High-pressure phase behavior of binary mixtures containing ionic liquid [HMP][Tf2N], [OMP][Tf2N] and carbon dioxide

High-pressure phase behavior of binary mixtures containing ionic liquid [HMP][Tf2N], [OMP][Tf2N] and carbon dioxide

Fluid Phase Equilibria 308 (2011) 147–152 Contents lists available at ScienceDirect Fluid Phase Equilibria journal homepage: www.elsevier.com/locate...

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Fluid Phase Equilibria 308 (2011) 147–152

Contents lists available at ScienceDirect

Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid

High-pressure phase behavior of binary mixtures containing ionic liquid [HMP][Tf2 N], [OMP][Tf2 N] and carbon dioxide Joon-Hyuk Yim a , Ha Na Song a , Byung-Chul Lee b , Jong Sung Lim a,∗ a b

Department of Chemical and Biological Engineering, Sogang University, 1 Sinsu-Dong, Mapo-Gu, Seoul, South Korea Department of Chemical Engineering and Nano-Bio Technology, Hannam University, 461-6 Jeonmin-dong, Yuseong-gu, Daejeon 305-811, South Korea

a r t i c l e

i n f o

Article history: Received 15 January 2011 Received in revised form 7 June 2011 Accepted 17 June 2011 Available online 24 June 2011 Keywords: Solubility Ionic liquid Carbon dioxide [HMP][Tf2 N] [OMP][Tf2 N]

a b s t r a c t This paper presents bubble-point pressure data for CO2 in ionic liquids 1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([HMP][Tf2 N]) and 1-octyl-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([OMP][Tf2 N]) at pressures up to approximately 62 MPa and temperatures between 303.15 and 373.15 K. The solubility of CO2 in ionic liquids was measured with a high-pressure variable-volume view cell. At high CO2 concentrations in ionic liquids, the equilibrium pressure increased sharply with increasing CO2 concentrations while the solubility of CO2 in the ionic liquids decreased commensurate to increases in temperature. We have observed that in the [Tf2 N] anion-based ionic liquids, the shorter the alkyl group chain in cation is, the larger the solubility of CO2 in ionic liquid become. The experimental data for the CO2 + ionic liquid system were relatively well correlated using the Peng–Robinson equation of state. © 2011 Elsevier B.V. All rights reserved.

1. Introduction The many advantages of ionic liquids have garnered great attention in various chemical industries as green solvents. Ionic liquids are beneficial for the replacement of traditional organic solvents in organic synthesis and extraction. Ionic liquids can be used as solvents because of their low melting point, and, because of their ionic structure. When ionic liquids are employed as solvents, superior selectivity is obtained when compared to other conventional organic solvents [1,2]. Some product recovery techniques and separation employing ionic liquids are currently under investigation. Distillation exploits the lack of ionic liquids vapor pressure, allowing for facile recovery of volatile products. Hydrophilic products are easily extracted from hydrophobic ionic liquids with water; however, the problem of cross-contamination between the streams has yet to be fully explored. Recovery of nonvolatile or thermally sensitive products from an ionic liquid using diethyl ether and hexane, although successful, can negate the overall goal of organic emission reduction. Based on the desire to greatly reduce or eliminate traditional organic solvents, experiments utilizing another green solvent, supercritical CO2 , for product recovery have been undertaken [5]. In supercritical fluid extraction, ionic liquid/CO2 solutions are vital to the recovery of solutes [3]. For these processes, to choose

