Elsevier

Fluid Phase Equilibria

Volume 397, 15 July 2015, Pages 50-57
Fluid Phase Equilibria

Liquid–liquid equilibria for water + 1-propanol (or 1-butanol) + potassium chloride + ammonium chloride quaternary systems at 298.15 K

https://doi.org/10.1016/j.fluid.2015.03.050Get rights and content

Highlights

  • Investigate phase behavior of water + 1-propanol (or 1-butanol) + KCl + NH4Cl systems at 298.15 K.

  • Good agreement has been obtained with several equations and models.

  • Phase-separation ability is 1-butanol > 1-propanol and salting-out ability is KCl > NH4Cl.

  • Liquid–liquid regions increase with the increasing of KCl/NH4Cl mass-fraction ratio.

Abstract

Liquid–liquid equilibria (LLE) for quaternary systems of (water + 1-propanol + KCl + NH4Cl) and (water + 1-butanol + KCl + NH4Cl) were investigated at 298.15 K. Variation of phase behavior was studied by two integrated phase diagrams, the solvation abilities of salts and the polarities of alcohols. Binodal curves were fitted by three-parameter equation at different salt (KCl and NH4Cl) mass-fraction rations (0/1, 1/3, 1/1, 3/1 and 1/0). Tie-lines data of four related ternary systems (salt mass-fraction ratios 0/1 and 1/0) were successfully described by Othmer–Tobias and Hand equations, while the tie-lines data and saturated equilibrium data of quaternary systems (salt mass-fraction ratios 1/3, 1/1, 3/1) were correlated using the modified Eisen–Joffe equation.

Introduction

Liquid–liquid equilibrium (LLE) investigations for ternary and quaternary mixtures are frequently encountered in industrial separation and purification, such as the processes of liquid extraction, crystallization and azeotropic distillation. The separation by solvent extraction is a challenge as the tie-line becomes parallel to the solvent axis, especially in solutropic solutions. The mutual solubility can be significantly changed by adding adequate salt to the system, which benefits to modify the slope of the tie-lines, even to the extent of eliminating the solutrope. The formation of two phases is generally considered to be the attribution of the salting-out effect.

The salting-out effect in mixed ternary systems for water + organic solvent + salt have been systematically studied [1], [2], [3], [4], [5], [6], [7]. Equilibria for some quaternary systems (water + two organic solvent + salt) [8], [9], [10] and (water + organic solvent + two inorganic salts) [11], [12], [13] have also been investigated. Different effect of inorganic salt on equilibrium is generally caused by different physical and chemical properties of salt. But as two common inorganic salts, potassium chloride (KCl) and ammonium chloride (NH4Cl) share the same chemical properties, and it is easy for them to enter into both crystal lattices to form a solid solution. During our previous study, the methods of water–1-propanol–KCl–NH4Cl aqueous two-phase system (ATPSs) and reactive extraction with tributylamine were used for the separation of KCl and NH4Cl from aqueous solution [14], [15]. However, the variation of the equilibrium under different proportions of inorganic salts in the separation process is not clear yet.

The aim of present work is to systematically investigate the liquid–liquid equilibria for quaternary systems of (water + 1-propanol + KCl + NH4Cl) and (water + 1-butanol + KCl + NH4Cl). To observe equilibrium under different proportion of inorganic salts, different mass ratios for KCl/NH4Cl (0/1, 1/3, 1/1, 3/1 and 1/0, respectively) were prepared. The experimental binodal and tie-lines data at 298.15 K were reported, which were respectively correlated by parametric equation and thermodynamic models (Othmer–Tobias and Hand equations [16], [17] for ternary systems and modified Eisen–Joffe equation [9], [10], [18] for quaternary systems). The effect of different alcohols and cations on the phase-formation ability of the studied systems were discussed considering the intermolecular interactions with water and Gibbs free energy of hydration of ions (ΔhydG). The salting-out effect of different salt was also verified by the partition coefficient (K) and the selectivity factor (S) of the aliphatic alcohol, which benefits to understand the factors that determine the partition of solute and solvent in organic or aqueous phases.

Section snippets

Materials

1-Propanol (>99.5 mass%, analytical grade) and 1-butanol (>99.5 mass%, analytical grade) were purchased from Tianjin BoDi Chemical Reagent Factory (Tianjin, China). The purity of these materials was checked by gas chromatography. NH4Cl and KCl were supplied by Da Mao Chemical Reagent Factory (Tianjin, China). These reagents had a minimum mass fraction purity of 0.99. All chemicals were used without further purification. Water used in experiments was double distilled. Description of chemical

Integrated phase diagrams of quaternary systems

Based on the studied ternary systems (water + 1-propanol + KCl) and (water + 1-butanol + NH4Cl) [12], [22], we investigate other two ternary systems (water + 1-propanol + NH4Cl) and (water + 1-butanol + KCl) at 298.15 K. Table 2 provides the solubility data for KCl and NH4Cl in water, while the solubility of inorganic salts in aliphatic alcohol are not presented as they are slight soluble in organic solvents. The binodal curves of ternary systems can be obtained from the data listed in Appendix A (Supplementary

Conclusion

The liquid–liquid equilibria for water + 1-propanol (or 1-butanol) + potassium chloride + ammonium chloride were systematically investigated at 298.15 K. The two-phase formation ability of different alcohols in the order: 1-butanol > 1-propanol, which is due to the weaker intermolecular interactions of partial miscible alcohol (1-butanol) with water.

Furthermore, liquid–liquid regions increase with the increasing of KCl/NH4Cl ratios, which is attributed to the more positive ΔhydG of potassium. Thus,

Acknowledgement

Thanks the supports by National Natural Science Foundation of China (21276063, 21306037, 51309074 and 21476059).

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