(31g) The Impact of Algal Growth Conditions on the Hydrothermal Liquefaction Products

Hydrothermal liquefaction (HTL) of algae has become a promising method to creating a biocrude product.  One key challenge to overcome for the commercialization of HTL is the optimization of its co-products.  It has been shown that HTL of wastewater-cultivated algae (WWC-algae) yields a higher-value, solid co-product that has been identified as hydroxyapatite (HAp).  While primarily used in biomaterial applications for bone and teeth regeneration, HAp has also shown promise as a green catalyst for dehydration and dehydrogenation reactions due to its acid-base chemistry.  Because of its catalytic characteristics, it is postulated that HAP can enhance the oil properties of the biocrude product in-situ of the HTL process.   This paper focuses on the impact of the algae growth conditions of the formation of HAp and the resultant HAp properties.  Chlorella kessleri microalgae was grown in 15 L light rack tanks with varying growth conditions.  The algae were extracted by either centrifugation or induced auto-flocculation that occurred when increasing the pH.  Preliminary results show a higher ash and char yield, similar to WWC-algae, when grown in conditions with high alkalinity, 100 mg/L CaCO₃ and extracted by auto-flocculation.  Furthermore, silica may be acting as a seed crystal for the formation of HAp.  Detailed characterization of the algae, HTL solid product properties, and impact of the solid product on the biocrude properties will be presented.