Diapositiva 1

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VAPOR-LIQUID-EQUILIBRIA FOR THE BINARY SYSTEMS
CYCLOHEXANE DIETHYL CARBONATE AND CYCLOHEXENE
DIETHYL CARBONATE Beatriz Marrufoa, Sonia
Lorasb and Margarita Sanchotellob aDepartamento
de Ingeniería Química Básica, Universidad del
Zulia, 4001, Maracaibo, Venezuela bDepartamento
de Ingeniería Química, ETSE, Universitat de
València, 46100 Burjassot, Valencia, España
Introduction 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.
Experimental Section 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.
Experimental Results 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.
Thermodynamic Modeling 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.
Conclusion 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. Contact e-mail sonia.loras_at_uv.es 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. Contact e-mail sonia.loras_at_uv.es

• Figure 1
• Immersion heater
• Cottrell pump
• Column
• Mixing chamber
• Magnetic stirrer
• Solenoid coil and valve hood
• Pt-100 sensor

Figure 2. T-x-y diagram at 100 kPa cyclohexane
(1) DEC (2)
Figure 3. T-x-y diagram at 100 kPa cyclohexene
(1) DEC (2)
Table 1. Correlation of Binary Systems for
Different GE Models
Figure 4. Residual curve map with NRTLmodel at
100 kPa