Experimental Determination and Prediction of Gas Solubility Data for

Figure 1 Experimental and predicted Henry coefficients for CH4 (1) in H2O (2): experimental data from this work (▫); different authors (Dortmund Dat...
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Ind. Eng. Chem. Res. 2003, 42, 5392-5398

Experimental Determination and Prediction of Gas Solubility Data for Methane + Water Solutions Containing Different Monovalent Electrolytes Jo1 rn Kiepe,† Sven Horstmann,‡ Kai Fischer,‡ and Ju 1 rgen Gmehling*,† Department of Industrial Chemistry, University of Oldenburg, D-26 111 Oldenburg, Germany, and Laboratory for Thermophysical Properties (LTP GmbH), Institute at the University of Oldenburg, D-26111 Oldenburg, Germany

Gas solubility data of methane (CH4) in aqueous electrolyte solutions were measured using the static synthetic method in a temperature range from 313 to 373 K, at pressures up to 10 MPa, and with molalities up to 8 mol‚(kg of water)-1. The experimental P-x data were used to fit interaction parameters for an equation of state approach, which consists of a combination of the predictive Soave-Redlich-Kwong (PSRK) group contribution equation of state and the LIFAC method for the prediction of vapor-liquid equilibria in systems with strong electrolytes. Furthermore, Henry coefficients were derived from these experimental P-x data and compared to the results of the extended PSRK model. 1. Introduction For many applications, the influence of electrolytes on the phase equilibrium behavior has to be considered for the design of the industrial processes. Important examples are the gas antisolvent salt crystallization, petroleum and natural gas exploitation, formation of gas hydrates, and various absorption processes in petroleum refining, the gas processing industry, coal gasification, and environmental protection. For nonelectrolyte systems, the predictive Soave-Redlich-Kwong (PSRK) group contribution equation of state (EoS)1,2 is widely integrated in process simulations for the prediction of vapor-liquid and gas-liquid equilibria. Therefore, the PSRK EoS was extended by combination with the LIFAC group contribution method3 in order to calculate also the phase equilibrium of systems containing strong electrolytes and supercritical components. Hereby, the influence of the strong electrolytes on the activity coefficients of the nonelectrolytes is considered using the LIFAC model in the PSRK mixing rule.4 Whereas the published group interaction parameters of the PSRK and the LIFAC model can directly be used, only the new gas-ion interaction parameters introduced have to be fitted to experimental data. A large number of gas solubility data for the systems CO2 + H2O containing several potassium and sodium salts obtained with the static synthetic technique have already been presented in former papers.5,6 In this work, the solubilities of methane in several aqueous electrolyte solutions at temperatures between 40 and 100 °C and pressures up to 10 MPa are measured as an ongoing process for the extension of the new PSRK method. The experimental data are presented in comparison to PSRK * To whom correspondence should be addressed. Tel.: +49-(0)441-798-3831. Fax: +49-(0)441-798-3330. E-mail: [email protected]. † University of Oldenburg. ‡ Institute at the University of Oldenburg.

calculations using the obtained PSRK parameters to show the influence of the different ionic species on the phase equilibrium behavior. The reliability of the experimental approach has been proved on the basis of experimental data for the salt-free system at temperatures where data are available. 2. Experimental Section 2.1. Materials. Water was distilled twice and then degassed as described before.7 Methane (MG, purity 99.995%) was used without any further purification. Potassium chloride and bromide as well as lithium chloride and bromide (Fluka, purity >99.5%) were dried in a vacuum oven at 80 °C. 2.2. Apparatus and Procedure. For the measurement of the gas solubility, the same static apparatus was used as that described by Kiepe et al.5 The system pressure is measured at constant temperature for different overall compositions using this synthetic method. The apparatus used, which is previously described in detail by Fischer and Wilken,8 can be operated at temperatures between 200 and 500 K and pressures up to 15 MPa. To determine the feed compositions, the quantities of pure substances charged into the stirred equilibrium cell have to be known precisely. Before evacuation, the salts are weighed into the cell, which is mounted in a thermoregulated oil bath. Additionally, the purified and degassed water is charged into the cell using a piston injector (model 2200-801, Ruska), which allows the precise recording of volume differences. After equilibrium has been reached, the pressure inside the cell is measured with a pressure sensor (model PDCR 911, Druck; range: 0-13.5 MPa) and the temperature is monitored with a Pt100 resistance thermometer (model 1560, Hart Scientific). Methane is kept in a thermoregulated gas storage of 300 cm3 and can be added stepwise into the cell containing the aqueous electrolyte solution. The precise amount of gas

