Study On The Production Of Ethanol From Agricultural Residues By Organosolv Pretreatment

Lignocellulose is widely existed in the nature of renewable resources, among which there are a large number of agricultural residues such as straw, corncobs, therefore effective reuse of the agricultural residues is significant. As the typical agricultural residues, corncob is low-cost and abundant, it has been regarded as the ideal raw material for bioethanol production. In this thesis, the whole process of bioethanol production by the agricultural residues has been studied, including pretreatment, enzymatic hydrolysis, simutanueous saccharification and fermentation (SSF), and immobilization of cellulose. The purpose is to improve the ethanol yields and reduce the cost of the whole process.The results showed that the optimal pretreatment conditions of sulfuric acid-ethanol pretreatment is sulfuric acid mass fraction 2%, ethanol concentration 50%, pretreatment temperature 120℃, pretreatment time 60min, ratio of solid to liquid 1:10. The enzymatic saccharification rate of corncob is 68.48%. The optimal pretreatment conditions of sodium hydroxide-ethanol pretreatment is sodium hydroxide mass fraction 2%, ethanol concentration 50%, pretreatment temperature 60℃, pretreatment time 60min, ratio of solid to liquid 1:10. Under the optimal contions,74.48% of lignin can be apparently removed and the percentage of cellulose in corncob is significantly increased to 73.11%. The enzymatic saccharification rate of pretreated corncob is 77.29% and the experimental conditions are relatively mild.In this paper, we selected sodium alginate as the carrier and glutaraldehyde as the cross linking agent to immobilize cellulase. The experiment carried the research on the effects of different glutaraldehyde concentration, the amount of cellulase, coupling time, coupling temperature with one target:activity. Some characters of free cellulase and the immobilized cellulase, such as optimum temperature, optimum pH, the thermal stability, the stabilities for researvation and the operational stabilities have been studied. The results showed that:the optimum temperature of immobilized cellulase is 60℃, and the optimum reaction pH is 5.8. The thermal stability, the operational stabilities and the stability for reservation of immobilized cellulase are significantly improved.The SSF experiment of corncob after sodium hydroxide-ethanol pretreatment was carried out. The results showed that:the optimal strategy was determined to be:substrate concentration of 5%(w/v), cellulose dosage 20FPU/g, fermentation temperature of 38℃, fermentation time of 72h. The final ethanol concentration was increased to be 12.93 g/L with ethanol yield from substrate of 62.28%. A pre-saccharify process was developed which decreased the fermentation time to 36h. When the pre-saccharify time is 12h, the ethanol concentration is 12.97g/L. When using the fed-batch process in high substrate concentration of SSF, the ethanol concentration can reach 19.13g/L.The kinetic model of reducing sugar change in SSF process was derived by the previous models. The adaptive PSO algorithm with non-linear changed inertia weight was applied to identify the parameters of kinetic models and fit with the experimental data in the SSF process of corncob. The results showed that the simulated values fitted well with the experimental data.