VAPOR-LIQUID-EQUILIBRIA FOR THE BINARY SYSTEMS CYCLOHEXANE + MORPHOLINE AND CYCLOHEXENE + MORPHOLINE Beatriz Marrufo a, Sonia Loras b and Margarita Sanchotello b a Departamento de Ingeniería Química Básica, Universidad del Zulia, 4001, Maracaibo, Venezuela b Departamento de Ingeniería Química, ETSE, Universitat de València, Burjassot, Valencia, España Introduction  Distillation processes are by nature expensive to construct and operate. These costs are elevated when the systems being separated form azeotropes or they have close 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 [1]; in this work, the behaviour of morpholine as a possible entrainer is investigated at 100 kPa since it is recommended as a good entrainer for separating this kind of mixtures [2]. For the system cyclohexane + morpholine, isobaric VLE data have been reported in the literature at kPa [3, 4].  No VLE data are published previously for the binary system cyclohexene + morpholine. 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  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. In order to investigate the behavior of morpholine 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. Cyclohexane is an unstable node (where residue curves begin), morpholine is a stable node (where residue curves terminate), and cyclohexene is a saddle (where residue curves are deflected). So, cyclohexane would be obtained as overhead product (unstable node), and as bottom product (stable nodes) it could be obtained morpholine, as it was to be expected according to the boiling points of the three pure components. The actual compositions of the final products obviously will depend on the number of plates, feed, reflux and reboil ratios, etc.  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 morpholine (3). Conclusion In this case the residue curve map gives a little valuable information. On the other hand, it can be concluded the extractive distillation of cyclohexane/cyclohexene using morpholine as entrainer could be a process with good economic viability because it enhances the relative volatility of the binary mixture (  12 ) from to as it is shown in Figure 5. [1] B. Marrufo, S. Loras, M. Sanchotello, J. Chem. Eng. Data, (2009) in press, DOI: /je900259b. [2] G. Preusser, K. Ritchter, M. Schulze. Ger. Offen. 2,013,298, [3] T.E. Vittal Prasad, S. Suchil Kumar, M. Bhanu Pratap Goud, P. Anil Kumar, A. Srinivas, P. Subrahmaneswara Reddy, D.H.L. Prassad. J. Chem. Eng. Data 48, (2003), [4] T.E. Vittal Prasad, S. Suchil Kumar, M. Bhanu Pratap Goud, P. Anil Kumar, A. Srinivas, P. Subrahmaneswara Reddy, D.H.L. Prassad. J. Chem. Eng. Data 49, (2004), 740. [5] B. Marrufo, S. Loras, M. Sanchotello, Fluid Phase Equilibria 279, (2009), Acknowledgements. Financial support from the Ministerio de Ciencia y Tecnología of Spain, through project CTQ /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 Table 1. Correlation of Binary Systems for Different G E Models Figure 1 1. Immersion heater 2. Cottrell pump 3. Column 4. Mixing chamber 5. Magnetic stirrer 6. Solenoid coil and valve hood 7. Pt-100 sensor Figure 2. T-x-y diagram at 100 kPa: cyclohexane (1) + morpholine (2) Figure 3. T-x-y diagram at 100 kPa: cyclohexene (1) + morpholine (2) Figure 4. Residual curve map with NRTL model at 100 kPa Figure 5. VLE data plotted on a solvent-free basis for the system cyclohexane (1) + cyclohexene (2) + morpholine (3) at kPa. (  ) for x 3 = 0.0 [5] ; (  ) for x 3 = 0.4 and (  ) for x 3 = 0.7, calculated using NRTL model.