Reverse Osmosis Membrane Lateral Leakage Reduction
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Solution Overview
Problem
Spiral wound reverse osmosis devices experience side seal leakage due to incomplete penetration of adhesive through the microporous coating layer, leading to infiltration of seawater into the glue bond, especially under high pressure gradients during seawater desalination, which degrades permeate water quality.
Innovation Solution
A longitudinal indentation is created in the composite reverse osmosis membrane along each side of the membrane leaf, compressing the microporous coating to a nonporous state, which, in combination with a polyurethane bonding adhesive, prevents lateral movement of raw feed water through the microporous layer, and this is achieved using embossing rollers in the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adhesive is applied to bond membrane edges in spiral wound devices, then membrane leaves are held together and sealed, but incomplete penetration of adhesive through microporous coating causes lateral leakage of feed water
Solution Approach 1:
The microporous coating is pre-treated with a plasma process before adhesive application. This preliminary action modifies the surface properties of the coating, increasing its affinity for the adhesive and ensuring complete penetration. The plasma treatment creates a more receptive surface that allows the adhesive to fully penetrate through the microporous layer, eliminating lateral leakage pathways while maintaining ease of manufacture.
Solution Approach 2:
The adhesive formulation is modified by changing its chemical parameters, specifically using a plasma-responsive adhesive that reacts with the plasma-treated surface. This parameter change in adhesive chemistry enables complete penetration through the microporous coating by creating strong chemical interactions with the treated surface, thereby ensuring reliable sealing without compromising manufacturability.
2Productivity
If high operating pressure is applied during seawater desalination, then permeate production increases, but pressure gradient forces feed water infiltration through defective glue bonds
Solution Approach 1:
The microporous coating undergoes plasma treatment before adhesive bonding, creating a pre-modified surface that ensures complete adhesive penetration. This preliminary surface modification eliminates defects in the glue bond that would otherwise allow feed water infiltration under high pressure, enabling the system to operate at high pressures for maximum permeate production without suffering from leakage.
Solution Approach 2:
The plasma treatment is a temporary, surface-level modification that does not require permanent structural changes to the membrane or adhesive. This cost-effective, short-duration treatment process creates sufficient surface receptivity for complete adhesive penetration, providing a simple solution to prevent feed water infiltration under high operating pressures without complex or expensive modifications.
3Ease of operation
If microporous coating is used on membrane carrier, then permeate drainage function is provided, but lateral migration of raw feed water occurs through the porous layer at glue bonds
Solution Approach 1:
The microporous coating is pre-treated with plasma before adhesive application, modifying its surface properties to enhance adhesive penetration while preserving the bulk porous structure. This preliminary treatment ensures that the adhesive completely penetrates the coating to create reliable seals, preventing lateral feed water migration, while the coating's permeate drainage function remains intact for efficient operation.
Solution Approach 2:
The plasma treatment creates localized surface modification only at the regions where adhesive penetration is needed, specifically at the membrane edges and glue bond zones. This local quality change ensures complete adhesive penetration at critical sealing locations to prevent lateral leakage, while the rest of the microporous coating maintains its original permeable structure for effective permeate drainage.
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 solution effectively eliminates most or all lateral migration of raw feed water through the microporous layer, enhancing the integrity of the glue bond and maintaining high water quality by preventing seawater infiltration, even under high pressure conditions.
Implementation Method 1
A longitudinal indentation is created in the composite reverse osmosis membrane along each side of the membrane leaf, compressing the microporous coating to a nonporous state
Implementation Method 2
Two-part urethane adhesives are typically the glue of choice. The adhesive is desired to penetrate the nonwoven support web of each of the two adjacent folds, bonding them together along with the permeate channel spacer
Implementation Method 3
Reverse osmosis developed into an economically feasible process approximately in the late 1960's. Reverse osmosis membranes capable of desalting seawater generally consist of a nonwoven polyester web carrier coated with a thin layer of a microporous plastic
Data Source
AI summary
Spiral wound reverse osmosis devices with reduced lateral leakage and thereby increased salt rejection are made by compacting a microporous layer within a composite reverse osmosis membrane longitudinally along its lengthwise periphery. Means and method for causing longitudinal indentations in composite membranes during manufacturing operations are disclosed and described.