Polyamide Semipermeable Membrane With Amino Density Gradient
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Solution Overview
Problem
Existing composite semipermeable membranes face a trade-off between water permeability and solute removability, with increased water permeability leading to decreased removability, necessitating an improvement in both properties.
Innovation Solution
A composite semipermeable membrane with a separation functional layer containing crosslinked polyamide, featuring a controlled amino group density gradient and specific structural characteristics, including a thickness of 9.0 nm to 13.0 nm, and a ratio of amino to carboxy and amide groups, optimized for high water permeability and removability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If water permeability of the composite semipermeable membrane is increased, then energy saving during operation is improved, but removability of solutes decreases
Solution Approach 1:
The invention applies local quality by creating a gradient structure within the separation functional layer where amino group density varies through the thickness. The surface region has lower amino group density for high removability, while the inner region has higher amino group density for high water permeability. This spatial variation in composition allows simultaneous optimization of both removability and water permeability, resolving the technical contradiction.
Solution Approach 2:
The invention changes the parameter of amino group density distribution within the separation functional layer. By controlling the ratio Nb/Nd (amino group density at surface/amino group density at inner region) to be 0.40 or less, the membrane achieves optimal balance between removability and water permeability, thereby improving energy efficiency without sacrificing solute removal performance.
2Productivity
If water permeability is improved, then productivity is increased, but removability decreases
Solution Approach 1:
The separation functional layer is designed with non-uniform amino group density distribution, where the surface region (lower density) provides high removability and the inner region (higher density) provides high water permeability. This local differentiation allows the membrane to simultaneously achieve high productivity and high removability, breaking the traditional trade-off between these parameters.
Solution Approach 2:
The invention creates a composite structure within the separation functional layer that combines regions with different amino group densities. This composite approach, achieved through controlled interfacial polycondensation, allows the membrane to exhibit both high water permeability (from the inner region) and high removability (from the surface region), simultaneously improving productivity and reliability.
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 water permeability and solute removal rates, with silica removal rates of 99.3% or more, boron removal rates of 60% or more, and sodium chloride removal rates of 99.5% or more, while maintaining low resistance to water permeation.
Implementation Method 1
membrane separation method has become increasingly used as an energy- and resource-saving process
Implementation Method 2
a composite semipermeable membrane useful for selective separation of a liquid mixture... can be suitably used for desalination of, for example, seawater and brackish water
Implementation Method 3
The separation functional layer is formed on the porous support membrane by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide
Data Source
AI summary
The present invention relates to a composite semipermeable membrane including a porous support layer and a separation functional layer provided on the porous support layer, in which the composite semipermeable membrane has a first surface which is a surface on a separation functional layer side and a second surface which is a surface opposite to the first surface, the separation functional layer contains a crosslinked polyamide, and an amino group density measured by a scanning transmission electron microscope (STEM) in a cross section in a thickness direction of the separation functional layer satisfies Nb/Nd≤0.40, provided that Nb and Nd are defined in the description.