Influence of water vapor on silica membranes: Effect of sorption and percolation

Silica-based membranes are regarded as promising way of hydrogen separation at elevated temperatures because of their high H2 permeance, excellent selectivity and relative ease to scale up. This really is particularly relevant because of their applications in coal gasification and steam reforming where water vapor exists. The membranes studied listed here are made up of three layers: macroporous Al2O3 as the support, mesoporous Al2O 3 as the intermediate layer and microporous amorphous silica while the separation layer. In this report, the influence of water vapor on the transport through silica membrane has been investigated when it comes to adsorption and percolation effect at relatively low temperatures (i. e. 50 and 90┬░C). The selected temperatures maximize the big difference of mobility between That he and H2O molecules and steer clear of the structural change. He’s regarded as a mobile component, while H2O is definitely an immobile one when both of these gases transported under the specified conditions…

Contents: Influence of water vapor on silica membranes: Effect of sorption and percolation

1.1 Membranes for hydrogen separation
1.2 Gas transport in the porous materials
1.2.1 Single-component transport
1.2.1.1 Viscous flow
1.2.1.2 Knudsen diffusion
1.2.1.3 Surface diffusion
1.2.2 Multi-component transport
1.2.2.1 Gaseous diffusion in the macroporous materials
1.2.2.2 Micropore diffusion
1.2.2.3 Maxwell-Stefan equation
1.2.3 Percolation effect
1.3 Silica membrane
1.3.1 Synthesis of the silica membrane
1.3.2 Influence of water vapor on the gas permeance through silica membrane
1.4 Gas sorption
1.4.1 Introduction
1.4.2 Adsorption isotherm
1.4.3 Langmuir isotherm
1.4.4 Adsorption of water vapor on the unsupported porous silica materials
1.4.4.1 Active groups on the surface of silica materials
1.4.4.2 Adsorption on the porous silica materials
1.5 Sorption measurements in the thin layer by the
1.5.1 The principle of ellipsometry
1.5.2 Sorption of water vapor on silica layers by the ellipsometry
Chapter 2 Sample preparation and experiments
2.1 Samples
2.2 Experimental methods and setups
2.2.1 Water vapor generator
2.2.2 Gas permeation
2.2.3 Ellipsometry
Chapter 3 Results
3.1 Gas permeation in the presence of water vapor
3.2 Water vapor adsorption in the microporous silica layer
Chapter 4 Discussion
4.1 Influence of water vapor on gas permeation
4.2 water vapor adsorption in the microporous silica layer
4.3 Percolation effect
Chapter 5 Conclusions…

Source: University of Twente

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