Carbon Molecular Sieve Membrane Pyrolysis Control
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Solution Overview
Problem
Current carbon molecular sieve (CMS) membranes face challenges in achieving an optimal balance between selectivity and permeability, particularly for gases with similar molecular sizes, and there is a need for improved methods to produce CMS membranes that address these limitations.
Innovation Solution
A method involving the use of polyimide precursor polymers, heated to a final pyrolysis temperature of 600° C. to 700° C. at a controlled heating rate of 3 to 7° C./minute in a non-oxidizing atmosphere, followed by accelerated cooling, to produce CMS membranes with enhanced selectivity and permeance for gas separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pyrolysis temperature and thermal soak time are increased to improve selectivity, then selectivity increases but permeability decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling pyrolysis temperature (600-700°C range), heating rate (3-7°C/minute), and thermal soak time (at most 60 minutes) to achieve optimal balance between selectivity and permeability. This systematic parameter optimization resolves the contradiction by finding the specific parameter window where both selectivity and permeability are maximized simultaneously.
Solution Approach 2:
The patent introduces dynamic control of the pyrolysis process through controlled heating rates and variable thermal soak times. The dynamic adjustment of temperature profile and residence time allows the membrane structure to develop optimally, achieving both high selectivity and maintained permeability that static high-temperature processing cannot achieve.
2Manufacturing precision
If a tightly packed precursor polymer structure is used to improve selectivity, then selectivity increases but permeability decreases
Solution Approach 1:
The patent changes the physical-chemical parameters of the precursor polymer by selecting polyimides with specific glass transition temperatures and molecular structures. This parameter selection enables the precursor to form an optimal carbon matrix structure during pyrolysis that provides both tight molecular sieving (high selectivity) and adequate gas transport pathways (high permeability).
3Reliability
If pyrolysis is performed in vacuum or inert atmosphere to improve membrane quality, then separation performance improves but process complexity increases
Solution Approach 1:
The patent employs an inert atmosphere (nitrogen or argon) during pyrolysis to prevent oxidation of the carbonizing polymer and ensure consistent membrane quality. This approach maintains high separation performance while simplifying the process compared to vacuum pyrolysis, as inert gas flow is easier to control and maintain than high vacuum conditions.
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 results in CMS membranes with improved selectivity and permeance, specifically for gases like ethylene/ethane and propylene/propane, while maintaining stability over time, making it suitable for separating gases with similar molecular sizes and in natural gas feeds.
Implementation Method 1
heating, in a furnace, said polyimide precursor polymer to a final pyrolysis temperature of 600° C. to 700° C. at a pyrolysis heating rate of 3 to 7° C./minute from 400° C. to the final pyrolysis temperature
Implementation Method 2
Gas transport through such membranes is commonly modeled by the sorption-diffusion mechanism
Implementation Method 3
CMS membranes have been shown to have attractive separation performance properties exceeding that of polymeric membranes
Data Source
AI summary
The invention is an improved method of making a carbon molecular sieve (CMS) membrane in which a polyimide precursor polymer is pyrolyzed to form a carbon molecular sieve membrane by heating, in a furnace, said polyimide precursor polymer to a final pyrolysis temperature of 600 C to 700 C at a pyrolysis heating rate of 3 to 7 C/minute from 400 C to the final pyrolysis temperature, the final pyrolysis temperature being held for a pyrolysis time of at most 60 minutes in a non-oxidizing atmosphere. In a particular embodiment, the cooling rate from the pyrolysis temperature is accelerated by methods to remove heat. The CMS membranes have shown an improved combination of selectivity and permeance as well as being particularly suitable to separate gases in gas streams such methane from natural gas, oxygen from air and ethylene or propylene from light hydrocarbon streams.