Microsoft Word - contents_2.doc HUNGARIAN JOURNAL OF INDUSTRIAL CHEMISTRY VESZPRÉM Vol. 31. pp. 23-29 (2003) VAPOR PRESSURE, DENSITY, VISCOSITY AND REFRACTIVE INDEX OF DIMETHYL SULFOXIDE + 1,4-DIMETHYLBENZENE SYSTEM O. CIOCIRLAN, O. IULIAN Department of Applied Physical Chemistry and Electrochemistry, Faculty of Industrial Chemistry, “Politehnica” University of Bucharest, 313 Splaiul Independentei, 060042, Romania This work reports the experimental results of the isothermal vapor-liquid equilibrium data between 303.15 K and 333.15 K, densities, viscosities and refractive indices from 298.15 to 323.15 K of the dimethyl sulfoxide + 1,4-dimethylbenzene system over the entire range of mixture composition. The obtained PTX data were correlated and estimated by the Wilson, NRTL and UNIFAC models. The excess Gibbs energy and activity coefficients were calculated and compared with the others excess properties. Excess molar volumes, viscosity deviations and deviations in refractivity were calculated from experimental data; all the computed quantities were fitted to the Redlich-Kister equation. The resulting excess functions were interpreted in terms of the interactions between the molecules in the binary system. Keywords: VLE data, mixture properties, correlative and predictive methods, molecular interactions Introduction Continuing our work on the thermodynamic of the nonelectrolite systems, the present paper is a part of a study of the binary systems containing dimethyl sulfoxide (DMSO) and aromatic hydrocarbons, interesting as mixed solvents [1]. Dimethyl sulfoxide is a versatile nonaqueous, aprotic, highly polar self-associated solvent (having a dipole moment µ =3.90 D at 298.15 K) used extensively in kinetic studies, electrochemistry and as a solvent for polymers. Binary mixtures of DMSO with aromatic solvents are interesting in studies of polymer miscibility, polymer phase diagrams, and preferential interactions in mixed solvents [2]. This work reports isothermal experimental vapor liquid equilibrium (VLE) data at temperatures in the range from 303.15 K to 333.15 K and experimental data of density, viscosity and refractive index in the temperature range from 298.15 to 323.15 K for the dimethyl sulfoxide + 1,4-dimethylbenzene system. The VLE data were correlated by means of Wilson [3] and NRTL [4] models; this work has also served to test the predictive capacity of the group contribution methods: original UNIFAC [5] and UNIFAC-Dortmund [6,7]. Excess molar volumes, viscosity deviations and deviations in refractivity were calculated from experimental data; all the computed quantities were fitted to the Redlich-Kister equation. After our knowledge, VLE data for this binary system are not numerous [8]; there is only one source in the literature [9]. No literature data on densities, viscosities and refractive indices are available for this system, except on densities at 303.15 K [10]. Experimental Materials The used substances were purified by distillation. Dimethyl sulfoxide was distilled under vacuum at 0.8-0.9 kPa and 338.65 K. The analytical-reagent- grade 1,4-dimethylbenzene from Fluka (p.a.) was used without further purification. The purity was checked by refractive index, density and gas chromatography. It was better than 99.5 mass per 24 cent. The experimental values of density, refractive index and viscosity of the pure components are presented in Table 1 and compared with literature values. Table 1. Experimental and literature values for density (ρ), refractive index (nD) and viscosity (η) of the pure components 10-3 ρ, kg·m-3 nD η, mPa·s T, K lit. exptl lit. exptl lit. exptl dimethyl sulfoxide 293.15 1.1005013, 