Mercaptan management in selective hydrodesulfurization of fcc naphtha

Abstract

A process for reducing the sulfur content of FCC naphtha is described. The process includes introducing a FCC naphtha feed to a selective hydrogenation zone to form a hydrogenated feed. The hydrogenated feed is separated into light fraction and a heavy fraction. The heavy fraction is introduced into a selective hydrodesulfurization zone to form a desulfurized stream which contains mercaptans. The desulfurized stream is separated into a mercaptan rich stream and a mercaptan lean stream. The mercaptan rich stream is treated with a caustic extraction process, a hydrodesulfurization reaction zone, a selective hydrogenation process, an adsorption process, or an ionic liquid extraction process to remove at least a portion of the mercaptan compounds to form a second mercaptan lean stream.

What is claimed is: 
     
         1 . A process for reducing the sulfur content of full range naphtha comprising:
 introducing a naphtha feed into a selective hydrogenation zone in the presence of hydrogen and a hydrogenation catalyst under selective hydrogenation conditions to form a hydrogenated feed;   separating the hydrogenated feed into at least two fractions, a light fraction and a heavy fraction;   introducing the heavy fraction to a selective hydrodesulfurization zone in the presence of hydrogen and a hydrodesulfurization catalyst under selective hydrodesulfurization conditions to form a desulfurized stream, the desulfurized stream containing mercaptans;   separating at least a portion of the desulfurized stream into at least two streams, a mercaptan rich stream and a first mercaptan lean stream; and   treating at least a portion of the mercaptan rich stream to remove at least a portion of the mercaptan compounds to form a second mercaptan lean stream.   
     
     
         2 . The process of  claim 1  wherein treating the at least the portion of the mercaptan rich stream comprises introducing the mercaptan rich stream into at least one of a caustic extraction zone, a hydrodesulfurization reaction zone, the selective hydrogenation zone, an adsorption zone, and an ionic liquid extraction zone. 
     
     
         3 . The process of  claim 1  further comprising combining the first mercaptan lean stream with the second mercaptan lean stream. 
     
     
         4 . The process of  claim 1  further comprising combining the light fraction with at least one of the first mercaptan lean stream and the second mercaptan lean stream. 
     
     
         5 . The process of  claim 1  wherein separating the at least the portion of the desulfurized stream into at least two streams comprises separating the at least the portion of the desulfurized stream into the mercaptan rich stream and the first mercaptan lean stream. 
     
     
         6 . The process of  claim 5  wherein the mercaptan rich stream has a boiling point in a range of about 60° C. to about 100° C., and the first mercaptan lean stream has a boiling point in a range of about 100° C. to about 220° C. 
     
     
         7 . The process of  claim 1  wherein separating the at least the portion of the desulfurized stream into at least two streams comprises separating the at least the portion of the desulfurized stream into the mercaptan rich stream and at least two first mercaptan lean streams, a low boiling first mercaptan lean stream having a boiling point range lower than a boiling point range of the mercaptan rich stream and a high boiling first mercaptan stream having a boiling point range greater than the boiling point range of the mercaptan rich stream. 
     
     
         8 . The process of  claim 7  wherein the mercaptan rich stream has a boiling point in a range of about 85° C. to about 100° C., and the low boiling first mercaptan lean stream has a boiling point in a range of about 60° C. to about 85° C., and the high boiling first mercaptan lean stream has a boiling point in a range of about 100° C. to about 220° C. 
     
     
         9 . The process of  claim 1  wherein the mercaptan rich stream has a boiling point in a range of about 60° C. to about 100° C. and the first mercaptan lean stream has a boiling point in a range of about 100° C. to about 220° C., and wherein treating the mercaptan rich stream comprises introducing the mercaptan rich stream into a caustic extraction zone. 
     
     
         10 . The process of  claim 1  and further comprising:
 separating the desulfurized stream into a gas stream and a liquid stream in a first side of a divided wall separator and wherein separating the at least the portion of the desulfurized stream into the at least two streams comprises separating the liquid stream into at least the mercaptan rich stream and at least two first mercaptan lean streams, 
 wherein the mercaptan rich stream has a boiling point in a range of about 85° C. to about 100° C., and the at least two first mercaptan lean streams comprise a low boiling first mercaptan lean stream having a boiling point in a range of about 60° C. to about 85° C., and a high boiling mercaptan lean stream having a boiling point in a range of about 100° C. to about 220° C., and 
 wherein treating the at least the portion of the mercaptan rich stream comprises introducing at least the portion of the mercaptan rich stream into a hydrodesulfurization reaction zone forming a hydrodesulfurization reaction zone effluent; 
 and further comprising: 
 separating the hydrodesulfurization reaction zone effluent into a gas stream and a liquid stream in the second side of the divided wall separator; 
 stripping the liquid stream in a stripping zone to form a third mercaptan lean stream. 
 
     
     
         11 . The process of  claim 1  wherein separating the at least the portion of the desulfurized stream into at least two streams comprises separating the at least the portion of the desulfurized stream into at least the mercaptan rich stream and at least two mercaptan lean streams,
 wherein the mercaptan rich stream has a boiling point in a range of about 85° C. to about 100° C., and the at least two first mercaptan lean streams comprise a low boiling first mercaptan lean stream having a boiling point in a range of about 60° C. to about 85° C., and a high boiling mercaptan lean stream having a boiling point in a range of about 100° C. to about 220° C., and 
 wherein treating the at least the portion of the mercaptan rich stream comprises introducing the at least the portion of the mercaptan rich stream into the selective hydrogenation zone. 
 
