Super Wetting Multi-stage Structure Nanofiber Membrane Design And Oil-water Separation Research

The massive discharge of oil-water mixtures in family life and industrial production has caused huge economic losses and waste of resources,seriously endangering ecological balance and environmental safety.The traditional oil-water separation strategy has the disadvantages of low separation efficiency,high operating cost and easy to cause secondary pollution in the separation process,and it is unable to separate the surfactant-stabilized emulsion,which is gradually being replaced by the emerging membrane separation technology.However,due to the lack of oil-water separation membrane materials with high permeability and high antifouling performance,the application of membrane separation technology in the world is hindered.At this stage,most of the research on the wettability of the membrane surface is focused on the surface coating and surface graft modification.This modification strategy on based membrane surface is not only cumbersome,but in the main stage of the separation process will damage the separation capacity of the membrane system.Therefore,the development of an environmentally friendly,economical,and efficient oil-water separation membrane to effectively treat surfactant-stabilized emulsions is a global problem that needs to be solved urgently.For oil-in-water emulsions,the research team used electrospinning technology to construct an asymmetric super-hydrophilic multi-layer PAN nanofiber membrane to achieve ultra-fast separation of oil-in-water emulsion.By introducing a new type of hydrophilic cross-linking network into the PAN nanofiber,the hydrophilicity of the membrane surface and the ability to combine with water molecules to form a hydrated layer are enhanced.At the same time,the introduction of cross-linking network can realize the fine adjustment of the pore diameter of the nanofiber membrane,and through the design of the asymmetric structure nanofiber to reduce the mass transfer resistance in the process of oil-water separation and improve the water production rate.Studies have shown that the effective pore size of the asymmetric nanofiber membrane introduced into the hydrophilic cross-linked network is about 2μm,the porosity is as high as 91%,water droplets can pass quickly within 0.3s,the underwater oil contact angle is 155±1°,and demonstrate excellent resistance to oil droplets adhesion.The permeance of this nanofiber membrane to n-octane emulsion（particle size in the range of 78nm-2300nm）and toluene emulsion（particle size between 78nm-342nm）is 22206 L·m^-2·h^-1·bar^-1 and29840 L·m^-2·h^-1·bar^-1 respectively,the separation efficiency exceeds 99.2%.In the circulating oil-water separation test,the flux decline rate of the nanofiber membrane is about 77.1%,the flux recovery rate is as high as 98.8±1%,and the irreversible scaling rate is less than 1.6±1%,which shows a broad application prospect in the treatment of oily wastewater.For the water-in-oil emulsion,this topic uses coaxial electrospinning technology to design silicon-containing microspheres modified super-hydrophobic multi-layer polyvinylidene fluoride nanofiber membrane.Studies have shown that polydimethylsiloxane molecules crosslink and aggregate into microspheres under the action of an electric field,and polyvinylidene fluoride molecules phase change into nanofiber membranes.The microsphere structure and the nanofiber structure interweave each other,giving the membrane surface super-hydrophobic properties.The nanofiber membrane has a porosity of about 86.2%and a hydrophobic angle of up to 154.9±0.5°.Due to the unique asymmetric fiber structure and surface characteristics,the permeance of this super-hydrophobic polyvinylidene fluoride nanofiber membrane to water-in-n-octane emulsion reaches 21816 L m^-2 h^-1 bar^-1.The water removal rate is as high as 99.65%.In the circulating oil-water separation test,the flux decline rate of the nanofiber membrane is about 97.2%,the flux recovery rate is as high as 85.3%,and the irreversible pollution scale rate is less than 14.1%,which shows a broad application prospect in the oil refining process.