Catalytic waste Kraft lignin hydrodeoxygenation to liquid fuels over a hollow Ni-Fe catalyst

Abstract

Conversion of Kraft lignin (KL) into liquid fuels is critically attractive but hampered by the inherent recalcitrant structure of KL. The phenolic intermediates formed during depolymerization of KL are prone to rapid repolymerization generating undesired repolymerization products (heavy oil and/or coke). In this work, KL depolymerization coupled with demethoxylation was achieved via a novel hollow Ni-Fe (H-NiFe2O4) catalyst under mild conditions. The liquid product yield reached 90 wt% with minimum coke yield of 3.4 wt% at 320 °C for 24 h. The petroleum ether soluble product has a yield of 70 wt%, molecular weight of 222 g/mol and a HHV of 35.3 MJ/kg. The H-NiFe2O4 catalyst exhibited excellent activity in promoting lignin depolymerization while depressing condensation. The meticulous characterization and control experiments indicated the catalytic performance of H-NiFe2O4 benefits from the synergy of Ni and Fe. Additionally, plausible reaction pathways of KL depolymerization over H-NiFe2O4 are discussed.