SoaveRedlichKwong

Soave-Redlich-Kwong (SRK) is a cubic equation of state used to model the P-V-T behavior of fluids, particularly hydrocarbon systems, by combining the Redlich-Kwong framework with a temperature-dependent attraction term. It was introduced by Soave in 1972 as an improvement over the Redlich-Kwong equation.

The SRK equation in molar form is P = RT/(V − b) − a α(T) / [V (V + b)], where V is molar volume, R is the gas constant, P is pressure, and T is temperature. The parameters a and b are functions of critical properties: a = 0.42747 R^2 T_c^2 / P_c and b = 0.08664 R T_c / P_c. The temperature dependence is captured by α(T) = [1 + m (1 − √T_r)]^2, with m = 0.480 + 1.574 ω − 0.176 ω^2 and T_r = T / T_c; ω is the acentric factor. Solving for V or the compressibility factor Z from P = ZRT / V_m yields a cubic equation in Z.

For mixtures, a and b are obtained via mixing rules, often using a binary interaction parameter k_ij; α(T) is typically computed from the mixture’s components and their critical properties. SRK is widely used in chemical process design and simulation due to its balance of simplicity and accuracy for nonpolar and mildly polar systems. Limitations include reduced accuracy for highly polar or associating compounds (such as water or alcohols) and near the critical point, where more advanced models or corrections may be required.