Insights into the Degradation of 4-Methyl-1-Cyclohexane Carboxylic Acid by Ozone Using a Copper – Magnesium Phosphate Catalyst – The Role of Reactive Oxygen Species, Reaction Network, and Biodegradability Assessment

A probe-based kinetic study was conducted for the oxidation of a model naphthenic acid compound, i.e. 4-Methyl-1-cyclohexane carboxylic acid (4MCH), by ozone using a copper-magnesium phosphate catalyst. The second order reaction rate constant of hydroxyl radicals with 4MCH was 4.85 × 109 M−1 s−1, followed by superoxide radicals and ozone at 1.54 × 108 and 4.29 M−1 s−1, respectively. On average, 57% of 4MCH molecules were oxidized by hydroxyl radicals, while only 33% and 10% of 4MCH molecules were oxidized by ozone and superoxide radicals, respectively. Singlet oxygen had no reactivity toward 4MCH. The catalyst lowered the total organic carbon (TOC) and chemical oxygen demand (COD) of 4MCH by 94% and 98%, respectively, in 215 min. 18,124 and 4859 mg of ozone was consumed for the removal of 1 g of TOC and COD, respectively. The ozone utilization efficiency was 18%. The by-products of the reaction were found to be easily biodegradable after 155 min of the reaction. The by-products were identified, and a reaction network was proposed for the oxidation of 4MCH. Meta addition was the dominant mechanism for the reaction between 4MCH and hydroxyl and superoxide radicals, while the reaction between ozone and 4MCH was initiated through a stepwise hydrogen abstraction mechanism.