A DYNAMIC STUDY ON AXIAL-DISPERSION AND ADSORPTION IN CATALYTIC MONOLITHS

A dynamic procedure was used for the measurement of the axial dispersi on coefficient, as well as the adsorption equilibrium and rate constan ts of CO, O-2, CH4, and C3H6 tracers on a monolithic catalyst washcoat ed by Pt-Al(2)O3. Using a transient axial dispersion model, moment exp ressions were derived for the inert and adsorbing tracers. From the se cond central moment of inert tracer response peaks, an average value o f the axial dispersion coefficient was determined as 2.65 x 10(-4) m(2 )/s for a ceramic monolith containing cells with square cross section. The results indicated that axial dispersion in such a monolith is hig her than the corresponding value in a circular tube. The adsorption eq uilibrium constants of the adsorbing tracers (CO, O-2, CH4, C3H6) and the heat of adsorptions were determined from the time delay of the res ponse curves measured in the temperature range of 76-300 degrees C, wh ile the adsorption rate parameters were evaluated from the second cent ral moments, A detailed analysis of the results indicated that pore di ffusion resistance in the Pt-Al2O3 layer is negligible and also that f ilm mass-transfer resistance is much smaller than the adsorption resis tance.