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.

Automated summary

Radioactive iodine can be released in both organic and inorganic forms during the normal operation and severe accident of a nuclear power plant. Methyl iodide is formed through the reaction between radioactive iodine and organic products present in the containment. Activated carbon impregnated with hexamethylenetetramine (HMTA) and triethylenediamine (TEDA) showed significant adsorption capacity for methyl iodide. TEDA-IAC was more effective at low temperatures, adsorbing up to 473 mg/g, while HMTA-IAC had a higher adsorption capacity at high temperatures due to its stability, adsorbing up to 245 mg/g of methyl iodide. The adsorption capacity of both TEDA and HMTA impregnated activated carbons improved by up to 64% and 54%, respectively, compared to raw activated carbon. The Langmuir model fitted well to the adsorption equilibrium data, and the second-order model explained the adsorption kinetics. Thermodynamic parameters confirmed the exothermic and spontaneous nature of the reaction.