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

Abstract

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.