∗ Corresponding author. Tel.: +82 2 705 8918; fax: +82 2 705 7899. E-mail address: [email protected] (J.S. Lim). 0378-3812/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2011.06.023

effective ionic liquid for separation, it is important to know the solubility of gas in the ionic liquid that we seek to utilize. The supercritical carbon dioxide (scCO2 ) is the most widely used solvent in various supercritical fluid industries: polymer manufacturing, decaffeination of coffee beans, solvents for extraction, and so on [4]. This is because of non-flammability, non-toxic, non-polar, low critical temperature and pressure values and its affordability. As green solvents, the scCO2 are used in innumerable separation processes [5]. In our research, we studied the solubilities of CO2 in pyrrolidinium based ionic liquids with the [Tf2 N] anion. We measured the solubility of CO2 in ionic liquids, 1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([HMP][Tf2 N]), 1-octylbis(trifluoromethylsulfonyl)imide methylpyrrolidinium ([OMP][Tf2 N]). The range of temperature for the experimental measurements was 303.15–373.15 K in 10 K intervals. The solubility of CO2 was determined by measuring the bubble-point pressure at fixed temperature. 2. Experimental 2.1. Materials The ionic liquids [HMP][Tf2 N] and [OMP][Tf2 N] were purchased from C-TRI (Korea). The purity data of [HMP][Tf2 N] and [OMP][Tf2 N] are shown in Table 1. The ionic liquid sample was placed into the high pressure variable volume view cell for solubility measurement and evacuated by vacuum pump at room temperature for several days. Coulometric Karl Fischer titration

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Table 1 Purity data of [HMP][Tf2 N] and [OMP][Tf2 N]. Ionic liquid

[HMP][Tf2 N]

[OMP][Tf2 N]

Description Water contents Chloride content Assay

Pale yellowish liquid 29 ppm 14 ppm >99%

Brownish liquid 35 ppm 16 ppm >99%

(Metrohm model 684) was performed on a sample of the evacuated ionic liquid. The water mass fraction was about 29 × 10−6 for [HMP][Tf2 N] and less than 35 × 10−6 for [OMP][Tf2 N]. The high purity (99.995%) carbon dioxide (CO2 ) used in our measurements was purchased from Deokyang Gas Co. (Korea). The ionic liquids and CO2 gas were used without further purification. 2.2. Apparatus The solubilities of CO2 in ionic liquids ([HMP][Tf2 N] and [OMP][Tf2 N]) were measured with the high-pressure variablevolume view cell. Fig. 1 shows a schematic diagram of the experimental apparatus for measuring the solubilities of CO2 in ionic liquids. The experimental apparatus used in this work was the same as that used in our earlier research [6,7]. At the heart of the system is the high-pressure variable-volume view cell. The main feature of the variable-volume cell apparatus is that it keeps the overall composition of the system constant throughout the experiment. The cell has a dimension of 16 mm i.d. × 70 mm o.d. and an internal working volume of about 31 cm3 . A piston is placed inside the cell to adjust the cell volume. A pressure generator (High Pressure Equipment Co. model 50-6-15) is used to pressurize water and

there from displace the piston. A change in the cell volume causes a change in the system pressure. A sapphire window is inserted into the view cell to observe the interior of the cell. The system pressure was measured with a high-precision pressure gauge (Dresser Heise model CC-12-G-A-02B, ±0.05 MPa accuracy) placed between the pressure generator and the view cell. The system temperature was measured to within ±0.1 K with an RTD temperature probe inserted into the interior of the cell. A temperature-controlled forced-convection air bath was used to keep the system temperature constant. A visual observation of the interior of the cell through the sapphire window was carried out with borescope (Olympus model R080-044-000-50) and a CCD camera connected to a monitor. A magnetic stirring system was equipped under the cell body to mix the contents of the cell. A stirring bar in the cell was activated by a samarium–cobalt magnet located below the cell, and the magnet was driven by an electric motor. 2.3. Methods An ionic liquid sample was loaded into the high pressure variable-volume view cell. The amount of sample was about 8–9 g. It makes adequate space to agitate the stirring bar in the variable view cell. The piston, stirring bar and sapphire window are inserted into the variable view cell. A piston creates space inside the cell with the pressure generator used to pressurize water. We were able to observe the cell interior though the sapphire window. To remove any entrapped air present in the cell and any dissolved gas and water in the ionic liquid, the cell was evacuated by vacuum pump at room temperature for several days before the experiment. Once the vapor space of the system was fully evacuated, a

Fig. 1. A schematic diagram of the experimental apparatus: (1) water for pressing; (2) pressure generator; (3) pressure gauge; (4) piston; (5) sapphire window; (6) magnetic bar; (7) stirrer; (8) air bath; (9) variable-volume view cell; (10) light source; (11) borescope; (12) CCD camera; (13) monitor; (14) temperature gauge; (15) heater; (16) heating controller.

