Cation-Exchange Fluorinated Membrane with Anode Protrusions
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Solution Overview
Problem
Conventional ion-exchange membranes for electrolyzing alkali chloride solutions struggle to maintain stable electrolysis performance and mechanical strength while reducing impurities in produced alkali hydroxide, particularly alkali chloride, which is essential for high-purity applications like rayon, pulp, and chemical production.
Innovation Solution
A cation-exchange membrane with projecting parts made of a fluorine-containing polymer and a porous substrate on the anode side, featuring specific height, distribution density, and area fractions, is developed to enhance the supply of alkali chloride solution and reduce impurities, achieved through an embossed release paper process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the water content of the layer facing to the anode side is increased to lower electric resistance, then the electric resistance is reduced, but the strength of the membrane decreases and the concentration of impurities in alkali hydroxide increases
Solution Approach 1:
The membrane structure is divided into multiple layers with different water contents and ion-exchange capacities. The layer facing the anode side has controlled water content (6-12%) to maintain strength, while other layers have higher water content (15-30%) to provide low electric resistance. This local differentiation allows each layer to optimize its function without compromising overall performance.
Solution Approach 2:
The membrane is segmented into multiple functional layers: a first layer with carboxylic acid groups, a second layer with sulfonic acid groups, and optionally a third layer. Each layer has specific water content ranges and ion-exchange capacities that are optimized independently, allowing the system to achieve low overall electric resistance while maintaining structural integrity through the layered architecture.
2Loss of energy
If the ion-exchange capacity of the layer containing carboxylic acid group is increased to lower electric resistance, then the electric resistance is reduced, but current efficiency is lowered and impurities in alkali hydroxide increase
Solution Approach 1:
The first layer containing carboxylic acid groups is designed with specific ion-exchange capacity (0.8-1.5 meq/g) and water content (6-12%) to balance electric resistance and current efficiency. The second layer with sulfonic acid groups has higher ion-exchange capacity (1.2-2.0 meq/g) to provide additional conduction pathways without compromising selectivity, as sulfonic acid groups maintain better ion selectivity at higher capacities.
3Loss of energy
If the ion-exchange capacity of the layer containing sulfonic acid group is increased to lower electric resistance, then the electric resistance is reduced, but impurities in alkali hydroxide increase and membrane strength remarkably decreases
Solution Approach 1:
The second layer containing sulfonic acid groups is designed with controlled ion-exchange capacity (1.2-2.0 meq/g) and water content (15-30%) to achieve low electric resistance while maintaining adequate strength. The fluorinated polymer backbone provides inherent mechanical strength, and the crosslinking density is optimized to prevent excessive swelling that would compromise structural integrity.
4Strength
If a porous substrate made from PTFE is embedded into the membrane to improve strength, then the membrane strength is improved, but the resin layer thickness must be reduced which lowers the strength further
Solution Approach 1:
A porous substrate made from PTFE or similar fluorinated polymers is embedded within the membrane structure to provide mechanical support. The porous structure allows ion transport while the substrate framework prevents excessive swelling and maintains dimensional stability. The resin layers are applied over this substrate, creating a composite structure that leverages the strength of the porous substrate while maintaining the ion-exchange functionality of the resin layers.
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 effectively reduces impurities in alkali hydroxide production while maintaining electrochemical and mechanical strength, ensuring high-quality alkali hydroxide over a long period and contributing to cost reduction and purity provision.
Implementation Method 1
a fluorine-containing polymer having an ion-exchange group
Implementation Method 2
electrolyzing an aqueous solution of an alkali chloride
Implementation Method 3
the membrane has projecting parts comprising a polymer having an ion-exchange group on the surface of an anode side
Data Source
AI summary
A cation-exchange membrane for electrolysis which comprises a fluoropolymer having ion-exchange groups and a porous base. It is characterized by having, on the anode-side surface of the membrane, protrusions comprising a polymer having ion-exchange groups. It is further characterized in that: when the average value of the heights of the tops of the protrusions from the anode-side surface of the membrane is expressed as h (μm), then 20≦h≦150; when the density of the protrusions distributed is expressed as P (protrusions per cm2), then 50≦P≦1,200; when the average proportion of the areas of those bottom parts of the protrusions which are on the same level as the anode-side surface of the membrane to the area of the anode-side surface of the membrane is expressed as S (cm2/cm2), then 0.001≦S≦0.6; and when the average proportion of the areas of the top parts of the protrusions to the area of the anode-side surface of the membrane is expressed as T (cm2/cm2), then T≦0.05.