Sequential catalytic-mixed-milling and thermohydrolysis of cassava starch improved ethanol fermentation

Abstract

© 2018 Cassava starch is an abundant feedstock for biological transformation to ethanol, however, its industrial processing needs further improvements to enhance efficiency and cost-effectiveness. In the present study, a low-cost catalyst (CC–SO3H) was synthesized by partial carbonization and sulfonation of crystalline cellulose, which was thermally stable and reactive at 160 °C in 5 times repeated batch of thermohydrolysis of cassava starch. The catalyst was studied for its potential role in the hydrolysis of cassava starch as a standard feedstock. It was shown that the milling of cassava starch in the presence of the CC–SO3H catalyst improved the solid-state reaction that enhanced porosity, increased surface area and decreased crystallinity of the starch granules. These phenomena caused the rapid thermohydrolysis of starch with an exceptionally high starch conversion rate (96.43%), glucose yield (93.12%), and glucose selectivity (95.32%) within 2 h of reaction at 160 °C, 10 bar. The highest ethanol yield (0.43 g ethanol/g total reducing sugars) was achieved at 96 h of fermentation corresponding to the highest ethanol concentration of 15.41 g/L from the fermentation of hydrolysate of mixed-milling/thermo-hydrolysis at 160 °C for 2 h of cassava starch. In addition, the reaction kinetics showed the feasibility of this process for robust bioethanol production from starchy feedstocks.