Composite Semipermeable Membrane Coating for Abrasion Without Flux Loss
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Solution Overview
Problem
Existing composite semipermeable membranes face issues with abrasion leading to decreased separation performance, and existing solutions either compromise abrasion resistance or water-permeating performance.
Innovation Solution
A composite semipermeable membrane design featuring a support membrane, a separation functional layer with crosslinked polyamide, and a coating layer with specific friction coefficients and surface characteristics, including a vinyl alcohol-based polymer, to enhance abrasion resistance and water-permeating performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating layer is added to prevent abrasion of the separation functional layer, then abrasion resistance is improved, but water-permeating performance decreases
Solution Approach 1:
The coating layer is designed with specific local properties: a controlled developed area ratio (Sdr) of 60%-200% and specific friction coefficient range (μs: 0.40-1.30, μd: 0.25-0.73). This local quality control allows the coating to provide abrasion protection while maintaining water permeability by optimizing the surface structure and friction characteristics rather than simply adding a thick coating layer.
Solution Approach 2:
The invention changes key parameters of the coating layer to resolve the contradiction. By controlling the developed area ratio within 60%-200% and the static friction coefficient within 0.40-1.30, the coating layer achieves both abrasion resistance and acceptable water permeability. This parameter optimization transforms the coating from a performance-degrading addition to a functional protective layer.
2Reliability
If the amount of polyamide in the separation functional layer is increased to prevent abrasion, then abrasion resistance is improved, but water-permeating performance decreases
Solution Approach 1:
The coating layer acts as an intermediary between the separation functional layer and the external environment. Instead of increasing polyamide content in the separation layer, the coating layer provides the abrasion resistance function, allowing the separation layer to maintain its original polyamide content and thus preserve water-permeating performance while still achieving protection against abrasion.
3Productivity
If the separation functional layer is made thin to improve water-permeating performance, then water-permeating performance is improved, but abrasion resistance decreases
Solution Approach 1:
The membrane structure is segmented into distinct functional layers: the separation functional layer (thin, for high permeability) and the coating layer (protective, for abrasion resistance). This segmentation allows each layer to be optimized for its specific function - the separation layer can be kept thin to maximize water permeability while the coating layer provides the necessary mechanical protection against abrasion.
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 excellent abrasion resistance and good water-permeating performance, maintaining separation efficiency despite mechanical stresses.
Implementation Method 1
a static friction coefficient μs between the coating layer-side surface of the composite semipermeable membrane and a lapping film abrasive having a particle size of # 2000 is 0.40 to 1.30
Implementation Method 2
membrane separation methods using a semipermeable membrane such as a reverse osmosis membrane or a nanofiltration membrane
Data Source
Figure 1~2(b)
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AI summary
The present invention provides a composite semipermeable membrane that has excellent water permeability performance while having exceptional abrasion resistance. This composite semipermeable membrane comprises a support membrane, a separation function layer that contains a cross-linking polyamide, and a coating layer that is positioned on the separation function layer, the developed interfacial area ratio Sdr of the coating-layer-side surface being 60-200%, and the coefficient of static friction µs between the coating-layer-side surface and a wrapping film having a #2000 grain size being 0.40-1.30.