Cation Exchange Membrane Potassium Sodium Ion Composition
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Solution Overview
Problem
Cation exchange membranes used in the ion-exchange membrane method for producing potassium hydroxide from potassium chloride solutions tend to swell and elongate during electrolysis, leading to membrane damage and increased electrolysis voltage, requiring pre-swelling operations that are labor-intensive and inconvenient.
Innovation Solution
A cation exchange membrane with a composition of at least 99 mol % potassium and sodium ions, specifically 80 to 98 mol % potassium and 2 to 20 mol % sodium, made from perfluorocarbon polymers with alkali metal salt form carboxylic acid and sulfonic acid groups, which reduces swelling and elongation during electrolysis without the need for pre-swelling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a cation exchange membrane of potassium salt form is used in the ion-exchange membrane method, then potassium hydroxide aqueous solution can be produced by electrolyzing potassium chloride aqueous solution, but the membrane swells and expands during electrolysis causing wrinkles to form
Solution Approach 1:
The invention changes the cation composition parameter of the membrane by introducing sodium ions (2-20 mol%) alongside potassium ions (80-98 mol%). This compositional parameter change modifies the membrane's physical properties, specifically reducing swelling and expansion during electrolysis while maintaining its function in producing potassium hydroxide aqueous solution
Solution Approach 2:
The invention creates a composite cation exchange membrane containing both potassium ions and sodium ions in specific proportions. This composite ionic structure combines the benefits of potassium ions for hydroxide production with sodium ions for reduced swelling, resolving the contradiction between manufacturing ease and compositional stability
2Ease of operation
If the cation exchange membrane is fixed along the peripheral edge to the frame, then the membrane can be installed in the electrolyzer, but wrinkles are formed when the membrane swells and expands
Solution Approach 1:
By changing the ionic composition parameter to include 2-20 mol% sodium ions, the membrane's dimensional stability is improved, reducing swelling and expansion during operation. This allows the membrane to maintain its shape when fixed to the frame, preventing wrinkle formation while remaining easy to install
3Reliability
If wrinkles are formed in the cation exchange membrane, then the membrane structure is compromised, but the membrane is damaged by contact with electrodes and electrolysis voltage rises
Solution Approach 1:
The compositional parameter change (adding 2-20 mol% sodium ions) enhances the membrane's dimensional stability and reduces wrinkle formation. This maintains structural integrity, preventing contact damage with electrodes and avoiding electrolysis voltage increases, thereby improving reliability and reducing harmful effects
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 membrane remains stable during electrolysis, preventing damage and voltage increases, allowing for stable production of potassium hydroxide without the need for pre-swelling operations, thus simplifying the process and ensuring consistent membrane performance.
Implementation Method 1
a cation exchange membrane of potassium salt form as a diaphragm is installed to divide inside of the electrolyzer into a cathode compartment on the cathode side and an anode compartment on the anode side; and a potassium chloride aqueous solution is supplied to the anode compartment, and a potassium hydroxide aqueous solution is supplied to the cathode compartment, to electrolyze the potassium chloride aqueous solution
Implementation Method 2
the membrane is likely to be swollen and expanded during electrolysis of the potassium chloride aqueous solution. In the electrolyzer, the cation exchange membrane of potassium salt form is fixed along the peripheral edge to the frame, and therefore, if the membrane is swollen and expanded, wrinkles will be formed in the membrane
Implementation Method 3
a potassium chloride aqueous solution is supplied to the anode compartment, and a potassium hydroxide aqueous solution is supplied to the cathode compartment, to electrolyze the potassium chloride aqueous solution while maintaining the concentration of the aqueous potassium hydroxide solution discharged from the cathode chamber
Data Source
AI summary
To provide a cation exchange membrane which is less susceptible to swelling or elongation during electrolysis of a potassium chloride aqueous solution even without permitting water absorption or swelling immediately prior to mounting it in an electrolyzer, and a method whereby it possible to stably produce a potassium hydroxide aqueous solution without necessity to conduct an operation for water absorption or swelling immediately prior to mounting the membrane in the electrolyzer. A cation exchange membrane comprising a polymer having cation exchange groups, wherein in cations (100 mol %) contained in the cation exchange membrane, the total of potassium ions and sodium ions is at least 99 mol %, and in the total (100 mol %) of potassium ions and sodium ions contained in the cation exchange membrane, the potassium ions are 80-98 mol % and the sodium ions are 20-2 mol %.