Continuous Cu/keto-ABNO catalyzed aerobic oxidation of ethyl lactate to ethyl pyruvate in a micro-packed bed reactor: Process optimization and reaction kinetics

Pyruvic acid and its esters are increasingly utilized as precursors for synthesizing antioxidations or dietary supplement in the pharmaceutical industry. The selectivity of oxidation step holds paramount importance in the synthesis route. In this study, a continuous micro-packed bed reactor platform is developed to determine the kinetic parameters of Cu/keto-ABNO catalyzed aerobic ethyl lactate (EL) oxidation. Initially, various operating parameters including types of nitroxyl radical, phase ratio, pressure and temperature were systematically studied to reveal their effect on the oxidation performance. The Cu/keto-ABNO catalyzed aerobic oxidation method can efficiently transform EL to ethyl pyruvate (EP) without hydrolysis. Comparing the aerobic oxidation performances in batch reactors, the reaction time was shortened to 1/15 and the space time yield was increased by 6 times in micro-packed bed reactors, which is due to the enhanced gas–liquid mass transfer. Finally, the kinetic parameters of this reaction were promptly determined and the supplementary validation experiments were conducted to confirm the applicability and accuracy of the kinetic model.