Processes for recovering paraxylene

Patent metadata

Field	Value
Publication number	US-10351489-B2
Application number	US-201715600494-A
Country	US
Kind code	B2
Filing date	May 19, 2017
Priority date	Jun 30, 2016
Publication date	Jul 16, 2019
Grant date	Jul 16, 2019

Abstract

Disclosed is a process for recovering paraxylene in which a first simulated moving bed adsorption unit is used to produce two extract streams—one rich in paraxylene and a paraxylene-rich extract stream that is lean in ethylbenzene and an ethylbenzene-rich extract stream that is lean in paraxylene- and a paraxylene-depleted raffinate stream. A significant amount of the ethylbenzene is removed in the ethylbenzene-rich extract stream (at least enough to limit buildup in the isomerization loop), so the paraxylene-depleted raffinate stream may be isomerized in the liquid phase. Avoiding vapor phase isomerization saves energy and capital, as liquid phase isomerization requires less energy and capital than the vapor phase isomerization process due to the requirement of vaporizing the paraxylene-depleted stream and the use of hydrogen, which requires an energy and capital intensive hydrogen recycle loop.

First claim

The invention claimed is:

1. A process for recovering paraxylene, the process comprising:
(a) introducing a first hydrocarbon feed stream into a first simulated moving bed adsorption unit, wherein the first hydrocarbon feed stream comprises a mixture of paraxylene (PX), metaxylene (MX), orthoxylene (OX), and ethylbenzene (EB);
(b) introducing a desorbent stream into the first simulated moving bed adsorption unit, wherein the desorbent stream comprises a desorbent;
(c) withdrawing a first PX-rich extract stream, which comprises desorbent and PX, from the first simulated moving bed adsorption unit, wherein the first PX-rich extract stream is withdrawn at a location downstream of a desorbent introduction location and upstream of a feed introduction location;
(d) withdrawing an EB-rich extract stream, which comprises desorbent, EB, and PX, from the first simulated moving bed adsorption unit, wherein the EB-rich extract stream is withdrawn at a location downstream of the first PX-rich extract stream withdrawal location and upstream of the feed introduction location;
(e) withdrawing a first PX-depleted raffinate stream, which comprises desorbent, MX, OX, and EB, from the first simulated moving bed adsorption unit;
(f) isomerizing at least a portion of the first PX-depleted raffinate stream at least partially in a liquid phase to produce a first isomerized stream having a higher PX concentration than the first PX-depleted raffinate stream;
(g) recycling at least a portion of the first isomerized stream to the first simulated moving bed adsorption unit; and
(h) providing the EB-rich extract stream to a PX recovery unit to produce a second PX-rich extract stream, wherein the PX recovery unit comprises a second simulated moving bed adsorption unit or a crystallizer.

2. The process of claim 1 , further comprising:
(i) providing the first PX-rich extract stream to a first extract column to remove desorbent and produce a desorbent-free PX-rich extract stream; and
(j) providing the desorbent-free PX-rich extract stream to a first finishing column to produce a first pure PX stream.

3. The process of claim 2 , wherein the second PX-rich extract stream is provided to the first extract column of step (i).

4. The process of claim 3 , wherein the second simulated moving bed adsorption unit produces a second PX-depleted raffinate stream, and further comprising recovering a pure EB stream from the second PX-depleted raffinate stream in a distillation column.

5. The process of claim 4 , further comprising removing desorbent from the EB-rich extract stream before step (h).

6. The process of claim 4 , wherein the second simulated moving bed adsorption unit comprises a different adsorbent than the first simulated moving bed adsorption unit, and wherein the adsorbent of the second moving bed adsorption unit has a higher affinity for EB and PX than the adsorbent of the first moving bed adsorption unit.

7. The process of claim 4 , wherein a conventional simulated moving bed adsorption unit comprising 24 adsorbent beds, divided into two columns of 12 adsorbent beds each, is retrofitted such that the first column functions as the first simulated moving bed adsorption unit and the second column functions as the second simulated moving bed adsorption unit.

8. The process of claim 4 , wherein the EB-rich extract stream is combined with a second hydrocarbon feed stream before step (h).

