Using Solvents to Reduce the Metal Content in Crude Bio-oil from Hydrothermal Liquefaction of Microalgae

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.