An Empirical Equation for Thermodynamic Properties of Light Hydrocarbons and Their Mixtures II. Mixtures of Methane, Ethane, Propane, and n-Butane

An empirical equation is given for the isothermal variation with density of the work content of hydrocarbon mixtures in the gaseous or liquid state. From this fundamental equation are derived (a) an equation of state, (b) an equation for the fugacity, (c) an equation for the isothermal variation of the enthalpy, and (d) an equation for the isothermal variation of the entropy. These equations summarize P-V-T-x properties of the gaseous or liquid phase, liquid-vapor equilibria, critical properties, latent heats of evaporation, and heats of mixing. The equation is a generalization to mixtures of the equation for pure hydrocarbons given in the first paper of this series. Methods are proposed for determining the parameters in the equation for mixtures from the parameters in the equation for pure hydrocarbons. A comparison is made between observed properties of mixtures and those predicted by the equations. These comparisons show that the equations provide a satisfactory practical summary of the volumetric properties and liquid-vapor equilibria of mixtures of methane, ethane, propane, and n-butane.