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466265 Ionic Liquids As Entrainers for the Separation of Aliphatic/Aromatic Mixtures By Extractive Distillation Systems: Rigorous Model Based Process Optimization

In this work, we presented the study of how ionic liquids can increase the efficiency of n-heptane/toluene mixtures separation. We have made a screening of potential ionic liquids to be used with the COSMOTherm software and selected a small group of them. Then, following the previously described methodology we have implemented such components in the Aspen Properties databanks by specifying the required properties. Rigorous process simulations of the extractive distillation column can be then developed. IL Mixture design was carried out by defining an optimization problem in Matlab and solved using derivative-free optimization methods. A COM interface was needed in order to connect Matlab with the Aspen Plus software. The objective function implemented to design the entrainer mixture took into account both separation an economic criteria.

Besides, we have correlated the experimental liquid-liquid equilibrium [4] and vapor-liquid equilibrium [5] data of some ionic liquid – solvent systems to conventional activity coefficient thermodynamic models (NRTL) in order to evaluate COSMO predictions. Binary interaction parameters were then implemented in Aspen Plus and some process simulations were carried out in order to determine the deviation between the regressive thermodynamic model (NRTL) and the predictions of the COSMO based simulations.

Sothis work is structured as follows: First a short introduction to ionic liquids and to the COSMO based model is shown, then the methodology employed to couple quantum calculations with Aspen Plus and the optimization strategy is described. Third, a detailed comparison of COSMOSAC predictions against regressive thermodynamic models (NRTL) is shown in terms of process simulation results. The next section addresses the optimization problem of the extractive distillation process selecting the best ionic liquid or mixture for the separation proposed and finally the main conclusions of the work are inferred.[1] Navarro, P., Larriba, M., García, J., Rodríguez, F. Vapor-liquid equilibria for n-heptane + (benzene, toluene, p-xylene, or ethylbenzene) + [4empy][Tf2N] (0.3) + [emim][DCA] (0.7) binary ionic liquid mixture. Fluid 540 Phase Equilibria 2016;417:421

[2] Klamt, A. and F. Eckert, COSMO-RS: a novel and efficient method for the a priori prediction of thermophysical data of liquids. Fluid Phase Equilibria, 2000. 172(1): p. 43-72.

[3] Lin, S.-T. and S.I. Sandler, A Priori Phase Equilibrium Prediction from a Segment Contribution Solvation Model. Industrial & Engineering Chemistry Research, 2002. 41(5): p. 899-913.

[4] Larriba, M., Navarro, P., Garcia, J., Rodríguez, F.. Liquid-liquid extraction of btex from reformer gasoline using binary mixtures of [4empy][tf2n] and [emim][dca] ionic liquids. Energy and Fuels 2014;28(10):6666:6676

[5] Navarro, P., Larriba, M., García, J., González, E.J., Rodríguez, F. Vapor-liquid equilibria of n-heptane+ toluene+ [emim][DCA]g system by headspace gas chromatography. Fluid Phase Equilibria 2015;387:209:216.

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