PURPOSE: To enable to dilute the components less volatile than water in a distillation bottom by providing a pump and a reverse osmotic membrane type separator in a reflux pipe.
CONSTITUTION: The pump 6 and the reverse osmotic membrane type separator 7 are provided in th reflux pipe 5. A vapor consisting mainly of water and organic compounds less volatile than water is taken out from a vapor phase part 2 of a distillation column 1, then it is condensed to a liquid, which is pressurized by the pump 6 and fed to the separator 7 under pressure. A penetrated liquid, that is, the liquid penetrated through the reverse osmotic membrane of the separator 7 is taken out to the exterior of the system through a discharge pipe 8 in such a condition that the concentration of the organic compounds therein is still lower than that in the condensed liquid. The liquid concentrated with reference to the organic compounds which can not permeate through the membrane of the separator 7 is returned into the distillation column 1 after lowering its pressure to a predetermined pressure.
TOUDA YASOJI
SHIYOUJI MASAAKI
