Evaluation of vapor—liquid equilibrium of CO 2 binary systems using UNIQUAC-based Huron—Vidal mixing rules

Abstract

Since Huron and Vidal [M.J. Huron, J. Vidal, Fluid Phase Equilib. 3 (1979) 255] developed the basic idea of the so-called G E mixing rules, similar models have been proposed by different authors. In most of them, a group-contribution method like the UNIFAC model is used with the equation of state to enable the description of vapor-liquid equilibrium (VLE) at high temperatures and pressures including supercritical compounds. In this work we intended to use the UNIQUAC instead of the UNIFAC method as G E model in SRK equation of state. For comparison between Huron-Vidal-type mixing rules, we selected the modified Huron-Vidal first-order (MHV1) and second-order (MHV2) mixing rules proposed by Michelsen [M.L. Michelsen, Fluid Phase Equilib. 60 (1990a) 213; M.L. Michelsen, Fluid Phase Equilib. 60 (1990b) 42.] and PSRK mixing rule proposed by Holderbaum and Gmehling [T. Holderbaum, J. Gmehling, Fluid Phase Equilib. 70 (1991) 251.]. In other words, this paper investigates the ability of several mixing rules to predict and correlate the high-pressure vapor-liquid equilibrium used in combination with the UNIFAC and UNIQUAC models. For comparison of these mixing rules, the carbon dioxide binary mixtures have been chosen because carbon dioxide has numerous applications in supercritical fluid processes. The missing interaction parameters of UNIFAC and UNIQUAC were estimated through the regression of experimental vapor-liquid equilibrium data. For comparison of UNIQUAC-based mixing rules with each other, the interaction parameters of 51 carbon dioxide binary systems have been determined. Furthermore, a comparison between UNIFAC- and UNIQUAC-based SRK equation of state is presented. The results show that all of the UNIFAC- and UNIQUAC-based mixing rules, with parameters derived from VLE, can be used for reliable calculations of phase equilibrium. It is shown that the PSRK/UNIQUAC mixing rule can correlate the data for the best VLE results. Also, it is shown that the use of the second-order mixing rule in UNIQUAC-based SRK equation of state does not necessarily improve the results of VLE calculations.