Details

The bubble-point and dew-point pressures are calculated from Raoult's law:

,

,

,

The saturation pressures are calculated using the Antoine equations:

,

where , and are Antoine constants and is temperature.

The Peng–Robinson equation of state for mixtures is used to determine the phase envelope and the critical locus. The critical point is where the bubble and dew curves meet; connecting these points is the critical locus. The -values are calculated:

,

.

The fugacity coefficient is calculated:

,

,

,

where is the compressibility factor, the superscript is for liquid and vapor, and are constants, and is pressure.

For a mixture:

,

,

,

,

,

,

where and are the attraction and repulsion factors for the mixture, and are the attraction and repulsion parameters for the pure component, is the binary interaction parameter, and are the critical temperature and pressure, is a simplification term, and is the acentric factor.

The equation is solved for the compressibility factor,

,

,

,

where , and are constants.

Reference

[1] J. R. Elliott and C. T. Lira, Introductory Chemical Engineering Thermodynamics, 2nd ed., Upper Saddle River, NJ: Prentice Hall, 2012 pp. 626–628.