JP7648345B2 - Pure water production method and production equipment - Google Patents

Description

The present invention relates to a method and apparatus for producing pure water.

Conventionally, ultrapure water with extremely low impurity content such as ionic substances, fine particles, organic matter, dissolved gas, and live bacteria has been used in the manufacturing process of electronic parts such as semiconductor devices, liquid crystal displays, silicon wafers, and printed circuit boards, as well as in the manufacturing process of pharmaceuticals. In particular, a large amount of ultrapure water is used in the manufacturing process of electronic parts, including semiconductor devices, and as the integration density of semiconductor devices increases, the requirements for the purity of ultrapure water are becoming increasingly strict. For example, ultrapure water for semiconductor manufacturing requires specifications such as a resistivity of 18.2 MΩ·cm or more, less than 1 fine particle of 0.05 μm or more per mL, total organic carbon (TOC) of less than 1 μg/L, and metal components of less than 1 ng/L, and the required water quality tends to become even stricter.

In particular, in recent years there has been a demand for the reduction of trace impurities such as boron and TOC. In general, it is difficult to completely remove boron using ultrapure water production equipment (subsystems) that only have non-regenerative ion exchange equipment, and removal of boron using primary pure water systems has been considered. Regenerative ion exchange equipment that uses acids and alkalis as regenerants is widely used as a method for removing boron and TOC in primary pure water systems. However, regenerative ion exchange equipment is isolated from the primary pure water system and is placed on standby for a certain period of time after the regeneration operation is performed before operation can begin. During this standby time, some of the organic parent material may dissolve from the ion exchanger, potentially affecting the quality of the treated water.

Patent Document 1 discloses a method for storing a demineralization tower in a condensate demineralization unit of a thermal power plant after regeneration. After the regeneration of the cation layer and anion layer is completed, they are separated by backwashing, and then washing water is passed through the cation layer and anion layer continuously or intermittently. This prevents organic components eluted from the cation resin from contaminating the anion resin.

Japanese Unexamined Patent Publication No. 7-116526

The storage method for a demineralization tower after regeneration described in Patent Document 1 aims to quickly stabilize the water quality of the condensate, and is not a method for producing pure water.

The object of the present invention is to provide a method for producing pure water that can start up a regenerative ion exchange device quickly and with low leaching.

The method for producing pure water of the present invention comprises alternating between a plurality of ion exchange devices arranged in parallel and filled with regenerative ion exchangers between an operating state in which water to be treated is treated and a regeneration standby state in which the supply of the water to be treated is stopped, the ion exchangers are regenerated, and the system waits until the next operating state, and in the regeneration standby state of each of the plurality of ion exchange devices , wash water is passed through the ion exchangers continuously until the timing when the next operating state begins after the regeneration of the ion exchangers is completed.

The present invention provides a method for producing pure water that allows a regenerative ion exchange device to be started up quickly and with low leaching.

FIG. 1 is a schematic diagram of a pure water production system according to an embodiment of the present invention (when tower A is in operation). FIG. 1 is a schematic diagram of a pure water producing system according to one embodiment of the present invention (when tower A cation resin is being regenerated). FIG. 2 is a schematic diagram of a pure water producing system according to one embodiment of the present invention (when tower A anion resin is being regenerated). FIG. 1 is a schematic diagram of a pure water production system according to an embodiment of the present invention (when tower A is on standby). FIG. 2 is a schematic diagram of a pure water production system according to one embodiment of the present invention (when tower A is restarted from operation). FIG. 2 is a schematic diagram of a test device in the examples and comparative examples. 1 is a graph showing the relationship between the amount of water passing through and the TOC of the treated water in an example and a comparative example.

