Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C7/00—Purification; Separation; Use of additives
  • C07C7/14—Purification; Separation; Use of additives by crystallisation; Purification or separation of the crystals
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C7/00—Purification; Separation; Use of additives
  • C07C7/12—Purification; Separation; Use of additives by adsorption, i.e. purification or separation of hydrocarbons with the aid of solids, e.g. with ion-exchangers
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
  • C07C5/22—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by isomerisation
  • C07C5/27—Rearrangement of carbon atoms in the hydrocarbon skeleton
  • C07C5/2729—Changing the branching point of an open chain or the point of substitution on a ring
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C7/00—Purification; Separation; Use of additives
  • C07C7/005—Processes comprising at least two steps in series
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C7/00—Purification; Separation; Use of additives
  • C07C7/12—Purification; Separation; Use of additives by adsorption, i.e. purification or separation of hydrocarbons with the aid of solids, e.g. with ion-exchangers
  • C07C7/13—Purification; Separation; Use of additives by adsorption, i.e. purification or separation of hydrocarbons with the aid of solids, e.g. with ion-exchangers by molecular-sieve technique

Definitions

• the invention relates to a process for producing paraxylene including xylene isomerization, and to an apparatus for the practice of said process.
• the xylene isomers are important intermediates, which find wide and varied application in chemical syntheses.
• paraxylene (PX) is a feedstock for terephthalic acid which finds use in the manufacture of synthetic fibers
• metaxylene (MX) is used in the manufacture of dyes
• orthoxylene (OX) is used as a feedstock for phthalic anhydride, which finds use in the manufacture of plasticizers.
• Xylenes are found in various fractions such as coal tar distillate, petroleum reformates and pyrolysis liquids in admixture with other compounds of like boiling point.
• the aromatic components are readily separated from non-aromatics by methods such as solvent extraction.
• a fraction may then be obtained readily such as by distillation, consisting essentially of C8 aromatics.
• C8 aromatics aromatic hydrocarbons having 8 carbon atoms, including particularly ethylbenzene and the xylene isomers paraxylene (p- xylene or PX), orthoxylene (o-xylene or OX), and metaxylene (m-xylene or MX).
• the feed stream or streams used in the system shown in Figure 1 may come from a variety of sources, such as one or more sources selected from C8+ Reformate 1, C8+ Selective Toluene Disproportionation Product 17, C8+ Trans alky lation Product 2, C8+ Toluene Disproportionation Product 15, and any other streams that contain C8 aromatics, such as products from toluene methylation with methanol.
• sources such as one or more sources selected from C8+ Reformate 1, C8+ Selective Toluene Disproportionation Product 17, C8+ Trans alky lation Product 2, C8+ Toluene Disproportionation Product 15, and any other streams that contain C8 aromatics, such as products from toluene methylation with methanol.
• Each of these sources is per se well-known in the art.
• These streams typically comprise the four C8 isomers and heavier aromatics (C9+ aromatics) which are processed along with a recycle stream 10, in one or more fractionators in C8/C9+ Aromatics
• C8/C9+ Aromatics Fractionation in 16 thus yields C8 Aromatics stream 6 which typically contains between 10 and 95 wt% paraxylene, and bottoms product 3 comprising C9+ aromatics.
• the C8 aromatics stream 6 is processed to selectively recover paraxylene by one or both of selective adsorption or crystallization which is shown as Paraxylene Recovery unit 12 in Figure 1.
• a Paraxylene Product, which may comprise as much as 99.7 wt% or even higher of paraxylene is recovered as Stream 7, with the balance of C8 aromatics passing via conduit 8 to Vapor Phase Xylenes Isomerization 13.
• Vapor Phase Xylenes Isomerization 13 establishes a near-equilibrium balance of xylene isomers in Stream 19 using one or more of a variety of catalysts which may also convert ethylbenzene to benzene and ethane or may convert ethylbenzene to near-equilibrium xylene isomers.
• Vapor phase processes and catalysts therefore are per se well-known in the art.
• the Xylenes Isomerization Product 19 passes to Detoluenization Fractionation 18 which removes C7 and lighter materials (C7-) in Stream 11 to yield Isomerate Recycle Stream 10.
• Isomerate Recycle Stream 10 is recycled to the C8/C9+ Aromatics Fractionation 16.
• U.S. Patent No. 3,856,874 describes splitting the effluent stream from PX separation, passing the independent streams over different catalysts, then combining the isomerized streams and recycling.
• U.S. Patent No. 7,439,412 teaches a process for recovering one or more high purity xylene isomers from a C8+ aromatic feedstream, including the use of an isomerization unit under liquid phase conditions.
