| In last decades,inorganic membranes have gotten extensive attention,especially in high temperature and harsh working conditions due to their superior mechanical strength,thermal stability and anti-corrosive ability.Compared with other inorganic membranes,stainless steel membranes possess numerous properties,such as superior mechanical durability,impervious to hostile fluids,withstand high temperature and high pressure,easily-sealed and long service life.However,the development and application of stainless steel membranes are restricted by their rough surfaces and large pore size distribution.In this study,single-channel and three-channel stainless steel hollow fiber membranes were prepared through non-solvent induced phase separation combined with temperature-programmed sintering technique.Then superhydrophilic stainless steel hollow fiber microfiltration membranes with narrow pore size and smooth surfaces were fabricated through simple dip-coating technique.Lastly,MFI zeolite membranes on stainless steel supports were synthesized through secondary growth hydrothermal synthesis.The main results in this study were summarized as follows:Firstly,single-channel stainless steel hollow fiber membranes were prepared through nonsolvent induced phase separation combined with temperature-programmed sintering technique.The effects of stainless steel powders content and polymer content on the morphology,mechanical strength,porosity,density,maximum pore size and pure water flux of stainless steel hollow fibers were investigated systematically.The effect of steric hindrance in dope solution was improved with the increase of polymer content,which reduced the aggregation and sedimentation of stainless steel powders.As a result,the stability of dope solution was promoted.Meanwhile,the viscosity of dope solution was improved with the increase of polymer content.Sponge-like structures were easily formed due to the slow exchange rate between solvent and non-solvent and the slow mobile rate of polymer chains which resulted from the high viscosity of dope solution.The structure of stainless steel membranes would densify with the increase of stainless steel powders.Meanwhile,the viscosity of dope solution was improved with the increase of polymer content.Sponge-like structures were easily formed due to the slow exchange rate between solvent and non-solvent and the slow mobile rate of polymer chains which resulted from the high viscosity of dope solution.In conclusion,the whole performance of stainless steel hollow fibers was optimal when the polymer content was 3.2 wt.%and the stainless steel powders content was 80 wt.%,which were the pure water flux of 11500 L/(m2·h·bar),the mechanical strength of 115 MP a,the porosity of 35%and the maximum pore size of 3.5 ?m.Secondly,three-channel stainless steel hollow fibers were prepared through three-channel spinneret.The effects of sintering temperature on the morphology,fractural loading,pore size distribution and permeation(nitrogen permeation and pure water flux)of stainless steel membranes were investigated systematically.Three-channel stainless steel membranes were applied to the separation of starch wastewater.The fractural loading of stainless steel membrane increased firstly and then decreased.The maximum value of fractural loading was 18.2N at 1100?.The nitrogen permeation and pure water flux also increased firstly and then decreased.The maximum value of nitrogen permeation and pure water flux were 32.2× 10-5 mol/(m2·s·Pa)and 27.1 m3/(m2·h·bar)at 1200?.The finger-like structures collapsed gradually and some pinholes appeared on the surface of metal crystals with the increase of temperature.The metal crystals collapsed obviously and lots of pinholes appeared on the surface when temperature was raised to 1300?,which led to the immediate decrease of the performance.The effect of sintering temperature on the pore size distribution was minor.Anti-corrosive tests proved that stainless steel membranes could be applied in a wide pH range.The separation tests of starch wastewater proved that stainless steel membranes could be applied in the field of separation of suspend substances and could be recycled by simple washing steps.In addition,superhydrophilic and under water superoleophobicity stainless steel hollow fibers were fabricated through simple dip-coating technique.The positive effect of piperazine on the formation of a continuous membrane was proved.The morphology,wettability,pore size distribution,crystal structure,mechanical strength and permeation(nitrogen permeation and pure water flux)of stainless steel microfiltration membranes were investigated systematically.Stainless steel microfiltration membranes were applied to anti-fouling fields.The surfaces of stainless steel microfiltration membranes with piperazine in its coating suspension were continuous and the mean pore size was 244 nm.The mechanical strength of stainless steel microfiltration membranes was two times higher than that of stainless steel substrates.Contact angle tests and XRD patterns showed that the crystal structure of TiO2 layer was anatase and the membrane surface possessed the properties of superhydrophilic and under water superoleophobicity.For oil in water emulsion,the rejection of stainless steel microfiltration membranes was as high as 99%and the pure water flux could recover up to 90%after the washing steps.For sodium alginate solution,the rejection of stainless steel microfiltration membranes was 90%and the pure water flux could recover up to 90%after the washing steps.For bovine serum albumin solution,the rejection of stainless steel microfiltration membranes was 90%within certain operation time.However,due to the severe concentration polarization and the adsorption of proteins onto TiO2 surface,the flux decline in the operation process was obvious.Lastly,MFI zeolite membranes on macropore stainless steel supports were synthesized through secondary growth hydrothermal synthesis.The effects of the compositions of synthesis solution,synthesis temperature and synthesis time on the morphology and pervaporation performance of MFI membranes were investigated systematically.The effects of feed temperature and feed concentration on pervaporation performance were also studied.High tetramethylammonium hydroxide(TPAOH)content contributed to the growth of c-oriented crystals.However,there would be defects on membrane surface if the nutrient(tetraethoxysilane)was insufficient.High synthesis temperature contributed to the growth of coriented crystals and the crystals would grow randomly at low synthesis temperature.The performance of zeolite membranes synthesized at high temperature was superior to that synthesized at low temperature.The optimal separation factor of 65 and flux of 1.68 kg/(m2·h)for at 60? for ethanol-water mixture were obtained.Compared with different zeolite membranes on supports with different microstructure,high porosity and large area of fingerlike structures contributed to a high performance zeolite membranes.The separation performance of zeolite membranes for butanol-water mixture was also investigated.A high separation factor of 207 and a good flux of 218 g/(m2·h)at 80? for butanol-water mixture were measured,which showed that MFI zeolite membranes got the potential in butanol separation process. |
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