Esterification of propanoic acid by butanol and 2-ethylhexanol catalyzed by heteropolyacids pure or supported on carbon

The esterification of propanoic acid by butanol or 2-ethylhexanol is catalyzed by heteropolyacids pure or supported on carbon supports. A detailed study of the homogeneous reaction has been carried out, showing that the reaction rate is proportional to the concentration of protons and that the catalyst can be easily recycled by distillation of the reaction medium. When the heteropolyacid is supported on carbon, different behaviors are observed, depending on both the heteropolyacid and the carbon support. However, in all cases, the activity is lower than that of the pure heteropolyacid. The activity loss increases with the surface area of the carbon support and, for a given support, it decreases with the polyanion loading. A study of the recycling of these catalysts has shown that a deactivation occurs, due to the redissolution of the polyanion in the reaction medium. This phenomenom is more important for the catalysts having the highest activity per Keggin unit, due to a smaller interaction of the polyanion with the support.