Two-stage alkaline hydrothermal liquefaction of wood to biocrude in a continuous bench-scale system

Feedstock pumpability is one of the main obstacles for continuous processing of biomass through hydrothermal liquefaction (HTL), due to their tendency to form heterogeneous slurries. In this work, a novel strategy is proposed to ensure lignocellulosic feed pumpability in HTL processing, even while applying elevated biomass loadings. In the first stage, a pumpable feed is prepared by an alkaline treatment of coarse wood chips at 180 °C, 120-min reaction time, and 0.35 NaOH-to-wood ratio. In a subsequent stage, the treated feedstock is converted into a biocrude in a continuously operated 20 kg/h scale unit. In total, 100 kg of wood paste with 25% dry matter is processed at 400 °C and 30 MPa, demonstrating the usefulness of this two-stage liquefaction strategy. An additional advantage liquefaction of such pretreated wood shows increased biocrude yields with approximately 10% compared to the case where non-pretreated wood is liquefied.