Influence of the Thermodynamic State on Cyclohexane Oxidation Kinetics in Carbon Dioxide Medium

Cyclohexane has been oxidized in supercritical carbon dioxide (SC CO2) medium in the presence of oxygen to give the main products, cyclohexanone and cyclohexanol. Kinetic studies have been performed to study the effects of the proximity to the plait point, nature of the phase and initial feed concentration on the product profiles, selectivities, and rates of product formation. The initial reaction conditions have been chosen to be at different regions of space on the ternary-phase diagram of the initial reaction mixture comprising cyclohexane, oxygen, and carbon dioxide. These conditions encompass different thermodynamic phases such as (i) the homogeneous subcritical (mixture) phase rich in SC CO2, (ii) the homogeneous supercritical (mixture) phase, (iii) the SC CO2-rich vapor−liquid two phase, and (iv) the CO2 dissolved liquid phase. It has been observed that the density and the proximity to the plait point of the reaction mixture influence the reaction conversion, rates, and pathways. The first-order rate constants are observed to be dependent on the thermodynamics state of the feed.