Alkaline Stable N-Spirocyclic Positively Charged Membranes for Food and Bioprocessing

Positively charged membranes, with high selectivity by allowing anions to transport through and excellent anti-fouling ability by repelling cations, have potential applications as separation membrane for food and bioprocessing. N-spirocyclic quaternary ammonium is a highly stable cation category even in concentrated alkaline. To overcome the poor membrane-forming ability as the reported N-spirocyclic functionalized membranes caused by rigid N-spiro, two strategies are proposed. One is in-situ thermal cross-linking of the chloromethylated polysulfone backbone (CrASU-PSF), and another is to graft amine containing N-spirocyclic side chain with different spacer length (GrASU-PSF). Both strategies obtain excellent membrane strength and alkaline stability (hydroxide conductivity retains over 95% after immersing in 1 M KOH at 80 ^oC for 720 h). The Cr-ASU-PSF1.92 membrane exhibits conductivity of about 78.8 mS cm^-1 at 80 ^oC, while the conductivity of the Gr6-ASU-PSF1.59 membrane with 6 alkyl spacer increase to about 108.0 mS cm^-1 at 80 ^oC with a relatively low swelling ratio of less than 30%.

Key words:

Charged membrane; N-spirocyclic quaternary ammonium cation; Cross-linking; Alkaline stability; Conductivity