1.1005314 1.10073 298.15 1.096211, 1.095412 1.09574 1.477011 1.4768 2.0388 303.15 1.0905015 1.09074 1.475214 1.4733 1.83014 1.8405 313.15 1.0804616 1.08075 1.470014 1.4694 1.53414 1.5373 1,4-dimethylbenzene 293.15 0.861017 0.86144 298.15 0.856519, 0.8567020 0.85712 1.4932010, 1.4928619, 1.493021 1.4930 0.60318 0.6281 Vapor pressure The total vapor pressure of the binary mixture was measured at temperatures between 303.15 K and 333.15 K by a static method, with a glass isoteniscope of the Smith and Menzies type, with some modifications [22], which allows the measurements of VLE at subatmospheric pressures at temperatures up to 423.15 K. Vapor pressures are measured by means of a Hg manometer and a cathetometer, readings accurate to within 0.026 kPa. The temperature was controlled by a U-10 type thermostat and measured with an Hg thermometer with an estimate accuracy of 0.05 K. The substances were degassed prior to the measurements by freezing-thawing processes under vacuum. The vapor phase volume of the apparatus being relatively small, calculation showed that the error in composition due to vaporization is within this limit. Density, Viscosity and Refractive Index Densities, ρ, of the pure solvents and the mixtures were measured with an Anton Paar DMA 4500 densimeter with a precision of ±0.00005 g cm-3, between 298.15 and 323.15 K. The DMA cell was calibrated with ultra pure water at atmospheric pressure. The sample size was 0.7 cm3, and the sample thermostat was controlled to ±0.01 K. Kinematic viscosities, ν, of the pure components and their mixtures were determined at 298.15, 303.15, 313.15 and 323.15 K using an Ubbelohde capillary viscosimeter for which the uncertainty of the flow time measurement was ±0.1 s; the corresponding uncertainty in the kinematic viscosity was ± 0.001 10-6 m2 s-1. At least four times flow measurements were performed for each composition and temperature, and the results were averaged. The viscosimeter was calibrated using double distilled water; it was placed in a thermostat maintained constant within ± 0.05 K. Refractive indices values for the D-line, nD, were measured with a thermostated Abbe refractometer with a precision of ±0.0001. All measurements were done in a thermostat maintained at ± 0.05 K. The binary mixtures were prepared by mass; the precision of the mole fraction is estimated to be better than ± 0.0002. Results and Discussion The measurements of the total pressure were carried out at various compositions on the large temperature range. For each binary mixture the dependencies between experimental pressure and temperature were established. The functions P = f(T) obtained by polynomial regression were used to calculate the VLE data at 303.15 K, 313.15 K, 323.15 K and 333.15 K. The smoothed data resulted from experimental measurements are reported in Table 2. Table 2 Vapor-liquid equilibrium data for the binary dimethyl sulfoxide (1) + 1,4-dimethylbenzene (2) system from 303.15 to 333.15 K. Smoothed values of the pressure by polynomial regression P, kPa T, K X1 303.15 313.15 323.15 333.15 0.0000 1.55 2.65 4.34 6.86 0.1235 1.67 2.50 4.33 7.21 0.2098 1.50 2.41 4.37 7.20 0.3029 1.19 2.19 4.00 6.93 0.4059 1.36 2.10 3.86 6.64 0.6348 1.09 1.91 3.60 6.17 0.8022 1.09 1.71 3.05 5.11 0.9078 0.74 1.40 2.35 3.59 0.9554 0.64 0.85 1.47 2.48 1.0000 0.11 0.22 0.41 0.73 The temperature dependence of the pure component vapor pressures, Pio, was calculated using the Antoine equation: i i i o i CKT B AkPaP − −= )( )(ln (1) where the Antoine constants Ai, Bi and Ci are reported in Table 3. 