[en] Highlights: • Densities of reline + methanol mixtures were measured from 293.15 to 323.15 K. • All of the studied mixtures have negative excess molar volumes. • The volume related derivative properties of the mixtures were calculated. Deep Eutectic Solvents (DESs) have been introduced recently as a new generation of green solvents. DESs have great potential to be used in different fields and applications, and so, it is important to have information on the properties of DESs and their mixtures. Up to now, the volumetric properties of only aqueous mixtures of DESs have been investigated. In this study, we measured the densities of pseudo-binary mixtures of methanol and choline chloride + urea (1:2) (reline) at atmospheric pressure over the temperature range of 293.15–323.15 K. Based on the measured density data, excess molar volumes of the mixtures were calculated. All of the excess molar volumes had negative values, which show the stronger solvation interactions of the mixture molecules compared to the interactions within pure reline or methanol. Furthermore, the volumetric properties of partial molar volume, excess partial molar volume, partial molar volume at infinite dilution, excess partial molar volume at infinite dilution, and isobaric volume expansion were calculated. By comparing the excess partial molar volumes at infinite dilution of reline and methanol, it is concluded that each prefers to be surrounded by the other, and this tendency is stronger for reline molecules.

[en] Research highlights: → A model is presented to predict dissociation pressures of gas hydrates at various temperatures. → The present model is applicable on a wide range of equilibrium conditions. → The simple calculation procedure presented here saves considerably the calculation time. - Abstract: One of the major assumptions of the original van der Waals-Platteeuw (vdWP) model is the single occupancy of hydrate cavities. In this work, the vdWP model is modified to also account for multiple occupancies of hydrate cavities by small molecules. The developed model is evaluated by calculating the hydrate equilibrium conditions with either oxygen or nitrogen as guest molecules in pure form, as well as mixtures of nitrogen and propane (molecules of these pure gases and those in (nitrogen + propane) have double occupancy in large cavities of structure II up to a certain concentration of propane). The results of this modified model show good agreement with the experimental data reported in the literature.

[en] Highlights: • Densities of aqueous solutions of 1 ChCl + 4 Phenol were measured from 20 to 50 °C. • A comprehensive volumetric investigation was carried out on the investigated mixtures. • All of the investigated mixtures showed negative excess molar volumes. In this study, the densities of the pseudo-binary systems of water and the deep eutectic solvent, 1 choline chloride + 4 phenol were measured and reported for the first time in literature, and a comprehensive investigation on the various volumetric properties was carried out. Nine mixtures, with different compositions of water, were prepared. The densities of the prepared mixtures, as well as pure water and pure deep eutectic solvent (DES) were measured within a temperature range of 293.15–333.15 K at atmospheric pressure. Various volumetric properties, such as excess molar volumes and isobaric volume expansions, partial molar volumes and excess partial molar volumes were calculated for the investigated compositions. Furthermore, partial molar volumes and excess partial molar volumes at infinite dilution were estimated for water and the DES. By analysing the calculated properties, the interstitial accommodation effect was suggested for the investigated mixtures. The stronger tendency of water to be solvated in the mixture, as compared to the DES, was observed for all investigated temperatures. This suggests that, most probably, hydrogen bonds in the investigated mixtures are established in a manner in which water molecules are located at central positions, surrounded by the DES pseudo-molecules.