Experimental determination and modeling of the phase behavior for the selective oxidation of benzyl alcohol in supercritical CO2

In this study the phase behavior of mixtures relevant to the selective catalytic oxidation of benzyl alcohol to benzaldehyde by molecular oxygen in supercritical CO2 is investigated. Initially, the solubility of N2 in benzaldehyde as well as the dew points of CO2–benzyl alcohol–O2 and CO2–benzaldehyde–water ternary mixtures were experimentally determined. The cubic plus association (CPA) equation of state was used to model the phase behavior of the experimentally investigated systems as well as the phase behavior of relevant mixtures that can exist inside the reactor during the reaction time. In this direction, the CPA binary interaction parameters were estimated from the corresponding binary systems and the phase behavior of two ternary systems, i.e. CO2–benzyl alcohol–O2 (reacting mixture) and CO2–benzaldehyde–water (mixture of products) as well as the phase behavior of multicomponent mixtures containing both reactants and products were predicted. CPA was proved to be a versatile model that can predict the complex phase behavior of the aforementioned systems. The results reveal that the ternary mixture of products (CO2–benzaldehyde–water) and the intermediate multicomponent mixtures containing both products and reactants require lower pressure than the corresponding mixture of the reactants (CO2–benzyl alcohol–O2) in order to be in a single phase.