Process for Removing a Contaminant from an Aromatic Selective Solvent

Abstract

The invention is a process and apparatus for removing a contaminant from an aromatic selective solvent. A feed stream comprising an aromatic hydrocarbon and a non-aromatic hydrocarbon is contacted with the aromatic selective solvent in an extractive distillation zone to produce a raffinate stream comprising the non-aromatic hydrocarbon, and a rich solvent stream comprising the aromatic hydrocarbon and the solvent. The rich solvent stream is separated in a second distillation zone to produce an extract stream comprising the aromatic hydrocarbon, and a lean solvent stream comprising the contaminant and the aromatic selective solvent. At least a portion of the lean solvent stream is washed with a non-aromatic hydrocarbon to produce a clean solvent stream, at least a portion of which is passed to at least one of the extractive distillation zone and the second distillation zone.

1 . A process for removing a contaminant from an aromatic selective solvent, the process comprising:
 (a) contacting a feed stream comprising a non-aromatic hydrocarbon and an aromatic hydrocarbon with the aromatic selective solvent in an extractive distillation zone to produce a raffinate stream comprising the non-aromatic hydrocarbon, and a rich solvent stream comprising the aromatic hydrocarbon and the aromatic selective solvent;   (b) separating the rich solvent stream in a second distillation zone to produce an extract stream comprising the aromatic hydrocarbon, and a lean solvent stream comprising the contaminant and the aromatic selective solvent;   (c) washing at least a portion of the lean solvent stream with a washing stream comprising a second non-aromatic hydrocarbon to produce a clean solvent stream comprising the aromatic selective solvent, and a first by-product stream comprising the contaminant and the second non-aromatic hydrocarbon; and   (d) introducing at least a portion of the clean solvent stream to at least one of the extractive distillation zone and the second distillation zone.   
     
     
         2 . The process of  claim 1  wherein the aromatic selective solvent is selected from the group consisting of 1,1-dioxide tetrahydrothiofuran, 2-sulfolene, 3-sulfolene, 2-methylsulfolane, 2-4-dimethyl-sulfolane, methyl-2-sulfonylether, an N-aryl-3-sulfonylamine, ethyl-3-sulfonyl sulfide, 2-sulfonylacetate, diethyleneglycol, a polyethyleneglycol, a dipropyleneglycol, a polypropyleneglycol, a dimethylsulfoxide, an N-methylpyrrolidone, a glycol-amine, glycols, glycol ethers, an N-methyl-2-pyrrolidone, and an N-formyl morpholine, and combinations thereof. 
     
     
         3 . The process of  claim 1  wherein the lean solvent stream comprises the contaminant in an amount not more than about 25 wt % of the lean solvent stream. 
     
     
         4 . The process of  claim 1  wherein the portion of the lean solvent stream washed in step (c) ranges from about 0.1% to about 60% of the lean solvent stream produced in step (b). 
     
     
         5 . The process of  claim 1  wherein the conditions of the lean solvent washing step (c) include a temperature from about 10° C. to about 95° C. 
     
     
         6 . The process of  claim 1  wherein the weight ratio of the second non-aromatic hydrocarbon to the at least a portion of the lean solvent stream in lean solvent washing step (c) ranges from about 0.02 to about 10. 
     
     
         7 . The process of  claim 1  wherein the lean solvent washing step (c) further comprises the presence of water. 
     
     
         8 . The process of  claim 7  wherein the amount of water in lean solvent washing step (c) is insufficient to form an aqueous phase. 
     
     
         9 . The process of  claim 1  wherein at least a portion of the raffinate stream from step (a) provides at least a portion of the washing stream in lean solvent washing step (c). 
     
     
         10 . The process of  claim 1  wherein the first by-product stream comprises from about 10% to about 99% of the contaminant in the at least a portion of the lean solvent stream washed in lean solvent washing step (c). 
     
     
         11 . The process of  claim 1  wherein the feed stream further comprises the contaminant and the rich solvent stream further comprises the contaminant. 
     
     
         12 . The process of  claim 11  wherein the aromatic hydrocarbon comprises at least one of benzene, toluene, and xylene; and the contaminant comprises a C9+ aromatic hydrocarbon. 
     
     
         13 . The process of  claim 1  wherein the first by-product stream comprises the aromatic selective solvent in an amount not more than about 5 wt % of the first by-product stream. 
     
     
         14 . The process of  claim 1  wherein the first by-product stream further comprises the aromatic selective solvent, the process further comprising:
 (e) washing at least a portion of the first by-product stream with a second solvent stream comprising water to produce a second by-product stream comprising the contaminant and the second non-aromatic hydrocarbon, and an aqueous solvent stream comprising water and the aromatic selective solvent.   
     
     
         15 . The process of  claim 14  wherein the conditions of the by-product washing step (e) include a temperature from about 10° C. to about 95° C. and a pressure sufficient to ensure a liquid phase. 
     
     
         16 . The process of  claim 14  wherein the weight ratio of the second solvent stream to the at least a portion of the first by-product stream in the by-product washing step (e) ranges from about 0.01 to about 10. 
     
     
         17 . The process of  claim 14  further comprising passing at least a portion of the aqueous solvent stream to at least one of the extractive distillation zone of step (a) and the second distillation zone of step (b). 
     
     
         18 . The process of  claim 14  further comprising introducing water to at least one of the extractive distillation zone and the second distillation zone to produce a first stream comprising water from at least one of the extractive distillation zone and the second distillation zone; at least a portion of the first stream providing at least a portion of the second solvent stream in the by-product washing step (e). 
     
     
         19 . The process of  claim 14  wherein the aqueous solvent stream comprises at least about 90% of the aromatic selective solvent in the at least a portion of the first by-product stream being washed in the by-product washing step (e). 
     
     
         20 . A process for removing a contaminant from an aromatic selective solvent, the process comprising:
 (a) contacting a feed stream comprising a non-aromatic hydrocarbon, an aromatic hydrocarbon, and the contaminant with the aromatic selective solvent in an extractive distillation zone to produce a raffinate stream comprising the non-aromatic hydrocarbon, and a rich solvent stream comprising the aromatic hydrocarbon, the contaminant, and the aromatic selective solvent;   (b) separating the rich solvent stream in a second distillation zone to produce an extract stream comprising the aromatic hydrocarbon, and a lean solvent stream comprising the contaminant and the aromatic selective solvent;   (c) washing at least a portion of the lean solvent stream with at least a portion of the raffinate stream to produce a clean solvent stream comprising the aromatic selective solvent, and a first by-product stream comprising the contaminant and the non-aromatic hydrocarbon;   (d) introducing at least a portion of the clean solvent stream to at least one of the extractive distillation zone and the second distillation zone; and   (e) washing at least a portion of the first by-product stream with water to produce a second by-product stream comprising the contaminant and the non-aromatic hydrocarbon, and an aqueous solvent stream comprising water and the aromatic selective solvent.