Silica Membranes for Hydrogen Separation from Coal Gas. Final Report PDF Download
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Languages : en
Pages : 69
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Book Description
This project is a continuation of a previous DOE-UCR project (DE-FG22- 89PC89765) dealing with the preparation of silica membranes highly permselective to hydrogen at elevated temperatures, suitable for hydrogen separation from coal gas. The membranes prepared in the previous project had very high selectivity but relatively low permeance. Therefore, the general objectives of this project were to improve the permeance of these membranes and to obtain fundamental information about membrane structure and properties. The specific objectives were: (1) to explore new silylation reagents and reaction conditions with the purpose of reducing the thickness and increasing the permeance of silica membranes prepared by chemical vapor deposition (CVD), (2) to characterize the membrane structure, (3) to delineate mechanism and kinetics of deposition, (4) to measure the permeability of silica layers at different extents of deposition, and (5) to mathematically model the relationship between structure and deposition kinetics.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 69
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Book Description
This project is a continuation of a previous DOE-UCR project (DE-FG22- 89PC89765) dealing with the preparation of silica membranes highly permselective to hydrogen at elevated temperatures, suitable for hydrogen separation from coal gas. The membranes prepared in the previous project had very high selectivity but relatively low permeance. Therefore, the general objectives of this project were to improve the permeance of these membranes and to obtain fundamental information about membrane structure and properties. The specific objectives were: (1) to explore new silylation reagents and reaction conditions with the purpose of reducing the thickness and increasing the permeance of silica membranes prepared by chemical vapor deposition (CVD), (2) to characterize the membrane structure, (3) to delineate mechanism and kinetics of deposition, (4) to measure the permeability of silica layers at different extents of deposition, and (5) to mathematically model the relationship between structure and deposition kinetics.
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Category :
Languages : en
Pages :
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Book Description
Author:
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Category :
Languages : en
Pages : 97
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Book Description
The general objective of this project was to synthesize permselective membranes suitable for hydrogen separation from coal gas. The specific objectives were: (i) to synthesize membranes by chemical vapor deposition (CVD) of SiO2 or other oxides on porous support tubes, (ii) characterize the membranes by permeation measurements of various gases and by electron microscopy, and (iii) obtain information about the mechanism and kinetics Of SiO2 deposition, and model the process of membrane formation. Silica glass and certain other glasses, in dense (nonporous) form, are highly selective to hydrogen permeation. Since this high selectivity is accompanied by low permeability, however, a practical membrane must have a composite structure consisting of a thin layer of the active oxide supported on a porous tube or plate providing mechanical support. In this project the membranes were synthesized by chemical vapor deposition (CVD) of SiO2, TiO2, Al2O3 and B2O3 layers inside the walls of porous Vycor tubes (5 mm ID, 7 mm OD, 40 Å mean pore diameter). Deposition of the oxide layer was carried out using the reaction of SiCl4 (or TiCl4, AlCl3, BCl3) and water vapor at elevated temperatures. The porous support tube was inserted concentrically into a larger quartz tube and fitted with flow lines and pressure gauges. The flow of the two reactant streams was regulated by mass flow controllers, while the temperature was controlled by placing the reactor into a split-tube electric furnace.
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Languages : en
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Languages : en
Pages : 4
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A new reactor system was constructed which can be used for CVD Of SiO2 layers on porous Vycor tubes. The system is suitable for the usual one-sided deposition and for alternating (or layer-by-layer) deposition whereby the silylating agent and water are passed one at a time in alternating periods. The main advantage of alternating deposition is that it allows membrane deposition using silica precursors for which the homogeneous hydrolysis is fast. As we have demonstrated in earlier work, fast homogeneous reaction interferes with membrane formation. The disadvantage of alternating deposition is the longer time required for membrane formation. Figure 1 is a schematic of the new reactor constructed for homogeneous deposition. In each silylation period the space inside and outside of the support tube is evacuated and a small and accurately controlled amount of reactant (e.g. SiCl4) is allowed to flow from a storage glass flask 4 into the reactor annulus by opening valve 5 for a few seconds. The silylation reaction is allowed to proceed for the desired time interval (about one minute) after which the reactor is evacuated and flow of water vapor commences by opening valve 7. After the completion of one cycle of silylation and hydrolysis, the nitrogen permeance of the support tube is measured by the techniques used in our earlier work (bubble flow meter or pressure transducer). After the nitrogen permeance has decreased by a specified factor (about thirty) from its initial value, the reactions are terminated and the membrane is annealed at 700°C for about ten hours after which the nitrogen and hydrogen permeances are measured at several temperatures.
