Behavior of catalytic pellets at high reaction rates. The effect of edges

Abstract

The diffusion and reaction problem in catalytic pellets of any shape subject to diffusive transport limitations is undertaken in this contribution. Effective reaction rates in three-dimensional (3D) catalysts can be evaluated through a series solution written in terms of powers of (1/Φ) when strong diffusion limitations are present. In a recent paper, Keegan et al. [Chem. Eng. J. 2005, 110, 41] have clearly demonstrated for smooth catalysts that the second-order term [in (1/Φ)2] depends essentially on the shape of the pellet. In this context, the purpose of this paper is to develop expressions of the second-order term for two-dimensional (2D) or 3D catalytic bodies showing edges. While the first-order term allows definition of the proper size of a catalyst, the second-order term provides a characterization for the shape of the catalyst. The possibility of using this characterization of catalyst shape in a geometrical one-dimensional (1D) model to approximate the behavior of given 2D or 3D pellets is analyzed. Also, the direct use of the two-term truncated series for complementing the numerical evaluation of the conservation equation is described.