Degradation of a Model Naphthenic Acid, Cyclohexanoic Acid, by Vacuum UV (172 nm) and UV (254 nm)/H₂O₂

Abstract

The mechanism of hydroxyl radical initiated degradation of a typical oil sands process water (OSPW) alicyclic carboxylic acid was studied using cyclohexanoic acid (CHA) as a model compound. By use of vacuum ultraviolet irradiation (VUV, 172 nm) and ultraviolet irradiation in the presence of hydrogen peroxide UV(254 nm)/H(2)O(2), it was established that CHA undergoes degradation through a peroxyl radical. In both processes the decay of the peroxyl radical leads predominantly to the formation of 4-oxo-CHA, and minor amounts of hydroxy-CHA (detected only in UV/H(2)O(2)). In UV/H(2)O(2), additional 4-oxo-CHA may also have been formed by direct reaction of the oxyl radical with H(2)O(2). The oxyl radical can be formed during decay of the peroxyl-CHA radical or reaction of hydroxy-CHA with hydroxyl radical. Oxo- and hydroxy-CHA further degraded to various dihydroxy-CHAs. Scission of the cyclohexane ring was also observed, on the basis of the observation of acyclic byproducts including heptadioic acid and various short-chain carboxylic acids. Overall, the hydroxyl radical induced degradation of CHA proceeded through several steps, involving more than one hydroxyl radical reaction, thus efficiency of the UV/H(2)O(2) reaction will depend on the rate of generation of hydroxyl radical throughout the process. In real applications to OSPW, concentrations of H(2)O(2) will need to be carefully optimized and the environmental fate and effects of the various degradation products of naphthenic acids considered.

A solar-driven UV/Chlorine advanced oxidation process

“…This process was first assessed at the bench scale using a narrow band interference filter (303 AE 8 nm) representative of the lower end of the solar UV region, where the quantum yields and hydroxyl radial yield factor were determined. The solar-driven AOP was first applied to the photobleaching of MB [a model compound for organic dyes] and then to the photodegradation of CHA [a simple model compound for the potentially toxic naphthenic acids present in typical oil sands process-affected water (Drzewicz et al, 2010;Gamal El-Din et al, 2011;Martin et al, 2010;Pé rez-Estrada et al, 2011;Pourrezaei et al, 2011)] at the bench scale and under actual sunlight in Edmonton, Alberta, Canada, along with theoretical calculations.…”

Two‐step persulfate and Fenton oxidation of naphthenic acids in water

“…Different techniques addressed to the removal of NAs from aqueous wastes have been investigated 14 . Those include adsorption 15 , biodegradation 16 and advanced oxidation processes (AOPs) 9,17,18 . Adsorption, being a non-destructive operation, gives rise to secondary wastes while conventional biological treatments are limited by the toxicity and recalcitrant character of NAs 2 20,21 and their oxides 22 , or by some energy source, including thermal 23 , light (UV 24,25 /solar 26 /LED 27 ) and electricity 28 .…”

Naphthenic acids removal from high TDS produced water by persulfate mediated iron oxide functionalized catalytic membrane, and by nanofiltration

“…Hydroxyl radical reacts with the aliphatic carboxylic acids through abstraction of hydrogen from the aliphatic chain of the acids [37]. On the other hand, Madhavan et.…”