Extraction Of Lactic Acid During Fermentation Mixture

The lactic acid (α-hydroxyl propionic acid) is an important organic acid, with long history of extensive usage in the food, medicine and chemical industries. Especially in recent years, with employment of green solvent (lactate ester) and products of degradable plastics, the demand for the lactic acid is increasing significantly.There are two mainstream ways to produce lactic acid: fermentation and chemical synthesis. The chemical synthetic method has been seldom used because of serious environmental issues. Polylactic acid synthesis needs higher monomer (lactic acid) purity, so the extraction and purification of lactic acid from the fermentation liquid is a problem at the present time. Traditional lactic acid extraction method involves acidification of calcium lactate, solvent extract, ion exchange, membrane technology and absorb fermentation etc. Because these methods are with expensive and the lactic acid is of low in purity, its application is limited. The esterification and hydrolysis method is used extensively at present time. it has generally been adopted for getting high purity lactic acid. It includes three steps: first esterifying ammonium lactate (NH4LA) in a fermentation broth with the alcohol to produce lactate ester, second purifying lactate ester, third hydrolyzing the purified lactate ester into LA.In the dissertation, the extraction of LA is carried out by esterification and hydrolysis method. Through experiments on simulative fermentative mixture, the optimum conditions for esterification were determined as followed: reaction time was 6h, ratio between alcohol and lactic acid was 3:1 and initial concentration of lactic acid was 30%(w/w), the butanol was used as a reactant and the solid acid (MSAC01) as a catalyst, which was prepared by ourselves. Under the conditions, the esterification yield of to simulant kitchen garbage fermentative mixture was 87.7%, and the esterification yield of actual kitchen garbage fermentative mixture was 82%. For hydrolysis reaction, the strong acid cation resin in H+ form is used as catalyst, the optimum conditions for hydrolysis was: hydrolysis time 4 hours, the ratio of water to ester 15:1, mixer rotational speed 450r/min, content of catalyst 2.5%. Under above conditions, the hydrolysis yield was 89.7%.