- Email: [email protected]
High-pressure vapor–liquid equilibrium of binary systems with R236fa1
Fluid Phase Equilibria 161 Ž1999. 305–313
High-pressure vapor–liquid equilibrium of binary systems with R236fa 1 Sergio Bobbo
a, )
, Roberto Camporese a , Roman Stryjek
b
a
b
Institute of Refrigeration, National Research Council, Corso Stati Uniti, 4, I-35127, Padua, Italy Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44r52, 01-224, Warsaw, Poland Received 1 September 1998; accepted 23 February 1999
Abstract Within the European Union Joule project aimed at the substitution of R114 in high temperature heat pumps with chlorine-free, environmentally benign fluids, R236fa has been chosen as one of the components of mixtures to consider as alternative fluids for R114 Ž1,2-dichlorotetrafluoroethane.. The results of VLE measurements performed at our laboratory on mixtures including R236fa are summarized and discussed for the systems R600a Žisobutane. q R236fa Ž1,1,1,3,3,3-hexafluoropropane. at 303 K, RE170 Ždimethyl ether. q R236fa at 303 and 323 K, R134a Ž1,1,1,2-tetrafluorethane. q R236fa at 283 and 303 K, R32 Ždifluoromethane. q R236fa and R125 Žpentafluoroethane. q R236fa, both at 303 and 323 K. All data were correlated by means of the CSD EOS. Generally small deviations between experimental and calculated vapor compositions confirm the thermodynamic consistency of the experimental results and the model used for data reduction. An extensive discussion of the deviations from Raoult’s law is performed through analysis of the excess Gibbs energy. All systems formed by HFCs show a very small g E , with small deviation from Raoult’s law. A much higher g E is shown by the systems R600aq R236fa, with a positive deviation from Raoult’s law, and RE170q R236fa, with a negative deviation clearly coming from the hydrogen bonding. q 1999 Elsevier Science B.V. All rights reserved. Keywords: R236fa; Vapor–liquid equilibria; Gibbs energy
1. Experimental apparatus and measurement methodology The apparatus Ž Fig. 1. and the measuring methods have already been described in detail elsewhere w1–4x and are briefly reiterated here. They were practically the same for all the systems considered. ) 1
Corresponding author. Tel.: q39-49-829-5736; fax: q39-49-829-5728; e-mail: [email protected] Paper presented at the 5th Asian Thermophysical Properties Conference.
0378-3812r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 8 1 2 Ž 9 9 . 0 0 1 9 4 - 6
306
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
Fig. 1. Schematic diagram of the apparatus. Components are labeled as follows: cooler ŽCR., resistance thermometer for temperature control ŽCT., diaphragm ŽDP., equilibrium cell ŽEC., heating resistor ŽHR., magnetic pump ŽMP., resistance thermometer for temperature measurement ŽMT., nitrogen bottle ŽNB., pure refrigerant bottle ŽPB., pressure control pack ŽPCP., pressure gauge ŽPG., stirrer ŽST., sampling valve ŽSV., vacuum pump ŽVP..
The VLE measurements were taken in a stainless steel recirculation equilibrium cell equipped with two windows and a magnetic pump for forcing the vapor through the liquid. The VLE cell with the magnetic pump was immersed in a liquid thermostat of about 100 l capacity. Pressure was measured with a 3500 kPa full-scale pressure gauge. A diaphragm immersed in the bath was mounted to separate the reagents from the quartz sensor of the pressure gauge. The accuracy of the pressure measurement was estimated to be generally within "0.3 kPa. Temperature was measured with a 100 V platinum resistance thermometer and was continuously recorded during the experiments. A long-term temperature stability within "1 mK was achieved in the thermostatic bath. The accuracy of the temperature measurement was estimated to be within "5 mK. The composition of the phases was determined by means of a gas chromatograph connected on-line to the VLE cell. The response of the flame ionization detector was carefully calibrated using mixtures prepared gravimetrically by weighing with a standard analytical balance. The GC response was continuously recalibrated, and small changes in actual GC response due to GC parameter instability were observed and taken into account. A very good resolution and short total analysis time in isothermal conditions were obtained for all systems. The results of calibration were regressed with functions expressing the mole fraction of the lower boiling temperature compound as a function of the percentage of its peak area.
