Isothermal Vapor–Liquid Equilibrium Data for the Binary System 1, 1, 2

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Isothermal Vapor−Liquid Equilibrium Data for the Binary System 1,1,2,3,3,3-Hexafluoro-1-propene (R1216) + 2,2,3-Trifluoro-3(trifluoromethyl)oxirane from (268.13 to 308.19) K Wayne Michael Nelson, Mark Williams-Wynn, Shalendra Clinton Subramoney, and Deresh Ramjugernath* Thermodynamics Research Unit, School of Engineering, University of KwaZulu-Natal, Howard College Campus, Durban, South Africa ABSTRACT: Isothermal vapor−liquid equilibrium data were measured for the binary system 1,1,2,3,3,3-hexafluoro-1-propene +2,2,3-trifluoro-3-(trifluoromethyl)oxirane from (268 to 308) K using an apparatus based on the “static-analytic” method. The expanded uncertainties in the measurements were evaluated as 0.05 K, 0.6 kPa, 0.002, and 0.003 for the temperature, pressure, and liquid and vapor mole fractions, respectively. The experimental data were correlated with the Peng− Robinson equation of state using the classical mixing rule and the Mathias− Copeman alpha function. No azeotropes were observed within the temperature and pressure range studied; however, the binary mixture had relative volatilities close to unity, indicating that separation of the mixture via standard distillation is not feasible.

1. INTRODUCTION 2,2,3-Trifluoro-3-(trifluoromethyl)-oxirane (commonly known as hexafluoropropylene oxide, or HFPO) is an important fluorochemical intermediate, which can be used to produce high value materials.1,2 Traditional methods for the production of HFPO from 1,1,2,3,3,3-hexafluoro-1-propene (hexafluoropropene or R1216) are based on batch processes.1 Recently, Lokhat3 proposed a continuous process for the gas phase epoxidation of R1216 with molecular oxygen to produce HFPO. Both the continuous and the batch processes result in process streams consisting of HFPO, unreacted R1216, and low concentrations of side-products. The subsequent removal of the R1216 and the side-products is required to produce a high-purity HFPO product. To assess whether conventional distillation or extractive distillation can be used to facilitate the separation of HFPO from R1216,4−6 vapor−liquid equilibrium data for the HFPO + R1216 is required. Extractive distillation is generally applicable to systems with relative volatilities that are below 1.1, but greater than 0.9.7 Vapor−liquid equilibrium (VLE) data of high reliability and accuracy is imperative for optimization of distillation and distillation-type operations. However, the measurement of VLE data for close-boiling systems is immensely difficult.8 For compounds of similar volatility the conditions at equilibrium must be measured with high precision and accuracy. In general, VLE data published for close-boiling systems are sparse and often not consistent.8 This is probably the reason why there are no VLE data sets for the R1216 + HFPO binary system available in the open literature, and thus, all VLE data presented herein constitutes new data. © XXXX American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Materials. 1,1,2,3,3,3-Hexafluoro-1-propene (C3F6, CAS No. 116-15-4) and 2,2,3-trifluoro-3-(trifluoromethyl)oxirane (C3F6O, CAS No. 428-59-1) used in these measurements were supplied by the South African Nuclear Energy Corporation (NECSA). Both the chemical purities and the critical properties for the compounds are listed in Table 1. Table 1. Chemical Purities and Critical Properties for R1216 and HFPO chemical purity 21

R1216 HFPO22

critical properties21,22

suppliera

TCD area %b

ω

Tc/K

pc/MPa

0.999 0.997

99.85 99.70

0.3529 0.3338

358.9 359.3

3.136 2.931

a

Volume fraction stated by the Nuclear Energy Corporation of South Africa. bArea percentage of component identified by gas chromatography using a thermal conductivity detector (TCD) and a 5% Krytox CarboBlack B column.

