Method for producing lactic acid, method for producing lactide, methods for producing polylactic acid, lactic acid, lactide and polylactic acids

摘要

Lactic acid obtained by a method for producing lactic acid, the method comprising: (A) a step of continuous fermentation wherein a fermentation culture medium of a microorganism having an ability of lactic acid fermentation is filtered through a porous membrane having an average pore size of not less than 0.01 µm and less than 1 µm with a transmembrane pressure difference within the range of 0.1 to 20 kPa, and the permeate is collected, while retaining the non-permeated liquid in or returning the non-permeated liquid to the culture, and adding a fermentation feedstock to the culture; (B) a step of filtering the permeate obtained in Step (A) through a nanofiltration membrane; and (C) a step of distilling the permeate obtained in Step (B) under a pressure of not less than 1 Pa and not more than atmospheric pressure, at 25°C to 200°C to recover lactic acid; comprises only small amounts of impurities, and a polylactic acid obtained using the lactic acid as a raw material has excellent thermal stability, mechanical strength and hue.