Measurements of Bubble Point Pressures for the Binary Mixture of

Nov 4, 2013 - Measurements of Bubble Point Pressures for the Binary Mixture of ... Zhi-qiang Yang , Lian-gang Kou , Wei Mao , Jing Lu , Wei Zhang , an...
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Measurements of Bubble Point Pressures for the Binary Mixture of Pentafluoroethane with Chloropentafluoroethane Wei Zhang, Zhi-qiang Yang, Wei Mao, and Jian Lu* Xi’an Modern Chemistry Research Institute, Xi’an, Shaanxi 710065, People’s Republic of China ABSTRACT: Bubble point pressures for the binary mixture of pentafluoroethane (HFC-125) with chloropentafluoroethane (CFC115) were measured at the temperature ranges from (243.15 to 333.15) K using a static apparatus. The uncertainties of measurements were estimated to be less than 20 mK in temperature, 1.2 kPa in pressure, and 0.001 in liquid-phase mole fraction. The experimental data were correlated with the Peng−Robinson equation of state with van der Waals mixing rules. The correlation results have a good agreement with the experimental results. The overall average absolute deviation was 0.36 % between measured pressures and calculated results from the Peng−Robinson (PR) equation of state. The interaction parameter k12 was obtained for different temperatures, and the relationship between k12 and the temperature was correlated with the deviation of ± 0.5 %. The azeotropic compositions and pressures at specified temperatures were calculated.

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INTRODUCTION Pentafluoroethane (HFC-125) is an important component in some alternative refrigerants that are promising replacements for HCFC-22.1−3 The fluorination of tetrachloroethene or 1,1,1-trifluoro-2,2-dichloroethane is the commercial process for manufacture of HFC-125,4−6 and chloropentafluoroethane (CFC-115) is the primary byproduct during this process. Vapor−liquid equilibrium (VLE) data of the mixture of CFC115 and HFC-125 are indispensable to design the purification process of HFC-125. However, to our knowledge, the VLE data for binary system of CFC-115 + HFC-125 are not reported as yet. In this work, the bubble point pressures for the binary mixture CFC-115 + HFC-125 were measured at (243.15, 253.15, 263.15, 273.15, 283.15, 293.15, 303.15, 313.5, 323.5, and 333.15) K. The experimental data were correlated with the Peng−Robinson equation of state (PR EOS) with van der Waals one-fluid mixing rules.7−10 The azeotropic compositions and pressures at specified temperatures were calculated.

Table 1. Specifications of the Chemicals Used chemicals HFC-125 CFC-115 a

Zhejiang Chemical Industry Research Institute Zhejiang Chemical Industry Research Institute

mass fraction purity

analysis method

0.999

GCa

0.999

GC

Gas chromatography.

differential pressure transducer (Xi’an Instrument, China; 1151DP) and an absolute pressure sensor (GE, PMP4051). The data were recorded using an Agilent 34970A acquisition/ switch unit and a personal computer. The total uncertainties of measurements were estimated less than ± 20 mK for temperature and ± 1.2 kPa for pressure at a confidence level of approximately 95 % (k = 2). The mass of each component introduced into the cell was determined with a digital balance (Sartorius Inc., BSA423S) having an accuracy of 0.001 g. The sample cell with a volume of 53.275 mL was used in this work. The sample cell was initially charged with the binary mixtures at a temperature of 243.15 K. About 30 g of CFC-115 and HFC-125 were added into the sample cell, and less than 15 mg of sample was lost in the pipes of the mixing apparatus during this process. Therefore, the absolute deviation of mass fraction was below 0.05 % for one component. The compositions of the liquid phase were calculated from the total composition by correction for the mass of each component existing in the vapor phase.12 The densities of the both phases were estimated by using the Peng− Robinson (PR) equation of state with van der Waals mixing rules without binary interaction parameter. The estimated

