JP2594286B2 - Method for producing quaternary ammonium hydroxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an electrolytic cell for synthesizing high-purity quaternary ammonium hydroxide from a quaternary ammonium salt by electrolysis using an ion exchange membrane. The present invention relates to a method of operating continuously and stably.

(Problems to be Solved by the Related Art and the Invention) Quaternary ammonium hydroxide is useful as a standard solution of a base in nonaqueous solvent titration, including a phase transfer catalyst, or as an organic alkaline agent in organic synthesis. It is a compound and is used as a processing agent for cleaning, etching, developing resists, and the like for semiconductor substrates in the manufacture of integrated circuits and large-scale integrated circuits. In particular, in recent years, due to the tendency toward higher integration of semiconductor devices, a semiconductor substrate is contaminated when impurities are mixed in a developer for semiconductors. Therefore, high-purity quaternary ammonium hydroxide containing no impurities is required. ing.

By the way, as a method for producing quaternary ammonium hydroxide, there is a method of electrolyzing a raw material quaternary ammonium salt using an electrolytic cell partitioned into an anode chamber and a cathode chamber by one cation exchange membrane. Are known. However, when this method is used, high-purity quaternary ammonium hydroxide was not obtained because chlorine ions pass through the ion-exchange membrane and are mixed with the target quaternary ammonium hydroxide. . Therefore, a method has been proposed in which the amount of diffusion of the chloride ions is reduced by using two or more cation exchange membranes (Japanese Patent Laid-Open No. 60-131986). According to this method, quaternary ammonium hydroxide containing less chloride ions can be obtained.However, when the operation is continued, the amount of liquid in the intermediate chamber gradually decreases, the voltage increases, and finally the operation must be stopped. A problem that must be solved.

(Means for Solving the Problem) The present inventors have studied the cause of the increase in the voltage of the intermediate chamber described above. As a result, a room for supplying a quaternary ammonium salt as a raw material (hereinafter, also referred to as a raw material room) is provided.
The inventors have found that pH is related to an increase in the voltage of the intermediate chamber, and have completed the present invention.

That is, the present invention uses an electrolytic cell partitioned into an anode chamber, an intermediate chamber and a cathode chamber by arranging at least two cation exchange membranes between the anode and the cathode, and a quaternary cell in the anode chamber. An aqueous solution of ammonium salt is supplied, a quaternary ammonium hydroxide aqueous solution is present in the intermediate chamber, and a basic compound is added in the electrolysis to take out the quaternary ammonium hydroxide aqueous solution from the cathode chamber to raise the pH of the anode chamber to 8 or more. A method for producing quaternary ammonium hydroxide, comprising continuously performing electrolysis while maintaining the temperature.

As the quaternary ammonium salt used as a raw material in the present invention, known compounds are used without any limitation.
A quaternary ammonium salt generally preferably used is represented by the following general formula [I] It is a compound shown by these. In the above general formula, the number of carbon atoms of the alkyl group and the hydroxyalkyl group is not particularly limited, but is generally preferably 1 to 6. Further, as the aryl group, a phenyl group, a tolyl group, a xylyl group,
Examples include a naphthyl group, a phenanthryl group and an anthryl group. Further, as the monovalent carboxylate ion, an aliphatic carboxylate ion such as a formate ion, an acetate ion, a propionate ion, and a butyrate ion is preferable.

Specific examples of such quaternary ammonium salts include tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide, tetraethylammonium chloride, tetramethylammonium hydrogencarbonate, tetraethylammonium hydrogensulfate, and tetramethylammonium formate. Ammonium, tetramethylammonium acetate, tetraethylammonium carbonate, tetramethylammonium sulfate and the like.

The quaternary ammonium hydroxide obtained by the method of the present invention has the following general formula [II] It is a compound shown by these. Specific examples include tetramethylammonium hydroxide and tetraethylammonium hydroxide.

The electrolytic cell used in the present invention is an electrolytic cell having at least one intermediate chamber between an anode chamber and a cathode chamber by disposing at least two cation exchange membranes between an anode and a cathode. is there. The basic structure of such an electrolytic cell is divided into three chambers, an anode chamber, an intermediate chamber and a cathode chamber, by disposing two cation exchange membranes between an anode and a cathode. Alternatively, a structure in which two or more intermediate chambers are provided by partitioning with a cation exchange membrane may be employed.