     
     
         12 . The process of  claim 1  wherein separating at least the portion of the desulfurized stream into at least two streams comprises separating at least the portion of the desulfurized stream into at least the mercaptan rich stream and at least two mercaptan lean streams,
 wherein the mercaptan rich stream has a boiling point in a range of about 85° C. to about 100° C., and the at least two first mercaptan lean streams comprise a low boiling first mercaptan lean stream having a boiling point in a range of about 60° C. to about 85° C., and a high boiling mercaptan lean stream having a boiling point in a range of about 100° C. to about 220° C., and 
 wherein treating the at least the portion of the mercaptan rich stream comprises introducing the at least the portion of the mercaptan rich stream into an adsorption zone. 
 
     
     
         13 . The process of  claim 1  wherein separating at least the portion of the desulfurized stream into at least two streams comprises separating at least the portion of the desulfurized stream into at least the mercaptan rich stream and at least two mercaptan lean streams,
 wherein the mercaptan rich stream has a boiling point in a range of about 85° C. to about 100° C., and the at least two first mercaptan lean streams comprise a low boiling first mercaptan lean stream having a boiling point in a range of about 60° C. to about 85° C., and a high boiling mercaptan lean stream having a boiling point in a range of about 100° C. to about 220° C., and 
 wherein treating the at least the portion of the mercaptan rich stream comprising introducing the at least the portion of the mercaptan rich stream into an ionic liquid extraction zone. 
 
     
     
         14 . A process for reducing the sulfur content of full range FCC naphtha comprising:
 introducing a FCC naphtha feed into a selective hydrogenation zone in the presence of hydrogen and a hydrogenation catalyst under selective hydrogenation conditions to form a hydrogenated feed;   separating the hydrogenated feed into at least two fractions, a lighter fraction and a heavier fraction;   introducing the heavier fraction to a selective hydrodesulfurization zone in the presence of hydrogen and a hydrodesulfurization catalyst under selective hydrodesulfurization conditions to form a desulfurized stream, the desulfurized stream containing mercaptans;   separating at least a portion of the desulfurized stream into at least two streams, a mercaptan rich stream and a first mercaptan lean stream; and   treating at least a portion of the mercaptan rich stream to remove at least a portion of the mercaptan compounds to form a second mercaptan lean stream, wherein treating the at least the portion of the mercaptan rich stream comprises introducing the at least the portion of the mercaptan rich stream into at least one of a caustic extraction zone, a hydrodesulfurization reaction zone, the selective hydrogenation zone, an adsorption zone, and an ionic liquid extraction zone.   
     
     
         15 . The process of  claim 14  further comprising at least one of:
 combining the first mercaptan lean stream with the second mercaptan lean stream; and combining the lighter fraction with at least one of the first mercaptan lean stream and the second mercaptan lean stream. 
 
     
     
         16 . The process of  claim 14  wherein separating the at least the portion of the desulfurized stream into at least two streams comprises separating the at least the portion of the desulfurized stream into the mercaptan rich stream and the first mercaptan lean stream. 
     
     
         17 . The process of  claim 16  wherein the mercaptan rich stream has a boiling point about 60° C. to about 100° C. and the first mercaptan lean stream has a boiling point in a range of about 100° C. to about 220° C. 
     
     
         18 . The process of  claim 14  wherein separating the at least the portion of the desulfurized stream into at least two streams comprises separating the at least the portion of the desulfurized stream into the mercaptan rich stream and at least two first mercaptan lean streams, a low boiling first mercaptan lean stream having a boiling point range lower than a boiling point range of the mercaptan rich stream and a high boiling first mercaptan stream having a boiling point range greater than the boiling range of the mercaptan rich stream. 
     
     
         19 . The process of  claim 18  wherein the boiling point range of the mercaptan rich stream is about 85° C. to about 100° C., and the boiling point range of the low boiling first mercaptan lean stream is about 60° C. to about 85° C., and the boiling point range of the high boiling first mercaptan lean stream is about 100° C. to about 220° C. 
     
     
         20 . A process for reducing the sulfur content of full range FCC naphtha comprising:
 introducing a FCC naphtha feed into a selective hydrogenation zone in the presence of hydrogen and a hydrogenation catalyst under selective hydrogenation conditions to form a hydrogenated feed;   separating the hydrogenated feed into at least two fractions, a lighter fraction and a heavier fraction;   introducing the heavier fraction to a selective hydrodesulfurization zone in the presence of hydrogen and a hydrodesulfurization catalyst under selective hydrodesulfurization conditions to form a desulfurized stream, the desulfurized stream containing mercaptans;   separating at least a portion of the desulfurized stream into at least a mercaptan rich stream, a low boiling mercaptan lean stream having a boiling point range lower than a boiling point range of the mercaptan rich stream, and a high boiling first mercaptan stream having a boiling point range greater than the boiling range of the mercaptan rich stream; and   treating at least a portion of the mercaptan rich stream to remove at least a portion of the mercaptan compounds to form a second mercaptan lean stream, wherein treating the at least the portion of the mercaptan rich stream comprises introducing the at least the portion of the mercaptan rich stream into at least one of a caustic extraction zone, a hydrodesulfurization reaction zone, the selective hydrogenation zone, an adsorption zone, and an ionic liquid extraction zone.