Energy Fuels 2009, 23, 4701–4708 Published on Web 08/19/2009
: DOI:10.1021/ef900649c
Separation of Carbon Dioxide and Sulfur Dioxide Gases Using Room-Temperature Ionic Liquid [hmim][Tf2N] A. Yokozeki† and Mark B. Shiflett*,‡ †
109-C Congressional Drive, Wilmington, Delaware 19807, U.S.A, and ‡DuPont Central Research and Development, Experimental Station, Wilmington, Delaware 19880, U.S.A. Received June 26, 2009. Revised Manuscript Received July 31, 2009
To understand capturing and/or enhanced gaseous selectivity of industrial flue gases containing CO2 and SO2 using room-temperature ionic liquids, we have developed a ternary equation of state (EOS) model for a CO2/SO2/1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]) system. The present model is based on a generic RK (Redlich-Kwong) EOS, with empirical binary interaction parameters of each binary system. These interaction parameters have been determined using our measured VLE (vapor-liquid-equilibrium) data for SO2/[hmim][Tf2N] and CO2/[hmim][Tf2N] and literature data for CO2/SO2. The validity of the present EOS has been checked by conducting ternary VLE experiments for the present system. With this EOS, isothermal ternary phase diagrams and solubility (VLE) behaviors have been calculated for various (T, P, and feed compositions) conditions. For large and equimolar CO2/ SO2 mole ratios, the gaseous selectivity is nearly independent of the amount of the ionic liquid addition. However, for small CO2/SO2 mole ratios the addition of the ionic liquid significantly increases the selectivity. The strong absorption of CO2 and SO2 in this ionic liquid may be practical for the simultaneous capture of these acid gases.
Solubility studies of CO2 in many RTILs have been reported,17-29 and significantly high solubilities are observed even in the physical absorption, relative to those of simple hydrocarbons and N2. In the case of SO2, only a few RTILs have been examined for the binary phase PTx (pressure-temperature-composition) behavior,14 and all of them show much higher solubility of SO2, compared with CO2. For example, Henry’s law constants are 31.30 and 1.64 bar at 298 K for CO2 and SO2 in RTIL, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]), respectively.14 This large difference in the Henry’s law constant suggests the selective capturing of these acid gases. Some authors report on the high SO2 selectivity of separation from CO2 using
1. Introduction Removal of CO2 and SO2 from industrial flue gases in the combustion of fossil fuels is highly important due to their adverse environmental effects. Apart from the conventional removal techniques using limestones1,2 or organic solvents,3,4 room-temperature ionic liquids (RTILs) are being considered as possible candidates for capturing these acidic flue gases.5-16 *To whom correspondence should be addressed. Phone: 302-6952572. Fax: 302-695-4414. E-mail:
[email protected]. (1) Ryu, H. J.; Grace, J. R.; Lim, C. J. Energy Fuels 2006, 20, 1621– 1628. (2) Wu, S.; Uddin, Md. A.; Su, C.; Nagamine, S.; Sasaoka, E. Ind. Eng. Chem. Res. 2002, 41, 5455–5458. (3) Boniface, J.; Shi, Q.; Li, Y. Q.; Cheung, J. L.; Rattigan, O. V.; Davidovits, P.; Worsnop, D. R.; Jayne, J. T.; Kolb, C. E. J. Phys. Chem. A 2000, 104, 7502–7510. (4) DuPont BELCOÒ Clean Air Technologies sells Labsorb regenerative scrubbing systems to remove sulfur dioxide from gas streams while minimizing solid and liquid discharges. http//:www.belcotech. com. (5) Brennecke, J. F.; Maginn, E. J. Purification of gas with liquid ionic compounds; U.S. Patent 6579343, 2003. (6) Wang, Y.; Pan, H.; Li, H.; Wang, C. J. Phys. Chem. B 2007, 111, 10461–10467. (7) Shi, W.; Maginn, E. J. J. Phys. Chem. B 2008, 112, 16710–16720. (8) Wu, W.; Han, B.; Gao, H.; Liu, Z.; Jiang, T.; Huang, J. Angew. Chem., Int. Ed. 2004, 43, 2415–2417. (9) Yuan, X. L.; Zhang, S. J.; Lu, X. M. J. Chem. Eng. Data 2007, 52, 596–599. (10) Mochizuki, Y.; Sugawara, K. Energy Fuels 2008, 22, 3303–3307. (11) Ando, R. A.; Siqueira, L. J. A.; Bazito, F. C.; Torrest, R. M.; Santos, P. S. J. Phys. Chem. 2007, 111, 8717–8719. (12) Huang, J.; Riisager, A.; Wasserscheid, P.; Fehrmann, R. Chem. Commun. 