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Vapor–liquid equilibria and densities of ternary mixtures of fluorinated ethers with hydrofluorocarbons as R22 alternatives
Fluid Phase Equilibria 222–223 (2004) 231–237
Vapor–liquid equilibria and densities of ternary mixtures of fluorinated ethers with hydrofluorocarbons as R22 alternatives Ismail Kul a,1 , Adolph L. Beyerlein b,∗ , Darryl D. DesMarteau b b
a Department of Chemistry, Widener University, One University Place, Chester, PA 19013, USA Department of Chemistry, Hunter Laboratories, Clemson University, Clemson, SC 29634-0973, USA
Available online 24 July 2004
Abstract Vapor pressure data below the normal boiling point are presented for ternary mixtures that are prepared from the following chemicals: perfluoro[methylethyl ether] (RE-218), pentafluorodimethylether (RE-125), 1,1,1-trifluorodimethylether (RE-143a), dimethylether (RE-170), 1,1,1,2-tetrafluoroethane (R-134a), 1,1,1-trifluoroethane (R-143a), 1,1-difluoroethane (R-152a), fluoroethane (R-161), and difluoromethane (R-32). Liquid–liquid phase separation in the binary mixtures RE-218/RE-170 and RE-218/R-161 is eliminated with the ternary mixtures, RE-218/RE-143a/RE-170 and RE-218/R-134a/R-161. A sufficient amount of vapor pressure data was obtained for these ternary mixtures to calculate vapor–liquid phase relations using van Laar equations for ternary mixtures. Vapor pressure data are also reported for a number of ternary mixtures containing RE-125. Liquid density data and the critical parameters are reported for the equimolar mixtures, RE-218/R-134a/R-161, RE-125/R-32/R-152a, and RE-125/R-32/R-134a, which are judged to have a high potential as R-22 alternatives based on their boiling point and critical temperature. © 2004 Elsevier B.V. All rights reserved. Keywords: Vapor–liquid equilibria; Vapor pressure; Perfluoro[ethylmethylether]; Pentafluorodimethylether; R-22; Refrigerants
1. Introduction The search for R-22 replacements has identified binary azeotropic mixtures of perfluoro[ethylmethylether] (RE-218) with partially fluorinated ethane derivatives or the partially fluorinated ether, 1,1,1-trifluoromethylmethylether (RE-143a). These mixtures have boiling points lower than −30 ◦ C and critical temperatures higher than 80 ◦ C [1–3]. The boiling points and critical temperatures should be compared to those of R-22, −40.1 and 96 ◦ C, respectively. However, other binary mixtures investigated, such as RE-218/R-161 or RE-218/RE-170, (R-161 and RE-170 refer to fluoroethane and dimethylether, respectively). that yields low boiling points approaching that of R-22 have high liquid–liquid phase separation temperatures which may be a factor in refrigeration applications. ∗
Corresponding author. Tel.: +1 864 654 4128; fax: +1 864 656 6613. E-mail addresses: [email protected] (I. Kul), [email protected] (A.L. Beyerlein), [email protected] (D.D. DesMarteau). 1 Completed portions of this work in partial fulfillment of the requirements of a Ph.D. in Chemistry at Clemson University. Thesis is available from University Microfilms, Ann Arbor, MI, with Order No. 3095424. 0378-3812/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2004.06.024
In order to eliminate the liquid–liquid phase separation temperatures for binary mixtures containing RE-218, 1,1,1,2-tetrafluoroethane (R-134a) or RE-143a are added to the binary mixtures producing the ternary mixtures, RE-218/RE-143a/RE-170 and RE-218/R-134a/R-161 and the vapor pressures of these mixtures at various compositions are studied. In addition ternary mixtures containing pentafluorodimethyl ether (RE-125) are investigated to determine if lower boiling points and higher critical temperatures that approach those of R-22 can be achieved. It is the purpose of this paper to report the results of these investigations.
2. Experimental methods and results For a description of the experimental methods the reader is referred to the authors’ previous publications [2–5]. Briefly the vapor pressures below the boiling point were measured to within ±0.5 kPa using MKS capacitance pressure sensors and the temperatures were measured within ±0.1 K using a copper constantan thermocouple calibrated against a precision Guildline platinum resistance thermometer. The mix-
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Table 1 Experimental vapor pressure below the normal boiling point as a function of temperature and mole fraction ratio for RE-218/RE-143a/RE-170 mixtures 70:15:15 t (◦ C) P (kPa) 31.5 38.1 45.3 53.3 61.2 69.6 80.9 88.8 94.1 98.5
P (kPa)
−58.9 −55.6 −52.5 −49.2 −46.5 −43.5 −41.4 −38.9 −37.3 −35.9 −34.5 −33.5
26.1 31.6 38.1 45.3 52.1 60.8 67.7 76.5 82.1 87.9 93.6 98.5
45:35:20
40:20:40
t (◦ C)
P (kPa)
−52.0 −50.0 −48.0 −45.7 −43.7 −41.9 −40.5 −38.2 −36.2 −34.1 −32.4
36.9 41.2 46.4 52.4 57.9 63.3 68.1 76.0 83.5 92.1 99.3
35:35:30
t (◦ C)
P (kPa)
−57.0 −54.9 −52.8 −51.2 −49.2 −47.3 −45.6 −43.8 −42.3 −40.5 −38.7 −37.0 −36.0 −34.9
31.5 35.6 40.1 43.9 48.8 53.7 58.8 64.5 69.7 76.1 82.8 89.5 93.9 98.4
t (◦ C)
P (kPa)
−62.8 −58.1 −54.5 −51.5 −48.7 −46.1 −43.8 −41.6 −39.4 −37.6 −35.4 −34.4 −33.0
20.0 26.9 33.1 39.2 45.9 52.7 59.3 66.3 73.5 80.5 88.5 93.1 98.8
33:33:33 t (◦ C) P (kPa) −57.1 −53.0 −50.6 −48.0 −45.4 −43.1 −40.9 −38.3 −37.2 −35.4 −34.0 −32.7
28.0 35.5 40.5 46.8 53.6 60.1 67.1 76.8 80.5 87.1 93.3 98.5
30:30:40
25.5:25.5:49
t (◦ C)
P (kPa)
−64.6 −60.2 −56.2 −53.3 −50.4 −47.6 −45.1 −42.5 −40.0 −38.4 −36.7 −35.0 −34.0
18.8 24.8 31.3 37.1 43.9 50.8 57.5 65.9 74.4 80.3 86.8 93.3 98.0
20:20:60
20:60:20
15:15:70
10:10:80
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
−59.8 −56.0 −53.1 −50.6 −48.0 −45.5 −43.1 −41.0 −38.7 −37.0 −35.4 −34.3
25.5 32.0 38.3 43.9 50.5 57.6 65.2 72.1 80.5 87.2 93.3 99.1
−59.8 −56.2 −53.4 −50.7 −48.5 −46.3 −44.0 −42.1 −40.4 −37.2 −36.4 −35.0
25.9 32.7 38.5 45.3 51.1 57.3 64.4 70.8 77.3 89.3 93.1 98.9
−62.8 −56.9 −53.3 −49.7 −45.9 −42.6 −39.2 −37.2 −34.8 −32.6 −31.6 −30.5
17.5 25.3 31.3 38.8 47.5 55.5 65.5 72.4 80.8 88.9 93.5 98.7
