Vapor–Liquid Equilibrium Data for 1-Methyl-2-Pyrrolidone + (1

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Vapor−Liquid Equilibrium Data for 1‑Methyl-2-Pyrrolidone + (1-Butanol or 1‑Hexene or Water) Binary Mixtures Ranjeetha Hirawan, Sumit Sinha, Samuel A. Iwarere, J. David Raal, Paramespri Naidoo, and Deresh Ramjugernath* Thermodynamics Research Unit, School of Engineering, University of KwaZulu-Natal, King George V Avenue, Durban 4041, South Africa ABSTRACT: The unusual properties of 1-methyl-2-pyrrolidone or N-methyl-2-pyrrolidone (NMP) make it a solvent of interest in industrial extractive distillation processes. To augment available data, vapor−liquid equilibrium (VLE) measurements were made for NMP + 1-hexene at (313.15, 335.15, and 363.15) K, for NMP + water at (343.15, 363.15, and 380.15) K, and for NMP + 1-butanol at (10, 25, and 50) kPa using a dynamic recirculating apparatus. Limiting activity coefficients are reported for water and n-hexene as solutes in NMP. Activity coefficient minima were found for 1-butanol as solvent in NMP in the very dilute regions at (10 and 25) kPa. All systems were modeled satisfactorily with the nonrandom two-liquid (NRTL) equation for the Gibbs excess energy with a variable alpha parameter. Thermodynamic consistency testing of the isothermal data with the Van Ness (Van Ness, H. C. Pure Appl. Chem. 1995, 67, 859−872) direct test is discussed.

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INTRODUCTION The properties of 1-methyl-2-pyrrolidone (NMP), such as miscibility with water and organic solvents, polarity, and temperature and composition stability, make it a solvent of great interest in extractive distillation. The Fischer−Tropsch synthesis process used by South African petrochemical company SASOL produces mixtures of hexene and branched olefins together with branched alcohols, aldehydes, and ketones, and so forth. For separation and purification of such multicomponent mixtures, NMP as a solvent is of great interest. Isobaric VLE data for the NMP + water system are available from several studies, as referenced by Noll et al.2 The latter authors have presented very precise P−x isothermal data for this system at (351.01 and 380.24) K, and excess enthalpies at (363.15, 413.15, and 416.15) K, to extend the available NMP + water data available in the literature available at temperatures between (278.15 and 353.15) K. Extensive isothermal VLE data are also available from Fischer and Gmehling3 for NMP with eight paraffinic or olefinic hydrocarbons. In their studies, two sets of isothermal data were measured for NMP + 1-hexene at (363.15 and 413.15) K. Their very precise data for the latter temperature were compared with our measurements at subatmospheric pressures as a test of our apparatus and procedures. Other authors such as Gierycz et al.,4 Gonzalez et al.5 as well as Domańska and Łachwa6 have reported isothermal VLE data for the binary mixtures of NMP with some aliphatic alkanes, cycloalkanes, benzene, and their derivatives, P−x isothermal data for NMP + (2-propanol and 2-butanol) systems, and NMP with three ketones, respectively. A list of existing literature for binary systems of NMP + water and NMP + 1-hexene with the type of © 2014 American Chemical Society

Table 1. List of Existing Data for Water + NMP and 1-Hexene + NMP in Literature systems reported in literature water + N-methyl-2pyrrolidone water + N-methyl-2pyrrolidone water + N-methyl-2pyrrolidone N-methyl-2-pyrrolidone + water water + N-methyl-2pyrrolidone 1-hexene + N-methyl-2pyrrolidone

data type and condition

reference

isobaric, 101.33 kPa

Bogoslovskii et al.18

isobaric, 53.33 kPa and 101.33 kPa isobaric, 760 mmHg

Golubkov et al.19

isobaric, 101.325 kPa

Zhiyu et al.21

P−x data (isothermal), 351.01 K and 380.24 K P−x data (isothermal), 363.15 K and 413.15 K

Noll et al.2

Gupta and Rawat20

Fischer and Gmehling3

data and the conditions at which the data were measured are presented in Table 1. In this study, isobaric VLE data were measured for NMP + 1-butanol at (10, 25, and 50) kPa, NMP + 1-hexene at (313.15, 335.15, and 363.15) K, and for NMP + water at (343.15, 363.15, and 380.15) K. Measurement of VLE for systems of such large relative volatilities with the equipment available for the study (a glass recirculation still of advanced design) poses a considerable challenge, particularly for the dilute regions, and limited the system pressures to 1 bar. For the NMP + 1-butanol system, activity Received: January 27, 2014 Accepted: March 19, 2014 Published: April 2, 2014 1643

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Table 2. Refractive Indices and Purities of Chemicals Used in this Study

component 1-butanol N-methyl-2pyrrolidone 1-hexene water

lit.

b

GC peak area fraction

minimum purity claimedc

supplier

exp.

