EFFECT OF DISSOLVED INORGANIC SALTS ON THE VAPOR-LIQUID EQUILIBRIA AND ENTHALPY OF MIXING OF THE METHANOL-ETHYL ACETATE SYSTEM

Abstract

The effect of three inorganic chloride salts, namely, sodium chloride, calcium chloride and zinc chloride on the vapor-liquid equilibria (VLE) and heat of mixing (h.o.m) of the methanol-ethyl acetate system has been investigated under the atmospheric conditions of 760 ± 3 mm Hg pressure. In the experimentation for VLE a Smith and Bonner type equilibrium still was used while in h.o.m. determination a calorimeter connected to a microprocessor-based control unit (MIPROC) which displays digitally the heat of mixing values in calories was employed. All the three salts dissolved to various concentration levels in the solvent mixture brought about a decrease in the azeotropic composition (expressed in terms of mole fraction of methanol) from 0.75 to values like 0.50, 0.37 and 0.18 depending upon the salt added and its concentration level. The salts sodium chloride and calcium chloride which are more soluble in methanol have been found to salt-in that component but with a peculiarity in that, in methanol-rich region the salting-in effect was substantial while in the methanol-lean region it is only marginal. The addition of salt zinc chloride which is more soluble in ethyl acetate results in an anomalous behaviour. As for the salt effect on h.o.m., the addition of calcium chloride brought about a significant enhancement in the h.o.m values while the salts sodium chloride and zinc chloride (which could be added only to about 5% by weight concentration due to the experimental difficulties) entailed a decrease and lateral shift respectively in the h.o.m. values. The VLE and h.o.m data which were found to be thermodynamically consistent have been correlated respectively by NRTL, Wilson and by a model similar to the Scatchard series type equation.