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
307
Fig. 2. VLE of R236faqhydrofluorocarbons at 303 K.
At least five analyses were performed for each phase and the average value was considered as corresponding to the equilibrium. Considering the margin of error and the reproducibility of GC, we generally estimated an overall accuracy in the measurements of the composition of "0.002 Ž"0.0035 in the worst case. in the mole fraction for both the liquid and the vapor phases. 2. Discussion The results of our measurements for the systems R600aq R236fa at 303 K, RE170q R236fa at 303 and 323 K, R134aq R236fa at 283 and 303 K, R32 q R236fa and R125 q R236fa, both at 303 and 323 K, are presented elsewhere w1–4x. A representation of the VLE data measured at 303 K is given in Figs. 2–4 for all systems.
Fig. 3. VLE of R600aŽ1.qR236fa at 303 K.
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
308
Fig. 4. VLE of RE170Ž1.qR236fa at 303 K.
The experimental VLE data were correlated, as described in Ref. w4x, by means of the CSD EOS w5x, with the combining rules proposed therein with one adjustable parameter, k i j , per each binary system. The calculated k i j are reported in Table 1. Equation coefficients for pure compounds were adopted from Ref. w7x. The VLE data were reduced taking T, p, x as independent variables minimizing the following objective function F: Np
Fs
Ý
D prpexp
2
Ž1.
is1
where Np is the number of experimental points, D p s pexp y pcal , pexp is the experimental pressure and pcal is the calculated pressure. Analysis of the results for the R32 q R236fa, R125 q R236fa and R134a q R236fa systems demonstrated that the data are well represented by the CSD EOS. The system pressure showed not systematic, but only random error deviations, as shown in Fig. 5 with reference to the liquid composition. Deviations in vapor composition were also randomly distributed, being within "0.003
Table 1 Binary interaction coefficients, k i j , for the studied systems Binary mixture
k 12
Source
R600aqR236fa RE170qR236fa R134aqR236fa R125qR236fa R32qR236fa R22qRE170
0.1368 y0.0900 y0.0073 y0.0008 y0.0325 y0.1203
a
a b
This work, experimental VLE data from Ref. w1,2x. This work, experimental VLE data from Ref. w6x.
w4x a
w3x w3x b
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
309
Fig. 5. Deviations of pressure for all data.
in mole fraction for each of these systems ŽFig. 6.. This value is far below "0.005 that can be considered as the limit to state the thermodynamic consistency between the experimental data and the model used for the correlation. A good representation of the pressure was also achieved for the system R600aq R236fa, but the deviations in vapor compositions were higher, though still within the limit of "0.005. For the RE170q R236fa system, S-shaped deviations were evident for the pressure Ž Fig. 5. and the deviations for the vapor composition were above "0.005 in mole fraction, as well as being clearly systematic. In our opinion, they cannot be attributed to experimental errors, but rather to the performance of the model involved. To verify our hypothesis, we compared the results of fitting the VLE data for the RE170q R22 Žchlorodifluoromethane. system w6x; the respective deviations are shown in Figs. 7 and 8. The systematic deviations for the RE170q R22 system are even more evident, clearly above the accuracy declared by the authors.
Fig. 6. Deviations of vapor composition for all data.
310
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
Fig. 7. Deviations of pressure for the system RE170Ž1.qR22 at 283 K Žv . and 323 K Ž`. with CSD EOS. Experimental data from Ref. w6x.
