Homogeneous catalysis in the oxidation of p-chlorophenol in supercritical water

Abstract

The kinetics of the uncatalyzed and homogeneously catalyzed oxidation of p-chlorophenol in water near the critical point (374 °C, 218 atm) was investigated. Under the conditions of the experiments, the rate of disappearance of chlorophenol appears to be first order at low concentrations, second order at high concentrations, and independent of the concentration of oxygen. This was observed at both subcritical and supercritical conditions. Trace metals as a result of reactor corrosion were found in the reaction mixture and may have acted as catalysts. Further addition of copper(II) and manganese(II) salts as homogeneous catalysts resulted in modest increases in the oxidation rate. The presence of the added catalyst did not appear to alter the mechanism. A pronounced surface effect was evident. Increasing the surface-to-volume ratio of the reactor enhances the rate, possibly due to wall initiation. Feasible mechanisms are postulated, which include solvolysis and free-radical oxidation.

Kinetics of phenol oxidation in supercritical water

“…In a more recent study involving a model organic pollutant, Yang and Eckert (1988) oxidized p-chlorophenol in near-critical and supercritical water in a plug-flow reactor. They examined the dependence of the average reaction rate (average rate = A[p-chlorophenol]/.r) on the p-chlorophenol and oxygen concentrations, and reported that the reaction was first order in p-chlorophenol at low concentrations, second order at high concentrations, and always zero order in oxygen.…”

“…did not report the conversions for each experiment, but she did report that the maximump-chlorophenol conversion was 95%. If the conversions from many of the experiments were frequently high, then the rate constants reported by and Yang and Eckert (1988) must be viewed as being only approximate.…”

Methane and methanol oxidation in supercritical water: Chemical kinetics and hydrothermal flame studies

“…The same was found for phenol (Thornton and Savage, 1990), acetamide, and acetic acid . In light of our results, it is interesting to note that Yang and Eckert (1988) found a reaction order for p-chlorophenol that increased from 1 to 2 as concentration was increased.…”

Modeling of supercritical oxidation of aqueous wastes in a deep‐well reactor

“…First-order dependence of the rate on the concentration of the organic component was reported in the literature for supercritical-water oxidation Tester, 1987, 1988;Yang and Eckert, 1988;Webley and Tester, 1989). Thus, we assume that the rate is given by r = k, exp( -E,,,/RT)C,, where A (the organic component) is the limiting reactant.…”