Hydrophilic pretreatment of furfural residues to improve enzymatic hydrolysis

Furfural residues (FRs) is an industrial waste material with an enormous potential for bio-ethanol production. In this study, FRs were pretreated with green liquor (GL) combined with hydrogen peroxide (GL–H₂O₂) or ethanol (GL-ethanol). The wettability and electrostatic contributions of untreated and pretreated FRs was investigated as well as that of isolated lignin cellulolytic enzyme lignin (CEL) and cellulose. The results showed that the hydrophilicity of FRs was increased after GL–H₂O₂and GL-ethanol pretreatment. Lignin is the key factor that affects the hydrophilicity of substrate. The cellulase binding for lignin was reduced due to the increase of hydrophilicity of lignin, resulting in the improvement of enzymatic hydrolysis. The electrostatic contributions was also an important factor that influenced the cellulase binding of lignin. After pretreatments, the negative charge of lignin was decreased. Accordingly, the cellulase binding capacity was reduced. This effect was more significant after the GL-ethanol pretreatment. Thus, the glucose yield of the substrate obtained from the GL-ethanol pretreatment (86.1 %) was larger than that from the GL–H₂O₂pretreatment (82.2 %). Unlike the CEL, GL–H₂O₂pretreatment increased the negative charge of cellulose. And the increase of negative charge improved the affinity of cellulose to cellulase via electrostatic attraction. The XPS analyses indicated that the carbonyl groups from lignin play an important role in decreasing the hydrophobicity of the substrates.