The excess Gibbs energy, g E , values were calculated from the CSD EOS using the following function: g E s RT Ž ln f y Ý x i ln f i . Ž2. where R is the gas constant, T is the absolute temperature, f is the fugacity coefficient of the mixture and f i is the fugacity coefficient of the ith component of the mixture at the same temperature and pressure. The character of the properties of the systems considered is clearly evident when the excess Gibbs energy, g E , is plotted as a function of composition at 303 K ŽFig. 9.. All systems formed by HFCs show a very small g E within "40 Jrmol at most. A much higher g E is shown by the systems R600aq R236fa Žabout 870 Jrmol at most., and RE170q R236fa Žabout y470 Jrmol at most.. The negative value of g E for the last system clearly comes from the hydrogen bonding.
Fig. 8. Deviations of vapor composition for the system RE170Ž1.qR22 at 283 K Žv . and 323 K Ž`.. Experimental data from Ref. w6x.
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
311
Fig. 9. Excess Gibbs energy at 303 K of the systems with R236fa.
It is worth pointing out that strong hydrogen bonding of RE170 with partially fluorinated hydrocarbons was reported in literature on the basis of VLE measurements for two systems, RE170q R22 w6x and RE170q R236fa w4x. The strong proton donor properties of chloroform are well-known and the partial replacement of chlorine atoms with fluorine atoms Žthat are more electronegative. can therefore be expected to cause the formation of hydrogen bonding by R22. As for the second system, the proton donor property of hydrogen results from the molecular structure of R236fa which, in order to induce a strong hydrogen bonding, has to be not linear, but bent —and consequently polar, with a smaller steric hindrance to the proton acceptor. A comparison between the g E produced by these two systems is shown in Fig. 10. For the former system, the g E values at 303 K were calculated again using the CSD EOS with the k 12 values that we had calculated. Clearly the g E for the RE170q R22 mixture is more negative than that for the RE170q R236fa. The behavior of the systems illustrated in Figs. 2–4 prompts the following remarks, classifying the systems into three groups: Ža. Mixtures of R236fa with hydrofluorocarbons ŽHFC. : these all show small deviations from Raoult’s law; no dependence was detected on differences in molecular parameters, such as ratio of critical volume, difference in critical temperatures and, probably, differences in dipole moment.
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
312
Fig. 10. Excess Gibbs energy for the systems RE170Ž1.qR236fa and RE170Ž1.qR22.
Žb. System of R236fa with hydrocarbon Ž HC. shows a strong positive deviation from Raoult’s law; a qualitatively similar deviation is also shown by other systems belonging to this group, for which data are reported in the literature. Žc. Mixture of R236fa with dimethyl ether shows a strong negative deviations from Raoult’s law that can be attributed to hydrogen bonding. Our results suggest that the phenomenon of hydrogen bonding is more frequent between some HFC and compounds with proton acceptor. This means that the hydrogen bonding may also play an important part in the solubility of refrigerants in polyester and polyether oils, which also have proton acceptor groups.
3. Conclusions The main findings emerging from the series of VLE measurements for mixtures including R236fa was a new positive azeotrope for the mixture R600aq R236fa and the proton-donor properties of R236fa, with the ability to induce hydrogen bonding with proton acceptor compounds. Finally, the systems with various HFCs followed Raoult’s law well. For these latter mixtures, temperature glide depends solely on the differences in saturated pressure of the second component of the systems.
4. Nomenclature CSD EOS F HFC g k p
Carnahan–Starling–De Santis Equation of state objective function hydrofluorocarbon Gibbs energy ŽJrmol. binary interaction parameter pressure ŽkPa.
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
R T
gas constant 8.3144 ŽJrmol K. temperature ŽK.
Greek letters D f x y
deviation Žexperimentaly calculated. fugacity coefficient Ž – . liquid molar fraction vapor molar fraction
Subscripts cal exp i, j
calculated experimental ith, jth component of the mixture
Superscripts E
excess
313
Acknowledgements The CNR-ITEF is grateful to the European Community Commission for supporting this research. Mauro Scattolini is gratefully acknowledged for his collaboration in the experiments.
