Experimental and Modeling Study of the Phase Behavior of (Methane + CO₂+ Water) Mixtures

Abstract

In this work we report phase equilibrium measurements on the system (methane + carbon dioxide + water) carried out with a high-pressure quasi-static-analytical apparatus. The measurements have been made under conditions of two-phase vapor-liquid equilibrium, three-phase vapor-liquid-liquid equilibrium (VLLE), and four-phase vapor-liquid-liquid-hydrate equilibrium. The compositions of three coexisting fluid phases have been obtained along eight isotherms at temperatures from (285.15 to 303.5) K and at pressures up to either the upper critical end point (UCEP) or up to the hydrate formation locus. Compositions of coexisting vapor and liquid phases have been obtained along three isotherms at temperatures from (323.15 to 423.15) K and pressures up to 20 MPa. The quadruple curve, along which hydrates coexist with the three fluid phases, was also measured along its entire length. The VLLE data obtained for this mixture have been compared with the predictions of the statistical associating fluid theory for potentials of variable range (SAFT-VR), implemented with the square-well potential and using parameters fitted to pure-component and binary-mixture data. Specifically, we used the SAFT-VR parameters reported by Mı́guez and co-workers [Mı́guez, J. M.; dos Ramos, M. C.; Piñeiro, M. M.; Blas, F. J. J. Phys. Chem. B 2011, 115, 9604]. The pressure along the quadruple curve was compared with the predictions of two different thermodynamic models. Furthermore, a detailed study of the ternary mixtures was carried out based on comparison with available ternary data of the type (CO2 + n-alkane + water) and available data for the constituent binary subsystems. In this way, we analyzed the observed effects on the solubility when the n-alkane component was changed or a third component was added.

Phase Equilibria of the CH4-CO2 Binary and the CH4-CO2-H2O Ternary Mixtures in the Presence of a CO2-Rich Liquid Phase

“…The Q 2 for a CH 4 molar fraction of 0.225 has been estimated by Bi et al [19] to be at 287.9 K and 8.4 MPa. Thus, the Q 2 zone is accurately described by several authors [17][18][19]32] (Table 2) (Figure 1, "+" orange symbols).…”

“…This binary mixture exhibits a diagram of Type I in the classification of van Konynenburg [32,36]. Thus, in the pressure-composition space, the vapor-liquid equilibrium (VLE) envelopes are characterized by critical points located along a continuous line linking the critical points of CH 4 (190.55 K; 4.60 MPa) and CO 2 (304.21 K; 7.38 MPa) [37].…”

“…Al Ghafri et al [32] did a very interesting study of this mixture at VLE, vapor-liquid-liquid equilibrium (VLLE), liquid-liquid equilibrium (LLE), and hydrate-vapor-liquid-liquid equilibrium (HVLLE). Indeed, in the p-T diagram, the VLLE region delimited by the Quadruple curve, the upper-critical end point (UCEP) curve, and the CO 2 vaporization curve has been studied by Al Ghafri et al [32], with composition measurements for all phases.…”

Phase behavior of (CO2+H2) and (CO2+N2) at temperatures between (218.15 and 303.15)K at pressures up to 15MPa

“…The uncertainties associated with this calibration method have been discussed in detail by Al Ghafri et al [26]. For the purposes of the uncertainty analysis, the small quadratic term in Eq.…”

“…It is shown in [26] that the uncertainty u(xi) in the mole fraction xi associated with both the measurement and the calibration steps, but excluding the effects of uncertainties in temperature and pressure, is given by…”