Study On The Separation And Purification Process Of Food-grade L-lactic Acid

Lactic acid and its derivatives, widely used in the chemical, food, pharmaceutical industries, are promising products. For food and pharmaceutical purposes, however, with high optical purity L- lactic with lower content of impurities are required. Currently, L- lactic acid is mainly produced by fermentation method, which suffers some difficulties such as complex separation process, poor recovery rate and low efficiency.This thesis focused on the downstream purification process of lactic acid produced by Rhizopus oryaze 3.819 from sweet potato starch. For lactic acid clarification and purification, a series of technologies were introduced, which covered ultrafiltration membrane with 5000D retention molecular weight for protein removal, particle active charcoal in combination with macroporous AB-8 resin for sugar and pigments removal , and gradual temperature decrease for calcium lactate crystallization. Firstly, fast and accurate assays related to purification process were established for the main components analysis. Secondly, the key factors in every process were further researched. Finally, the process of food-grade lactic acid and its parameters were optimized.The results were as follows: by using particle active charcoal and AB-8 macroporous adsorbent resin for color and sugar removal, the loss rate of calcium lactate in the process was only 7.8%, which was much lower than that of 20-30% in the conventional process caused by powder charcoal. In addition, most sugar and pigments were removed. For ultrafiltration technique, it had advantages in separating protein over traditional process. Its retention rate of protein and the loss rate of calcium lactate were about 91.56% and 2%, respectively. Gradual temperature decrease and crystal seeds addition were adopted for crystallization of calcium lactate, in which crystallization rate could be up to 67.4%. Furthermore, its mother liquid can be reused for crystallizing.The optimized process of food-grade lactic acid had some advantages such as lower energy consumption, simpler operation requirements and better continuity. The recovery rate of lactic acid could reach 70%. Revealed from the results of paper chromatography and optical polarity, the content of refined lactic acid was 90% with optical purity of 95%, and its stability was superior.