The chemicals were degassed before measurements were undertaken. The degassing procedure involved repeatedly allowing vapor phase formation and then purging of the vapor from the equilibrium cell. This technique is only valid for the removal of light residual gases from the compounds and cannot remove heavier impurities or close-boiling components. Received: July 24, 2014 Accepted: December 17, 2014

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2.2. Experimental Apparatus. A “static-analytic” type equilibrium cell was used to perform the isothermal vapor−liquid equilibrium measurements. The equilibrium cell is a replica of the cell that was developed by Narasigadu et al.9 A sapphire tube enclosed at either end with stainless steel flanges forms the equilibrium cell which has an internal volume of approximately 18 cm3. The equilibrium cell was submerged in a 50 L steel bath filled with an antifreeze and water solution. The temperature of this fluid was maintained with an immersion circulator (Polyscience; model 7312). Polyscience states that this controller has a temperature stability of ± 0.01 K. Two 100 Ω platinum resistance thermometer (Pt100) probes (WIKA Instruments; model REB 1/10 DIN) were used to measure the temperature of the cell. One of these Pt100 probes was inserted into a well drilled into the top flange and the other into an identical well drilled into the bottom flange. The pressure within the cell was measured with a (0 to 6) MPa pressure transmitter (WIKA Instruments; model P-10). The linearity of the pressure transmitter as stated by WIKA Instruments is ≤ 0.05 % of the span. The pressure transmitter was housed within a heated aluminum block, maintained at a constant temperature of 313 K. This was to ensure that fluctuations in the ambient temperature did not disturb the pressure readings (temperature compensation between (273 and 323) K is also incorporated into the P-10 pressure transmitter). The portion of the line from the cell to the pressure transmitter that was not submerged in the isothermal bath fluid was heat traced to prevent condensation of vapors and subsequent pressure gradients within it. The signals from the Pt100 probes and the pressure transmitter were retrieved by a data acquisition unit (Agilent; model 34970A). This unit was connected to an I/O port of a desktop computer and was used to log the data in real-time. A Shimadzu GC-2010 gas chromatograph was used to analyze the compositions of the vapor and liquid samples from the equilibrium cell. The gas chromatograph was operated with a thermal conductivity detector (TCD) and a Restek CarboBlack B column containing a 5% Krytox packing (length, 2 m; i.d., 2 mm). Helium (baseline 5.0), supplied by Afrox (Pty) Ltd (South Africa), was used as a carrier gas for the gas chromatograph. The equilibrium phases were sampled directly from within the cell with a single rapid online sampler-injector (ROLSI).10 The configuration of the ROLSI attached to the equilibrium cell allowed for sampling of either the liquid or the vapor phase by moving the position of the tip of the ROLSI capillary.9 2.3. Calibrations. The two Pt100 probes were calibrated against a standard temperature probe (WIKA Instruments; model CTH 6500). The standard temperature probe was stated by WIKA Instruments to have a maximum uncertainty of 0.02 K. The (0−6) MPa pressure transmitter was calibrated against a standard pressure transmitter (WIKA Instruments; model CPT 6000). The linearity of the standard pressure transmitter, as stated by WIKA Instruments, is ≤0.025% of the span. Within the pressure range studied for the calibration, the standard pressure transmitter was stated by WIKA Instruments to have a maximum uncertainty of 0.02 kPa. The TCD of the gas chromatograph was calibrated using a modified direct injection technique. The standard direct injection calibration technique fits the number of moles of a component, which must be calculated from the state variables, using an equation of state, against the response of the detector. This method is subject to a fair amount of uncertainty, as it is very difficult to accurately describe the state variables. To overcome these inadequacies, a modified direction injection method

