Mechanism Of Degradation Of 2-Chlorophenol By Electro-Heterocatalysis Reactor

Chlorophenol is a typical refractory and toxic organic pollutant, and it can remain in the environment for a long time. Electro-heterocatalysis shows a wonderful prospect in industrialization since it has characteristics from both electro-oxidation and heterogeneous catalysis. It overcomes the concentration polarization phenomena as well as the high conditions heterogeneous catalysis needed, and has advantage in ratio of area to volume, mass transfer, and current efficiency. This paper started with the degradation efficiency of 2-chlorophenol (2-CP), mainly investigated the yield of hydroxyl radical (·OH) and the degradation pathways of 2-CP, finally, elaborated the degradation mechanism of 2-CP by electro-heterocatalysis reactor.2-CP and TOC were rapidly degraded by electro-heterocatalysis reactor which use Ti/SnO₂+Sb₂O₄ as anode, stainless steel as cathode andγ-Al₂O₃/Sb₂O₄+SnO₂ as particle electrode. Different initial pH value had slightly influence on the degradation rate of 2-CP and TOC. In alkaline environment, a relatively higher degradation rate appeared, 2-CP removal rate reached 97% after 90 min and the TOC removal rate reached 58.9% under our experimental condition. Particle electrode increased 70% of the current efficiency compared with the reactor without particle electrode in the beginning. Hydroxyl radical is the main active species in electro-heterocatalysis system, it was measured by monitoring products resulted from attack of p-hydroxybenzoic acid by·OH. Acid initial solution had a higher·OH yield than neutral initial solution or alkaline had. Higher current density lead to higher·OH yield, but current efficiency reduced. Hydroxyl radical production reached the highest level at 0.02 mol/L Na₂SO₄ concentration under constant current conditions, and then the production decreased as the electrolyte concentration increased. However, low electrolyte concentration required a higher output voltage which means excessive energy consumption was needed to reach the specified current density. The relational expression between·OH yield and input energy was k_·OH= 0.109×10^-7 mol/(L·s·W) under current of 0.5 A, electrolyte concentration of 0.05 mol/L, aeration rate 0.4 m³/h, initial pH=3.56.Degradation pathway of 2-CP by electro-heterocatalysis reactor was divided into three steps: Firstly, 2-CP experienced electronic transfer and·OH attack, then it became 2-Cl-p(o)-hydroquinone which was further oxidized to 2-Cl-p(o)-benzoquinone. Secondly, the ring was opened and 2-Cl-p(o)-benzoquinone formed aliphatic hydrocarbons which soon decomposed into succinic acid, acetic acid, and other small organic acids after dechloridation. Finally, further oxidation of organic acids formed the end products: carbon dioxide and water.