Blockage, diffusion paths

The approach was extended to include diffusional limitations. The fo3rm of the continuity equations for the reactant A corresponded to that for a continuum model, but the effect of the structure of the catalyst was introduced through P. Blockage increases the tortuosity of the diffusion path, thus affecting the effective diffusivities. This was also accounted for. Both parallel and consecutive coking were investigated. In the latter case non monotonic internal coke profiles were obtained, as for the single... 

The decoration of CNTs tends to lower the porosity of the ACF from 1,065 to 565 m /g. The adsorption of BVIO onto ACF and CNTs/ACF was 162.4 and 220 mg/g, respectively. This finding indicates that the total microporosity of ACF cannot be fully accessed by the dye molecules. Therefore, the appearance of CNTs plays a positive role in (i) facilitating the pore accessibility to adsorbates and (ii) providing more adsorptive sites for the liquid-phase adsorption. This reflects that CNTs/ACF contains a large number of mesopore channels, thus preventing the pore blockage from the diffusion path of micropores for adsorbates to penetrate [72-73]. 

It was therefore concluded that the changes in diffusion which occur on drawing result from shorter jumps between activation sites as a result of greater blockage of available paths. 

A Bethe-tree is a particular case of more general networks considered in percolation theory. Sahimi and Tsotsis [1985] applied percolation theory and Monte Carlo simulation to deactivation in zeolites, approximated by a simple cubic lattice. Beyne and Froment [1990, 1993] applied percolation theory to reaction, diffusion and deactivation in the real ZSM-5 lattice. The finite rate of growth was described in terms of a polymerization mechanism. Pore blockage was reached in this small pore zeolite. It also affects the path followed by the diffusing molecules that becomes more tortuous, so that the effective diffusivity has to be expressed in terms of the blockage probability. 

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