JPH0421604B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing high-purity sulfuric acid suitable for use in semiconductor manufacturing, electronic industry, etc. using purified oleum as a starting material. Conventional technology In recent years, high-purity sulfuric acid has been widely used in semiconductor manufacturing and the electronics industry, etc., but with the advancement of these electronic technologies, highly pure sulfuric acid with extremely low content of impurities and foreign substances and without coloration has been used. The demand for sulfuric acid is increasing. Previous attempts have been made to industrially produce such high-purity sulfuric acid by using fuming sulfuric acid as a starting material, extracting the sulfur trioxide (SO ₃ ) vapor that volatilizes from the fuming sulfuric acid, and absorbing it into purified sulfuric acid. However, impurities (particularly components such as O ₃ , As, and Hg) are entrained during this process, and even if some of the volatilized sulfur trioxide is refluxed (cooled and decomposed and removed), fuming sulfuric acid High-purity sulfuric acid, which is a starting material, inevitably contains a certain amount of impurities. Problems to be Solved by the Invention As a result of studying the production of high-purity sulfuric acid using fuming sulfuric acid as a starting material, the inventor found that NO ₃ , which is a particular problem with sulfuric acid used in semiconductor manufacturing and the electronic industry, etc. Since impurities such as As and Hg are contained in fuming sulfuric acid, some of them will volatilize and enter high-purity sulfuric acid when sulfur trioxide is volatilized from the fuming sulfuric acid, although there are differences depending on the volatilization temperature. become. That is, in order to reduce the impurities in high-purity sulfuric acid, it depends on how much the impurities in the starting raw material, fuming sulfuric acid, can be reduced. Therefore, by heating purified oleum with extremely low impurity content,
Knowledge that high-purity sulfuric acid with substantially minimal impurity content can be obtained by volatilizing SO ₃ , absorbing this volatile SO ₃ in high-purity sulfuric acid, and diluting it with ultrapure water. As a result, the present invention was completed. Therefore, the main object of the present invention is to use purified fuming sulfuric acid as a starting material to produce high-purity products with extremely low content of impurities and foreign substances, and without coloring, which are particularly suitable for use in semiconductor manufacturing, electronic industry, etc. The object of the present invention is to provide a method for industrially advantageously producing sulfuric acid. The present invention will be explained in detail below. Structure of the Invention The structural feature of the present invention is that the raw material gas containing sulfur trioxide at the outlet of the converter is brought into contact with oleum, guided to a purified smoke tower, absorbed into the purified fuming sulfuric acid, and then purified concentrated sulfuric acid ( The purified fuming sulfuric acid is diluted with concentrated sulfuric acid (hereinafter referred to as concentrate) to adjust the fume concentration, and the sulfur trioxide remaining in the outlet gas of the purified smoke tower is guided to a high-purity sulfuric acid absorption tower that circulates the concentrated sulfuric acid. , absorb into the concentrate, return a part of the concentrate after absorption to the purified smoke tower, dilute the purified fuming sulfuric acid as described above, and then reduce the sulfuric acid concentration in the concentrate with pure water and/or ultrapure water. The purpose is to generate, absorb and recover sulfur trioxide from purified fuming sulfuric acid. Means for Solving the Problem The free SO ₃ concentration of purified fuming sulfuric acid used as a starting material differs depending on the amount of _sulfur trioxide dissolved in it. It is convenient to use sulfuric acid with a concentration of 105.6% to 106.8%. In the present invention, it is preferable to charge the purified fuming sulfuric acid into an SO ₃ volatilization device and heat it to about 150°C to volatilize SO ₃ to the extent that the concentration of oleum is reduced by about 5% to 10%. In terms of free SO ₃ concentration, for example, fuming sulfuric acid with a free SO ₃ concentration of 25% (concentration
105.6%) as the starting material, the above concentration is
This will be done until the concentration reaches 20% (104.5% as fuming sulfuric acid concentration). Note that the purified fuming sulfuric acid after volatilizing SO ₃ can be led to a purification smoke tower or a smoke absorption tower to further improve the purification and yield of high-purity sulfuric acid. In the present invention, SO ₃ volatilized as described above is used.
