry liquid to form a fourth reslurry stream; and in one or more of the first crystallization zone, the second crystallization zone, and the third crystallization zone, filtering the solid/liquid mixture through at least one filter in a filter column, the filter having an effective pore size larger than the fourth effective pore size, to form a filtrate comprising mother liquor and a product stream comprising solid p-xylene, and then slurrying the product stream in a reslurry liquid to form a reslurry stream, wherein the crystallization zone effluent comprises the filtrate.

[0009] In certain embodiments as otherwise described herein, the first solid/liquid mixture is filtered through at least one filter in a first filter column in the first crystallization zone to form a first filtrate comprising mother liquor and a first product stream comprising solid p-xylene, the filter having a first effective pore size larger (e.g., at least 25%, at least 50%, at least 100%, at least 200%, or at least 300% larger) than the fourth effective pore size, and then the first product stream is slurried in a reslurry liquid to form a first reslurry stream; and the first crystallization zone effluent comprises the first filtrate.

[0010] In certain embodiments as otherwise described herein, p-xylene is present in the first filtrate in an amount that is at least 1 wt.% (e.g., 1-5 wt.%) greater than the p-xylene solubility limit of the first filtrate.

[0011] In certain embodiments as otherwise described herein, the second solid/liquid mixture is filtered through at least one filter in a filter column in the second crystallization zone to form a second filtrate comprising mother liquor and a second product stream comprising solid p-xylene, the filter having a second effective pore size larger (e.g., at least 25%, at least 50%, at least 100%, at least 200%, or at least 300% larger) than the fourth effective pore size, and then the second product stream is slurried in a reslurry liquid to form a second reslurry stream; and the second crystallization zone effluent comprises the second filtrate.

[0012] In certain embodiments as otherwise described herein, p-xylene is present in the second filtrate in an amount that is at least 1 wt.% (e.g., 1-5 wt.%) greater than the p-xylene solubility limit of the second filtrate.

[0013] In certain embodiments as otherwise described herein, the third solid/liquid mixture is filtered through at least one filter in a filter column in the third crystallization zone to form a third filtrate comprising mother liquor and a third product stream comprising solid p- xylene, the filter having a third effective pore size larger (e.g., at least 25%, at least 50%, at least 100 at least 200%, or at least 300% larger) than the fourth effective pore size, and then the third product stream is slurried in a reslurry liquid to form a third reslurry stream; and the third crystallization zone effluent comprises the third filtrate.

[0014] In certain embodiments as otherwise described herein, p-xylene is present in the third filtrate in an amount that is at least 1 wt.% (e.g., 1-5 wt.%) greater than the p-xylene solubility limit of the third filtrate.

[0015] In certain embodiments as otherwise described herein, p-xylene is present in the fourth filtrate in an amount that is at most 1 wt.% (e.g., 0.1-0.9 wt.%) greater than the p- xylene solubility limit of the fourth filtrate.

[0016] In certain embodiments as otherwise described herein, solid p-xylene is present in the fourth product stream in an amount that is at most 67% (e.g., at most 60% or at most 50%) of a total amount of solid p-xylene present in the first product stream, second product stream, third product stream, and fourth product stream.

[0017] In certain embodiments as otherwise described herein, at least a portion of the fourth reslurry stream and at least a portion of one or more of the first reslurry stream, second reslurry stream, and third reslurry stream are transferred to an efficiency-stage slurry drum of an efficiency zone. [0018] In certain embodiments as otherwise described herein, at least a portion of an effluent of the efficiency-stage slurry drum is separated to form a fifth filtrate comprising reslurry liquid and a fifth product stream comprising solid p-xylene; at least a portion of the fifth product stream is slurried in a reslurry liquid to form a fifth reslurry stream; at least a portion of the fifth reslurry stream is transferred to a product-stage slurry drum of a product zone; and at least a portion of an effluent of the product-stage slurry drum is separated to form a sixth filtrate comprising reslurry liquid and a sixth product stream comprising p-xylene.

[0019] In certain embodiments as otherwise described herein, at least a portion of the fifth filtrate is transferred to the first crystallization zone.

[0020] In certain embodiments as otherwise described herein, the reslurry liquid of one or more of the first crystallization zone, second crystallization zone, third crystallization zone, and recovery zone comprises at least a portion of the fifth filtrate or sixth filtrate.

[0021] In certain embodiments as otherwise described herein, the reslurry liquid comprising the fifth reslurry stream includes at least a portion of the sixth filtrate.

[0022] In another aspect, the disclosure provides an apparatus for recovering p-xylene, comprising a first crystallizer; a second crystallizer in fluid communication with the first crystallizer; a third crystallizer in fluid communication with the second crystallizer; and a fourth filter unit comprising at least one filter column, each filter column in fluid communication with the third crystallizer, each filter column including at least one filter, each filter having a fourth effective pore size; and further comprising at least one of a first filter unit comprising at least one filter column, each filter column providing the fluid communication between the first crystallizer and the second crystallizer, each filter column including at least one filter, each filter having a first effective pore size; a second filter unit comprising at least one filter column, each filter column providing the fluid communication between the second crystallizer and the third crystallizer, each filter column including at least one filter, each filter having a second effective pore size; and a third filter unit comprising at least one filter column, each filter column providing the fluid communication between the third crystallizer and the fourth filter unit, each filter column including at least one filter, each filter having a third effective pore size.

[0023] In certain embodiments as otherwise described herein, the apparatus further comprises an efficiency-stage slurry drum in fluid communication with the fourth filter unit; a fifth filter unit comprising at least one filter column, each filter column in fluid communication with the efficiency-stage slurry drum, each filter column including at least one filter, each filter having a fifth effective pore size; a product-stage slurry drum in fluid communication with the fifth filter unit; and a sixth filter unit comprising at least one wash column, each wash column in fluid communication with the product-stage slurry drum.

[0024] In certain embodiments as otherwise described herein, the apparatus comprises the second filter unit, and the second effective pore size is larger (e.g., at least 25%, at least 50%, at least 100%, at least 200%, or at least 300% larger) than the fourth effective pore size.

[0025] In certain embodiments as otherwise described herein, the second filter unit comprises 3-5 filter columns, and the fourth filter unit comprises 3-5 filter columns.

[0026] In certain embodiments as otherwise described herein, the apparatus comprises the first filter unit, and the first effective pore size is larger (e.g., at least 25%, at least 50%, at least 100%, at least 200%, or at least 300% larger) than the fourth effective pore size. [0027] In certain embodiments as otherwise described herein, the first filter unit comprises 2-4 filter columns, and the fourth filter unit comprises 4-8 filter columns.

[0028] Other aspects of the disclosure will be apparent to those skilled in the art in view of the description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS [0029] FIG. 1 is a process flow diagram for the separation and recovery of p-xylene in accordance with one embodiment of the present disclosure.

