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We determined the effects of different hydrothermal liquefaction (HTL) process variables (temperature, holding time, algae loading, and water loading) on 13 different elements in biocrude and the aqueous phase co-product. Reaction conditions included both fast and isothermal HTL. The concentrations of P, Mg, Na, and Ca in the biocrude had their highest values at the mildest HTL conditions explored, and the concentrations decreased precipitously as even moderate HTL conditions were used. The concentrations of Zn, Cu, and Ni do not show much variation with HTL severity, whereas the concentration of Fe in the biocrude first increases and then decreases. P and Na were the most abundant elements in the biocrude from fast HTL, but Fe was the most abundant from isothermal HTL. These results show that the HTL conditions can influence the concentrations of different metals and inorganic species in algal biocrude from HTL.Special Issue: 6th Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies

We produced biocrude oil from microalgae at two hydrothermal liquefaction conditions and recovered the biocrude with eight different organic solvents to explore their influence on biocrude yields and metal content. We also determined how preventing contact between the organic solvent and the aqueous phase product influenced the metal contents in the biocrude, as this approach would likely be employed at scale. For all solvents tested save dichloromethane, the bio-oil yield is higher when the solvent and aqueous phase do not come into contact. For all solvents tested, the alkali metal contents of the biocrudes are 1 or 2 orders of magnitude higher when there is no contact between solvent and aqueous phase product. The choice of solvent can reduce the biocrude iron content by half and make a significant difference in other metals as well. Using MTBE alone or a combination of hexane and ethanol and not allowing the solvents to contact the aqueous phase gives the best results in terms of high biocrude yield and low metal contents.

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