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 (R i,water ∞ ) 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 (γ i,aqueous ∞ ), 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 R i,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 (p i SAT /p water SAT ) 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.

Framework for correlating the effect of temperature on nonelectrolyte and ionic liquid activity coefficients

“…In the case of glycol ethers, the molecule has a hydrophilic hydroxyl end group that can form hydrogen bonds with water and a hydrophobic alkyl ether end group with an entropic repulsion to water. For example, the propylene glycol n ‐butyl ether (PnB) + water binary is characterized by = 81 at 50°C and = 130 at 80°C . Both and increase in magnitude with increasing temperature, assuming θ ij is constant (Table ).…”

Isobaric vapour–liquid equilibria of binary 1-propoxy-2-propanol mixtures with water and alcohols at reduced pressure

“…(12) to be 7.3 compared to ∞ PnP in the other binary systems with values lower than 1.3. Whether hydrophobic or hydrophilic interactions dominate in water + glycol ether liquid mixtures depends strongly upon temperature and structure of the ether [15]. A higher LCST value indicates a glycol ether with greater hydrophilic character.…”

“…Studies of the solubility behaviour of several C i EO j and PGAE in water exhibit that these mixtures have lower critical solution temperatures (LCST) [13,15]. The appearance of a LCST is characteristic for systems, in which hydrogen bonds are the dominating interactions.…”

Use of Glycol Ethers for Selective Release of Periplasmic Proteins from Gram-Negative Bacteria

“…The value of the LCST typically will change somewhat as other components such as dissolved organic solutes or salts are added to the solution. The LCST value is a measure of the hydrophilic and hydrophobic nature of the organic compound in aqueous solution; a higher LCST value indicates a more hydrophilic compound (22,33). Table 2 lists LCST values for selected glycol ethers.…”

“…Well-known methods that may be used to remove the remaining glycol ether from the aqueous product include the use of buffer exchange by diafiltration, the use of chromatography to retain the product and allow solvent residues to flow through without being retained, and the use of adsorbents to preferentially adsorb solvent residues. Options for recovering glycol ether residues from the wash water or other aqueous effluent steams produced by these processes are described elsewhere (22).…”