10.1021/ie030386x CCC: $25.00 © 2003 American Chemical Society Published on Web 08/21/2003

Ind. Eng. Chem. Res., Vol. 42, No. 21, 2003 5393

taken from the storage can be determined by the difference in the pressure in the gas storage before and after filling. The pressure sensors of the equilibrium cell, the piston injector, and the gas storage were calibrated for the different temperatures considered using a pressure balance (model 21000, Desgranges & Huot). The evaluation procedure is quite complex and described in detail by Fischer and Wilken8 because only temperature, pressure, total loadings, and total volumes are measured. Therefore, the compositions of the coexisting phases have to be determined by evaluation of the raw data. Necessarily, liquid densities of aqueous electrolyte mixtures were measured as a function of the temperature and salt content using a vibrating tube densimeter (model DMA 4500, Anton Paar)9 in order to determine the exact volume of the liquid phase. From the total volume of the cell, the remaining gas-phase volume can be calculated precisely. At given equilibrium conditions (temperature, gas-phase volume, and pressure), the amounts of CH4 in the gas and thus in the liquid phase can be obtained. Because of the small solubility of methane in water, the liquid volume of the sample had to be as large as possible. The optimum of the liquid phase was found to be 90% of the total volume of the cell. Several effects such as small amounts of solvents in the gas phase, the compressibility of the solvent under the gas pressure, the partial molar volume of the dissolved gas, and the solvent activity coefficient cannot be neglected because they have an influence on the resulting liquid-phase compositions. They can be taken into account in two different ways as described by Fischer and Wilken.8 In the first approach, an iterative isothermal and isochoric algorithm solving the mass and volume balances is used, whereas in the second one, EoS models, which offer the probability of providing the auxiliary desired quantities given above directly, are taken advantage of. For the systems considered, the reliability of the data treatment in both methods was tested, whereby identical results were obtained. 3. Results and Discussion For the salt-free methane + water system, the experimental gas solubilities obtained using the EoS raw data treatment approach are listed in Table 1. The experimental results for the electrolyte systems can be found in Tables 2-10. Henry coefficients H12 were derived using the EoS data treatment by calculating

H12 ) lim

x1f0

f1 ) φ∞1 Ps2 x1

where f1 is the fugacity of the gas in the gas phase, x1 the mole fraction of the gas in the liquid phase, φ∞1 the fugacity coefficient of the gas at infinite dilution, and Ps2 the vapor pressure of the mixture (water + salt). The values are given in Table 11. Experimental and predicted Henry coefficients (PSRK) are plotted as a function of temperature in Figure 1, whereby a typical temperature dependence of the Henry coefficients is observed. The Henry coefficients increase

Table 1. Experimental Gas Solubility Data for the System CH4 (1) + H2O (2) 313.35 K

353.18 K

373.29 K

x1

P/kPa

x1

P/kPa

xl

P/kPa

0.000 00 0.000 09 0.000 23 0.000 28 0.000 32 0.000 71 0.000 86 0.001 15 0.001 26 0.001 45 0.001 54

7.28 432.97 1097.9 1307.4 1517.7 3491.2 4307.1 6001.0 6646.3 7821.3 8425.7

0.000 00 0.000 05 0.000 10 0.000 14 0.000 42 0.000 59 0.000 84 0.000 98 0.001 17 0.001 24

