1098
J. Chem. Eng. Data 2002, 47, 1098-1102
Articles Isobaric Vapor-Liquid Equilibria of Diethyl Carbonate with Four Alkanes at 101.3 kPa A. Rodrı´guez, J. Canosa, A. Domı´nguez, and J. Tojo* Chemical Engineering Department, Vigo University, 36200 Vigo, Spain
Isobaric vapor-liquid equilibria have been measured for the four binary systems hexane + diethyl carbonate (DEC), DEC + heptane, DEC + octane, and cyclohexane + DEC at 101.3 kPa. The activity coefficients were found to be thermodynamically consistent and were satisfactorily correlated with the Wilson and UNIQUAC equations. They were also compared with results obtained from the application of the ASOG and UNIFAC group contribution methods.
1. Introduction papers1,2
Currently, have been published related to dialkyl carbonates because of the possible use of oxygenated volatile organic compounds as fuel additives. This paper is a continuation of our work on the determination of the thermodynamic properties of dialkyl carbonates.3-8 To ascertain dialkyl carbonate properties with other components, we present experimental isobaric vapor-liquid equilibria (VLE) data for the binary systems hexane + diethyl carbonate (DEC), DEC + heptane, DEC + octane, and cyclohexane + DEC at 101.3 kPa. No VLE data have been previously published at this pressure. The experimental results have been compared with those correlated through the Wilson9 and UNIQUAC10 equations. The interaction parameters of the functional group OCOO- with CH3- and -CH2cy- in the ASOG11 model and of the group -OCOO- with CH3- in the UNIFAC12 model have been determined previously.13 ASOG and UNIFAC group contribution methods have been employed to predict the binary systems. 2. Experimental Section Chemicals. Except for diethyl carbonate, which was supplied by Fluka, the pure components were supplied by Merck. They were degassed by ultrasound and dried over molecular sieves Type 4 Å (supplied by Aldrich) and kept in an inert argon (with a maximum content of water of 2 × 10-6 by mass fraction) atmosphere. Their mass fraction purities were >99.5 mass % for diethyl carbonate, >99.5 mass % for hexane, >99.5 mass % for heptane, >99 mass % for octane, and >99.5 mass % for cyclohexane. Close agreement with recent published density and refractive index values, shown in Table 1, confirms their purity. Apparatus and Procedure. A glass Fischer LABODEST VLE 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. This pump ensures that both liquid and * To whom correspondence should be addressed. E-mail: jtojo@ uvigo.es.
Table 1. Comparison of Density G and Refractive Index nD with Literature Data for Pure Components at 298.15 K F/(g‚cm-3)
nD
component
expt
lit.
expt
lit.
diethyl carbonate
0.9691
1.382 40
hexane heptane octane cyclohexane
0.6548 0.6794 0.6985 0.7738
0.969 26a 0.969 24b 0.654 84a,d 0.679 46a,d 0.698 62a,d 0.773 89a
1.382 87a 1.382 84c 1.372 26a,d 1.385 11a,d 1.395 05a,d 1.423 54a
a Riddick et al.23 et al.25
b
Francesconi et al.24
1.372 26 1.385 12 1.395 05 1.423 63 c
Cocero et al.22
d
Das
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 Yokogawa model 7563 thermometer with an accuracy of (0.01 K. The apparatus is equipped with a glass temperature probe PT 100 with an accuracy of (0.01 K. For the pressure measurement, a digital pressure controller Ruska model 7218 with an accuracy of (0.001 kPa was used. Equilibrium conditions were assumed when constant temperature and pressure were obtained for 30 min or longer. Then, samples of liquid and condensate were taken for analysis. The composition analysis of both samples was determined using an Anton-Paar DSA-48 digital vibrating tube densimeter. Densimetry was used to establish standard curves for each binary system after the densitycomposition curves for the mixtures had been plotted. The root-mean-square deviation in the mole fraction was usually
