Elucidating the Influence of N Doping on Production of ε-Caprolactone Catalyzed by Nanocarbon: A Kinetic Model from Batch to Semibatch and Continuous-Flow Operations

Nanocarbons have been identified as effective catalysts to promote the Baeyer–Villiger (BV) oxidation of cyclohexanone (Cy═O) toward ε-caprolactone (ε-CL). To effectively enlarge the production capacity of ε-CL, a kinetic model with simplified two main reactions (BV oxidation and aldehyde self-oxidation) catalyzed by carbon nanotubes (CNTs) and N-doped CNTs was established. The enhancement of N dopants was observed to facilitate the rate constant (k) and lower the energy barrier (Ea). Meanwhile, the negative value of reaction order for the BV oxidation was obtained, implying competitive adsorption between ketone and aldehyde on the carbon surface, as confirmed by the density functional theory simulations. Also, the high ratio of ketone/aldehyde favored the formation of ε-CL and improved the aldehyde efficiency (η). Based on the established kinetic model in the batch reaction, the semibatch and continuous-flow reactions were performed, validating the rationality and feasibility of the reaction model.