Development of a highly hydrophilic nanofiltration membrane for desalination and water treatment

Thin film composite (TFC) co-polyamide membranes were modified by adding carboxyl group to the polypiperazinamide backbone. The sodium chloride, sodium sulphate, magnesium chloride and magnesium sulphate rejections were measured at various feed pressures for the modified and unmodified membranes. The pure water permeability was improved as much as 20% for the modified membrane. Besides, the membrane rejection ability towards divalent ions was excellent compared to the monovalent ions. The rejection of multivalent ions was more than 96% at the operating pressure as low as 450 kPa. The modified membrane was more negatively charged compared to the unmodified membrane. The membranes developed can be used for pre-treatment in a desalination plant as well as for hardness removal in water treatment process at a higher production rate.

By incorporating 3,5-diaminobenzoic acid, the hydrophilicity of the membrane was increased. The highly hydrophilic membrane could improve the water permeability as much as 23% which indicates that the product rate could be increased. Besides, the membrane rejection ability towards divalent ions was excellent compared to the monovalent ions. The rejection of multivalent ions especially sulphate-containing salt was more than 95% at the operating pressure as low as 450 kPa. The modified membrane was more negatively charged compared to the unmodified membrane. However, the rejection ability of divalent counterions was not reduced. The membranes developed could open up the avenue for pre-treatment in a desalination plant. It can also be applied to reduce k k’ r Robs Rreal ω — Concentration in permeate, mol m–3 — Bulk diffusivity, m2s–1 — Volume flux (based on membrane area), m3m–2s–1 — Mass transfer constant, ms–1 — Mass transfer constant defined by Eq. (4) — Radius of stirrer, m — Observed rejection — Real rejection — Stirring speed, rad.s–1