JPH0649141B2 - Method of regenerating ultrafiltration membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention uses ultrafiltration membrane to remove fine particles, colloidal substances, high molecular weight organic substances, exothermic substances, etc. in primary pure water to obtain ultrapure water. Continuation of the treatment during manufacturing may cause contaminants to adhere to the ultrafiltration membrane and reduce the amount of permeated water, or bacteria may propagate on the ultrafiltration membrane and live bacteria may leak into the permeated water. The present invention relates to a method for regenerating an ultrafiltration membrane at the time.

<Prior Art> Conventionally, an ultrafiltration membrane device has been used for the purpose of removing fine particles, colloidal substances, high molecular weight organic substances, exothermic substances, etc. in water to be treated, but in recent years, it has produced LSIs and ultra LSIs. It is often used for producing ultrapure water as water for cleaning semiconductor wafers or chips (hereinafter referred to as semiconductor wafers) in the electronic industry.

Water for cleaning such semiconductor wafers is usually produced by the following flow. That is, the raw water is treated with a primary side pure water device such as a coagulating sedimentation device, sand filtration, an activated carbon filter device, a reverse osmosis membrane device, a two-bed, three-column pure water production device, a mixed-bed polisher, and a precision filter. Immediately before washing the semiconductor wafer, the primary pure water is treated with an ultraviolet irradiator and / or a mixed bed type polisher, and then treated with an ultrafiltration membrane device to obtain fine particles remaining in the primary pure water, colloidal substances, So-called ultrapure water is obtained by removing viable bacteria and the like as much as possible.

The ultrafiltration membrane device used for such an application has the treated water that is primary pure water obtained by the primary side water supply device, and is also irradiating with ultraviolet light immediately before, The permeation treatment for a long time reduces the amount of permeated water, or viable bacteria leak into the permeated water.

The cause of this is that a very small amount of high molecular weight organic matter or the like remains in the primary pure water which is the water to be treated of the ultrafiltration membrane device, or adheres to the membrane surface of the ultrafiltration membrane, or has resistance to ultraviolet rays. It is considered that general bacteria propagate on the membrane surface.

Therefore, when the ultrafiltration membrane to be used is contaminated as described above, it is necessary to perform some regenerative treatment to restore the performance of the ultrafiltration membrane and sterilize it.

The regenerative treatment of the ultrafiltration membrane that has been conventionally performed is 1 to 5
% Hydrogen peroxide solution, a method of immersing in an oxidant such as sodium hypochlorite solution, or a method of washing with a passing solution, a method of immersing in an acid such as about 3% nitric acid, hydrochloric acid, or a method of washing with a passing solution, Although there is a method of immersing in an alkali such as caustic soda solution of about 3% or washing by passing it through, the regenerative treatment using such an oxidizing agent, acid or alkali deteriorates the ultrafiltration membrane or the components of the device. In addition, there are drawbacks such as using a large amount of pure water for cleaning after the regenerative treatment, and the regenerative treatment effect is not sufficient. Furthermore, since a relatively large amount of oxidizing agent, acid and alkali are used, there is a problem that the chemical cost and the waste liquid processing cost are high.

On the other hand, as a regenerative treatment that does not deteriorate the ultrafiltration membrane or the components of the device and that can be washed relatively easily after the regenerative treatment,
A method of washing the ultrafiltration membrane with hot water is also used, but this method has a drawback that the regenerative treatment effect is small.

<Problems to be Solved by the Invention> In the present invention, a polymer organic substance or the like adheres to the ultrafiltration membrane surface,
Alternatively, it solves the drawbacks of conventional regenerative processing when general bacteria multiply and its processing performance deteriorates.It does not deteriorate the ultrafiltration membrane or the components of the device, and facilitates cleaning after regenerative processing. It is an object of the present invention to provide a regenerative treatment method which can be carried out at low cost, and which has excellent regenerative treatment effects.

<Means for Solving Problems> Cleaning with hot water in the conventional regenerative treatment method described above
It utilizes the solubility and releasability of high molecular weight organic substances attached to the film surface of hot water and the bactericidal property, but if the regenerative treatment effect is excellent, it is easy to wash after the regenerative treatment. And has advantages such as not deteriorating the ultrafiltration membrane, and is an excellent method for regenerating the ultrafiltration membrane for producing ultrapure water as water for cleaning semiconductor wafers.

