SEPARATING MEMBRANE EXCELLENT IN ACID RESISTANCE

PURPOSE:To enhance the acid resistance of a membrane by a method wherein a furan resin is uniformed being deposited on the inside and outside surfaces of a separating membrane including a PVA-based polymer as a base and also on the inside surfaces of pores of the membrane. CONSTITUTION:The separating membrane in which the base consists of a PVA polymer having a microstructure with an average pore diameter of 0.01-1mu is impregnated with a solution of a furfuryl alcohol monomer or a monomeric mixture of furfuryl alcohol and furfural, and the solution thus impregnated is hardened so that the furan resin is uniformly deposited on the inside and outside surfaces of the membrane and the inside surfaces of the pores of the membrane, in an amount of 5-90wt% of the base. The hardening of the furan resin is effected by heating in the presence of sulfuric acid, nitric acid, phosphoric acid, Lewis acid or the like as a condensation catalyst. The monomer is used by dissolving it in a solvent prepared by mixing water-soluble polymers such as polyethylene glycol. The membrane has its acid resistance enhanced without sacrificing permeability performance and is excellent in strength and Young's modulus.