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Table 2 The critical properties and acentric factor of ionic liquids calculated with a modified Lydersen–Joback–Reid method [12]. Ionic liquids

M (g/mol)

Tb (K)

Tc (K)

Pc (MPa)

ω

[HMP][Tf2 N] [OMP][Tf2 N]

450.46 478.52

879.06 924.82

1235.15 1263.019

2.1694 1.9219

0.4090 0.5011

known amount of CO2 was loaded into the cell. The exact amount of CO2 gas introduced into the cell was determined by weighing the CO2 sample cylinder before and after loading using a balance (Precisa model 1212 M) with accuracy of ±1 mg. To prevent any loss of CO2 gas in the feed line during loading, the CO2 gas in the feed line was recovered into the CO2 sample cylinder by dipping the cylinder into a Dewar flask filled with liquid nitrogen. The uncertainties in measuring ionic liquid and CO2 are 0.2 and 2 mg, respectively. The uncertainty analysis for the composition measurement for each component was performed in accordance with the International Organization of Standardization (ISO) guidelines [8] and was analyzed within ±0.005 mol fraction for each component. The mole fraction of CO2 in ionic liquid was calculated on the basis of known amount of CO2 . Ionic liquid and CO2 were agitated by stirring bar to makes single phase. As the pressure increased, CO2 and ionic liquid reached a homogenous phase. After which, the pressure was slowly reduced until the first CO2 bubble was observed from the solution. At this moment, we measured the pressure of the cell and we noted this pressure as the bubble-point pressure at a fixed CO2 mole fraction and temperature. The pressure reduction rates for the determinations of the bubble-point pressure ranged approximately from 0.05 MPa s−1 for the highest bubble-point pressure case to 0.001 MPa s−1 for the lowest bubblepoint pressure case. The reduction rate was so slow that the effect of the rate on the results of the bubble-point pressure was not observed. After one set of experiments from 303.15 to 373.15 K was finished at a fixed CO2 mole fraction, more CO2 was charged into the cell and a CO2 mole fraction of a new set of experimental systems was recalculated. All the other experiments having increasing CO2 mole fractions were performed in this manner. Every measurement was repeated more than three times at each temperature to obtain accurate data. The uncertainty of the temperature measurement was ±0.1 K and the bubble-point pressure measurement was ±0.01 MPa.

The experimental (CO2 + ionic liquid) data were correlated with the Peng–Robinson equation of state (PR-EoS) [9]. RT



v−b

a(T ) V (V − b) + b(V − b)

(1)

The mixture parameters in ionic liquid phase are calculated from the following four mixing rules: a=

 i

xi xj aij

j

aij = (aii ajj )1/2 (1 − kij ) b=

 i

 bij =

(2)

xi xj bij

(3) (4)

j

bi + bj 2

 (1 − lij )

(5)

In Eqs. (3) and (4), lij and kij are the binary interaction parameters. In Eq. (4), bii = bi and bjj = bj .

Pci





1 + 0.37464 + 1.54226ωi −

0.26992ωi2



  2

 1−

T Tci

(6)

bi =

0.077796RTci Pci

(7)

To calculate the parameters of the PR-EoS, critical temperature (Tc ), critical pressure (Pc ) and acentric factor (ω) of both components CO2 and ionic liquids were needed. Those properties of CO2 are easily obtained from the literature [10], however, those of ionic liquids are not available. Therefore, critical properties of ionic liquids have to be estimated. In this work, to estimate the critical properties of ionic liquids, we used the modified Lydersen–Joback–Reid method [11,12] which is a group contribution method and is known to give a relatively good result especially for the molecules having high molecular weights [12]. Tb /K :

