JPH0761412B2 - Ultrapure water production system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ultrapure water production system, and in particular, it is suitable for use in the semiconductor manufacturing industry, and has a fine particle content of 0.1 μm or less, tens of particles / cm. ^It relates to an ultrapure water production system of ³ or less.

[Conventional technology]

Conventionally, non-porous membranes have been used for gas separation, the gas supply side was used to produce a mixed gas by adjusting the pressure difference on the permeate side, but after selectively permeating only vapor, There was no idea to condense and use it as pure water. Recently, as the gas separation membrane itself and the separation mechanism have been elucidated, it has become known that water vapor can be relatively easily eliminated. However, there is no example in which a non-porous membrane is applied to a vapor-steam system and put into practical use as any device (Japanese Patent Laid-Open No. 54-130483).
Issue).

[Problems to be solved by the invention]

The above-mentioned prior art is concerned with gas separation itself, and there is no consideration of producing pure water, that is, selectively permeating water vapor and forcibly condensing it. Also,
Another conventional technique is a reverse permeable membrane separation method using a non-porous membrane, but this is because of the direct contact between the liquid and the membrane.
It has been difficult to avoid the problem of clogging due to the trapping of fine particles in the solution by the membrane. Further, in order to increase the treatment amount, it was necessary to treat at a high pressure of 10 to 30 atm. This high pressure pushes the fine particles in the solution toward the permeate side, and there is also a problem that the particles are contaminated by larger particles than expected. Therefore, even if the reverse osmosis membrane separation method is used, the limit is that the number of fine particles around 0.1 μm is removed to about ^{30 to} 50 particles / cm ³ .

The object of the present invention is to significantly reduce the content of fine particles,
An object of the present invention is to provide an ultrapure water production system capable of increasing the amount of treatment in the water vapor separation means.

[Means for solving problems]

The characteristics of the present invention to achieve the above-mentioned object are steam generating means for generating steam, steam separating means having a non-porous membrane for permeating the steam introduced from the steam generating means, and the non-porous membrane. Means for cooling the water vapor that has permeated through the water vapor, and the total pressure of the first area on the water vapor introduction side and the second area on the water vapor permeation side in the water vapor separation means separated by the non-porous membrane as a boundary. And a means for adjusting the pressure in the second region with a gas having a boiling point lower than that of the water vapor so that the difference from the pressure does not exceed the pressure difference that the non-porous membrane can withstand.

[Action]

Since the water vapor is guided to the non-porous membrane arranged in the gas, the amount of fine particles that permeate the non-porous membrane is significantly reduced. Also,
Since the pressure difference between the total pressure in the first region and the total pressure in the second region does not exceed the pressure difference that the non-porous membrane can withstand, the pressure in the second region is adjusted by the gas having a lower boiling point than that of water vapor. ,
The non-porous membrane can be made thin, and the permeation area of the non-porous membrane does not decrease. Since the non-porous membrane can be made thin and the permeation area of the non-porous membrane does not decrease, the throughput of the steam separation means can be increased.

〔Example〕

In order to remove the fine particles in the water and obtain ultrapure water, it is possible to use a membrane having a pore size equal to or smaller than that of the fine particles, but the membrane is quite flexible and in reality it is difficult to completely remove it.
One reason is that since the solution and the film are in direct contact with each other, the state in which the particles are forced into the film and forcibly used in a kind of clogging locally occurs. This can be solved by a so-called non-contact method in which the solution and the film are used separately.
A non-porous film is preferable for removing fine particles of 0.1 μm or less. A non-porous membrane is a membrane in which the gaps (free volume) of polymer chains are mainly used for gas diffusion,
Sufficient for water molecules to escape.