The following describes an embodiment of the pure water production method and pure water production apparatus of the present invention with reference to the drawings. Figures 1A to 1E show the schematic configuration of the pure water production apparatus 1 and the regeneration method of the regenerative ion exchange apparatus 2. In each figure, the thick lines indicate the lines through which the water to be treated, the treated water, or the cleaning water flows. The pure water production apparatus (primary system) constitutes an ultrapure water production apparatus together with the upstream pretreatment system and the downstream subsystem (secondary system). The regenerative ion exchange apparatus 2 requires periodic regeneration, but ultrapure water used in semiconductor manufacturing processes and the like needs to be produced continuously. For this reason, in this embodiment, three resin towers (hereinafter referred to as tower A 2A, tower B 2B, and tower C 2C) are provided in parallel, and the three towers are alternately switched between an operating state and a regeneration standby state so that two towers are operating and one tower is isolated from the pure water production apparatus 1. In the following explanation, a method is described for switching tower A 2A from an operating state to a regeneration standby state, waiting for a predetermined time after regeneration, and then switching it to an operating state.

Figure 1A shows a pure water production system 1 in which A tower 2A and B tower 2B are in operation and C tower 2C is in a standby state for regeneration. The pure water production system 1 of this embodiment has a raw water tank 3, a raw water pump 4, a filter 5, an activated carbon tower 6, a cation resin tower 7, a decarbonation device 8, an anion resin tower 9, a reverse osmosis membrane device 10, a reverse osmosis membrane device treated water tank (hereinafter referred to as RO treated water tank) 11, a reverse osmosis membrane device treated water transfer pump (hereinafter referred to as RO treated water pump) 12, and an ultraviolet oxidation device 13, which are arranged in series along a line L1 from upstream to downstream in the flow direction D of the water to be treated. The raw water (hereinafter referred to as water to be treated) produced in the pretreatment system and stored in the raw water tank 3 is pressurized by the raw water pump 4, and then relatively large particle size dust and the like are removed by the filter 5, and impurities such as hydrogen peroxide, chlorine, and organic matter are removed by the activated carbon tower 6. The water to be treated has its cationic components removed in the cation resin tower 7, its carbon dioxide removed in the decarbonation device 8, and its anionic components removed in the anion resin tower 9, and then its ionic components are further removed in the reverse osmosis membrane device 10. The treated water from the reverse osmosis membrane device 10 is then sent to the RO treated water tank 11, where it is pressurized by the RO treated water pump 12, after which the organic components are decomposed by the ultraviolet oxidation device 13, and then sent to the regenerative ion exchange device 2.

Towers A 2A, B 2B, and C 2C of the regenerative ion exchange device 2 are filled with regenerative ion exchangers, which in this embodiment are ion exchange resins. The ion exchange resins remove organic components and ionic components from the water being treated. In particular, boron has a weak adsorption force to resins, so it is easy to remove from the resin. The ion exchange devices installed in the subsystems are usually cartridge-type non-regenerative devices, partly because the ionic load of the water being treated is small. Non-regenerative ion exchange devices are used for long periods of time until their ion exchange performance deteriorates and they need to be replaced, so the captured boron is likely to flow into the water being treated. In contrast, the regenerative ion exchange device 2 is effective as a means of removing boron, because the boron captured in the resin can be removed by regeneration before it breaks through the resin.

As all three resin towers (Tower A 2A, Tower B 2B, Tower C 2C) have the same configuration, the following explanation will mainly focus on Tower A 2A. Although explanation will be omitted, lines L6 to L9 and valves V3 to V8 are also provided in Tower B 2B and Tower C 2C in the same way. Tower A 2A, Tower B 2B, and Tower C 2C are connected at the inlet to lines L2A, L2B, and L2C, respectively, which branch off from line L1, and at the outlet to lines L3A, L3B, and L3C, respectively, which merge with line L4. Line L4 is connected to line L5, which connects to the subsystem. Lines L2A, L2B, and L2C are provided with valves V1A, V1B, and V1C, respectively, and lines L3A, L3B, and L3C are provided with valves V2A, V2B, and V2C, respectively. Valves V1A, V1B and V2A, V2B are open, and valves V1C, V2C are closed. Therefore, towers A 2A and B 2B are in operation to treat the water to be treated, and tower C 2C is in a standby state for regeneration, isolated from the pure water production system 1.