46.47 340.43 657.24 952.84 2841.1 4032.8 5858.9 6926.9 8417.6 9025.3

0.000 00 0.000 07 0.000 16 0.000 26 0.000 52 0.000 93 0.001 08 0.001 25

101.42 544.59 1137.1 1793.4 3637.0 6695.3 7831.5 9259.5

Table 2. Experimental Gas Solubility Data for the System CH4 (1) + H2O (2) + KCl (3) at 40 °C and Different Salt Concentrations m ) 0.99 mol‚(kg of water)-1 and T ) 313.51 K

m ) 2.49 mol‚(kg of water)-1 and T ) 313.17 K

m ) 3.99 mol‚(kg of water)-1 and T ) 313.15 K

x1,salt-free

P/kPa

x1,salt-free

P/kPa

x1,salt-free

P/kPa

0.000 00 0.000 09 0.000 18 0.000 24 0.000 31 0.000 59 0.000 78 0.001 02 0.001 14 0.001 31 0.001 52

6.87 480.84 904.99 1220.2 1592.3 3184.5 4306.8 5792.1 6530.9 7703.4 9180.3

0.000 00 0.000 07 0.000 14 0.000 19 0.000 28 0.000 50 0.000 69 0.000 94 0.001 07 0.001 22 0.001 36

6.27 419.39 795.51 1129.1 1616.4 2993.1 4262.3 6016.9 7094.4 8203.0 9341.0

0.000 00 0.000 07 0.000 15 0.000 20 0.000 24 0.000 48 0.000 66 0.000 89 0.000 98 0.001 10 0.001 21

5.78 435.03 932.23 1219.0 1480.4 3093.6 4337.0 6055.2 6817.3 7762.2 8735.2

Table 3. Experimental Gas Solubility Data for the System CH4 (1) + H2O (2) + KCl (3) at 80 °C and Different Salt Concentrations m ) 0.99 mol‚(kg of water)-1 and T ) 353.29 K

m ) 2.50 mol‚(kg of water)-1 and T ) 353.17 K

m ) 3.99 mol‚(kg of water)-1 and T ) 353.13 K

x1,salt-free

P/kPa

x1,salt-free

P/kPa

x1,salt-free

P/kPa

0.000 00 0.000 07 0.000 15 0.000 20 0.000 29 0.000 46 0.000 63 0.000 79 0.001 09 0.001 24

45.28 511.56 1056.7 1416.6 2048.1 3245.5 4528.6 5714.5 8202.3 9512.8

0.000 00 0.000 07 0.000 11 0.000 15 0.000 21 0.000 42 0.000 60 0.000 73 0.000 95 0.001 07 0.001 13

42.85 536.94 886.93 1180.0 1603.3 3202.4 4731.1 5819.9 7844.2 8919.7 9552.1

0.000 00 0.000 08 0.000 12 0.000 18 0.000 24 0.000 66 0.000 69 0.000 83 0.000 93 0.001 01

41.86 696.76 1000.4 1473.3 1977.5 5797.1 6055.8 7423.7 8494.3 9241.7

with the temperature (reduction of the methane solubility) until a maximum value is reached. A further increase of the temperature leads to decreasing values. The variety of literature values is in good agreement with the Henry coefficients derived from the new experimental data, which can be seen as proof for the reliability of the data measured in this work. All available data for methane + water systems taken from the Dortmund Data Bank (DDB 2003) were evaluated, reduced, and finally used to optimize the required interaction parameters given in Table 12. These parameters provide a reliable calculation within a large range of temperatures and pressures up to the critical point of water (see Figure 1). In Figure 2, experimental P-x data for the salt-free system

5394 Ind. Eng. Chem. Res., Vol. 42, No. 21, 2003 Table 4. Experimental Gas Solubility Data for the System CH4 (1) + H2O (2) + KCl (3) at 100 °C and Different Salt Concentrations

