A novel highly sensitive test reaction for micromixing: Acid-base neutralization and alkaline hydrolysis of ethyl oxalate

Micromixing in chemical reactors can be characterized through test reactions that are sensitive to mixing. A new pair of parallel competitive reactions, including acid–base neutralization and diethyl oxalate hydrolysis, is proposed in this work. It has clear principles and high sensitivity to micromixing with quantitative accuracy and operational simplicity. The measurement results obtained from stopped-flow spectra show that the alkaline hydrolysis of diethyl oxalate follows second-order kinetics, and the rate constant conforms to the Arrhenius equation k₂ = 2.331 × 10⁸ exp(−26.92 × 10³/RT) (L/mol/s). The estimated half-life of hydrolysis is approximately 3 × 10⁻⁴ s under the selected concentration combinations, which provides significant advantages for the micromixing assessment in the strong turbulent fluid environment. In the same stirred tank, the critical feed time of new test reaction is shorter than that of the Villermaux–Dushman reaction. Overall, this work provides practical ideas for screening other desired esters for fast hydrolysis to construct more test reactions for micromixing.