Production of low sulfur syngas from natural gas with C4+/C5+ hydrocarbon recovery

Abstract

Sour natural gas is processed to remove the sulfur compounds and recover C 4+ /C 5+ hydrocarbons by scrubbing the gas with an amine solution to remove most of the sulfur, followed cooling the gas to remove C 4+ /C 5+ hydrocarbons and more sulfur compounds as liquid condensate to produce a gas having less than 20 vppm of total sulfur. The condensate is sent to a fractionator to recover the C 4+ /C 5+ hydrocarbons. The sulfur and hydrocarbon reduced gas is contacted first with zinc oxide and then nickel, to produce a gas having less than 10 vppb of total sulfur which is passed into a synthesis gas generating unit to form a very low sulfur synthesis gas comprising a mixture of H 2 and CO. This synthesis gas is useful for hydrocarbon synthesis with increased life of the hydrocarbon synthesis catalyst and greater hydrocarbon production from the hydrocarbon synthesis reactor. Contacting the synthesis gas with zinc oxide further reduces the sulfur content to below 3 vppb.

What is claimed is:  
     
         1 . A process for removing sulfur from sour natural gas containing C 4+ /C 5+  hydrocarbons, with recovery of said hydrocarbons, comprises: 
 (i) contacting said sour gas with a liquid sulfur absorbent to remove most of the sulfur and form a sulfur reduced gas;  
 (ii) cooling said sulfur reduced gas to condense more sulfur compounds and said C 4+ /C 5+  hydrocarbons as liquid;  
 (iii) separating said liquid from said gas and recovering said C 3+ /C 4+  hydrocarbons to produce a sulfur and hydrocarbon reduced gas, and  
 (iv) contacting the said sulfur and hydrocarbon reduced gas with one or more sulfur removing adsorbents or absorbents to produce a gas having less than 0.1 vppm of sulfur.  
 
     
     
         2 . A process according to claim one wherein said sulfur includes H 2 S and organic sulfur compounds.  
     
     
         3 . A process according to  claim 2  wherein CO 2  is also removed from said gas with said liquid absorbent.  
     
     
         4 . A process according to  claim 5  wherein said liquid absorbent comprises a hindered amine.  
     
     
         5 . A process according to  claim 4  wherein said organic sulfur compounds include mercaptans and COS.  
     
     
         6 . A process according to  claim 5  wherein said sulfur and hydrocarbon reduced gas is contacted first with zinc oxide and then nickel absorbents to produce said gas having less than 0.1 vppm of sulfur.  
     
     
         7 . A process according to  claim 6  wherein said gas has less than 80 vppb of sulfur.  
     
     
         8 . A process according to  claim 7  wherein said cooling is accomplished by Joule-Thomson expansion of said gas.  
     
     
         9 . A process according to  claim 7  wherein said gas is passed as hydrocarbon feed into a synthesis gas generator to form a synthesis gas comprising a mixture of H 2  and CO.  
     
     
         10 . A process for producing a synthesis gas comprising a mixture of H 2  and CO from a sour natural gas comprising mostly methane which also contains C 4+ /C 5+  hydrocarbons, CO 2 , H 2 S, C 2+  mercaptans and COS, with recovery of said C 4+ /C 5+  hydrocarbons from said gas, which comprises: 
 (a) contacting said gas with an aqueous amine solution to remove most of said H 2 S and organic sulfur compounds to produce a sulfur reduced gas containing less than 2 vppm of total sulfur compounds;  
 (b) cooling said gas to a temperature sufficient to condense said C 4+ /C 5+  hydrocarbons and some of the remaining sulfur compounds to liquids;  
 (c) separating said condensed liquids from said cool gas;  
 (d) recovering said C 4+ /C 5+  hydrocarbons;  
 (e) heating said cool gas to a temperature of at least about 100° F;  
 (f) contacting said heated gas with ZnO and then with nickel to remove more sulfur compounds from said gas and produce a very low sulfur content gas comprising methane which contains less than 0.1 vppm of sulfur compounds;  
 (g) passing said gas produced in (f) into a synthesis gas generating zone in which it reacts with oxygen to form said synthesis gas.  
 
     
     
         11 . A process according to  claim 10  wherein said gas reacts with oxygen and steam in said synthesis gas generating zone to produce said syngas.  
     
     
         12 . A process according to  claim 11  wherein said synthesis gas is contacted with zinc oxide to reduce the sulfur content to less than 10 vppm.  
     
     
         13 . A process according to  claim 12  wherein said synthesis gas is reacted in the presence of a sulfur sensitive hydrocarbon synthesis catalyst at reaction conditions effective to form hydrocarbons, at least a portion of which are solid at standard conditions of room temperature and pressure and wherein said catalyst has a half life of at least 30 days.  
     
     
         14 . A process according to  claim 13  wherein at least a portion of said synthesized hydrocarbons are upgraded by one or more hydroconversion operations.  
     
     
         15 . A process according to  claim 14  wherein said sulfur content of said syngas is less than 3 vppb and wherein said hydrocarbon synthesis catalyst half life is at least 150 days.  
     
     
         16 . A hydrocarbon synthesis process which comprises reacting a synthesis gas comprising a mixture of H 2  and CO in the presence of a sulfur sensitive hydrocarbon synthesis catalyst at conditions effective to form hydrocarbons, at least a portion of which are solid at standard conditions of room temperature and pressure, in which said gas has a sulfur content of less than 10 vppb and wherein said catalyst has a half life of greater than 30 days.  
     
     
         17 . A process according to  claim 16  wherein at least a portion of said said hydrocarbons are upgraded to more valuable product by one or more hydroconversion operations.  
     
     
         18 . A process according to  claim 17  wherein said catalyst half life is at least 80 days.  
     
     
         19 . A process according to  claim 18  wherein said catalyst half life is at least 150 days.  
     
     
         20 . A process according to  claim 19  wherein said synthesis gas has a sulfur content of less than 3 vppb.