EXCESS HEAT-CAPACITY SURFACES FOR WATER-ALKANOL MIXTURES BY THE UNIQUAC MODEL

Hydroorganic mixtures are industrial solvents that can serve as media to solubilize either water in hydrocarbon or a hydrophobic substance i n water. In many cases the solubilizing capability is obtained via a h omogeneous complex aqueous mixtures,containing an alcohol. Since exces s heat capacity, C-p(E), is very sensitive to structural changes in mi xtures, concentration and temperature dependence of C-p(E) have been c alculated by using the UNIQUAC model for the mixtures methanol(1)-wate r(2), ethanol(1)-water(2), and 1-propanol(1)-water(2). The temperature -dependent parameters of the model estimated directly from C-p(E) data at more than one different isotherm are used in the calculations. The overall deviations between the calculated and experimental data point s change in the range 6.52-10.15%, which indicates the satisfactory re presentation of C-p(E) data by the model for engineering calculations. The temperature range of experimental data for the mixtures is 288.15 and 308.15 K. Surfaces of reduced, apparent, and partial molar excess heat capacities are also derived. The concentration and temperature d ependencies of these functions suggest the existence of transitions of microstructure in the water-rich region, qualitatively similar to mic ellization. The surface of these thermodynamic functions facilitates a better understanding of thermodynamic properties and association of a lcohol-water mixtures over a whole or certain concentration and temper ature range. Such thermodynamic surfaces may be represented satisfacto rily by the UNIQUAC model at low pressures.