Liquid-Liquid Equilibrium Data Correlation Using NRTL Model for Different Types of Binary Systems: Upper Critical Solution Temperature, Lower Critical Solution Temperature, and Closed Miscibility Loops

In this work, liquid-liquid equilibrium (LLE) data at different temperatures have been correlated for 30 binary systems that presented different miscibility behaviors: 15 upper critical solution temperature (UCST), 5 lower critical solution temperature (LCST), and 10 closed loop LLE region systems. The NRTL model along with an expression frequently used in the literature for the temperature dependence in the binary interaction has allowed an acceptable fitting of all the systems. The parameters obtained have been validated by the inspection of the Gibbs energy of mixing function regarding the fulfillment of the Gibbs common tangent equilibrium condition, and also by the stability of the solution to avoid possible metastable equilibrium solutions. The critical solution temperatures have been calculated by extrapolation using the NRTL parameters obtained for all selected binary systems. Moreover, the NRTL parameter values have been analyzed using some proposed representations that also include the boundary curve between miscible (L) and partially miscible (LLE) regions. These graphical representations are useful because they show the parameter value requirements to reproduce UCST, LCST, or closed loop behaviors.