Solvent properties of supercritical CO2/HFC134a mixtures

The dipolarity/polarizability parameter, pi*, of Kamlet and Taft is used to characterize the solvent properties of CO2/1,1,1,2- tetrafluoroethane (HFC 134a) mixtures in the supercritical state. It is shown that: preferential s olvation of the solute by HFC134a occurs. The local composition of the pola r constituent is shown to steadily decrease as the pressure is increased, b ut: the local pi* value does not decrease below that of the bulk fluid. A m ixture of 30 mol % HFC134a in CO2 has properties similar to these of bulk H FC134a at high densities. Such a mixture is extremely useful for extraction purposes, as it has a critical temperature that is 42 degrees C lower than bulk HFC134a.