JPH04254595A - Production of high-grade quaternary ammonium hydroxide - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for producing quaternary ammonium hydroxide, and more specifically, the present invention relates to a method for producing quaternary ammonium hydroxide. This invention relates to a method for producing high-purity quaternary ammonium hydroxide by using an insoluble electrode coated with iridium oxide on a treated titanium substrate as an anode.

Quaternary ammonium hydroxide is used in a wide range of applications in the electronic and semiconductor industries, including wafer cleaning solutions, etching solutions, and developing solutions in IC and LSI manufacturing processes.

[Prior art and its problems]

In recent years, as the degree of integration increases in semiconductor manufacturing processes, chemicals used are increasingly required to be highly purified.

Quaternary ammonium hydroxide is no exception; high purity is required, and high purity is now required of the entire raw material used and its manufacturing method.

Conventionally, as a method for electrolytically producing quaternary ammonium hydroxide, for example, JP-A-57-155390, JP-A-57
-181385, JP 57-155390, JP 57-181385, JP 59-193288, JP 60-100690, JP 60-1319
No. 86, JP-A-62-142792, JP-A-63-1
No. 34684, JP-A-64-87792, JP-A-64
A large number of methods have been proposed, such as No.-87795 and Japanese Unexamined Patent Publication No. 64-87797.

However, in the conventional method described above, quaternary ammonium halide salts, quaternary ammonium sulfates, etc. are mainly used as quaternary ammonium salts to be subjected to electrolysis, and when quaternary ammonium halide salts are used, Due to factors such as some of the halide ions passing through the cation exchange membrane and entering the catholyte side and getting mixed into the product, and halogen gas generated during electrolysis corroding the anode itself, high purity It is difficult to obtain quaternary ammonium hydroxide.

Furthermore, since the generated halogen gas is harmful, equipment for removing it or neutralization processing equipment is required.

Furthermore, when quaternary ammonium sulfate is used as a raw material, it is difficult to handle the raw material alkyl sulfate, and there are also problems such as the sulfuric acid generated during electrolysis corroding the electrodes and equipment. In some cases, it is difficult to obtain highly pure quaternary ammonium hydroxide.

Furthermore, even when a quaternary ammonium organic carboxylate salt as in JP-A-60-100690 is used as a raw material, there is a risk that the organic carboxylic acid generated during electrolysis will corrode the anode itself, which is not preferable. There is a possibility that a part of the organic carboxylic acid generated during electrolysis may be mixed into the product quaternary ammonium hydroxide through the cation exchange membrane, which may cause a decrease in purity.

However, in Japanese Patent Application Laid-Open No. 63-134684, high purity quaternary It is illustrated that ammonium hydroxide is obtained.

When producing quaternary ammonium hydroxide by these conventional electrolysis methods, the conventional anode used in the electrolytic cell is usually one that is stable in an oxidizing atmosphere, such as a carbon electrode or a platinum electrode. So-called insoluble electrodes, such as titanium electrodes coated with platinum, Ru, Ir, etc., are used.

However, even with such insoluble electrodes, especially at high current densities, elution of platinum is observed in the case of platinum electrodes, and the electrodes have short lifespans.

[Problems to be solved by the present invention]

The present invention solves the problems observed in the conventional methods as described above, and uses an anode that has a long life and generates extremely little pollution, thereby producing quaternary ammonium hydroxide with higher purity. It provides law.

[Means to solve the problem]

In view of the above circumstances, the present inventors conducted intensive studies on a method for obtaining high-purity quaternary ammonium hydroxide. In the method of producing quaternary ammonium hydroxide by electrolyzing quaternary ammonium salt using a tank, the life of the anode can be extended by using an electrode coated with iridium oxide on a titanium substrate treated with chemicals as an anode. The present invention was completed based on the discovery that higher purity quaternary ammonium hydroxide can be obtained over a long period of time.

Conventionally, the iridium oxide-coated titanium substrate used as an anode is a titanium substrate whose surface is blast-treated and coated with iridium oxide. With such electrodes, elution of iridium is observed when operating at high current density, which contaminates the product and has a short life as an electrode, making long-term operation impossible, which is industrially inconvenient. It is.

Therefore, the present inventors conducted various studies to create a long-life electrode that can be used continuously for a long period of time by suppressing the elution of iridium as much as possible, and as a result, the surface of the titanium substrate was treated with chemicals to coat it with iridium oxide. It was confirmed that the anode has extremely low elution of iridium, can be used for a long time even when used continuously at high current density, and has an extremely long life.

That is, the present invention provides a quaternary ammonium salt, preferably a quaternary ammonium bicarbonate represented by the following general formula (wherein R1, R2, R3 and R4 may be the same or different, each representing an alkyl group or hydroxyalkyl group having 1 to 8 carbon atoms, an alkoxyalkyl group having 2 to 9 carbon atoms, an aryl group, or a hydroxyaryl group) is divided into an anode chamber and a cathode chamber by a cation exchange membrane, The present invention relates to a method for producing high-purity quaternary ammonium hydroxide in which electrolysis is carried out using an electrolytic cell, which is an electrode in which a titanium substrate treated with chemicals and coated with iridium oxide serves as an anode.

