| Oil/water emulsion?O/W emulsion?is a common pollutant,which is very harmful to the ecological environment and human health.Chemical demulsification is a frequently-used efficient method in traditional oil/water emulsion treatment,but the demulsifier remains in water,which is prone to secondary pollution and high energy consumption in the treatment process.Although membrane separation technology is a kind of environmental friendly and low energy consumption sewage treatment technology,there are some problems of low separation efficiency and serious membrane pollution when the membrane separation technology is used to treat oily wastewater,especially the oil/water emulsion with stable kinetics.In order to overcome the problems in the application of demulsifier and membrane separation technology,the hyperbranched phenol-amine resin block polyether demulsifier?AE2311?with demulsification effect was grafted on the surface of polyvinylidene fluoride?PVDF?membrane in this study,constructing the functional PVDF membrane with demulsification function and combining the chemical demulsification to the membrane separation,with a view to realizing the separation of O/W emulsion from oil and water.In this study,PVDF and styrene maleic anhydride?SMA?were firstly used as blend membrane materials,N'N-dimethylacetamide?DMAc?as solvent and lithium chloride?Li Cl?as pore-forming agent to prepare SMA/PVDF blend membrane by immersion precipitation phase conversion.The effects of PVDF concentration,coagulation bath temperature and SMA content on membrane structure and properties were investigated.The results showed that when the PVDF content was 16 wt%and the SMA content was 7 wt%,the blend membrane exhibited typically asymmetric structure with porosity of 70.3%,water contact angle of 68.5°,pure water flux of 548.34L·m-2·h-1 and BSA rejection of 100%.Secondly,the hyperbranched phenol-amine resin block polyether demulsifier AE2311 was grafted onto surface of SMA/PVDF membrane via the alcoholysis reaction between maleic anhydride on membrane surface and terminal hydroxyl group on AE2311.The successful preparation of the demulsifier modified PVDF membrane was charaterized by X-rayphotoelectron spectroscopy?XPS?,attenuated total reflectance-fourier transform infrared spectroscopy?ATR-FTIR?,scanning electron microscopy?SEM?and atomic force microscope?AFM?.The effects of grafting time on grafting ratio,pore size,hydrophilicity,permeability and anti-fouling properties of the modified membranes were investigated.The results showed that the obtained AE2311@SMA/PVDF membrane with grafting time of 9 h exhibited superhydrophilic?water contact angle of 0°?and underwater superoleophobic properties?underwater oil contact angle over 150°?.The modified membrane also obtained the grafting ratio of422.5 mg·g-1,the porosity of 62.33%,the average pore size of 41.98 nm and the water flux of 362.14 L·m-2·h-1.After three cyclic filtration experiments,the flux recovery ratio?FRR?of the modified membrane reached 92.36%,with excellent anti-fouling performance.Finally,the AE2311@SMA/PVDF membrane was used to investigate its separation efficiency for different oil-in-water emulsions,and to evaluate the oil resistance,long-term operational stability and membrane demulsification efficiency of the modified membrane.It was found that the oil/water separation ratio of the modified membrane to kerosene/water,dichloroethane/water,petroleum ether/water and toluene/water emulsion were all more than 99%,which exhibited excellent oil/water separation performance.After three filtration experiments,FRR of the membrane reached 96.56%,which indicated that the membrane pocessed excellent oil resistance.In addition,the modified membrane can be reused and has long-term operational stability.The membrane demulsification experiment proved that the modified membrane surface can destroy the O/W emulsion,and the separation ratio of the emulsion reached 57.4%without membrane filtration.The mechanism of the oil/water separation membrane combineded the chemical demulsification effect of AE2311,the superhydrophilicity and underwater superoleophobic properties of the membrane surface,and the screening effect of the ultrafiltration membrane.Therefore,the demulsifier functionalized membrane prepared in this study can effectively separate the O/W emulsion,the efficiency is not significantly reduced undergoing cyclic separation,which proved that the AE2311@SMA/PVDF modified membrane had a good application prospect in oil/water separation and had potential application value for large-scale separation of oil-water emulsion. |
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