Conversion of phenol intermediates into aromatic hydrocarbons over various zeolites during lignin pyrolysis

Abstract

The goal of this study was to investigate conversion features of phenol intermediates produced in lignin pyrolysis into aromatic hydrocarbons (AH) over zeolite catalysts. Ten lignin-derived monomeric phenols were selected and classified into three groups on the basis of their structures: NP (phenols without side chains), SP (phenols with saturated side chains), and OP (phenols with oxygenated functional groups). Each compound was pyrolyzed in the temperature range from 600 to 800 °C over three zeolite catalysts (Y, BETA, and ZSM-5). Benzene, toluene, xylenes (BTX), and naphthalene were produced as the main AH. This study revealed that phenol structure had a significant influence on formation of AH during catalytic pyrolysis. In particular, the yield of AH was considerably higher from SP type phenols (70–140 µg/mg) than other types (30–70 µg/mg). Pyrolysis temperature also affected the amount of benzene produced because a higher pyrolysis temperature promoted cleavage of side chains on the aromatic ring, which could be converted into AH over acidic sites in the zeolite catalyst. Based on these results, possible conversion pathways of lignin-derived phenols were suggested. Among the three types of zeolite catalysts, the Y type was found to be the most effective for producing monocyclic AH due to its suitable pore size and highest acidity/surface area. Meanwhile, BETA was the most effective catalyst for formation of naphthalene.