The Study On Separation And Purification Of L-lactic Acid From Fermentation Broth

This paper studied the extraction and purification of L-lactic acid from fermentation broth. First, the fermentation broth was pretreated for the next step. It was kept in the65℃water for40minutes then thallium and protein such high molecular weight substance would deposit at the bottom. Next the top lucid liquid was decolored by the actived carbon. The process was that we put the actived carbon in a tube then let the fermentation broth through it at the flow rate13ml/min. The final decolor rate could achieve96%.There was little fermentation broth in the deposit. In order to fully use the deposite we centrifuge the deposit at the4800rpm for3-5minutes. The deposit was separate clearly from the liquid. We took the top liquid then discard the deposit.In this paper we studied the extraction of L-lactic acid by the n-butyl. After studied the different condition such as the temperature, mixture time, the concentration of lactic acid in fermentation broth, dose of the extract, then we got the optimize the condition was pH=2, T=25℃, lactic acid:butyl alcohol=1:1, the concentration of lactic acid in fermentation broth is30%, mix time2minutes,3times extraction.Then we used the extract phase as the substance to esterify to get the n-butyl lacated.At present the molecular distillation equipment is expensive and most of them are export from the oversea such as Germany and America. After many times experience in Wuxi and Tianjin and discuss with the agent and company of making molecular evaporate we got the concrete reference for our fermentation broth. So we book a suit of equipment include thin film evaporate and molecular evaporate from Tianjin. We used the thin film distillation and molecular distillation to purify the lactic acid. First, we dewater and degas by the thin film evaporate to get the high vacuum in the molecular distillation. Else the purity and recovery was low if the vacuum can not be enough higher. Also we studied the effect of the different pretreatment of fermentation broth to purity and recovery of product.We analyzed the product of L-lactic acid according GB2023-80and FCC criterion. And we make compare between the standard and the product by mass spectrum. The product can perfectly match the standard. At the same time, we analyzed other request in the criterion and they can meet the criterion.