Activity coefficients at infinite dilution, physicochemical and thermodynamic properties for organic solutes and water in the ionic liquid ethyl-dimethyl-(2-methoxyethyl)ammonium trifluorotris-(perfluoroethyl)phosphate

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Highlights

  • γ and KL for 65 solutes in the IL [COC2N1,1,2][FAP] were determined by IGC.

  • ΔG1E,, ΔH1E, and ΔS1E, were calculated.

  • LFER system constants as a function of T for [COC2N1,1,2][FAP] were determined.

  • Results were compared to other ILs based on the same cation and anion.

Abstract

New values of activity coefficients at infinite dilution, γ for 65 different solutes including alkanes, alkenes, alkynes, cycloalkanes, aromatic hydrocarbons, alcohols, thiophene, ethers, ketones, aldehydes, esters and water in the ionic liquid ethyl-dimethyl-(2-methoxyethyl)ammonium trifluorotris(perfluoroethyl)phosphate, were determined using inverse gas chromatography within the temperature range from (318.15 to 368.15) K. This is a continuation our study of ionic liquids based on this anion and 2-hydroxyethyl cation substituent. The experimental γ values were used to calculate thermodynamics functions such as partial molar excess Gibbs energy ΔG1E,, enthalpy ΔH1E, and entropy ΔS1E,. Additionally the (gas + liquid) partition coefficients of the solutes, KL were calculated and were used to determine the linear Gibbs energy relationship (LFER) system constants as a function of temperature. Values of the selectivity and capacity at infinite dilution for alkanes/thiophene extraction problems were also calculated. Results were compared to ionic liquids investigated previously with the same anion.

Introduction

In this work the activity coefficients at infinite dilution for different organic solutes and water in the ionic liquid ethyl-dimethyl-(2-methoxyethyl)ammonium trifluorotris(perfluoroethyl)phosphate, [COC2N1,1,2][FAP] were determined within the temperature range from (318.15 to 368.15) K using inverse gas chromatography (IGC). This is a continuation of our systematic study on thermodynamic properties of ionic liquid. Our recent research focuses on ionic liquids with the [FAP] and [NTf2] anions and cations with methoxyethyl substituent, namely: 4-(2-methoxyethyl)-4-methylmorpholinium trifluorotris(perfluoroethyl)phosphate, [COC2mMOR][FAP] [1]]; 1-(2-methoxyethyl)-1-methylpiperidinium trifluorotris(perfluoroethyl)phosphate, [COC2mPIP][FAP] [2]]; 1-(2-methoxyethyl)-1-methylpyrrolidinium trifluorotris(perfluoroethyl)phosphate, [COC2mPYR][FAP] [3]]; 4-(2-methoxyethyl)-4-methylmorpholinium bis(trifluoromethylsulfonyl)-amide, [COC2mMOR][NTf2] [4]]; 1-(2-methoxyethyl)-1-methylpiperidinium bis(trifluoromethylsulfonyl)-amide, [COC2mPIP][NTf2] [5]]; 1-(2-methoxyethyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)-amide, [COC2mPYR][NTf2] [6]]. The work noted above [1], [2], [3], [4], [5], [6] concern activity coefficients at infinite dilution. Additionally for these ILs, the ternary (liquid + liquid) equilibria were examined [7], [8], [9], [10], [11], [12], [13].

Additionally, based on retention data, the (gas + liquid) partition coefficients, KL, and basic thermodynamic functions such as partial molar excess Gibbs ΔG1E,, enthalpy ΔH1E, and entropy ΔS1E, at infinite dilution were determined for [COC2N1,1,2][FAP].

Ionic liquids have several particular properties such as a wide temperature range of the liquid state; high thermal stability; high conductivity and a wide electrochemical window; adjustable physicochemical properties by modification of the structure of both the cation as well as the anion, or by mixing two or more different ionic liquids; and extremely low vapour pressure [14], [15], [16](for example 10−3 to 10−1 Pa above T = 400 K for imidazolium ionic liquids [17]]). For environmental reasons, the last mentioned property is especially important since it prevents volatilization of these compounds to the atmosphere. Therefore the ILs can be used as solvents in extraction processes. To use an IL as an extractant, the information about interactions of the IL with different compounds is needed. Such information is provided from γ measurements. From the values of activity coefficients at infinite dilution, the selectivity (Sij=γi/γj) and capacity (kj=1/γj) can be directly calculated for different separation problems. Ionic liquids are considered as entrainers in separation of sulfur compounds from fuels [18], [19], [20], [21]. Therefore the values of selectivity and capacity for alkanes/thiophene extraction problems were calculated for the IL investigated and compared to other [FAP] anion based ILs. [22], [23], [24], [25], [26].

Section snippets

Materials

The ionic liquid [COC2N1,1,2][FAP] had a purity of >0.995 mass fraction and was supplied by Merck. The water content was analysed by the Karl-Fischer titration technique described previously [11]. The results obtained have shown the water content to be less than 200 · 10−6. Density as a function of temperature, necessary to calculate KL, was measured previously [11]. Due to the high purity of solutes and in fact that the IGC technique separated any impurities on the column solutes were used

Results and discussion

The experimental activity coefficients at infinite dilution in [COC2N1,1,2][FAP] for 65 organic solutes and water within the temperature range from (318.15 to 368.15) K are presented in table 1. Table 2S provides information about the mean column pressure, p, inlet column pressure, pi, outlet column pressure, po and standard state of solutes at given temperatures. Over the experimental temperature range, the logarithm of γ is a linear function of inverse temperature, therefore results obtained

Conclusions

Activity coefficients at infinite dilution and the (gas + liquid) partition coefficients for various solutes in the ionic liquid ethyl-dimethyl-(2-methoxyethyl)ammonium trifluorotris(perfluoroethyl)phosphate were measured by inverse gas chromatography technique at wide temperature range. It was found that interactions with wide range of compounds for investigated IL is similar to previously investigated [COC2mPIP][FAP] and [COC2mPYR][FAP] ILs. Additionally the extraction properties of

Acknowledgement

Funding for this research was provided by the National Science Centre in years 2011–2014 (Grant No. 2011/01/B/ST5/00800).

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