• the product of the liquid phase isomerization unit is returned to the first fractionation tower in the system. See also U.S. Patent No. 7,626,065.
• U.S. Patent No. 7,553,998 teaches a process for recovering one or more high- purity xylene isomers from a feed having substantial content of C9+ aromatic hydrocarbons comprising de-ethylation of heavy aromatics followed by fractionation and then passing the stream to a C8 aromatic isomer recovery to recover high-purity xylene isomer with lowered energy costs.
• Streams passing through an isomerization unit under liquid isomerization conditions are split, with a portion sent to an isomer recovery unit and a portion is purged.
• U.S. Application Serial No. 12/612,007 (published as 2010/0152508) describes a process for producing a PX-rich product, the process comprising: (a) providing a PX-depleted stream; (b) isomerizing at least a portion of the PX-depleted stream to produce an isomerized stream having a PX concentration greater than the PX-depleted stream and a benzene concentration of less than 1,000 ppm and a C9+ hydrocarbons concentration of less than 5,000 ppm; and (c) separating the isomerized stream by selective adsorption.
• Provisional Application No. 61/326,445, filed April 21, 2010, is directed to a xylenes isomerization process, including a liquid phase isomerization, for the production of equilibrium or near-equilibrium xylenes, wherein the process conditions include a temperature of less than 295°C and a pressure sufficient to maintain the xylenes in liquid phase.
• the present inventors have surprisingly discovered a process which significantly reduces the energy required to produce high purity xylene isomers by providing parallel configuration of vapor phase and liquid phase isomerization systems.
• the invention is directed to a process for producing paraxylene comprising first separating a feed comprising C8+ aromatics into an overhead or first stream comprising xylene isomers and a bottoms product or second stream comprising C9+ aromatics, separating the xylene stream in a PX recovery unit to recover a PX-rich stream and a PX- depeleted stream, then separating said PX depleted (C8 aromatics) stream through a parallel configuration of vapor phase xylenes isomerization and liquid phase xylenes isomerization.
• a benzene separation step occurs between the C8/C9+ fractionation and the PX recovery unit, and/or a benzene separation step downstream from the isomerization step(s). There may also be, in embodiments, a toluene separation step, such as downstream of said isomerization step(s).
• the liquid phase isomerization product is recycled to one or more of the C8/C9+ fractionation, the benzene separation step (where present) and the PX recovery step.
• the invention also relates to an apparatus for the production of paraxylene comprising a first fractionation column operating at conditions suitable for the separation of a C8+ aromatics stream into an overheads comprising xylenes and a bottoms product comprising C9+ aromatics, the overheads stream fluidly connected with a PX recovery unit, wherein said PX recovery unit provides a PX-enriched stream and a PX-depleted stream, the improvement comprising dividing a conduit carrying said PX-depleted stream so that a portion of said PX-depleted stream is passed to a vapor phase isomerization unit and another portion of said PX-depleted stream is passed to a liquid phase isomerization unit.
• said liquid phase isomerization unit is fluidly connected so as to provide liquid phase isomerate recycle to said first fractionation column and/or to said PX recovery unit.
• said PX recovery unit is selected from at least one of a crystallizer and an adsorptive separator.
• At least one other fractionator upstream of said first fractionator, wherein said at least one other fractionator operates under conditions suitable for removing benzene from a stream comprising xylenes or for removing toluene from a stream comprising xylenes, and optionally wherein both said fractionator for removing benzene and said fractionator for removing toluene are provided upstream of said first fractionator.
• Figure 1 is a schematic illustrating a prior art flow configuration for xylenes isomerization.
• Figure 2 is a schematic illustrating an embodiment of the invention.
• Figures 3 and 4 represent a comparison of two systems, each embodiments of the present invention, the former returning liquid isomerization product to the rerun tower and the latter returning liquid isomerization product to PX recovery unit.
• a hydrocarbon stream comprising C8+ aromatics is separated into a stream comprising C8 aromatics and a stream comprising C9+ aromatics.
• the C8 stream optionally passed through a benzene separation unit, is then passed to a PX recovery unit to provide two streams, one having an increased PX concentration and the other having a decreased PX concentration.
• the PX-depleted stream is then divided and then isomerized, in parallel, in at least one liquid isomerization unit and in at least one vapor phase isomerization unit.
• the feed stream(s) to the system shown in Figure 2 may come from one or more sources comprising C8+ aromatic hydrocarbons, including C8+ reformate 1, C8+ Selective Toluene Disproportionation Product 17, C8+ transalkylation product 2, C8+ toluene disproportionation product 15, and any other streams that contain C8 aromatics such as products from toluene methylation with methanol.
