Sequential dilute acid/alkali pretreatment of corncobs for ethanol production

Abstract

ABSTRACT A two-step pretreatment using sequential dilute acid/alkali was applied in this study to improve the hydrolysis of corncobs. 88.6% of the hemicellulose was selectively removed by dilute sulfuric acid hydrolysis (DA) in the first step, 88% of the lignin was effectively extracted by sodium hydroxide in the second step. Consequently, a high content of glucan (74.4%), corresponding to 94.6% recovery, remained in the pretreated biomass. The substrate enzymatic digestibilities (SED) of the two-step pretreated biomass were 64%, 80%, 91%, and 93% after 72 h hydrolysis with enzyme loadings of 5, 10, 15, and 20 FPU/g substrate, respectively, which were much higher than those of the DA-pretreated material. The ethanol concentration after the simultaneous saccharification and fermentation (SSF) process at 15% (w/w) solids loading reached 52 g/L, equivalent to 77.2% of the theoretical ethanol yield based on an untreated corncobs glucan content. The changes to the chemical and physical structures of the residues detected by SEM, FTIR, and the DPv test were correlated with the improved enzymatic digestibility.