Highly active and magnetically recoverable heterogeneous catalyst for hydrothermal liquefaction of biomass into high quality bio-oil

[Display omitted] •A cheap, magnetic Fe3O4 catalyst for hydrothermal liquefaction of draff.•Mass and carbon recovery increased by 49.3% and 34.8%, respectively compared to non-catalytic.•82.0 % carbon recovery to bio-oil, with 87.2 % deoxygenation and HHV of 37.7 MJ kg−1.•Catalyst was successfully separated from solid ash products after reaction.•Catalyst was active and recoverable even up to 5 reaction cycles. This article reports a safe, low-cost, and industrially applicable magnetite supported on activated carbon catalyst that can be magnetically retrieved from the solid and reused multiple times without the need of a regeneration step. The FeOx/C catalyst improved the bio-oil yield by 19.7 ± 0.96 % when compared to the uncatalysed reaction at 320 °C for the HTL of draff (brewer’s spent grains). The use of homogeneous Na2CO3 base as a catalyst and co-catalyst, improved carbon extraction into the aqueous phase. The exceptional catalytic activity can be attributed to the Fe3O4 phase which can produce in-situ H2 that improves the biomass decomposition and oil property with an energy recovery of ∼84 %. The FeOx/C catalyst was separated using magnetic retrieval and maintained its catalytic activity even up to 5 reaction cycles showing potential as a cheap catalyst for HTL reactions and can be scaled-up for industrial applications.