JPH0771668B2 - Method for removing trace organic substances in ultrapure water - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for removing a trace amount of organic matter from ultrapure water used in the electronic industry, the pharmaceutical industry and the like.

(Prior Art) The ultrapure water used in the above fields is required to have various organic substances as well as various ions and colloidal substances. In particular, in the electronic industry that manufactures ICs, LSIs, and VLSIs, ultrapure water used as cleaning water for semiconductor wafers, if organic matter remains in the water, creates stains of silicon carbide on the mirror-finished silicon wafer, Bacteria that have grown in the supply pipes, etc., using organic matter as a nutrient source are released during cleaning, causing problems such as short-circuiting of submicron-order circuits, which affects the yield of products. Countermeasures for the removal of trace organic substances have become an important issue in this field.

Ultrapure water is produced by further refining primary pure water obtained through processing operations such as reverse osmosis, ion exchange, and microfiltration. In this ultrapure water purification step, for example, as shown in the flow chart of FIG. 2, the primary pure water from the primary pure water system shown in (1) is received in the storage tank (2) so that the water does not become stagnant. The pump (3) constantly circulates in the loop piping system (4). Then, circulating water is passed through a purification device (9) consisting of an ultraviolet sterilizer (5), a non-regenerative ion exchanger (6), a microfilter (7), and a limit filter (8) arranged in a loop piping system. The purified water is supplied as ultrapure water from the downstream side to each point of use through each branch pipe (10). The primary pure water is replenished to the storage tank (2) by controlling the liquid level by the amount of the ultrapure water taken out of the system from the branch pipe (10).

In the ultrapure water purified in this way, various ions and colloidal substances have been almost completely removed, so the specific resistance value is 17 to 18 M, which is close to the theoretical pure water of H ₂ O of 18.24.
Although Ω-cm can be easily obtained, the amount of TOC (total organic carbon) in the ultrapure water can be calculated as a few because the elution of organic substances from the ion exchange resin and various organic materials in the purification process may occur. It is difficult to keep it below 10 ppb.

(Problems to be solved by the invention) In ultrapure water, bacteria may constantly invade due to leaks from the purification equipment and reverse pollution from the point of use. As a nutrient source, the flow of water such as piping to the use point stagnates and adheres to the inner wall of the piping to grow, so in the above ultrapure water purification process, bacterial treatment with chemicals or hot water is regularly performed. Has been done.

However, chemical sterilization requires a complicated operation and time to feed and retain the chemicals in each pipe, and consumes a large amount of ultrapure water for cleaning and discharging the chemicals. On the other hand, hot water sterilization increases the elution amount of organic substances from the ion exchange resin and the organic material, and therefore is not a fundamental measure against the propagation of sterilization products.

Therefore, it has been desired to establish an inexpensive and reliable treatment method for preventing the breeding of the sterilization number in ultrapure water and removing the organic substances that cause the breeding.

As a method for removing organic matter in water, there are conventionally known an activated carbon adsorption method and a reverse osmosis treatment method. When activated carbon is used in the purification process of ultrapure water, organic matter can be adsorbed and removed well, but the resistivity of ultrapure water is significantly reduced by elution of inorganic substances from activated carbon, and the activated carbon bed becomes a hotbed for bacteria. There are problems such as clogging of the subsequent ultrafilter.

On the other hand, in the reverse osmosis treatment method, many organic compounds in ultrapure water have relatively low molecular weight, so it cannot be expected that the reverse osmosis membrane sufficiently blocks the organic substances, and the reverse osmosis treatment method requires high-pressure operation. Therefore, energy consumption is large, and there is a risk that bacteria will adhere to the reverse osmosis membrane surface and further increase pressure loss.

(Means for Solving Problems) The present invention has been made as a result of various studies on solving the above-mentioned problems, and most of the organic substances in ultrapure water are used for increasing the specific resistance. Focusing on the fact that it is an organic substance eluted from the regenerated ion exchange resin part, in the process of purifying ultrapure water, it is necessary to pass water through the mixed bed of the ion exchange resin and activated carbon to simultaneously remove the organic substances together with various ions. It has a feature.

More specifically, referring to an actual example, FIG. 1 shows an example of a flow for carrying out the method of the present invention, and a primary pure water from a primary pure water system (1) is stored in a storage tank (2). The pump (3) constantly circulates it in the loop piping system (4A). An ultrapure water purifying device (9A) is arranged in this loop piping system (4A), and the circulating water passes through the ultraviolet sterilizer (5) and is replaced with a non-regenerative ion exchanger, and the ion exchange resin is effectively used in the device. Diameter 0.5m
It is passed through a mixing tower (11) in which m-shaped spherical activated carbon is mixed and packed in a volume ratio of, for example, 1: 1. Then, it is passed through the microfilter (7) and the ultrafilter (8), and supplied as ultrapure water from each branch pipe (10) to the use point. The primary pure water is replenished to the storage tank (2) by the liquid level control by the amount of the ultrapure water taken out of the system from the branch pipe (10).

As the activated carbon to be mixed and filled in the mixing tower (11), molded activated carbon that is hard to be crushed and has little wear is used. Before mixing with the ion-exchange resin, it is thoroughly washed with ultrapure water to cause ash content. It is desirable to remove as much of the eluted components as possible.

