Composite Ion Exchange Membrane Low Crosslinking Nitrate Removal
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Solution Overview
Problem
Ion exchange membranes used in processes like electrodialysis struggle to achieve high selectivity for monovalent ions and low electrical resistance, especially when removing nitrate from water at low concentrations, due to limitations in existing surface treatment methods.
Innovation Solution
A composite ion exchange membrane is created by reacting an ionically-charged membrane with a composition containing a monofunctional ethylenically unsaturated monomer and a crosslinking agent, with a molar ratio of crosslinking agent to monomer less than 0.04 or zero, resulting in improved selectivity and low electrical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional surface treatment methods using high crosslinking agent ratios are used, then membrane structure stability is improved, but selectivity for monovalent ions and limiting current density deteriorate
Solution Approach 1:
The patent changes the key parameter of crosslinking agent ratio from conventional high ratios (0.54-0.86) to a low ratio (less than 0.04). This parameter change resolves the contradiction by achieving sufficient structural stability through alternative means (surface treatment with oppositely charged species) while maintaining high ion selectivity and limiting current density that are compromised by excessive crosslinking.
Solution Approach 2:
The patent extracts the crosslinking agent from the surface treatment composition, using instead oppositely charged species that provide stabilization without the harmful effects of high crosslinking. This extraction allows the membrane to achieve stability through electrostatic interactions rather than covalent crosslinking, preserving ion transport properties.
2Duration of action of stationary object
If conventional surface treatment with high crosslinking agent ratios is applied, then membrane durability is improved, but electrical resistance increases
Solution Approach 1:
The patent applies parameter change by reducing the crosslinking agent ratio to less than 0.04, which maintains membrane durability through surface treatment with oppositely charged species while preventing the increase in electrical resistance that occurs with conventional high crosslinking ratios.
Solution Approach 2:
The patent introduces oppositely charged species as an intermediary that provides membrane stabilization and durability without the adverse electrical effects of crosslinking agents. These species act as a mediator between the membrane and the environment, providing protection while maintaining electrical conductivity.
3Strength
If high crosslinking agent ratios are used in surface treatment, then membrane structural integrity is improved, but performance in removing low concentration nitrate deteriorates
Solution Approach 1:
The patent changes the crosslinking agent ratio parameter to less than 0.04, achieving sufficient structural integrity through surface treatment with oppositely charged species while maintaining the membrane's ability to effectively remove low concentration nitrate, which is compromised by high crosslinking.
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 composite membrane exhibits high selectivity for monovalent ions, high limiting current density, and low electrical resistance, effectively removing nitrate from water even at low concentrations, making it suitable for water purification applications.
Implementation Method 1
Ion exchange membranes are generally categorized as cation exchange membranes or anion exchange membranes, depending on their predominant charge. Cation exchange membranes comprise negatively charged groups that allow the passage of cations but reject anions, while anion exchange membranes comprise positively charged groups that allow the passage of anions but reject cations.
Implementation Method 2
a monofunctional ethylenically unsaturated monomer having an ionic charge opposite to the charge of the ionically-charged membrane; and (b) a crosslinking agent comprising two or more ethylenically unsaturated groups
Data Source
AI summary
A composite ion exchange membrane obtainable by a process comprising reacting an ionically-charged membrane with a composition comprising: (a) a monofunctional ethylenically unsaturated monomer having an ionic charge opposite to the charge of the ionically-charged membrane; and (b) a crosslinking agent comprising two or more ethylenically unsaturated groups; wherein the molar ratio of (b):(a) is lower than 0.04 or is zero.