VAPOR-LIQUID-EQUILIBRIA FOR THE BINARY
SYSTEMS CYCLOHEXANE + DIETHYL CARBONATE AND
CYCLOHEXENE + DIETHYL CARBONATE
Beatriz Marrufoa, Sonia Lorasb and Margarita Sanchotellob
aDepartamento
bDepartamento
Introduction
Experimental
Section
Experimental
Results
de Ingeniería Química Básica, Universidad del Zulia, 4001, Maracaibo, Venezuela
de Ingeniería Química, ETSE, Universitat de València, 46100 Burjassot, Valencia, España
 The separation of paraffins and olefins is a specific problem in the area of hydrocarbon processing due to the close proximity of
their boiling points. Extractive distillation is a process potentially suitable for this kind of separation since the addition of a
solvent, known as entrainer, modifies the relative volatility of the mixture to be separated. A good solvent selection for
extractive distillations must be made from accurate vapor-liquid equilibrium (VLE) data.
 The present work was undertaken as a part of thermodynamic research on the separation of cyclohexane and cyclohexene using
different solvents. In this work, the behaviour of diethyl carbonate (DEC) as a possible entrainer is investigated. Isobaric VLE
data for the binary systems cyclohexane (1) + DEC (3) and cyclohexene (2) + DEC (3) have been measured at 100 kPa. In a previous
work [1], we reported VLE data for the binary system cyclohexane (1) + cyclohexene (2) at (30, 60 and 101.3) kPa. For the system
cyclohexane + DEC, isobaric and isothermal VLE data have been reported in the literature [2-3]. No VLE data are published
previously for the binary system cyclohexene + DEC.
Figure 1
 A dynamic-recirculating still equipped with a Cottrell
circulation pump was used in the equilibrium determinations
(Figure 1). The system was kept at the boiling point for at
least 30 min to ensure that the steady state was reached.
Then, samples of liquid and condensate were taken for
analysis.
 Compositions of the liquid and condensed vapor phase samples
were determined by gas chromatography.
 The accuracy of experimental measurements was 0.02 K in
temperature, 0.1 kPa in pressure, and 0.001 in mole
fraction.
1.
2.
3.
4.
5.
6.
7.
Immersion heater
Cottrell pump
Column
Mixing chamber
Magnetic stirrer
Solenoid coil and valve hood
Pt-100 sensor
 According to the results (Figures 2 and 3), both binary systems shown moderate positive deviations from ideal behaviour and do
not present any azeotrope.
 The VLE data for the binary systems were found to be thermodynamically consistent using the Fredenslund test.
400
400
390
390
T/K
T/K
380
380
370
370
360
360
350
0,0
0,2
0,4
0,6
0,8
350
1,0
0,0
x1 , y1
0,4
0,6
1,0
Figure 3. T-x-y diagram at 100 kPa:
cyclohexene (1) + DEC (2)
 The activity coefficients of the solutions were well correlated by Wilson, NRTL and UNIQUAC models. The results of this
correlation are shown in Table 1, where: cyclohexane (1), cyclohexene (2) and diethyl carbaonate (3).
 In order to investigate the behavior of diethyl carbonate as an entrainer in the separation of the mixture
cyclohexane/cyclohexene, the residual curve map for the ternary system has been simutaled by Aspen split v2006 using the NRTL
model. The residual curve map is shown in Figure 4.
cyclohexene
Table 1. Correlation of Binary Systems for Different GE Models
UNIQUAC
a
0.036
0.075
1+3
625.49
2323.56
0.121
0.274
2+3
310.35
1839.14
0.117
0.595
1+2c
-1195.08
1403.45
0.2
0.038
0.847
1+3
2937.34
-74.83
0.3
0.139
0.539
2+3
2846.94
-682.42
0.3
0.119
c
-365.51
422.30
0.038
0.777
1+3
1424.53
-589.94
0.127
0.638
2+3
1442.37
-791.98
0.114
>
>
0.2
0.8
0.4
0.6
0.6
>
>
-598.78
0.4
<
0.8
<
0.2
0.4
0.2
>
<
1.0
0.0
>
>
100·y1b
831.37
1.0
>
ARDT a(%)
1+2c
1+2
0.0
Bubble point
>
ij
>
Aji
(J.mol-1)
<
Aij
(J.mol-1)
>
>
Wilson
System
i+j
< <
Model
Conclusion
0,8
x1 , y1
Figure 2. T-x-y diagram at 100 kPa:
cyclohexane (1) + DEC (2)
Thermodynamic
Modeling
0,2
0.6
0.8
1.0
0.0
Figure 4. Residual
curve map with NRTLmodel
at 100 kPa
cyclohexane
2-methoxyethanol
b
Average absolute deviation in temperature. Average absolute deviation in vapor phase composition.
Residual curve map shows two distillation zones delimited by a separatrice which links both binary azeotropes. For the separation of
homogeneous mixtures by simple distillation, this separatrice cannot be crossed. So, it can be concluded that 2-methoxyethanol is
not a good entrainer for the separation cyclohexane/cyclohexene, since neither pure cyclohexane nor pure cyclohexene can be
obtained easily due to the presence of the two found binary azeotropes.
[1] www.brix-berg.com
Acknowledgements. Financial support from the Ministerio de Ciencia y Tecnología of Spain, through project CTQ2007-61400/PPQ, FEDER European Program and the Conselleria de Cultura,
Educació i Esport (Generalitat Valenciana) of Valencia (Spain). Beatriz Marrufo has a grant from La Universidad del Zulia, Venezuela.