Hydrothermally-Stable Silica Composite Membranes
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Solution Overview
Problem
Silica-based membranes for hydrogen separation are not hydrothermally stable, experiencing significant permeability loss when exposed to moisture at high temperatures due to densification of Si—O—Si bonds, leading to reduced selectivity and permeance.
Innovation Solution
The development of composite silica-based membranes with mixed elements like alumina and titania, deposited on graded mesoporous gamma-alumina substrates using a dual-element chemical vapor deposition technique, which provides a uniform surface and enhances hydrothermal stability while maintaining high selectivity and permeance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If pure silica membranes are used for hydrogen separation, then high selectivity is achieved, but hydrothermal stability deteriorates due to densification upon exposure to water vapor at elevated temperatures
Solution Approach 1:
The patent applies composite materials by combining silica with other inorganic oxides (alumina, titania, zirconia, magnesia) to create composite membranes that maintain the hydrogen separation selectivity of silica while improving hydrothermal stability. The composite structure prevents the densification that occurs in pure silica membranes when exposed to water vapor at elevated temperatures, thereby retaining permeability and achieving both high selectivity and stability.
2Reliability
If silica membranes are exposed to water vapor at high temperature, then hydrogen separation function is maintained, but permeability decreases due to pore shrinkage from Si-O-Si bond formation
Solution Approach 1:
The composite membrane structure with silica combined with other inorganic oxides prevents the harmful densification reaction (formation of Si-O-Si bonds leading to pore shrinkage) that occurs in pure silica membranes. This composite approach maintains both the hydrogen separation function and the permeance by stabilizing the pore structure against water vapor-induced densification at high temperatures.
3Stability of the object's composition
If sol-gel methods are used to prepare composite membranes with inorganic oxides, then hydrothermal stability improves, but selectivity decreases due to spaces between particles
Solution Approach 1:
The patent uses an intermediate mesoporous substrate as a mediator to support the composite membrane layer. This substrate provides a continuous, defect-free framework that eliminates the spaces between particles inherent in sol-gel methods. The composite membrane is deposited on this intermediate layer, achieving both high selectivity (by eliminating particle gaps) and hydrothermal stability (through the composite composition).
Solution Approach 2:
The patent replaces the sol-gel deposition method with chemical vapor deposition (CVD). This substitution creates a continuous, defect-free membrane layer without the particle spaces that characterize sol-gel membranes. The CVD process deposits the composite membrane material in a uniform, continuous manner, achieving both high selectivity and hydrothermal stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composite membranes exhibit improved hydrothermal stability, with H2 permeance stabilization after initial exposure to water vapor, and maintain high selectivity over CH4 and CO2, outperforming pure silica membranes in humid environments.
Implementation Method 1
The composite membrane comprises an overcoat of a silica-based composite placed on optional porous substrates deposited on a porous support. The invention also includes methods for preparing such composite membranes. composite membranes prepared by chemical vapor deposition (CVD)
Implementation Method 2
Membranes may be defined as thin, solid materials that permit the selective transport of certain chemical species over others. Silva membranes prepared by chemical vapor deposition (CVD) or sol-gel methods on mesoporous supports are effective for selective hydrogen permeation
Implementation Method 3
Silva membranes prepared by chemical vapor deposition (CVD) or sol-gel methods on mesoporous supports are effective for selective hydrogen permeation
Data Source
AI summary
Thin layers of a mixed composition are deposited on a porous substrate by chemical vapor deposition in an inert atmosphere at high temperature. The resulting membrane has excellent stability to water vapor at high temperatures. An exemplary membrane comprises an amorphous mixed-element surface layer comprising silica and at least one oxide of additional element, an optional porous substrate on which said surface layer is deposited, and a porous support on which said substrate or mixed-element surface layer is deposited, wherein the permeance of the membrane is higher than 1×10−7 mol m−2s−1Pa−1 and the selectivity of H2 over CO, CO2, and CH4 is larger than 100, and wherein the H2 permeance of the membrane after exposure to a stream containing 60 mol % water vapor at 673 K for 120 h is at least 50% of its initial H2 permeance.