A Research On Ethanol And Methane Production From Biomass Pretreated By Subcritical Water Pretreatment

Due to the rapid population growth and industrialization, energy problems became thefocus worldwide. The limited reserves of fossil energy make renewable energy become ahotspot, fuel ethanol is one kind of renewable energy sources. Traditionally, fuel ethanol isproduced from grains, such as corn and sugarcane, however it may lead to potential foodcrisis because the materials themselves are the main resoures for food and animal feed,therefore production of ethanol from waste straw residuals reach a consensus in manycountries. However, there are still some problems in ethanol production from biomass, forexample, the pretreatment technology, low cost and efficient cellulase technology, pentoseand hexose co-fermentation technology and so on. Appropriate pretreatment technology canimprove the utilization rate of lignocellulosic materials and enhance the ethanol yield offermentation. In this study, subcritical water pretreatment method was employed to pretreatdifferent kinds of materials, subsequently the compositions of various materials wereanalyzed, finally the ethanol fermentation of pretreated residuals and methane fermentation ofhydrolysates were studied. The main results were as follows:1. The optimization of subcritical water pretreatment process. Central composite designwere employed to optimize the pretreatment time and temperature, it revealed that theoptimal pretreatment conditions for switchgrass, wheat straw and corn stover were200℃，0min;194℃,0min and190℃,0min, respectively. Under the optimal pretreatment conditions,the maxmum reducing sugar contents of the material hydrolysates were3203mg,2082mg and1858mg, respectively.2. Compositions analysis of biomass residuals pretreated under optimal conditions. Afterdetermination of lignin, hemicellulose and cellulose contents of raw materials and pretreatedresiduals, it indicated that the removal rates of hemicellulose of switchgrass, wheat straw andcorn stover were90%,74.7%and69.5%, and the removal rates of lignin of differentmaterials were40%，44.9%and34.2%,respectively. meanwhile, the retention rates of cellulose were85%，95.1%and92.8%. The results were conincidence with fourier transforminfrared spectroscopy (FTIR) analysis. Scanning electron microscope (SEM) analysis showedthat the cellulose crystal structures of biomass residuals were broken after pretreatment.Consequently, the subcritical water pretreatment can remove the hemicelluloses and ligninseffectively, furthermore, it can reserve most of the celluloses and break the cellulose crystalstructures which can benefit the enzymolysis process and fermentation process of residualsand hydrolysate.3. The enzymolysis of biomass residuals pretreated under different conditions. Theenzymolysis experiments results of residuals pretreated under different conditions showedthat the enzymolysis rate increased as the subcritical water pretreatment temperature and timerised. The enzymolysis rates of the residuals pretreated under optimal conditions ofswitchgrass, wheat straw and corn stover were34%,35%and28.8%, respectively.4. The fermentation of biomass residuals and hydrolysates obtained at optimalpretreatment conditions. The residuals were fermented to produce bioethanol by simultaneoussaccharification fermentation (SSF) method, the ultimate ethanol concentrations ofswitchgrass, wheat straw and corn stover were20.76g/L,12.8g/L and10.4g/L. In methanefermentation tests, only the hydrolysates derived from switchgrass produced biogas, the totalvolumn of biogas was390mL and the methane yield was46%.