Use of Ultrasound in the Determination of Isobaric LLV, SLV, and SLLV Equilibrium Data. Application to the Determination of the Water + Na2SO4 or K2SO4 + 2-Methylpropan-2-ol Systems at 101.3 kPa and Boiling Conditions

Abstract

The importance of good dispersion and homogenization of liquid and solid phases in the determination of isobaric liquid–liquid–vapor (LLV), solid–liquid–vapor (SLV), and solid–liquid–liquid–vapor (SLLV) equilibrium data is shown by analyzing the fluctuations observed during the LLV equilibrium determination of the heterogeneous azeotrope of the water + 1-butanol and water + cyclohexane systems, explaining the causes of these fluctuations, studying how to avoid them, and extending them to systems with solid phases. The LLV, SLV, and SLLV equilibrium data of systems that are easily dispersed (similar phase densities and low interfacial tension) can be determined by using the traditional equipment for determination of LV equilibria. In contrast, mixtures that are difficult to homogenize require more sophisticated equipment because it is difficult to obtain good phase dispersion of the liquid phases by mere agitation. In most cases, this type of system could be dispersed by coupling an ultrasonic homogenizer to the boiling flask of the equipment. This apparatus, with ultrasonic waves and modifications to control the temperature of the recirculated phases, has been applied to the determination of the water + Na2SO4 or K2SO4 + 2-methylpropan-2-ol system at 101.3 kPa and boiling conditions. Comparison of both systems shows the size of the LLV region is larger in the system containing Na2SO4. The determined experimental data of these systems were correctly predicted by the extended UNIQUAC model for electrolytes, in spite of several interaction parameters having been obtained without their experimental data.