Research Of Inhibitors From Corn Stalks With Steam Explosion And The Optimization Of Enzymatic Hydrolysis

As a new energy, cellulosic ethanol is a good material to solve the crisis of energy. pretreatment is one of the most important step in the production of ethanol. Steam pretreatment is seemed to be one of the best pretreatment. However pretreatment requires high temperature and high pressure, so under this condition ,some biological molecules degrade and some of these degradation products can inhibite the process of hydrolysis and fermentation. These inhibitors affect the ethanol yield severely.In this study, we use Hebi steam explosion machine to pretreat corn straw in the condition of 2.5MP, 5min. We found some inhibitors’ concentrations are very high, they are formic acid, acetic acid, furfural, 5-hydroxymethyl furfural . So the effects of these four inhibitors on Saccharomyces cerecisiae growth and fermentation is the main purpose.We optimize the best conditions of the yeast without inhibitors, then study the effects of every inhibitor on Saccharomyces cerecisiae growth and fermentation. Thenwe use response surface to study the interaction of the inhibitors. On this basis we established a kinetic model of yeast fermentation inhibitors.Enzyme kinetics of steam explosion corn straw are analyzed, and some of hydrolysis conditions were optimized and achieved good results.The main conclusions of this thesis included the following five parts:1)he best conditions of yeast growth were optimized: the best time to inoculate is 12h; the best pH is 5.0; the best temperature is 35℃and the best rotation speed is 150rpm.2) In the condition of 5% inoculation, 8% initial glucose concentration , 5.0 initial pH, 35℃and 150rpm, the effects of each inhibitor on yeast growth and fermentation are studied. The results show that the maximum concentrations are formic acid 10g/L, acetic acid 20g/L, 5-hydroxymethylfurfural 5g/L and furfural 3g/L. We also find that formic acid and acetic acid are not consumed, however 5-hydroxymethylfurfural and furfural are consumed. The stongest inhibitor is furfural.3)Under the same fermentation conditions, we use central composite response surface design experiments to test the four inhibitors. The result shows that formic acid, acetic acid, furfural have great negative effects on the biomass and ethanol fermentation, and the effects of interaction among them is very significant. 4) By response surface design export, the optimal conditions are found. The result shows that the best enzyme loading is 30FPU/g; the best pH is 5.0; the best temperature is 43.8℃and the best rotation speed is 200rpm. Reducing sugar production increase 12%.