Refining L-lactic Acid By Centrifugal Molecular Distillation And Simulation Of Its Liquid Film Flow Using CFD Technique

The fermentation of glucose to L-lactic acid was conducted using Lactobacillus fermentum. The effects of glucose concentration, temperature, PH, and fermentation time on L-lactic acid production were investigated during the batch fermentation. The results showed that the optimal glucose concentration was 100g/L, and the optimal operation parameters were 37℃, pH 6.8 and 64h. The batch fermentation process was studied in a 5L system under the optimal conditions, the fermentation broth was post-processed and separated to obtain high pure L-lactic acid.A physic model was designed according to the molecular distillation equipment and the fluid flow of centrifugal molecular distillation was simulated by the software of Fluent. The effects of feed rate and rotor speed on film pattern of evaporation surface were studied and satisfactory results were gained.Purification of L-lactic acid by molecular distillation was studied. The effects of operation pressure, feed rate, evaporating temperature and separation series on purity and yield of L-lactic acid were investigated. The results showed that molecular distillation was an efficient method for purification of L-lactic acid. The purity of production was higher than 91%.The feasibility was investigated to the application of simplified recovery method with molecular distillation technique for the preparation of high purity L-lactic acid at laboratory scale. Sulfuric acid was directly taken into fermentation broth without crystallization, conventional decolorization and ion exchange. The crude L-lactic acid produced was concentrated directly by rotary evaporator, and the enriched material was extracted by butanol and purified in molecular evaporator. The results showed that high pure L-lactic acid can be obtained under the proper condition. The operation units of the recovery method were greatly decreased, and the yield of production was also increased.