Isobaric vapor–liquid equilibrium and isothermal surface tension for hexane + cyclopentyl methyl ether binary mixture: Experimental determinations and theoretical predictions

Abstract

This work reports the measurements and the theoretical predictions of the vapor–liquid equilibrium (VLE) at the isobaric conditions of 50, 75, and 94 kPa and over the temperature range from 332 K to 372 K and the surface tensions (ST) at atmospheric pressure (101.3 kPa) and the isothermal condition of 298.15 K in the whole mole fraction range for the hexane + cyclopentyl methyl ether binary mixture. The experimental determinations of VLE are carried out in a dynamic all-glass Guillespie type cell, where both vapor and liquid phases are circulating. The ST measurements are obtained from a maximum differential bubble pressure tensiometer. The theoretical predictions of VLE and ST are carried out by applying the square gradient theory to the Peng–Robinson Stryjek-Vera equation of state, appropriately extended to mixtures with a modified Huron–Vidal mixing rule, where the excess Gibbs energy is obtained from classical models whose parameters are obtained from the VLE data reported here.Experimental results of VLE show that this mixture is zeotropic and exhibits a slight positive deviation from ideal behavior over the experimental range. ST, in turn, exhibits negative deviation from the linear behavior. The measured VLE data of this binary mixture satisfy the Fredenlund's consistency test and are well-correlated by classical activity coefficients models (e.g., the Wohl, nonrandom two-liquid (NRTL), Wilson, and universal quasichemical (UNIQUAC)) for all of the isobaric conditions. According to the results, the NRTL activity coefficients model is the most appropriate model to describe the VLE of this semi-ideal binary mixture. The dependence of surface tensions on mole fraction is satisfactorily smoothed using the Myers-Scott equation.The theoretical approach uses the pure fluids properties and the NRTL activity coefficients model to predict both VLE and ST. According to the results, this full predictive schema is able to reproduce VLE and ST with an absolute average deviation of 1.0% and 1.2%, respectively. Additionally, the square gradient theory describes a surface activity of hexane, which increases with the bulk mole fraction of hexane until it reaches a maximum value at 0.63 mol fraction of hexane. This interfacial behavior enhances the concentration of hexane at the interfacial region over the corresponding bulk phases concentration.