Polyimide Gas Separation Membrane Resisting Densification
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Solution Overview
Problem
Existing gas separation membranes face a trade-off between gas permeability and selectivity, and impurities like benzene, toluene, and xylene cause membrane plasticization or densification, leading to impaired performance when processing gases with low impurity content over time.
Innovation Solution
A gas separation membrane with a polyimide compound containing specific repeating units, including fluorine-substituted alkyl and acyl groups, is designed to maintain high permeability and selectivity, even when treating gases with low impurities, by using a composite structure with a gas-permeable support layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a gas separation membrane uses conventional polyimide compounds, then gas permeability can be improved, but gas separation selectivity deteriorates
Solution Approach 1:
The patent modifies the chemical structure of polyimide compounds by introducing specific repeating units with fluorine-substituted alkyl groups and acyl groups at defined positions. This structural parameter change enables simultaneous achievement of high gas permeability and high gas separation selectivity, resolving the trade-off between these two properties that plagues conventional polyimide membranes.
Solution Approach 2:
The patent creates a composite membrane structure consisting of a gas separation layer made from the modified polyimide compound and a support layer. This composite structure allows the gas separation layer to be made thin for high permeability while the support layer provides mechanical strength, achieving both high gas permeability and maintained selectivity.
2Reliability
If a gas separation membrane processes mixed gases with low impurity content over time, then stable operation is required, but membrane densification occurs causing gas permeability to deteriorate
Solution Approach 1:
The patent introduces specific repeating units with fluorine-substituted alkyl groups and acyl groups into the polyimide structure before membrane formation. These pre-introduced structural features prevent membrane densification from occurring during long-term operation with low-impurity gases, thereby maintaining stable gas permeability over time and preventing the deterioration that would otherwise occur.
Solution Approach 2:
By changing the chemical composition parameters of the polyimide compound to include specific repeating units (where R represents fluorine-substituted alkyl groups and L2 represents acyl groups), the patent fundamentally alters the membrane's resistance to densification, enabling long-term stable operation without gas permeability loss.
3Productivity
If the gas separation layer is made thin to achieve high gas permeability, then productivity improves, but mechanical strength deteriorates
Solution Approach 1:
The patent divides the membrane into two functional segments: a thin gas separation layer for high permeability and a separate support layer for mechanical strength. This segmentation allows each layer to be optimized independently, with the gas separation layer being thin enough for high productivity while the support layer provides the necessary mechanical integrity.
Solution Approach 2:
The patent employs a composite membrane structure where a gas separation layer made from modified polyimide is combined with a support layer. This composite construction enables the gas separation layer to be made thin for high gas permeability while the support layer compensates for the reduced mechanical strength, achieving both high productivity and adequate strength.
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 membrane achieves stable high permeability and selectivity for carbon dioxide in mixed gases with low impurities, preventing membrane densification and maintaining performance over extended periods.
Implementation Method 1
Materials made of polymer compounds have gas permeability specific to each material. Due to this nature, selective permeation and separation of a gas component of interest can be achieved by using a membrane formed of a specific polymer compound.
Data Source
AI summary
Provided are a polyimide compound including a repeating unit having an aromatic diamine component having a specific structure in which a side-chain benzylic position is regioselectively brominated, a gas separation membrane having a gas separation layer containing the polyimide compound, and a gas separation module and a gas separation apparatus each having the gas separation membrane.