Destruction of Aqueous-phase Carbon Tetrachloride Using an Electrochemical Reactor

Lei Wang, Doctoral candidate (presenter)
Department of Chemical & Environmental Engineering
University of Arizona

Dr. A. Eduardo Saez
Department of Chemical & Environmental Engineering
University of Arizona

Dr. Wendell P. Ela
Department of Chemical & Environmental Engineering
University of Arizona

Dr. Robert G. Arnold
Department of Chemical & Environmental Engineering
University of Arizona

ABSTRACT

A continuous-flow, laboratory-scale (3-inch diameter) electrochemical reactor was developed to destroy aqueous-phase carbon tetrachloride (CT) via electrochemical reduction. The reactor consisted of a cylindrical metal (Cu or Ni) foam cathode (95% porosity) through which the contaminated catholyte flowed. The cathode was surrounded by a concentric anode that consisted of carbon cloth. A polysulfone membrane separated the catholyte and anolyte solutions. The total cathode length was nine inches. The CT concentration distribution was measured at various axial and radial positions in the metal foam cathode. During continuous-flow operation, over 70% destruction of CT was obtained using either cathode material under the following conditions: Applied cathode potential -0.3V or lower, influent conductivity 0.05S/m (like tap water), detention time 15 minutes. However, radial concentration profiles showed that CT was rapidly transformed near the anode (i.e., near the reactor perimeter) and that conversion near the reactor center was slow. Thus, an appreciable portion of the reactor worked at very low efficiency. An electrochemical reactor model was developed to simulate the performance of the reactor. Simulations suggested that the steady aqueous-phase pH should vary significantly in the radial direction, typically from acidic values at the reactor perimeter to neutral or slightly alkaline values along the reactor centerline. It is proposed that useful cathode surface area of the metal foam is sensitive to solution pH. At neutral and alkaline pH values, corrosion of the metal cathode reduces the surface area that is available for CT reduction. No corrosion occurs at pH values lower than 2-3, so that virtually the entire cathode surface remains active only in the perimeter region of the foam material. The analysis suggests that reactor utility can be enhanced dramatically if cathode materials can be obtained that resist corrosion in the neutral pH range