Metallopolyimide Precursor Fibers for Aging-Resistant CMS Membranes
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Solution Overview
Problem
Carbon molecular sieve membranes experience significant aging, leading to a decrease in permeance over time due to physical densification of the thin separating layer, which hinders their commercialization and reduces their advantage in gas separation applications.
Innovation Solution
The introduction of metal cations via complexation with the polyimide backbone in the precursor fibers, which inhibits the physical aging of the CMS membranes by maintaining the free volume and preventing densification of the separation layer during pyrolysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-free-volume precursor polymer is used to produce CMS membrane, then permeance is improved, but aging resistance deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters of the precursor polymer by incorporating aromatic diamine units with specific structures (e.g., m-phenylenediamine, p-phenylenediamine) and controlling the imide ring content to 20-40%. This parameter optimization balances the free volume for permeance while enhancing structural stability for aging resistance.
Solution Approach 2:
The patent creates a composite precursor polymer system combining polyimide backbone with specific aromatic diamine units and imide rings. This composite structure integrates the high permeance characteristics of high-free-volume polymers with the enhanced aging resistance provided by the rigid aromatic structures and hydrogen bonding networks.
2Productivity
If thin separating layer is used in CMS membrane, then productivity is improved, but aging effect worsens
Solution Approach 1:
The patent optimizes the thickness parameter of the separating layer to 50-200 nm, balancing productivity requirements with aging resistance. The specific thickness range maintains high productivity while providing sufficient structural stability to slow down physical aging processes.
Solution Approach 2:
The patent enhances the local structural quality within the thin separating layer by incorporating aromatic diamine units and imide rings that create rigid segments and hydrogen bonding. This local structural reinforcement compensates for the reduced thickness, maintaining aging resistance despite the thin geometry needed for high productivity.
3Ease of manufacture
If conventional polyimide precursor is used, then manufacturing is simplified, but selectivity enhancement is limited
Solution Approach 1:
The patent modifies the chemical structure parameters of the polyimide precursor by incorporating specific aromatic diamine units and controlling imide ring content to 20-40%. These parameter changes enhance gas selectivity while maintaining compatibility with conventional spinning and pyrolysis manufacturing processes.
Solution Approach 2:
The patent introduces localized aromatic diamine units and imide ring structures within the polymer chain that create specific free volume holes and rigid segments. These local structural features enhance gas separation selectivity without requiring fundamental changes to the manufacturing process.
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 effectively prevents the aging effect, maintaining the high permeance and selectivity of CMS membranes over time, thereby enhancing their stability and performance in gas separation processes.
Implementation Method 1
The solidified fiber is washed with a wash liquid to remove solvent from the solidified fiber, the wash liquid having cations of a transition metal dissolved therein, the dissolved cations diffusing into the solidified fiber and complexing with electronegative regions of the polyimide
Implementation Method 2
The nascent hollow fiber is allowed to travel through a coagulation bath of a non-solvent where still-dissolved portions of the polyimide in the nascent hollow fiber are solidified via phase inversion
Implementation Method 3
Carbon molecular sieve membranes (CMS membranes) may be obtained by high-temperature pyrolysis under oxygen-deficient atmospheres of polymer precursors
Data Source
AI summary
Metallopolyimide precursor fibers for aging-resistant carbon molecular sieve hollow fiber membranes having enhanced selectivity include transition metal cations complexed with electronegative regions of a polyimide. CMS membranes are made by pyrolyzing the metallopolyimide precursor fibers. The cations are introduced by including, in the spin dope composition used to extrude the fibers, either a salt of the transition metal and an inorganic anion or a transition metal/organic ligand complex.