JPH0419891B

PURPOSE:To obtain a composite membrane prevented from the delamination of a membrane layer and excellent in gas separation capacity and gas permeability, by interposing an extremely thin membrane crosslinked by a tetrafunctional or more silane or silaxane crosslinking agent between a porous support and an extremely thin membrane. CONSTITUTION:A tetrafunctional or more silane or siloxane crosslinking agent, for example, tetraacetoxysilane or ethyl polysilicate, polyorganosiloxane and a catalyst are dissolved in a non-aqueous solvent. The resulting solution is thinly and uniformly applied to a porous support and dried by hot air to form a composite membrane. Next, a solution, which is prepared by dissolving a polymer having a high gas separation property such as poly(4-methylpentene-1) in cyclohexane, is develoved on a water surface to form a membrane which is, in turn, supported by the surface of the membrane of the pre-fabricated polyorganosiloxane composite membrane to obtain a gas separating composite membrane.