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EXPERIMENTAL SECTION Chemicals. The samples of HFC-125 and CFC-115 were supplied by Zhejiang Chemical Industry Research Institute. The specifications of the chemicals used are summarized in Table 1. The manufacturers stated that the purities of both HFC-125 and CFC-115 were above 0.999 in mass fraction. These samples were used in this study without further purification. Apparatus. The experimental data were measured using a static apparatus. The apparatus used in this work was similar to that described by Wang et al.11 Figure 1 depicts the scheme of our experimental apparatus. The temperature was measured by a platinum-resistance thermometer (Yunnan Instrument, China; no. 4349), while the pressure was measured by a © 2013 American Chemical Society

supplier

Received: September 18, 2013 Accepted: October 25, 2013 Published: November 4, 2013 3304

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Figure 1. Scheme of the apparatus. A, pressure sensors; B, digital multimeter; C, pressure bumper; CL, cooler; D, nitrogen bottle; DP, differential pressure detector; E, vacuum pump; F, pressure gauge; G, pressure balance controller; H, sample cell; HT, heater; J, thermostatic bath; K, auxiliary cooler; PC, computer; PT, platinum resistance thermometer; SP, standard platinum resistance thermometer; V1 to V9, valves.

Table 2. Experimental Data of Bubble Point Pressure P/kPa at Various Compositions and Temperatures for CFC-115 (1) + HFC-125 (2) Mixturesa T/K

a

x1

243.15

253.15

263.15

273.15

283.15

293.15

303.15

313.15

323.15

333.15

0 0.106 0.174 0.341 0.421 0.659 0.797 1

228.1 233.0 233.9 231.1 227.8 209.8 192.0 148.6

337.3 343.2 344.0 339.1 333.8 306.8 281.0 219.9

482.5 489.3 489.7 481.5 473.6 434.5 398.1 314.6

670.5 677.9 677.7 664.9 653.4 598.3 548.5 439.4

908.8 916.4 915.1 896.0 879.8 804.2 737.7 594.92

1205.2 1212.6 1209.7 1182.3 1160.1 1058.4 971.4 789.3

1568.5 1575.3 1570.1 1531.7 1501.6 1367.6 1255.7 1028.4

2008.5 2013.9 2005.8 1953.4 1913.3 1739.0 1597.3 1317.9

2536.8 2540.5 2528.6 2458.2 2405.4 2180.8 2003.5 1664.9

3170.3 3172.5 3146 3051.8 2991.9 2702.8 2482.9 2077.5

Standard uncertainties (k = 2) are u(T) = 0.02 K, u(P) = 1.2 kPa, and u(x1) = 0.001.

where P is the pressure, T is the temperature, R is the universal gas constant (8.314 J·mol−1·K−1), v is the mole volume, a(T) is the energy parameter which is a function of the absolute temperature, b is the excluded volume parameter, Pc is the critical pressure, Tc is the critical temperature, and ω is the acentric factor. Tc, Pc, and ω for HFC-125 and CFC-115 are provided in Table 3. Further, the mixing coefficients am and bm

uncertainties of the liquid-phase mole fraction was 0.001 at a confidence level of approximately 95 % (k = 2).

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RESULTS AND DISCUSSION Table 2 exhibits the experimental data of bubble point pressures for the binary system of CFC-115 (1) + HFC-125 (2) measured at the temperature ranges from (243.15 to 333.15) K with 10 K intervals and several mole fractions x1. The measured data of bubble point pressures were correlated with the following Peng−Robinson equation of state: P=

a(T ) RT − v−b v(v + b) + b(v − b)

Table 3. Critical Properties and Acentric Factors for Pure Chemicals13

(1)

a(T ) = (0.457235R2Tc2Pc)α(T )

(2)

b = 0.077796RTc/Pc

(3)

chemicals

Tc/K

Pc/kPa

ω

HFC-125 CFC-115

339.17 353.10

3617.7 3120.0

0.3052 0.2520

were estimated by using the van der Waals one-fluid mixing rule in this study. They are expressed as: N

with α(T ) = [1 + κ(1 − Tγ0.5)]2

am = (4)

i=1 i=1

(6)

N

and κ = 0.37464 + 1.54226ω − 0.26992ω 2

N

∑ ∑ yyi j aij

bm =

(5)

∑ yb i i i=1

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Article

aiaj (1 − kij)

