Solubilities and thermodynamic properties of CO2 in choline-chloride based deep eutectic solvents

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Highlights

Abstract

The solubilities of CO2 in three kinds of deep eutectic solvents, (choline chloride + phenol), (choline chloride + diethylene glycol) and (choline chloride + triethylene glycol), were determined at temperatures ranging from 293.15 K to 323.15 K under pressures up to 600.0 kPa using isochoric saturation method. The mole ratios of choline chloride to phenol were selected as 1:2, 1:3 and 1:4, the others as 1:3 and 1:4. Henry’s constants and thermodynamic properties such as standard Gibbs free energy, enthalpy, and entropy changes of CO2 solvation were calculated from the correlation of solubility data. Results revealed that the solubility of CO2 increased with increasing pressure and decreased with increasing temperature. The enthalpies of solution were negative at all conditions.

Introduction

In the recent years, emissions of CO2 mainly caused by energy production and consumption lead to various environmental problems such as increasing global temperature, rising sea levels, flooding, drought, changing patterns of precipitation and infectious diseases [1], [2]. Therefore, the removal of CO2 from industrial flue gases is of particular importance for a sustainable society and has become a hotpot of research. Among CO2 capture technologies, amine absorption was proved to be the most practical technologies before 2030 [3]. However, the utilization of these solutions has several serious drawbacks including high equipment corrosion, intensive energy demand and high cost in the operations [4], [5], [6], [7], [8].

After numerous works of searching for new solvents which could serve as alternatives to amine absorbents, the ability of room-temperature ionic liquids (RTILs) to absorb CO2 was superior compared to other organic solvents [9]. RTILs typically composed of large, delocalized cations and anions are characterized by low vapor pressure, high thermal and chemical stability, non-flammability, and high solvation capacity [10], [11], [12], [13], [14], [15], [16]. Their unique properties, which could be influenced by modifying cation and anion, make them an ideal class of separation media for various sample preparation techniques [17], [18], [19], [20]. However, they have not been widely used because of high cost in bulk application and low tolerance to moisture. In addition to that, some studies revealed the toxic nature of RTILs [21], [22].

To overcome the limitations of RTILs, deep eutectic solvents (DESs) were put forward as versatile alternatives [23]. Being a new class of ionic liquids, they are prepared by mixing substituted quaternary ammonium salt with metal halide or hydrogen bond donor (HBD) and possess much lower melting point than either of their components [24]. DESs consist of at least one HBD and one hydrogen bond acceptor (HBA) counterpart. Their properties can be adjusted by selecting the nature and ratio of the hydrogen bond counterparts. They often share many interesting characteristics with green solvents RTILs with the outstanding features of low price and biodegradability. The first DES was reported by mixing choline chloride with urea [25]. Other similar DESs were also developed and applied to different areas such as solvents or catalysts in reactions or bio-transformations, liquid separations, and metal electro-deposition [26], [27], [28], [29], [30]. DESs were also explored as mediums for CO2 capture in recent studies [31], [32]. Up to date, Li et al. [33] reported the solubilities of CO2 in choline chloride-urea mixture at temperature ranging from 313.15 K to 333.15 K under pressure up to 13 MPa. Leron et al. [34] studied the solubility of CO2 in the DES composed of choline chloride and urea with the mole ratio of 1:2 under more wider temperature of T = (303.15 to 343.15) K. Recently, Leron et al. [35] extended the DESs scope to the mixture of choline chloride and ethylene glycol for CO2 dissolution with satisfactory results. Francisco et al. [36] reported the CO2 capture using DES composed of choline chloride and natural lactic acid (1:2 mole ratio). However, systematic research and the detailed thermodynamic properties are still absent. In addition, the solubility study at a relative low temperature (<300 K) is overlooked.

