Study On The Purification Process Of Lactic Acid By Esterification

This study was focused on the purification process of lactic acid by esterification.The effects of ethanol/lactic acid ratio, cyclohexane/lactic acid ratio,catalyst loading,incubation period, heat temperature on the esterification yield of lactic acid and ethanolwere discussed. Response surface design (RSD) was used to optimize the conditions,and a mathematics model was founded. The esterification conditions were as follows:ethanol/lactic acid ratio was 4:1,cyclohexane/lactic acid ratio was 0.8:l,catalyst loading was2%,incubation period was 3h,heating temperature was 110℃.The mathematics model was tested,the relative coefficient of predict values and experimental values were 0.988.The mathematic modelwas considered effectual. The ethyl lactate was recovered from solution of esterificationreaction by vacuum distillation. The effects of temperature, neutralizer, residual acids onthe recover yield of ethyl lactate were discussed. The best recovered method was asfollows: the calcium carbonate was used as neutralizer to neutralize the catalyst and theresidual acids, the ethanol, water and cyclohexane were distillated at atmosphericpressure, and vacuum distillation was carried out at 110℃. The product of vacuumdistillation was hydrolyzed. The effects of hydrolysis method, hydrolysis terminus, ratioof water/ester on the hydrolysis rate of ethyl lactate were studied. The conclusion fromthe was that hydrolysis-internal rectification process was used, the water/ester ratio was20,the heating temperature was controlled to keep the speed of distillation between0.2~0.3mL/min,the hydrolysis could be stopped when the temperature of top towerreached to 98℃.The refined lactic acid was obtained by condensing the hydrolysissolution.This technics was applied on the purification of fermented L-lactic acid. The fermentation broth was processed by different pre-treatment. The effects of process and impurity on the refine yield of lactic acid were studied. According to the results, the effect of different processes on the refine yield of lactic acid could be attributed to the production of impurities, and decrease of any impurities could redound to enhance the refine yield of lactic acid. Took loss rate and refine yield into account, the traditional technics was improved. The calcium salt recovery process was used to pre-treat the fermentation broth. The lactic acid was purified by esterification. The concentration ofthe final production was 88%, which was better than the product buying from market. The production was checked by GC which indicated that there was no ethyl lactate in the lactic acid.