Removal of gaseous methyl iodide using hexamethylenetetramine and triethylenediamine impregnated activated carbon: A comparative study

Radioactive iodine may be released into off-gas streams during both, the normal operation and severe accident of nuclear power plant in both organic and inorganic forms. Methyl iodide formation results from the reaction between radioactive iodine and organic products (like paint and cable coatings) present within the containment. For the removal of methyl iodide (MeI) gas, activated carbon (AC) was impregnated with 2, 5, 8 and 10 wt% of hexamethylenetetramine (HMTA) and triethylenediamine (TEDA). Characterization of the raw and impregnated activated carbon (IAC) was done by XRD, SEM, Raman, BET and TGA. Removal efficiency of MeI was evaluated using breakthrough experiments by varying weight percent of TEDA and HMTA. Both TEDA and HMTA-rich AC exhibited significant MeI adsorption capacity. TEDA-IAC was more effective for the elimination of MeI which adsorbed maximum 473 mg/g at low temperatures, whereas HMTA-IAC with high porosity had a comparatively high adsorption capacity at high temperatures due to its stability as compared to TEDA-IAC and adsorbed maximum 245 mg/g MeI. When raw AC was compared to IACs, results demonstrated that adsorption capacity of MeI improved up to 64 % for TEDA and 54 % for HMTA impregnated ACs. Langmuir model was well fitted to adsorption equilibrium data, and second-order model explained adsorption kinetics. Thermodynamic parameters study confirmed that the reaction is exothermic and spontaneous in nature.