Diverse Pretreatment Of Corn Stover And Saccharification And Fermentation

Cellulosic ethanol produced from various lignocellulosic materials is a renewable energy and has the potential to be a valuable substitute forgasoline. Owing to these structural characteristics, pretreatment is an essential step to enhance enzymes accessibility to the cellulose. Besides digestibility of cellulose, it is also necessary to consider other non-cellulose components application for achieving biomass biorefinery during pretreatment. In this thesis, to consider application of cellulose and hemicellulose, pretreatment of corn stover and bioethanol fermentation were studied.First, the dilute acid pretreatment of corn stover was studied. The effects of acid concentration and solid-liquid ratio on the removal and recovery of hemicellulose and cellulose hydrolysis were researched. The results showed that the optimum pretreatment conditions (dilute acid concentration 0.8%, ratio of solid to liquid 1:10, pretreatment temperature 150℃, pretreatment time 50 min) were identified. Under this pretreatment conditions, the hemicellulose content of 3.0% in the solid residues and the xylose yield of 93.0% in the pretreatment solution were obtained. The conversion of cellulose to glucose was 71.6% at 72 hours in the subsequent enzymatic hydrolysis with cellulase.After dilute acid pretreatment, the solid residues of corn stover were further treated with alkaline sulfite to remove residual lignin for decreasing inhibition of lignin on enzymatic hydrolysis of cellulose. The conditions of pretreatment with alkaline sulfite for the solid residues from dilute acid pretreated corn stover were optimized by single factor experiment, and were as follows:alkaline sulfite charge 15%, sodium hydroxide charge 5%, treatment temperature 140℃, solid to liquid ratio 1:6, treatment time 1 h. Under this pretreatment condition, the delignification rate of 85.0% was obtained. The conversion of cellulose to glucose at 72 h reached to 85.4% for the pretreated corn stover by the two step treatment The addtion of sodium anthraquinone-2-benzene sulfonate and sodium dodecyl benzene sulfonate could protect carbohydrates from degradation while couldn’t promote the delignification. The ethanol concentration of 48.5 g/L was obtained at substrate concentration of 18.1% when the pretreated corn stover was used as substrate after fed-batch fermentation. The conversion of cellulose to ethanol was 77.2%, which increased by 16.8% compared with that of dilute acid pretreatment.Finally, the ammonium sulfite was used to pretreat corn stover to remove lignin and the solid residues from the pretreatment process, which mainly contain cellulose and hemicelluloses, was used as substrate for ethanol production by a process of enzymatic hydrolysis and co-fermentation of glucose and xylose. The results showed the lignin content of 8.7%, the cellulose conversion of 86.6% and the hemicellulose conversion of approximately 100% were achieved under the condition of ammonium sulfate charge 10%, sodium hydroxide charge 3%, pretreatment temperature 170℃, solid to liquid ratio 1:6 and pretreatment time 1 h. Ethanol concentration reached 50 g/L, and conversion of total sugars (glucose and xylose) to ethanol was 64.7% using simultaneous saccharification and co-fermentation process with strain XH7. The optimum fermentation temperature of XH7 strains was 36℃ and enzyme loading was 15 FPU/g substrate.