Thermo-responsive copolymers with ionic group as novel draw solutes for forward osmosis processes

Thermo-responsive copolymers containing ionic groups (P(MT_xEO_y), where x and y are the feed molar percent of [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MTAC) and 2-(2-methoxyethoxy)ethyl methacrylate (MEO), respectively) were synthesized via free radical polymerization using MTAC and MEO as monomers, in order to use the copolymers as a draw solute in a forward osmosis (FO) system. The osmotic pressure and lower critical solution temperature (LCST) could be controlled by changing the composition of the copolymers. For example, P(MT₂₅EO₇₅) shows a relatively high osmotic pressure of 0.909 Osmol/kg at 0.2 g/mL, and P(MT₅EO₉₅) shows a LCST close to room temperature at 32 °C. When P(MT₂₀EO₈₀) was used as a draw solute in the FO system, a reasonable water permeation flux value of 5.45 Lm⁻²h⁻¹ at 0.1 g/mL was observed and the draw solute (P(MT₂₀EO₈₀)) could be recovered with a very large draw solute recovery value of 99.80% from the draw solutions by heating to 70 °C, above the LCST, followed by a microfiltration process. Therefore, it is expected that such copolymer system could be a prospective candidate as a draw solute in the FO system.