Monovalent-Selective Membrane Stack for Desalination
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Solution Overview
Problem
Current electrodialysis metathesis (EDM) systems face challenges in producing potable water from seawater with high yield due to large concentration differences between ion diluting and ion concentrating compartments, leading to high water loss and increased costs from sodium chloride supply, which also reduces desalination capacity.
Innovation Solution
A membrane stack design with two ion diluting compartments, two ion concentrating compartments, and alternating cation and anion exchange membranes with higher monovalent ion selectivity, allowing fluid communication between compartments to optimize ion transport and reduce energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional EDM systems use standard cation and anion exchange membranes in a four-compartment design, then ion transport occurs, but large concentration differences between ion diluting and ion concentrating compartments cause high water loss through osmosis
Solution Approach 1:
The patent applies local quality by differentiating membrane properties in different locations. Monovalent-selective membranes are placed specifically in compartments (a) and (b) where feed fluid enters, while standard membranes are used in other compartments. This localized differentiation optimizes ion selectivity where needed while maintaining overall system functionality, thereby reducing water loss through osmosis while preserving desalination yield.
Solution Approach 2:
The patent segments the ion exchange membrane system into two types: monovalent-selective membranes and standard membranes. This segmentation allows different functional zones within the EDM unit - compartments (a) and (b) use monovalent-selective membranes for selective ion transport, while other compartments use standard membranes for general ion exchange, thus optimizing water loss prevention without sacrificing productivity.
2Ease of manufacture
If conventional EDM systems supply additional sodium chloride to maintain ion concentration, then ion transport is maintained, but operational costs increase
Solution Approach 1:
The patent implements self-service by enabling the EDM system to maintain ion transport stability through the selective transport properties of monovalent-selective membranes. These membranes preferentially transport monovalent ions (Na+, Cl-) over divalent ions, naturally maintaining the ion balance needed for continuous operation without requiring external sodium chloride supplementation, thereby reducing operational costs while maintaining reliability.
Solution Approach 2:
The patent changes the selective parameter of the ion exchange membranes by using monovalent-selective membranes with higher selectivity coefficients for monovalent ions. This parameter change enables the system to maintain stable ion transport through selective ion preference rather than through external chemical supplementation, reducing operational costs while ensuring transport stability.
3Use of energy by moving object
If conventional EDM systems use standard membranes with lower monovalent ion selectivity, then system complexity is reduced, but energy consumption increases due to less efficient ion transport
Solution Approach 1:
The patent applies local quality by strategically placing monovalent-selective membranes in specific compartments (a) and (b) where feed fluid enters and initial ion separation occurs. This localized high-selectivity configuration maximizes energy efficiency where it is most needed for feed fluid treatment, while using standard membranes in other compartments maintains overall system simplicity, thus reducing energy consumption without excessive device complexity.
Solution Approach 2:
The patent segments the membrane system to use monovalent-selective membranes only in compartments (a) and (b) for feed fluid processing, while standard membranes are used in compartments (c) and (d). This segmentation optimizes energy consumption in the most critical zones while maintaining overall system simplicity, achieving better energy efficiency without proportionally increasing device complexity.
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 design enhances desalination efficiency, reduces water loss, and eliminates the need for additional sodium chloride supply, resulting in a more cost-effective and efficient desalination process with higher yield of desalinated water.
Implementation Method 1
When a feed fluid passes through the cells and a DC voltage is applied across the electrodes, dissolved cations pass through the cation exchange membrane and towards the cathode, whereas dissolved anions pass through the anion exchange membrane and towards the anode
Implementation Method 2
Each cell comprises a wall made from a negatively charged cation exchange membrane and a wall made from a positively charged anion exchange membrane
Implementation Method 3
large concentration differences between ion diluting and ion concentrating compartments, leading to high water loss
Data Source
AI summary
A membrane stack comprising the following components: (a) a first ion diluting compartment (D1); (b) a second ion diluting compartment (D2); (c) a first ion concentrating compartment (C1); (d) a second ion concentrating compartment (C2); and (e) a membrane wall (CEM1, mAEM, mCEM, AEM, CEM2) between each compartment and on the outside of the first and last compartment of the stack; wherein: (i) each membrane wall comprises a cation exchange membrane (CEM1, mCEM, CEM2) or an anion exchange membrane (mAEM, AEM) and the order of the cation and anion exchange membranes alternates from each wall to the next; (ii) the membrane walls (mAEM, mCEM) on each side of compartment (a) both have a higher monovalent ion selectivity than the corresponding membrane walls (AEM, CEM2) on each side of compartment (b); and (iii) the stack further comprises a means for communicating fluid between compartments (a) and (b).