2006, 4027–4029. (13) Huang, J.; Riisager, A.; Berg, R. W.; Fehrmann, R. J. Mol. Catalysis A 2008, 279, 170–176. (14) Anderson, J. L.; Dixon, J. K.; Maginn, E. J.; Brennecke, J. F. J. Phys. Chem. B 2006, 110, 15059–15062. (15) Jiang, Y.-Y.; Zhou, Z.; Jiao, Z.; Li, L.; Wu, Y.-T.; Zhang, Z.-B. J. Phys. Chem. B 2007, 111, 5057–5061. (16) Jiang, X.; Nie, Y.; Li, C.; Wang, Z. Fuel 2008, 87, 79–84. r 2009 American Chemical Society
(17) Shiflett, M. B.; Yokozeki, A. J. Phys. Chem. B 2007, 111, 2070– 2074. (18) Shiflett, M. B.; Kasprzak, D. J.; Junk, C. P.; Yokozeki, A. J. Chem. Thermodyn. 2008, 40, 25–31. (19) Yokozeki, A.; Shiflett, M. B.; Junk, C. P.; Grieco, L. M.; Foo, T. J. Phys. Chem. B 2008, 112, 16654–16663. (20) Shiflett, M. B.; Yokozeki, A. Ind. Eng. Chem. Res. 2005, 44, 4453–4464. Tuma, D.; Xia, J.; Maurer, G. J. Chem. (21) Perez-Salado Kamps, A; Eng. Data 2003, 48, 746–749. (22) Husson-Borg, P.; Majer, V.; Costa Gomes, M. F. J. Chem. Eng. Data 2003, 48, 480–485. (23) Shariati, A.; Peters, C. J. J. Supercrit. Fluids 2004, 30, 139–144. (24) Scovazzo, P.; Camper, D.; Hieft, J.; Poshusta, J.; Koval, C.; Noble, R. Ind. Eng. Chem. Res. 2004, 43, 6855–6860. (25) Liu, Z.; Wu, W.; Han, B.; Dong, Z.; Zhao, G.; Wang, J.; Jiang, T.; Yang, G. Chem.;Eur. J. 2003, 9, 3897–3903. (26) Aki, S. N. V. K.; Mellein, B. R.; Saurer, E. M.; Brennecke, J. F. J. Phys. Chem. B 2004, 108, 20355–20365. (27) Blanchard, L. A.; Gu, G.; Brennecke, J. F. J. Phys. Chem. B 2001, 105, 2437–2444. (28) Shiflett, M. B.; Yokozeki, A. J. Chem. Eng. Data 2009, 54, 108– 114. (29) Carvalho, P. J.; Alvarez, V. H.; Schroder, B.; Gil, A. M.; Marrucho, I. M.; Aznar, M.; Santos, L. M. N. B. F.; Coutinho, J. A. P. J. Phys. Chem. B 2009, 113, 6803–6812.
4701
pubs.acs.org/EF
Energy Fuels 2009, 23, 4701–4708
: DOI:10.1021/ef900649c
Yokozeki and Shiflett
Figure 1. Chemical structure of [hmim][Tf2N].
supported ionic liquid membranes: assuming the ideal selectively without considering the SO2 and CO2 interactions.15 However, the selective capturing of these gases may be misleading as stated in reference 14. Shi and Maginn7 have made similar conclusions, based on their molecular dynamics simulations, although the conditions (T, P, and feed compositions) for their simulations were limited (i.e., with only two cases). In the present study, we clarify these points by constructing the ternary phase diagrams of CO2 þ SO2 þ [hmim][Tf2N] for the first time, using our cubic equation-of-state (EOS) method.17,30 The ternary EOS is based on interaction parameters of each binary system, and the binary interaction parameters were determined from our present VLE (vapor-liquidequilibrium) measurements for SO2/[hmim][Tf2N], our previous measurements17 for CO2/[hmim][Tf2N], and literature data31 for CO2/SO2. To check the validity of the present ternary EOS, VLE experiments for the present ternary system were performed under various T, P, and feed compositions, and the EOS validity was satisfactorily confirmed. Then, the capturing and selectivity of these acid gases with RTIL [hmim][Tf2N] are calculated at several feed, T, and P conditions. The selectivity advantage using this RTIL and the simultaneous CO2/SO2 capture characteristics are discussed based on the present ternary phase calculations.
