“Modeling of Surface Tension and Phase Equilibria for Water + Amine Mixtures from (298.15 to 323.15) K Using Different Thermodynamic Models”

The main aim of this work is to study phase equilibria, surface tension, and adsorption of water + amine mixtures. To achieve this aim, the surface tension was studied for following mixtures: water + monoethanolamine (MEA), water + diethanolamine (DEA), water + triethanolamine (TEA), water + n-methyldiethanolamine (MDEA), and water + 2-amino-2-methyl-1-propanol (AMP) in the temperature range of 298.15 K to 323.15 K. Peng–Robinson–Stryjek–Vera equation of state (PRSV-EOS) was used to model the phase equilibria of the binary mixtures. The binary interaction parameters were adjusted to the experimental information of the phase equilibria to correctly model the properties of the phase equilibria. The surface tension of all mixtures was calculated by using linear gradient theory (LGT) + PRSV-EOS, Shereshefsky model (SM), and Lamperski model (LM). LGT + PRSV-EOS as fitted approach correctly modeled the surface tension of the water + amine mixtures. Overall deviation for all the mixtures is 0.66%, and our results were better than those published in the literature. The surface tensions of binary mixtures were correlated by SM and excellent results were obtained. The average percent deviation in correlation of surface tension of studied mixtures was 2.2%. Based on Shereshefsky model, the standard Gibbs energy of adsorption (Δ G^o) and the free energy change (Δ G_s) in the surface region were calculated. The free energy change was used to obtain the excess number of molecular layers in the surface region. The magnitude of Δ G_s and Δ G^o was discussed in terms of nature and type of intermolecular interactions in binary mixtures. Additionally, the Lampersky model was used to predict the surface tension of studied mixtures and surface compositions. The surface compositions were used together with Shereshefsky model results to identify the adsorption of the amine at surface layer.