JP3304412B2 - Pure water production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing pure water by subjecting mixed raw water for semiconductor production and industrial water to ion exchange and membrane separation treatment.

[0002]

2. Description of the Related Art Ultrapure water used in a semiconductor manufacturing process or the like generally comprises a primary pure water manufacturing process comprising ion exchange and membrane separation, and a secondary pure water production process comprising ultraviolet oxidation, mixed-bed ion exchange and ultrafiltration. It is manufactured through a pure water manufacturing process (also called a subsystem). As raw water supplied to such an ultrapure water production process, in addition to industrial water, semiconductor production effluent discharged from a semiconductor production process at a semiconductor production plant or the like is collected and used as raw water.

However, since both contain different components, pure water is produced by another treatment method. That is, when semiconductor manufacturing wastewater is used as raw water, primary pure water is produced through the steps of activated carbon treatment, weak basic anion exchange, strong acidic cation exchange, strong basic anion exchange, and membrane separation.
On the other hand, when industrial water is used as raw water, activated carbon treatment,
Primary pure water is produced through the steps of strongly acidic cation exchange, degassing, strong basic anion exchange, and membrane separation.

[0004]

In the conventional ultrapure water production process, since the primary pure water is produced by a different treatment method for each raw water, the treatment apparatus and operation are complicated, and the production cost is increased. There is a problem. In order to improve this point, if both raw waters are mixed and treated, there is a problem that scale adheres to the membrane separation device, thereby reducing the amount of treated water and the quality of treated water.

It is an object of the present invention to prevent a decrease in the amount of treated water and the quality of treated water due to the generation of scale in a membrane separation apparatus even when raw water is produced by mixing wastewater for producing semiconductors and industrial water, thereby enabling simple treatment. An object of the present invention is to propose a pure water production method capable of producing high-quality pure water at a high treated water amount by using an apparatus and operation.

[0006]

According to the present invention , an anion exchange resin is produced from a semiconductor manufacturing wastewater without cation exchange.
This is a method for producing pure water, which comprises introducing an anion-exchange column into a packed anion exchange column, exchanging anions, mixing with industrial water, and subjecting the mixed raw water to ion exchange and membrane separation.

The semiconductor manufacturing wastewater used as raw water in the present invention is cleaning wastewater or other wastewater discharged from a semiconductor manufacturing process, and is wastewater containing fluorine ions. The semiconductor manufacturing wastewater can be subjected to pretreatment such as activated carbon treatment in advance. As other industrial water used as raw water, tap water, groundwater, river water, and the like generally used as raw water for producing pure water can be used as they are. This industrial water can also be subjected to a pretreatment such as a coagulation sedimentation treatment.

When ion exchange and membrane separation treatment are performed by mixing such semiconductor production wastewater and industrial water, scale is generated in the membrane separation apparatus, and the amount of treated water and the quality of treated water are reduced. However, fluorine ions in semiconductor manufacturing wastewater and calcium ions in industrial water react to produce calcium fluoride, and [Ca]
[F] ² = 4 × 10 ^-11 or more was found to be due to the formation of colloid.

That is, when calcium fluoride colloid is formed by mixing both raw waters, the dissociation constant is low.
It is not removed in the ion exchange step, but flows directly into the membrane separation device to be scaled. When calcium fluoride adheres to the separation membrane, the performance does not easily recover even when chemical cleaning is performed, and the amount of treated water is reduced, and the attached matter is gradually eluted, and the quality of treated water is reduced.

In the present invention, in order to prevent such generation of calcium fluoride, semiconductor production wastewater is previously subjected to anion exchange to remove fluorine ions, and then mixed with industrial water to obtain a mixed raw water. The mixing ratio of both is arbitrary.
Mixing can be performed by introducing both into a storage tank.

The anion exchange resin used for the anion exchange of the waste water for producing semiconductors may be a weakly basic anion exchange resin or a strongly basic anion exchange resin, and may be a gel type or a porous type. Since fluorine ions in semiconductor manufacturing wastewater are usually contained in the form of hydrofluoric acid, regeneration is easier if a weakly basic anion exchange resin is used. In the anion exchange, the resin is packed in the tower, and the semiconductor manufacturing wastewater is SV10
It can be carried out by passing water at ３０30 hr ⁻¹ . The anion-exchange treated water of semiconductor production wastewater can be mixed with industrial water after post-treatment such as ultraviolet oxidation if necessary.

Ion exchange of mixed raw water is an operation of decationizing and deanionizing with a cation exchange resin and an anion exchange resin. A strongly acidic cation exchange resin is used as the cation exchange resin, and a strongly basic anion exchange resin is used as the anion exchange resin. In some cases, a weak acid or weakly basic resin may be used in combination. These resins may be of a gel type or a porous type.

