On-purpose production of propane fuel gas from the hydrothermal reactions of n-butanol over Pt/Al₂O₃ catalyst: A parametric and mechanistic study

Production of components of liquefied petroleum gases (LPG) from biomass can become a sustainable pathway towards the defossilisation of off-grid locations for heating and transport applications. The reactions of butanol in the presence of 5 wt% Pt/Al₂O₃ across a set of reaction temperatures (200 °C to 300 °C), reaction times (up to 2 h), n-butanol concentrations (up to 30 wt%) and various feedstock-to-catalyst mass ratios were investigated and optimised. High conversion of n-butanol to gas products (99.91 wt%), high yield of propane (63.56 wt%) and propane hydrocarbon selectivity of 88.87 % were achieved in a batch reactor after 2 h of reaction at 300 °C. The formation of propane appeared to be from several mechanisms including decarbonylation, dehydration, C–O and C–C hydrogenolysis and hydrogenation. Significant yields of hydrogen and butane were formed, which may support the complex mechanistic pathways involved in n-butanol conversion. The 5 wt% Pt/Al₂O₃ catalyst was stable for up to two reaction cycles under the conditions investigated before mainly deactivating via hydrolysis of the alumina support and coke formation. This present work shows that n-butanol is a potential bio-derived feedstock to produce on-purpose biopropane fuel gas via catalytic hydrothermal processing.