about 67 mg of [hmim][Tf2N] was loaded into the sample container and heated to 348.15 K under a vacuum of about 10-9 MPa for 24 h to remove trace amounts of water and other volatile impurities. To prevent any corrosion or damage to the microbalance caused by exposure to the SO2, a molecular sieve trap was installed to remove trace amounts (0.9998, CAS No. 7446-09-5) and carbon dioxide (mole fraction purity >0.9999, CAS No. 124-38-9) were purchased from MG Industries (Philadelphia, Pennsylvania). The [hmim][Tf2N] (C12H19N3F6O4S2, Lot No. L58130031 842, CAS No. 382150-50-7) was obtained from EMD Chemicals, Inc. (Gibbstown, New Jersey). Figure 1 provides the chemical structure. The [hmim][Tf2N] ionic liquid sample was dried and degassed by first placing the sample in a borosilicate glass tube and pulling a course vacuum on the sample with a diaphragm pump (Pfeiffer, model MVP055-3) for about 3 h. Next, the sample was fully evacuated using a turbopump (Pfeiffer, model TSH-071) to a pressure of about 4 10-7 kPa while simultaneously heating and stirring the ionic liquid at a temperature of about 348 K for 48 h. The final water content was measured by Karl Fischer titration (Aqua-Star C3000, solutions AquaStar Coulomat C and A), and the ionic liquid contained less than 1 10-4 mass fraction of water. Binary VLE Measurements. We have conducted gas solubility experiments for SO2 and [hmim]Tf2N] using a gravimetric microbalance20 (Hiden Isochema Ltd., IGA 003). Initially, (30) Yokozeki, A. Int. J. Thermophys. 2001, 22, 1057–1071. (31) Dortmund Data Bank (DDB). 2008; http://www.dechema.de.
4702
Energy Fuels 2009, 23, 4701–4708
: DOI:10.1021/ef900649c
Yokozeki and Shiflett
Table 1. Experimental Solubility (PTx) Data for SO2 (1) þ [hmim][Tf2N]2 T/K
P/MPa
100x1
283.2 282.4 283.5 282.8 283.3 283.4 283.5 298.1 298.1 298.1 298.2 298.1 298.1 298.1 298.1 298.1 298.1 298.2 298.1 298.1 298.1 298.1 323.1 323.1 323.1 323.1 323.1 323.1 323.2 323.1 348.2 348.1 348.1 348.1 348.2 348.2 348.1 348.1
0.0107 0.0503 0.0753 0.1002 0.1252 0.1501 0.1750 0.0109 0.0505 0.0753 0.1003 0.1504 0.2004 0.2502 0.3002 0.2505 0.2005 0.1503 0.1004 0.0761 0.0502 0.0111 0.0109 0.0505 0.0754 0.1003 0.1502 0.2001 0.2503 0.3002 0.0110 0.0504 0.0756 0.1003 0.1508 0.2003 0.2500 0.3003
17.1 51.2 61.6 70.6 76.7 82.5 87.5 12.4 37.7 47.7 55.3 66.7 75.2 82.0 88.1 82.1a 75.5a 67.0a 55.5a 48.1a 37.9a 12.9a 4.9 19.2 26.6 32.9 43.1 51.3 58.1 63.9 3.7 12.4 16.9 21.0 28.0 34.3 40.1 45.7
a
Figure 2. Schematic diagram of a sample cell.
