Ethanol Production from Sugarcane Bagasse Using Phosphoric Acid-Catalyzed Steam Explosion

The steam explosion was carried out in the absence (autohydrolysis) and presence of phosphoric acid to evaluate the effects of temperature (180 and 210 °C), acid concentration (0 and 19 mg g-1, dry basis) and pretreatment time (5 and 10 min) on the structure and reactivity of sugarcane bagasse. Glucan recovery was used as the main response factor for pretreatment optimization through a central composite design. Autohydrolysis at 210 °C for 10 min had a good pretreatment performance but phosphoric acid catalysis (19 mg g-1) resulted in better yields under considerably milder conditions (180 °C, 5 min). Hydrolysis of both substrates for 96 h using 8 wt.% total solids and 30 mg g-1 Cellic® CTec2 (Novozymes) provided total glucose yields of 75% in average. The production of cellulosic ethanol was assessed by both separate and simultaneous hydrolysis and fermentation using Saccharomyces cerevisiae. Freeze-drying of pretreatment water solubles reduced the concentration of furfural, hydroxymethylfurfural and acetic acid by more than 80% and this eliminated their inhibitory effect on yeast fermentation.