Application Of Poly(Phthalazinone Ether Sulfone) Nanofiltration Membrane In Seawater Softening

Nano filtration (NF) membrane surface has a special charge performance. The rejection of the NF membrane is higher for divalent ions than monovalent ions. The NF membrane is proved to be effective in removing the divalent ions that is easy to scale in seawater, and is suitable for the separation of particle size in the range of0.01m to0.001m. As seawater pretreatment unit, NF can provide the required water quality for subsequent desalination process which makes it possible to reduce energy consumption and to raise water recovery.In this paper, simulated seawater is confected on the basis of the actual ion content in Dalian seawater. The performance of poly(phthalazinone ether sulfone) nanofiltration membranes were evaluated when the operating pressure was1.OMPa and recovery rate was30%. For NF1membrane:the rejection of Mg2+、Ca2+、hardness、SO42-、Cl-in simulated seawater reached to43%、25%、40%、94%、15%、For NF2membrane:the rejection of Mg2+Ca2+、hardness、SO42-、Cr in simulated seawater reached to70%、60%、68%、96%、21%. Compared to other membranes, NF1and NF2have more excellent performance. The seawater softening performance of NF1and NF2as the experimental membrane were discussed and compared.To the actual seawater system, the effects of pressure, recovery rate and temperature on the permeate flux and the rejection of ions in seawater were discussed. The rejections of ions and the flux increased as the pressure increased from0.5to1.3MPa. At1.3MPa, the NFl membrane removed ions of Mg2+、Ca2+、SO42-、Cl-and total hardness by28%、35%、82%、18%and29%respectively, while the NF2membrane removed ions of Mg2+、Ca2+SO42-、Cl-and total hardness by81%、69%、90%、37%and79%, respectively. During the operation period, operating pressure was kept constant at1.3MPa, the ions rejections of the membrane decrease with the increase of recovery rate. Under the condition of solution permeate recovery of7%, the NF1membrane removed ions ofMg2+、Ca2+、SO42-、Cl-and total hardness by36%、38%、93%、22%and37%, respectively. The brine Langelier saturation index is-0.03, which indicates that no calcium carbonate scaling would occur. When the temperature of feed solution increased from20to85℃, solution permeates flux of NF1membrane increased while the rejection of the membrane decreased. NF2membrane were operated under the identical conditions of recovery of20%-70%, the permeate water Langelier saturation index is less than zero, which indicates that no calcium carbonate scaling would occur. NF2have more excellent membrane performance than NF1,so it is more suitable for seawater softening process.