Process for the production of purified xylene isomers

Patent metadata

Field	Value
Publication number	US-9309169-B2
Application number	US-201314080963-A
Country	US
Kind code	B2
Filing date	Nov 15, 2013
Priority date	Nov 30, 2012
Publication date	Apr 12, 2016
Grant date	Apr 12, 2016

Abstract

The invention is directed to a process to produce para-xylene and optionally, ortho-xylene, including coupling a C 9 + -aromatics-removal system with an isomerization system or with a parallel configuration of two isomerization systems to reduce xylenes recycle for energy savings and/or productivity increases.

First claim

What is claimed is:

1. A process for producing para-xylene, PX, the process comprising:
(a) supplying at least one hydrocarbon feed comprising C 8 + aromatics to a PX production system comprising a C 9 + -aromatics-removal system, a PX-recovery system, a first isomerization system, a second isomerization system, and a C 7 − hydrocarbons-removal system;
(b) separating C 9 + -aromatics from said feed in said C 9 + -aromatics-removal system to recover at least one C 8 -aromatics stream, at least one PX-lean stream having a lower PX concentration than said C 8 -aromatics stream, and at least one C 9 + -aromatics-rich stream;
(c) separating said C 8 -aromatics stream in said PX-recovery system to recover a PX-rich stream and a PX-depleted stream;
(d) isomerizing at least partially in the vapor phase said PX-depleted stream in said first isomerization system to produce a first isomerized stream having a higher PX concentration than said PX-depleted stream;
(e) separating C 7 − hydrocarbons from said first isomerized stream in said C 7 − hydrocarbons-removal system to produce a C 7 − hydrocarbons-rich stream and a C 7 − hydrocarbons-depleted isomerized stream having a lower C 7 − hydrocarbons concentration than said first isomerized stream;
(f) recycling said C 7 − hydrocarbons-depleted isomerized stream to said C 9 + -aromatics-removal system;
(g) isomerizing at least partially in the liquid phase said PX-lean stream in said second isomerization system to produce a second isomerized stream having a higher PX concentration than said PX-lean stream; and
(h) recycling said second isomerized stream to said C 9 + -aromatics-removal system.

2. The process of claim 1 further comprising isomerizing at least partially in the liquid phase at least a portion of said PX-depleted stream in said second isomerization system to produce at least a portion of said second isomerized stream having a higher PX concentration than said PX-depleted stream.

3. The process of claim 1 further comprising reacting at least partially in the vapor phase at least a portion of said PX-lean stream in said first isomerization system to produce at least a portion of said first isomerized stream having a higher PX concentration than said PX-lean stream.

4. The process of claim 1 further comprising separating C 7 − hydrocarbons from at least a portion of said second isomerized stream in said C 7 − hydrocarbons-removal system to generate at least a portion of said C 7 − hydrocarbons-depleted isomerized stream having a lower C 7 − hydrocarbons concentration than said second isomerized stream.

5. The process of claim 1 further comprising sending at least a portion of said second isomerized stream to said PX-recovery system.

6. The process of claim 1 further comprising separating benzene from at least a portion of said second isomerized stream in a benzene removal system to produce a benzene-rich stream and a benzene-depleted stream.

7. The process of claim 6 and further comprising sending at least a portion of said benzene-depleted stream to said PX-recovery system.

8. The process of claim 6 and further comprising sending at least a portion of said benzene-depleted stream to said C 9 + -aromatics-removal system.

9. The process of claim 1 , wherein said C 9 + -aromatics-removal system comprises at least one distillation unit.

10. The process of claim 9 , wherein the C 9 + -aromatics-removal system produces an overhead stream comprising a C 8 -aromatics stream and a bottoms stream comprising a C 9 + -aromatics-rich stream.

11. The process of claim 9 , wherein said PX-lean stream comprises, at least partially, the liquid drawn from a drawing tray of which the tray number is in between 30% to 80% of the total tray number of said distillation unit(s).

12. The process of claim 11 , wherein at least a portion of said second isomerized stream and/or benzene-depleted stream is recycled to said C 9 + -aromatics-removal system at the same location as the drawing tray.

13. The process of claim 11 , wherein at least a portion of said second isomerized stream and/or benzene-depleted stream is recycled to said C 9 + -aromatics-removal system at a tray located above said drawing tray.

14. The process of claim 9 , wherein said distillation unit comprises at least one dividing-wall distillation unit.

15. The process of claim 9 , wherein at least a portion of said second isomerization system is installed inside said distillation unit in the form of catalytic distillation to effect said isomerization and said separation.

16. The process of claim 1 , wherein said C 7 − hydrocarbons-removal system comprises at least one distillation unit.

17. The process of claim 1 , wherein said PX recovery system comprises a fractional crystallization unit and/or a selective adsorption unit for recovering said PX-rich stream.

18. The process of claim 1 , wherein each of said isomerizations comprise at least one of xylenes isomerization, ethylbenzene dealkylation, and ethylbenzene isomerization.

19. The process of claim 1 further including separating said C 9 + -aromatics-rich stream in an ortho-xylene-recovery system to produce an ortho-xylene-rich stream and an ortho-xylene-depleted C 9 + -aromatics stream.

20. The process of claim 1 , wherein the PX concentration among the xylenes in said C 8 -aromatics stream is above the PX equilibrium concentration.

21. The process of claim 1 , wherein said feed comprising C 8 + aromatics includes at least one feed selected from the group consisting of a C 8 + selective toluene disproportionation product, a C 8 + transalkylation product, a C 8 + reformate product, a C 8 + toluene disproportionation product, and a C 8 + toluene methylation product, and a C 8 + benzene methylation product.

Assignees

• Exxonmobil Chem Patents Inc

Inventors

• Ou John Di-Yi
• Demartino Ronald L
• Abichandani Jeevan S

Classifications

• C07C15/08

  Xylenes · CPC title

• C07C7/04

  by distillation · CPC title

• C07C2529/70

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

• C07C4/18 Primary

  Catalytic processes · CPC title