Many industrial processes such as printing, metal cleaning or painting produce waste air streams containing low concentrations of organic solvents, such as acetone, toluene, perchloroethane, xylene, etc. The total value of the solvent lost with the waste air is considerable. In addition, these solvents represent a significant pollution problem, and in recent years several procedures for recovering solvents from air, such as carbon adsorption, incineration, etc. have been introduced in the industry. All of them show some draw-backs in terms of efficiency, reliability and costs. In this paper a membrane process is described, which provides an attractive alternative to the conventional methods. In a basic study the permeabilities of acetone, toluene, xylene, dichloroethane and dichloromethane through a homogeneous polydimethylsiloxane (PDMS) membrane have been determined using a pressure difference between 400 and 1000 mbar as driving force. The selectivity of the membrane for the various solvents and their dependence on the solvent concentration in a mixture with nitrogen were studied.

The selectivities of the PDMS membrane for the solvent/nitrogen mixtures were in the range of S = 70-160, depending on the solvent and its concentration in the feed mixture. Based on these data a pilot plant process has been designed in which a solvent is recovered from a waste air stream and the depleted air is recycled into the waste air producing process. The solvent which has permeated the membrane is recovered as a liquid by condensation. Thus, complete recycling of air and solvents is possible. In a cost analysis it has been demonstrated that the membrane process is indeed an attractive alternative to conventional air cleaning techniques.

Read the full research of Removal of organic vapors from air

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Silicone rubber has very different properties from general synthetic rubber.

Physical properties

It has properties such as heat resistance and high electrical insulation. It does not harden even at low temperatures. It is resistant to ultraviolet rays, and physiologically inactive. These characteristics are due to the difference in silicone rubber’s molecular structure from general rubber.

Chemical properties

General rubber is a bond of carbon and carbon, but silicone rubber is a bond of silicon and oxygen. This bond is called a siloxane bond, and the characteristic properties of silicone rubber are due to this siloxane bond.
The binding energy of Si—O in silicone rubber is considerably larger than that of CC and CO bonds, so it is chemically stable. In addition, the Si—O bond has about 50% ionic bond property compared to the CC bond, which consists of 100% covalent bond, and can be said to be located between organic and inorganic. It is thought that the presence of this ionic bond strengthens the bond between CH of the methyl group which directly bonded to silicon and contributes to stabilization.

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Nagasep has excellent permeability of VOC (volatile organic solvent) as well as gas molecules, so the target component can be separated and recovered from the atmosphere or water. The standard size of the hollow fiber membrane and the permeability of various gases are displayed below.

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The amount of oxygen dissolved in water under atmospheric pressure is approximately 8 ppm at 25 ° C.

Metals will get rusted by water and oxygen. The reaction of iron rusting process happens like this : When iron comes into contact with water, it dissolves in water as iron ions, and at the same time, dissolved oxygen produces hydroxide ions. Iron (II) hydroxide is formed by the reaction of iron ions and hydroxide ions. This is oxidized by dissolved oxygen, thus produces ferric hydroxide containing hydroxide called red rust.

Red rust on pipes can be prevented by removing dissolved oxygen using NAGASEP. In addition, the flow of degassed water through the pipe would naturally create a film of triiron tetroxide called black rust. This black rust is formed on the surface of the iron and won’t react with moisture or oxygen, which can suppress the occurrence of red rust.

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1. Degassing of recycled water Using NAGASEP (internal perfusion modules) for recycled water in buildings to prevent pipe rusting.

2. Degassing of tap water Using NAGASEP (external perfusion modules) for tap water, besides degassing, harmful chlorine compounds are also removed at the same time.

What makes NAGASEP exceptional?

NAGASEP can deal with the rusty water without rebuilding the whole pipe system. You only need to put one or several modules into the tank and it will start producing non-oxygenated water. We have a real case that NAGASEP is installed where tank water enters into pipe and turns the water into degassed water. The degassed water can be a natural cleaner for the rusty pipe and can prevent rust in the future.

Why degassed water can reduce the red rust to black rust?

In normal water, the chemical reaction goes like: 4Fe + 3O2 + 2H2O → 4FeOOH

In degassed water, the chemical reaction goes like: 6FeOOH + 2e- → 2Fe3O4　＋ 2H2O + 2OH

What is frequency for changing a new module?

Whenever there is leak in the old module you should change for a new one. The reason for the damage to silicone is mainly because of oganochloride. Thus, the expected changing frequency for the module will be determined by the water quality.

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This research has used our product NAGASEP.

What is chlorealla?
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A hollow fiber culture system has been proposed for supplying the carbon dioxide to the microalgae, to replace the conventional air bubbling system which has been adopted to supply carbon dioxide in most conventional microalgal culture. In order to examine the usefulness of hollow fiber membranes for the microalgal culture, the microalgal growth rate for Chlorella sp. and the effective mass transfer coefficient of carbon dioxide through the hollow fiber membranes have been measured using the proposed photobioreactor filled with hollow fibers.

The microalgal growth rate using hollow fiber membranes was found to be three times greater than that observed in the conventional non-membrane photobioreactor. An experimental investigation has been conducted so as to evaluate the effect of the volume flow rate of the carbon dioxide and its concentration of the feed air through the hollow fibers on the microalgal growth rate. The present study clearly indicates that the hollow fiber membrane is quite useful for the microalgae culture in terms of enhancing both microalgal growth rate and dissolution rate of the carbon dioxide.

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In an inkjet printer, ink is ejected onto paper from the tip of a thin nozzle called an ink head to print. At this time, if gas is dissolved in the ink, it will become bubbles and cause print misalignment or nozzle clogging during ejection. These problems can be prevented by degassing the ink before printing using NAGASEP, so that the print finish will be beautiful.

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Resin: PVC, PC, ABS, PP
Metal: aluminum, stainless

Above are the optional material for the housing of module.

For test modules, resin housing is cheaper. However, the resins listed above are not highly resistant to organic solvents.

If your application is recycling of organic solvent from waste liquid or there will be organic solvent, we would recommend you to use metal-based housing.

Also, for autoclave sterilization (120 ℃), it is reasonable to choose metal or polycarbonate(PC), since PVC and ABS has a lower working temperature.

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The removal of dissolved oxygen (DO) from water was studied using a silicone rubber hollow-fiber membrane module. Dissolved oxygen in water was effectively reduced by the vacuum degassing or pervaporation process through a non-porous membrane. The controlling transport property, gas permeability through the membrane, was independently measured by a method using a differential transformer. A gas-phase driving force model was presented based on the permeabilities of the permeates through the hollow-fiber. Experimental results of the oxygen removal from water were compared with the model calculations. The present model proved to explain the effects of the pressure condition and the operation mode on the removal of oxygen from water. Although the liquid-phase mass transfer resistance was shown to have a large effect on the removal performance of the membrane module, the membrane permeation step controlled the mass transfer during vacuum degassing.

Ⓒ 1998 Elsevier Science B.V.

Keywords: Fiber membranes; Gas and vapor permeation; Pervaporation; Water treatment; Dissolved oxygen

To read the entire essay, please download this PDF file.

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In a 20℃ environment, oxygen can dissolve at 8ppm nitrogen at 15ppm. When temperature arise, less air dissolve in water. The dissolved oxygen is necessary for the creatures living underwater, but since oxygen would create scale buildup and corrosion of the pipes, for industries it’s ideal to remove the oxygen from water.

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