Study on the Alternative Solvent of Methylbenzene in the Total Acid Number Titration of Current Jet Fuels

[Image: see text] Evaluation of the acidic characteristics of a jet fuel, especially for the total acid number (TAN), is of great significance to ensure flight safety. Methylbenzene is commonly used as the titration solvent; however, it is poisonous and harmful to the environment. It is highly desirable to develop an alternative solvent for methylbenzene to extract the acidic compounds from the jet fuel during the determination of the TAN. Here, we develop a desirable alternative solvent of a mixed ethanol–water solution with the volume ratio of ethanol to water of 99:1, which exhibits a value of TAN similar to that of the solvent of methylbenzene in potentiometric titration and acid–base titration methods. The TAN value derived from the different titration solvents was in the order of 2.96 μg KOH g(–1) (V(cyclohexane)/V(isopropanol)/V(water) = 100:99:1) > 2.68 μg KOH g(–1) (V(methylbenzene)/V(isopropanol)/V(water) = 100:99:1) ≈ 2.6 μg KOH g(–1) (V(absolute ethanol)/V(water) = 99:1) > 2.34 μg KOH g(–1) (V(isopropanol)/V(water) = 99:1). The current report presents a nontoxic and eco-friendly alternative solvent for methylbenzene, which may open up an avenue for evaluating the TAN of jet fuels.