Thermoresponsive cationic copolymer microgels as high performance draw agents in forward osmosis desalination

• Novel applications of thermo-responsive cationic microgels for forward osmosis desalination.
• The chemical structure of cationic comonomers affects the water flux and recovery performance.
• Improved overall performance of microgel-based forward osmosis desalination.
• Hansen solubility parameters are used to estimate the performance of microgel-driven forward osmosis desalination.

Thermoresponsive cationic copolymer microgels with aliphatic and aromatic cationic comonomers are synthesized and applied as the draw agents in forward osmosis (FO) desalination for the first time. The results show the FO desalination performance depends on the chemical structures and the dissociation constants (pKa) of the cationic comonomers. Cationic copolymer microgel containing 2-(diethylamino) ethyl methacrylate has the best overall performance with an initial water flux of 45.6 LMH and water recovery of 44.8%. This microgel also shows the shortest equilibrium swelling time which in turn reveals significant improvement in apparent flux of 5.5 LMH compared to other cationic and anionic copolymer microgels. Furthermore, Hansen solubility parameters are used to correlate the solvation behavior of these cationic microgels and their performance in forward osmosis desalination. Our results show Hansen solubility parameters and the dissociation constants of cationic comonomers can be used to estimate the performance of microgels in microgel-driven FO desalination systems.

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