Liquid-liquid equilibrium of 2-methyltetrahydrofuran/water over wide temperature range: Measurements and rigorous regression

• LLE data for water-2MTHF from 293 to 423 K are reported.
• NRTL parameter values for water-2MTHF are obtained.
• Data regression with conventional tools may violate stability.
• Aspen reports saddle point of Gibbs free energy as phase split.
• BOARPET guarantees thermodynamic stability in regression.

The liquid-liquid equilibrium (LLE) of the binary system 2-methyltetrahydrofuran (2MTHF)-water was determined experimentally and the Non-Random-Two-Liquid (NRTL) model was fitted to the experiments. To our knowledge, this work is the first i) to report measurement data in the temperature range from 293 K to 423 K, and ii) to present a thermodynamic model including parameter values, capturing the LLE of this fluid system. The model fitting was conducted with both Aspen Properties and our in-house tool BOARPET that is based on the work of Mitsos et al. (A. Mitsos, G. M. Bollas, and P. I. Barton. Chem. Eng. Sci., 2009). From the regressed parameter values the Gibbs free energy was calculated in order to check thermodynamic stability. It was found that the results of Aspen violate thermodynamic stability even locally and thus, are not utilizable. In particular, Aspen determines phase compositions for which the Gibbs free energy is locally concave. This gives a hitherto unknown motivation to use rigorous problem formulation in parameter estimation. From experimental results it is evident that 2MTHF-water exhibits a stable biphasic system over a wide temperature range which makes it a promising solvent system candidate for reacting systems.

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