Isobaric vapor-liquid equilibria of water-pyridine and water-pyridine-calcium chloride mixtures

Isobaric vapor-liquid equilibrium data at 705 +/- 1 mm Hg for the systems water-pyridine and water-pyridine-CaCl2 were obtained using the modified Othmer circulation still. The experimental data for the water-pyridine system exhibited an azeotropic point at a water composition of 75.0 mol% and a temperature of 92.60 degreesC. The isobaric salt-free binary data were compared with predicted vapor-liquid equilibrium (VLE) data using the UNIFAC model. Good agreement between the experimental and the predicted results was obtained, with a root-mean-square-deviation (RMSD) in predicted bubble-point temperature and predicted vapor-phase composition of 0.28 K and 0.007, respectively. In addition to that, the experimental data were correlated with the Wilson, the NRTL and the UNIQUAC models. The calculated VLE data using the parameters found by these models were in good agreement with the experimental results. The VLE of water-pyridine mixtures in the presence of calcium chloride at different concentrations was found to be dramatically different from that of the salt-fret mixtures. Calcium chloride had showed a salting-out effect on water and could eliminate the azeotropic point of the system when used under saturated conditions. In addition, analysis of the data showed that the salt resulted in "splitting" the liquid mixtures into two different liquid phases. (C) 2001 Elsevier Science B.V. All rights reserved.