25 Table 3 Result of correlation and prediction with Wilson, NRTL and UNIFAC models for dimethyl sulfoxide (1) + 1,4- dimethylbenzene (2) system Compound Ai Bi Ci dimethyl sulfoxide23 15.86168 4717.396 41.59 1,4-dimethylbenzene24 14.08127 3346.646 57.84 The various models are used for correlation and prediction of binary VLE data: the equations based on local composition concept (Wilson and NRTL) and the group contribution methods UNIFAC. The results of correlation with Wilson and NRTL models are presented in Table 4, which includes the model parameters values and the statistical parameters: average percentage deviation in pressure, ∆P, and standard deviation, σ. Prediction of VLE for the binary system at 303.15, 313.15, 323.15 and 333.15 K has been carried out by the original UNIFAC method and its modification, UNIFAC-Dortmund. The group interaction parameters were those published by Reid [25], Hansen [26] and Gmehling [6,7]. The results of prediction are also presented in Table 4. The Wilson and NRTL give a similar and good representation of experimental data (except at 303.15 K temperature); σ and ∆P characterise the data as satisfactory. It can be observed that the description of this system by the original UNIFAC method shows good agreement with the experimental data, like Wilson and NRTL models; the modified UNIFAC gives less satisfactory results, especially at high temperature. The experimental and calculated (with Wilson model) total pressures vs. liquid and vapor compositions for 303.15 K, 313.15 K, 323.15 K and 333.15 K are presented in Figure 1. In the same phase diagram the curves represent calculated data and the points, experimental data. The activity coefficients were calculated with Wilson equation for binary systems. Figure 2 presents the dependence of the activity coefficients of the composition at 313.15 K, the limiting values at infinite dilution of these coefficients being given. We have also computed and represented the variation of the excess Gibbs energy of the system, which shows positive deviations from the ideal. The comparison of maximum obtained value of GE with literature, at 313.15 K, is satisfactory [9]. Table 4 Experimental values of density, kinematic viscosity and refractive index of dimethyl sulfoxide (1) + 1,4- dimethylbenzene (2) system from 298.15 to 323.15 K Statistical parameters Model Parameters, J mol-1 σ a, mmHg ∆P b, % 303.15 K Wilson ∆λ12=4143.8± 770 ∆λ21=2412.5±1004 0.86 7.14 NRTL (α=0.3) ∆g12=4067.7±1113 ∆g21=1442.6± 891 0.91 7.54 UNIFAC Original UNIFAC UNIFAC-Dortmund 6.25 9.92 313.15 K Wilson ∆λ12=3764.3±217 ∆λ21= 346.4±326 0.41 2.64 NRTL (α=0.3) ∆g12=4444.2±309 ∆g21= 969.4±222 0.37 2.10 UNIFAC Original UNIFAC UNIFAC-Dortmund 7.99 4.54 323.15 K Wilson ∆λ12=6261.8±431 ∆λ21=1163.9±284 0.86 2.27 NRTL (α=0.3) ∆g12=2620.0±435 ∆g21=3451.0±535 1.15 2.93 UNIFAC Original UNIFAC UNIFAC-Dortmund 3.79 10.20 333.15 K Wilson ∆λ12=9770.9±728 ∆λ21= 455.2±172 1.07 1.91 NRTL (α=0.3) ∆g12=1649.8±343 ∆g21=5777.3±636 2.00 3.85 UNIFAC Original UNIFAC UNIFAC-Dortmund 3.48 14.20 a Standard deviation σ ={Σi N (Pcalc(i)- Pexp(i)) 2/(N-M)}0.5 (N: number of data points and M: number of estimated parameters). b Average percentage deviation in pressure ∆P=(100/N)·Σi N |Pcalc(i)- Pexp(i)|/ Pexp(i) 0 2 4 6 8 0 0.2 0.4 0.6 0.8 1 X2, Y2 P , k P a Fig. 1 Experimental vapor pressures of dimethyl sulfoxide (1) + 1,4-dimethylbenzene (2) system at 303.15 K (□); 313.15 K (∆); 323.15 K (o); 333.15 K (×); correlation with Wilson model (―) 26 0 1 2 3 4 5 6 7 8 9 10 0 0.2 0.4 0.6 0.8 1 X2 1, 2 0 200 400 600 800 1000 1200 G E , J m ol -1 Fig. 2 Activity coefficients and excess Gibbs energy for the dimethyl sulfoxide (1) + 1,4-dimethylbenzene (2) system calculated with Wilson model at 313.15 K Densities, viscosities