Optimization of the acid pretreatment of rice hulls to obtain fermentable sugars for bioethanol production

The structural complexity of the lignocellulosic materials hinders enzymatic hydrolysis for what their conversion to bioethanol requires a pretreatment step. The aim of this work was to optimize the pretreatment of rice hulls with diluted acid. A Central Composite Design (CCD) was used to obtain regression equations in function of the variables: acid concentration and heating time. Optimal conditions were obtained by the Desirability function. As a strategy to obtain the best solid material for the production of ethanol by fermentation minimizing sugars degradation, the optimization of the pretreatments was performed following three scenarios. The optimum was established as the conditions that maximize glucans in the solid and xylose in the liquid (0.3% (w/v) of sulfuric acid and a 33 min). The pretreated rice hull in those conditions was treated enzymatically. The performance of the enzymatic hydrolysis was about 50% (25% of total sugars present) over a period of 48 h of reaction, and the efficiency of conversion of dissolved sugars to bioethanol was of 84%.

► Report of the optimization of the acid pretreatment of rice hulls to obtain fermentable sugars for bioethanol production. ► Optimum acid pretreatment of rice hulls with 0.3% (w/v) H2SO4 for 33 min. ► Considerable purification of glucans (18.7% increases) by extraction of xylans (14.7%). ► Mild enzymatic conversion of glucans to glucose (50%) and good efficiency of bioethanol production (84%).