Research On Heat And Mass Transfer Characteristics Of Alumina Membrane Coated Activated Carbon With Core-shell Sturcture

Recently, the catalyst materials with core-shell structure have attracted much attention due to its unique stability, catalytic activity and selectivity. Coated with a layer of a defective-free and compact inorganic membrane, the catalyst materials are improved in both mechanical strength and catalytic performance. From the viewpoint of application, it is necessary to study on the heat and mass transfer characteristics of composite catalyst materials with core-shell structure. This thesis has prepared activated carbon coated with alumina membrane. Then the preparation method of the new catalyst material with shell-core structure has been optimized. Besides the heat and mass transfer characteristics have been studied, and a useful heat transfer model has been set up and derived.In this thesis, a series of alumina membrane coated activated carbon with core-shell structure has been synthesized by spraying process with different layer thicknesses. In order to get a complete, uniform and compact membrane, the experimental conditions have been optimized. The result has shown that the volume ratio of the sol and the ethanol should be less than1:6; the spraying should be operated more than10times; the drying temperature should be about120℃.The effective thermal conductivity of particle bed was determined by hot-wire method. And the particle thermal conductivity was calculated by using the model of effective thermal conductivity in fixed-bed. The results have indicated that the particle thermal conductivity decreases with increasing coated alumina. In addition, the decreasing tendency is greater in core-shell structure than that in physical mixed cases. Using the series and parallel theory, a heat transfer model has been developed to deduce the particle thermal conductivity of catalyst materials with core-shell structure, which agree well with the experimental data. The expression is λp=0.51vsλs+1/2.03vs/λs+1.02vc/λc. The developed model in this paper has provided a method for studying heat transfer characteristics and predicting the particle thermal conductivity of catalyst materials with core-shell structure.Finally, the saturated adsorption and adsorption kinetics of CO2on the catalyst materials have been studied in this thesis. The result has shown that the CO2adsorption on alumina is weaker than that on activated carbon, and coating alumina on activated carbon will reduce the saturated adsorption of CO2on the materials. In addition, the alumina shell, which is mostly mesoporous material, will increase the mass transfer length inside the catalyst material. The inside mass transfer resistance of activated carbon will be strengthened by coating alumina with the longer mass transfer length and weaker affinity of CO2on the inside surface of pore.