Influence of Fe/HZSM-5 catalyst on elemental distribution and product properties during hydrothermal liquefaction of Nannochloropsis sp.

Hydrothermal liquefaction (HTL) is a promising thermochemical technology to produce biocrude oil from algae; however, further improvement of the process efficiency is still required. In this study, we used a cost-effective catalyst (Fe/HZSM-5) during HTL of microalgae Nannochloropsis sp. The highest biocrude oil yield (38.1 ± 3.2%) was achieved at 365 °C with the inclusion of Fe/HZSM-5, which improved the biocrude oil yield by 25% compared with the non-catalyzed group. In addition, Fe/HZSM-5 showed a positive effect on influencing element migration during the HTL process. An increase of carbon in the biocrude oil and increase of nitrogen in the aqueous phase were observed, which would benefit downstream processing, including biocrude oil upgrading and nutrients recovery. Furthermore, the presence of low-molecular weight ketones, acids, amides and phenols in the biocrude oil indicated improvement of the oil quality. Hence, Fe/HZSM-5 could be a promising catalyst for the HTL of algae, enhancing biocrude oil production and regulating the distribution of carbon and nitrogen in the product fractions.