Table 7. Experimental Gas Solubility Data for the System CH4 (1) + H2O (2) + LiCl (3) at 40 °C and Different Salt Concentrations

m ) 1.01 mol‚(kg of water)-1 and T ) 373.17 K

m ) 2.49 mol‚(kg of water)-1 and T ) 373.21 K

m ) 3.99 mol‚(kg of water)-1 and T ) 373.19 K

m ) 2.49 mol‚(kg of water)-1 and T ) 313.20 K

m ) 4.99 mol‚(kg of water)-1 and T ) 313.12 K

m ) 7.99 mol‚(kg of water)-1 and T ) 313.09 K

x1,salt-free

P/kPa

x1,salt-free

P/kPa

x1,salt-free

P/kPa

x1,salt-free

P/kPa

x1,salt-free

P/kPa

x1,salt-free

P/kPa

0.000 00 0.000 06 0.000 10 0.000 12 0.000 17 0.000 22 0.000 43 0.000 79 0.000 98 0.001 17 0.001 29

97.55 501.37 806.39 933.72 1288.9 1641.0 3125.5 5748.5 7205.2 8695.3 9665.7

0.000 00 0.000 06 0.000 12 0.000 17 0.000 23 0.000 46 0.000 81 0.000 89 0.001 05 0.001 16

91.59 559.71 1003.8 1387.5 1798.3 3595.6 6519.4 7244.8 8617.6 9665.4

0.000 00 0.000 06 0.000 11 0.000 15 0.000 21 0.000 52 0.000 67 0.000 86 0.001 02 0.001 11

87.21 530.79 971.13 1257.3 1803.6 4368.6 5724.8 7433.9 8967.7 9790.5

0.000 00 0.000 08 0.000 13 0.000 18 0.000 22 0.000 36 0.000 63 0.000 73 0.000 92 0.000 99 0.001 03

5.67 507.22 877.96 1233.0 1534.3 2502.9 4586.4 5392.6 7029.4 7692.5 8102.8

0.000 00 0.000 06 0.000 09 0.000 12 0.000 17

4.70 473.03 814.33 1022.0 1444.8

0.000 00 0.000 04 0.000 08 0.000 14 0.000 25 0.000 37 0.000 47 0.000 54 0.000 64 0.000 72

3.45 481.79 903.85 1548.4 2881.9 4312.1 5642.9 6619.3 8098.0 9483.0

Table 5. Experimental Gas Solubility Data for the System CH4 (1) + H2O (2) + KBr (3) at 40 °C and Different Salt Concentrations m ) 2.51 mol‚(kg of water)-1 and T ) 313.17 K

m ) 5.01 mol‚(kg of water)-1 and T ) 313.15 K

Table 8. Experimental Gas Solubility Data for the System CH4 (1) + H2O (2) + LiCl (3) at 80 °C and Different Salt Concentrations m ) 2.50 mol‚(kg of water)-1 and T ) 353.21 K

m ) 4.85 mol‚(kg of water)-1 and T ) 353.28 K

x1,salt-free

P/kPa

x1,salt-free

P/kPa

x1,salt-free

P/kPa

x1,salt-free

P/kPa

0.000 00 0.000 09 0.000 15 0.000 30 0.000 51 0.000 71 0.000 93 0.001 09

6.98 496.74 837.08 1680.5 2924.7 4141.4 5660.0 6723.4

0.000 00 0.000 10 0.000 13 0.000 21 0.000 37 0.000 57 0.000 69 0.000 85 0.001 00

6.01 678.74 891.11 1495.4 2719.3 4274.9 5296.7 6738.4 8153.3

0.000 00 0.000 06 0.000 11 0.000 15 0.000 22 0.000 39 0.000 57 0.000 66 0.000 80 0.000 90

