| As the oil resources become scarce and the global environmental pollution is increasing, the renewable energy is to be developed. Currently, fuel ethanol is one of the oil energy alternatives, and sweet sorghum has the advance of non-food energy crops and not accounting for good farmland, so it is the ideal alternative material. The merits of the strain heavily effect the fermentation, so it is very important to screen out the good strain and the strain’s optimization. In that case, we can achieve large-scale industrial production of the alcohol, even we can solve the energy crisis.1. Breeding the fermentation strain. The yeast FFCC2167 is the original strain. First, the strain is domesticated in order to improve the ability of high glucose tolerance. Then using X-ray and DES composite mutagenesis and differential medium to select mutants. At last, the wanted strain named FXD-3 was got through the ethanol tolerance test, which has higher yield of alcohol and higher tolerance to ethanol. Using the sweet sorghum stem juice by general formula as the fermentation medium. The optimum conditions of fermentation:inoculum 10%v/v,30℃, pH=4.5, fermentation period 36h, ethanol production is 92.98g/L, the yield of alchol is 90.03%。2. The optimization of the mutant strain fermentation conditions. Designing experiment by Minitab software optimize fermentation conditions. Using partial derivative method found optimal dosage and intuitive analysis of the interaction that has significance. Results showed that:In the optimum fermentation conditions, the initial total sugar in the sweet sorghum juice is 220g/L, the amount of nutrients in the fermentation medium:CO(NH2)24.8318g/L, MgSO41.3734g/L, KH2PO44.8114g/L, CaCl25.8571g/L and FeCl30.6962g/L. The fermentation period of the yeast strain FXD-3 is 36h, Residual reducing sugar is 9.24 g/L, the utilization of the sugar is 95.8%, the ethanol production is 100.44g/L, the yield of alcohol is 93.46%. Compared to not mutagenic, total sugar is down by 8%, the utilization of the total sugar increased by 0.92%. The ethanol production increased by 21.15g/L. The yield of alcohol increased by 26.67%.3. Establishing the model of the kinetics of batch fermentation to produce ethanol by using sweet sorghum stem juice. Established the model of the kinetics of the cell growth, the generation of alcohol and the substrate consumption. Tracking testing batch fermentation process, establishing logistic equation by Unary linear regression to the experiment results, fitting by Michael-Marquardt method and solution through Matrix-linear, then we got the model parameters. The result of the fitting is excellant, which show that the selected model well reflect the process of batch fermentation to produce ethanol by using sweet sorghum stem juice and the kinetic mechanism. So we can design the large-scale fermentation process.the model of the kinetics of the yeast cell growth:the model of the kinetics of the yeast cell growth:the model of the kinetics of the Substrate consumption:... |