References w1x S. Bobbo, R. Stryjek, N. Elvassore, A. Bertucco, A recirculation apparatus for vapor–liquid equilibrium measurements of refrigerants. Binary Mixtures of R600a, R134a and R236fa, 13th Symposium on Thermophysical Properties, Boulder, Colorado June 22–27, 1997. w2x S. Bobbo, R. Stryjek, N. Elvassore, A. Bertucco, Fluid Phase Equilibria 150–151 Ž1998. 343–352. w3x S. Bobbo, R. Camporese, R. Stryjek, Vapor–liquid equilibria for difluoromethane ŽR-32.q, and pentafluoroethane ŽR-125.q1,1,1,3,3,3-hexafluoropropane ŽR-236fa. at 303.2 K and 323.3 K, J. Chem. Eng. Data, accepted for publication. w4x S. Bobbo, R. Camporese, R. Stryjek, Vaporqliquid equilibrium measurements and correlations of the refrigerant mixture dimethyl ether ŽRE170.q1,1,1,3,3,3-hexafluoropropane ŽR236fa.4 at the temperatures of Ž303.68 and 323.75. K, J. Chem. Thermodyn. 30 Ž1998. 1041–1046. w5x R. De Santis, F. Gironi, L. Marrelli, Vapor–liquid equilibria from a hard sphere equation of state, Ind. Eng. Chem. Fundam. 15 Ž1976. 183–189. w6x J.R. Noles, J.A. Zollweg, Vapor–liquid equilibrium for chlorodifluoromethaneqdimethyl ether from 283 to 395 K at pressures to 5.0 MPa, J. Chem. Eng. Data 37 Ž1992. 306–310. w7x M. Huber, J. Gallagher, M. McLinden, G. Morrison, NIST thermodynamic properties of refrigerants and refrigerant mixtures database ŽREFPROP., Version 5.0, National Institute of Standards and Technology, Thermophysics Division, Gaithersburg, MD, 1996.
High-pressure vapor–liquid equilibrium of binary systems with R236fa 1 Sergio Bobbo
a, )
, Roberto Camporese a , Roman Stryjek
b
a
b
Institute of Refrigeration, National Research Council, Corso Stati Uniti, 4, I-35127, Padua, Italy Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44r52, 01-224, Warsaw, Poland Received 1 September 1998; accepted 23 February 1999
Abstract Within the European Union Joule project aimed at the substitution of R114 in high temperature heat pumps with chlorine-free, environmentally benign fluids, R236fa has been chosen as one of the components of mixtures to consider as alternative fluids for R114 Ž1,2-dichlorotetrafluoroethane.. The results of VLE measurements performed at our laboratory on mixtures including R236fa are summarized and discussed for the systems R600a Žisobutane. q R236fa Ž1,1,1,3,3,3-hexafluoropropane. at 303 K, RE170 Ždimethyl ether. q R236fa at 303 and 323 K, R134a Ž1,1,1,2-tetrafluorethane. q R236fa at 283 and 303 K, R32 Ždifluoromethane. q R236fa and R125 Žpentafluoroethane. q R236fa, both at 303 and 323 K. All data were correlated by means of the CSD EOS. Generally small deviations between experimental and calculated vapor compositions confirm the thermodynamic consistency of the experimental results and the model used for data reduction. An extensive discussion of the deviations from Raoult’s law is performed through analysis of the excess Gibbs energy. All systems formed by HFCs show a very small g E , with small deviation from Raoult’s law. A much higher g E is shown by the systems R600aq R236fa, with a positive deviation from Raoult’s law, and RE170q R236fa, with a negative deviation clearly coming from the hydrogen bonding. q 1999 Elsevier Science B.V. All rights reserved. Keywords: R236fa; Vapor–liquid equilibria; Gibbs energy
1. Experimental apparatus and measurement methodology The apparatus Ž Fig. 1. and the measuring methods have already been described in detail elsewhere w1–4x and are briefly reiterated here. They were practically the same for all the systems considered. ) 1
Corresponding author. Tel.: q39-49-829-5736; fax: q39-49-829-5728; e-mail: [email protected] Paper presented at the 5th Asian Thermophysical Properties Conference.