41.57 513.00 872.80 1267.7 1799.9 3250.9 4784.1 5636.5 6945.0 7940.7

0.000 00 0.000 03 0.000 07 0.000 11 0.000 15 0.000 29 0.000 41 0.000 52 0.000 67

38.75 342.28 770.49 1124.7 1578.8 3042.4 4383.3 5647.5 7582.2

Table 6. Experimental Gas Solubility Data for the System CH4 (1) + H2O (2) + KBr (3) at 80 °C and Different Salt Concentrations m ) 2.57 mol‚(kg of water)-1 and T ) 353.23 K

m ) 5.01 mol‚(kg of water)-1 and T ) 353.22 K

x1,salt-free

P/kPa

x1,salt-free

P/kPa

0.000 00 0.000 04 0.000 06 0.000 10 0.000 21 0.000 40 0.000 59 0.000 72 0.000 88 0.001 07

44.52 303.98 490.67 745.15 1510.6 2945.2 4437.3 5438.4 6807.0 8406.2

0.000 00 0.000 04 0.000 09 0.000 26 0.000 47 0.000 61 0.000 71 0.000 80

38.79 382.66 842.23 2351.4 4387.9 5852.0 6893.2 7950.1

methane + water are compared with data taken from the literature10,11 and predictions using the PSRK method. As can be seen, the experimental data of this work are in good agreement with the data of the other authors and the PSRK calculations. For the system CH4 + H2O + KCl, experimental gas solubility data at several fixed salt concentrations up to 4 mol‚(kg of water)-1 were determined experimentally at 40, 80, and 100 °C. In Figure 3a-c, they are compared to the results of the salt-free system and the results of the PSRK model using the interaction parameters fitted. A salting-out effect leading to smaller CH4 solubilities with increasing salt concentration is observed. Parts a-c of Figure 4 show a comparison of the results for

Table 9. Experimental Gas Solubility Data for the System CH4 (1) + H2O (2) + LiBr (3) at 40 °C and Different Salt Concentrations m ) 1.00 mol‚(kg of water)-1 and T ) 313.17 K

m ) 2.50 mol‚(kg of water)-1 and T ) 313.17 K

m ) 5.00 mol‚(kg of water)-1 and T ) 313.17 K

x1,salt-free

P/kPa

x1,salt-free

P/kPa

x1,salt-free

P/kPa

0.000 00 0.000 07 0.000 11 0.000 15 0.000 28 0.000 48 0.000 68

6.85 389.92 619.36 830.99 1582.5 2828.3 4075.6

0.000 00 0.000 89 0.001 75 0.003 16 0.004 41 0.007 34 0.010 13 0.014 32

5.78 335.81 600.20 861.13 1617.4 2786.3 4035.0

0.000 00 0.000 07 0.000 12 0.000 17 0.000 30 0.000 48 0.000 68 0.000 81 0.000 95 0.001 01

4.95 496.26 878.53 1237.7 2245.6 3804.5 5554.2 6784.2 8136.5 8776.9

CH4 + H2O + LiCl, LiBr, and KBr, respectively, at 40 °C and different salt concentrations. It can be seen that the predictions performed by the extended PSRK approach are also in good agreement with the experimental data. Furthermore, it is shown that LiCl has the strongest salting-out effect, followed by LiBr, KCl, and KBr, which is also illustrated in Table 11 regarding the derived Henry coefficients [H12(LiCl) > H12(LiBr) > H12(KCl) > H12(KBr)]. The regressed interaction parameters are given in Table 13, whereby for systems containing methane and water, no further short-range parameters had to be fitted for the gas-cation or gas-anion interactions because the middle-range

