Isobaric Vapor-Liquid Equilibria of Heptane + 1-Butanol and Heptane + 1-Pentanol Systems at (53.3 and 91.3) kPa M. Mohsen-Nia* and M. R. Memarzadeh Thermodynamic Research Laboratory, University of Kashan, Kashan, Iran Isobaric vapor-liquid equilibrium (VLE) data have been determined at (53.3 and 91.3) kPa for the binary mixtures of heptane + 1-butanol and heptane + 1-pentanol. The VLE data of binary systems were found to be thermodynamically consistent. In addition, the experimental VLE data were correlated by using the Wilson, nonrandom two-liquid (NRTL), and universal quasi-chemical (UNIQUAC) activity coefficient models for the liquid phases. The binary interaction parameters of the activity coefficient models have been determined and reported. A comparison of model performances has been made by using the criterion of the average absolute deviation (AAD) in boiling-point and vapor-phase composition. The obtained results indicate that the used activity coefficient models satisfactorily correlate the VLE data of the studied systems. Introduction Considering environmental protection strategies, production costs, and different requests for the industrial production of chemicals involves purification and recovery of the products, byproducts, and unreacted raw materials. The presence of some specific groups, particularly polar groups (oxygen, nitrogen), in most liquid mixtures of organic components forms nonideal systems. The separation of nonideal mixtures especially azeo- tropic mixtures is a topic of great practical and industrial interest. 1,2 Distillation is clearly the dominating separation process, accounting for more applications than all of the other separation processes, such as extraction, adsorption, crystal- lization, and membrane-based technologies. For the development of efficient distillation processes for the non-ideal mixtures, there is a great need for vapor-liquid equilibrium (VLE) data. 3,4 In recent years it has become increasingly important to develop new thermodynamic research on the VLE of mixtures formed by hydrocarbons and oxygenated additives (ethers and alkanols) to unleaded gasoline. There are various models to estimate the VLE of non-ideal systems, but for new systems especially in the final design step the necessary VLE data needs to be determined experimentally. 5-7 In this work, to improve our knowledge of the phase behavior of alkanes with 1-butanol and 1-pentanol mixtures, we measured isobaric VLE data for the (heptane + 1-butanol) and (heptane + 1-pentanol) systems at (53.3 and 91.3) kPa. The obtained VLE data of binary systems and the activity coefficients were found to be thermodynamically consistent. The experimental data were correlated with using the Wilson, 8 nonrandom two- liquid (NRTL), 9 and universal quasi-chemical (UNIQUAC) 10 equations for the liquid-phase activity coefficients. The cor- related parameters of the models are given. Experimental Section Materials. All materials were supplied by Merck. The purity of the pure components was checked on the basis of its refractive index at 293.15 K. The refractive index was measured using a thermostatically controlled Abbe refractometer (Atago 1T/4T) equipped with a digital thermometer, with an uncertainty of ( 0.05 °C, with an uncertainty of ( 0.0001 n D . The measured physical properties are listed in Table 1 along with values from the literature. 11,12 Boiling point measurements were obtained by using a Fischer boiling-point measurement. The estimated uncertainty in the boiling point measurements was 0.05 K. The materials were used directly without further purification. Apparatus and Procedure. In the dynamic equilibrium still the binary mixture was brought to a boil under controlled pressure. The pressure was fixed and held constant by using a vacuum pump. In each VLE experiment, the vapor and liquid mixture was separated in the equilibrium glass cell, and the vapor phase was condensed and returned to the boiling cell. The composition of the boiling liquid and the vapor changed with time until a steady state was achieved. The system was kept at the boiling point at least for 20 min to ensure that the steady state was reached. Then, samples of liquid and condensate were taken for analysis. The equilibrium compositions were determined by the refractometry method. The refractive index measurements were done by an Abbe refractometer (Atago 1T/ 4T). The refractometer was frequently calibrated by using double-distilled water. Water was circulated into the instrument through a thermostatically controlled bath maintained constant to ( 0.01 °C. At least three analyses were made for each sample. The measured refractive index data of the binary mixtures of heptane + 1-butanol and heptane + 1-pentanol at 293.15 K are reported in Table 2. The maximum deviations from the average value were less than 0.1 %. The uncertainties of the pressure, equilibrium composition measurements, and temperature were ( 0.1 kPa, ( 0.006 mol fraction, and ( 0.05 K, respectively. The vapor pressures of the pure components were measured with the same recirculating still. * Corresponding author. E-mail: m.mohsennia@kashanu.ac.ir. Table 1. Normal Boiling Temperature and Refractive Index of the Chemicals a heptane 1-butanol 1-pentanol T b lit /K 371.55 390.88 411.13 T b exp /K 371.65 390.95 411.10 n D lit 1.3877 1.3993 1.4100 n D exp 1.3876 1.3992 1.4101 a T b and n D data are taken from Lide 11 and Dean, 12 respectively. J. Chem. Eng. Data 2010, 55, 2140–2144 2140 10.1021/je9006629  2010 American Chemical Society Published on Web 01/22/2010