Catalytic fast pyrolysis of lignin to produce aromatic hydrocarbons: optimal conditions and reaction mechanism

Catalytic fast pyrolysis of lignin with zeolite catalysts is a promising method to produce aromatic hydrocarbons. In this paper, alkali lignin was used as a model compound to pyrolyze with HZSM-5 (silica to alumina ratio, SAR = 23), HZSM-5(50), HZSM-5(80), HY and Hβ. Non-condensable vapours and condensable fractions were determined and quantified by GC/FID and GC/MS respectively. 7.63 wt% of aromatic hydrocarbons and 3.34 wt% of C1–C4 alkanes and alkenes were acquired. The effects of catalysts and pyrolysis parameters were studied in this work. Different reaction pathways were compared and discussed by combining density functional theory (DFT) calculations. Cyclization reactions to form aromatic hydrocarbons were thought to be the main reaction pathway, while direct demethylation, demethoxylation and dehydration reactions were the secondary reaction pathway to convert phenolic lignin monomers to non-oxygenated aromatic hydrocarbons.