JP6527960B2 - Process and apparatus for producing paraxylene - Google Patents

Description

Inventors Tinger, Robert Zee; Period, Dana Lynn and Molinje, Michel
CROSS-REFERENCES TO RELATED APPLICATIONS This application is related to US Provisional Patent Application Nos. 62 / 154,774 filed on April 30, 2015 and European Patent Application No. 15171577.8 filed on June 11, 2015. Claim the benefits of priority.
Technical field

  The present application relates to improved processes and apparatus for producing para-xylene, in particular to recovering para-xylene from multiple streams having different amounts of ethylbenzene.

Ethylbenzene (EB), paraxylene (PX), ortho-xylene (OX) and meta-xylene (MX) is present together in C ₈ aromatics product stream from chemical plants and oil refineries often. Although high purity EB is an important raw material for styrene production, and all of the high-purity EB feedstock used in the production of styrene is not due for various reasons to recover from C ₈ aromatic product stream, ethylene Manufactured by the alkylation of benzene with Of the three xylene isomers, PX has the largest commercial market and is mainly used for the preparation of terephthalic acid and terephthalic acid esters, which are various polymers such as poly (ethylene terephthalate), poly (propylene terephthalate) And poly (butene terephthalate). While OX and MX are useful as solvents and raw materials for making products such as phthalic anhydride and isophthalic acid, the market demand for OX and MX and their downstream derivatives is much smaller than that of PX.

Given the higher PX demand compared to other isomers, it has been directed significant commercial interest in maximizing the production from a given source PX of the C ₈ aromatic feed. However, achieving this goal of maximizing PX manufacturing presents many important technical challenges that must be overcome. For example, C ₈ aromatics four, especially three xylene isomers typically present in a concentration which is determined by the C ₈ thermodynamics of production of aromatic stream at a particular plant or oil refinery. As a result, the increased amount of additional processing steps are used in PX, and / or to be improved PX recovery efficiency, production of PX to the amount originally present in the C ₈ aromatics stream at most It is limited. Various methods of increasing the concentration of PX in C ₈ aromatics stream is known. These processes typically use a C ₈ aromatic stream, a separation step where at least a portion of PX is recovered to produce a PX poor stream, and a PX content in PX poor stream is returned to equilibrium concentration. It comprises the steps of circulating between the isomerization steps.

In a typical aromatic plant, a stream of liquid feed, typically a C ₈₊ aromatic feed stream, as shown in FIG. 1, is processed by previously known methods to provide C _{7 -species} species. (In particular benzene and toluene) have already been removed and are fed via conduit 1 to the xylene re-distillation column 3. The xylene re-distillation column (or, more simply, the fractionation column) evaporates the feed to bring the C ₈ aromatics to the overhead mixture 5 of xylene (OX, MX and PX) and ethylbenzene (EB), And a bottom product 61 containing C ₉₊ aromatics. The overhead mixture typically has a composition of about 40 to 50% metaxylene (MX), 15 to 25% PX, 15 to 25% OX and 10 to 20% EB. In the present specification, percentages are by weight unless otherwise specified.

  The overhead mixture 5 may then be sent to a PX recovery unit 15, where crystallization, adsorption or membrane separation techniques may be used. These techniques can separate PX from its isomers to produce up to 99.9% high purity PX, which is removed from apparatus 15 via conduit 17. If the device 15 is an adsorptive separation device, such as a ParexTM or an EluxylTM device, the extract 17 contains a desorbent, such as paradiethylbenzene (PDEB), which is distilled, for example, by distillation. It is necessary to separate from the desired extract PX in column 19. Distillation column 19 produces high purity PX stream 27, which may contain light impurities such as toluene, non-aromatics and water, which are downstream of the distillation column (shown in FIG. Not removed) to further improve the PX purity. Desorbent is returned to the PX recovery system 15 via conduit 21.

Raffinate 65 mainly contains MX, OX, EB, and this raffinate 65 and desorbent are sent to fractionation tower 37, which contains stream 35 and bottoms containing MX, OX and EB. Generate 63 The desorbent in the bottom product 63 is returned to the PX recovery unit 15. Note that the term "raffinate" as used herein refers to the part recovered from the PX recovery unit 15, whether the technique used is adsorption separation, crystallization or membrane separation. . Stream 35 is sent to isomerization unit 43 to isomerize MX and OX and optionally EB to an equilibrium mixture of 4 isomers. The isomerization unit 43 may be a gas phase or liquid phase isomerization unit or both. Product isomerization unit 43 is sent via conduit 51 to _{C 7-} distillation column _{53, C 7-} distillation column 53 the isomerization product, and bottoms stream 59 containing the equilibrium _{xylene, C 7-} It is separated into an overhead, 47 containing aromatics such as benzene and toluene. Thereafter, the bottom product 59 of the distillation column 53 is sent to the xylene redistillation column 3, where it is combined with the feed 1 as shown in the figure or by means of a separate inlet (not shown). It may be introduced.

However, when the EB is present in the C ₈ aromatics stream, which may affect the efficiency of the particular process. In particular, when the adsorptive separation device is used for the recovery of PX, although the adsorbent has a higher affinity for PX, the adsorbent may also adsorb EB to a considerable extent, thereby The capacity of the adsorbent for adsorbing PX decreases. Therefore, to avoid conflicts EB with respect to the suction capacity, in order to increase the efficiency of adsorption of PX, it is desirable to reduce or minimize the amount of EB in C ₈ aromatics stream is sent to the adsorption separation unit. Moreover, liquid phase isomerization converts little or no EB in the poor stream to PX, resulting in an increase in the amount of EB in the xylene loop to very high levels. Therefore, it is also desirable to control the amount of EB in a PX poor stream subjected to liquid phase isomerization to maximize the use of liquid phase isomerization.

The present invention is an improved process for producing PX, in particular the process of methylating toluene and / or benzene to selectively produce PX, with multiple streams of PX having different amounts of EB. Process, including being processed separately. A first hydrocarbon feedstock comprising xylene and EB is provided to a first PX adsorption section where a first PX rich stream and a first PX poor stream are recovered from the feedstock. A second hydrocarbon feedstock comprising xylene and less EB than the first hydrocarbon feedstock is provided to a second PX adsorption zone where a second PX rich stream and a second PX are provided. Poor streams are recovered from the feedstock. Separating multiple feeds with different EB content increases the overall efficiency of the adsorption of PX by the adsorber. The first and second PX adsorption compartments may be two separate adsorption towers of two separate PX adsorbers or one PX adsorber. In some embodiments, the first hydrocarbon feedstock is passed through a first xylene fractionation column prior to the PX adsorption section to produce a first overhead stream comprising C ₈ hydrocarbons and C _A first bottom stream comprising ₉₊ hydrocarbons may be produced, the first top stream being sent to a first PX adsorption section. Similarly, the second hydrocarbon feedstock is passed through a second xylene fractionation column to produce a second overhead stream containing C ₈ hydrocarbons and a second column containing C _{9 +} hydrocarbons. A bottoms stream may be produced, the second overhead stream being sent to a second PX adsorption section.

