Method for dehydration and concentration of aqueous solution containing organic compound

A method for dehydration and concentration of an aqueous solution containing an organic compound which is in the form of a liquid at 25.degree. C. and has a boiling point of not higher than 200.degree. C., comprising the steps of:

• evaporating the aqueous solution to produce a gaseous mixture comprising vapor of the organic compound and vapor of water;
• selectively separating the water vapor from the gaseous mixture by bringing the gaseous mixture into contact with a first side of an aromatic polyimide gas separation membrane at a temperature of 70.degree. C. or higher to cause selective permeation of water vapor through the membrane to a second side whereby the water vapor passes selectively into the second side of the membrane, while the gaseous mixture from which water content is reduced is left on the first side where the gaseous mixture was introduced;
• and
• recovering the gaseous mixture from which water vapor content is reduced from the first side of the membrane.