KR20130056357A - Process for the production of paraxylene - Google Patents

Abstract

The present invention provides a process for purifying an aromatic feed stream to produce paraxylene, comprising separating the C8 + aromatic feed stream into a stream comprising C8 aromatic species and a stream comprising C9 + aromatic species. It is about. After separating PX from the C8 aromatic stream, the PX-deficient stream is separated and processed simultaneously in the liquid isomerization unit and the vapor phase isomerization unit.

Description

Production method of para xylene {PROCESS FOR THE PRODUCTION OF PARAXYLENE}

The present invention relates to a process for the preparation of paraxylene comprising xylene isomerization, and an apparatus for carrying out the method.

Priority claim

This application claims the advantages and priorities of US Provisional Application No. 61 / 408,097, filed October 29, 2010, and European Application No. 10192327.4, filed November 24, 2010.

Xylene isomers are important intermediates that are widely found and widely applied in chemical synthesis. As an example, paraxylene (PX) is a feedstock for terephthalic acid used in the manufacture of synthetic fibers, metaxylene (MX) is used for the manufacture of dyes, orthoxylene (OX) is used for the preparation of plasticizers. Used as feedstock for phthalic anhydride.

Xylene is found in pyrolysis liquids mixed with various fractions, such as coal tar distillates, petroleum reform oils, and other compounds of similar boiling point. The aromatic component is easily separated from the nonaromatic component by a method such as solvent extraction. Subsequently, the fraction consisting essentially of C8 aromatics can be easily obtained, for example by distillation. "C8 aromatic" means aromatic hydrocarbons having 8 carbon atoms, in particular ethylbenzene and xylene isomers [paraxylene (p-xylene or PX), orthoxylene (o-xylene or OX) and meta Xylene (m-xylene or MX)].

Due to its similar chemical structure and physical properties and the same molecular weight, it is difficult to separate, but various methods have been used to separate the isomers, for example OX can be separated from other C8 aromatics by fractional distillation and PX is fractionated crystal or Can be separated by selective sorption. Current demand is primarily for PX, and it is desirable to convert MX, the main xylene present in the feed stream, and also convert OX to PX to meet market demand. At room temperature where xylene is processed in a typical petrochemical plant, the thermodynamic equilibrium content is about 24 mol% PX, 56 mol% MX and 20 mol% OX based on the total amount of xylene in the feed.

The production of paraxylene and orthoxylene in conventional aromatic complexes is energy intensive. This is due in part to a sufficient amount of recycle that has been reprocessed through orthoxylene and C9 + aromatics removal. A typical commercial process is shown in FIG. 1, which comprises a stream comprising C8 + aromatics (C8 aromatic hydrocarbons and aromatic hydrocarbons of higher carbon number) comprising PX in an amount exceeding that found in an equilibrium mixture of xylenes. To treat the stream at least partially for recovery.

The feed stream or the stream used in the system shown in FIG. 1 can be a variety of sources, such as C8 + reformate ( 1 ), C8 + selective toluene disproportionation product ( 17 ), C8 + transalkylation product ( 2 ), C8 + toluene disproportionation reaction Product 15 and any other stream containing C8 aromatics, such as one or more sources selected from products from toluene methylation using methanol. Each of these sources is inherently well known in the art. These streams typically comprise four C8 isomers and heavier aromatics (C9 + aromatics), which follow the recycle stream ( 10 ) in at least one of the C8 / C9 + aromatic fractions ( 16 ) to remove the C9 + aromatics into the stream ( 3 ). Processed). If not removed from the feed stream by this fractionation, C9 + and heavier aromatics may have an adverse effect on downstream paraxylene recovery ( 12 ) and vapor phase xylene isomerization ( 13 ).

