Sustainable production of aromatic-rich biofuel via catalytic co-pyrolysis of lignin and waste polyoxymethylene over commercial Al2O3 catalyst

Abstract

Co-valorization of biomass and multiple solid wastes is essential to environment protection and energy security. Herein, aromatic-rich biofuel was produced from lignin and waste polyoxymethylene (POM) via catalytic co-pyrolysis process. Commercial and cheap γ-Al2O3 catalyst exhibited good catalytic performance. Series characterizations and bench-top pyrolysis experiments were conducted to illustrate the synergism between raw materials and the mechanism of aromatics formation. The TG analysis and thermodynamics calculation revealed that a remarkably positive synergistic effect existed between lignin and POM, which reduce the activation energies and make the reaction more conducive in terms of thermodynamics. Meanwhile, the yields of biochar and bio-oil increased considerably. Additionally, the operating conditions affected the product distributions significantly. The suitable mixing ratio of lignin to POM was around equal (5:5) with the bio-oil yield increased to 28.3 % and aromatic hydrocarbons selectivity increased to > 95 %. Moreover, POM, the precursor for alkylating reagents and hydrogen donors, could promote the deoxygenation reactions of phenolic intermediates and result into aromatic hydrocarbons. The acid sites of γ-Al2O3 promoted series secondary cracking reactions (alkylation, deoxygenation), and thus improved bio-oil quality. Finally, the stability test showed that commercial γ-Al2O3 catalyst was slightly deactivated after 4 cycles because of coke deposits and acid sites loss.