Peng-Robinson
The Peng-Robinson equation of state is a two-fold
modification of the PR equation of state that extends the application of
the original PR method for moderately non-ideal systems. It has been
shown to match vapour pressures curves of pure components and
mixtures more accurately than the PR method, especially at low vapour
pressures.
It has been successfully extended to handle non-ideal systems giving
results as good as those obtained using excess Gibbs energy functions
like the Wilson, NRTL or UNIQUAC equations.
One of the proposed modifications to the PR equation of state by
Stryjek and Vera was an expanded alpha, "α", term that became a
function of acentricity and an empirical parameter, κi
, used for fitting
pure component vapour pressures