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NAGASEP is a separation membrane module made of silicone (silicon rubber; scientific name “polydimethylsiloxane”) hollow fiber homogeneous membrane ※1.
It bundles ultrafine tubes with an inner diameter of about 200 μm (0.2 mm) and a film thickness of 20 to 80 μm (0.02 to 0.08 mm) for each size, so a large separation membrane area can be secured with a relatively small volume.
NAGASEP’s hollow fiber membrane, silicone (silicon rubber), is physiologically inactive, so it maintains its normal physical properties in a wide temperature range from -60 ° C to over 150 ° C. Also, it has electrical insulation and is highly resistant to ultraviolet rays.
※1 A “homogeneous membrane” refers to a membrane with no pores in which polymer chains have gaps at the molecular level.
First, the clogging problem.Porous membranes separate substances by permeating various components according to the size of the pores formed in the membrane. Therefore, during operation, membrane performance deterioration often occurs due to pore clogging and countermeasures are required.There is no hole in the homogeneous membrane, so no need to worry about clogging.
Second, silicone membranes have better dissolution rate for larger molecules. The solubility in silicone membrane increases with the size of the molecule. The larger the molecule, the greater the condensability. This helps the molecule to dissolve better into the membrane. On the other hand, For porous membranes, the diffusivity in the film is generally smaller when the resistance increase.
Silicone (silicone rubber) has excellent resistance to inorganic chemicals such as various acids, bases, salts, oxidizers, and polar organic compounds such as alcohol or animal and vegetable oils, but will swell with non-polar organic compounds such as gasoline, toluene, carbon tetrachloride and insulating oil, etc.
It is hardly affected by dilute acids, dilute alkalis, alcohols, acetone, nitrobenzene, aniline, etc., and its volume increases by 10 to 15%.
Although it swells to some extent in benzene, toluene, gasoline, carbon tetrachloride, etc. Unlike general organic rubber, it does not dissolve the material but will return to its original state when the solvent is removed.
It also has excellent oil resistance at high temperatures.
During production, a small amount of silica powder is applied to the surface of the membrane to prevent the hollow fibers from sticking together, but it is not treated with chemicals.
Silica is a general term for substances composed of silicon dioxide (SiO2), which is contained in large quantities in the natural world or even in the living body, though in small amounts.
In industrial use, silica is widely used in industry such as fillers for rubber and paper, additives for foods, cosmetics, and pharmaceuticals, and desiccants for sweets.
Silicone (silicon rubber) is hydrophobic and has a water absorption rate of less than 1% even when immersed in water for a long time.
Unlike general rubber, silicone (silicon rubber) has a chemically stable molecular structure because its main chain consists of siloxane bonds of silicon and oxygen.
By permeation (pervaporation ※2) method in which the mixed solution is supplied to the silicone (silicon rubber) membrane module and the pressure on the opposite side of the membrane is reduced by a vacuum pump to liquefy the vapor that has permeated through a cooling trap. The mixed solvent can be separated and collected.
※2 The name pervaporation has come to be called pervaporation because the process of pervaporation consists of two processes, permeation and evaporation.
There are two methods for VOC (Volatile Organic Compounds) emission measures: combustion method and separation/recovery method. Separation/recovery method include adsorption with activated carbon and membrane separation with selective permeation membrane.
The silicone (silicon rubber) hollow fiber membrane adopted by NAGASEP has excellent characteristics for separating and concentrating VOCs.
The device has a simple structure in which a vacuum pump and a vapor recovery container are installed in the membrane module, and the VOC can be continuously concentrated and collected by reducing the pressure on the permeate side of the membrane while maintaining atmospheric pressure on the membrane supply side.
Most VOC is contained as a solvent in adhesives, paints, inks, etc. Chemical components manufacturers and printing facilities, electronic components and metalworking manufacturers that use VOC as a cleaning agent. Also, VOC is emitted from the storage tanks of and petroleum such as gasoline. If it is released into the atmosphere, it may cause pollution such as health damage. In 2004, a revised Air Pollution Control Act enforced Regulations are in place for major emission facilities.
Dissolved gas in water can be continuously removed by flushing water into the silicone (silicon rubber) hollow fiber while depressurizing the outside with a vacuum pump.
Generally, 8 ppm of oxygen and 15 ppm of nitrogen are dissolved at a water temperature of 20 ° C, but by using a silicone (silicon rubber) hollow fiber membrane it possible to degas them to ppb.
It is easy to concentrate oxygen and carbon dioxide from the atmosphere using a device applied with silicone (silicon rubber) membrane.
By supplying indoor air (oxygen concentration 21%, carbon dioxide concentration 400ppm) to the silicone (silicon rubber) membrane module and reducing the pressure on the air side, the permeated air is concentrated to oxygen concentration 30%, carbon dioxide concentration 1,500ppm.
Concentrated carbon dioxide can be used as a carbon dioxide supply device for greenhouses in greenhouse cultivation.
Since animal cells are breathing, it is necessary to maintain a high oxygen concentration and the discharge of carbon dioxide in the medium.
The silicone (silicon rubber) hollow fiber membranes that make up NAGASEP are
(1) The area of the gas exchange membranes can be efficiently secured within the limited volume.
(2) Good permeability of oxygen and carbon dioxide
(3) No entry route for mold and other bacteria
(4) Gas exchange is possible without bubbles regardless of supply pressure
(5) Autoclave sterilization is possible
Given the features above, it is suitable for gas exchangers.
When water and organic solvent are separated, because silicone (silicone rubber) is hydrophobic, the organic solvent permeates first.
Trihalomethanes (chlorine compounds) such as trichlorethylene, chloroform and carbon tetrachloride, which are harmful in tap water and groundwater, can be removed at the same time.
The detergent should be chosen depending on the dirt, generally the following detergents are recommended. Pump these detergents through the module, then rinse with water.
[Microorganism]
Sodium hydroxide (pH 10-12), sodium hypochlorite (100-1000ppm), hydrogen peroxide (1-3%)
[Proteins, polysaccharides, etc.]
Sodium hydroxide (pH 10-12), sodium hypochlorite (100-1000ppm), surfactant (0.1-0.2%)
[Fats and oils]
Sodium hydroxide (pH 10-12), surfactant (0.1-0.2%), warm water (-80 ° C)
[Scale (inorganic)]
Hydrochloric acid, sulfuric acid, nitric acid (about 2%)
The pervaporation (pervaporation * 2) method is to supply an aqueous solution to one side of the membrane and reduce the pressure on the other side with a vacuum pump to allow a specific liquid component to permeate the membrane as vapor, then this vapor can be cooled and taken out.
Imagine the cross-section of the membrane in the thickness direction, it consists of two layers. On the liquid side, the liquid has permeated the membrane and formed a solution phase. On the gas side, a vapor phase in which this liquid becomes vapor is formed.
There are three separation processes: <dissolution> → <diffusion> → <evaporation></evaporation></diffusion></dissolution> Therefore, the principle of the pervaporation method is, as in the case of the gas separation membrane, that separation is performed by utilizing the difference in the dissolution / diffusion rate with respect to the membrane, or so to say the interaction between the permeation component and the membrane.
Therefore, it has the advantage that an azeotropic mixture that cannot be separated by the distillation method that separates due to the difference in boiling points, can be separated by selecting the membrane, and that it is not affected by the osmotic pressure unlike the reverse osmosis membrane.
※2 The name pervaporation has come to be called pervaporation because the process of pervaporation consists of two processes, permeation and evaporation.
