NOVELTY - A crystalline silicoaluminophosphate-34 (SAPO-34) membrane is made by applying a first quantity of SAPO-34 crystalline material to a part of a surface of a porous support; preparing an aqueous SAPO-34 forming gel containing two organic templating agents; aging the gel for greater than or equal to 24 hours; contacting the porous support with the aged gel; heating the porous support and the gel to form a second quantity of SAPO-34 crystalline material on the support, thus forming a cumulative layer of SAPO-34 crystals on the surface of the support; and calcining the SAPO-34 layer to remove the templating agents.    USE - Method for manufacturing a crystalline SAPO-34 membrane (claimed) for use in gas separations.    ADVANTAGE - The method is capable of producing supported SAPO-34 membranes with improved CO2/CH4 selectivities and higher CO2 permeances as compared to separation selectivities previously reported for SAPO-34 membranes. The obtained SAPO-34 membranes have superior thermal, mechanical and chemical stability, good erosion resistance, and high pressure stability as compared to conventional polymeric membranes.    DETAILED DESCRIPTION - Manufacture of a crystalline silicoaluminophosphate-34 (SAPO-34) membrane includes:    (A) applying a first quantity of SAPO-34 crystalline material to a part of a surface of a porous support prior to a contacting step, where the first quantity of crystalline material is in the form of loose SAPO-34 crystals;    (B) preparing an aqueous SAPO-34 forming gel, where the gel comprises aluminum, phosphorus, silicon, oxygen, first and second organic templating agents and water, with the ratio of silicon to aluminum being greater than 0.1;    (C) aging the gel for greater than or equal to 24 hours;    (D) contacting the porous support with the aged gel;    (E) heating the porous support and the gel to form a second quantity of SAPO-34 crystalline material on the support, thus forming a cumulative layer of SAPO-34 crystals on the surface of the support; and    (F) calcining the SAPO-34 layer to remove the templating agents.    The gel is aged from 40-60 degrees C prior to the contacting step, or aged from 4-28 days. The porous support and the gel are heated to 453-553 degrees K for 20-25 hours. The contacting and heating steps are repeated until the SAPO layer is impermeable to nitrogen (N2) before performing the calcining step. INDEPENDENT CLAIMS are included for:    (1) a supported membrane comprising SAPO-34 crystals on a porous support made by the method; and    (2) a method of separating a first gas component from a gas mixture containing at least first and second gas components, comprising providing the SAPO-34 membrane having feed and permeate sides and being selectively permeable to the first gas component over the second gas component; applying a feed stream including the first and second gas components to the feed side; and providing a driving force sufficient for permeation of the first gas component through the membrane, thus producing a permeate stream enriched in the first gas component from the permeate side of the membrane.    A separation index of the supported membrane is greater than or equal to 5 for approximately 50/50 carbon dioxide (CO2)/methane (CH4) mixture at 295 degrees K, a feed pressure of 222 kPa and a pressure drop of 138 kPa.