Process to Maximize Methane Content in Natural Gas Stream

Abstract

The present invention relates to a hydrogenolysis process and catalyst for conversion of ethane to methane in a natural gas stream when such streams contain large quantities of ethane. Such natural gas streams include the product of the in situ treatment of oil shale to produce oil and gas. Hydrogenolysis catalysts have been identified that produce high yields of ethane at low light-off temperatures.

1 . A process for increasing methane content in a natural gas feed stream comprising:
 a) providing a gaseous feed stream comprising a first quantity of methane, ethane, propane and hydrogen wherein said ethane and propane comprise about 6 to 30 vol-% of said gaseous feed stream; and   b) sending said gaseous feed stream to a conversion unit wherein a hydrogenolysis reaction takes place wherein said natural gas feed stream is contacted with at least one hydrogenolysis catalyst at a temperature and pressure sufficient to substantially convert said ethane to a second quantity of methane.   
     
     
         2 . The process of  claim 1  further comprising separating said first quantity of methane and said second quantity of methane from other components within said gaseous feed stream to form a purified natural gas feed stream. 
     
     
         3 . The process of  claim 1  wherein said hydrogen and said ethane are present in a molar ratio of about 0.8:1 to 10:1. 
     
     
         4 . The process of  claim 1  wherein said feed stream further comprises carbon oxides. 
     
     
         5 . The process of  claim 1  wherein said feed stream further comprises higher hydrocarbons than ethane. 
     
     
         6 . The process of  claim 1  wherein said hydrogenolysis catalyst comprises at least one transition metal selected from the group consisting of nickel, cobalt, osmium, iridium, rhodium, ruthenium, rhenium and iron on a metal oxide support. 
     
     
         7 . The process of  claim 1  wherein said first quantity of methane is separated from said gaseous feed stream before said gaseous feed stream is sent to said conversion unit. 
     
     
         8 . The process of  claim 1  wherein at least 50% of said ethane and propane are converted to methane. 
     
     
         9 . The process of  claim 1  wherein at least 90% of said ethane and propane are converted to methane. 
     
     
         10 . The process of  claim 1  wherein a portion of said CO and CO 2  are converted to methane within said conversion unit. 
     
     
         11 . The process of  claim 1  wherein after said hydrogenolysis reaction takes place, carbon oxides are added to a resulting gaseous stream and then the resulting gaseous stream is subjected to a methanation reaction to react said carbon oxides with hydrogen to produce a third quantity of methane. 
     
     
         12 . The process of  claim 1  wherein said natural gas feed stream is a product of thermal treatment of oil or carbon containing rocks or sand. 
     
     
         13 . The process of  claim 1  wherein said hydrogenolysis reaction has a light-off temperature between about 300° and 375° C. 
     
     
         14 . The process of  claim 1  wherein said temperature for conversion of said higher carbon hydrocarbons than methane to methane is from about 2500 to 600° C. 
     
     
         15 . The process of  claim 1  wherein said gaseous feed stream comprises about 10 to 25 vol-% combined ethane and propane. 
     
     
         16 . The process of  claim 1  wherein said gaseous feed stream comprises about 20 to 25 vol-% combined ethane and propane. 
     
     
         17 . The process of  claim 1  wherein said gaseous feed stream is sent to at least two of said conversion units sequentially. 
     
     
         18 . The process of  claim 17  wherein said gaseous feed stream is divided into a first gaseous feed stream and a second gaseous feed stream prior to passing to said at least two of said conversion units, said first gaseous feed stream is heated to a hydrogenolysis reaction temperature, then said first gaseous feed stream is sent to a first conversion unit to produce a first enhanced methane stream, then said first enhanced methane stream is cooled upon being mixed with said second gaseous feed stream to form a combined gaseous feed stream, and then said combined gaseous feed stream is sent to a second conversion unit to be converted to a second enhanced methane stream. 
     
     
         19 . The process of  claim 1  further comprising sending said gaseous feed stream to a reactor to convert said carbon dioxide and carbon monoxide to methane. 
     
     
         20 . The process of  claim 1  wherein said purified natural gas stream is sent into a natural gas pipeline to be transported.