J. Chem. Eng. zyxwvutsrq Data zyxwvut 1988, 33, 263-265 Liquid-Liquid Equilibria for the Ternary Systems y-Butyrolactone-n -Heptane-Benzene, y-Butyrolactone-n-Heptane-Toluene, and y-Butyrolactone-n -Heptane-p -Xylene Akl M. Awwad," Muna A. Salman, and Fatln A. Hassan Scientific Research Council, Petroleum Research Center, Jadiriyah, P. 0. Box 70039, Baghdad, Iraq Liquid-liquid equilibrium data for the system y-butyrolactone-n -heptane-benzene, y-butyrolactone-n -heptane-toluene, and y-butyrolactone-n-heptane-p -xylene are obtalned at 298.15 K. Dlstrlbutlon coefflclents and selectlvlty at 298.15 K were calculated. The selectlvlty for extraction of benzene from n-heptane by extraction with y-butyrolactone Is better than that for extraction of toluene or p -xylene from n -heptane. Introduction In recent years, the petroleum industry has given much at- tention to the highly polar, high density, and high boiling point solvents such as dimethyl sulfoxide ( 7), N-formylmorpholine (2), N-methylpyrrolidone zyxwvutsrqp (3), glycols (4), and sulfolane (5). This interest has resulted from their high selectivity and solvency for low molar mass monocyclic aromatic hydrocarbons (c'49). y8utyrolactone (C,H,02) is a new solvent for the recovery of aromatic hydrocarbons. Therefore, we have initiated a program to study its efficiency for extraction of benzene, toluene, and xylenes from reformates. Ternary phase equilibrium data are essential for the proper understanding of solvent extraction processes. To our knowledge phase equilibrium data on these systems have not been published in the literature. The present work reports the phase diagrams, distribution coefficients, tie line data, and selectivity for the systems y-butyrolactone-n - heptane-benzene, y-butyrolactone-n-heptane-toluene, and y-butyrolactone-n-heptane-p -xylene at 298.15 K. Experlmental Section Materials. The n-heptane (stated purity of 99.5 mol zyxwvut YO), benzene (stated purity of 99.5 mol %), toluene (stated purity of 99.5 mol %), p-xylene (stated purity of 99.5 mol %), and y-butyrolactone (stated purity of 99 mol %) were obtained zyxwvuts from Fluka AG and used without further purification. All liquids were kept over freshly activated molecular sieve of Type 4A (Union Carbide) and filtered before use. The purity of all the liquids was confirmed by gas-liquid chromatographic analysis. Densities, p, and refractive indices, zyxwvutsrqp n,, of the pure liquids at 298.15 K are compared with data from the literature in Table I. Procedure. Liquid-liquid equilibria data for the ternary sys- tems were determined by a standard turbidimetric method (9) using an apparatus similar to that described elsewhere (70). Blnodal Curves Determination. Homogeneous synthetic mixtures of known compositions of n -heptane-benzene, n - heptane-toluene, n-heptane-p -xylene, y-butyrolactone-benz- ene, y-butyrolactone-toluene, and y-butyrolactone-p -xylene were titrated in a thermostated bottle to the appearance of turbidity. The thermostat temperature was controlled by a temperature controller and maintained a constant temperature 0021-956818811733-0263$01.50/0 Table I. Physical Properties of the Pure Liquids at 298.15 K 263 PIP nD liquid obsd lit. obsd lit. n-heptane 0.679 50 0.67951' 1.38509 1.3851" benzene 0.873 66 0.87363c 1.479 99 1.49792b toluene 0.862 10 0.86222' 1.493 88 1.493gb p-xylene 0.85661 0.8566gb 1.493 22 1.49325b y-butyrolactone 1.124 21 1.1254d 1.434 zyx 77 1.4348d "Reference 7. bReference 6. 'Reference 8. dReference 12. within fO.O1 OC. The temperature was measured with a Hewlett-Packard quartz thermometer calibrated against a gal- lium temperature standard. The addition of y-butyrolactone to a miscible mixture of n-heptane-benzene, n-heptane-toluene, n -heptane-p -xylene and the addition of n-heptane to a ho- mogeneous mixture of y-butyrolactone-benzene, y-butyro- lactone-toluene, and y-butyrolactone-p -xylene rendered the systems immiscible. The titrant was added in small increments from the jacketed microburet and the contents of the bottle were mixed for proper mixing and equilibrium with a Teflon- coated magnetic rod. The amount of titrant thus added was calculated from its volume and density measured at 298.15 K with an Anton Paar digital dosimeter (Model DMA 60). Com- position of the ternary mixture at the first appearance of tur- bidity gave one point on the binodal curve. Tie Line Data Determination. Tie lines for the present systems were obtained by mixing a known weight of the n- heptane-benzene, n-heptane-toluene, and n-heptane-p -xylene mixtures with an equal weight of y-butyrolactone in a thermo- stated cell. The two-phase mixture was stirred for at least 2 h and allowed to settle for at least 6 h. Once equilibrium had been reached, samples of both phases were carefully with- drawn with glass syringes. The samples were analyzed by gas-liquid chromatography (Pye Unican, Model 204) equipped with a flame ionization detector and connected to an integration unit (Spectra Physics). A 6 ft X '/8 in. stainless steel column packed with Carbowax 20M on Chromsorb W and operating at 160 OC was used for analysis. The flow rate of nitrogen carrier gas was kept constant at 30 cm3 min-'. Samples of known concentration were injected for calibration purposes. Mass fraction measurements were reproducible to within f0.004. Results and Discussion Experimental data for the binodal curves for the systems y-butyrolactone-n-heptane-benzene, y-butyrolactone-n-hep- tane-toluene, and y-butyrolactone-n -heptane-p -xylene at 298.15 K are illustrated in Figures 1, 2, and 3. The tie line data indicating the composition of the two phases are reported in Tables 11, 111, and IV. Plait points were determined by a construction method ( 7 7) in the rectangular coordinate system. The projection points corresponding to the ends of the tie lines were found to tie on a smooth curve within the limits of ex- 0 1988 American Chemical Society