Styrene hydroformylation in supercritical carbon dioxide: Rate and selectivity control

Supercritical fluids have the unique characteristic of density-tuned physicochemical properties that can affect reaction rates and selectivities. We have studied homogeneously catalyzed styrene hydroformylation in supercritical carbon dioxide (scCO(2)) and have shown that the reaction rate and the regioselectivity can be varied by changes in pressure at constant temperature. This rate and selectivity change is explained in terms of the transition state theory. We have determined the partial molar volumes of the reaction products based on the Peng-Robinson equation of state for an infinite-dilution solution model, a real solution model, and a real solution model with regressed interaction coefficients. Then, the estimated partial molar volumes were used to predict the experimentally observed selectivity behavior. Through these simulations, an understanding of the reaction rate and selectivity control by adjustment of the pressure was developed.