The A tower 2A is a double-bed ion exchange resin tower in which the lower part is filled with an anion layer 21 made of anion exchange resin, and the upper part is filled with a cation layer 22 made of cation exchange resin. The anion layer 21 and the cation layer 22 may be formed of ion exchange fibers, monolithic ion exchangers, etc. Between the anion layer 21 and the cation layer 22, a header 23 is provided for supplying a regenerant for the anion layer 21. The line L2A is connected to the bottom of the A tower 2A, and the line L3A is connected to the top of the A tower 2A. Therefore, the treated water is introduced into the A tower 2A as an upward flow, the anion components are removed in the anion layer 21, then the cation components are removed in the cation layer 22, and then the treated water is discharged from the line L3A. The regenerative ion exchange device 2 may be a mixed bed type in which the cation exchange resin and the anion exchange resin are mixed and packed in one resin tower, or a two-bed, two-tower type in which the cation exchange resin and the anion exchange resin are packed in different resin towers and these resin towers are connected in series. Alternatively, the cation layer 22 may be packed in the lower portion and the anion layer 21 may be packed in the upper portion, and the water to be treated may be supplied as a downward flow.

Line L6 is provided between valve V1A and A tower 2A, branching off from line L2A. Line L6 joins line L1 via RO treated water tank 11. The position where line L6 joins line L1 may be the inlet side of reverse osmosis membrane device 10 (between anion resin tower 9 and reverse osmosis membrane device 10), the inlet side of cation resin tower 7 (between activated carbon tower 6 and cation resin tower 7), or the inlet side of ultraviolet oxidation device 13 (between RO treated water pump 12 and ultraviolet oxidation device 13). It is desirable to return the eluted components from at least A tower 2A (regenerative ion exchange device 2) to the upstream stage of a device that has one or more functions for removing them. During operation of A tower 2A, valves V6 and V8 on line L6 are closed.

Line L7, which supplies hydrochloric acid, merges with line L3A. When A tower 2A is in operation, valve V3 on line L7 is closed. Line L8, which is connected to header 23 and supplies caustic soda, is provided on the side wall of A tower 2A. When A tower 2A is in operation, valve V4 on line L8 is closed. Line L9, which is a drainage line, branches off from line L8, and valve V5 on line L9 is closed. Line L10, which is a drainage line, branches off from line L6, and valve V7 on line L10 is closed.

Next, the regeneration method of A tower 2A will be described. As shown in FIG. 1B, valves V1A and V2A are closed to isolate A tower 2A, and valves V1C and V2C are opened to operate C tower 2C. Valves V3 and V5 are opened, and hydrochloric acid is supplied to A tower 2A from line L7 to regenerate the cation exchange resin with hydrochloric acid. The hydrochloric acid supplied from line L7 is supplied to the top of A tower 2A, flows through the inside of the cation layer 22 as a downward flow, and is recovered in a wastewater tank (not shown) through header 23, line L8, and line L9. By flowing hydrochloric acid in the opposite direction to the water to be treated, the cationic components captured by the cation exchange resin can be removed more effectively. That is, since the lower part of the cation layer 22 is the inlet side of the water to be treated, more cationic components are captured than in the upper part, which is the outlet side. By flowing hydrochloric acid from top to bottom, the cationic components are prevented from flowing back to the upper side and contaminating the upper part of the cation layer 22. When regenerating the cation layer 22 with hydrochloric acid, water from the RO treated water tank 11 is supplied in an upward flow from the bottom of the anion layer 21 to prevent the hydrochloric acid from coming into contact with the anion layer 21. Next, the remaining hydrochloric acid is washed away with water from the RO treated water tank 11 using the same line as the hydrochloric acid (not shown).

Next, as shown in FIG. 1C, valves V3 and V5 are closed, valves V4, V7, and V8 are opened, and caustic soda is supplied to A tower 2A from line L8 to regenerate the anion exchange resin with caustic soda. The caustic soda supplied from line L8 is supplied to the top of the anion layer 21 of A tower 2A through the header 23, flows through the anion layer 21 as a downward flow, passes through line L10, and is collected in a wastewater tank (not shown). The reason for flowing caustic soda in the opposite direction to the water to be treated is the same as in the case of hydrochloric acid described above. When regenerating the anion layer 21 with caustic soda, water from the RO treated water tank 11 is supplied in a downward flow from the top of the cationic layer 22 to prevent caustic soda from contacting the cationic layer 22. Next, the remaining caustic soda is washed using the water from the RO treated water tank 11 using a similar line (not shown).