is introduced into a high-purity sulfuric acid absorption tower in which high-purity concentrated sulfuric acid is circulated and absorbed. The sulfuric acid obtained by absorbing SO ₃ as described above has extremely low content of impurities such as As, Hg, and NO ₃ , so it can be said to be high-purity sulfuric acid. In the present invention, as described above, the high purity sulfuric acid obtained in this way is adjusted to the desired concentration using ultrapure water or pure water, and then an inert gas such as nitrogen or clean air gas is blown into it. remain in
The degree of purification can be further increased by removing SO ₂ . The high-purity sulfuric acid obtained as described above is packaged into a product in a clean room using containers thoroughly washed with ultrapure water. The obtained products are suitable for use in the manufacture of semiconductors that require high purity and the manufacture of various electronic devices. Effects of the Invention As described above, according to the present invention, a purified fuming tower and a concentrated absorption tower are newly installed from the raw material gas containing many impurities to obtain purified fuming sulfuric acid with increased purity in advance, and the sulfuric acid is volatilized. By evaporating SO ₃ through treatment and absorbing it into high-purity concentrated sulfuric acid, high-purity sulfuric acid with extremely low impurity content can be advantageously produced using purified oleum as a starting material. It can be said that it is useful as an industrial manufacturing method. EXAMPLES The present invention will be explained in more detail with reference to Examples below. Example 1 A description will be given below with reference to FIG. 1. Fuming absorption tower 1 (50 mmφ x 2300 mmh) 35% oleum was circulated at a rate of 0.4/min, and the converter outlet gas (7 to 8% SO ₃ ) was passed through this at a rate of 10/min. The SO ₃ concentration after passing through the smoke absorption tower 1 is 8
It was ~10%. Thereafter, after passing through the mist separator 2, it was absorbed in 30% fuming sulfuric acid in a purification smoke tower 3 (50 mmφ x 2300 mmh). This outlet gas contained 2 to 2.5% SO ₃ and was led to the concentrated absorption tower 4 to absorb the SO ₃ gas, and the concentration was adjusted to 98.5% with pure water. The produced concentrate was supplied to a refining smoke tower. The 30% fuming sulfuric acid extracted from the purified smoke tower is converted into SO ₃ volatilizer 5 (100 mm
φ×100mmh) and SO ₃ by external heater
The volatilization temperature was controlled at 150°C. The 30% fuming sulfuric acid became about 25% and overflowed from the SO ₃ volatilization device, a part of which was returned to the purification smoke tower 3, and the rest went to the smoke absorption tower. The generated SO ₃ gas was introduced into a high-purity sulfuric acid absorption tower 6 made entirely of Teflon, brought into contact with purified concentrated sulfuric acid, and absorbed. Ultrapure water was used to adjust the concentration of sulfuric acid. Of the high-purity sulfuric acid produced, 10 times the amount of purified concentrated sulfuric acid (approximately 6 kg) used initially was discarded, and then 100 kg
of high-purity sulfuric acid was produced. The analytical values of this high purity sulfuric acid are shown in A of Table 1. After that, desorption using _N2 gas passed through a dust filter.
SO ₂ treatment was performed in SO ₂ gas removal tower 7. The analytical values of this high purity sulfuric acid are shown in B of Table 1. As is clear from Table 1, it is possible to obtain high-purity sulfuric acid with a lower impurity level of 1/10 or less than that of commercially available high-purity sulfuric acid (obtained by the treatment described in JP-A-56-22608). I understand.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 shows a layout diagram of an embodiment of the present invention. In the figure, 1 is a smoke absorption tower, 2 is a mist separator, and 3
4 is a purification smoke tower, 4 is a concentrated absorption tower, 5 is an SO ₃ volatilization device, 6 is a high-purity sulfuric acid absorption tower, 7 is an SO ₂ gas removal tower, and 8 is a circulating acid pump.

Claims (1)

[Claims] 1 After contacting the raw material gas containing sulfur trioxide at the converter outlet with oleum, it is led to a purified oleum and absorbed into the purified oleum, and then purified oleum is purified with purified concentrated sulfuric acid (hereinafter referred to as concentrated sulfuric acid). After diluting and adjusting the smoke concentration, the sulfur trioxide remaining in the outlet gas of the purified smoke tower is guided to a high-purity sulfuric acid absorption tower in which concentrated concentrate is circulated, and absorbed into the concentrated concentrate. A portion of the concentrated oleum is returned to the purified oleum and the purified oleum is diluted as described above, and then the sulfuric acid concentration of the concentrated sulfuric acid is adjusted with pure water and/or ultrapure water to remove sulfur trioxide from the purified oleum. A method for producing high-purity sulfuric acid, which is characterized by generation, absorption and recovery.