(721h) Influence of Solvents on Metal Contents in Biocrude Oil from Hydrothermal Liquefaction of Microalgae

Algal biocrude oil is a complex matrix composed of tens of thousands of molecules including organic compounds containing inorganic elements such as S, P, and metals. Depending on the product workup methods, the most abundant metals can be alkali metals (Na and K) or Fe. Metals in crude oil can cause problems in refineries such as fouling, corrosion, and catalyst deactivation. Different interventions can be employed to reduce metal contents in the crude oil [1], and one of the post-HTL methods is to use different organic solvents for oil recovery. This approach is akin to solvent extraction methods that can be applied in petroleum demetallation [2].

In this study, we used two hydrothermal liquefaction conditions that gave high biocrude yields and lower iron contents [3]. We selected eight organic solvents with different polarities and boiling points. For product recovery, we determined how preventing contact between the solvent and the aqueous-phase product influenced the metal contents in the biocrude [4], as this approach would probably be employed in a large-scale operation. We observed a large influence on bio-oil yields when using different solvents, and that the alkali metal contents are at least two orders of magnitude higher when the solvent and aqueous phase never came into contact. The choice of solvent can reduce iron content by half and can make a significant difference in other metals as well. The effect of solvent demetallation cannot be contributed to one single solvent property but multiple factors such as polarity, solubility, and dielectric constant need to be considered.

Reference

[1] Jiang, J., and P. E. Savage. "Influence of Process Conditions and Interventions on Metals Content in Biocrude from Hydrothermal Liquefaction of Microalgae." Algal Research 26 (2017): 131-134.

[2] Savastano, C. A. "The solvent extraction approach to petroleum demetallation." Fuel science & technology international 9.7 (1991): 855-871.

[3] Jiang, J., and P. E. Savage. "Metals and Other Elements in Biocrude from Fast and Isothermal Hydrothermal Liquefaction of Microalgae." Energy & Fuels (2017). 10.1021/acs.energyfuels.7b03144

[4] Xu, D., and P. E. Savage. "Characterization of biocrudes recovered with and without solvent after hydrothermal liquefaction of algae." Algal Research 6 (2014): 1-7.