JP2005177564A - Ultrapure water production method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce maintenance costs by lowering the concentration of boron and reducing the regeneration frequency of an anion exchange resin or mixed bed ion exchange resin device in ultrapure water production processes. <P>SOLUTION: A heat exchanger is disposed ahead of the anion exchange device or the mixed bed ion exchange device in an ultrapure production system to control the temperature of water to be treated, fed to the anion exchange device or the mixed bed ion exchange device, at ≤25°C, preferably at ≤20°C. A reduction in water temperature enables a prolongation of a period until boron ions begin to flow out to extend a regenerative cycle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for producing ultrapure water, and more specifically, in a field requiring high purity water such as a pharmaceutical production process, a liquid crystal substrate production process, and a semiconductor production process, It is related with the manufacturing method and apparatus of the ultrapure water which can extend boron and can reduce a boron to very low concentration.

  Conventionally, so-called ultrapure water has been used in fields requiring high-purity water quality such as pharmaceutical manufacturing processes, liquid crystal substrate manufacturing processes, and semiconductor manufacturing processes.

  Ultrapure water is usually produced by an ultrapure water production apparatus consisting of two stages, a primary pure water system and a secondary pure water system.

  The primary pure water system includes, for example, raw water such as tap water and well water, a membrane pretreatment device, a first pH adjustment device that adds acid to the treatment water of the membrane pretreatment device, and a first pH adjustment device. Degassing device for decarboxylating treated water, second pH adjusting device for adding alkali to decarboxylated treated water, reverse osmosis membrane device for treating treated water of second pH adjusting device with reverse osmosis membrane, reverse osmosis membrane It consists of a mixed bed type ion exchange device that removes the ion component of the permeated water of the device. In addition to the above configuration, the primary pure water system may further use an anion exchange device, a cation exchange device, an ultraviolet decomposition device, a vacuum deaeration device, or the like. The treated water of the primary pure water system is temporarily stored in the primary pure water tank.

  The secondary pure water system is an ultraviolet decomposition device that decomposes the organic components of the treated water of the primary pure water system into ion components, and a mixed bed ion exchange device that removes the ion components generated by the decomposition of the organic components by the ultraviolet decomposition device. The treated water, which is composed of an ultrafiltration membrane device or the like and is not normally used at the point of use, is recycled and reused as the treated water of the secondary pure water system.

  Among the devices used in these primary pure water systems and secondary pure water systems, when an ion exchange device adsorbs a certain amount of ions, it no longer adsorbs ions and ions flow out into the treated water. Therefore, it is necessary to regenerate at an appropriate timing before the outflow of ions starts.

The ease of adsorption of ions to the anion exchange resin differs depending on the type of ion, and the ease of adsorption is usually in the order of SO4 ²⁻ > NO 3 ⁻ > Cl ⁻ > F ⁻ > ionic silica> B.

  For this reason, the boron concentration of treated water is also used as a standard for resin regeneration in an anion exchanger and mixed bed ion exchanger.

  Recently, ultrapure water with higher purity has been required for ultrapure water used in semiconductor manufacturing sites. In particular, boron ions that exist as impurities in ultrapure water are semiconductor devices. Since it is one of the impurities used in the PN junction, it has been required to keep the boron ion concentration at a very low level.

Boron is considered a typical semi-metallic element with intermediate attributes between metals and non-metals with negative charges, but boric acid tends to form anionic compounds rather than cationic compounds. In deionized water, it reacts with water as in the following formula to generate borate ions (hereinafter simply referred to as boron ions) and hydrogen ions.

  This boron ion can be removed by an anion exchange device or a mixed bed type ion exchange device. However, as described above, boron ions are not easily adsorbed by the ion exchange resin, and boron ions in the treated water of the ultrapure water production system are very difficult to absorb. In order to keep it at a very low level, it is necessary to frequently regenerate the ion exchange resin, which causes a problem that the maintenance cost of the ultrapure water production system becomes high.

A technique using a boron-selective ion exchange resin that selectively removes boron ions has also been proposed (Patent Document 1). However, in this method, another ion exchange resin tower must be installed. In addition, since an ion exchange resin tower is required separately, it is not an essential solution for reducing maintenance costs.
Japanese Patent Application Laid-Open No. 8-8496

  As described above, it has recently been required to reduce the concentration of boron ions in ultrapure water. However, since boron ions are difficult to be adsorbed on ion exchange resins, in order to reduce boron ions, However, it is necessary to frequently regenerate the ion exchange resin, which causes a problem that the maintenance cost of the ultrapure water production system increases.

