Catalytic hydrothermal deoxygenation of palmitic acid

Abstract

We herein report a new approach to convert fatty acids to hydrocarbons in near- or supercritical water. We tested several different metal salts, bases, and high-surface-area supported metal catalysts for activity toward deoxygenation of palmitic acid in a hydrothermal reaction medium. Two heterogeneous catalysts, 5% platinum on activated carbon (Pt/C) and 5% palladium on activated carbon (Pd/C), proved to be very effective for hydrothermal deoxygenation of palmitic acid. The reactions were done in water with no added H₂. The catalysts can be reused without significant activity loss, and the selectivity was more than 90% toward pentadecane, the deoxygenation product. We examined the effect of the catalyst loading, reactant loading, batch holding time, and reaction temperature on the Pt/C-catalyzed deoxygenation rate. The results show that the reaction is first-order in palmitic acid, and the rate constants displayed Arrhenius behavior with an activation energy of 79 kJ mol⁻¹.