Vapour - liquid and liquid - liquid equilibria of mixtures of water and alcohols: measurements and correlations

The ternary systems of water with 2-ethyl-1-hexanol and 1-butanol or ethanol, important in industrial applications, have been chosen for investigating the vapour-liquid equilibria (VLE) of systems with highly associating components and liquid-liquid separation (VLLE). A static equilibrium apparatus with two vibrating tube densimeters (made of glass) for measuring the densities of vapour and liquid developed by Rott (1990, PhD thesis, Universitat-GH-Paderborn) has been modified and tested up to 30 bar and 200°C (for densities only up to 150°C). Vapour and liquid are circulated through the densimeters and the equilibrium cell by two micrometering pumps. All parts of the apparatus containing the test fluid are temperature-controlled at phase equilibrium temperature. Samples of vapour and liquid(s) are analysed by gas chromatography (GC-MSD). The VLE and VLLE of the ternary systems water - 1-butanol-2-ethyl-l-hexanol, ethanol-water - 1-butanol, and ethanol - water - 2-ethyl-l-hexanol and of the pertaining binaries have been investigated between 100 and 200°C. Parallel to the measurements, the VLE and VLLE have been calculated by cubic equations of state (CEOS) of Trebble - Bishnoi - Salim (TBS) type. The deviations between the measurements and calculations for the saturation pressure and the densities and compositions of vapour and liquid at equilibrium do not exceed a few percent. Currently, association terms are being incorporated in the CEOS in order to reduce the deviations.