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Apr 17, 2012 - Department of Chemistry, Andhra Loyola College, Vijayawada, Andhra Pradesh, India. ABSTRACT: Isobaric vapor−liquid equilibrium (VLE) ...
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Activity Coefficients and Excess Gibbs Energies for Binary Mixtures of N-Methyl-2-pyrrolidone with Some Substituted Ethanols K. Rayapa Reddy,† D. Bala Karuna Kumar,† G. Srinivasa Rao,‡ P. V. S. Sairam,‡ P. Anila,§ and C. Rambabu*,† †

Department of Chemistry, Acharya Nagarjuna University, PG Centre, Nuzvid, Andhra Pradesh, India Department of Physics, Andhra Loyola College, Vijayawada, Andhra Pradesh, India § Department of Chemistry, Andhra Loyola College, Vijayawada, Andhra Pradesh, India ‡

ABSTRACT: Isobaric vapor−liquid equilibrium (VLE) data is determined for the binary mixtures of N-methyl-2-pyrrolidone + aminoethanol, N-methyl-2-pyrrolidone + chloroethanol, and N-methyl-2-pyrrolidone + phenylethanol at 95.3 kPa over the entire composition range using a Swietoslawski type ebulliometer. All three systems investigated show negative deviations from Raoult's law, and none of the binary systems formed azeotropic mixtures. The experimental VLE data of the three binary mixtures are correlated using the Wilson model. The computed vapor phase mole fractions, activity coefficients, and Gibbs energy along with optimum Wilson parameters are presented. The studies indicate that all three binary systems are nonideal liquid mixtures deviating from Raoult's law exhibiting negative values of excess Gibbs energies due to strong intermolecular hydrogen bonding between unlike molecules.

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INTRODUCTION Over the past few decades, process modeling has gained a great deal of attention as a reliable tool for attaining effective, clean, and optimal new technologies.1 Because of pressure from the growth of chemical and related industries, the increasing development of process design requires ecofriendly and less energy-consuming conditions. Modeling is primarily dependent on accurate knowledge of the thermodynamical behavior of the chemicals involved; therefore, the availability of suitable methods and the availability of reliable physical property data are basic requirements to achieve a proper design.2,3 Among various thermophysical properties needed for the modeling for solvent mixtures, vapor−liquid equilibrium (VLE) data are key to the design of industrial plants of the liquids involved. Calculations of VLE in chemical engineering have traditionally been performed with an equation of state (EOS). These EOS models are based on pure phase properties, are easy to use, and require little computational effort and yield qualitative predictions of binary mixture VLE. It is well-known that, for the simulation and operation of the extractive distillation process and also for determining the optimal values of parameters in the thermodynamic models,4,5 VLE data are vital. Liquid solvents play an important role in a number of chemical equations.6 The choice of a proper solvent for a particular process primarily depends on the availability of physical properties.7 Among such solvents, N-methyl-2-pyrrolidone (NMP) is an important solvent as it has a low volatility and high polarity, is chemically and thermally stable, and is completely miscible with water and most organic solvents. It is a cyclic lactam with a nonpolar region and a donor−acceptor CO−NH peptide © 2012 American Chemical Society

bond, and for this reason, it is frequently used to study hydrophobic interactions8 and to model proteins.9 The favorable toxicological and environmental properties convert NMP into a candidate to replace advantageously chlorinated solvents.10 Also NMP, either in pure or mixed states, is widely used in chemical engineering,11 extractive distillation,12 absorption,13 gas desulfurization,14 and coal extraction.15 Among the substituted ethanols, 2-aminoethanol (AE) is used for the alkalinization of water in steam cycles of power plants, including nuclear power plants with pressurized water reactors to control the corrosion16 of metal components of a reactor. 2-Chloroethanol (CE), a precursor for ethylene oxide, is widely used in a number of synthetic reactions including the manufacturing of dyes,17 drugs, pesticides, and plasticizers. 2-Phenylethanol (PE) is used as a common ingredient in perfumes when rose smell is desired and as a preservative in soaps18 due to its stability in basic conditions. The literature survey shows that studies on the phase equilibrium and the corresponding VLE data of the binary liquid mixtures of NMP + AE, NMP + CE, and NMP + PE are very scarce. In this investigation, we report the isobaric VLE data on activity coefficients useful for the simulation and design of distillation process and excess Gibbs energy for all three binary systems along with the vapor composition of the mixtures at 95.3 kPa, and the data are correlated with Wilson's model. Received: November 24, 2011 Accepted: April 3, 2012 Published: April 17, 2012 1412

