Preparation Characterization And Hydrogen Separation Of Cobalt-doped Silica Memebranes

Silica membranes have draw a great deal of attention in the field of membrane separation and energy chemical industry due to their high thermal stability,large mechanical strength and ease to limit the pore size in the range of gas molecule diameter. Studies show that in the hot and humid environment,water vapour adsorption on the membrane surface will result in a collapse of microporous strcture, , leading to a reduced gas permeation and and separation performance.The poor hydrothermal stability of silica membrane materials limits their application in water gas shift reaction(WGS).Cobalt-doped silica membranes were prepared by various methods to improve the hydrothermal stability of materials.But due to the larger size of the Co ions, it is easy to change the pore size when Si atoms are replaced by a fraction of Co after modification, so that the pore size control remains a challenge. In this thesis, cobalt-doped silica membranes was prepared by the sol-gel technique using tetraethyl orthosilicate(TEOS) and nitrate hexahydrate (Co(NO₃)₂·6H₂O) as precursors. The pore structure be controlled by the amount of water.The supported silica membranes were prepared on the top ofγ-Al₂O₃/α-Al₂O₃ ceramic by the dip-coating thchnology under clean room condition. The status of Co,the pore structure and the gas permeation were investigated by means of FT-IR, XRD and N2 adsorption. Gas permeation and separation performance of the doped silica membranes was studied with a home-made setup.The results show that cobalt atoms are covalently linked to oxygen atoms by replacing a fraction of silicon atoms in the framework. Silica membranes doped with 10% cobalt have a typical microporous structure, with a pore size centered at 5(?) and narrowly distributed between 4(?) and 5.5(?),and a pore volume of 0.119cm³g·^-1.The hydrogen transport in the co-doped silica membranes was subjected to a Knudsen diffusion mechanism at low temperatures and complies with an activated diffusion mechanism at temperatures higher than 100℃,The membranes possess a H2 permeance of 6.41×10^-7mol·m^-2s·^-1·Pa^-1 and a H₂/CO₂ permselectivity of 6.61 at 300℃,which is higher than that of Knudsen diffusion.