The effect of hemicelluloses and lignin on acid hydrolysis of cellulose

In acid hydrolysis of plant biomass, polysaccharides are converted to monosaccharides, which is basic raw material for biorefinery for fermentation based process. These monosaccharides, however, are not stable in acidic reaction medium, and are converted to organic acids via furans. Impact of hemicelluloses and lignin on acid hydrolysis of cellulose was investigated to focus on monosaccharide production with different degrees of cellulose purity. Two-step concentrated sulphuric acid process was applied to biomass for monosaccharide conversion. Kinetics of cellulose hydrolysis was analysed using 1H NMR spectroscopy. Higher reaction temperature in secondary hydrolysis caused severe degradation of the monosaccharides. In pure and holocellulose, further reaction of glucose in acidic reaction medium produced formic acid and levulinic acid. However, lignocellulosic biomass generated much less formic acid and levulinic acid under the same reaction condition. Humin (or pseudo-lignin) was also formed by the condensation of lignin and furans from monosaccharides in acidic reaction condition. Thus, the fermentation inhibitors, furans and formic acid, were generated in low quantities by lignocellulosic biomass than by delignified biomass such as pure cellulose or holocellulose.