0378-3812r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 8 1 2 Ž 9 9 . 0 0 1 9 4 - 6
306
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
Fig. 1. Schematic diagram of the apparatus. Components are labeled as follows: cooler ŽCR., resistance thermometer for temperature control ŽCT., diaphragm ŽDP., equilibrium cell ŽEC., heating resistor ŽHR., magnetic pump ŽMP., resistance thermometer for temperature measurement ŽMT., nitrogen bottle ŽNB., pure refrigerant bottle ŽPB., pressure control pack ŽPCP., pressure gauge ŽPG., stirrer ŽST., sampling valve ŽSV., vacuum pump ŽVP..
The VLE measurements were taken in a stainless steel recirculation equilibrium cell equipped with two windows and a magnetic pump for forcing the vapor through the liquid. The VLE cell with the magnetic pump was immersed in a liquid thermostat of about 100 l capacity. Pressure was measured with a 3500 kPa full-scale pressure gauge. A diaphragm immersed in the bath was mounted to separate the reagents from the quartz sensor of the pressure gauge. The accuracy of the pressure measurement was estimated to be generally within "0.3 kPa. Temperature was measured with a 100 V platinum resistance thermometer and was continuously recorded during the experiments. A long-term temperature stability within "1 mK was achieved in the thermostatic bath. The accuracy of the temperature measurement was estimated to be within "5 mK. The composition of the phases was determined by means of a gas chromatograph connected on-line to the VLE cell. The response of the flame ionization detector was carefully calibrated using mixtures prepared gravimetrically by weighing with a standard analytical balance. The GC response was continuously recalibrated, and small changes in actual GC response due to GC parameter instability were observed and taken into account. A very good resolution and short total analysis time in isothermal conditions were obtained for all systems. The results of calibration were regressed with functions expressing the mole fraction of the lower boiling temperature compound as a function of the percentage of its peak area.
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
307
Fig. 2. VLE of R236faqhydrofluorocarbons at 303 K.
At least five analyses were performed for each phase and the average value was considered as corresponding to the equilibrium. Considering the margin of error and the reproducibility of GC, we generally estimated an overall accuracy in the measurements of the composition of "0.002 Ž"0.0035 in the worst case. in the mole fraction for both the liquid and the vapor phases. 2. Discussion The results of our measurements for the systems R600aq R236fa at 303 K, RE170q R236fa at 303 and 323 K, R134aq R236fa at 283 and 303 K, R32 q R236fa and R125 q R236fa, both at 303 and 323 K, are presented elsewhere w1–4x. A representation of the VLE data measured at 303 K is given in Figs. 2–4 for all systems.
Fig. 3. VLE of R600aŽ1.qR236fa at 303 K.
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
308
Fig. 4. VLE of RE170Ž1.qR236fa at 303 K.
The experimental VLE data were correlated, as described in Ref. w4x, by means of the CSD EOS w5x, with the combining rules proposed therein with one adjustable parameter, k i j , per each binary system. The calculated k i j are reported in Table 1. Equation coefficients for pure compounds were adopted from Ref. w7x. The VLE data were reduced taking T, p, x as independent variables minimizing the following objective function F: Np
Fs
Ý
D prpexp
2
Ž1.