[0030] FIG. 2 is a schematic view of a crystallization zone in accordance with one embodiment of the present disclosure.

[0031] FIG. 3 is a schematic view of a crystallization zone in accordance with one embodiment of the present disclosure.

[0032] FIG. 4 is a side view cross-section of a filter column in accordance with one embodiment of the present disclosure.

DETAILED DESCRIPTION

[0033] In various aspects, the processes of the disclosure provide for improved separation of p-xylene.

[0034] Additional features of the processes of the disclosure will now be described in reference to the drawing figures.

[0035] The present inventors have determined that high-purity p-xylene can be efficiently recovered by filtering crystallized p-xylene in a filter column having a relatively large pore size in one or more crystallization zones upstream of a recovery zone, and then filtering the crystallization zone effluent in the recovery zone, in a filter column having a relatively small pore size. Because the large-pore filter column can reliably recover substantial amounts of solid p-xylene at high throughput, the filtration duty of the small-pore filter column (which operates at lower throughput, and can be prone to failure) is desirably reduced. Surprisingly, then, filtering crystallized p-xylene at one or more stages of crystallization in addition to filtering in a downstream recovery zone can decrease the total number of filter columns necessary for an industrially useful p-xylene recovery process.

[0036] Accordingly, one aspect of the disclosure provides a process comprising, in a crystallizer of a first crystallization zone, cooling a liquid feed stream comprising p-xylene to form a first solid/liquid mixture comprising solid p-xylene and mother liquor; transferring an effluent of the first crystallization zone to a second crystallization zone; in a crystallizer of the second crystallization zone, cooling at least a portion of the effluent to form a second solid/liquid mixture comprising solid p-xylene and mother liquor; transferring an effluent of the second crystallization zone to a third crystallization zone; in a crystallizer of the third crystallization zone, cooling at least a portion of the effluent to form a third solid/liquid mixture comprising solid p-xylene and mother liquor; transferring an effluent of the third crystallization zone to a recovery zone; and in the recovery zone, filtering at least a portion of the effluent through at least one filter of a filter column of the recovery zone, the filter having a fourth effective pore size, to form a fourth filtrate comprising mother liquor and a fourth product stream comprising solid p-xylene, and then slurrying the fourth product stream in a reslurry liquid to form a fourth reslurry stream. In one or more of the first crystallization zone, the second crystallization zone, and the third crystallization zone, the solid/liquid mixture is filtered through at least one filter in a filter column, the filter having an effective pore size larger than the fourth effective pore size, to form a filtrate comprising mother liquor and a product stream comprising solid p-xylene, and then the product stream is slurried in a reslurry liquid to form a reslurry stream, and the crystallization zone effluent comprises the filtrate. As described below, the inventors have determined that using one or more larger- effective pore size filter columns in earlier filtering stages can provide improved process efficiency.

[0037] FIG. 1 is a process flow diagram for separating and recovering p-xylene from a liquid feed stream in accordance with one embodiment of the present disclosure. As shown in FIG. 1, a system for performing a method 100 includes a first crystallization zone 110 including at least one crystallizer (not shown) capable of cooling a liquid feed stream 101 comprising p-xylene to form a first solid/liquid mixture comprising solid p-xylene and mother liquor; a second crystallization zone 120 including at least one crystallizer (not shown) capable of cooling an effluent 111 of the first crystallizer zone 110 to form a second solid/liquid mixture comprising solid p-xylene and mother liquor; a third crystallization zone 130 including at least one crystallizer (not shown) capable of cooling an effluent 121 of the second crystallizer zone 120 to form a third solid/liquid mixture comprising solid p-xylene and mother liquor; a recovery zone 140 including a filter column 142 capable of filtering an effluent 131 of the third crystallizer zone 130 to form a fourth filtrate 141 comprising mother liquor and a fourth product stream comprising solid p-xylene, the filter column 142 further capable of slurrying the fourth product stream in a reslurry liquid to form a fourth reslurry stream 143; an efficiency zone 150 including an efficiency-stage slurry drum 152 capable of receiving the fourth reslurry stream 143, and a filter column 154 capable of separating an effluent 151 of the efficiency-stage slurry drum 152 to form a fifth filtrate 153 comprising reslurry liquid and a fifth product stream comprising solid p-xylene, the filter column 154 further capable of slurrying the fifth product stream to form a fifth reslurry stream 155; and a product zone 160 including a product-stage slurry drum 162 capable of receiving the fifth reslurry stream 155, and a wash column 164 capable of separating an effluent 161 of the product-stage slurry drum 162 to form a sixth filtrate 163 comprising reslurry liquid and a sixth product stream 165 comprising p-xylene.

[0038] The person of ordinary skill in the art will appreciate that a variety of liquids can be used as reslurry liquids. Typically, reslurry liquids are provided by filtrates from the efficiency stage and/or the product stage.

[0039] Streams and materials used in the method represented in FIG. 1 may be directed and transferred through suitable transfer lines, conduits, and piping constructed, for example, from materials appropriate for process use and safety. It will be understood that particular elements may be physically juxtaposed and, where appropriate, may be have flexible regions, rigid regions, or a combination of both. In directed streams, intervening apparatuses and/or optional treatments may be included. By way of example, pumps, valves, manifolds, gas and liquid flow meters and distributors, sampling and sensing devices, and other equipment (e.g., for monitoring, controlling, adjusting, and/or diverting pressures, flows and other operating parameters) may be present.

[0040] In the embodiment of FIG. 1, a liquid feed stream 101 comprising p-xylene is transferred to the first crystallization zone 110. In certain embodiments as otherwise described herein, the liquid feed stream comprises a product stream including p-xylene from a selective or non-selective toluene disproportionation reactor, a selective or non-selective alkylation reactor, a selective or non-selective transalkylation reactor, a catalytic reformer, or a distillation column capable of fractionating, for example, pyrolysis gasoline. In certain embodiments as otherwise described herein, the liquid feed stream comprises a product stream including p-xylene from a reaction zone or a fractionation zone of a xylenes isomerization system.

[0041] In certain embodiments as otherwise described herein, the liquid feed stream comprises 10-70 wt.% p-xylene, e.g., 10-60 wt.%, or 10-50 wt.%, or 10-40 wt.%, or 10-30 wt.%, or 15-70 wt.%, or 20-70 wt.%, or 25-70 wt.%, or 15-60 wt.%, or 15-50 wt.%, or 15- 40 wt.%, or 15-30 wt.% p-xylene. For example, in certain such embodiments, the liquid feed stream comprises 20-30 wt.% p-xylene, 40-60 wt.% m-xylene, and 20-30 wt.% o-xylene. In certain embodiments as otherwise described herein, the feed stream comprises 40-99 wt.% xylenes (e.g., in a near-equilibrium distribution of p-xylene, m-xylene, and o-xylene) and 1- 60 wt.% of a combined amount of benzene, toluene, ethylbenzene, and Cg ₊ aromatic compounds. In certain embodiments as otherwise described herein, the liquid feed stream is substantially free (e.g., comprises less than 2 wt.%, or less than 1 wt.%, or less than 0.5 wt.%, or less than 0.1 wt.%) of solids. Of course, in other embodiments, the liquid feed stream comprises solid p-xylene (e.g., 2-5 wt.% solid p-xylene). [0042] In the first crystallization zone 110, the liquid feed stream 101 is cooled in a crystallizer to form a first solid/liquid mixture comprising solid p-xylene and mother liquor. In certain embodiments as otherwise described herein, the first crystallization zone includes two or more (e.g., two or three) crystallizers configured to operate in parallel.

