This report summarizes results obtained as part of a larger effort to demonstrate the applicability of electrolytic procedures for the direct anodic (oxidative) degradation of toxic organic wastes. We refer to this process as "electrochemical incineration" (ECI) because the ultimate degradation products, e.g., carbon dioxide, are equivalent to those achieved by thermal incineration processes. In this work, the ECI of 4-chlorophenol is achieved in an aqueous medium using a platinum anode coated with a quaternary metal oxide film containing Ti, Ru, Sn, and Sb oxides. The electrode is stable and active when used with a solid Nafion membrane without the addition of soluble supporting electrolyte. Liquid chromatography (LC), including reverse phase and ion exchange chromatography, is coupled with electrospray mass spectrometry (ES-MS) and used, along with gas chromatography-mass spectrometry (GC-MS) and measurements of pH, chemical oxygen demand (COD), and total organic carbon (TOC), to study the reaction and identify the intermediate products from the ECI of 4-chlorophenol. Twenty-six intermediate products are identified and reported. The most abundant of these products are benzoquinone, 4-chlorocatechol, maleic acid, succinic acid, malonic acid, and the inorganic anions chloride, chlorate, and perchlorate. After 24 h of ECI, a solution that initially contained 108 ppm 4-chlorophenol yields only 1 ppm TOC with 98% of the original chlorine remaining in the specified inorganic forms. LC-ES-MS and direct infusion ES-MS detection limits are between 80 ppb and 4 ppm for these intermediate products. Elemental analysis of the electrolyzed solutions by inductively coupled plasma mass spectrometry ICP-MS showed that only trace amounts (<25 ppb) of the metallic elements comprising the metal oxide film were present in the solution.

The electrochemical performance of several anode materials is compared for the electrochemical incineration of p-benzoquinone in acetate buffer media (pH 5). The chemical oxygen demand (COD) estimated for benzoquinone by titration with standard permanganate solution can be decreased to virtually zero by electrolysis at electrodes comprised of Fe(III)-doped ~-PbO2 films on Ti substrates. Carbon dioxide is a product of the electrochemical process; however, the possibility of other volatile products cannot be dismissed. Addition of solid benzoquinone to acetate media is followed by slow formation of a brownish black color that is concluded to result from one or more humic compounds produced by condensation of benzoquinone; however, it cannot be concluded whether the condensation reaction is a necessary prerequisite to successful electrochemical incineration of benzoquinone. Optimal operating conditions suggested for electrochemical incineration of benzoquinone in acetate buffer include heating of the anode (e.g., 60~ to increase the rate of anodic discharge of H20 and, thereby, decrease the anodic overpotential. Evidence also is presented that the.rate of electrochemical incineration is enhanced, slightly by the addition of a traces of Fe(III) with reduction of dioxygen (O2) to hydrogen peroxide (I-I202) at a cooled stainless steel cathode (e.g., 15~ in an undivided cell.