Polyimide Blend Membranes for Gas Separation
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Solution Overview
Problem
Current polyimide membranes for gas separation face challenges in achieving high selectivity and permeability due to defects and delamination issues in thin film composite membranes, and difficulties in fabricating defect-free integrally skinned polyimide membranes.
Innovation Solution
Development of polyimide blend membranes comprising a miscible blend of aromatic polyimides with UV cross-linkable benzophenone functional groups, which are processed using phase inversion and UV cross-linking to create asymmetric integrally skinned or thin film composite membranes with improved selectivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If thin film composite membranes are used for gas separation, then permeability is improved, but selectivity deteriorates due to defects and delamination
Solution Approach 1:
The patent uses a composite structure combining polyimide blend (providing permeability) with porous support layer (providing mechanical strength and stability). This composite approach allows the membrane to achieve high permeability while maintaining structural integrity that prevents defects and delamination, thereby resolving the contradiction between permeability and selectivity.
Solution Approach 2:
The patent applies different properties to different layers: the thin polyimide blend skin layer provides high permeability for gas separation, while the thicker porous support layer provides mechanical strength and dimensional stability. This local differentiation of properties allows each layer to optimize its function without compromising the other, resolving the contradiction between permeability and structural reliability.
2Reliability
If integrally skinned polyimide membranes are fabricated, then selectivity is improved, but manufacturing difficulty increases due to shrinkage during casting
Solution Approach 1:
The patent modifies the polyimide composition by creating a blend with specific molecular weights and incorporating UV cross-linkable groups. This changes the material parameters to reduce shrinkage during casting while maintaining the ability to form integral skin structures. The UV cross-linking step further stabilizes the membrane structure, making fabrication more controllable and reliable.
Solution Approach 2:
The patent incorporates UV cross-linkable benzophenone groups into the polyimide structure before membrane formation. This preliminary chemical modification allows subsequent UV cross-linking to stabilize the membrane structure during or after casting, preventing shrinkage-related fabrication failures and enabling reliable production of integrally skinned membranes with high selectivity.
3Productivity
If membrane surface area is increased to improve separation capacity, then productivity is improved, but capital cost increases
Solution Approach 1:
The patent optimizes the polyimide blend composition and UV cross-linking parameters to achieve peak performance in permeability and selectivity. By maximizing the membrane's intrinsic separation capacity through optimized material parameters, the required membrane surface area is minimized, thereby reducing capital costs while maintaining high productivity.
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 polyimide blend membranes exhibit enhanced permeability and selectivity, with superior chemical and thermal stability, and are suitable for various gas separations such as H2/CH4, CO2/CH4, and O2/N2, reducing the need for large membrane surface areas and increasing purity of the product gas.
Implementation Method 1
Separation is based on a solution-diffusion mechanism. This mechanism involves molecular-scale interactions of the permeating gas with the membrane polymer. The mechanism assumes that in a membrane having two opposing surfaces, each component is sorbed by the membrane at one surface, transported by a gas concentration gradient, and desorbed at the opposing surface.
Implementation Method 2
The polyimide blend membranes in the present invention have UV cross-linkable benzophenone functional groups. The cross-linked polyimide blend membranes comprise polymer chain segments where at least part of these polymer chain segments are cross-linked to each other through possible direct covalent bonds by exposure to UV radiation.
Data Source
AI summary
The polyimide blend membrane in the present invention was prepared by blending a first aromatic polyimide with high permeability and a second aromatic polyimide with high selectivity for gas separation. The polyimide blend membrane in the present invention showed improved permeability compared to membranes made from the second aromatic polyimide and improved selectivity compared to membranes made from the first aromatic polyimide.