In the production of quaternary ammonium hydroxide by electrolysis of quaternary ammonium bicarbonate in the present invention, as shown by the following formula, in addition to quaternary ammonium hydroxide, only carbon dioxide gas is produced. Furthermore, no corrosive substances are produced during electrolysis, making it suitable as a method for producing high-purity quaternary ammonium hydroxide.

The quaternary ammonium bicarbonate used in the present invention is a compound represented by the following formula (R1, R2, R3 and R4 are the same as above), and specifically, tetramethylammonium bicarbonate, Tetraethylammonium bicarbonate, tetrapropylammonium bicarbonate, trimethylpropylammonium bicarbonate, trimethylbutylammonium bicarbonate, trimethylbenzylammonium bicarbonate,
Examples include trimethylhydroxyethylammonium bicarbonate, trimethylmethoxyammonium bicarbonate, dimethyldiethylammonium bicarbonate, dimethyldihydroxyethylammonium bicarbonate, methyltriethylammonium bicarbonate, methyltrihydroxyethylammonium bicarbonate, and the like. .

Such quaternary ammonium bicarbonates can be easily prepared by reacting dialkyl or diaryl carbonates with tertiary amines and water, or by reacting quaternary ammonium monoalkyl or monoaryl carbonates with water. can be obtained.

In the present invention, an electrolytic cell which is usually divided into an anode chamber and a cathode chamber by a cation exchange membrane is used, but in addition to this, at least two electrolytic cells are used.
It is also possible to use an electrolytic cell which is divided by two cation exchange membranes into an anode chamber, a cathode chamber and one or more intermediate chambers.

The anode used in the present invention uses an insoluble electrode coated with iridium oxide on a titanium substrate treated with chemicals. The chemicals used when treating the titanium substrate with chemicals are strong acids such as phosphoric acid, nitric acid, hydrochloric acid, sulfuric acid, tamamizu, and hydrofluoric acid.

For chemical treatment, the above acid concentration is 20 to 80% by weight,
It is carried out at 50 to 150°C for several minutes to several hours.

Further, in order to improve the adhesion between the iridium oxide and the titanium substrate, oxides such as tantalum and niobium may be contained.

As the cathode used in the present invention, an electrode used as a cathode in this type of electrolysis, such as stainless steel or nickel, is used. These anodes and cathodes can be used in any shape such as a plate, rod, net, or perforated plate.

As the cation exchange membrane used in the present invention, a corrosion-resistant fluororesin-based membrane having a cation exchange group such as a sulfonic acid group or a carboxylic acid group is preferably used.
In addition to these, styrene-divinylbenzene copolymers having the above-mentioned exchange groups may also be used.

The material of the electrolytic cell, storage tank, piping, valves, etc. of the present invention is preferably a corrosion-resistant material such as fluororesin or polypropylene resin.

In the present invention, electrolysis in the electrolytic cell is performed by applying a DC voltage, and the current density is 1 to 100 A.
/dm3, preferably 5 to 80 A/dm3.

Moreover, it is preferable that the temperature during electrolysis is in the range of 10 to 50°C. The electrolysis in the present invention can be carried out either batchwise or continuously, and the concentration of the raw material supplied to the anode chamber is set at 1 to 60% by weight, preferably 3 to 40% by weight.

In addition, ultrapure water is supplied to the cathode chamber, but at the start of operation, ultrapure water alone has low electrical conductivity and is difficult to cause electrolysis, so a small amount of the target quaternary ammonium hydroxide, for example, It is desirable to use a liquid containing 0.01 to 5% by weight.

Since the purpose of the present invention is to produce high-purity quaternary ammonium hydroxide, it is natural to use high-purity quaternary ammonium bicarbonate to be used as a raw material. It is.

Furthermore, prior to electrolysis, it is necessary to thoroughly clean the inside of the apparatus, and during electrolysis, it is desirable to perform the electrolysis under an atmosphere of clean inert gas such as nitrogen or argon.

〔Effect of the invention〕

According to the present invention, by using an iridium oxide coated electrode treated with chemicals as an anode, there is little elution of the anode material, so the degree of contamination of products is low and it can be used for a long period of time.

Therefore, it is possible to produce highly pure quaternary ammonium hydroxide over a long period of time.

Next, examples of the present invention will be shown.

Example 1 Nafion 324 (manufactured by DuPont, fluororesin cation exchange membrane) was used as the cation exchange resin, and an apparatus was used in which the electrolytic cell was divided into an anode chamber and a cathode chamber.

An electrode made of a titanium substrate treated with sulfuric acid and coated with iridium oxide was used as the anode, and nickel was used as the cathode.

A 30% by weight solution of tetramethylammonium bicarbonate in ultrapure water was circulated through the anode chamber.

A 0.5% by weight solution of tetramethylammonium hydroxide dissolved in ultrapure water is circulated in the cathode chamber.

