Vapor-Liquid Equilibrium for Binary System of Diethyl Sulfide + n-Heptane and Diethyl Sulfide + 2,2,4-Trimethylpentane at (363.15 and 353.15) K Erlin Sapei,* ,² Anna Zaytseva, ² Petri Uusi-Kyyny, ² Kari I. Keskinen, ²,‡ and Juhani Aittamaa ² Department of Chemical Technology, Helsinki University of Technology, P.O. Box 6100, FI-02015 HUT, Finland, and Neste Jacobs Oy, P.O. Box 310, FI-06101, Porvoo, Finland Isothermal vapor-liquid equilibrium (VLE) for diethyl sulfide + n-heptane and diethyl sulfide + 2,2,4- trimethylpentane at (363.15 and 353.15) K were measured with a circulation still. Maximum pressure azeotropes were found in both systems. The experimental results were correlated with the temperature-dependent Wilson model and also compared with the original UNIFAC and COSMO-RS predictive models. The measured diethyl sulfide + n-heptane VLE have been used simultaneously with the excess enthalpy from literature for a correlation of temperature-dependent Wilson parameters. Analyses of liquid- and vapor-phase composition were determined with a gas chromatograph and a refractometer. All VLE measurements passed the three thermodynamic consistency tests used. Introduction Increasing concerns on air pollution have led many countries to adopt more stringent regulations, which impose an ultralow concentration of sulfur in gasoline. 1 Design of separation processes to accomplish the removal of sulfur requires the knowledge of the vapor-liquid equilibrium (VLE) of sulfur compounds with hydrocarbons. Real gasoline is a rather complex hydrocarbon mixture composed of alkanes, olefins, cycloalkanes, and aromatics ranging from C 5 to C 14 . Sulfides are one of the major impurities present in crude oils and are also found in distillates and in products from cracking, coking, and alkylation processes. 2 The quantities of these compounds in the distillates are varying, depending on oil source and distillation operation. The VLE measurements of sulfides and hydrocarbon mixtures are very scarce in the literature. In this work, isothermal VLE measurements for binary system of diethyl sulfide + n-heptane and of diethyl sulfide + 2,2,4-trimethylpentane were performed at (363.15 and 353.15) K with a circulation still. Similar measurements studied in this work were not found in the open literature. Lecat 3 has measured the azeotropic point of diethyl sulfide + n-heptane at 101.32 kPa by using the distillation method. Didaoui-Nemouchi and Ait Kaci 4 have measured the excess molar enthalpies of diethyl sulfide with heptane at 303.15 K. Desty and Fidler 5 have measured the azeotropic point of diethyl sulfide + 2,2,4-trimethylpentane at 101.32 kPa by using the distillation method. Experimental Section Materials. Diethyl sulfide, n-heptane, 2,2,4-trimethylpentane, and toluene were purchased from Sigma Aldrich, Finland. The purities of the chemicals were checked with a gas chromatograph (GC) equipped with a flame ionization detector. n-Heptane, 2,2,4-trimethylpentane, and toluene were dried over molecular sieves (Merck 3Å) for 24 h. Diethyl sulfide was used as purchased without further purification. The refractive index (n D ) of the pure liquids were measured at 298.15 K with automatic refractometer (ABBEMAT-HP, Dr. Kernchen, Germany) with accuracy ( 0.00002, and the water contents were determined with a Karl Fischer titrator (DL38, Mettler Toledo). The purity, water content, and measured refractive indexes are presented in Table 1. The measured refractive indexes corresponded well with literature values. 6 Apparatus. The VLE runs were carried out with a circulation still of the Yerazunis-type 7 built at the glass workshop of the Helsinki University of Technology with minor modifications to the original design. 8 The experimental setup is described in detail in previous works. 8,9 Approximately 80 mL of reagent was needed to run the apparatus. Temperatures were measured with a Pt-100 resistance tem- perature probe, which was located at the bottom of the packed section of the equilibrium chamber and connected to thermom- eter (F200, Tempcontrol) with an accuracy of ( 0.02 K, and the calibration uncertainty was ( 0.01 K. The uncertainty of the whole temperature measurement system was estimated to be ( 0.05 K. Pressure was measured with a pressure transducer (PMP 4070, Druck) (0 to 100 kPa) connected to a Red Lion panel meter. The inaccuracy of the instruments was reported to be ( 0.07 kPa by the manufacturer. The pressure measurement system was calibrated against a BEAMEX PC 105-1166 pressure calibrator. The inaccuracy of the whole pressure measurement system including the calibration uncertainty is expected to be less than ( 0.17 kPa. To improve mixing in the sampling chambers and * Corresponding author. E-mail: sapei@cc.hut.fi. ² Helsinki University of Technology. ‡ Neste Jacobs Oy. Table 1. Purity, Water Content, and Refractive Indexes (nD) of Pure Components GC purity water content nD (298.15 K) component (mass %) (mass %) exptl lit. 6 diethyl sulfide 99.72 0.01 1.4400 1.4402 n-heptane 99.28 0.01 1.3853 1.3851 2,2,4-trimethylpentane 99.78 0.01 1.3890 1.3890 toluene 99.97 0.02 1.4939 1.4941 192 J. Chem. Eng. Data 2007, 52, 192-198 10.1021/je060351e CCC: $37.00 © 2007 American Chemical Society Published on Web 12/05/2006