| High-temperature flue gas filtration technology is an important part of the solutions of exhaust gas emissions,and ceramic filter material is the key issue in the field of hot gas filtration.However,the traditional ceramic filter material has high pressure drop,low removal efficiency for submicron particles,and high preparation cost.Therefore,in this study,mullite fibrous composite membranes with excellent filtration performance such as low filtration resistance,high filtration efficiency and low-cost are prepared,which are very promising for PM pollution control in the field of hot gas filtration.In the first time,we developed silica/mullite fiber(labeled Si/MF)composite membranes with double-layer pore gradient structure by a simple vacuum procedure.The support with three-dimensional skeleton structure exhibited high porosity(higher than 90%)and low density(lower than 0.25 g/cm3).By controlling the mass ratio of silica sol to mullite fiber,we can obtain uniform and complete filtering layers with different thicknesses.The composite membranes exhibited high PM filtration efficiency with 99%for 1–10?m,97%for 0.5?m and 90%for 0.3?m.These samples had high air flow with very low pressure drop(lower than 600 Pa when airflow velocity reached 1.1 m/s).In order to further improve the filtration efficiency of the composite membrane for sub-micrometer particles,in this study,kaolin particles were introduced into the raw material system including the mullite fiber and silica-sol,and kaolin-silica/mullite fiber(labeled Kaolin-Si/MF)composite membranes with three-layer gradient pore structure was prepared by vacuum filtration procedure.The support is also a three-dimensional network structure.However,compared with the support of Si/MF composite membrane,the addition of kaolin makes the porosity and average pore size of the composite membrane slightly lower,and the high temperature compressive strength is greatly improved.The top layer of Kaolin-Si/MF composite membrane contains kaolin separation layer and silica-gel transition layer that its pore size between the support and the separation layer.Compared with Si/MF composite membrane,Kaolin-Si/MF composite membrane has higher PM0.3 filtration efficiency(>99.97%),the filtration resistance of the Kaolin-Si/MF composite membrane is also larger than Si/MF composite membrane at the same airflow rate.When the airflow rate is 0.3 m/s,the Kaolin-Si/MF composite membrane has a larger quality factor(QF)value than the Si/MF composite membrane,and the overall filtration performance is better. |
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