(Parker Instruments, 0 to 0.75 MPa). The internal volume of each cell was calculated by measuring the mass of methanol required to completely fill the cell and knowing the density of methanol at the fill temperature. The internal volume of each cell (VT) was 90 ( 2.5 cm3. Ionic liquid was loaded by mass (1.5-25 g) and weighed on an analytical balance with a resolution of 0.1 mg (Mettler Toledo AB304-S) inside a nitrogenpurged drybox. To load ionic liquid in the cell, the pressure gauge was removed and a stainless steel syringe needle (Popper and Son, Inc. model 7937, 18 152.4 mm pipetting needle) that fit through the open ball valve (valve 1) was used for filling. The ball valve was closed, the pressure gauge reconnected, and the cell was removed from the drybox. The cell was connected to the diaphragm pump, with both ball valves open, to remove residual nitrogen. Once evacuated, the ball valve (valve 2) was closed and the cell was weighed to obtain the initial ionic liquid mass. The CO2/SO2 gas mixtures were also loaded by mass (0.31.5 g) from a high pressure gas cylinder. Three CO2/SO2 gas mixtures (9.4/90.6, 49.7/50.3, and 91.8/8.2 mol % CO2/SO2) were prepared by weight and analyzed by gas chromatography (GC) (Hewlett-Packard HP6890) using an isothermal (80 °C) method (GS-GASPRO capillary column, 60 m length, 0.32 mm i.d., model 113-4362, Aiglent Technologies, inlet injector temperature 200 °C, thermal conductivity detector temperature 250 °C, helium carrier gas, flow rate of 55 cm3 min-1 with a 20:1 split ratio, injection volume of 25 μL). Special care must be taken when preparing the CO2/SO2 gas mixtures to prevent the SO2 from condensing. The saturation vapor pressure for CO2 at 293 K is 6.0 MPa; however, the saturation pressure for SO2 at 293 K is much lower at 0.35 MPa. Therefore, the total pressure for the three gas mixtures (9.4/90.6, 49.7/50.3, and 91.8/8.2 mol % CO2/SO2) were 0.31, 0.48, and 0.60 MPa, respectively. The five sample cells were placed inside a Plexiglas tank, and the temperature was controlled with an external temperature bath (VWR International, Model 1160S) that circulated water through a copper coil inside the tank. The bath was stirred with an agitator (Arrow Engineering Co., Inc. model 1750), and the temperature was measured with a thermocouple (Fluke 52II thermometer). The temperature was initially set at about 295 K.
Desorption measurements.
systematic errors have been estimated to be less than 0.006 mol fraction at a given T and P. One of the largest sources of uncertainty in the present solubility experiments is due to the buoyancy correction in the data analysis. Analysis of the buoyancy effects requires an accurate measurement of the [hmim][Tf2N] liquid density and SO2 gas density. The NIST REFPROP32 program was used to calculate the SO2 gas density. Accurate liquid density data for [hmim][Tf2N] have been measured by Kumezan et al.33 and were used in our analysis. In the case of SO2 absorption in [hmim][Tf2N] the change in molar liquid volume at the measured T and P conditions is from 0 to -75%, with a minimal affect on the final solubility measurements of 0 to þ0.1% (in mole %). A detailed description of the buoyancy correction is provided in our previous reports. 20,34 The corrected solubility (PTx) data are shown in Table 1 for SO2 in the [hmim][Tf2N] ionic liquid. Ternary VLE Measurement. We have also conducted VLE experiments for the present ternary system (CO2/SO2/[hmim][Tf2N]) at several thermodynamic conditions in order to verify the present EOS model. Five sample cells have been constructed as shown in Figure 2. Each cell was made using Swagelok fittings, two Swagelok ball valves (SS-426S4), stainless steel cylinder, and a pressure gauge (32) Lemmon, E. W.; McLinden, M. O.; Huber, M. L. Standard Reference Data Program REFPROP, version 8.0; National Institute of Standards and Technology: Gaithersburg, MD, 2008. Tuma, D.; Maurer, G. (33) Kumezan, J.; Perez-Salado Kamps, A.; J. Chem. Thermodyn. 2006, 38, 1396–1401. (34) Shiflett, M. B.; Yokozeki, A. AIChE J. 2006, 52, 1205–1219.
4703
Energy Fuels 2009, 23, 4701–4708
: DOI:10.1021/ef900649c
Yokozeki and Shiflett
Table 2. EOS Constants for Pure Compounds Used in the Present Study sulfur dioxide carbon dioxide [hmim][Tf2N]a -1
molar mass /g 3 mol Tc/K Pc/MPa β0 β1 β2 β3 a
64.07 430.64 7.8840 1.002 22 0.450 287 -0.048 279 0.001 2512
44.01 304.13 7.377 1.000 49 0.438 66 -0.104 98 0.062 50
447.42 815.0 1.611 1.0 0.500 36
Taken from our previous work, see ref 17.
Table 3. Optimal Binary Interaction Parameters in Equations 6-8 system (1)/(2)
l12
l21
CO2/[hmim][Tf2N]* 0.348 80 0.322 17 SO2/[hmim][Tf2N] -0.098 62 -0.138 57 0.031 95 0.905 96 CO2/SO2 *
m12 = m21 τ12 = τ21/K -0.409 39 0.151 81 0.0
95.07 0 -2.853
Taken from our previous work, see ref 17.