(8)

where kij = kji, kii = 0, y is the mole fraction, and subscripts i and j denote the components. The binary interaction parameters kij was determined by minimizing the following objective function to fit the experimental bubble point pressure data: objective function =

1 n

n

∑

(Pi ,expt − Pi ,calc)

i=1

Pi ,expt

·100 % (9)

where n is the number of experimental points at the same temperature and pexpt and pcalc are the experimental pressure and calculated pressure, respectively. The correlation results are shown in Table 4. AAD is the average absolute deviation of pressure, and its definition is the same with the object function. Table 4. Interaction Parameter kij for CFC-115 (1) + HFC125 (2) and the Average Absolute Deviations for Pressure T/K

no. points

kij

AAD/%

243.15 253.15 263.15 273.15 283.15 293.15 303.15 313.15 323.15 333.15 average

8 8 8 8 8 8 8 8 8 8

0.0624 0.0629 0.0632 0.0636 0.0639 0.0641 0.0642 0.0645 0.0648 0.0652

0.36 0.36 0.34 0.36 0.32 0.31 0.33 0.38 0.40 0.43 0.36

Figure 2. Bubble point pressure for the CFC-115 (1) + HFC-125 (2) system at temperatures from (243.15 to 283.15) K (a) and from (293.15 to 333.15) K (b): ▲, 243.15 K; ▼, 253.15 K; ●, 263.15 K; ■, 273.15 K; ◆, 283.15 K; △, 293.15 K; ▽, 303.15 K; ○, 313.15 K; □, 323.15 K; ◇, 333.15 K; , bubble point pressure values calculated by the PR EOS; - - -, dew point pressure values calculated by PR EOS.

Figure 2 gives the bubble and dew point pressures estimated from the PR EOS for the binary mixtures of CFC-115 (1) + HFC-125 (2) at different temperatures against the compositions of CFC-115. Figure 3 shows the relative deviation from PR EOS. From Table 4 and Figures 2 and 3, it can be seen that the calculated values of PR EOS were consistent with the experimental data. The relative deviations were within ± 1 % between the experimental and calculated values for pressures, and the average absolute deviations were less than 0.5 % at temperatures from (243.15 to 333.15) K. The overall average absolute deviation of pressure was 0.36 %. The interaction parameters k12 increases as the temperature T increases, and the relationship between k12 and 1/T is approximately linear as shown in Figure 4. It was fitted by the following expression: k12 = 0.720 − 23.212/(T /K)

(10)

where T is the temperature. The relative deviation from the correlated values of k12 was less than ± 0.5 % at temperature from (243.15 to 333.15) K. When the PR EOS was calculated in the whole composition range with k12, it can be found that the binary system of CFC115 (1) + HFC-125 (2) had the azeotropic point. Table 5 displays the azeotropic compositions and pressures at specified temperatures from the calculated data. Figures 5 and 6 show the variation of the azeotropic compositions and pressures for the CFC-115 + HFC-125 binary mixtures, respectively. Azeotropic data of this mixture determined in the temperature of (243.15 to 333.15) K were 0.0661 to 0.2002 mole fraction of

Figure 3. Relative deviations of bubble point pressures from the PR EOS.

CFC-115 in composition and (324.6 to 3189.1) kPa in pressure. The results reveal that azeotropic composition and pressures depended on the temperature. In the experimental 3306

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Figure 4. Relationship between binary interaction parameters and temperatures: ▲, correlated k12; , predicted k12.

Figure 6. Variation of the calculated azeotropic pressure for the CFC115 (1) + HFC-125 (2) mixtures: ▲, this work; , predicted.

Table 5. Calculated Azeotropic Composition and Pressure of the CFC-115 (1) + HFC-125 (2) Mixture T/K

P/kPa

x1

T/K

P/kPa

x1

243.15 253.15 263.15 273.15 283.15

234.6 344.4 490.1 678.7 917.8

0.2002 0.1853 0.1695 0.1535 0.1374

293.15 303.15 313.15 323.15 333.15

1215.8 1581.7 2025.4 2557.3 3189.1

0.1213 0.105 0.0898 0.0766 0.0661

interaction parameter k12 was obtained at different temperatures, and the relationship between k12 and the temperature was correlated. The azeotropic compositions and pressures were calculated at specified temperatures. Temperature dependence correlation equations were proposed for the azeotropic compositions and azeotropic pressures.

