Polysiloxaneimide membranes for removal of VOCs from water by pervaporation

For the separation of volatile organic compounds (VOCs) from water by pervaporation, three polysiloxaneimide (PSI) membranes were prepared by polycondensation of three aromatic dianhydrides of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), and pyromellitic dianhydride (PMDA) with a siloxane-containing diamine. The PSI membranes were characterized using 1H-NMR, ATR/IR, DSC, XRD, and a Rame-Hart goniometer for contact angles. The degrees of sorption and sorption selectivity of the PSI membranes for pure organic compounds and organic aqueous solutions were investigated. The pervaporation properties of the PSI membrane were investigated in connection with the nature of organic aqueous solutions. The effects of feed concentration, feed temperature, permeate pressure, and membrane thickness on pervaporation performance were also investigated. The PSI membranes prepared have high pervaporation selectivity and permeation flux towards hydrophobic organic compounds. The PSI membranes with 150-μm thickness exhibit a high pervaporation selectivity of 6000–9000 and a high permeation flux of 0.031–0.047 kg/m2 h for 0.05 wt % of the toluene/water mixture.