Sigma Aldrich Merck

1.3992

1.3993

1.0000

≥ 0.990

1.4703

1.4700

0.9990

≥ 0.995

Merck

1.3838 1.33299

1.3837 1.33299

0.9909 1.0000

≥ 0.990

EXPERIMENTAL SECTION

Chemicals. The 1-hexene and NMP used in this study were supplied by Merck and the 1-butanol by Fluka-Sigma Aldrich, with mass fraction purities as reported in Table 2. Distilled water was produced in our laboratories. The experimental refractive index measurements for the chemicals were undertaken with an ATAGO Abbe refractometer, model RX-7000α. The uncertainty in measurement of the refractive index is 0.0004. Measured and literature refractive index values are also listed in Table 2. Apparatus and Procedure. VLE data were measured using the dynamic apparatus of Raal7 which was modified by Joseph et al.8 This apparatus has been used for many studies in the Thermodynamics Research Unit at the University of KwazuluNatal, and a detailed diagram and experimental procedure are provided in the references provided. The system pressure was measured with a WIKA P10 pressure transmitter, and a WIKA grade A 4-wire Pt-100 temperature sensor was used with

refractive index at 293.15 K

a

Article

a

Refractive index at 293.15 K, U(nD) = 0.0004. bLiterature: Weast et al.22 at 293.15 K. cAs stated by the supplier.

coefficient minima were found in the NMP-rich regions at pressures of (10 and 25) kPa, as discussed further below.

Table 3. Physical Properties for the Pure Components Used in This Study pure component property

1-butanol

N-methyl-2-pyrrolidone

1-hexene

water

Tc12/K Pc12/kPa Vc12/cm3·mol−1 compressibility factor (Zc) dipole moment23/debye radius of gyration23/Å acentric factor (ω)23 A12 B12 C12

562.9 4417.77 274.0 0.2586 1.66 3.225 0.5900 16.2409 3724.479 203.296

721.7 4519.10 310.8 0.2341 4.09 3.541 0.3577 15.3656 4558.383 222.200

504.0 3206.0 350.0 0.2678 0.4 3.647 0.2839 14.0205 2779.91 232.154

647.3 22048.32 56.0 0.2294 1.85 0.615 0.3440 16.5700 3984.92 233.426

Table 4. Vapor−Liquid Equilibrium Data for the Binary Mixture of 1-Hexene (1) + N-Methyl-2-pyrrolidone (2) at (313.15, 335.15, and 363.15) K: Liquid-Phase Mole Fraction (x1), Vapor-Phase Mole Fraction (y1), and Pressure (p)a T/K = 313.15

a

T/K = 335.15

p/kPa

x1

y1

γ1

0.13 30.32 33.28 37.52 39.05 40.76 42.07 43.48 45.01

0.000 0.212 0.295 0.468 0.543 0.666 0.811 0.948 1.000

0.000 0.996 0.996 0.997 0.997 0.998 0.998 0.998 1.000

3.19 2.51 1.78 1.60 1.36 1.15 1.02

T/K = 363.15

p/kPa

x1

y1

γ1

0.51 39.21 44.92 56.03 67.24 73.84 81.75 85.35 86.35 86.96 88.26 90.06 90.65 90.88 91.03 91.36 91.58 91.96 92.24 92.46 92.86 93.46 95.26 96.56

0.000 0.103 0.129 0.202 0.309 0.384 0.502 0.578 0.590 0.607 0.650 0.695 0.715 0.729 0.748 0.762 0.783 0.819 0.845 0.881 0.896 0.935 0.989 1.000

0.000 0.990 0.991 0.991 0.991 0.992 0.992 0.993 0.991 0.994 0.994 0.999 0.999 0.996 0.994 0.996 0.992 0.995 0.996 0.997 0.997 0.998 0.998 1.000

