Sweet Sorghum Biorefinery for Production of Fuel Ethanol and Value-Added Co-products

Abstract. An integrated process has been proposed for a sweet sorghum biorefinery in which all carbohydrate components of the feedstock were used for production of fuel ethanol and industrial chemicals. In the first step, the juice was extracted from the stalks. The resultant bagasse was then pretreated using the soaking in aqueous ammonia (SAA) process, which did not result in significant loss of cellulose and hemicellulose, to enhance subsequent enzyme hydrolysis for production of fermentable sugars. Following pretreatment, the bagasse was hydrolyzed with a commercial enzyme product containing high hemicellulase activity (Accellerase XY). The xylose-rich solution obtained after solid/liquid separation was used for production of value-added co-products using suitable microorganisms. The value-added co-products produced to demonstrate the feasibility were astaxanthin and D-ribose. The residual solids were then hydrolyzed with a commercial enzyme product containing high cellulase activity (Accellerase 1500), with the juice extracted in the first step used as make-up water. By combining the sugar in the juice with the glucose released from the residual solids by enzyme hydrolysis, high ethanol concentrations could be achieved, which resulted in lower distillation cost than if pure water were used for enzyme hydrolysis and subsequent fermentation, as normally performed in cellulosic ethanol production.