Thus, the C8 / C9 + aromatic fraction in ( 16 ) typically produces a C8 aromatic stream 6 containing 10 to 95% by weight paraxylene, and a bottom product 3 comprising C9 + aromatics. The C8 aromatic stream 6 is processed to selectively recover paraxylene by one or both of the selective adsorption or crystallization shown as PX recovery apparatus 12 in FIG. 1. Paraxylene product, which may comprise at least 99.7% by weight of paraxylene, is recovered in stream ( 7 ) and the balance of the C8 aromatic stream is passed through vapor phase xylene isomerization ( 13 ) through conduit (8). Optionally, in the presence of hydrogen provided by stream 9 , vapor phase xylene isomerization 13 establishes a near-equilibrium balance of xylene isomers in stream 19 using one or more various catalysts, and The catalyst may also convert ethylbenzene to benzene and ethane or convert ethylbenzene to near-equivalent xylene isomers. Thus, vapor phase processes and catalysts are inherently well known in the art.

Subsequent to the system shown in FIG. 1, xylene isomerization product 19 is passed through a detoluthiation fractionation 18 that removes C7 and lighter material C7- in stream 11 and isomer recycle stream ( 10 ). Isomere recycle stream 10 is recycled to C8 / C9 + aromatic fractions 16 .

Improving this energy-intensive process is an active area of research, but this is not a simple matter of optimizing each individual step, as one step of optimization can negatively affect more than one step in the overall system. Examples of proposed improvement methods include the following.

US Pat. No. 3,856,874 describes a process for splitting the effluent stream from PX separation, passing the independent stream on different catalysts, and then combining and recycling the isomerized streams.

US Pat. No. 7,439,412 teaches a method of recovering one or more high purity xylene isomers from a C8 + aromatic feed stream comprising the use of an isomerization apparatus under liquid phase conditions. In an example, the product of the liquid phase isomerization apparatus is returned to the first fractionation tower of the system. See also US Pat. No. 7,626,065.

U.S. Pat.No. 7,553,998 has a substantial content of C9 + aromatic hydrocarbons comprising deethylating and then fractionating the heavy aromatics and then passing the stream through C8 aromatic isomer recovery to recover high purity xylene isomers at low energy costs. A method of recovering one or more high purity xylene isomers from the feed is taught. The stream passing through the isomerization device under liquid isomerization conditions is divided into a portion that is sent to the isomer recovery device and a portion that is purged.

US patent application Ser. No. 12 / 612,007 (published as 2010/0152508) includes (a) providing a PX-deficient stream; (b) isomerizing at least a portion of the PX-deficient stream to produce an isomerized stream having a greater PX concentration, less than 1,000 ppm benzene concentration, and less than 5,000 ppm C9 + hydrocarbon concentration than the PX-deficient stream; And (c) separating the isomerized stream by selective adsorption.

US Provisional Application No. 61 / 326,445 dated April 21, 2010, relates to a xylene isomerization process comprising liquid phase isomerization for the production of equilibrium or near-equilibrium xylenes, wherein the process conditions are at temperatures below 295 ° C. And pressure sufficient to maintain xylene in the liquid phase of the embodiment, which uses hydrogen at levels of only ppm or less and can be regenerated several times by a very simple in situ procedure.

Other interesting references include US Patent Application Publication No. 2008/0262282; US2009 / 0149686; US2009 / 0182182; US Patent No. 6,448,459; No. 6,872,866; And 7,368,620.

Surprisingly, the inventors have discovered a method of significantly reducing the energy required to produce high purity xylene isomers by providing parallel arrangements of vapor and liquid isomerization systems.

The present invention comprises a first step of separating a feed comprising C8 + aromatics into an overhead, or a first stream comprising xylene isomers and bottom products, or a second stream comprising C9 + aromatics; After separating the xylene stream in a PX recovery unit to recover the PX-rich stream and the PX-deficient stream, the PX-deficient (C8 aromatic) stream is passed through a parallel arrangement of vapor phase xylene isomerization and liquid phase xylene isomerization. It relates to a method for producing para xylene, comprising the step of separating the.

