Self-Cross-Linked Polyimide Membranes for Gas Separation
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Solution Overview
Problem
Current polymeric membrane materials for gas separation face limitations in combining high selectivity and permeability with thermal and hydrolytic stability, particularly due to issues like plasticization and difficulty in controlling cross-linking in thin selective layers, which affects their performance in separating gases such as CO2/CH4 and H2/CH4.
Innovation Solution
Development of self-cross-linkable and self-cross-linked aromatic polyimide membranes with both hydroxyl and carboxylic acid functional groups that can form covalent ester bonds upon heating, allowing for the creation of membranes with improved mechanical stability and resistance to hydrocarbons, while maintaining high selectivity and permeability for gas separation applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymeric membranes are used for gas separation, then selectivity and permeability can be achieved, but thermal and hydrolytic stability deteriorates due to plasticization and lack of cross-linking control
Solution Approach 1:
The polyimide polymer contains both hydroxyl and carboxylic acid functional groups that automatically react with each other upon heating to form covalent ester cross-links. This self-cross-linking mechanism eliminates the need for external cross-linking agents or complex multi-step processes, while providing controlled thermal stability and resistance to plasticization by condensable gases.
Solution Approach 2:
The invention creates a composite structure within the polyimide membrane by forming ester cross-links between functional groups of the same polymer chains. This internal cross-linked network combines the gas separation capabilities of polyimide with enhanced thermal and hydrolytic stability, effectively creating a composite material system that addresses both selectivity and stability requirements.
2Strength
If cross-linking is applied to improve membrane stability, then thermal and mechanical properties improve, but control of cross-linking in thin selective layers becomes difficult
Solution Approach 1:
The polyimide polymer contains both hydroxyl and carboxylic acid functional groups that automatically react with each other upon heating to form covalent ester cross-links. This self-cross-linking mechanism eliminates the need for external cross-linking agents or complex multi-step processes, while providing controlled thermal stability and resistance to plasticization by condensable gases.
Solution Approach 2:
The cross-linking process is controlled by changing the temperature parameter. Upon heating to appropriate temperatures, the hydroxyl and carboxylic acid groups react to form ester cross-links. This temperature-controlled mechanism provides precise control over cross-linking in thin selective layers, avoiding the difficulties associated with chemical cross-linking agents.
3Manufacturing precision
If asymmetric integrally skinned polyimide membranes are fabricated, then selectivity can be improved, but fabrication becomes difficult due to high shrinkage during casting and drying
Solution Approach 1:
The self-cross-linking reaction is performed preliminarily during the membrane fabrication process itself, rather than as a separate post-treatment step. The hydroxyl and carboxylic acid groups react to form ester cross-links during casting and drying, pre-establishing the cross-linked structure before the membrane is put into service. This preliminary cross-linking compensates for shrinkage and facilitates successful fabrication of asymmetric integrally skinned membranes.
Solution Approach 2:
The cross-linking process is controlled by changing the temperature parameter. Upon heating to appropriate temperatures, the hydroxyl and carboxylic acid groups react to form ester cross-links. This temperature-controlled mechanism provides precise control over cross-linking in thin selective layers, avoiding the difficulties associated with chemical cross-linking agents.
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 self-cross-linked aromatic polyimide membranes exhibit enhanced CO2/CH4, H2/CH4, and He/CH4 separation performance, with specific examples showing high permeance and selectivity, and demonstrate resistance to hydrocarbons and high CO2 concentrations, addressing the productivity-selectivity trade-off and stability issues of existing membranes.
Implementation Method 1
The self-cross-linkable aromatic polyimide polymer comprises both hydroxyl functional groups and carboxylic acid functional groups wherein the carboxylic acid functional groups can react with the hydroxyl functional groups via heating to form a cross-linked polyimide polymer
Implementation Method 2
Separation is based on a solution-diffusion mechanism. This mechanism involves molecular-scale interactions of the permeating gas with the membrane polymer
Data Source
AI summary
This invention relates to self-cross-linkable and self-cross-linked aromatic polyimide polymers, their membranes and methods for making and using these polymers and membranes. The self-cross-linkable aromatic polyimide polymer described in the present invention comprises both hydroxyl functional groups and carboxylic acid functional groups. The self-cross-linked aromatic polyimide was formed via heating the self-cross-linkable aromatic polyimide polymer at ≦300° C. The self-cross-linked aromatic polyimide membranes exhibit high selectivity in separation of mixtures of gases and liquids.