Although any type of ion exchange such as a two-column system, a double-bed system, and a mixed-bed system can be adopted, it is preferable to perform degassing of carbon dioxide gas or the like at this stage. A method such as a tower type or a four-bed five-column type is preferable. As the degassing tower, any of decarboxylation type, vacuum degassing type, and N ₂ degassing type may be used. The operation of the ion exchange treatment using these is the same as the ordinary pure water production method.

The purpose of the membrane separation treatment is to mainly remove relatively high-molecular-weight organic substances leaking from the ion-exchange step, but also to remove low-molecular-weight organic substances, solid substances, inorganic ions and the like. Good. The separation membrane used here is preferably a reverse osmosis membrane such as polyamide or cellulose acetate, but may be a UF membrane or MF membrane. The operation pressure for membrane separation is 10 to 20 kgf / cm ² G,
It is preferred to operate at a recovery of 70% or more.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a flow chart showing an embodiment of the pure water production method of the present invention.

In FIG. 1, reference numeral 1 denotes a semiconductor manufacturing drainage tank, and 2 denotes an activated carbon treatment tank in which an activated carbon layer 2a is formed. Reference numeral 3 denotes an anion exchange tower on which an OH-type weakly basic anion exchange resin layer 3a is formed. Reference numeral 4 denotes a mixed raw water tank, and reference numeral 5 denotes an activated carbon treatment tank in which an activated carbon layer 5a is formed. Reference numeral 6 denotes a cation exchange tower on which an H-type strongly acidic cation exchange resin layer 6a is formed. Reference numeral 7 denotes a degassing tower, which is of a decarboxylation type. Reference numeral 8 denotes an anion exchange tower, which uses an OH type strongly basic anion exchange resin 8a. 9 is a desalination water tank, 10
Is a membrane separation device having a built-in separation membrane 10a made of a reverse osmosis membrane.

The method of producing pure water is as follows.
From 1, semiconductor manufacturing wastewater is introduced into the semiconductor manufacturing drainage tank 1. Then, a part thereof is introduced from the connecting pipe 12 into the activated carbon treatment tank 2 to perform activated carbon treatment, and organic substances and other impurities are adsorbed and removed by the activated carbon layer 2a. This activated carbon treatment tank 2
May be omitted, and the activated carbon treatment tank 5 may perform the action.

The treated water in the activated carbon treatment tank 2 is introduced into the anion exchange tower 3 through the connecting pipe 13, and fluorine ions and other anions are removed by the anion exchange resin layer 3a. The anion exchange treatment may be either upward flow or downward flow.
It is preferable to pass water at ３０30 hr ⁻¹ . Regeneration is performed using an acid such as hydrochloric acid or sulfuric acid, and may be either cocurrent regeneration or countercurrent regeneration. The anion exchange treated water is introduced into the mixed raw water tank 4 through the connecting pipe 14.

On the other hand, industrial water is introduced into the mixed raw water tank 4 from the industrial water pipe 15 and mixed with the anion exchange-treated water to form mixed raw water. Industrial water contains calcium ions, but since fluoride ions are not contained in the anion exchange treated water, no calcium fluoride colloid is formed.

The mixed raw water is supplied from the connecting pipe 16 to the activated carbon treatment tank 5.
To perform activated carbon treatment with the activated carbon layer 5a to adsorb and remove free chlorine, organic substances, and other impurities. If these impurities are not contained in the raw water due to pretreatment or the like, this treatment can be omitted.

The activated carbon treated water is introduced into the cation exchange tower 6 through the communication pipe 17 and is brought into contact with the cation exchange resin layer 6a to perform decation. This operation may be either upward flow or downward flow, and it is preferable to pass water at an SV of 10 to 30 hr ^-1 . Regeneration may be either a cocurrent or countercurrent regeneration method.

The cation-exchanged water is introduced into the degassing tower 7 from the connecting pipe 18 and sprayed on the filler layer 7a, and air is sent from the air pipe 19 to dissipate carbon dioxide gas and other gases for degassing. Do. If oxygen must not be contained in the degassed water, vacuum degassing, N ₂ degassing, etc. are performed.

The degassed water is supplied from the connecting pipe 20 to the anion exchange tower 8.
To be brought into contact with the anion exchange resin layer 8a for deanionization. This operation may be either an upward flow or a downward flow, and it is preferable to pass water at an SV of 10 to 30 hr ^-1 .
Regeneration may be either a cocurrent or countercurrent regeneration method.

