Estimation of high-pressure fugacity coefficients of pure gaseous fluids by a modified SRK equation of state

Soave, G., Barolo, M. and Bertucco, A., 1993. Estimation of high-pressure fugacity coefficients of pure gaseous fluids by a modified SRK equation of state. Fluid Phase Equilibria, 91: 87-100. This paper considers the prediction of pure-compound fugacity coefficients at high temperature and high pressure by a modified form of the Redlich -Kwong equation of state (G. Soave, Chem. Eng. Sci., 27: 1197), with an added volume shift as proposed by A. Peneloux and E. Rauzy, Fluid Phase Equilibria, 8: 7-23. Two quantities are involved: a volume translation σ and an attractive parameter α. At each temperature and pressure, they were first determined from the corresponding experimental Z, φ values; outside the critical area, σ is independent of temperature and pressure and a depends on temperature only. Since the value of σ is close to that determined from liquid densities, the value was assumed from the liquid density at 20°C or at the boiling point. Experimental Z, φ values were regressed directly, to determine the best values of α at each temperature. Owing to the small correction of σ, it was impossible to reproduce satisfactorily both Z and φ data, so it was decided to consider fugacity coefficients alone. Several literature equations for a were considered. When parameters were determined by regression of experimental vapor pressures, none of the equations were finally satisfactory; 12α gives a linear function of 12T, as in the one-parameter expression proposed in 1972 by Soave, which was selected. A criterion was found to estimate the single parameter m from the value of the acentric factor, with a negligible loss of accuracy. Fugucity coefficients can be predicted accurately for non-polar compounds; for alcohols and polar compounds they are less satisfactory, but a good accuracy can be attained by adjusting both m and σ on experimental data.