is1
where Np is the number of experimental points, D p s pexp y pcal , pexp is the experimental pressure and pcal is the calculated pressure. Analysis of the results for the R32 q R236fa, R125 q R236fa and R134a q R236fa systems demonstrated that the data are well represented by the CSD EOS. The system pressure showed not systematic, but only random error deviations, as shown in Fig. 5 with reference to the liquid composition. Deviations in vapor composition were also randomly distributed, being within "0.003
Table 1 Binary interaction coefficients, k i j , for the studied systems Binary mixture
k 12
Source
R600aqR236fa RE170qR236fa R134aqR236fa R125qR236fa R32qR236fa R22qRE170
0.1368 y0.0900 y0.0073 y0.0008 y0.0325 y0.1203
a
a b
This work, experimental VLE data from Ref. w1,2x. This work, experimental VLE data from Ref. w6x.
w4x a
w3x w3x b
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
309
Fig. 5. Deviations of pressure for all data.
in mole fraction for each of these systems ŽFig. 6.. This value is far below "0.005 that can be considered as the limit to state the thermodynamic consistency between the experimental data and the model used for the correlation. A good representation of the pressure was also achieved for the system R600aq R236fa, but the deviations in vapor compositions were higher, though still within the limit of "0.005. For the RE170q R236fa system, S-shaped deviations were evident for the pressure Ž Fig. 5. and the deviations for the vapor composition were above "0.005 in mole fraction, as well as being clearly systematic. In our opinion, they cannot be attributed to experimental errors, but rather to the performance of the model involved. To verify our hypothesis, we compared the results of fitting the VLE data for the RE170q R22 Žchlorodifluoromethane. system w6x; the respective deviations are shown in Figs. 7 and 8. The systematic deviations for the RE170q R22 system are even more evident, clearly above the accuracy declared by the authors.
Fig. 6. Deviations of vapor composition for all data.
310
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
Fig. 7. Deviations of pressure for the system RE170Ž1.qR22 at 283 K Žv . and 323 K Ž`. with CSD EOS. Experimental data from Ref. w6x.
The excess Gibbs energy, g E , values were calculated from the CSD EOS using the following function: g E s RT Ž ln f y Ý x i ln f i . Ž2. where R is the gas constant, T is the absolute temperature, f is the fugacity coefficient of the mixture and f i is the fugacity coefficient of the ith component of the mixture at the same temperature and pressure. The character of the properties of the systems considered is clearly evident when the excess Gibbs energy, g E , is plotted as a function of composition at 303 K ŽFig. 9.. All systems formed by HFCs show a very small g E within "40 Jrmol at most. A much higher g E is shown by the systems R600aq R236fa Žabout 870 Jrmol at most., and RE170q R236fa Žabout y470 Jrmol at most.. The negative value of g E for the last system clearly comes from the hydrogen bonding.
Fig. 8. Deviations of vapor composition for the system RE170Ž1.qR22 at 283 K Žv . and 323 K Ž`.. Experimental data from Ref. w6x.
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
311
Fig. 9. Excess Gibbs energy at 303 K of the systems with R236fa.
It is worth pointing out that strong hydrogen bonding of RE170 with partially fluorinated hydrocarbons was reported in literature on the basis of VLE measurements for two systems, RE170q R22 w6x and RE170q R236fa w4x. The strong proton donor properties of chloroform are well-known and the partial replacement of chlorine atoms with fluorine atoms Žthat are more electronegative. can therefore be expected to cause the formation of hydrogen bonding by R22. As for the second system, the proton donor property of hydrogen results from the molecular structure of R236fa which, in order to induce a strong hydrogen bonding, has to be not linear, but bent —and consequently polar, with a smaller steric hindrance to the proton acceptor. A comparison between the g E produced by these two systems is shown in Fig. 10. For the former system, the g E values at 303 K were calculated again using the CSD EOS with the k 12 values that we had calculated. Clearly the g E for the RE170q R22 mixture is more negative than that for the RE170q R236fa. The behavior of the systems illustrated in Figs. 2–4 prompts the following remarks, classifying the systems into three groups: Ža. Mixtures of R236fa with hydrofluorocarbons ŽHFC. : these all show small deviations from Raoult’s law; no dependence was detected on differences in molecular parameters, such as ratio of critical volume, difference in critical temperatures and, probably, differences in dipole moment.
