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Twu-Sim-Tassone equation of state

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Twu, Sim and Tassone presented a cubic equation of state for accurate representation of hydrocarbons that has become known as the Twu-Sim-Tassone or TST equation of state[1]. With a critical compressibility factor of (Eq. 5)

Z_c = \frac{p_cv_c}{RT_c} =   0.296296

it better represents the compressibility than many of than the Redlich-Kwong equation of states, including the Soave modified version, and the Peng and Robinson equation of state.

The equation follows the general cubic form resulting in the equation (Eq. 2):


where V_m is the molar volume, R is the molar gas constant, T is the temperature, p is the pressure, 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 (Eqs. 3 and 4):

a_c=0.470507   \frac{ R^2T_c^2}{p_c}
b_c=0.0740740  \frac{ RT_c}{p_c}


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