Polyquaternium-7 Enhances Monovalent Selectivity in Electrodialysis Membranes
Li, Jian, et al. Journal of Membrane Science 486 (2015): 89-96.
Challenge: Multivalent ions such as Ca2+ and Mg2+ can deposit on cation exchange membranes (CEMs) in electrodialysis, reducing the effectiveness and service life.
Solution: Modified commercial CEMs using degraded polyquaternium-7 (PQ7), a cationic polymer surfactant, to create a highly selective surface layer. A key innovation was forming covalent sulfonamide bonds between PQ7's amine groups and the membrane surface via chlorosulfonation/amination chemistry, ensuring long-term stability.
Key Results:
· Monovalent Selectivity: PQ7's cationic nature creates a surface charge barrier preferentially rejecting multivalent cations.
· Durable Bonding: The sulfonamide linkage formed via PQ7's amine groups prevents layer detachment, ensuring sustained performance.
· Superior Ion Selectivity: Modified membranes showed drastically reduced leakage of multivalent ions, including Zn2+ leakage decreased from 22.0% to 14.2%, and significant reduction in Ca2+ and Mg2+ leakage (seawater application). Diffusion dialysis confirmed reduced electrolyte leakage.
· Improved Transport Properties: Modified membranes exhibited reduced limiting current and increased Ohmic/electro-convection resistance.
Polyquaternium-7 Increases Water Permeability and Fouling Resistance in Polyamide Nanofiltration Membranes
Zhan, Zi-Ming, et al. Industrial & Engineering Chemistry Research 60.39 (2021): 14297-14306.
Challenge: Conventional polyamide nanofiltration (NF) membranes exhibit a trade-off among their water permeability, divalent ion rejection (softening), and antifouling properties, which significantly restricts their applications in water desalination.
Solution: A solution is to surface-graft polyquaternium-7 (PQ7), a cationic copolymer of dimethyl diallyl ammonium chloride and acrylamide, onto polyamide NF membranes. Simply grafting PQ7 onto polyamide NF membranes took advantage of its unique chemical structure and improved multiple performance.
Key Results:
· Electrostatic Repulsion: Positive charges of quaternary ammonium groups on PQ7 improved the electrostatic repulsion of divalent cations (Ca2+, Mg2+).
· Surface Modification: The surface hydrophilicity and roughness were enhanced by grafting of PQ7, while the membrane thickness was not changed.
· Economical Process: Simple grafting process using a cheap modifier (PQ7).
· Substantial Increase in Permeability: Water flux increased 66% (from 47.8 to 79.6 L m-2 h-1 at 5 bar).
· Superior Ion Rejection: Rejection of divalent ions reached exceptionally high levels due to enhanced positive surface charge.
· Excellent Antifouling Performance: PQ7-grafted membranes demonstrated superior flux recovery after fouling, and strong resistance to both organic foulants (sodium alginate) and protein foulants (bovine serum albumin).