experimental

1
SOLUBILITY OF WATER IN LIQUID PERFLUOROCARBONS M. G. Freire 1 , L. M. N. B. F. Santos 2 , I.M. Marrucho 1 and J.A.P. Coutinho 1 1 CICECO, Departamento de Química, Universidade de Aveiro, Aveiro, Portugal 2 Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Porto, Portugal H º/(KJ.m ol -1 ) G º/(KJ.m ol -1 ) Sº/(J.K -1 .mol -1 ) C 6 F 14 39.5 20.2 64.8 C 8 F 18 37.0 19.9 57.2 C 9 F 20 36.0 19.8 54.1 C 10 F 18 36.9 20.0 56.5 C 6 F 6 28.1 15.3 41.5 C 7 H 16 35.7 18.6 56.5 2 0 ) ln( T R H T x i Fluorinated molecules such as perfluorocarbons (PFCs) and their derivates represent a very interesting and stimulating class of chemicals in the physical chemistry and polymer science due to their specific and unusual properties. It is however in the biomedical field where most of the relevant applications of PFCs are found. They can be used in tissue oxygenation as blood substitutes, anti-tumural agents and perfusates for isolated organs, gas-carriers in eye surgery, diagnostic imaging agents, drug delivery and in the aeration of biological reactors [1]. The aim of this work is the study of water solubility in liquid perfluorocarbons at several temperatures since data of this property are extremely scarce in the literature. A 737 model Karl Fisher titrator was used and it has been adapted for measuring the low solubility of water in the perfluorocarbons solvents. The study of pure perfluorocarbons is based in measurements of the solubility of water in linear, cyclic and aromatic perfluorocarbons in the temperature range between 295.7 and 309.6 K and at atmospheric pressure. Since to our knowledge there are no known data in literature for the PFCs, the method was validated with the determination of the n-heptane solubility in water in the same temperature range comparing the measures with literature data. Experimental values of water solubility in PFCs, expressed in mol fractions, are presented in Table 1. Table 1. Solubility of water in liquid PFCs Experimental C 6 F 14 C 8 F 18 C 9 F 20 C 10 F 18 C 6 F 6 C 7 H 16 T/(K ) 10 -4 (x ± σ a ) 10 -4 (x ± σ a ) 10 -4 (x ± σ a ) 10 -4 (x ± σ a ) 10 -3 (x ± σ a ) 10 -4 (x ± σ a ) 295.7 2.6 ± 0.1 2.8 ± 0.1 3.08 ± 0.09 2.72 ± 0.09 1.60 ± 0.01 4.25 ± 0.02 298.2 2.93 ± 0.08 3.3 ± 0.1 3.3 ± 0.2 3.1 ± 0.2 1.76 ± 0.02 4.97 ± 0.04 303.2 4.11 ± 0.07 4.35 ± 0.09 4.52 ± 0.05 3.9 ± 0.1 2.08 ± 0.01 --- 305.8 4.51 ± 0.08 4.6 ± 0.1 5.38 ± 0.09 4.1 ± 0.1 2.37 ± 0.02 6.71 ± 0.06 309.6 5.2 ± 0.2 5.6 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 2.66 ± 0.02 9.09 ± 0.07 From the Gibbs-Duhem equation, assuming that for such a diluted solution both the activity coefficient for water in the water phase and that for the organic component in the organic phase are equal to one, it’s possible to obtain the following approximation [2]: The linear dependence of ln(x) with temperature for an individual case (C 6 F 6 ) and for the linear compounds studied is shown in Figures 1 and 2, respectively. Experimental data is well described by the linear representation of ln(x) with temperature for all the studied cases. The solubility of water in the linear PFCs is fairly insensitive to the carbon number (CN), rising just slightly with increasing CN because it seems to be primarily influenced by the breaking of hydrogen bonds in water. The water solubility in PFCs is strongly dependent on the temperature. Whose integration, assuming that H i is constant with temperature, leads to Figure 1. ln(x) dependence of temperature for water solubility (x) in C 6 Figure 2. ln(x) dependence of temperature for water solubility (x) in the linear PFCs studied a Standard deviation of experimental data Thermodynamic Parameters The determination of water solubility has a particular significance since it may be a way to access to thermodynamic properties of these systems. Solubility measurements at different temperatures allow the determination of thermodynamic parameters of the solution that are difficult to obtain using direct methods, such as ∆Hº. The thermodynamic parameters are presented in Table 2. Table 2. Thermodynamic parameters at 298.2 K for the water dissolution in PFCs The heat of solution for water in PFCs is always positive and is nearly the same for all the PFC compounds and slightly higher than the heat of solution for the n- alkanes. This increase may be due to the larger size of the PFC molecules increasing the difficulty of the dissolution of water. Typical values for the energy of a “normal” hydrogen bond range between 20 and 40 KJ.mol -1 suggests that the dissolution of n water molecules leads to the breaking of n hydrogen bonds, which to a good approximation is independent of both carbon number and temperature. The lone pair electrons of oxygen interaction with the system of the hexafluorobenzene ring reduces the heat of [1] Dias AMA, Pàmies JC, Coutinho JAP, Marrucho IM, Vega LF, J Phys. Chem. B (2004) 108: 1450 [2] Tsonopoulos C, Fluid Phase Equilibria (1999) 156: 21 The authors thank financial support from Fundação para a Ciência e a Tecnologia (POCTI/EQU/44427/2002) M. G. Freire acknowledges the scholarship SFRH / BD / 14134 / 2003 References & Acknowledgments Introduction Results & Discussion T B A x ) ln( -6,5 -6,4 -6,3 -6,2 -6,1 -6,0 -5,9 0,00321 0,00323 0,00325 0,00327 0,00329 0,00331 0,00333 0,00335 0,00337 0,00339 1/T/(K -1 ) ln(x) -8,4 -8,3 -8,2 -8,1 -8,0 -7,9 -7,8 -7,7 -7,6 -7,5 -7,4 -7,3 0,00322 0,00324 0,00326 0,00328 0,00330 0,00332 0,00334 0,00336 0,00338 0,00340 1/T/(K -1 ) ln(x) ln(x)in C 6F14 ln(x)in C 8F18 ln(x)in C 9F20

