Solvent effect on HZSM-5 catalyzed solvolytic depolymerization of industrial waste lignin to phenols: superiority of the water–methanol system over methanol

Abstract

Kraft lignin from industrial black liquor was subjected to one-pot solvolytic depolymerization and hydrodeoxygenation over zeolite HZSM-5 as catalyst and NaOH as co-catalyst at 220 °C. The effect of methanol and a water–methanol (1 : 1) mixture as solvent on the lignin depolymerization products was studied. The products were characterized by infrared spectroscopy and numerical indices based on IR spectra of the product mixture were defined to study the functional group transformations occurring in the reaction. Compared to NaOH in pure methanol, NaOH in water–methanol was found to be efficient in suppressing char formation and enhancing product quality and quantity. Alkyl substituted phenols were found to be the major product (14.1 wt%). Other than phenols, formation of long chain aliphatic compounds was also observed.