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Languages : en
Pages : 2
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Book Description
The project objectives are (1) to explore new silylation reagents and reaction conditions with the purpose of reducing the thickness and increasing the permeance of silica membranes, (2) to delineate mechanism and kinetics of silica deposition, (3) to measure the permeability of silica layers at different extents of deposition and (4) to mathematically model the relationship of permeability and membrane structure. Study of the literature has suggested the use of certain ultrafast silylation reagents for the purpose of achieving thinner deposit layers and, hence, increase membrane permeance. The silylation reagents available commercially are suitable for grafting only one molecule per silanol ( -OH) group on the solid surface. The silylation reagents needed for our purposes must contain hydrolyzable groups such that the -OH groups can be regenerated and the reaction continued to build a multilayer deposit. During the reporting period we have started to explore the synthesis of silylation reagents suitable for multilayer formation. A systematic series of kinetic experiments were carried out using a thermogravimetric analysis system (TGA) to measure the reaction rate of SiCl4 with surface -OH groups, the rate of H2O with surface chloride groups and the rates of condensation reactions between two -OH groups and between an -OH group and a -Cl group.
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Category :
Languages : en
Pages : 97
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Book Description
The general objective of this project was to synthesize permselective membranes suitable for hydrogen separation from coal gas. The specific objectives were: (i) to synthesize membranes by chemical vapor deposition (CVD) of SiO[sub 2] or other oxides on porous support tubes, (ii) characterize the membranes by permeation measurements of various gases and by electron microscopy, and (iii) obtain information about the mechanism and kinetics Of SiO[sub 2] deposition, and model the process of membrane formation. Silica glass and certain other glasses, in dense (nonporous) form, are highly selective to hydrogen permeation. Since this high selectivity is accompanied by low permeability, however, a practical membrane must have a composite structure consisting of a thin layer of the active oxide supported on a porous tube or plate providing mechanical support. In this project the membranes were synthesized by chemical vapor deposition (CVD) of SiO[sub 2], TiO[sub 2], Al[sub 2]O[sub 3] and B[sub 2]O[sub 3] layers inside the walls of porous Vycor tubes (5 mm ID, 7 mm OD, 40 [Angstrom] mean pore diameter). Deposition of the oxide layer was carried out using the reaction of SiCl[sub 4] (or TiCl[sub 4], AlCl[sub 3], BCl[sub 3]) and water vapor at elevated temperatures. The porous support tube was inserted concentrically into a larger quartz tube and fitted with flow lines and pressure gauges. The flow of the two reactant streams was regulated by mass flow controllers, while the temperature was controlled by placing the reactor into a split-tube electric furnace.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 4
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Book Description
A new reactor system was constructed which can be used for CVD Of SiO[sub 2] layers on porous Vycor tubes. The system is suitable for the usual one-sided deposition and for alternating (or layer-by-layer) deposition whereby the silylating agent and water are passed one at a time in alternating periods. The main advantage of alternating deposition is that it allows membrane deposition using silica precursors for which the homogeneous hydrolysis is fast. As we have demonstrated in earlier work, fast homogeneous reaction interferes with membrane formation. The disadvantage of alternating deposition is the longer time required for membrane formation. Figure 1 is a schematic of the new reactor constructed for homogeneous deposition. In each silylation period the space inside and outside of the support tube is evacuated and a small and accurately controlled amount of reactant (e.g. SiCl[sub 4]) is allowed to flow from a storage glass flask 4 into the reactor annulus by opening valve 5 for a few seconds. The silylation reaction is allowed to proceed for the desired time interval (about one minute) after which the reactor is evacuated and flow of water vapor commences by opening valve 7. After the completion of one cycle of silylation and hydrolysis, the nitrogen permeance of the support tube is measured by the techniques used in our earlier work (bubble flow meter or pressure transducer). After the nitrogen permeance has decreased by a specified factor (about thirty) from its initial value, the reactions are terminated and the membrane is annealed at 700[degrees]C for about ten hours after which the nitrogen and hydrogen permeances are measured at several temperatures.
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Category :
Languages : en
Pages : 4
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Book Description
Project Objectives are to develop hydrogen-permselective ceramic membranes for water-gas shift membrane-reactor suitable for hydrogen production from coal gas and evaluate the technical and economic potential of the membrane-reactor. During the reporting period exploratory experiments begun on a membrane preparation technique aimed at providing higher membrane permeance. The new preparation technique involves two stages. The first stage is the formation of a layer of silica gel by a two-phase interfacial reaction within the pores of the substrate. The gel is then dried and calcined yielding a microporous (pore diameter below 10 Å) silica layer within the pores of the substrate tube. The second stage involves one-sided chemical vapor deposition using the SiCl4-H2O reaction to close up the micropores of the gel layer and produce the final hydrogen permselective membrane. Chemical reactions involved are described.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 4
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Book Description
Project Objectives are to develop hydrogen-permselective ceramic membranes for water-gas shift membrane-reactor suitable for hydrogen production from coal gas and evaluate the technical and economic potential of the membrane-reactor. During the reporting period exploratory experiments begun on a membrane preparation technique aimed at providing higher membrane permeance. The new preparation technique involves two stages. The first stage is the formation of a layer of silica gel by a two-phase interfacial reaction within the pores of the substrate. The gel is then dried and calcined yielding a microporous (pore diameter below 10 [Angstrom]) silica layer within the pores of the substrate tube. The second stage involves one-sided chemical vapor deposition using the SiCl[sub 4]-H[sub 2]O reaction to close up the micropores of the gel layer and produce the final hydrogen permselective membrane. Chemical reactions involved are described.