−60.0 −56.4 −53.4 −51.2 −49.0 −46.8 −44.6 −42.5 −40.7 −38.9 −37.1 −35.6
27.1 33.3 39.5 44.8 50.7 57.1 63.7 70.8 77.7 84.1 92.3 98.5
t (◦ C)
P (kPa)
−57.4 −54.5 −51.5 −49.2 −46.5 −45.6 −43.9 −42.4 −41.0 −39.5 −37.8 −36.5 −35.6
31.3 37.5 44.8 50.9 58.9 61.7 66.9 72.0 77.5 83.3 89.6 95.1 98.4
Table 2 Experimental vapor pressure below the normal boiling point as a function of temperature and mole fraction ratio for RE-218/R-134a/RE-161 mixtures 74:10.5:15.5
60:15:25
50:18.6:31.4
45:45:10
40:22.1:37.9
33.3:33.3:33.3
30:30:40
20.7:56:23.3
15:20:65
t (◦ C)
85:5:10 P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
40:40:20 P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
30:26:44 P (kPa)
t (◦ C)
25:30:45 P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
10:10:80 P (kPa)
t (◦ C)
10:80:10 P (kPa)
−47.6 −45.7 −44.0 −42.1 −40.7 −39.5 −38.2 −37.0 −35.8 −34.7 −33.5 −32.8
54.9 59.1 62.7 67.2 71.3 75.1 79.1 83.2 87.1 91.6 95.7 98.3
−47.7 −46.1 −45.0 −43.2 −42.0 −40.9 −39.6 −38.3 −37.0 −36.0
60.5 64.3 67.9 72.9 76.8 80.7 84.7 89.5 94.8 98.7
−54.2 −52.3 −50.5 −48.4 −47.0 −45.6 −43.7 −42.3 −40.9 −39.7 −38.2
47.3 52.1 56.8 62.8 67.2 72.0 78.0 83.3 88.4 93.2 99.2
−55.2 −53.7 −52.2 −50.3 −48.9 −47.5 −46.0 −44.5 −43.2 −42.0 −40.8 −39.6 −38.7
42.8 46.7 50.8 56.3 60.5 64.9 69.7 75.2 79.9 85.2 89.9 94.1 98.5
−48.4 −46.9 −45.6 −44.2 −42.7 −41.4 −39.9 −38.6 −37.3 −36.0 −35.2 −34.2
48.8 52.9 56.8 61.2 65.7 70.3 75.6 80.1 85.6 90.9 94.7 98.8
−54.4 −52.5 −50.6 −48.8 −46.6 −45.0 −43.1 −40.9 −38.3 −36.7 −35.3
37.6 41.7 46.3 51.1 57.2 62.4 68.7 76.4 86.4 93.1 99.7
−52.8 −51.3 −50.0 −49.0 −47.9 −46.7 −45.6 −44.2 −43.2 −42.2 −41.0 −39.9 −38.8
49.2 53.6 57.3 60.5 64.4 68.1 72.0 76.8 80.7 84.5 89.9 94.0 98.5
−55.1 −52.5 −50.8 −49.0 −47.2 −45.7 −44.1 −42.2 −40.8 −38.7 −37.3
40.0 46.0 50.5 55.6 61.3 66.1 71.5 78.4 83.6 92.3 98.7
−54.0 −52.5 −51.0 −49.5 −48.1 −46.6 −45.2 −43.5 −42.0 −40.8 −39.6 −38.4
44.8 48.9 53.1 57.3 61.9 66.8 71.7 77.7 83.5 88.5 93.3 98.8
−57.7 −55.4 −53.8 −51.3 −50.1 −48.8 −47.8 −46.7 −45.4 −43.9 −42.6 −41.4 −40.1 −38.9
37.7 42.9 46.9 54.0 57.7 61.5 64.8 68.7 73.3 78.4 83.7 88.9 93.7 99.3
−53.7 −52.4 −50.7 −48.9 −47.4 −45.7 −43.4 −41.9 −40.8 −39.6 −38.4
45.3 48.9 53.7 59.1 63.9 69.7 78.3 83.2 88.3 93.5 98.1
−49.5 −48.0 −46.0 −44.3 −42.9 −41.3 −39.8 −38.3 −36.7 −35.5 −34.5
45.9 50.5 55.9 61.2 66.1 71.5 76.9 82.3 88.8 93.9 98.5
−54.8 −53.4 −51.8 −50.1 −48.6 −46.9 −45.5 −44.1 −42.6 −41.4 −40.3
47.6 51.2 56.3 61.5 66.7 72.1 77.5 83.3 88.8 94.1 98.5
−58.0 −56.0 −54.1 −52.3 −50.7 −48.8 −47.4 −45.8 −44.4 −42.9 −41.5
43.3 48.5 54.1 58.9 64.5 70.1 75.7 81.6 87.3 93.3 99.1
−48.6 −47.0 −45.3 −43.8 −42.3 −39.9 −38.4 −37.1 −35.6 −34.4 −32.9 −31.0
42.0 45.6 49.6 53.9 58.1 65.3 69.9 74.8 79.9 85.3 90.9 99.5
I. Kul et al. / Fluid Phase Equilibria 222–223 (2004) 231–237
−55.6 −52.2 −48.9 −45.7 −42.9 −40.2 −36.8 −34.9 −33.5 −32.5
47.1:26.4:26.4
t (◦ C)
32.3 38.4 44.5 51.5 59.1 65.9 73.9 86.0 97.9 −54.3 −51.3 −48.6 −45.7 −43.0 −40.8 −38.3 −35.2 −32.4 46.1 50.3 54.1 59.5 64.8 70.1 74.9 80.4 86.4 90.9 94.5 98.8 −52.4 −50.7 −49.1 −47.3 −45.5 −43.9 −42.5 −41.0 −39.4 −38.2 −37.4 −36.4 41.3 45.6 51.1 56.0 60.8 66.7 76.1 80.7 86.8 92.8 100.3 −58.1 −56.3 −54.3 −52.5 −50.9 −49.2 −46.6 −45.3 −43.8 −42.3 −40.6 40.4 44.9 49.9 54.4 58.7 63.6 69.7 74.9 80.4 86.3 92.0 99.5 37.6 42.9 47.3 52.1 56.8 62.3 66.1 71.7 81.6 90.1 95.2 100.3 −61.2 −59.0 −56.9 −54.8 −52.9 −50.9 −49.1 −47.3 −45.5 −44.0 −42.8 −41.4 −40.2
34.3 38.4 43.2 48.1 53.2 59.1 64.8 70.5 77.5 83.1 88.3 93.5 98.9
−52.1 −50.3 −48.3 −45.9 −44.7 −43.5 −42.3 −40.9 −39.7 −38.3 −37.2
48.4 53.2 58.9 66.3 70.4 74.4 78.5 84.0 88.1 94.4 98.9
−59.7 −57.1 −54.6 −52.9 −50.9 −48.8 −46.0 −44.3 −42.6 −41.1 −39.5 −37.5
31.9 36.7 41.9 46.4 51.6 57.9 66.0 71.9 78.4 83.9 90.5 99.1
−62.4 −60.2 −58.4 −56.7 −54.9 −53.3 −52.1 −50.5 −47.8 −45.8 −44.7 −43.5
−58.5 −56.6 −54.7 −53.1 −51.6 −50.0 −48.3 −46.9 −45.3 −43.9 −42.3 −40.8
P (kPa) t (◦ C) P (kPa) t P (kPa) t P (kPa) t P (kPa) t P (kPa) t P (kPa) t P (kPa) t
RE-125/RE-143a/R-143a
(◦ C) (◦ C)
RE-125/R-32/R-134a RE-125/R-32/R-152a
(◦ C) (◦ C)
RE-125/R-32/R-161 RE-125/R-143a/R-134a
(◦ C) (◦ C)
RE-125/R-143a/R-152a RE-125/R-143a/R-161
Table 3 Experimental vapor pressures below the boiling point for equimolar ternary mixtures containing RE-125
(◦ C)
RE-125/RE-143a/R-161
I. Kul et al. / Fluid Phase Equilibria 222–223 (2004) 231–237
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tures were prepared to a prescribed mole fraction within 0.5% accuracy by condensing the components of the mixture into the sample bulb from a calibrated volume. The critical temperature was measured by slowly raising the temperature of the sample in a sealed tube until the disappearance of the meniscus was observed. The saturated liquid density, ρL , and rectilinear diameters, ρ [= (ρL + ρg )/2, ρg being the saturated vapor density], were measured as function of temperature within 1 kg/m3 by preparing several samples of differing weight in a precision bore tube (25 cm in length) and measuring the displacement of the meniscus from the bottom of the tube with a Gaertner cathetometer. The chemicals used in this work were synthesized to 99.5% purity, excepting R-161 (CH3 CH2 F) which was purchased from PCR. The purity of R-161 was verified to be 99.5% by a combination of 1 H and 19 F NMR spectroscopy, FT-IR spectroscopy, and GC–MS spectroscopy. The results of the vapor measurements are presented in Tables 1–4 and the results of the density measurements are presented in Table 5. The vapor pressures of the ternary mixtures containing RE-218 are presented in Tables 1 and 2 at a number of compositions. One of these ternary mixtures contains RE-218 which is perfluorinated and RE-170 which contains no fluorine. These two components would form very non-ideal binary mixtures whose boiling point in principle could be sufficiently lowered below those of the pure components to approach the boiling point of R-22. However, the non-ideality of these mixtures is so great that liquid–liquid phase separation would occur up to temperatures above the normal boiling point. The liquid–liquid phase separation is eliminated by adding the third component, RE-143a (CF3 OCH3 ), with an intermediate fluorine content. Effectively, the non-ideality could be tuned by adjusting the content of RE-143a to produce the optimal boiling point for Table 4 Experimental vapor pressure measurements as a function of temperature for selected ternary mixtures between the normal boiling point and critical temperature RE218/R134a/R161 t
