ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Application of extended NRTL equation for ternary liquid-liquid and vapor-liquid-liquid equilibria description

Pavol Steltenpohl and Elena Graczová

Institute of Chemical and Environmental Engineering, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, 812 37 Bratislava, Slovak Republic

E-mail: pavol.steltenpohl@stuba.sk

Received: 1 October 2009  Revised: 25 November 2009  Accepted: 29 November 2009

Abstract: Simulation of a hydrocarbons mixture separation by extractive distillation was based on binary vapor-liquid as well as liquid-liquid equilibrium data. Sulfolane was considered as extractive solvent for the selective toluene separation from a model mixture with heptane. For simulation of the chosen hydrocarbons mixture separation in the presence of an extractive solvent, the NRTL model was considered. A set of temperature-dependent binary NRTL parameters was evaluated independently by fitting the experimental vapor-liquid and liquid-liquid equilibrium data of the respective binary subsystems. In order to improve the description of the ternary vapor-liquid equilibrium, original NRTL model extended by the ternary contribution term was used. Parameters of the ternary contribution were obtained by direct fitting of available ternary liquid-liquid equilibrium data while employing the original binary NRTL parameters. Quality of the ternary vapor-liquid-liquid equilibrium description using the original and the extended excess Gibbs energy models was assessed by comparing the calculated compositions of conjugate liquid phases with experimental data. Using the extended NRTL model, mean deviation of the computed mole fractions decreased by approximately four times (9.73 × 10⁻³) compared to the value obtained using the original NRTL model. Both original and extended NRTL models were employed for the simulation of a model mixture separation by extractive distillation. At chosen experimental conditions, high purity distillate (x ₁ > 0.999) was obtained. Results of the aromatics extractive distillation in the presence of sulfolane were compared to those obtained with N-methylpyrrolidone as the extractive solvent.

Keywords: vapor-liquid-liquid equilibrium - ternary contribution - extractive distillation - simulation - sulfolane -  N-methylpyrrolidone

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-010-0006-x

Chemical Papers 64 (3) 310–317 (2010)