Static and dynamic assessments of polysulfonamide and poly(amide-sulfonamide) acid-stable membranes

Polysulfonamide (PSA) and poly(amide-sulfonamide) (PASA) thin film composite (TFC) membranes as the novel acid-stable membranes have been prepared by two aromatic and cycloaliphatic diamines. The acid-stable membranes were synthesized by interfacial polymerization of the diamines with benzene-1,3-disulfonyl chloride (BDSC) and/or trimesoyl chloride (TMC) on PES support membrane and their structures and performance were compared with polyamide (PA) TFC membranes. The stability of the TFC membranes in acids were studied by static acid soaking tests in two strong acids of 2.5% (w/w) HNO3 and 10% (w/w) H2SO4 at high temperature of 55 °C for 24 h. The dynamic permeation experiments were also done by 500 ppm MgSO4 at 0.5 MPa in deionized water and in 5% (w/w) H2SO4 solution. The acid retention in all of the membranes was very low. In contrast, the salt rejection was high in both water and acid solutions. The salt rejection was enhanced in acid solution filtration test because of the positive surface charge of the membranes in very low acidic pHs. The PSA membranes showed very good stability in high temperature acids while the PA membranes were completely degraded after acid soaking tests. Despite of the MPD-PA membranes which showed higher salt rejections than PIP-PA, the MPD-PSA membranes had lower rejections of 32% compared to PIP-PSA one (46%). The percent changes of salt rejection in water were −54%, −71%, −9.6% and −22% in H2SO4 and −29%, −54%, −2.1% and −13% in HNO3 for PIP-PASA, MPD-PASA, PIP-PSA and MPD-PSA membranes, respectively. The high molecular weight PSA polymers with improved acid stability and salt rejection were obtained from aliphatic diamine of PIP compared to aromatic MPD.