[0043] In certain embodiments as otherwise described herein, the liquid feed stream is cooled to a temperature below -40 °F (e.g., below -50 °F, or below -60 °F). In certain embodiments as otherwise described herein, the first solid/liquid mixture comprises 5-15 wt.%, e.g., 5-12.5 wt.%, or 5-10 wt.%, or 7.5-15 wt.%, or 10-15 wt.%, or 7.5-12.5 wt.% solid p-xylene.

[0044] FIG. 2 is a schematic view of a crystallization zone in accordance with one embodiment of the present disclosure. In the embodiment of FIG. 2, a crystallization zone

210 includes a crystallizer 212. In operation, a liquid feed stream 201 is cooled in the crystallizer 212 to form a solid/liquid mixture, the solid/liquid mixture comprising the effluent

211 of the crystallization zone 210.

[0045] Accordingly, in certain embodiments as otherwise described herein, the effluent of the first crystallization zone comprises the first solid/liquid mixture (e.g., comprising 5-15 wt.% solid p-xylene).

[0046] FIG. 3 is a schematic view of a crystallization zone in accordance with another embodiment of the present disclosure. In the embodiment of FIG. 3, a crystallization zone 310 includes a crystallizer 312 and a filter column 314. In operation, a liquid feed stream 301 is cooled in the crystallizer 312 to form a solid/liquid mixture 311. The solid/liquid mixture 311 is filtered in the filter column 314 to form a product stream (not shown) and a filtrate 313, and then the product stream is slurried to form a reslurry stream, the reslurry stream comprising the effluent 315 of the crystallization zone 310.

[0047] FIG. 4 is a side view cross-section of a filter column in accordance with one embodiment of the present disclosure. In the embodiment of FIG. 4, a filter column 400 includes a substantially hollow cavity 402 having a closed end 404 and an open end 406.

The cavity 402 can be substantially tubular or cylindrical in shape. Within the cavity 402, at least one filter tube 408 extends in an axial direction, the filter tube 408 having a top portion 410 and a bottom portion 412. The top portion 410 is closed. The filter tube 408 is generally situated in substantial proximity to an inner wall 414 of the column 400. The bottom portion 412 of the filter tube 408 extends through the closed end 404 of the substantially hollow cavity 402, the bottom portion 412 having an opening 416 at a terminal end. The filter tube 408 includes at least one filter 418, attached, integrated, or otherwise affixed to the filter tube 408, forming a connection for flow of a substantially liquid portion of a solid/liquid mixture between the interior of the hollow cavity 402 and the interior of filter tube 408. A product chute 426 extends from the open end 406 of the cavity 402, and includes a reslurry zone 428.

[0048] In operation, a stream 401 comprising a solid/liquid mixture is introduced into a filtration zone 420 of the hollow cavity 402 through an inlet 422. The solid/liquid mixture moves towards the open end 406 of the hollow cavity 402. A substantially liquid portion of the solid/liquid mixture passes through the filter 418 and through opening 416, and is removed from the filter column 400 through outlet 424 as filtrate stream 403. As the substantially liquid portion of the solid/liquid mixture continues to pass through the filter 418, a substantially solid portion of the solid/liquid mixture forms a packed bed within the hollow cavity 402. As the substantially solid portion accumulates, the packed bed increases in size, filling the section between at least one filter tube 408 and the inner wall 414. When the packed bed reaches the open end 406 of the hollow cavity 402, a portion of the packed bed falls into the chute 426. Once the filter column 400 is operating at steady state, the amount of separated solids falling into the chute 426 is about equal to the amount of solids entering the cavity 402 through inlet 422 (i.e. , in the solid/liquid mixture of stream 401). A reslurry liquid stream 405 is introduced into the chute 426 through inlet 430 and mixed with the separated solids in the reslurry zone 428 to form a slurry, which is removed from the filter column 400 through outlet 432 as reslurry stream 407. Of course, the person of ordinary skill in the art will appreciate that suitable filter column configurations other than that depicted in FIG. 4 are generally known in the art. Filter columns are further described in U.S. Patents nos. 7,812,206; 8,211,319; 8,530,716 and 8,962,906, each of which is hereby incorporated herein by reference in its entirety. As used herein, an “effective pore size” of a column is the 90 ^th percentile narrowest cross-sectional dimension of a pores (i.e. , as counted among all pores. This narrowest cross-sectional dimension would be, for example, 100 microns for a rectangular slot/pore that is 100 microns wide and 300 microns long. A circular pore 100 microns in diameter, would also have a pore size of 100 microns.

[0049] Accordingly, in certain embodiments, the first solid/liquid mixture is filtered through at least one filter in a first filter column in the first crystallization zone to form a first filtrate comprising mother liquor and a first product stream comprising solid p-xylene, the filter having a first effective pore size larger than the fourth effective pore size, and then the first product stream is slurried in a reslurry liquid to form a first reslurry stream. In such embodiments, the first crystallization zone effluent comprises the first filtrate. In certain embodiments as otherwise described herein, the first effective pore size is at least 25%, or at least 50%, or at least 100%, or at least 200%, or at least 300% larger than the fourth effective pore size (i.e., of the at least one filter in a filter column of the recovery zone). In certain embodiments as otherwise described herein, the first crystallization zone includes two or more (e.g., 2-4) filter columns configured to operate in parallel.

[0050] In certain embodiments as otherwise described herein, the at least one filter of the first filter column has a length (i.e., along a vertical axis of the filtration zone) of at least 4 in., e.g., at least 5 in., or at least 6 in., or 4-12 in., or 4-8 in., or 6-10 in. In certain such embodiments, the at least one filter comprises a filter tube having a length (i.e., along a vertical axis of the filtration zone) of at least 48 in., e.g., at least 60 in., or 48-96 in., or 48-84 in., or 48-72 in., or 60-96 in, or 72-96 in., or 60-84 in., or 60-72 in. In certain embodiments as otherwise described herein, the first filter column includes one filter tube (e.g., comprising one filter). In other embodiments, the first filter column comprises two or more (e.g., 4-6) filter tubes, each filter tube comprising one or more (e.g., one) filters.

