Xylene separation process

Patent metadata

Field	Value
Publication number	US-9522863-B2
Application number	US-201414580452-A
Country	US
Kind code	B2
Filing date	Dec 23, 2014
Priority date	Feb 28, 2014
Publication date	Dec 20, 2016
Grant date	Dec 20, 2016

Abstract

A process is described for separating paraxylene from a multicomponent fluid mixture of C8 aromatics, and more particularly to a process for separating paraxylene from such a fluid mixture by means of adsorption apparatus, such as moving-bed or simulated moving-bed adsorption apparatus. A process is also described for making paraxylene by making a mixture of C8 aromatics and separating paraxylene from the mixture by means of a simulated moving-bed adsorption apparatus.

First claim

What is claimed is:

1. A process for separating paraxylene from at least one multicomponent feed by simulated countercurrent adsorptive separation in an apparatus comprising at least one column comprising multiple adsorbent bed chambers comprising adsorbent beds stacked one on too of the other, wherein a circulating bulk fluid flows into the top of an adsorbent bed chamber, through the adsorbent bed and down to the top of the next adsorbent bed chamber, said process comprising the steps of:
(a) passing said multicomponent feed through a conduit into an absorbent bed in an adsorbent bed chamber to adsorb paraxylene on said adsorbent, wherein the multicomponent feed comprises a C8 aromatic mixture of paraxylene, orthoxylene, metaxylene, and ethylbenzene, said C8 aromatic mixture comprising from 15 to 30 volume percent of paraxylene,
(b) passing at least one first flushing medium into conduit of step (a) in fluid communication with the adsorbent bed chamber to flush residue of the multicomponent feed from the conduit and into the adsorbent bed of the adsorbent bed chamber comprising adsorbed paraxylene, wherein
the first flushing medium comprises from 10 to 95 volume percent, based on the total volume of the first flushing medium, of a C8 aromatic mixture and from 5 to 70 volume percent of a non-C8 aromatic liquid, which is miscible with C8 aromatics, and wherein the C8 aromatic mixture in the first flushing medium comprises from 75 to 98 volume percent of paraxylene;
(c) passing at least one second flushing medium into the conduit of step (b) in fluid communication with the adsorbent bed chamber to flush residue of the first flushing medium from the conduit into the adsorbent bed of the adsorbent bed chamber, wherein
the second flushing medium comprises less than 1 volume percent of ethylbenzene, less than 2 volume percent of orthoxylene, and less than 2 volume percent of metaxylene; and
(d) withdrawing an extract stream comprising paraxylene from the conduit of step (c) after the second adsorbent bed has been subjected to said second flushing step (c).

2. The process of claim 1 , wherein the sum of orthoxylene, metaxylene, and ethylbenzene make up 70 to 85 volume percent of the multicomponent feed of step (a), and wherein the volume of the C8 aromatic mixture introduced into the conduit during step (b) is from 10 to 100 percent of the volume of the conduit.

3. The process of claim 1 , wherein the volume of the C8 aromatic mixture introduced into the conduit during step (b) is from 30 to 95 percent of the volume of the conduit.

4. The process of claim 1 , wherein the first flushing step of step (b) comprises introducing the C8 aromatics and the non-C8 aromatics into the conduit together.

5. The process of claim 1 , wherein the first flushing step of step (b) comprises sequentially passing into the conduit the C8 aromatic mixture, followed by passing the non-C8 aromatic liquid into the conduit.

6. The process of claim 1 , wherein the non-C8 aromatic liquid and the second flushing medium comprises at least one hydrocarbon selected from the group consisting of paradiethylbenzene, toluene, tetralin, cyclohexane, and paraffins having from 6 to 20 carbon atoms.

7. The process of claim 1 , wherein said apparatus further comprises at least one rotary valve,
wherein the conduit of steps (a), (b), and (c) provides fluid communication between the adsorbent bed chamber and the at least one rotary valve, and
wherein the at least one rotary valve controls the direction of fluid flow through the conduit of steps (a), (b), and (c).

