Removal of p-chlorophenol in mist by DC corona discharge plasma

Volatile organic pollutants in mist are becoming of great concern around the world. In the present study, removal of p-chlorophenol (4-CP) in mist by corona discharge plasma was investigated using a link tooth wheel-cylinder plasma reactor energized by a positive DC power supply. The results indicate that the corona discharge is effective in removal of 4-CP in mist. The removal of 4-CP and TOC (total organic carbon) improves as input power increases. With the help of Gaussian03 package program combined with frontier orbital theory and density functional theory, it was speculated that 4-chlorocatechol was the dominating hydroxylated intermediate and C-Cl would be initially attacked by the plasma species to form Cl^- due to its longest bond length, which is verified by HPLC and IC analysis results of 4-CP degradation products. Most of the chlorine atoms are released from the removed 4-CP to form Cl^-. The Cl^- takes up more than 93% while the 4-chlorocatechol accounts for less than 1% of the reacted chlorine. The ring-opening (maleic and oxalic acids) and ring-containing products (mainly 4-chlorocatechol) account for less than 50% and 1% of the converted carbon respectively under the investigated conditions, with the other converted carbon being contained in inorganic products such as CO₂ and CO. Both short-living and long-living plasma species contribute to 4-CP degradation. Based on the analysis of 4-CP degradation products and the roles of active species in 4-CP degradation, possible pathways of 4-CP degradation in mist were proposed.