(203j) High-Pressure Phase Equilibrium Calculation By Cubic Equation of State with Various ?-Functions

Knowledge of phase equilibria are key information for design of chemical processes. A theoretical model of phase equilibria such as a cubic equation of state can be useful for understanding the phase behavior for the mixture targeted in the wide range of temperatures and pressures. The phase equilibrium calculation by the cubic equation of state needs the binary interaction parameter fitted to the experimental data at various temperature. The binary interaction parameters should be the functions of temperature. A large number of phase equilibrium data at various temperatures are required for fitting of the binary interaction parameters. The interaction parameter in the cubic equation of state contains an alpha-function that present the temperature dependence of the interaction parameter. Guennec et al., have investigated the consistency of the alpha-function of the cubic equation of state [1]. A new alfa-function of Peng-Robinson equation [2] of state has been proposed to improve the thermodynamic properties of fluids by Sun et al. [3]. They have claimed that the types of alpha function affect the calculated results of the fluid thermodynamic properties. This work provides the effect of alpha-function of Peng-Robinson equation of state on the high-pressure phase equilibria, vapor-liquid, solid-vapor and solid-vapor-liquid equilibria. The results in this work will be useful knowledge for the selection of the suitable alpha-function for the targeted mixtures and temperature region.

Peng-Robinson equation of state was used for the high-pressure phase equilibrium calculation, vapor-liquid, solid-vapor and solid-vapor-liquid equilibrium for carbon dioxide systems. The four types of the alpha-function proposed by Soave [4], Twu et al. [5], Boston et al. [6] and Gasem et al. [7] are used for the phase equilibrium calculations. The binary interaction parameters are fitted to the phase equilibrium data and given in the function of temperatures. For carbon dioxide, the interaction parameters calculated by the alpha-function by Boston et al. [5] are deviated largely from those by other types at the temperature over the critical temperature. It is found that this temperature dependence of the interaction parameter affects the results of the vapor-liquid equilibria for carbon dioxide + methanol binary system. The other phase equilibrium calculations are also evaluated using the four alpha-functions of the interaction parameters in Peng-Robinson equation of state.

References

[1] Gunnec, Y. L. et al., Fluid Phase Equilibria, 427 (2016) 513 – 538., [2] Peng, D. Y, Robinson, D. B., Ind. Eng. Chem. Fund., 15 (1976) 59 – 64., [3] Sun, X., Fang, Y., Zhao, W., Xiang, S., ACS Omega, 7 (2022) 5332 – 5339., [4] Soave, G., Chem. Eng. Sci., 27 (1972) 1197 – 1203., [5] Twu, C. H. et al., Fluid Phase Equilibria, 105 (1995) 45 – 59., [6] Boston, J. F. et al., Phase Equilibria and Fluid Properties in the Chemical Industry (1980) 823 – 849., [7] Gasem, K. A. M. et al., Fluid Phase Equilibria 108 (2001) 113 – 125.