Mixed-acid and organic-amine pretreatments for effective sugar production from corncob

Abstract

Effective pretreatment is essential for producing fermentable sugars from lignocellulosic biomass. In this study, mixed-acid and organic-amine pretreatments were conducted for corncob deconstruction, component fractionation, lignin removal, and enzymatic saccharification. The sulfuric acid/maleic acid system (1:1, w/w) efficiently hydrolyzed hemicellulose, achieving glucose and xylose yields of 78.5% and 99.56%, respectively. 2D HSQC NMR analysis showed a clear decrease in the Cβ signal of β-O-4 linkages in G-type lignin units, indicating acid-catalyzed ether-bond cleavage. However, delignification in the acid system was limited to a maximum of 26.2%. In contrast, aqueous triethylamine pretreatment selectively removed lignin by cleaving ester and ether linkages in lignin-carbohydrate complexes while retaining most cellulose and hemicellulose. 2D HSQC NMR analysis revealed substantially weakened β-O-4 signals after amine pretreatment, indicating selective depolymerization with intact S and G units. Pretreatment with 30% triethylamine achieved 74% lignin removal. Enzymatic hydrolysis of the amine-pretreated residue gave 99.4% glucose, 89.1% xylose, and 93.7% total sugar yields. DFT calculations demonstrated that the amine system exhibits significantly stronger interactions with the lignin model (−32.78 kcal/mol) than organic acids (−18.52 and −15.08 kcal/mol), explaining its superior lignin affinity. These results show that mixed-acid pretreatment is suitable for xylose-oriented fractionation, whereas amine pretreatment is more suitable for delignification and glucose-oriented saccharification.