Exploring The Low Enzyme Loading Pretreatment And High Solid Loading Fermentation Process Of Lignocellulose

Lignocellulosic ethanol,produced from lignocellulosic biomass,is an important renewable energy source with many good properties,such as moderate energy density,easy storage and transportation,easy production and mixing with fossil fuel.Although the cellulosic ethanol production process is already in place,it still encounters many obstacles to its industrialization,including harsh pretreatment process conditions and low fermentation efficiency at high solid loading and so on.This study mainly improves the biomass conversion rate and reduces the production cost of lignocellulosic ethanol from the two aspects: pretreatment process innovation and fermentation process innovation.There are some challenges in simultaneous saccharification and co-fermentation(SSc F)process at high solid loading: the difference between the optimum temperature of cellulase and fermentation strain;the efficient utilization of glucose and xylose in the present of inhibitors.Thus,a novel co-culture fermentation system was developed.Through investigating the effects of temperature distribution fermentation period,inoculation time,inoculation ratio and synergistic interaction mechanism on the SSc F process,this novel co-fermentation process was established and optimized.The ethanol yield and final concentration reached to 0.44 g ethanol/g sugar and 70.2 g/L by using this novel fermentation system at 25% solid loading.Tracing back to the source,the inhibitor problem in SSc F process is mainly due to the presence of lignin in lignocellulose biomass(inhibiting the enzymatic hydrolysis)and excessive degradation of fermentable sugars caused by severe pretreatment conditions in the pretreatment process(inhibiting the fermentation strain).The high temperature ethylenediamine(EDA)pretreatment showed extremely high lignin removal efficiency,and the removal rate of lignin reached 86.1%.High temperature EDA pretreatment significantly improved the surface roughness of corn stover,improved its pore structure and increased its porosity.Thus,the productive adsorption to cellulase of pretreated corn stover significantly increased by 35.2%.In SSc F at 15% glucan loading with high temperature EDA pretreated corn stover,up to 82.2 g/L ethanol was achieved with a relatively low enzyme loading of 3.6 FPU/g dry matter.A novel mild stepwise pretreatment process was also developed in this study.It could effectively address the issues of excessive degradation of fermentable sugars in severe pretreatment process and low efficiency in reducing the resistance of lignocellulosic biomass in mild pretreatment process.More than 95% glucan and 85% xylan were reserved in the pretreated solid after stepwise pretreatment.The glucan and xylan conversion of pretreated solid reached 94.18% and 72.81%,respectively,with a low enzyme loading of 10 mg cellulase/g glucan.In stepwise mild pretreatment process,aqueous ammonia pretreatment enhanced productive enzyme adsorption on biomass mainly by increasing specific surface area,while EDA pretreatment improved productive enzyme adsorption by the coalescence and re-localization of lignin to expose more accessible surface.