Separation of Glycol Ethers and Similar LCST-Type Hydrogen-Bonding Organics from Aqueous Solution Using Distillation or Liquid−Liquid Extraction

Abstract

Infinite-dilution relative volatilities ( ) were measured at 50 °C and 80 °C using a Rayleigh distillation apparatus for dilute solutions of propylene glycol n-butyl ether (PnB), propylene glycol n-propyl ether (PnP), and dipropylene glycol n-butyl ether (DPnB) dissolved in water and brine (3 wt % NaCl). The data were analyzed to determine infinite-dilution activity coefficients ( ), Henry's Law constants, partial molar enthalpies of mixing, and Setschenow constants. Partition ratios (K values) for extraction of PnP also were measured using 14 hydrophobic organic extraction solvents, including alcohols, ketones, ethers, chlorinated hydrocarbons, aromatics, and aliphatics. An interpretation of molecular interactions in solution is given based on the analysis of activity coefficients, as a function of temperature and salt concentration. General rules are proposed for the class of hydrogen-bonding organic compounds characterized by the presence of a lower critical solution temperature (LCST) in the organic + water phase diagram. The value of αi,water is likely to increase as the temperature increases for stripping volatile LCST-type hydrogen-bonding organics from dilute aqueous solution, provided the pure-component vapor pressure relative to water ( / ) also increases or stays approximately the same. For extraction of LCST-type compounds from aqueous solution, K is likely to increase as the temperature increases, provided that the mutual solubility between phases is low.