Tb [K] = 198.2 +

Tc /K :

Tc [K] =

Pc /MPa :



nTbM

(8) Tb

0.5703 + 1.0121

Pc [bar] =



nTM −

M



0.2573 +



nPM



nTM

2

2

(9)

(10)

where M is the molecular weight in ionic liquid. The groups considered for the modified Lydersen–Joback–Reid method are presented in the literature [11]. The acentric factor is calculated as [11] ω=

3. Correlation

P=

aii =

0.457235R2 Tci2

(Tb − 43)(Tc − 43) Pc log Pb (Tc − Tb )(0.7Tc − 43) + log

P  c

Pb

−1





(Tc − 43) Pc log Pb (Tc − Tb )



(11)

Acentric factor is calculated by critical properties and normal boiling temperature (Tb for Pb = 0.1 MPa). All the calculated critical properties, the normal boiling temperature and acentric factors of ionic liquids are listed in Table 2. 4. Results and discussion In this paper, the high pressure phase behavior of carbon dioxide in [HMP][Tf2 N] and [OMP][Tf2 N] were measured in the temperature range from 303.15 to 373.15 K in 10 K intervals. The experimental results are given in Tables 3 and 4. Figs. 2a, b, 3a and b also show their bubble-point pressures versus the temperature and CO2 mole fraction, respectively. As can be seen in Fig. 2, the bubblepoint pressure increases linearly with rises in temperature at a fixed CO2 mole fraction. This means that at a fixed pressure, the solubility of CO2 in ionic liquid decreases with rising temperature. Additionally, at a fixed CO2 mole fraction, the CO2 solubility in ionic liquid is dramatically affected by temperature. Fig. 3 shows that as the CO2 mole fraction increases, the bubble-point pressures increase dra-

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Table 3 Solubility data for the [HMP][Tf2 N] + CO2 system. x(CO2 )

T (K)

P (MPa)

x(CO2 )

T (K)

P (MPa)

0.2778

303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15

1.06 1.29 1.55 1.73 1.92 2.22 2.55 2.87 1.68 2.07 2.49 2.86 3.29 3.72 4.18 4.62 2.12 2.59 3.07 3.58 4.13 4.67 5.20 5.83 3.26 3.92 4.68 5.59 6.53 7.52 8.53 9.62

0.6138

303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15

4.04 4.88 5.87 6.96 8.28 9.55 10.95 12.28 4.90 6.10 7.60 9.26 11.17 13.34 15.03 17.06 6.29 9.12 12.50 16.00 19.10 22.67 25.57 28.00 21.72 26.00 30.53 34.73 38.02 41.56 44.63 47.55

0.3827

0.4416

0.5699

0.6797

0.7478

0.8105

matically. So the slope of the solubility pressure with temperature increased sharply with increases in CO2 mole fraction. The bubblepoint pressures also increased with increasing CO2 mole fraction at fixed temperature.

Calculated binary interaction parameters from 303.15 to 373.15 K in 10 K intervals for each system are provided in Table 5. The calculated results from the PR-EoS with mixing rules are illustrated in Fig. 3 along with the experimental data. The correlation

Table 4 Solubility data for the [OMP][Tf2 N] + CO2 system. x(CO2 )

T (K)

P (MPa)

x(CO2 )

T (K)

P (MPa)

x(CO2 )

T (K)

P (MPa)

0.2409

303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15

0.51 0.62 0.74 0.86 0.99 1.17 1.30 1.51 1.02 1.31 1.61 1.87 2.18 2.44 2.69 3.02 1.86 2.22 2.62 3.10 3.52 4.03 4.50 5.03 2.48 3.05 3.62 4.22 4.83 5.48 6.17 6.78

0.6193

303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15

3.51 4.27 5.06 6.00 7.00 8.03 8.99 10.20 4.10 5.17 6.12 7.50 8.75 10.15 11.60 12.99 5.90 7.30 9.18 11.44 13.51 16.08 18.00 20.10 7.35 10.20 13.39 16.45 19.35 22.21 24.30 26.60

