Solubilities of isobutane and cyclopropane in ionic liquids

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Highlights

  • Solubilities of isobutane and cyclopropane in two ionic liquids were reported.

  • Solubilities were measured from T = (302 to 344) K and from (0.03 to 1.16) MPa.

  • The effects of temperature and pressure on the solubilities were investigated.

  • Solubilities of hydrocarbons in [HMIM][Tf2N] and [P(14)666][TMPP] were compared.

  • A modified Krichevsky–Kasarnovsky equation was used to model experimental data.

Abstract

In this work, we presented the solubilities of isobutane and cyclopropane in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][Tf2N]) and trihexyl tetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate ([P(14)666][TMPP]) from T = (302 to 344) K up to 1.16 MPa. Henry’s constants for isobutane and cyclopropane in [HMIM][Tf2N] and [P(14)666][TMPP] were calculated from experimental results. Solubilities of isobutane and cyclopropane in [HMIM][Tf2N] are apparently smaller than those in [P(14)666][TMPP]. The effects of temperature, pressure and the number of carbon atoms in the hydrocarbons on the solubility were investigated in detail. A modified Krichevsky–Kasarnovsky equation was successfully applied to correlate the experimental results. The mean absolute relative deviations and the maximum absolute relative deviations are less than (2.4 and 4.6)%, respectively.

Graphical abstract

Henry’s constants for isobutane and cyclopropane in [HMIM][Tf2N] and [P(14)666][TMPP].

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Introduction

Ionic liquids are a class of liquid salts at room temperature [1], which have lots of potential applications in separation [2], battery [3] and refrigeration [4], [5] due to their good stability, high conductivity, low vapor pressure, and low melting point, etc. Ionic liquids can be tuned for different properties by changing their cations and anions. Small hydrocarbons and organic solvents have attracted widespread attentions as working pairs for the absorption refrigeration cycles owing to their good thermophysical properties, heat transfer characteristics, low toxicity and low global warming potential [6], [7]. However, the flammability of hydrocarbons limited their applications. Ionic liquids may help to solve this problem as absorbents. Moreover, ionic liquid can be used to store and separate hydrocarbons [8], [9].

Solubilities of hydrocarbons in ionic liquids are required for designing the refrigeration, storage and separation processes. Literatures [10], [11] have reviewed the solubilities of methane, ethane, ethylene, propane, propylene, butane, benzene and 1-butene in ionic liquids. However, there are no data for the solubilities of isobutane and cyclopropane in ionic liquids, although they are important refrigerants.

In this work, we presented new experimental data for the solubilities of isobutane and cyclopropane in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][Tf2N]) and trihexyl tetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate ([P(14)666][TMPP]). The measurements were carried out at temperature range from (302 to 344) K and at pressures up to 1.16 MPa. [HMIM][Tf2N] and [P(14)666][TMPP] were chosen because they have high solubilities for hydrocarbons [10]. High solubility is helpful for improving the efficiency of refrigeration, storage and separation. A modified Krichevsky–Kasarnovsky equation was used to model the experimental results.

Section snippets

Materials

Isobutane and cyclopropane were provided by Zhejiang Sinoloong Refrigerant Company Limited and Beijing Hengye Zhongyuan Chemical Company Limited, respectively. The purities are 99.9% in mass fraction. They were used without further purification. [HMIM][Tf2N] was purchased from Shanghai Cheng Jie Chemical Company Limited with a purity ⩾99.0% in mass fraction, formula is C12H19F6N3O4S2. [P(14)666][TMPP] was purchased from Strem Chemicals, incorporated with a purity ⩾95.0% in mass fraction,

Results and discussion

Solubilities of isobutane and cyclopropane in [HMIM][Tf2N] and [P(14)666][TMPP] at temperature from (302 to 344) K and at pressure from (0.03 to 1.16) MPa were given in TABLE 2, TABLE 3. FIGURE 2, FIGURE 3, FIGURE 4, FIGURE 5 show the px data of isobutane and cyclopropane in [P(14)666][TMPP] and [HMIM][Tf2N]. figure 6 and table 4 show the Henry’s constants for isobutane and cyclopropane in [P(14)666][TMPP] and [HMIM][Tf2N] which were calculated from the experimental results. As shown in FIGURE 2

Conclusions

In this work, we presented the solubilities of isobutane and cyclopropane in [HMIM][Tf2N] and [P(14)666][TMPP] at temperatures between (302 and 344) K and at pressures up to 1.16 MPa. [P(14)666][TMPP] has higher solubilities for isobutane and cyclopropane than [HMIM][Tf2N]. Solubilities of isobutane and cyclopropane in [P(14)666][TMPP] and [HMIM][Tf2N] increase with the increasing pressure, and decrease with the increasing temperature. Solubilities of hydrocarbons in [HMIM][Tf2N] increase as the

Acknowledgements

The authors are very grateful to Prof. John M. Prausnitz of University of California, Berkeley and Dr. Waheed Afzal of University of the Punjab, Pakistan for their help concerning this work. The supports provided by the National Natural Science Foundation of China (No. 51376141) for the present work are gratefully acknowledged.

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