Taylor Series for Peng-Robinson Equilibrium Properties Using Similarity Variables

The Peng-Robinson (PR) equation of state (EoS) is used to determine vapor pressure in addition to PVT properties. In this work, a dimensionless version of the PR equation has been simplified by combining the temperature and acentric factor into a similarity variable, η, termed the adjusted temperature. Other new dimensionless variables were defined by combining pressure and temperature into a dependent variable, Ψ, termed the adjusted pressure, and by defining a reduced density variable, ρr', relative to the maximum liquid density in the low temperature limit. A Taylor series expansion in the similarity variable η was used to express reduced phase densities and vapor pressure by simple polynomials. The truncation error of these series was characterized. This work resulted in a simpler method of estimating PVT properties and vapor pressure that would be predicted by the PR equation for any substance.