JP4854323B2 - Manufacturing method of high purity sulfuric acid - Google Patents

Description

The present invention relates to a method for producing high-purity sulfuric acid, for example, a method for producing high-purity sulfuric acid from which sulfurous acid gas (SO ₂ sulfur dioxide) which is an impurity is highly removed.

  Sulfuric acid is used as a cleaning solution for silicon wafers used in semiconductor factories. When sulfurous acid gas is present as an impurity in sulfuric acid used for this purpose, there arises a problem that the electrical characteristics of the silicon wafer are deteriorated. Therefore, the sulfuric acid used for such applications is required to have a low sulfurous acid gas concentration. As a method for producing high-purity sulfuric acid having a low impurity concentration, for example, a method disclosed in JP-A-8-337406 (Patent Document 1) can be mentioned. The above-mentioned patent document discloses a method for producing high-purity sulfuric acid from gaseous sulfuric anhydride containing sulfurous acid gas as an impurity and water, which includes an absorption step, a transport step, and a stripping step. . Specifically, crude sulfuric acid is obtained by absorbing anhydrous sulfuric acid in water in the absorption step. In the transporting process, the obtained crude sulfuric acid is transported to the stripping tower. In the stripping step, the crude sulfuric acid in the crude sulfuric acid is separated and removed from the sulfuric acid by stripping the crude sulfuric acid with air by stripping in the stripping tower. For example, as shown in FIG. 5, in the stripping tower 300, crude sulfuric acid 301 is supplied from the upper part, air 302 is supplied from the lower part, and the sulfurous acid gas 303 is separated and removed by bringing them into contact with each other, thereby producing high-purity sulfuric acid 304. Manufacture. According to the method for producing high-purity sulfuric acid disclosed in Patent Document 1, the concentration of sulfurous acid gas in the crude sulfuric acid can be reduced to 1 ppm by weight or less. FIG. 5 is a schematic diagram showing a conventional stripping tower.

However, in the method for producing high-purity sulfuric acid of Patent Document 1, only the liquid temperature of the crude sulfuric acid supplied to the stripping tower is disclosed, and the amount of air used and the contact time of the gas-liquid are disclosed. Not. Since sulfuric acid generally has a high viscosity, the sulfurous acid gas component dissolved in sulfuric acid is difficult to diffuse, which causes a problem that the liquid-side mass transfer rate is lowered. Therefore, in order to obtain the expected diffusion effect, there is a problem that the height of the stripping tower is higher than the height of a general apparatus, the gas-liquid contact area is increased, and a large amount of air must be used. is there. In addition, when a large amount of air is used, there is a problem that impurities are mixed from the air into the high purity sulfuric acid and the quality of the high purity sulfuric acid is deteriorated.
JP-A-8-337406

  Therefore, the present invention has been made to solve the above-described problems, and an object of the present invention is to reduce the amount of air necessary for removing sulfurous acid gas and to form sulfurous acid gas in sulfuric acid. It is to provide a method for producing high-purity sulfuric acid, in which high-quality, high-purity sulfuric acid is produced by efficiently removing the catalyst.

  The method for producing high-purity sulfuric acid according to the present invention is a stripping tower having a liquid reservoir at the lower part, in which a crude sulfuric acid containing sulfurous acid gas and a gas inert to sulfuric acid are brought into countercurrent contact with each other to produce sulfur dioxide gas from the crude sulfuric acid Is a method for producing high-purity sulfuric acid by removing crude sulfuric acid, a crude sulfuric acid supply step for supplying crude sulfuric acid from the upper part of the stripping tower, a gas is supplied to the liquid reservoir, and the crude sulfuric acid and gas are supplied to the liquid reservoir. And a gas supply process for countercurrent contact.

  According to the method for producing high-purity sulfuric acid of the present invention, crude sulfuric acid and gas can be efficiently and directly contacted in the liquid reservoir. Therefore, the amount of air required for removing sulfurous acid gas can be reduced, and sulfurous acid gas in sulfuric acid can be efficiently removed to produce high-quality high-purity sulfuric acid.

  Preferably, in the method for producing high-purity sulfuric acid, the flow rate (kg / h) of crude sulfuric acid (L) supplied in the crude sulfuric acid supply step and the flow rate (kg / h) of gas (G) supplied in the gas supply step The gas-liquid ratio (L / G) is 10 to 50 kg / kg, the residence time of the crude sulfuric acid in the liquid reservoir is 1 to 20 minutes, and the temperature of the crude sulfuric acid in the liquid reservoir is 10 to 130 ° C. It is characterized by being.

  By setting the gas-liquid ratio (L / G), the retention time of the crude sulfuric acid, and the temperature of the crude sulfuric acid within the above ranges, the crude sulfuric acid containing sulfurous acid gas is retained in the liquid reservoir, so that it does not react with sulfuric acid. When active gas is dispersed, sulfurous acid gas can be efficiently removed. Therefore, the amount of gas that is inert to sulfuric acid can be reduced, and high-quality high-purity sulfuric acid can be produced.

  Preferably, in the method for producing high-purity sulfuric acid, the gas supply step is performed with a sparger including a spout composed of a small hole group having a diameter of 5 mm or less.

  Thereby, the contact area between the crude sulfuric acid and the gas can be increased, and the mass transfer capacity coefficient can be increased. Therefore, the sulfurous acid gas in the crude sulfuric acid can be removed more efficiently.