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AUTHOR INFORMATION

Corresponding Author

*Fax: +86-29-88291213. Tel.: +86-29-88291213. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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(1) Kul, I.; DesMarteau, D. D.; Beyerlein, A. L. Vapor-liquid equilibria of novel chemicals and their mixtures as R-22 alternatives. Fluid Phase Equilib. 2000, 173, 263−276. (2) Han, X.; Chen, G.; Cui, X.; Wang, Q. Vapor−liquid equilibrium data for the binary mixture difluoroethane (HFC-32) + pentafluoroethane (HFC-125) of an alternative refrigerant. J. Chem. Eng. Data 2007, 52, 2112−2116. (3) Meng, L.; Duan, Y. Y.; Chen, Q. PVTx properties in the gas phase for difluoromethane (HFC-32) + pentafluoroethane (HFC-125). J. Chem. Eng. Data 2004, 49, 1821−1826. (4) Reshetnikov, S. I.; Zirka, A. A.; Petrov, R. V.; Ivanov, E. A. Kinetics study of the perchloroethylene hydrofluorination into pentafluoroethane (Freon 125) over chromium-based catalyst. Chem. Eng. J. 2011, 176, 22−25. (5) Lee, B. G.; Kim, H. S.; Kim, H.; Lee, S. D.; Sao, I. The fluorination of 1,1,1-trifluoro-2,2-dichloroethane to pentafluoroethane over Cr-based catalyst. J. Ind. Eng. Chem. 1997, 3, 160−164. (6) Coulson, D. R. Kinetics of the fluorination/chlorination of 1chloro-1,2,2,2-tetrafluoroethane. J. Catal. 1993, 142, 289−302. (7) Peng, D. Y.; Robinson, D. B. A new two-constant equation of state. Ind. Eng. Chem. Fundam. 1976, 15, 59−64. (8) Perry, R. H.; Green, D. W. Perry’s Chemical Engineering Handbook; McGraw-Hill: New York, 2001. (9) Smith, J. M.; van Ness, H.; Abbott, M. M. Introduction to Chemical Engineering Thermodynamics; McGraw-Hill: Boston, 2001. (10) Guo, J.; Wu, X.; Jing, S.; Zhang, Q.; Zheng, D. Vapor-liquid equilibrium of ethylene + mesitylene system and process simulation for ethylene recovery. Chin. J. Chem. Eng. 2011, 19, 543−548. (11) Wang, Z.; Duan, Y. Vapor pressures of 1,1,1,3,3-pentafluoropropane (HFC-245fa) and 1,1,1,2,3,3,3-heptafluoropropane (HFC227ea). J. Chem. Eng. Data 2004, 49, 1581−1585.

Figure 5. Variation of the calculated azeotropic composition for the CFC-115 (1) + HFC-125 (2) mixtures: ▲, this work; , predicted.

temperature range, the mole fraction of CFC-115 in azeotropic compositions was correlated by the empirical equation: x1,azeo = 0.57193 − 0.00153(T /K)

(11)

and azeotropic pressures were correlated by the equation: Pazeo = 18621.7302 − 153.8893(T /K) + 0.3225(T /K)2

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REFERENCES

(12)

CONCLUSIONS Measurements of bubble point pressures for binary mixtures of CFC-115 + HFC-125 were investigated at (253.15, 263.15, 273.15, 283.15, 293.15, 303.15, 313.15, 323.15, and 333.15) K. The experimental data were correlated with the PR EOS. The overall average absolute deviation was 0.36 % between measured and calculated bubble point pressures. The 3307

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(12) Chen, J. X.; Chen, Z. S.; Hu, P.; Jiang, B.; Li, Z. Vapor-liquid equilibria for the binary system pentafluoroethane (HFC-125) +isobutane (HC-600a) at temperatures from (243.15 to 333.15) K. J. Chem. Eng. Data 2007, 52, 2159−2162. (13) NIST Chemistry WebBook. http://webbook.nist.gov/ (2013).

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