was used with the aid of a Chaney Adaptor attached to a Hamilton gastight syringe. The Chaney Adaptor allowed for the precise reproduction of the volume for both of the gases. The accuracy of the injected volume is unfortunately, still subject to errors (adsorption, manufacturer errors, injection technique, etc.). For the modified direct injection method used in this work, identical volumes of each component were injected into the gas chromatograph via the Chaney Adaptor, and the response ratios of the detector were calculated. The ratio of the TCD responses to each component is equivalent to that which would result from an equimolar mixture, as the two components were injected within a short time frame, and thus, the temperature and the pressure of the injected gases were assumed to be equal. In this manner, the calibration technique is less dependent upon the state variables. The ratio of the detector response can be fitted to the equimolar composition. However, for the estimation of the uncertainty in composition it is more convenient to have the detector response related to the mole number; this can be accomplished by utilizing the response ratio. It is critical to note that this technique is only valid for systems where the components are gases at ambient conditions, and where the response of the detector for the individual components is linear. The linearity of the response ratio was checked by injecting a range of different volumes (20, 30, ..., 100) μL of the “equimolar” mixtures using both a (0 to 50) μL and a (0 to 100) μL Hamilton gastight syringe. Furthermore, at equilibrium different volumes of sample were withdrawn to further validate the linear response of the TCD within the working range. 2.4. Experimental Procedure. Before the equilibrium measurements were undertaken, the cell was cleaned and subjected to vacuum overnight, to ensure that any components absorbed into the gasket materials were removed. The line from the equilibrium cell to the pressure transmitter was maintained at a temperature of 5 K above the temperature of the fluid in the isothermal bath, for the duration of the measurements. The vapor pressures of the individual components were measured to validate both the calibration and degassing procedures. The required amounts of each component were charged into the equilibrium cell and further degassed in situ. The VLE measurements began with the mixture containing a large fraction of one component. With each subsequent loading, the fraction of the second component present in the mixture was increased. This allowed for the datum points along the entire P−x−y envelope to be measured. After each loading, the binary mixture in the cell was held at the required temperature while being stirred. Vapor−liquid equilibrium was assumed to be achieved when the pressure readings stabilized and the average value recorded from the pressure transmitter was constant (within experimental uncertainty) for at least 20 min. Each phase was individually sampled at least six times to check for measurement repeatability at equilibrium. 2.5. Experimental Uncertainty. The expanded uncertainty for the temperature, pressure, and composition measurements are critically estimated in accordance with the guidelines given by the National Institute of Standards and Technology (NIST).11,12 The combined uncertainty for the pressure measurements were quantified by including the maximum error in the calibration polynomial, errors intrinsic to the reference transmitter, and the repeatability of the measurements at equilibrium. Similarly, the combined uncertainty for the temperature measurements were estimated by taking into account errors inherent to the calibration polynomial, errors intrinsic to the B

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the experimental pressures (or temperatures) at which the vapor and liquid compositions were analyzed. To capture such deviations we use a fairly strict assessment and treat the two averaged values of pressure and temperature as a normal rectangular (type B) distribution. Similarly, we use a rectangular distribution to account for deviations in the repeatability of composition measurements at equilibrium. The uncertainty in the composition resulting from the calibration of the TCD was evaluated using the law of propagation of errors.12 In this manner, the influence of the errors in the pressure, the temperature, and the volume upon the magnitude of the number of moles of the injected gas can be calculated, as ni = f(p,T,V), related in our work through the ideal gas equation. However, the modified direct injection calibration method used in this work is reliant upon injections of high precision rather than injections of high accuracy, and thus the standard uncertainties for the p, V, and T data used here represent precision and not accuracy. The law of propagation of errors can also be applied to estimate the uncertainty in composition, since xi = f(ni,nj), and similarly, the uncertainty in the relative volatility αij, since αij = f(xi,yi). The standard uncertainty uc(θi) can be converted to an expanded uncertainty Uc(θi) by applying a coverage factor, k. A coverage factor of 2 was applied to calculate the expanded uncertainties. Unfortunately, we do not incorporate chemical purities into the estimation of the experimental uncertainty as the impurities within the pure components were unknown. The expanded uncertainty on average for temperature, pressure, and both liquid and vapor phase compositions are U(T) = 0.05 K, U(p) = 0.6 kPa, U(x) = 0.002, and U(y) = 0.003, respectively.

reference temperature probe, axial thermal gradients present in the isothermal bath fluid between the cell top and bottom, and the repeatability of the measurements at equilibrium. For the uncertainty in composition we incorporate errors from the calibration polynomial, potential errors inherent to the modified direct injection technique, and the repeatability of samples withdrawn from each phase at equilibrium. The standard uncertainties for each of these aforementioned items are listed in Table 2. Table 2. Standard Uncertainty Estimates and Influences for the Variables of this Study source of uncertainty

estimate

standard pressure transmitter correlation for P standard temperature probe correlation for T axial thermal gradients at T = 268 K axial thermal gradients at T = 278 K axial thermal gradients at T = (288 to 298) K correlation for ni of R-1216 correlation for ni of HFPO V of injected gas from syringe T of injected gas from syringe P of injected gas from syringe

influence

0.02 kPa 0.5 kPa 0.02 K 0.04 K 0.04 K 0.03 K 0.02 K

p p T T T T T

0.6 0.5 0.5 0.5 0.5

x, x, x, x, x,

% % % K kPa

distribution p/√3 p/√3 T/√3 T/√3 T/√6 T/√6 T/√6

y y y y y

ni/√3 ni/√3 V/√3 T/√3 p/√3

The pressure and temperature data recorded during the sampling of the liquid and vapor phases were logged separately. Thus, for each mixture at equilibrium we obtained two sets of pressure and temperature data, for the liquid and vapor phase compositions, respectively. Slight variations may exist between