As the cation exchange membrane used in the electrolytic cell, a known cation exchange membrane can be used without particular limitation. For example, a cation exchange membrane having a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, or the like as an ion exchange group and a base material of, for example, a hydrocarbon-based, fluorocarbon-based, or perfluorocarbon-based resin is used. In particular, as the cation exchange membrane constituting the cathode chamber, a cation exchange membrane which is stable in a basic atmosphere and has a base made of a perfluorocarbon resin having excellent durability is preferable. Also, at least a carboxylic acid group is bonded as a cation exchange group to the side facing the cathode, and a sulfonic acid group is bonded to the remaining part. A cation exchange membrane having an anisotropic structure in which sulfonic acid groups corresponding to an exchange capacity of 2/3 or less are bonded is desirable. A cation exchange membrane having a thin cationic layer on the side of the membrane facing the anode is preferred. The cationic thin layer is not particularly limited, but is composed of a layer in which a strongly basic exchange group is bonded to a molecule constituting the ion exchange membrane by ionic bond or molecular bond, and generally has a thickness of 10 to 50,000.
Å, preferably 20 to 10000Å.

As the anode of the electrolytic cell used in the present invention, an anode that is stable in an oxidizing atmosphere is used. For example, a so-called insoluble anode in which carbon, platinum-coated titanium, Ru, Ir, or the like is coated on a titanium plate is preferably used. As the cathode, those which are stable in a strongly basic atmosphere and have a low overvoltage are selected, for example, an active cathode widely used in insoluble salt electrolysis such as SUS316, platinum and Raney nickel is used without any limitation. .

As the structure of the electrode, a known shape such as a plate shape or a net shape, a perforated plate shape such as an expanded metal, a rod shape such as a sump is used.

In the above-described electrolytic cell, the quaternary ammonium salt as a raw material is supplied to the anode chamber as an aqueous solution, and in the intermediate chamber and the cathode chamber, both sides of which are partitioned by a cation exchange membrane,
An aqueous solution of quaternary ammonium hydroxide is provided.

The concentration of the aqueous solution of the raw material quaternary ammonium salt is
In general, it is preferably 0.2 to 4.0 N from the viewpoints of electric resistance and viscosity of the aqueous solution. Further, the concentration of the aqueous solution of quaternary ammonium hydroxide supplied to the intermediate chamber and the cathode chamber partitioned by the two cation exchange membranes is 0.2 to 0.2 for the same reason.
It is preferable to select from the range of 4.5N. As the aqueous solution of quaternary ammonium hydroxide, the aqueous solution of quaternary ammonium hydroxide obtained in the cathode chamber is used as it is or after its concentration is adjusted.

The greatest feature of the present invention is that the pH of a room for supplying a quaternary ammonium salt as a raw material in the electrolytic cell, that is, the pH of the anode chamber is maintained at 8 or more. As is clear from the examples and comparative examples described later,
Is 8 or more, the voltage of the intermediate chamber partitioned by the two cation exchange membranes hardly changes even after a long operation. However, when the pH is less than 8, the voltage of the intermediate chamber increases, and this tendency becomes more significant as the pH decreases.

In the present invention, a specific method for maintaining the pH of the room for supplying the raw materials at 6 or more is not particularly limited, and any method may be used. But,
The method preferably employed in the present invention is a method in which a basic compound is added to a room for supplying raw materials. That is, as the basic compound, the same compound as that of the quaternary ammonium hydroxide, which is a product of electrolysis, or a compound such as ammonia that can be easily removed by heating can be used. preferable.

The electrolysis is performed under appropriate conditions according to the concentration of the aqueous solution of the quaternary ammonium salt as a raw material. Generally, it is preferable to carry out the process at a current density of 1 to 50 A / dm ² and a temperature in the battery case not exceeding 90 ° C.

By such electrolysis, the product, quaternary ammonium hydroxide, is generally obtained at a desired concentration in the range of 0.1 to 4.5N.

