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

Abstract

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 FeO_x/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 FeO_x/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.

Keywords: Biomass waste; Catalyst reusability; Hydrothermal liquefaction; Magnetic separation; Magnetite.