CO2-Responsive Low Molecular Weight Polymer with High Osmotic Pressure as a Draw Solute for Forward Osmosis

Maedeh Ramezani; Sarah N Ellis; Anna Riabtseva; Michael F Cunningham; Philip G Jessop

doi:10.1021/acsomega.3c07644

CO₂-Responsive Low Molecular Weight Polymer with High Osmotic Pressure as a Draw Solute for Forward Osmosis

ACS Omega. 2023 Dec 13;8(51):49259-49269. doi: 10.1021/acsomega.3c07644. eCollection 2023 Dec 26.

Authors

Maedeh Ramezani^{1

2}, Sarah N Ellis¹, Anna Riabtseva^{1

2}, Michael F Cunningham², Philip G Jessop¹

Affiliations

¹ Department of Chemistry, Queen's University, Kingston, ON K7L 3N6,Canada.
² Department of Chemical Engineering, Queen's University, Kingston, ON K7L 3N6,Canada.

Abstract

A key challenge in the development of forward osmosis (FO) technology is to identify a suitable draw solute that can generate a large osmotic pressure with favorable water flux while being easy to recover after the FO process with a minimum of energy expenditure. While the CO₂- and thermo-responsive linear poly(N,N-dimethylallylamine) polymer (l-PDMAAm) has been reported as a promising draw agent for forward osmosis desalination, the draw solutions sufficiently concentrated to have high osmotic pressure were too viscous to be usable in industrial operations. We now compare the viscosities and osmotic pressures of solutions of these polymers at low and high molecular weights and with/without branching. The best combination of high osmotic pressures with low viscosity can be obtained by using low molecular weights rather than branching. Aqueous solutions of the synthesized polymer showed a high osmotic pressure of 170 bar under CO₂ (π_CO2) at 50 wt% loading, generating a high water flux against NaCl feed solutions in the FO process. Under air, however, the same polymer showed a low osmotic pressure and a cloud point between 26 and 33 °C (depending on concentration), which facilitates the recovery of the polymer after it has been used as a draw agent in the FO process upon removal of CO₂ from the system.