(387c) Bioconversion of Lignocellulose Into Bioethanol: Process Intensification and Mechanism Research

Bioethanol is one of the most potential renewable energies. For large-scale usage, lignocellulosic material is a promising choice to produce a second generation bioethanol fuel. However, there are a number of obstacles such as slow reaction rate, high production costs, non-cellulosic material block, and low ethanol concentration, which diminishing the enzyme performance and hinder the progress of biomass industrialization. This paper summarizes our work on bioconversion of lignocellulose into bioethanol aiming to enhance enzyamtic hydrolysis efficiency and increase final ethanol concentration. Process Intensification. (1) Optimization of enzyme complex: The digestion of cellulose was increased by enzyme complexes of cellulase and accessory enzymes including â-glucosidase, xylanase and pectinase to hydrolyze cellobiose, hemicellulose and pectin, respectively. (2) Cellulase recovery: In order to reduce the high cost of enzymes, different strategies were used to decrease use cost by enzyme recycling and reuse. By optimize the operation condition, cellulase, mainly cellobiohydrolase (CBH) can be recycled and the recovery efficiency was reached 85% by the process of cellulase adsorption onto fresh material; â-glucosidase can be reused four times by immobilization; and by the method of fed-enzyme membrane bioreactor (MBR), utilize efficiency was 3.31-fold of conventional batch reator (CBR), and 1.32-fold of fed-CBR for corn stover pretreated by diluted sulfuric acid?sodium hydroxide. (3) High solids SSF: High dry matter is essential to increase production concentration. High ethanol concentration up to 84.7 g/L was obtained at high DM concentration of 25% in fed-batch simultaneous saccharification and fermentation of corncob treated by combination of acid and alkali, which was higher than 4% (v/v), the low level of economically feasible distillation. Moreover, simultaneous saccharification and co-fermentation with a recombined Z.mobilis was carried on and a final ethanol concentration of 60.52 g/L was obtained for 10% DM supplementation giving a total DM of 25%. Reaction mechanism. On the other hand, in order to explore the reaction mechanism and direct the process development, multi-scale properties of substrate during enzymatic hydrolsis were investigated. (1) Hydrolysis behavior of Cellulases: By the established method of SEC/MALLS coupled with differential refractive index, microcrystalline cellulose and filter paper cellulose were characterized to reflect different reaction pattern of cellobiohydrolase (CBH) and endoglucanase (EG) on substrate. It was found that EG digestion follows a random scission pattern, while CBH digestion follows a layer-by-layer solubilisation pattern, which probably be the major reason for low efficiency of cellulase. (2) Substrate Limitation: Key factors of substrate that limit cellulose hydrolysis were characterized by different detection techniques. According to results of the partial least square analysis, the most important factor for cellulose digestion was accessible interior surface area, followed by delignification and the destruction of the hydrogen bonds.