(◦ C)
14.2 20.7 25.0 30.1 35.1 40.2 45.5 50.5 56.3 60.5 65.4 70.1 74.3 77.4
RE125/R32/R134a (◦ C)
P (kPa)
t
698.3 839.6 944.9 1082.6 1235.1 1402.7 1596.9 1797.7 2046.5 2249.4 2499.7 2763.2 3015.5 3214.0
14.6 17.2 20.2 24.9 30.2 35.2 40.0 46.3 50.2 55.2 60.1 66.1 71.1 74.0 80.8
RE125/R32/R152a
P (kPa)
t (◦ C)
P (kPa)
811.5 875.2 951.9 1080.9 1243.7 1409.7 1585.5 1832.0 2000.5 2230.9 2471.5 2789.6 3074.7 3245.3 3675.8
11.6 16.8 22.0 27.2 32.4 37.6 42.8 48.0 53.2 58.3 63.5 68.7 73.9 79.1 84.3 89.5
736 859 996 1148 1317 1503 1709 1935 2182 2453 2748 3071 3423 3807 4226 4682
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I. Kul et al. / Fluid Phase Equilibria 222–223 (2004) 231–237
Table 5 Measured saturated liquid densities and diameters between the boiling point and critical temperature for selected ternary mixtures RE218/R134a/R161 t
(◦ C)
24.1 31.0 35.5 40.7 45.6 51.6 55.5 60.4
ρL
(kg/m3 )
1133.1 1102.3 1080.4 1053.4 1038.3 1002.0 978.5 947.8
RE125/R32/R134a ρ
(kg/m3 )
593.1 583.5 577.3 570.1 563.3 555.0 549.6 542.8
t
(◦ C)
22.4 27.7 36.1 41.2 46.6 51.3 58.8
ρL
RE125/R32/R152a ρ
(kg/m3 )
1176.2 1150.2 1111.5 1087.4 1060.5 1035.9 999.5
the resulting ternary mixture. For this reason we have investigated numerous compositions of these mixtures and the measured vapor pressures are given in Table 1. Likewise, the vapor pressures of RE-218/R-134a/R-161 are examined at a number of compositions and are presented in Table 2. Unlike mixtures containing RE-218, the vapor pressure of mixtures containing RE-125 exhibit nearly ideal behavior [3]. Therefore, detailed composition studies of these mixtures were not performed. Rather a number of ternary mixtures were examined which contained RE-125 and various other components in equimolar amounts. The vapor pressure measurements from these studies are presented in Table 3. From these investigations it was judged based on boiling point and critical temperature that three of the equimolar mixtures, RE-218/R-134a/R-161, RE-125/R-134a/R-161 and RE-125/R-32/R-152, have high potential as R-22 alternatives. Vapor pressure measurements for these mixtures were extended to temperatures above the boiling point, approaching the gas–liquid critical temperature and are presented in Table 4. The saturated liquid density and
(kg/m3 )
611.1 603.4 591.1 583.6 575.8 568.9 557.9
t (◦ C)
ρL (kg/m3 )
ρ (kg/m3 )
22.7 30.6 35.8 41.9 50.8 56.8 61.1
1150.3 1125.2 1104.9 1075.8 1034.0 993.1 968.8
591.1 580.1 572.8 564.2 551.8 543.4 537.4
3. Discussion of results In order to analyze the vapor–liquid phase diagram for the ternary mixtures containing RE-218 and identify possible azeotropic compositions, a three-component van Laar analysis described by Wohl [6] was applied to the vapor pressure data in Tables 1 and 2. It begins by fitting the vapor pressure data to the following van Laar equations by the least-squares method: P = P10 x1 γ1 + P20 x2 γ2 + P30 x3 γ3
(1)
where γ 1 , γ 2 and γ 3 are the activity coefficients of components 1, 2 and 3, respectively. P10 , P20 and P30 are the vapor pressures for pure components 1–3 and x1 , x2 and x3 the liquid mole fractions of the components, respectively. The vapor phase mole fractions, y1 and y2 are estimated from y1 =
x1 P10 γ1 P
(2)
x2 P20 γ2 (3) P The activity coefficients for ternary liquid mixtures are given by y2 =
log γ1 = 2 x2 A1–2 (A2–1 /A1–2 )2 + x32 A1–3 (A3–1 /A1–3 )2 + x2 x3 (A2–1 /A1–2 )(A3–1 /A1–3 )(A1–2 + A1–3 − A3–2 (A1–3 /A3–1 )) × (x1 + x2 (A2–1 /A1–2 ) + x3 (A3–1 /A1–3 ))2 (4) log γ2 = 2 x3 A2–3 (A3–2 /A2–3 )2 + x12 A2–1 (A1–2 /A2–1 )2 + x3 x1 (A3–2 /A2–3 )(A1–2 /A2–1 )(A2–3 + A2–1 − A1–3 (A2–1 /A1–2 )) × (x2 + x3 (A3–2 /A2–3 ) + x1 (A1–2 /A2–1 ))2 (5) log γ3 = 2 x1 A3–1 (A1–3 /A3–1 )2 + x22 A3–2 (A2–3 /A3–2 )2 + x1 x2 (A1–3 /A3–1 )(A2–3 /A3–2 )(A3–1 + A3–2 − A2–1 (A3–2 /A2–3 )) × (x3 + x1 (A1–3 /A3–1 ) + x2 (A2–3 /A3–2 ))2 (6) rectilinear diameters measured for these mixtures are presented in Table 5.
where A1–2 , A2–1 , A1–3 , A3–1 , A2–3 and A3–2 represent the van Laar parameters as proposed by Wohl [6]. Eqs. (1)–(6)
I. Kul et al. / Fluid Phase Equilibria 222–223 (2004) 231–237
Fig. 1. Boiling point diagram of the RE-218/RE-143a/RE-170 ternary mixtures vs. mole fractions of liquid components.
assume that the vapor fugacity is equal to the partial vapor pressure of the corresponding components. The temperature dependence of the van Laar coefficients are assumed to be linear with the reciprocal Kelvin temperature. The results of fitting the vapor pressure data in Tables 1 and 2 to these van Laar equations by least-squares calculation is given in Table 6. The pure component vapor pressure data needed for these calculations is taken from our previous publications [1,3,7], i.e. vapor pressure data for RE-218, RE-143a, R-161 were obtained from Kul and co-workers [1], for R-134a from Kul and co-workers [3], and for RE-170 from Kul [7]. In addition vapor pressure data from Kul et al. [8] for the binary mixtures, RE-218/RE-143a were also utilized. Using the van Laar Equations and the temperature-dependence of the van Laar coefficients, ternary compositions with the same boiling point were calculated and these compositions for various boiling points are presented in ternary composition diagrams (Figs. 1 and 2). One can view the lines of constant boiling point on these 2D diagrams as points on a sheet or surface of a three-dimensional
Fig. 2. Boiling point diagram of the RE-218/R-134a/R-161 ternary mixtures vs. mole fractions of liquid components.
