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Vapor−Liquid Equilibrium of Three Hydrofluorocarbons with [HMIM][Tf2N] Xiangyang Liu, Maogang He,* Nan Lv, Xuetao Qi, and Chao Su Key Laboratory of Thermal Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China ABSTRACT: New experimental data for the vapor−liquid equilibrium of 1-hexyl3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][Tf2N]) with difluoromethane (R-32), 1,1-difluoroethane (R-152a), and pentafluoroethane (R-125) were presented. Measurements were performed using an isochoric saturation method at temperatures from (302.3 to 344.1) K and at pressures between (0.03 to 1.22) MPa. The relative expanded uncertainty in solubility measurement is less than 4 %. Within the investigated temperature and pressure range, the order of the solubilities for R-32, R-152a, and R-125 in [HMIM][Tf2N] is R-152a > R-32 > R-125. The experimental results were successfully correlated with the Krichevsky−Kasarnovsky equation. The AAD between the experimental data and calculated values for the solubilities of R-152a, R-32, and R-125 in [HMIM][Tf2N] are 1.4 %, 1.5 %, and 0.8 %, respectively. hydrochlorofluorocarbons (HCFCs), fluorocarbons (FCs), hydrofluoroethers (HFEs), and chlorofluorocarbons (CFCs) in ionic liquids were also studied.10,19,28−30 In this work, we present new experimental data for the solubilities of R-32, R-152a, and R-125 in [HMIM][Tf2N] at temperatures between (302.3 to 344.1) K and at pressures between (0.03 to 1.22) MPa which were measured with an isochoric saturation method. The Krichevsky−Kasarnovsky equation was used to model the experimental data.

1. INTRODUCTION Ionic liquids have a variety of applications in industry such as electrolyte in batteries,1 lubricants,2 solvents for separation processes,3 etc., because many of them have negligible vapor pressure at room temperature, are nonflammable, and possess good chemical stability.4 Recently, ionic liquids + hydrofluorocarbons (HFCs) were used as working pairs for absorption refrigeration cycles,5−7 which can be driven by low-grade energy.8 Ionic liquids + HFCs can overcome the disadvantages of NH3+ H2O and H2O+LiBr, such as toxicity, crystallization, and corrosivity. In addition, ionic liquids have been shown to be an effective solvent in the extractive distillation process for the separation of azeotropic mixtures of hydrofluorocarbons.9 Vapor−liquid equilibrium data of refrigerants in absorbents are the most important data for the applications of ionic liquids and HFC gases. However, the solubility data of HFCs in ionic liquids are still scarce. Most of the known data were reported by Shiflett et al.10−20 They have measured the solubilities of R-1141, R-134, R-134a, R-161, R-32, R-41, R-125, R-143a, R-23, and R-152a in various ionic liquids. Dong et al.,21 Shariati and Peters,22,23 and Ren et al.9,24,25 reported the solubilities of R-152a, R134a, R-32, and R-23 in 1-n-alkyl-3-methylimidazolium ionic liquid with different anions containing trifluoromethanesulfonate, hexafluorophosphate, and bis(trifluoromethylsulfonyl)imide. Granjo et al.26,27 studied the solubilities of R-23, R-32, and R-41 in seven imidazolium-based, phosphonium-based, and ammonium-based ionic liquids. Their results show that ionic liquids have high solubilities for HFCs when the anions have fluorinated groups, such as [PF6] and [Tf2N]. When the length of fluoroalkyl chains on the anion and the alkyl chains on the cation increases, the solubilities of HFCs in ionic liquid will be improved. Solubilities of some © 2015 American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Materials. R-32, R-152a, and R-125 were provided by Zhejiang Sinoloong Refrigerant CO., LTD with purities ≥ 99.9 % in mass fraction. Carbon dioxide was purchased from Praxair with a purity ≥ 99.999 % in mass fraction. They were used without further purification. [HMIM][Tf2N] is purchased from Shanghai Cheng Jie Chemical CO., LTD, with a purity ≥ 99.0 % in mass fraction. The ionic liquid was dried at 393 K for 48 h under vacuum before being used in order to remove volatile impurities. The chemicals used in this study are summarized in Table 1. 2.2. Gas Solubility Apparatus. The gas solubility measurements were carried out with an isochoric saturation method; the apparatus mainly consists of the equilibrium cell, the gas reservoir, the data acquisition system, the vacuum pump, the magnetic stirrer, the thermostat, and the temperature and pressure sensors, as shown in Figure 1. The experimental method is similar to that used in the literature.31,32 The gas reservoir was made of copper to keep the temperature of gas in it uniform and stable. The volume of the equilibrium cell and Received: November 25, 2014 Accepted: April 8, 2015 Published: April 17, 2015 1354

