Adsorption and desorption of methyl iodide in a triethylenediamine-impregnated activated carbon bed

Abstract

As a relevant technique for controlling radioactive organic iodines, the adsorption and desorption of methyl iodide was investigated in a TEDA (triethylenediamine)-impregnated activated carbon bed. The amount of adsorption was quantitatively divided into two parts: reversible physical adsorption and strongly bonded chemisorption. This was confirmed by thermo-gravimetric and differential thermal analysis technique. The physical adsorption obeyed the Langmuir equation and the amount of chemisorption was stoichiometrically proportional to the amount of impregnant. A nonequilibrium dynamic model was developed based on both the physical adsorption and the bimolecular reaction between adsorbate and impregnant. The dynamic model successfully simulated the adsorption and desorption behavior of methyl iodide. The effect of humidity on the adsorption and desorption of methyl iodide was also investigated. The amounts of chemisorption and physical adsorption of methyl iodide were measured in different humidity levels for base and TEDA-impregnated activated carbons. The physical adsorption of methyl iodide in the presence of water vapor was well fitted with the potential theory-based Dubinin-Polanyi equation. On the other hand, the adsorption of water vapor showed typical S-shaped isotherm curve and was not well represented by any of isotherm equations. The considerable amount of chemisorption even in high humidity conditions confirmed the effectiveness of TEDA-impregnation for trapping methyl iodide permanently. The dynamic model developed for a single component system was extended to the mixture adsorption of methyl iodide and water vapor. This generalized dynamic model can be used successfully for mixture system of organic compound and water vapor in which chemisorption and physical adsorption occur simultaneously.