After the desalinated water is stored in the desalting water tank 9 from the connecting pipe 21, a part of the water is introduced into the membrane separation device 10 through the connecting pipe 22, and the membrane is separated by the separation membrane 10 a, and organic matter, solid matter, and inorganic matter are separated. The remaining impurities such as ions are removed. The membrane separation is performed at an operation pressure of 10 to 20 kgf / cm ² G and a recovery of 70% or more. Since calcium fluoride does not exist in the desalted water flowing into the membrane separation device 10, there is no scaling with calcium fluoride colloid as in the conventional case, and the treated water amount does not decrease for a long time.

The permeated water of the membrane separator 10 is taken out of the pure water pipe 23 as pure water. This pure water can be used as it is or after any post-treatment, and can be used for general pure water. Can be offered. The concentrate of the membrane separation device 10 is discharged from the concentrate tube 24.

Example 1 pH 4.0, fluorine ion 20 mg / l, total cation 3
0 mg / l (CaCO _ThreeAs), total anion 100m
g / l (CaCO_ThreeAs) semiconductor manufacturing wastewater, OH
Weakly basic anion exchange resin DIAION WA-30
(Mitsubishi Kasei Co., Ltd., trademark)
Anion exchange by passing water through the on-exchange tower at 500 liter / hr
After the exchange, pH 7.3, calcium ion 30 mg /
l, total cation 120mg / l (CaCO_ThreeAs)
130 mg / l of total anions (CaCO_ThreeAs) industry
It was mixed with service water (tap water) to obtain mixed raw water.

An activated carbon tank filled with 100 liters of Kuraray Coal (trade name, manufactured by Kuraray Co., Ltd.) was mixed with the mixed raw water, H-type strongly acidic cation exchange resin Diaion SK1B.
A cation exchange tower filled with 50 liters (trademark, manufactured by Mitsubishi Kasei Co., Ltd.), a deaeration tower for blowing air countercurrently at 5 Nm ³ / hr, and an OH type strong basic anion exchange resin Diaion SA10 (Mitsubishi Kasei Corporation) Through a series of anion exchange columns filled with 70 liters of Toray Industries, Inc., and a spiral type reverse osmosis membrane module SU-710 (Toray Industries, Inc.)
Operating pressure of 15 kgf /
The membrane was separated at a supply rate of 90 cm ² G and a recovery rate of 90% to produce pure water.

As a result, the specific resistance of the pure water at the outlet of the membrane separation device after the operation for 3 hours and after the operation for 70 hours was 18.02 Ω ·
cm, the amount of treated water was 28 m ³ / d, and the quality of treated water and the amount of treated water did not decrease.

Comparative Example 1 A test was conducted under the same conditions as in Example 1 except that the anion exchange of the semiconductor production wastewater was not carried out. The specific resistance of the pure water at the outlet of the membrane separation device was 18.02 Ω · after 3 hours of operation. c
m after the 70-hour operation.
cm and the treated water volume is 28 m ³ after 3 hours of operation.
/ D, but 23 m ³ / d after 70 hours of operation
Has dropped.

From the above results, it is possible to prevent a decrease in the quality of the treated water and a decrease in the amount of treated water by mixing the wastewater for semiconductor production with an industrial water after anion exchange.

[0031]

According to the present invention, a semiconductor manufacturing waste water, mosquitoes
Filled with anion exchange resin without thione exchange
After being introduced into the anion exchange column and anion exchanged, it is mixed with industrial water to perform ion exchange and membrane separation treatment, thereby preventing scaling of the membrane separation device due to formation of calcium fluoride colloid. Thus, it is possible to prevent a reduction in the amount of treated water and the quality of treated water, and it is possible to produce high-purity pure water at a high treated water amount and at low cost by using a simple treatment apparatus and operation.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a pure water production method according to an embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor production drain tank 2, 5 activated carbon treatment tank 3, 8 anion exchange tower 4 mixed raw water tank 6 cation exchange tower 7 degassing tower 9 demineralized water tank 10 membrane separation device 11 semiconductor production drain pipe 15 industrial water pipe 19 air pipe 23 Pure water pipe 24 Concentrated liquid pipe

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) C02F 1/44 B01D 61/04 B01D 61/16 C02F 1/42 C02F 9/00

Claims (1)

(57) [Claims] 1. A method for cation exchange of semiconductor manufacturing wastewater .
To an anion exchange tower filled with anion exchange resin
A method for producing pure water, comprising introducing, after anion exchange, mixing with industrial water, and subjecting the mixed raw water to ion exchange and membrane separation treatment.