JPH03213103A - Gas or low melting point volatile organic substance-removing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for removing gases or low-boiling volatile organic substances dissolved in an aqueous solution.

[Prior Art and Problems to be Solved by the Invention] When using an aqueous solution, there are many fields in which it is necessary to remove gases or organic substances dissolved therein.

For example, regarding analytical equipment, liquid chromatography,
Automated clinical chemistry analysis, degassing of medical spectrophotometers, etc.
Industrial applications include deaeration of ion exchange water processes, ultrapure water systems, boiler water, nuclear power plant water, turbine water, etc.

For example, in liquid chromatography, if air is dissolved in the solvent, bubbles will form inside the pump, around valves, and inside the detector, causing trouble. Dissolved oxygen can also cause chemical reactions with solutes.

In automated clinical chemistry analysis, as the amount of sample becomes smaller, even a small amount of dissolved oxygen has a negative impact on analysis accuracy.

In addition, spectrophotometers are greatly affected by absorption by dissolved oxygen in the ultraviolet short wavelength region. On the other hand, in the ion exchange water process, dissolved oxygen and carbon dioxide gas in the liquid shorten the life of the ion exchange resin. Furthermore, dissolved oxygen in boiler water and nuclear power plant water accelerates corrosion of containers, pipes, etc.

BACKGROUND ART Conventionally, methods such as a heating boiling method, a depressurization method, an ultrasonic method, a helium method, and the like have been known for degassing gases dissolved in a liquid. However, the heating boiling method is highly dangerous due to its high temperature operation, the decompression method and ultrasonic method have low degassing ability, and the helium method has high operating costs, so it has never been an effective or economical method.

More specifically, for example, gases dissolved in boiler water, mainly dissolved oxygen, are the main cause of pitting corrosion in boiler pre-boiler systems, so treatment to remove them is necessary. For such deoxidation, there are two methods: mechanical deoxidation using a deaerator using a heating boiling method, a vacuum method, etc., and a method of chemically reducing dissolved oxygen, for example, by injecting an oxygen scavenger such as hydrazine or sodium sulfite. There are various methods, and unless these methods are used in combination, the deoxidation efficiency cannot be increased, and this process is especially essential for medium and high pressure boilers.

Furthermore, dissolved gases, mainly dissolved oxygen, in drinking water and building water supplies are the main cause of corrosion in water supply pipes, and this corrosion leads to the occurrence of red water. Red water causes sensory problems such as taste and causes problems such as discoloration of laundry, so if its occurrence is recognized, it is necessary to consider some countermeasures. Currently, countermeasures against such red water include re-laying water supply pipes, replacing pipes with linings, and continuously injecting rust preventive agents for water supply. These red water prevention measures are both economical and
It is not necessarily sufficient in terms of reliability, safety, etc., and comes with various limitations. Therefore, an inexpensive, simple, and reliable prevention method is desired.

Conventionally, the purpose of deaeration in ultrapure water systems can be roughly divided into two types. One is removing dissolved carbon dioxide to extend the life of the anion exchange resin during the ion exchange process, and the other is removing dissolved oxygen to suppress the generation of viable bacteria in ultrapure water. . In semiconductor manufacturing,
When the memory capacity reached the 256-bit level, a level of 0.5 ppm was sufficient as the dissolved oxygen concentration (hereinafter referred to as DO value) for the above purpose. the result,
A vacuum deaeration method has been used as a deaeration method.

However, in recent years, 4M bits and 1
Semiconductors with 6M pins are being developed.

In the manufacture of these large-capacity semiconductors, in addition to the above two points, the purpose of degassing is to prevent the formation of an oxide film on the silicon wafer due to dissolved oxygen. In order to prevent oxidation of the silicon wafer due to this dissolved oxygen, the Do value should be 0.01 to 0. O5ppm is required. Furthermore, since it is necessary to perform degassing near the point of use, a relatively small degassing device is required.

However, conventional vacuum deaerators have disadvantages in that their ability to remove dissolved oxygen is insufficient and the size of the device is also quite large.

Beverage manufacturing water, which is the raw water used to manufacture beverages such as beer, juice, and coffee, and the water used in those manufacturing processes, is generally sterilized by removing dissolved oxygen to prevent product deterioration and oxidation. Preferably.

Conventionally, in order to produce water for such purposes, water to be treated is desorbed by heating and boiling, depressurization, or by contacting the water with carbon dioxide gas or a mixed gas of carbon dioxide gas and an inert gas. Know how to care.

