Vapor‐Liquid Equilibrium of Carbon Dioxide + Ethanol: Experimental Measurements with Acoustic Method and Thermodynamic Modeling

Abstract

Phase behavior of systems composed by supercritical carbon dioxide and ethanol is of great interest, especially in the processes involving supercritical extraction in which ethanol is used as a cosolvent. The development of an apparatus, which is able to perform the measurements of vapor-liquid equilibrium (VLE) at high pressure using a combination of the visual and the acoustic methods, was successful and was proven to be suited for determining the isothermal VLE data of this system. The acoustic method, based on the variation of the amplitude of an ultra-sound signal passing through a mixture during a phase transition, was applied to investigate the phase equilibria of the system carbon dioxide + ethanol at temperatures ranging from 298.2 K to 323.2 K and pressures from 3.0 MPa to 9.0 MPa. The VLE data were correlated with Peng-Robinson equation of state combined with two different mixing rules and the SAFT equations of state as well. The compositions calculated with the models are in good agreement with the experimental data for the isotherms evaluated.

Experimental measurements and predictions of density, viscosity, and carbon dioxide solubility in methanol, ethanol, and 1-propanol

“…The Cambridge [16] 263 to 373 0.8 to 12 Vapour-liquid compositions Sih et al [17] 298 to 313 0.1 to 7 Viscosity of gas-expanded methanol Schwinghammer et al [20] 303 0.8 to 5.5 Vapour-liquid compositions Xie et al [23] 313 1 to 8 Solubility Xia et al [24] 313 to 395 Up to 9.7 Solubility and molality Bezanehtak et al [28] 278 to 308 1.5 to 7.4 Vapour-liquid compositions and saturated liquid density Gao et al [29] 323 to 473 6 to 16.2 Vapour-liquid compositions Smith et al [30] 313 to 323 10 to 20 ensity of gas-Dexpanded methanol Joung et al [34] 313 to 343 0.6 to 12 Vapour-liquid compositions Yeo et al [36] 298 to 430 Up to 17.5 Dew, bubble and critical points Elbaccouch et al [38] 313 1 to 7.5 Vapour-liquid compositions Chang et al [41] 291 to 313 Up to 8 Vapour-liquid compositions and saturated phase densities Reighard et al [44] 298 to 373 1.5 to 15 Vapour-liquid compositions Schlichting et al [48] 283 to 242 Up to 3.5 Vapour phase solubility Yoon et al [49] 313 0.7 to 8 Vapour-liquid compositions Ethanol (C 2 H 5 OH) Sima et al [6] 333 to 373 1.1 to 14.1 Solubility and critical data Mehl et al [7] 298 to 323 3 to 9 Solubility (bubble point) Tochigi et al [8] 313 0.5 to 4.0 Vapour-liquid compositions Seifried and Temelli [9] 313 to 343 0.1 to 11.2 Density of gas-expanded ethanol Kato et al [10] 313 1 to 10 Solubility and saturated liquid density Sih et al [11] 298 to 313 0.1 to 7.7 Viscosity of gas-expanded ethanol Chiu et al [12] 291 to 313 2.4 to 7.8 Vapour-liquid boundaries Knez et al [13] 313 to 353 1 to 14 Vapour-liquid compositions Secuianu et al [14] 293 to 353 Up to 11.1 Vapour-liquid compositions Dalmolin et al [18] 288 to 323 Up to 0.6 Solubility Wu et al [19] 333 to 572 6.7 to 14.8 Phase boundaries Kodama and Kato [21] 291 2 to 5.4 Vapour-liquid compositions and saturated phase densities Stievano and Elvassore [22] 291 to 323 3.3 to 8.1 Solubility and saturated liquid density Tsivintzelis et al [25] 313 to 328 0.6 to 9.4 Vapour-liquid c...…”

Influence of Modifiers on Supercritical Fluid Chromatography (SFC) and Supercritical Fluid Extraction (SFE), Part I

“…However, ethanol is less toxic for the operator and the environment; it has been used in up to 30% molar volume in isocratic mode [18]. The practical experiments and data described in [19] are considered very important because of the large volumes of ethanol used as modifier. Multicomponent mixtures of CO 2 , ethanol, and diethylamine, described in [18], are not unique.…”

“…The ethanol solubility y (T, P) in gaseous CO 2 has been calculated based on theoretical estimations from [19] for the CO 2 molar share in a gaseous ethanol-CO 2 system at temperatures of 25˚C, 40˚C, 45˚C, and 50˚C. In [19], the authors used four theoretical models and achieved the best performance with the Peng-Robinson/Mathias-Klotz-Prausnitz approach [41] to estimate the molar share of CO 2 in the gaseous CO 2 -ethanol system. Figure 12 demonstrates a good qualitative correspondence of the ethanol solubility pressure dependence with the theory of three types of solubility for polar substances in sub-and supercritical CO 2 .…”

“…This transformation may occur when the pressure falls to the bubble pressure (discussed in [19]). At the point of this transformation in the chromatography column with a CO 2 -modifier system, the modifier's molar share may be different for the liquid-like and gaseous sections.…”

“…Under equilibrium conditions, at the bubble pressure, from the two-component liquid-like SF system in the gaseous bubble enters mainly CO 2 , and the modifier's molar share y gas in the bubble becomes much lower than y liq in the liquid-like section. This is illustrated in Figure 13, built on the basis of data from [19], where y gas is multiplied by a factor of 100 to compare it with the y liq values at the same pressure. Figure 13 shows that the 20% -30% modifier content in the liquid CO 2 -ethanol section of the chromatography column may be transformed to the gas phase, with only 1% of modifier in it.…”