235
ternary diagram in which the normal boiling point would be third-dimension. The approximate location of minima or troughs or valleys on this sheet are identified by directed lines in Figs. 1 and 2. For the RE-218/RE-143a/RE-170 mixtures (Fig. 1) the trough begins with the azeotropic minimum boiling (−30 ◦ C) composition of binary mixture, RE-218/RE-143a, and extends towards increasing mole fractions of the third component, RE-170. The boiling points along the trough decrease to −34 ◦ C. The calculated liquid and vapor phase compositions at one point along the trough are nearly equal, i.e. the liquid phase mole fractions are: x1 = 0.472, x2 = 0.264 and x3 = 0.264 with a boiling point of −32.8 ◦ C and the corresponding vapor phase compositions are y1 = 0.508, y2 = 0.237 and y3 = 0.255, where RE-218, RE-143a and RE-170 are components 1, 2 and 3, respectively. Although, this composition is not a true ternary azeotropic composition, it does have azeotropic like behavior and the terminology of ‘near azeotropic’ composition is used. Fig. 2 illustrates that the boiling point behavior of the mixture, RE-218/R-134a/R-161, parallels that of RE-218/RE-143a/RE-170. An azeotropic line or ‘trough’ begins with the azeotropic composition, 0.48 mole fraction of RE-218, of the binary mixture, RE-218/R-134a, whose azeotropic boiling point is −32 ◦ C. The azeotropic line extends towards increasing concentrations of the third component, R-161. As one increases the concentration of R-161, the boiling point rapidly decreases to −42 ◦ C at which point liquid–liquid phase separation occurs. The composition along the azeotropic line which is judged the best composition for R-22 refrigerant applications is at equimolar concentrations of the three components. This composition has a boiling point, −36.7 ◦ C that is well below that of the binary mixture, RE-218/R-134a. It is also expected to be non-flammable by the rule that the total number of C–F bonds in the mixture exceeds the sum of the total number of C–C and C–H bonds [9]. Mixtures with lower boiling points are expected to be flammable and to have high liquid–liquid phase separation temperatures. The vapor phase composition at the equimolar liquid composition indicates fractionation of the low boiling, R-161 component. Consequently, the “near azeotropic” behavior of these mixtures is poorer than RE-218/RE-143a/RE170 mixtures. However, because of their lower boiling point and higher critical temperature, the RE-218/R-134a/R-161 mixture is expected to have a higher potential as an R-22 alternative. The boiling point of the various ternary mixtures containing RE-125 was obtained by fitting the vapor pressure data in Table 3 to the following empirical relation: c ln P = a + b ln T + (7) T The results are summarized in Table 7 along with related results from prior work [2]. For comparison purposes we have also included in Table 7, results for ternary mixtures
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Table 6 Results of the van Laar analysis of the vapor pressure data below the boiling point A12
A21
A13
A31
A23
A32
RE-218 (1)/RE-143a (2)/RE-170 (3) mixtures (RMS Dev. = 2%) −0.2307 + (249.2/T) 5.9947 − (1080.4/T) −4.3277 + (1751.9/T)
5.474 − (813.4/T)
2.8439 − (663.3/T)
0.2278 − (53.17/T)
RE-218 (1)/R-134a (2)/R-161 (3) mixtures (RMS Dev. = 1%) −2.9947 + (1076.5/T) 2.6721 − (329.74/T) 1.3458 + (282.53/T)
−6.506 + (1825.5/T)
14.225 − (3407.5/T)
10.231 − (2485.6/T)
Table 7 Parameters of Eq. (7) obtained by a least-squares calculation on vapor pressures measured below the boiling point for equimolar ternary mixtures Mixture
Empirical parameters (Eq. (7))
RE-125/RE-143a/R-161a RE-125/R-134a/R-161a RE-218/RE-143a/RE-170 RE-125/RE-143a/R-143a RE-125/R-143a/R-152a RE-218/R-134a/R-161 RE-125/R-143a/R-134a RE-125/R-143a/R-161 RE-125/R-32/R-152a RE-125/R-32/R-134a RE-125/R-32/R-161 a
a
b
c
47.4876 77.9263 67.5142 19.0488 88.7409 82.5243 47.4327 13.0778 89.0983 91.9289 67.3819
−4.9541 −9.6493 −8.0479 −0.6094 −11.4379 −10.4078 −4.9688 0.3573 −11.4834 −11.9164 −8.1109
−3789.5 −4916.6 −4520.2 −2633.8 −5109.6 −4970.6 −3698.5 −2429.4 −5097.1 −5206.0 −4289.6
Boiling point (◦ C)
RMS Dev. (%)
−31.6 −31.8 −32.1 −35.8 −36.6 −36.7 −37.0 −39.7 −40.3 −40.4 −43.3
0.3 0.3 0.3 0.2 0.2 0.2 0.4 0.3 0.3 0.2 0.3
Data taken from Kul et al. [2].
Table 8 Empirical representations for liquid density, boiling point and critical constants for ternary mixtures with high potential for R-22 replacement Mixture
Liquid density (kg/m3 ) (t = celsius temperature)
tb (◦ C)
tc (◦ C)
ρc (kg/m3 )
Pc (kPa)
RE-218/R-134a/R-161 RE-125/R-32/R-134a RE-125/R-32/R-152a
1210.7−2.5911t−0.02869t2
−36.7 −40.4 −40.3
87.6 86.2 89.5
504 515 498
3930 4038 4682
1276.0−4.3302t−0.00642t2 1189.4−0.59099t−0.04965t2
containing RE-218 that were investigated in this work. The results are ordered with decreasing boiling point.
4. Summary of conclusions The ternary mixture van Laar analysis [6] are useful for identifying azeotropic and near azeotropic compositions for the non-ideal mixtures. A near azeotropic composition is determined for the ternary mixture, RE-218/RE-143a/RE-170 with a mole fraction ratio of 0.472:0.264:0.264 and a boiling point of −32.8 ◦ C. However, based on the boiling point, the optimal mixture for R-22 replacement that contains RE-218 is the equimolar mixture of RE-218/R-134a/R-161 (see Table 7) with a boiling point of −36.7 ◦ C. The optimal mixtures that contain RE-125 are the equimolar mixtures RE-125/R-32/R-134a and RE-125/R-32/R-152a with boiling points of −40.4 and −40.3 ◦ C, respectively (see Table 7). Saturated liquid densities and diameters were measured for these mixtures. Also the vapor pressures were measured upto temperatures approaching the critical temperature (see Table 4).
A parametric representation of the liquid density data along with the critical constants is presented in Table 8. The critical density in Table 8 was obtained by extrapolating the diameters to the critical temperature and the critical pressure is calculated from the Riedel vapor pressure equation (ln P = α + β/Tr + γ ln Tr + δTr6 , where Tr = T/Tc ) [10] which has been fitted to vapor pressure data (see Table 4) for temperatures ranging from the boiling point upto near the critical temperature. These data along with vapor pressure data, Benson et al. database for ideal gas heat capacities [11], and modified corresponding states methods [4] can be used to estimate the coefficient of performance of these mixtures as refrigerants using methods described in Bare [12] and Morrison and McLinden [13]. Such estimates are beyond the scope of this present paper and will be reported in a future publication [14]. List of symbols a, b, c parameters of the vapor pressure equation (7) Ai –j parameters of the van Laar equations (4)–(6)
I. Kul et al. / Fluid Phase Equilibria 222–223 (2004) 231–237
P Pi0 Pc T t Tb Tc xi yi Greek γi ρc ρg ρL ρ
vapor pressure vapor pressure of pure component i gas–liquid critical pressure Kelvin temperature Celsius temperature normal boiling point critical temperature liquid phase mole fraction of component i vapor phase mole fraction of component i letters activity coefficient of component i gas–liquid critical density saturated vapor density saturated liquid density (ρL + ρg )/2 rectilinear diameter
Acknowledgements The authors gratefully acknowledge the Electric Power Research Institute in Palo Alto, California, for supporting this research.