8. The process of claim 7 , further comprising the step of:
(e) passing a desorbent through a rotary valve and the conduit to the adsorbent bed chamber after the extract stream has been withdrawn from the adsorbent bed chamber according to step (d).

9. The process of claim 8 , further comprising the step of:
(f) withdrawing a portion of the liquid from the adsorbent bed chamber through the conduit and a rotary valve before desorbent has been passed through the conduit into the adsorbent bed chamber according to step (e) and after a liquid stream has been removed from said chamber through the conduit according to step (d).

10. The process of claim 1 , wherein said second flushing medium of step (c) comprises less than 1.0 volume percent of the sum of paraxylene, orthoxylene, metaxylene, and ethylbenzene, and wherein the second flushing medium comprises at least 99 volume percent of the desorbent used in step (e).

11. The process of claim 9 , wherein at least of a portion of the liquid withdrawn according to step (f) is used as the second flushing fluid of step (c).

12. The process of claim 7 ,
wherein separate conduits provide fluid communication between each adsorbent bed chamber and the at least one rotary valve.

13. The process of claim 12 , wherein the flow of liquids through conduits to and from adsorbent bed chambers are controlled by the at least one rotary valve, such that, over time, each of steps (a), (b), (c), (d), (e), and (f) take place in each of the adsorbent bed chambers of the apparatus.

14. The process of claim 13 , wherein, at the same time that the multicomponent feed is passed through a rotary valve through a first conduit into a first adsorbent bed in a first adsorbent bed chamber according to step (a), the following steps occur:
(b′) the at least one first flushing medium is passed through a rotary valve and then into a second conduit in fluid communication with a second adsorbent bed chamber to flush residue of the multicomponent feed from the second conduit and into the adsorbent bed of the second adsorbent bed chamber, wherein the second adsorbent bed chamber is located upstream from the first adsorbent bed chamber, based on the direction of the flow of the circulating bulk fluid;
(c′) the at least one second flushing medium s passed through a rotary valve and then into a third conduit in fluid communication with a third adsorbent bed chamber to flush residue of the first flushing medium the third conduit into the adsorbent bed of the third adsorbent bed chamber, wherein the third adsorbent bed chamber is located upstream from the second adsorbent bed chamber, based on the direction of the flow of the circulating bulk fluid;
(d′) an extract stream is passed through a fourth conduit and then into a rotary valve, wherein the fourth conduit is in fluid communication with a fourth adsorbent bed chamber, wherein the fourth adsorbent bed chamber is located upstream from the third adsorbent bed chamber, based on the direction of the flow of the circulating bulk fluid; and
(e′) the desorbent is passed through a rotary valve and then into a fifth conduit in to fluid communication with a fifth adsorbent bed chamber located above said fourth adsorbent bed chamber, wherein the fifth adsorbent bed chamber is located upstream from the fourth adsorbent bed chamber, based on the direction of the flow of the circulating bulk fluid.

15. The process of claim 14 , further comprising the step of:
(f) withdrawing a liquid from a sixth adsorbent bed chamber into a sixth conduit and then through a rotary valve, wherein the sixth adsorbent bed chamber is located upstream from the fourth adsorbent bed chamber and downstream from the fifth adsorbent bed chamber, based on the direction of the flow of circulating bulk fluid, and wherein at least a portion of the liquid withdrawn according to step (f) is used as at least a portion of the at least one second flushing medium.

16. The process of claim 15 , wherein at least one adsorbent bed chamber is located upstream, based on the dir

Assignees

• Exxonmobil Chemical Patents Inc

Inventors

• Bender Timothy P

Classifications

• C07C7/13 Primary

  by molecular-sieve technique · CPC title

• C07C6/123

  of only one hydrocarbon · CPC title

• C07C15/08

  Xylenes · CPC title