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
312
Fig. 10. Excess Gibbs energy for the systems RE170Ž1.qR236fa and RE170Ž1.qR22.
Žb. System of R236fa with hydrocarbon Ž HC. shows a strong positive deviation from Raoult’s law; a qualitatively similar deviation is also shown by other systems belonging to this group, for which data are reported in the literature. Žc. Mixture of R236fa with dimethyl ether shows a strong negative deviations from Raoult’s law that can be attributed to hydrogen bonding. Our results suggest that the phenomenon of hydrogen bonding is more frequent between some HFC and compounds with proton acceptor. This means that the hydrogen bonding may also play an important part in the solubility of refrigerants in polyester and polyether oils, which also have proton acceptor groups.
3. Conclusions The main findings emerging from the series of VLE measurements for mixtures including R236fa was a new positive azeotrope for the mixture R600aq R236fa and the proton-donor properties of R236fa, with the ability to induce hydrogen bonding with proton acceptor compounds. Finally, the systems with various HFCs followed Raoult’s law well. For these latter mixtures, temperature glide depends solely on the differences in saturated pressure of the second component of the systems.
4. Nomenclature CSD EOS F HFC g k p
Carnahan–Starling–De Santis Equation of state objective function hydrofluorocarbon Gibbs energy ŽJrmol. binary interaction parameter pressure ŽkPa.
S. Bobbo et al.r Fluid Phase Equilibria 161 (1999) 305–313
R T
gas constant 8.3144 ŽJrmol K. temperature ŽK.
Greek letters D f x y
deviation Žexperimentaly calculated. fugacity coefficient Ž – . liquid molar fraction vapor molar fraction
Subscripts cal exp i, j
calculated experimental ith, jth component of the mixture
Superscripts E
excess
313
Acknowledgements The CNR-ITEF is grateful to the European Community Commission for supporting this research. Mauro Scattolini is gratefully acknowledged for his collaboration in the experiments.
References w1x S. Bobbo, R. Stryjek, N. Elvassore, A. Bertucco, A recirculation apparatus for vapor–liquid equilibrium measurements of refrigerants. Binary Mixtures of R600a, R134a and R236fa, 13th Symposium on Thermophysical Properties, Boulder, Colorado June 22–27, 1997. w2x S. Bobbo, R. Stryjek, N. Elvassore, A. Bertucco, Fluid Phase Equilibria 150–151 Ž1998. 343–352. w3x S. Bobbo, R. Camporese, R. Stryjek, Vapor–liquid equilibria for difluoromethane ŽR-32.q, and pentafluoroethane ŽR-125.q1,1,1,3,3,3-hexafluoropropane ŽR-236fa. at 303.2 K and 323.3 K, J. Chem. Eng. Data, accepted for publication. w4x S. Bobbo, R. Camporese, R. Stryjek, Vaporqliquid equilibrium measurements and correlations of the refrigerant mixture dimethyl ether ŽRE170.q1,1,1,3,3,3-hexafluoropropane ŽR236fa.4 at the temperatures of Ž303.68 and 323.75. K, J. Chem. Thermodyn. 30 Ž1998. 1041–1046. w5x R. De Santis, F. Gironi, L. Marrelli, Vapor–liquid equilibria from a hard sphere equation of state, Ind. Eng. Chem. Fundam. 15 Ž1976. 183–189. w6x J.R. Noles, J.A. Zollweg, Vapor–liquid equilibrium for chlorodifluoromethaneqdimethyl ether from 283 to 395 K at pressures to 5.0 MPa, J. Chem. Eng. Data 37 Ž1992. 306–310. w7x M. Huber, J. Gallagher, M. McLinden, G. Morrison, NIST thermodynamic properties of refrigerants and refrigerant mixtures database ŽREFPROP., Version 5.0, National Institute of Standards and Technology, Thermophysics Division, Gaithersburg, MD, 1996.