[0051] In certain embodiments as otherwise described herein, the at least one filter of the first filter column comprises rectangular pores having a length along a vertical axis of the filtration zone and a width perpendicular thereto. In certain such embodiments, the first pore height is 2-8 mm, or 2-6 mm, or 2-4 mm, or 4-8 mm, or 6-8 mm, and the first pore width is 0.2-0.4 mm, or 0.2-0.3 mm, or 0.3-0.4 mm. In certain such embodiments, the at least one filter of the filter column of the recovery zone comprises rectangular pores having a fourth pore height of 1-7 mm, or 1-5 mm, or 1-3 mm, or 3-7 mm, or 5-7 mm, and a fourth pore width of 0.1-0.3 mm, or 0.1-0.2 mm, or 0.2-0.3 mm. In certain such embodiments, the area of at least a portion of the rectangular pores comprising the at least one filter of the first filter column is at least 200%, or at least 300% larger than that of the rectangular pores comprising the at least one filter of the filter column of the recovery zone.

[0052] In certain embodiments as otherwise described herein, p-xylene is present in the first filtrate in an amount that is at least 1 wt.%, e.g., 1-4 wt.%, or 1-3 wt.%, or 1-2 wt.%, or 2-5 wt.%, or 3-5 wt.%, or 4-5 wt.% greater than the p-xylene solubility limit of the first filtrate. The person of ordinary skill in the art can determine the p-xylene solubility limit of a liquid (e.g., the first filtrate) based on its physical properties, such as chemical composition, temperature, etc.

[0053] In certain embodiments as otherwise described herein, the first solid/liquid mixture is filtered in a first filter column in the first crystallization zone to form a first filtrate comprising mother liquor and a first product stream comprising solid p-xylene, and the effluent of the first crystallization zone including the first filtrate is transferred to a crystallizer of the second crystallization zone. Notably, transferring the filtrate to a downstream crystallizer desirably avoids p-xylene losses otherwise attributable to the relatively poor filtration efficiency of the first filter column, which can reliably separate solid p-xylene from the first solid/liquid mixture at a desirably high throughput (accordingly lowering the filtration duty of the downstream recovery zone). Moreover, the present inventors have determined that solid p-xylene present in the filtrate can “seed” the downstream crystallizer, advantageously improving the crystallization yield therein.

[0054] In the second crystallization zone 120, an effluent 111 of the first crystallization zone 110 (e.g., comprising the first solid/liquid mixture or the first filtrate) is cooled in a crystallizer to form a second solid/liquid mixture comprising solid p-xylene and mother liquor. In certain embodiments as otherwise described herein, the second crystallization zone includes two or more (e.g., two or three) crystallizers configured to operate in parallel.

[0055] In certain embodiments as otherwise described herein, the effluent of the first crystallization zone is cooled to a temperature below -50 °F (e.g., below -60 °F, or below -70 °F). In certain embodiments as otherwise described herein, the first crystallization effluent comprises the first solid/liquid mixture, and the second solid/liquid mixture comprises 10-20 wt.%, e.g., 10-17.5 wt.%, or 10-15 wt.%, or 12.5-20 wt.%, or 15-20 wt.%, or 12.5-17.5 wt.% solid p-xylene. In other embodiments, the first crystallization effluent comprises the first filtrate, and the second solid/liquid mixture comprises 2-10 wt.%, e.g., 2-8 wt.%, or 2-6 wt.%, or 4-10 wt.%, 6-10 wt.% solid p-xylene.

[0056] In certain embodiments as otherwise described herein, the effluent of the second crystallization zone comprises the second solid/liquid mixture (e.g., comprising 2-10 wt.%, or 10-20 wt.% solid p-xylene).

[0057] In certain embodiments as otherwise described herein, the second solid/liquid mixture is filtered through at least one filter in a second filter column in the second crystallization zone to form a second filtrate comprising mother liquor and a second product stream comprising solid p-xylene, the filter having a second effective pore size larger than the fourth effective pore size, and then the second product stream is slurried in a reslurry liquid to form a second reslurry stream. In such embodiments, the second crystallization zone effluent comprises the second filtrate. In certain embodiments as otherwise described herein, the second effective pore size is at least 25%, or at least 50%, or at least 100%, or at least 200%, or at least 300% larger than the fourth effective pore size (i.e., of the at least one filter in a filter column of the recovery zone). In certain embodiments as otherwise described herein, the second crystallization zone includes two or more (e.g., 3-5) filter columns configured to operate in parallel.

[0058] In certain embodiments as otherwise described herein, the at least one filter of the second filter column has a length (i.e., along a vertical axis of the filtration zone) of at least 4 in., e.g., at least 5 in., or at least 6 in., or 4-12 in., or 4-8 in., or 6-10 in. In certain such embodiments, the at least one filter comprises a filter tube having a length (i.e., along a vertical axis of the filtration zone) of at least 48 in., e.g., at least 60 in., or 48-96 in., or 48-84 in., or 48-72 in., or 60-96 in, or 72-96 in., or 60-84 in., or 60-72 in. In certain embodiments as otherwise described herein, the second filter column includes one filter tube (e.g., comprising one filter). In other embodiments, the second filter column comprises two or more (e.g., 4-6) filter tubes, each filter tube comprising one or more (e.g., one) filters.

[0059] In certain embodiments as otherwise described herein, the at least one filter of the second filter column comprises rectangular pores having a length along a vertical axis of the filtration zone and a width perpendicular thereto. In certain such embodiments, the second pore height is 2-8 mm, or 2-6 mm, or 2-4 mm, or 4-8 mm, or 6-8 mm, and the second pore width is 0.2-0.4 mm, or 0.2-0.3 mm, or 0.3-0.4 mm. In certain such embodiments, the at least one filter of the filter column of the recovery zone comprises rectangular pores having a fourth pore height of 1-7 mm, or 1-5 mm, or 1-3 mm, or 3-7 mm, or 5-7 mm, and a fourth pore width of 0.05-0.2 mm, or 0.05-0.1 mm, or 0.1-0.2 mm.

In certain such embodiments, the area of at least a portion of the rectangular pores comprising the at least one filter of the second filter column is at least 200%, or at least 300% larger than that of the rectangular pores comprising the at least one filter of the filter column of the recovery zone.

[0060] In certain embodiments as otherwise described herein, p-xylene is present in the second filtrate in an amount that is at least 1 wt.%, e.g., 1-4 wt.%, or 1-3 wt.%, or 1-2 wt.%, or 2-5 wt.%, or 3-5 wt.%, or 4-5 wt.% greater than the p-xylene solubility limit of the second filtrate.

[0061] In certain embodiments as otherwise described herein, the second solid/liquid mixture is filtered in a second filter column in the second crystallization zone to form a second filtrate comprising mother liquor and a second product stream comprising solid p- xylene, and an effluent of the second crystallization zone including the second filtrate is transferred to a crystallizer of the second crystallization zone. In certain such embodiments, the first solid/liquid mixture is filtered in a first filter column in the first crystallization zone to form a first filtrate comprising mother liquor and a first product stream comprising solid p- xylene, and the effluent of the first crystallization zone including the first filtrate is transferred to a crystallizer of the second crystallization zone. In other such embodiments, the effluent of the first crystallization zone including the first solid/liquid mixture is transferred to a crystallizer of the second crystallization zone.