DOI: 10.1021/je501069b J. Chem. Eng. Data 2015, 60, 1354−1361

Journal of Chemical & Engineering Data

Article

Table 1. Chemicals Used in This Work

a

chemical name

supplier

purity in mass fraction

purification method

water content in mass fraction

[HMIM][Tf2N]a difluoromethane (R-32) pentafluoroethane (R-125) 1,1-difluoroethane (R-152a) carbon dioxide

Shanghai Cheng Jie Chemical CO., Ltd. Zhejiang Sinoloong Refrigerant CO., Ltd. Zhejiang Sinoloong Refrigerant CO., Ltd. Zhejiang Sinoloong Refrigerant CO., Ltd. Praxair

≥ 99 % ≥ 99.9 % ≥ 99.9 % ≥ 99.9 % ≥ 99.999 %

vacuum drying none none none none

0.008 %b

1-Hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. bMeasured with Metrohm 831 Karl Fischer titrator.

2.4. Calculation of Gas Solubility. The solubility of gas in an ionic liquid can be expressed by the mole fraction of gas dissolved in the ionic liquid, which is calculated by

x=

ngl nl + ngl

(1)

nlg

where nl is the mole number of ionic liquid; is the mole number of gas dissolved in the ionic liquid, which is calculated by ngl = n in − ngv = (n i − n f ) − ngv

(2)

nvg

where is the mole number of gas in the equilibrium cell after the equilibrium is reached; nin is the mole number of gas loaded into the equilibrium cell from the gas reservoir; ni and nf are the mole number of gas in the gas reservoir before and after loading gas into the equilibrium cell, respectively. Equation 2 can be rewritten as Figure 1. Schematic of the experimental apparatus.

ngl = VGC(ρi − ρf ) − ρg (VEC − Vl )

the gas reservoir was calibrated prior to the gas solubility measurement by filling the cell and reservoir with liquid water at room temperature. The volume measured includes the volume of all connections. The mass of water was determined with a Mettler Toledo ME4002 balance; the expanded uncertainty is 0.02 g (coverage factor k = 2).33 The density of water was obtained from REFPROP 9.1.34 The relative expanded uncertainties of the volume of the equilibrium cell and the gas reservoir are estimated to be within 0.1 % (k = 2). The temperature inside the equilibrium cell and the gas reservoir was measured with platinum resistant thermometers (Fluke 5608) with an uncertainty of 0.02 K (k = 2). The temperature of the equilibrium cell is controlled with the thermostat. The temperature stability is less than ± 0.04 K/30 min. The expanded uncertainty of the temperature in the equilibrium cell is less than 0.1 K (k = 2). Pressure sensors (Keller 33X) were used to measure the pressure in the equilibrium cell and the gas reservoir. Different pressure sensors with the full scale 3 and 10 MPa were used for different range of measurement; the expanded uncertainties are 0.4 and 1.2 kPa, respectively. 2.3. Experiment Procedure. Initially, the dried ionic liquid was loaded into the equilibrium cell, which was placed under vacuum. A Mettler Toledo ME 204 balance (uncertainty is 0.0002 g) was used to measure the mass of ionic liquid in the equilibrium cell. The equilibrium cell was filled with gas from the gas reservoir and the temperature and pressure in the gas reservoir before and after releasing gas from the gas reservoir was recorded. With the gas dissolving into the ionic liquid, the pressure in the equilibrium cell was decreased at fixed temperatures. A magnetic stirrer was used to accelerate the dissolve process. Equilibrium was attained when the pressure did not change. The temperature and pressure in the equilibrium cell were recorded.

