Crosslinked Polyimide Membranes for High-Polarity Solvent Separation
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Solution Overview
Problem
Conventional membrane separation processes using PTFE, ceramic, or glass fiber membranes have poor processability and are limited to microfiltration, lacking resistance to high-polarity solvents for applications in pervaporation (PV) and vapor permeation (VP).
Innovation Solution
A polyimide composition comprising a dissolvable polyimide, a crosslinking agent, and a solvent is used to create a separation membrane with good solvent resistance and processability, achieved through a crosslinking process and dry phase inversion, allowing the membrane to be coated on a substrate and used in PV and VP processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PTFE, ceramic, or glass fiber membranes are used for membrane separation, then good resistance to high-polarity solvents is achieved, but poor processability and limitation to microfiltration only occur
Solution Approach 1:
The patent uses a composite material system consisting of polyimide polymer matrix combined with specific crosslinking agents (such as hexamethylene diisocyanate or trimethylolpropane trimethacrylate). This composite approach creates a membrane that combines the solvent resistance of crosslinked structures with the processability of polymer materials, resolving the contradiction between reliability and ease of manufacture.
Solution Approach 2:
The patent employs parameter changes by controlling the crosslinking degree and membrane formation conditions (such as casting parameters and thermal treatment). By adjusting these parameters, the membrane achieves both good solvent resistance and improved processability, including the ability to be formed into various configurations and used in different separation modes beyond just microfiltration.
2Reliability
If PTFE, ceramic, or glass fiber membranes are used for membrane separation, then good resistance to high-polarity solvents is achieved, but limitation to microfiltration only occurs
Solution Approach 1:
The polyimide-crosslinking agent composite system enables the membrane to be adapted for multiple separation applications. The crosslinked polyimide structure maintains solvent resistance while allowing the membrane to be used in microfiltration, ultrafiltration, reverse osmosis, and other separation modes, thus expanding adaptability without sacrificing reliability.
Solution Approach 2:
By changing parameters such as membrane thickness, pore size, and crosslinking density, the same polyimide-based membrane material can be optimized for different separation applications. This enables versatility across multiple separation technologies while maintaining good resistance to high-polarity solvents.
3Reliability
If crosslinking process is performed on polyimide composition, then good resistance to high-polarity solvents is achieved, but increased manufacturing complexity occurs
Solution Approach 1:
The crosslinking agent is pre-mixed with the polyimide solution before membrane casting. This preliminary action ensures uniform distribution of the crosslinking agent throughout the membrane matrix, so that when crosslinking occurs during or after membrane formation, it proceeds uniformly without requiring complex multi-step processing, thus reducing manufacturing complexity while achieving good solvent resistance.
Solution Approach 2:
The crosslinking agent acts as an intermediary that bridges the polyimide chains to form a crosslinked network. By selecting crosslinking agents that react under mild conditions (such as isocyanates or epoxies that crosslink at moderate temperatures), the manufacturing process remains relatively simple while still achieving the desired solvent resistance through the crosslinked structure.
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 excellent resistance to high-polarity solvents, porosity, and processability, making it suitable for PV and VP applications with stable performance and efficient mass transfer.
Implementation Method 1
a crosslinking process is performed on the polyimide composition
Implementation Method 2
a dry phase inversion process is performed on the polyimide membrane
Data Source
AI summary
A preparation method of separation membrane is provided. First, a polyimide composition including a dissolvable polyimide, a crosslinking agent, and a solvent is provided. The dissolvable polyimide is represented by formula 1:wherein B is a tetravalent organic group derived from a tetracarboxylic dianhydride containing aromatic group, A is a divalent organic group derived from a diamine containing aromatic group, A′ is a divalent organic group derived from a diamine containing aromatic group and carboxylic acid group, and 0.1≤X≤0.9. The crosslinking agent is an aziridine crosslinking agent, an isocyanate crosslinking agent, an epoxy crosslinking agent, a diamine crosslinking agent, or a triamine crosslinking agent. A crosslinking process is performed on the polyimide composition. The polyimide composition which has been subjected to the crosslinking process is coated on a substrate to form a polyimide membrane. A dry phase inversion process is performed on the polyimide membrane.