Preparation Of Resistant To Pollutional Membranes For Forward Osmosis And Application Of Seawater Desalination

Cellulose acetate (CA) is a kind of widespread man-made fiber, which has the advantagesof low cost, high thermal stability, chemical stability and strong mechanical properties.However, the further application of CA in desalination is limited due to its poor stain resistanceand degradation. In this study, CA was used to prepare forward osmosis membrane by addinggrapheneoxide and nano-Titania, and then the prepared membranes were modified. The purewater flux, surface contact angle and structure of the forward osmosis membrane were tested.Also, the application of the prepared forward osmosis membrane in seawater desalination wasinvestigated.The influence of CA content, solvent ratio, additive content, support layer mesh numberand coagulation bath temperature on the pure water flux and reverse salt flux were initiallystudied. In addition, the optimum parameters of the forward osmosis membrane were examinedand the results showed that the optimum mass fraction of CA was16%, DMF and acetonevolume ratio was1:0.6, the mass fraction of PEG400was4%, support layer mesh number was120, and the coagulation bath temperature was60℃. The pure water flux was15L/m2·h after1h and the reverse salt flux was below7.5g/m2·h.Based on the optimum parameters of CA forward osmosis membrane, the effect ofgraphene oxide content and blending temperature on the performance of the forward osmosismembrane were investigated. The data showed that the best graphene oxide content was0.15%and the blending temperature was50℃. In the test time of1h, using1M NaCl as the drawsolution and deionized water as feed solution, the pure water flux was about16L/m2·h and thereverse salt flux was below7g/m2·h.The effects of TiO2content and blending temperature on the membrane performance werethen investigated. It was found that the optimum parameters for titanium dioxide/celluloseacetate blending forward osmosis membrane were TiO2content of1.25%at the blendingtemperature of60℃. In the test time of1h, using1M NaCl as the draw solution and deionizedwater as feed solution, the pure water flux was more than10L/m2·h and the reverse salt fluxwas below5g/m2·h. The contact angle of the forward osmosis membrane was tested by contact angleinstrument, which illustrated the contact angle of CA forward osmosis membrane was71.6°.The graphene oxide/cellulose acetate blending forward osmosis membrane contact angle was58.2°, indicating that the graphene oxide/cellulose acetate blending forward osmosis membranehad better hydrophilicity than CA forward osmosis membrane. The nano-titaniumdioxide/cellulose acetate blending forward osmosis membrane contact angle was54.2°with thebest hydrophilicity. It could be seen from the results that additives could enhance thehydrophilicity of the forward osmosis membrane, and the hydrophilic of nano-titanium dioxidewas better than the graphene oxide.In the end, the preparation of forward osmosis membrane were used for seawaterdesalination. In the test time of1h, using2M glucose solution as the draw solution and BoHaiseawater as the feed solution, and the overall change of pure water flux for CA forward osmosismembrane was little, basically stable at20L/m2·h. The pure water flux of grapheneoxide/cellulose acetate blending forward osmosis membrane was relatively large, about30L/m2·h. And the pure water flux declined with filtration time. Finally, the flux wasapproximately equal to the pure water flux of CA forward osmosis membrane. The pure waterflux of the nano-titanium dioxide/cellulose acetate blending forward osmosis membrane wasabout25L/m2·h and relatively stable.