Preparation Of Polyamide Composite Ro Membrane With Oxidation Resistance

During the reverse osmosis operation,the polyamide separation layer is susceptible to degradation by the attack of active chlorine and OH-radicals in the feed solution,which degrades the performance and reduces the service life of membranes.To address this problem,this project will prepare an aromatic polyamide reverse osmosis membrane with 2,4-diaminotoluene（MMPD）as a functional monomer for exploring the improvement in the oxidation resistance and separation performance of the membrane using the method of persulfate modification.PES ultrafiltration membrane as the support layer of the reverse osmosis membrane,MMPD as aqueous phase monomer,and trimesoyl chloride（TMC）dissolved in hexane as organic phase monomer were used in this project.The separation layer of the composite membrane was prepared through secondary interfacial polymerization,and the composite membrane was modified by immersing in aqueous potassium sulfate（K₂S₂O₈）.The composite membrane was characterized by a scanning electron microscopy（SEM）,a contact angle tester（CA）,and an attenuated total reflection Fourier transform infrared spectrometer（ART-FTIR）.The influence of the conditions of interfacial polymerization on the performance of the composite membrane was investigated based on the variation of pure water flux and desalination rate.The following influential factors of interfacial polymerization were controlled:pore size and porosity of the ultrafiltration membrane,the concentration of monomer,temperature and time of interfacial polymerization,and the concentration of potassium persulfate and immersing time for modifying the composite membrane.The optimum condition for membrane preparation obtained was the aqueous phase solution consisting of:2.5 wt.%of MMPD,1.0 wt.%of trimethylamine,2.0 wt.%of camsilate,and 0.2 wt.%of organic phase monomer（TMC）,with hexane as solvent.The interfacial polymerization temperature was controlled at 50℃,the reaction time of primary interfacial polymerization was 90 s,and the reaction time of secondary interfacial polymerization was 30 s.The heat treatment was carried out at 80℃ for 600 s.At 60℃,the optimum modification condition was immersing in 1.0 wt.%of K₂S₂O₈solution for 100 min.The pure water flux and desalination rate of the prepared polyamide reverse osmosis composite membrane were 52.8 L·m^-2·h^-1·MPa^-1and 97.6%,respectively.Finally,the modified reverse osmosis membrane prepared was immersed in 35 wt.%of aqueous hydrogen peroxide.After 12 days of oxidation treatment,the pure water flux and desalination rate of the modified membrane had not significantly changed,indicating that the modified polyamide reverse osmosis composite membrane has good oxidation resistance.