Study On High Permeability And High Selectivity Polyamide Composite Nanofiltration Membrane

Nanofiltration,as a new type of pressure-driven membrane separation technology,has been widely used in many fields such as wastewater treatment,seawater desalination,drinking water purification,product purification and concentration due to its advantages of low energy consumption,high separation accuracy,wide separation objects,and high separation efficiency.The thin-film composite membranes prepared by interfacial polymerization are currently the mainstream products of commercial nanofiltration membranes.However,how to further improve the permeability and selectivity of nanofiltration membranes has always been a common concern of industry and academia.Herein,two strategies,solvent activation and the incorporation of dendritic amphiphilic hyperbranched macromolecules were proposed to improve the permeability and selectivity of polyamide composite nanofiltration membranes.The specific research contents are shown as follows:?1?Ethyl acetate?EAC?,acetone?ACT?and tetrahydrofuran?THF?were used as activation solvents,which were added to the organic phase to investigate the effects of the types and contents of the activation solvents on the structure and performance of the polyamide nanofiltration membranes.The results show that the activated solvent can increase the porosity of the substrate,widen the interfacial polymerization reaction zone and promote the diffusion rate of the monomer during interfacial polymerization,thereby improving the structure and performance of the nanofiltration membranes.Besides,the water flux reaches 114 L·m^-2·h^-1 when the activation solvent THF?10 vol%?was added,which is about 2.6 times higher than the pristine membrane.The selectivity of Na Cl/Na₂SO₄ is 59.1 at the same time.Compared with the commercial nanofiltration membranes,the membrane exhibits more excellent permeability and selectivity.?2?The hyperbranched polyester acid chloride?HPE-COCl?was prepared by a one-step acid chloride method with a dendritic carboxyl-terminated hyperbranched polyester?HPE?as raw material,and then the HPE-COCl was crosslinked in the polyamide layer via conventional interfacial polymerization,further preparing the polyamide nanofiltration membranes based on hyperbranched molecules.The results show that it's more conducive for HPE-COCl to exert its unique hyperbranched structure by using ethyl acetate as co-solvent due to its low solubility in water.Moreover,the incorporation of the hyperbranched macromolecule into the polyamide skin layer can synergistically improve the permeability and selectivity of the membrane due to it's unique dendritic,hydrophilic-hydrophobic alternating structure and high-density hydrophilic groups.Besides,the water flux reaches 78 L·m^-2·h^-1 when the HPE-COCl content is 0.07%w/v,which is about 1.45 times higher than the pristine membrane.Furthermore,the selectivity of Cl^-/SO₄^2-and Fe³⁺/Na⁺simultaneously improve by about1.7 times and 5.1 times,respectively.In summary,the permeability and selectivity of the conventional composite nanofiltration membranes were simultaneously improved by solvent activation and the incorporation of the dendritic amphiphilic hyperbranched polyester acyl chloride macromolecule.Thus,this work provides new ideas and methods for the development of composite nanofiltration membranes with excellent comprehensive performance.