Feedstock pumpability is one of the main obstacles for continuous processing of biomass through hydrothermal liquefaction, 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 a first stage, a pumpable feed is prepared by an alkaline treatment of coarse wood chips at 180 °C, 120 minutes reaction time and 0.35 NaOH-to-wood ratio. In a subsequent stage the treated feedstock is converted into a bio-crude 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. As 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.

This work proposes a novel strategy to improve the continuous processing of wood slurries in hydrothermal liquefaction systems by co-processing with algae. Of all algae tested, brown seaweeds and microalgae perform best in preventing slurries dewatering, the main reason for pumpability issues with wood slurries. Rheological tests (viscosity-shear rate profile) indicate that the addition of these two algae to the wood slurry causes the highest increase in viscosity, which coincides with improved wood slurries stability and pumpability. Hydrothermal liquefaction of wood-algae slurries at 400 °C and 15 minutes in 10 mL tubular batch reactors shows that macroalgae slightly decrease the biocrude yield from 28.5 wt% to 21.6-25.5 wt% while microalgae increase the biocrude yield with more than 40 % relative to pure wood liquefaction. Another benefit of microalgae addition is that the total biomass loading and the organic mass fraction of the slurry can be increased by 100 % and 90 % respectively. Therefore, when co-processed with wood, microalgae can improve the wood feedstock pumpability, biomass loading, organic matter and the biocrude yield.

A major challenge for the implementation of hydrothermal liquefaction (HTL) as a continuous process is the formulation of lignocellulosic feedstock, which is prone to phase separation into water and biomass parts when pressurized. One approach to remedy such phase separation is to reduce the dry matter content; however, as this approach is detrimental to process cost efficiency, designing an appropriate pretreatment step to ensure pumpability at high dry matter content is preferable. This paper evaluated the effect of various pretreatment methods on product distribution and composition resulting from the HTL of willow and proposes short rotation coppice as an alternative biomass feedstock for biofuels production. Alkaline-thermal pretreatment, besides making high dry matter pumpable feedstock slurries, also led to an increase in the production of the bio-crude product with an oxygen content lower than 8wt% and a higher concentration of aromatics and phenolic compounds.

No abstract

No abstract