Rapid Formation And Performance Of Alumina Ceramic Filtration Membrane

In recent decades,lack of water resources and environmental pollution are becoming increasingly serious in the world.Ceramic filtration membranes,as a class of new and efficient clean separation equipment,have been successfully used in many industry areas,such as waste solution treatment,food industry and high temperature flue gas treatment,etc.,and show a good application prospect.Ceramic membrane is usually prepared by dip-coating method.The precursor or suspension of alumina,silica,zirconia or titania were coated on porous supports through dip-coating process.After drying and firing,the wet membranes became to ceramic membranes.To achieve sufficient filtration efficiency,ceramic filtration membranes are usually designed a gradual multiple layer structure.This pore size gradually decreases from macro-porous support to intermediate layer and separation layer.The preparation of intermediate layer and separation layer involves high-temperature treatment and drying process several times.These complex and time-consuming processes made the fabrication of ceramic filtration membranes extremely expensive.Therefore,it is necessary to develop new preparation methods to shorten the preparation cycle of the ceramic filter membrane and reduce the cost.The main research contents of this paper can be concluded into three aspects.The first one is based on the method of freeze-casting using camphene as freezing media.The effects of surface air flow rate,freezing temperature and solid content on the micro-structure and performance of membrane had been studied.The support and membrane are simultaneously formed in the rapid preparation process by controlling the crystallization and evaporation of camphene during cooling process.The second one is based on the method of dip-coating.The effect of ratio of the support pore size to the diameter of the membrane-forming particles on filtration performance was studied.And the ratio was optimized to prepare high flux ceramic membrane.The last one is the research to rapidly prepare high quality green membranes via UV curing technique.The effects of photosensitive composition contents,firing temperature and drying process on the performance of membrane were discussed.The alumina ultra-filtration membrane was prepared in one step by freezing-casting method for the first time.In this method,camphene andα-alumina(d₅₀=0.169μm)were used as freezing media and membrane-forming material.The slurry containing camphene,α-alumina and dispersants was mixed at 60⁶5℃,then poured into a mold at room temperature and quickly transferred to a freeze device.Both the surface contacted with the bottom cold plate（copper plate）and the surface contacted with air can form filtration membranes under certain conditions.The formation mechanism of the surface contacted with the copper sheet is supercooling crystallization mechanism,and the other surface is controlled by the supercooling crystallization mechanizm and the surface evaporation mechanizm.The properties of the filtration membrane can be regulated by the gas flow rate on the surface and the freezing temperature of the copper sheet.The results show that the pure water flux and pore size of ceramic membrane decreased as the freezing temperature decreased or the surface gas flow rate increased.The membrane can obtain a higher permeation flux by controlling the surface flow rate when the most frequent pore size is similar.At the same time,it can narrow the membrane pore size distribution.Under the conditions of solid content of 35vol%,freezing temperature of 35^oC,surface gas flow rate of 3.5m/s and fired at 1150^oC for 2h,the membrane with the most frequent pore size of 33.0nm was made which had a pure water flux of 458.0 L m^-22 h^-11 bar^-1,and a bending strength of 36.5MPa.The membrane possessed a high rejection rate of 99.6%for Direct Red 80 and a permeate flux of 230.3 L m^-22 h^-11 under applied pressure of 2bar.Dip-coating is widely utilized to form ceramic filtration membranes.The effect of the ratio of support pore size to the diameter of membrane-forming particles on the filtration performance was studied.The results showed that the pure water flux of the ceramic membrane increased as the ratio decreased.This is mainly due to the agglomerates formed among the membrane forming particles which mainly was caused by PVA,so that the support pore size is similar with the agglomerates,which effectively reduces the penetration of the membrane forming particles.When the ratio was about 3.9:1,the prepared membrane had an average pore size of 184.6nm and a pure water flux of 1438 L m^-22 h^-11 bar^-1.In order to shorten the drying period and improve the performance of membrane,the application of UV curing in rapid formation of membrane was studied.Photosensitive resin and photoinitiator were added into the membrane forming suspension.Under the action of free radicals excited by ultraviolet light,a green membrane with high strength is formed on the porous support surface rapidly,which is able to withstand the tension caused by fast drying that makes it possible to shorten the drying process and prevented drying defects.When the membrane-forming suspension contained 20wt%α-alumina,5wt%photosensitive resin,0.05wt%photoinitiator,1wt%PVA,0.8wt%glycerin and 0.2wt%dispersant,the wet membrane prepared by dip-coating had been solidified after cured under a high pressure mercury lamp for 30s.Only dried at 150℃for 30min the membrane was fired at 1100^oC for2h.The membrane prepared above exhibited a narrow pore size distribution centered at about65.2nm and a rejection rate of 98.5%for 100nm monosize PS microsphere,and has a good water permeance of 887 L m^-22 h^-11 bar^-1.