Decomposition of 2-Chlorophenol at a Process Combining Pyrolysis with NaOH prior to Oxidation in Supercritical Water

Abstract
The aim of this research is to overcome difficulties of a conventional supercritical water oxidation (SCWO) process, which suffers from severe corrosion of the reactor and the hazardous intermediates such as polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzodioxins (PCDDs) at a low temperature. To overcome these problems, a new process (SCWP/O) which combines a pyrolysis reactor prior to SCWO is proposed. 2-chlorophenol (2CP) was selected as a reactant, which is known as a precursor to form PCDDs and PCDFs. Sodium hydroxide (NaOH) was selected as an alkali, which is used for neutralization of acids in the conventional SCWO process.
Experiments were conducted under four conditions, which are 2CP oxidation, 2CP pyrolysis with NaOH in supercritical water, 2CP pyrolysis and oxidation in a combined process suggested in this study, and the conventional SCWO process (2CP oxidation with NaOH) . The comparison between the conventional SCWO process and the combined process is particularly interesting. The conversion of 2CP at the combined process was higher than that at the conventional SCWO. A variety of reaction products were detected using a GC/MS. Dimers such as 1-chlorodibenzodioxin, dichlorophenoxyphenol and 2,7-dichlorodibenzodioxin were detected from the samples of the conventional SCWO process. On the other hand, dimers were not detected from ones of the combined process, but phenol and cresols were mainly detected as the reaction products. The results of experiments show a possibility that the problems of SCWO can be solved by the combination of pyrolysis reactor.

Key words: supercritical water oxidation, 2-chlorophenol, sodium hydroxide, pyrolysis, dioxins