In an embodiment, the benzene separation step occurs between the C8 / C9 + fractionation and PX recovery apparatus, and / or the benzene separation step downstream of the isomerization step. In an embodiment, the benzene separation step may also be a toluene separation step, for example downstream of the isomerization step.

In an embodiment, the liquid isomerization product is recycled to one or more of the C8 / C9 + fractionation, benzene separation step (if present) and PX recovery step.

The invention also provides a first fractionation column operating under conditions suitable for separating a C8 + aromatic stream into an overhead comprising xylene and a bottom product comprising C9 + aromatics; A device for the production of paraxylene comprising an overhead stream fluidly connected with a PX recovery device, wherein the PX recovery device provides a PX-rich stream and a PX-deficient stream and is part of the PX-deficient stream. An improvement is that the conduit carrying the PX-deficient stream passes through the vapor phase isomerization apparatus and another portion of the PX-deficient stream passes through the liquid phase isomerization apparatus.

In an embodiment, the liquid phase isomerization apparatus is fluidly connected to provide recycling of the liquid phase isomers to the first fractionation column and / or to the PX recovery apparatus.

In an embodiment, the PX recovery device is selected from one or more of a crystallizer and an adsorptive separator.

In an embodiment, one or more other fractionators are provided upstream of the first fractionator, wherein the one or more other fractionators are suitable for removing benzene from a stream comprising xylenes or removing toluene from a stream comprising xylenes. Operating under conditions, optionally a fractionator for removing benzene and a fractionator for removing toluene are provided upstream of the first fractionator.

It is an object of the present invention to significantly reduce the energy required to produce paraxylene and orthoxylene by minimizing the recycle of isomers from vapor phase xylene isomerization.

These and other objects, features and advantages of the present invention will become apparent from the following detailed description, preferred embodiments, examples and references described in the claims.

In the accompanying drawings, like reference numerals are used to indicate like parts throughout the several views.
1 diagrammatically shows a prior art flow arrangement for xylene isomerization.
2 diagrammatically illustrates an embodiment of the invention.
3 and 4 show a comparison of the two systems of each embodiment of the present invention, FIG. 3 returns the liquid isomerization product to the tower and FIG. 4 returns the liquid isomerization product to the PX recovery apparatus.

According to the invention, the hydrocarbon stream comprising C8 + aromatics is separated into a stream comprising C8 aromatics and a stream comprising C9 + aromatics. The C8 stream, optionally passing through the benzene separation unit, then passes through the PX recovery unit to provide two streams: one stream with increased PX concentration and the other with reduced PX concentration. The PX-deficient stream is then split and then isomerized in at least one liquid isomerization device and at least one vapor isomerization device at the same time.

The invention will be better understood with reference to the specific embodiment shown in FIG. 2. It will be well understood by those skilled in the art based on the present disclosure that many variations can be made and that the embodiments do not limit the invention described in the claimed claims.

The feed streams of the system shown in FIG. 2 are for example C8 + reformate ( 1 ), C8 + selective toluene disproportionation product ( 17 ), C8 + transalkylation product ( 2 ), C8 + toluene disproportionation product ( 15 ) and C8 aromatic May be produced from one or more sources including C8 + aromatic hydrocarbons including products from toluene methylation with methanol, such as methanol.

In the flow arrangement shown in FIG. 2, the energy consumption is determined by minimizing the amount of isomer recycle ( 10 ) from vapor phase xylene isomerization ( 13 ) and the amount of C9 + aromatics treated in the C8 / C9 + aromatic fractionation ( 16 ). Reduced by the controlling step. The novel process batch includes parallel processing of the PX-deficient C8 aromatic stream 8 via vapor phase xylene isomerization and liquid phase xylene isomerization 20 . PX- deficient aromatic C8 stream of stream (8) is vapor phase xylene isomerization is minimized through (13) the vapor phase xylene isomerization and the amount of the opposite sex PX- deficiency C8 aromatic stream 30 evaporates from 13 Energy is minimized by reducing the associated amount of nitride recycle stream 10 , which contains by-products of much higher concentrations of C9 + aromatics than liquid phase xylene isomerization products. The LP isomer recycle stream ( 21 ), a product from the liquid phase xylene isomerization ( 20 ), is sent to the C8 / C9 + aromatic fraction ( 16 ) at the higher feed position to minimize energy consumption due to its low concentration of C9 + aromatics. . The energy savings of the C8 / C9 + aromatic fraction ( 16 ) can result in a 75% reduction in the overall energy consumption of the paraxylene production process.