[0062] In the third crystallization zone 130, an effluent 121 of the second crystallization zone 120 (e.g., comprising the second solid/liquid mixture or the second filtrate) is cooled in a crystallizer to form a third solid/liquid mixture comprising solid p-xylene and mother liquor. In certain embodiments as otherwise described herein, the third crystallization zone includes two or more (e.g., two or three) crystallizers configured to operate in parallel.

[0063] In certain embodiments as otherwise described herein, the effluent of the second crystallization zone is cooled to a temperature below -60 °F (e.g., below -70 °F, or below -80 °F). In certain embodiments as otherwise described herein, the second crystallization zone effluent comprises the second solid/liquid mixture, and the third solid/liquid mixture comprises 10-20 wt.%, e.g., 10 17.5 wt.%, or 10-15 wt.%, or 12 5-20 wt.%, or 15-20 wt.%, or 12 5 17.5 wt.% solid p-xylene. In other embodiments, the second crystallization effluent comprises the second filtrate, and the third solid/liquid mixture comprises 2-10 wt.%, e.g., 2-8 wt.%, or 2-6 wt.%, or 4-10 wt.%, 6-10 wt.% solid p-xylene. [0064] In certain embodiments as otherwise described herein, the effluent of the third crystallization zone comprises the third solid/liquid mixture (e.g., comprising 2-10 wt.%, or 10-20 wt.% solid p-xylene).

[0065] In certain embodiments as otherwise described herein, the third solid/liquid mixture is filtered through at least one filter in a third filter column in the third crystallization zone to form a third filtrate comprising mother liquor and a third product stream comprising solid p-xylene, the filter having a third effective pore size larger than the fourth effective pore size, and then the third product stream is slurried in a reslurry liquid to form a third reslurry stream. In such embodiments, the third crystallization zone effluent comprises the third filtrate. In certain embodiments as otherwise described herein, the third effective pore size is at least 25%, or at least 50%, or at least 100%, or at least 200%, or at least 300% larger than the fourth effective pore size (i.e. , of the at least one filter in a filter column of the recovery zone). In certain embodiments as otherwise described herein, the third crystallization zone includes two or more (e.g., 2-6) filter columns configured to operate in parallel.

[0066] In certain embodiments as otherwise described herein, the at least one filter of the third filter column has a length (i.e., along a vertical axis of the filtration zone) of at least 4 in., e.g., at least 5 in., or at least 6 in., or 4-12 in., or 4-8 in., or 6-10 in. In certain such embodiments, the at least one filter comprises a filter tube having a length (i.e., along a vertical axis of the filtration zone) of at least 48 in., e.g., at least 60 in., or 48-96 in., or 48-84 in., or 48-72 in., or 60-96 in, or 72-96 in., or 60-84 in., or 60-72 in. In certain embodiments as otherwise described herein, the third filter column includes one filter tube (e.g., comprising one filter). In other embodiments, the third filter column comprises two or more (e.g., 4-6) filter tubes, each filter tube comprising one or more (e.g., one) filters.

[0067] In certain embodiments as otherwise described herein, the at least one filter of the third filter column comprises rectangular pores having a length along a vertical axis of the filtration zone and a width perpendicular thereto. In certain such embodiments, the third pore height is 2-8 mm, or 2-6 mm, or 2-4 mm, or 4-8 mm, or 6-8 mm, and the third pore width is 0.2-0.4 mm, or 0.2-0.3 mm, or 0.3-0.4 mm. In certain such embodiments, the at least one filter of the filter column of the recovery zone comprises rectangular pores having a fourth pore height of 1-7 mm, or 1-5 mm, or 1-3 mm, or 3-7 mm, or 5-7 mm, and a fourth pore width of 0.05-0.2 mm, or 0.05-0.1 mm, or 0.1-0.2 mm. In certain such embodiments, the area of at least a portion of the rectangular pores comprising the at least one filter of the third filter column is at least 200%, or at least 300% larger than that of the rectangular pores comprising the at least one filter of the filter column of the recovery zone.

[0068] In certain embodiments as otherwise described herein, p-xylene is present in the third filtrate in an amount that is at least 1 wt.%, e.g., 1-4 wt.%, or 1-3 wt.%, or 1-2 wt.%, or 2-5 wt.%, or 3-5 wt.%, or 4-5 wt.% greater than the p-xylene solubility limit of the third filtrate.

[0069] In certain embodiments as otherwise described herein, the third solid/liquid mixture is filtered in a third filter column in the third crystallization zone to form a third filtrate comprising mother liquor and a third product stream comprising solid p-xylene, and an effluent of the third crystallization zone including the third filtrate is transferred to a filter column of a recovery zone. In certain such embodiments, the first solid/liquid mixture is filtered in a first filter column in the first crystallization zone to form a first filtrate comprising mother liquor and a first product stream comprising solid p-xylene, and the effluent of the first crystallization zone including the first filtrate is transferred to a crystallizer of the second crystallization zone. In other such embodiments, the effluent of the first crystallization zone including the first solid/liquid mixture is transferred to a crystallizer of the second crystallization zone. In certain such embodiments, the second solid/liquid mixture is filtered in a second filter column in the second crystallization zone to form a second filtrate comprising mother liquor and a second product stream comprising solid p-xylene, and the effluent of the second crystallization zone including the second filtrate is transferred to a crystallizer of the third crystallization zone. In other such embodiments, the effluent of the second crystallization zone including the second solid/liquid mixture is transferred to a crystallizer of the third crystallization zone.

[0070] In the recovery zone 140, an effluent 131 of the third crystallization zone 130 (e.g., comprising the third solid/liquid mixture or the third filtrate) is filtered through at least one filter in a filter column to form a fourth filtrate 141 comprising mother liquor and a fourth product stream comprising solid p-xylene, the filter having a fourth effective pore size (i.e., smaller than the first effective pore size, the second effective pore size, and/or the third effective pore size), and then slurrying the fourth product stream in a reslurry liquid to form a fourth reslurry stream 143. In certain embodiments as otherwise described herein, the recovery zone includes two or more (e.g., 3-8) filter columns configured to operate in parallel.

[0071] In certain embodiments as otherwise described herein, the at least one filter of the filter column of the recovery zone has a length (i.e., along a vertical axis of the filtration zone) of at least 4 in., e.g., at least 5 in., or at least 6 in., or 4-12 in., or 4-8 in., or 6-10 in.