  As a result of diligent research to solve such problems, the present inventors have found that when the temperature of the water to be treated is lowered, the time until breakthrough of boron ions in the ion exchange resin becomes longer.

  The present invention has been made on the basis of such knowledge, and a heat exchanger is disposed in front of the anion exchange device or the mixed bed ion exchange device in the ultrapure water production system, and the anion exchange device or the mixed bed ion exchange is provided. It is characterized in that the temperature of the water to be treated in the apparatus is controlled to 25 ° C. or lower, preferably 20 ° C. or lower.

  The effect of the present invention increases as the temperature of the water to be treated of the anion exchange device or the mixed bed ion exchange device decreases, but the cost required for cooling increases as the temperature of the water to be treated decreases. Therefore, it is desirable to set the cooling temperature to an appropriate temperature in view of the reduction in the regeneration cost due to the reduction in the regeneration frequency and the increase in the cost for cooling. In general, if the cooling temperature exceeds 10 ° C. from the original water temperature, the increase in the cooling cost will offset the effect of reducing the regeneration cost. Therefore, the cooling of the water to be treated can be set within the range of 10 ° C. from the original water temperature. desirable.

  As a heat exchanger used in the present invention, a rectangular pipe is divided into a plurality of partitions by a partition plate made of a metal plate having good heat conductivity to form a plurality of water channels, and the water to be treated and the cooling water are placed in adjacent water channels. A flat plate heat exchanger configured to pass countercurrent to each other is suitable.

  The anion exchange apparatus or mixed bed type ion exchange apparatus used in the present invention includes an anion exchange resin apparatus filled with an anion exchange resin or a mixed bed type ion exchange resin filled with a mixture of an anion exchange resin and a cation exchange resin. The device is suitable.

  The heat exchanger can be installed in the primary pure water system, the secondary pure water system, or both if it is a front stage of the anion exchange device or the mixed bed type ion exchange device. It is more effective to install it in the front stage of the anion exchanger or mixed bed ion exchanger of the pure water system.

  The heat exchanger does not need to be placed immediately before the anion exchange device or the mixed bed type ion exchange device. If the treated water entering the anion exchange device or the mixed bed type ion exchange device is 25 ° C. or less, the heat exchanger It is also possible to interpose the apparatus between the heat exchanger and the anion exchange apparatus or the mixed bed type ion exchange apparatus.

  According to the present invention, it is possible to extend the regeneration time of the ion exchange device and reduce boron to a very low concentration.

The best mode for carrying out the invention will be described below.
In addition, although the following form is an example applied to the primary pure water system of the ultrapure water manufacturing apparatus which supplies ultrapure water to a semiconductor manufacturing apparatus, this invention is not limited to this Example. .

  FIG. 1 is a configuration diagram of an embodiment in which the present invention is applied to a primary pure water system of an ultrapure water production system.

  As shown in the figure, the ultrapure water production apparatus of this embodiment includes a membrane pretreatment device 1 comprising a hollow fiber membrane, a first pH adjusting device 2 comprising an acid storage tank 2a and a pump 2b, and a decarbonation gas tower 3. From the second pH adjusting device 4 comprising the alkaline storage tank 4a and the pump 4b, the first reverse osmosis membrane device 7a, the second reverse osmosis membrane device 7b, the flat plate heat exchanger 8, and the mixed bed ion exchange device 9. The main part is composed.

  In this embodiment, the raw water (Atsugi City water, Kanagawa Prefecture) supplied to the ultrapure water production apparatus is pretreated by the membrane pretreatment apparatus 1 and then the pH of the treated water by a pH meter not shown. Is measured, the amount of sulfuric acid aqueous solution to obtain a predetermined pH value is calculated by a pH adjusting device (not shown), and the sulfuric acid aqueous solution is poured from the first pH adjusting device 2 to adjust the pH to 4-5. .

  Next, the city water whose pH is adjusted to 4 to 5 is degassed and decarboxylated by the decarboxylation device 3. In the decarboxylated treated water, the amount of aqueous sodium hydroxide solution for calculating a predetermined pH value is calculated by a pH adjusting device (not shown), and the aqueous sodium hydroxide solution is added from the alkaline storage tank 4a by the pump 4b. Is adjusted to 6-7. The treated water whose pH is adjusted to 6 to 7 is supplied to the first reverse osmosis membrane device [Toray Industries, Inc. SU-710] 7a, and the permeated water is further supplied to the second reverse osmosis membrane device 7b. Reverse osmosis membrane treatment is performed.