(3)

where VGC and VEC are the volume of the gas reservoir and the equilibrium cell, respectively; Vl is the volume of ionic liquid in the equilibrium cell, which was obtained from the mass and density of ionic liquid; ρi and ρf are the molar densities of gas in the gas reservoir before and after loading gas into the equilibrium cell; ρg is the molar density of gas in the equilibrium cell when equilibrium is reached. ρi, ρf, and ρg were obtained from the REFPROP 9.1.34 The density data of [HMIM][Tf2N] have been reported in the literature;35 the uncertainty is 0.0001 g·cm−3. The volume change of gas-dissolved ionic liquid was neglected, because it has a small effect on the solubility.21,36 The densities of [HMIM][Tf2N] can be represented by ρ = − 9.0525·10‐4T + 1.6415

(4)

where ρ is in g·cm−3 and T is in K. From eqs 1 and 3, we can get x=

VGC(ρi − ρf ) − ρg (VEC − Vl ) nl + VGC(ρi − ρf ) − ρg (VEC − Vl )

(5)

The expanded uncertainty in mole fraction can be obtained from21 U (x) = ku(x) 2 ⎡⎛ ⎛ ∂x ⎞2 ∂x ⎞ 2 ⎢ =k ⎜ ⎟ u(VGC) + ⎜⎜ ⎟⎟ u(ρi )2 ⎢⎣⎝ ∂VGC ⎠ ⎝ ∂ρi ⎠ ⎛ ⎞2 ⎛ ∂x ⎞2 ⎛ ∂x ⎞2 ∂x 2 ⎟⎟ u(ρf ) + ⎜⎜ ⎟⎟ u(ρg )2 + ⎜ + ⎜⎜ ⎟ u(VEC)2 ∂ ∂ ∂ V ρ ρ ⎝ ⎝ f⎠ EC ⎠ ⎝ g⎠ ⎤1/2 ⎛ ∂x ⎞2 ⎛ ∂x ⎞2 2 2⎥ + ⎜ ⎟ u(V1) + ⎜ ⎟ u(nl) ⎥⎦ ⎝ ∂Vl ⎠ ⎝ ∂nl ⎠ 1355

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where u(x) is the standard uncertainty in mole fraction; u(VGC), u(VEC), u(V1), u(ρi), u(ρf), u(ρg), and u(n1) are the standard uncertainty in VGC, VEC, V1, ρi, ρf, ρg, and n1, respectively. The relative expanded uncertainty in solubility measurement Ur(x) = U(x)/x including random error is estimated to be less than 4 % (k = 2).

data at different pressures are in good agreement with those reported in the literature. Solubilities of R-32, R-152a, and R-125 in [HMIM][Tf2N] were measured at temperatures from (302.3 to 344.1) K and at pressures between (0.03 and 1.22) MPa. The experimental results are given in Table 3. Figures 3−5 show the p−x data of R-32, R-152a, and R-125 in [HMIM][Tf2N] at different temperatures. Obviously, the solubilities of R-32, R-152a, and R-125 in [HMIM][Tf2N] increase with pressure, but temperature has a negative and relative smaller effect on the solubilities. Solubilities of R-32, R-152a, and R-125 in [HMIM][Tf2N] were compared with those of other refrigerants including carbon dioxide, R-134a,24 methane,41 ethane,42 and propane.43 The result is shown in Figure 6. Solubilities of the four hydrofluorocarbons in [HMIM][Tf2N] are apparently larger than those of carbon dioxide and small hydrocarbons. The solubilities of propane in [HMIM][Tf2N] are larger than those of carbon dioxide.42 Therefore, the order of the solubilities of these gases in [HMIM][Tf2N] is R-152a > R-134a > R-32 > R-125 > propane > carbon dioxide > ethane > methane. Figure 7 compares the solubilities of R-152a in 1-butyl-3methylimidazolium hexafluorophosphate ([BMIM][PF6]),15 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIM][TfO]),21 1-butyl-3-methylimidazolium trifluoromethylsulfonate ([BMIM][TfO])21 and [HMIM][Tf2N] at 323 K. It shows that [HMIM][Tf2N] has higher solubilities for R-152a than the other three ionic liquids. This result may be caused by two reasons:14,26 one is the longer alkyl chains on the cation which will increase the free volume in the ionic liquid, another is that the hydrogen bond (H−F) plays an important role between the hydrogen atoms in the HFCs and the fluorine atoms on the anion, as well as the fluorine atoms of the HFCs and the hydrogen atoms on the cation. [HMIM][Tf2N] has longer alkyl chains on the cation and more fluorine atoms on the anion than [BMIM][PF6], [EMIM][TfO], and [BMIM][TfO], so it has higher solubilities for R-152a. Figure 8 presents the solubilities of R-32 in 1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf2N]),14 1-heptyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate ([HMIM][TFES]),14 and [HMIM][Tf2N] at 298 K. From the experimental results in the literature,14,21 we can conclude that imidazolium-based ionic liquids have lower solubilities for R-32 at higher temperature. Solubilities of R-32 in [HMIM][Tf2N] at 303 K are higher than those in [EMIM][Tf2N] at 298 K, indicating that the solubility of R-32 in 1-n-alkyl-3-methylimidazolium ionic liquid with the anion [Tf2N] increases with the increasing number of carbon atoms on the cation. The solubilities of R-32 in [HMIM][TFES] are lower than those of R-32 in [HMIM][Tf2N] and [EMIM][Tf2N] although [HMIM][TFES] has longer alkyl chains on the cation than [EMIM][Tf2N]. The result is consistent with the conclusion that the solubilities of HFCs increase with the increase in the length of fluoroalkyl chains on the anion.26 The experimental solubility data of R-32, R-125 and R-152a in [HMIM][Tf2N] were correlated by the KK equation. The partial molar volume at infinite dilution V∞ 1 and Henry’s constant H at a fixed temperature for R-32, R-152a, and R-125 in [HMIM][Tf2N] were obtained from the intercept and slope of a plot of ln( f/x) vs pressure. The results are shown in Table 4 and Figures 9 and 10. Figure 9 shows that H values for R-32, R-125, and R-152a in [HMIM][Tf2N] increase with temperature, and can be correlated well by

