Study the effect of zeolite pore size and acidity on the catalytic pyrolysis of Kraft lignin

Abstract

In this study, three zeolites with different pore sizes and acidity, H-Beta, HY and HZSM-5, were used for the preparation of bio-oil by catalytic pyrolysis of Kraft lignin at 600 °C. The three-dimensional sizes and kinetic diameters of the bio-oil components were calculated using quantum chemical calculations, and the bio-oil was analyzed by heteronuclear single quantum coherence nuclear magnetic resonance (HSQC-NMR). The effects of zeolite acidity and pore size on the bio-oil upgrading process were studied for the pyrolysis products of Kraft lignin. The results showed that optimum pore size of the zeolites ranged from 6.500 Å–8.400 Å during the catalyzed pyrolysis of lignin. Among the zeolites, the H-Beta zeolite is the most effective in the lignin pyrolysis. The results also showed that the pore size and acidity of the zeolites had a significant effect on the product yields, coking and deoxygenation. The pore size affects the coking and dehydration reactions, while the acidity can promote the rearrangement of ether bonds or the breaking of lignin side chains and deoxygenation reactions. This study would be beneficial to improve the zeolite catalytic activity and minimize the oxygen content in bio-oil produced from the pyrolysis of Kraft lignin.