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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, 3030–290 Coimbra, Portugal. 2 Electrical Engineering Department, Institute Polytechnique of Coimbra , 3030-199 Coimbra, Portugal. * e-mail: [email protected] 1.E-01 Abstract Results This work is inserted in a research program that consists mainly1.E-02 in the experimental and theoretical study of the effect of association [1] between solute and solvent molecules in the solubility of gases in 1.E-03 liquids. To measure the solubility of gases in liquids an automated apparatus based on Ben-Naim-Baer and Tominaga et al designs has been 1.E-04 implemented [2]. The accuracy of the experimental method was checked 280 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]. X2 CHF3 CH3F CH2F2 CF4 Methanol 290 Ethanol 300 1.E-01 310 1.E-01 T/K 1.E-02 X2 X2 1.E-02 1.E-03 1.E-03 1.E-04 1.E-05 280 290 300 310 1.E-04 280 320 290 300 1-Butanol 1-Propanol 1.E-01 1.E-01 1.E-02 X2 X2 1.E-02 1.E-03 1.E-03 Automated apparatus [2,3] (which embodies a volumetric method) 320 T/K T/K Experimental 310 1.E-04 280 290 300 310 1.E-04 280 320 290 300 310 T/K T/K PE LA CHF3 PT TC T 1.E-01 TRAP DIF V5 butanol propanol etanol metanol X2 Gas V1 V3 V2 Vacuum V4 V6 GB 1.E-02 280 EQ 290 310 T/K TB SAT 300 PC AGIT E 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, System AAD (%) Ref. CH2F2 / Methanol 3.9 [4] CH2F2 / Ethanol 3.2 [4] CF4 / 1-Butanol 1.9 [5],[6] elevator. AAD = (1 / N) 100 (x2 - x2lit / x2lit) i Calculations Table 1 Thermodynamic functions (J Gas (2) CHF3 CH3F CH2F2 CF4 mol-1) Conclusions obtained from Rlnx2 = A + B/T + ClnT, at 298 K. Solvent (1) G20 H20 S20 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 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 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 1-Propanol 18622.35 -1211.84 -66.56 1-Butanol 18480.83 -1636.01 -67.51 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 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. 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.