However, in the heating boiling method, dissolved oxygen in water is
It is necessary to heat the water to be treated to a temperature of 104°C or higher in order to reduce the amount to 104°C. This heating increases energy costs, and long-term operation causes scale to deposit on various parts of the equipment, making cleaning difficult. It requires a lot of effort. The depressurization method has the disadvantage that it can only reduce dissolved oxygen in water to about 0.2 ppm and has a low degassing ability. In addition, the method of bringing carbon dioxide gas into contact with the water to be treated reduces dissolved oxygen in the water to 0. In order to reduce the amount to about 1 ppm, it is necessary to fill the device with a filler such as Raschchlinig and raise the temperature to a high temperature of about 70° C., and cleaning this filler requires a lot of effort. Furthermore, when used as water for brewing coffee or the like, delicious and flavorful coffee cannot be obtained because carbon dioxide is dissolved in the water. In addition, in a method in which a mixed gas of carbon dioxide gas and an inert gas is brought into contact with the water to be treated, dissolved oxygen in the water is reduced to 0. To reduce O to about 5ppm, heat the water to be treated to 101°C.
It is necessary to heat the coffee to a higher level, and in this case as well, there is a problem in that the energy cost due to heating is high and, like the above, delicious and flavorful coffee cannot be obtained.

Furthermore, in semiconductor-related fields, low-boiling volatile organic substances such as chloroform, trichloroethane, trichloroethylene, carbon tetrachloride, carbon tetrachloride, and tetrachloroethylene contained in wastewater must be recovered from the viewpoint of environmental issues. However, in the currently used activated carbon adsorption method, since the wastewater is a dilute aqueous solution, the recovery cost is extremely high and it is not economical.

Even in the field of drinking water, pollution of water sources such as rivers and lakes has caused
Low boiling point volatile organic substances, which were not previously included, now exceed environmental standards, and as contamination progresses, the amount of chlorine used for chlorine disinfection increases, and chlorine-based organic substances are produced by chemical reactions. It is now generated. However, with increasing interest in drinking water in recent years,
Despite the need for advanced processing, the current situation is that effective processing is not carried out due to cost issues.

As mentioned above, there are many fields that require the removal of gaseous or low-boiling volatile organic substances, and there has been no satisfactory removal method in any of these fields.

In recent years, a degassing method using a tube (hollow) membrane made of synthetic resin such as silicone or polytetrafluoroethylene has been proposed (Japanese Patent Application Laid-Open No. 60-25514, Utility Model Application No. 63-43609, etc.). ).

However, thin films made of such synthetic resins have limits in terms of mechanical strength and moldability, and in order to be used practically as a degassing membrane, the film thickness must be increased as the degassing rate, which determines economic efficiency, decreases. There was a problem that it had to be done.

[Means for Solving the Problems] As a result of intensive research to solve the above-mentioned problems in removing gases or low-boiling volatile organic substances dissolved in various aqueous solutions, the present inventors have developed a water-impermeable membrane. The present invention was achieved by discovering that the above component can be efficiently removed by bringing the vapor pressure of the other aqueous component close to zero through the above steps.

That is, the present invention allows the water to permeate through a water-impermeable membrane by contacting one side with a gas-dissolved aqueous solution or a low-boiling volatile organic substance-dissolved aqueous solution and bringing the vapor pressure of the aqueous solution components close to zero on the other side. Provided is a method for removing gases or low-boiling volatile organic substances, which is characterized by removing dissolved components.

The aqueous solution to which the present invention is applied is not particularly limited as long as it contains a gas dissolved therein or a low-boiling volatile organic substance dissolved therein.

For example, liquid chromatography, automated clinical chemistry analysis,
Industrial applications such as analytical instruments such as medical spectrophotometers, ion exchange water processes, ultrapure water systems for semiconductor manufacturing, power generation, general industry, boiler water used in ship boilers, nuclear power plant water, turbine water, etc. Examples include liquids and wastewater used in connection. These liquids usually include river water, well water, tap water, industrial water, pharmacopoeia regular water, etc.
It is a liquid containing 76, cations such as Ca, Mg, Na, etc., anions such as chlorine ions, sulfate ions, hydrogen carbonate ions, etc., and organic matter that has been putrefied and decomposed. Also,
Also included are liquids containing substances that are not soluble in water, such as colloidal particles and suspended particles.

The present invention can also be applied to drinking water flowing inside general household water pipes, building water supply pipes, cooling towers, circulating water pipes, etc. and building water supply.

The present invention can also be applied to water used in the production of soy sauce, raw water used in the production of beverages such as beer, alcohol, juice, coffee, and water used in the production process.

The gases dissolved in the various aqueous solutions mentioned above include oxygen, carbon dioxide, nitrogen, chlorine, and ammonia.

