Process and system for reducing the olefin content of a fischer-tropsch product stream

Abstract

A method is provided for converting synthesis gas to liquid hydrocarbon mixtures useful as distillate fuel and/or lube base oil. The synthesis gas is contacted with a synthesis gas conversion catalyst comprising a Fischer-Tropsch synthesis component in an upstream catalyst bed thereby producing an intermediate hydrocarbon mixture containing olefins and C 21+ normal paraffins. The intermediate hydrocarbon mixture is subsequently contacted with a hydroisomerization catalyst and an olefin saturation catalyst, thereby resulting in a product containing no greater than about 25 wt % olefins and containing no greater than about 5 wt % C 21+ normal paraffins. The hydroisomerization and olefin saturation catalysts may be in separate beds or mixed in a single bed downstream of the synthesis gas conversion catalyst.

1 . A process for converting synthesis gas to a hydrocarbon mixture comprising contacting a feed comprising a mixture of carbon monoxide and hydrogen with, in sequence:
 a. a synthesis gas conversion catalyst in an upstream bed, wherein a first intermediate hydrocarbon mixture containing olefins and C 21+  normal paraffins is formed over the synthesis gas conversion catalyst,   b. a hydroisomerization catalyst containing a metal promoter and an acidic component in an intermediate catalyst bed downstream of the upstream catalyst bed, wherein said C 21+  normal paraffins of the first intermediate hydrocarbon mixture are hydroisomerized over the hydroisomerization catalyst thus forming a second intermediate hydrocarbon mixture containing olefins and no greater than about 5 wt % C 21+  normal paraffins, and   c. an olefin saturation catalyst in a downstream catalyst bed downstream of the intermediate catalyst bed, wherein said olefins are saturated over the olefin saturation catalyst,   thereby resulting in a final hydrocarbon mixture containing no greater than about 25 wt % olefins and containing no greater than about 5 wt % C 21+  normal paraffins.   
     
     
         2 . The process of  claim 1  wherein the final hydrocarbon mixture contains no greater than about 5 wt % olefins. 
     
     
         3 . The process of  claim 1  wherein the final hydrocarbon mixture contains essentially no olefins. 
     
     
         4 . The process of  claim 1  wherein the upstream bed and the intermediate beds are within a single reactor and have an essentially common reactor temperature and an essentially common reactor pressure. 
     
     
         5 . The process of  claim 4  wherein the single reactor further comprises the downstream bed. 
     
     
         6 . The process of  claim 1  wherein the synthesis gas conversion catalyst comprises cobalt, iron or ruthenium on a solid oxide support. 
     
     
         7 . The process of  claim 6  wherein the solid oxide support is selected from the group consisting of alumina, silica, titania and mixtures thereof. 
     
     
         8 . The process of  claim 1  wherein the hydroisomerization catalyst comprises a zeolite of the SSZ-32 family. 
     
     
         9 . The process of  claim 1  wherein the intermediate bed further comprises a hydrocracking catalyst selected from the group consisting of amorphous silica-alumina, tungstated zirconia, zeolitic molecular sieve and non-zeolitic crystalline molecular sieve. 
     
     
         10 . The process of  claim 1  wherein the hydroisomerization catalyst further comprises a metal promoter selected from the group consisting of cobalt, nickel, copper, ruthenium, rhodium, rhenium, palladium, silver, osmium, iridium, platinum, gold, molybdenum, tungsten, and oxides, and combinations thereof. 
     
     
         11 . The process of  claim 11  wherein the hydrocracking catalyst further comprises a metal promoter selected from the group consisting of cobalt, nickel, copper, ruthenium, rhodium, rhenium, palladium, silver, osmium, iridium, platinum, gold, molybdenum, tungsten, and oxides, and combinations thereof. 
     
     
         12 . The process of  claim 1  wherein the synthesis gas conversion catalyst further comprises a promoter selected from the group consisting of ruthenium, rhenium, platinum, palladium, gold, and silver. 
     
     
         13 . The process of  claim 1  wherein the gaseous hourly space velocity is between about 100 and about 5000 volumes of gas per volume of catalyst per hour. 
     
