Method for condensing water-soluble organic matter and device for condensing water-soluble organic matter

A method for condensing a water-soluble organic matter by distillation and membrane separation, comprising:

• a distillation step in which a raw material including a mixture of water and a water-soluble organic matter having a lower boiling point than water or a mixture of water and a water-soluble organic matter which forms an azeotrope with water and the azeotrope of which with water has a lower boiling point than water, is input into a distillation column and the raw material is distilled;
• and
• a membrane separation step in which column top vapor obtained in the distillation step is introduced into a separation membrane device having a plurality of stages of vapor-permeation separation membranes through which water vapor goes selectively, and the water-soluble organic matter having a required concentration of more than 99.0% by mass is obtained from a final outlet on a non-permeation side in the separation membrane device by membrane separation of the vapor-permeation separation membrane, wherein
• when the permeability of water is referred to as K—W and the permeability of the water-soluble organic matter is referred to as K—A in the vapor-permeation separation membrane, the permeability ratio K—W/K—A of a vapor-permeation separation membrane disposed at least immediately before the final outlet on the non-permeation side in the separation membrane device is lower than those of the other vapor-permeation separation membranes.