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In this study, liquid–liquid equilibrium measurements were performed for the ternary (water/non-ionic surfactant/decane) systems at T = 298.15 K and atmospheric pressure. Propylene glycol mono propyl ether and ethylene glycol monobutyl ether were selected as surfactant; the first one is propylene glycol ether, while the second one is ethylene glycol ether. New experimental liquid–liquid equilibrium data were presented for the corresponding systems. Effect of salinity and surfactant structure (EO or PO functional group) on the phase behavior of such systems has been studied by both experimental measurements and thermodynamic modeling. The experimental phase behavior data were predicted by the perturbed hard sphere chain (PHSC) equation of state. In the presence of electrolyte, mean spherical approximation (MSA) term has been coupled with the PHSC EoS to account the contribution of long-range interactions. The calculated results indicate acceptable qualitative agreement of PHSC results with the experimental data. [ABSTRACT FROM AUTHOR]

In this study, vapor-liquid and liquid-liquid equilibrium in mixtures containing glycol ether surfactant, non-polar and polar compounds are calculated using Perturbed Hard Sphere Chain (PHSC) equation of state (EoS). Pure liquid density and vapor pressure of surfactants are used for parameter estimation of glycol ether surfactants. The PHSC parameters are calculated for both ethylene glycol ether and propylene glycol ether surfactants. Glycol ether surfactant molecules are modeled as associating components by considering two association sites for each molecule. The results show that the PHSC model is capable of correlating thermodynamic behavior of binary (polar + surfactant) and (non-polar + surfactant) systems. Upper critical solution temperature (UCST) for hydrocarbon + surfactant and lower critical solution temperature (LCST) for water + surfactant systems are accurately calculated. The critical temperatures and the extent of immiscibility are in good agreement with the available experimental data. [ABSTRACT FROM AUTHOR]