Polyamide Membrane Chlorine Resistance via Droplet Polymerization
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Solution Overview
Problem
Existing water-treatment separating membranes have a short chlorine resistance duration and require separate post-treatment processes to maintain high salt rejection and permeation flux, which complicates their operation and maintenance.
Innovation Solution
A water-treatment separating membrane is manufactured by forming an aqueous amine solution layer on a porous support and dropping droplets of an organic solution containing an acyl halide compound, creating a polyamide active layer with varying thickness and surface roughness, which increases the specific surface area without the need for additional post-treatment processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin film of polyamide active layer is formed by interfacial polymerization, then high salt rejection and high permeation flux are achieved, but chlorine resistance decreases rapidly over time
Solution Approach 1:
The patent applies local quality by creating a polyamide active layer with non-uniform thickness through controlled droplet formation. The layer has varying thickness across the surface, with thinner regions providing high permeation flux and thicker regions providing enhanced chlorine resistance. This local variation in layer properties allows simultaneous optimization of both salt rejection performance and durability against chlorine degradation.
Solution Approach 2:
The patent introduces dynamics by using a two-stage polymerization process. First, a thin polyamide layer is formed by interfacial polymerization between aqueous amine solution and organic acyl halide solution. Then, the layer is further polymerized by treating with additional acyl halide solution, dynamically evolving the layer structure to enhance chlorine resistance while maintaining the initial high-performance characteristics.
2Duration of action of stationary object
If the specific surface area of the active layer is increased to improve chlorine resistance, then a separate post-treatment process is required to coat the surface with electrically neutral polymer
Solution Approach 1:
The patent merges multiple functions into a single integrated process. The polyamide active layer formation and chlorine resistance enhancement are combined into one continuous process without requiring separate post-treatment steps. The controlled droplet polymerization inherently creates the desired layer structure that simultaneously provides both separation performance and chlorine resistance, eliminating the need for additional coating processes.
Solution Approach 2:
The patent applies self-service by designing a process where the polyamide active layer automatically develops the necessary properties during formation. The controlled droplet polymerization process inherently creates a layer with appropriate surface characteristics and thickness distribution that provides chlorine resistance without requiring external intervention or separate treatment steps to coat the surface with neutral polymers.
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 method results in a membrane with extended chlorine resistance and maintained high salt rejection and permeation flux over time, eliminating the need for separate post-treatment processes and enhancing surface roughness and specific surface area.
Implementation Method 1
impregnating the minute and porous support with an organic solution including trimesoyl chloride (TMC) so that the mPD contacts the TMC to allow interfacial polymerization and to form a polyamide layer
Implementation Method 2
When a level of external pressure, higher than osmotic pressure, is applied, the solvent may move from the solution having the higher concentration of the solute to the solution having the lower concentration of the solute. This phenomenon is known as reverse osmosis.
Data Source
Figure 1A~1C
Figure 2A~2C
Figure 3A~3C
AI summary
A water-treatment separating membrane includes a polyamide active layer formed on a porous support. The ratio of a maximum value with respect to a minimum value of a ratio of a peak height of a C=O double bond of a carboxyl group (-COOH) with respect to a peak height of a C=O double bond combined with an amide group (-CONH-) is from 1.2 to 4, when measured after acid treating the polyamide active layer and by using a Fourier transform infrared spectrometer (FTIR).