JPH0818022B2 - Heat sterilization method of final filter for ultrapure water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a method for heat sterilization of a final filter for ultrapure water used in the electronics industry and the like, and more specifically,
The present invention relates to a method for heat sterilizing a final filter for ultrapure water, which enables heat sterilization in a short time and with a simple operation without using chemicals or the like.

[Conventional technology]

Today, the progress of VLSI is remarkable, and 1M bit devices have already been shipped. In the manufacturing process of these VLSIs,
Ultrapure water is used to clean semi-finished VLSI products. Since the quality of ultrapure water affects the yield of products,
With the recent progress in manufacturing technology, the water quality has improved dramatically.

 FIG. 1 shows an example of the recent ultrapure water production process.

According to FIG. 1, most of the suspended matter is removed from the raw water supplied to the raw water tank by the coagulation filter 2. Next, after passing through the reverse osmosis membrane 3 to remove most of suspended matter, dissolved organic matter (TOC), dissolved inorganic matter, and ionic substances, residual ionic substances are removed by the ion exchanger 4. Furthermore, the bacteria that are alive are sterilized by the ultraviolet sterilization lamp 5, the ionic substances are completely removed through the high-performance ion exchanger 6, and finally the ultrafiltration membrane 7 is passed to remove dead bodies and fine particles of the bacterium due to sterilization. Remove to obtain ultrapure water. Except for the required amount of water that has passed through the ultrafiltration membrane, by returning to the previous step of the ultraviolet germicidal lamp 5 and circulating it,
Prevents accumulation of dirt.

The quality of ultrapure water obtained in the above steps is usually
Water temperature 20 ~ 30 ℃, specific resistance 18MΩ ・ cm or more, TOC 50ppb or less,
Viable count 0.1 / ml or less, particle size 0.1μm or more 50 /
It is less than or equal to ml. However, with the recent progress in LSI integration, the water quality above the above, that is, the resistivity of
Ω ・ cm or more, TOC 10 ppb or less, viable cell count 0.001 cells / ml or less,
There has been a demand for ultrapure water having a water quality improved to 50 particles / ml or less having a particle diameter of 0.05 μm or more.

By the way, the ultrapure water obtained by the process of FIG.
I Circulate inside the manufacturing site with loop piping. Since this pipe is usually very long and has many use points, the purity of the ultrapure water obtained from the above process gradually decreases due to the pollution from the pipe and the reverse pollution from the use points. It is known that such pollutants are fine particles and live bacteria.

For this reason, recently, a point of use filter is attached to the position shown by 8 in FIG. 2, that is, immediately before the ultrapure water supply port to cope with the above-mentioned contamination. Such a filter is a final filter and is called a final filter.

Since live bacteria and the like accumulate in this final filter, it is necessary to sterilize it appropriately.

[Problems to be solved by the invention]

As a sterilization method of the final filter, a chemical sterilization method in which a chemical such as formaldehyde or hydrogen peroxide is filled in the filter for a certain period of time is known. However, this method has a drawback that it takes a long time not only to sterilize but also to wash the chemicals, so that it cannot meet the rapid demand for ultrapure water. On the other hand, it is said that the bacteria that grow in ultrapure water will be completely killed if kept at a water temperature of 80 ° C for about 1 hour.
The sterilization method using hot water is drawing attention.

However, few heat exchangers that adjust the temperature while maintaining the quality of ultrapure water are known, and heat sterilization of only the final filter is rarely performed due to reasons such as complicated equipment. It was

Therefore, an object of the present invention is to provide a heat sterilization method of a final filter for ultrapure water, which is easy to sterilize and can be treated in a short time.

[Means for solving problems]

The inventors diligently studied to solve the above problems.
Research has led to the completion of the present invention.

That is, the present invention, while the final filter for ultrapure water is attached to the pipe, supplies hot water of 80 ° C. or more to the inlet pipe of the final filter to filter the whole amount, and permeates from the use point of the permeated water pipe outlet. The operation of draining water
It is intended to provide a method for heat sterilizing a final filter for ultrapure water, which is characterized by allowing the temperature of permeated water to be 80 ° C. or higher and continuing it for 60 minutes or longer.