3.89 3.69 2.94 2.33 2.04 1.71 1.54 1.52 1.49 1.41 1.34 1.31 1.29 1.25 1.24 1.20 1.16 1.12 1.08 1.07 1.03 1.00

p/kPa

x1

y1

γ1

2.18 13.89 25.70 35.20 54.41 71.94 85.30 96.26 218.59

0.000 0.013 0.027 0.038 0.064 0.091 0.110 0.133 1.000

0.000 0.845 0.915 0.941 0.969 0.971 0.978 0.980 1.000

4.47 4.29 4.28 4.01 3.72 3.66 3.40

U(T) = 0.072 K (k = 2); U(p) = 0.13 kPa (k = 2); U(x, y) = 0.0057 (k = 2). 1644

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Table 5. Vapor−Liquid Equilibrium Data for the Binary Mixture of 1-Butanol (1) + N-Methyl-2-pyrrolidone (2) at (10, 25, and 50) kPaa p/kPa = 10

a

p/kPa = 25

T/K

x1

y1

γ1

399.53 397.98 397.06 393.15 388.47 383.73 380.51 377.39 372.68 365.38 350.55 347.35 343.89 340.65 339.22 337.80

0.000 0.011 0.016 0.045 0.083 0.135 0.159 0.185 0.249 0.341 0.568 0.655 0.740 0.865 0.927 1.000

0.000 0.087 0.124 0.278 0.440 0.577 0.626 0.682 0.764 0.855 0.955 0.970 0.975 0.992 0.998 1.000

0.619 0.622 0.572 0.582 0.578 0.583 0.598 0.616 0.667 0.820 0.886 0.945 1.012 1.015 1.000

p/kPa = 50

T/K

x1

y1

γ1

425.91 423.60 422.54 418.32 416.11 411.16 407.16 401.60 393.54 389.56 384.68 374.41 370.44 367.98 365.31 358.90 357.27 355.78

0.000 0.013 0.021 0.049 0.063 0.102 0.130 0.182 0.271 0.316 0.371 0.513 0.579 0.635 0.686 0.873 0.928 1.000

0.000 0.091 0.131 0.252 0.314 0.441 0.562 0.671 0.779 0.824 0.867 0.933 0.953 0.968 0.975 0.990 0.995 1.000

0.618 0.573 0.537 0.552 0.561 0.624 0.640 0.664 0.689 0.722 0.817 0.868 0.915 0.954 1.032 1.023 1.000

T/K

x1

y1

γ1

448.97 446.08 444.56 439.55 436.22 430.81 421.48 411.75 406.06 393.37 386.84 383.86 378.08 376.60 371.94

0.000 0.014 0.019 0.052 0.069 0.109 0.182 0.286 0.348 0.528 0.655 0.708 0.855 0.890 1.000

0.000 0.087 0.150 0.282 0.370 0.462 0.648 0.766 0.839 0.934 0.964 0.977 0.986 0.992 1.000

0.615 0.799 0.635 0.673 0.620 0.667 0.678 0.716 0.792 0.852 0.884 0.903 0.971 1.000

U(T) = 0.072 K (k = 2); U(p) = 0.13 kPa (k = 2); U(x, y) = 0.0057 (k = 2).

Table 6. Vapor−Liquid Equilibrium Data for the Binary Mixture of Water (1) + N-Methyl-2-pyrrolidone (2) at (343.15, 363.15, and 380.15) Ka T/K = 343.15

a

T/K = 363.15

T/K = 380.15

p/kPa

x1

y1

γ1

p/kPa

x1

y1

γ1

p/kPa

x1

y1

γ1

0.79 9.01 12.69 14.79 17.49 19.29 21.70 24.90 28.40 31.10

0.000 0.340 0.462 0.523 0.605 0.657 0.733 0.812 0.923 1.000

0.000 0.948 0.968 0.980 0.989 0.993 0.994 0.996 0.996 1.000

0.811 0.857 0.893 0.921 0.939 0.947 0.983 0.986 1.000

2.17 11.39 20.90 26.09 34.81 45.22 54.04 61.73 67.24 70.14

0.000 0.182 0.322 0.407 0.519 0.674 0.782 0.879 0.959 1.000

0.000 0.843 0.936 0.954 0.971 0.991 0.995 0.997 0.998 1.000

0.758 0.872 0.877 0.933 0.951 0.983 0.999 0.998 1.000

4.98 17.29 30.20 44.22 54.07 63.03 68.14 77.95 91.03 129.90

0.000 0.120 0.231 0.330 0.405 0.472 0.504 0.577 0.682 1.000

0.000 0.767 0.879 0.927 0.948 0.966 0.971 0.980 0.985 1.000

0.879 0.920 0.959 0.983 1.006 1.038 1.025 1.02 1.000

U(T) = 0.072 K (k = 2); U(p) = 0.13 kPa (k = 2); U(x, y) = 0.0057 (k = 2).

