| D-lactic acid is an important optically active chiral intermediate and a monomer for polylactic acid,which widely used in the fields of agriculture,chemical industry and medicine.Microorganisms fermentation is the mainly method to produce D-lactic acid for industrial production,and the use of glycerol for the production of D-lactic acid is a highlight.However,there are some problems,such as slow growth and low concentration of bacteria,low acid production rate,low product concentration,substrate repression and so on.In order to solve these problems,this study were decolorized the raw glycerol,and fermented with sole carbon source,including a certain proportion of glucose and glycerol.The product of D-lactic acid was separated and purified by ion exchange method combined with vacuum distillation.The main research contents and results are as follows:With treated with activated carbon under different conditions,the decolorization effect of crude glycerol was evaluated by fermentation,which using bleached glycerol.The optimum conditions for decolorization of crude glycerol were as follows: the amount of activated carbon was 3.5%,the adsorption time was 2 h,under these conditions,the decolorization rate of glycerol and glycerol was 94.35% and 93.8%,respectively..The fermentation was carried out with 4%,6%,8%,10% decolorization glycerol as the carbon source,and 5% calcium carbonate as the neutralization agent for72 h,which the fermentation temperature was 37℃ and the rotation speed was 150r/min.The yield of D-lactic acid was 21.4 g/L,26.1 g /L,24.6 g/L,and 23.8 g/ L,respectively.The effect of initial glycerol concentration on the yield of D-lactic acid was explored.The results showed that,the optimum carbon source content was 5%.Under the 5% total carbon source,the influence of mixed carbon sources with different proportions of glycerol and glucose on fermentation were studied..When the glucose concentration in the mixed carbon source was 10 g/L and the content of glycerol was 40g/L,the production of D-lactic acid was faster and the high yield was 25.9 g/L.Fermentation was carried out in a 7 L fermentor,and by adding with 3 mo/L of calcium hydroxide as neutralizing agent,and E.coli D303 was fermented to about 23 h with 10g/L glucose and 40 g/L glycerol as the substrate.When the fermentation time was to about 23 h,the gulcose depleted.The yield of D-lactic acid was 40.8 g/L,the remaining glycerol concentration was about 4 g/L,and the conversion rate of sugar acid was81.6%,which the time to 60 h.The product of D-lactic acid was separated by ion exchange resin,and the eluate was purified by distillation under reduced pressure,wherein the adsorption conditions and elution conditions of the anion exchange resin were studied.The main results were as follows: the cation was removed by 001×8 strongly acidic styrene cation exchange resin.When the lactic acid in fermentation broth was separated by the D371 styreneanion exchange resin,the adsorption flow rate was 1.4 mL/min,and the adsorption temperature was 25℃,which obtained better adsorption effect.When the eluent was water,the elution temperature was 90℃ and the elution flow rate was 1.4 m L/min,the elution was the best.The D-lactic acid with the chemical purity of more than 99% was obtained by two decompression distillation. |
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