GAS SOLUBILITY OF HFCs IN ORGANIC SOLVENTSJ.P.B. Almeida1, H.C. Fachada2, I. M. A. Fonseca1*

1 Chemical Engineering Department, University of Coimbra, Pólo II, Pinhal de Marrocos, 3030–290

Coimbra, Portugal.2 Electrical Engineering Department, Institute Polytechnique of Coimbra , 3030-199 Coimbra, Portugal.* e-mail: fonseca@eq.uc.pt

The solubilities of HFCs in the alcohols decrease in the order:

CHF3 > CH2F2 > CH3F > CF4. This is corroborated by the values of Gº2 in

Table 1.

This can be explained by the formation of a complex between solute/solvent

molecules by means of hydrogen-bonding. Actually the presence of the

strongly electron-attracting halogen atom(s) on the carbon of the solute

molecule looses the hydrogen(s) and makes it available for coordination to the

donor atom (of the solvent molecule). For each HFC the solubility increases with the C- content of the alcohol

increases. This is related to H-bonding or association in the alcohol; i.e.

solvents with strong H-bonding tendencies dissolve less the same gas those

with weaker H-bonding tendencies. The comparison of the solubility with literature values in Table 2 shows a

satisfactory agreement.

[1] J.M. Prausnitz, R.N. Lichtenthaler, E.G. Azevedo, Molecular Thermodynamics

of Fluid-Phase Equilibria, 3rd ed., Prentice Hall, Englewood Cliffs, 1999.

[2] I.M.A Fonseca, J.P.B. Almeida, H.C. Fachada, Automated apparatus for gas

solubility measurements, J. Chem. Thermodynamics 39 (2007) 1407-1411.

[3] H.L. Clever, R. Battino, The Experimental Determination of Solubilities, edited

by G.T. Hefter and R.P.T. Tomkins, Wiley, 2003, pp. 101-150.

[4] M. Takenouchi, R. Kato, H. Nishiumi, J. Chem. Eng. Data 46 (2001) 746-749.

[5] S. Bo, R. Battino, E. Wilhelm, J. Chem. Eng. Data 38 (1993) 611-616.

[6] J. Pardo, M.C. Lopez, J. Santafe, F.M. Royo, J.S. Urieta, Fluid Phase

Equilibria 109 (1995) 29-37.

This work is inserted in a research program that consists mainly in the

experimental and theoretical study of the effect of association [1]

between solute and solvent molecules in the solubility of gases in

liquids.

To measure the solubility of gases in liquids an automated apparatus

based on Ben-Naim-Baer and Tominaga et al designs has been

implemented [2]. The accuracy of the experimental method was checked

by measuring the solubility of carbon dioxide and nitrous oxide in water,

being found to be 0.6%.

The solubilities of hydrofluorocarbons, HFCs, (CH3F, CH2F2, CHF3 and

CF4) in lower alcohols (methanol, ethanol, 1-propanol, 1-butanol) have

been determined in the temperature range [285, 310] K, at atmospheric

pressure.

To represent the temperature dependence of the mole fraction

solubilities, the equation Rlnx2 = A + B/T + ClnT was used. From this

equation the experimental Gibbs energies, enthalpies and entropies of

solution at 298 K were calculated [3].

Solubility apparatus: TB, thermostated bath; TC, temperature controller;

T, thermometer; PT, pressure transducer; LA, linear actuator; PC,

pressure controller; PE, Penning gauge; DIF, diffusion oil pump; TRAP,

liquid N2 trap; EQ, equilibrium vessel with connector; GB, gas burette;

V1,…V6, high vacuum Teflon stopcocks; AGIT, magnetic stirrer; E,

elevator.

Experimental Automated apparatus [2,3] (which embodies a volumetric method)

Results

1-Butanol

1.E-04

1.E-03

1.E-02

1.E-01

280 290 300 310

T/K

X2

1-Propanol

1.E-04

1.E-03

1.E-02

1.E-01

280 290 300 310 320

T/K

X2

Ethanol

1.E-04

1.E-03

1.E-02

1.E-01

280 290 300 310 320

T/K

X2

Methanol

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

280 290 300 310 320

T/K

X2

1.E-04

1.E-03

1.E-02

1.E-01

280 290 300 310

CHF3

CH3F

CH2F2

CF4

Calculations

System AAD (%) Ref.

CH2F2 / Methanol 3.9 [4]

CH2F2 / Ethanol 3.2 [4]

CF4 / 1-Butanol 1.9 [5],[6]

Table 2 Comparison of solubility results with literature values

Table 1 Thermodynamic functions (J mol-1) obtained from Rlnx2 = A + B/T + ClnT, at 298 K.

Gas (2) Solvent (1) G20 H2

0 S20

CHF3

Methanol 9254.09 -7168.81 -55.11

Ethanol 8884.89 -11726.59 -69.17

1-Propanol 8250.34 -9517.25 -59.62

1-Butanol 7720.77 -13872.79 -72.46

CH3F

Methanol 20486.50 -244659.00 -889.75

Ethanol 15920.76 -57274.00 -245.62

1-Propanol 14628.30 -8124.00 -76.35

1-Butanol 14330.02 -19192.00 -112.49

CH2F2

Methanol 10196.86 -11570.75 -73.05

Ethanol 9639.87 -18034.80 -92.87

1-Propanol 8869.65 -9407.77 -61.33

1-Butanol 8390.15 -7527.62 -53.42

CF4

1-Propanol 18622.35 -1211.84 -66.56

1-Butanol 18480.83 -1636.01 -67.51

Abstract

CHF3

1.E-02

1.E-01

280 290 300 310

T/K

X2

butanol propanoletanolmetanol

Conclusions

AAD = (1 / N) i

100 (x2 - x2lit / x2lit)

References

Acknowledgements

This work was carried out under Research Project POCI/EQU 44056/2002 financed by FCT –

Fundação para a Ciência e Tecnologia (Portugal) and FEDER