Production of aromatic hydrocarbons from lignin derivatives by catalytic cracking over a SiO₂-Al₂O₃ catalyst

Catalytic cracking of phenolic compounds to aromatic hydrocarbons is vital to the utilization of lignin. In this work, pristine amorphous SiO₂-Al₂O₃ was used as a catalyst to produce aromatic hydrocarbons from lignin-derived phenolics by catalytic cracking using methanol as the solvent. These catalysts were characterized by various techniques (XRD, NH₃-TPD, Py-IR, etc.) and evaluated on a fixed bed reactor using guaiacol as a model compound. The effects of reaction temperature, the flow of carrier gas, the molar ratio of guaiacol to methanol, and WHSV were investigated. 33-SA (SiO₂-Al₂O₃ with the SiO₂ content of 33%) exhibited the best catalytic activity due to its high content of Lewis acid sites (168.47 μmol g^-1). Co-feeding with methanol promoted the removal of oxygen atoms and improved the reaction system H/C_eff. Under the optimal conditions of 400 °C, 25 mL min^-1 N₂, a molar ratio of methanol to guaiacol of 25, and WHSV of 8/3 h^-1, the yield of aromatic hydrocarbons reached 57.93%. The deactivating species in the transformation of guaiacol into aromatic hydrocarbons on catalysts were also studied.