Table 3. Experimental, Literature, and Modelled Vapor Pressure Data for R1216 and HFPO experimental dataa Texp/K

literature datab

pexp/kPa

268.13 278.14 288.14 298.14 308.19 318.22

278.57 394.08 542.58 729.82 963.24 1251.16

271.33 387.00 536.57 726.03 963.02 1252.90

268.13 278.13 288.15 298.17 308.20 318.21

258.47 365.66 503.71 678.24 894.42 1160.25

259.29 366.69 505.29 680.36 898.06 1164.13

modeled data Δp/kPac

pcal/kPa

R1216 7.2 7.1 6.0 3.8 0.2 −1.7 HFPO −0.8 −1.0 −1.6 −2.2 −3.7 −3.8

pcal/kPa

Δp/kPab

(Δp/pexp)/%

278.78 393.88 542.03 729.60 963.98 1251.17

−0.21 0.20 0.55 0.22 −0.74 −0.01

−0.08 0.05 0.10 0.03 −0.08 −0.01

258.49 365.63 503.69 678.14 894.90 1160.25

−0.02 0.03 0.02 0.10 −0.48 0.00

−0.01 0.01 0.01 0.01 −0.05 0.01

a

U(T) = 0.05 K, U(p) = 0.6 kPa. bLiterature data of Coquelet et al.21 and Dicko et al.22 modeled using the Peng−Robinson equation of state and Mathias−Copeman alpha function for R1216 and HFPO, respectively. cΔp = pexp − pcal, where pexp and pcal are the experimental and calculated vapor pressures, respectively.

Table 4. Model Parameters and Statistical Analysis of the Data-Fit for the Binary System of R1216 (1) + HFPO (2) T = (268.13 to 308.18) K model a

PR Raoult’s Law a

statistical analysis

model parameters

AAD(p)/kPa

AARD(p)/%

AAD(y)

AARD(y)/%

k12 = 0.002

0.24 1.35

0.05 0.23

0.0010 0.0026

0.44 0.72

PR EoS (MC alpha function) coupled with classical mixing rule. C

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Table 5. Experimental P−x−y and Relative Volatility Data, Including the Expanded Uncertainties for the Binary System of R1216 (1) + HFPO (2) T/K

p/kPa

x1

y1

α12

U(T)/K

U(p)/kPa

U(x1)

U(y1)

U(α12)

268.13 268.13 268.13 268.14 268.14 268.14 268.13 268.14 268.13 268.12 268.14 268.14 278.15 278.15 278.15 278.13 278.15 278.16 278.15 278.15 278.14 278.14 278.14 288.14 288.15 288.16 288.16 288.16 288.16 288.14 288.15 288.14 288.14 288.15 298.15 298.17 298.16 298.17 298.15 298.15 298.16 298.18 298.17 298.19 298.15 298.16 298.17 308.18 308.18 308.18 308.19 308.18 308.19 308.19 308.19 308.18 308.18 308.19 308.19 308.19 308.18 308.18

259.68 261.83 263.86 265.55 268.16 270.07 271.82 273.95 275.56 276.21 277.73 278.28 366.58 368.21 372.22 376.63 380.28 385.05 386.91 388.72 391.87 392.50 393.24 504.65 508.33 513.67 517.03 521.40 527.26 528.48 537.13 538.29 539.66 541.68 679.93 683.72 689.38 692.57 696.82 703.53 706.37 709.19 709.97 717.96 722.58 726.83 729.55 895.33 897.97 900.90 908.22 912.35 918.65 923.91 931.20 939.14 944.90 950.20 955.17 959.98 960.90 961.97

0.0486 0.1427 0.2304 0.3122 0.4331 0.5259 0.6244 0.7347 0.8302 0.8670 0.9584 0.9848 0.0272 0.0740 0.1926 0.3328 0.4581 0.6285 0.7019 0.7722 0.9064 0.9356 0.9622 0.0196 0.0974 0.2168 0.2953 0.4009 0.5483 0.5825 0.8344 0.8669 0.9064 0.9673 0.0315 0.0932 0.1873 0.2426 0.3150 0.4390 0.4906 0.5425 0.5619 0.7150 0.8286 0.9315 0.9900 0.0025 0.0360 0.0693 0.1631 0.2250 0.3079 0.3781 0.4838 0.6001 0.6910 0.7768 0.8603 0.9372 0.9514 0.9736

