Composite Membrane Protrusions for Stable Reverse Osmosis
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Solution Overview
Problem
Composite semipermeable membranes used in reverse osmosis experience decreased water permeability and salt removability when pressure fluctuations occur due to frequent operation and stop conditions.
Innovation Solution
A composite semipermeable membrane with a microporous support layer and a separation functional layer featuring cross-linked aromatic polyamide protrusions, optimized in terms of density, deformation, and group ratios, is developed to maintain performance under fluctuating pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a composite semipermeable membrane with a separation functional layer is used to achieve high salt removability, then salt removability is improved, but water permeability decreases when pressure fluctuates due to frequent operation and stop
Solution Approach 1:
The separation functional layer is divided into multiple protrusions distributed across the support membrane surface. Each protrusion acts as an independent separation unit, allowing water to pass through while blocking salt ions. This segmentation maintains high salt removability while the distributed structure prevents compaction under pressure fluctuations, preserving water permeability.
Solution Approach 2:
The protrusions are designed with specific local properties: a height of 0.05-2.0 μm, a top diameter of 5-50 nm, and a bottom diameter of 50-200 nm. These localized structural characteristics create regions of high selective separation capability while maintaining overall membrane flexibility and resistance to compaction under varying pressure conditions.
2Reliability
If the separation functional layer is made denser to improve salt removability, then salt removability is improved, but the membrane becomes more susceptible to compaction under pressure fluctuations
Solution Approach 1:
The protrusions feature a curved, dome-like shape with a spherical cap structure. This curvature distributes mechanical stress uniformly across the protrusion surface during pressure fluctuations, preventing localized compaction and maintaining structural stability. The rounded geometry allows the protrusions to flex elastically under pressure while maintaining their separation function.
Solution Approach 2:
The membrane employs a composite structure combining a porous support membrane with a separation functional layer containing cross-linked polyamide protrusions. This composite architecture provides both the density needed for high salt removability and the structural flexibility to resist compaction, as the cross-linked network maintains protrusion integrity under varying pressure conditions.
3Reliability
If the protrusions are made taller to improve separation performance, then salt removability is improved, but the membrane becomes more vulnerable to damage under pressure fluctuations
Solution Approach 1:
The protrusion dimensions are optimized within specific parameter ranges: height of 0.05-2.0 μm, top diameter of 5-50 nm, and bottom diameter of 50-200 nm. These parameter specifications balance separation performance with mechanical durability, ensuring that protrusions are tall enough to provide effective salt rejection but not so tall as to be vulnerable to collapse or damage under pressure fluctuations.
Solution Approach 2:
The separation functional layer utilizes cross-linked polyamide material forming the protrusions. The cross-linking creates a three-dimensional network structure that enhances the mechanical strength and elasticity of the protrusions, allowing them to maintain their shape and function under repeated pressure cycles without degradation or damage.
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 achieves high salt removability and water permeability even under conditions of frequent pressure changes, ensuring stable performance and durability.
Implementation Method 1
a separation functional layer provided on the microporous support layer, in which the separation functional layer includes a plurality of protrusions formed of a thin membrane including a cross-linked aromatic polyamide
Implementation Method 2
a microporous support layer
Implementation Method 3
microporous support layer
Data Source
AI summary
The present invention relates to a composite semipermeable membrane including: a microporous support layer; and a separation functional layer provided on the microporous support layer, in which the separation functional layer includes a plurality of protrusions formed of a thin membrane including a cross-linked aromatic polyamide, in arbitrary ten cross sections perpendicular to a membrane surface direction and having a length of 2.0 μm in the membrane surface direction, an average number density of the protrusions whose height with respect to a surface of the support layer as reference is one-fifth or more of a ten-point average surface roughness of the separation functional layer is 13.0 protrusions/μm or more, and an average value of a deformation amount when the protrusions are pressed with a force of 5 nN is 2.2 nm or less, and a standard deviation of the deformation amount is 1.2 nm or less.