Mass transfer in monolith catalysts - CO oxidation experiments and simulations

From CO oxidation measurements in monoliths: and subsequent three-dimensional CFD simulations, the gas-solid mass transfer in square monolith channels with rounded corners was studied. Generally, the measured conversions were higher than the simulated conversions, especially at high flow rates. The following expression for the mass transfer rate, expressed as the average Sh number, was obtained from the experiments: Sh = 3.53 exp (0.0298 Re d(h)/L Sc). This expression predicts higher Sh numbers compared with the analytical values for laminar flow, and a somewhat stronger dependence on the Re number. The possibility of these high mass transfer-rates being due to turbulent effects is discussed. By measuring the CO oxidation rate on monoliths with an inactive washcoat layer on top of an active one, the effective diffusion coefficient through the porous washcoat on the monolith walls was estimated. However, the uncertainties of this method were large, mainly due to difficulties in characterising the washcoat distribution. (C) 1998 Elsevier Science Ltd. All rights reserved.