Even if the maximum gap is about 10 to 60Å, it can be fully used. The throughput problem can be solved by increasing the vapor partial pressure difference before and after the membrane, and the pressure resistance problem of the membrane can be solved by enclosing a low boiling point gas so that the total pressure is balanced on the permeate side. Since the non-porous membrane as described above is placed in non-contact with the solution, it is possible to produce ultrapure water in which the number of fine particles (impurities) is less than tens per cm ^{3 of} pure water.

An embodiment of the present invention will be described below with reference to FIG. Here, the basic part of the ultrapure water production system of the present invention will be described. The pretreated water is introduced into the evaporator 1 via the pump 9. The evaporator 1 is equipped with a heating device 8 to heat the water in the evaporator 1 to a predetermined temperature to generate steam.
The generated vapor passes through the gas-liquid separation device 7 and the membrane module 2
Be introduced to. A non-porous membrane 3 is installed on the membrane module 2, and water molecules diffuse in the non-porous membrane 3 to be separated from the fine particles that have always flown.
The pressure on the vapor introduction side of the membrane module is adjusted to, for example, 5 atm. Dry pure N ₂ on the permeate side of the membrane module
It is filled with gas and the pressure is set to a value slightly below 5 atm (eg 4.95 atm). The vapor that has permeated the non-porous membrane is always introduced into the condenser 4 from the upper part of the module together with the N ₂ gas and is condensed. The condensed vapor becomes water at about 30 ° C, and the partial pressure of water vapor in the condenser and on the permeate side is 0.05 atm. The condensed water is immediately stored in the receiving tank 5 installed in the lower part. The ultrapure water 6 thus obtained contains about 50 fine particles of 0.1 μm or less per cm ³ . Ultrapure water is sent from the receiving tank 5 through the valve 10 to each use point.

Next, the water permeation principle using the non-porous membrane used in the membrane module will be described. When the gas permeates the non-porous film, first, the gas is dissolved on the surface of the non-porous film and then diffuses inside the non-porous film to permeate. And the driving force for gas permeation is the partial pressure difference of the permeated gas before and after the non-porous membrane, that is,
It is the difference in concentration. For example, in FIG. 2, the supply side is set to the atmospheric pressure of water vapor, and the permeation side is set to a water vapor partial pressure of 0.05 at 30 ° C.
At atmospheric pressure, a-0.05 atm becomes a differential pressure that promotes permeation. Since the non-porous membrane is weak to pressure here, a gas other than water vapor having a lower boiling point than water vapor on the permeate side, for example,
A material such as N ₂ is filled so that the total pressure difference before and after the non-porous membrane does not occur. The non-porous membrane has no pressure difference between the front and back, or has a very small value at all, so that a thin non-porous membrane or a thin non-porous membrane stretched on an appropriate support can be used.

Even after being adjusted in this way, water vapor continuously escapes to the permeate side because a differential pressure is generated before and after the non-porous membrane. Of course, N ₂ leaks from the permeate side to the supply side, but it is about 10 ⁻³ times that of water vapor permeation, so it is not a big problem.

Next, the case of using a porous film will be described. Even a porous film can be applied to the present invention if it is coated on the surface to form a non-porous layer. That is, as shown in FIG. 3, the porous film material 11 has many voids 13. Some tetrafluoroethylene membranes have voids of 50% or more. If the porous membrane is used as it is, gas and water vapor will escape through the voids. Most of these voids have an average pore diameter of 0.1 μm or more and cannot be used for the purpose of sieving fine particles of 0.1 μm or less. Therefore, the non-porous coating material 12 is coated on the surface of the porous membrane material to form an apparently non-porous membrane. At the time of use, it is used as the coating surface and the steam supply side.

Next, the pressure adjusting gas used on the permeate side will be described.
As already described in FIG. 2, gas permeation through a non-porous membrane is a rate-determining step where the gas is dissolved on the membrane surface.

