Comparative Study of Chemical Pretreatments and Acid Saccharification of Bagasse of Sugar Crops for Ethanol Production

Abstract

The bagasse of two sugar crops i.e. sugarcane (variety CoJ 83) and sweet sorghum (variety RSSV 9) were evaluated for their potential for the production of bioethanol. Different chemical pretreatments were carried out with 2 % H2O2, 1 % NaOH and 2 % H2O2 + 1 % NaOH solutions each with pH 11.5 and 13 for 24, 48 and 72 h followed by saccharification of pretreated bagasse with sulfuric acid (0.8 and 1 M) for 50 min. Bagasse hydrolysates were then fermented with Saccharomyces cerevisiae var ellipsoideus for ethanol production. The amounts of cellulose, hemicellulose and lignin were 47.1, 29.2, 11.2 % in sugarcane and 45.8, 28.1, 14.0 % in sweet sorghum respectively. Loss of weight in alkaline pretreatment was found more in sugarcane (45.4 %) than in sweet sorghum (43.1 %). The maximum amounts of reducing sugars 528.8 and 504.8 mg/g were obtained by saccharification of pretreated bagasse of sugarcane and sweet sorghum respectively, after saccharification with 0.8 M H2SO4. Bioethanol production was found maximum 30.5 and 26.2 ml/100 g pretreated bagasse in sugarcane and sweet sorghum with pretreatment conditions of (2 % H2O2 + 1 % NaOH; pH 11.5, 72 h) and (2 % H2O2 + 1 % NaOH; pH 13, 72 h) respectively, followed by saccharification with 0.8 M H2SO4, and fermentation for 72 h. But when estimated ethanol production on unit weight basis of crops, it was found higher in sweet sorghum (25.4 L/ton stalks) crop than in sugarcane (21.4 L/ton stalks).