Vapour-Liquid equilibrium constants up to the critical point for binary hydrocarbon systems

Abstract

Correlations have been developed that enable the calculation of vapour-liquid equilibrium constants for both components of binary hydrocarbon systems up to and including the critical point of the mixture. The calculation of these constants requires the determination of the ratio of the activity coefficients, ξ = γ l/γ v, and of the fugacities of the pure components in the liquid and vapour states. These correlations have been developed from the extensive work of K ay on the binary systems: n-butane - n-heptane, ethane- n-butane and ethane- n-heptane. The method developed in this study has been tested on the three systems used in its development and on the following five additional hydrocarbon systems: methane-ethane, methane-propane, propane- isopentane, propane-benzene, and ethane- cyclohexane. An average deviation of 6·2 per cent from the corresponding experimental values resulted for 104 vapour-liquid equilibrium constants for the eight hydrocarbon systems considered. In addition, this method has been applied to the following three non-hydrocarbonsystems : nitrogen -oxygen, hydrogen sulphide- n-pentane, and carbon dioxide- n-butane. For these systems the average deviations were found to be 5·0, 16·0 and 13·4 per cent, respectively, for a total of fifty experimental values considered. The method developed in this study is particularly useful for the calculation of equilibrium constants for binary hydrocarbon systems in the vicinity of the critical point. These correlations can also be used for the calculation of critical temperatures and pressures of binary hydrocarbon systems.