2 shows a benzene removal device 23 (subsidiary benzene stream 22 ) through a conduit 50 at one or more locations where the liquid isomer nitride recycle stream 21 optionally comprises a C8 aromatic / C9 + aromatic fraction ( 16 ). ), And through the conduit ( 60 ) directly to the recovery of paraxylene ( 12 ). The amount sent to each location is determined by the amount of by-products containing benzene and the amount needed to remove the C9 + aromatics. By-products from the liquid phase xylene isomerization ( 20 ) in the liquid phase isomer recycle stream ( 21 ) may be removed to a level acceptable for paraxylene recovery ( 12 ), especially when selective adsorption is used to recover the paraxylene. . The C9 + aromatics can be removed in the C8 / C9 + aromatic fractionation ( 16 ) or in one or more devices using separation techniques such as membranes, extraction and adsorption. Similarly, benzene can be removed using one or more devices using separation techniques such as distillation, extraction, membranes and adsorption. Optionally, the C9 + aromatics and benzene can be removed using simultaneously one or more devices utilizing separation techniques such as distillation, extraction, membranes and adsorption.

Vapor phase xylene isomerization ( 13 ), optionally in the presence of hydrogen in stream ( 9 ), essentially balances the near-equilibrium balance of xylene isomers in stream ( 19 ) using one or more of various catalysts well known in the art. This can also be achieved by converting ethylbenzene to benzene and ethane or converting ethylbenzene to near-equivalent xylene isomers. Xylene and the isomerization product stream 19 is passed through the de-toluene fractionation screen 18 to remove the hard material than this and C7 of stream 11 produces a binary nitride recycle stream (10). Isomer recycle recycle stream 10 is processed in OX and C9 + aromatics removal device 16 .

Regarding the separation of xylene during PX recovery, two preferred methods are fractional crystallization and selective adsorption, the details of which are essentially known to those skilled in the art. In this regard, reference is made, for example, to US Pat. No. 7,439,412 and also the references mentioned in the Background section above. Details of crystallization and selective adsorption are not inherently subject matter herein.

Likewise, details of vapor phase xylene isomerization and liquid phase xylene isomerization are also essentially known in the art. In this regard, for example, US Pat. No. 6,180,550; No. 6,448,459; No. 6,872,866; No. 7,244,409; 7,371,913; 6,076,366; No. 7,495,137; No. 7,592,499; US Patent Application Publication No. 2009-0182182; See US patent application Ser. No. 12 / 612,007, and US provisional application Ser. No. 61 / 326,445, issued April 21, 2010.

Computer simulations using commercial software Pro II programs are performed to demonstrate the benefits of the present invention. For example, an appropriate assumption was made with reference to US Pat. No. 7,439,412 by the skilled artisan. A plant with a PX capacity of 540 kta is provided as a base case (FIG. 1). The simulation studied two process arrangements, process A shown in FIG. 3 and process B shown in FIG. 4. In both processes A and B, the PX-deficient stream of C8 aromatics from the PX recovery unit 12 is split into two equal fractions and sent one of them to the liquid phase xylene isomerization unit 20 while the other Is sent to the vapor phase xylene isomerization device ( 13 ). As shown in the figure, process A (FIG. 3) directs the product from the liquid isomerization device 20 to the tower 16 , while process B (FIG. 4) from the liquid phase xylene isomerization device 20 . The product is sent to a PX recovery device 12 (Parex® adsorptive separation device essentially known to those skilled in the art). 1 and 2, both 3 and 4 pass through a detoluene fractionator 18 to remove toluene and send the equilibrium or near-equilibrium xylene isomer back to the tower 16 . The simulation shows significant energy savings of 3.10 MW (mega watts) for Process B (FIG. 4) and 12.45 MW for Process A (FIG. 3) compared to the base case of FIG. 1 using the process according to the invention. .