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EXPERIMENTAL SECTION Chemicals. NMP (Merck, India, > 0.995 mole fraction purity) is distilled at low pressure and stored over freshly activated 0.3 nm molecular sieves.19 2-Aminoethanol (SD Fine Chemicals, India, > 0.995 mole fraction purity) is purified by distillation at low pressures, and 2-chloroethanol (SD Fine Chemicals, India, > 0.995 mole fraction purity) is purified by using a fractionating column. The middle fractions are used for the experiment, and 2-phenylethanol (Sigma Aldrich, > 0.995 mole fraction purity) is used without further purification. The purity of the chemicals is verified by comparing the densities of the pure compounds and is reported in Table 1, along with literature values.20−26

is brought back to the required temperature. The composition of the mixture is verified both at the beginning and at the end of each experiment by taking a gas chromatograph (GC-17A, Shimadzu), and the analysis is carried out by using a thermal conductivity detector fitted with an SE-30 column. An Anton Paar DMA 4500 digital vibrating U-tube densimeter, with automatic viscosity correction, is used to measure the densities of the components. The densities of the samples are observed with a reproducibility of ± 1·10−5 g·cm−3. The uncertainty in the density measurement, as reported by the equipment manufacturer, is 1·10−5 g·cm−3 at a confidence level of 95 %, and the accuracy for the density measurement is ± 5·10−5 g·cm−3. For the period of vibration (τ), the densities (ρ) of the mixtures are determined using the relationship ρ = a + bτ2, where a and b are the instrument constants and are determined by calibration with degassed and bidistilled water and dry air.28 With a solid state thermostat (Peltier) the temperature in the cell is regulated to ± 0.01 K. All of the measurements are made at (303.15 and 308.15) K and at atmospheric pressure.

Table 1. Comparison of the Density (ρ/kg·m−3) of the Pure Liquids with Literature Data at (303.15 and 308.15) K 303.15 K

308.15 K

chemical

exp

lit.

exp

lit.

N-methyl-2-pyrrolidone aminoethanol chloroethanol phenylethanol

1023.45 1008.12 1192.48 1012.65

1023.4220 1008.122 1192.424

1019.34 1005.08 1186.44 1008.68

1019.32921 1005.0323 1186.625 1008.6326

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RESULTS AND DISCUSSION VLE data, that is, vapor and liquid phase compositions, temperature, activity coefficients, and Gibbs energy for all three binary systems measured at a pressure of 95.3 kPa are reported in Table 2. The experimental data are correlated by the Wilson method from which the activity coefficients are calculated taking into account the nonideal behavior of the vapor−liquid phases. The adjustable binary parameters assumed in these equations are estimated by a nonlinear regression method. According to the Wilson model, the activity coefficients γ1 and γ2 can be expressed as

Apparatus and Procedure. A Swietoslawski type ebulliometer similar to the one described by Hala et al.27 is used to determine the VLE data, at constant pressure as a function of the liquid-phase mole fraction. A dry nitrogen gas cylinder and a vacuum pump are connected to the ebulliometer with a closed end manometer in line for the maintenance and measurement of the total pressure of the system at a required level. By adjusting the opening of the needle valve of the gas cylinder or the bypass line of the vacuum pump, the required pressure is maintained. In this set of experiments the total pressure is maintained within ± 0.05 kPa of the required value, by applying the needed adjustment and frequently reading the mercury columns of the manometer. The equilibrium temperature with an accuracy of ± 0.05 K is measured with a mercuryin-glass thermometer which is calibrated by means of point-topoint comparison with a standard platinum resistance thermometer (certified by the National Institute of Standards and Technology). The thermometer is kept in the thermo-well filled with mercury to note the steady-state temperature of the (vapor + liquid) mixture impinging on the Cottrell tube. The mixtures are prepared gravimetrically by using an electronic balance (Sartorius BT224s) with an uncertainty of ± 1·10−4 g and are stored in airtight glass bottles. The uncertainty in mole fraction is estimated to be 1·10−4. It is ensured that the components are adequately mixed before being transferred into the ebulliometer and each binary mixture is used immediately after the preparation. After the binary mixture is transferred into the ebulliometer, in accordance with the suggestion of Hala et al., the heating rate is slowly increased and adjusted to produce the required boil-up rate so that a drop count of about 30 drops per minute is achieved. The equilibrium temperature is noted after a steady state is achieved, judged by the constancy of the equilibrium temperature, and the uniformity of the drop rate is maintained at least for 30 min. Before starting the actual experiment, to attain the constancy of composition of the binary mixture, the mixture is subjected to the maximum temperature that the mixture is expected to be subjected during the experiment and

