Fluid-Solid Reaction Kinetics for Solids of Nonbasic Geometries and Determination of the Appropriate Shape Factors

The rate analysis involving a solid of nonbasic geometry in general requires a complex numerical solution. A closed-form expression of the reaction rate for such a solid would be very convenient and greatly simplify the analysis. A method for this purpose was developed in this work for solids with shapes of finite cylinders and finite rectangular parallelepipeds reacting under the rate control by chemical reaction or mass transfer, which may be extended to other irregular shapes. In this method, an appropriate shape factor is first obtained under the conditions of a topochemical reaction, which is then applied to the unified rate expressions previously obtained for solids of three basic shapes. Good agreements between the rates predicted with the appropriate shape factors and the exact or numerical solutions were obtained for both reaction-controlled and pore-diffusion-controlled reactions.