The invention has been described above with reference to a number of embodiments and specific examples. Many variations will suggest themselves to those skilled in the art in light of the above details.

The present invention has been described above to refer to various embodiments and specific examples. Many modifications will be suggested to those skilled in the art in view of the above details.

In another embodiment, the invention relates to:

1. (a) separating a feed comprising C8 + aromatics in a first fractionation step into a first stream comprising xylene isomers and a second stream comprising C9 + aromatics;

(b) recovering the PX-rich stream PX-deficient stream by separating the first stream in a paraxylene (PX) recovery apparatus;

(c) a first portion of the PX-deficient stream through a vapor phase xylene isomerization apparatus to produce a first isomerization stream, and a PX- through liquid phase xylene isomerization apparatus to produce a second isomerization stream. Passing through the second portion of the deficient stream; And

(d) optionally further comprising a benzene separation step wherein the benzene is separated from the stream comprising xylene

Including, the manufacturing method of PX.

2. in the above paragraph 1,

And at least one benzene separation step selected from a benzene separation step between the liquid phase xylene isomerization unit and the first fractionation step and a benzene separation step between the liquid phase isomerization unit and the PX recovery unit.

3. The above paragraph 1 or 2,

Wherein the second isomer nitride stream is recycled to one or more of one fractionation step, one or more benzene separation steps (if present), and a PX recovery unit.

4. The paragraph according to any one of paragraphs 1 to 3 above,

Wherein the product of at least a portion of the liquid phase isomerization apparatus is recycled to the first fractionation step.

5. The method according to any one of paragraphs 2 to 4 above,

At least part of the product of the liquid phase isomerization apparatus is recycled to the benzene separation stage.

6. The paragraph according to any one of paragraphs 1 to 5 above,

A process wherein the product of the liquid phase isomerization apparatus is recycled to the PX recovery step.

7. The paragraph according to any one of paragraphs 1 to 6 above,

The production method wherein the PX recovery step includes a crystallization device.

8. The paragraph of any of paragraphs 1-7 above,

Wherein the PX recovery step comprises selective adsorption.

9. The paragraph according to any one of paragraphs 1 to 8 above,

And, if present in the stream, further comprising the step of fractionating the isomer recycle stream to remove toluene.

10. The apparatus according to any one of paragraphs 1 to 9 above,

Wherein the feed comprising C8 + aromatics comprises at least one feed selected from the group consisting of C8 + selective toluene disproportionation products, C8 + transalkylation products, C8 + reformate products and C8 + toluene disproportionation products.

11. Apparatus for the production of paraxylene (PX),

A first fractionation column operating under conditions suitable for separating the C8 + aromatic stream into an overhead stream comprising xylene and a bottom product stream comprising C9 + aromatics;

The overhead stream is fluidly connected with a PX recovery device providing a PX-rich stream and a PX-deficient stream;

Wherein the conduit carrying the PX-deficient stream is divided such that a portion of the PX-deficient stream is passed to the vapor phase isomerization apparatus and another portion of the PX-deficient stream is passed to the liquid phase isomerization apparatus.

12. The paragraph 11 above,

Wherein the liquid isomerization device is fluidly connected to provide liquid isomer nitride recycle to the first fractionation column and / or the PX recovery device.

13. The paragraph 11 above,

Wherein the PX recovery device is selected from at least one of a crystallizer and an adsorptive separator.

