Aromatic hydrocarbon production by catalytic pyrolysis of palm kernel shell waste using a bifunctional Fe/HBeta catalyst: effect of lignin-derived phenolics on zeolite deactivation
Conversion of lignin to aromatic hydrocarbons over zeolites is a challenging issue due to low reactivity of lignin-derived phenolic compounds over zeolites as well as their high potential for strong adsorption on zeolite acid sites. Hence, pure zeolites are not appropriate catalysts for upgrading of the lignocellulosic biomass with high content of lignin. In this research, a bifunctional Fe/HBeta catalyst showed to be efficient for production of aromatic hydrocarbons in catalytic pyrolysis of palm kernel shell waste with a high lignin content of about 50 wt%. Lignin-derived phenolics were deoxygenated through a hydrogenolysis reaction promoted by Fe active sites. A comparison between catalytic behaviour of HBeta and HZSM-5 in conversion of palm kernel shells showed that catalyst deactivation via occupation of zeolite acid sites by lignin-derived phenolics is affected by catalyst pore size and strength of zeolite acid sites. Meanwhile, cellulose and lignin were compared in terms of reactivity over zeolite acid sites and influence on zeolite deactivation. It was also shown that the yield of aromatic hydrocarbons obtained from conversion of lignin was remarkably enhanced by incorporation of iron into the HBeta structure. However, both HBeta and Fe/HBeta resulted in approximately similar aromatic yield from conversion of cellulose.