     
         14 . The process of  claim 4  wherein the reactor pressure is between about 3 atmospheres and about 35 atmospheres. 
     
     
         15 . The process of  claim 4  wherein process water is not separated from the reactor during the hydroisomerization of said C 21+  normal paraffins. 
     
     
         16 . The process of  claim 4  wherein no hydrogen in addition to the mixture of carbon monoxide and hydrogen is added to the reactor. 
     
     
         17 . The process of  claim 1  wherein the hydrocarbon mixture is substantially free of solid wax at ambient conditions. 
     
     
         18 . The process of  claim 1  wherein the hydrocarbon mixture has an isomerized C 21+  paraffin concentration of at least 30 weight % based on the weight of the C 21+  fraction. 
     
     
         19 . The process of  claim 1  wherein the hydrocarbon mixture has a cloud point no greater than 15° C. 
     
     
         20 . The process of  claim 1  wherein between the intermediate catalyst bed and the downstream catalyst bed, the second intermediate hydrocarbon mixture is passed through a separator and separated into gas which is recycled to the upstream catalyst bed, water which is removed and liquid hydrocarbons which are passed to the downstream catalyst bed. 
     
     
         21 . The process of  claim 4  wherein the single reactor is a multi-tubular fixed bed reactor. 
     
     
         22 . The process of  claim 1  wherein the olefin saturation catalyst is selected from the group consisting of metals selected from Group IB noble metals and Group VIII noble metals and combinations thereof. 
     
     
         23 . The process of  claim 1  wherein the olefin saturation catalyst is selected from the group consisting of platinum, palladium, rhodium, iridium, silver, osmium and gold, and combinations thereof. 
     
     
         24 . The process of  claim 20  wherein the olefin saturation catalyst is selected from the group consisting of metals selected from Group VIII noble and non-noble metals and Group VIB metals, and combinations thereof. 
     
     
         25 . The process of  claim 20  wherein the olefin saturation catalyst is selected from the group consisting of molybdenum, tungsten, nickel, iron, zinc, copper, lead, cobalt, nickel-molybdenum, cobalt-molybdenum, nickel-tungsten, and cobalt-tungsten. 
     
     
         26 . The process of  claim 20  wherein the olefin saturation catalyst comprises a metal sulfide. 
     
     
         27 . The process of  claim 1  wherein the olefin saturation catalyst comprises a refractory inorganic oxide support. 
     
     
         28 . The process of  claim 27  wherein the refractory inorganic oxide support comprises a zeolite. 
     
     
         29 . The process of  claim 1  wherein the olefin saturation catalyst comprises a zeolite comprising SSZ-32. 
     
     
         30 . The process of  claim 1  wherein the upstream catalyst bed temperature is between about 160° C. and about 260° C. 
     
     
         31 . The process of  claim 1  wherein the upstream catalyst bed temperature is between about 175° C. and about 250° C. 
     
     
         32 . The process of  claim 1  wherein the upstream catalyst bed temperature is between about 185° C. and about 235° C. 
     
     
         33 . The process of  claim 4  wherein the temperature of the upstream catalyst bed and the temperature of the intermediate catalyst bed differ by no more than about 20° C. 
     
     
         34 . The process of  claim 1  wherein the final hydrocarbon mixture produced comprises:
 0-20 wt % CH 4 ; 
 0-20 wt % C 2 -C 4 ; and 
 60-95 wt % C 5+ . 
 
     
     
         35 . A process for converting synthesis gas to a hydrocarbon mixture comprising contacting a feed comprising a mixture of carbon monoxide and hydrogen with, in sequence:
 a. a synthesis gas conversion catalyst in an upstream bed, wherein an intermediate hydrocarbon mixture containing olefins and C 21+  normal paraffins is formed over the synthesis gas conversion catalyst, and   b. a mixture of an olefin saturation catalyst and a hydroisomerization catalyst containing a metal promoter and an acidic component in a downstream catalyst bed, whereby said C 21+  normal paraffins of the intermediate hydrocarbon mixture are hydroisomerized and said olefins are saturated thus forming a hydrocarbon mixture containing no greater than about 25 wt % olefins and no greater than about 5 wt % C 21+  normal paraffins.