  The first and second PX poor streams are provided on opposite sides of the dividing walls of the dividing wall raffinate distillation column and then separated into EB rich and EB poor streams. At least a portion of the EB rich stream is then fed to the xylene isomerization unit where the EB rich stream is isomerized under at least partial gas phase conditions to be poor in the first and second PX A first isomerized stream is produced having a PX concentration higher than the stream. At least a portion of the EB-poor stream is then fed to the xylene isomerization unit where the EB-poor stream is isomerized under at least partial liquid phase conditions to deplete the first and second PX A second isomerized stream is produced having a PX concentration higher than the stream. Gas phase isomerization is more efficient in converting EB than liquid phase isomerization, but because liquid phase isomerization is more energy efficient, it splits poor streams into PX based on EB content, respectively Subjecting to a suitable isomerization process maximizes the efficiency and effectiveness of the process. At least a portion of the first isomerized stream is then recycled to the first PX adsorption section or optionally to the first xylene fractionation column, and at least a portion of the second isomerized stream Is then recycled to the second PX adsorption section or optionally to the second xylene fractionation column to recover additional PX. This process is then repeated to define the so-called xylene isomerization loop.

  The invention also includes an apparatus for carrying out the process of the invention comprising a first PX adsorption zone and a second PX adsorption zone, the first PX adsorption zone being from a first hydrocarbon feedstock. A first PX rich stream and a first PX poor stream are produced, and a second PX adsorption section is a second hydrocarbon rich feedstock from a second hydrocarbon feed and a second PX rich stream and a second PX poor stream Manufacture. The first and second PX adsorption sections are fluidly connected to a dividing wall raffinate distillation column, where the first and second PX poor streams are separated into an EB rich stream and an EB poor stream. Fluidly connected to the dividing wall raffinate distillation column are a gas phase isomerizer and a liquid phase isomerizer, and the gas phase isomerizer isomerizes the EB rich stream and is poor in first and second PX The first isomerized stream is produced with a PX concentration higher than the stream, and the liquid phase isomerization unit isomerizes the poor stream in EB to a PX concentration higher than the poor stream in the first and second PX To produce a second isomerized stream. In some embodiments, the first xylene fractionation column is fluidly connected downstream of the gas phase isomerization unit and upstream of the first PX adsorption section, and the second xylene fractionation column is liquid It is fluidly connected downstream of the isomerization unit and upstream of the second PX adsorption section.

Figure 1 is a flow diagram of a conventional para-xylene (PX) production and extraction process using liquid phase xylene isomerization and gas phase xylene isomerization.

1 is a flow diagram of a first embodiment of the process of the present invention.

5 is a flow diagram of a second embodiment of the process of the present invention.

5 is a flow chart of a third embodiment of the process of the present invention.

7 is a flow chart of a fourth embodiment of the process of the present invention.

As used herein, the term "C _n " hydrocarbon refers to a hydrocarbon in which n is a positive integer and has n carbon atoms per molecule. For example, the C ₈ aromatic hydrocarbon means a mixture of aromatic hydrocarbons or aromatic hydrocarbons having eight carbon atoms per molecule. The term "C _n +" hydrocarbon means a hydrocarbon where n is a positive integer and has at least n carbon atoms per molecule, while the term "C _n- " hydrocarbon means n Is a positive integer and means a hydrocarbon having n or less carbon atoms per molecule.

The present invention is an improved process and apparatus for producing PX, in particular methylating toluene and / or benzene to selectively produce PX, wherein multiple streams with different amounts of EB are separated The process comprises the steps of: treating to increase the efficiency of recovery of PX. Referring to FIG. 2, a first hydrocarbon feedstock 102 comprising xylene and EB is provided to a first para-xylene adsorption section 130 where it is poor in first PX rich stream 132 and first PX Stream 134 is recovered from the feedstock. A second hydrocarbon feedstock 104 comprising xylene and less EB than the first hydrocarbon feedstock 102 is provided to a second para-xylene adsorption section 140 where a second PX rich stream 142 and A second PX poor stream 144 is recovered from the feed. The first and second PX poor streams 134 and 144 are then separated in the dividing wall raffinate distillation column 170 into EB rich streams 172 and EB poor streams 174. At least a portion of the EB-rich stream 172 is then fed to the xylene isomerization unit 180 where the EB-rich stream 172 is isomerized under at least partial gas phase conditions to produce first and second PX A first isomerized stream 182 is produced having a PX concentration higher than the poor stream 134, 144. At least a portion of the EB-poor stream 174 is then fed to the xylene isomerization unit 190 where the EB-poor stream 174 is isomerized under at least partial liquid phase conditions to form the first and second PXs. A second isomerized stream 192 is produced having a PX concentration higher than the poor stream 134,144. At least a portion of the first isomerized stream 182 is then recycled to the first para-xylene adsorption section 130 and at least a portion of the second isomerized stream 192 is then It is recycled to the para-xylene adsorption section 140 to recover additional PX. Thus the process is repeated and a so-called xylene isomerization loop is defined.
Hydrocarbon feed

  The first hydrocarbon feedstock 102 used in the process of the present invention is any hydrocarbon stream comprising xylene and EB, such as a reformate stream (product stream of a reformate split distillation column), a hydrogenation A cracked product stream, a reaction product stream of xylene or EB, an aromatic disproportionation stream, an aromatic transalkylated stream, a CyclarTM process stream and / or an imported product stream may be, but is not limited to these. The first feedstock 102 is at least 1.0 wt%, at least 2.0 wt%, at least 3.0 wt%, at least 5.0 wt%, at least 7.5 wt% or at least 10.0 wt%. It may contain EB.

The second hydrocarbon feedstock 104 is a hydrocarbon stream containing xylene and less EB than the first hydrocarbon feedstock 102, such as PX selective aromatic alkylation product stream, non-selective (equilibrium PX) Aromatic alkylation product stream, aromatic disproportionation stream, aromatic transalkylation stream, methanol / dimethyl ether to aromatic product stream, syngas to aromatic product stream, C ₂ -C ₄ alkane / alkene • Two aromatic product streams, imported product streams and / or off-spec PX streams from a PX recovery unit may be, but is not limited to these. The second hydrocarbon feedstock 104 is less than 10.0 wt%, less than 7.5 wt%, less than 5.0 wt% as long as its EB content is less than the EB content of the first feedstock 102 May contain an EB content of less than 3.0% by weight, less than 2.0% by weight or less than 1.0% by weight.