Fig. 4 shows the relationship between the boiling points of various gases and the solubility coefficient for natural rubber. The tendency of the solubility coefficient for natural rubber is
The same tendency is shown for non-porous membranes and coating materials. The water vapor (boiling point of water) is 100 ° C (375 ° K)
The value is 100 to 1000 times higher than that of He, N ₂ and O ₂ . That is, H
Compared to e, N ₂ and O ₂ , water vapor is easily transmitted by two or three orders of magnitude. Therefore, it is considered that N ₂ is suitable for the pressure adjusting gas on the permeate side. However, in principle, it is less than water vapor, that is, the boiling point is 100.
It is considered that a gas having a temperature lower than ℃ can be a pressure adjusting gas.

Finally, a method for producing ultrapure water according to the present invention will be described with reference to the flow sheet shown in FIG. Pretreated water is introduced into storage tank 15 via valve 14. It is introduced from a tank 15 via a pump 16 into an evaporator 17 having a high pressure. Vaporized in an evaporator 17 and introduced into a membrane module 18 using a non-porous membrane. Pump on the supply side via pressure regulating valve 19
Excess gas is discharged through 20 at startup, and excess steam is discharged during operation. The permeate side of the membrane module 18 is connected by a pipe 28 to a condenser 21. Further, the cooling water in the condenser is cooled by the chiller unit 22 and is recycled.

In the condenser 21, the water is cooled to, for example, 30 ° C. or less. N ₂ gas for pressure adjustment on the permeate side is a cylinder 27, or
Pump through the gas purifier 26 from the liquid nitrogen evaporator
It is sent into the system from 25. The pressure of the N ₂ gas on the permeate side is regulated by the pressure regulating valve 19 so as to have the above-mentioned differential pressure at the time of starting. Pure water that has been transmitted and condensed by the condenser 21 is stored in the receiving tank 23.

It is sent from the tank 23 to the point of use via the valve 24.

〔The invention's effect〕

According to the present invention, since the water vapor is guided to the non-porous membrane arranged in the gas, the amount of fine particles that permeate the non-porous membrane is significantly reduced. Further, since the non-porous membrane can be made thin and the permeation area of the non-porous membrane does not decrease, the throughput of the steam separation means can be increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic form of an ultrapure water producing apparatus according to an embodiment of the present invention, FIG. 2 is a permeation principle diagram of a non-porous membrane, and FIG. 3 is a porous membrane coated with a non-porous membrane. Cross-sectional view of the membrane, Fig. 4 is a graph showing the relationship between the boiling point of gas and the solubility coefficient of natural rubber at 25 ° C, and Fig. 5 is ultrapure water pretreated by using the present invention. 3 is a flow sheet showing a method for manufacturing the. 1 ... Evaporator, 2 ... Membrane module, 3 ... Non-porous membrane, 4 ...
Condenser, 5 ... Receiving tank, 6 ... Ultrapure water.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ichimichi Suzuki 1168 Moriyama-cho, Hitachi-shi, Ibaraki Prefecture Energy Research Laboratory, Hiritsu Manufacturing Co., Ltd. (56) References JP-A-63-162003 (JP, A)

Claims (3)

[Claims] 1. A steam generating unit for generating steam, a steam separating unit having a non-porous membrane for permeating the steam introduced from the steam generating unit, and cooling the steam for permeating the non-porous membrane. Means and the total pressure of the first region on the water vapor introduction side and the total pressure of the second region on the water vapor permeation side in the water vapor separation means separated by the non-porous membrane as a boundary. An ultrapure water producing apparatus comprising: a means for adjusting the pressure in the second region with a gas having a boiling point lower than that of the water vapor so that the pressure does not exceed a pressure difference that the porous membrane can withstand. 2. The apparatus for producing ultrapure water according to claim 1, wherein the gas having a boiling point lower than that of the water vapor is a gas that does not chemically react with the non-porous film. 3. The non-porous membrane is a membrane having a surface which is apparently non-porous by coating a substance that allows water vapor to permeate either the porous membrane or the porous support. The ultrapure water production system according to item 1 or 2.