Preparation And Investigation Of PA/MPD Double-layer Composite Membrane Based On PES Membrane

Membrane separation technology uses a membrane with selective permeation as a separation medium,and relies on the concentration difference,chemical potential difference,or pressure difference on both sides of the membrane as the driving force to selectively permeate a certain component in the mixed liquid and retain The other components in the mixed solution have achieved the purposes of separation,purification,and concentration.With its simple separation process,easy operation,and no secondary pollution,it has been widely used in water treatment,food processing,biopharmaceutical and other fields.The advantages of low energy consumption and high efficiency in the membrane filtration process are widely used in water treatment.However,as the separation system becomes more and more complex,the filter membrane also has problems of low flux and poor selectivity in practical applications.Therefore,it is of great significance to study the membrane structure and separation performance from the method of membrane preparation.In this paper,polyethersulfone(PES)ultrafiltration membrane as the support layer,piperazine(PIP)as the water phase monomer,terephthaloyl chloride(TPC)as the organic phase monomer,m-phenylenediamine(MPD)was made to the first Dihydrate phase monomer.The polyamide(PA)produced by the first interfacial polymerization was prepared by secondary interfacial polymerization to prepare a PA/MPD double-layer composite nanofiltration membrane.The surface structure,chemical composition,hydrophilicity and chargeability of the membrane surface were characterized by surface contact angle tester,Zeta potential tester,Fourier infrared spectrometer and scanning electron microscope.The separation performance of the single-layer composite membrane and the two-layer composite membrane was compared using a cross-flow separation test.Concluded as follow:(1)The PA/MPD double-layer composite nanofiltration membrane can be prepared by secondary interfacial polymerization of the residual acid chloride group on the loose PA separation layer formed by one-time interfacial polymerization and the MPD aqueous phase.Infrared spectroscopy indicated that the secondary interfacial polymerization was carried out by reacting the amino group on the MPD molecule with the residual acid chloride on the PA separation layer to form a dense MPD separation layer.The zeta potential and the static contact angle of the membrane surface indicate that the formed MPD separation layer makes the composite nanofiltration membrane composite.The charge is increased,the electronegativity is enhanced and the hydrophilicity is lowered.Infrared spectroscopy indicated that the secondary interfacial polymerization was carried out by reacting an amino group on the MPD molecule with a residual acid chloride on the PA separation layer to form a dense MPD separation layer.(2)Compared with the loose PA monolayer composite membrane,the PA/MPD double-layer composite nanofiltration membrane has a smaller pore size,and the membrane surface electronegativity and retention capacity are improved.The pore size decreased from 1.150 nm to 0.839 nm;the molecular weight cutoff also decreased from 460 Da to 270 Da.Compared with the PA single-layer composite nanofiltration membrane,the permeation flux of the PA/MPD double-layer composite nanofiltration membrane is even higher at the same rejection rate:PA/MPD double-layer composite nanoparticle at a rejection rate of 85%The flux of the membrane is 1.44 times that of the PA monolayer composite membrane;when the flux is 42L·m-2·h-1,the retention ratio of the PA/MPD double-layer composite nanofiltration membrane compared to the PA monolayer composite membrane It increased by 18.5%to reach 93.1%.After a long period of filtration test,the PA/MPD double-layer composite nanofiltration membrane showed good filtration stability.(3)The separation test of the dyes found that the PA/MPD double-layer composite nanofiltration membrane and the PA single-layer composite nanofiltration membrane have high interception ability for the dye.However,in the initial analysis of flux and flux loss,the PA/MPD double-layer composite nanofiltration membrane has higher initial flux and smaller flux loss,so the separation ability of the dye is stronger.