Binodal and spinodal curves of ternary systems containing lignin using the NRTL and UNIQUAC models

Abstract

This communication outlines a modelling study conducted on the liquid-liquid equilibrium (LLE) data for three ternary systems comprising lignin, water, and a solvent, utilizing the NRTL and UNIQUAC models. The approach involved estimating binary interaction parameters through regression analysis on the LLE data, followed by the drawing of binodal curves. The obtained interaction parameters were used to calculate the spinodal curves and plait points. The NRTL model results indicate percent deviations in lignin composition (mass fraction) at the lignin-rich phase ranging from 11.8 to 46.3, in solvent composition at the lignin-rich phase ranging from 6.9 to 10.2, in lignin composition at the lignin-lean phase ranging from 18.1 to 86.7, and in solvent composition at the lignin-lean phase ranging from 0.6 to 7.5. Similarly, for the UNIQUAC model, the percent deviations in lignin composition at the lignin-rich phase were found to range from 10.3 to 60.2, in solvent composition at the lignin-rich phase from 10.0 to 15.4, in lignin composition at the lignin-lean phase from 18.4 to 88.5, and in solvent composition at the lignin-lean phase from 0.8 to 7.9. Moreover, the UNIQUAC model calculated plait point for the lignin-ethanol-water system at 45°C exhibits serious disagreement with experimental data. In contrast, for systems containing acetic acid and acetone, the NRTL model partially demonstrates superior performance, and there is good agreement between the experimental and calculated values by both models. Additionally, in the lignin-ethanol-water system, the UNIQUAC model provides better coverage of experimental data in the vicinity of the mixture's plait point.