Engineering strategies to control liquid phase oxidation of hydrocarbons to produce value-added chemicals (Manuscript # 699f)

Industrially important liquid-phase oxidation of hydrocarbons with molecular oxygen or air follows a free radical pathway that includes initiation, propagation, and termination. The main challenge of this process is to control product selectivity as the reactants are present in different phases, heat management due to exothermic reactions, and steps progress at different rates. This study highlights how engineering strategies can be used to manipulate various stages of free radical processes. Initiation is the first step of the free radical process which is recognized as the slowest step and kinetically controlled. However, with the improved reactor technology, it was possible to change the initiation process. For instance, an experiment demonstrated in a microfluidic reactor revealed that the initiation process can be significantly improved by controlling the gas-liquid interface (a), which ensures very high oxygen availability. Moreover, experiments performed in batch reactors showed that the rate of initiation was much higher in cases of higher gas-liquid interfacial area, followed by low interfacial area, and little or no initiation in circumstances of no gas-liquid interface. Propagation and termination steps are fast, and proper control of these steps would lead to the formation of desired products. Ensuring oxygen would lead to the oxygenates formation while oxygen deficiency leads to the form addition product (R-R). A microfluidic reactor study maintaining Taylor flow revealed that ensuring oxygen availability increased ketone to alcohol in primary oxidation products from 1:1 to 14:1 at nearly constant conversion. This selectivity increase was noticeably greater than in batch and semi-batch reactors. The size and shape of the microfluidic reactors have varied effects on mass transfer and mixing and hence affect the conversion and selectivity in different ways. Overall, the controlled autoxidation method holds promise for turning lower-value hydrocarbons into value-added products, and engineering strategies can play a crucial role in controlling free radical chemistry.