9. The process of claim 4 , wherein the withdrawal location of the EB-rich extract stream from the first simulated moving bed adsorption unit is selected to minimize a desorbent content in the EB-rich extract stream, and the EB-rich extract stream comprises the entirety of a feed stream to the second simulated moving bed adsorption unit.

10. The process of claim 4 , wherein the withdrawal location of the EB-rich extract stream from the first simulated moving bed adsorption unit is at least 3 beds away from the first PX-rich extract stream withdrawal location.

11. The process of claim 3 , wherein the second simulated moving bed adsorption unit produces a second PX-depleted raffinate stream, and further comprising:
(k) isomerizing at least a portion of the second PX-depleted raffinate stream in a vapor phase to produce a second isomerized stream having a higher PX concentration than the second PX-depleted raffinate stream; and
(l) recycling at least a portion of the second isomerized stream to one or both of the first simulated moving bed adsorption unit and the second simulated moving bed adsorption unit.

12. The process of claim 3 , wherein the second simulated moving bed adsorption unit produces an EB-rich raffinate stream and an EB-lean raffinate stream, and further comprising:
(m) recycling at least a portion of the EB-lean raffinate stream to step (f); and
(o) isomerizing at least a portion of the EB-rich raffinate stream in a vapor phase to produce a second isomerized stream having a higher PX concentration than the EB-rich raffinate stream.

13. The process of claim 2 , wherein the PX recovery unit further comprises a crystallizer.

14. The process of claim 13 , wherein the second PX-rich extract stream is provided to the first extract column of step (i).

15. The process of claim 14 , wherein the crystallizer produces an EB-rich liquid product, which is sent to a refinery stream.

16. A process for recovering paraxylene, the process comprising:
(a) providing a first hydrocarbon feed stream and a desorbent stream to a first simulated moving bed adsorption unit, wherein the first hydrocarbon feed stream comprises a mixture of paraxylene (PX), metaxylene (MX), orthoxylene (OX), and ethylbenzene (EB), and wherein the desorbent stream comprises desorbent;
(b) withdrawing from the first simulated moving bed adsorption unit:
(i) a first PX-rich extract stream, which comprises desorbent and PX;
(ii) an EB-rich extract stream, which comprises desorbent, EB, and PX; and
(iii) a first PX-depleted raffinate stream, which comprises desorbent, MX, OX, and EB,

wherein the first PX-rich extract stream is withdrawn at a location downstream of a desorbent introduction location and upstream of a feed introduction location and the EB-rich extract stream is withdrawn at a location downstream of the first PX-rich extract stream withdrawal location and upstream of the feed introduction location;
(c) isomerizing at least a portion of the first PX-depleted raffinate stream at least partially in a liquid phase to produce a first isomerized stream having a higher PX concentration than the first PX-depleted raffinate stream;
(d) recycling at least a portion of the first isomerized stream to the first simulated moving bed adsorption unit;
(e) providing the EB-rich extract stream to a second simulated moving bed adsorption unit to produce a second PX-rich extract stream and a second PX-depleted raffinate stream; and
(f) recovering a pure EB stream from the second PX-depleted raffinate stream in a distillation column.

17. The process of claim 16 , further comprising removing desorbent from the EB-rich extract stream before step (e).

18. The process of claim 16 , wherein the EB-rich extract stream is combined with a second hydrocarbon feed stream before step (e).

19. The process of claim 16 , further comprising removing C 9+ hydrocarbons from the first hydrocarbon feed stream in a xylenes fractionation column prior to step (a).

20. A process for recovering paraxylene, the process comprising:
(a) providing a first hydrocarbon feed stream and a desorbent stream to a first s

Assignees

• Exxonmobil Chemical Patents Inc

Inventors

• Salciccioli Michael
• Agrawal Gaurav
• Weber Michael W
• Pilliod Dana L
• Dorsi Catherine M

Classifications

• C07C7/12

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

• C07C5/277

  Catalytic processes · CPC title

• C07C7/148

  by treatment giving rise to a chemical modification of at least one compound · CPC title

• C07C7/11

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

• C07C2601/16

  the ring being unsaturated · CPC title