Hydrothermal Liquefaction of Pinewood Sawdust: Influence of Reaction Atmosphere

Abstract

Hydrothermal liquefaction (HTL) is a thermochemical process for production of biocrude oils, commonly from wet biomass under inert atmosphere (N2). Influence of reaction atmosphere on HTL of pinewood sawdust was investigated in this work, at 300 °C for 60 min with the presence of KOH or H2SO4 catalyst under N2, H2, and O2 atmosphere, respectively. Very interestingly, the reaction atmosphere showed significant influence on both products distribution and properties of the biocrude oils. Generally, H2 atmosphere enhanced biomass degradation in the presence of either KOH or H2SO4 catalyst, producing the highest biocrude oil yield, lowest solid residue yield, and the best oil quality in terms of total acid number (TAN), viscosity and average molecular weights (Mn, Mw). Whereas the HTL in O2 atmosphere showed the poorest performance in terms of yields and properties of biocrude oils. The highest quality of biocrude oil was produced using KOH catalyst in H2 atmosphere with the maximum biocrude yield (approx. 34 wt.%) and the highest energy recovery (ER) in biocrude (ER = 73.14%). The measured properties of the oil are as follows: TAN = 40.2 mg KOH/g, viscosity = 51.2 cp, Mn = 470 g/mol, Mw = 767 g/mol. In addition, the biocrude oils produced in H2 atmosphere contain more light oil (naphtha) fraction (23.9 wt.% with KOH and 16.5 wt.% with H2SO4) with lower boiling points, while those generated in O2 atmosphere have more carboxylic acid compounds.