Improved Recovery of Propylene Glycol Monomethyl Ether (PGME) and Propylene Glycol Monomethyl Ether Acetate (PGMEA) from an Aqueous Salt Solution with Molecular Interaction Analysis

Abstract

Propylene glycol monomethyl ether (PGME) and propylene glycol monomethyl ether acetate (PGMEA) are widely used photoresist thinners that generate wastewater during semiconductor production. However, the removal of these components from water is challenging. This study investigated the phase equilibria of the water + PGME + PGMEA system with NaCl, KCl, or LiCl to identify a suitable salt for improving separation. Liquid–liquid equilibrium (LLE) data for the quaternary systems were measured at 303.15 and 313.15 K under atmospheric pressure. At 5 wt % salt, the binodal region expanded, enhancing PGME and PGMEA separation. Salting-out effectiveness followed the order NaCl > KCl > LiCl. The eNRTL model accurately correlated the experimental LLE data and slightly outperformed the ion-specific ePC-SAFT model, although ePC-SAFT required fewer binary interaction parameters and successfully predicted electrolyte-induced phase splitting. Sigma-profile analysis further explained molecular interactions and effectively reproduced salting-out trends, demonstrating potential for predicting salt effects on LLE.