Adsorption mechanism of methyl iodide by triethylenediamine and quinuclidine-impregnated activated carbons at extremely low pressures

Abstract

Activated carbons impregnated with 1, 5, and 10 wt% triethylenediamine (TEDA) and quinuclidine (QD) were prepared for the removal of methyl iodide (CH3I) gas. The textural properties of the impregnated activated carbons were characterized by N2 and CO2 isotherms at 77 K and 273 K, respectively. The adsorption isotherms of CH3I was obtained at 283, 293, and 303 K and at pressures up to 250 Pa using a self-made volumetric system with resolution of 10−3 Pa. All the experimental isotherms were fitted by the Langmuir and Toth models, and the initial part of the uptake curve was fitted by the Fick’s diffusion model. Furthermore, the adsorption heats were analyzed by the van’t Hoff and Clausius–Clapeyron equations. The adsorption characteristics of TEDA- and QD-impregnated activated carbons, such as the isotherms, thermodynamic heats, and adsorption rate, were compared at very low pressures (less than 20 Pa). The adsorption behaviors are affected by the type and amount of impregnant and textural properties. The impregnant-rich activated carbon is beneficial for the removal of CH3I at low pressures, while the less impregnated AC with high porosity shows a relatively high adsorption capacity under a high pressure. It indicates that the physisorption and chemisorption of CH3I occur simultaneously, but the contribution of chemisorption to the removal of CH3I increases with the amount of impregnant. The adsorption rate is more affected by alkylated (chemisorbed) products than impregnants.