0.8176

303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15

16.11 19.99 23.38 26.78 29.50 32.35 34.45 35.92

0.3418

0.4424

0.5230

0.6779

0.7309

0.7758

J.-H. Yim et al. / Fluid Phase Equilibria 308 (2011) 147–152

151

Table 5 Binary interaction parameters for the ionic liquids system. Temperature (K)

[HMP][Tf2 N]

303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15

[OMP][Tf2 N]

k12

k12

l12

l12

0.0640304 0.0623102 0.0624202 0.0635930 0.0636309 0.0643910 0.0632633 0.0621991

0.0473313 0.0481142 0.0473567 0.0499004 0.0515407 0.0496988 0.0466393 0.0423891

0.0578881 0.0561900 0.0546185 0.0537269 0.0515407 0.0496988 0.0466393 0.0423891

0.0561975 0.0556733 0.0560889 0.0571311 0.0581478 0.0584917 0.0601003 0.0594022

model successfully predicts the solubility pressure data at lower mole fraction of CO2 . The mole fraction of CO2 increases, however, the deviation between experimental data and calculated results become grow. Deviations between experimental and calculated values are shown in Table 6. We calculate the average absolute deviation in percentage (AAD%) for each system. As temperature increases the AAD% values of [HMP][Tf2 N] decreased. Whereas the AAD% values of [OMP][Tf2 N] were all similar in temperature range. Fig. 4 compares the solubility data for the [BMP][Tf2 N] [7] + CO2 , [HMP][Tf2 N] + CO2 , [OMP][Tf2 N] + CO2 and [P14,6,6,6][Tf2 N] [6] + CO2 systems at 333.15 K. It shows the effects of different cation on the solubility of CO2 in the [Tf2 N] anion-based ionic liquids. As can be seen in this figure, at lower mole fraction of CO2 under 0.5x1 , the differences of solubility of CO2 in different ionic liquids are not large. But at higher CO2 mole fraction over than 0.5x1 ,

60

50 40

P (MPa)

a

P (MPa)

a

the differences of solubility of CO2 in ionic liquid become larger and larger. The sequence of magnitude of bubble point pressure is [BMP][Tf2 N] [7] > [HMP][Tf2 N] > [OMP][Tf2 N] > [P14,6,6,6][Tf2 N] [6]. This means that the sequence of magnitude of solubility of CO2 is [P14,6,6,6][Tf2 N] [6] > [BMP][Tf2 N] [7] > [HMP][Tf2 N] > [OMP][Tf2 N]. This illustrates that the solubility of CO2 decreases commensurate to alkyl group chain length in cation. That is, the shorter the alkyl group chain in cation is, the larger the solubility of CO2 in ionic liquid become. And in

30

40

20

20 10

0

0.2

300

b

320

340

360

380

0.6

0.8

b

40

T (K) 40

30

P (MPa)

30

P (MPa)

0.4

Mole fraction of CO2, x1

0

20

10

20

10

0

0 300

320

340

360

380

T (K) Fig. 2. P–T graph of CO2 solubilities of the CO2 + ionic liquid system: (a) CO2 + [HMP][Tf2 N]: 0.2778 ( ); 0.3827 (); 0.4416 (); 0.5699 (); 0.6138 (); 0.6797 (); 0.7478 (♦); 0.8105 ( ). (b) CO2 + [OMP][Tf2 N]: 0.2409 (䊉); 0.3418 (); 0.4424 ( ); 0.5230 (); 0.6193 (); 0.6779 (); 0.7307 (); 0.7758 (); 0.8176 ( ).

0.2

0.4

0.6

0.8

Mole fraction of CO2, x1 Fig. 3. P–x1 graph of CO2 solubilities of the CO2 + ionic liquid system: (a) [HMP][Tf2 N] and (b) [OMP][Tf2 N]. 303.15 K (䊉); 313.15 K (); 323.15 K (); 333.15 K (♦); 343.15 K (); 353.15 K (); 363.15 K (); and 373.15 K (); calculated by P–R EOS (—) [9].

