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J. Chem. Eng. Data 2007, 52, 1488-1491
Activity Coefficients at Infinite Dilution of Alkanes, Alkenes, and Alkyl Benzenes in 1-Propyl-2,3-dimethylimidazolium Tetrafluoroborate Using Gas-Liquid Chromatography Ming-Hui Wang, Jun-Sheng Wu,* Li-Sheng Wang, and Mi-Yi Li School of Chemical Engineering & Environment, Beijing Institute of Technology, Beijing 100081, People’s Republic of China
Activity coefficients at infinite dilution, γ∞i , have been determined for 17 organic solutes, alkanes, alkenes, and alkyl benzenes, in the ionic liquid 1-propyl-2,3-dimethylimidazolium tetrafluoroborate ([PDMIM][BF4]) by the gas-liquid chromatographic method with the ionic liquid as the stationary phase. The measurements were carried out in the temperature range of 303.15 K to 363.15 K. The partial molar excess enthalpies at infinite dilution, ∞ HE,∞ i , were also determined for the solutes from the temperature dependence of the γi values.
Introduction This work is a continuation of our studies on the determination of activity coefficients at infinite dilution by the gasliquid chromatographic (GLC) method for ionic liquids.1,2
Experimental Section The ionic liquid 1-propyl-2,3-dimethylimidazolium tetrafluoroborate ([PDMIM][BF4]) was purchased from Hang Zhou Chemer Chemical Co., Ltd. Its purity was above 99 % (mass), with the following certified amounts of impurities: [Cl-] < 500 ppm, water < 1000 ppm. The hydrocarbons provided by Beijing Chemical Reagents Company were analytical reagents. The solutes were used without further purification. The GLC apparatus, column preparation, packing method, and experimental process in this work are the same as those described by Zhou.1,2 In this work, dry nitrogen was used as the carrier gas, and ethanol was used as solvent to coat the ionic liquid onto the solid support. The values of infinite dilution, γ∞i , were obtained by the equation proposed by Cruickshank et al.3 and Everett.4 For all solutes, values of the vapor pressure of the pure liquid solute (i), P0i , were calculated from the Antoine equation, with Antoine coefficients given by Boublik et al.,5 which are given in Table 1. The liquid molar volumes of pure solute, V0i , were estimated using experimental values of their densities; the partial molar volumes of the solute, V∞i , have been assumed to be equal to V0i . Values of B11 and B12 have been estimated according to the Tsonopolous method6 with an uncertainty of < ( 10 cm3‚mol-1. The critical parameters needed for the calculations were available from the literature,6 which are given in Table 2. The mixed critical properties, Pcij, Tcij, Vcij, and Zcij and mixed acentric factor ωij were calculated by using equations given in the literature.6,7 The pressure drop was recorded by GC automatically with an uncertainty of ( 0.2 kPa. The errors in the γ∞i were obtained from the law of propagation of errors. The uncertainties in the measured and derived quantities are listed in Table 3. * Corresponding author. E-mail:
[email protected].
∞ Figure 1. Plot of ln γi,3 vs 1/T for the solutes: 9, pentane; b, hexane; 2, heptane; 1, octane; [, nonane; solid triangle pointing left, decane; solid triangle pointing right, cyclohexane; solid oval, methylcyclohexane; f, 2,2,4-trimethylpentane.
∞ Figure 2. Plot of ln γi,3 vs 1/T for the solutes: 9, benzene; b, toluene; 2, ethyl benzene; 1, m-xylene; [, p-xylene; solid triangle pointing left, o-xylene.
