Competitive effects in the adsorption of CH 3I on KI-impregnated activated carbons in the presence of CO 2

Abstract

This paper describes an investigation of the adsorption of CH 3I on a KI-impregnated carbon and the influence of competitive adsorption on the process. A gravimetric method was used to study the equilibrium capacity and kinetics for the adsorption of CO 2 and CH 3I in the presence of He, and CH 3I in the presence of CO 2 on the carbon. The results of these experiments were compared with those obtained from measurements carried out using a McBain spring apparatus to obtain the equilibrium uptake of CH 3I vapour on the KI-impregnated carbon at 293 K. The adsorption kinetic results covering the range 275–333 K show that the rates of adsorption are only weakly dependent on the temperature. The apparent activation energies for adsorption of CO 2 and CH 3I in the presence of He, and CH 3I in the presence of CO 2 were 20.0 ± 1.1, 6.5 ± 0.3 and 10.0 ± 0.5 kJ mol −1, respectively. The rates of adsorption of CH 3I in the presence of CO 2 were about half the corresponding rate of the adsorption of CH 3I in the presence of He. However, the equilibrium capacities were very similar in both cases. Adsorption experiments carried out over a CH 3I partial pressure range, 3.08–38.5 kPa in CO 2 showed that the initial adsorption rate constant was linearly dependent on the CH 3I concentration. The results are discussed in terms of competitive adsorption in the CH 3I-CO 2 system.