The present inventor has conducted various studies on the improvement of the performance of regenerative treatment in conventional hot water washing. As a result, a small amount of acid is added to hot water to obtain acidic hot water having a pH of 3 or less, and such an acidic hot water is used for the ultrafiltration membrane. It was found that the performance after the regenerative treatment was dramatically improved when the product was washed.

The present invention is based on the above knowledge, and in the process of producing ultrapure water by treating primary pure water at least with an ultraviolet irradiation device and then with ultrafiltration membrane device, the performance of the ultrafiltration membrane device is When the temperature decreases, the method for regenerating an ultrafiltration membrane is characterized in that the ultrafiltration membrane is washed with acidic hot water having a pH of 3 or lower and a temperature of 70 ° C. or higher.

<Action> The reason why the regenerative treatment effect of acid hot water is higher than that of neutral hot water is probably due to the following reasons. That is, generally, the growth of microorganisms is influenced by the pH of the environment, and each microorganism has a pH range suitable for its growth. For example, general bacteria are neutral to weakly alkaline (p
H7-8), and yeasts and molds are said to have an optimum pH range for weak acidity (pH 6-7). In other words, optimum pH
If it shifts from the zone to the acidic side or the alkaline side, the growth of microorganisms is suppressed and the microorganisms eventually die.

Therefore, it is considered that general bacteria that propagate on the membrane surface can be effectively sterilized by the synergistic action of the sterilizing power of the original hot water and the sterilizing power of the acidic water. Solubility and releasability against
It is considered that this can be further improved by making the pH of hot water acidic. Note that the pH is in the weakly alkaline pH range.
Although it is possible to use hot water that is more alkaline than 7 to 8 as washing water, its effect is smaller than that of acidic hot water as shown in Example 2.

The present invention cleans the membrane surface by passing acidic hot water whose pH is adjusted to 3 or less through an ultrafiltration membrane when the amount of permeated water decreases or live bacteria leak into the permeated water. However, when acidic hot water having a high acid concentration is used, the film is deteriorated. Therefore, it is usually preferable to use acidic hot water having a pH of 1 to 3. The temperature of the acidic hot water is preferably 70 ° C. or higher, usually around 90 ° C. It should be noted that a temperature of 70 ° C. or lower is not preferable because the regenerative effect becomes small.

Next, the cleaning time is required to be at least 15 minutes or more, and normally about 30 minutes is sufficient, and acidic hot water whose pH is adjusted is passed in the same direction as the water to be treated permeates, Alternatively, the reverse direction of permeation of the water to be treated, in other words, water is passed from the permeate side to the non-permeate side of the membrane, and the entire amount of cleaning wastewater (permeate and non-permeate) obtained during treatment is blown. Preferably. In addition, depending on the case, a circulation process can also be implemented.

As the pH adjuster in the present invention, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, oxalic acid, tartaric acid or the like can be used.

Further, the ultrafiltration membrane can be applied to ultrafiltration membranes having various shapes such as a flat membrane shape, a tubular membrane shape, a spiral shape, and a hollow fiber shape.

Embodiments of the present invention will be described below based on a flow of an ultrafiltration membrane device used in an ultrapure water production process for cleaning a semiconductor wafer as an example.

In the figure, 1 is a pure water tank, 2 is a mixed bed polisher, 3 is an ultraviolet irradiation device, 4 is a heat exchanger, and 5 is an ultrafiltration membrane device. Coagulation sedimentation device, sand filter, activated carbon filtrate, reverse osmosis membrane device,
The primary pure water obtained by the primary side water supply device consisting of a two-bed, three-tower pure water production system, a mixed-bed polisher, a precision filter, etc. is once received in the pure water tank 1, and the primary pure water is used for cleaning semiconductor wafers. The following treatment is performed to obtain pure water.

That is, after treating the primary pure water of the pure water tank 1 with the mixed bed polisher 2 and the ultraviolet irradiation device 3 using the pump 6, the valve 8 is closed, the valve 7 is opened, and the heat exchanger 4 is bypassed by the bypass passage 9. Then, the permeated water 10 is obtained by treating with the ultrafiltration membrane device 5, the permeated water 10 is used as ultrapure water for cleaning semiconductor wafers, and the non-permeated water 11 is circulated in the pure water tank 1 or Alternatively, it is circulated and recovered to the primary side water supply device. When the amount of permeated water of the ultrafiltration membrane device 5 is reduced by such a treatment, or when viable bacteria are leaked into the permeated water 10,
The regenerative treatment of the present invention is performed.