range, of 0.1 kPa. Therefore, the combined standard uncertainty for the pressure measurement, U(p), is 0.13 kPa. The uncertainties in composition measurement arise from measurement of GC peak areas, from reproducibility of samples at a given temperature or pressure, from GC calibration by the area ratio method and, most seriously, (for systems of large relative volatility particularly in the dilute regions), from failure to reach true equilibrium in a single pass. The combined standard uncertainty for both x and y measurement is thus estimated to be 0.0057 of a mole fraction.

installation near the bottom of the packed section of the equilibrium chamber to minimize errors from conductive heat losses from the glass bulb and its leads to the lowertemperature surroundings. Resistance was measured on a Fluka 8840A multimeter with a 0.004 % claimed accuracy, equivalent to 0.005 ohms in the measurement range, that is, 0.013 K uncertainty. Equilibrium was assumed to have been reached when the temperature and/or pressure remained constant for at least 45 min. Vapor and liquid samples were analyzed on a Shimadzu GC-2010 with thermal conductivity detector and a Cwax 20 M Bonded capillary column. Estimates of uncertainties in the pressure, temperature, and composition are as follows: Uncertainties in temperature measurement arise from failure of the sensor bulb to reach the liquid equilibrium temperature due to conductive heat losses, uncertainties in resistance measurement and from calibration with a WIKA temperature standard; thus the combined standard uncertainty of the temperature measurement, U(T) is 0.072 K. Uncertainties in pressure measurement arise from transmitter error, from repeatability and from calibration against a WIKA pressure standard with claimed uncertainty, in the pressure

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DATA REDUCTION Measured P−x−y or T−x−y data were modeled using the NRTL equation for the liquid phase with the alpha parameter included as an adjustable variable and the regression method of Marquardt.9 Vapor phase corrections were made using the virial equation of state and the Pitzer−Curl10 correlation for the second virial coefficient: BPc = Bο + ωB1 RTc 1645

(1)

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Figure 4. Activity coefficient plot (γ1) versus x1 for 1-hexene (1) + NMP (2) at 335.15 K: ●, this study.

Figure 1. P−x−y VLE data for 1-hexene (1) + NMP (2) at 313.15 K: ●, this study; - - -, NRTL equation.

Figure 5. P−x−y VLE plot for water (1) + NMP (2) at 363.15 K: ●, this study; - - -, NRTL equation.

Figure 2. P−x−y VLE data for 1-hexene (1) + NMP (2) at 335.15 K: ●, this study; - - -, NRTL equation.

Figure 6. P−x−y VLE plot for water (1) + NMP (2) at 380.15 K: ●, this study; - - -, NRTL equation; ○, Noll et al.2

Figure 3. P−x−y VLE data for 1-hexene (1) + NMP (2) at 363.15 K: --●--, this study; ○, Fischer and Gmehling.3

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and

(3)

RESULTS AND DISCUSSION Physical properties of the pure components are given in Table 3. The Antoine equation constants are those reported in the DDB12 for the equation: B ln P(kPa) = A − t(°C) + C (4)

Liquid molar volumes required in eq 3 were calculated from the Rackett equation. Virial cross-coefficients were estimated using the Prausnitz et al.11 rules.

Measured pure component vapor pressures were in good agreement with those from the above equation. Measured VLE data, including activity coefficients for the more volatile component (γ1) are presented in Tables 4 to 6 for NMP + 1-hexene, NMP + 1-butanol, and NMP + water, respectively. P−x−y or T−x−y plots are shown for NMP + 1-hexene at

yi ΦiP = xiγipisat

(2)

with ⎡ (B − V L)(P − psat ) + Py 2 δ ⎤ ii i i j ij ⎥ Φi = ⎢ ⎥ ⎢ RT ⎦ ⎣

and

δij = 2Bij − Bii − Bjj

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Figure 7. Isobaric T−x−y VLE data for n-butanol (1) + NMP (2) at 50 kPa: ●, this study; - - -, NRTL equation.

Figure 10. Deviation pressure plot ((x1x2)/PD versus x1) for 1-hexene (1) + NMP (2) at 313.15 K.

Figure 8. Activity coefficient plot (γ1) versus x1 for n-butanol (1) + NMP (2) at 10 kPa: ●, this study; - - -, NRTL equation.

Figure 11. Deviation pressure plot ((x1x2)/PD versus x1) for 1-hexene (1) + NMP (2) at 335.15 K.

