Copper/TEMPO-catalyzed continuous aerobic alcohol oxidation in a micro-packed bed reactor

Abstract

Aerobic oxidation of alcohols to aldehydes and ketones provides a green and sustainable method for the pharmaceutical and fragrance industries. For the industrial application of aerobic oxidations, safety and mass transfer limitations are two significant concerns. With the prominent features of a small inventory of hazardous chemicals and the short diffusion distance, micro-reactors provide an approach to address safety issues and accelerate gas–liquid mass transfer for the aerobic oxidation process. In this work, a highly-efficient micro-packed bed reactor is demonstrated for Cu/TEMPO-catalyzed aerobic alcohol oxidation. A dilute oxygen source (9% O₂ in N₂) is used to ensure that the oxygen/organic mixture never enters the explosive regime. Under the optimized process conditions, the space–time yield for the aerobic oxidation of benzyl alcohol is 7318.4 mol m⁻³ h⁻¹, which is about one order of magnitude higher than that of batch reactors. The kinetic parameters are also determined with this flow system, and a pivotal kinetic model is established to provide guidance for the enhancement of this oxidation process. In addition, with the implementation of the micro-packed bed, several alcohols, including allylic, aromatic, and aliphatic derivatives, can achieve higher oxidation rates compared to slug flow micro-reactors. This continuous flow technology provides a new option for aerobic alcohol oxidation in a more efficient and safer way.