14. The paragraph 11 above,

An apparatus further comprising one or more other fractionators upstream of the first fractionator, wherein the one or more other fractionators remove benzene from a stream comprising xylenes or to remove toluene from a stream comprising xylenes. Or operating under conditions suitable for removing both, wherein the at least one other fractionator is upstream of the first fractionator.

Trademark names used herein are referred to as "trademarks" or "registered trademarks," which indicate that a trademark name may be protected by a particular trademark, for example, a trademark name registered in various jurisdictions. All patents and patent applications, test procedures (e.g., Certificate of Priority, ASTM method, UL method, etc.), and other documents cited herein, to the extent that such disclosure is not contrary to the present invention and its incorporation is permitted for all jurisdictions. All are incorporated by reference. Where lower and upper numerical limits are listed herein, ranges from any lower limit to any upper limit are contemplated.

Claims (14)

(a) separating a feed comprising C8 + aromatics in a first fractionation step into a first stream comprising xylene isomers and a second stream comprising C9 + aromatics;
(b) separating the first stream in a paraxylene (PX) recovery unit to recover the PX-rich stream and the PX-deficient stream;
(c) a first portion of the PX-deficient stream through the vapor phase xylene isomerization apparatus to produce a first isomerate stream, and a liquid phase xylene isomerization apparatus to generate a second isomerization stream. Passing through the second portion of the PX-deficient stream; And
(d) optionally further comprising a benzene separation step wherein the benzene is separated from the stream comprising xylene
Method for producing a PX comprising a. The method of claim 1,
And at least one benzene separation step selected from a benzene separation step between the liquid phase xylene isomerization unit and the first fractionation step and a benzene separation step between the liquid phase isomerization unit and the PX recovery unit. 3. The method according to claim 1 or 2,
Wherein the second isomer nitride stream is recycled to one or more of the first fractionation stage, one or more benzene separation stages (if present), and the PX recovery stage. The method according to any one of claims 1 to 3,
Wherein the product of at least a portion of the liquid phase isomerization apparatus is recycled to the first fractionation step. 5. The method according to any one of claims 2 to 4,
Wherein the product of at least a portion of the liquid phase isomerization apparatus is recycled to one or more benzene separation stages. 6. The method according to any one of claims 1 to 5,
A process wherein the product of the liquid phase isomerization apparatus is recycled to the PX recovery step. 7. The method according to any one of claims 1 to 6,
The production method wherein the PX recovery step includes a crystallization device. The method according to any one of claims 1 to 7,
Wherein the PX recovery step comprises selective adsorption. The method according to any one of claims 1 to 8,
If present in the stream, further comprising the step of fractionating the isomer recycle stream to remove toluene. 10. The method according to any one of claims 1 to 9,
Wherein the feed comprising C8 + aromatics comprises at least one feed selected from the group consisting of C8 + selective toluene disproportionation products, C8 + transalkylation products, C8 + reformate products and C8 + toluene disproportionation products. Apparatus for the production of paraxylene (PX),
A first fractionation column operating under conditions suitable for separating the C8 + aromatic stream into an overhead stream comprising xylene and a bottom product stream comprising C9 + aromatics;
The overhead stream is fluidly connected with a PX recovery device providing a PX-rich stream and a PX-deficient stream;
Wherein the conduit carrying the PX-deficient stream is divided such that a portion of the PX-deficient stream is passed to the vapor phase isomerization apparatus and another portion of the PX-deficient stream is passed to the liquid phase isomerization apparatus. The method of claim 11,
Wherein the liquid isomerization device is fluidly connected to provide recycling of the liquid isomer to the first fractionation column and / or to the PX recovery device. The method of claim 11,
Wherein the PX recovery device is selected from at least one of a crystallizer and an adsorptive separator. The method of claim 11,
An apparatus further comprising one or more other fractionators upstream of the first fractionator, wherein the one or more other fractionators remove benzene from a stream comprising xylenes or to remove toluene from a stream comprising xylenes. Or operating under conditions suitable for removing both, wherein the at least one other fractionator is upstream of the first fractionator.

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