Effect of Intradiffusion Resistance on the Chemical Process in a Nonspherical Catalyst Pellet

Abstract

The problem of a three-dimensional catalyst pellet with three characteristic sizes a, b, and c under conditions of intradiffusion resistance and a first-order reaction has been discussed. Using an exact solution in the Cartesian coordinate system, dependences for calculating the equivalent size and effectiveness factor of the pellet on Thiele parameter ψ have been proposed. A specific feature of the solution is the dependence of the pellet shape on the Thiele parameter. In dimensionless coordinates, at ψ → 0, the pellet surface tends to a sphere with unit radius; at ψ → ∞, it assumes the shape of a regular octahedron, the vertices of which are localized on the coordinate axes at a unit distance from the origin. In dimensional coordinates, depending on the ratio of parameters a, b, and c, the pellet can assume shapes similar to those of ellipsoids, discs, or “cigars.” At high Thiele parameter values, the effectiveness factor of nonspherical and spherical pellets is described by a single dependence equal to 3/ψ.