Pleated Semipermeable Composite Membrane for Low Pressure Desalination
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Solution Overview
Problem
Conventional composite semipermeable membranes exhibit insufficient salt removal performance and water permeation performance under low pressure conditions.
Innovation Solution
A composite semipermeable membrane with a microporous support layer and a separation functional layer containing crosslinked aromatic polyamide, featuring a pleated structure with specific convex and concave parts, is developed. The membrane is formed through a process involving an aqueous polyfunctional amine solution, an aliphatic carboxylic acid, and a polyfunctional acid halide, with a compound like ethylene glycol ether added after a controlled time frame, satisfying specific infrared absorption and temperature modulated DSC conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional composite semipermeable membranes are used, then manufacturing is straightforward, but salt removal performance and water permeation performance are insufficient under low pressure conditions
Solution Approach 1:
The invention introduces a pleated structure with convex and concave parts in the separation functional layer, creating local variations in surface morphology. This local structural differentiation optimizes water permeation pathways while maintaining salt rejection, achieving high performance under low pressure conditions without requiring complete structural redesign
Solution Approach 2:
The invention uses a composite semipermeable membrane consisting of a microporous support layer and a separation functional layer containing crosslinked aromatic polyamide. This composite structure combines the mechanical strength of the support layer with the selective separation properties of the polyamide layer, achieving both durability and high salt removal performance
2Reliability
If polymerization is performed in the presence of organic additives or monofunctional acid halides, then membrane formation is facilitated, but salt removal performance and water permeation performance remain insufficient
Solution Approach 1:
The invention changes the chemical parameters of the polymerization system by using polyfunctional acid halides (with 2 or more functional groups) instead of conventional monofunctional acid halides. This parameter change creates a crosslinked polyamide network structure that enhances both salt removal and water permeation performance while maintaining manufacturability through controlled polymerization
3Productivity
If the separation functional layer is made thinner to improve water permeation, then water permeation performance increases, but salt removal performance may deteriorate
Solution Approach 1:
The invention addresses the thickness-performance tradeoff by introducing a pleated structure with convex and concave parts, effectively adding a third dimension to the thin film. This creates extended permeation pathways and increased effective surface area without increasing linear thickness, allowing both high water permeation and salt removal performance to coexist in a thin separation layer
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 removal performance and water permeation performance while maintaining durability, even under low pressure conditions, by optimizing the ratio of free and bound water interaction with the polymer.
Implementation Method 1
the composite semipermeable membrane containing a crosslinked polyamide polymer as a separation active layer has been proposed... suitable for use for, for example, desalination of seawater or brackish water
Implementation Method 2
the ratio between the amount of free water that weakly interacts with a polymer contained in the separation functional layer, and the amount of bound water that strongly interacts with the polymer and is low in permeability is appropriate
Data Source
Figure 1
AI summary
The present invention pertains to a semipermeable composite membrane having a support film and a separation function layer, wherein, (A) in a semipermeable composite membrane equilibrated under specific conditions, the half value width H of an absorption peak between 3900 cm-1 and 2900 cm-1 in a difference spectrum Sd obtained by subtracting IR spectrum S2 from IR spectrum S1 is 355-373, and (B) in the IR spectrum S1, the value F obtained by dividing the area of the absorption intensity between 3900 cm-1 and 2900 cm-1 by the absorbance at the peak top between 1690 cm-1 and 1630 cm-1 is at least 850.