Reverse Osmosis Membrane with Carbon Nanotubes for Chlorine Resistance
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Solution Overview
Problem
Reverse osmosis membranes using aromatic polyamide suffer from low chlorine resistance, leading to reduced desalination performance after washing with oxidizing chlorine, and existing carbon nanotube-based membranes do not offer significant improvements in performance or resistance.
Innovation Solution
A reverse osmosis composite membrane is developed with disentangled carbon nanotubes embedded in a crosslinked polyamide matrix, featuring a specific distribution of carbon nanotubes and a molecularly-oriented crosslinked aromatic polyamide layer that enhances chlorine resistance and maintains high permeate flux and NaCl rejection rates even after exposure to oxidizing chlorine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If aromatic polyamide reverse osmosis membrane is used for desalination, then high NaCl rejection rate is achieved, but chlorine resistance is low causing performance deterioration after washing
Solution Approach 1:
The patent uses a composite structure combining aromatic polyamide with carbon nanotubes and crosslinking agents. The carbon nanotubes are dispersed within the polyamide matrix, creating a composite material that maintains the high rejection properties of polyamide while adding chlorine resistance through the carbon nanotube network and crosslinked structure.
Solution Approach 2:
The patent modifies the chemical structure of the polyamide by introducing crosslinking through agents like triethylene glycol dimethyl ether. This crosslinking changes the physical and chemical parameters of the membrane, improving its stability and resistance to oxidizing agents like chlorine while maintaining porosity and rejection properties.
2Ease of operation
If oxidizing chlorine washing is applied to restore membrane performance, then dirt and protein components are removed, but membrane deterioration occurs due to low chlorine resistance
Solution Approach 1:
The patent converts the harmful effect of chlorine (which normally deteriorates polyamide membranes) into a beneficial washing method. The carbon nanotube-enhanced membrane can withstand chlorine exposure, allowing the use of strong oxidizing agents for effective cleaning without damaging the membrane structure, thus enabling thorough removal of organic fouling.
Solution Approach 2:
The crosslinking density and carbon nanotube content are optimized to achieve the right balance between membrane permeability, rejection properties, and chlorine resistance. This parameter optimization allows the membrane to withstand repeated chlorine washing cycles while maintaining performance.
3Reliability
If carbon nanotubes are incorporated into polyamide membrane, then chlorine resistance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent incorporates carbon nanotubes into the polyamide matrix during the membrane formation process itself, rather than as a separate post-treatment step. The carbon nanotubes are mixed with the polyamide solution before phase inversion, ensuring uniform distribution and simplifying the manufacturing process while achieving the desired chlorine resistance.
Solution Approach 2:
The patent utilizes the porous structure formed during phase inversion to accommodate carbon nanotubes. The phase inversion process creates a sponge-like structure with interconnected pores that naturally incorporate the carbon nanotubes, eliminating the need for complex additional processing steps to integrate the nanotubes into the membrane.
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 a permeate flux of 0.8 m3/(m2·day·MPa) and a NaCl rejection rate of 95% or more, with less than 10% reduction in rejection rate after immersion in sodium hypochlorite, and maintains antifouling properties and chlorine resistance.
Implementation Method 1
a reverse osmosis membrane arranged on the porous support and containing a crosslinked polyamide and carbon nanotubes
Implementation Method 2
the reverse osmosis membrane containing disentangled carbon nanotubes in the crosslinked polyamide... excellent in chlorine resistance
Data Source
AI summary
A method of manufacturing a reverse osmosis composite membrane, including: (i) bringing a mixed liquid containing carbon nanotubes, water, and an amine component into contact with a porous support, the mixed liquid being produced through a step of pressurizing and compressing an aqueous solution containing the carbon nanotubes while flowing the aqueous solution, followed by releasing or reducing a pressure to return a volume of the aqueous solution to an original volume to mix the carbon nanotubes; and then (ii) subjecting the amine component in the mixed liquid adhering to the porous support to a crosslinking reaction.