• sources comprising C8+ aromatic hydrocarbons, including C8+ reformate 1, C8+ Selective Toluene Disproportionation Product 17, C8+ transalkylation product 2, C8+ toluene disproportionation product 15, and any other streams that contain C8 aromatics such as products from toluene methylation with methanol.
• the flow of Paraxylene Depleted C8 Aromatics Stream 8 is minimized through Vapor Phase Xylenes Isomerization 13 to minimize energy by reducing the amount of Paraxylene Depleted C8 Aromatics Stream 30 that is vaporized in Vapor Phase Xylenes Isomerization 13 and the associated amount of Isomerate Recycle Stream 10, which contains a much higher concentration of by-product C9+ aromatics than Liquid Phase Xylenes Isomerization product.
• LP Isomerate Recycle Stream 21 which is the product from Liquid Phase Xylenes Isomerization 20 is sent to C8/C9+ Aromatics Fractionation 16 at a higher feed location to minimize energy consumption due to its lower concentration of C9+ aromatics.
• the amount of energy savings on the C8/C9+ Aromatics Fractionation 16 can result in as much as a 75% reduction in the overall energy consumption of the process for the production of paraxylene.
• FIG. 2 shows that the Liquid Phase Isomerate Recycle Stream 21 can be optionally sent to one or more locations which include C8 Aromatics/C9+ Aromatics Fractionation 16, via conduit 50 to Benzene Removal unit 23 (with attendant benzene stream 22) and via conduit 60 directly to Paraxylene Recovery 12.
• the amount sent to each location is determined by the need to remove by-products which include benzene, and C9+ aromatics.
• the by-products from Liquid Phase Xylenes Isomerization 20 in the Liquid Phase Isomerate Recycle Stream 21 may need to be removed down to a level that is acceptable for Paraxylene Recovery 12, especially if selective adsorption is used for recovering paraxylene.
• the C9+ aromatics can be removed in the C8/C9+ Aromatics Fractionation 16 or in one or more devices that employ separation techniques such as membrane, extraction, and adsorption.
• benzene can be removed using one or more devices that employ separation techniques such as distillation, extraction, membrane, and adsorption.
• the C9+ aromatics and benzene can be removed simultaneously using one or more devices that employ separation techniques such as distillation, extraction, membrane, and adsorption.
• Vapor Phase Xylenes Isomerization 13 establishes a near-equilibrium balance of xylene isomers in stream 19 using one or more of a variety of catalysts, per se well-known in the art, which may also convert ethylbenzene to benzene and ethane or may convert ethylbenzene to near-equilibrium xylene isomers.
• the xylenes isomerization product stream 19 passes to detoluenization fractionation 18 which removes C7 and lighter materials in stream 11 to yield isomerate recycle stream 10.
• Isomerate recycle stream 10 is processed in the OX and C9+ aromatics removal unit 16.
• Process A ( Figure 3) sent the product from the Liquid Phase Xylenes Isomerization unit 20 to the rerun tower 16, while Process B ( Figure 4) sent the product from Liquid Phase Xylenes Isomerization unit 20 to the PX recovery unit 12 (a ParexTM absorptive separation unit, per se well-known in the art).
• a process for producing paraxylene comprising:
• said feed comprising C8+ aromatics includes at least one feed selected from the group consisting of a C8+ selective toluene disproportionation product, a C8+ trans alky ation product, a C8+ reformate product, and a C8+ toluene disproportionation product.
• PX paraxylene
• a first fractionation column operating at conditions suitable for the separation of a C8+ aromatics stream into an overheads comprising xylenes and a bottoms product stream comprising C9+ aromatics, the overheads stream fluidly connected with a PX recovery unit, wherein said PX recovery unit provides a PX-enriched stream and a PX-depleted stream, the improvement comprising dividing a conduit carrying said PX-depleted stream so that a portion of said PX-depleted stream is passed to a vapor phase isomerization unit and another portion of said PX-depleted stream is passed to a liquid phase isomerization unit.
• PX paraxylene
• liquid phase isomerization unit is fluidly connected so as to provide liquid phase isomerate recycle to said first fractionation column and/or to said PX recovery unit.

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• 2011
  • 2011-10-21 EP EP11836894.3A patent/EP2632880A4/de not_active Withdrawn
  • 2011-10-21 SG SG10201508779UA patent/SG10201508779UA/en unknown
  • 2011-10-21 CN CN201180052392.0A patent/CN103201240B/zh active Active
  • 2011-10-21 JP JP2013536681A patent/JP5876883B2/ja active Active
  • 2011-10-21 KR KR1020137010675A patent/KR20130056357A/ko not_active Ceased
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  • 2011-10-21 WO PCT/US2011/057240 patent/WO2012058108A2/en not_active Ceased
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