Investigation On The Production Of Cellulose Ethanol From Rice Straw By Simultaneous Saccharification And Fermentation

Oil, coal and other traditional energy sources have become depleted and resulted in environmental pollution. To solve the imminent energy crisis and environmental pollution, the use of rice straw preparation of bio-fuel ethanol fermentation to alleviate the above-mentioned crisis. Production,application and extension along with many others of fuel ethanol have been made over years. However, there are many key obstacle factors especially three sides in it today. One is serious environmental pollution and high cost caused by pretreatment of materials, the other is the lower conversional rate of fuel ethanol during sugar fermentation. Thirdly, due to inhibitory effect of glucose on cellulase, conversional rate of cellulose and reducing sugar of saccharification liquid is lower, resulting in higher production cost.These problems can be solved through adopting green pretreatment process, screening yeast strains of high-temperature tolerance and high-alcoholicity endurance , breeding strains of excreting cellulase and optimizing process conditions of simultaneous saccharifiction and fermentation. Accordingly,lots of experiments have been done and period-conclusion have been made in this paper. The research results are as follows:(1) the study on pretreatment conditions of straw cellulose. The effects of pretreating straw cellulose on enzyme hydrolysis were investigated through mechanically crushing pretreatment, microwave pretreatment, acid-alkali pretreatment, Glycerin Pretreatment and microwave-assisted Glycerin pretreatment. The results show that straw powder(1g) of microwave-assisted ( power 320w) Glycerin(7g) pretreatment was choosed as experimental material of simultaneous saccharifiction and fermentation.(2) study on breeding of excreting cellulase strain and biological characteristics. Gram-negative bacteria JX-2 of excreting more cellulase was isolated and purificated through a lot of expriments. The stain was primarily determiated as cytophata whose optimum growth pH and temperature were 9.0～11.0, 37℃,aerobe. The filter paper enzyme activity of cellolase excreted by JX-2 arrived at 1158.6U·ml-1,which showed better industry application prospect.(3) study on breeding of yeast strains of high-temperature tolerance and high-alcoholicity endurance. P1,5min,P2,10min were chosen as high-temperature tolerance and high-alcoholicity endurance through plenty of screening work. P1,5min could grow in solid-medium of 16% alcohol concentration under 52℃,and it's production rate was 2.96% under high teperature of 52℃. P2,10min was similar to P1,5min and it's production rate was 2.86%.(4) study on simultaneous saccharifiction and fermentation producing fuel ethanol by straw powder. The effects of temperature, pH, yeast concentration, enzyme concentration, fermentation time on fermentation process were investigated and their optimum conditions were found out. Based on single-factor results, orthogonal experiments were implemented. The final results showed that best fermentation conditions were temperature 36℃, pH6.0, yeast concentration 7%, enzyme concentration 22ml.(5) optimization of SSF process based on response surface. The effects of temperature, Yeast Concentration, enzyme concentration on ethanol production were studied based on response surface method. The first- order model was established between SSF conditions and ethanol rate through a lot of experiments model fitting. It's as follows: y = 21.782 + 0.804x 1 + 0.124x 2 + 0.526x3Upward data design for the best work point, the production rate of ethanol approached to best value under fermentation temperature 38℃, enzyme concentration 16.386u/g, yeast concentration3.962%. Meanwhile, the second-order model was established and it was as follows:After analysing variance of the model, the effect of three variables on response was determinated. Moreover, the second- order model consists of interaction factors. The optimum conditions are fermentation temperature 39.16℃, enzyme concentration 15.74u/g, yeast concentration4.16%. It was best process condition that the study were looking for through regular analysis and experiment validation.There are 37 figures, 30 tables and 122 references in this Doctor paper.