Exercise 2
Ionic liquids (ILs) have recently attracted considerable attention for their unique attributes, e.g.
negligible vapour pressure, good stability, and ionic property in contrast to the conventional
molecular solvents, and some encouraging results have been achieved with respect to their
utilization as a benign medium and/or solvent in a reaction and/or separation process. Vapour
pressure data indicate that volatility of solvents can be changed dramatically by the addition
of ionic liquid, while the variation extent is different depending on the nature of both solvent
and ionic liquid involved. As a result, the relative volatility of a component is changed and
even the azeotrope of a binary liquid mixture eliminated.
In literature, the vapour pressure data were measured for three binary systems containing
water, methanol or ethanol with an ionic liquid (IL) 1-ethyl-3-ethylimidazolium
diethylphosphate ([EEIM][DEP]) at varying temperature and IL-content ranging from mass
fraction of 0.10 to 0.85 (mole fraction from 0.0071 to 0.4849) by a quasi-static method and
listed in Tables 1 to 3. The vapour pressures of the pure component at system temperature can
be calculated by Antoine equation with Antoine constants listed in Table 4.
For these binary systems, the vapour phase is fully composed of solvent vapour due to the
non-volatility of IL, and thus the vapour phase composition y1 = 1. Since the vapour phase
composition for such a binary system and for the pure solvent are the same, and the pressure
difference between them is relatively small, the fugacity coefficient correction can be
cancelled out.
According to the data in Tables 1 to 4, pleases to calculate the experimental activity
coefficient of the solvent in an IL-containing binary liquid mixture.
To observe the variation trend of vapour pressure with temperature at different IL-content,
pleases plot the experimental vapour pressure against reciprocal temperature for the binary
system listed at different values of mole fraction [EEIM][DEP], and to evaluate the
evaporation enthalpy of corresponding solvent.
To study the effect of IL on the evaporation enthalpy, you can to construct figures to plot the
enthalpy against the mole fraction of IL for all the mixtures listed.
Table 1, Vapour pressure data of binary system {water (1) + [EEIM][DEP] (2)}
T/K
P/kPa
T/K
P/kPa
T/K
P/kPa
T/K
x1=0.9929
0.9734
0.9392
0.7348
317.63
9.313
318.64
9.352
322.37
9.999
335.67
323.32
12.417
328.63
15.336
328.73
13.708
343.03
330.04
17.104
333.95
19.706
334.78
18.237
348.57
337.05
23.601
338.47
24.119
340.58
23.740
354.81
343.15
30.859
344.41
31.311
346.28
30.475
360.40
348.44
38.586
349.69
38.853
350.76
36.793
366.55
353.97
48.377
354.52
47.442
355.06
43.825
371.31
358.10
57.075
358.11
54.915
359.05
51.389
P/kPa
9.576
13.588
17.498
22.917
29.158
37.269
44.949
Table 2, Vapour pressure data of binary system {methanol (1) + [EEIM][DEP] (2)}
T/K
P/kPa
T/K
P/kPa
T/K
P/kPa
T/K
x1=0.9874
0.9530
0.8968
0.6052
299.20
17.386
300.90
17.011
304.41
15.977
330.07
302.90
21.011
303.56
19.485
309.04
20.320
335.85
306.70
25.347
307.06
23.240
312.75
24.418
341.15
310.58
30.529
311.51
28.841
316.39
29.051
346.66
314.13
36.039
315.46
34.748
320.25
34.773
351.65
317.92
42.869
319.41
41.695
324.51
42.231
356.22
321.32
49.884
323.44
49.950
327.72
48.525
361.20
324.75
57.891
326.85
57.898
331.26
56.515
366.19
Table 3 Vapour pressure data of binary system {ethanol (1) + [EEIM][DEP] (2)}
T/K
P/kPa
T/K
P/kPa
T/K
P/kPa
T/K
x1=0.9817
0.9338
0.8580
0.5151
309.96
14.808
309.80
13.490
310.59
11.648
344.56
314.00
18.301
313.92
16.741
316.24
15.641
349.59
319.06
23.625
318.49
21.170
318.57
17.646
355.84
323.19
28.909
321.24
24.276
323.93
22.978
359.82
327.26
35.060
325.40
29.674
329.23
29.635
365.11
330.78
41.264
329.03
35.216
333.85
36.689
370.80
334.37
48.506
333.54
43.290
339.15
46.313
337.91
56.716
338.72
54.395
342.93
54.503
P/kPa
14.336
18.745
23.771
29.985
37.048
44.985
54.429
65.452
P/kPa
9.139
11.648
15.641
18.686
23.205
29.875
Table 4 Antoine vapour pressure constants of pure compounds
Component
Antoine constants
A
B
C
Ethanol
8.1122
1592.864
226.184
Methanol
8.08097
1582.271
239.726
Water
8.07131
1730.63
233.426
sat
sat
Antoine equation logP = A- B/(t + C), where P is in Torr, and t is temperature in oC.
Reference:
Xiao-Chuan Jiang, Jun-Feng Wang, Chun-Xi Li*, La-Mei Wang, Zi-Hao Wang
Vapour pressure measurement for binary and ternary systems containing water methanol
ethanol and an ionic liquid 1-ethyl-3-ethylimidazolium diethylphosphate
J. Chem. Thermodynamics 39 (2007) 841–846