Isobaric vapor–liquid equilibria for the system 1-pentanol–1-propanol–water at 101.3 kPa

Isobaric vapor–liquid equilibria for the system 1-pentanol–1-propanol–water at 101.3 kPa

Fluid Phase Equilibria 180 (2001) 205–210 Isobaric vapor–liquid equilibria for the system 1-pentanol–1-propanol–water at 101.3 kPa S. Loras a , M.J. ...

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Fluid Phase Equilibria 180 (2001) 205–210

Isobaric vapor–liquid equilibria for the system 1-pentanol–1-propanol–water at 101.3 kPa S. Loras a , M.J. Fernández-Torres b,∗ , V. Gomis-Yagües b , F. Ru´ız-Beviá b a

Departamento de Ingenier´ıa Qu´ımica, Facultad de Qu´ımica, Universitat de València, 46100 Burjassot, Valencia, Spain b Departamento de Ingenier´ıa Qu´ımica, Universidad de Alicante, Apdo 99, Alicante, Spain Received 8 September 2000; accepted 8 January 2001

Abstract Consistent vapor–liquid equilibrium data for the ternary system 1-pentanol–1-propanol–water is reported at 101.3 kPa at temperatures in the range of 362–393 K. The VLE data were satisfactorily correlated with UNIQUAC model. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Data; Vapor–liquid equilibria; UNIQUAC; Correlation; Alcohols; Water

1. Introduction Distillation is the most common operation in the chemical industry used for the separation of liquid mixtures. The correct design of distillation columns requires the availability of accurate vapor–liquid equilibria (VLE) data and the use of generalized methods to predict the properties of the mixtures. Experimental data of VLE for ternary or higher mixtures are quite scarce due to the experimental effort necessary to obtain a complete description of the system. This paper reports the results of measurements of VLE for the system 1-pentanol–1-propanol–water at normal atmospheric pressure. No measurements of VLE for this system have been previously reported. 2. Experimental section 2.1. Chemicals Water (resistivity = 18 M cm) was purified using a Milli-Q Plus system. The 1-pentanol (Panreac) and 1-propanol (Merck) had nominal purities of >99.0 and >99.5 mass%, respectively. The chemicals were used without further purification after chromatography failed to show any significant impurities. ∗ Corresponding author. Tel.: +34-96-590-3867; fax: +34-96-590-3826. E-mail address: [email protected] (M.J. Fern´andez-Torres).

0378-3812/01/$20.00 © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 8 1 2 ( 0 1 ) 0 0 3 5 0 - 8

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2.2. Apparatus and procedure An all-glass Fischer LABODEST vapor–liquid equilibrium apparatus model 602/D, manufactured by Fischer Labor und Verfahrenstechnik (Germany), was used in the equilibrium determinations. The equilibrium vessel was a dynamic-recirculating still described by Walas [1], equipped with a Cottrell circulation pump. The is still capable of handling pressures from 0.25 to 400 kPa and temperatures up to 523 K. The Cottrell pump ensures that both liquid and vapor phases are in intimate contact during boiling and also in contact with the temperature sensing element. The equilibrium temperature was measured with a digital Fischer thermometer with an accuracy of ±0.1 K. For the pressure measurement, a digital manometer with an accuracy of ±0.01 kPa was used. The temperature probe has been verified in two points, the ice and steam points of distilled water. The manometers were tested using the vapor pressure of ultrapure water. This was still operated under constant pressure until equilibrium was reached. Equilibrium conditions were assumed when constant temperature and pressure were obtained for 60 min or longer. Then, samples of liquid and condensate vapor were taken for analysis. The sample extractions were carried out with special syringes, which withdrew small-volume samples (1.0 ␮l) from the system. The composition analysis of the liquid and condensed vapor phase samples were determined using a Varian Star 3400 CX gas chromatograph (GC), after calibration with gravimetrically prepared standard solutions. A thermal conductivity detector was used together with a 2 m, 3.175 mm i.d., packed column, Porapak P. The GC response peaks were processed with a star chromatography station. The column and detector temperatures were 473 and 503 K, respectively. Very good separation was achieved under these conditions, and calibration analyses were carried out to convert the peak ratio to the mass composition of the sample. At least three analyses were made of each liquid and vapor composition. The standard deviation in the mole fraction was usually <0.001. 3. Results and discussion Isobaric VLE data were only determined for the totally miscible mixtures of the three components. The experimentally determined compositions of the liquid and vapor phases, and the corresponding equilibrium temperatures, are listed in Table 1 and represented on Fig. 1. The binodal curve data (dashed line) shown in the figure is taken from a previous study [2] and marks the miscibility limit of the three liquid components at 358.15 K. The reason for having selected this temperature value is because it is closer to the bubble point of the mixtures presented in Table 1. The ternary data were found to be thermodynamically consistent as tested by the point to point L–W method of Wisniak [3]. All the values of L/W are between 0.97 and 1.00. Vapor pressures were calculated with the Antoine equation, whose parameters Ai , Bi and Ci for 1-pentanol, 1-propanol and water were obtained from Reid et al. [4]. The UNIQUAC equation was used to correlate the 34 ternary experimental data presented in this paper. In the correlation, 23 isobaric data previously published in the constituents binary mixtures were also included (nine data of the system 1-propanol–water [5], nine of 1-pentanol–1-propanol [6] and five of 1-pentanol–water [7]). The pure component molecular structure constants for the UNIQUAC equation are those given by Sorensen and Arlt [8]. For the purpose of fitting the parameters, a nonlinear optimization method was used to minimize the following objective function.