⎞ ⎛ Λ 21 Λ12 ln γ1 = −ln(x1 + Λ12x 2) + x 2⎜ − ⎟ x 2 + Λ 21x1 ⎠ ⎝ x1 + Λ12x 2 (1)

⎞ ⎛ Λ 21 Λ12 ln γ2 = −ln(x 2 + Λ 21x1) + x1⎜ − ⎟ x1 + Λ12x 2 ⎠ ⎝ x 2 + Λ 21x1 (2)

where the adjustable parameters Λ12 and Λ21 are given by Λ12 =

V2 L V1L

⎛ λ − λ11 ⎞ ⎟ exp⎜ − 12 ⎝ RT ⎠

(3)

⎛ λ − λ 22 ⎞ ⎟ exp⎜ − 12 ⎝ RT ⎠

(4)

and Λ 21 =

V1L V2L

The nonlinear regression analysis method, described by Kuester and Mize,29 with the Nelder−Mead optimization technique is used for the determination of optimum Wilson parameters by minimizing the optimum function: Φ = [(Pcal /Pexp) − 1}]2

(5)

where Pcal = γ1(Wilson)x1P10 + γ2(Wilson)x 2P2 0

(6)

30,31

Antoine constants are used (Table 3) to determine the available pure liquid−vapor pressure data with an average deviation of 0.5 %. From the liquid density data given in 1413

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Table 1 molar volumes of the pure liquids are calculated at 303.15 K. The interaction parameters computed based on the Wilson model are presented in Table 4. Figure 1 represents the variation of the boiling point temperature with the mole fraction of NMP in both liquid and vapor phases for all three binary systems under investigation; from the figures, it can be concluded that azeotropic mixtures

Table 2. Temperature−Mole Fraction (T−x) Data for the Binary Systems N-Methyl-2-pyrrolidone (1) + Substituted Ethanols (2) at 95.3 kPaa x1

T/K

0.0000 0.0650 0.1352 0.2114 0.2943 0.3848 0.4841 0.5934 0.7145 0.7800 0.8492 0.8853 0.9224 0.9606 1.0000 0.0000 0.0719 0.1485 0.2301 0.3174 0.4108 0.5112 0.6194 0.7361 0.7980 0.8626 0.9161 0.9436 0.9716 1.0000 0.0000 0.0615 0.1216 0.1802 0.2374 0.2934 0.3480 0.4014 0.4536 0.5547 0.6513 0.7440 0.8328 0.9181 1.0000

y1

γ1

γ2

N-Methyl-2-pyrrolidone (1) + Aminoethanol (2) 442.28 0.0000 1.000 444.20 0.0189 0.654 0.996 446.21 0.0459 0.723 0.985 448.36 0.0830 0.786 0.969 450.67 0.1327 0.842 0.947 453.21 0.1981 0.890 0.921 456.06 0.2836 0.930 0.892 459.35 0.3947 0.961 0.860 463.28 0.5402 0.983 0.826 465.55 0.6297 0.990 0.808 468.11 0.7336 0.996 0.790 469.02 0.7923 0.998 0.780 470.35 0.8557 0.999 0.771 471.78 0.9246 1.000 0.762 474.01 1.0000 1.000 N-Methyl-2-pyrrolidone (1) + Chloroethanol (2) 399.89 0.0000 1.000 403.91 0.0066 0.795 0.998 406.26 0.0157 0.838 0.992 408.99 0.0283 0.877 0.982 412.25 0.0461 0.910 0.969 416.20 0.0714 0.938 0.953 421.16 0.1090 0.961 0.935 427.63 0.1680 0.978 0.915 436.58 0.2688 0.990 0.893 443.21 0.3497 0.995 0.883 450.32 0.4686 0.998 0.872 459.33 0.6122 0.999 0.863 464.34 0.7105 1.000 0.859 469.02 0.8357 1.000 0.855 474.01 1.0000 1.000 N-Methyl-2-pyrrolidone (1) + Phenylethanol (2) 489.79 0.0000 1.000 488.92 0.0837 0.953 1.000 488.25 0.1630 0.958 0.999 487.39 0.2378 0.962 0.999 486.34 0.3086 0.966 0.997 485.46 0.3753 0.970 0.996 484.53 0.4382 0.974 0.994 483.68 0.4973 0.977 0.992 482.83 0.5528 0.981 0.989 481.23 0.6541 0.986 0.983 479.72 0.7429 0.991 0.976 478.29 0.8209 0.995 0.967 476.95 0.8889 0.998 0.957 475.68 0.9484 0.999 0.946 474.01 1.0000 1.000