In one embodiment, the second hydrocarbon feedstock 104 is a selective alkylation product in a methylation reactor of benzene and / or toluene with methanol and / or dimethyl ether. The reactor may be a fluidized bed, a moving bed, a fixed bed, a circulating bed or any combination thereof. One fluid bed methylation reactor is described in US Pat. Nos. 6,423,879 and 6,504,072, the entire contents of which are incorporated herein by reference and the fluid bed methylated reactor Reactor has a diffusion parameter for 2,2-dimethylbutane of about 0.1 to 15 seconds ^-1 when measured at a temperature of 120 ° C. and a 2,2-dimethylbutane pressure of 60 Torr (8 kPa) A catalyst containing porous crystalline material is used. The porous crystalline material may be a mesoporous zeolite, such as ZSM-5, which is at least one to control the reduction of the pore volume of the material during the steaming process. C., and heavily steamed at a temperature of at least 950.degree. C. in the presence of those containing phosphorous. An example of a fixed bed process and catalyst is described in U.S. Patent Nos. 7,304,194 and 8,558,046, which are steamed at a temperature of 150-350.degree. C. for selectivity to para-xylene Discloses an increased phosphorus modified ZSM-5 catalyst.

The feedstock may further comprise recycle stream (s) from isomerization step (s) and / or various separation steps. The hydrocarbon feed contains PX together with MX, OX and EB. In addition to xylene and EB, the hydrocarbon feedstock may also contain some amount of other aromatics or even non-aromatics. Examples of such aromatic compounds are C7 _- hydrocarbons such as benzene and toluene, and _{C9 +} aromatics such as mesitylene, pseudocumene and the like. These types of feed stream (s) are described in the "Oil Refining Process Handbook", Robert A. Myers, Ed., McGraw-Hill Book, Inc., Second Edition.

Depending on the composition of the first and second hydrocarbon feedstock 102, 104, the first separation step of 1 or more which serves to remove the C _7- and C ₉₊ hydrocarbons from feedstock, first and second A second hydrocarbon feedstock 102, 104 may be present prior to providing the first and second para-xylene adsorption sections 130, 140. In general, the first separation step may comprise fractional distillation, crystallization, adsorption, reactive separation, membrane separation, extraction or any combination thereof. In one embodiment, the first hydrocarbon feedstock 102 is passed through the first xylene fractionation column 110 prior to being passed through the first para-xylene adsorption section 130. The first xylene fractionation column 110 produces a first overhead stream 112 containing C ₈ hydrocarbons and a first bottom stream 114 comprising C _{9 +} hydrocarbons, and the first overhead stream Stream 112 may be sent to a first paraxylene adsorption section 130 and first bottom stream 114 may be sent to a transalkylation unit (not shown).

Similarly, the second hydrocarbon feedstock 104 is passed through the second xylene fractionation column 120 before being passed through the second para-xylene adsorption section 140. The second xylene fractionation column 120 produces a second overhead stream 122 containing C ₈ hydrocarbons and a second bottom stream 124 comprising C _{9 +} hydrocarbons, and the second overhead stream Stream 122 is sent to the second para-xylene adsorption section 140. The second hydrocarbon feedstock 104 is described in the phenol and styrene removal steps, such as in US Patent Application Publication Nos. 2013/0324779 and 2013/0324780, before or after the second xylene fractionation column 120. , The entire contents of which are incorporated herein by reference. The second bottom stream 124 is also optionally phenol prior to being passed through the transalkylation unit (not shown) and optionally through the first bottom stream 114. And styrene removal steps such as those described in US Patent Application Publication Nos. 2013/0324779 and 2013/0324780.

Depending on the mass balance and equipment requirements, a portion of the first hydrocarbon feedstock 102 may be combined with the second hydrocarbon feedstock 104 prior to the xylene fractionation device or vice versa . Similarly, a portion of the overhead stream 112 may be combined with the overhead stream 122 before the PX adsorption section 130, 140 or vice versa.
Paraxylene recovery

First hydrocarbon feed 102 first overhead stream 112 containing the C ₈ hydrocarbons or in the first embodiment xylene fractionator is used, is the first para-xylene adsorption zone 130 As supplied, the first PX rich product stream 132 and the first PX poor stream 134 are produced. A second hydrocarbon feedstock 104, or a second overhead stream 122 containing C ₈ hydrocarbons in embodiments where a first xylene fractionation unit is used, passes to the second para-xylene adsorption section 140. Supplied to produce a second PX rich product stream 142 and a second PX poor stream 144. In one embodiment, the first and second PX rich product streams 132, 142 are at least 10 wt% PX, preferably at least 50 wt% PX, more preferably at least 50 wt% PX based on the total weight of the PX rich product stream Contains at least 70% by weight PX, even more preferably at least 80% by weight PX, most preferably at least 90% by weight PX and ideally at least 95% by weight PX.

  The first and second para-xylene adsorption sections 130, 140 are preferably simulated moving bed adsorption devices, such as PAREXTM devices or ELUXYLTM devices. These types of separation devices and their designs are described in "Perry's Handbook of Chemical Engineers", R.S. H. Perry, D .; W. Green and J.A. O. Maloney, Ed., McGraw-Hill Book, 6th ed., 1984, and the aforementioned "Oil Refining Process Handbook". In a typical simulated moving bed adsorber, an adsorbent bed consisting of several subbeds is housed in two adsorption towers connected in series. In one embodiment, the first paraxylene adsorption section 130 and the second paraxylene adsorption section 140 are separate simulated moving bed adsorption devices with two adsorption columns in each section. In another embodiment, the first para-xylene adsorption section 130 and the second para-xylene adsorption section 140 each comprise one adsorption tower of one simulated moving bed adsorber.

  Separately processing feedstocks with different EB content, eg, feedstocks with less than 1.0 wt% EB and feedstocks with more than 1.0 wt% EB, result in more efficient adsorption of PX Be Although the adsorbent has a higher affinity to PX, the adsorbent may also adsorb EB to a significant extent, thereby reducing the capacity of the adsorbent to adsorb PX. Thus, applying a lower amount of EB, ie, a feedstock with less than 1.0 wt% EB, to another PX adsorption compartment minimizes the amount of competing EB for the adsorption capacity in that adsorption compartment. It is able to increase the efficiency of PX adsorption, resulting in more efficient adsorption of the entire PX.

In FIG. 2 in a conventional simulated moving bed plant arrangement, the first and second PX rich product streams 132, 142 containing PX and desorbent are sent to the extract distillation column 150 for separation, Extract distillation column 150 produces PX stream 152 and first desorbent stream 154. The first desorbent stream 154 is recycled to the first and second paraxylene adsorption sections 130, 140, optionally through the desorbent vessel. The PX stream 152 is then sent to a finishing distillation column 160, which produces a purified PX product 162. The toluene stream 164 may be recovered from the finishing distillation column 160 as a top product and recycled to the PX manufacturing process, preferably to the selective alkylation process of benzene and / or toluene with methanol and / or dimethyl ether. In a conventional simulated moving bed plant arrangement, PX poor streams containing MX, OX, EB and desorbent are sent to a raffinate distillation column, while in the process of the present invention a dividing wall raffinate distillation column is a conventional raffinate distillation Replacing the tower, this process is described below.
Divided wall raffinate distillation tower

  With continuing reference to FIG. 2, the first and second PX poor streams 134, 144 are passed through dividing wall raffinate distillation column 170, which replaces the conventional raffinate distillation column (fractionation column 37 in FIG. 1), The dividing wall raffinate distillation column 170 separates the first and second PX poor streams 134, 144 into three streams: an EB rich stream 172, an EB poor stream 174 and a second desorbent stream 176. As the name implies, the term "split-wall distillation column" refers to a particular known form of distillation column that includes dividing walls. The dividing wall vertically bisects a portion of the interior of the distillation column but does not extend to either the top and bottom sections of the distillation column, and thus, like the conventional distillation column The distillation column is allowed to reflux and reboil. The dividing wall provides a fluid impermeable baffle that separates the interior of the distillation column. The dividing wall distillation column can be configured for multiple processes, even though the inlet to the distillation column is located on one side of the dividing wall and one or more sidestream outlets are on the opposite side. Wells or inlets may be placed on both sides of the dividing wall distillation column and multiple withdrawals may be from the top or bottom of the distillation column, or any combination thereof.