Results and Discussion The values of γ∞i of different solutes in [PDMIM][BF4] obtained over a temperature range of 303.15 K to 363.15 K were listed in Table 4. The results of γ∞i were correlated with temperature by the following equation ln γ∞i ) a +
10.1021/je6005696 CCC: $37.00 © 2007 American Chemical Society Published on Web 06/13/2007
b (T/K)
(1)
Journal of Chemical and Engineering Data, Vol. 52, No. 4, 2007 1489 Table 1. Vapor Pressure P0i of the Solutes (i) from T ) 303.15 K to 363.15 K P0i /kPa solutes (i)
T/K ) 303.15
T/K ) 313.15
pentane hexane heptane octane nonane decane 2,2,4-trimethylpentane cyclohexane methylcyclohexane
82.0 24.9 7.79 2.46 0.782 0.245 8.33 16.2 7.83
116 37.3 12.3 4.14 1.41 0.473 13.0 24.6 12.2
cyclohexene styrene
16.0 1.08
benzene toluene ethylbenzene o-xylene m-xylene p-xylene
15.9 4.89 1.68 1.78 1.49 1.55
T/K ) 323.15
T/K ) 333.15
T/K ) 343.15
T/K ) 353.15
T/K ) 363.15
Alkanes 159 54.1 18.9 6.69 2.41 0.865 19.5 36.3 18.4
214 76.4 28.1 10.5 4.03 1.51 28.6 51.9 27.0
283 105 40.5 15.9 6.31 2.52 43.5 72.5 38.6
367 143 57.1 23.1 9.81 4.06 56.8 99.0 53.9
480 189 78.6 33.4 14.5 6.33 77.4 132 73.6
22.6 1.89
Alkenes 35.4 3.18
48.1 5.14
70.4 8.02
92.7 12.1
129 17.8
24.3 7.89 2.87 2.04 2.55 2.27
Alkyl Benzenes 36.2 12.3 4.69 3.40 4.18 4.34
52.2 18.6 7.40 5.44 6.63 6.94
73.5 27.2 11.3 8.43 10.2 10.5
101 38.9 16.8 12.7 15.2 15.6
136 54.3 24.3 18.6 22.0 22.7
Table 2. Critical Constants Zc, Tc, Pc, and Vc and Acentric Factors ω of the Solutes and the Carrier Gas Used in the Calculation of the Virial Coefficients Tc
Pc
Vc
K
bar
cm3·mol-1
ω
solute (i)
Zc
pentane hexane heptane octane nonane decane cyclohexane methylcyclohexane 2,2,4-trimethylpentane
0.268 0.264 0.261 0.259 0.252 0.256 0.273 0.268 0.266
Alkanes 470 508 540 569 595 618 554 572 544
33.7 30.3 27.4 24.9 22.9 21.1 40.7 34.7 25.7
311 368 428 492 555 624 308 368 470
0.252 0.30 0.350 0.399 0.445 0.49 0.211 0.235 0.304
cyclohexene styrene
0.27 0.274
Alkenes 560 647
42.9 39.4
292 374
0.210 0.257
benzene toluene ethyl benzene o-xylene m-xylene p-xylene nitrogen
Alkyl Benzenes 0.268 562 49.0 0.264 592 41.1 0.263 617 36.1 0.263 630 37.3 0.259 617 35.4 0.259 616 35.1 0.290 126 33.5
256 316 374 370 375 378 89.5
0.210 0.264 0.304 0.312 0.327 0.322 0.0400
Table 3. Uncertainties in the Measured and Derived Quantities parameters
uncertainty
tr-tG U0 Pi Po J P0i n3 ∞ γi,3
( 3.3 % ( 0.5 % ( 0.6 % ( 0.02 % (1% ( 0.01 % to ( 0.25 % ( 0.5 % (4%
According to the Gibbs-Helmholtz equation, the value for the partial molar excess enthalpy at infinite dilution, HE,∞ i , can be obtained from the slope of a straight line derived from eq 1.
∞ Figure 3. Plot of ln γi,3 vs 1/T for the solutes: 9, cyclohexene; b, styrene.