Ind. Eng. Chem. Res., Vol. 42, No. 21, 2003 5395 Table 10. Experimental Gas Solubility Data for the System CH4 (1) + H2O (2) + LiBr (3) at 80 °C and Different Salt Concentrations m ) 0.99 mol‚(kg of water)-1 and T ) 353.15 K

m ) 2.47 mol‚(kg of water)-1 and T ) 353.17 K

m ) 4.99 mol‚(kg of water)-1 and T ) 353.22 K

x1,salt-free

P/kPa

x1,salt-free

P/kPa

x1,salt-free

P/kPa

0.000 00 0.000 04 0.000 08 0.000 14 0.000 25 0.000 45 0.000 65 0.000 87 0.001 25

46.03 311.37 607.62 1026.3 1812.9 3269.3 4857.7 6635.2 9964.6

0.000 00 0.000 05 0.000 09 0.000 18 0.000 32 0.000 49 0.000 73 0.000 93 0.001 07 0.001 16

43.85 388.94 726.16 1340.7 2416.7 3756.1 5796.7 7756.7 9232.6 10232

0.000 00 0.000 03 0.000 05 0.000 10 0.000 39 0.000 49 0.000 64 0.000 75 0.000 80

38.95 325.06 510.73 954.23 3838.2 4894.3 6529.5 7881.6 8427.2

Table 11. Experimental and Predicted Henry Coefficients of CH4 in the Different Solutions Figure 1. Experimental and predicted Henry coefficients for CH4 (1) in H2O (2): experimental data from this work (9); different authors (Dortmund Data Bank, DDB 2003) (+); original PSRK (s).

Figure 2. Experimental and predicted P-x data for the system CH4 (1) + H2O (2): Experimental data from this work at 313.35 K (]), 353.18 K (0), 373.29 K (O); Davis and Mcketta10 at 310.93 K (+); Carroll et al.11 at 373.15 K (*); PSRK at 313.35 K (s), at 353.18 K (- - -), and at 373.29 K (‚‚‚).

term provides sufficient information about the temperature dependence of the salt effect of the systems considered. Parts a-d of Figure 5 show a comparison of the experimental Henry coefficients for methane in the different solutions at 40 and 80 °C and the results calculated by PSRK. For the Henry coefficients, good results are obtained again and a prediction of the different salt effects of LiCl, LiBr, KCl, and KBr is possible. 4. Conclusions Using a synthetic method, reliable gas solubility data of methane in several aqueous solutions (LiCl, LiBr, KCl, and KBr) were measured up to 10 MPa in a wide concentration and temperature range. The reliability of

system

m/mol‚(kg of water)-1

T/K

Hexp/ MPa

Hcalc/MPa (PSRK)

CH4 (1) + H2O (2)

0 0 0

313.35 353.18 373.29

4595 6296 6449

4688 6184 6352

CH4 (1) + H2O (2) + KCl (3)

0.99 0.99 1.01 2.49 2.50 2.49 3.99 3.99 3.99

313.51 353.29 373.17 313.17 353.17 373.21 313.15 353.13 373.19

5026 6573 6680 5643 6928 7222 6009 7852 7950

5081 6451 6657 5397 6640 6856 6071 7392 7641

CH4 (1) + H2O (2) + KBr (3)

2.51 2.57 5.01 5.01

313.17 353.23 313.15 353.22

5380 6928 6861 8696

5207 6417 6497 7867

CH4 (1) + H2O (2) + LiCl (3)

2.49 2.50 4.99 4.85 7.99

313.20 6597 353.21 7760 313.12 8324 353.28 9932 313.09 10690

6557 8198 8101 9897 11152

CH4 (1) + H2O (2) + LiBr (3)

1.00 0.99 2.50 2.47 5.00 4.99

313.17 353.15 313.17 353.17 313.17 353.22

5525 6848 5832 7161 7245 9174

5673 7210 6156 7682 7318 9077

the new data was validated by a comparison to the experimental results for the salt-free system from other authors and, furthermore, has already been proven before for carbon dioxide in several aqueous electrolyte mixtures.5 The required gas-solvent interaction parameters for the PSRK method were regressed to the new experimental and literature data, and the gas solubility data obtained from the electrolyte systems were used to fit the gas-ion interaction parameters. The salting-out effect as well as the temperature dependence is represented correctly using these parameters. All systems examined can be described with this set of interactions parameters, which can be seen as a proof of the consistency of the model. The temperature dependence of the different ionic species on the phase equilibria is given correctly without fitting further shortrange parameters for the gas-ion interactions. Concluding, it was possible to apply the PSRK model successfully to electrolyte systems by linking this method

