Polyimide Membrane Structure for High-Flux Stable Desalination
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Solution Overview
Problem
Existing polyimide membranes face challenges in achieving high flux, exceptional permeability, and stable rejection performance for desalination applications, particularly in membrane distillation processes.
Innovation Solution
A method for producing a polyimide membrane involving the polymerization of dianhydride and phenylenediamine monomers, followed by precipitation and application on a substrate, using solvents like water or alcohol to form a polyimide membrane with specific thickness, porosity, and hydrophobicity, optimized for use in air gap membrane distillation systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional membrane distillation membranes are used, then basic desalination function is achieved, but permeate flux and salt rejection performance are insufficient
Solution Approach 1:
The patent changes the physical and chemical parameters of the membrane by controlling pore size (0.03-0.1 μm), hydrophobicity (water contact angle 80-110°), and thermal stability through polyimide material selection and phase inversion process optimization, achieving both high flux and stable salt rejection
Solution Approach 2:
The patent uses composite polyimide materials with specific molecular structures (containing aromatic rings, imide groups, and hydrophobic side chains) to create a membrane that combines high flux, excellent salt rejection, and thermal stability in a single integrated material system
2Reliability
If pore diameter is reduced to prevent pore wetting, then salt rejection improves, but permeate flux decreases
Solution Approach 1:
The patent optimizes the pore size parameter to a specific range (0.03-0.1 μm) that balances salt rejection and water vapor permeation, and adjusts hydrophobicity parameters (water contact angle 80-110°) to prevent pore wetting while maintaining adequate flux
Solution Approach 2:
The patent creates a membrane surface with specific local hydrophobic properties through polyimide material selection and surface morphology control, making the pore surfaces highly hydrophobic to repel liquid water while allowing water vapor passage, thus achieving high salt rejection without sacrificing flux
3Reliability
If hydrophobicity is enhanced to prevent pore wetting, then membrane stability improves, but manufacturing complexity increases
Solution Approach 1:
The patent achieves enhanced hydrophobicity by selecting polyimide materials with specific molecular structures containing hydrophobic groups and optimizing the phase inversion process parameters (solvent selection, non-solvent type, coagulation bath temperature), creating a straightforward manufacturing process that produces membranes with water contact angles of 80-110°
Solution Approach 2:
The patent uses homogeneous polyimide polymer materials with consistent molecular structure and properties throughout the membrane matrix, ensuring uniform hydrophobicity and stability across the entire membrane surface, which simplifies manufacturing by eliminating the need for complex surface treatments or multi-layer structures
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 polyimide membrane exhibits improved permeate flux and stable salt rejection, suitable for desalinating highly saline water with up to 99.97% salt rejection and 12 Kg/m² h permeate flux, demonstrating enhanced performance in desalination processes.
Implementation Method 1
Membrane distillation (MD) is a thermally-driven process, wherein only vapor molecules can transport across the porous membranes under a vapor pressure gradient
Implementation Method 2
Pore wetting of membranes can be improved by reducing the pore diameter and enhancing the hydrophobicity of membranes
Implementation Method 3
The characteristics of the polymer determine the selectivity and permeability for separation purposes, including gas and liquid applications
Data Source
AI summary
A method of making a polyimide membrane includes mixing dianhydride and phenylenediamine monomers in a first solvent to form a mixture; heating the mixture thereby polymerizing to form a polyimide polymer in a crude mixture; precipitating and separating the polyimide polymer from the crude mixture; mixing and dissolving the polyimide polymer in a second solvent to form a polyimide solution; applying the polyimide solution onto a surface of a substrate to form a polyimide liquid layer on the substrate; immersing the substrate after the applying in at least one liquid medium selected from the group consisting of water and alcohol, thereby precipitating the polyimide polymer from the polyimide solution to form the polyimide membrane disposed on the surface of the substrate. A desalination system containing the polyimide membrane, and a desalination process.