This is a cubic EOS containing the repulsion term of the van der Waals EOS. The original Patel–Teja EOS [1] uses Soave's temperature dependence of the attraction term and can therefore not be used at very high reduced temperatures (this can become a problem with helium, neon, and hydrogen). The modified version of the EOS uses a more flexible temperature function containing 4 (!) adjustable parameters.

The equation gives good vapour pressure curves and liquid densities for many compounds.

The critical compression factor of this EOS is variable and can, in principle, be fitted to experimental data. But this is not advisable, as this causes a massive deterioration of the liquid volumes.

adjustable parameters: 4 (original) or 7 (modified)

[1] N.C. Patel and A.S. Teja, Chem. Eng. Sci. 77 (1982) 463–473.

[2] N.C. Patel, Int. J. Thermophys. 17 (1996) 673–682.

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