5396 Ind. Eng. Chem. Res., Vol. 42, No. 21, 2003

Figure 3. Experimental and predicted P-x data for the system CH4 (1) + H2O (2) + KCl (3). (a) At 40 °C, experimental data from this work: m ) 0 mol‚(kg of water)-1 (2), m ) 0.99 mol‚(kg of water)-1 (9), m ) 2.49 mol‚(kg of water)-1 (b), m ) 3.99 mol‚(kg of water)-1 ([). (b) At 80 °C, experimental data from this work: m ) 0 mol‚(kg of water)-1 (2), m ) 0.99 mol‚ (kg of water)-1 (9), m ) 2.50 mol‚(kg of water)-1 (b), m ) 3.99 mol‚(kg of water)-1 ([). (c) At 100 °C, experimental data from this work: m ) 0 mol‚(kg of water)-1 (2), m ) 1.01 mol‚(kg of water)-1 (9), m ) 2.49 mol‚(kg of water)-1 (b), m ) 3.99 mol‚ (kg of water)-1 ([); PSRK (s).

Figure 4. Experimental and predicted P-x data at 40 °C for the following systems. (a) For CH4 (1) in H2O (2) + LiCl (3), experimental data from this work: m ) 2.49 mol‚(kg of water)-1 (b), m ) 4.99 mol‚(kg of water)-1 ([); m ) 7.99 mol‚(kg of water)-1 (2). (b) For CH4 (1) in H2O (2) + LiBr (3), experimental data from this work: m ) 1.00 mol‚ (kg of water)-1 (9), m ) 2.50 mol‚(kg of water)-1 (b), m ) 5.00 mol‚(kg of water)-1 ([). (c) For CH4 (1) in H2O (2) + KBr (3), experimental data from this work: m ) 2.51 mol‚ (kg of water)-1 (b), m ) 5.01 mol‚(kg of water)-1 ([); PSRK (s); PSRK salt-free (‚‚‚).

Ind. Eng. Chem. Res., Vol. 42, No. 21, 2003 5397

Figure 5. Experimental and predicted Henry coefficients. (a) For CH4 (1) in H2O (2) + LiCl (3), (b) For CH4 (1) in H2O (2) + KCl (3), (c) For CH4 (1) in H2O (2) + LiBr (3), (d) For CH4 (1) in H2O (2) + KBr (3), experimental data from this work; 40 °C ([), 80 °C (b); PSRK (s). Table 12. Regressed Gas-Solvent Interaction Parametersa for the PSRK Model Used in This Work

a

i

j

aij /K

aj i /K

bij

bj i

cij /K-1

cj i /K-1

CH4

H2O

-1149.10

-1573.20

5.860 40

11.993

-0.005 122

-0.012 25

parij ) aij + bij T + cij T 2.

Table 13. Regressed Gas-Ion Interaction Parameters for the PSRK Model short-range (SR) interaction parameters

middle-range (MR) interaction parameters

i

j

aij /K

aj i /K

bij

bj i

Rij

βij

CH4 CH4 CH4 CH4

K+ Li+ ClBr-

0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0

0.152 48 0.320 13 0.222 75 0.146 40

1.906 52 1.172 90 0.301 54 0.318 83

with the LIFAC model considering systems with very poor solubilities. Acknowledgment The authors thank the “Bundesministerium fur Wirtschaft” via “Arbeitsgemeinschaft industrieller Forschungsvereinigungen” (AIF Project 12219N) for financial support.

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Received for review May 1, 2003 Accepted July 16, 2003 IE030386X