Composite hollow fiber type separation membranes processes for the preparation thereof and their use

Claim 1

A process for producing a composite hollow fiber type separation membrane, comprising the steps of: (A) extruding through an annular orifice a spinning solution of (1) a matrix polymer, for forming an ultra-microporous layer and a porous layer of the hollow fiber separation membrane and (2) a pore-making polymer capable of being extracted after formation of the hollow fiber, said matrix polymer and said pore-making polymer dissolved in a common solvent, wherein the ratio of matrix polymer to pore-making polymer (by weight) is from about 100:25 to 100:200; (B) rapidly coagulating the inner surface of said hollow fiber, thereby forming an inner surface which is non-porous and flat; then (C) applying a solution of a polymer for forming a selective separation layer dissolved in a solvent to the core portion of said hollow fiber, thereby bringing said solution into contact with said non-porous inner surface of the hollow fiber; (D) after removing the excess liquid passing a gas over the thus prepared inner surface of the hollow fiber to form on the non-porous, inner surface a non-porous, dense, selective separation layer having an average thickness of 0.01-2 μ and a coefficient of variation in thickness of less than or equal to 25%; (E) contacting the outer surface of the hollow fiber with a solvent which is a non-solvent for said matrix polymer, but an effective solvent for said pore-making polymer and extracting and removing said pore making polymer, thereby forming a hollow fiber having said selective separation layer as the innermost layer of the hollow fiber, and having an ultra-microporous layer having a surface comprising pores which are not observable, even with scanning electron microscopy of 24,000 X magnification, and having a fluid permeability of at least 10 times that of said selective separation layer and a thickness of less than or equal to 0.08 μ and a porous layer comprising pores of 0.1-1μ in pore diameter except for macrovoids and having a porosity of at least 50% and a thickness of 10-500μ.