Composite Semipermeable Membrane for Pressure-Cycle Durability
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Solution Overview
Problem
In water treatment systems like ZLD, frequent switching between running and stopping due to variable wastewater flow rates leads to premature deterioration of composite semipermeable membranes, reducing their rejection performance and requiring increased energy consumption to compensate for reduced permeate flux.
Innovation Solution
A composite semipermeable membrane with an elastic modulus of 250 MPa to 500 MPa and a coating of hydrophilic polymers, combined with permeate-side flow path materials of adjusted knitting density, to withstand repeated pressure changes without damage, extending membrane life and maintaining permeate flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If permeate-side flow path materials with high knitting density are used to reduce membrane damage, then membrane reliability is improved, but permeate flux decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the elastic modulus of the membrane surface within 250-500 MPa and the knitting density of permeate-side flow path materials within 30-60 wales/5 cm and 30-50 courses/5 cm. This optimization resolves the contradiction by finding the optimal parameter range that provides sufficient mechanical protection while maintaining adequate permeate flux
Solution Approach 2:
The patent uses composite materials by combining the membrane with permeate-side flow path materials having specific knitting structures. The composite structure of the membrane and the knitted material with controlled wales and courses provides both mechanical durability against pressure changes and sufficient permeability for water flux
2Productivity
If operating pressure is increased to compensate for reduced permeate flux, then permeate flux is improved, but energy consumption increases
Solution Approach 1:
The patent changes the structural parameters of the permeate-side flow path materials (knitting density, wales, courses) to optimize permeate flux. By adjusting these parameters, the system achieves adequate flux without requiring excessive operating pressure, thereby reducing energy consumption while maintaining productivity
3Reliability
If the system is stopped when buffer tank water level is low, then membrane damage from pressure changes is reduced, but treatment efficiency decreases due to frequent stoppings
Solution Approach 1:
The patent applies beforehand cushioning by using permeate-side flow path materials with optimized knitting density as a protective buffer. This cushioning structure absorbs and mitigates the mechanical stress from frequent pressure changes during system start-stop operations, protecting the membrane while allowing the system to operate according to buffer tank levels
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 enhances membrane durability and maintains salt rejection performance over time, reducing energy consumption and operational costs by minimizing membrane damage from pressure fluctuations.
Implementation Method 1
a membrane surface of the composite semipermeable membrane has an elastic modulus of 250 MPa or more and 500 MPa or less as calculated by force curve measurement using AFM in water
Implementation Method 2
composite semipermeable membrane includes: a porous support membrane; and a skin layer supported by the porous support membrane
Data Source
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AI summary
A composite semipermeable membrane 12 of the present invention includes a porous support membrane 12a and a skin layer 12b supported by the porous support membrane 12a. The membrane surface of the composite semipermeable membrane 12 has an elastic modulus of 250 MPa or more and 500 MPa or less as calculated by force curve measurement using AFM in water. A spiral membrane element 20 of the present invention includes the composite semipermeable membrane 12 of the present invention. A water treatment system 100 of the present invention includes the spiral membrane element 20 of the present invention.