Composite membrane for use in gas separation

Claim 1

A composite membrane for use in the separation of a gas from a mixture of gases which comprises: a polysulfone type resin porous membrane capable of rejecting 90% or more of dextran molecules having a weight average molecular weight of 70,000; and a styrene type resin coated on at least one surface of said polysulfone type resin porous membrane, said styrene type resin being a member selected from the group consisting of: (I) a linear polymer having a weight average molecular weight of 1×10 5 or more comprising 0 to 100 mol % of a structural unit (a), 0 to 100 mol % of structural unit (b) and 0 to 30 mol % of a structural unit (c), provided that the total amount of said structural units (a), (b) and (c) is 100 mol %, said structural unit (a) being represented by the formula ##STR15## wherein L 1 is selected from the group consisting of a hydrogen atom, a halogen atom and a straight or branched, hydrocarbon radical having 1 to 10 carbon atoms, and L 1 ' is selected from the group consisting of hydrogen atom, a halogen atom, and a straight or branched hydrocarbon radical having 1 to 6 carbon atoms, said structural unit (b) being represented by the formula ##STR16## wherein L 2 is selected from the group consisting of a hydrogen atom, halogen atom and a straight or branched hydrocarbon radical having 1 to 8 carbon atoms, said structural unit (c) being represented by the formula ##STR17## wherein X is selected from the group consisting of a hydrogen atom, halogen atom, a methyl group and a cyano group, and Y is selected from the group consisting of (i) ##STR18## wherein L 3 is selected from the group consisting of a straight or branched hydrocarbon radical having 1 to 20 carbon atoms, (ii) a cyano group, (iii) a nitro group, (iv) a pyridyl group, (v) ##STR19## wherein L 4 is selected from the group consisting of a straight or branched hydrocarbon radical having 1 to 12 carbon atoms and (vi) ##STR20## wherein L 5 and L 6 each independently are selected from the group consisting of a hydrogen atom, a straight or branched hydrocarbon radical having 1 to 12 carbon atoms, a phenyl group and a cyclohexyl group, (II) a blend polymer prepared by blending at least two different linear polymers (I) each as defined above, and (III) a crosslinked polymer selected from the group consisting of: (i) a crosslinked polymer prepared by crosslinking a linear polymer having a weight average molecular weight of 1×10 3 or more comprising 0 to 100 mol % of a structural unit (a) as defined above, 0 to 100 mol % of a structural unit (b) as defined above and 0 to 30 mol % of a structural unit (c) as defined above, provided that the total amount of said structural units (a), (b) and (c) is 100 mol %, and (ii) a crosslinked polymer prepared by crosslinking a blend polymer prepared by blending at least two different linear polymers each having a weight average moelcular weight of 1×10 3 or more, said linear polymers each comprising 0 to 100 mol % of a structural unit (a) as defined above, 0 to 100 mol % of a structural unit (b) as defined above and 0 to 30 mol % of a structural unit (c) as defined above, provided that the total amount of said structural units (a), (b) and (c) is 100 mol %, said styrene type resin having a selective gas permeability of not smaller than that of said polysulfone type resin porous membrane, said styrene type resin being coated on said polysulfone type resin porous membrane in a thickness of 5 μm or less and in an mount of at least 1.0×10 -7 g/cm 2 of said polysulfone type resin porous membrane.