Study on PPTA/PEMs/PA composite NF membranes for highly efficient desalination of high-saline Kevlar® brine and long-term anti-scaling performance

It produces a large number of organic brine during the polymerization process of Kevlar®, which contains N-(1-Methyl-2-pyrrolidinone) (NMP) and high concentrations of CaCl₂ and NaCl. The wastewater will cause serious pollution of water and soil resources if discharged directly. The separation and recycling of inorganic salts have been an industrial difficulty. In this paper, based on the novel concept of green self-recycling, we used Poly (p-phenylene terephthamide) (PPTA, resin of Kevlar®) ultrafiltration membrane as the substrate, composited the loose and curled polyelectrolyte multilayers (PEMs) as interlayers and formed a homogeneous polyamide separation layer through interfacial polymerization, from which we obtained the homogeneous reinforcement aramid composite nanofiltration (NF) membrane. The composite NF membranes with different interlayer numbers showed different advantages. For single-component brine, the retentions of PEMs-1/PA membrane were 93 % and 98.4 % for 10 g/L CaCl₂ and MgSO₄ respectively. For mixed brine of 20 g/L CaCl₂ and NaCl, the retentions of PEMs-3/PA membrane were 87.13 % and 1.05 % for CaCl₂ and NaCl respectively with the separation factor as high as 82.95. In the test of long-term service stability, PEMs-3/PA maintained stable performance in 4 cycles total of 160 h. And the permeance could almost fully recover after pure water backwash of only 0.5 h. In addition, the structural stability and anti-scaling performance of the PEMs-3/PA membrane were further verified in high-temperature brine. Surprisingly, the obtained PPTA NF membrane in this work could effectively treat the high-saline brine in the Kevlar® polymerization process and would have more promising prospects in the treatment of industrial wastewater of brine.