Thermodynamics and activity coefficients at infinite dilution for organic compounds and water in the ionic liquid 1-butyl-3-methylimidazolium perchlorate
Graphical abstract
Introduction
Ionic liquids (ILs) as a new green solvents have been garnered plenty of attentions in recent years. Compared to conventional organic solvents such as volatile organic compounds, ILs have a number of unique advantages: low vapor pressure, high thermal stability, wide range of solubility, non-flammability, high conductivity properties and wide electrochemical window. They are made up of two components: the anion and the cation. As both the anion and cation can be varied, these solvents can be designed for a particular end use in mind or for a particular set of properties to meet the requirements of the applications of interests. They have been widely used in various fields of chemical industry and improved many traditional production processes, especially ILs can be used as novel solvents systems for organic separation, synthesis processes, and electrochemistry [1], [2], [3], [4], [5]. Activity coefficients at infinite dilution () can measure the nonideality response of the solution, and is one of important thermodynamic parameters for the chemical engineering. It reflects the solubility and selectivity of solvent on solute and can be applied to extractive distillation, liquid-liquid extraction and absorption in the design and use of unit operation. The activity coefficients at infinite dilution can characterize the interaction between solute molecules and solvent molecules and is the key parameter to evaluate the performance of the solvent separation. This work is a continuation of our studies on the determination of activity coefficients at infinite dilution by the gas-liquid chromatographic (GLC) method for ionic liquids [6], [7]. In recent years, the anions studied were BF4−, PF6−, NTf2−, CF3COO− and other perfluorinated anions. Most of these ionic liquids had higher synthesis costs and were difficult to realize industrial production and application. This IL 1-butyl-3-methylimidazolium perchlorate ([BMIM][ClO4]) is chosen because it is relatively simple and cheap to synthesize. It also has a high thermal stability, low viscosity, high electrical conductivity, and is soluble in most conventional solvents [8], [9], [10]. Moreover, the study of perchlorate as an anion has barely been reported. In this paper, we report the activity coefficients at infinite dilution for 34 solutes, including alkanes, cycloalkanes, alkenes, aromatic hydrocarbons, acetonitrile, acetone, tetrahydrofuran, ethyl acetate, 1,4-dioxane, chloromethanes, alcohols, and water in the IL [BMIM][ClO4]. Values of were determined at 10 K intervals from 303.15 to 353.15 K. The values of the partial molar excess enthalpies at infinite dilution () were derived from the temperature dependence of the values. The entropies () and Gibbs energies () of organic solutes at a reference temperature = 298.15 K were also determined from the values. The gas-liquid partition coefficients for the same set of 34 selected solutes as a function of temperature is reported.
The solubility parameters of [BMIM][ClO4] were calculated as a function of temperature with the regular solution theory (RST). The selectivity () and the capacity () at infinite dilution directly calculated from offer an important means to evaluate the performance of ILs as solvents in various separation problems. and at T = 323.15 K for ILs [BMIM][ClO4] have been also calculated for n-hexane (i)/benzene (j), cyclohexane (i)/benzene (j). The results were analyzed in comparison to previously published literature data for other 1-butyl-3-methylimidazolium-based ILs. For three isomeric xylenes separation problems, selectivity at T = 323.15 K were also obtained from the values.
Section snippets
Chemicals and materials
The ionic liquid [BMIM][ClO4] was supplied by Shanghai Chengjie Chemical Co., Ltd. and had a purity of >0.99 mass fraction according to manufacturer’s specifications, with the following certified mass fraction of impurities: w(Cl) < 410−4, water <10−3. Before use, the IL was subjected to vacuum evaporation at T = (323–333) K over 24 h to remove possible traces of solvents and moisture. The water content was of <0.0004 mass fraction, as determined by Karl Fisher titration. The different organic
Activity coefficients at infinite dilution () and gas-liquid partition coefficients ()
In (gas-liquid) chromatography, the activity coefficients at infinite dilution were obtained by the equation proposed by Cruickshank et al. [17] and Everett [18].where is the activity coefficient of solute at infinite dilution in the stationary phase (3), is the vapor pressure of the pure liquid solute i, is the number of moles of the stationary phase component on the column, and is the standardized retention volume obtained by
Activity coefficients at infinite dilution() and gas-liquid partition coefficients (KL)
Experimental results of for 34 solutes in the column with 45.68 mass% of the support material in the temperature range of (303.15–353.15) K are presented in Table 1. The measurement results for 10 selected solutes in the column with 36.40 mass% of the support material at 323.15 K and 343.15 K are listed in Table 4S. It gave similar results to that in the column of 45.68 mass%. The difference between both sets of values is of the order of the experimental uncertainty. The values for the
Conclusions
In this work, we determined the activity coefficients at infinite dilution of organic solutes and water in the IL [BMIM][ClO4] through GLC measurements. The values of gas-liquid partition coefficients and partial molar excess enthalpies at infinite dilution were derived. The entropies and Gibbs energies of organic solutes at a reference temperature = 298.15 K were calculated from the values. The Hildebrand’s solubility parameters of [BMIM][ClO4] were also determined by the regular
Acknowledgment
This work was supported by China National Science & Technology Pillar Program (2015BAK16B03), 2016 Beijing Institute of Petrochemical Technology Graduate Program for Innovation Activity, and Beijing Institute of Petrochemical Technology URT Program of National Level (Grant No. 2015X00004).
References (49)
- et al.
J. Chem. Thermodyn.
(2016) - et al.
J. Chem. Thermodyn.
(2016) - et al.
J. Chem. Thermodyn.
(2014) - et al.
J. Chem. Thermodyn.
(2015) - et al.
Trans. Nonferrous Met. Soc. China
(2010) - et al.
Chin. Chem. Lett.
(2016) - et al.
J. Chem. Thermodyn.
(2013) - et al.
J. Chem. Eng. Data
(2005) - et al.
J. Chem. Thermodyn.
(2005) - et al.
Fluid Phase Equilibria.
(2016)