Process for separating higher hydrocarbons from natural or produced gas streams

A gas separation process, comprising the steps of:

• passing a first gas mixture comprising methane as its major constituent, and further comprising at least one gas from the group consisting of ethane and heavier hydrocarbons, across the feed side of a membrane having a feed side and a permeate side, said membrane comprising a microporous support layer and an ultrathin permselective layer, and wherein said membrane has a selectivity for propane over methane of 8 or more;
• withdrawing from said permeate side a second gas mixture enriched in at least one gas from the group consisting of ethane and heavier hydrocarbons compared with said first gas mixture, wherein the ratio of the volume flows of said second gas mixture and said first gas mixture is less than about 27%, and
• withdrawing from said feed side a third gas mixture enriched in methane compared with said first gas mixture;
• wherein the proportion of methane retained on said feed side in said third gas mixture is at least about 80%.

A process for controlling the Btu value of a gas stream, comprising the steps of:

• passing a first gas mixture comprising methane as its major constituent, and further comprising at least one gas from the group consisting of ethane and heavier hydrocarbons, and having a Btu value greater than 1050 Btu/cubic foot, across the feed side of a membrane having a feed side and a permeate side, said membrane comprising a microporous support layer and an ultrathin permselective layer, and wherein said membrane has a selectivity for propane over methane of 8 or more;
• withdrawing from said permeate side a second gas mixture enriched in at least one gas from the group consisting of ethane and heavier hydrocarbons compared with said first gas mixture, wherein the ratio of the volume flows of said second gas mixture and said first gas mixture is less than about 27%;
• and
• withdrawing from said feed side a third gas mixture enriched in methane compared with said first gas mixture, and having a Btu value less than 1050 Btu/cubic foot.

A hydrocarbon recovery process, comprising the steps of:

• passing a first gas mixture comprising methane as its major constituent, and further comprising at least one gas from the group consisting of ethane and heavier hydrocarbons, across the feed side of a membrane having a feed side and a permeate side, wherein said membrane has a selectivity for propane over methane of 8 or more;
• withdrawing from said permeate side a second gas mixture enriched in at least one gas from the group consisting of ethane and heavier hydrocarbons compared with said first gas mixture, wherein the ratio of the volume flows of said second gas mixture and said first gas mixture is less than about 27%;
• and
• withdrawing from said feed side a third gas mixture enriched in methane compared with said first gas mixture, wherein the proportion of said one gas retained on said feed side in said third gas mixture is less than 30%.