Sem t

1
GAS SOLUBILITY OF HFCs IN ORGANIC SOLVENTS
J.P.B. Almeida1, H.C. Fachada2, I. M. A.
Fonseca1 1 Chemical Engineering Department,
University of Coimbra, Pólo II, Pinhal de
Marrocos, 3030290 Coimbra, Portugal. 2
Electrical Engineering Department, Institute
Polytechnique of Coimbra , 3030-199 Coimbra,
Portugal. e-mail fonseca_at_eq.uc.pt
Results
Abstract
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.
Experimental Automated apparatus 2,3 (which
embodies a volumetric method)


Table 2 Comparison of solubility results with
literature values
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.
System AAD () Ref.
CH2F2 / Methanol 3.9 4
CH2F2 / Ethanol 3.2 4
CF4 / 1-Butanol 1.9 5,6
AAD (1 / N)
100 (?x2 - x2lit? / x2lit)
Calculations
Conclusions
Table 1 Thermodynamic functions (J mol-1)
obtained from Rlnx2 A B/T ClnT, at 298 K.

• The solubilities of HFCs in the alcohols
  decrease in the order
• CHF3 gt CH2F2 gt CH3F gt 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.

Gas (2) Solvent (1) ?G20 ?H20 ?S20
CHF3 Methanol 9254.09 -7168.81 -55.11
CHF3 Ethanol 8884.89 -11726.59 -69.17
CHF3 1-Propanol 8250.34 -9517.25 -59.62
CHF3 1-Butanol 7720.77 -13872.79 -72.46
CH3F Methanol 20486.50 -244659.00 -889.75
CH3F Ethanol 15920.76 -57274.00 -245.62
CH3F 1-Propanol 14628.30 -8124.00 -76.35
CH3F 1-Butanol 14330.02 -19192.00 -112.49
CH2F2 Methanol 10196.86 -11570.75 -73.05
CH2F2 Ethanol 9639.87 -18034.80 -92.87
CH2F2 1-Propanol 8869.65 -9407.77 -61.33
CH2F2 1-Butanol 8390.15 -7527.62 -53.42
CF4 1-Propanol 18622.35 -1211.84 -66.56
CF4 1-Butanol 18480.83 -1636.01 -67.51
References
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.
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