Transient rates of gas sorption. III. Pore structure, adsorption isotherms, and calculated rates at constant volume

Abstract

The pore structure has been determined for the thoria, alumina monohydrate, and γ-alumina adsorbents of Part I of this Series ; also the Henry's law constants when the adsorbate is water vapour at 140 °C. Using these quantities in the equations given in Part II it is shown how the calculated rate of Knudsen flow, accompanied by rapid adsorption on the pore walls, can account for the experimental rates of gas uptake by the two aluminas. None of the equations can account for the dependence of the rate of uptake by thoria on the square (or higher power) of the mass of the bed. It is suggested that a poisoning phenomenon may be responsible. In deciding the nature of the limiting step in gas uptake by an adsorbent, the dependence of the rate on the mass of the bed is a useful criterion. The temperature coefficient is not informative unless it is positive. The methods and results described in Parts I, II, and III can be applied in the study of gas adsorption and flow in the catalyst pellets of a fixed-bed industrial reactor. They should also be capable of predicting the unsteady reaction rates within a granule in a fluidized bed.