3. CORRELATION Experimental solubilities are fitted to the Krichevsky− Kasarnovsky (KK) equation,37 which is expressed as ln

V1∞(p − p2S ) f = ln H + RT x

(7)

where f is the fugacity of gas which is obtained from literature;34 H is Henry’s constant; V∞ 1 is the partial molar volume of solute in the solvent at infinite dilution; p is pressure; pS2 is the saturated vapor pressure of solvent. For ionic liquid at room temperature, pS2 is considered to be to zero. Therefore, eq 5 becomes ln

V ∞p f = ln H + 1 x RT

(8)

4. RESULTS AND DISCUSSION The reliability of our experimental apparatus was validated by determining the solubilities of CO2 at 323 K. The experimental results and the data available in the literature36,38−40 are listed in Table 2 and Figure 2. It can be seen that our experimental Table 2. Mole Fraction x of CO2 in [HMIM][Tf2N] at Temperature T and Pressure pa T/K

p/MPa

x

323.4 324.6 323.2 324.0 323.4

1.650 2.487 2.927 3.814 4.649

0.2640 0.3550 0.4081 0.4763 0.5337

a

Expanded uncertainties U are U(T) = 0.1 K, U(p) = 1 kPa; the relative expanded uncertainty Ur is Ur(x) = 4%. The level of confidence is 0.95 (k = 2).

Figure 2. Solubilities of carbon dioxide in [HMIM][Tf2N] at 323 K: ●, our work; ○, Muldoon et al.;36 □, Shiflett and Yokozeki;38 △, Raeissi et al.;39 ◊, Yim and Lim.40

ln H = 1356

A +B T

(9) DOI: 10.1021/je501069b J. Chem. Eng. Data 2015, 60, 1354−1361


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Table 3. Mole Fraction x of R-32, R-152a, and R-125 in [HMIM][Tf2N] at Temperature T and Pressure pa T/K

p/MPa

x

T/K

R-32 302.7 303.3 302.9 302.5 302.9 303.4 303.5 313.9 313.2 313.0 313.9 312.5 312.2 313.4 323.6 323.9 323.2 323.9 322.6 324.1 322.4 332.6 333.4 332.6 332.6 333.5 333.7 333.0 343.2 342.9 343.3 343.3 343.1 344.1 342.6 a