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References [1] A.L. Beyerlein, D.D. DesMarteau, I. Kul, G. Zhao, Fluid Phase Equilib. 150–151 (1998) 287–296. [2] I. Kul, D.D. DesMarteau, A.L. Beyerlein, Fluid Phase Equilib. 173 (2000) 263–276. [3] I. Kul, D.D. DesMarteau, A.L. Beyerlein, Fluid Phase Equilib. 185 (2001) 241–253. [4] A.L. Beyerlein, D.D. DesMarteau, S.-H. Hwang, N.D. Smith, P.A. Joyner, ASHRAE Trans. 99 (1) (1993) 368–379. [5] A.L. Beyerlein, D.D. DesMarteau, K. Naik, Y. Xie, ASHRAE Trans. 102 (1) (1996) 358–366. [6] K. Wohl, AIChE Trans. 42 (1946) 215. [7] I. Kul, Ph.D. Thesis, Clemson University, 2001, available from University Microfilms, Ann Arbor, MI with Order no. 3095424. [8] N.D. Smith, K. Ratanaphruks, M.W. Tufts, A.S. Ng, ASHRAE J. 35 (2) (1993) 19–23. [9] I. Kul, D.D. DesMarteau, A.L. Beyerlein, ASHRAE Trans. 106 (1) (1999) 351–357. [10] L. Riedel, Chem. Eng. Tech. 26 (1954) 83–89. [11] S.W. Benson, F.R. Cruickshank, D.M. Golden, G.R. Haugen, H.E. O’Neal, A.S. Rodgers, R. Shaw, R. Walsh, Chem. Rev. 69 (1969) 279. [12] J.C. Bare, ASHRAE Trans. 99 (1) (1993) 397. [13] G. Morrison, M.O. McLinden, NBS Technical Note 1226, National Institute of Standards and Technology, Gaithersburg, MD, Order No. PB87-104410/GAR, 1986. [14] I. Kul, D.D. DesMarteau, A.L. Beyerlein, ASHRAE Trans. 110 (2) (2004).
Vapor–liquid equilibria and densities of ternary mixtures of fluorinated ethers with hydrofluorocarbons as R22 alternatives Ismail Kul a,1 , Adolph L. Beyerlein b,∗ , Darryl D. DesMarteau b b
a Department of Chemistry, Widener University, One University Place, Chester, PA 19013, USA Department of Chemistry, Hunter Laboratories, Clemson University, Clemson, SC 29634-0973, USA
Available online 24 July 2004
Abstract Vapor pressure data below the normal boiling point are presented for ternary mixtures that are prepared from the following chemicals: perfluoro[methylethyl ether] (RE-218), pentafluorodimethylether (RE-125), 1,1,1-trifluorodimethylether (RE-143a), dimethylether (RE-170), 1,1,1,2-tetrafluoroethane (R-134a), 1,1,1-trifluoroethane (R-143a), 1,1-difluoroethane (R-152a), fluoroethane (R-161), and difluoromethane (R-32). Liquid–liquid phase separation in the binary mixtures RE-218/RE-170 and RE-218/R-161 is eliminated with the ternary mixtures, RE-218/RE-143a/RE-170 and RE-218/R-134a/R-161. A sufficient amount of vapor pressure data was obtained for these ternary mixtures to calculate vapor–liquid phase relations using van Laar equations for ternary mixtures. Vapor pressure data are also reported for a number of ternary mixtures containing RE-125. Liquid density data and the critical parameters are reported for the equimolar mixtures, RE-218/R-134a/R-161, RE-125/R-32/R-152a, and RE-125/R-32/R-134a, which are judged to have a high potential as R-22 alternatives based on their boiling point and critical temperature. © 2004 Elsevier B.V. All rights reserved. Keywords: Vapor–liquid equilibria; Vapor pressure; Perfluoro[ethylmethylether]; Pentafluorodimethylether; R-22; Refrigerants
1. Introduction The search for R-22 replacements has identified binary azeotropic mixtures of perfluoro[ethylmethylether] (RE-218) with partially fluorinated ethane derivatives or the partially fluorinated ether, 1,1,1-trifluoromethylmethylether (RE-143a). These mixtures have boiling points lower than −30 ◦ C and critical temperatures higher than 80 ◦ C [1–3]. The boiling points and critical temperatures should be compared to those of R-22, −40.1 and 96 ◦ C, respectively. However, other binary mixtures investigated, such as RE-218/R-161 or RE-218/RE-170, (R-161 and RE-170 refer to fluoroethane and dimethylether, respectively). that yields low boiling points approaching that of R-22 have high liquid–liquid phase separation temperatures which may be a factor in refrigeration applications. ∗
Corresponding author. Tel.: +1 864 654 4128; fax: +1 864 656 6613. E-mail addresses: [email protected] (I. Kul), [email protected] (A.L. Beyerlein), [email protected] (D.D. DesMarteau). 1 Completed portions of this work in partial fulfillment of the requirements of a Ph.D. in Chemistry at Clemson University. Thesis is available from University Microfilms, Ann Arbor, MI, with Order No. 3095424. 0378-3812/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2004.06.024
In order to eliminate the liquid–liquid phase separation temperatures for binary mixtures containing RE-218, 1,1,1,2-tetrafluoroethane (R-134a) or RE-143a are added to the binary mixtures producing the ternary mixtures, RE-218/RE-143a/RE-170 and RE-218/R-134a/R-161 and the vapor pressures of these mixtures at various compositions are studied. In addition ternary mixtures containing pentafluorodimethyl ether (RE-125) are investigated to determine if lower boiling points and higher critical temperatures that approach those of R-22 can be achieved. It is the purpose of this paper to report the results of these investigations.
2. Experimental methods and results For a description of the experimental methods the reader is referred to the authors’ previous publications [2–5]. Briefly the vapor pressures below the boiling point were measured to within ±0.5 kPa using MKS capacitance pressure sensors and the temperatures were measured within ±0.1 K using a copper constantan thermocouple calibrated against a precision Guildline platinum resistance thermometer. The mix-
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Table 1 Experimental vapor pressure below the normal boiling point as a function of temperature and mole fraction ratio for RE-218/RE-143a/RE-170 mixtures 70:15:15 t (◦ C) P (kPa) 31.5 38.1 45.3 53.3 61.2 69.6 80.9 88.8 94.1 98.5
P (kPa)
−58.9 −55.6 −52.5 −49.2 −46.5 −43.5 −41.4 −38.9 −37.3 −35.9 −34.5 −33.5
26.1 31.6 38.1 45.3 52.1 60.8 67.7 76.5 82.1 87.9 93.6 98.5
45:35:20
40:20:40
t (◦ C)
P (kPa)
−52.0 −50.0 −48.0 −45.7 −43.7 −41.9 −40.5 −38.2 −36.2 −34.1 −32.4
36.9 41.2 46.4 52.4 57.9 63.3 68.1 76.0 83.5 92.1 99.3
35:35:30
t (◦ C)
P (kPa)
−57.0 −54.9 −52.8 −51.2 −49.2 −47.3 −45.6 −43.8 −42.3 −40.5 −38.7 −37.0 −36.0 −34.9
31.5 35.6 40.1 43.9 48.8 53.7 58.8 64.5 69.7 76.1 82.8 89.5 93.9 98.4
t (◦ C)
P (kPa)
−62.8 −58.1 −54.5 −51.5 −48.7 −46.1 −43.8 −41.6 −39.4 −37.6 −35.4 −34.4 −33.0
20.0 26.9 33.1 39.2 45.9 52.7 59.3 66.3 73.5 80.5 88.5 93.1 98.8
