Catalytic conversion of guaiacol as a model compound for aromatic hydrocarbon production

Guaiacol, a mono-aromatic compound containing a hydroxyl and a methoxyl group, is one of the main products from lignin pyrolysis. In order to investigate the feasibility of aromatic hydrocarbons production from lignin, guaiacol was employed as the model compound for the catalytic conversion over HZSM-5 zeolites with different Si/Al ratios in a fixed-bed reactor under the temperatures from 500 °C to 800 °C. With the increased temperature, the yield of both aromatic hydrocarbons (such as benzene, toluene, styrene, naphthalene and 2-methylnaphtalene) and coke was increased from the mass fraction of 1.83%-24.27% and from 1.17% to 12.81%, respectively. At 600 °C, the yield of benzene was promoted by the HZSM-5 catalyst with high Si/Al ratio (200) by the mass fraction of 2.94% and up to 1.94% for that of toluene. The production of monocyclic aromatic hydrocarbons (especially for benzene and p-xylene) was favored with the loading of Ni on HZSM-5(25), while the formation of polycyclic aromatic hydrocarbons was notably inhabited. The coke deposition was slightly increased with the increased loading of Ni during the catalytic conversion of guaiacol. The demethoxylation and dehydroxylation reactions were considered to be promoted by the increase of Brønsted acid sites, while the methyl substitution reaction was slightly influenced by the total acidity of catalyst. The experimental results provided the conceptual and technical support for the catalytic pyrolysis of lignin to produce aromatic hydrocarbons.