Supercritical-fluid-assisted oxidation of oleic acid with ozone and potassium permanganate

Abstract

The goal of this research was to determine if any advantages could be realized by conducting the oxidation of oleic acid with ozone and potassium permanganate in supercritical carbon dioxide (SC-CO₂). The ozonolysis of oleic acid without SC-CO₂ at 313.15 K and ambient pressure resulted in complete conversion of the oleic acid within 2 hrs. The reaction was zero-order, indicating the system was mass-transfer limited, and the rate of oleic acid disappearance was 0.077 mol s⁻¹ m⁻³. Due to experimental limitations, no reaction was observed in the case of ozone in SC-CO₂. However, oxidation of oleic acid with potassium permanganate in SC-CO₂ at 12.2 MPa resulted in an increase in oleic acid conversion from 50.8% to 95.1% at 308.15 K and 51.7% to 95.6% at 318.15 K. Oleic acid oxidation with potassium permanganate in supercritical carbon dioxide was found to have a reaction order of 1.75 with rate constants of 5.33 × 10⁻⁵ m^2.25 s⁻¹ mol^−0.75 and 1.43 × 10⁻⁴ m^2.25 s⁻¹ mol^−0.75 at 308.15 K and 318.15 K, respectively. Also, increased yields of the target products, azelaic acid and pelargonic acid, were obtained when compared to the oxidation without SC-CO₂. In terms of greenness, the addition of SC-CO₂ allows product separation to be combined with reaction, which reduces the need for other energy-intensive separations, such as distillation, which are traditionally used. In comparing the two oxidizers, ozone is more efficient, but the use of potassium permanganate would eliminate concerns associated with fugitive emissions of ozone into the environment.