TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The permeate gas mixture comprises carbon dioxide.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The feed gas mixture comprises carbon dioxide and methane.    TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The silicone composition is a hydrosilylation-curable silicone composition comprising a silicone-polyether copolymer having two or more silicon-bonded hydrogen atoms per molecule, a crosslinking agent having two or more aliphatic unsaturated carbon-carbon bonds per molecule and a hydrosilylation catalyst. The ratio of the number of moles of silicon-bonded hydrogen atoms in the organohydrogenpolysiloxane with respect to number of moles of aliphatic unsaturated carbon-carbon bonds in the crosslinking agent is 0.1-20. The crosslinking agent is organic compound(s) having two or more aliphatic unsaturated carbon-carbon bonds per molecule, organosilane(s) having two or more silicon-bonded aliphatic unsaturated carbon-carbon bond-containing groups per molecule, silicone resin(s) having two or more silicon-bonded aliphatic unsaturated carbon-carbon bond-containing groups per molecule, and/or organosiloxane(s) having two or more silicon-bonded aliphatic unsaturated carbon-carbon bond-containing groups per molecule. The silicone-polyether copolymer is linear block copolymer of formula: X(R12SiO(R12SiO)mR12Si-R2-O(CnH2nO)p-R2-)q(R12SiO)rR12SiX, or graft copolymer, preferably graft copolymer. The graft copolymer comprises 0-99 mol% siloxy units of formula: R12SiO2/2 (I), 1-100 mol% siloxy units of formula: R1ESiO2/2 (II), 0-80 mol% siloxy units of formula: HR1SiO2/2 (III), and 0-66 mol% siloxy units of formula: R13SiO1/2 (IV). The silicone composition is an epoxy/amine-curable silicone composition comprising a silicone-polyether copolymer having an average of at least two silicon-bonded epoxy-substituted organic groups per molecule and a polyamine, or a condensation-curable silicone composition comprising a silicone-polyether copolymer having an average of at least two silicon-bonded hydrogen atoms, hydroxy groups, or hydrolyzable groups per molecule, and a condensation catalyst.R1=1-10C (halo)hydrocarbyl;R2=1-10C hydrocarbylene;X=curable silicon-bonded group chosen from H, hydroxy, hydrolyzable group, radiation-curable group, free radical-curable group, epoxide-containing group and/or aliphatic unsaturated carbon-carbon bond-containing group;m,r=0-100;n=2-4;p,q=1-100;E=-R2O(CnH2nO)pR3 or group of formula (i);andR3=R1, H, or curable group which makes E as silicon-bonded curable group.Preferred Process: During separation of gas components in feed gas mixture, a combustible output stream comprising portion(s) of the retentate gas mixture and portion(s) of the feed gas mixture is generated. The combustible output stream comprises 20-100 volume/volume% methane. The separation of gas components in feed gas mixture further involves burning permeate in a gas turbine generator, contacting an additional membrane which is a cured product of the silicone composition with at least one of the retentate gas mixture and the permeate gas mixture, contacting primary side of a secondary membrane with portion(s) of the primary retentate gas mixture to produce a secondary permeate gas mixture on secondary side of the secondary membrane and secondary retentate gas mixture on the primary side of the secondary membrane, contacting primary side of a tertiary membrane comprising cured product of a silicone composition with portion(s) of retentate gas mixtures or permeate gas mixtures.