Isobaric Vapor-Liquid Equilibria for the Binary Mixtures of Styrene with Ethylbenzene, o-Xylene, m-Xylene, and p-Xylene Antonio Aucejo, Sonia Loras,* Vicente Martı ´nez-Soria, Nils Becht, and Gustavo Del Rı ´o Departamento de Ingenierı ´a Quı ´mica, Escuela Te ´cnica Superior de Ingenierı ´a, Universitat de Vale `ncia, 46100 Burjassot, Valencia, Spain Consistent vapor-liquid equilibria (VLE) data have been determined at (5 and 15) kPa for the binary systems styrene + ethylbenzene, + o-xylene, + m-xylene, and + p-xylene in the temperature range (324 to 359) K. The binary systems exhibit very slight deviations from ideal behavior, and no azeotrope is present. The VLE data were well-correlated by the Wilson, NRTL, and UNIQUAC equations. Introduction Mixtures of styrene with ethylbenzene and xylene isomers are frequently found in industrial processes, for instance, in the production of styrene by catalytic dehydrogenation of ethyl- benzene. For correct design of separation processes, the knowledge of accurate vapor-liquid equilibria (VLE) data is essential. Additionally, the separation of these mixtures is further complicated due to similar boiling points of the components and the tendency of styrene to polymerize quickly. To minimize or even totally eliminate undesirable polymerization, the distil- lation of these mixtures is usually carried out at low temperatures and, therefore, low pressures. The pressure range used for industrial applications normally is between 5 kPa and 15 kPa. 1 The present work was undertaken to measure VLE data of the binary systems ethylbenzene (1) + styrene (2), o-xylene (1) + styrene (2), m-xylene (1) + styrene (2), and p-xylene (1) + styrene (2) at (5 and 15) kPa. For the system ethylbenzene + styrene, isobaric and isothermal VLE data have been reported in the literature. References 2 to 8 report isobaric VLE data, but not at (5 and 15) kPa; refs 9 to 11 report isothermal VLE data. References 12 and 13 are the only ones for the systems o-xylene + styrene and m-xylene + styrene, respectively. Both of them report isobaric VLE data at 60 mmHg. For the system p-xylene + styrene, no VLE data have been previously published. Experimental Section Chemicals. Styrene (99.5+ %) and o-xylene (99+ %) were purchased from Fluka Chemie, and ethylbenzene (99 %), m-xylene (99+ %; anhydrous), and p-xylene (99+ %, HPLC grade) were supplied by Aldrich. The reagents were used without further purification after chromatography failed to show any significant impurities. The densities of pure liquids were measured at 298.15 K using an Anton Paar DMA 55 densimeter. Temperature was controlled to ( 0.01 K with a thermostated bath. The uncertanties in density and refractive index measure- ments are ( 0.01 kg‚m -3 and ( 0.0002, respectively. The experimental values of these properties are given in Table 1 together with those given in the literature. 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, equipped with a Cottrell circulation pump. The still is capable of handling pressures from (0.25 to 400) kPa and temperature 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 Hart Scientific thermometer model 1502A and a Pt 100 probe Hart Scientific model 5622 calibrated at the Spanish Instituto Nacional de Te ´cnica Aeroespacial. The uncertainty is estimated to be ( 0.02 K. For the pressure measurement, a digital manometer with an uncertainty of ( 0.05 kPa is used. The temperature probe was calibrated against the ice and steam points of distilled water. The manometers were calibrated using the vapor pressure of ultrapure water. In each VLE experiment, the pressure was fixed and held constant by using a vacuum pump, and the heating and shaking * Corresponding author. E-mail: Sonia.Loras@uv.es. Fax: +34 963 544898. Table 1. Density (d) and Refractive Index (nD) of the Chemicals d (298.15 K)/kg‚m -3 nD (298.15 K) component expt lit a expt lit a styrene 902.30 901.40 1.5438 1.5440 ethylbenzene 862.74 862.57 1.4932 1.4932 o-xylene 875.99 875.63 1.5020 1.5030 m-xylene 859.80 859.86 1.4944 1.4946 p-xylene 856.55 856.70 1.4930 1.4933 a Ref 19. Table 2. Experimental Vapor Pressure Data for Pure Components styrene ethylbenzene o-xylene m-xylene p-xylene T/K P/kPa T/K P/kPa T/K P/kPa T/K P/kPa T/K P/kPa 313.06 2.0 305.49 2.0 316.01 2.5 307.84 2.0 306.95 2.0 327.14 4.0 319.24 4.0 330.78 5.0 321.77 4.0 320.77 4.0 336.09 6.0 328.05 6.0 340.03 7.5 330.64 6.0 329.64 6.0 342.72 8.0 334.62 8.0 346.93 10.0 337.24 8.0 336.26 8.0 348.10 10.0 339.90 10.0 352.52 12.5 342.57 10.0 341.60 10.0 352.62 12.0 344.38 12.0 357.26 15.0 347.07 12.0 346.10 12.0 356.55 14.0 348.27 14.0 361.36 17.5 350.98 14.0 350.02 14.0 360.07 16.0 351.73 16.0 365.02 20.0 354.46 16.0 353.51 16.0 363.22 18.0 354.86 18.0 368.29 22.5 357.59 18.0 356.65 18.0 366.06 20.0 357.68 20.0 371.27 25.0 360.42 20.0 359.49 20.0 368.71 22.0 360.28 22.0 374.04 27.5 363.04 22.0 362.14 22.0 371.17 24.0 362.70 24.0 376.58 30.0 365.44 24.0 364.55 24.0 373.43 26.0 364.94 26.0 367.74 26.0 366.83 26.0 367.06 28.0 369.85 28.0 368.96 28.0 369.04 30.0 371.87 30.0 371.00 30.0 1051 J. Chem. Eng. Data 2006, 51, 1051-1055 10.1021/je050523s CCC: $33.50 © 2006 American Chemical Society Published on Web 03/28/2006