PURPOSE: To modify a porous membrane composed of a high-molecular polymer into a separation membrane having excellent separation performance, by depositing a trace amount of a specified modifying org. solvent on said porous membrane and then removing said solvent.
CONSTITUTION: A trace amount of a modifying org. solvent is deposited on the entire surface of a porous membrane composed of a high-molecular polymer such as an arom. polyimide or PVA, said solvent being selected from a dissolving org. solvent such as phenol or 3-chlorophenol capable of dissolving at least 1wt% high-molecular polymer constituting said membrane and a shrinking org. solvent such as dimethylformamide or aniline capable of shrinking said membrane to an extent of at least 15% when said membane is wetted with said solvent and then dried. Then the resulting porous membrane is dried and/or heated to gradually remove the solvent. In this way, the porous membrane can be modified by a very simple method to impart a similar performance to that of an unsymmetrical separation membrane exhibiting excellent permeability and separation performance when used for gas or liquid separation.
KUSUKI YOSHIHIRO
HARADA TAKASHI
SHIMAZAKI HIROSHI
ISHIDA TOSHIO