In certain such embodiments, the at least one filter comprises a filter tube having a length (i.e., along a vertical axis of the filtration zone) of at least 48 in., e.g., at least 60 in., or 48-96 in., or 48-84 in., or 48-72 in., or 60-96 in, or 72-96 in., or 60-84 in., or 60-72 in. In certain embodiments as otherwise described herein, the filter column of the recovery zone includes one filter tube (e.g., comprising one filter). In other embodiments, the filter column of the recovery zone comprises two or more (e.g., 4-6) filter tubes, each filter tube comprising one or more (e.g., one) filters.

[0072] In certain embodiments as otherwise described herein, the at least one filter of the filter column of the recovery zone comprises rectangular pores having a length along a vertical axis of the filtration zone and a width perpendicular thereto. In certain such embodiments, the fourth pore height is 1-7 mm, or 1-5 mm, or 1-3 mm, or 3-7 mm, or 5-7 mm, and the fourth pore width is 0.05-0.2 mm, or 0.05-0.1 mm, or 0.1-0.2 mm. [0073] In certain embodiments as otherwise described herein, p-xylene is present in the fourth filtrate in an amount that is at most 1 wt.%, e.g., 0.1-0.9 wt.%, or 0.1-0.8 wt.%, or 0.1-0.7 wt.% greater than the p-xylene solubility limit of the fourth filtrate. In certain embodiments as otherwise described herein, at least a portion of the fourth filtrate is transferred to a reaction zone of a xylenes isomerization system.

[0074] As noted above, the present inventors have determined that filtering crystallized p-xylene in a filter column having a relatively large pore size in one or more crystallization zones upstream of a recovery zone can desirably reduce the filtration duty of the recovery zone. Accordingly, in certain embodiments as otherwise described herein, solid p-xylene is present in the fourth product stream in an amount that is at most 67% (e.g., at most 60%, or at most 55%, or at most 50%, or at most 45%) of a total amount of solid p-xylene present in the first product stream, second product stream, and/or third product stream, and the fourth product stream. For example, in certain embodiments, solid p-xylene is present in the fourth product stream in an amount that is at most 67% (e.g., at most 60%, or at most 55%, or at most 50%, or at most 45%) of a total amount of solid p-xylene present in the first product stream and the fourth product stream, or a total amount of solid p-xylene present in the second product stream and the fourth product stream, or a total amount of solid p-xylene present in the third product stream and the fourth product stream, or a total amount of solid p-xylene present in the first product stream, the second product stream, and the fourth product stream, or a total amount of solid p-xylene present in the first product stream, the third product stream, and the fourth product stream, or a total amount of solid p-xylene present in the second product stream, the third product stream, and fourth product stream, or a total amount of solid p-xylene present in the first product stream, the second product stream, the third product stream, and the fourth product stream.

[0075] The fourth reslurry stream 143 and the first reslurry stream, the second reslurry stream, and/or the third reslurry stream (not shown) are transferred to an efficiency-stage slurry drum 152 of the efficiency zone 150. For example, in certain embodiments, the fourth reslurry stream and the first reslurry stream; or the fourth reslurry stream and the second reslurry stream; or the fourth reslurry stream and the third reslurry stream; or the fourth reslurry stream, the first reslurry stream, and the second reslurry stream; or the fourth reslurry stream, the first reslurry stream, and the third reslurry stream; or the fourth reslurry stream, the second reslurry stream, and the third reslurry stream; or the fourth reslurry stream, the first reslurry stream, the second reslurry stream, and the third reslurry stream are transferred to the efficiency-stage slurry drum. In certain embodiments, the two or more reslurry streams are combined and then transferred to the efficiency-stage slurry drum. In other embodiments, each reslurry stream is individually transferred to the efficiency-stage slurry drum. Advantageously, drums fed from filter columns as described herein can have less plugging and other operational problems than drums fed from centrifuges.

[0076] In the embodiment of FIG. 1 , an effluent 151 of the efficiency-stage slurry drum 152 is filtered through at least one filter in a filter column 154 of the efficiency zone 150 to form a fifth filtrate 153 comprising reslurry liquid and a fifth product stream comprising solid p-xylene, the filter having a fifth effective pore size smaller than the first effective pore size, the second effective pore size, and/or the third effective pore size, and then the fifth product stream is slurried in a reslurry liquid to form a fifth reslurry stream 153. In certain embodiments as otherwise described herein, the effluent of the efficiency-stage slurry drum comprises at least 40 wt.%, e.g., at least 45 wt.%, or at least 50 wt.%, or 40-70 wt.%, or 40- 60 wt.%, or 45-70 wt.%, or 50-70 wt.% p-xylene.

[0077] In certain embodiments as otherwise described herein, the efficiency zone includes two or more (e.g., two) filter columns configured to operate in parallel.

[0078] In certain embodiments as otherwise described herein, the at least one filter of the filter column of the efficiency zone has a length (i.e. , along a vertical axis of the filtration zone) of at least 4 in., e.g., at least 5 in., or at least 6 in., or 4-12 in., or 4-8 in., or 6-10 in.

In certain such embodiments, the at least one filter comprises a filter tube having a length (i.e., along a vertical axis of the filtration zone) of at least 48 in., e.g., at least 60 in., or 48-96 in., or 48-84 in., or 48-72 in., or 60-96 in, or 72-96 in., or 60-84 in., or 60-72 in. In certain embodiments as otherwise described herein, the filter column of the efficiency zone includes one filter tube (e.g., comprising one filter). In other embodiments, the filter column of the efficiency zone comprises two or more (e.g., 4-6) filter tubes, each filter tube comprising one or more (e.g., one) filters.

[0079] In certain embodiments as otherwise described herein, the at least one filter of the filter column of the efficiency zone comprises rectangular pores having a length along a vertical axis of the filtration zone and a width perpendicular thereto. In certain such embodiments, the fifth pore height is 1-7 mm, or 1-5 mm, or 1-3 mm, or 3-7 mm, or 5-7 mm, and the fifth pore width is 0.05-0.2 mm, or 0.05-0.1 mm, or 0.1-0.2 mm.

[0080] In certain embodiments as otherwise described herein, p-xylene is present in the fifth filtrate in an amount that is at most 0.5 wt.%, e.g., 0.05-0.4 wt.%, or 0.05-0.3 wt.%, or 0.05-0.2 wt.% greater than the p-xylene solubility limit of the fifth filtrate. In certain embodiments as otherwise described herein, at least a portion of the fifth filtrate is transferred to a crystallizer of the first crystallization zone. In certain embodiments as otherwise described herein, the reslurry liquid of the first crystallization zone, the second crystallization zone, and/or the third crystallization zone comprises at least a portion of the fifth filtrate.

[0081] As described above, in certain embodiments, separating at least a portion of an effluent of the efficiency-stage slurry drum comprises filtering the effluent in a filter column.

In other embodiments, separating at least a portion of an effluent of the efficiency-stage drum comprises separating in a centrifuge (e.g., a pusher centrifuge, or a screen-bowl centrifuge, or a solid-bowl centrifuge).

