(546i) Single-Stage Hydroconversion of Algal Oil to Sustainable Aviation Fuel (SAF)

There has been an increasing consensus on the urgent need to reduce the aviation industry's carbon footprint and its reliance on petroleum fossil fuels due to rising demand and environmental concerns. Sustainable aviation fuels (SAFs) have gained attention as a promising solution to reduce greenhouse gas (GHG) emissions owing to their distinct advantages over other alternative energy sources. Unlike other energy sources that require extensive infrastructure changes, SAFs comply with ASTM specifications for conventional jet fuels, making them compatible with existing infrastructure. As a result, SAFs can be utilized as drop-in replacements for petroleum jet fuels, potentially reducing carbon emissions.

Microalga have garnered a lot of attention in the field of bioenergy production and are considered a promising alternative biomass source for aviation fuel production. This interest is due to several factors, including the high growth rate and lipid yields of certain species, the ability to cultivate microalgae in non-arable regions, and the advantage of not competing with food resources. Among the various fuel precursors derived from microalgae, algal lipids have gained the most attention. These lipids can be extracted and converted to biojet fuel using the hydroprocessed esters/fatty acids (HEFA) technology, which involves hydrodeoxygenation of oils followed by cracking and isomerization.

The HEFA pathway can be achieved in a single stage or in two stages. For a two-stage hydroconversion process, hydrodeoxygenation is conducted first to reduce the oxygen content of the fatty acids using a hydrotreating catalyst. Cracking and isomerization is then conducted on the hydrotreated feed to obtain jet-range hydrocarbons. In our current study, we have shown that a two-stage hydroconversion pathway for the upgrading of algal oil to SAF using base metal catalysts (sulfided NiMo/γ-Al₂O₃ and NiMo/HZSM-5 for hydrodeoxygenation, and cracking and isomerization respectively) yields biojet fuel that is compatible with Jet A, the jet fuel used for commercial flights. Therefore, with the right distillation process, jet fuel from algal oil can serve as a fuel blend for Jet A for commercial use. The two-stage hydroconversion process was also optimized in terms of temperature, pressure, hydrogen-to-feed ratio and liquid hourly space velocity (LHSV) to maximize the yield of product obtained.

However, to reduce the multi-step process which would require high investment for system equipment, a single stage hydroconversion of algal oil to SAF using bifunctional precious metal catalysts is proposed in this study. These catalysts will be synthesized in the lab using the incipient wetness impregnation (IWI) method. Evaluation and optimization studies will be conducted, and their performance will be compared with the yields obtained in the two-stage hydroconversion pathway. Previous research in the lab showed that precious metal-based hydrotreating catalysts were superior in performance to sulfided NiMo/γ-Al₂O₃ during the hydrodeoxygenation step. Therefore, it is expected that the bifunctional precious metal catalysts would have comparable yields to the two-stage hydroconversion pathway, aiding in the simplification of the overall process. Findings from the study will aid in the selection of a suitable catalyst and optimal process conditions for the overall efficiency of the process.