Lower critical solution temperature (LCST) phase separation of glycol ethers for forward osmotic control

Abstract

Lower critical solution temperature (LCST) phase transition of glycol ether (GE)-water mixtures induces an abrupt change in osmotic pressure driven by a mild temperature change. The temperature-controlled osmotic change was applied for the forward osmosis (FO) desalination. Among three GEs evaluated, di(ethylene glycol) n-hexyl ether (DEH) was selected as a potential FO draw solute. A DEH-water mixture with a high osmotic pressure could draw fresh water from a high-salt feed solution such as seawater through a semipermeable membrane at around 10 °C. The water-drawn DEH-water mixture was phase-separated into a water-rich phase and a DEH-rich phase at around 30 °C. The water-rich phase with a much reduced osmotic pressure released water into a low-salt solution, and the DEH-rich phase was recovered into the initial DEH-water mixture. The phase separation behaviour, the residual GE concentration in the water-rich phase, the osmotic pressure of the DEH-water mixture, and the osmotic flux between the DEH-water mixture and salt solutions were carefully analysed for FO desalination. The liquid-liquid phase separation of the GE-water mixture driven by the mild temperature change between 10 °C and 30 °C is very attractive for the development of an ideal draw solute for future practical FO desalination.

Energy-efficient desalination by forward osmosis using responsive ionic liquid draw solutes

“…The water flux study corroborates well with the trend predicted using osmolality values. It is worth mentioning that the osmolality was measured by a cryoscopic method at subzero degree Celsius, thus the actual osmolality values of such LCST-type draw solutions at room temperature might be lower 27 due to stronger molecular interactions at higher temperatures. It can be observed in Fig.…”

Concentration dependent speciation and mass transport properties of switchable polarity solvents

“…68 Density and apparent molar properties Solutions at greater concentration than 3.68 mol kg À1 visually foamed when agitated by the osmometer and thus did not freeze properly for a measurement, limiting the scope of the freezing point study.…”

A Thermodynamical Approach for Evaluating Energy Consumption of the Forward Osmosis Process Using Various Draw Solutes

“…PB was once evaluated by Nakayama et al [17] and the advantages of using glycol ethers as draw solutes include low viscosities, low pH values, low volatilities, etc. On the contrary, the high pH value of the aqueous DP solution might cause potential damage to the membrane, and more caution needs to be taken during the operation because of the volatility and toxicity of DP.…”

“…Other examples of utilizing low-grade heat in draw solute recovery are the solutes with a lower critical solution temperature (LCST) point that exhibit liquid-liquid phase separation with water at high temperature. For example, Nakayama et al demonstrated that some types of glycol ethers including di(ethylene glycol) n-hexyl ether (DEH), propylene glycol n-butyl ether (PB) and di(propylene glycol) n-propyl ether (DPP) can be used as draw solutes [17]. LCST ionic liquids as draw solutes were reported to be able to treat feed solutions with NaCl concentrations of up to 1.6 mol·L −1 by Cai et al [18].…”