Resins macroreticular, diffusion

Macroporous cation exchangers, 14 387 Macroporous gels, 13 738 Macroporous molecular sieves, 16 849 Macroporous particles, apparent effective diffusivity and, 15 730 Macroporous resins, 14 393, 397 Macroreticular sulfonated styrene-... 

Paul et al. (25) observed that for polymer volume fractions less than 0.8, the functional dependence of the diffusion coefficients on the polymer volume fraction was, generally, in accordance with Equation 40. Muhr and Blanshard (26) provide additional supporting data on different polymers than those reported by Paul et al, Roucls and Ekerdt (27) measured the diffusion of cyclic hydrocarbons in benzene-swollen polystyrene beads their diffusion coefficients satisfy the general form of Equation 40. The effective dlffuslvltles of organic substrates in crossllnked polystyrene reported by Marconi and Ford (17) also follow trends predicted in Equation 40. In the absence of experimental data, it appears that Equation 40 provides a reasonable, and the simplest, means to estimate D for use in detailed modeling or in estimation methods such as Equation 38. Equation 40 was used by Dooley et al. (11) in their study of substrate diffusion and reaction in a macroreticular sulfonic acid resin which involved vapor phase reactants. 

Substrate limitations have been documented and quantitatively described ( U, 2, 17 ). Dooley et al. (11) present an excellent description of modeling a reaction in macroreticular resin under conditions where diffusion coefficients are not constant. Their study was complicated by the fact that not all the intrinsic variables could be measured independently several intrinsic parameters were found by fitting the substrate transport with reaction model to the experimental data. Roucls and Ekerdt (16) studied olefin hydrogenation in a gel-form resin. They were able to measure the intrinsic kinetic parameters and the diffusion coefficient independently and demonstrate that the substrate transport with reaction model presented earlier is applicable to polymer-immobilized catalysts. Finally, Marconi and Ford (17) employed the same formalism discussed here to an immobilized phase transfer catalyst. The reaction was first-order and their study presents a very readable application of the principles as well as presents techniques for interpreting substrate limitations in trlphase systems. 

Film diffusion is usually the controlling step in dilute solutions which are moving at a low superficial velocity through the fixed bed whereas internal diffusion is limiting in high concentration solutions. Dealing with macroreticular resins with a permanent pore volume, BET surface and a defined pore size distribution, pore diffusion can be described by an approach which is based on the conservation of ions in a spherical shell and diffusion steps. 

The macroreticular resins, however, have the advantages of (1) ease of filtration from the reaction medium after reaction (2) more accessible reactive groups, and (3) large pore sizes which offer less hindrance to the diffusion of the reactants. 

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