That is, the valve 7 is closed and the valve 8 is opened to pass hot water after ultraviolet irradiation through the heat exchanger 4 to obtain hot pure water at about 90 ° C., and the hot pure water is charged with the acid in the chemical solution tank 12. Acid hot water having a pH of 1 to 3 is injected by the injection pump 13, and the hot water is passed through the ultrafiltration membrane device 5, and the permeated water and the non-permeated water obtained at this time are all blown out of the system.

After the ultrafiltration membrane was washed with acidic hot water for about 30 minutes, the valve 8 was closed and the valve 7 was opened to allow the pure water at room temperature to pass through the bypass passage 9 and the injection of the acid by the injection pump 13 to stop, so that the pure water at room temperature was removed. Water is passed through the ultrafiltration membrane device 5, and when the water quality of the permeated water 10 becomes stable, the permeation treatment is performed.

Although the injection pump 13 is used to inject the acid in the drawing, the acid can be added by using the suction force of the ejector, and the primary pure water is further irradiated with the ultraviolet irradiation device 3.
It is also possible to process the mixed bed polisher 2 in that order.

<Effects> As described above, according to the present invention, the ultrafiltration membrane is washed with acidic hot water obtained by adding a small amount of acid to hot water. Therefore, the regeneration treatment is effectively performed without degrading the ultrafiltration membrane. can do.

Examples will be described below in order to clarify the effects of the present invention.

Example-1 The effect of the present invention was confirmed based on the flow shown in the drawings.

That is, the primary pure water obtained in the primary side water supply device was treated with a mixed bed polisher and an ultraviolet irradiation device, and then treated with a polysulfone-based hollow fiber ultrafiltration membrane to obtain 100 live cells (colonies) in the permeated water. ) / 100 m or more, the treatment is interrupted, and the method of the present invention is performed in which the ultrafiltration membrane is washed with acidic hot water at a temperature of 90 ° C. adjusted to pH 3 by injecting a small amount of nitric acid into primary pure water. Then, in the same manner, the primary pure water was passed through to measure the viable bacteria in the permeated water after the regeneration treatment.

For comparison, immersion in 1% hydrogen peroxide solution (normal temperature) (2 hours), immersion in 3% nitric acid (normal temperature) (2 hours),
After washing with 90 ° C neutral hot water (30 minutes of water passage) and normal temperature acidic water with pH adjusted to 3 by injecting nitric acid (30 minutes of water passage), in the same manner after the regeneration treatment. The primary pure water was passed through to measure the viable bacteria in the permeated water after the regeneration treatment. The results are shown in Table 1.

[Example-2] Using the same ultrafiltration membrane as in Example-1, the primary pure water was permeated in the same manner, and the treatment was interrupted when the permeated water amount decreased to 30 from the initial 100. As the method of the present invention, acidic hot water having a temperature of 90 ° C. adjusted to pH 3 by injecting a small amount of nitric acid into pure water, and a temperature adjusted to pH 12 by injecting a small amount of sodium hydroxide into pure water as a comparative example. The ultrafiltration membrane was washed with alkaline hot water at 90 ° C., and then primary pure water was passed through in the same manner to measure the permeated water retention rate after the regeneration treatment.

The permeated water retention rate is calculated by the following formula.

Further, for comparison, regenerative treatment was carried out by the same conventional method as shown in Example-1, and the permeated water retention rate after the regenerative treatment was measured. The results are shown in Table 2.

[Brief description of drawings]

 Drawing is explanatory drawing which shows the flow of embodiment of this invention. DESCRIPTION OF SYMBOLS 1 ... Pure water tank, 2 ... Mixed-bed polisher 3 ... Ultraviolet irradiation device, 4 ... Heat exchanger 5 ... Ultrafiltration membrane device, 6 ... Pump 7, 8 ... Valve, 9 ... Bypass passage 10 ... Permeate, 11 ... Non-permeable water 12 ... Chemical liquid tank, 13 ... Injection pump

Claims (1)

[Claims] 1. In a step of producing ultrapure water by treating primary pure water at least with an ultraviolet irradiation device and then with an ultrafiltration membrane device, when the performance of the ultrafiltration membrane device deteriorates. A method for regenerating an ultrafiltration membrane, which comprises washing the ultrafiltration membrane with acidic hot water having a pH of 3 or lower and a temperature of 70 ° C. or higher.