Role of TEDA as an activated carbon impregnant for the removal of cyanogen chloride from air streams: Synergistic effect with Cu(ii)

The hydrolysis and fate of cyanogen chloride (CK) in the presence of triethylenediamine (TEDA) - a widely used carbon impregnant - in aqueous and nonaqueous (acetonitrile) media has been determined. In the presence of water, anticipated TEDA substitution is not observed; rather, simple base-catalyzed (OH^-) hydrolysis to cyanic acid (HOCN; unstable in water, decomposing to CO₂ and NH₃) is the major reaction, accompanied by a series of complex side reactions (not involving TEDA) to form several persistent compounds. Thus, the role of TEDA, in the presence of water, is primarily a source of OH^-. CK substitution at TEDA is observed in acetonitrile, again forming several complex, but quite different, species. Studies examining the removal of CK from humidified air streams by carbon impregnated with TEDA and/or basic Cu²⁺ (another common carbon impregnant) are consistent with simple hydrolysis being the major CK-removal mechanism; no TEDA substitution is observed in the presence of humidity/water. Considering the reaction stoichiometry apparent at CK breakthrough for the impregnated carbons, the combination of TEDA and Cu²⁺ is much more effective than the individual impregnants themselves. This synergism is attributed to dissolution of basic Cu²⁺ by TEDA to form soluble complexes of the type [Cu(TEDA)₂(OH)(H₂O)]^- in the carbon-adsorbed water layer, thus greatly increasing the dispersion and effectiveness of the basic Cu²⁺ impregnant.