In the present invention, it is not necessary to detach the module of the final filter from the pipe or to pull out the membrane from the module, and the final filter may be used in the mounted state.

In the method of the present invention, as a means for supplying hot water, after supplying water to the inlet pipe of the final filter and passing through the final filter, it is received in a heatable hot water tank and heated to 80 ° C. or higher. After that, the hot water is preferably sent again to the inlet pipe of the final filter by a pump to circulate the hot water between the final filter and the hot water tank.

As another means for supplying hot water, ultrapure water is externally supplied to a heatable hot water tank, heated to 80 ° C. or higher, and then the hot water is supplied to the inlet pipe of the final filter. preferable.

Further, as another means, it is preferable to install an appropriate heater heating section inside the inlet pipe of the final filter. This heater is operated only during heat sterilization, and stopped during normal ultrapure water supply.

It is preferable that the heater capacity used in any of the above means is appropriately designed in consideration of the supply amount of hot water so that the temperature of the final filter becomes 80 ° C. or higher.

Further, the final filter used in the present invention includes an ultrafiltration membrane type and a microfiltration membrane type, but if the particle size of the fine particles to be removed is 0.05 μm or less, the ultrafiltration membrane is practically used. .

In the present invention, the water supplied to the inlet pipe of the final filter is ultrapure water obtained from the ultrapure water production step,
Alternatively, water or hot water supplied from the outside to the inlet pipe of the final filter may be used.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Example 1 As shown in FIG. 3, inner diameter 77 mm, outer diameter 83 mm, length 26
Inner diameter 400 μm, outer diameter 68 in 0 mm polysulfone case
500 μm of polyethersulfone ultrafiltration hollow fiber membrane 9
A final filter 8 containing 0 pieces was prepared. This final filter 8 is an external pressure type, and the internal volume is
1050 ml, initial filtration flow rate is 1200 kg at inlet pressure 1 kg / cm ² , 25 ° C
It was / h. The design flow rate is 500 / h.

FIG. 4 is a layout diagram showing a state in which such a final filter is mounted in the final filtration step of FIG. 2 and the relationship with the apparatus used in the present invention. In FIG.
The ultrapure water that has flowed into the final filter 8 through the inlet pipe 35 is discharged from the permeated water pipe 34. The discharged water is directly stored in a hot water tank 37 with a capacity of 2 equipped with a temperature controller 39 and an electric heater 38 with a capacity of 1 KW, and after the temperature is adjusted to a predetermined level, an inlet pipe 35 is provided by a circulation pump 36 with a flow rate of 60 / h. Is reintroduced via joint 30. A cleaning valve 32 is installed between the circulation pump 36 and the joint 30.
A valve for limiting the inflow of ultrapure water is provided on the upstream side of
But they are installed respectively.

In order to carry out the heat sterilization method of the present invention using the apparatus as described above, the cleaning valve 32 is closed and the hot water tank 37 is filled with the necessary amount of ultrapure water. Next, the valve 31 is closed, the heater is turned on, and the temperature of the hot water tank 37 is adjusted to 90 ° C with the temperature controller 39.
Adjust to. Then, the valve 32 is opened to operate the circulation pump. At this time, the result of measuring the temperature of the permeated water pipe of the final filter is shown in FIG. The initial water temperature is
It was 25 ° C. After 20 minutes, the temperature reached 85 ° C, and after 30 minutes, it reached 89 ° C and became constant. Since heat sterilization only needs to be performed at 80 ° C. or higher for 1 hour, this heat sterilization was completed in 80 minutes. After switching off the heater, stopping the pump and closing the valve 32, the valve 31 was opened and ultrapure water was supplied at a flow rate of 500 / h.

As a result of continuous measurement of the specific resistance of the permeated water pipe of the final filter, the purity recovered to the same level as the raw water in about 10 minutes. Therefore, the total time required for complete sterilization was 90 minutes.

Example 2 In the apparatus of Example 1, the valve 31 was closed and the hot water tank 37 was used.
To this, ultrapure water at 25 ° C. was continuously supplied from an external ultrapure water supply source, and all the permeated water that passed through the final filter was discharged so as not to return to the hot water tank 37. Also, the heater 38 of the hot water tank was changed to one with a capacity of 2KW.

