Paraxylene separation process

Patent metadata

Field	Value
Publication number	US-9725378-B2
Application number	US-201514624861-A
Country	US
Kind code	B2
Filing date	Feb 18, 2015
Priority date	Mar 20, 2014
Publication date	Aug 8, 2017
Grant date	Aug 8, 2017

Abstract

The invention relates to a p-xylene separation process wherein at least a portion of ethylbenzene present in an aromatics-containing feed is removed prior to isomerization. Aspects of the invention provide a process for producing p-xylene. The process includes providing a first mixture comprising ≧5.0 wt. % of aromatic C 8 isomers, the C 8 isomers comprising p-xylene and ethylbenzene. A p-xylene-containing portion and an ethylbenzene-containing portion are separated from the first mixture in a first separation stage to form a p-xylene-depleted raffinate. The first separation stage can include at least one simulated moving-bed adsorptive separation stage. At least a portion the p-xylene-depleted raffinate in the liquid phase is reacted to produce a reactor effluent comprising aromatic C 8 isomers. The first mixture can be combined with ≧50.0 wt. % of the reactor effluent's aromatic C 8 isomers. The combining can be carried out before and/or during the separating of the p-xylene and ethylbenzene portions.

First claim

What is claimed is:

1. A process for producing p-xylene, the process comprising:
(a) providing a first mixture comprising aromatic C 8 isomers;
(b) separating from the first mixture in a first stage:
(i) a p-xylene-depleted raffinate;
(ii) a p-xylene-containing portion comprising ≧10.0 wt. % of the mixture's p-xylene; and
(iii) an ethylbenzene-containing portion comprising ≧10.0 wt. % of the mixture's ethylbenzene; wherein the first separation stage includes at least one simulated moving-bed adsorption chromatographic separation;

(c) conducting away at least a portion of the separated p-xylene;
(d) reacting at least a portion of the p-xylene-depleted raffinate in the liquid phase to produce a first reactor effluent comprising aromatic C 8 isomers;
(e) separating from the first reactor effluent in a second separation stage a toluene-containing fraction and a xylene-enriched raffinate;
(f) separating from the xylene-enriched raffinate an o-xylene-containing distillate;
(g) recycling at least a portion of the o-xylene-containing distillate directly to the reacting in (d);
(h) conducting away ≧50.0 wt. % of the ethylbenzene separated in (b)(iii); and
(i) exposing ≦10.0 wt. % of aromatic C 8 isomers in the process to vapor-phase isomerization to produce a second reactor effluent comprising aromatic C 8 isomers.

2. The process of claim 1 , wherein the first mixture comprises ≧50.0 wt. % of a mixture of p-xylene, ethylbenzene, m-xylene, and o-xylene.

3. The process of claim 1 , wherein the first mixture comprises about 17 wt. % to 27 wt. % p-xylene, 40 wt. % to 50 wt. % m-xylene, 18 wt. % to 28 wt. % o-xylene, and 5 wt. % to 15 wt. % ethylbenzene.

4. The process of claim 1 , wherein reacting at least a portion the p-xylene-depleted raffinate in the liquid phase includes one or more transalkylation reactions.

5. The process of claim 1 , further comprising:
(j) separating from the first reactor effluent in the second separation stage at least a portion of any C 1 -C 7 compounds produced during the reacting in (d); and
(k) conducting the separated C 1 -C 7 compounds away from the process.

6. The process of claim 1 , further comprising separating from the first mixture in the first separation stage ≧50.0 wt. % of any non-aromatic hydrocarbon molecules.

7. The process of claim 1 , wherein the reacting in (d) includes liquid-phase isomerization, and wherein ≦10.0 wt. % of the p-xylene-depleted raffinate is in the vapor phase during the reacting.

8. The process of claim 1 , wherein ≦1.0 wt. % of the p-xylene-depleted raffinate is in the vapor phase during the reacting.

9. The process of claim 1 , wherein (i) ≧90.0 wt. % of the first mixture's ethylbenzene is separated by chromatographic separation in the first separation stage, (ii) ≧90.0 wt. % of the separated ethylbenzene is conducted away from the process, and (iii) ≧90.0 wt. % of the reactor effluent's aromatic C 8 isomers are combined with the first mixture in step (d).

10. The process of claim 1 ,
wherein the p-xylene-containing portion further comprises a desorbent from the separating in (b);
wherein the process further comprises:
(l) separating from the p-xylene containing portion a distillate fraction comprising the desorbent; and
(m) recycling the distillate fraction to the separating in (b).

11. The process of claim 10 , further comprising:
(n) separating from the p-xylene-containing portion a residue comprising p-xylene during the separating in (l); and
(o) concentrating a p-xylene content of the residue in a crystallization zone to produce a concentrated p-xylene stream and a liquid stream;
(p) recycling the liquid stream to the separating in (b).

Assignees

• Exxonmobil Chemical Patents Inc

Inventors

• Ou John D
• Abichandani Jeevan S

Classifications

• C07C7/12 Primary

  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

• C07C4/02

  by cracking a single hydrocarbon or a mixture of individually defined hydrocarbons or a normally gaseous hydrocarbon fraction · CPC title

• C07C15/08

  Xylenes · CPC title

• C07C2529/40

  of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11 · CPC title