Magnetically recoverable catalysts and base recycling for sustainable hydrothermal liquefaction of woodchips

This study investigates the hydrothermal liquefaction (HTL) of complex lignocellulosic woodchips (WC) using low-cost, magnetically recoverable carbon-supported magnetite (ACM) catalysts combined with homogenous Na 2 CO 3 (SC) base catalyst. While the presence of SC was essential to improve bio-oil yields from 4.5 % to 11.8 %, the addition of ACM under optimised conditions (7.5 % Fe/C, 1:1 catalyst ratio) further increased bio-oil yields to 15.6 %, representing a fourfold increase over non-catalytic HTL conditions. At the same time, the higher heating value (HHV) of the oil was increased from 30.0 to 34.3 MJ kg −1 , with a corresponding H/C value of 0.84. This improved performance is attributed to the combined effects of ACM, which promotes deoxygenation and cracking reactions, and SC, which enhances hydrolysis of the lignocellulosic matrix and stabilises intermediates. The magnetic properties of ACM enabled facile recovery and reuse, with the catalyst maintaining> 80 % activity across five cycles. AP recycling was successfully used to recover >50 % of base catalyst and led to a further 2 % increase in oil yield. These findings demonstrate that the ACM/SC tandem system offers a promising, recyclable and scalable approach for improving HTL oil yields and quality, though further studies are needed to assess long-term stability and industrial viability under continuous-flow conditions. • New recyclable dual catalyst system for HTL of lignocellulosic biomass (woodchips). • Four times bio-oil yields (4.5 %–15.6 %) with improved HHV (30.0–34.3 MJ kg −1 ). • Na 2 CO 3 (SC) promotes hydrolysis and can be recycled with HTL aqueous phase. • Supported magnetite catalyst (Fe 3 O 4 /C) facilitates deoxygenation and cracking. • Fe 3 O 4 /C's magnetic properties enable catalyst recovery and reuse over 5 cycles.