  In certain embodiments, the dividing wall is low enough to provide an optimal ratio of low EB product to high EB product on the tray from its top to the bottom of the distillation column. Extending to the person skilled in the art can ascertain its requirements using simulation tools. The first PX poor stream 134 from the first hydrocarbon feedstock 102 with higher EB concentration is fed to one side of the dividing wall of the dividing wall raffinate distillation column 170 and has lower EB concentration The second PX poor stream 134 from the second hydrocarbon feedstock 104 is fed to the opposite side of the dividing wall of the dividing wall raffinate distillation column 170. EB-rich stream 172 and EB-poor stream 174 are withdrawn from the top of the distillation column or near the top of the distillation column to remove light components such as water. Each overhead stream may be processed by a separate overhead product unit (not shown), and part of the EB rich stream 172 and the EB poor stream 174 may be a dividing wall raffinate distillation column It may be returned as a reflux at 170. Using a dividing wall distillation column as a raffinate distillation column further improves the separation of EBs in a PX poor stream and allows more efficient use of the isomerization process.

At least a portion of the EB rich stream 172 is sent to the isomerization unit 180 and at least a portion of the EB poor stream 174 is sent to the isomerization unit 190. In other embodiments in which the amount of EB in the EB rich stream is minimal, the EB rich stream may be purged towards the fuel blend. The second desorbent stream 176 may optionally be recycled to the first and second para-xylene adsorption sections 130, 140, through the desorbent vessel.
Xylene isomerization

In a preferred embodiment, the EB rich stream 172 is sent to the isomerization unit 180 and the isomerization unit 180 is operated in the gas phase, as liquid phase isomerization converts little or no EB in PX poor stream . Also, the EB-poor stream 174 is sent to the isomerization unit 190, which operates in the liquid phase. Energy and capital are saved by minimizing the amount of stream poor in PX subjected to gas phase isomerization. Because gas phase isomerization requires steaming a stream poor in PX and the use of hydrogen, the use of hydrogen requires an energy intensive and capital intensive hydrogen recycling loop. The gas phase isomerization process requires more energy and capital than liquid phase isomerization.
Gas phase isomerization

The EB rich stream 172 is fed to the xylene isomerization unit 180 where the EB rich stream 172 is at least partially effective to isomerize the PX poor EB rich stream 172 back to the equilibrium concentration of xylene isomers. The catalyst is contacted with a xylene isomerization catalyst under conditions of a substantially gas phase. In general, there are two types of gas phase isomerization catalysts, one dealkylates EB to produce benzene and ethylene and isomerizes xylene isomers, and the other four, including EB Different C ₈ aromatics are isomerized to their equilibrium concentrations. Any catalyst may be used in the gas phase isomerization unit 180.
EB dealkylation

In one embodiment, the EB-rich stream 172 is subjected to xylene isomerization, where the EBs in the stream can be dealkylated to produce benzene. In this embodiment ethylbenzene is removed by the cracking / disproportionation, poor C ₈ stream to paraxylene conveniently supplied to the multi-bed reactor, the multi-bed reactor at least a first containing an ethylbenzene conversion catalyst bed And a second bed downstream of the first bed and containing a xylene isomerization catalyst. These beds can be in the same or different reactors. Alternatively, the ethylbenzene conversion catalyst and the xylene isomerization catalyst may be contained in a single bed reactor.

  The ethylbenzene conversion catalyst typically has a constraint index in the range of 1 to 12, a molar ratio of silica to alumina of at least about 5, for example at least about 12, for example at least 20, and an alpha value of at least 5, for example 75 to 5000 Containing medium pore size zeolite. The restraint index and its method of measurement are disclosed in U.S. Pat. No. 4,016,218, the contents of which are incorporated herein by reference while the test method for alpha values is U.S. Pat. No. 3,354,078. No. and Journal of Catalysis, Vol. 4, p. 527 (1965); Vol. 6, p. 278 (1966); and Vol. 61, p. 395 (1980). Hereby incorporated by reference. The experimental conditions of the test used herein include a constant temperature of 538 ° C. and a fluctuating flow rate as described in detail in the Journal of Catalysis, vol. 61, p. 395. Higher alpha values correspond to more active cracking catalysts.

  Examples of suitable medium pore size zeolites include ZSM-5 (US Pat. Nos. 3,702,886 and Reissue Pat. No. 29,948), ZSM-11 (US Pat. No. 3,709,979) ZSM-12 (US Patent 3,832,449), ZSM-22 (US Patent 4,556,477), ZSM-23 (US Patent 4,076,842), ZSM-35. (US Pat. No. 4,016,245), ZSM-48 (US Pat. No. 4,397,827), ZSM-57 (US Pat. No. 4,046,685), ZSM-58 (US Pat. No. 4) , 417, 780), EU-1 and mordenite. The entire contents of the above references are incorporated herein by reference. Preferred zeolites are ZSM-5, ZSM-12 or EU-1.

  The zeolite used for the ethylbenzene conversion catalyst typically has a crystal size of at least 0.2 microns, a xylene pressure of 120 ° C. and 4.5 ± 0.8 mm mercury and (at the same conditions of temperature and pressure) ) For xylenes which can be either para, meta, ortho or mixtures thereof, with an ortho-xylene adsorption time corresponding to 30 percent of its equilibrium ortho-xylene adsorption capacity measured at ortho-xylene adsorption times greater than 1200 minutes Exhibit an equilibrium adsorption capacity of at least 1 gram per 100 grams of zeolite. The determination of the amount adsorbed may also be carried out gravimetrically in thermal equilibrium. Adsorption tests are described in U.S. Pat. Nos. 4,117,026, 4,159,282, 5,173,461 and Re. 31,782, each of which is incorporated herein by reference. Incorporated in the specification.