Figure 4. Isothermal VLE Pxy (pressure-liquid-vapor composition) diagrams of the binary SO2/CO2 system. Lines: the present EOS calculations; solid lines = bubble point curves; broken lines = dew point curves. Symbols: data from REFPROP program.32 (a) T = 273.15 K. (b) T = 333.15 K.
measured. In most cases the cells reached equilibrium in 12 to 24 h. The process was repeated at a higher temperature of about 322 K. The pressure gauges were calibrated using the Paroscientific Model 765-1K pressure transducer. The Fluke thermometer was calibrated using the standard platinum resistance thermometer (SPRT model 5699, Hart Scientific, range 73 to 933 K) and readout (Blackstack model 1560 with SPRT module 2560). The temperature and pressure uncertainties were (0.1 K and (0.005 MPa, respectively. The vapor space of each sample was analyzed by placing a rubber septum over the end of the valve and inserting a hypodermic needle to remove a small sample (25 μL) which was analyzed by GC. The CO2 and SO2 peaks appear at about 3.5 and 12.2 min with a total method run time of 15 min.
3. Thermodynamic Model
Figure 3. Isothermal Px (pressure-liquid composition) phase diagram, or solubility chart. (a) SO2 þ [hmim][Tf2N] binary system, lines: the present EOS model calculations, symbols: the present experimental data; (b) CO2 þ [hmim][Tf2N] binary system, lines: the present EOS calculations, symbols: experimental data taken from refs 17 and 33.
To study the phase behavior of a ternary system of CO2/ SO2/[hmim][Tf2N], we have developed for the first time thermodynamic models based on equations of state (EOS), which have been successfully applied for refrigerant/lubricant oil mixtures30 and various hydrofluorocarbons and CO2 mixtures with ionic liquids.17-20 It is based on a generic Redlich-Kwong (RK) type of cubic EOS: RT aðTÞ P ¼ ð1Þ V - b VðV þ bÞ
The sample cells were vigorously shaken to assist with mixing prior to being immersed in the tank. The water level in the tank was adjusted such that the entire cell was underwater, including the bottom 2 cm of the pressure gauge. The pressure in each cell was recorded until no change in pressure was measured. To ensure the samples were at equilibrium and properly mixed, the cells were momentarily removed from the water bath and vigorously shaken. The cells were placed back in the bath and the process was repeated until no change in pressure was
aðTÞ ¼ 0:427480 4704
R2 Tc2 RðTÞ Pc
ð2Þ
Energy Fuels 2009, 23, 4701–4708
: DOI:10.1021/ef900649c
Yokozeki and Shiflett
Figure 6. Comparison of experimental and calculated VLE data for the ternary CO2/SO2/[hmim][Tf2N] system. Calculated vapor-phase compositions of SO2 (CO2 mole % = 100 - SO2 mole %) are compared with observed SO2 vapor compositions for various experimental conditions (see Table 4). Symbols: open symbols = about 295 K; solid symbols = about 321 K; circle symbols = 9.4/ 90.6 mol % CO2/SO2 feed; square symbols = 49.7/50.3 mol % CO2/ SO2 feed; diamond symbols = 91.8/8.2 mol % CO2/SO2 feed.
kij ¼
b ¼
lij lji ðxi þ xj Þ , lji xi þ lij xj
ð3Þ
The temperature-dependent part of the a parameter in the EOS for pure compounds is modeled by the following empirical form:17-20 e3 X RðTÞ ¼ βk ð1=Tr -Tr Þk , ðTr T=Tc Þ ð4Þ k ¼0
where 0 ai Dna Dni
The coefficients, βk, are determined so as to reproduce the vapor pressure of each pure compound. The a and b parameters for general N-component mixtures are modeled in terms of their respective binary interaction parameters.17-20 N X pffiffiffiffiffiffiffiffi a ¼ ai aj fij ðTÞð1 - kij Þxi xj , i, j ¼1 ai ¼ 0:427480 fij ðTÞ ¼ 1 þ τij=T,
RTci Pci
ð8Þ
where mij = mji, mii = 0, Tci is the critical temperature of the i-th species, Pci is the critical pressure of the i-th species, R is the universal gas constant, and xi is the mole fraction of the ith species. In the above model, there are a maximum of four binary interaction parameters: lij, lji, mij, and τij for each binary pair. However, only two or three parameters are sufficient for most cases. The fugacity coefficient φi of the ith species for the present EOS model, which is needed for the phase equilibrium calculation, is given by: RT 1 a 0 þ bi ln φi ¼ ln PðV -bÞ V - b RTbðV þ bÞ ! 0 0 a ai bi V ð9Þ þ 1 ln þ RTb a Vþb b
Figure 5. Isothermal ternary CO2/SO2/[hmim][Tf2N] phase diagrams calculated by the present EOS model. (a) T = 273.15 K (b) T = 298.15 K.