and refractive indices were measured in the temperature range from 298.15 to 323.15 K and the measured values were listed in Table 5. The values of excess molar volume, VE, viscosity deviation, ∆ν, and deviation in molar refractivity, ∆R, were calculated from the experimental data according to the following equations: ∑ = −= 2 1i iim E XVVV (2) ∑ = −=∆ 2 1i iim Xννν (3) ∑ = −=∆ 2 1i iim RRR ϕ (4) where Xi and φi represent the mole fraction and volume fraction, respectively; Vm, νm, Rm, the properties of mixtures, Vi, νi, Ri, the properties of the pure components. The values of R were calculated from the Lorentz-Lorenz equation [27]. The experimental values of VE, ∆ν, and ∆R have been fitted to the Redlich-Kister [28] type polynomials: ( ) kn k k XAXXY ∑ = −= 0 121 12 (5) where Y represent the excess molar volume, viscosity deviation and deviation in molar refractivity, and Ak represents the parameters. A nonlinear least-squares method was used to estimate the adjustable parameters Ak. The values of Ak and standard deviation σ are given in Table 6. Table 5 Parameters of Eq. 5 and standard deviations of excess functions of dimethyl sulfoxide (1) + 1,4-dimethylbenzene (2) system X1 10-3·ρ, kg·m-3 106·ν, m2·s-1 nD X1 10-3·ρ, kg·m-3 106·ν, m2·s-1 nD 298.15 K 0.0000 0.85712 0.855 1.4930 0.5969 0.96896 1.236 1.4858 0.1056 0.87326 0.902 1.4927 0.7009 0.99631 1.337 1.4836 0.1975 0.88813 0.950 1.4920 0.8022 1.02625 1.447 1.4813 0.2988 0.90577 1.010 1.4908 0.8978 1.05785 1.561 1.4791 0.4033 0.92574 1.079 1.4893 1.0000 1.09574 1.698 1.4768 0.5126 0.94902 1.163 1.4875 303.15 K 0.0000 0.85277 0.692 1.4907 0.5969 0.96423 1.110 1.4835 0.1056 0.86880 0.745 1.4901 0.7009 0.99151 1.227 1.4813 0.1975 0.88363 0.797 1.4893 0.8022 1.02138 1.360 1.4790 0.2988 0.90121 0.861 1.4882 0.8978 1.05292 1.506 1.4765 0.4033 0.92112 0.936 1.4868 1.0000 1.09074 1.687 1.4733 0.5126 0.94434 1.028 1.4851 313.15 K 0.0000 0.84405 0.746 1.4854 0.5969 0.95490 1.012 1.4792 0.1056 0.85999 0.782 1.4847 0.7009 0.98205 1.079 1.4772 0.1975 0.87472 0.816 1.4840 0.8022 1.01179 1.152 1.4749 0.2988 0.89220 0.858 1.4831 0.8978 1.04318 1.227 1.4723 0.4033 0.91200 0.906 1.4820 1.0000 1.08075 1.316 1.4694 0.5126 0.93510 0.963 1.4805 323.15 K 0.0000 0.83526 0.578 0.5969 0.94543 0.857 0.1056 0.85108 0.612 0.7009 0.97244 0.934 0.1975 0.86571 0.647 0.8022 1.00203 1.020 0.2988 0.88308 0.690 0.8978 1.03326 1.113 0.4033 0.90276 0.740 1.0000 1.07075 1.227 0.5126 0.92574 0.802 Table 6 Function A0 A1 A2 A3 σ a 298.15 K 106·VE, m3·mol-1 -0.7875 0.0235 -0.7956 0.1458 0.0007 106·∆ν, m2·s-1 -0.4946 -0.0705 0.0004 106·∆R, m3·mol-1 -8.6332 2.0491 -0.5638 0.1739 0.0022 303.15 K 106·VE, m3·mol-1 -0.7718 0.0122 -0.7718 0.1051 0.0011 106·∆ν, m2·s-1 -0.4112 -0.1051 0.0130 0.0002 106·∆R, m3·mol-1 -8.6048 2.2879 -0.7394 0.0058 313.15 K 106·VE, m3·mol-1 -0.7908 -0.0116 -0.8715 0.0009 106·∆ν, m2·s-1 -0.3002 -0.0443 0.0002 106·∆R, m3·mol-1 -8.5246 2.1822 -0.8037 0.5005 0.0041 323.15 K 106·VE, m3·mol-1 -0.7815 -0.0221 -0.9102 0.0026 106·∆ν, m2·s-1 -0.2340 -0.0220 0.0017 0.0001 106·∆R, m3·mol-1 a Standard deviation σ ={Σi N (Ycalc(i)- Yexp(i)) 2/(N-M)}0.5 (N: number of data points and M: number of estimated parameters). The dependence of excess molar volume VE on the mole fraction of DMSO is presented in Figure 3. The negative values of VE suggest the presence of specific interactions between the mixing components. VE shows negligible temperature dependence. Plots of excess viscosity versus the mole fraction of DMSO are shown in Figure 4. The ∆ν are negative over the whole composition range; a 27 -0.25 -0.2 -0.15 -0.1 -0.05 0 0 0.2 0.4 0.6 0.8 1 X2 10 6 V E , m 3 m ol -1 -0.13 -0.11 -0.09 -0.07 -0.05 -0.03 -0.01 0 0.2 0.4 0.6 0.8 1 X2 6 , m m 2 s- 1 -2.5 -2 -1.5 -1 -0.5 0 0.5 0 0.2 0.4 0.6 0.8 1 X2 6 R , m 3 m ol -1 rise of temperature makes an increase of ∆ν. The viscosity of a mixture depends on the molecular interactions between components: generally, mixtures with strong interactions between different molecules show positive viscosity deviations, while for mixtures without specific strong interactions, viscosity deviations are negative. In our mixtures the breaking of dipole-dipole interactions of DMSO contributes to the reduction of the viscosity during the mixing process. On the other hand, self-association of DMSO and “π electron interactions” in DMSO + 1,4-dimethyl- benzene system [29] increase the viscosity, but the effect is not as important as the breaking of self- interactions. Consequently, the excess viscosity of all our mixtures is moderately negative; similarly, VE values remain negative. The presence of intramolecular interaction is reflected in positive deviations from Raoult’s law, therefore, positive values for GE. The excess molar refractivity is shown in Figure 5. The ∆R values are negative for the whole composition range for all mixtures. The values are independent of temperature, as predicted by the theory, the molar refractivity depending only on the wavelength of light used for measurement. Fig. 3 Excess molar volumes for dimethyl sulfoxide (1) + 1,4- dimethylbenzene (2) system at 298.15 (◊); 303.15 K (□); 313.15 K (∆); 323.15 K (o); correlation with Redlich-Kister equation (―) Fig. 4 Viscosity deviations for dimethyl sulfoxide (1) + 1,4- dimethylbenzene (2) system for the temperatures given in Figure 3; correlation with Redlich-Kister equation (―) Fig. 5 Deviations in molar refractivity for dimethyl sulfoxide (1) + 1,4-dimethylbenzene (2) system for the temperatures given in Figure 3; correlation with Redlich-Kister equation (―) Conclusions The experimental data concerning the isothermal vapor-liquid equilibria in the binary 1,4- dimethylbenzene + DMSO system have been presented. Eight various mixtures containing 1,4- dimethylbenzene + DMSO have been analyzed. A good agreement between experimental and calculated values of the pressure has been observed for Wilson and NRTL correlative methods and for original UNIFAC- predictive method. Experimental densities, kinematic viscosities and refractive indices data for the binary system DMSO + 1,4-dimethylbenzene have been measured at atmospheric pressure between 298.15 K and 323.15 K. Excess functions have been calculated and fitted to the Redlich-Kister equation. The behaviour of this mixture has been discussed in terms of inter and intramolecular interactions. 28 SYMBOLS Ai, Bi, Ci Antoine’s equation parameters Ak Redlich-Kister’s parameters G E excess Gibbs energy gij parameters of NRTL equation M number of model parameters N number of experimental points nD refractive index ∆P average percentage deviation in pressure expP experimental total pressure calcP computed total pressure o iP vapor pressure of i-th pure component ∆R deviation in molar refractivity Rm molar refractivity of mixture Ri molar refractivity of the i-th pure component T absolute temperature VE excess molar volume Vm molar volume of mixture Vi molar volume of the i-th pure component X i liquid-phase mole fractions γ k activity coefficients λ ij parameters of Wilson equation µ dipole moment η, ν dynamic and cinematic viscosity, respectively ∆ν viscosity deviation νm kinematic viscosity of mixture νi kinematic viscosity of the i-th pure component ρ density σ standard deviation φi volume fraction REFERENCES 1. 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