PURPOSE: To make effectively remain more condensed org. oxygen compd.-contg. liq. by passing an aq. feed liq. contg. org. oxygen compd. while bring it into contact to a high pressure side of a porous membrane layer of polyimine cross- linked with an aliphatic polyhalide and proceeding a pervaporation maintaining a pressure drop through the layer.

CONSTITUTION: The aq. feed liq. contg. org. oxygen compd. (e.g., isopropyl alcohol) is passed while being in contact to high pressure side of a porous membrane layer of polyimine cross-linked with aliphatic polyhalides, and the pressure drop is maintained through the layer. By the process of pervaporation is proceeded as a rarefied mixture contg. less org. oxygen compd. than the aq. feed liq. to pass the separation layer and a liq. contg. more concd. org. oxygen compd is remained. As the result, an aq. soln of org. oxygen compd. can be effectively dehydrated.