Furthermore, a low-boiling volatile organic substance refers to a substance that has a boiling point lower than that of water and has a large vapor pressure at the same temperature. For example, lower alcohols such as methanol, ethanol, butanol, propatool, carbon tetrachloride, chloroform,
Halogen hydrocarbons such as chlorofluorocarbons, other methyl ethers,
Ethers such as ethyl ether, methyl ethyl ketone,
Examples include ketones such as acetone.

In the present invention, the permeating dissolved components are removed by bringing the aqueous solution into contact with one side of the water-impermeable membrane and bringing the vapor pressure of the aqueous solution components close to zero on the other side.

The method of bringing the vapor pressure of the aqueous solution component close to zero is not particularly limited, but examples include a method of mechanically removing the permeate component using a vacuum pump, a method of removing the permeate component by flowing an inert gas, and a method of removing the permeate component by flowing an inert gas. A method of removing permeated components by causing a chemical reaction and flowing a substance that does not evaporate the permeated components;
Examples include a method of removing the permeated component by flowing a solvent in which the permeated component has a higher solubility than water.

Here, when the permeated components are mechanically removed using a vacuum pump or the like, water vapor may permeate in addition to the components to be removed as the permeated components, increasing the load on the vacuum pump and increasing the operating cost. Furthermore, when the permeated components are removed by flowing an inert gas, water vapor other than the components to be removed may permeate the inert gas, which may reduce the removal efficiency of the target component. Therefore, when using a vacuum pump, make sure not to increase the degree of vacuum above saturated steam at the operating temperature, and when using an inert gas, use moist inert gas that has been pre-impregnated with water vapor at the operating temperature. That is, it is preferable to flow an inert gas that is in equilibrium with saturated water vapor at the operating temperature, thereby allowing more efficient removal of permeated components.

The inert gas used in the present invention is not particularly limited, but typically includes nitrogen, argon, helium, etc., and air, carbon dioxide, etc. can also be used depending on the permeate component.

Further, the component used in the present invention that chemically reacts with the permeation component is appropriately selected depending on the permeation component. For example, when the permeation component is oxygen, hydrazine, sodium sulfite, etc. are used.

In addition, the solvent used in the present invention that dissolves the permeate component is also appropriately selected depending on the permeate component. For example, for an aqueous solution containing ethanol as a low-boiling volatile organic substance, ethers such as methyl ether and ethyl ether is used.

The water-impermeable membrane used in the present invention is not particularly limited in its structure, but includes, for example, a homogeneous membrane consisting of a non-porous active thin membrane, a dense layer or an active dense layer and a porous layer that integrally supports it. An asymmetric membrane, a composite membrane formed by forming a non-porous active thin film on such an asymmetric membrane, preferably a composite membrane formed by partially penetrating the non-porous active thin film into the dense layer of the asymmetric membrane, etc. be. Here, activity means
This means that it has the property of separating dissolved substances and liquid.

The nitrogen gas permeation rate of the water-impermeable membrane at 30°C is 7 Xl0-'~2 XIO2Nm/nl, h
, atm, preferably 3 Xl0-3 to 5 Xl0O
Nrd/rtr-h-atm. If the nitrogen gas permeation rate is less than 7X10-'Nn(/bo・h-atIll), the permeation rate of dissolved substances may become small; on the other hand, if it is greater than 2X102Nrrr/rrf・h・atm, the water impermeability may decrease. Specific examples of the above-mentioned homogeneous membranes and non-porous active thin membranes, which are undesirable because they may become unsustainable, include silicone, poly(4-methylpentene-1), natural rubber,
Examples include poly(2,6-dimethylphenylene oxide, Teflon, neorene, polyethylene, polystyrene, polypropylene, etc.).

Furthermore, the asymmetric membrane used in the present invention is not particularly limited, but examples include aromatic polysulfone, aromatic polyamide, and aromatic polyimide. Aromatic polysulfones are preferably used because of their durability.

Although the shape of the water-impermeable membrane is not particularly limited, it is preferably hollow or flat, and may be formed on a reinforcing material such as a nonwoven fabric.

Although the shape of the water-impermeable module 112 and the module containing the membrane thereof are not limited in any way, a so-called hollow fiber membrane module in which hollow fiber membranes are usually bundled and incorporated therein is preferably used. In addition, a so-called spiral type module formed by winding a sheet-like membrane or a module having another structure can also be used.

[Effects of the Invention] According to the method of the present invention, compared to the case of using conventional synthetic resin tubes, the vapor transmission rate can be increased and the permeation of water vapor can be suppressed, so equipment costs and operating costs can be reduced. This has the advantage that maintenance costs can be reduced.