33:33:33 t (◦ C) P (kPa) −57.1 −53.0 −50.6 −48.0 −45.4 −43.1 −40.9 −38.3 −37.2 −35.4 −34.0 −32.7
28.0 35.5 40.5 46.8 53.6 60.1 67.1 76.8 80.5 87.1 93.3 98.5
30:30:40
25.5:25.5:49
t (◦ C)
P (kPa)
−64.6 −60.2 −56.2 −53.3 −50.4 −47.6 −45.1 −42.5 −40.0 −38.4 −36.7 −35.0 −34.0
18.8 24.8 31.3 37.1 43.9 50.8 57.5 65.9 74.4 80.3 86.8 93.3 98.0
20:20:60
20:60:20
15:15:70
10:10:80
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
−59.8 −56.0 −53.1 −50.6 −48.0 −45.5 −43.1 −41.0 −38.7 −37.0 −35.4 −34.3
25.5 32.0 38.3 43.9 50.5 57.6 65.2 72.1 80.5 87.2 93.3 99.1
−59.8 −56.2 −53.4 −50.7 −48.5 −46.3 −44.0 −42.1 −40.4 −37.2 −36.4 −35.0
25.9 32.7 38.5 45.3 51.1 57.3 64.4 70.8 77.3 89.3 93.1 98.9
−62.8 −56.9 −53.3 −49.7 −45.9 −42.6 −39.2 −37.2 −34.8 −32.6 −31.6 −30.5
17.5 25.3 31.3 38.8 47.5 55.5 65.5 72.4 80.8 88.9 93.5 98.7
−60.0 −56.4 −53.4 −51.2 −49.0 −46.8 −44.6 −42.5 −40.7 −38.9 −37.1 −35.6
27.1 33.3 39.5 44.8 50.7 57.1 63.7 70.8 77.7 84.1 92.3 98.5
t (◦ C)
P (kPa)
−57.4 −54.5 −51.5 −49.2 −46.5 −45.6 −43.9 −42.4 −41.0 −39.5 −37.8 −36.5 −35.6
31.3 37.5 44.8 50.9 58.9 61.7 66.9 72.0 77.5 83.3 89.6 95.1 98.4
Table 2 Experimental vapor pressure below the normal boiling point as a function of temperature and mole fraction ratio for RE-218/R-134a/RE-161 mixtures 74:10.5:15.5
60:15:25
50:18.6:31.4
45:45:10
40:22.1:37.9
33.3:33.3:33.3
30:30:40
20.7:56:23.3
15:20:65
t (◦ C)
85:5:10 P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
40:40:20 P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
30:26:44 P (kPa)
t (◦ C)
25:30:45 P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
P (kPa)
t (◦ C)
10:10:80 P (kPa)
t (◦ C)
10:80:10 P (kPa)
−47.6 −45.7 −44.0 −42.1 −40.7 −39.5 −38.2 −37.0 −35.8 −34.7 −33.5 −32.8
54.9 59.1 62.7 67.2 71.3 75.1 79.1 83.2 87.1 91.6 95.7 98.3
−47.7 −46.1 −45.0 −43.2 −42.0 −40.9 −39.6 −38.3 −37.0 −36.0
60.5 64.3 67.9 72.9 76.8 80.7 84.7 89.5 94.8 98.7
−54.2 −52.3 −50.5 −48.4 −47.0 −45.6 −43.7 −42.3 −40.9 −39.7 −38.2
47.3 52.1 56.8 62.8 67.2 72.0 78.0 83.3 88.4 93.2 99.2
−55.2 −53.7 −52.2 −50.3 −48.9 −47.5 −46.0 −44.5 −43.2 −42.0 −40.8 −39.6 −38.7
42.8 46.7 50.8 56.3 60.5 64.9 69.7 75.2 79.9 85.2 89.9 94.1 98.5
−48.4 −46.9 −45.6 −44.2 −42.7 −41.4 −39.9 −38.6 −37.3 −36.0 −35.2 −34.2
48.8 52.9 56.8 61.2 65.7 70.3 75.6 80.1 85.6 90.9 94.7 98.8
−54.4 −52.5 −50.6 −48.8 −46.6 −45.0 −43.1 −40.9 −38.3 −36.7 −35.3
37.6 41.7 46.3 51.1 57.2 62.4 68.7 76.4 86.4 93.1 99.7
−52.8 −51.3 −50.0 −49.0 −47.9 −46.7 −45.6 −44.2 −43.2 −42.2 −41.0 −39.9 −38.8
49.2 53.6 57.3 60.5 64.4 68.1 72.0 76.8 80.7 84.5 89.9 94.0 98.5
−55.1 −52.5 −50.8 −49.0 −47.2 −45.7 −44.1 −42.2 −40.8 −38.7 −37.3
40.0 46.0 50.5 55.6 61.3 66.1 71.5 78.4 83.6 92.3 98.7
−54.0 −52.5 −51.0 −49.5 −48.1 −46.6 −45.2 −43.5 −42.0 −40.8 −39.6 −38.4
44.8 48.9 53.1 57.3 61.9 66.8 71.7 77.7 83.5 88.5 93.3 98.8
−57.7 −55.4 −53.8 −51.3 −50.1 −48.8 −47.8 −46.7 −45.4 −43.9 −42.6 −41.4 −40.1 −38.9
37.7 42.9 46.9 54.0 57.7 61.5 64.8 68.7 73.3 78.4 83.7 88.9 93.7 99.3
−53.7 −52.4 −50.7 −48.9 −47.4 −45.7 −43.4 −41.9 −40.8 −39.6 −38.4
45.3 48.9 53.7 59.1 63.9 69.7 78.3 83.2 88.3 93.5 98.1
−49.5 −48.0 −46.0 −44.3 −42.9 −41.3 −39.8 −38.3 −36.7 −35.5 −34.5
45.9 50.5 55.9 61.2 66.1 71.5 76.9 82.3 88.8 93.9 98.5
−54.8 −53.4 −51.8 −50.1 −48.6 −46.9 −45.5 −44.1 −42.6 −41.4 −40.3
47.6 51.2 56.3 61.5 66.7 72.1 77.5 83.3 88.8 94.1 98.5
−58.0 −56.0 −54.1 −52.3 −50.7 −48.8 −47.4 −45.8 −44.4 −42.9 −41.5
43.3 48.5 54.1 58.9 64.5 70.1 75.7 81.6 87.3 93.3 99.1
−48.6 −47.0 −45.3 −43.8 −42.3 −39.9 −38.4 −37.1 −35.6 −34.4 −32.9 −31.0
42.0 45.6 49.6 53.9 58.1 65.3 69.9 74.8 79.9 85.3 90.9 99.5
I. Kul et al. / Fluid Phase Equilibria 222–223 (2004) 231–237
−55.6 −52.2 −48.9 −45.7 −42.9 −40.2 −36.8 −34.9 −33.5 −32.5
47.1:26.4:26.4
t (◦ C)
32.3 38.4 44.5 51.5 59.1 65.9 73.9 86.0 97.9 −54.3 −51.3 −48.6 −45.7 −43.0 −40.8 −38.3 −35.2 −32.4 46.1 50.3 54.1 59.5 64.8 70.1 74.9 80.4 86.4 90.9 94.5 98.8 −52.4 −50.7 −49.1 −47.3 −45.5 −43.9 −42.5 −41.0 −39.4 −38.2 −37.4 −36.4 41.3 45.6 51.1 56.0 60.8 66.7 76.1 80.7 86.8 92.8 100.3 −58.1 −56.3 −54.3 −52.5 −50.9 −49.2 −46.6 −45.3 −43.8 −42.3 −40.6 40.4 44.9 49.9 54.4 58.7 63.6 69.7 74.9 80.4 86.3 92.0 99.5 37.6 42.9 47.3 52.1 56.8 62.3 66.1 71.7 81.6 90.1 95.2 100.3 −61.2 −59.0 −56.9 −54.8 −52.9 −50.9 −49.1 −47.3 −45.5 −44.0 −42.8 −41.4 −40.2
34.3 38.4 43.2 48.1 53.2 59.1 64.8 70.5 77.5 83.1 88.3 93.5 98.9
−52.1 −50.3 −48.3 −45.9 −44.7 −43.5 −42.3 −40.9 −39.7 −38.3 −37.2
48.4 53.2 58.9 66.3 70.4 74.4 78.5 84.0 88.1 94.4 98.9
−59.7 −57.1 −54.6 −52.9 −50.9 −48.8 −46.0 −44.3 −42.6 −41.1 −39.5 −37.5
31.9 36.7 41.9 46.4 51.6 57.9 66.0 71.9 78.4 83.9 90.5 99.1
−62.4 −60.2 −58.4 −56.7 −54.9 −53.3 −52.1 −50.5 −47.8 −45.8 −44.7 −43.5
−58.5 −56.6 −54.7 −53.1 −51.6 −50.0 −48.3 −46.9 −45.3 −43.9 −42.3 −40.8
P (kPa) t (◦ C) P (kPa) t P (kPa) t P (kPa) t P (kPa) t P (kPa) t P (kPa) t P (kPa) t
RE-125/RE-143a/R-143a
(◦ C) (◦ C)
RE-125/R-32/R-134a RE-125/R-32/R-152a
(◦ C) (◦ C)
RE-125/R-32/R-161 RE-125/R-143a/R-134a
(◦ C) (◦ C)
RE-125/R-143a/R-152a RE-125/R-143a/R-161
Table 3 Experimental vapor pressures below the boiling point for equimolar ternary mixtures containing RE-125
(◦ C)
RE-125/RE-143a/R-161
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tures were prepared to a prescribed mole fraction within 0.5% accuracy by condensing the components of the mixture into the sample bulb from a calibrated volume. The critical temperature was measured by slowly raising the temperature of the sample in a sealed tube until the disappearance of the meniscus was observed. The saturated liquid density, ρL , and rectilinear diameters, ρ [= (ρL + ρg )/2, ρg being the saturated vapor density], were measured as function of temperature within 1 kg/m3 by preparing several samples of differing weight in a precision bore tube (25 cm in length) and measuring the displacement of the meniscus from the bottom of the tube with a Gaertner cathetometer. The chemicals used in this work were synthesized to 99.5% purity, excepting R-161 (CH3 CH2 F) which was purchased from PCR. The purity of R-161 was verified to be 99.5% by a combination of 1 H and 19 F NMR spectroscopy, FT-IR spectroscopy, and GC–MS spectroscopy. The results of the vapor measurements are presented in Tables 1–4 and the results of the density measurements are presented in Table 5. The vapor pressures of the ternary mixtures containing RE-218 are presented in Tables 1 and 2 at a number of compositions. One of these ternary mixtures contains RE-218 which is perfluorinated and RE-170 which contains no fluorine. These two components would form very non-ideal binary mixtures whose boiling point in principle could be sufficiently lowered below those of the pure components to approach the boiling point of R-22. However, the non-ideality of these mixtures is so great that liquid–liquid phase separation would occur up to temperatures above the normal boiling point. The liquid–liquid phase separation is eliminated by adding the third component, RE-143a (CF3 OCH3 ), with an intermediate fluorine content. Effectively, the non-ideality could be tuned by adjusting the content of RE-143a to produce the optimal boiling point for Table 4 Experimental vapor pressure measurements as a function of temperature for selected ternary mixtures between the normal boiling point and critical temperature RE218/R134a/R161 t