The coefficients a and b, the correlation coefficient R2, the standard deviation σ of the fitted equation, γ∞i at 298.15 K calculated using eq 1, and values of HE,∞ derived from eq 1 are i listed in Table 5. The plots of measured ln γ∞i vs 1/T values are given in Figures 1 to 3, which showed a fairly good fitting quality of eq 1. The selectivity S∞ij is defined below8 S∞ij
)
γi,3∞ γj,3∞
(2)
The values of selectivity, S∞ij , for the separation of a hexane (i)/benzene (j) mixture at T ) 298.15 K using different ILs and some very polar solvents obtained from the literature9,10 and from this work are presented in Table 6. The results indicated that [PDMIM][BF4] is an ideal extraction solvent for separation of the hexane and benzene binary system. A more accurate treatment for infinite dilution activity coefficient measurement by GC was discussed in the work of Nutelet and Jaubert,11 and the retention mechanism of neutral organic compounds on the polar liquid stationary phase was investigated by Ali and Poole.12 On the basis of their analysis,
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Journal of Chemical and Engineering Data, Vol. 52, No. 4, 2007
Table 4. Experimental Activity Coefficients at Infinite Dilution for Various Solutes in the Ionic Liquid 1-Propyl-2,3-dimethylimidazolium Tetrafluoroborate as the Stationary Phase at Temperatures of 303.15 K to 363.15 K T/K ) 303.15
solutes (i) pentane hexane heptane octane nonane decane cyclohexane methylcyclohexane 2,2,4-trimethylpentane
T/K ) 313.15
236.7 364.4 644.7 864.8 1843 9813 149.2 251.5 611.6
T/K ) 323.15
T/K ) 333.15
T/K ) 343.15
T/K ) 353.15
T/K ) 363.15
92.81 142.7 227.4 369.4 297.0 2579 64.7 103.2 259.6
71.52 111.0 173.8 299.1 170.4 1566 52.2 82.1 208.6
59.77 90.25 134.6 244.2 102.6 1164 43.2 66.1 169.7
48.47 75.11 109.5 202.9 69.5 814.2 36.1 54.2 142.0
Alkanes 120.5 187.0 307.8 475.1 602.3 3788 83.3 134.3 333.4
162.0 250.5 441.1 634.4 944.0 5975 112.8 182.6 439.9
cyclohexene styrene
47.24 6.606
37.13 5.314
benzene toluene ethylbenzene o-xylene m-xylene p-xylene
4.239 7.082 16.81 11.33 14.93 14.22
3.551 6.048 13.50 9.341 12.11 11.50
Alkenes 30.18 4.587 Alkyl Benzenes 3.123 5.351 11.16 7.855 10.21 9.645
24.34 3.817
20.65 3.378
17.31 2.967
14.62 2.653
2.745 4.594 9.630 6.793 8.773 8.414
2.436 4.323 8.356 6.022 7.734 7.367
2.193 3.861 7.396 5.455 6.948 6.576
2.011 3.514 6.616 4.970 6.253 5.980
Table 5. Coefficients of Equation 1, a and b, Correlation Coefficient R2, γ∞i at 298.15 K Calculated Using Equation 1, Values of HE,∞ Derived i from Equation 1, and Standard Deviation σ b HE,∞ i
b solute i
R2
K
-4.07 -3.67 -4.34 -2.02 -12.7 -5.93 -3.68 -3.78 -2.42
2874 2885 3264 2653 6118 4580 2625 2813 2667
Alkane 0.998 0.998 0.999 0.999 0.999 0.999 0.999 0.999 0.999
cyclohexene styrene
-3.21 -3.62
2138 1662
Alkene 0.999 0.998
benzene toluene ethylbenzene o-xylene m-xylene p-xylene
-3.07 -2.28 -2.81 -2.55 -2.58 -2.58
1362 1278 1696 1582 1576 1509
pentane hexane heptane octane nonane decane cyclohexane methylcyclohexane 2,2,4-trimethylpentane
a
a
Alkyl Benzenes 0.9987 0.9975 0.9975 0.9967 0.9967 0.9962
kJ·mol-1
σ
262.3 406.0 740.6 971.9 2490 1.247‚103 168.1 285.7 682.1
23.89 23.99 27.14 22.06 50.87 38.08 21.82 23.39 22.17
0.0411 0.0384 0.0350 0.0266 0.0654 0.0347 0.0288 0.0246 0.0283
52.50 7.060
17.78 13.82
0.0100 0.0210
4.473 7.437 17.79 15.74 14.97 11.96
11.32 10.63 14.10 13.15 13.10 12.55
0.0145 0.0193 0.0256 0.0266 0.0276 0.0284
Range of uncertainties is within ( 4 %. b Range of uncertainties is within ( 6 %.
