Unveiling the Constraints of COSMO-SAC for PEG-Water Liquid-Liquid Equilibrium Prediction

Area of Science:

• Physical Chemistry
• Polymer Science
• Thermodynamics

Background:

• Liquid-liquid equilibrium (LLE) is crucial for understanding polymer-solvent phase behavior.
• Polyethylene glycol (PEG) and water mixtures exhibit complex phase diagrams, including closed-loop behavior.
• Accurate predictive models are needed for designing separation processes involving these systems.

Purpose of the Study:

• To evaluate the predictive capabilities of the COSMO-SAC model for PEG-water LLE.
• To investigate the impact of polymer end groups and model parameters on LLE predictions.
• To assess the model's performance in predicting closed-loop diagrams and lower critical solution temperature (LCST).

Main Methods:

• Extended COSMO-SAC methodology to incorporate polymer end groups in σ-profile construction.
• Employed a global optimization approach for LLE prediction across the entire composition range.
• Analyzed the influence of end groups, hydrogen bond energies, and volume effects on LLE.

Main Results:

• COSMO-SAC qualitatively predicted the phase behavior of PEG-water systems, including the closed-loop diagram.
• The model achieved a first-time prediction of the closed-loop diagram for PEG-water systems.
• Significant deviations from experimental data were observed for the lower critical solution temperature (LCST).

Conclusions:

• The COSMO-SAC model shows promise for qualitatively predicting PEG-water LLE but requires refinement.
• Improvements in both combinatorial and residual terms are necessary for enhanced predictive accuracy.
• Further model development is essential for complex polymer-solvent systems.