(38e) Effects of Process Conditions on Metal Content in 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. Iron is found to plug the head of the catalyst beds that are used to hydrotreat algal biocrude oil [1]. Metal impurities in crude bio-oil can also cause catalyst deactivation, coke formation, corrosion, and deposition. Thus, further studies are required to understand how the HTL conditions influence metal content and to develop methods to reduce the metal content in algal biocrude for downstream processing operations.

We hydrothermally treated microalgae using different processing conditions (isothermal reaction vs. rapid heating, different temperatures and reaction times, different reactor loadings) and determined the amounts of thirteen different metals in the biocrude oil as well as in the other product phases. The metal content in biocrude oil undergoes dramatic change within the first 5 minutes of HTL reaction. Generally, lighter elements are transferred into bio-oil faster than heavier metals. Iron in bio-oil behaves differently than many of the other metals, and is the target metal to be removed due to its abundance. As the reaction conditions become more severe, less iron resides in bio-oil phase. Optimum reaction conditions could be identified in terms of a high bio-oil yield and low metal concentration in the bio-oil. The results from this study provide the first glimpse into how and whether HTL process conditions can be used to manipulate metal content in algae biocrude.

Reference

[1] Jarvis, Jacqueline M., et al. "Impact of iron porphyrin complexes when hydroprocessing algal HTL biocrude." Fuel 182 (2016): 411-418.