Preparation And Properties Of Low-cost Tubular SiC Ceramic Membranes

With the continuous development of the economy and society,frequent industrial activities have led to the discharge of a large amount of waste without strict treatment,resulting in serious ecological and environmental pollution.Ceramic membrane is a kind of separation membrane material,which is often used in the field of separation and purification.Because of the good thermal stability,chemical stability and high mechanical strength,it is easier to adapt to harsh working environments.Particularly,silicon carbide(SiC)ceramic membrane has become a new material in the membrane market due to its excellent hydrophilicity,thermal shock resistance and pollution resistance.However,it is difficult to combine SiC ceramics below 2000℃ due to the high binding energy of Si-C covalent bond,which leads to the high cost of pure SiC membranes prepared by recrystallization sintering,limiting the market promotion and application..Reactive sintering can effectively reduce sintering temperature and production cost caused by high temperature sintering by introducing sintering additives,which has become a research hotspot of SiC ceramic membrane.The traditional ceramic sintering aid is metal oxide.In order to futher reduce costs,this paper used coal gangue waste as sintering aid to prepare SiC ceramic membrane support by reactive sintering at a lower temperature.Then,the pure SiC ceramic membrane separation layer was prepared on the surface of the support by dipping and pulling,and its performance was investigated.Firstly,a series of SiC supports with different pore sizes were successfully prepared using coal gangue waste as a sintering aid,SiC with an average particle size of 11.72 μm as raw material,graphite as a pore forming agent,and hydroxypropylmethylcellulose(HPMC)as a binder under air atmosphere.The effects of sintering temperature and coal gangue ratio on the properties of the support were investigated.The results show that the optimal sintering temperature is 1300℃ and the coal gangue ratio is 12 wt%.The SiC support has a porosity of 47.08%,an average pore size of 2.78 μm,and exhibits a pure water permeability of 83967 L.m-2·h-1·bar-1 and a flexural strength of 34.01 MPa.When used for solid-liquid separation,the SiC solid particles with a particle size range of D50=0.87-11.72 μm can be completely removed.At the same time,the SiC ceramic support can be regenerated through simple ultrasonic treatment.The steady-state permeability was almost constant after three cycles,which proves that the polluted ceramic membrane can be regenerated by physical methods.Secondly,the suspension was prepared using SiC powder with an average particle size of 0.87 μm as the raw material and polyvinylic acid(PAA)as the dispersant.By adjusting the pH and the content of the dispersant,the sedimentation height was observed,and the effect on the stability of the suspension was investigated.The results show that SiC powder with an average particle size of 0.87 μm has an isoelectric point of pH=3.6,and when the suspension pH=11,the absolute value of Zeta potential is the largest,which is more conducive to the dispersion of the suspension.Therefore,when pH=11 and the addition amount of dispersant is 0.8 wt%,a SiC suspension with uniform dispersion and good stability can be prepared.Finally,the coating solution was prepared by using SiC powder with an average particle size of 0.87μm as the raw material,polyvinyl acid(PAA)as the dispersant,and polyvinyl alcohol(PVA)as the binder.The membrane was coated on a home-made SiC support with an average pore diameter of 0.64 μm by dipping and pulling,and the separation layer was prepared by sintering in an argon atmosphere.The effects of solid content of suspension,coating time,and sintering temperature on the performance of the separation layer were investigated.The results show that when the solid content of the suspension is 2.5 wt%,the separation layer is difficult to cover the surface of the support.With the increase of solid content,the average pore diameter decreases from 0.52 μm to 0.28 μm,the permeability of pure water decreases from 2300 L·m-2·h-1·bar-1 to 950 L·m-2·h-1·bar-1.When the solid content of the suspension is 10 wt%,with the increase of coating time,the average pore size has little change,only decreasing from 0.46 μm to 0.39 μm,the permeability of pure water decreases from 1550 L·m-2·h-1·bar-1to 1300 L·m-2·h-1·bar-1.When the solid content of the suspension is 10 wt%,the coating time is 10 s,and the sintering temperature increases from 1050μ℃ to 1250 ℃ in an argon atmosphere,SiC particles will not undergo oxidation reaction,nor will evaporation and condensation occur.The particles accumulate into pores,which will not lead to changes in phase composition and microstructure,and their average pore size and pure water permeability are basically unchanged.