Anion Exchange Membrane Synthesis Without Chloromethyl Ether
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Solution Overview
Problem
The preparation of anion exchange membranes (AEMs) for water desalination using chloromethyl ether is costly and hazardous due to its carcinogenic nature, necessitating the development of alternative methods that avoid its use while maintaining membrane performance.
Innovation Solution
The synthesis of quaternized, cross-linked copolymers from polyacrylonitrile (PAN) and poly(2-dimethylaminoethyl)methacrylate (PDMA), optionally with poly-n-butyl acrylate (PnBA), using free radical polymerization and subsequent quaternization with alkyl halides and diamine, to create AEMs suitable for electrodialysis without relying on chloromethyl ether.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If chloromethyl ether is used in the preparation of anion exchange membranes, then the membrane can be produced through conventional two-step process, but the process becomes costly and hazardous due to carcinogenic nature of chloromethyl ether
Solution Approach 1:
The invention extracts and removes the harmful chloromethyl ether step from the conventional two-step process. Instead of using chloromethyl ether for chloromethylation followed by quaternary amination, the patent employs a one-step quaternary amination process that directly introduces quaternary ammonium groups without requiring the carcinogenic intermediate step, thereby eliminating the harmful factor while maintaining manufacturing capability
Solution Approach 2:
The patent replaces the expensive and hazardous chloromethyl ether with safer, more economical alternatives such as alkyl halides (methyl iodide, ethyl bromide) or alkyl sulfonates. These substitutes are less toxic, more readily available, and eliminate the need for specialized handling and disposal procedures required for carcinogenic substances, making the process both cheaper and safer
2Reliability
If conventional two-step process with chloromethylation is used, then AEM can be prepared, but the process becomes complicated and costly
Solution Approach 1:
The invention merges the two separate steps of chloromethylation and quaternary amination into a single unified quaternary amination step. By using monomers that already contain the necessary functional groups or by performing direct quaternary amination on polymer backbones, the process eliminates the intermediate chloromethylation step, reducing procedural complexity while maintaining the reliability of producing functional anion exchange membranes
Solution Approach 2:
The patent employs preliminary action by pre-functionalizing the polymer backbone with appropriate groups during the polymerization stage or by selecting polymers that inherently possess the necessary reactivity. This allows the quaternary amination to proceed directly without requiring prior chloromethylation, simplifying the overall process while ensuring reliable membrane formation
3Productivity
If styrene-divinyl benzene copolymer is used for AEM preparation, then industrial AEM can be produced, but the process requires carcinogenic chloromethyl ether
Solution Approach 1:
The invention changes the chemical parameters of the polymer system by transitioning from styrene-divinyl benzene copolymers requiring chloromethylation to polymers with alternative functional groups that can undergo direct quaternary amination. This parameter change includes using polymers with amino groups, hydroxyl groups, or other nucleophilic groups that can react directly with alkyl halides or sulfonates, eliminating the need for carcinogenic chloromethyl ether while maintaining industrial productivity
Solution Approach 2:
The patent employs composite material strategies by combining polymer matrices with quaternary ammonium functional groups introduced through alternative chemistry. This may involve using copolymers with multiple functional groups, incorporating cross-linking agents, or creating composite structures that achieve the desired ion exchange properties without relying on the conventional chloromethyl ether pathway, thus maintaining productivity while eliminating carcinogenic harm
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
This method produces AEMs with high current efficiency (63-92%) and low power consumption (0.73-1.35 KWh/Kg) during water desalination, demonstrating equivalent performance to conventional styrene-divinyl benzene-based membranes while avoiding the use of carcinogenic reagents.
Implementation Method 1
The synthesis of quaternized, cross-linked copolymers from polyacrylonitrile (PAN) and poly(2-dimethylaminoethyl)methacrylate (PDMA), optionally with poly-n-butyl acrylate (PnBA), using free radical polymerization
Implementation Method 2
subsequent quaternization with alkyl halides and diamine, to create AEMs suitable for electrodialysis
Implementation Method 3
Anion exchange membrane (AEM) for water desalination by electrodialysis
Data Source
AI summary
The present invention relates to the preparation of novel anion exchange membranes from bicomponent or tricomponent copolymers containing both quaternizable and cross-linkable moieties. The bicomponent copolymers consisted with polyacrylonitrile and poly(2-dimethylaminoethyl) methacrylate and the tricomponent copolymers consisted with polyacryloniterle and poly2-dimethylaminoethyl) methacrylate and polyn-butyl acrylate. Quaternization of dimethyl amino groups of copolymer by methyl iodide followed by cross-linking of acrylonitrile groups of copolymer by hydrazine hydrate resulted anion exchange membrane with desired properties such as high ion exchange capacity (1.30-1.50 meqg−1), high transport number (0.92-0.93) for direct use in electrodyalysis unit. The tricomponent anion exchange membrane containing 32 wt % PDMA, 17 wt % PnBA, and 51 wt % PAN exhibited improved performance mainly in terms of low power consumption and high current efficiency during desalination of water.