Process for xylenes isomerization

Patent metadata

Field	Value
Publication number	US-9809509-B2
Application number	US-201615296878-A
Country	US
Kind code	B2
Filing date	Oct 18, 2016
Priority date	Dec 15, 2015
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

A process for the isomerization of a para-xylene depleted, meta-xylene rich stream under at least partially liquid phase conditions using ZSM-23 with an external surface area of at least 75 m 2 /g (indicating a small crystallite size), and a SiO 2 /Al 2 O 3 ratio between 15 and 75 that produces a higher than equilibrium amount of para-xylene, i.e., more than about 24 wt % of para-xylene, based on the total amount of xylenes.

First claim

The invention claimed is:

1. A process for producing para-xylene from a C8 aromatic hydrocarbon mixture, the process comprising:
(a) providing a C8 aromatic hydrocarbon mixture comprising para-xylene, ortho-xylene and meta-xylene to an ortho-xylene splitter to produce a first stream comprising para-xylene and meta-xylene and a second stream comprising ortho-xylene;
(b) passing the first stream comprising para-xylene and meta-xylene to a para-xylene recovery unit to recover a para-xylene product stream and produce a para-xylene-depleted stream consisting essentially of meta-xylene;
(c) contacting the para-xylene-depleted stream comprising meta-xylene with a catalyst under at least partially liquid phase conditions effective to produce a first isomerized stream having a para-xylene content of more than 24 wt.%, based on the total amount of xylenes in the first isomerized stream; and first isomerized stream, wherein the catalyst comprises ZSM-23 with a SiO 2 /A 1 2 O 3 ratio between 15 and 50 and an external surface area of 75-115 m 2 /g; and
(d) recycling at least a portion of the first isomerized stream back to the para-xylene recovery unit.

2. The process of claim 1 , wherein the catalyst in step (c) is self-bound.

3. The process of claim 1 , wherein at least a portion of the first isomerized stream is recycled back to the ortho-xylene splitter.

4. The process of claim 1 , further comprising:
(e) contacting the second stream comprising ortho-xylene with a catalyst comprising ZSM-5 having an alpha value of at least 300 under at least partially liquid phase conditions effective to produce a second isomerized stream; and
(f) recycling at least a portion of the second isomerized stream back to the ortho-xylene splitter.

5. The process of claim 4 , wherein the liquid phase conditions of step (c) and (e) comprise a temperature from 400° F. (204° C.) to 1,000° F. (538° C.), a pressure of from 0 to 1,000 psig, a weight hourly space velocity (WHSV) of from 0.5 to 100 hr −1 .

6. The process of claim 4 , wherein the liquid phase conditions of step (c) comprise a temperature from 482° F. (250° C.) to 572° F. (300° C.), a pressure from 350 psig (2.41 MPa) to 500 psig (3.45 MPa), and a weight hourly space velocity (WHSV) from 0.5 to 10 hr −1 .

7. The process of claim 1 , wherein the C 8 aromatic hydrocarbon mixture further comprises ethylbenzene and the process further comprises a step of reducing the ethylbenzene.

8. The process of claim 7 , wherein the ethylbenzene is removed prior to the ortho-xylene splitter by an ethylbenzene removal unit or an ethylbenzene conversion unit.

9. The process of claim 8 , wherein the ethylbenzene removal unit comprises a fractionation column or an adsorption unit equipped with an ethylbenzene-selective adsorbent.

10. The process of claim 8 , wherein the ethylbenzene conversion unit comprises a catalytic system effective to dealkylate ethylbenzene to benzene and produce an ethylbenzene-depleted stream.

11. The process of claim 7 , wherein the ethylbenzene is removed by a purge stream from the para-xylene-depleted stream comprising meta-xylene prior to step (c) or from the second isomerized stream after step (c).

Assignees

• Exxonmobil Chemical Patents Inc

Inventors

• Weiss Brian M
• Lacy Darryl D
• Weigel Scott J

Classifications

• C07C2529/40

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

• C07C5/2737 Primary

  with crystalline alumino-silicates, e.g. molecular sieves · CPC title

• C07C2529/70

  of types characterised by their specific structure not provided for in groups C07C2529/08 - C07C2529/65 · CPC title

• C07C4/18

  Catalytic processes · CPC title

• B01J29/7046

  MTT-type, e.g. ZSM-23, KZ-1, ISI-4 or EU-13 · CPC title