Patent ID: 8053610

Claim:
A method for purifying an aqueous solution of fermentation alcohol to give anhydrous alcohol, comprising: (step 1) feeding an aqueous solution of fermentation alcohol to a mash column, distilling a distillate containing an alcohol/water mixed vapor by heating an aqueous solution of fermentation alcohol in the mash column, and feeding the distillate or a first condensate obtained by condensing the distillate into a distillation column; (step 2) distilling an alcohol/water mixed vapor from the distillation column by heating the distillate or the first condensate in the distillation column, refluxing a second condensate obtained by condensing a part of the mixed vapor to the distillation column, and superheating the remaining part of the mixed vapor to a temperature at which the mixed vapor does not condense in a membrane separator and then feeding to the membrane separator; and then, (step 3) selectively removing a water vapor from the alcohol/water mixed vapor in the membrane separator, wherein the mash column is controlled in such a manner that an alcohol concentration of the alcohol/water mixed vapor distilled from the mash column is less than 50% by weight in step 1, and an operating pressure in the distillation column is 150 kPa (absolute pressure) or more, and a reflux amount of the second condensate to the distillation column is controlled in such a manner that an alcohol concentration of the alcohol/water mixed vapor distilled from the distillation column is 55 to 85% by weight in step 2.