Next, as shown in FIG. 1D, valves V4 and V7 are closed, valves V2A and V6 are opened, and washing water is supplied to A tower 2A through lines L4 and L3A. At this time, lines L3B, L3C, L4, and L3A function as washing water supply lines that supply washing water to A tower 2A. The washing water is the outlet water of B tower 2B and C tower 2C, that is, pure water, so it has high purity. It is preferable that the flow rate of the washing water is between 0.5 and 5% of the total flow rate of the pure water discharged from B tower 2B and C tower 2C. The pure water used as washing water flows in the order of cation layer 22 and anion layer 21, and is returned to RO treated water tank 11 through line L6, which is the return line. At this time, lines L2A and L6 function as washing water recovery lines that recover washing water. Since the washing water is reused in this way, the water recovery rate is hardly reduced. The washing water may be returned to a position other than the RO treated water tank 11 as long as it is upstream of the regenerative ion exchange device 2. However, since the wash water may contain organic matter that has eluted from the resin in Tower A 2A, as mentioned above, it is desirable to return it to the upstream stage of a device that has at least one function capable of removing eluted components from Tower A 2A.

Normally, the switching between A tower 2A, B tower 2B, and C tower 2C is performed on a weekly or monthly basis, but regeneration is completed in a few hours. Conventionally, after regeneration is completed, the resin tower is filled with pure water (i.e., the resin is immersed in the resin) and waits until the next operation starts until the timing of switching. However, if the waiting time is long, the resin matrix peels off and the peeled organic matter and fine particles are likely to flow into the immersion water in the resin tower. The leaked organic matter and fine particles may remain in the resin tower and may adhere to the inner wall and resin of the resin tower. For this reason, the water quality of the treated water (TOC, resistivity, number of fine particles, etc.) may become unstable for a while after the resin tower is connected to the pure water production device and the supply of the water to be treated is started. As a result, the load in the downstream subsystem may increase and the water quality at the point of use may fluctuate. In this embodiment, after regeneration is completed, cleaning water is circulated in a standby state until the next operation state, so that organic matter and fine particles peeled off from the resin are washed away by the cleaning water and are less likely to accumulate in the resin tower. Therefore, when the resin tower is connected to the pure water production system 1, the amount of organic matter and fine particles present in the resin tower is reduced, and the quality of the treated water is stabilized quickly after the supply of the water to be treated begins.

Next, as shown in Figure 1E, valves V6 and V8 are closed, valve V1A is opened, and operation of tower A 2A is resumed. At the same time, valves V1B and V2B are closed to isolate tower B 2B from the pure water production system 1. While tower A 2A and tower C 2C are operating, tower B 2B is regenerated and put into standby according to the procedure described above.

Since this embodiment can be implemented simply by changing the operating method of the existing equipment, there is no need to add new lines or valves. Since the wash water is pressurized by the upstream raw water pump 4 and RO treated water pump 12, there is no need to install a new pump. The simplest method is to use the outlet water of the resin towers in operation (tower B 2B and tower C 2C in this embodiment) as the wash water, but there are no particular limitations as long as the wash water has a certain purity and does not contaminate the resin of the regenerative ion exchange device 2 in standby. The wash water may be water that has a resistivity equal to or greater than that of the treated water generated by the regenerative ion exchange device 2.

(Example)
The effect of the present invention was confirmed using the device shown in FIG. 2. A φ25 mm acrylic column was filled with 300 mL of strongly acidic cation resin to create a cation tower. Similarly, a φ25 mm acrylic column was filled with 300 mL of strongly basic anion resin to create an anion tower. The anion tower and the cation tower were connected in series to create two systems of such a two-bed, two-tower ion exchange device. Hydrochloric acid was previously supplied to each cation tower in a downward flow to regenerate the strongly acidic cation resin. Similarly, caustic soda was previously supplied to each anion tower in a downward flow to regenerate the strongly basic anion resin. Next, the water to be treated, which was treated in sequence with city water from Sagamihara City, Kanagawa Prefecture, through a filter, an activated carbon device, an ion exchange device (a two-bed, three-tower type in which a cation exchange resin tower, a decarbonation device, and an anion exchange resin tower are connected in series, as in the embodiment), and a reverse osmosis membrane device, was passed through the anion tower and the cation tower in that order. In order to continuously obtain treated water, the lines 1 and 2 were operated alternately at a constant yield (operation -> regeneration -> standby while passing wash water -> operation).

