Crosslinked Thermally Rearranged Poly(benzoxazole-co-imide) Membrane for CO2/CH4 Separation
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Solution Overview
Problem
Conventional polybenzoxazole membranes for gas separation have limitations in carbon dioxide/methane selectivity and permeability, and existing methods for preparing these membranes do not adequately consider variations in free volume and gas separation quality due to different imidization methods of hydroxypolyimide precursors.
Innovation Solution
A crosslinked thermally rearranged poly(benzoxazole-co-imide) membrane is developed through a multi-step process involving azeotropic thermal imidization, transesterification crosslinking, and thermal rearrangement, using specific chemical formulas and reactants to enhance gas permeability and selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional solvent casting process is used to prepare polybenzoxazole membrane, then membrane preparation is simple and practical, but carbon dioxide permeability is 10-100 times lower than thermal rearrangement process
Solution Approach 1:
The invention changes the preparation method from solvent casting to thermal rearrangement process, transforming the chemical structure of the membrane to achieve dramatically higher CO2 permeability while maintaining practical manufacturability through controlled thermal processing
Solution Approach 2:
The invention utilizes thermal rearrangement phase transition of polyimide to polybenzoxazole structure through controlled heating, which fundamentally alters the membrane's free volume and chain packing to enhance gas permeability
2Reliability
If poly(styrenesulfonic acid) is added to improve CO2/CH4 selectivity, then selectivity improves by at most about 95%, but there is no disclosure about preparation method of polyimide precursor and variations in free volume factor are not considered
Solution Approach 1:
The invention performs preliminary action by systematically optimizing the polyimide precursor preparation method and crosslinking conditions before thermal rearrangement, ensuring controlled free volume development and consistent membrane quality without requiring poly(styrenesulfonic acid) additives
Solution Approach 2:
The invention changes key parameters including imidization method, crosslinking temperature, and thermal rearrangement conditions to achieve high selectivity through controlled free volume development in the membrane structure
3Quantity of substance
If rigid ladder-shaped structure is used to improve gas permeability, then diffusibility and adsorbability to small gas molecules are improved, but efficient packing in polymer chain space increases reducing mass transferability
Solution Approach 1:
The invention utilizes thermal rearrangement phase transition that transforms the rigid ladder-shaped polyimide structure into polybenzoxazole, fundamentally altering chain packing and free volume distribution to simultaneously achieve high permeability and maintained mass transferability
Solution Approach 2:
The invention changes the molecular structure through thermal rearrangement, transforming the rigid ladder structure into a new configuration with optimized free volume that enhances gas permeability while preventing excessive chain packing
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 resulting membrane exhibits improved gas separation quality, exceeding the 2008 upper bound in CO2/CH4 separation with increased permeability and selectivity, and is suitable for flue gas separation applications.
Implementation Method 1
thermal rearrangement of polyimide having a hydroxyl group at the ortho position thereof provides a carbon dioxide permeability 10-100 times higher
Implementation Method 2
gas separation based on the use of a membrane has been spotlighted as separation technology growing rapidly
Implementation Method 3
polymers having a high degree of free volume and known as microporous organic polymers have improved diffusibility in addition to adsorbability to small gas molecules
Implementation Method 4
crosslinked thermally rearranged poly(benzoxazole-co-imide) obtained by transesterification crosslinking between an ortho-hydroxy polyimide copolymer and a diol compound
Data Source
AI summary
Provided is a method for preparing a membrane for flue gas separation including a crosslinked thermally rearranged poly(benzoxazole-co-imide) through the transesterification crosslinking of an ortho-hydroxy polyimide copolymer and a diol compound, followed by thermal rearrangement. The membrane for flue gas separation including the crosslinked thermally rearranged poly(benzoxazole-co-imide) has excellent gas permeability and selectivity, and particularly provides gas separation quality corresponding to a level exceeding the so-called 2008 upper bound in terms of carbon dioxide/methane separation.