A cubic equation of state with group contributions for the calculation of vapor-liquid equilibria of mixtures of hydrofluorocarbons and lubricant oils

A method for calculating the vapor-liquid equilibria of mixtures between hydrofluorocarbons and lubricant oils is presented. A cubic equation of state is used (Sako, T.; et al. J. Appl. Polym. Sci. 1989, 38, 1839), containing three parameters: the attractive one, a, the volume parameter, b, and the number of external degrees of freedom per molecule, c. To allow calculation of the parameters of the high molecular weight components, whose critical constants and vapor pressure are unknown, a group-contribution approach is developed for a, b, and c. The extension to mixtures is achieved by applying Huron-Vidal mixing rules. A modified Uniquac model is used to evaluate infinite-pressure activity coefficients. With the proposed method, the density of pure heavy components (such as n-hexadecane and pentaerythritol esters) is predicted as a function of temperature. Vapor-liquid equilibria calculations are presented for binary mixtures between several hydrofluorocarbons and pentaerythritol esters or hexadecane; a comparison with the results obtained by available models is also outlined.