In such an apparatus, the heater power was turned on to successively heat ultrapure water supplied from the outside, and hot water was supplied to the final filter 8 by the pump 36 to perform thermal sterilization of the final filter. At this time, the flow rate of the pump 36 was appropriately adjusted and the relationship with the outlet temperature of the final filter was observed. FIG. 6 shows the relationship between the outlet temperature of the final filter and the flow rate of the pump. The reason why the temperature drops at the flow rate of 25 / h or more is considered to be due to the insufficient capacity of the heater. It is considered that the reason why the temperature does not reach 90 ° C at 25 / h or less is that the temperature drops due to heat dissipation from the piping and filter. In this example, it can be seen that the temperature can be sufficiently sterilized by flowing at a flow rate of 10 to 20 / h. A heater of 1 to 2 kW is sufficient for this.

Example 3 Using the same final filter as in Example 1,
As shown in FIG. 7, the heating part 40 of the heater having a capacity of 1 KW contained in the polysulfone container was inserted between the inlet valve 31 installed in the inlet pipe 35 and the final filter 8.

In such an arrangement, the temperature of the final filter could be maintained at 80 ° C. or higher by adjusting the flow rate to 11 to 14 / h by narrowing the valve 31 under heating by the heater. When not performing heat sterilization, turn off the heater power.

In Examples 1 to 3 of the present invention, the heater, pump, hot water tank, etc. used are preferably electrolytically-polished stainless steel or those coated with Teflon in order to prevent contamination of the final filter.

〔The invention's effect〕

According to the present invention, since the final filter is sterilized with hot water, the operation is simple, and the state in which ultrapure water can be supplied can be restored in a short time.

Furthermore, the heat sterilization method of the present invention in which hot water is circulated is an economically excellent method without requiring a large amount of hot water.

By carrying out the heat sterilization of the present invention once a week or so, the permeated water of the final filter can maintain a sufficiently sterile condition.

[Brief description of drawings]

FIG. 1 is a flow chart showing the steps for producing ultrapure water. FIG. 2 is a flowchart showing a process for producing ultrapure water in which a final filter is installed. FIG. 3 is a specific example of the final filter used in the present invention. FIG. 4 is a layout drawing of an apparatus for carrying out the heat sterilization method of the present invention. FIG. 5 is a graph showing the relationship between hot water circulation time and outlet water temperature in Example 1. FIG. 6 is a graph showing the relationship between the circulating flow rate of hot water and the outlet water temperature in the second embodiment. FIG. 7 is a layout of an apparatus for carrying out the heat sterilization method in the third embodiment. [Main reference numbers] 1 ... Raw water tank, 2 ... Coagulation filter, 3 ... Reverse osmosis membrane, 4 ... Ion exchanger, 5 ... Ultraviolet germicidal lamp, 6 ... High-performance ion exchanger, 7 …… Ultrafiltration membrane, 8 …… Final filter, 9 …… Hollow fiber membrane, 10 …… Sealant, 13 …… Polysulfone case, 31 …… Inlet valve, 32 …… Cleaning valve, 34 …… Permeation Water piping, 35 …… Inlet piping, 36 …… Circulation pump, 37 …… Hot water tank, 38 …… Heater, 39 …… Temperature controller, 40 …… Heater heating section

Claims (3)

[Claims] [Claim 1] With the final filter for ultrapure water attached to the pipe, to the inlet pipe of the final filter at 80 ° C.
It is characterized in that the operation of supplying the above hot water, filtering the whole amount, and discharging the permeated water from the use point of the permeated water piping outlet is continued for 60 minutes or more after the temperature of the permeated water becomes 80 ° C or more. Thermal sterilization method of final filter for ultrapure water. 2. The hot water of 80 ° C. or higher supplied to the inlet pipe of the final filter is heated by supplying permeated water of the final filter or ultrapure water from the outside to a hot water tank capable of being electrically heated. The ultrapure water according to claim 1, which is water, which is discharged after being passed through a final filter or is received by the heatable hot water tank and circulated between the final filter and the hot water tank. Sterilization method of final filter for shaving. 3. The final filter for ultrapure water according to claim 1, wherein the hot water supplied to the inlet pipe of the final filter is supplied by installing an electric heating section in the inlet pipe of the final filter. Heat sterilization method.