[Examples] The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples at all.

In the following, parts mean parts by weight.

Example 1 A composite membrane was obtained by forming poly(4-methylpentene-1) to a thickness of 1 μm on a polysulfone porous membrane formed on a nonwoven fabric. The nitrogen gas permeation rate of this composite membrane at 30°C is 0.75Nrrr/rd-h-a
It was tm.

On one side of such a membrane (membrane area r 140c+fl), dissolved oxygen 8. llppm (25°C) ultrapure water 250
- was circulated at a flow rate of 20 cm/s for 180 minutes, and the other side was maintained at a vacuum level of -759 mm and 11 g using a vacuum pump. As a result, the dissolved oxygen concentration was 0.008 PPm, and the amount of water vapor permeation was 2.
It became 1.2g/rrf-h-arm.

Example 2 The same procedure as in Example 1 was carried out except that the degree of vacuum was -737 mm and 11 g, excluding the saturated water vapor pressure of 23 mm and 11 g at 25°C. As a result, the dissolved oxygen concentration was 0.009 ppm, and the water vapor permeation was The amount is 1.5 g/r
l(-h - became atm.

Example 3 The same process as in Example 2 was performed except that the ultrapure water temperature in Example 2 was 50"C and the saturated water vapor pressure was -668 mm11 g excluding 92 mm11 g. As a result, the dissolved oxygen concentration was 0.007 ppm, Water vapor permeation amount is 15.3g/n
It became Lh-ATM.

Example 4 Using the membrane obtained in Example 1, a spiral type module with a membrane area of 6.65n was molded and the vacuum degree was -720M11 [
Dissolved oxygen in the state of 8. As a result of passing ultrapure water of 1ppm (25°C) at a flow rate of 12.5t/h, the outlet dissolved oxygen concentration was 0.495ppm.

Example 5 Instead of vacuum in Example 1, pure nitrogen gas (99,
The oxygen concentration of ultrapure water obtained in the same manner as in Example 1 except that 99χ) was flowed at a flow rate of 201/min was 0°O2.
It was 0 ppm.

Example 6 Results of treating pure nitrogen gas containing saturated water vapor in the same manner as in Example 5 by aerating pure nitrogen gas into sufficiently degassed ultrapure water at 25°C. , the obtained ultrapure water oxygen concentration was 0. O was 20 ppm.

Example 7 The dissolved oxygen concentration obtained in the same manner as in Example 1, except that instead of the vacuum in Example 1, a saturated aqueous sodium sulfite solution was flowed at a flow rate of 5 cyn/S, the dissolved oxygen concentration was 0.2
It was 35 ppm.

Example 8 The same procedure as in Example 1 was carried out except that a 2% aqueous ethanol solution was flowed instead of the ultrapure water in Example 1. As a result, the concentration of the obtained ethanol solution was 0.27%.

Example 9 The ethanol concentration of a solution obtained in the same manner as in Example 8 except that the ethanol concentration in Example 8 was 0.2% was 0.045%.

(that's all )

Claims (7)

[Claims] (1) Through a water-impermeable membrane, one side is brought into contact with an aqueous solution in which a gas or a low-boiling volatile organic substance is dissolved, and the other side is permeated by bringing the vapor pressure of the aqueous solution components close to zero. A method for removing gases or low-boiling volatile organic substances, characterized by removing dissolved components. (2) The method for removing gases or low-boiling volatile organic substances according to claim (1), wherein the method for bringing the vapor pressure of the aqueous solution components close to zero includes mechanically removing the permeated components using a vacuum pump or the like. (3) The method for removing gases or low-boiling volatile organic substances according to claim (2), characterized in that the amount of permeation of water vapor is suppressed by not lowering the degree of vacuum below the saturated water vapor pressure at the operating temperature. (4) The method for removing gases or low-boiling volatile organic substances according to claim (1), characterized in that the method for bringing the vapor pressure of the aqueous solution components close to zero is to remove the permeated components by flowing an inert gas. (5) The method for removing gases or low-boiling volatile organic substances according to claim (4), characterized in that the amount of permeation of water vapor is suppressed by flowing an inert gas that is in equilibrium with saturated water vapor at the operating temperature. (6) The gas or low-boiling volatile organic substance according to claim (1), characterized in that the method for bringing the vapor pressure of the aqueous solution component close to zero is to remove the permeated component by flowing a component that chemically reacts with the permeated component. How to remove. (7) The method of bringing the vapor pressure of the aqueous solution component close to zero is to remove the permeated component by flowing a solvent in which the permeated component has a higher solubility than water. How to remove organic matter.