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Introduction. Results & Discussion. Whose integration, assuming that ∆H i is constant with temperature, leads to. Experimental. Figure 1 . ln(x) dependence of temperature for water solubility (x) in C 6 F 6. a Standard deviation of experimental data. Thermodynamic Parameters. - PowerPoint PPT Presentation

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Page 1: Experimental

SOLUBILITY OF WATER IN LIQUID PERFLUOROCARBONSM. G. Freire1, L. M. N. B. F. Santos2, I.M. Marrucho1 and J.A.P. Coutinho1

1CICECO, Departamento de Química, Universidade de Aveiro, Aveiro, Portugal2Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências,

Universidade do Porto, Porto, Portugal

∆Hº / (KJ.mol -1) ∆Gº / (KJ.mol -1) ∆Sº / ( J.K-1.mol-1) C6F14 39.5 20.2 64.8 C8F18 37.0 19.9 57.2 C9F20 36.0 19.8 54.1 C10F18 36.9 20.0 56.5 C6F6 28.1 15.3 41.5

C7H16 35.7 18.6 56.5

2

0)ln(TRH

Tx i

Fluorinated molecules such as perfluorocarbons (PFCs) and their derivates represent a very interesting and stimulating class of chemicals in the physical chemistry and polymer science due to their specific and unusual properties. It is however in the biomedical field where most of the relevant applications of PFCs are found. They can be used in tissue oxygenation as blood substitutes, anti-tumural agents and perfusates for isolated organs, gas-carriers in eye surgery, diagnostic imaging agents, drug delivery and in the aeration of biological reactors [1].The aim of this work is the study of water solubility in liquid perfluorocarbons at several temperatures since data of this property are extremely scarce in the literature.

A 737 model Karl Fisher titrator was used and it has been adapted for measuring the low solubility of water in the perfluorocarbons solvents. The study of pure perfluorocarbons is based in measurements of the solubility of water in linear, cyclic and aromatic perfluorocarbons in the temperature range between 295.7 and 309.6 K and at atmospheric pressure.Since to our knowledge there are no known data in literature for the PFCs, the method was validated with the determination of the n-heptane solubility in water in the same temperature range comparing the measures with literature data.Experimental values of water solubility in PFCs, expressed in mol fractions, are presented in Table 1.

