Preparation Of Porous Mullite Ceramic Membrane Supports For Gas-solid Separation

Porous ceramic membranes play an important role in removing the fine particles of high-temperature exhaust gases. The support is the basis of the preparation and application of porous ceramic membranes, therefore, the pros and cons of its performance directly affects the performance of the membranes. At present, domestic supports have a low cost-performance ratio. Due to cheap price, sintered mullite was selected as main raw material to develop supports in the thesis. The processing of raw materials and the preparation process of supports were studied for improving the cost-performance ratio of supports.Firstly, the mullite particles were reshaped by ball milling. The study shows that when the method of ball milling designed in the paper is used, sharp corners of the surface of mullite particles are removed while mullite particles are not broken. The repeatability of preparation of supports is improved when the reshaped mullite particles are used.Secondly, a new preparation technology of supports with high pore connectivity was designed. It is called "coating layer by layer technology". The results show that the supports prepared by the technology have higher apparent porosity and pore connectivity than those prepared by traditional technology.Then, the technological parameters of the preparation of the supports with low cost and high pore connectivity were set. The phase diagram of Al2O3-K2O-SiO2 was used to design the sintering aid named "cf". The results of the study show that cf could melt at 1300 ℃ and that the melt could infiltrate mullite particles so that the cooled melt could connect the adjacent mullite skeleton particles.Finally, the influence of briquetting pressure, adding amount of cf and adding amount of charcoal powders on the properties of supports was studied. When additional w(charcoal powder)≤<8%, support greens can be well formed; when additional w(charcoal powder) is in the scope of 2%～-8%, compared with adding no charcoal powder, the cold compression strength of the dried support greens obviously increases; when additional w(charcoal powder)>8%, the cold compression strength of greens decreases. The apparent porosity of supports increases with the increase of charcoal adding amount, while the cold compression strength decreases. When additional w(charcoal powder) increases from 2% to 4%, the rangeability of both the apparent porosity and the cold compression of supports is smaller; when additional w(charcoal powder) increases from 0 to 2% and from 4% to 6%, both the apparent porosity and the cold compression strength of supports is bigger. The cold compression strength of supports increases with the increases of cf adding amount, while the apparent porosity decreases. When the additional w(cf)<12.5%, the rate of change of both apparent porosity and cold compression strength of supports is lower; When the additional w(cf)>12.5%, the rate of change of both apparent porosity and cold compression strength of supports is higher. When the briquetting pressure≥>20MPa an≤60MPa, the support greens could be formed well. And the cold compression strength of suports increases with the increase of briquetting pressure, while the apparent porosity of supports decreases. Three key parameters of briquetting pressure, adding amount of cf and adding amount of charcoal powders were determined by orthogonal experiment as following:briquetting pressure 40MPa, adding amount of cf 10wt%, adding amount charcoal powder 6 wt%.