Degradation of cyclohexanecarboxylic acid as a model naphthenic acid by the UV/chlorine process: Kinetics and by-products identification

Degradation kinetics, by-products identification and pathways of a model naphthenic acid, cyclohex-anecarboxylic acid (CHA), by the UV/Chlorine process were investigated in this study. Mathematical modeling indicated that the initial CHA decay rate increased rapidly with the chlorine dose when the chlorine dose was lower than 45 mg/L and decreased with further chlorine dose increases. Increasing the chlorine dose from 400 to 800 mg/L resulted in a steady increase in the total removal of CHA after 60 min of UV photolysis. By dividing the 700 mg/L chlorine dose into five separated doses (140 mg/L each) added at 10 min intervals, the total CHA removal increased from 72% to 91%. This implies that the ideal condition of the UV/Chlorine process in degrading CHA is to add chlorine continuously at a constant rate to compensate any chlorine consumption to reduce the radical scavenging effect. It was found that the CHA decay was mainly attributed to the hydroxyl radical (%OH) attack and the reactive chlorine species (RCS) contribution was relatively small. Various byproducts, including the mono-chlorinated and di-chlorinated by-products, were identified and the reaction pathway for CHA degradation during UV/Chlorine treatment was proposed.

Automated summary

The study found that the ideal condition for degrading CHA using the UV/Chlorine process is to continuously add chlorine at a constant rate to reduce chlorine consumption and minimize the radical scavenging effect, resulting in a higher removal rate.