Experimental and theoretical investigation of the mass transfer controlled regime in catalytic monoliths

We show that an accurate description of the mass transfer controlled regime in long catalytic monolith channels in which the flow is fully developed and laminar, requires the knowledge of two constants, namely, the asymptotic Sherwood number (Sh∞, or dimensionless mass transfer coefficient) and the first normalized Fourier weight, α1. While the first of these has received considerable attention in the literature, the second factor has been assumed to be unity. Because of this systematic error (of about 20% for common channel geometries), literature data and correlations for mass transfer in monoliths have large uncertainties. We present new experimental data that corroborates the theory and a new method for experimental estimation of the asymptotic constants for any arbitrary channel shape. For the case of a square channel we obtain experimental values for the constants of Sh∞=2.92±0.16 and α1=0.78±0.09, which are in excellent agreement with the theoretical values (Sh∞=2.977 and α1=0.8074). Using the asymptotic solutions of the convection–diffusion equation, we develop new correlations for mass transfer coefficients for the case of developing laminar flow that agree with numerical solutions of the Navier–Stokes equations, and theory in the limits.

[1]  V. Balakotaiah,et al.  Shape normalization and analysis of the mass transfer controlled regime in catalytic monoliths , 2002 .

[2]  Carmo J. Pereira,et al.  Computer-Aided Design of Catalysts , 1993 .

[3]  R. Shah.  Laminar Flow Forced convection in ducts , 1978 .

[4]  C. Pereira,et al.  External Mass Transfer Coefficients for Monolith Catalysts , 1996 .

[5]  Bruce A. Finlayson,et al.  Mathematical models of the monolith catalytic converter: Part I. Development of model and application of orthogonal collocation , 1976 .

[6]  J. Cavendish,et al.  Carbon Monoxide Oxidation in an Integral Reactor: Transient Response to Concentration Pulses in the Regime of Isothermal Multiplicities , 1978 .

[7]  Pio Forzatti,et al.  Adequacy of lumped parameter models for SCR reactors with monolith structure , 1992 .

[8]  Gerhart Eigenberger,et al.  Optimization of the cold-start behaviour of automotive catalysts using an electrically heated pre-catalyst , 1996 .

[9]  Pio Forzatti,et al.  Mathematical Models of Catalytic Combustors , 1999 .

[10]  Jacob A. Moulijn,et al.  Monoliths in Heterogeneous Catalysis , 1994 .

[11]  R. E. Hayes,et al.  Introduction to Catalytic Combustion , 1998 .

[12]  Nikunj Gupta,et al.  Heat and mass transfer coefficients in catalytic monoliths , 2001 .

[13]  James Wei,et al.  Mathematical modeling of monolithic catalysts , 1976 .

[14]  Alexander Bauer,et al.  Mass-transfer enhancement by static mixers in a wall-coated catalytic reactor , 2003 .

[15]  S. Oh,et al.  Multiple steady states in an isothermal, integral reactor: the catalytic oxidation of carbon monoxide over platinum--alumina , 1977 .

[16]  L. Hegedus.  Temperature excursions in catalytic monoliths , 1975 .

[17]  James Wei.  The Catalytic Muffler , 1975 .

[18]  B. Andersson,et al.  Mass transfer in monolith catalysts–CO oxidation experiments and simulations , 1998 .