Experimental determination and theoretical modeling of the vapor–liquid equilibrium and surface tensions of hexane + tetrahydro-2H-pyran

Isobaric vapor–liquid equilibrium (VLE) data have been measured for the binary system hexane + tetrahydro-2H-pyran at 50, 75, and 94 kPa and over the temperature range 321–358 K using a vapor–liquid equilibrium still with circulation of both phases. Atmospheric surface tension data have been also determined at 303.15 K using a maximum bubble pressure tensiometer. Experimental results show that the mixture is zeotropic and exhibits slight positive deviation from ideal behavior over the experimental range. Surface tensions, in turn, exhibit negative deviation from the linear behavior. E data of the binary mixture satisfy the Fredenlundʹs consistency test and were well-correlated by the Wohl, nonrandom two-liquid (NRTL), Wilson, and universal quasichemical (UNIQUAC) equations. The dependence of surface tensions on mole fraction was satisfactorily smoothed using the Redlich–Kister equation. perimental VLE and surface tension data were accurately predicted by applying the square gradient theory to the Peng–Robinson Stryjek–Vera equation of state (EoS), appropriately extended to mixtures with a modified Huron–Vidal mixing rule. This theoretical model was also applied to describe the surface activity of species along the interfacial region, from which it was concluded that hexane presents interfacial accumulation and, therefore, a positive relative Gibbs adsorption isotherm on THP.