Excess Heat Capacity Surfaces for Water-Alkanol Mixtures by the UNIQUAC Model

Yaşar Demire, Halime Paksoy

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2 Scopus citations


Hydroorganic mixtures are industrial solvents that can serve as media to solubilize either water in hydrocarbon or a hydrophobic substance in water. In many cases the solubilizing capability is obtained via a homogeneous complex aqueous mixtures containing an alcohol. Since excess heat capacity, CpE, is very sensitive to structural changes in mixtures, concentration and temperature dependence of CpE have been calculated by using the UNIQUAC model for the mixtures methanol(1)-water(2), ethanol(1)-water(2), and 1-propanol(1)-water(2). The temperature-dependent parameters of the model estimated directly from CpE data at more than one different isotherm are used in the calculations. The overall deviations between the calculated and experimental data points change in the range 6.52–10.15%, which indicates the satisfactory representation of CpE 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 dependencies of these functions suggest the existence of transitions of microstructure in the water-rich region, qualitatively similar to micellization. The surface of these thermodynamic functions facilitates a better understanding of thermodynamic properties and association of alcohol-water mixtures over a whole or certain concentration and temperature range. Such thermodynamic surfaces may be represented satisfactorily by the UNIQUAC model at low pressures.

Original languageEnglish (US)
Pages (from-to)921-927
Number of pages7
JournalIndustrial and Engineering Chemistry Research
Issue number3
StatePublished - Mar 1 1995

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Industrial and Manufacturing Engineering


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