Twu-Sim-Tassone equation of state

Twu, Sim and Tassone presented a cubic equation of state for accurate representation of hydrocarbon that has become known as the Twu-Sim-Tassone or TST equation of state. With a critical compressibility factor $Z_{c}$ of 0.2962, it better represents many the compressibility of than the Redlich-Kwong equation of state, including the Soave modified version, and the Peng and Robinson equation of state. This allows it to better represent long chain hydrocarbons.

The equation follows the general cubic form resulting in the equation:

$p={\frac {RT}{V_{m}-b}}-{\frac {a}{(V_{m}-0.5b)(V_{m}+3b)}}$

Where $V_{m}$ is the molar volume, and $a$ and $b$ are the attractive and repulsive parameters akin to those of the Van der Waals equation of state. Relations exists between $a$ and $b$ and the critical parameters $T_{c}$ and $P_{c}$ in the forms:

$a={\frac {0.427481R^{2}T_{c}^{2}}{P_{c}}}$

$b={\frac {0.086641RT_{c}}{P_{c}}}$