0.0536 0.1520 0.2457 0.3287 0.4524 0.5400 0.6391 0.7448 0.8385 0.8733 0.9603 0.9854 0.0286 0.0768 0.2021 0.3473 0.4732 0.6405 0.7145 0.7813 0.9103 0.9387 0.9641 0.0212 0.1034 0.2284 0.3088 0.4160 0.5635 0.5971 0.8435 0.8721 0.9103 0.9686 0.0338 0.0978 0.1975 0.2539 0.3285 0.4532 0.5033 0.5564 0.5752 0.7255 0.8351 0.9346 0.9903 0.0027 0.0381 0.0743 0.1697 0.2351 0.3187 0.3891 0.4920 0.6120 0.7009 0.7842 0.8650 0.9394 0.9529 0.9744

1.11 1.08 1.09 1.08 1.08 1.06 1.07 1.05 1.06 1.06 1.05 1.04 1.05 1.04 1.06 1.07 1.06 1.05 1.06 1.05 1.05 1.05 1.05 1.08 1.07 1.07 1.07 1.06 1.06 1.06 1.07 1.05 1.05 1.04 1.07 1.05 1.07 1.06 1.06 1.06 1.05 1.06 1.06 1.05 1.05 1.05 1.04 1.06 1.06 1.08 1.05 1.06 1.05 1.05 1.03 1.05 1.05 1.04 1.04 1.04 1.03 1.03

0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.05 0.05 0.05 0.05 0.05 0.05 0.06 0.05 0.06 0.05 0.06 0.06 0.06 0.06 0.06 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.06 0.05 0.06 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05

0.60 0.74 0.79 0.59 0.60 0.59 0.59 0.59 0.59 0.59 0.59 0.59 0.60 0.59 0.59 0.59 0.59 0.59 0.60 0.59 0.60 0.59 0.59 0.59 0.59 0.63 0.65 0.63 0.59 0.59 0.75 0.59 0.62 0.59 0.59 0.64 0.60 0.60 0.60 0.61 0.61 0.62 0.61 0.60 0.62 0.60 0.59 0.64 0.59 0.61 0.64 0.61 0.59 0.71 0.64 0.61 0.80 0.66 0.61 0.59 0.59 0.70

0.0028 0.0041 0.0034 0.0038 0.0040 0.0042 0.0045 0.0041 0.0028 0.0023 0.0006 0.0004 0.0005 0.0015 0.0024 0.0035 0.0038 0.0037 0.0033 0.0027 0.0014 0.0010 0.0007 0.0003 0.0022 0.0027 0.0032 0.0038 0.0039 0.0037 0.0021 0.0020 0.0014 0.0005 0.0005 0.0013 0.0024 0.0029 0.0035 0.0040 0.0039 0.0042 0.0040 0.0033 0.0023 0.0010 0.0002 0.0001 0.0013 0.0011 0.0023 0.0037 0.0039 0.0040 0.0041 0.0039 0.0036 0.0027 0.0019 0.0010 0.0011 0.0004

0.0017 0.0023 0.0036 0.0038 0.0038 0.0046 0.0036 0.0030 0.0023 0.0018 0.0006 0.0003 0.0006 0.0022 0.0025 0.0037 0.0040 0.0036 0.0033 0.0026 0.0013 0.0010 0.0007 0.0004 0.0019 0.0028 0.0034 0.0038 0.0039 0.0037 0.0022 0.0018 0.0016 0.0006 0.0005 0.0017 0.0028 0.0031 0.0036 0.0041 0.0039 0.0038 0.0042 0.0031 0.0022 0.0012 0.0002 0.0006 0.0008 0.0037 0.0028 0.0059 0.0035 0.0041 0.0065 0.0038 0.0033 0.0028 0.0022 0.0012 0.0007 0.0009

0.04 0.02 0.02 0.02 0.01 0.02 0.02 0.02 0.02 0.02 0.01 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.02 0.01 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.04 0.03 0.03 0.02 0.02 0.01 0.01 0.02 0.01 0.01 0.01 0.01 0.02 0.02 0.02

