Distillate production in a hydrocarbon synthesis process.

Abstract

A wax fraction from a hydrocarbon synthesis process is fractionated in a vacuum distillation column prior to any hydrocracking steps. A straight-run distillation fraction is isolated from the vacuum distillation. A heavy wax fraction from the vacuum distillation process is hydroprocessed, and a hydroprocessed distillate fraction is recovered. The straight-run distillate fraction and the hydroprocessed distillate fraction are combined to make a fraction that boils in the range of diesel fuel.

1 . A process for producing a distillate fuel, comprising;
 a. passing a heavy fraction from a hydrocarbon synthesis process to a vacuum distillation zone and recovering at least a first distillate fuel fraction and a heavy wax fraction;   b. passing the heavy wax fraction in combination with hydrogen to a hydrocracking reaction zone for cracking the carbon chain molecules in the heavy wax fraction to shorter molecules; and   c. recovering a first reaction zone effluent from the hydrocracking reaction zone.   
     
     
         2 . The process of  claim 1 , further comprising:
 a. passing a combination of the first reaction zone effluent and a light fraction from the hydrocarbon synthesis process to a hydrotreating reaction zone; and   b. recovering a second reaction zone effluent from the hydrotreating reaction zone.   
     
     
         3 . The process of  claim 2 , further comprising passing a portion of the second reaction zone effluent to an atmospheric distillation zone and recovering at least a second distillate fuel fraction. 
     
     
         4 . The process of  claim 3 , further comprising combining the first distillate fuel fraction and the second distillate fuel fraction to make a combined distillate fuel. 
     
     
         5 . The process of  claim 4 , further comprising passing the combined distillate fuel to a hydroisomerization reaction zone for decreasing the cloud point of the combined distillate fuel. 
     
     
         6 . The process of  claim 1 , further comprising:
 a. passing the first reaction zone effluent from the hydrocracking reaction zone to a hydroisomerization reaction zone and producing a hydroisomerization reaction zone effluent; and   b. passing at least a portion of the hydroisomerization reaction zone effluent to a hydrotreating reaction zone.   
     
     
         7 . A process for producing a distillate fuel from a hydrocarbon synthesis process, comprising:
 a. passing a heavy fraction from a hydrocarbon synthesis process in combination with a hydroprocessed bottoms product to a vacuum distillation zone and recovering at least a first distillate fuel and a heavy wax stream therefrom;   b. passing at least a portion of the heavy wax stream in combination with hydrogen to a hydrocracking reaction zone for cracking the carbon chain molecules in the wax product to shorter molecules, and recovering a first reaction zone effluent;   c. combining a light fraction from the hydrocarbon synthesis process with at least a portion of the first reaction zone effluent and passing the combined feed, in further combination with hydrogen, to a hydrotreating reaction zone for hydrotreating the combined feed, and recovering a second reaction zone effluent;   d. passing at least a portion of the second reaction zone effluent to an atmospheric distillation zone and recovering at least a second distillate fuel and the hydroprocessed bottoms product; and   e. combining the first distillate fuel with the second distillate fuel to form a combined distillate fuel.   
     
     
         8 . The process of  claim 7 , wherein the hydrocarbon synthesis process is a Fischer-Tropsch process. 
     
     
         9 . The process of  claim 7 , wherein the hydrocracking reaction zone contains one or more catalysts, each comprising a cracking component and a hydrogenation component on an oxide support material. 
     
     
         10 . The process of  claim 9  wherein the cracking component is selected from the group consisting of silica-alumina, Y-type zeolite, ultrastable Y-type zeolite and dealuminated zeolite. 
     
     
         11 . The process of  claim 9 , wherein the hydrogenation component comprises at least one metal component selected from the Group VIII elements and/or from the Group VI elements. 
     
     
         12 . The process of  claim 11 , wherein the Group VIII elements are selected from the group consisting of iron, cobalt, nickel, palladium and platinum. 
     
     
         13 . The process of  claim 11 , wherein the Group VI elements are selected from the group consisting of chromium, molybdenum and tungsten. 
     
     
         14 . The process of  claim 7 , wherein the hydrotreating reaction zone contains one or more catalysts, each comprising a composite of a Group VI metal or compound thereof with a Group VIII metal or compound thereof supported on a refractory base. 
     
     
         15 . The process of  claim 14 , wherein the Group VIII elements are selected from the group consisting of iron, cobalt, nickel, palladium and platinum. 
     
     
         16 . The process of  claim 14 , wherein the Group VI elements are selected from the group consisting of chromium, molybdenum and tungsten. 
     
     
         17 . The process of  claim 14 , wherein the refractory base is alumina. 
     
     
         18 . The process of  claim 7 , wherein the atmospheric distillation zone is maintained at a pressure in the range of greater than 15 psia to 150 psia. 
     
     
         19 . The process of  claim 7 , wherein the vacuum distillation zone is maintained at a pressure of less than 15 psia. 
     
     
         20 . The process of  claim 7 , wherein the combined distillate fuel has a normal boiling point range in the range of 350° F. to 750° F. 
     
     
         21 . The process of  claim 7 , wherein the combined distillate fuel is a diesel fuel. 
     
     
         22 . The process of  claim 7 , wherein the hydrocracking reaction zone and the hydrotreating reaction zone are in a single reactor vessel. 
     
     
         23 . The process of  claim 7 , wherein the hydrocracking reaction zone and the hydrotreating reaction zone are in separate reactor vessels. 
     
     
         24 . The process of  claim 7 , wherein the hydrocracking reaction zone is maintained at a pressure in the range of 200 to 4000 psig and at a temperature in the range of 600° F. to 900° F. 
     
     
         25 . The process of  claim 7 , wherein the hydrotreating reaction zone is maintained at a pressure in the range of 200 to 4000 psig and at a temperature in the range of 400° F. to 850° F.