  The zeolite used in the ethylbenzene conversion catalyst may be self-binding (without a binder) or may be complexed with an inorganic oxide binder, the ratio of both being about 1 to about 99 weight of the dry composite A zeolite content in the range of percent, more usually in the range of about 10 to about 80 weight percent, such as about 65% zeolite and about 35% binder. If a binder is used, the binder is preferably non-acidic, such as silica. Procedures for preparing silica bound ZSM-5 are described in US Pat. Nos. 4,582,815, 5,053,374 and 5,182,242, which are incorporated herein by reference Be

  In addition, the ethylbenzene conversion catalyst is typically about 0.001 to about 10 weight percent, such as about 0.05 to about 5 weight percent, such as about 0.1 to about 2 weight percent of the hydrogenation / dehydrogenation component. Contains. Examples of such components are oxides, hydroxides, sulfides or free metal (ie zero valence) forms of Group VIIIA metals (ie Pt, Pd, Ir, Rh, O, Ru, Ni, Co And Fe), Group VIIA metals (ie, Mn, Tc and Re), Group VIA metals (ie, Cr, Mo and W), Group VB metals (ie, Sb and Bi), Group IVB metals (ie, Sn and Pb) And Group IIIB metals (ie, Ga and In) and Group IB metals (ie, Cu, Ag and Au). Noble metals (ie, Pt, Pd, Ir, Rh, Os and Ru) are preferred hydrogenation / dehydrogenation components. Combinations of such noble metal or non-noble metal catalyst forms, such as Pt and Sn may be used. The metal may be in a reduced valence state, for example when this component is in the form of an oxide or hydroxide. This reduced valence state of the metal may be obtained in situ in the course of the reaction, if a reducing agent such as hydrogen is included in the feed to the reaction.

  The xylene isomerization catalyst used in this embodiment typically comprises medium pore size zeolites, such as those having a constraint index of 1 to 12, especially ZSM-5. The acidity of ZSM-5 of this catalyst, expressed as an alpha value, is generally less than about 150, such as less than about 100, such as about 5 to about 25. Such reduced alpha values can be obtained by steaming. Zeolites typically adsorb ortho-xylene in an amount equal to 30% of its equilibrium adsorption capacity for ortho-xylene at crystal sizes less than 0.2 microns and a xylene pressure of 120 ° C. and 4.5 ± 0.8 mm mercury. It has an ortho-xylene adsorption time that takes less than 50 minutes to complete. The xylene isomerization catalyst may be in self-bound form (without a binder) or may be complexed with an inorganic oxide binder such as alumina. Additionally, the xylene isomerization catalyst may contain the same hydrogenation / dehydrogenation components as the ethylbenzene conversion catalyst.

Using the above catalyst system, decomposition / disproportionation of ethylbenzene and isomerization of xylene are typically at temperatures of about 400 ° F. to about 1,000 ° F. (204 ° C. to 538 ° C.), about 0 Pressures of ̃1,000 psig (100-7,000 kPa), weight hourly space velocity (WHSV) of about 0.1 to about 200 h ⁻¹ , and hydrogen (H ₂ ) and hydrocarbons of about 0.1 to about 10 It carries out on the conditions containing the molar ratio with HC). Alternatively, the conversion conditions may be a temperature of about 650 ° F. to about 900 ° F. (343 ° C. to 482 ° C.), a pressure of about 50 to about 400 psig (446 to 2,859 kPa), a WHSV of about 3 to about 50 hr ^-1 . And a molar ratio of H ₂ to HC of about 0.5 to about 5 may be included. WHSV is based on the weight of the catalyst composition, ie the total weight of active catalyst plus binder for it, if used.
EB isomerization

In another embodiment, the EB-rich stream 172 is subjected to EB isomerization to produce a stream comprising C ₈ aromatics at equilibrium concentrations.

  Typically, the EB isomerization catalyst is a medium pore size molecular sieve having a constraint index that falls within the approximate range of 1 to 12, such as ZSM-5 (US Pat. No. 3,702,886 and Reissue Patent 29,948), ZSM-11 (US Patent 3,709,979), ZSM-12 (US Patent 3,832,449), ZSM-22 (US Patent 4,556,477) ZSM-23 (US Pat. No. 4,076,842), ZSM-35 (US Pat. No. 4,016,245), ZSM-48 (US Pat. No. 4,397,827), ZSM-57. (US Patent 4,046,685) and ZSM-58 (US Patent 4,417,780). Alternatively, the xylene isomerization catalyst may be MCM-22 (as described in US Pat. No. 4,954,325), PSH-3 (as described in US Pat. No. 4,439,409), SSZ- 25 (described in US Pat. No. 4,826,667), MCM-36 (described in US Pat. No. 5,250,277), MCM-49 (US Pat. No. 5,236,575). Molecular sieves) and MCM-56 (as described in US Pat. No. 5,362,697). The molecular sieve may also be a molecular sieve of EUO structural type, which is preferably EU-1 or mordenite. A preferred molecular sieve is one of the EUO structural types having a Si / Al ratio of about 10 to 25 as disclosed in U.S. Patent No. 7,893,309. The entire contents of the above references are incorporated herein by reference.

  It may be desirable to combine the molecular sieve of the xylene isomerization catalyst with another material that is resistant to the temperature and other conditions of the process of the present invention. Such matrix materials include inorganic materials such as clays, silica and / or metal oxides (eg titanium oxide or boron oxide) as well as synthetic or naturally occurring substances. The metal oxides may be naturally occurring or in the form of gelatinous precipitates or gels, such as mixtures of silica and metal oxides. Naturally occurring clays can be complexed with molecular sieves, and naturally occurring clays include montmorillonite and kaolinaceous clays, and these families include subbentonite clays and kaolin clays. These are usually known as Dixie, McNammy, Georgia and Florida Clay or others, the main mineral constituents of others being halloysite, kaolinite, dickite, nacrite or anauxite. Such clays can be used in their native as-mined state or can be first subjected to calcination, acid treatment or chemical modification.

  In addition to the above materials, molecular sieves are porous matrix materials such as alumina, zirconia, silica alumina, silica magnesia, silica zirconia, silica tria, silica beryllia, silica titania, aluminum phosphate, aluminum phosphate, titanium phosphate, zirconia zirconia, It may be complexed with ternary compounds such as silica alumina tria, silica alumina zirconia, silica alumina magnesia and silica magnesia zirconia. Mixtures of these components could also be used. The matrix may be in the form of cogel. The relative proportions of the molecular sieve component and the inorganic oxide gel matrix relative to anhydride may vary within wide limits, the molecular sieve content is in the range of about 1 to about 99 weight percent of the dry complex, more usually In the range of about 10 to about 80 weight percent.

  The EB isomerization catalyst also comprises at least one metal from group VIII of the Periodic Table of the Elements, and optionally at least one metal selected from metals from Groups IIIA, IVA and VIIB. The Group VIII metals present in the catalyst used in the isomerization process according to the invention are from iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, preferably from noble metals, very preferably palladium and platinum It is chosen from More preferably, the Group VIII metal is platinum. The metal optionally selected from Groups IIIA, IVA and VIIB is selected from gallium, indium, tin and rhenium, preferably from indium, tin and rhenium.