S. Loras et al. / Fluid Phase Equilibria 180 (2001) 205–210

OF = 1000



Pexp − Pcal Pexp

2 +



γexp − γcal γexp

207

2 (1)

where P is the pressure and γ the liquid-phase activity coefficients. Table 2 lists the optimized UNIQUAC binary interaction parameters aij (K) obtained. Mean absolute deviations (MAD) between experimental and calculated vapor phase mole fraction and pressures were MAD (y water ) = 0.04, MAD (y ethanol ) = 0.02 and MAD (P ) = 2.1 kPa. The model represents the experimental data successfully. The model parameters can be used to predict boiling points and vapor phase compositions from the liquid phase composition at the system pressure. Fig. 2 shows Table 1 Vapor–liquid equilibrium data for the system 1-pentanol (1); 1-propanol (2) and water (3) at 101.3 kPa being xi , the liquid phase mole fraction and yi , the vapor phase mole fraction T (K)

x1

x2

y1

y2

392.8 384.0 377.3 372.0 367.9 367.7 367.4 370.9 372.4 374.6 376.9 379.7 383.3 373.4 371.3 369.4 367.6 366.1 364.6 364.5 365.7 366.8 368.0 369.6 365.2 364.4 363.8 362.3 362.4 363.7 365.3 364.1 362.4 362.9

0.839 0.650 0.447 0.245 0.056 0.114 0.089 0.246 0.346 0.448 0.543 0.647 0.758 0.587 0.484 0.394 0.291 0.199 0.103 0.121 0.221 0.311 0.399 0.494 0.396 0.315 0.212 0.111 0.117 0.218 0.330 0.214 0.102 0.087

0.106 0.303 0.502 0.701 0.888 0.809 0.833 0.670 0.571 0.466 0.363 0.259 0.140 0.229 0.313 0.411 0.506 0.599 0.692 0.643 0.550 0.444 0.343 0.240 0.224 0.293 0.386 0.484 0.408 0.330 0.245 0.224 0.286 0.190

0.392 0.223 0.111 0.041 0.006 0.012 0.010 0.044 0.060 0.084 0.121 0.178 0.254 0.141 0.102 0.074 0.053 0.034 0.016 0.020 0.040 0.058 0.079 0.108 0.095 0.053 0.043 0.022 0.026 0.046 0.183 0.156 0.029 0.108

0.255 0.525 0.672 0.780 0.831 0.760 0.773 0.703 0.649 0.575 0.490 0.387 0.259 0.288 0.333 0.408 0.472 0.528 0.578 0.544 0.482 0.407 0.328 0.255 0.279 0.271 0.341 0.411 0.370 0.304 0.285 0.296 0.322 0.337

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Fig. 1. Vapor–liqud equilibrium tie lines for the 1-pentanol–1-propanol–water system at 101.3 kPa: ( ) vapor phase mole fractions.

Fig. 2. Vapor–liquid isotherms for the ternary system 1-pentanol–1-propanol–water at 101.3 kPa, calculated with the UNIQUAC equation, as a function of the liquid mole fraction.

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Table 2 Optimized UNIQUAC binary interaction parameters, aij (K) for the VLE data of the system 1-pentanol (1); 1-propanol (2) and water (3) a12 a13 a23 a21 a31 a32

−24.04 144.50 205.11 35.33 205.09 37.70

Fig. 3. Vapor phase composition for the ternary system 1-pentanol–1-propanol–water at 101.3 kPa, calculated with the UNIQUAC equation, as a function of the liquid mole fraction. The basic triangular grid represents the liquid composition (xi ). The parametric curves indicate equilibrium vapor mole fractions of 1-pentanol (· · · ) and 1-propanol (—).

the isotherms of the ternary system as a function of liquid mole fraction. In Fig. 3, the mole fraction of component i in the liquid, xi , is represented by the basic grid, and the vapor mole fraction, yi , in equilibrium with the liquid is shown as parametric curves. List of symbols aij UNIQUAC binary interaction parameters P pressure xi liquid phase mole fraction yi vapor phase mole fraction γ liquid phase activity coefficients

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Acknowledgements The authors wish to thank the Generalitat Valenciana (Spain) for the financial help of the Project GV-3174/95 and DGES for the financial aids of the Project PB96-0338. References [1] [2] [3] [4] [5] [6] [7] [8]

S.M. Walas, Phase Equilibria in Chemical Engineering, Butterworths, London, 1985. M.J. Fernández, V. Gomis, M. Ramos, F. Ru´ız, J. Chem. Eng. Data 45 (2000) 1053–1054. J. Wisniak, Ind. Eng. Chem. Res. 32 (1993) 1531–1533. R.C. Reid, J.M. Prausnitz, T.K. Sherwood, The Properties of Gases and Liquids, Their Estimation and Correlation, 3rd Edition, McGraw-Hill, New York, 1977. K. Kojima, K. Tochigi, H. Seki, K. Watase, Kagaku Kogaku 32 (1968) 149–150. J.E. Villa Rivera, Ph.D. thesis, Paris, 1983. T.-H. Cho, K. Ochi, K. Kojima, Kagaku Kogaku Robunshu 10 (1984) 181–182. J.M. Sorensen, W. Arlt, Liquid–Liquid Equilibrium. Data Collection. Binary Systems, DECHEMA Chemistry Data Series, Vol. V, 1979 (Part 1).