Paraxylene separation process

Patent metadata

Field	Value
Publication number	US-9850186-B2
Application number	US-201615375754-A
Country	US
Kind code	B2
Filing date	Dec 12, 2016
Priority date	Feb 26, 2016
Publication date	Dec 26, 2017
Grant date	Dec 26, 2017

Abstract

A process for producing paraxylene is provided. The process includes separating a first mixture of C 8 aromatic hydrocarbons in a simulated moving bed apparatus using a desorbent to produce (i) an extract comprising ≧50.0 wt % of the paraxylene in the first mixture; (ii) a desorbent-rich raffinate comprising ≧75 wt % of the desorbent withdrawn, and (iii) an desorbent-lean raffinate comprising ≦25 wt % of the desorbent withdrawn in the desorbent-rich and desorbent-lean raffinates. The desorbent-lean raffinate can then, without an intervening separation step, be passed to a refinery process or a vapor phase isomerization reaction to produce an effluent comprising paraxylene in a greater concentration than the desorbent-lean raffinate. The desorbent-rich raffinate can be passed to a liquid phase isomerization reaction to produce an effluent comprising paraxylene in a greater concentration than the desorbent-rich raffinate.

First claim

What is claimed is:

1. A process for producing paraxylene, the process comprising:
(a) providing a first mixture comprising ≧5.0 wt % of aromatic C 8 isomers, said C 8 isomers comprising paraxylene, metaxylene, orthoxylene, and ethylbenzene;
(b) separating the first mixture in a simulated moving bed apparatus comprising use of a desorbent to produce a paraxylene-rich extract, a desorbent-rich raffinate, and a desorbent-lean raffinate,
wherein the paraxylene-rich extract comprises ≧50.0 wt % of the paraxylene in the first mixture,
wherein the desorbent-rich raffinate comprises metaxylene, orthoxylene, ethylbenzene, and ≧75 wt % of the desorbent withdrawn in the desorbent-rich raffinate and the desorbent-lean raffinate, and
wherein the desorbent-lean raffinate comprises metaxylene, orthoxylene, ethylbenzene, and ≦25 wt % of the desorbent withdrawn in the desorbent-rich raffinate and the desorbent-lean raffinate;

(c) passing, without an intervening separation step, at least a portion of the desorbent-lean raffinate to (i) a vapor phase isomerization reaction to produce a first reaction effluent having a higher paraxylene concentration than the desorbent-lean raffinate, (ii) a refinery process, or both;
(d) passing at least a portion of the desorbent-rich raffinate to a liquid phase isomerization reaction to produce a second reaction effluent having a higher paraxylene concentration than the desorbent-rich raffinate; and
(e) recycling at least a portion of the second reaction effluent from step (d) to the separating of step (b).

2. The process of claim 1 , wherein step (c) comprises passing the desorbent-lean raffinate to a vapor phase isomerization reaction.

3. The process of claim 2 further comprising;
(f) recycling at least a portion of the first reaction effluent from step (c) to the separating of step (b).

4. The process of claim 1 , wherein the vapor phase isomerization reaction in step (c) comprises contacting the desorbent-lean raffinate with a catalyst and process conditions effective to deethylate the ethylbenzene and isomerize the metaxylene and orthoxylene.

5. The process of claim 1 , wherein the vapor phase isomerization reaction in step (c) comprises contacting the desorbent-lean raffinate with a catalyst and process conditions effective to isomerize the ethylbenzene, metaxylene, and orthoxylene.

6. The process of claim 1 , further comprising before step (e):
(d′) separating from the second reaction effluent of step (d) (i) at least a portion of C 1 -C 7 compounds, (ii) at least a portion of orthoxylene and/or C 9+ aromatics, or both.

7. The process of claim 3 , further comprising before step (f):
(c′) separating from the first reaction effluent of step (c) (i) at least a portion of C 1 -C 7 compounds, (ii) at least a portion of orthoxylene and/or C 9+ aromatics, or both.

8. The process of claim 1 , wherein the desorbent-lean raffinate comprises ≦10.0 wt % of the desorbent withdrawn in the desorbent-rich raffinate and a desorbent-lean raffinate.

9. The process of claim 8 , wherein the desorbent-lean raffinate comprises ≧30.0 wt % of the ethylbenzene in the first mixture.

10. The process of claim 1 , wherein the desorbent-rich raffinate comprises ≦40 wt % of the ethylbenzene in the first mixture.

11. The process of claim 1 , wherein the paraxylene-rich extract comprises ≧90.0 wt % of the paraxylene in the first mixture.

