Light olefin oligomerization process for the production of liquid fuels from paraffins

Abstract

A process and apparatus are presented for the conversion of light paraffins to heavier liquid fuels or distillate. The process and apparatus includes conversion of a paraffin stream to an olefinic stream. The olefinic stream is passed through a reactor zone to convert the olefins to heavier hydrocarbons, including branched paraffins and branched olefins. The process includes recycling a portion of the product to the reactors for controlling the heat and reaction rate of the dimerization or oligomerization process.

1 . A process for converting light paraffins to a liquid fuel, comprising:
 passing a light paraffins stream to a dehydrogenation zone to generate a first process stream comprising light olefins;   passing the first process stream as at least a portion of an oligomerization feed stream to an oligomerization zone to generate a second process stream comprising C 5 + olefins;   passing the second process stream to a second fractionation zone to generate an overhead third process stream comprising C 5 − hydrocarbons, and a bottoms fourth process stream, comprising olefinic C 5 + hydrocarbons;   passing the fourth stream to a third fractionation zone to generate an overhead fifth process stream, comprising a gasoline product, and a bottoms sixth process stream, comprising a distillate product, and;   recycling at least a portion of the third process stream back to the dehydrogenation zone as at least a part of the light paraffins stream.   
     
     
         2 . The process of  claim 1  wherein at least a portion of either the fourth process stream or the sixth process stream are recycled to the oligomerization zone as a portion of the oligomerization feed stream. 
     
     
         3 . The process of  claim 1  wherein the oligomerization feed stream comprises about 5 to about 80 wt % olefins. 
     
     
         4 . The process of  claim 3  wherein the light olefin concentration in the oligomerization feed stream is between about 10 wt % and about 40 wt % of the feed. 
     
     
         5 . The process of  claim 1  wherein at least a portion of the sixth process stream is passed to a first hydrogenation zone to generate a seventh process stream comprising a distillate with less than 0.1 wt % alkenes. 
     
     
         6 . The process of  claim 1  further comprising, before passing the light paraffins stream to the dehydrogenation zone, passing the light paraffins stream to a first fractionation zone comprising a deisobutanizer column to generate an overhead stream comprising isobutane which is passed to the dehydrogenation zone as at least a portion of the light paraffins stream. 
     
     
         7 . The process of  claim 6  further comprising passing the light paraffins stream to a hydrogenation zone prior to being passed to the first fractionation zone comprising a deisobutanizer column. 
     
     
         8 . The process of  claim 1  further comprising, prior to recycling at least a part of the third process stream to the dehydrogenation zone, passing the third process stream to a hydrogenation zone to generate a light paraffins stream. 
     
     
         9 . The process of  claim 1  wherein the oligomerization zone contains an oligomerization catalyst comprising a zeolite with a framework having a ten-ring pore structure. 
     
     
         10 . The process of  claim 9  wherein the oligomerization catalyst comprising a zeolite having a ten-ring pore structure comprises a uni-dimensional pore structure. 
     
     
         11 . The process of  claim 1  wherein the conditions in the dehydrogenation zone include an operating temperature in the range of from about 500° C. to about 700° C., an operating pressure of from about 7 to about 150 psig and a liquid hourly space velocity of from about 0.5 to about 50. 
     
     
         12 . The process of  claim 1  wherein the oligomerization zone comprises one or more reactors and where each oligomerization reactor should be operated to allow the temperature at the outlet to be over about 25° C. greater than the temperature at the inlet. 
     
     
         13 . The process of  claim 1  wherein the conditions in the oligomerization zone include an operating pressure of between about 2.1 MPa and about 10.5 MPa, a maximum bed temperature of between about 140° and about 300° C., a space velocity of between about 0.5 and about 5 hr−1 and where the reaction conditions are set to keep the reactants in the liquid phase. 
     
     
         14 . The process of  claim 1  wherein conversion of light olefins across the oligomerization zone is greater than 90 wt %. 
     
     
         15 . A process for converting light paraffins to a liquid fuel, comprising:
 passing a light paraffin stream to a fractionation zone comprising a deisobutanizer column to generate an overhead stream substantially comprising isobutane;   passing the overhead stream to a dehydrogenation zone to generate a first process stream comprising light olefins;   passing the first process stream as at least a portion of an oligomerization feed stream to an oligomerization zone to generate a second process stream comprising C 5 +olefins;   passing the second process stream to a second fractionation zone to generate an overhead third process stream, comprising C 5 − hydrocarbons, and a bottoms fourth process stream, comprising olefinic C 5 + hydrocarbons;   passing the fourth stream to a third fractionation zone to generate an overhead fifth process stream, comprising a gasoline product, and a bottoms sixth process stream, comprising a distillate product; and   recycling at least a portion of the third process stream back to the dehydrogenation zone as at least a part of the light paraffins stream.   
     
     
         16 . The process of  claim 15  wherein the light olefins comprising the first process stream substantially comprise isobutene. 
     
     
         17 . The process of  claim 15  wherein at least a portion of either the fourth process stream or the sixth process stream are recycled to the oligomerization zone as a portion of the oligomerization feed stream. 
     
     
         18 . A process for converting light paraffins to a liquid fuel, comprising:
 passing a light paraffin stream to a first fractionation zone comprising a deisobutanizer column to generate an overhead stream comprising isobutane;   passing the overhead stream to a dehydrogenation zone to generate a first process stream comprising light olefins;   passing the first process stream as at least a portion of an oligomerization feed stream to an oligomerization zone to generate a second process stream comprising C 5 + olefins;   passing the second process stream to a second fractionation zone to generate an overhead third process stream, comprising C 5 − hydrocarbons, and a bottoms fourth process stream, comprising olefinic C 5 + hydrocarbons;   passing the fourth process stream to a third fractionation zone to generate an overhead fifth process stream, comprising a gasoline product, and a bottoms sixth process stream, comprising a distillate product; and   recycling at least a portion of the third process stream to the first fractionation zone.   
     
     
         19 . The process of  claim 18  wherein the light paraffins stream comprises C 3  and C 4  hydrocarbons and the overhead stream from the first fractionation zone comprises propane and isobutane. 
     
     
         20 . The process of  claim 19  further comprising separating the second process stream into a C 3 − overhead stream and a C 4 + bottoms stream and passing the C 4 + bottoms stream to the second fractionation zone to generate the third and fourth process streams.