Figure 9. Activity coefficient plot (γ1) versus x1 for n-butanol (1) + NMP (2) at 25 kPa: ●, this study; - - -, NRTL equation.

Figure 12. Deviation pressure plot (PD/(x1x2) versus x1) for water (1) + NMP (2) at 380.15 K.

(313.15, 335.15, and 363.15) K in Figures 1 to 3, respectively, and an activity coefficient plot for the intermediate temperature in Figure 4. The present measurements are compared with those from static cell measurements by Fischer and Gmehling3 in Figure 3. In Figures 5 and 6 illustrative P−x−y plots are presented for NMP + water at (363.15 and 380.15) K, respectively. In Figure 6 our data at pressures up to 91 kPa are compared with the P−x data of Noll et al.2 at the same temperature. There is good agreement between our data and their static cell measurements. Isobaric T−x−y data for NMP + 1-butanol at 50 kPa are shown in Figure 7 and activity coefficient plots at the two lower pressures (10 and 25) kPa in Figures 8 and 9. The (rare) minima could not be confirmed at 50 kPa. Activity coefficients for NMP as solute (γ2) could not be satisfactorily calculated for any of the

three systems studied. There is too much scatter in the γ1−x1 plots for NMP + 1-butanol to permit reliable extrapolation of T−x1 or γ1 data to determine γ1∞ values. The limiting coefficients however appear to lie between 0.60 and 0.80 for the three pressures. In their VLE measurements on NMP with various hydrocarbons, using a very precise static cell method, Fischer and Gmehling3 also found that (γ2∞) values for the high-boiling NMP in the much lower boiling hydrocarbons could not be determined. Limiting activity coefficients (γi∞) can be computed from:13 ∞

γi = 1647

psat ⎡ ∞ j ⎢ Φi sat 1 pi ⎢⎣

∞ ⎤ 1 ⎛ ∂p ⎞ ⎥ + βj sat ⎜ ⎟ pj ⎝ ∂x1 ⎠x = 0 ⎥⎦ 1

(5)

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⎡ dP ⎤∞ ⎡ dPD ⎤∞ ⎡ PD ⎤∞ =⎢ =⎢ ⎥ − P1sat + P2sat ⎥ ⎥ ⎢ ⎣ x1x 2 ⎦x = 0 ⎣ dx1 ⎦x = 0 ⎣ x1 ⎦x = 0

Table 7. Limiting Activity Coefficients system

T/K

γ1∞ (measured)

1-hexene (1) + NMP (2)

313.15 335.15 363.15 343.15 363.15 380.15

9.49 ± 0.4 6.87 ± 0.3 4.63 ± 0.05 0.60 ± 0.03 0.71 ± 0.1 0.85 ± 0.05

water (1) + NMP (2)

γ1∞ (literature)

1

−1 ∞ ⎤ ⎡⎛ ⎡ x x ⎤∞ dPD ⎞ ⎥ 1 2 ⎢ = ⎜ ⎥ ⎢ ⎟ ⎣ PD ⎦x = 0 ⎢⎣⎝ dx1 ⎠x = 0 ⎥⎦ 1 1

0.8682

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DATA CORRELATION AND CONSISTENCY TESTING Data for all three systems were best correlated with the NRTL equation, with the alpha parameter as an additional correlating variable. The parameter values are shown in Table 8. Measurement of the vapor compositions permitted thermodynamic consistency testing for the two isothermal systems by the direct method of Van Ness.1 RMS values for the residuals δ ln(γ1/γ2) showed the data to be good and satisfactory for the NMP + 1-hexene and NMP + water systems at the higher temperatures, respectively. The very high relative volatilities (e.g., α > 900 at 313.15 K for NMP + 1-hexene) at the lower temperatures and the difficulty of calculating activity coefficients for the NMP as solute in the dilute regions prevented calculation of satisfactory

(6)

and ⎡ B − VL ⎤ jj j ⎥ βj = 1 + pjsat ⎢ ⎢⎣ RT ⎥⎦

(9)

