UV Cross-Linked Polyimide Membrane for CO2 Separation
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Solution Overview
Problem
Current polymeric gas separation membranes, such as cellulose acetate and polyimide membranes, face limitations in selectivity, permeability, and stability, making them inefficient for high-performance gas separations like CO2/CH4 and H2/CH4, due to defects and porosity in the selective skin layer.
Innovation Solution
Development of new polyimide membranes with high permeances and selectivities, specifically poly(3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride-2,4,6-trimethyl-m-phenylenediamine) and poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-pyromellitic dianhydride-2,4,6-trimethyl-m-phenylenediamine) polyimides, which are fabricated using specific dianhydrides and diamines, and undergo UV cross-linking to enhance selectivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional polymeric membranes (cellulose acetate, polyimide) are used, then low cost and ease of manufacture are achieved, but selectivity and permeability are limited due to defects and porosity in the selective skin layer
Solution Approach 1:
The patent uses composite materials by combining glassy polymer matrix with rigid rod polymer segments to create a hybrid structure that leverages the advantages of both material types, achieving high selectivity and permeability simultaneously
Solution Approach 2:
The patent changes the chemical structure parameters of the polymer by incorporating rigid rod segments with specific molecular configurations (e.g., -C6H4-C≡C-C6H4- units) to fundamentally alter the membrane's separation properties
2Reliability
If glassy polymers with stiff backbones are used, then selectivity for small molecules (H2, He) over large molecules (hydrocarbons) is improved, but permeability decreases
Solution Approach 1:
The patent applies local quality by creating regions with different polymer chain densities and mobilities within the membrane structure, where rigid rod segments create localized free volume that enhances permeability without compromising overall selectivity
Solution Approach 2:
The patent utilizes porous materials by creating a membrane structure with controlled free volume and nanoscale voids that facilitate gas transport while maintaining selective barriers through the rigid rod polymer architecture
3Productivity
If high performance polymers (polyimides, polytriazole) are used to improve selectivity and permeability, then gas separation performance is enhanced, but thermal and chemical stability deteriorate
Solution Approach 1:
The patent employs aromatic rings and triple bonds that create inherently stable, rigid structures resistant to thermal degradation and chemical attack, ensuring long-term membrane durability
Solution Approach 2:
The patent applies local quality by creating regions with different polymer chain densities and mobilities within the membrane structure, where rigid rod segments create localized free volume that enhances permeability without compromising overall selectivity
4Productivity
If asymmetric polymeric membranes with thin nonporous selective skin layer are used, then separation efficiency is improved, but manufacturing complexity increases due to defect-prone skin layer formation
Solution Approach 1:
The patent applies preliminary action by pre-organizing the polymer chains into rigid rod configurations during synthesis, which facilitates spontaneous formation of a defect-free selective skin layer during membrane fabrication without requiring complex post-processing
Solution Approach 2:
The patent changes the chemical structure parameters of the polymer by incorporating rigid rod segments with specific molecular configurations (e.g., -C6H4-C≡C-C6H4- units) to fundamentally alter the membrane's separation properties
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 new polyimide membranes exhibit improved CO2 and H2 permeability and selectivity, with CO2 permeability of at least 50 Barrers and single-gas CO2/CH4 selectivity of 15 at 50°C, reducing the need for large membrane areas and enhancing purity and durability for gas separation applications.
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
undergo UV cross-linking to enhance selectivity and stability
Data Source
AI summary
The present invention discloses a new type of polyimide membrane with high permeances and high selectivities for gas separations and particularly for CO2/CH4 and H2/CH4 separations. The polyimide membranes have CO2 permeability of 50 Barrers or higher and single-gas selectivity for CO2/CH4 of 15 or higher at 50° C. under 791 kPa for CO2/CH4 separation. The polyimide membranes have UV cross-linkable functional groups and can be used for the preparation of UV cross-linked polyimide membranes having CO2 permeability of 20 Barrers or higher and single-gas selectivity for CO2/CH4 of 35 or higher at 50° C. under 791 kPa for CO2/CH4 separation.