GE/J·mol−1 0.0 −115.3 −209.8 −282.8 −332.9 −358.3 −356.7 −324.9 −258.7 −211.0 −152.7 −119.2 −82.7 −43.1 0.0

Table 4. Representation of VLE Measurements by the Wilson Model mixture

[(λ12 − λ11)/R]

[(λ12 − λ22)/R]

σ

N-methyl-2-pyrrolidone (1) + aminoethanol (2) N-methyl-2-pyrrolidone (1) + chloroethanol (2) N-methyl-2-pyrrolidone (1) + phenylethanol (2)

202.8432

−193.0611

0.016

151.4330

−139.3501

0.009

−65.9814

67.8429

0.012

0.0 −62.2 −112.9 −151.5 −177.5 −189.8 −187.6 −169.4 −133.7 −108.6 −78.2 −49.9 −34.3 −17.7 0.0 0.0 −12.7 −23.7 −33.2 −41.2 −47.7 −52.8 −56.5 −59.0 −60.1 −56.5 −48.5 −36.2 −20.0 0.0

Figure 1. Experimental boiling point temperatures at 95.3 kPa versus mole fraction of NMP for the mixtures of (a) NMP + AE, (b) NMP + CE, and (c) NMP + PE.

Standard uncertainties u are: u(T) ∼1.5 K, u(p) = 0.05 kPa, and the combined standard uncertainty uc is uc(x1) = 0.0001. a

Table 3. Antoine Constants Used for the Equation: ln(P) = A − B/[(T/K) + C] substance

A

B

C

Tmin/K

Tmax/K

N-methyl-2-pyrrolidone 2-aminoethanol 2-chloroethanol 2-phenylethanol

14.327731 17.2430 17.2430 16.9930

3084.531 4877.630 4865.630 567030

−34.6231 −57.7630 −16.3630 −34.0530

183.00 10.50 −67.50 −26.15

550.00 364.85 311.85 410.85

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Figure 2. Variation of experimental boiling point temperatures versus mole fraction of NMP for the mixtures with estimated uncertainties (≈ 1.5 K): ▲, NMP + CE; ■, NMP + AE; ◆, NMP + PE.

it is understood that the intermolecular hydrogen bond between the like molecules of aminoethanol breaks and forms new hydrogen bonds with NMP molecules more readily; this may be due to the more electronegative nitrogen atom which withdraws electrons from the alcohol group, thereby weakening the intermolecular hydrogen bonding between the molecules of aminoethanols and simultaneously the formation of new hydrogen bonds between the unlike molecules of aminoethanol and NMP, whereas, in the system NMP + CE, chlorine withdraws electrons less when compared to the nitrogen atom of the amino group, thereby possessing less negative values of Gibbs energy. Meanwhile, in the system NMP + PE, the excess Gibbs energy values are much less negative than the other two systems perhaps due to less electron-withdrawing capacity of the phenyl group. In the three binary mixtures investigated the absolute excess Gibbs energy values follows the order: NMP + AE > NMP + CE > NMP + PE.

are not formed in any of the three systems under study. Figure 2 gives the variation of experimental boiling point temperatures with the mole fraction of NMP for the mixtures with the estimated uncertainties (≈ 1.5 K). An observation of the activity coefficients presented in Table 2 confirms that all of the systems are nonideal, and the nonideality falls in the order: (NMP + AE) > (NMP + CE) > (NMP + PE)

