Crosslinked Polyimide Membranes for Organic Solvent Nanofiltration
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Solution Overview
Problem
Existing asymmetric polyimide nanofiltration membranes are not stable in solvents where the base polyimide is soluble, leading to structural loss and low or no flux in solvents like DMF and dichloromethane, limiting their application in organic solvent nanofiltration.
Innovation Solution
The development of asymmetric polyimide nanofiltration membranes that are treated with a crosslinking agent and impregnated with a conditioning agent, formed through a process involving a polyimide dope solution, casting, coagulation, and washing, which results in membranes that are stable in solvents where the base polyimide is soluble and exhibit higher fluxes when processing mixtures of water and organic solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If asymmetric polyimide membranes are used for nanofiltration, then separation performance is improved, but stability in organic solvents deteriorates
Solution Approach 1:
The patent applies crosslinking chemistry to transform the polyimide membrane structure from linear chains to a crosslinked network, fundamentally changing the chemical parameters of the membrane material. This crosslinking modification enables the membrane to resist solvent swelling and dissolution while preserving nanofiltration separation performance, directly resolving the contradiction between separation capability and solvent stability
Solution Approach 2:
The patent creates a composite membrane system by combining crosslinked polyimide with a porous support substrate. The crosslinked polyimide layer provides both separation functionality and solvent resistance, while the support provides mechanical strength. This composite structure achieves both reliable separation performance and stability in organic solvents
2Stability of the object's composition
If crosslinking is applied to polyimide membranes, then solvent stability is improved, but flux may deteriorate
Solution Approach 1:
The patent creates an asymmetric membrane structure where the dense selective layer is crosslinked to provide solvent stability, while the support substrate remains porous to maintain high flux. This local differentiation of properties - crosslinked dense layer for stability, porous support for flow - resolves the contradiction between solvent stability and flux
Solution Approach 2:
The patent applies crosslinking selectively to the polyimide forming layer rather than the entire membrane structure. This partial crosslinking approach provides sufficient solvent stability while minimizing impact on flux, as the crosslinked network is confined to the selective layer where it is most needed for preventing solvent-induced structural collapse
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 crosslinked membranes maintain structural integrity and exhibit improved flux and rejection in solvents where traditional membranes fail, offering stability and performance in solvents like DMF and dichloromethane, and show higher fluxes in organic solvent nanofiltration applications.
Implementation Method 1
a phase inversion technique, which results in an ultra-thin top layer of the asymmetric membrane
Implementation Method 2
at least a fraction of the imide groups of the polyimide are crosslinked
Implementation Method 3
Nanofiltration is a membrane process utilising membranes whose pores are generally in the range 0.5-5 nm
Data Source
AI summary
Improved integrally skinned asymmetric membranes for organic solvent nanofiltration, and their methods of preparation and use are disclosed. Membranes are formed from polyimides by phase inversion and are then crosslinked by addition of amine crosslinking agents that react with the imide groups of the polyimide, creating amide bonds. These stabilize the membranes and allow solvent nanofiltration to be maintained even in the solvents from which the membranes were formed by phase inversion.