Optimum density and composition for catalytic pellets

Abstract

Optimization calculations are applied to the problem of selecting either a microporous support from the viewpoint of available surface area or a macroporous support from the viewpoint of permeability in order to achieve the largest reaction rate in a pellet of fixed geometry. A single reversible reaction of first order is considered under isothermal conditions. The calculations are carried out with a proposed diffusion model which can successfully correlate diffusion data in pellets formed from single supports over a wide range of conditions. Optimum compositions are determined for pellets formed from both supports at a fixed density. Optimum densities are calculated for pellets of fixed composition. The combined problem of optimum density and composition is also treated and is shown to reduce to one of the individual problems. The results include both local maxima in the reaction rate and maxima on the boundary of allowable values of composition and density. The location of the maxima depend upon the kinetic and diffusional characteristics of the supports and the diffusional parameters of the pellet.