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Table 6 Average absolute deviations (AAD%) between experimental data and calculated value for the [HMP][Tf2 N] + CO2 and [OMP][Tf2 N] + CO2 system. AAD%a

Temperature (K)

303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 Average a

5. Conclusion

[HMP][Tf2 N]

[OMP][Tf2 N]

9.40 11.49 10.10 9.01 8.02 7.57 7.98 7.65 8.90

5.17 5.95 6.46 6.14 6.33 6.03 5.69 5.63 5.93

In this paper, experimental results for the solubility of CO2 in ionic liquids [HMP][Tf2 N] and [OMP][Tf2 N] were observed from 303.15 to 373.15 K in 10 K intervals. The solubility of CO2 in ionic liquids was measured by using a high-pressure variable-volume view cell. Normal boiling temperature, the acentric factor and critical properties of ionic liquids were estimated with the modified Lydersen–Joback–Reid method. PR-EoS and mixing rules were used for calculate the solubility pressure. At lower mole fraction of CO2 , CO2 exhibited very high solubilities in ionic liquids. The bubblepoint pressure increased sharply at high mole fraction of CO2 and increases linearly with increasing temperatures at fixed mole fraction of CO2 .

Average absolute deviation in percentage:

1 AAD% = N

  N Picalc − Piexp   exp

i=1

Pi

all systems, as the CO2 mole fraction increases, the bubble point pressures increase dramatically.

× 100 (N = number of data).

Acknowledgement This work was supported by the Special Research Grant of Sogang University. 30

References 25

P (MPa)

20 15 10 5 0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Mole fraction of CO2, x1 Fig. 4. Comparison of P–x1 graph of CO2 solubilities in the [Tf2 N] based ionic liquids systems at 333.15 K: [BMP][Tf2 N] (䊉) (our previous work) [7]; [HMP][Tf2 N] (); [OMP][Tf2 N] (); [P14,6,6,6][Tf2 N] () (our previous work) [6].

[1] J.L. Anthony, E.J. Maginn, J.F. Brennecke, J. Phys. Chem. B 106 (2002) 315. [2] E.-K. Sin, B.-C. Lee, J.S. Lim, J. Supercrit. Fluids 45 (2008) 282. [3] A.E. Visser, R.P. Swatloski, W.M. Reichert, S.T. Griffin, R.D. Rogers, Ind. Eng. Chem. Res. 39 (2000) 3596. [4] Y. Ari, T. Sako, Y. Takebayashi, Supercritical Fluids: Molecular Interactions, Physical Properties and New Applications, Springer-Verlag, Berlin, Heidelberg, New York, 2001. [5] L.A. Blanchard, J.F. Brennecke, Ind. Eng. Chem. Res. 40 (2001) 287. [6] H.-N. Song, B.-C. Lee, J.S. Lim, J. Chem. Eng. Data 55 (2010) 891. [7] J.-H. Yim, H.-N. Song, K.-P. Yoo, J.S. Lim, J. Chem. Eng. Data 56 (2011) 1197–1203. [8] Guide to the Expression of Uncertainty in Measurement, International Organization of Standardization (ISO), Geneva, Switzerland, 1995. [9] D.Y. Peng, D.B. Robinson, Ind. Eng. Chem. Fundam. 15 (1976) 59. [10] M.O. McLinden, S.A. Klein, E.W. Lemmoon, A.P. Peskin, Thermodynamic Properties of Refrigerants and Refrigerant Mixtures Database (REFPROP) V.6.01, NIST, 1998. [11] J.O. Valderrama, W.W. Sanga, J.A. Lassús, Ind. Eng. Chem. Res. 47 (2008) 1318. [12] J.O. Valderrama, P.A. Robles, Ind. Eng. Chem. Res. 46 (2007) 1338.