Applying a direct current of 30 A/dm3 between the anode and cathode,
Electrolysis was performed at a temperature of 40°C. With an average current efficiency of 88%, 22% of tetramethylammonium hydroxide was added to the cathode chamber.
An 8% by weight aqueous solution was obtained.

As a result of examining the impurity concentration in the tetramethylammonium hydroxide aqueous solution obtained in the cathode chamber, it was found that Na, Fe, K,
Ca, Al, Ag, Co, Cr, Cu, Mn, Ni, Z
n, Mg was 3 ppb or less. Also, Ir is also 3pp
It was below b. Cl was 10 ppb or less.

On the other hand, the Ir concentration in the anode chamber was 120 ppb.

Comparative Example 1 A titanium substrate subjected to sandblasting as an anode,
The same equipment as in Example 1 was used except that electrodes coated with iridium oxide were used.

A 30% by weight solution of tetramethylammonium bicarbonate dissolved in ultrapure water was circulated in the anode chamber, and a 0.5% solution of tetramethylammonium hydroxide dissolved in ultrapure water was circulated in the cathode chamber.
Circulate the wt% solution.

Applying a direct current of 30 A/dm3 between the anode and cathode,
Electrolysis was performed at a temperature of 40°C. Average current efficiency 86%
23. of tetramethylammonium hydroxide in the cathode chamber.
A 1% by weight aqueous solution was obtained.

As a result of investigating the impurity concentration in the tetramethylammonium hydroxide obtained in the cathode chamber, it was found that Na, Fe, K, Ca,
Al, Ag, Co, Cr, Cu, Mn, Ni, Zn, M
g was 3 ppb or less, and Ir was 7 ppb. Cl was 10 ppb or less.

On the other hand, the Ir concentration in the anode was 380 ppb.

Comparative Example 2 The same apparatus as in Example 1 was used, except that instead of iridium oxide, an electrode coated with platinum was used on a titanium substrate treated with hydrochloric acid as an anode.

A 30% by weight solution of tetramethylammonium bicarbonate dissolved in ultrapure water was circulated in the anode chamber, and a 0.5% solution of tetramethylammonium hydroxide dissolved in ultrapure water was circulated in the cathode chamber.
Circulate the wt% solution.

A direct current of 30 A/dm3 was applied between the anode and the cathode, and electrolysis was carried out at a temperature of 40°C. With an average current efficiency of 78%, 23% of tetramethylammonium hydroxide was added to the cathode chamber.
A 2% by weight aqueous solution was obtained.

As a result of examining the impurity concentration in the tetramethylammonium hydroxide aqueous solution obtained in the cathode chamber, Na, Fe, K, and C were found.
a, Al, Ag, Co, Cr, Cu, Mn, Ni, Zn
, Mg was 3 ppb or less. Also, Pt is 85ppb
and Cl was 10 ppb or less.

On the other hand, the Pt concentration in the anode chamber was 8320 ppb.

A comparison with Example 1 shows that Pt is eluted in a significantly large amount.

Example 2 The concentration of tetramethylammonium bicarbonate in the anode chamber was set to 1
The same equipment as in Example 1 was used, except that the concentration was 5% by weight and a DC voltage of 50 A/dm3 was applied between the anode and cathode, and the same operations were carried out.

At an average current efficiency of 80%, a 24.1% by weight tetramethylammonium hydroxide aqueous solution was obtained in the cathode chamber.

As a result of examining the impurity concentration in the tetramethylammonium hydroxide aqueous solution obtained in the cathode chamber, it was found that Na, Fe, K, and C
a, Al, Ag, Co, Cr, Cu, Mn, Ni, Zn
, Mg was 3 ppb or less, and Ir was also 3 ppb or less. Cl was 10 ppb or less.

On the other hand, the Ir concentration in the anode chamber was 135 ppb.

Example 3 The iridium oxide-coated electrode used as the anode in Example 1 and Comparative Example 1 and the platinum-coated electrode used in Comparative Example 2 were used, and the same equipment and conditions as in Example 1 were used to test the electrode. Table 1 shows the results of examining the durability.

Patent applicant: Mitsubishi Gas Chemical Co., Ltd. Agent Sadafumi Kobori

Claims (2)

[Claims] Claim 1: A method for producing quaternary ammonium hydroxide by electrolyzing a quaternary ammonium salt, characterized in that an insoluble electrode in which a chemically treated titanium substrate is coated with iridium oxide is used as an anode. A method for producing high purity quaternary ammonium hydroxide. Claim 2: The quaternary ammonium salt has the following general formula (
In the formula, R1, R2, R3 and R4 may be the same or different, and each represents an alkyl group or hydroxyalkyl group having 1 to 8 carbon atoms, an alkoxyalkyl group having 2 to 9 carbon atoms, an aryl group, or hydroxyaryl. The method according to claim 1, wherein the quaternary ammonium bicarbonate is a quaternary ammonium bicarbonate represented by the following group.