Ozonation of Naphthenic Acids in Water: Kinetic Study

Abstract

The large amount of oil sands process-affected water (OSPW), produced from the extraction of oil from oil sands in Alberta, Canada, has demonstrated both acute and chronic toxicity to many species due to the presence of naphthenic acids (NAs). The “zero discharge” policy posted by the Alberta government presents a major challenge for the oil sands industries. In this study, ozonation was used to remove model NAs from water. It was found that the removal of NAs increased with the temperature. The kinetics of direct ozonation between molecular ozone and NAs was investigated in the presence of a radical scavenger, sodium bicarbonate. The rate constants of the direct ozonation at 5, 15 and 25 °C were determined to be 0.67, 2.71 and 8.85 M−1 s−1, respectively, and the activation energy of the direct ozonation was found to be 88.85 kJ mol−1. The kinetics of indirect ozonation was also studied. By using pCBA as a hydroxyl radical probe compound to determine the hydroxyl radical concentration and applying the ratio of hydroxyl radical concentration to dissolved ozone concentration, R ct, the rate constants of the indirect ozonation of NAs were found to be 1.12 × 108, 1.78 × 108 and 2.33 × 108 M−1 s−1 at 5, 15 and 25 °C, respectively. In addition, from the Arrhenius plot of the rate constants, the activation energy of the indirect ozonation was found to be 25.41 kJ mole−1.