Table 6. Selectivities, S∞ij , at Infinite Dilution of Various Solvents for the Hexane (i)/Benzene (j) Separation at T ) 298.15 K
a
γ∞i 298.15Ka
solvents
S∞ij
sulfolanea dimethylsulfoxidea diethylene glycola N-methyl-2-pyrrolidinonea anilinea [MMIM][BTI]b [EMIM][EtOSO3]a [BMIM][BTI]b [HMIM][PF6]a [HMIM][BF4]a [BMIM][BF4]c [MBPY][BF4]b [OMIM][Cl]b [PDMIM][BF4]d
30.5 22.7 15.4 12.5 11.2 27 41.4 15 21.6 23.1 63.7 18 9 90.77
Ref 9. b Ref 10. c Ref 1. d This work.
the values of γ∞i reported in this work might have a tendency of underestimation.
Literature Cited (1) Zhou, Q.; Wang, Li.-S. Activity Coefficients at Infinite Dilution of Alkanes, Alkenes and Alkyl benzenes in 1-Butyl-3-methylimidazolium Tetrafluoroborate Using Gas-Liquid Chromatography. J. Chem. Eng. Data 2006, 51, 1698-1701. (2) Zhou, Q.; Wang, L.-S.; Wu, J.-S.; Li, M.-Y. Activity Coefficients at Infinite Dilution of Polar Solutes in 1-Butyl-3-methylimidazolium Tetrafluoroborate Using Gas-Liquid Chromatography. J. Chem. Eng. Data 2007, 52, 131-134. (3) Cruickshank, A. J. B.; Windsor, M. L.; Young, C. L. The use of gasliquid chromatography to determine activity coefficients and second virial coefficients of mixtures. Proc. R. Soc. London 1966, A295, 259270. (4) Everett, D. H. Effect of gas imperfection of G. L. C. measurements: A refined method for determining activity coefficients and second virial coefficients. Trans. Faraday Soc. 1965, 61, 1637-1645. (5) Boublik, T.; Fried, V.; Hala, E. The Vapor Pressure of Pure Substances. Physical science data 17; Elsevier: Amsterdam, The Netherlands, 1984. (6) Reid, R. C.; Prausnitz, J. M.; Sherwood, T. K. The Properties of Gases and Liquids, 3rd ed.; McGraw-Hill Chemical Engineering Series: New York, 1977.
Journal of Chemical and Engineering Data, Vol. 52, No. 4, 2007 1491 (7) Prausnitz, J. M.; Lichtenthaler, R. N.; Azevedo, E. G. Molecular Thermodynamics of Fluid Phase Eqilibria, 2nd ed.; Prentice Hall: New York, 1986. (8) Tiegs, D.; Gmehling, J.; Medina, A.; Soares, M.; Bastos, J.; Alessi, P.; Kikic, I. DECHEMA Chemistry Data Series IX, Part 1. DECHEMA: Frankfurt/Main, 1986. (9) Letcher, T. M.; Marciniak, A.; Marciniak, M.; Doman´ska, U. Activity coefficients at infinite dilution measurements for organic solutes in the ionic liquid 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide using g.l.c. at T ) (298.15, 313.15, and 333.15) K. J. Chem. Thermodyn. 2005, 37, 1327-1331. (10) Deenadayalu, N.; Thango, S. H.; Letcher, T. M.; Ramjugernath, D. Measurement of activity coefficients at infinite dilution using polar and non-polar solutes in the ionic liquid 1-methyl-3-octyl-imidazolium
diethyleneglycolmonomethylethersulfate at T ) (288.15, 298.15, and 313.15) K. J. Chem. Thermodyn. 2006, 38, 542-546. (11) Nutelet, F.; Jaubert, J.-N. Accurate measurements of thermodynamic properties of solutes in ionic liquids using reverse gas chromatography. J. Chromatogr. A 2006, 1102, 256-267. (12) Ali, Z.; Poole, C. F.; Insights into the retention mechanism of neutral organic compounds on polar chemically bonded stationary phases in reversed phase liquid chromatography. J. Chromatogr. A 2004, 1052, 199-204. Received for review December 14, 2006. Accepted May 2, 2007.
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