Dilute acid hydrolysis of p-cresol-impregnated wood meal

Abstract

Dilute acid hydrolysis is typically conducted on wood to hydrolyze cellulose and hemicellulose into their compositional sugars, furfurals, or organic acids. However, lignin obtained in this process, also called hydrolysis lignin, cannot be generally used as a functional material. To overcome uncontrolled self-condensation of lignin, wood meal was impregnated with a small amount of p-cresol, and then, acid hydrolysis was performed with 1.1% sulfuric acid at 180 °C for 60 min. The cresol hardly changed the main products in the hydrolysate: glucose, formic acid, and levulinic acid. Much larger amount of lignin was extracted from the hydrolysis residue with tetrahydrofuran or by soda cooking than in the process without p-cresol impregnation. It seemed that the impregnated p-cresol was covalently bonded to lignin during acid hydrolysis and successfully prevented the self-condensation of lignin molecules, contributing improvement of the solubility of the resultant lignin in organic solvents or aqueous sodium hydroxide. Our hydrolysis process balances the valorization of carbohydrate with that of lignin.