Selection Of Yeast Strain For Fermentiong Xylose And The Technique Of The Ethanol Fermented By Corn Stalks

Since global energy crisis and pollution problems got worse and worse, the development of renewable and clean energy become one of the most effective methods to solve both of the problems. Xylose is the major sugar which is only second to glucose in lignocellulose Hydrolysate. Converting xylose from plant lignocellulosic materia to ethanol effectively mains a lot to bio-ethanol industrial production. In this paper the yeast strains which can ferment xylose efficiently to product ethanol were screened, the pretreatment of corn stalks was optimized and fermentation by isolated yeast strain was also studied. The main results were as follows:From 63 samples, including rotten wood, leaves and other rich lignocellulose soil samples 13 wild yeast strains which can ferment xylose to ethanol were selected. Nine of them were able to product ethanol at 25℃, and the ethanol yield of No 4, 5, 14-1strains can reach 4p.0 ~ 8.6 g / L after 72hs fermentation; only No 54 yeast strain can ferment xylose to ethanol at 37℃,The No4 and 5 strains had 100% and 99% max homology with typical Pichia stipitis strain, identified by 26S rDNA partial sequence and compared with the carbohydrate assimilation results of typical Pichia stipitis strains. The ethanol concentration of No.4 strain after 48h fermentation can be 21.0g/L.The technics of three pretreatment methods, such as lime, alkali-H2O2 and dilute sulfuric acid, of maize straw were optimized. Dilute sulfuric acid pretreatment method with 808.2 mg/g reducing sugars yield was achieved when the concentration of sulfuric acid was 1.5%, at 121℃for 60 minutes, and enzymatic hydrolyzed at 45℃and pH4.5,with 110.3 mg/g enzyme (cellulose and hemicelluloses 110.3 mg/g respectively) for 70.7 hours, better than the other two methods.Compared the fermentation of the three kinds of corn stalk of enzymatic hydrolyzed, The reducing sugar utilization rate of the calcium oxide pretreatment is higher, followed by alkaline hydrogen peroxide pretreatment, and the dilute sulfuric acid pretreatment has the lowest sugar utilization rate.The result revealed that ethanol yield and yeast concentrations had some positive correlation with reducing sugar utilization rate from the fermentation. The higher ethanol yield was got from the concentrated solution of oxidation calcium pretreatment hydrolyzed and alkaline peroxide preconditioning hydrolyzed, and the maximum ethanol yield was got at 48 h, earlier than the third method; and the largest ethanol yield were 13.3 g/L and 12.0 g/L, respectively.