Preparation And Properties Of Polyimide Nanofiltration Membrane Based On Porous Organic Polymer

As a new separation technology with pressure as the driving force,nanofiltration membrane has the advantages of low energy consumption and high separation property.It has been widely used in desalination,petrochemical,energy,food,environment,medicine,water treatment and other fields.Attributed to its simple operation and easy control interfacial polymerization has become the most effective method for preparing composite nanofiltration membranes.It plays an irreplaceable role in the field of nanofiltration membranes.A dense and thin polyimide thin separation layer was produced by interfacial polymerization.It has excellent retention effect on divalent salts and polyvalent salts.Therefore,it has been widely used in wastewater treatment,medicine,food and other fields.However,the membrane prepared by the traditional interfacial polymerization method tends to have low water permeability,and the high-voltage operation causes an increase in energy consumption.Therefore,this thesis aims to introduce a two-dimensional porous organic polymer material into the interfacial polymerization,and to modify the polyimide nanolayer by regulating the polyimide layer.The main research contents in this work are as follows:?1?Preparation of nanofiltration membrane based on HAzo-POP3An azo-coupling reaction between aryl tris/diamine and tris/diol in aqueous solution was carried out under mild conditions by ice-water bath method.A porous organic polymer material based on polyphenylene ring was designed and synthesized?o-hydroxy azo-hierarchical porous organic polymers?HAzo-POPs??.HAzo-POPs were characterized by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,atomic force microscope?AFM?,Fourier transform infrared spectroscopy?FIR?,powder X-ray diffraction?XRD?and nitrogen adsorption and desorption.The two-dimensional structure and porous properties were proved.Its porosity and?-?conjugated structure make two-dimensional HAzo-POPs with unique regulation in the application of interfacial polymerization membranes.Compared with insoluble two-dimensional COFs,HAzo-POPs has an excellent dispersibility in water,which is benefit of using in water treatment.Polyacrylonitrile?PAN?was used as support membrane,piperazine?PIP?and trimesoyl chloride?TMC?were used as the aqueous phase and organic phase monomer,and HAzo-POP3 with different concentration were added to the aqueous phase.The PA-POP3 organic hybrid negatively charged nanofiltration membrane was prepared by interfacial polymerization.The results show that the addition of HAzo-POP3 has effectively improved the water permeability of the membrane,which is high of 22.6 L m^-2h^-1bar^-1under pressure of 0.4 MPa.Membranes exhibit significant charge-negative properties.And the rejection rate of Na₂SO₄ reached97.3%,which had excellent desalting effect.?2?Preparation of nanofiltration membrane based on o-POPThe o-POP was dispersed in an aqueous phase solution containing PIP monomer.And the PA-o-POP hybrid negatively charged nanofiltration membrane was prepared by interfacial polymerization,using anhydrous piperazine?PIP?and trimesoyl chloride?TMC?as the aqueous phase and organic phase monomer and PAN as the support.The results indicated that the added of o-POP can greatly improve the water permeability and maintain high salt retention.The water permeability reached 29.9 L m^-22 h^-11 bar^-1,and the salt rejection rate for Na₂SO₄ reached 97.5%under the pressure of 0.4 MPa.This work overcomes the constraint relationship between water permeability and salt rejection in traditional nanofiltration membranes.