Biomass Hydrolysis Under Extremely Low Acids For Fuel Ethanol Production

The technology of fuel ethanol production from biomass is potential in liquid fuel supply at present, as will solve the problem caused by severe liquid fuel crisis. And, the two-step hydrolysis, first hydrolysis of hemicellulose under hot liquid water, followed by the hydrolysis of cellulose under extremely low acids, has gained more and more attentions. Founded by the National Natural Scientific Foundation (50025618) - "The mechanism research of biomass comprehensive utilization as a clean energy", a detailed research of two-step hydrolysis of biomass for fuel ethanol production was carried out, which will benefit the co-utilization of biomass hydrolysis and pyrolysis.First of all, quantitative paper and xylan were chosen to represent cellulose and hemicellulose to study the hydrolysis behavior of the two main components of biomass respectively. Then the green process of hemicellulose hydrolysis by hot liquid water followed by cellulose hydrolysis under extremely low acids was designed. The experimental research was carried out to study the effect of acid concentration and reaction time on conversion ratio and reducing sugars yield, to determine the optimum of reaction parameters. Three types of lignocellulosic biomass - pine, poplar and corn straw underwent hydrolysis and reached to 41.78%, 57.84% and 53.44% in the conversion ratio, while 39.28%, 42.83% and 23.82% in the total reducing sugars yield.The sugar components distribution of the liquid products was analyzed by HPLC with the KS-802 sugars column. The content of monosaccharide and oligosaccharide were determined quantitatively. Other small molecule organic products were detected by GC-MS analysis, as showed that there exists some polarity components with methyl, ethyl, methoxy and hydroxyl etc. The residues were observed by SEM, combined with component analysis and thermogravimetric analysis, the hydrolysis mechanism of cellulose, hemicellulose and biomass under extremely low acids was discussed.Based on the review of biomass hydrolysis model, concerned with the property of cellulose and hemicellulose, the experimental data were simulated by heterogeneous and pseudo-homogeneous consecutive first-order reactions model respectively. And with the components analysis of woody biomass, the experimental data of pine hydrolysis was consonant with the model well.Due to the relatively high reducing sugars yield and future large-scale utilization, the hydrolyzate of the two step hydrolysis from poplar underwent fermentation by Candida tropicalis 2.637 and Saccharomyces cerevisiae 2.699 respectively. Simultaneously the influences to the ethanol yield by pretreatment methods, such as Ca (OH)₂ neutralizing, over- neutralizing, active carbon absorbance and yeast training, were carried out. The ethanol yield of the second step hydrolyzate reached to nearly 40% by Saccharomyces cerevisiae 2.699. However the Candida tropicalis 2.637 has the potential to use the hydrolyzate rich in pentose to produce single cell protein.