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Simulation of Toluene Extractive Distillation from a Mixture with Heptane

P. Steltenpohl, M. Chlebovec, and E. Graczová

Department of Chemical and Biochemical Engineering, Faculty of Chemical and Food Technology, Slovak University of Technology, SK-812 37 Bratislava

 

E-mail: steltenp@cvt.stuba.sk

Abstract: Comparison of simulated equilibrium data and extractive distillation simulations accomplished by the use of different model parameters sources is presented. Sets of experimental binary vapourliquid and liquid-liquid equilibrium data were used to estimate the binary parameters of the NRTL model equation. Furthermore, UNIFAC method predicted binary NRTL parameters were obtained from the HYSYS simulation environment.
Both sets of model parameters were used to model the vapour-liquid equilibrium of ternary mixture containing heptane, toluene, and N-methylpyrrolidone (NMP). The influence of the NRTL model parameters on the efficiency of extractive distillation unit used for toluene separation from a mixture with heptane in the presence of NMP was further investigated.
Simulation of extractive distillation column gave similar results for both sets of NRTL model parameters when the use of a large quantity of extractive solvent was assumed. However, for solvent to feed ratio lower than 3, higher separation efficiency of the column was observed for original model parameters compared to HYSYS supplied ones. This fact seems to correlate with the feed component’s relative volatility variation with the amount of extractive solvent present in the mixture.
It was found that the source of model parameters influences essentially the quality of binary and ternary equilibria prediction. Important differences between experimental and modelled equilibrium data could be expected when unreliable model parameters are used. Especially, model parameters predicted by the UNIFAC LLE method gave mistaken liquid-liquid and vapour-liquid equilibrium data fit. As a consequence, at certain simulation conditions the choice of improper phase-equilibrium model parameters led to wrong separation unit design.

Full paper in Portable Document Format: 596aa421.pdf

 

Chemical Papers 59 (6a) 421–427 (2005)

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