12. The process of claim 1 , wherein the desorbent-rich raffinate and the desorbent-lean raffinate comprise ≧90.0 wt % of the ethylbenzene in the first mixture.

13. The process of claim 1 , wherein ≧50.0 wt % of the second reaction effluent from step (d) is recycled in step (f).

14. The process of claim 3 , wherein ≧50.0 wt % of the first reaction effluent from step (c) is recycled in step (e).

15. The process of claim 1 , wherein the first mixture comprises ≧50.0 wt % of a mixture of paraxylene, ethylbenzene, metaxylene, and orthoxylene.

16. The process of claim 1 , wherein the desorbent comprises at least one of para-diethylbenzene, toluene and tetralin.

17. A process for producing paraxylene, the process comprising:
(a) providing a first mixture comprising ≧5.0 wt % of aromatic C 8 isomers, said C 8 isomers comprising paraxylene, metaxylene, orthoxylene, and ethylbenzene, to a first separation stage to produce a C 8 aromatics stream and a C 9+ hydrocarbon stream;
(b) separating the C 8 aromatics stream in a second separation stage comprising a simulated moving bed apparatus comprising use of a desorbent to produce a paraxylene-rich extract, a desorbent-rich raffinate, and a desorbent-lean raffinate,
wherein the paraxylene-rich extract comprises ≧50.0 wt % of the paraxylene in the first mixture,
wherein the desorbent-rich raffinate comprises metaxylene, orthoxylene, ethylbenzene, and ≧75 wt % of the desorbent withdrawn in the desorbent-rich raffinate and the desorbent-lean raffinate, and
wherein the desorbent-lean raffinate comprises metaxylene, orthoxylene, ethylbenzene, and ≦25 wt % of the desorbent withdrawn in the desorbent-rich raffinate and the desorbent-lean raffinate;

(c) passing, without an intervening separation step, at least a portion of the desorbent-lean raffinate to a vapor phase isomerization reaction to produce a first reaction effluent having a higher paraxylene concentration than the desorbent-lean raffinate;
(d) passing at least a portion of the desorbent-rich raffinate to liquid phase isomerization reaction to produce a second reaction effluent having a higher paraxylene concentration than the desorbent-rich raffinate; and
(e) recycling at least a portion of the first reaction effluent from step (c) and the second reaction effluent from step (d) to the first separation stage of step (a) or the second separation stage of step (b).

18. The process of claim 17 further comprising:
(f) passing the paraxylene-rich extract to a third separation stage to remove the desorbent and produce a paraxylene extract;
(g) recycling the desorbent back to the second separation stage; and
(h) passing the paraxylene extract to a fourth separation stage to produce a paraxylene product.

19. The process of claim 17 , further comprising prior to step (d):
(d′) passing at least a portion of the desorbent-rich raffinate from to a fifth separation stage to remove the desorbent and produce a raffinate, wherein the raffinate is passed to the liquid phase isomerization reaction.

20. The process of claim 17 , wherein the first reaction effluent from is recycled to the first separation stage and the second reaction effluent is recycled to the second separation stage.

21. The process of claim 17 , wherein the vapor phase isomerization reaction of step (c) comprises contacting the desorbent-lean raffinate with a catalyst and process conditions effective to deethylate the ethylbenzene and isomerize the metaxylene and orthoxylene.

22. The process of claim 17 , wherein the vapor phase isomerization reaction of step (c) comprises contacting the desorbent-lean raffinate with a catalyst and process conditions effective to isomerize the ethylbenzene, metaxylene, and orthoxylene.

23. The process of claim 17 , wherein the desorbent-lean raffinate comprises ≦10.0 wt % of the desorbent withdrawn in the desorbent-rich raffinate and a desorbent-lean raffinate.

24. The process of claim 23 , wherein the desorbent-lean raffinate comprises ≧30.0 wt % of the ethylbenzene in the first mixture, and the

Assignees

• Exxonmobil Chemical Patents Inc

Inventors

• Agrawal Gaurav
• Weber Michael W
• Salciccioli Michael
• Porter John R
• Pilliod Dana L
• Bender Timothy P

Classifications

• C07C5/2767 Primary

  Changing the number of side-chains · CPC title

• C07C5/2729

  Changing the branching point of an open chain or the point of substitution on a ring · CPC title

• B01D15/1821 Primary

  Simulated moving beds · CPC title

• C07C5/2702

  Catalytic processes not covered by C07C5/2732 - C07C5/31; Catalytic processes covered by both C07C5/2732 and C07C5/277 simultaneously · CPC title

• C07C7/11

  by absorption, i.e. purification or separation of gaseous hydrocarbons with the aid of liquids · CPC title