Study On The Structure And Separation Performance Of Polyamide Nanofiltration Membrane Prepared By Controllable Interfacial Polymerization

With the intensification of human activities,the limited fresh water resources of the earth are seriously polluted,and the global water resources crisis seriously limits the development of human society.Membrane separation technology has the advantages of simple operation,low energy consumption and high separation efficiency,which has made a great contribution to address the water resources crisis.Nanofiltration is one kind of membrane separation technology and belongs to pressure-driven separation membrane.The separation accuracy of nanofiltration is between those of ultrafiltration and reverse osmosis,as those small molecular organic matters and divalent or high-valent ions with molecular weight of 200～1000 can be effectively separated.So,it’s widely used in municipal wastewater treatment and desalination.Polyamide nanofiltration membrane is the most successful commercial nanofiltration membrane at present,which consists of the support layer and the polyamide separation layer.The polyamide layer plays a critical role in the water flux and rejection of the nanofiltration membrane.So,optimizing the structure and morphology of the polyamide layer is the key to improve the separation performance of the nanofiltration membrane.Interfacial polymerization is the most common method to prepare polyamide layer,while the reaction is uncontrollable,making the structure and morphology of polyamide layer difficult to regulate.Therefore,it is an effective way to optimize the polyamide layer and improve the performance of nanofiltration membrane by deeply understanding the interfacial polymerization process and proposing a controllable interfacial polymerization method.This paper aims at the problem that the interfacial polymerization reaction is difficult to control.The controllability of the interfacial polymerization reaction was improved,the structure and morphology of the polyamide layer was optimized through designing a new interfacial polymerization process.Meanwhile,the separation performance of the nanofiltration membrane was tested.（1）Evaluation of structure and performance of polyamide nanofiltration membrane prepared by electrosprayed interfacial polymerizationThe interfacial polymerization was achieved by electrospray of piperazine（PIP）and trimesoyl chloride（TMC）monomers.A series of nanofiltration membranes were prepared by controlling the reaction conditions of electrosprayed interfacial polymerization,and also the performance was tested.It is found that the surface roughness and thickness of the polyamide layer can be regulated by electrosprayed interfacial polymerization.The water flux of the membrane prepared by electrosprayed interfacial polymerization was 83.0 L m^-2 h^-1 at operating pressure of 5 bar.,which is 4times higher than that prepared by traditional interfacial polymerization under the same conditions,and the rejection rate of sodium sulfate was 95.5%.additionally,we added Span 80 functional interlayer to further reduce the roughness of the membrane surface,improve the interfacial stability between the support layer and the separation layer as well as the removal efficiency of bisphenol A（97.8%）.The electrosprayed interfacial polymerization and functional interlayer strategy provide a new insight for constructing high performance composite nanofiltration membrane.（2）Evaluation of the structure and performance of polyamide composite nanofiltration membrane prepared by emulsion interfacial polymerizationA series of polyamide composite nanofiltration membranes were prepared by porous hydrophobic membrane-assisted interfacial polymerization,and their properties were tested.It is found that the reaction rate of interfacial polymerization can effectively slow down during this process,so that the roughness and thickness of polyamide layer can be regulated.The composite nanofiltration membrane prepared by this method has certain selective permeability,the maximum water flux can reach 46.5 L m^-2 h^-1 under5 bar operating pressure and the rejection rate of sodium sulfate can reach 92.3%.This novel interfacial polymerization method also provides a new insight for controllable interfacial polymerization.In this paper,aiming at the regulation of the morphology and structure of the polyamide layer,two kinds of polyamide nanofiltration membranes were prepared by controlling the reaction rate of interfacial polymerization.The effects of the two interfacial polymerization processes on the structure and morphology of the polyamide layer and the separation performance of the nanofiltration membrane were systematically tested.The obtained results provided a new idea for further controlling the interfacial polymerization reaction and optimizing the structure and morphology of the polyamide layer.