UV-Crosslinked Polyimide Membranes for Gas 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 fabricated from poly(3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride-2,4,6-trimethyl-m-phenylenediamine) and other derivatives, which incorporate UV cross-linkable sulfonic or carbonyl groups, enhancing selectivity and stability through improved membrane structure and cross-linking processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymeric membranes (cellulose acetate, polyimide) are used for gas separation, then the membrane structure provides basic separation capability, but defects and porosity in the selective skin layer reduce selectivity and permeability
Solution Approach 1:
The patent applies parameter changes by controlling the phase inversion process through specific parameters: polymer concentration (15-25 wt%), non-solvent concentration (80-95 vol%), temperature (0-25°C), and immersion time (5-30 minutes). These parameter optimizations enable the formation of a defect-free selective skin layer with enhanced selectivity and permeability for gas separation
Solution Approach 2:
The patent utilizes porous materials by creating a controlled porous structure in the support layer while maintaining a dense defect-free skin layer. The phase inversion process generates a membrane with a thin selective skin (0.1-2 μm) over a porous support, where the skin layer's porosity is minimized to prevent defects while the support layer provides mechanical strength
2Productivity
If the selective skin layer is made thinner to increase permeability, then gas flux improves, but the layer becomes more prone to defects reducing selectivity
Solution Approach 1:
The patent resolves this contradiction through parameter optimization in the phase inversion process, specifically controlling polymer concentration (15-25 wt%), non-solvent concentration (80-95 vol%), and immersion time (5-30 minutes). These parameters enable formation of an ultra-thin skin layer (0.1-2 μm) that maintains high permeability while remaining defect-free through controlled phase separation
Solution Approach 2:
The patent applies partial action by creating a dual-layer structure where only the thin skin layer (0.1-2 μm) provides selective separation, while the thicker support layer provides mechanical strength. This allows the selective layer to be extremely thin for high permeability without compromising overall membrane integrity
3Reliability
If new polyimide membranes with cross-linking are developed to improve selectivity and stability, then separation performance increases, but membrane fabrication complexity increases
Solution Approach 1:
The patent applies preliminary action by incorporating cross-linkable functional groups (sulfonic or carbonyl groups) into the polyimide polymer structure before membrane fabrication. This preliminary chemical modification enables subsequent cross-linking through UV irradiation or chemical agents, enhancing stability and selectivity without requiring complex multi-step fabrication processes
Solution Approach 2:
The patent uses composite materials by combining polyimide polymer with cross-linking agents or UV-curable components to create a composite membrane structure. The cross-linked polyimide network provides enhanced thermal and chemical stability while maintaining gas separation performance, effectively resolving the contradiction between stability and fabrication complexity
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 demonstrate significantly higher CO2 and H2 permeability and selectivity, reducing the membrane area required for gas separation and improving the purity and durability of the separation process, suitable for various gas and liquid separations.
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 membranes described herein have been cross-linked by chemical or UV cross-linking or other cross-linking process as known to one skilled in the art. A cross-linked polyimide membrane can be prepared by UV cross-linking of the polyimide membrane via exposure of the membrane to UV radiation.
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.