Ethanol Production From Glycerol Fermented By Microorganisms

Resently, great attention was paid to the renewable resources when petroleum are being depleted gradually. The technology of fuel-ethanol and biodiesel were exploitured. As an attractive biofuel, the biodiesel is hopeful to be industrialized after fuel-ethanol industrial. It is the main method by transesterification in the manufacture biodiesel, and glycerol was produced as by-product plentifully. The new problem was appeared that how to handle the numerous quantity of crude glycerol and how to make reasonable use of crude glycerol in the near futrure. A new method is explored in this study that ethanol was produced from crude glycerol by microorganisms. Finally, the problem of using glycerol will be solved, and a new way will be found that ethanol was produced by other substances instead of grains.The topic of this study is to explore a process for ethanol production from crude glycerol discharged after biodiesel manufacturing process by microorganisms.The analysis methods of glycerol and ethanol were established. The glycerol concentration in the fermentation liquid was determined by HPLC; the concentration of ethanol was measured by headspace GC. The method was simple and accurate. By strain screening, P.macerans was used as ethanol fermentation strain. The composition of seed culture medium was optimized as follows: glycerol 8g, glucose 12g, peptone 5g, yeast extract 5g, CaCO3 10g, H2O1L, pH9.0; the fermentation conditions were conducted at 41℃for 36h anaerobically with inoculum volume 10%. The optimized fermentation medium was as follows: glycerol 50g, glutamic acid 5g, peptone 5g, yeast extract 5g, NaCl 5g, ZnSO4·7H2O 1g, H2O 1L, pH8.0. Based on the optimized composition of medium, the fermentation conditons of ethanol was studied: In fed-batch fermentation, the inhibition of high concentration glycerol was eliminated, glycerol was utilized effectively.It is obvious that the fermentation time was shorten at the mixed fermentation of P.macerans and Monascus sp.9906. Based on mixed fermentation, in fed-batch fermentation the initial concentration of glycerol was 0.217mol/L, the experiment was carried out in 1L flasks with 700mL Moanscus broths; adding 0.217mol/L glycerol in Monascus broths with an interval of 60hours, 100mL Monascus broths was added at an interval and the fermentation lasted 360h. The concentration of ethanol reached 0.221mol/L, the total productivity of ethanol was 0.628mmol/h and ethanol conversion rate was obtained at 87%. In a 5L flask, the concentration of ethanol was 0.370mol/L, the utilization rate of glycerol was obtained at 82.3% and ethanol conversion rate reached 83.0%. Comparing with the fermentation by P.macerans, the utilization rate of glycerol and ethanol conversion rate were increased obviously by mixed fermentation.The mixed fermentation was adopted for ethanol fermentation using glycerol-containing wastes. In 0.109mol/L crude glycerol, ethanol conversion rate reached 80.7% that approached to real theory conversion rate 81.8%, but the concentration of ethanol was only 0.067mol/L. The main reason is that high concentration of glycerol inhibited the growth of P.macerans; and the high concentration of slat and residue fatty acid were harmful to the microorganisms.