Pretreatment of Rice Straw by Inorganic Salts and 1-Ethyl-3-methylimdazolium Acetate for Biofuel Production

Ionic liquid (IL) pretreatment is an efficient method to improve the enzymatic hydrolysis. The limitation of using IL is its high cost, thus there is a need for improvement to make it feasible for industrial applications. In this research, IL, 1-ethyl-3-methyl-acetate (Emim-AC), pretreatment of rice straw was conducted by mixing with inorganic salts to reduce the load of IL in the reaction, i.e. reduce the cost of the process. The aqueous mixtures of Emim-AC and 6 types of inorganic salts, including NaCl, KCl, MgCl2, NaNO3, KNO3 and Mg(NO3)2 were individually prepared and were tested at the same condition to pretreat rice straw. Among these salt mixtures, a combination between Emim-AC and NaCl was the best method providing the highest reducing sugar at 3.099 mg/ml. Then, the simplex lattice design was applied to find the optimum proportion of Emim-Ac, NaCl and water in the pretreatment mixture. The experimental data obtained from the design were analyzed with ANOVA and the mathematical model of mixture formulation was constructed with high correlation coefficient (R2). The highest yield of reducing sugar at 16.5967 mg/ml was obtained in the formulated mixture containing 0.9% of NaCl, 71.856% of Emim-AC and 9% of water. This work suggested the possibility to reduce the IL cost by reducing load of IL for bioconversion process of lignocellulosic biomass to value-added chemicals and biofuels.