RTc Pc
ð7Þ
N 1X ðbi þ bj Þð1 - kij Þð1 - mij Þxi xj , 2 i, j ¼1
bi ¼ 0:08664
b ¼ 0:08664
where kii ¼ 0
0
nj6¼i
and bi
Dnb Dni n n j6¼i
= total mole number, and
ni = mole number of the ith species (or xi = ni/n). The explicit forms of a0i and b0i may be useful for readers and are given as: ( ) N X lij lji ðlij - lji Þxi xj 0 pffiffiffiffiffiffiffiffi ai aj fij xj 1 - kij -a ð10Þ ai ¼ 2 ðlji xi þ lij xj Þ2 j ¼1
R2 T Ri ðTÞ Pci
ð5Þ
( ) N X lij lji ðlij - lji Þxi xj -b bi ¼ ðbi þ bj Þð1 - mij Þxj 1 - kij ðlji xi þ lij xj Þ2 j ¼1
where τij ¼ τji , and τii ¼ 0
ð6Þ
ð11Þ
0
4705
Energy Fuels 2009, 23, 4701–4708
: DOI:10.1021/ef900649c
Yokozeki and Shiflett
Table 4. Experimental VLE Data for Ternary Mixtures feed CO2/ feed SO2/ mol % mol % 8.15 6.62 6.03 4.51 8.15 6.62 6.03 42.20 32.81 27.78 7.99 27.78 7.99 76.06 62.26 47.40 34.42 22.49 76.06 62.26 47.40 34.42 22.49
66.73 54.25 51.83 43.67 66.73 54.25 51.83 42.63 33.14 28.06 8.08 28.06 8.08 6.80 5.57 4.24 3.08 2.01 6.80 5.57 4.24 3.08 2.01
feed [hmim] [Tf2N]/mol %
T/K
P/ liquid SO2 MPa calculated/mol %
25.13 39.13 42.13 51.81 25.13 39.13 42.13 15.18 34.05 44.16 83.93 44.16 83.93 17.14 32.17 48.36 62.50 75.50 17.14 32.17 48.36 62.50 75.50
295.2 296.7 294.8 294.5 322.1 322.1 322.1 295.7 294.7 295.2 295.3 320.6 320.6 296.0 296.0 296.0 296.0 296.1 321.5 321.5 321.1 320.2 320.1
0.143 0.115 0.132 0.105 0.172 0.168 0.201 0.391 0.263 0.253 0.119 0.298 0.132 0.384 0.363 0.358 0.356 0.350 0.413 0.398 0.377 0.412 0.419
60.2 50.0 50.7 42.8 44.1 41.9 45.0 59.3 40.5 32.9 8.2 29.1 7.8 14.9 9.6 6.0 3.8 2.2 10.1 7.4 5.1 3.5 2.2
liquid [hmim][Tf2N] calculated/mol %
vapor SO2 calculated/mol %
vapor SO2 measured/mol %
38.8 49.1 47.8 55.9 55.4 57.4 54.1 35.8 54.9 62.0 88.0 67.3 89.8 74.5 79.5 82.6 84.5 86.0 82.3 84.9 87.3 87.8 88.8
78.7 71.2 59.9 54.7 85.5 80.6 75.9 30.4 21.1 16.2 6.3 26.1 12.4 4.4 2.8 1.8 1.1 0.7 5.9 4.4 3.1 2.0 1.2
79.0a 71.7a 62.3a 52.9a 86.1a 80.2a 75.1a 31.0b 20.0b 16.0b 6.0b 27.1b 12.4b 4.3c 2.8c 2.3c 1.6c 1.0c 7.0c 5.0c 3.9c 2.4c 1.2c
a CO2/SO2 gas mixture: (9.4/90.6) mole %; b (49.7/50.3) mole %; c (91.8/8.2) mole %). Liquid CO2 mole % = (100 - Liquid SO2 mole % - Liquid [hmim][Tf2N] mole %). Vapor CO2 mole % = (100 - Vapor SO2 mole %, and Vapor [hmim][Tf2N] = 0 mol %).
The equilibrium solubility for the ternary VLE system can be obtained by solving the following equilibrium conditions: xi φLi ¼ yi φV i
ði ¼ 1, 2, 3Þ
ments (
