In-situ and ex-situ catalytic upgrading of vapors from microwave-assisted pyrolysis of lignin

In-situ and ex-situ catalytic upgrading with HZSM-5 of vapors from microwave-assisted pyrolysis of lignin were studied. The in-situ process produced higher bio-oil and less char than ex-situ process. The gas yield was similar for both processes. The ex-situ process had higher selectivity to aromatics and produced more syngas and less CO₂ than the in-situ process. Additional experiments on ex-situ process found that the bio-oil yield and coke deposition decreased while the gas yield increased at higher catalyst-to-lignin ratios and catalytic upgrading temperatures. The increased catalyst-to-lignin ratio from 0 to 0.3 reduced the selectivity of methoxy phenols from 73.7% to 22.6% while increased that of aromatics from 1.1% to 41.4%. The highest selectivity of alkyl phenols (31.9%) was obtained at 0.2 of catalyst-to-lignin ratio. Higher catalytic temperatures favored greater conversion of methoxy phenols to alkyl phenols and aromatics. Appropriate catalyst-to-lignin ratio (0.3) together with higher catalytic temperatures favored syngas formation.