Bulky Diamine Polyimide Membrane Permeance Retention
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Solution Overview
Problem
Existing crosslinked polyimide membranes experience significant loss in permeance, typically around 50% to 70%, during the transesterification process, which compromises their separation efficiency for gas mixtures like CO2 and CH4.
Innovation Solution
A high molecular weight, monoesterified polyimide polymer is developed using a small amount of bulky diamine, which is then crosslinked to maintain permeance and selectivity, with the bulky diamine inhibiting segmental motion and increasing the glass transition temperature, thereby reducing permeance loss during crosslinking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If crosslinked polyimide membranes are made using conventional methods, then selectivity is improved, but permeance drops significantly (50-70% loss)
Solution Approach 1:
The patent changes the chemical structure parameter by incorporating bulky diamine groups (such as 2,2'-bis(trifluoromethyl)benzidine) into the polyimide polymer at specific molar ratios (0.5-10 mol%). This structural modification alters the polymer's physical properties, specifically increasing the glass transition temperature and reducing segmental motion, which in turn minimizes permeance loss during crosslinking while maintaining selectivity.
Solution Approach 2:
The patent creates a composite polymer structure by combining conventional diamine monomers with bulky diamine monomers in a controlled ratio. This composite approach allows the bulky diamine components to provide structural rigidity and inhibit unwanted segmental motion, while the overall polymer matrix maintains its gas separation capabilities, achieving both selectivity and preserved permeance.
2Strength
If transesterification conditions are applied to create covalent ester crosslinks, then membrane strength is improved, but permeance loss increases (50-70% drop)
Solution Approach 1:
The patent modifies the polymer's glass transition temperature parameter by incorporating bulky diamine groups, which restrict segmental motion. This parameter change ensures that the polymer remains structurally stable during transesterification crosslinking, allowing crosslinks to form without causing excessive collapse of the polymer matrix and associated permeance loss.
Solution Approach 2:
The bulky diamine groups are incorporated into the polymer structure beforehand to provide pre-cushioning against the effects of crosslinking. These groups act as internal spacers that prevent excessive chain collapse during the crosslinking process, thereby cushioning the permeance against the harsh effects of transesterification conditions.
3Quantity of substance
If bulky diamine is added to inhibit segmental motion, then permeance loss is reduced, but polymer complexity increases
Solution Approach 1:
The patent uses parameter changes by controlling the molar ratio of bulky diamine to total diamine monomers within a specific range (0.5-10 mol%). This quantitative control optimizes the balance between achieving sufficient segmental motion inhibition (for permeance retention) and avoiding excessive structural complexity that would complicate synthesis and processing.
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 crosslinked membranes with minimal permeance loss (less than 10%) and retained selectivity, achieving CO2 permeance of at least 20 GPU and CO2/CH4 selectivity greater than 20, even after crosslinking, compared to membranes made without bulky diamines.
Implementation Method 1
the bulky diamine inhibiting segmental motion and increasing the glass transition temperature
Implementation Method 2
transesterifying the crosslinkable polyimide polymer within the fibers. More specifically, the crosslinkable polyimide polymer can be formed into crosslinkable fibers, which are then subjected to transesterification conditions to create covalent ester crosslinks
Implementation Method 3
crosslinked hollow fiber membranes have good selectivity... useful for the separation of fluid mixtures
Data Source
AI summary
One method as described herein relates to making a high molecular weight, monoesterified polyimide polymer using a small amount of bulky diamine. These high molecular weight, monoesterified polyimide polymers are useful in forming crosslinked polymer membranes with high permeance that are useful for the separation of fluid mixtures. Another method as described herein relates to making the crosslinked membranes from the high molecular weight, monoesterified polyimide polymer containing a small amount of bulky diamine. The small amount of bulky diamine allows for formation of both the high molecular weight polyimide polymer and for covalent ester crosslinks via reaction of the carboxylic acid groups with a diol crosslinking agent. This small amount of bulky diamines reduces chain mobility or segmental motion during crosslinking and reduces large loss of permeance. As such, this method provides a crosslinked membrane with good permeance and selectivity.