NOVELTY - A membrane comprises a cured product of a silicone composition containing a silicone-polyether copolymer having curable silicon-bonded groups, and free-standing unsupported membrane or a supported membrane comprising a porous or permeable substrate. The membrane is provided on the substrate.    USE - Membrane is used for separation of gas components in feed gas mixture (claimed). Uses include but are not limited to recovery of hydrogen gas in ammonia synthesis, recovery of hydrogen in petroleum refining, separation of methane from other components in biogas synthesis, enrichment of air with oxygen for medical applications, removal of water vapor from air and natural gas, removal of carbon dioxide from natural gas and biogas, removal of entrained gases from liquids, introduction of water vapor for humidification, and carbon-capture applications.    ADVANTAGE - The membrane has excellent carbon dioxide-methane and carbon dioxide-nitrogen selectivity, carbon dioxide permeability, physical strength, durability, rheological stability and oxidative stability. The carbon dioxide is effectively and quickly separated from mixture of gas, with high purity using the membrane.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method for separating gas components in feed gas mixture, which involves contacting side (325) of membrane (320) comprising a cured product of a silicone composition with a feed gas mixture (301) comprising gas component (C1) or gas component (C2), and producing a permeate gas mixture (340) on a side (330) of the membrane and a retentate gas mixture (335) on the side (325) of the membrane. The permeate gas mixture (340) is enriched with the gas component (C1). The retentate gas mixture is depleted in the gas component (C1). The silicone composition comprises a silicone-polyether copolymer having curable silicon-bonded groups.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of membrane separation system.    Feed gas mixture (301)    Membrane (320)    Sides (325, 330)    Retentate gas mixture (335)    Permeate gas mixture (340)