Solvent Resistant Nanofiltration Performance Of PTMSDPA And Its Derivatives

With excellent thermal stability and high gas permeability, Poly[1-(4-trimethyl silyl)phenyl-2-phenyl acetylene] (PTMSDPA) has become a promising solvent resistant nanofiltration membrane. In this paper, we explored the alcohol permeability and dye retention of PTMSDPA and Poly (diphenyl acetylene) membrane.PTMSDPA dense membrane was prepared by solvent evaporation method. The ethanol permeability of PTMSDPA membranes was explored. With the increase of experimental pressure and temperature, the solvent flux increased obviously. Meanwhile, the temperature effect on flux of ethanol was well correlated by an Arrhenius plot. The PTMSDPA membrane exhibited stable flux and no membrane compaction. The membrane swelling degree boosted when the carbon number of alcohol added, while solvent flux dropped. The diffusion ability of solvent was inferred to be the main reason that lead to the decrease of membrane flux. However, the Solution-Diffusion model cannot fully explain the mechanism of mass transfer.Dye retention of PTMSDPA membrane was carried out. The difference of solubility parameter between dye and membrane represented the interaction between dye and membrane which could also be characterized by the partition coefficient K. High solubility parameter difference value and low partition coefficient K illustrated a weak interaction between dye and membrane, thus resulting in a high rejection. The higher the solvent solubility parameter difference value between PTMSDPA membrane and solvent, the stronger the affinity of the membrane and solvent, therefore producing a higher membrane swelling degree. When the dye displayed a higher affinity to membrane (|δmembrane-δdye|<|δmembrane-δsolvent|) than solvent, the dye would pass through membrane more easily, and the permeate was therefore enriched with dye, providing a lower retention. Dye retention rate was not only influenced by the membrane charge, but also associated with the properties of dyes and solvents as well as the interaction between membrane with dye.PDPA membrane was obtained by means of desilication reaction where trifluoroacetic acid was used to get off the trimethylsilyl group of PTMSDPA. Fractional free volume of PDPA declined after desilication, the solvent flux dropped subsequently. It was found that PTMSDPA and PDPA demonstrated a similar performance and the interaction between dye and membrane played a major role in dye retention.