(178c) Demetallation of Biocrude from Hydrothermal Liquefaction of Microalgae

Hydrothermal liquefaction (HTL) converts wet biomass into a crude bio-oil that could be further treated to be acceptable for processing in petroleum refineries. HTL takes advantage of the properties of hot, compressed water near its critical point to break down biomacromolecules in the feedstock into smaller molecules. Several issues presently prevent the substitution of HTL biocrude for petroleum and one is the presence of metals in the crude bio-oil. Metals could cause problems such as corrosion, fouling, catalyst deactivation during downstream processing, etc. Metal impurities in crude bio-oil are unavoidable and metals will need to be removed if biocrude is used as transportation fuels. The most abundant metals in algal biocrude after HTL include Na and Fe. Na is present in typical growth media and Fe is an element essential for microalgae cultivation.

We hydrothermally treated microalgae using different processing conditions (isothermal, rapid heating and non-isothermal conditions, different temperatures and times) and determined the metal content in the biocrude oil as well as in the other product phases. We then studied the ability of different interventions to reduce this metal content. Process options explored include treatment in supercritical water in the absence of catalyst, use of different solvents for biocrude oil recovery after HTL, and use of heterogeneous catalysts during hydrothermal treatment. The Fe and Na content was reduced over 70% by use of specific organic solvents and reduced over 98% via application of heterogeneous catalysts. Additional catalytic studies with Fe model compounds permitted post-reaction catalyst characterization via techniques such as scanning electron microscopy and Mössbauer Spectroscopy.