(◦ C)
14.2 20.7 25.0 30.1 35.1 40.2 45.5 50.5 56.3 60.5 65.4 70.1 74.3 77.4
RE125/R32/R134a (◦ C)
P (kPa)
t
698.3 839.6 944.9 1082.6 1235.1 1402.7 1596.9 1797.7 2046.5 2249.4 2499.7 2763.2 3015.5 3214.0
14.6 17.2 20.2 24.9 30.2 35.2 40.0 46.3 50.2 55.2 60.1 66.1 71.1 74.0 80.8
RE125/R32/R152a
P (kPa)
t (◦ C)
P (kPa)
811.5 875.2 951.9 1080.9 1243.7 1409.7 1585.5 1832.0 2000.5 2230.9 2471.5 2789.6 3074.7 3245.3 3675.8
11.6 16.8 22.0 27.2 32.4 37.6 42.8 48.0 53.2 58.3 63.5 68.7 73.9 79.1 84.3 89.5
736 859 996 1148 1317 1503 1709 1935 2182 2453 2748 3071 3423 3807 4226 4682
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Table 5 Measured saturated liquid densities and diameters between the boiling point and critical temperature for selected ternary mixtures RE218/R134a/R161 t
(◦ C)
24.1 31.0 35.5 40.7 45.6 51.6 55.5 60.4
ρL
(kg/m3 )
1133.1 1102.3 1080.4 1053.4 1038.3 1002.0 978.5 947.8
RE125/R32/R134a ρ
(kg/m3 )
593.1 583.5 577.3 570.1 563.3 555.0 549.6 542.8
t
(◦ C)
22.4 27.7 36.1 41.2 46.6 51.3 58.8
ρL
RE125/R32/R152a ρ
(kg/m3 )
1176.2 1150.2 1111.5 1087.4 1060.5 1035.9 999.5
the resulting ternary mixture. For this reason we have investigated numerous compositions of these mixtures and the measured vapor pressures are given in Table 1. Likewise, the vapor pressures of RE-218/R-134a/R-161 are examined at a number of compositions and are presented in Table 2. Unlike mixtures containing RE-218, the vapor pressure of mixtures containing RE-125 exhibit nearly ideal behavior [3]. Therefore, detailed composition studies of these mixtures were not performed. Rather a number of ternary mixtures were examined which contained RE-125 and various other components in equimolar amounts. The vapor pressure measurements from these studies are presented in Table 3. From these investigations it was judged based on boiling point and critical temperature that three of the equimolar mixtures, RE-218/R-134a/R-161, RE-125/R-134a/R-161 and RE-125/R-32/R-152, have high potential as R-22 alternatives. Vapor pressure measurements for these mixtures were extended to temperatures above the boiling point, approaching the gas–liquid critical temperature and are presented in Table 4. The saturated liquid density and
(kg/m3 )
611.1 603.4 591.1 583.6 575.8 568.9 557.9
t (◦ C)
ρL (kg/m3 )
ρ (kg/m3 )
22.7 30.6 35.8 41.9 50.8 56.8 61.1
1150.3 1125.2 1104.9 1075.8 1034.0 993.1 968.8
591.1 580.1 572.8 564.2 551.8 543.4 537.4
3. Discussion of results In order to analyze the vapor–liquid phase diagram for the ternary mixtures containing RE-218 and identify possible azeotropic compositions, a three-component van Laar analysis described by Wohl [6] was applied to the vapor pressure data in Tables 1 and 2. It begins by fitting the vapor pressure data to the following van Laar equations by the least-squares method: P = P10 x1 γ1 + P20 x2 γ2 + P30 x3 γ3
(1)
where γ 1 , γ 2 and γ 3 are the activity coefficients of components 1, 2 and 3, respectively. P10 , P20 and P30 are the vapor pressures for pure components 1–3 and x1 , x2 and x3 the liquid mole fractions of the components, respectively. The vapor phase mole fractions, y1 and y2 are estimated from y1 =
x1 P10 γ1 P
(2)
x2 P20 γ2 (3) P The activity coefficients for ternary liquid mixtures are given by y2 =
log γ1 = 2 x2 A1–2 (A2–1 /A1–2 )2 + x32 A1–3 (A3–1 /A1–3 )2 + x2 x3 (A2–1 /A1–2 )(A3–1 /A1–3 )(A1–2 + A1–3 − A3–2 (A1–3 /A3–1 )) × (x1 + x2 (A2–1 /A1–2 ) + x3 (A3–1 /A1–3 ))2 (4) log γ2 = 2 x3 A2–3 (A3–2 /A2–3 )2 + x12 A2–1 (A1–2 /A2–1 )2 + x3 x1 (A3–2 /A2–3 )(A1–2 /A2–1 )(A2–3 + A2–1 − A1–3 (A2–1 /A1–2 )) × (x2 + x3 (A3–2 /A2–3 ) + x1 (A1–2 /A2–1 ))2 (5) log γ3 = 2 x1 A3–1 (A1–3 /A3–1 )2 + x22 A3–2 (A2–3 /A3–2 )2 + x1 x2 (A1–3 /A3–1 )(A2–3 /A3–2 )(A3–1 + A3–2 − A2–1 (A3–2 /A2–3 )) × (x3 + x1 (A1–3 /A3–1 ) + x2 (A2–3 /A3–2 ))2 (6) rectilinear diameters measured for these mixtures are presented in Table 5.
where A1–2 , A2–1 , A1–3 , A3–1 , A2–3 and A3–2 represent the van Laar parameters as proposed by Wohl [6]. Eqs. (1)–(6)
I. Kul et al. / Fluid Phase Equilibria 222–223 (2004) 231–237
Fig. 1. Boiling point diagram of the RE-218/RE-143a/RE-170 ternary mixtures vs. mole fractions of liquid components.
assume that the vapor fugacity is equal to the partial vapor pressure of the corresponding components. The temperature dependence of the van Laar coefficients are assumed to be linear with the reciprocal Kelvin temperature. The results of fitting the vapor pressure data in Tables 1 and 2 to these van Laar equations by least-squares calculation is given in Table 6. The pure component vapor pressure data needed for these calculations is taken from our previous publications [1,3,7], i.e. vapor pressure data for RE-218, RE-143a, R-161 were obtained from Kul and co-workers [1], for R-134a from Kul and co-workers [3], and for RE-170 from Kul [7]. In addition vapor pressure data from Kul et al. [8] for the binary mixtures, RE-218/RE-143a were also utilized. Using the van Laar Equations and the temperature-dependence of the van Laar coefficients, ternary compositions with the same boiling point were calculated and these compositions for various boiling points are presented in ternary composition diagrams (Figs. 1 and 2). One can view the lines of constant boiling point on these 2D diagrams as points on a sheet or surface of a three-dimensional
Fig. 2. Boiling point diagram of the RE-218/R-134a/R-161 ternary mixtures vs. mole fractions of liquid components.
