Surface Diffusion in Liquid-Filled Pores

Example S.5.e l Surface Diffusion in Liquid-Filled Pores 

Komiyama and Smith [70] have studied intraparticle mass transport of benzal-dehyde in polymeric porous amberlite particles. With methanol as the solvent, there was very little adsorption of the benzaldehyde, and the uptake data could be accurately represented by the usual constant diffusivity equation, Eq. 3.5.e-5a with a linear adsorption isotherm, as seen in Fig. 1. The porosity was about , = 0.5, and the tortuosity about t = 2.7, which is a reasonable value based on earlier discussion. 

However, with water as the solvent, there is much more adsorption, leading to both nonlinear isotherms and to significant surface diffusion. The uptake data now could only be adequately represented by the complete Eq. 3.5.e-S, as seen in Fig. 2. Line 1 is the result of assuming no surface diffusion and using the above 

As described in Sec. 35a, there are still many puzzling aspects of conf nra-tional diffusion that remain to be explained. About the only theoretical infcmna-tion available concerns the motion of spherical particles in liquids through cylindrical pores. Anderson and Quinn [71] have shown that the fective difiiirivity in straight, round pores (tortuosity t = 1.0) is given by  

Satterfield and Colton et al. [72, 73] have studied diffusion of several sugars and other types of molecules in microporous catalyst support solids and correlated their data with the relation 

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