(Effects) According to the method of the present invention, when the quaternary ammonium salt is electrolyzed using an electrolytic cell having an intermediate chamber partitioned by two cation exchange membranes, Ascent can be prevented. Therefore, the present invention provides a method for continuously producing quaternary ammonium hydroxide by electrolysis stably for a long time, and its industrial value is extremely large.

(Examples) Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 Two cation exchange membranes (manufactured by DuPont, trade name: Nafion 901) are arranged from the anode side between an anode obtained by plating platinum on a titanium plate and a cathode made of SUS 316, and an effective energization comprising three chambers is provided. An electrolytic cell having an area of 0.2 dm ² was constructed. The cation exchange membrane was installed with the surface having a carboxylic acid group facing the cathode.

Using the above electrolytic cell, a 2.5N tetramethylammonium chloride aqueous solution was placed in the cathode chamber, and a 1.7N tetramethylammonium hydroxide solution (manufactured by Tama Chemical Co., Ltd.) was placed in a room (intermediate chamber) formed by two cation exchange membranes. A 15.1% solution) and a 1.5N tetramethylammonium hydroxide solution (Tama Chemical: 15.1% solution diluent) were circulated in the cathode chamber, respectively, and electrolysis was continuously performed at a current density of 15 A / dm ² for 24 hours. .

Tetramethylammonium hydroxide generated in the cathode compartment
It is prepared and obtained to 1.5N, and the pH of the aqueous solution of tetramethylammonium chloride in the anode compartment is always 2, 4,
Change the amount to be 6, 8, and 12 and add 1.5 to the anode compartment.
The specified tetramethylammonium hydroxide was added.

As a result, the chloride ion concentration in the 1.5 N aqueous solution of tetramethylammonium hydroxide obtained from the cathode chamber was always 0.1 ppm or less at any pH, and tetramethylammonium hydroxide was obtained in the cathode chamber. The resulting current efficiency was 75%. However, the voltage of the intermediate chamber partitioned by the two cation exchange membranes was 3.0 V at just pH immediately after the start of electrolysis and after 24 hours of operation when the pH was 8 or more. V. However, when the pH is 4, the voltage rises to 5.0 V after 24 hours of operation, and when the pH is 2,
After running for 24 hours, it reached 12.8V.

FIG. 1 shows the relationship between the pH of the room for supplying the raw materials and the voltage of the intermediate room partitioned by two cation exchange membranes.

Example 2 The same procedure as in Example 1 was performed except that ammonium hydroxide was not added to the anode chamber, and the electrolysis was performed. As a result, the pH of the anode chamber was 4.5, and the voltage of the room formed by the two cation exchange membranes was 12%.
After the operation for 1 hour, the voltage reached 10.5 V, and the liquid volume in the intermediate chamber decreased over time.

On the other hand, pH was adjusted to 12 by adding ammonium hydroxide to the anode chamber.
, And the voltage at the same location was 3.0 V, and a tetramethylammonium hydroxide aqueous solution could be stably obtained from the cathode chamber.

Note Cl hydroxide in tetramethylammonium also be obtained from the cathode chamber if any ^- of the concentration was lower than 0.1ppm.

Example 3 Example 3 was carried out under the same conditions as in Example 2 except that tetramethylammonium carbonate was used as a raw material and tetramethylammonium hydroxide was added to the anode chamber so that the pH of the anode chamber was always 12. .

As a result, the concentration of carbonate ions in the 1.5 N aqueous solution of tetramethylammonium hydroxide obtained from the cathode chamber was always 0.05 ppm or less. The current efficiency of obtaining tetramethylammonium hydroxide in the cathode chamber is
At that time, the voltage of the intermediate room was 3.2 V and remained unchanged.

[Brief description of the drawings]

 FIG. 1 shows the relationship between the pH of the raw material chamber and the voltage of the intermediate chamber.

Claims (1)

(57) [Claims] An anolyte compartment, an intermediate compartment and a cathodic compartment each having at least two cation exchange membranes disposed between an anode and a cathode. A saline solution is supplied, a quaternary ammonium hydroxide aqueous solution is present in the intermediate chamber, and a basic compound is added in the electrolysis to take out the quaternary ammonium hydroxide aqueous solution from the cathode chamber to adjust the pH of the anode chamber to 8 or more. A method for producing quaternary ammonium hydroxide, comprising continuously performing electrolysis while maintaining the same.