Submitted to: Atmospheric Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/14/2000
Publication Date: 2/10/2001
Citation: Gan, J., Megonnell, N.E., Yates, S.R. 2001. Adsorption and catalytic decomposition of methyl bromide and methyl iodide on activated carbons. Atmospheric Environment. 34:941-947. Interpretive Summary: Methyl bromide (MeBr) is widely used as a fumigant for pest control in soil, commodity and structures. Studies have shown that 30-90% of the applied MeBr in soil fumigation, and 80-95% in commodity and structural fumigation, is emitted into the atmosphere. Methyl bromide is a potent stratospheric ozone depletor and much of its use will be discontinued soon. Methyl bromide fumigation is essential for commodity and structural fumigation. It is desirable to develop techniques for preventing MeBr emission, thus extending its use without inflicting any significant effects on the environment. In this study we investigated the use of activated carbon to recover MeBr and developed a simply approach to dispose the contaminated carbon. We showed that all activated carbons adsorb MeBr or methyl iodide (MeI)strongly, and the adsorbed chemicals may be destroyed simply by adding water and heating the carbon-water mixture at a higher temperature. This discovery should provide a convenient and inexpensive way for preventing fumigant emissions from commodity and structural treatments.
Technical Abstract: Methyl bromide (MeBr) is commonly used for fumigating structures and commodities. Emission of MeBr during such treatments is environmentally detrimental because of the reaction of MeBr with stratospheric ozone. In this study we evaluated adsorption of MeBr and methyl iodide (MeI) a potential MeBr replacement, on five commercial activated carbons, and studied water-initiated catalytic decomposition of adsorbed fumigants. All carbon samples showed great adsorption affinity to MeBr and MeI, with the adsorption capacity for MeI several times greater than that for MeBr on the same carbon. For the same fumigant, adsorption was affected by the type of carbon and the concentration of fumigant. Water initiated decomposition of both fumigants, liberating bromide or iodide as a transformation product. The rate of decomposition increased with increasing temperature, and was also influenced by the carbon type. The half-life of MeBr or MeI on Centaur, a catalytically-modified carbon, was less than 2 h at 80C. The rapid decomposition of MeBr and MeI on wet carbons at elevated temperatures may be used to detoxify these fumigants after adsorption on activated carbons.