Activity coefficients obtained by the Wilson model are used to compute excess Gibbs energies of the three binary systems under investigation through GE = RT (x1 ln γ1 + x 2 ln γ2)

(7)

Excess Gibbs energies of the three binary mixtures with the mole fraction of NMP are shown in Figure 3, and from the

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CONCLUSIONS VLE data of the binary mixtures {NMP (1) + AE (2)}, {NMP (1) + CE (2)}, and {NMP (1) + PE (2)} are studied at the local atmospheric pressure, 95.3 kPa, over the entire composition range in a Swietoslawski-type ebulliometer. The experimental results are found to be well-represented by the Wilson model. It is observed from the investigation that all three binary systems are nonideal liquid mixtures deviating from Raoult's law. Also, it is observed that all three binary systems under investigation exhibit negative values of excess Gibbs energies due to strong intermolecular hydrogen bonding between unlike molecules.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 08656-235200.

Figure 3. Variation of excess Gibbs energy with the mole fraction of NMP. ●, NMP + AE; ◆, NMP + CE; ■, NMP + PE.

Funding

One of the authors, K.R.R., wishes to thank the University Grants Commission of India for awarding a teacher fellowship under the FDP scheme and Director IICT, Hyderabad for providing laboratory facilities.

figure it can be concluded that strong intermolecular forces are operating between the unlike molecules. From the observed negative excess Gibbs energy values of the system NMP with AE, 1415

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Notes

(21) Dávila, M. J.; Aparicio, S.; Alcalde, R. Thermophysical Properties of Binary and Ternary Mixtures Containing Lactams and Methanol. Ind. Eng. Chem. Res. 2009, 48, 10065−10076. (22) Aguila-Hermnandez, J.; Trejo, A.; Garcia-Flores, B. E.; Molnar, R. Viscometric and Volumetric Behaviour of Binary Mixtures of Sulfolane and NMP with Monoethanolamine and Diethanolamine in the range 303−373 K. Fluid Phase Equilib. 2008, 267, 172−180. (23) Dean, R.; Moulins, J.; MacInnis, A.; Palepu, R. M. Excess Volumes, Partial Molar and Adiabatic Compressibilities of Binary Mixtures of n-Alcohols with Monoethanolamine. Phys. Chem. Liq. 2009, 47, 302−310. (24) Aminabhavi, T. M.; Banerjee, K. Density, Viscosity, Refractive Index, and Speed of Sound in Binary Mixtures of 2-Chloroethanol with Alkanols (C1-C6) at 298.15, 303.15, and 308.15 K. J. Chem. Eng. Data 1998, 43, 509−513. (25) Aralaguppi, M. I.; Jadar, C. V.; Aminabhavi, T. M. Density, Viscosity, Refractive Index, and Speed of Sound in Binary Mixtures of 2-Chloroethanol with Methyl Acetate, Ethyl Acetate, and n-Butyl Acetate. J. Chem. Eng. Data 1999, 44, 441−445. (26) Yeh, C.-T.; Tu, C. H. Densities, Viscosities, Refractive Indexes, and Surface Tensions for Binary Mixtures of 2-Propanol + Benzyl Alcohol, + 2- Phenylethanol and Benzyl Alcohol + 2- Phenylethanol at T = (298.15, 308.15 and 318.15) K. J. Chem. Eng. Data 2007, 52, 1760−1767. (27) Hala, E.; Pick, J.; Fried, V.; Villim, O. Vapour-Liquid Equilibrium; Pergamon Press: Oxford, 1967. (28) Anton Paar Digital Densimeter. Instruction Handbook; Anton Paar: Graz, Austria, 2002. (29) Kuester, R. T.; Mize, J. H. Optimization Techniques with FORTRAN; McGraw Hill: New York, 1973. (30) Yaws, C. L. The Yaws Handbook of Vapor Pressure: Antoine Coefficients; Gulf Publications: Houston, TX, 2007. (31) Palczewska-Tulinska, M.; Oracz, P. Vapor Pressures of 1-Methyl-2Pyrrolidone, 1-Methyl-azepan-2-one, and 1,2-Epoxy-3-chloropropane. J. Chem. Eng. Data 2007, 52, 2468−2471.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS K.R.R. expresses his gratefulness to Rev. Fr. Dr. Francis Xavier SJ, Principal, Andhra Loyola College, Vijayawada.

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REFERENCES

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