Kinetics of the Esterification Reaction between Pentanoic Acid and Methanol Catalyzed by Noncorrosive Cation Exchange Resin

The extensive demand for cleaner environment is forcing the chemical industry to use less hazardous materials. In this regard, solid catalysts have lately attracted the attention of scientists and researchers around the world.1–8 By using sufficient amounts of these heterogeneous catalysts, their catalytic activity for ester formation can be equivalent to that of conventional homogeneous catalysts. Solid catalysts have good properties in terms of their esterification efficiency.9,10 Amongst the wide variety of solid catalysts available, cation ion-exchange resin is widely used in esterification process because it is not corrosive and easy to separate from the reaction mixture.6,7 Many authors have studied the esterification reactions using ion exchange resins. In spite of many reports on the esterification reactions over ion exchange resins, however, few kinetic studies consider the effect of adsorption, desorption and partitioning phenomenon occurring between the interior and the exterior liquid phases with respect to the resins. For example, Sanz et al.11 have studied the kinetics of lactic acid esterification reaction with methanol, catalyzed by different acidic resins. These authors have interpreted their results by means of an Eley–Rideal (ER) and a Langmuir–Hinshelwood (LH) model. Ali and Merchant12 have reported kinetic results related to the esterification between acetic acid and 2-propanol on different resins interpreting the obtained data with various models: pseudo-homogeneous (PH), Eley–Rideal (ER), Langmuir–Hinshelwood (LH). One of the challenges in determining kinetic parameters for the esterification over solid acid catalysts is the proper handling of the water concentration.13 Yalcinyuva et al.14 demonstrated that the phase partitioning and the swelling phenomena cannot be neglected for an accurate description of an esterification process involving ionic exchange resins. In fact, they have investigated the esterification reaction of myristic acid with isopropyl alcohol catalyzed by Amberlyst 15, and they have shown that the water concentration slows down the conversion, but is found to be lower than the theoretical value calculated on the basis of the measured acid conversion. Lee et al.15 have studied the kinetics of the esterification reaction of acetic acid with methanol, in the presence of Amberlyst 36 as catalyst. According to their study, the magnitude of adsorption strengths follows the order of water > methanol > acetic acid > methyl acetate. Popken et al.16 and Song et al.17 have studied the esterification reaction of acetic acid with methanol also using Amberlyst 15 as catalyst. HowKinetics of the Esterification Reaction between Pentanoic Acid and Methanol Catalyzed by Noncorrosive Cation Exchange Resin