Integrated lignocellulosic bioprocess for co-production of ethanol and xylitol from sugarcane bagasse

Abstract

Economics of cellulosic ethanol production could be supported by high-value chemicals co-production, e.g. xylitol, which has high market value in food and pharmaceutical industries. Herein, we present an integrated sugarcane bagasse processing for the co-production of ethanol and xylitol from cellulose and hemicellulose, respectively. Process integration comprised pretreatment followed by separation of hemicellulosic hydrolysate and pretreated cellulose, in combination with enzymatic hydrolysis and fermentation. Saccharomyces cerevisiae was used for ethanol production in a simultaneous saccharification and fermentation process of pretreated cellulose, and Candida tropicalis was selected for xylitol fermentation of hemicellulosic hydrolysate. Batch process parameters were systematically optimized resulting in 7.5 FPU/g optimal enzyme load, 0.03 g/L and 0.035 g/g optimal inoculum size, 89 h−1 optimal kLa and 54 g/g optimal sugar-to-nitrogen ratio. Finally, fed-batch strategy was accomplished yielding maximum concentrations of ethanol by S. cerevisiae and xylitol by C. tropicalis at 56.1 g/L and 24.0 g/L, respectively. Of the total glucose and xylose available in bagasse, the product yield of 0.44 g/g (ethanol) and 0.50 g/g (xylitol) were reached. Economic analysis revealed that the incorporation of xylitol with ethanol in an integrated biorefinery together with fed-batch strategy for high-titer product could improve profitability by 2.3-folds compared to base case of cellulosic ethanol production. Hence, this integrated biorefinery for co-production could be attractive to current cellulosic ethanol for advancing economic feasibility.