A Kinetic Model for Cathodic Degradation of Explosives in a Flow-Through Electrochemical Reactor.

A laboratory-scale, flow-through, undivided cell electrochemical reactor hosting a stainless steel wire mesh cathode and downstream Ti/MMO anode was evaluated for its ability to degrade the dissolved explosives with diverse chemical properties and reactivities. Degradation efficiencies of RDX, NQ, DNAN, MNA, 2,4-DNT, HMX, TNT, and NTO were dependent on applied current, and 80-100% removal efficiency was achieved after a ~5.5 min detention time. A kinetic model was developed for explosives degradation along the cathode distance considering the processes of explosives reduction at the cathode surfaces, possible alkaline hydrolysis, and mass transfer limitations on cathodic reduction rates. Accordingly, intrinsic reaction rate coefficients for were derived, and their values ranged two orders of magnitude. Rate coefficients for the nitroaromatics increased as MNA<2,4-DNT<DNAN<TNT, which trends with increasing nitro group number and more positive one-electron reduction potentials, pointing to the more oxidized compounds having faster reactivities. For the nitramines, the six-membered ring compounds RDX and HMX had much lower rate coefficients than NQ and NTO. Alkaline hydrolysis was predicted to account for only up to a few percent of compound degradation. The model framework and reactivity information can be used for designing larger scale reactors operating at larger flow rates under similar water chemistry.