Tracking the Permanganate Oxidation of Ethanol and Its Implications for Ethanol-Blended Fuels

Ethanol-blended fuels are being adopted worldwide, including in Indonesia, where nationwide use is planned, which makes their chemical stability during storage increasingly important. Ethanol can oxidise to ethanoic acid, a corrosive compound with a lower theoretical energy yield than ethanol. This study investigated how oxidation time (0, 8, 16, 24, 32 and 40 minutes) affects the apparent concentration of ethanoic acid in 10% ethanol oxidised by acidified potassium permanganate. Ethanoic acid was quantified by acid–base titration with 0.2 M sodium hydroxide, using five repeated trials per time point. Apparent ethanoic acid concentration increased from 0.0648 ± 0.0003 mol dm⁻³ at 0 minutes to 0.130 ± 0.0005 mol dm⁻³ at 40 minutes, a twofold increase, and plateaued after about 32 minutes. The data were well described by a quadratic model (R² = 0.9922). The average rate of formation fell by 15%, from 0.00220 mol dm⁻³ min⁻¹ (0–20 minutes) to 0.00187 mol dm⁻³ min⁻¹ (20–32 minutes), consistent with collision theory. Although fuel efficiency was not measured directly, the results suggest that ethanol oxidation can produce acidic species that may increase corrosion risk and reduce combustion efficiency in ethanol-based fuels, underscoring the importance of proper storage and handling.