Sulfonic Mesostructured SBA-15 Silicas for the Solvent-Free Production of Bio-Jet Fuel Precursors via Aldol Dimerization of Levulinic Acid

Sulfonic acid-functionalized mesostructured silicas have been evaluated in the solvent-free aldol dimerization of biomass-derived levulinic acid into bio-jet fuel precursors. These compounds produce branched alkanes in a subsequent hydrodeoxygenation process, with suitable properties for being a renewable alternative to conventional fossil aviation fuels. The combination of activity and selectivity toward the desired condensation products achieved over sulfonic acid-functionalized SBA-15 materials is superior to those displayed by other commercial solid acid catalysts. Enhanced textural properties provided by the mesoporous SBA-15 support contribute to such improved catalytic performance. The strength and loading of the mesoporous silica-supported sulfonic acid moieties are also important factors affecting the catalytic performance of the materials. Reaction conditions (temperature, time, and catalyst loading) have been optimized for propylsulfonic acid-functionalized mesostructured silica (Pr-SBA-15) by means of a response surface methodology, leading to a maximum yield to levulinic acid dimerization products of 58.4% (145 °C, 0.15 g of catalyst, 24 h, no solvent). Under these reaction conditions, conversion of levulinic acid is 61.1%, indicating excellent selectivity toward bio-jet fuel precursors. A small catalytic activity decay has been detected in reutilization experiments, attributed to the formation of organic deposits onto the catalyst surface. A mild acid washing of the catalyst allowed a significant recovery of the initial activity.