In the embodiment, the treated water was passed through the ion exchange device of the line 1 at a space velocity of SV90. That is, the treated water was passed through the anion tower from the bottom to the top in an upward flow, and further passed through the cation tower from the bottom to the top in an upward flow. While the line 1 was in operation, the washing water was passed through the ion exchange device of the line 2 in a standby state at a space velocity of SV1. That is, a part of the treated water of the line 1 was passed through the washing line in a downward flow from the top of the cation tower, and further passed through the top of the anion tower in a downward flow (the flow of the washing water is shown by a broken line). The treated water was passed through the line 1 for 65 hours, and then the line 2 was switched to an operating state for alternate operation, and the TOC of the treated water of the line 2 was measured. The TOC was measured using a TOC meter SIEVERS M9e manufactured by Suez. The comparative example is the same as the embodiment, except that the water passing washing was not performed when the line 2 was in a standby state. The results are shown in FIG. 3. The horizontal axis shows the amount of water passing through per unit volume of resin, and the vertical axis shows the TOC of the treated water. In the example, because line 2 was cleaned by passing water through it during standby, the TOC of the treated water stabilized when about 500 times the volume of water had been passed through it compared to the resin volume. In the comparative example, it was necessary to pass about 1000 times the volume of water through it compared to the resin volume until the TOC of the treated water stabilized, and it was confirmed that the TOC stabilized in a shorter time in the example.

1 Pure water production equipment 2 Regenerative ion exchange equipment 2A, 2B, 2C Ion exchange resin towers (A tower, B tower, C tower)
21 Ion exchanger (anion layer)
22 Ion exchanger (cation layer)

Claims (8)

In a plurality of ion exchange devices filled with regenerative ion exchangers and arranged in parallel , an operating state in which water to be treated is treated and a regeneration standby state in which the supply of the water to be treated is stopped, the ion exchangers are regenerated, and the system is on standby until the next operating state are alternately repeated between the plurality of ion exchange devices ,
In the regeneration standby state, washing water is continuously passed through the ion exchanger until a next operating state is started after the regeneration of the ion exchanger is completed. The method for producing pure water according to claim 1, wherein the cleaning water and the regenerant supplied for regenerating the ion exchanger are passed in a direction opposite to the direction of the water to be treated. The method for producing pure water according to claim 1 or 2, wherein the cleaning water has a resistivity equal to or greater than that of the treated water produced by the ion exchange device. 2. The method for producing pure water according to claim 1 , wherein the cleaning water is treated water produced by the ion exchange device in the operating state. 5. The method for producing pure water according to claim 1, wherein the water used as the cleaning water is returned to a stage upstream of a device having one or more functions for removing components eluted from the ion exchange device. 6. The method for producing pure water according to claim 1 , wherein the space velocity of the wash water in the ion exchange device is lower than the space velocity of the water to be treated in the ion exchange device. a plurality of ion exchange devices filled with regenerative ion exchangers and arranged in parallel , the plurality of ion exchange devices being capable of alternately repeating between an operating state in which the water to be treated is treated and a regeneration standby state in which the supply of the water to be treated is stopped, the ion exchangers are regenerated, and the plurality of ion exchange devices are on standby until the next operating state;
a cleaning water supply line for continuously supplying cleaning water to the ion exchanger during the regeneration standby state until a next operating state is started after the regeneration of the ion exchanger is completed;
A pure water production apparatus having the above structure. The water purifying apparatus according to claim 7 ,
a pretreatment system provided upstream of the pure water production apparatus;
a subsystem provided downstream of the water purifying apparatus;
An ultrapure water production apparatus comprising:

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