Study On Solvent-resistant Polyamide Composite Nanofiltration Membranes

At present,the development of organic solvent recovery,purification and reuse technologies is critical to the implementation of cleaner production in chemical processes.Solvent-resistant nanofiltration membranes are expected to be used in the separation of many different solvent systems due to their low energy consumption and mild operating conditions.However,it is still a challenge to synthesize nanofiltration membrane materials with excellent separation performance and tolerance to different organic solvents.In this study,the solvent-resistant polyamide nanofiltration membrane was prepared by a new amine monomer,and then select different compounds to modify the surface of the nanofiltration membrane,so as to further improve the separation performance of the composite nanofiltration membrane.The main findings include:1)Solvent-resistant nanofiltration was synthesized by interfacial polymerization using crosslinked polyetherimide film（C-PEI）as support layer and 4,4’-diaminodiphenylmethane and trimesoyl chloride as monomers.The membrane is optimized for the concentration of amine monomer and acid chloride.The preferred solvent-resistant nanofiltration membrane showed the tetrahydrofuran（THF）permeance of 40.3 L m^-2 h^-1 MPa^-1 with the bromothymol blue（BTB）rejection of98.5%,it was also well tolerated in acetonitrile（ACN）,methanol（Me OH）,ethanol（Et OH）and ethyl acetate（EA）.The molecular weight cut-off of the composite nanofiltration membrane in tetrahydrofuran solvent is 332 g mol^-1,which maintains stable separation performance in tetrahydrofuran solvent within 48 h.2)The surface of the solvent-resistant nanofiltration membrane was modified by hydrophilic-hydrophobic chemical modification using Tris and 2,2,2-trifluoroethylamine,respectively.The surface modification did not affect the pore size,morphology and surface roughness of the membrane.However,the surface energy and surface tension of the membrane changed significantly.Nanofiltration membrane NF-2 has different effects on the permeance of strong polar and weak polar solvents after hydrophilic and hydrophobic modification.The permeance of hydrophilic modified nanofiltration membrane Phi-NF-2 to ACN and Me OH was 27.7,26.1 L m^-2 h^-1 MPa^-1,respectively,and the permeance increased to about 3.5,2.5 times of the original NF-2membrane.The permeance of hydrophobically modified nanofiltration membrane Pho-NF-2 to THF and EA were 66.4 L m^-2 h^-1 MPa^-1 and 11.9 L m^-2 h^-1 MPa^-1,respectively,and their permeance increased to about 1.6 and 1.5 times of the original NF-2 membrane,the hydrophobically modified nanofiltration membrane exhibited a high rejection of the erythrosine B（EB）dye.Furthermore,the effects of viscosity,dielectric constant,molar volume,membrane-solvent surface tension,solvent solubility parameters and swelling degree on the permeance of the solvent through the membrane were investigated.And considering the factors such as the swelling degree and the polar component of the solubility parameter,the correlation formula for predicting the membrane permeance is obtained.