Preparation And Application Of PVDF Hollow Fiber Membrane

Polyvinylidene fluoride?PVDF?has good chemical stability and high mechanical strength,and its good physicochemical properties make PVDF an preferred material for membrane preparation.In this paper,PVDF hollow filber membrane was prepared by non-solvent induced phase separation.The effects of casting solution composition?the PVDF polymer concentration,pore-foaming agent PEG mass fraction,solvent?and film making process?coagulation bath temperature and composition,and core liquid composition?on the structure and properties of PVDF membranes were systematically studied.The study shows that the flux and porosity of PVDF membrane increase at first and then decrease with the increasing pore-foaming agent PEG mass fraction.The water flux and porosity of PVDF membrane decreased gradually,however,the fracture strength of the membrane enhances gradually with the increasing of PVDF polymer concentration in the casting solution.In the same mass fraction of PVDF and PEG,the water flux of PVDF hollow fiber membrane decrease gradually when using N-methyl-2-pyrrolidone?NMP?,dimethylformamide?DMF?and dimethylacetamide?DMAc?as solvent,fracture strength of PVDF hollow fiber membrane was decrease gradually in this order:DMF>NMP>DMAc.The water flux,porosity and fracture strength of the membrane increase with the increasing the temperature of coagulation bath.The formation of the finger-like macrovoid is suppressed by increasing the concentration of ethanol in the coagulation bath,and the porous finger-like sturcture changed to a dense sponge-like structure.By adding 30%alcohol?methanol,ethanol,isopropanol?to the internal coagulat tank,the PVDF membrane becomes dense,the PVDF membrane have lower water flux and porosity,and the mechanical properties are poor.Secondly,The PVDF-inorganic hollow fiber membrane was prepared by blending modification method.The effects of inorganic particles of LiCl,Al₂O₃ and SiO₂ on the properties and structure of the blended modified membranes were investigated.The addition of LiCl increases the viscosity of the casting solution,slows the diffusion rate of non-solvent into the casting solution,inhibits the formation of the finger-like macrovoid,and facilitates the formation of the sponge structure.The low contents of Al₂O₃ particles can improve the water flux of the membrane.As the Al₂O₃ content increases,the finger-like macrovoid of the membrane is suppressed and develops toward the sponge-like structure.SiO₂ has its own unique physical properties.It can cross-link the PVDF polymer chains to each other,increaseing the density of interlacing the polymer chains and chains,effectively increase the breaking strength of the film.Finally,the membrane extractor made by 1%LiCl blended membrane was used to study the enrichment of rare earth ions Er³⁺by LiCl modified PVDF hollow fiber membrane.The results show that the extraction rate of rare earth ion Er³⁺first increases,then decreases with the increase of the carrier P507 concentration,the stripping agent hydrochloric acid concentration and two-phase flow rate,and decreases with the increase of initial H⁺concentration in the feed phase.The optimum extraction conditions for enrichment of Er³⁺were as follows:the initial H⁺concentration of in the feed phase was 0.065 mol/L,the stripping agent hydrochloric acid concentration was3.0 mol/L,the concentration of the carrier P507 was 0.25 mol/L,and the flow rates of the two-phase were 10 mL/min.Under these conditions,the influences of the membrane contactors made of three inorganic particles of LiCl,Al₂O₃ and SiO₂ blend modified membranes on the rare earth ion Er³⁺extraction were studied.LiCl and SiO₂ can effectively lock the liquid membrane phase,slowing loss of liquid membrane,and enhance extraction rate.However,the extraction rate was reduced adding Al2O3.When the content of LiCl is 0.5%,the extraction rate was 94.8%,and the content of SiO₂ is2%,the extraction rate was 97.6%.