Considering that application of green DESs to CO2 capture has potential prospects for various chemical processes, researches on dissolution of CO2 in DESs possess basic importance. In our previous work [37], the solubilities of CO2 in DESs of choline chloride and dihydric alcohols (including 1, 4-butanediol, 2, 3-butanediol, and 1, 2-propanediol) were determined. As persistent attention to and continuous work on the dissolution of CO2 in DESs, in the current work, we hope to extend the relevant research to the solubilities of CO2 in three kinds of choline chloride-based DESs at temperatures ranging from 293.15 K to 323.15 K under pressures up to 600.0 kPa using isochoric saturation methods. Furthermore, Henry’s constant was calculated from the solubility data. Thermodynamic properties such as standard Gibbs free energy, enthalpy, and entropy changes of solution of the gas were also obtained from the correlation of Henry’s constant with temperatures.

Section snippets

Chemicals

Purities are expressed as mass fraction. The CO2 (>0.9995) was supplied by Jingong Special Gas Co., Ltd. Choline chloride (>0.985) was produced by Jinan Hualing Pharmaceutical Co., Ltd. Phenol (⩾0.990), diethylene glycol (⩾0.990), and triethylene glycol (⩾0.990) were all produced by Sinopharm Chemical Reagent Co., Ltd. The summary of the chemicals used, their purities, and sources are listed in table 1. DESs were prepared by melting choline chloride with the corresponding phenol or alcohols at

Solubility data of CO2 in DESs

Densities of all the DESs under pressure p = 101.3 kPa and different temperatures are listed in table 2 along with the densities of (choline chloride + phenol) from the literature [40]. The density values from present experiment and literature are basically consistent, with the maximum relative deviation of 0.26 %. It can be found that the densities of all the DESs were affected by the kinds of HBD such as alcohols or phenol, mole ratios as well as temperatures. The densities of (choline chloride + 

Conclusions

In the present work, a series of DESs was synthesized and the solubility data of CO2 in these solutions were determined at temperatures ranging from 293.15 K to 323.15 K and pressures up to 0.6 MPa. The results imply that the solubility of CO2 in DESs increases with decreasing temperature and increasing pressure. Moreover, the DESs composed of triethylene glycol and choline chloride with the mole ratio of 4:1 demonstrated the highest capacity to dissolve CO2 among all the DESs. Henry’s law

Acknowledgments

The authors are grateful for the financial support by the Natural Science Foundation of Zhejiang Province (No. Y4100699) and the Natural Science Foundation of China (No. 21006095).

References (44)

  • M. Hasib-ur-Rahman et al.

    Chem. Eng. Process.

    (2010)
  • J. Kumelan et al.

    J. Chem. Thermodyn.

    (2006)
  • A. Latala et al.

    Aquat. Toxicol.

    (2005)
  • R.B. Leron et al.

    J. Chem. Thermodyn.

    (2012)
  • P. Cojocaru et al.

    Mater. Lett.

    (2011)
  • R.B. Leron et al.

    J. Chem. Thermodyn.

    (2013)
  • R.B. Leron et al.

    Inst. Chem. Eng.

    (2013)
  • R.B. Leron et al.

    Thermochim. Acta

    (2013)
  • M. Francisco et al.

    Fluid Phase Equilib.

    (2013)
  • J. Jacquemin et al.

    J. Chem. Thermodyn.

    (2006)
  • D.S. Deng et al.

    J. Chem. Thermodyn.

    (2013)
  • W.J. Choi et al.

    Green Chem.

    (2007)
  • J. Li et al.

    J. Chem. Eng. Data

    (2012)
  • C.H. Yu et al.

    Aerosol Air Qual. Res.

    (2012)
  • G.T. Rochelle

    Science

    (2009)
  • Q. Ye et al.

    Acta Phys. Chim. Sin.

    (2012)
  • A. Houshmand et al.

    Sep. Sci. Technol.

    (2011)
  • E. Groppo et al.

    Phys. Chem. Chem. Phys.

    (2012)
  • S.S.A. Talesh et al.

    Sep. Sci. Technol.

    (2011)
  • R.J. Bernot et al.

    Environ. Toxicol. Chem.

    (2005)
  • C. Pretti et al.

    Green Chem.

    (2006)
  • J.F. Brennecke, E.J. Maginn, United States Patent 6, 579, 343,...
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