PR — Peng-Robinson equation of state

The Peng-Robinson (PR) equation of state (EOS) is a modification of the Redlich-Kwong (RK) EOS and was published by Peng and Robinson in 1976[1]. It is similar to the Soave-Redlich-Kwong (SRK) EOS in many respects. As with the SRK EOS, the ac/Tr0.5 term in the RK EOS was replaced with a more general temperature-dependent term, a(Tr).

This equation provides accurate predictions for mixtures of hydrocarbons, but does not accurately predict the behavior of mixtures of polar components or hydrocarbons with light gases such as hydrogen. However, the simplicity of the equation, and its accuracy for calculating vapor-liquid equilibrium for hydrocarbon mixtures, allowed it to gain widespread industry popularity.

In addition to fugacity coefficients and K-values, the PR EOS can also predict the enthalpy, entropy, and density for the liquid and vapor phases.