Pentachlorophenol oxidation rates in supercritical water

Abstract

The oxidation rate of pentachlorophenol, [C₆HCl₅O] which is used to control termites and as a general herbicide and also as the probable human's carcinogen, was investigated in an isothermal continuous tubular reactor under supercritical water oxidation (SCWO) conditions. The experiments were conducted at a temperature of 400–550°C and a fixed pressure of 25 MPa, with a residence time that ranged from 6 s to 26 s. The conversion of PCP was monitored by analyzing total organic carbon (TOC) on the liquid effluent samples. The initial TOC concentrations of PCP were varied from 0.74 mmol/L to 2.91 mmol/L and the oxygen concentrations were varied from 0.46 mmol/L to 3.52 mmol/L. By taking into account the dependence of the oxidant and TOC concentration on the reaction rate, a global PCP oxidation rate was regressed from the data of 48 experiments, to a 95% confidence level. The resulting activation energy was determined to be 43.56 ± 1.47 kJ/mol, and the pre-exponential factor was (1.92 ± 0.46) × 10² L^1.16 mmol^−0.16 s⁻¹. The reaction orders for the PCP (based on TOC) and the oxidant were 0.74 ± 0.02 and 0.42 ± 0.05, respectively.

Keywords:

• Pentachlorophenol
• Supercritical water oxidation
• Oxidation rate
• TOC disappearance
• SCWO
• PCP

Acknowledgments

This work was supported by the Agency for Defense Development, Korea.

Notes

* The TOC and O₂ concentration at the reactor inlet was calculated from the feedstock concentration and flow rates of the feed streams with the process condition.