Twu-Sim-Tassone equation of state

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. 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):

\[p=\frac{RT}{V_m-b}-\frac{a}{(V_m-0.5b)(V_m+3b)}\]

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):

\[a_c=0.470507 \frac{ R^2T_c^2}{p_c}\]

\[b_c=0.0740740 \frac{ RT_c}{p_c}\]

References

Related reading

• Chorng H. Twu, Wayne D. Sim and Vince Tassone "Getting a Handle on Advanced Cubic Equation of State", Chemical Engineering Progress November pp. 58-65 (2002)