EFFECTS OF SOLUTE ADSORPTION ON HINDERED DIFFUSION UPTAKE RATES IN FINITE BATH EXPERIMENTS

This work investigates the effects of solute adsorption on hindered di ffusion behavior in porous catalysts. A mathematical model describing the adsorptive diffusion process is developed. The model, termed the s hrinking pore model, incorporates the local reduction in catalyst pore diameter due to the adsorption of solute molecules on the pore walls. The influence of the adsorbed solute layer is found to depend on two additional parameters, reflecting the relative degree of adsorption an d molecule/pore size ratio. Hindered diffusion experiments are perform ed for diffusion controlled adsorptive uptakes of two solute molecules , quinoline and polystyrene, from cyclohexane on a porous catalyst. Co mparison of the experimental data and model simulation results shows t hat for the larger polystyrene solute the shrinking pore model better represents the uptake behavior than the conventional model which assum es constant catalyst properties, e.g. pore diameter, during the uptake process. Experimental measurements were found to be in good agreement with model simulations after accounting for additional hindered diffu sional effects due to an adsorbed solute layer on the pore walls. The additional hindrance due to the adsorbed solute was found to be very s ignificant for the uptake of the larger polystyrene solute, whereas it was not significant for the smaller quinoline solute.