The conditions used in the EB isomerization process are generally temperatures from 300 to about 500 ° C., preferably about 320 to about 450 ° C., more preferably about 340 to about 430 ° C .; about 0.3 to about 1.5 MPa, preferably Is a hydrogen partial pressure of about 0.4 to about 1.2 MPa, more preferably about 0.7 to about 1.2 Mpa; about 0.45 to about 1.9 MPa, preferably about 0.6 to about 1.5 MPa And a weight hourly space velocity (WHSV) of about 0.25 to about 30 hr- ¹ , preferably about 1 to about 10 hr- ¹ , more preferably about 2 to about 6 hr- ¹ .

The product of the vapor phase xylene isomerization process 180 is a first isomerized stream 182 having a PX concentration higher than the first and second PX poor streams 134, 144. The first isomerized stream 182 is then recycled to the para-xylene adsorption section 130 to recover additional PX, and the process is repeated to form a so-called xylene isomerization loop. In some embodiments, the first isomerized stream 182 is passed through a de-toluene fractionator 184 to produce at least one C _{7 -isomerized} stream and a C _{8 +} isomerized stream 186 The C ₈₊ isomerized stream 186 is passed through the first xylene fractionation column 110 and then recycled to the first para-xylene adsorption section 130 to recover additional PX. Preferably, the de-toluene fractionation tower 184 produces two C7 _- isomerized streams, the two C7 _- isomerized streams comprising benzene and / or toluene streams 187 and light ends / hydrogen With stream 189, benzene and / or toluene stream 187 may be sent to the extraction and light end / hydrogen stream 189 may be sent to the fuel.
Liquid phase isomerization

The EB poor stream 174 is fed to the xylene isomerization unit 190 where the EB poor stream 174 is effective to isomerize the PX poor and EB poor stream 174 back to its equilibrium concentration of xylene isomers. Contact with a xylene isomerization catalyst at least partially under liquid phase conditions. Conditions suitable for liquid phase isomerization are about 200 ° C. to about 540 ° C., preferably about 230 ° C. to about 310 ° C., more preferably about 270 ° C. to about 300 ° C., about 0 to 6,895 kPa (g) , preferably at a pressure of about 1,300kPa (g) ~ about 3,500kPa (g), 0.5~100 h ^-1, the weight of preferably 1 to 20 hr ^-1, more preferably 1 to 10 hr ^-1 Includes space velocity (WHSV). Generally, these conditions, part of the C ₈ aromatics, preferably at least 25 wt%, more preferably at least 50 wt%, and ideally be expected to C ₈ aromatics 100% by weight is present in the liquid phase Be chosen to Low concentrations of hydrogen below the solubility limit may be added to the liquid phase isomerization process.

  While any catalyst capable of isomerizing xylene in the liquid phase can be used in the xylene isomerization unit, in one embodiment the medium pore size has a constraint index of 1 to 12 Contains zeolite. A restraint index and its method of measurement are described in US Pat. No. 4,016,218, the contents of which are incorporated herein by reference. Specific examples of suitable medium pore size zeolites include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48 and MCM-22, ZSM-5 and ZSM-11 are particularly preferred, in particular ZSM-5. The acidity of the zeolite, expressed as its alpha value, is preferably greater than 300, such as greater than 500, or greater than 1,000. The test method of alpha value is disclosed in U.S. Pat. No. 3,354,078; Journal of Catalysis, Vol. 4, p. 527 (1965); Vol. 6, p. 278 (1966); Vol. 61, p. 1980), each of which is incorporated herein by reference for its description. The experimental conditions of the test used to measure the alpha value cited herein include a constant temperature of 538 ° C. and a variable flow rate as described in detail in Journal of Catalysis, Volume 61, page 395. Preferred catalysts are described in US Pat. No. 8,569,559, the contents of which are incorporated herein by reference.

  The product of liquid phase xylene isomerization unit 190 is a second isomerized stream 192 having a PX concentration higher than the first and second PX poor streams 134, 144. The second isomerized stream 192 is then recycled to the first paraxylene adsorption section 130 or the second paraxylene adsorption section 140 to recover additional PX, and the process is repeated, so-called xylene isomerism Loop is formed. In order to control the level of EBs in the liquid phase isomerization loop and to prevent the accumulation of EBs, the purge stream 194 is a fixed time interval from the upstream or downstream of the liquid phase xylene isomerization unit 190 (this is determined by one skilled in the art May be withdrawn and transferred to the xylene isomerization unit 180 where EB may be converted.

Isomerization of xylene under liquid phase conditions produces less C ₉₊ aromatics than xylene isomerization under gas phase conditions. Thus, the second isomerized stream 192 may be provided to the second xylene fractionation column 120 at a higher tray location than the second hydrocarbon feedstock 104, with greater energy savings achieved. Ru. Furthermore, a significant portion of the second isomerized stream 192 bypasses the second xylene fractionation column 120 and is fed directly to the second para-xylene adsorption section 140, thereby re-fractionating Energy may be saved by avoiding it completely.

  In situations where only a single simulated moving bed unit is conventionally used, or in situations where it is not feasible to separate the feedstock by different levels of EB, US Pat. It is advantageous to separate high PX and low PX feedstocks as taught in US Pat. No. 5,529,757, the entire contents of which are incorporated herein by reference. A dividing wall distillation column may be used to provide the high PX feedstock separately to the low PX feedstock to the PX recovery unit and to avoid using a separate xylene fractionation column.

In the embodiment shown in FIG. 3, a hydrocarbon feed 202 comprising balanced xylene is provided to the dividing wall xylene fractionator 210 and also comprises a hydrocarbon feed comprising PX in an amount higher than the equilibrium concentration of xylene. Feed 204 is provided on the opposite side of the dividing wall of distillation column 210. Feedstock 204 may be fed at higher tray locations because of its higher PX concentration or lower C ₉₊ aromatic concentration typically found in toluene methylation or toluene disproportionation product streams. It can be determined by one skilled in the art. The feedstock 202 is any hydrocarbon stream containing xylene at its equilibrium concentration, ie, about 22 to 24 wt% PX, such as a reformate stream (product stream of a reformate split distillation column), hydrogenation Decomposition product stream, reaction product stream of xylene or EB, aromatic disproportionation stream, aromatic transalkylation stream, nonselective aromatic alkylation product stream, methanol-to-aromatic product stream, CyclarTM process It may be a stream and / or an imported product stream. Feedstock 204 is a hydrocarbon stream containing greater than about 22 to 24 wt% PX, such as PX selective aromatic alkylation product stream, aromatic disproportionation stream, aromatic transalkylation stream, PX recovery unit Out-of-spec PX flow, intermediate flow from crystallizer and / or imported product flow.

