2-Chlorophenol oxidation in supercritical water: Global kinetics and reaction products

Abstract

2-Chlorophenol (2CP) was oxidized in near-critical and supercritical water in a high-pressure plug-flow reactor. The global kinetics for 2CP disappearance were described by a rate law that was 0.88±0.06 order in 2CP, 0.41±0.12 order in O 2 , and 0.34±0.17 order in water. The activation energy was 11.0±3.8 kcal/mol, and the Arrhenius pre-exponential factor was 10 2.0±1.2 M −0.63 S −1 . The uncertainties represent 95% confidence intervals. The products of 2CP oxidation included CO, CO 2 , HCl, other chlorophenols, chlorohydroxybenzaldehydes, dichlorophenoxyphenols, dichlorobiphenols, and chlorinated dibenzodioxins and dibenzofuran. The molar yields of the organic products were determined for a set of experiments at 380°C and 278 atm. The most abundant products were 2CP dimers such as dichlorophenoxyphenols and dichlorobiphenols, and the highest yield observed for any individual product was 0.6%. Although the yields of these products were low, their selectivities were high. For example, at 3.6 s, the shortest residence time studied under these conditions, about 50% of the carbon in the 2CP that reacted appeared in 2CP dimers, 18% appeared as CO 2 , and the balance (32%) was presumably in single-ring and ring-opening products. A reaction pathway analysis using the Delplot methodology revealed that the evolution of products from 2CP oxidation in supercritical water was consistent with a reaction network comprising two parallel primary reactions. One primary reaction path led to dichlorophenoxyphenols and dichlorobiphenols whereas the second primary reaction led to single-ring and ring-opening products. The 2CP dimers were convereted to single-ring and ring-opening products, which were, in turn, ultimately oxidized to CO 2 .