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ternary diagram in which the normal boiling point would be third-dimension. The approximate location of minima or troughs or valleys on this sheet are identified by directed lines in Figs. 1 and 2. For the RE-218/RE-143a/RE-170 mixtures (Fig. 1) the trough begins with the azeotropic minimum boiling (−30 ◦ C) composition of binary mixture, RE-218/RE-143a, and extends towards increasing mole fractions of the third component, RE-170. The boiling points along the trough decrease to −34 ◦ C. The calculated liquid and vapor phase compositions at one point along the trough are nearly equal, i.e. the liquid phase mole fractions are: x1 = 0.472, x2 = 0.264 and x3 = 0.264 with a boiling point of −32.8 ◦ C and the corresponding vapor phase compositions are y1 = 0.508, y2 = 0.237 and y3 = 0.255, where RE-218, RE-143a and RE-170 are components 1, 2 and 3, respectively. Although, this composition is not a true ternary azeotropic composition, it does have azeotropic like behavior and the terminology of ‘near azeotropic’ composition is used. Fig. 2 illustrates that the boiling point behavior of the mixture, RE-218/R-134a/R-161, parallels that of RE-218/RE-143a/RE-170. An azeotropic line or ‘trough’ begins with the azeotropic composition, 0.48 mole fraction of RE-218, of the binary mixture, RE-218/R-134a, whose azeotropic boiling point is −32 ◦ C. The azeotropic line extends towards increasing concentrations of the third component, R-161. As one increases the concentration of R-161, the boiling point rapidly decreases to −42 ◦ C at which point liquid–liquid phase separation occurs. The composition along the azeotropic line which is judged the best composition for R-22 refrigerant applications is at equimolar concentrations of the three components. This composition has a boiling point, −36.7 ◦ C that is well below that of the binary mixture, RE-218/R-134a. It is also expected to be non-flammable by the rule that the total number of C–F bonds in the mixture exceeds the sum of the total number of C–C and C–H bonds [9]. Mixtures with lower boiling points are expected to be flammable and to have high liquid–liquid phase separation temperatures. The vapor phase composition at the equimolar liquid composition indicates fractionation of the low boiling, R-161 component. Consequently, the “near azeotropic” behavior of these mixtures is poorer than RE-218/RE-143a/RE170 mixtures. However, because of their lower boiling point and higher critical temperature, the RE-218/R-134a/R-161 mixture is expected to have a higher potential as an R-22 alternative. The boiling point of the various ternary mixtures containing RE-125 was obtained by fitting the vapor pressure data in Table 3 to the following empirical relation: c ln P = a + b ln T + (7) T The results are summarized in Table 7 along with related results from prior work [2]. For comparison purposes we have also included in Table 7, results for ternary mixtures
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Table 6 Results of the van Laar analysis of the vapor pressure data below the boiling point A12
A21
A13
A31
A23
A32
RE-218 (1)/RE-143a (2)/RE-170 (3) mixtures (RMS Dev. = 2%) −0.2307 + (249.2/T) 5.9947 − (1080.4/T) −4.3277 + (1751.9/T)
5.474 − (813.4/T)
2.8439 − (663.3/T)
0.2278 − (53.17/T)
RE-218 (1)/R-134a (2)/R-161 (3) mixtures (RMS Dev. = 1%) −2.9947 + (1076.5/T) 2.6721 − (329.74/T) 1.3458 + (282.53/T)
−6.506 + (1825.5/T)
14.225 − (3407.5/T)
10.231 − (2485.6/T)
Table 7 Parameters of Eq. (7) obtained by a least-squares calculation on vapor pressures measured below the boiling point for equimolar ternary mixtures Mixture
Empirical parameters (Eq. (7))
RE-125/RE-143a/R-161a RE-125/R-134a/R-161a RE-218/RE-143a/RE-170 RE-125/RE-143a/R-143a RE-125/R-143a/R-152a RE-218/R-134a/R-161 RE-125/R-143a/R-134a RE-125/R-143a/R-161 RE-125/R-32/R-152a RE-125/R-32/R-134a RE-125/R-32/R-161 a
a
b
c
47.4876 77.9263 67.5142 19.0488 88.7409 82.5243 47.4327 13.0778 89.0983 91.9289 67.3819
−4.9541 −9.6493 −8.0479 −0.6094 −11.4379 −10.4078 −4.9688 0.3573 −11.4834 −11.9164 −8.1109
−3789.5 −4916.6 −4520.2 −2633.8 −5109.6 −4970.6 −3698.5 −2429.4 −5097.1 −5206.0 −4289.6
Boiling point (◦ C)
RMS Dev. (%)
−31.6 −31.8 −32.1 −35.8 −36.6 −36.7 −37.0 −39.7 −40.3 −40.4 −43.3
0.3 0.3 0.3 0.2 0.2 0.2 0.4 0.3 0.3 0.2 0.3
Data taken from Kul et al. [2].
Table 8 Empirical representations for liquid density, boiling point and critical constants for ternary mixtures with high potential for R-22 replacement Mixture
Liquid density (kg/m3 ) (t = celsius temperature)
tb (◦ C)
tc (◦ C)
ρc (kg/m3 )
Pc (kPa)
RE-218/R-134a/R-161 RE-125/R-32/R-134a RE-125/R-32/R-152a
1210.7−2.5911t−0.02869t2
−36.7 −40.4 −40.3
87.6 86.2 89.5
504 515 498
3930 4038 4682
1276.0−4.3302t−0.00642t2 1189.4−0.59099t−0.04965t2
containing RE-218 that were investigated in this work. The results are ordered with decreasing boiling point.
4. Summary of conclusions The ternary mixture van Laar analysis [6] are useful for identifying azeotropic and near azeotropic compositions for the non-ideal mixtures. A near azeotropic composition is determined for the ternary mixture, RE-218/RE-143a/RE-170 with a mole fraction ratio of 0.472:0.264:0.264 and a boiling point of −32.8 ◦ C. However, based on the boiling point, the optimal mixture for R-22 replacement that contains RE-218 is the equimolar mixture of RE-218/R-134a/R-161 (see Table 7) with a boiling point of −36.7 ◦ C. The optimal mixtures that contain RE-125 are the equimolar mixtures RE-125/R-32/R-134a and RE-125/R-32/R-152a with boiling points of −40.4 and −40.3 ◦ C, respectively (see Table 7). Saturated liquid densities and diameters were measured for these mixtures. Also the vapor pressures were measured upto temperatures approaching the critical temperature (see Table 4).
A parametric representation of the liquid density data along with the critical constants is presented in Table 8. The critical density in Table 8 was obtained by extrapolating the diameters to the critical temperature and the critical pressure is calculated from the Riedel vapor pressure equation (ln P = α + β/Tr + γ ln Tr + δTr6 , where Tr = T/Tc ) [10] which has been fitted to vapor pressure data (see Table 4) for temperatures ranging from the boiling point upto near the critical temperature. These data along with vapor pressure data, Benson et al. database for ideal gas heat capacities [11], and modified corresponding states methods [4] can be used to estimate the coefficient of performance of these mixtures as refrigerants using methods described in Bare [12] and Morrison and McLinden [13]. Such estimates are beyond the scope of this present paper and will be reported in a future publication [14]. List of symbols a, b, c parameters of the vapor pressure equation (7) Ai –j parameters of the van Laar equations (4)–(6)
I. Kul et al. / Fluid Phase Equilibria 222–223 (2004) 231–237
P Pi0 Pc T t Tb Tc xi yi Greek γi ρc ρg ρL ρ
vapor pressure vapor pressure of pure component i gas–liquid critical pressure Kelvin temperature Celsius temperature normal boiling point critical temperature liquid phase mole fraction of component i vapor phase mole fraction of component i letters activity coefficient of component i gas–liquid critical density saturated vapor density saturated liquid density (ρL + ρg )/2 rectilinear diameter
Acknowledgements The authors gratefully acknowledge the Electric Power Research Institute in Palo Alto, California, for supporting this research.
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