Examples are shown in Figures 10 and 11 for the NMP + 1-hexene system and in Figure 12 for the NMP + water system. Limiting activity coefficients are listed in Table 7 and compared with available literature data. Figure 13 shows a comparison of our (γ1∞) values for NMP + 1-hexene as a function of temperature with those of Fischer and Gmehling3 from either static cell (P−x) measurements or from GC measurements. Accurate limiting coefficients, of considerable importance in distillation design for high-purity products, are difficult to measure for water + hydrocarbon or water + alcohol systems, as illustrated by Dohnal15 for n-butanol + water. Literature data for this system ((γi∞) as f(T)) from five different sources and procedures differed by more than 100 % for the same temperature in some regions and did not permit determination of temperature dependence. Our activity coefficients for NMP + water showed appreciably more scatter than for NMP + 1-hexene and suggest that a dynamic still in which the equilibrium mechanism is a bubbling chamber16,17 may be more suited. [Such an apparatus, which does not require achievement of equilibrium in a single pass, will be recommissioned in our laboratories for aqueous systems of high relative volatility soon].

where ⎡ (B − V L)(psat − psat ) + (δ psat ) ⎤ ii i ij j j i ⎥ = exp⎢ ⎢ ⎥ RT ⎣ ⎦

(8)

1

and 4.743

Figure 13. Plot of ln γ1∞ versus 103/T (K) for 1-hexene (1) + NMP (2): ●, this study; Fischer and Gmehling:3 □, from static cell measurements; △, from GLC measurements.

Φ∞ i

1

(7)

The limiting slope (∂P/∂x1)∞ is conveniently determined if good linear plots of (PD/x1x2) (or its inverse) vs x1 can be obtained from the data (PD = deviation pressure, = P − [p2sat + (p1sat − p2sat)x1]). The limiting values for the plots of (PD/x1x2) or its inverse) vs x1 are as follows:14 14

Table 8. Correlation Parameters Δg12, Δg21, and α12 for NRTL Model and Average Absolute Deviations (AAD) for Temperature and Vapor Compositions for the Newly Measured Binary Systemsa model NRTL

a

p/kPa

T/K

10.0 25.0 50.0

α12 0.5365 0.5365 0.5365

NRTL

313.15 335.15 363.15

0.5467 0.5467 0.5467

NRTL

343.15 363.15 380.15

0.4554 0.4554 0.4554

Δg12/(J·mol−1)

Δg21/(J·mol−1)

1-Butanol (1) + NMP (2) 8640.81 9778.83 3364.90 1-Hexene (1) + NMP (2) 5851.28 6763.56 6865.15 Water (1) + NMP (2) 657.83 3747.53 5344.77

−4267.92 −4251.48 −3808.47

ΔT/K

Δp/kPa

0.4525 0.2864 0.3465

Δy 0.0086 0.0089 0.0077

4295.19 3039.88 2853.87

0.0353 0.5534 1.0697

0.0002 0.0017 0.0032

−1689.87 −3039.93 −3055.86

0.0892 0.2839 0.3957

0.0022 0.0026 0.0028

n exp n exp ΔT/K = 1/n∑ni |Texp − Tcalc − Pcalc − ycalc i i |; Δp/kPa = 1/n∑i |Pi i |; Δy = 1/n∑i |yi i |.

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REFERENCES

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Figure 14. Van Ness1 direct consistency test for water (1) + NMP (2) at 380.15 K.

Figure 15. Van Ness1 direct consistency test for 1-hexene (1) + NMP (2) at 363.15 K.

residuals. Two examples are plotted in Figures 14 and 15, for NMP + water at 380.15 K and for NMP + 1-hexene at 363.15 K.

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CONCLUSIONS Isothermal P−x−y data are presented for the NMP + 1-hexene and NMP + water systems at three temperatures for each system, to augment what is available in the literature. Isobaric data are provided for NMP + 1-butanol at three pressures. Measurement of vapor compositions permitted rigorous thermodynamic consistency testing by the Van Ness1 direct method and indicated good to satisfactory consistency for the two isothermal systems at the two highest temperatures. Isobaric T−x−y data for NMP + 1-butanol produced activity coefficients for 1-butanol as solute with a minima in the very dilute regions at (10 and 25) kPa.

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Article

AUTHOR INFORMATION

Corresponding Author

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

The authors wish to thank the National Research Foundation (NRF), SASOL and the South African Research Chair Programme for financial support. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank glassblower P. Siegling for his expert craftsmanship. 1649

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(22) Weast, R C.; Astle, M. J.; Beyer, W. H. Handbook of Chemistry and Physics, 64th ed.; CRC Press: Boca Raton, FL, 1983−1984. (23) Prausnitz, J. M.; Anderson, T. F.; Grens, E. A.; Eckert, C. A.; Hsieh, R.; O’Connell, J. P. Computer Calculations for Multicomponent Vapor-Liquid and Liquid-Liquid Equilibria; Prentice Hall: Englewood Cliffs, NJ, 1980.

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