Ethanol Production from Hydrolyzed Soybean Molasses

The aim of this work was to produce ethanol using the acid hydrolysis of soybean molasses followed by alcoholic fermentation via submerged Saccharomyces cerevisiae . The influence of the acid type, pH, and absolute pressure of the hydrolysis on the ethanol yield and the total residual sugar concentration was evaluated using a factorial design (FD). The absolute pressure ranged from 1 to 2 atm; the pH ranged from 3 to 5; and three different acids were studied in the hydrolysis process: sulfuric, hydrochloric, and nitric acids. The experiments were conducted in an Applicon batch reactor with a useful volume of 1.5 L at a stirring speed of 230 rpm and with an inoculum concentration of 30 g/L. The inoculum volume used was 30% of the total volume. The best results, as determined by FD, were obtained at pH 4 and an absolute pressure of 1.5 atm for all of the acids studied. The highest ethanol yield was 46% for sulfuric acid, 48% for hydrochloric acid, and 54% for nitric acid. After the concentration of inoculum and the fermentation kinetics profiles were investigated, a 62% yield relative to the initial sugar content was obtained under optimum conditions after 14 h of fermentation and an inoculum concentration of 35 g/L.