Wet and Coarse: The Robustness of Two-Stage Crude Glycerol Mediated Solvothermal Liquefaction of Residual Biomass

Biomass residues were liquefied via two stage crude glycerol (CG) mediated solvothermal liquefaction (STL) at moderate temperatures with intention for industry-friendly production and direct biopolyol utilisation. Digested sewage sludge, hemp stalk hurd and sugar beet pulp were chosen as the local case feedstocks. The study goal was to investigate how robust CG-mediated STL is in terms of different feedstocks, powder particle size (< 0.2 to 0.5-1 mm) and dry matter content (20-100%). Sugar beet pulp performed best in terms of biomass conversion, followed by hemp stalk hurds and digested sewage sludge at 80%, 56% and 42%, respectively. Digested sewage sludge and sugar beet pulp liquefaction runs indicate that the extent of the base catalysed step could be lessened for some feedstocks. Hydroxyl numbers of the slightly alkaline biopolyols varied from 77 to 282 mgKOH/g. The process is shown to be robust universally with respect to feedstock particle size, while varied dry matter content has differing effects on the three residual biomass resources.