Carbon Molecular Sieve Membrane Conditioning for Gas Separation
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Solution Overview
Problem
Carbon molecular sieve (CMS) membranes suffer from reduced permeance and selectivity over time due to aging, and existing methods do not effectively optimize selectivity and permeance for specific gas molecules while maintaining stability during storage and use.
Innovation Solution
A method involving the pyrolysis of precursor polymers to form CMS membranes, followed by exposure to a conditioning atmosphere comprising a target permeate gas molecule, which improves selectivity and permeance, and enhances the stability of the membranes by maintaining permeance and selectivity over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CMS membranes are used for gas separation, then separation performance exceeds polymeric membranes, but permeance and selectivity decrease over time due to aging
Solution Approach 1:
The patent applies preliminary action by exposing the CMS membrane to a conditioning atmosphere (such as CO2, CH4, or H2) during the manufacturing process, specifically during pyrolysis or cooling stages. This pre-conditioning stabilizes the membrane structure before actual use, preventing subsequent performance degradation during storage and operation. The conditioning gas interacts with the membrane pores to establish a stable configuration that resists aging effects.
2Manufacturing precision
If pyrolysis temperature and thermal soak time are increased, then selectivity improves, but permeance decreases
Solution Approach 1:
The patent applies parameter changes by introducing the conditioning atmosphere parameter during pyrolysis or cooling. This additional parameter allows optimization of membrane performance independent of pyrolysis temperature and soak time. By controlling the conditioning gas exposure, the patent can achieve high selectivity without necessarily requiring extreme pyrolysis conditions that would overly reduce permeance.
3Manufacturing precision
If a rigid, tightly packed precursor polymer structure is used, then CMS membrane selectivity increases, but permeance is reduced
Solution Approach 1:
The patent applies preliminary action by exposing the membrane to conditioning atmosphere during or after formation. This pre-conditioning step allows the membrane to achieve optimal pore configuration and gas interaction characteristics before actual separation service. The conditioning process stabilizes the rigid structure to maintain selectivity while improving permeance by establishing favorable gas-membrane interactions in advance.
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 method achieves improved selectivity and permeance for similar-sized gas molecules, such as ethylene/ethane and propylene/propane, while maintaining stability, resulting in CMS membranes that retain performance over extended periods.
Implementation Method 1
heating said precursor polymer to a temperature where the precursor polymer undergoes pyrolysis to form the carbon molecular sieve membrane
Implementation Method 2
Gas transport through such membranes is commonly modeled by the sorption-diffusion mechanism
Implementation Method 3
Gas transport through such membranes is commonly modeled by the sorption-diffusion mechanism
Data Source
AI summary
The invention is an improved method of making a carbon molecular sieve (CMS) membrane in which a precursor polymer is pyrolyzed to form a carbon molecular sieve membrane that is then exposed to a conditioning atmosphere comprised of a target permeate gas molecule such as ethylene when the membrane is desired to separate it from a light hydrocarbon gas stream. The exposure to the ethylene desirably occurs prior to the CMS permeance and selectivity combination substantially changing (e.g., within 5 days) of cooling from the pyrolyzing temperature. The CMS membranes have shown an improved combination of selectivity and permeance as well as stability and are useful to separate gases in gas streams such methane from natural gas, oxygen from air and ethylene or propylene from light hydrocarbon streams.