Preparation Of Polyamide Reverse Osmosis Membrane With High Chlorine Resistance

Reverse osmosis(RO)technology is an efficient and mature membrane separation technology,and its core is the high functional RO membrane.However,in order to prevent the bio-fouling of the membrane,researchers of reverse osmosis usually adopt preliminary sterilization by adding active chlorine into the feed liquid.The conventional polyamide RO membrane is susceptible to free chlorine due to the chemical structure.The free chlorine in RO feed stream can cause deterioration of membrane performance,which shortens membrane life and greatly limits the development and application of RO technology.Therefore,it is of great significance to develop RO membrane with high chlorine resistance.In this work,the chlorination mechanism of polyamide RO membrane was clarified and monomer methyl-m-phenylenediamine(MMPD)was selected to prepare the composite RO membrane via interfacial polymerization and reaction with polyacyl chloride TMC.It was considerated that the aromatic diamine compound MMPD with a CH3 substituent at the ortho position of the amino would produce the polyamide possessing an improved chlorine resistance.The effects of monomer concentration,pH of aqueous solution,interfacial polymerization time,curing temperature and curing time on membrane separation performance were investigated.The optimal preparation conditions were determined:the aqueous phase monomer(MMPD)concentration is 2.0 wt.%,the organic phase monomer(TMC)concentration is 0.20 wt.%,aqueous solution pH value is 9.0,interfacial polymerization time is 60 s,curing temperature is 80℃,curing time is 10 min.The optimal conditions for preparing the RO membrane in the feed concentration of 2 g·L-1 and the pressure under the condition of 1.2 MPa,the retention rate of NaCl is 95.1%,reverse osmosis membrane flux is 36.3 L·m-2·h-1MPa-1.The RO performance of MMPD-TMC membrane was comparable to that of MPD-TMC membrane.The MMPD-TMC membrane was characterized by SEM,CA,XRD and TGA.In addition,the chlorine resistance of MMPD-TMC membrane was analyzed by adjusting the concentration of sodium hypochlorite.After the MMPD-TMC membranes were treated with 20000 ppm·h chlorine,the chlorination of crosslinked aromatic polyamides can be neglected as compared with the chlorination of MPD-TMC membranes,and the water flux and salt rejection remained stable.That is to say,compared with commercial RO membrane,MMPD-TMC membrane possessed relatively high chlorine resistance.