Proton Conducting Ceramic Membrane for CO2-Stable Dehydrogenation
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Solution Overview
Problem
Existing proton conducting ceramic membranes face challenges such as fragility, poor hydrogen selectivity, high cost, and instability in the presence of carbon-containing gases, limiting their effectiveness in dehydrogenation reactions like alkane to alkene transformation and steam reforming.
Innovation Solution
A proton conducting ceramic membrane is developed using a combination of rare-earth tungstates and mixed metal oxides, specifically a mixture of rare-earth tungstates and doped lanthanum chromates or spinel mixed metal oxides, which enhances ambipolar conductivity and stability, allowing for increased hydrogen permeation and resistance to carbon dioxide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Ba- and Sr-based perovskite ceramic membranes are used for proton conduction, then proton conducting capability is achieved, but stability deteriorates due to reaction with CO2, H2S, SO2, SO3, and H2O forming carbonates, sulphates, and hydroxides
Solution Approach 1:
The patent changes the chemical composition parameters by replacing Ba/Sr perovskites with rare-earth tungstates (Ln6-xWO12-δ) that have different chemical properties. These tungstates maintain proton conducting capability while being stable in CO2 and acidic gas environments, preventing the formation of carbonates and hydroxides that plague perovskite membranes.
Solution Approach 2:
The patent creates a composite membrane structure combining rare-earth tungstate (proton conductor) with mixed metal oxide (electronic conductor). This composite approach allows the membrane to achieve both high proton conductivity and chemical stability, with the tungstate providing proton transport and the mixed metal oxide providing electronic conduction and structural stability.
2Ease of manufacture
If microporous membranes are used for hydrogen separation, then membrane formation is simplified, but hydrogen selectivity deteriorates and mechanical strength decreases
Solution Approach 1:
The patent employs a dense ceramic membrane structure rather than microporous membranes. The rare-earth tungstate membrane provides inherent hydrogen selectivity through its proton conducting mechanism, where hydrogen is transported as protons through the crystal lattice. This dense structure eliminates the fragility and poor selectivity issues of microporous membranes while maintaining manufacturability through conventional ceramic processing.
3Reliability
If Pd-Ag composite membranes are used for hydrogen permeation, then hydrogen selectivity is improved, but cost increases due to expensive metal content
Solution Approach 1:
The patent replaces expensive Pd-Ag metal membranes with a cost-effective ceramic membrane made from rare-earth tungstate and mixed metal oxide. The ceramic material provides comparable hydrogen selectivity through proton conduction mechanisms while being significantly cheaper and more stable in carbon-containing gas environments, eliminating the need for expensive precious metals.
4Productivity
If hydrogen permeation is increased through membrane thinning, then productivity improves, but mechanical strength and stability deteriorate
Solution Approach 1:
The patent optimizes the membrane thickness parameter to achieve high hydrogen permeation flux while maintaining mechanical integrity. The rare-earth tungstate membrane is formulated with appropriate thickness (typically 1-10 micrometers) and compositional parameters that balance proton conductivity with mechanical strength, allowing high productivity without sacrificing 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 membrane achieves up to 5-fold increase in hydrogen permeation flux and maintains stability in CO2-rich environments, enabling efficient dehydrogenation reactions and steam reforming with improved selectivity and durability.
Implementation Method 1
proton conducting ceramic membrane which can be used to enable dehydrogenation reactions... Ceramic materials selected from a group of rare-earth tungstates... have been known to have proton conducting properties... The membrane achieves up to 5-fold increase in hydrogen permeation flux
Implementation Method 2
hydrogen selective membrane in the process stream should therefore increase the yield considerably. The removal of hydrogen can be achieved using hydrogen permeable membranes... allowing for increased hydrogen permeation
Implementation Method 3
these types of ceramic membranes comprise at least two layers, each comprising a different tungstate material... exhibit mixed proton and electron conductivity (n-type conductivity) in reducing atmospheres and mixed proton and electron hole conductivity (p-type conductivity) under oxidizing conditions... enhances ambipolar conductivity
Implementation Method 4
Mixed metal tungstates offers an ideal solution to this problem. These materials are stable in the presence of carbon dioxide and acidic gases in general making them usable in the presence of air... maintains stability in CO2-rich environments
Data Source
AI summary
A proton conducting ceramic membrane comprising a conducting layer, wherein said conducting layer comprises a mixture of a rare-earth tungstate as herein defined and a mixed metal oxide as herein defined. The invention also relates to a reactor comprising said membrane and the use of said membrane in a dehydrogenation process.