0.1144 0.2108 0.3021 0.4142 0.5136 0.5854 0.6395 0.1390 0.2507 0.3633 0.5097 0.6137 0.6931 0.7787 0.1615 0.2957 0.4284 0.6002 0.7404 0.8482 0.9028 0.1826 0.3387 0.4921 0.6826 0.8613 0.9776 1.0686 0.2081 0.3815 0.5634 0.7914 0.9794 1.1307 1.2208

p/MPa

x

T/K

R-152a 0.1114 0.1980 0.2806 0.3621 0.4192 0.4548 0.4972 0.1060 0.1907 0.2714 0.3504 0.4088 0.4447 0.4858 0.1013 0.1829 0.2618 0.3396 0.3954 0.4304 0.4760 0.0971 0.1755 0.2527 0.3299 0.3834 0.4186 0.4626 0.0923 0.1687 0.2430 0.3173 0.3717 0.4046 0.4506

302.4 302.9 303.2 302.8 303.2 302.3 313.5 312.3 313.4 313.4 312.2 313.4 322.8 323.5 323.6 322.2 323.7 322.3 333.1 332.8 333.8 333.4 332.5 332.9 343.3 343.0 342.6 342.7 342.8 343.4

0.0376 0.0559 0.0738 0.0962 0.1154 0.1344 0.0478 0.0689 0.0931 0.1226 0.1413 0.1748 0.0575 0.0862 0.1145 0.1469 0.1803 0.2096 0.0685 0.1010 0.1373 0.1810 0.2109 0.2564 0.0798 0.1183 0.1578 0.2101 0.2521 0.3074

p/MPa

x

R-125 0.0672 0.0999 0.1367 0.1814 0.2122 0.2528 0.0646 0.0968 0.1324 0.1761 0.2074 0.2459 0.0629 0.0929 0.1279 0.1714 0.2003 0.2402 0.0598 0.0897 0.1233 0.1650 0.1950 0.2326 0.0573 0.0861 0.1193 0.1598 0.1880 0.2247

303.1 303.3 303.2 302.6 303.1 303.5 312.4 312.7 313.5 312.5 312.3 312.7 322.6 323.4 323.3 323.2 322.3 322.5 332.7 332.5 332.6 332.5 332.5 332.8 342.9 343.0 342.8 343.0 342.5 343.2

0.1091 0.2124 0.2913 0.4092 0.4732 0.5435 0.1264 0.2517 0.3559 0.4977 0.5664 0.6537 0.1491 0.3020 0.4188 0.5987 0.6781 0.7811 0.1723 0.3444 0.4807 0.6893 0.7956 0.9172 0.1949 0.3935 0.5486 0.7934 0.9113 1.0592

0.0720 0.1410 0.1885 0.2610 0.2936 0.3282 0.0679 0.1326 0.1757 0.2458 0.2787 0.3186 0.0627 0.1220 0.1636 0.2286 0.2608 0.2927 0.0576 0.1136 0.1521 0.2135 0.2422 0.2756 0.0530 0.1043 0.1399 0.1966 0.2243 0.2550

Expanded uncertainties U are U(T) = 0.1 K, U(p) = 0.3 kPa; the relative expanded uncertainty Ur is Ur(x) = 4 %. The level of confidence is 0.95 (k = 2).

Figure 4. Solubilities of R-32 in [HMIM][Tf2N]: ◊, 303 K; □, 313 K; △, 323 K; ○, 333 K; +, 343 K; −, calculations from the general KK equation.

Figure 3. Solubilities of R-152a in [HMIM][Tf2N]: ◊, 303 K; □, 313 K; △, 323 K; ○, 333 K; +, 343 K; −, calculations from the general KK equation. 1357



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Figure 7. Solubilities of R-152a in different ionic liquids at 323 K: △, [BMIM][PF6];15 ◊, [BMIM][TfO];21 □, [EMIM][TfO];21 ●, [HMIM][Tf2N].

Figure 5. Solubilities of R-125 in [HMIM][Tf2N]: ◊, 303 K; □, 313 K; △, 323 K; ○, 333 K; +, 343 K; −, calculations from the general KK equation.

Figure 8. Solubilities of R-32 in different ionic liquids at 298.15 K: ●, [HMIM][Tf2N] at 303 K; △, [EMIM][Tf2N];14 ○, [HMIM][TFES].14 Figure 6. Solubilities of the gases in [HMIM][Tf2N] at 323 K: ▲, R-152a; ⧫, R-134a;24 ●, R-32; ■, R-125; ◊, methane at 293.3 K;41 △, ethane;42 □, propane at 298.15 K;43 ○, carbon dioxide.

