Dilute acid hydrolysis of sweet sorghum bagasse and fermentability of the hemicellulosic hydrolysate

Abstract

This study aimed to determine the best dilute acid hydrolysis condition for the hemicellulosic fraction of sweet sorghum bagasse for ethanol production by Scheffersomyces stipitis. The experiment followed a 23 factorial design with four central points, and had as variables: sulfuric acid concentration, temperature and hydrolysis time. Sorghum bagasse presented the following chemical composition: 24.77% of lignin, 31.28% of hemicellulose and 34.80% of cellulose. The hydrolysis that resulted in the highest sugars concentration (14.22 g/L of xylose and 2.42 g/L glucose) was 1.75% H2SO4, 121 °C and 40 minutes. This same condition provided low concentrations of toxic compounds (1.34 g/L of acetic acid, 0.90 g/L of phenol; 124.54 mg/L of hydroxymethylfurfural (HMF) and 978 mg/L of furfural). The fermentation of the hemicellulose-derived sugars by S. stiptis resulted in 22 g/L of ethanol, YP/S 0.40 g/g and Qp 0.34 g/L.h.