Multi-Response Optimization of Thermochemical Pretreatment of Soybean Hulls for 2G-Bioethanol Production

Soybean is a major crop used in the production of human food. The soybean hull (SH) is also known as the seed coat and it constitutes about 5-8% of the total seed on a dry weight basis, depending on the variety and the seed size. Dilute sulfuric acid was employed for the thermochemical pretreatment of SH prior to enzymatic saccharification and alcoholic fermentation. Empirical modeling of response surface, severity factor and multi-response desirability function methodology, were used to perform the process optimization. Temperature, acid concentration and reaction time were defined as operational variables, while furfural, 5-hydroxymethylfurfural and solubilized hemicellulose and cellulose were defined as response variables. Mathematical models satisfactorily described the process and optimal conditions were found at 121 ?; 2.5% w/v H2SO4 and 60 min. More than 80% and 90% of hemicelluloses and celluloses, respectively, were able to solubilize at this point. The fermentation performance of an industrial Saccharomyces cerevisiae strain was also evaluated. The glucose available in the hydrolysates was completely consumed in less than 12 h, with an average ethanol yield of 0.45 g(ethanol)/g(glucose). Thus, the thermochemical conditioning of SH with dilute sulfuric acid is a suitable operation for 2G-bioethanol production.