Table 1. Solubility of water in liquid PFCs

Experimental

C6F14 C8F18 C9F20 C10F18 C6F6 C7H16

T/(K) 10-4 (x ± σa) 10-4 (x ± σa) 10-4 (x ± σa) 10-4 (x ± σa) 10-3 (x ± σa) 10-4 (x ± σa)

295.7 2.6 ± 0.1 2.8 ± 0.1 3.08 ± 0.09 2.72 ± 0.09 1.60 ± 0.01 4.25 ± 0.02

298.2 2.93 ± 0.08 3.3 ± 0.1 3.3 ± 0.2 3.1 ± 0.2 1.76 ± 0.02 4.97 ± 0.04

303.2 4.11 ± 0.07 4.35 ± 0.09 4.52 ± 0.05 3.9 ± 0.1 2.08 ± 0.01 ---

305.8 4.51 ± 0.08 4.6 ± 0.1 5.38 ± 0.09 4.1 ± 0.1 2.37 ± 0.02 6.71 ± 0.06

309.6 5.2 ± 0.2 5.6 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 2.66 ± 0.02 9.09 ± 0.07

From the Gibbs-Duhem equation, assuming that for such a diluted solution both the activity coefficient for water in the water phase and that for the organic component in the organic phase are equal to one, it’s possible to obtain the following approximation [2]:

The linear dependence of ln(x) with temperature for an individual case (C6F6) and for the linear compounds studied is shown in Figures 1 and 2, respectively.

Experimental data is well described by the linear representation of ln(x) with temperature for all the studied cases.The solubility of water in the linear PFCs is fairly insensitive to the carbon number (CN), rising just slightly with increasing CN because it seems to be primarily influenced by the breaking of hydrogen bonds in water. The water solubility in PFCs is strongly dependent on the temperature.

Whose integration, assuming that ∆Hi is constant with temperature, leads to

Figure 1. ln(x) dependence of temperature for water solubility (x) in C6F6

Figure 2. ln(x) dependence of temperature for water solubility (x) in the linear PFCs studied

a Standard deviation of experimental data

Thermodynamic Parameters

The determination of water solubility has a particular significance since it may be a way to access to thermodynamic properties of these systems. Solubility measurements at different temperatures allow the determination of thermodynamic parameters of the solution that are difficult to obtain using direct methods, such as ∆Hº. The thermodynamic parameters are presented in Table 2.

Table 2. Thermodynamic parameters at 298.2 K for the water dissolution in PFCs

The heat of solution for water in PFCs is always positive and is nearly the same for all the PFC compounds and slightly higher than the heat of solution for the n-alkanes. This increase may be due to the larger size of the PFC molecules increasing the difficulty of the dissolution of water. Typical values for the energy of a “normal” hydrogen bond range between 20 and 40 KJ.mol-1 suggests that the dissolution of n water molecules leads to the breaking of n hydrogen bonds, which to a good approximation is independent of both carbon number and temperature.The lone pair electrons of oxygen interaction with the system of the hexafluorobenzene ring reduces the heat of solution increasing the solubility of water on this compound.

[1] Dias AMA, Pàmies JC, Coutinho JAP, Marrucho IM, Vega LF, J Phys. Chem. B (2004) 108: 1450

[2] Tsonopoulos C, Fluid Phase Equilibria (1999) 156: 21

The authors thank financial support from Fundação para a Ciência e a Tecnologia (POCTI/EQU/44427/2002)

M. G. Freire acknowledges the scholarship SFRH / BD / 14134 / 2003

References & Acknowledgments

Introduction Results & Discussion

TBAx )ln(

-6,5

-6,4

-6,3

-6,2

-6,1

-6,0

-5,9

0,00321 0,00323 0,00325 0,00327 0,00329 0,00331 0,00333 0,00335 0,00337 0,00339

1/T/(K-1)

ln(x

)

-8,4

-8,3

-8,2

-8,1

-8,0

-7,9

-7,8

-7,7

-7,6

-7,5

-7,4

-7,3

0,00322 0,00324 0,00326 0,00328 0,00330 0,00332 0,00334 0,00336 0,00338 0,00340

1/T/(K-1)

ln(x

)

ln(x) in C6F14

ln(x) in C8F18

ln(x) in C9F20