The mixing tower (11) may be additionally installed on the outlet side of the non-regenerative ion exchanger (6) of FIG. 2 instead of being installed alone as shown in FIG. (6),
The ultraviolet sterilizer (5) and the mixing tower (11) are arranged in this order, and a part of the organic substances eluted from the non-regenerative ion exchanger (6) are decomposed by ultraviolet rays, and then water is passed through the mixing tower (11). You may do it. It is also possible to change the mixing ratio of the ion exchange resin and the activated carbon depending on the water quality conditions and the like.

(Function) In the mixing bed of the ion exchange resin and the activated carbon in the mixing tower (11), the ions exchanged in the ultrapure water and the inorganic substances eluted from the activated carbon are captured by the ion exchange resin and separated from the ion exchange resin and other organic materials. Since the activated carbon captures the eluted organic matter, the actions of the ion exchange resin and the activated carbon complement each other, and the inorganic matter and the organic matter are simultaneously removed. Further, it is known that the ion exchange resin has an action of adsorbing bacteria and a bactericidal action in ultrapure water, and an effect of preventing sterilization and breeding in the mixed bed can be expected.

(Example) Next, the Example of this invention is shown with a comparative example.

[A] Comparative Example I Specific resistance of 2 to 15 MΩ to cm, TOC
Replenish primary pure water of 100 to 700 ppb, mix and fill anion-exchange resin and cation-exchange resin in a tower-shaped non-regeneration type ion exchanger (6), and circulate water at a flow rate of SV5 to 50 / H. did.

In this case, the specific resistance of the ultrapure water obtained is 17 to 18 MΩ-cm, but the TOC is only about 50 to 150 ppb (average 100 ppb).

[B] Comparative Example II A packed tower (not shown) containing only activated carbon was installed on the outlet side of the non-regenerative ion exchanger (6) in the flow of FIG.
Water was passed under the same conditions.

In the ultrapure water in this case, the TOC was reduced to 1/4 to 1/5 of that of Comparative Example I, but the specific resistance was increased due to the elution of the inorganic substances from the activated carbon.
It dropped to 4 MΩ-cm.

[C] Inventive Example In the flow chart shown in FIG. 1, in the mixing tower (11) having the same shape as the non-regenerative ion exchange tower (6) of Comparative Examples I and II, an ion exchange resin having a mixing ratio of 1: 1 was used. SV5 ~ 80 / H mixed and filled with activated carbon
The method of the present invention was carried out by circulating water at a flow rate of (average 40 / H).

The resistivity of ultrapure water has been improved to 18-18.2 MΩ-cm, and the TOC is 5-
It was reduced to 15ppb (10ppb on average).

In this case, as compared with Comparative Example I, even though the amount of the ion-exchange resin is half, the reason why the specific resistance value is improved in this way is that the organic substance contains a chargeable substance. It is considered that this is because this is adsorbed and removed by activated carbon. In the range of the circulation flow rate, the change in flow rate has almost no effect on the quality of treated water, and the ultrapure water purification capacity of the mixing tower (11) does not change even after 3 months of operation. From this, it was confirmed that the synergistic effect of the action of the ion exchange resin and the activated carbon was sufficiently exhibited in the mixing tower (11), and the organic matter was adsorbed and removed without lowering the specific resistance of the ultrapure water. .

(Effect of the invention) As described above, according to the method of the present invention, in the conventional ultrapure water purification step, simply by installing the mixing tower (11) in which the ion exchange resin and the activated carbon are mixed and packed, The original effective effect of both is exerted, and the synergistic effect of mutually correcting the accompanying deteriorating effect occurs, and the purity of ultrapure water is significantly improved.
Since the growth of bacteria caused by trace organic substances is suppressed,
The required frequency of sterilization cleaning can be reduced accordingly.

[Brief description of drawings]

FIG. 1 is a row diagram for explaining an embodiment of a method for removing a trace amount of organic substances in ultrapure water according to the present invention, and FIG. 2 is a flow chart of a conventional ultrapure water purification process. (1) …… Primary pure water system, (2) …… Storage tank, (3)…
… Pump, (4) (4A) …… Loop piping system, (5) ……
UV sterilizer, (6) …… Non-regenerative ion exchanger,
(7) ... Microfilter, (8) ... Ultrafilter, (9)
(9A) …… Refining equipment, (10) …… Branching pipe, (11) …… Mixing tower.

Claims (2)

[Claims] 1. A trace amount in ultrapure water characterized in that, in the process of purifying primary pure water into ultrapure water, water in the purification process is passed through a mixed bed of ion exchange resin and activated carbon. How to remove organic matter. 2. A process of purifying primary pure water into ultrapure water
Performed in a loop piping purification system in which the next pure water circulates, and by circulating water by arranging the mixed bed in the loop piping purification system as a mixing tower in which a non-regenerative ion exchange resin and activated carbon are mixed and packed, The method for removing a trace amount of organic matter in ultrapure water according to claim 1, wherein the removal of various ions in the circulating water is carried out at the same time as the adsorption of organic matter.