Elsevier

Fluid Phase Equilibria

Volume 465, 15 June 2018, Pages 51-57
Fluid Phase Equilibria

SLLE and SLLVE of the water + NH4Cl + 1-propanol system at 101.3 kPa

https://doi.org/10.1016/j.fluid.2018.03.003Get rights and content

Highlights

  • Multiphase equilibrium for water+1-propanol + NH4CL.

  • LL, SL and SLL and LLV, SLV and SLLV equilibrium data are determined at 298.15 K and at boiling temperature.

  • Inconsistency of previous results is shown.

  • Results are compared with the equilibrium phase diagram of water + NaCl + 1-propanol.

  • Extended UNIQUAC modeling of three - phase equilibrium including solid.

Abstract

The equilibrium of the ternary electrolyte system at 101.3 kPa, water + 1-propanol + ammonium chloride (NH4Cl), has been investigated at 298.15 K and at the boiling temperature to determine the shape of equilibrium surfaces and regions on the phase diagram. The data obtained have been compared with previously published experimental data showing their inconsistency.

Moreover, the results obtained allow us to study the shape of the phase diagram of the system, to analyze the evolution with the temperature of this equilibrium diagram and to show the differences with a similar system such as water + NaCl + 1-propanol.

Finally, it has been shown that the extended UNIQUAC model for electrolytes predicts the different equilibrium regions and boiling temperatures but there are great discrepancies between experimental and calculated equilibrium concentrations.

Introduction

An investigation on industrial requirements for thermodynamic and transport properties carried out by the Working Party on Thermodynamic and Transport properties of the European Federation of Chemical Engineering, EFCE [1] showed the acute need for accurate, reliable, and thermodynamically consistent experimental data.

One of the fields where the lack of experimental data is notorious is the mixed solvent electrolyte systems. This type of mixture is found in many processes including extractive distillation, crystallization, regeneration of solvents and liquid-liquid extraction of mixtures containing salts. The literature available on these systems is scant, the relatively small amount of existing experimental data is incomplete and some of them contain important inconsistencies as shown in a previous paper [2]. Consequently, the users of thermodynamic models such as the electrolyte NRTL model [3] or the extended UNIQUAC model for electrolytes [4] applied to represent these systems have difficulties to find experimental equilibrium data to calculate the model parameters.

In this sense, we previously studied the equilibrium diagram of the water + NaCl + 1-propanol system at 101.3 kPa [2] in order to examine the shapes of the various equilibrium surfaces and regions that arise in it. The electrolyte was NaCl whose solubility in water changes little with temperature: only 6.7% in 100 K (from 26.28 wt% at 273.15 K to 28.05 wt% at 373.15 K) [5]. The objective of the present paper is to extend that study to another similar system involving a salt such as NH4Cl whose solubility in water changes a lot with temperature: 88.7% in 100 K (from 22.92 wt% at 273.15 K a 43.24 wt% at 373.15 K) [5]. This fact could make the phase diagrams of both systems and their evolution with the temperature very different.

In this work, LL, SL and SLL equilibrium data at 298.15 K and 101.3 kPa and LV, LLV, SLV and SLLV equilibrium data of the water + NH4Cl + 1-propanol system at boiling temperature and 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, show the inconsistency of previous results, compare it with that of a similar system such as water + NaCl + 1-propanol and verify the accuracy of calculations done by using a model such as the extended UNIQUAC.

Section snippets

Chemicals

Table 1 presents the description of the chemicals used. It includes ethanol since this 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. Ultrapure water obtained by means of a MiliQPlus system was used. Its conductivity was lesser than 1 μS/cm.

Phase equilibrium determinations at 298.15 K and 101.3 kPa

Equilibrium measurements were made by preparing mixtures of known overall compositions by weighing different

Phase equilibrium at 298.15 K and 101.3 kPa

Water and 1-propanol are completely miscible but the presence of NH4Cl can split the mixture into two liquid phases in equilibrium. Consequently, the phase equilibrium diagram has the following regions: one LL region, two SL regions (organic and aqueous branch) and one SLL that is invariant (3 phases, 3 components, 2° of freedom = pressure and temperature). Table 2 and Fig. 1 show the equilibrium data determined for each region.

On the same Fig. 1, the experimental equilibrium data at 298.15 K

Conclusions

The phase equilibria of the water + NH4Cl + 1-propanol system at 101.3 kPa have been studied at 298.15 K and at the boiling temperatures. The data obtained have been compared with previously published experimental data showing their inconsistency.

The equilibrium diagrams at 298.15 K and at the boiling points show a smaller size of the equilibrium region with two liquids without solid phase at 298.15 K; a consequence of the great change of the NH4Cl solubility in water with temperature.

For the

Acknowledgment

The authors wish to thank Dr. Kaj Thomsen for his collaboration and help with the AQSOL software used in the calculations. In addition, we would like to thank the DGICYT of Spain for the financial support of project CTQ2014-59496.

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  • Effect of temperature on the phase-separation ability of KCl in aqueous two-phase systems composed of propanols: Determination of the critical temperature and extension of the results to other salts

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    Evidently, the SLLV region remained invariant, and the isotherms and vapor iso-composition lines of the SL and LL regions were straight lines. As in the previously studied systems (W + NaCl + 1P, W + NaCl + 2P, W + NH4Cl + 1P and W + NH4Cl + 2P) [13–15,32], the boiling temperatures of the binary azeotrope of water + alcohol, the plait point of the LLV region, and the invariant SLLV mixture are very similar. This feature explains why a large fraction of the mixtures in each of the systems boil within a very narrow range of temperatures, of only 1 K.

  • Influence of the temperature on the equilibrium phase diagram of the ternary system water + ammonium chloride + 2-propanol at 101.3 kPa

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    Consequently, the thermodynamic models that can be used to represent them, such as the OLI MSE model of Wang et al. [2], the extended UNIQUAC model for electrolytes [3], or the electrolyte NRTL model of Chen et al. [4], do not include enough equilibrium data to permit the correct calculation of model parameters. Moreover, not only is the amount of previous experimental data insufficient and incomplete, but some of the published data [5,6] also contain great inconsistencies as it is demonstrated in Ref. [7,8]. One of these mixed solvent electrolyte systems is the ternary mixture water + NH4Cl + 2-propanol.

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