Catalytic Pyrolysis of Lignin for Directional Production of p-Xylene over Metal Oxides-Modified HZSM-5 Catalysts

Abstract

Para-xylene (p-xylene) is an important bulk chemical in petrochemical industry, and the production of biomass-based p-xylene is of great significance in both academic and industrial arenas. This work proves the one step process for the production of p-xylene through the catalytic pyrolysis of lignin into the aromatic monomers, together with the alkylation of light aromatics and the isomerization of xylenes isomers into p-xylene over metal oxides-modified HZSM-5 catalysts. The modified catalysts by adding the La, Mg, Ce, and Zn elements into HZSM-5 promoted the alkylation of light aromatics (like benzene and toluene) into xylenes, and the isomerization of m-/o-xylenes to p-xylene, due to the modulations of the acid strength and the strong acid sites. Co-catalytic pyrolysis of lignin and methanol significantly enhanced the production of p-xylene during the catalytic pyrolysis of lignin. The highest p-xylene yield of 13.9% with a p-xylene/xylenes ratio of 82.7% was obtained by the co-catalytic pyrolysis of lignin with 33 wt% methanol over the 20% La2O3/HZSM-5 catalyst. The reaction pathway for the formation of p-xylene from lignin was addressed based on the identified products and the characterization of catalysts.