The Preparation Of PVA Composite Nanofiltration Membrane

Thin-film composite membranes were prepared by coating polyvinyl alcohol on porous polysulfone or polyacrylonitrile support membrane and following further crosslinked with glutaraldehyde, oxalic acid and citric acid. This research aimed at developing a nanofiltration membrane exhibiting high salt rejection and high permeate flux combined with good chlorine resistance and chemical stability. The experiments showed that some factors had effect on the composite membrane performance, such as the kind of substrate membrane, catalyst, cross-linking agent, the concentration of PVA, heat-treatment and coating time. The nanofiltration membrane showing better performance was prepared by using 2 wt% PVA crosslinking with 1 wt% glutaraldehyde agent for 10min and adding sulfuric acid as catalyst in the crosslinking process. The above membrane exhibited 98.9% rejection to xylenol orange (M_W=760.6) when tested at 0.6MPa and the room temperature on the 0.2g/L solution. Under the same condition, the rejection of NaCl was 49.3%, 93.6% to Na₂SO₄ and 93.4% to PEG600. The fluxes of the above solutions were all over 14.6 L/(m²Â·h).The physicochemical characteristics of PVA thin-film composite membranes were also studied. The results showed the composite membrane had better resistance to chlorine and high temperature, and the flux of the membrane kept almost stable in the long-term continuous running. Moreover, the separation characteristics of composite membranes under different operation pressures were also investigated. The flux of water was proportional to the operation pressure, and the rejection of inorganic salts and xylenol orange increased with increasing the operation pressure. The separation of various inorganic electrolytes and organic solutes was conducted. The orders of rejection were Na₂SO₄> MgSO₄> KCl> NaCl> CaCl₂> MgCl₂ and xylenol orange > PEG600. The retention and flux of inorganic substance decreased with increasing thesolute concentration.Finally, the membrane structure was characterized by Fourier Transform Infrared Adsorption Spectrum (FFIR) and Scanning Electron Microscopy (SEM). FTIR spectrum showed that the ester bond had been formed after crosslinking reaction. And the SEM showed the clear thin dense layer on the support membrane.