ENP Newswire -
Release date- 24022014 -
At the same time, the newly developed RO membrane is highly durable (the ability to sustain its performance to remove substances) against chemical cleaning, which is carried out during operation of water treatment plant to clean membranes when they become clogged with foreign substances in raw water. The membrane is expected to contribute to reduction of water treatment cost in applications such as brackish water desalination and wastewater treatment where chemical cleaning is required even more frequently because of the low quality of raw water.
In recent years, RO membranes have gained popularity in water treatment plants around the world for addressing water problems (water shortage, water quality deterioration, etc.). There has been increasing requirement for improving removal properties to secure high quality water and enhancing water permeability to carry out the treatment with low energy. Demand for enhancement of durability of RO membranes against chemical cleaning and in long-term use has been especially strong to ensure consistent supply of high quality water from raw water with varying qualities, as the use of RO membranes expands significantly.
To meet the demands,
The technological highlights of the newly developed ultralow pressure, highly durable RO membrane are the two key points based on which microstructure control was performed.
1. Stabilization of fine pore structure through control of the primary structure
Functional layer of a reverse osmosis membrane is formed of a material of cross-linked polyamide4) with fine pore structure.
This time, it carried out in-depth analysis of the primary structure8) of cross-linked polyamide using nuclear magnetic resonance spectrometry9) and succeeded in establishment of the precise interfacial polymerization10) to stabilize the primary structure based on the information obtained in the analysis. This enabled the formulation of the functional polyamide layer whose fine pore structure is stable in changing environment and stronger against chemicals including acids, alkalis, and small amount of chlorine.
2. Increased number of fine pores by controlling intermolecular interactions
The development of the ultralow pressure, highly durable RO membrane further diversifies the solutions it offers and is expected to contribute to solving the global water-related problems.
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1) Reverse osmosis membrane (RO membrane)
When a concentrated solution is separated from a dilute solution by semi-permeable membrane, water penetrates from the dilute solution phase to the concentrated solution due to the osmotic pressure generated by the concentration difference. When a pressure higher than the osmotic pressure is applied on the concentrated solution, water passes through the semi-permeable membrane into the dilute side. Membrane separation method on the basis of this phenomenon is called reverse osmosis method. RO membranes used in this method can remove positive metal ions such as sodium and calcium, negative ions such as chloride ion and sulfate ion as well as low molecular weight organic compounds such as agricultural chemicals.
2) Sub-nanometer scale
One nanometer is one billionth of a meter. Sub-nanometer is one tenth of a nanometer.
Sub-nanometer scale refers to this infinitesimally small world.
3) Highly durable RO membrane
4) Cross-linked polyamide
Polyamide can be largely divided into linear polyamides, whose chemical structure is straight chain shaped, and cross-linked polyamide, whose chemical structure has a mesh-like appearance. Cross-linked polyamide is the mainstream material for the functional layer of RO membrane.
Boron is known to cause damping-off of citrus fruits and also infertility and there is a need for technology that can efficiently remove the substance during seawater desalination and waste water treatment.
6) Positronium annihilation lifetime spectroscopy (PALS)
Positronium, an elementary particle with the same mass and negative charge of electron, self-destructs while releasing gamma rays on collision with electron. Positronium annihilation lifetime spectroscopy (PALS) determines the pore size of a material through lifetime measured by injecting positronium into it.
The smaller pore size of the material, the higher the probability of collision with electrons existing outside of the pores, which in turn means shorter positronium annihilation lifetime.
PALS technology can be used to measure pore sizes in the range of a sub-nanometer to ten nanometers.
7) Molecular dynamics simulation method
Molecular dynamics simulation method is a method to calculate polymer dynamics using computer. It enables us to obtain data on polymer molecule, movement and existence of water and solute in RO membrane by simulating position of each atom in molecule through Newton's laws of motion.
8) Primary structure
The primary structure of polyamide denotes repeating units and functional end groups of polyamide.
9) Nuclear magnetic resonance spectrometry
Nuclear magnetic resonance spectrometry is an effective method to analyze the chemical structure of organic molecules.
10) Precise interfacial polymerization
The cross-linked polyamide of RO membranes is made using a technology called interfacial polymerization that polymerizes monomers at the interface of water and oil.
11) Low fouling RO membrane
If organic compounds or microorganisms are present in raw water, it creates a phenomenon known as fouling, wherein these substances stick to the membrane surface, causing reduced water production. The low fouling RO membrane is a result of basic analysis of the fouling phenomenon and reduces the possibility of such substances sticking on the surface.
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