volume-translated Peng–Robinson

This equation was developed from the Peng–Robinson EOS by substituting a Twu temperature function for the Soave function and by using Peneloux' volume translation for improving the representation of liquid densities.

The amount of the volume translation is usually calculated from
liquid volumes at 0.7 *T*_{c}, and it is
temperature-independent. Consequently the EOS gives indeed better
density results for many compounds. But the volume shift is usually
not appropriate for the critical region. The critical compression
factor is usually off, and it is not advisable to use the critical
molar volume for parameter fitting.

adjustable parameters: 6

For mixture calculations the following mixing theories are available:

- UNIFAC: the authors' scheme for determining EOS parameters from the UNIFAC group contribution method [1]

[1] J. Ahlers and J. Gmehling, *Ind. Eng. Chem. Res.* 41
(2002) 3489–3498.

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