[0082] The fifth reslurry stream 153 is transferred to a product-stage slurry drum 162 of the product zone 160. In the embodiment of FIG. 1, an effluent 161 of the product-stage slurry drum 162 is separated in a wash column 164 of the product zone 160 to form a sixth filtrate 163 comprising reslurry liquid and a sixth product stream 165 comprising p-xylene. In certain embodiments as otherwise described herein, the product zone includes two or more (e.g., 6-8) wash columns configured to operate in parallel.

[0083] As the person of ordinary skill in the art will appreciate, a wash column (or a hydraulic wash column) is a solid-liquid separation apparatus for concentrating a suspension. A wash column separates solids from a solid/liquid mixture by directing the mixture into a first end of a wash column and a wash liquid into a second end of the wash column in countercurrent flow to the suspension, forming a bed of the solids. In the embodiment of FIG. 1, solid p-xylene of the bed is melted to form the sixth product stream 165.

[0084] In other embodiments, separating an effluent of the product-stage slurry drum is separated using a centrifuge (e.g., a pusher centrifuge, or a screen-bowl centrifuge, or a solid-bowl centrifuge) to form the sixth filtrate and the sixth product stream.

[0085] In certain embodiments as otherwise described herein, the effluent of the product-stage slurry drum comprises at least 60 wt.%, e.g., at least 70 wt.%, or at least 80 wt.%, or 60-95 wt.%, or 60-90 wt.%, or 70-95 wt.%, or 08-90 wt.% p-xylene.

[0086] In certain embodiments as otherwise described herein, the sixth product stream comprises at least 97 wt.%, e.g., at least 98 wt.%, or at least 99 wt.%, or at least 99.5 wt.%, or at least 99.7 wt.%, or at least 99.8 wt.% p-xylene.

[0087] In certain embodiments as otherwise described herein, the sixth filtrate comprises 50-90 wt.%, e.g., 60-90 wt.%, or 70-90 wt.% p-xylene. In certain embodiments as otherwise described herein, the reslurry liquid of the first crystallization zone, the second crystallization zone, the third crystallization zone, and/or the efficiency zone comprises at least a portion of the fifth filtrate.

[0088] Another aspect of the disclosure provides an apparatus for recovering p-xylene (e.g., according to a method described herein) comprising a first crystallizer; a second crystallizer in fluid communication with the first crystallizer; a third crystallizer in fluid communication with the second crystallizer; and a fourth filter unit comprising at least one filter column, each filter column in fluid communication with the third crystallizer, each filter column including at least one filter, each filter having a fourth effective pore size; and further comprising at least one of a first filter unit comprising at least one filter column, each filter column providing the fluid communication between the first crystallizer and the second crystallizer, each filter column including at least one filter, each filter having a first effective pore size; a second filter unit comprising at least one filter column, each filter column providing the fluid communication between the second crystallizer and the third crystallizer, each filter column including at least one filter, each filter having a second effective pore size; and a third filter unit comprising at least one filter column, each filter column providing the fluid communication between the third crystallizer and the fourth filter unit, each filter column including at least one filter, each filter having a third effective pore size.

[0089] For example, in certain embodiments as otherwise described herein, the apparatus comprises the first filter unit; or the second filter unit; or the third filter unit; or the first filter unit and the second filter unit; or the first filter unit and the third filter unit; or the second filter unit and the third filter unit; or the first filter unit, the second filter unit, and the third filter unit. The properties of the various components of the apparatus can be as otherwise described above with respect to the methods of the disclosure.

[0090] In certain embodiments as otherwise described herein, the apparatus further comprises an efficiency-stage slurry drum in fluid communication with the fourth filter unit; a fifth filter unit comprising at least one filter column, each filter column including at least one filter, each filter having a fifth effective pore size; a product-stage slurry drum in fluid communication with the fifth filter unit; and a sixth filter unit comprising at least one wash column, each wash column in fluid communication with the product stage slurry drum.

[0091] In certain embodiments as otherwise described herein, the apparatus comprises the second filter unit, and the second effective pore size is larger (e.g., at least 25%, at least 50%, at least 100%, or at least 200% larger) than the fourth effective pore size. In certain such embodiments, the second filter unit comprises 3-5 filter columns, and the fourth filter unit comprises 3-5 filter columns.

[0092] In certain embodiments as otherwise described herein, the apparatus comprises the first filter unit, and the first effective pore size is larger (e.g., at least 25%, at least 50%, at least 100%, or at least 200% larger) than the fourth effective pore size. In certain such embodiments, the first filter unit comprises 2-4 filter columns, and the fourth filter unit comprises 4-8 filter columns.

EXAMPLES

[0093] The Examples that follow are illustrative of specific embodiments of the invention, and various uses thereof. They are set forth for explanatory purposes only, and are not to be taken as limiting the invention.

Example 1. p-xylene Recovery Method

[0094] The p-xylene recovery process of FIG. 1 was modeled with ASPEN Plus (Aspen Technology Inc., Bedford, MA). Recovery processes 1-7, which included filtering in a filter column of one or more of the first crystallization zone, the second crystallization zone, and the third crystallization zone, were compared to a control process C, as shown in Table 1, below. The capacity of each process was 700 Ibs/hr.

Table 1. Recovery Processes

*lncludes filter columns; **lncludes wash columns

[0095] As shown in Table 1, filtering in a large-pore filter column of one or more of the first crystallization zone, the second crystallization zone, and the third crystallization zone, and then filtering in a small-pore filter column in the recovery zone, the total number of columns required by the recovery process was decreased, providing cost savings per unit p- xylene recovered from the feedstream.

[0096] Additional aspects of the disclosure are provided by the following enumerated embodiments, which can be combined in any number and in any fashion that is not technically or logically inconsistent.

Embodiment 1. A method for recovering p-xylene, comprising in a crystallizer of a first crystallization zone, cooling a liquid feed stream comprising p-xylene to form a first solid/liquid mixture comprising solid p-xylene and mother liquor; transferring an effluent of the first crystallization zone to a second crystallization zone; in a crystallizer of the second crystallization zone, cooling at least a portion of the effluent to form a second solid/liquid mixture comprising solid p-xylene and mother liquor; transferring an effluent of the second crystallization zone to a third crystallization zone; in a crystallizer of the third crystallization zone, cooling at least a portion of the effluent to form a third solid/liquid mixture comprising solid p-xylene and mother liquor; transferring an effluent of the third crystallization zone to a recovery zone; in the recovery zone, filtering at least a portion of the effluent through at least one filter of a filter column of the recovery zone, the filter having a fourth effective pore size, to form a fourth filtrate comprising mother liquor and a fourth product stream comprising solid p-xylene, and then slurrying the fourth product stream in a reslurry liquid to form a fourth reslurry stream; and in one or more of the first crystallization zone, the second crystallization zone, and the third crystallization zone, filtering the solid/liquid mixture through at least one filter in a filter column, the filter having an effective pore size larger than the fourth effective pore size, to form a filtrate comprising mother liquor and a product stream comprising solid p-xylene, and then slurrying the product stream in a reslurry liquid to form a reslurry stream, wherein the crystallization zone effluent comprises the filtrate.

