NOVELTY - Making a crystalline silicoaluminophosphate-34 (SAPO-34) membrane (I), comprises: providing a porous support having a pore size greater than about 0.1 micron; optionally, applying a first quantity of SAPO-34 crystalline material to the surface of the support, before step (e); preparing an aqueous SAPO-34 forming gel comprising an organic templating agent; aging the gel; contacting the support with the gel; heating; and calcining the SAPO-34 layer, where the gel comprises aluminum, phosphorus, silicon, oxygen, templating agent and water.    USE - (I) is useful for separating a first gas component from a gas mixture containing at least a first and a second gas component, where the first gas component is carbon dioxide and the second gas component is methane (claimed).    ADVANTAGE - The carbon dioxide/methane separation selectivity is greater than 90 (preferably 150) for an approximately 50/50 carbon dioxide/methane mixture at 295 K with a pressure differential across the membrane of 138 kPa. The permeance of carbon dioxide is greater than 3x10-7 mol/(m2 S Pa) for an approximately 50/50 carbon dioxide/methane mixture at 295 K with a pressure differential across the membrane of 138 kPa (all claimed). The process is an improved process to make (I) with improved separation selectivities. (I) has superior thermal, mechanical and chemical stability, good erosion resistance, and high pressure stability. (I) has high flux.    DETAILED DESCRIPTION - Making a crystalline silicoaluminophosphate-34 (SAPO-34) membrane, comprises: (a) providing a porous support having a pore size greater than about 0.1 micron; (b) optionally, applying a first quantity of SAPO-34 crystalline material to at least part of the surface of the porous support, before step (e), where the first quantity of crystalline material is in the form of SAPO-34 crystals; (c) preparing an aqueous SAPO-34 forming gel comprising an organic templating agent; (d) aging the gel; (e) contacting the porous support with the gel; (f) heating the porous support and the aged gel to form a second quantity of SAPO-34 crystalline material on the support, and a cumulative layer of SAPO-34 crystals on the surface of the support; and (g) calcining the SAPO-34 layer to remove the templating agent, where the gel comprises aluminum, phosphorus, silicon, oxygen, templating agent and water, with the ratio of silicon to aluminum being greater than 0.1 and less than or equal to 0.6, and during step (f) the support and the gel are heated to 453-533 K. INDEPENDENT CLAIMS are included for:    (1) a supported membrane made by the process; and    (2) a process for separating a first gas component from a gas mixture containing at least a first and a second gas component, comprising: providing (I) having a feed and a permeate side and being selectively permeable to the first gas component over the second gas component; applying a feed stream including the first and the second gas components to the feed side of the membrane; and providing a driving force sufficient for permeation of the first gas component through the membrane, to produce a permeate stream enriched in the first gas component from the permeate side of the membrane.