Diffusion pore-fissure

To explain this D(y) relation, it is necessary to assume overlapping of 2 diffusion mechanisms a "pore—fissure diffusion and a diffusion by simultaneous position interchange between cations. In both cases, cation motion would be along the walls of cavities, since cations are strongly attracted by the negatively charged zeolite lattice. Rate of diffusion is smaller in the interchange mechanisms than in pore-fissure diffusion. 

But cation diffusion always can occur by the interchange mechanism, whereas in pore—fissure diffusion it depends on the presence of unoccupied cation positions in a certain number and a definite distribution. Accordingly, the coefficients of internal diffusion are maximal when both diffusion mechanisms are operating at the same time, and minimal when diffusion is occurring only by the interchange mechanism. 

Dissolving out the organic materials which are not part of the main coal structure depends upon the size of the micropore. It may become the ratecontrolling step and represent the diffusion of the solution of the organic material in the solvent tetralin, from out of the pore, which implies that the process of solution will be first order with respect both to the coal and solvent. If, however, the material dissolves in a large port or fissure, then the diffusion process may be so rapid that the reaction will be first order with respect to the coal only. 

We now establish the coupled clay cluster/macro-pore model at the meso-scale. For the sake of simplicity we adopt a particular form of mesostructure wherein the clay clusters are isolated from each other by the fissure (macropore) system.. Denote Vj. C, D. Jj the velocity, concentration and diffusion coefficient and the overall flux of species (NaCl), the governing equations in Q f reduce to... 

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