Xylene separation processes using a membrane separator

Patent metadata

Field	Value
Publication number	US-11673848-B2
Application number	US-202117795901-A
Country	US
Kind code	B2
Filing date	Jan 11, 2021
Priority date	Feb 27, 2020
Publication date	Jun 13, 2023
Grant date	Jun 13, 2023

Abstract

A process and system for separating paraxylene from a mixture of paraxylene, metaxylene, orthoxylene, and ethylbenzene in a simulated moving bed apparatus using a membrane to separate non-aromatics from a desorbent stream. The lower nonaromatics content in the desorbent improves paraxylene product purity, increases paraxylene production at the same desorbent rate, reduces the desorbent rate, and/or reduces energy consumption in the product tower.

First claim

What is claimed is:

1. A process for separating paraxylene (PX) from a mixture of PX, metaxylene (MX), orthoxylene (OX), and ethylbenzene (EB), comprising the steps of:
(i) processing a feed stream, comprising the mixture, and a desorbent supply stream, comprising desorbent, in a simulated moving bed adsorption apparatus to produce an extract stream comprising desorbent enriched in PX and a raffinate stream comprising desorbent lean in PX;
(ii) fractionating the extract stream to produce a first desorbent-rich stream and a PX-rich stream;
(iii) fractionating the raffinate stream to produce a second desorbent-rich stream and a mixed-C8-aromatic-rich stream;
(iv) introducing a supply stream comprising at least a portion of one or both of the first desorbent-rich stream, the second desorbent-rich stream, or a combination thereof to a membrane separator to produce a permeate stream and a retentate stream, wherein the retentate stream is rich in non-aromatics relative to the permeate stream;
(v) supplying the permeate stream and any remaining portion(s) of the first desorbent-rich stream, the second desorbent-rich stream, or the combination thereof, to the desorbent supply stream to the simulated moving bed adsorption apparatus; and
(vi) purging the retentate stream from the process.

2. The process of claim 1 , wherein the desorbent comprises toluene, preferably wherein the desorbent stream comprises at least 90 percent by weight toluene, based on the total weight of the desorbent stream.

3. The process of claim 1 , wherein the first and second desorbent-rich streams comprise different levels of non-aromatics, and wherein the membrane separator supply stream comprises the one of the first and second desorbent-rich streams having the greater level of non-aromatics.

4. The process of claim 1 , wherein the membrane separator supply stream constitutes from 0.5 to 50 weight percent of the total weight of the first and second desorbent-rich streams.

5. The process of claim 4 , wherein the membrane separator supply stream constitutes from 1 to 20 weight percent of the total weight of the first and second desorbent-rich streams.

6. The process of claim 4 , wherein the membrane separator supply stream constitutes from 2 to 10 weight percent of the total weight of the first and second desorbent-rich streams.

7. The process of claim 1 , wherein the weight ratio of the permeate stream to the retentate stream is from 1 to 20.

8. The process of claim 7 , wherein the weight ratio of the permeate stream to the retentate stream from 1 to 10.

9. The process of claim 1 , wherein the retentate stream comprises from 0.1 to 10 wt % non-aromatics, based on the total weight of the retentate stream.

10. The process of claim 9 , wherein the retentate stream comprises from 0.2 to 5 wt % non-aromatics, based on the total weight of the retentate stream.

11. The process of claim 1 , wherein the weight ratio of the feed stream to the desorbent stream is from 0.05 to 5.

12. The process of claim 11 , wherein the weight ratio of the feed stream to the desorbent stream is from 0.1 to 2.

13. The process of claim 11 , wherein the weight ratio of the feed stream to the desorbent stream is from 0.4 to 2.

14. The process of claim 11 , the weight ratio of the feed stream to the desorbent stream is from 0.67 to 1.5.

15. The process of claim 1 , wherein the membrane separator comprises a polyimide membrane treated with a conditioning agent comprising a lubricating oil.

16. The process of claim 1 , wherein the membrane separator comprises a liquid membrane, preferably a supported ionic liquid membrane.

17. The process of claim 1 , wherein the total mass flow of desorbent in the feed stream and any makeup desorbent stream matches the total mass flow of desorbent in the retentate stream and any purge stream.

18. The process of claim 1 , wherein steps (iv)-(vi) improve PX product quality by reducing non-aromatics in the PX-rich product stream.

19. The process of claim 18 , wherein operation of the simulated moving bed adsorption apparatus is modulated to increase MX, OX, and/or EB in the extract stream up to an amount offsetting the reduction of non-aromatics in the PX-rich product stream, preferably wherein the modulation increases the quantity of the PX-rich product stream relative to the desorbent stream, and more preferably wherein the modulation further comprises reducing a quantity of the desorbent stream.

20. The process of claim 18 , further comprising modulating operation of the extract fractionation tower for energy conservation by increasing a toluene content in the PX-rich product stream up to an amount offsetting the reduction of non-aromatics in the PX-rich product stream.

21. A system for separating paraxylene (PX) from a mixture of PX, metaxylene (MX), orthoxylene (OX), and ethylbenzene (EB), comprising:
(i) a simulated moving bed adsorption apparatus to process a feed stream, comprising the mixture, and a desorbent supply stream, comprising desorbent, to produce an extract stream comprising desorbent enriched in PX and a raffinate stream comprising desorbent lean in PX;
(ii) an extract fractionation tower to fractionate the extract stream to produce a first desorbent-rich stream and a PX-rich product stream;
(iii) a raffinate fractionation tower to fractionate the raffinate stream to produce a second desorbent-rich stream and a mixed-C8-aromatic-rich product stream;
(iv) a membrane separator to produce a permeate stream and a retentate stream, wherein the retentate stream is rich in non-aromatics relative to the permeate stream;
(v) a supply line to supply the desorbent supply stream to the membrane separator, wherein the desorbent supply stream comprises at least a portion of one or both of the first desorbent-rich stream, the second desorbent-rich stream, or the combination thereof;
(vi) a return line to return the permeate stream and any remaining portion(s) of the first desorbent-rich stream, the second desorbent-rich stream, or the combination thereof, to the desorbent stream to the simulated moving bed adsorption apparatus; and
(vii) a purge line to purge the retentate stream from the system.

22. The system of claim 21 , wherein the desorbent comprises toluene, preferably wherein the desorbent stream comprises at least 90 percent by weight toluene.

23. The system of claim 21 , wherein the first and second desorbent-rich streams comprise different levels of non-aromatics, and wherein the membrane separator supply stream comprises the one of the first and second desorbent-rich streams having the greater level of non-aromatics.

24. The system of claim 21 , wherein the membrane separator comprises a polyimide membrane treated with a conditioning agent comprising a lubricating oil.

25. The system of claim 21 , wherein the membrane separator comprises a liquid membrane, preferably a supported liquid membrane.

Assignees

• Exxonmobil Chemical Patents Inc

Inventors

• Adebayo-Ige Oluwagbogo
• Tinger Robert G
• Detjen Todd E
• Minhas Bhupender S

Classifications

• Y02P20/50

  Improvements relating to the production of bulk chemicals · CPC title

• C07C7/144

  using membranes, e.g. selective permeation · CPC title

• C07C7/12 Primary

  by adsorption, i.e. purification or separation of hydrocarbons with the aid of solids, e.g. with ion-exchangers · CPC title

• B01D69/142

  with "carriers" · CPC title

• C07C15/08

  Xylenes · CPC title