NOVELTY - Preparation (P1) of a crystalline silicoaluminophosphate (SAPO) membrane (M1) involves: (A) providing a porous support having a first and a second side; (B) preparing aqueous SAPO forming membrane gel comprising aluminum, phosphorus, silicon, oxygen, organic templating agent, and water; (C) contacting at least one side of support with membrane forming gel; (D) heating support and membrane gel to form membrane layer of SAPO crystals on porous support; and (E) heating membrane layer at 600-1050 degrees K in oxygen-reduced or oxygen-free atmosphere to remove templating agent from the membrane layer.    USE - For the preparation of a crystalline silicoaluminophosphate (SAPO) membrane, useful for separating a gas component from a gas mixture containing at least two gas components, preferably for separating carbon dioxide from the mixture of carbon dioxide and methane (claimed), useful for large scale separations in petrochemical and chemical industries; for natural gas sweetening and carbon dioxide sequestration.    ADVANTAGE - The membrane has a carbon dioxide/methane (CO2/CH4) separation selectivity of greater than or equal to 50 (preferably greater than or equal to 55) for an approximately 50/50 molar CO2/CH4 mixture at room temperature with a feed pressure of 4.6 MPa and a permeate pressure of 84 kPa. The membrane has a CO2 permeance of at least 7.5x 10-7 (preferably at least 8.2x 10-7) mol/(m2.second.Pa) for an approximately 50/50 molar CO2/CH4 mixture at room temperature with a feed pressure of 4.6 MPa and a permeate pressure of 84 kPa. The membrane has at least 30% greater CO2 permeance over membranes prepared in the same manner except that the templating agent was removed in the presence of O2. The membrane has improved performance at high temperatures.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) crystalline silicoaluminophosphate (SAPO) membrane prepared by the process (P1); and    (2) separating (P2) a first gas component from a gas mixture containing at least a first and a second gas component, involving: (a) providing the crystalline (SAPO) membrane having a feed and a permeate side and being selectively permeable to the first gas component over the second gas component, where the SAPO membrane is made by the process (P1), (b) applying a feed stream including the first and the second gas components to the feed side of the membrane; and (c) providing a driving force 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.