Laboratory study demonstrates temperature-dependent osmotic pressure shifts in LCST polyether solutions, indicating efficient low-pressure reverse osmosis reconcentration without precipitation.
Aqueous solutions of thermoresponsive polymers can exhibit reversible changes in osmotic pressure (π), making them attractive draw solutes for forward osmosis followed by reverse osmosis (FO-RO) water purification processes─FO followed by RO reconcentration of the draw solution. This study evaluated the temperature dependence of π for aqueous solutions of lower critical solution temperature (LCST) thermoresponsive polyethers. These solutions exhibit higher π at ambient temperature, which promotes effective filtration during FO, and lower π upon heating, which aids the RO step [e.g., PPG–PEG-3900:44.6 bar (16 °C) and 5.1 bar (50 °C)]. The π of these solutions decreased significantly before reaching their respective cloud points, indicating that precipitation is not required to obtain a low π. It is possible to use RO with a low applied pressure at a temperature below the cloud point to reconcentrate the draw solution, making it possible to use thermoresponsive materials with relatively high cloud points for FO.
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Korchinsky et al. (2026) studied this question.
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