Absorption of water/methanol binary system on ion‐exchange resins

Polymeric ion-exchange resins are widely used in important industrial processes for both separation and reaction applications. Due to their particular cross-linked structure, these materials are subjected to a remarkable swelling phenomena when are contacted with polar solvents like methanol or water. The high liquid volume retained and the selectivity towards the absorption of particular substances can results in a significant alteration of the liquid reactive mixture composition when polymeric resins are used as catalysts. In this situation the bulk liquid phase and the absorbed phase are different in composition and the kinetics could be strongly affected as the chemical reaction occurs mainly on the internal surface of the resin particles. The correct description of the kinetics for such systems requires additional information regarding the phase partitioning of the various components between the liquid and the absorbed phase. In this work, experimental absorption data, concerning the binary system methanol-water partitioned in the presence of Amberlyst 15 and Relite CFS, two sulphonic ion-exchange resins, typically used as esterification catalysts, are presented. This mixture is of great interest in the esterification reaction of free fatty acids (FFAs) that is nowadays considered a suitable pre-treatment of cheap feedstock for biodiesel production. The data collected on binary systems water-methanol, at different temperatures, have then been successfully correlated by a multicomponent competitive absorption model that could be useful, in the future, in a wider kinetic study. The same model has also been tested on data taken from the literature.