Effectiveness factors of porous catalysts

In a large number of chemical processes, particularly in the petrochemical industry, solid catalysts are used. TTiese usually have the form of veiy porous particles, with sizes in the range of 0.1 - 10 nun. There are also other chemical processes where a reaction takes place inside porous solid particles, e.g., 

The reactants present in the continuous phase (a gas or a liquid) are transported toward the catalytic surface, are adsorbed there, and undergo a chemical reaction while in the adsorbed state. The reaction products are subsequently desorbed and transported away from the surface. The rate of a reaction at a given catalyst is in principle proportional to its total surface area. To obtain sufficienfly high 

These transport mechanisms can be considered separately from each other. 

However, the diffusion through the pores occurs simultaneously with the chemical reaction at the pore walls. There is an important similarity between this situation and the simultaneous reaction and diffusion in liquids in two phase systems. The porous solid can be considered as a quasi homogeneous phase, the concentration of the reactant(s) at the outer particle surface is a boundary condition for both the external and internal transport processes, that can be considered as processes in series. 

To be able to model the processes of diffusion and reaction, one needs to know some parameters describing the porous catalyst structure. One characteristic parameter is the internal surface area, that can be determined with adsorption experiments. This is frequently expressed as units of area per gram of catalyst. In this text the specific internal surface area a. is used, with dimension m/tti or m  

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The influence of reactant adsorption on the effectiveness factor of porous catalyst pellets In section 5.2.1 the effect of reactant adso tion on the multiplicity of the steady slate for a catalyst pellet was investigated using a lumped model that neglected intraparticle... 

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