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3. DATA TREATMENT Both the vapor pressure and VLE data were modeled by the direct method (phi−phi approach) using the data regression tools available in Aspen Plus V8.0.13 The vapor pressures were modeled using the Peng−Robinson (PR) equation of state14 and the Mathias−Copeman (MC) alpha function,15 using an ordinary least-squares type objection function (minimizing the sum of the pressure and temperature residuals). The VLE data were modeled using the PR equation of state with the classical mixing rule and the MC alpha function. The Britt−Luecke algorithm (rigorous maximum likelihood method) was used to minimize an ordinary least-squares type objective function (minimizing the sum of the pressure and vapor phase composition residuals for isothermal data).16 The quality of the data-fit was assessed using the average absolute deviation (AAD) and the average absolute relative deviation (AARD). The AAD is AAD (θ ̅ ) =

1 Np

Np

̅ | ∑ |θexp̅ − θcalc 1

Figure 1. p−x−y data for the R1216 (1) + HFPO (2) binary system at △ 268.13 K; ◊, 278.15 K; □, 288.15K; ×, 298.17 K; ○, 308.18 K. Modeled data (p−x and p−y) using the PR equation of state, MC alpha function, and classical mixing rule represented by the solid black line.

(1)

where θ̅exp and θ̅calc are the experimental and calculated values of a measure and θ̅ (in this case P and y1), and Np is the total number of data points. The AARD is defined as AARD (θ ̅ ) =

1 Np

Np

∑ 1

R1216 and HFPO displays slight positive deviation from Raoult’s law. Although the two components exhibit highly similar volatilities, the molecular interactions between the two components do not induce the formation of an azeotrope. However, the binary systems do still present unfavorable separation factors, as the relative volatility was consistently observed to remain below 1.1 (listed in Table 5). Therefore, within the temperature range studied, conventional distillation would not be a feasible option for the purification of the binary mixture of R1216 and HFPO.

|θexp ̅ − θcalc ̅ | θexp ̅

(2)

4. RESULTS AND DISCUSSION Saturated vapor pressure data for R1216 have been reported by Whipple,17 Li et al.,18 Feng et al.,19 Subramoney et al.,20 and Coquelet et al.21 Saturated vapor pressure data for HFPO have been reported by Subramoney et al.20 and Dicko et al.22 Our experimental vapor pressure data for both R1216 and HFPO are in fair agreement to the of Coquelet et al.21 and Dicko et al.,22 respectively. The experimental and literature vapor pressure data are listed in Table 3. The pressure deviations of experimental vapor pressure data measured in this study from the modeled literature data (PR equation of state, MC alpha function) are also listed in Table 3. The PR equation of state coupled with the MC alpha function accurately represents the vapor pressure data for R1216 and HFPO; the regressed model parameters and the pressure deviations for our experimental data are listed in Table 3. The AAD for pressure using the aforementioned model for R1216 and HFPO are 0.3 and 0.1 kPa, respectively. The PR equation of state with the classical mixing rule provides an excellent fit to the experimental VLE data. A single binary interaction parameter (kij = 0.002) is sufficient to provide an accurate description of the measured data. Low deviations are observed between the experimental and modeled pressures and vapor phase compositions, as listed in Table 4. In fact, Raoult’s law can represent the VLE data to within the experimental uncertainty due to the quasi-ideal nature of the phase behavior of this binary system. Owing to the close boiling nature of the binary system, the data presented herein is extremely sensitive to fluctuations in pressure and vapor phase composition. Consequentially, the data tabulated in Table 5 is displayed to decimal places beyond the experimental uncertainty. The phase envelopes for the experimental and modeled data are displayed in Figure 1. Within the temperature and pressure ranges that were studied, the binary system of

5. CONCLUSIONS Isothermal VLE data are reported for the binary mixture of 1,1,2,3,3,3-hexafluoroprop-1-ene and 2,2,3-trifluoro-3(trifluoromethyl)oxirane at temperatures ranging from (268.13 to 308.19) K. The data are well correlated using a single set of binary interaction parameters for Peng−Robinson equation of state using the classical mixing rule. No azeotrope was observed at the measured conditions; however, the binary system does not exhibit favorable separation factors.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +27 31 2603128. Fax: +27 31 2601118. Funding

This work is based upon research supported by the National Research Foundation of South Africa under the South African Research Chair Initiative of the Department of Science and Technology and the National Research Foundation Thuthuka Programme. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Millauer, H.; Schwertfeger, W.; Siegemund, G. Hexafluoropropene oxide: A key compound in organofluorine chemistry. Angew. Chem., Int. Ed. Engl. 1985, 24, 161−179.

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DOI: 10.1021/je5006938 J. Chem. Eng. Data XXXX, XXX, XXX−XXX