Hydrodeoxygenation of Microbial Oil to Diesel-Range Alkanes over Palladium-Supported Zeolite Catalysts: Experimental and Kinetic Modeling Study

Abstract

Catalytic hydrodeoxygenation is a promising route to convert biomass-derived fatty acids into drop-in biofuels like jet fuel and diesel. Here, we report a bespoke Pd nanoparticle (NP)-supported HUSY zeolite catalyst (PdNP/HUSY-DA), designed to promote the cascade hydrodeoxygenation of the fatty acid to the corresponding long-chain alkane, representing the novel integration of metal–acid functionality toward an enhanced HDO pathway for complex feedstocks. The objective of this study was to investigate the efficiency of PdNP/HUSY-DA for converting fatty acids, specifically real bio-oils, to diesel-range alkanes (C15–C18) and to develop a validated kinetic model for the process. Hydrodeoxygenation of the model compounds of palmitic and oleic acids revealed significant activity of PdNP/HUSY-DA, with overall reactant conversions of 87.2 ± 4.4 and 93.7 ± 4.7 mol %, respectively, within 2 h. This excellent activity translated to good performance when conducting HDO of real bio-oils (palm oil and microbial oil from Yarrowia lipolytica), exhibiting a triglyceride-to-alkane conversion of 83.9 ± 4.2 mol % within 24 h. A mechanistically informed kinetic model was developed based on the current understanding of the reaction mechanism and validated experimentally over windows of 453.15–493.15 K, 28–35 bar, and 0.125–0.25 w/v% (catalyst loading). Based on the experimental and model optimization studies, the hydrodeoxygenation of real bio-oil over PdNP/HUSY could achieve a maximum bio-oil conversion of 93.1 ± 4.6 mol % along with a total alkane yield of 83.3 ± 4.2 mol % under the optimum reaction conditions of 473.15 K, 35 bar (H2 pressure), and catalyst loading of 0.25 w/v%. Thus, these results demonstrate the potential of palladium-supported zeolite catalysts for the efficient production of diesel fuel from lipid-based feedstocks.