| The fresh water scarcity has gradually become one of the problems which threatens the global economic development.due to population growth,economic development,industrial expansion and other reasons.Seawater desalination is an important strategy to alleviate the shortage of water resources,which is mostly based on reverse osmosis technology.Although the current polyamide reverse osmosis membrane has high water flux and high salt rejection rate,how to further improve its rejection of high concentration salt solution and neutral substances under acceptable cost condition is a great challenge.Aimming at solving the above problems,this paper starts from the optimization of interfacial polymerization process,aiming at the trade-off limit between the flux/rejection of reverse osmosis membrane.The seawater desalination polyamide reverse osmosis membrane with high rejection was successfully prepared by a on-line“swelling and filling”method.In this paper,m-phenylenediamine(MPD)was used as the water-phase polymerization monomer,and trimethyl chloride(TMC)was used as the organic-phase polymerization monomer for the interfacial polymerization,and meanwhile,1,3,6-naphthalene trisulfonyl chloride(NTSC)and xylene were mixed in organic-phase solution.High rejection polyamide reverse osmosis composite membrane was prepared by interfacial polymerization on polysulfone ultrafiltration membrane.The reverse osmosis performance was tested using a 35000 ppm Na Cl and 5 ppm boric acid solution at 25.0?and 5.5 MPa,At the same time,we studied the effect of heating the organic solutions to 90?and introducing xylene into the organic phase on the surface chemical structure,properties,morphology and separation performance of the prepared polyamide reverse osmosis composite membrane.The main conclusions are as follows:(1)The organic phase heating can increase the crosslinking degree,At the same time the blade structure of the composite membrane become larger,the roughness increases,the water contact angle decreases,the negative charge on the surface of the membrane decreases,the thickness of the polyamide active layer decreases,the free volume decreases,and the mass of the active layer slightly decreases.We see the water flux,Na Cl rejection and boric acid rejection increase simultaneously.(2)The addition of xylene enhances the miscibility of the organic phase with water,thereby increasing the diffusion rate of MPD and forming a thicker interface reaction zone,so that the degree of crosslinking will be further increased,and heating of the organic phase will further promote crosslinking.As a result,the water flux of TFC-x membrane is increased to 66.57 Lm-2h-1,the rejection of Na Cl is 99.82%,and the rejection of boric acid is 88.23%.The water flux of TFC-x-h membrane is 57.17Lm-2h-1,the rejection of Na Cl is 99.83%,and the rejection of boric acid is 91.24%.(3)NTSC does not react with MPD to generate sulfonamide bonds due to its low reactivity,but is embedded in the polyamide network to reduce the free volume.The water flux of the final optimized reverse osmosis membrane is 37.85 Lm-2h-1,the rejection of Na Cl is significantly increased to 99.90%,and the rejection of boric acid is 92.39%.It is proved that the seawater desalination reverse osmosis membrane with high rejection can be successfully prepared by a in situ“swelling and filling”method. |
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