Surface Tensions for Binary Mixtures of Alkyl Levulinate + Alkanol: Measurement and Modeling

The surface tensions of binary mixtures alkyl levulinate (methyl levulinate and ethyl levulinate) + n-alkanols (methanol, ethanol, 1-propanol, and 1-butanol) at several temperatures (283.15 K, 298.15 K, and 313.15 K) and at atmospheric pressure were reported. For each binary mixture, the surface tension deviations were obtained and correlated with composition by using the Redlich–Kister polynomial expansion. These surface tension deviations vary from positive values for methanol to negative ones for 1-butanol. Regarding the behavior of surface tension deviation with alkyl levulinate, ethyl levulinate presents higher positive values or less negative ones than methyl levulinate. The computation of the surface tension was obtained with the linear square gradient theory plus the Peng–Robinson–Stryjek–Vera (PRSV-EoS). Phase equilibria for all the mixtures were predicted, because k₁₂= 0 was set. Then, the densities of the homogeneous phases were obtained and used in the calculation of the surface tension, which was obtained according to two approaches, i.e., prediction and fitted, and using values constant and correlations for the parameters for both approaches. The predictive approach was not adequate because a high global deviation was obtained (3.97 %), while two adjustable parameters for the mixture in LSGT improved the representation of the variation of experimental surface tension with temperature (deviation = 1.08 %). Therefore, the simplified version of square gradient theory named LSGT guarantees good results of fitting the experimental data.