Kinetic and mechanistic studies of Pt/C-catalysed hydrothermal conversion of butyric acid for on-purpose production of renewable propane

Catalytic hydrothermal decarboxylation of butyric acid represents a promising pathway to produce renewable propane as a major product. The decarboxylation reaction of butyric acid, which can be sourced from biomass at industrial scale, has demonstrated the potential to yield significant amounts of propane, making the process attractive for commercialisation. However, the development of industrial-scale process for the butyric acid-propane route requires the availability of accurate data on reaction kinetics, thermodynamics and equilibria. This present study examines the kinetics of butyric acid hydrothermal decarboxylation to produce propane using a 5 wt% Pt/C catalyst. Reactions were conducted between temperatures of 513 K and 533 K using a non-stirred batch reactor. To confirm that the results reflected true reaction kinetics, potential limitations due to both external and internal mass transport were thoroughly evaluated. A second-order rate expression with respect to butyric acid, with an activation energy value of 118 kJ mol−1 was obtained via power-law fitting of the experimental data. Additionally, a Langmuir-Hinshelwood mechanism-based kinetic model yielded a value of 113 kJ mol−1 for activation energy, closely aligning with the power-law data. Furthermore, a low adsorption enthalpy value of −35.14 kJ mol−1 obtained from this work, indicating weak interaction between butyric acid and the surface of the catalyst. The kinetic data and models developed offer valuable insights for process optimisation, reactor design and scale-up, contributing to the advancement of sustainable biopropane production.