Scalable fabrication of poly(urea-thiourea) nanofiltration membrane elements for extreme pH conditions and efficient alkali recovery

Researchers have developed pH-stable nanofiltration membranes with polyamine or polyurea selective layers to meet the challenges posed by extreme pH conditions. However, their limited overall separation capacity constrains their effectiveness in alkali resource recovery. In the present study, we report the fabrication of an innovative pH stable nanofiltration membrane via interfacial polymerization between isocyanates and amines. The strategic modulation of isocyanates, varying in molecular structure and reactivity, enabled fine-tuning of the resultant poly(urea-thiourea) selective layer’s molecular architecture. 1.8″ × 12″ sized spiral wound membrane elements were fabricated and their potential for recovering alkali resources from mercerizing wastewater was evaluated. The membrane elements achieved a COD rejection of 80 %, an OH⁻ permeability of 92 %, with a water flux of 6.5 L/h under 1 MPa. The results underscore their superior comprehensive separation capabilities. These innovative membranes may facilitate impactful pollution mitigation and carbon footprint reduction in the textile industry, by promoting efficient resource recovery and reuse of treated water, thereby promising significant economic and environmental benefits.