The dividing wall xylene fractionation column 210 divides the feeds 202, 204 into three streams: an equilibrated PX stream 212, an enriched PX stream 214, and a bottom stream 216 containing C ₉₊ hydrocarbons. Bottom stream 216 containing C _{9 +} hydrocarbons may be sent to a transalkylation unit to produce additional benzene, toluene and / or xylene. The equilibrium PX flow 212 and the enriched PX flow 214 are provided to a PX recovery unit 230, which is preferably a simulated moving bed adsorption unit, which is a stream 234 poor in PX rich product streams 232 and PX. Manufacture. A PX rich product stream 232 containing PX and desorbent is sent to an extract distillation column 250 for separation, which produces a PX stream 252 and a desorbent stream 254. Desorbent stream 254 is optionally recycled to the PX recovery unit 230 through the desorbent tank. The PX stream 252 is then sent to a finishing distillation column 260, which produces a purified PX product 262. The toluene stream 264 is recovered from the finishing distillation column 260 as overhead product and may be recycled to the PX manufacturing process, preferably the selective alkylation process of benzene and / or toluene with methanol and / or dimethyl ether. In a conventional simulated moving bed plant arrangement, a PX poor stream containing MX, OX, EB and desorbent is sent to a raffinate distillation column. However, in the process of the present invention, dividing wall raffinate distillation columns replace conventional raffinate distillation columns.

  The PX poor stream 234 is passed through a dividing wall raffinate distillation column 270 which replaces the conventional raffinate distillation column (fractionator column 37 in FIG. 1), and the dividing wall raffinate distillation column 270 is a PX poor stream 234 with three streams. Split into EB rich stream 272, EB poor stream 274 and desorbent stream 276. At least a portion of the EB rich stream 272 is sent to the isomerization unit 280, which operates in the gas phase. Also, at least a portion of the EB-poor stream 274 is sent to the isomerization unit 290, which operates in the liquid phase. Desorbent stream 276 is recycled to the PX recovery unit 230, optionally through the desorbent tank.

The product of gas phase xylene isomerization unit 280 is a gas phase isomerized stream 282 having a PX concentration higher than stream 234 which is poor in PX. The gas phase isomerized stream 282 is then recycled to the PX recovery unit 230 to recover additional PX, and the process is repeated to form a so-called xylene isomerization loop. In some embodiments, gas phase isomerized stream 282 is passed through de-toluene fractionator 284 to obtain at least one C _{7 -isomerized} stream, and C _{8 +} isomerized stream 286 The C ₈₊ isomerized stream 286 produced is passed through the dividing wall xylene fractionator 210 and then recycled to the PX recovery unit 230 to recover additional PX. Preferably, the de-toluene fractionation column 284 produces two C ₇ -isomerized streams, ie benzene and / or toluene stream 287 and light end / hydrogen stream 289, benzene and / or toluene stream 287 The light end / hydrogen stream 289 may be sent to the fuel, which may be sent for extraction.

  The product of liquid phase xylene isomerization unit 290 is liquid phase isomerized stream 292 having a PX concentration higher than stream 234 which is poor in PX. The liquid phase isomerized stream 292 is then recycled to the PX recovery unit 230 to recover additional PX, and the process is repeated to form a so-called xylene isomerization loop. In order to control the level of EB in the liquid phase isomerization loop and to prevent the accumulation of EB, the purge stream 294 is a constant time interval from the upstream or downstream of the liquid phase xylene isomerization device 290 (this is determined by one skilled in the art May be withdrawn and transferred to xylene isomerization unit 280 where EB may be converted. The liquid phase isomerized stream 292 may first be passed through the dividing wall xylene fractionation column 210, either side of the dividing wall, or into the PX recovery unit 230, to increase the equilibrium PX flow 212 or concentration. It may be provided with any of the provided PX streams 214.

FIG. 4 shows an embodiment where a dividing wall xylene fractionation column is used with two PX adsorption sections. The corresponding elements from FIG. 3 use the same reference numerals in FIG. The hydrocarbon feedstock 202 containing equilibrated xylene is provided to the dividing wall xylene fractionation column 210 and the hydrocarbon feedstock 204 containing PX in an amount higher than the equilibrium concentration of xylene is part of the distillation column 210 Provided on the other side of the wall. The dividing wall xylene fractionation column 210 divides the feeds 202, 204 into three streams: an equilibrated PX stream 212, an enriched PX stream 214, and a bottom stream 216 containing C ₉₊ hydrocarbons. .

  The equilibrium PX stream 212 is provided to a first PX recovery unit 230, which is preferably a simulated moving bed adsorption unit, which is a PX rich product stream 232 and a PX poor stream 234. Manufacture. The concentrated PX stream 214 is provided to a second PX recovery unit 240, which is preferably a simulated moving bed adsorption unit, which is a PX rich product stream 242 and PX The scarce stream 244 is produced. The PX rich product stream 232, 242, containing PX and desorbent, is sent to the extract distillation column 250 for separation, and the PX poor stream 234, 244 is passed to the dividing wall raffinate distillation column 270. Be done. The remaining steps are similar to those described in FIG. 3 above.

FIG. 5 shows an embodiment where a crystallizer is used to recover PX from the product of selective alkylation of benzene and / or toluene with methanol and / or dimethyl ether. Corresponding elements from FIGS. 3 and 4 use the same reference numerals in FIG. The product stream 502 from the selective alkylation of benzene and / or toluene with methanol and / or dimethyl ether in the methylation reactor is provided to the toluene fractionation column 510, which is also provided with fresh toluene 504 May be The toluene fractionation column produces overhead toluene stream 506 and C ₈₊ bottoms stream 508, which is recycled to the methylation reactor (not shown) and C ₈₊ bottoms stream 508 is crystallized. Provided to the analyzer 520. The C ₈₊ bottoms stream 508 may contain C ₉₊ aromatics, such as trimethylbenzene, methylethylbenzene, tetramethylbenzene, naphthalene and heavy oxygenates, but US Pat. No. 8,907,152 The C ₈₊ bottoms stream 508 may contain up to 10% by weight of C ₉₊ aromatics that would need to be fractionated upstream of the crystallizer 520 as taught in US _Pat . Optionally, C ₈₊ bottoms stream 508 may be provided to dividing wall xylene fractionator 210.

  The crystallizer 520 may be operated at about -20 ° F. (-28.9 ° C.) with propylene refrigeration or at about -80 ° F. (-62.2 ° C.) with ethylene refrigeration, as one skilled in the art Can be determined. Operating the crystallizer 520 at about −20 ° F. (−28.9 ° C.) using propylene refrigeration produces a filtrate 524 having about 30% by weight PX and about 3 to 4% by weight EB, On the other hand, operating the crystallizer 520 at about -80 ° F (-62.2 ° C) using ethylene refrigeration produces a filtrate 524 having about 10% by weight PX and about 4 to 5% by weight EB. Be done.

  If the filtrate 524 contains less than about 22 to 24 wt% PX, for example when ethylene refrigeration is used, the filtrate 524 is sent to the liquid phase isomerization unit 290 to isomerize the xylene . If the filtrate 524 contains more than about 22 to 24 wt% PX, for example when propylene refrigeration is used, the filtrate 524 is sent to the dividing wall xylene fractionation tower 210. The remaining steps follow the embodiment shown in FIGS. The PX recovery compartment of FIG. 5 is shown as a PX recovery unit 230 and may also be in accordance with the single PX recovery embodiment shown in FIG. 3 or the two compartment PX recovery unit shown in FIG. Good.