R-152a in [HMIM][Tf2N]. The AAD and the MD are defined by AAD =

where H is in MPa and T is in K. Figure 10 shows that the ∞ absolute values of V∞ 1 decrease with temperature. V1 can be represented by a function of temperature: V1∞

= C + DT + ET

2

MD = max

(10)

where A, B, C, D, and E are coefficients which are listed in Table 5. Combining eqs 6 to 8, we can get the general KK equation ln

p(C + DT + ET 2) f A = +B+ x T RT

1 N

N

∑

xcal − xexp xexp

i

(12)

xcal − xexp xexp

(13)

where N is the total number of experimental points; xcal and xexp are the calculated value from the general KK equation and the experimental result for mole fraction, respectively. Figures 3 to 5 show the calculations from the general KK equation for the solubilities of R-32, R-125, and R-152a in [HMIM][Tf2N]. It can be found that the general KK equation has a good agreement with experiment. The AAD between the experimental results and the calculations from the general KK equation for the solubilities of R-152a, R-32, and R-125 in [HMIM][Tf2N] are 1.4 %, 1.5 %, and 0.8 %, respectively.

(11)

Table 4 shows the mean absolute relative deviations (AAD) and the maximum relative absolute deviations (MD) between experimental results and the predictions from the general KK equation for the solubilities of R-32, R-125, and 1358



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Table 4. Henry’s Constants H and Partial Molar Volumes V∞ 1 for R-152a, R-32, and R-125 in [HMIM][Tf2N] at Temperature T T/K 302.8 313.0 323.0 333.1 343.0 303.0 313.1 323.4 333.0 343.2 303.1 312.7 322.9 332.6 342.9

H/MPa R-152a 0.57 0.73 0.94 1.15 1.37 R-32 0.96 1.22 1.49 1.76 2.10 R-125 1.46 1.83 2.35 2.91 3.60

3 −1 V∞ 1 /(cm ·mol )

−1823 −1395 −1337 −1080 −619 880 622 535 507 428

Figure 10. Partial molar volume of R-152a, R-32, and R-125 in [HMIM][Tf2N] at infinite dilution: ◊, R-125; □, R-152a; △, R-32; −, calculations from eq 10.

164 159 138 127 125

Table 5. Coefficients A, B, C, D, E and Results of eq 11 A B C D E AADa/% MDb/%

R-152a

R-32

R-125

−2294 7.024 0.1963 −99.68 10423 1.4 3.7

−2010 6.603 0.2910 −198.24 34210 1.5 3.8

−2371 8.194 0.01251 −9.188 1802 0.8 2.2

a

AAD is the mean absolute relative deviation between eq 11 and experimental solubility data. bMD is the maximum relative absolute deviation between eq 11 and experimental solubility data.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +86-29-8266-3863. Fax: +86-29-8266-3863. E-mail: [email protected]. Notes

The authors declare no competing financial interest. Funding

Support provided by the National Natural Science Foundation of China (No. 51376141) for the present work is gratefully acknowledged.

Figure 9. Henry’s constants for R-152a, R-32, and R-125 in [HMIM][Tf2N]: ◊, R-125; □, R-152a; △, R-32; −, calculations from eq 9.

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ACKNOWLEDGMENTS 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.

5. CONCLUSIONS In this work, we presented the solubilities of R-32, R-125, and R-152a in [HMIM][Tf2N] at temperatures between (302.3 and 344.1) K and at pressures between (0.03 and 1.22) MPa. Compared with carbon dioxide and small hydrocarbons, R-32, R-152a, and R125 are more soluble in [HMIM][Tf2N], their solubilities are in the order R-152a > R-32 > R-125. Low temperature, high pressure, long alkyl chains on the cation, and long fluoroalkyl chains on the anion can improve the solubilities of HFCs in ionic liquids. A general Krichevsky−Kasarnovsky equation was obtained for the solubilities for R-32, R-152a, and R125 in [HMIM][Tf2N], the calculations agree well with our experimental results.

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REFERENCES

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