Liquid-Liquid Equilibrium for the 1-Butanol-Water System

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Consider the partially miscible binary mixture composed of -butanol and water at 101.325 °C. The nonrandom two-liquid (NRTL) model developed by Renon and Prausnitz [1, 2] is adequate for determining liquid-liquid equilibrium (LLE) data. Since this mixture presents a heteroazeotrope with a boiling point of 93.49 °C, we consider only temperatures below this threshold value. The magenta-shaded region indicates where the validity of our simulation fails. Indeed, for °C we have, in addition to the two liquid phases, a third vapor phase.


This Demonstration calculates the LLE curve as well as tie lines. The arc-length continuation technique is used to generate all data in a single calculation. In addition, for a user-specified value of the temperature, the compositions of the 1-butanol-rich phase and the 1-butanol-lean phase are displayed.

Our results are validated by benchmarking them with their counterparts obtained from the Aspen-HYSYS process simulator [3] and shown in the diagram by the black triangles.


Contributed by: Housam Binous and Ahmed Bellagi (December 2016)
Open content licensed under CC BY-NC-SA




[1] J. M. Smith, H. C. Van Ness and M. M. Abbott, Introduction to Chemical Engineering Thermodynamics, 7th ed., Boston: McGraw-Hill, 2005.

[2] H. Renon and J. M. Prausnitz, "Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures," AIChE Journal, 14(1), 1968 pp. 135–144. doi:10.1002/aic.690140124.

[3] Aspentech. "Aspen-HYSYS." (Dec 15, 2016)

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