Study On Preparation Process And Filtration Performance Of Ceramic Membrane Which Was Made From Fly Ash Floating Beads With MMA-gelcasting Method

Due to the excellent properties such as mechanical strength,corrosion resistance,high-temperature resistant and durability,composite ceramic membrane is playing a more and more important role in many fields of human activities.It is significant to study a green,low cost,high efficiency preparation technology of the composite ceramic membrane.And the separation application of ceramic membrane is of great significance.In this paper,fly ash floating beads with fewer impurities,larger yield,lower price,lower sintering temperature,was selected as the raw material for preparing ceramic membrane.This project was designed to provide reliable experimental data and theoretical support for the recycle treatment of the fly ash and the optimization of ceramic membrane preparation process.Support of ceramic membrane was prepared by slip-casting.The plasticizer,dispersant,pore former were Polyvinyl alcohol(PVC),Polyethylene glycol(PEG20000),soluble starch.Increasing the amount of pore former could help to increase the porosity of support,but that led to enlarge pore diameter and uneven pore size distribution.The experimental results showed that the ideal mass fraction of pore former was 15%.Therefore,the slurry was made of PVC,PEG20000,soluble starch,fly ash powder and distilled water with a ratio of 3:1:15:100:70.We got support with 44.20% porosity,33.00 MPa bending strength,average pore diameter of 3.74 ?m,3278.4 L·m-2·h-1 water flux when green sintered at 1050? for 2h.Separation layer of ceramic membrane was prepared by gelcasting.In order to improve the traditional gelcasting monomer system,this paper studied the nonaqueous-based gelcasting using methyl methacrylate(MMA)as organic.The MMA bulk polymerization could fix the ceramic powder rapidly.Pre-polymerization of MMA and effect of prepolymer solution proportion on gelcasting were mainly investigated.We found that microwave can shorten the induction period and accelerate MMA polymerization,while more initiator dosage(BPO)could accelerate the reaction rate,which had no effect on the Gel solidification time.In addition,prolonging the pre-polymerization time could be helpful to shorten the Gel solidification time,reduce the volume shrinkage of slurry and improve the conversion rate of monomer.And increasing the proportion of MMA prepolymer solution in slurry could lead to the increase of porosity,but decrease of bending strength,average pore size and the uniformity of pore size distribution.Moreover,the rheological property of the slurry would be decreased by increasing the proportion of MMA prepolymer solution prepolymer.It is suitable for coating to control the viscosity of slurry between 3000~6500m Pa·s.Integrated above factors,it is optimal to conduct MMA pre-polymerization at 340 W microwave and adding 1.0wt% BPO for 6min.The ideal properties of MMA prepolymer solution were about 0.80×104 viscosity average molecular weight,8.68 m L/g intrinsic viscosity and 1075 m Pa·s dynamic viscosity.The mass fraction of MMA in the slurry was 45%~50%,which was the most favorable coating condition.The support and separation layer green bodies had the same phase composition and microstructure change during sintering.When the sintering temperature increased from 1000? to 1100?,the Si O2 in the powder begin to melt and reaction with Al2O3 and Fe O to produce cordierite gradually.The diffusion of molten liquid phase and the growth of mullite and cordierite grain lead to the densification of the microstructure of the ceramic membrane.With the increase of sintering temperature,the bending strength and corrosion resistance of ceramic membrane increased,but the porosity,the concentration of heavy metal leaching and the average pore size decreased,the pore size distribution become narrow.The composite ceramic membrane green body can be co-firing sintered and the optimum sintering temperature is 1050?.In this case,the porosity,bending strength,pure water flux and aci/alkali corrosion mass loss rate of the composite ceramic membrane were 43.16%,36.04 MPa,2661.91 L·m-2·h-1 and 0.27%/0.10%.The average pore diameter of separation layer downed to 0.86?m.In order to improve the filtering efficiency of composite ceramic membrane with microfiltration performance,in this paper the multi walled carbon nanotubes(MWNTs)dynamic membrane was studied while using composite ceramic membrane as the basement membrane.The effect of MWNTs size,coating solution concentration and transmembrane pressure on the filtration performance of dynamic membrane were discussed.The results showed that MWNTs-S with smaller size could fill in the basement membrane pores and narrower the aperture of ceraic membrane.As a result,the water flux of dynamic membrane decreased and its retention ability improved.The optimal concentration of dynamic membrane coating solution was 0.4g/L,and the ideal transmembrane pressure was 0.20 MPa.In this case,the removal rate of disperse red dye,disperse blue dye,direct red dye,direct blue dye,PEG20000,turbidity and UV254 by dynamic membrane increased to 97.4%,94.2%,75.7%,71.4%,41.6%,99.9% and 58.2%.MWNTs Dynamic membrane significantly enhanced the filtration performance of basement membrane and showed considerable practical value.