Embodiment 2. The method of embodiment 1, including filtering the first solid/liquid mixture through at least one filter in a first filter column in the first crystallization zone to form a first filtrate comprising mother liquor and a first product stream comprising solid p-xylene, the filter having a first effective pore size larger (e.g., at least 25%, at least 50%, at least 100%, at least 200%, or at least 300% larger) than the fourth effective pore size, and then slurrying the first product stream in a reslurry liquid to form a first reslurry stream; wherein the first crystallization zone effluent comprises the first filtrate. Embodiment 3. The method of embodiment 2, wherein p-xylene is present in the first filtrate in an amount that is at least 1 wt.% (e.g., 1-5 wt.%) greater than the p-xylene solubility limit of the first filtrate.

Embodiment 4. The method of any of embodiments 1-3, including filtering the second solid/liquid mixture through at least one filter in a filter column in the second crystallization zone to form a second filtrate comprising mother liquor and a second product stream comprising solid p-xylene, the filter having a second effective pore size larger (e.g., at least 25%, at least 50%, at least 100%, at least 200%, or at least 300% larger) than the fourth effective pore size, and then slurrying the second product stream in a reslurry liquid to form a second reslurry stream; wherein the second crystallization zone effluent comprises the second filtrate.

Embodiment 5. The method of embodiment 4, wherein p-xylene is present in the second filtrate in an amount that is at least 1 wt.% (e.g., 1-5 wt.%) greater than the p-xylene solubility limit of the second filtrate.

Embodiment 6. The method of any of embodiments 1-5, including filtering the third solid/liquid mixture through at least one filter in a filter column in the third crystallization zone to form a third filtrate comprising mother liquor and a third product stream comprising solid p- xylene, the filter having a third effective pore size larger (e.g., at least 25%, at least 50%, at least 100 at least 200%, or at least 300% larger) than the fourth effective pore size, and then slurrying the third product stream in a reslurry liquid to form a third reslurry stream; wherein the third crystallization zone effluent comprises the third filtrate.

Embodiment 7. The method of embodiment 6, wherein p-xylene is present in the third filtrate in an amount that is at least 1 wt.% (e.g., 1-5 wt.%) greater than the p-xylene solubility limit of the third filtrate. Embodiment 8. The method of any of embodiments 1-7, wherein p-xylene is present in the fourth filtrate in an amount that is at most 1 wt.% (e.g., 0.1-0.9 wt.%) greater than the p-xylene solubility limit of the fourth filtrate.

Embodiment 9. The method of any of embodiments 1-8, wherein solid p-xylene is present in the fourth product stream in an amount that is at most 67% (e.g., at most 60% or at most 50%) of a total amount of solid p-xylene present in the first product stream, second product stream, third product stream, and fourth product stream.

Embodiment 10. The method of any of embodiments 1-9, further comprising transferring at least a portion of the fourth reslurry stream and at least a portion of one or more of the first reslurry stream, second reslurry stream, and third reslurry stream to an efficiency-stage slurry drum of an efficiency zone.

Embodiment 11. The method of embodiment 10, further comprising separating at least a portion of an effluent of the efficiency-stage slurry drum to form a fifth filtrate comprising reslurry liquid and a fifth product stream comprising solid p-xylene; slurrying at least a portion of the fifth product stream in a reslurry liquid to form a fifth reslurry stream; transferring at least a portion of the fifth reslurry stream to a product-stage slurry drum of a product zone; and separating at least a portion of an effluent of the product-stage slurry drum to form a sixth filtrate comprising reslurry liquid and a sixth product stream comprising p-xylene.

Embodiment 12. The method of embodiment 11, further comprising transferring at least a portion of the fifth filtrate to the first crystallization zone. Embodiment 13. The method of embodiment 11, wherein the reslurry liquid of one or more of the first crystallization zone, second crystallization zone, third crystallization zone, and recovery zone comprises at least a portion of the fifth filtrate or sixth filtrate.

Embodiment 14. The method of any of embodiments 11-13, wherein the reslurry liquid comprising the fifth reslurry stream includes at least a portion of the sixth filtrate.

Embodiment 15. An apparatus for recovering p-xylene, comprising a first crystallizer; a second crystallizer in fluid communication with the first crystallizer; a third crystallizer in fluid communication with the second crystallizer; and a fourth filter unit comprising at least one filter column, each filter column in fluid communication with the third crystallizer, each filter column including at least one filter, each filter having a fourth effective pore size; and further comprising at least one of a first filter unit comprising at least one filter column, each filter column providing the fluid communication between the first crystallizer and the second crystallizer, each filter column including at least one filter, each filter having a first effective pore size; a second filter unit comprising at least one filter column, each filter column providing the fluid communication between the second crystallizer and the third crystallizer, each filter column including at least one filter, each filter having a second effective pore size; and a third filter unit comprising at least one filter column, each filter column providing the fluid communication between the third crystallizer and the fourth filter unit, each filter column including at least one filter, each filter having a third effective pore size. Embodiment 16. The apparatus of embodiment 15, further comprising an efficiency-stage slurry drum in fluid communication with the fourth filter unit; a fifth filter unit comprising at least one filter column, each filter column in fluid communication with the efficiency-stage slurry drum, each filter column including at least one filter, each filter having a fifth effective pore size; a product-stage slurry drum in fluid communication with the fifth filter unit; and a sixth filter unit comprising at least one wash column, each wash column in fluid communication with the product-stage slurry drum.

Embodiment 17. The apparatus of embodiment 15 or 16, comprising the second filter unit, wherein the second effective pore size is larger (e.g., at least 25%, at least 50%, at least 100%, at least 200%, or at least 300% larger) than the fourth effective pore size.

Embodiment 18. The apparatus of embodiment 17, wherein the second filter unit comprises 3-5 filter columns, and the fourth filter unit comprises 3-5 filter columns.

Embodiment 19. The apparatus of embodiment 15 or 16, comprising the first filter unit, wherein the first effective pore size is larger (e.g., at least 25%, at least 50%, at least 100%, at least 200%, or at least 300% larger) than the fourth effective pore size.

Embodiment 20. The apparatus of embodiment 19, wherein the first filter unit comprises 2-4 filter columns, and the fourth filter unit comprises 4-8 filter columns.

[0097] The foregoing detailed description and the accompanying drawings have been provided by way of explanation and illustration, and are not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

[0098] It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present disclosure. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims can, alternatively, be made to depend in the alternative from any preceding claim — whether independent or dependent — and that such new combinations are to be understood as forming a part of the present specification.