Consistency of experimental data in SLLV equilibrium of ternary systems with electrolyte. Application to the water + NaCl + 2-propanol system at 101.3 kPa
Introduction
The knowledge of the equilibrium phase diagram of mixed solvent electrolyte systems is important because this type of mixture is found in many processes. These processes include regeneration of solvents, liquid-liquid extraction of mixtures containing salts and extractive distillation and crystallization. For example, the salt effect distillation is used commercially in the concentration of aqueous nitric acid, using the salt magnesium nitrate as the separating agent. Other commercial applications include acetone-methanol separation using calcium chloride and isopropanol-water separation using the same salt [1].
However, the literature available on the mixed solvent electrolyte systems is scarce. Moreover, the relatively small amount of existing experimental data is incomplete and some of them containing important inconsistencies as shown in a previous paper [2].
Finally, the thermodynamic models used to represent these systems, such as the extended UNIQUAC model for electrolytes [3], or the electrolyte NRTL model [4] all need the equilibrium data to calculate the model parameters.
In two previous papers [2], [5], we studied the equilibrium diagram of the water + NaCl + 1-butanol and water + NaCl + 1-propanol systems at 101.3 kPa in order to examine the shapes of the various equilibrium surfaces and regions that occur in them. To do this, a detailed analysis of the evolution with temperature of the different equilibrium regions of these systems was carried out. The influence of salt on the equilibrium was investigated demonstrating that many of the previously published data were inconsistent and inaccurate. It is really important to have reliable experimental data suitable for the development of new thermodynamic models or obtaining new binary interaction parameters with the existing models.
In the previously studied systems, the electrolyte was NaCl although there was an important difference between them: the 1-butanol is partly miscible with water while 1-propanol is completely miscible. The objective of the present paper is to extend those studies with NaCl to another system involving a completely miscible solvent in order to verify the inconsistency of previously published data and to analyze once again the evolution with temperature of the different equilibrium regions. The chosen system is water + NaCl + 2-propanol at 101.3 kPa whose equilibrium phase diagram could be in principle similar to that with 1-propanol since both systems contain a binary water + propanol with a homogeneous minimum boiling azeotrope. However, as shown in Fig. 1, the azeotropic composition of the two systems is quite different: 0.69 mol fraction in 2-propanol [6], [7] for one of them and 0.43 in 1-propanol [8], [9] for the other one. This fact could make the phase diagrams of both systems and their evolution with the temperature very different.
In this work, LV (liquid-vapor), LLV (liquid-liquid-vapor), SLV (solid-liquid-vapor) and SLLV (solid-liquid-liquid-vapor) equilibrium data of the water + NaCl + 2-propanol system at 101.3 kPa have been determined experimentally. The results obtained permit us to carry out a study of the shape of the phase diagram of the system, to show the inconsistency of previous results, to analyze the evolution with temperature of the phase diagram and to compare it with that of a similar system as water + NaCl + 1-propanol.
Section snippets
Previous experimental equilibrium studies of the system and inconsistencies
The water + NaCl + 2-propanol system at 101.3 kPa includes the water + 2-propanol binary system with many experimental LV equilibrium data in bibliography (for example: [10], [11]) and two SLV binaries 2-propanol + NaCl and water + NaCl [9], [10]. It also includes the SLLE and LLE ternary equilibrium diagram at a temperature below boiling conditions which has been determined by several authors [12], [13], [14], [15], [16]. Fig. 2 shows the equilibrium data at 298.15 K, showing the different
Chemicals
Ultrapure water obtained by means of a MiliQPlus system was used. Its conductivity was less than 1 µS/cm. With respect to the rest of chemicals, Table 1 presents their description and includes ethanol since it was used as an internal standard for quantitative chromatographic analysis. The water content of the organic compounds presented in the table was determined by the Karl Fischer technique.
Apparatus and procedures
A modified vapor-liquid Fischer Labodest unit (Fischer Labor und Verfahrenstechnik) was used in the
Experimental results
Equilibrium data and boiling temperature of different mixtures are shown in Table 2, Table 3, Table 4, Table 5, Table 6 corresponding to the different regions of the equilibrium diagram. Fig. 4 shows some of these data: the LLVE region is represented by continuous tie lines joining the two liquid phases in equilibrium, and dashed lines joining the organic liquids with the point that is representative of the vapor phase. In the same way, the organic SLVE region is represented by continuous lines
Conclusions
The SLLV phase equilibria of the water + NaCl + 2-propanol mixture have been studied at 101.3 kPa and the influence analyzed of the salt on the vapor-liquid-liquid-solid equilibrium. The shape of the phase diagram at boiling temperatures is very similar to that of the water + NaCl + 1-propanol system but the evolution with temperature of this equilibrium diagram is very different.
Previously published experimental data have been compared with the data obtained in this work and it has been
Acknowledgment
The authors wish to thank the DGICYT of Spain for the financial support of project CTQ2014-59496.
References (19)
- et al.
Phase diagram of the vapor-liquid-liquid-solid equilibrium of the water + NaCl + 1-propanol system at 101.3 kPa
J. Chem. Therm.
(2018) - et al.
Extended UNIQUAC model for correlation and prediction of vapor-liquid-liquid-solid equilibria in aqueous salt systems containing non-electrolytes. Part B. Alcohol (ethanol, propanols, butanols)-water-salt systems
Chem. Eng. Sci.
(2004) - et al.
Isobaric vapor–liquid–liquid–solid equilibrium of the water + NaCl + 1-butanol system at 101.3 kPa
J. Chem. Therm.
(2016) - et al.
(Vapour + liquid) equilibrium of (DIPE + IPA + water) at 101.32 kPa
J. Chem. Therm.
(2003) - et al.
Liquid-liquid equilibria in wáter-aliphatic alcohol systems in the presence of sodium chloride
Chem. Eng. J.
(1976) - et al.
Liquid-liquid-solid equilibria for the ternary systems water-sodium chloride or potassium chloride-1-propanol or 2-propanol
Fluid Phase Equilib.
(1994) - et al.
Salt effect in phase equilibria: effect of dissolved inorganic salts on the liquid-liquid equilibria of benzene - 2-propanol-water system and the vapor-liquid equilibria of its constituent binaries
Fluid Phase Equilib.
(1989) - et al.
The application of ultrasound in the determination of isobaric vapour–liquid–liquid equilibrium data
Fluid Phase Equilib.
(2000) - McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, S.v. “salt-effect distillation.” Retrieved March 26 2018...
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