FORMATION OF ISOPYCNIC PHASES IN H2O CO2/ETHOXYLATED ALCOHOL SURFACTANT MIXTURES/

Citation
Rg. Zielinski et al., FORMATION OF ISOPYCNIC PHASES IN H2O CO2/ETHOXYLATED ALCOHOL SURFACTANT MIXTURES/, Journal of physical chemistry, 100(22), 1996, pp. 9465-9470
Citations number
37
Categorie Soggetti
Chemistry Physical
ISSN journal
00223654
Volume
100
Issue
22
Year of publication
1996
Pages
9465 - 9470
Database
ISI
SICI code
0022-3654(1996)100:22<9465:FOIPIH>2.0.ZU;2-W
Abstract
Ternary mixtures of H2O and CO2 with ethoxylated alcohol (C(i)E(j)) su rfactants can form three coexisting liquid phases at conditions where two of the phases have the same density (isopycnic phases). Isopycnic phase behavior has been observed for mixtures containing the surfactan ts C(8)E(5), C(10)E(6), and C(12)E(6), but not for those mixtures cont aining either C(4)E(1) or C(8)E(3). Pressure-temperature (PT) projecti ons for this isopycnic three-phase equilibrium were determined for H2O /CO2/C(8)E(5) and H2O/CO2/C(10)E(6) mixtures at temperatures from appr oximately 25 to 33 degrees C and pressures between 90 and 350 bar. Con ditions for density-matched phases were measured by observing an inver sion of the two liquid phases of interest as a function of pressure at constant temperature. For the H2O/CO2/C(8)E(5) mixtures, the isopycni c pressure at 30.0 degrees C was also determined by measuring densitie s of these two phases with increasing pressure across the inversion. T his pressure was found to be in very good agreement with the value obt ained by observing the phase inversion. A recent modification of the P eng-Robinson equation of state was used to predict liquid densities fo r H2O/CO2/C(8)E(5) ternary mixtures on the basis of densities measured for the two constituent binary mixtures containing surfactants and fr om literature values for the H2O/CO2 binary mixture. These predictions show that isopycnic phase formation is a direct consequence of the de nsity maximum calculated for binary mixtures of H2O and CO2 as a funct ion of composition. The enhanced mutual solubility of H2O and CO2 brou ght about by the addition of surfactant and the pure-component density of the surfactant are also important contributing factors to isopycni c phase formation.