  The permeated water of the second reverse osmosis membrane device 7b is supplied to the flat plate heat exchanger 8, the water temperature is adjusted to a predetermined temperature, and then supplied to the mixed bed type ion exchanger 9 as treated water to be removed. Ion treatment is performed.

  The mixed bed type ion exchange device 9 is a container having an inner diameter of 50 mm and a height of 1500 mm filled with 1.5 liters of mixed bed type ion exchange resin [Rohm and Haas, MBGP]. It is carried out as a downward flow with a flow rate of 60 liters / h.

  The concentration of boron ions in the treated water when treated at 28 ° C. (Comparative Example), 25 ° C. (Example 1), and 20 ° C. (Example 2) every day in the mixed-bed ion exchanger 9 The results when measured at regular times are shown in FIG.

  As is apparent from the graph of FIG. 2, in Example 1 (25 ° C.), the outflow period of boron ions in Comparative Example (28 ° C.) was 3 days, but it was extended to 60 days by 5 days. In Example 2, it was confirmed that the frequency of regeneration could be reduced by that much because the period of use of 133% was extended to 7 days.

  In addition, although the example which used the mixed bed type | mold ion exchange apparatus as an ion exchange apparatus was demonstrated in the above Example, the same effect can be acquired also when an anion exchange apparatus is used.

  The above embodiment is an example in which the present invention is applied to a primary pure water system of an ultrapure water production apparatus for semiconductors. However, the pharmaceutical production process, the liquid crystal substrate production process, and other high-purity products can be used outside the semiconductor production site. It can be applied to fields where water is required.

The figure which shows the structure of the principal part of the ultrapure water manufacturing apparatus of one Example of invention, It is a graph for showing the effect of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Membrane pretreatment apparatus, 2 ... 1st pH adjustment apparatus, 3 ... Decarbonation gas tower, 4 ... 2nd pH adjustment apparatus, 7a ... 1st reverse osmosis membrane apparatus, 7b ... 2nd reverse osmosis membrane Apparatus: 8 ... Flat plate type heat exchanger, 9 ... Mixed bed type ion exchanger.

Claims (7)

  A heat exchanger is disposed in front of the anion exchanger or mixed bed ion exchanger in the ultrapure water production system, and the temperature of the water to be treated that passes through the anion exchanger or mixed bed ion exchanger is 25 ° C. or lower. A method for producing ultrapure water, characterized in that the method is controlled.   The method for producing ultrapure water according to claim 1, wherein the temperature of water to be treated which is passed through the anion exchanger or the mixed bed ion exchanger is controlled to 20 ° C or lower.   A heat exchanger is disposed in front of the anion exchanger or mixed bed ion exchanger in the ultrapure water production system, and the water temperature of the treated water of the anion exchanger or mixed bed ion exchanger is 10 ° C. from the original water temperature. The method for producing ultrapure water according to claim 1, wherein the water content is lowered within a range.   The method for producing ultrapure water according to any one of claims 1 to 3, wherein the heat exchanger is a flat plate heat exchanger.   The method for producing ultrapure water according to any one of claims 1 to 4, wherein the anion exchange device or the mixed bed type ion exchange device is an anion exchange resin device or a mixed bed type ion exchange resin device.   The method for producing ultrapure water according to any one of claims 1 to 5, wherein the ultrapure water production system is a primary pure water system. A pretreatment device that performs membrane pretreatment on raw water;
A first pH adjusting device that adds acid to the treated water of the pretreatment device to make the pH less than 7,
A degassing device for degassing the treated water of the first pH adjusting device;
A second pH adjuster for adjusting the pH to 7 or more by adding alkali to the treated water in the degassing step;
A reverse osmosis membrane device for treating the treated water of the second pH adjusting device with a reverse osmosis membrane;
A water temperature adjusting device for adjusting the temperature of the treated water of the reverse osmosis membrane device to 25 ° C. or less;
An apparatus for producing ultrapure water, comprising: an anion exchange device or a mixed bed type ion exchange device that removes an ion component of treated water whose temperature is adjusted by the water temperature adjustment device.

Images