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 productivity in industrial gas separations.
Innovation Solution
Incorporating transition metal cations into the polyimide hollow fiber membranes through complexation with electronegative regions, which inhibits the densification of the membrane structure during pyrolysis, thereby preventing the aging effect and maintaining high permeance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional polyimide hollow fiber membranes are used as precursors for CMS membranes, then high permeance can be achieved initially, but severe aging behavior occurs leading to significant reduction in gas permeance over time
Solution Approach 1:
Metal cations serve as intermediary agents that complex with electronegative regions of the polyimide chains, acting as cross-linking bridges that prevent physical aging densification. These metal cations are introduced into the hollow fiber membrane during the spinning process and remain as structural stabilizers throughout the membrane lifecycle.
Solution Approach 2:
The invention creates a composite structure by combining polyimide matrix with metal cation cross-links. This composite approach modifies the physical aging behavior of the pure polyimide, resulting in a stabilized precursor membrane that maintains its free volume and permeance characteristics over time.
2Measurement precision
If the thin separating layer is made denser to improve selectivity, then gas separation performance improves, but permeance decreases due to reduced free volume
Solution Approach 1:
The invention changes the physical state and structural parameters of the membrane by introducing metal cation cross-links, which modify the density and free volume distribution. This allows the membrane to maintain a dense enough structure for high selectivity while preserving sufficient free volume for high permeance through the cross-linking effect.
3Productivity
If the separating layer is made thinner to increase productivity per unit volume, then module productivity improves, but aging-induced densification occurs more rapidly
Solution Approach 1:
The metal cation cross-linking is performed in advance during the membrane spinning process, creating a pre-stabilized structure before the membrane is put into service. This preliminary action prevents subsequent aging densification, allowing thin membranes to maintain their performance throughout their operational lifespan.
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 immobilization of metal cations within the membrane structure prevents the reduction in free volume and separation layer densification, effectively inhibiting the aging effect and maintaining high permeance over time, thus enhancing the stability and performance of carbon molecular sieve membranes.
Implementation Method 1
cations of a transition metal being dissolved in the bore fluid... the transition metal cations diffuse into the hollow and complex with electronegative regions of the polyimide
Implementation Method 2
The extruded core spin dope composition is allowed to traverse an air or inert gas gap to produce a nascent hollow fiber. 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
Implementation Method 4
the transition metal cations diffuse into the hollow and complex with electronegative regions of the polyimide
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 bore fluid used to extrude the fibers, either a salt of the transition metal and an inorganic anion or a transition metal/organic ligand complex.