Reactions catalysed by organic polymer-based cation exchangers

3 Reactions catalysed by organic polymer-based cation exchangers 

In order to account for the well known sorption and swelling properties of polymer ion exchangers, Helfferich s model [427] is frequently used for liquid phase reactions. According to this, the pore liquid of the resin, where the reaction occurs, is treated as a homogeneous system and the reactant is assumed to be distributed according to a distribution coefficient 

In Helfferich s relation it is implicitly assumed that the diffusion of the reactants through the pore liquid is fast enough so that equilibrium between the pore liquid and the supernatant solutions exists. Several papers, however, report a particle size effect on the esterification rate [428— 

433] indicating diffusional limitations attempts to describe-quantitatively the transport situation in the polymer mass are less frequent (e.g. ref. 

For the liquid phase kinetic studies of esterification, with a few exceptions [402,435—437] only the standard (non-porous, see Sect. 1.2.5) ion exchangers were used. The macroreticular (porous) ion exchangers with a large inner surface area are prefered for vapour phase reactions, especially in more recent studies [436—443]. The authors claimed that diffusion was not the limiting process under their conditions. This observation cannot be generalised, however, and even with vapour phase reactions and macroreticular polymers, the possibility of transport limitations through the pores or the polymer mass cannot be excluded a priori. 

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