Capability study of 1-butyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide and trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate as solvents in the separation of 1-propanol from water
Introduction
In order to recycle and reuse the chemical compounds used in a chemical process, which results in an economic and environmental benefit, their recovery is an essential part of the process. The separation operations are not always easy and their complexity increases when the separation components form azeotropic mixtures or have relative volatilities close to unity.
The total separation of an azeotropic mixture is impossible by conventional distillation, whereas the addition of an adequate solvent to the azeotropic mixture allows more effective separation, obtaining products with greater purity [1]. There are organic solvents that work well as separation agents but their environmental contamination is a major problem. Therefore, the search for ways to make these separations easier and cause less environmental damage and health hazards is of great interest [2].
The more restrictive environmental regulations and greater environmental awareness have led to ionic liquids (ILs) being researched as an alternative to conventional solvents [[3], [4], [5], [6]]. ILs are usually composed of a large organic cation and a small inorganic polyatomic anion, and the possibility of combining different cations and anions, in what are known as designer solvents, results in solvents with the necessary properties to optimize the efficiency and cost of the process. The high azeotropic breaking capacity, negligible vapour pressure and easy recovery, with hardly any loss of the solvent to atmosphere or any contamination to the environment, are the most remarkable properties of the ILs [7]. Depending on whether the IL is immiscible or partially miscible with any of the mixture components, the separation process will be carried out by extractive distillation or liquid–liquid extraction [8,9].
The previous knowledge of the equilibrium, their behaviour and the values of the thermodynamic parameters make the simulation and design of the process easier, with less possibility of error. For this reason, our research group has studied the liquid–liquid equilibrium (LLE) and vapour–liquid equilibrium (VLE) of ethanol, 1-propanol and 2-propanol with water and different ILs [[10], [11], [12], [13], [14]]. In order to find the ideal IL to separate the azeotropic mixture of water + 1-propanol [15], the experimental LLE with two different ILs, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) (CAS:174899-83-3) and trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate ([TDTHP][Phosph]) (CAS:465527-58-6), was studied in this work at atmospheric pressure and at different temperatures, covering the working range and studying its influence. The chemical structure for both ionic liquids was provided in the Supplementary data (Fig. 1). The thermodynamic parameters were calculated correlating the LLE data by the non-random two-liquid (NRTL) [16] and universal quasichemical (UNIQUAC) [17] activity coefficient models. Besides that, the selectivity and distribution coefficient for both ILs was determined in order to know their solvent capability in the azeotropic mixture of water + 1-propanol. Furthermore, the LLE of the aqueous mixture with [TDTHP][Phosph] at different temperatures was compared with experimental data provided in the literature for the same ternary mixture at 298.15 K [18]. Finally, the LLE of water + 1-propanol with the different ILs studied by our research group at 303.2 K was compared [12,13].
The ILs [bmim][Tf2N] and [TDTHP][Phosph] were chosen due to their hydrophobic nature, the values of the activity coefficients at infinite dilutions with 1-propanol and water provided by the literature [19,20], and the excellent results obtained in the extraction of 1-propanol from water in a previous work [18].
Section snippets
Chemicals
Both ILs, [bmim][Tf2N] (>0.9900 mass fraction) and [TDTHP][Phosph] (>0.9800 mass fraction), were supplied by Iolitec. 1-Propanol (w ≥ 0.9950 mass fraction), ethanol (≥0.9990 mass fraction) and bidistilled water were provided by Fluka. The purity of the 1-propanol and ethanol was checked by gas chromatography.
The alcohols were dried over molecular sieves (Union Carbide, type 4 Å, 1/6 in. pellets) and degassed. All reagents were used without further purification, and only appropriate precautions
Experimental data
The LLE for the ternary systems water (1) + 1-propanol (2) + [bmim][Tf2N] (3) and water (1) + 1-propanol (2) + [TDTHP][Phosph] (4) were determined at 283.2 K, 303.2 K and 323.2 K at atmospheric pressure. Table 2, Table 3 and Fig. 1, Fig. 2 show the results, in which the concentrations are expressed in molar fraction.
In Fig. 1, Fig. 2 it is possible to observe that both ternary systems were formed by two miscible subsystems, water + 1-propanol and 1-propanol + IL, and one partially miscible
Conclusion
The liquid–liquid equilibria of the ternary systems water (1) + 1-propanol (2) + [bmim][Tf2N] (3) and water (1) + 1-propanol (2) + [TDTHP][Phosph] (4) at 283.2, 303.2 and 323.2 K at atmospheric pressure were studied in order to know their behaviour and the capability of the ILs to achieve the separation of 1-propanol from water. Also, this study identifies the real values of their thermodynamic parameters, which are essential requirements to perform a realistic design of the process.
The
Acknowledgments
Financial support from the Ministerio de Ciencia y Tecnología of Spain (project No. CTQ2010-18848/PPQ) and the Universitat de València (project No. UV-INV-AE15-340195) is gratefully acknowledged.
References (28)
- et al.
J. Chem. Thermodyn.
(2012) - et al.
Fluid Phase Equil.
(2016) - et al.
Fluid Phase Equil.
(2016) - et al.
Fluid Phase Equil.
(2013) - et al.
Fluid Phase Equil.
(2008) - et al.
J. Chem. Thermodyn.
(2012) - et al.
J. Chem. Thermodyn.
(2018) Phase Equilibria in Chemical Engineering
(1984)Clean solvents chapter 1
ACS Symp. Ser.
(2009)- et al.
Ionic-liquids-industrial applications to green chemistry