Polyphenol-Polyamine Membrane for Magnesium-Lithium Separation
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Solution Overview
Problem
Existing commercial nanofiltration membranes have low efficiency for magnesium-lithium separation in salt lake water, with a separation coefficient of less than 5, making them unsuitable for extracting lithium from salt lake brine.
Innovation Solution
A separation membrane composed of a base material layer, porous support layer, and polyamide layer with a modification layer formed by cross-linked polymers from polyphenols and polyamines, featuring a pore size of 0.1-0.5 nm and Zeta potential of -5 mV to 30 mV, prepared through a self-assembly process under controlled pressures and fluid conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing commercial nanofiltration membrane is used for magnesium-lithium separation, then the membrane structure is simple and easy to manufacture, but the separation efficiency is extremely low with coefficient less than 5
Solution Approach 1:
The patent applies composite materials by combining polyamide layer with modification layer containing polyphenol and polyamine cross-linked polymers. This composite structure enables the membrane to achieve high magnesium-lithium separation coefficient (70-250) while maintaining manufacturability through established membrane fabrication processes.
Solution Approach 2:
The patent changes key parameters including pore size control (0.1-0.5 nm) and surface Zeta potential adjustment (-5 mV to 30 mV) through the modification layer. These parameter changes transform the membrane's separation performance from coefficient <5 to coefficient 70-250, directly addressing the separation efficiency requirement.
2Manufacturing precision
If pore size is reduced to improve separation efficiency, then magnesium-lithium separation coefficient increases, but water flux decreases
Solution Approach 1:
The patent applies local quality by creating a modification layer with specific cross-linked polymer structures on the polyamide layer surface. This localized modification maintains the bulk pore structure for water flux while creating a selective barrier layer with controlled local properties (pore size 0.1-0.5 nm, Zeta potential -5 mV to 30 mV) for high magnesium-lithium separation coefficient 70-250.
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 magnesium-lithium separation efficiency with a separation coefficient of 70-250 and high water flux, effectively intercepting magnesium ions while allowing lithium ions to pass through, with a desalination rate of MgCl2 exceeding 99%.
Implementation Method 1
a surface Zeta potential of the separation membrane is within the range from −5 mV to 30 mV... can desirably intercept magnesium ions
Implementation Method 2
a pore size of the separation membrane is within the range of 0.1-0.5 nm... effectively intercepting magnesium ions while allowing lithium ions to pass through
Implementation Method 3
a method for preparing the modification layer comprising: under a first pressure, and under conditions in which a polyphenol solution remains fluid, subjecting the polyamide layer side of a material... to a first contact with the polyphenol solution; then under a second pressure, and under conditions in which a polyamine solution remains fluid, subjecting the polyamide layer side of the material to a second contact with the polyamine solution to complete a self-assembly reaction
Data Source
AI summary
A separation membrane, a preparation method therefor and a use thereof in magnesium and lithium separation are provided. The separation membrane includes, in sequence, a base material layer, a porous support layer, a polyamide layer and a modification layer. Cross-linked polymers forming the modification layer has structural units provided by polyphenols and polyamines, at least some of the structural units provided by the polyphenols are connected to the polyamide layer via ortho positions of phenolic hydroxyl groups. The preparation method includes sequentially preparing the porous support layer, the polyamide layer and the modification layer on the base material layer. The method of preparing the modification layer includes under a first pressure, bringing one side of the polyamide layer into first contact with the polyphenol solution; then under a second pressure, bringing one side of the polyamide layer into second contact with the polyamine solution, to complete a self-assembly reaction.