Catalytic Oxidation of Phenol in Aqueous Solution over Copper Oxide Ajit Sadana and James R. Katrer* Department of Chemical Engineering, University of Delaware, Newark, Del. 7971 7
Catalytic oxidation of phenol in aqueous solution over supported copper oxide was studied in t h e batchwise mode at atmospheric and above-atmospheric pressure and between 369 and 419°K. T h e reaction undergoes an induction period and transition to a much higher, steady-state activity regime. T h e reaction is first order with respect to phenol in both regimes, but t h e oxygen dependency decreases from first to one-half order in shifting from t h e induction period to t h e steady-state activity regime. The rate shows other than first-order behavior with respect to catalyst loading. T h e reaction is proposed to involve a free-radical mechanism. Oxidation rates at atmospheric pressure conditions are too slow to be of practical interest but can easily be brought into the range of practical importance by only moderate increases in temperature and operating pressure. Introduction Many waste water streams originating in the chemical process industry contain high concentrations of organic materials which may be difficult to oxidize biologically. Phenols are one of the most common and important of these because they are extremely toxic to aquatic life and impart a strong disagreeable taste and odor to water particularly after chlorination. To meet present and future demands for improved water quality and increased water reuse improved treatment technology is desirable. Eisenhauer (1964, 1968) studied the oxidation of phenol in aqueous solution with ozone, hydrogen peroxide, chlorine and Fenton's reagent. He demonstrated a multistep consecutive reaction with high conversion to several intermediates as reaction proceeded and defined several of the important parameters affecting the rate and efficiency of the process. Shibaeva, et al. (1969a,b) have investigated the free-radical nature of homogeneous phenol oxidation with oxygen and hydrogen peroxide. The cost of such homogeneous oxidations is economically attractive only as a polishing step because of high reagent costs (Hall and Nellist, 1965; Hiubers, et al., 1969; Peppler and Fern, 1959). Borkowski (1967) found copper oxide on alumina to be the most active of many catalysts studied for the vaporphase oxidation of phenols in vaporized effluents with air and showed that between 573 and 673°K oxidation was essentially complete to COz and H20 at a space velocity of --9ooo hr-1. Walsh and Katzer (1973) determined the kinetics of the vapor-phase oxidation of phenol in dilute concentration in air-water mixtures over copper oxide between 423 and 543°K. At 523°K and 4000 hr-l space velocity conversion was essentially complete to COz and
HzO. Little information is available on aqueous-phase catalytic oxidation. Hamilton, et al. (1969), report on a process for aqueous-phase oxidation of organics over manganese dioxide at typically 373°K or less. A commercial process for the catalytic oxidation of organics in waste water has been announced (Krupp, 1972). Operating conditions are mild (
