Separation of CO₂ and CH₄ through two types of polyimide membrane

Two asymmetric polyimide membranes that have a thermal stability up to 550 K and good resistance to solvents were prepared. Some membrane-forming conditions such as coagulation solution, evaporation and immersion time were examined. Regarding the coagulation solution, a water-methanol mixture gives good membranes in eleven solutions tested. The permeabilities of two asymmetric polyimide membranes for CO₂ and CH₄ pure gases were determined at 25°C and at applied pressures up to 0.25 MPa. The prepared polyimide membranes, 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)-4,4′-diaminodiphenyl ether (ODA) and 1,2,3,4-butanetetracarboxylic dianhydride (BDA)-4,4′-diaminodiphenyl ether (ODA) exhibited higher selectivity and permeability for CO₂/CH₄.