Preparation Of Porous Mullite-based Ceramics And Application Of Oil-in-water Separation

With the promotion of global industrialization,the problem of waste gas and wastewater needs to be solved urgently.Compared with other separation technologies,membrane technology has the advantages of environment-friendly and low energy consumption,so it plays an increasingly important role in environmental separation applications.Compared with organic membrane,inorganic ceramic separation membrane has the advantages of good chemical stability,good thermal stability,high mechanical strength,strong anti-pollution ability,long service life and friendly environment.It is irreplaceable under high temperature,high pressure,strong acid and alkali,and it has a broad application prospect in high temperature gas-solid phase separation and environmental waste liquid treatment.At present,membranes cost and membranes fouling are the main technical bottlenecks in the development of ceramic membrane technology.The development of low-cost ceramic membrane and high performance ceramic membrane is the main development direction of inorganic ceramic separation membrane.Mullite ceramics have the advantages of low thermal expansion coefficient,high mechanical strength,acid-base corrosion resistance and low material cost.It is one of the main low cost membrane material systems developed in recent years.A low-cost and high pure water permeation flux fly ash-based porous ceramic membrane support was prepared in this paper with fly ash as main raw material.The effects of sintering temperature on porosity,mechanical strength,pore size distribution and pure water flux of fly ash-based support were revealed by studying the sintering process and phase reaction mechanism of ceramic support.When the sintering temperature exceeds 1400℃,the phase composition of ceramic support is single mullite phase.the growth of mullite inhibits the densification behavior at high sintering temperature.The porosity of porous mullite ceramic support after sintering at 1400℃is37.37±0.17%,the average pore size is 1.40μm,and the mechanical strength is48.84±2.93 MPa.The maximum pure water permeation flux reached 7.89 L·m^-2·s^-1when the transmembrane pressure was 0.25 MPa.The whisker ceramic membrane has the characteristics of high porosity,high flux and low tortuosity.Highly porous mullite whisker ceramic microfiltration membranes for the treatment of emulsified oily wastewater were prepared using Al（OH）₃ and coal gangue as primary materials and Mo O₃ as the whisker growth catalyst.By a comparative study on the ceramic membranes with and without Mo O₃ addition,the sintering reaction process,thermal shrinkage behavior,microstructure,open porosity,flexural strength and pore size distribution of the ceramic membranes were illuminated.The Mo O₃ addition significantly enhances mullitization reaction and promotes mullite whisker growth.Through changing the sintering temperature so as to control mullitization reaction and mullite whisker growth,the satisfactory porosity and pore size are achieved for the mullite whisker ceramic membrane sintered at 1400°C.The mullite whisker ceramic microfiltration membrane,possessed a high open porosity of47.21±0.48%,the average pore size of 185.3 nm and flexural strength of 34±2.5 MPa,shows the highest permeability of 35.8 m L·m^-2·s^-1 and above 97%oil rejection when operating at 0.1 MPa trans-membrane pressure in oil-in-water separation experiments.To further improve the properties of porous mullite ceramics,high purity mullite-based porous ceramics with high flux and high strength were prepared using commercial mullite powers as raw materials and different proportions Si C powders as additives.The reaction mechanism,dynamic shrinkage,porosity,mechanical strength,pore size distribution and pure water flux of the porous ceramics were characterized,and Si C influence on the properties of mullite porous ceramics was investigated.In the porous ceramics prepared in this experiment,maximum mechanical strength（1500℃-10%Si C）was 93.70±2.28 MPa,the highest porosity（1300℃-3%Si C）was43.8±0.22%.Considering mechanical strength,porosity and pore size distribution,the best porous mullite ceramics were selected as the synthetic conditions of 1350℃-7%Si C.The mechanical strength of this porous ceramic is 56.07±3.92 MPa,the porosity was 41.27±0.19%and the average pore size was 2.11μm,the pure water flux was 44.08L·m^-2·s^-1 when the trans-membrane pressure was 0.2 MPa.The porous mullite ceramic support/membrane prepared in this paper has ultra-high pure water flux and outstanding oil droplet rejection.It has certain competitiveness in the application field of liquid phase separation such as oil-water separation.In this paper,the porous ceramic synthetic raw material is solid waste such as fly ash and coal gangue,which not only realizes the resource utilization of solid waste,but also synthesizes products with high added value,and realizes the double harvest of environment and economic benefit.