Preparation Of Oil/water Emulsion Separating Membrane And Research On Key Factors Influencing Separation And Fouling Performance

As the water pollution caused by oil spill and oily wastewater discharge is one of the most serious problems in the world,oil/water separation technology became an important topic.Generally speaking,oily wastewater can be divided into layered oil/water mixture and emulsion.Since the latter one has smaller particle size and higher stability,it is more difficult to be separated.Thus,the separation of surfactant-stabilized oil/water emulsions with a droplet size below 20μm can be a great challenge.In this paper,microfiltration membrane was modified via UV-initiated polymerization,and the key factors influencing separation efficiency and membrane fouling have been systematically studied.1.Polytetrafluoroethylene（PTFE）microfiltration membrane with hydrophilicity and underwater oleophobicity was prepared.Poly（oligo（ethylene glycol）methacrylate）（pOEGMA）was grafted on the surface of PTFE membrane by UV-initiated polymerization technology.High efficiency,high flux and long-term stability were achieved during the oil-in-water emulsion separation process.The separation efficiency reached nearly 100%and the water flux was 1500L·m^-2·h^-1.The effect of surface wettability and membrane pore size on the demulsification and separation was studied.It was demonstrated that the emulsion separation is not only an interface problem,but also related to the pore structure of filtration membrane.Due to the high surface hydrophilicity and underwater oleophobicity,the membranes exhibited outstanding anti-fouling property and long-term performance.2.The influence of membrane surface charge on the emulsion separation and fouling resistant performance was studied.Poly（2-dimethylaminoethyl methacrylate）（pDMAEMA）and pOEGMA was grafted onto polyethylene（PP）membrane via UV-initiated polymerization.The pDMAEMA-grafted membrane showed strong positivity due to the protonation of secondary amine group in water（weakly acid）,whereas the pOEGMA-grafted one was negatively charged.Three types of oil-in-water（O/W）emulsions were prepared using ionic surfactant,nonionic surfactant and cationic surfactant,respectively.The separation efficiencies and fouling behaviors of differently charged membrane were studied.For all positively and negatively charged emulsions,the separation efficiency of pDMAEMA grafted membrane was the highest.And for negatively charged emulsions,the antifouling capability of p OEGMA was the highest.3.In a further step,pDMAEMA-grafted membrane with reversible surface charges in response to pH changes was used for emulsion separation and intelligent antifouling.The pDMAEMA-grafted membrane was positively charged in water,and deprotonated in alkaline conditions.The membrane fouling was investigated using reactive dyes and anionic surfactants as the model molecules.The membranes were easily contaminated by these anioic foulants,which afterwards could be removed in alkali solution（pH=9）.The removal ratio achieved above90%,and it remained at a high level after five circulation experiments.The membrane possessed high emulsion separation efficiency（>90%）and high flux recovery ratio（nearly 100%）by being washed with alkaline solution each time.Therefore,efficient separating membrane with long-term pollution resistance is obtained.Our studies provide new strategies for the surface design and construction of emulsion separation membrane for practical use.