  Although the invention has been described and illustrated by reference to specific embodiments, those skilled in the art will appreciate that the invention is useful for variations and modifications without necessarily departing from the spirit and scope of the invention. It will be understood that it is not only the ones exemplified in the book.

  The trade names used herein are indicated by the symbol TM or the symbol (R), indicating that the name may be protected by a particular trademark right, for example, these trade names May be registered trademarks in various jurisdictions. All patents and patent applications, test procedures (e.g. ASTM method, UL method etc) and other documents cited herein are fully incorporated herein by reference, but such disclosure content is incorporated herein by reference. It is limited to cover all jurisdictions that are consistent with the present invention and that such incorporation is permitted. Where numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated.

Claims (10)

A process for producing para-xylene, wherein the process comprises: (a) providing a first hydrocarbon feedstock comprising xylene and ethylbenzene to a first para-xylene adsorption zone;
(B) feeding a second hydrocarbon feedstock comprising xylene and less ethylbenzene than the first hydrocarbon feedstock to the second paraxylene adsorption zone;
(C) recovering a first paraxylene rich stream and a first paraxylene poor stream from said first hydrocarbon feedstock in said first paraxylene adsorption section;
(D) recovering a second paraxylene rich stream and a second paraxylene poor stream from said second hydrocarbon feedstock in said second paraxylene adsorption section;
(E) separating the first and second paraxylene poor streams into ethylbenzene rich and ethylbenzene poor streams in a dividing wall raffinate distillation column, wherein the first and second paraxylenes are poor The flow being provided on opposite sides of the dividing walls of the dividing wall raffinate distillation column;
(F) at least partially isomerizing at least a portion of the ethylbenzene rich stream in the gas phase to produce a first isomerization having a higher paraxylene concentration than the stream poor in the first and second paraxylenes Producing a flow which has been
(G) at least partially isomerizing at least a portion of the ethylbenzene poor stream in the liquid phase to a second isomerization having a higher paraxylene concentration than the first and second paraxylene poor streams Producing a flow which has been
(H) recycling at least a portion of the first isomerized stream to the first para-xylene adsorption zone; and (i) at least a portion of the second isomerized stream A process comprising recycling to the paraxylene adsorption zone of 2.   The process according to claim 1, wherein the first and second paraxylene adsorption sections each comprise either two simulated moving bed adsorbers or one simulated moving bed adsorber. The first includes a 1 0.0 wt% of ethylbenzene is also a hydrocarbon feedstock with less the second hydrocarbon feedstock comprises ethylbenzene of less than 1 0.0% by weight, claim Process described in 1 or 2.   The process according to any one of claims 1 to 3, wherein step (f) is carried out under ethylbenzene dealkylation conditions or ethylbenzene isomerization conditions. Wherein the first hydrocarbon feedstock, reformate flow, hydrocracking product stream, xylene or the reaction product stream, aromatic disproportionation stream, aromatic transalkylation flow Leo spare / or imported products flow EB Selected from the group consisting of and said second hydrocarbon feedstock is a para-xylene selective aromatic alkylation product stream, a non-selective aromatic alkylation product stream, an aromatic disproportionation stream, an aromatic transalkyl Flow, methanol / dimethylether to aromatic product stream, syngas to aromatic product stream, C ₂ -C ₄ alkane / alkene to aromatic product stream, import product stream and / or from PX recovery unit 5. The process according to any one of the preceding claims, wherein the process is selected from the group consisting of: off-spec PX flow. The process of claim 1, wherein the second hydrocarbon feedstock comprises a selective benzene and / or toluene methylation product stream, wherein the selective benzene and / or toluene methylation product stream is , In a fluidized bed, fixed bed, moving bed or circulating bed reactor, the process being carried out prior to step (h) at least one of said first isomerized streams in a de-toluene fractionation column The method further comprises the step of separating the C ₇ -isomerized stream, wherein step (a) comprises a first xylene fraction prior to providing the first hydrocarbon feedstock to the first para-xylene adsorption zone. Separating the C ₉₊ stream from the first hydrocarbon feedstock in a distillation column, and step (b) provides the second hydrocarbon feedstock to the second paraxylene adsorption zone before Further comprising the step of separating the C ₉₊ flow from said second hydrocarbon feedstock in the second xylene fractionation column, the process according to claim 1.   7. The process of claim 6, further comprising the step of providing the first isomerized stream to the first xylene fractionation column prior to step (h).   Prior to step (i), further comprising providing the second isomerized stream to the second xylene fractionation column, wherein the second isomerized stream is the second xylene 7. The process of claim 6, provided to a fractionation column at a higher elevation than the second hydrocarbon feedstock. An apparatus for producing para-xylene, wherein the apparatus comprises a first hydrocarbon feedstock and a first para-xylene adsorption zone producing a first para-xylene rich stream and a first para-xylene poor stream. And a second paraxylene adsorption section for producing a second paraxylene rich stream and a second paraxylene poor stream from a second hydrocarbon feedstock, said first and second paraxylenes An adsorption section is fluidly connected to a dividing wall raffinate distillation column, and the dividing wall raffinate distillation column is provided with streams poor on the first and second paraxylene on opposite sides of the dividing wall to be an ethylbenzene rich stream and ethylbenzene First and second paraxylene adsorption compartments separated into poor streams;
A gas phase isomerization apparatus fluidly connected to the dividing wall raffinate distillation column, wherein the gas phase isomerization apparatus isomerizes the ethylbenzene rich stream to produce a stream poorer than the first and second paraxylenes A liquid phase isomerization apparatus fluidly coupled to said dividing wall raffinate distillation column for producing a first isomerized stream having also high para-xylene concentration; Liquid phase isomerization apparatus, wherein an isomerizer isomerizes the stream poor in ethylbenzene to produce a second isomerized stream having a higher paraxylene concentration than the stream poorer in the first and second para-xylenes Containing devices. The apparatus according to claim 9, wherein the first and second paraxylene adsorption sections are either (1) two simulated moving bed adsorption towers or (2) one simulated moving bed adsorption towers, respectively. And the device comprises
A first xylene fractionation column fluidly connected to the gas phase isomerization unit and the first paraxylene adsorption section, the first xylene fractionation column being downstream of the gas phase isomerization unit And a first xylene fractionation column upstream of said first para-xylene adsorption zone;
A second xylene fractionation column fluidly connected to the liquid phase isomerization unit and the second paraxylene adsorption zone, the second xylene fractionation column being downstream of the liquid phase isomerization unit And a second xylene fractionation tower upstream of said second para-xylene adsorption zone; and a de-toluene fractionation tower fluidly connected to said gas phase isomerization unit and said first xylene fractionation tower 10. The method of claim 9, further comprising: removing toluene fractionation tower downstream of the gas phase isomerization unit and upstream of the first xylene fractionation tower. Device described.

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