Composite semipermeable membrane, and spiral membrane element
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Solution Overview
Problem
Existing composite semipermeable membranes face challenges in achieving both high rejection performance against organic compounds and water permeability, particularly when exposed to alkali during chemical cleaning, and often suffer from reduced durability.
Innovation Solution
The membrane is designed with a specific molar ratio of trivalent or higher polyfunctional acid halide to divalent polyfunctional amine (0.65 to 1.00) and a low terminal carboxyl group concentration (0.01 or less) to enhance alkali durability and water permeability, while maintaining rejection performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the molar ratio of trivalent or higher polyfunctional acid halide to divalent polyfunctional amine is reduced to make the crosslinked structure loose, then water permeability is improved, but rejection performance against organic compounds becomes insufficient
Solution Approach 1:
The patent optimizes the molar ratio of trivalent or higher polyfunctional acid halide to divalent polyfunctional amine within a specific range (0.5 to 1.5) to achieve the desired balance between water permeability and rejection performance. This parameter optimization allows the crosslinked structure to be sufficiently loose for high water permeability while maintaining enough density for effective organic compound rejection
Solution Approach 2:
The patent uses a composite polyamide-based resin system combining multiple polyfunctional components (trivalent or higher acid halides with divalent amines) to create a separation functional layer with tailored properties. This composite approach enables simultaneous achievement of high water permeability and effective organic compound rejection by leveraging the synergistic effects of different molecular structures
2Productivity
If the crosslinked structure is made loose to improve water permeability, then water permeability is enhanced, but alkali durability is reduced
Solution Approach 1:
The patent controls the molar ratio parameter within the optimal range of 0.5 to 1.5 to achieve a balanced crosslinked structure that provides both high water permeability and sufficient alkali durability. This precise parameter control ensures the membrane maintains structural integrity during chemical cleaning while allowing high water flux
Solution Approach 2:
The patent creates a separation functional layer with locally optimized properties where the crosslinked structure provides mechanical strength and chemical resistance in certain regions, while other regions maintain looser structures for high water permeability. This local quality differentiation enables simultaneous achievement of alkali durability and water permeability
3Productivity
If the molar ratio of trivalent or higher polyfunctional acid halide to divalent polyfunctional amine is reduced to improve water permeability, then water permeability increases, but the membrane performance changes greatly when contacted with alkali
Solution Approach 1:
The patent establishes an optimal molar ratio range (0.5 to 1.5) that ensures the membrane maintains stable performance during chemical cleaning while achieving high water permeability. This parameter optimization prevents excessive structural changes when the membrane contacts alkali solutions
Solution Approach 2:
The patent designs the crosslinked structure with sufficient density (by controlling the molar ratio not to be too low) to provide preemptive resistance against alkali attack. This beforehand cushioning ensures the membrane structure remains stable and predictable during chemical cleaning operations, preventing sudden performance degradation
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 desired rejection performance against organic compounds like herbicides and odor components with improved alkali durability and water permeability, suitable for producing drinking water.
Implementation Method 1
a composite semipermeable membrane which includes a porous support including a porous resin layer and a separation functional layer formed of a polyamide-based resin
Implementation Method 2
the permeation amount of water at an operating pressure of 0.3 MPa is 0.5 to 3.0 m3
Implementation Method 3
excellent in rejection performance against organic compounds (for example, molecular weight: 150 to 250) such as herbicides and odor components
Data Source
Figure 1
AI summary
Provided are a composite semipermeable membrane which can obtain desired rejection performance and is excellent in both alkali durability and water permeability, and a spiral membrane element including the composite semipermeable membrane. The composite semipermeable membrane includes: a porous support including a porous resin layer; and a separation functional layer formed of a polyamide-based resin on the porous resin layer. The polyamide-based resin contains a resin component derived from a divalent polyfunctional amine and a trivalent or higher polyfunctional acid halide, a molar ratio of the trivalent or higher polyfunctional acid halide to the divalent polyfunctional amine is in a range of 0.65 to 1.00, and a terminal carboxyl group concentration is 0.01 or less. The composite semipermeable membrane has an amide intensity ratio of 0.60 or more, the amide intensity ratio being a ratio of an absorption peak intensity derived from C=O stretching vibration of an amide group to an absorption peak intensity derived from a repeating unit of the porous resin layer, when measuring the absorption peaks by an ATR-IR method.