(268c) Analytical Method of Lines for Predicting Multiple and Asymmetric Steady States in Catalytic Monolith Reactors - Diffusive Transport

Monolith reactors are suitable for carrying out fast reactions in applications where space is a constraint. Important examples are car exhausts, fuel cell reforming, oxidation of volatile organic compounds (VOCs) and gas-liquid reactions. Advantages of monoliths include, absence of a need for filtering, a high geometrical surface area, safer operations, easier scale up and reduced misdistribution problems. Modeling transport in catalytic monolith reactors is still an active area of research1-3 because of the existence of multiple and asymmetric steady states. A rigorous numerical solution for the models governing these reactors are not efficient because [1] There exists multiple, meaningful solutions [2] Initial guess needs to be good [3] Number of node points needs to be very high because of possible steep gradients in the radial direction.

We have developed a novel efficient analytical method of lines (AMOL) approach for simulating transport in monolith reactors. The AMOL method involves converting a given elliptic PDE (x,y) to N 2nd order Ordinary differential equations in one of the independent space variables (say, y). The derivatives in x are approximated using finite differences accurate to order h2. The resulting system of coupled ordinary differential equations in y is integrated using the matrix methods to get a closed-form solution in y and the system parameters.4,5

The advantages and disadvantages of the proposed method in predicting multiple steady states for various modes of transport will be discussed.

References:

1. K. Ramanathan, V. Balakotaiah, and D. H. West, "Light-of criterion and transient analysis of catalytic monoliths", Chem. Engng. Sci., 58, 1381-1405 (2003).

2. Gupta, N. and V. Balakotaiah, "Heat and Mass Transfer Coefficients in Catalytic Monoliths", Chem. Eng. Sci., 56, 4771- 4786 (2001)

3. Gupta, N., D.H.West and V. Balakotaiah, "Bifurcation Analysis of a Two-dimensional Catalytic Monolith Reactor Model", Chem. Eng. Sci., 56, 1435-1442 (2001)

4. V. R. Subramanian and R. E. White, "A Semianalytical Method for Predicting Primary and Secondary Current Density Distributions: Linear and Nonlinear Boundary Conditions," J. Electrochem. Soc., 147 (5), 1636-1644 (2000).

5. V. R. Subramanian and R. E. White, "Semianalytical Method of Lines for Solving Elliptic Partial Differential Equations" Chem. Eng. Sci., 59(4), 781 (2004). asymmetric