Paraxylene Separation Process

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.

What is claimed is: 
     
         1 . A process for producing p-xylene, the process comprising:
 (a) providing a first mixture comprising ≧5.0 wt. % of aromatic C 8  isomers, the C 8  isomers comprising p-xylene and ethylbenzene;   (b) separating from the first mixture in a first separation stage a p-xylene-containing portion and (i) an ethylbenzene-containing portion and/or (ii) a non-aromatic containing portion, to form a p-xylene-depleted raffinate;   (c) reacting at least a portion the p-xylene-depleted raffinate in the liquid phase to produce a reactor effluent comprising aromatic C 8  isomers;   (d) combining with the first mixture ≧50.0 wt. % of the reactor effluent's aromatic C 8  isomers, the combining being carried out before and/or during the separating of (b), and   (e) conducting away at least part of the separated ethylbenzene-containing portion and/or conducting away at least part of the separated non-aromatic containing portion.   
     
     
         2 . The process of  claim 1 , wherein the separating step (b) includes separating from the first mixture:
 i. the p-xylene-containing portion comprising ≧10.0 wt. % of the first mixture's p-xylene; and   ii. the ethylbenzene-containing portion comprising ≧10.0 wt. % of the first mixture's ethylbenzene.   
     
     
         3 . The process of  claim 1 , further including conducting away at least a portion of the separated p-xylene-containing portion. 
     
     
         4 . The process of  claim 1 , further including conducting away ≧50.0 wt. % of the separated ethylbenzene-containing portion. 
     
     
         5 . 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. 
     
     
         6 . The process of  claim 1 , wherein the first mixture comprises 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. 
     
     
         7 . The process of  claim 1 , wherein the reacting at least a portion the p-xylene-depleted raffinate in the liquid phase includes at least one of (i) one or more reforming reactions, (ii) one or more disproportionation reactions, (iii) one or more transalkylation reactions, and (iv) one or more cracking reactions. 
     
     
         8 . The process of  claim 1 , further comprising:
 (f) separating from the reactor effluent in a second separation stage at least a portion of any C 1 -C 7  compounds produced during the reacting step (c), the step (e) being carried out before the combining step (d); and   (g) conducting the separated C 1 -C 7  compounds away from the process.   
     
     
         9 . The process  claim 8 , wherein the process further comprises:
 (h) removing from the first mixture (1) at least a portion of any o-xylene and/or (2) at least a portion of any C 9+  aromatics; and/or   (i) separating from the reactor effluent in a third separation stage one or more of toluene, o-xylene or C 9+  aromatics, and conducting away at least a portion of one or more of the separated toluene, the separated o-xylene, and the separated C 9+  aromatics.   
     
     
         10 . The process of  claim 1 , further comprising conducting away ≧50.0 wt. % of the non-aromatic containing portion separated in step (b), based on the total weight of the separated non-aromatic portion. 
     
     
         11 . The process of  claim 1 , wherein the reacting of step (c) includes liquid-phase isomerization, and wherein ≦10.0 wt. % of the p-xylene-depleted raffinate is in the vapor phase during the reacting. 
     
     
         12 . The process of  claim 1 , wherein ≦1.0 wt. % of the p-xylene-depleted raffinate is in the vapor phase during the reacting. 
     
     
         13 . 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). 
     
     
         14 . A process for producing p-xylene, the process comprising,
 (a) providing a first mixture comprising ≧5.0 wt. % of aromatic C 8  isomers, said C 8  isomers comprising p-xylene and ethylbenzene;   (b) separating from the first mixture in a first separation stage wherein the first separation stage includes at least one simulated moving-bed adsorptive separation stage:
 i. a p-xylene-depleted raffinate; 
 ii. a p-xylene-containing portion comprising ≧10.0 wt. % of the first mixture's p-xylene; and 
 iii. an ethylbenzene-containing portion comprising ≧10.0 wt. % of the first mixture's ethylbenzene; 
   (c) conducting away at least a portion of the p-xylene-containing portion;   (d) conducting away ≧50.0 wt. % of the ethylbenzene-containing portion;   (e) isomerizing at least a portion the p-xylene-depleted raffinate in the liquid phase wherein ≦10.0 wt. %, e.g., ≦1.0 wt. % or ≦0.1 wt. %, of the p-xylene-depleted raffinate is in the vapor phase during the isomerizing, to produce a reactor effluent comprising ≧90.0 wt. % p-xylene; and   (f) combining with the first mixture at least a portion of the reactor effluent, the combining being carried out before and/or during the separating of (b).   
     
     
         15 . The process of  claim 14 , further comprising:
 (g) removing from the first mixture (1) at least a portion of any o-xylene and/or (2) at least a portion of any C 9+  aromatics; and/or   (h) separating from the reactor effluent in a third separation stage one or more of toluene, o-xylene or C 9+  aromatics, and conducting away at least a portion of one or more of the separated toluene, the separated o-xylene, and the separated C 9+  aromatics; and   wherein the separating of step (b) further includes (iv) a non-aromatic hydrocarbon portion, comprising ≧50.0 wt. %, of the first mixture's non-aromatic hydrocarbon molecules.