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The liquid-phase acetic acid esterification kinetics with methanol to methyl acetate and water catalyzed by gel (Lewatit K1221) and macroporous (Lewatit K2629) ion exchange resins have been investigated and compared with literature reported data acquired on Amberlyst 15. The effects of the resin swelling, the initial molar methanol to acetic acid ratio (1:1 – 10:1) and the temperature (303 – 333 K) on the reaction kinetics were investigated. The gel type resin exhibits a remarkably higher catalytic activity compared to the macroporous resins, despite its similar number of sulfonic acid groups. This can be attributed to the differences in active site accessibility during reaction and, hence, in resin swelling, especially when it is in contact with polar components, such as water and methanol. The differences in catalytic behavior between the considered resins have been assessed using an exchange based Eley-Rideal model in which it is assumed that (1) all the active sites are occupied, (2) the acid undergoes a proton exchange with the protonated methanol and (3) the reaction occurs according to an Eley-Rideal mechanism with the surface reaction between protonated acetic acid and methanol from the bulk as rate-determining step. This model, which implicitly accounts for resin swelling, could describe the observed differences between the various resins. The activation energy was determined at 47 kJ mol-1, irrespective of the resin used.

Kinetic Study of Acetic Acid Esterification with Methanol Catalyzed by Gel and Macroporous Resins