PURPOSE: To minimize the decrease in the fluid permeability of a titled membrane and to improve sepn. performance and durabilty by heat treating a permselective hollow fiber membrane in an aq. soln. of halide of alkaline (earth) metals to decrease the moisture content thereof.
CONSTITUTION: A permselective hollow fiber membrane is heat treated in an aq. soln of a halide of alkali metals or alkaline earth metals or both thereof to decrease the moisture content thereof to 50W90% moisture content before immersion in the halide. Then the sepn. performance of the permselective hollow membrane is improved with virtually no decrease in the fluid permeability thereof and the mechanical strength of the membrane as well as the durability to heat, pressure and high salt concn. is improved.
MATSUMOTO HIROSHI
UKAI TETSUO