  Preferably, in the above-described method for producing high-purity sulfuric acid, the sparger spouts gas from the outlet toward the tower bottom of the diffusion tower, and the height from the tower bottom of the outlet is higher than the tower bottom of the liquid reservoir. The sparger is arranged to be 30% or less of the length. Preferably, in the method for producing high-purity sulfuric acid, the sparger spouts gas from the outlet toward the bottom of the stripping tower, and the height from the bottom of the outlet is 30 mm or more from the bottom. The sparger is arranged in

  Since the sparger is arranged so that the height of the jet outlet from the tower bottom is 30% or less of the height of the liquid reservoir from the tower bottom, the gas jetted from the jet outlet and the liquid reservoir It is possible to sufficiently contact the crude sulfuric acid retained in the part. By disposing the sparger so that the height of the jet outlet from the tower bottom is 30 mm or more from the tower bottom, it is possible to prevent destruction of gas bubbles effective for gas-liquid contact. Therefore, the sulfurous acid gas in the crude sulfuric acid can be removed more efficiently.

  Preferably, in the method for producing high-purity sulfuric acid, the liquid reservoir has a nozzle on a wall surface at a relatively high position, and further includes a step of discharging the high-purity sulfuric acid from the nozzle.

  Thereby, high purity sulfuric acid can be discharged from the nozzle by overflow means. Therefore, high purity sulfuric acid can be discharged without entraining bubbles. Therefore, high quality high purity sulfuric acid can be produced.

  Thus, according to the method for producing high-purity sulfuric acid of the present invention, the sulfur-sulfur gas can be removed by specifying the gas-liquid ratio (L / G), the residence time of the crude sulfuric acid, and the temperature of the crude sulfuric acid. The required amount of air used can be reduced, and sulfurous acid gas in the crude sulfuric acid can be efficiently removed to produce high-quality high-purity sulfuric acid.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a flowchart showing a method for producing high-purity sulfuric acid in an embodiment of the present invention. FIG. 2 is a diagram for explaining a method for producing high-purity sulfuric acid in the embodiment of the present invention. With reference to FIG. 1 and FIG. 2, the manufacturing method of the high purity sulfuric acid in embodiment of this invention is demonstrated.

  As shown in FIG. 1 and FIG. 2, the high purity sulfuric acid production method in the embodiment is inert with respect to crude sulfuric acid 203 containing sulfurous acid gas and sulfuric acid in a stripping tower 110 having a liquid reservoir 111 at the bottom. This is a method for producing high-purity sulfuric acid 206 by removing the sulfurous acid gas 205 from the crude sulfuric acid 203 by countercurrent contact with a gas 204, comprising a crude sulfuric acid supply step (S21) and a gas supply step (S22). ing. In the crude sulfuric acid supply step (S21), the crude sulfuric acid 203 is supplied from the upper part of the stripping tower 110. In the gas supply step (S 22), the gas 204 is supplied to the liquid reservoir 111, and the crude sulfuric acid 203 and the gas 204 are brought into countercurrent contact with the liquid reservoir 111. The flow rate (kg / h) of the crude sulfuric acid (L) 203 supplied in the crude sulfuric acid supply step (S21) and the flow rate (kg / h) of the gas (G) 204 supplied in the gas supply step (S22). The liquid ratio (L / G) is 10 to 50 kg / kg. The residence time of the crude sulfuric acid 203 in the liquid reservoir 111 is 1 to 20 minutes. The temperature of the crude sulfuric acid 203 in the liquid reservoir 111 is 10 to 130 ° C.

In the embodiment, as shown in FIG. 1, first, an absorption step (S10) for obtaining crude sulfuric acid containing sulfurous acid gas as an impurity is performed. In the absorption step (S10), crude sulfuric acid is obtained by absorbing water and / or dilute sulfuric acid in anhydrous sulfuric acid (SO ₃ ).

  Specifically, as shown in FIG. 2, for example, gaseous sulfuric anhydride 202 is supplied from the lower part of the absorption tower 101, and water and / or dilute sulfuric acid 201 is supplied from the upper part. And both are made to contact in the absorption tower 101, and the crude sulfuric acid 203 containing a sulfurous acid gas is obtained.

  As the raw material, anhydrous sulfuric acid 202, which is usually produced in a factory, can be used as it is through a pipe, and usually contains about 10 to 100 ppm by weight of sulfurous acid gas. Therefore, the crude sulfuric acid 203 obtained in the absorption step (S10) contains several ppm of sulfurous acid gas derived from anhydrous sulfuric acid 202.

  In addition, as the water 201 supplied in the absorption step (S10), for example, so-called ultrapure water is preferably used from the viewpoint that impurities are not mixed.

  As the absorption tower 101, a normal one such as a packed tower can be used, and the absorption tower 101 is generally filled with a packing such as Raschig ring.

  In addition, in the absorption tower 101, inactive gas with respect to a sulfuric acid can also be supplied from the lower part in order to remove sulfurous acid gas.

  Next, a step (S20) of removing sulfurous acid gas from the crude sulfuric acid is performed. In the step (S20), as shown in FIG. 2, in the stripping tower 110 having a liquid reservoir 111 at the bottom, the crude sulfuric acid 203 containing sulfurous acid gas and the gas 204 inert to sulfuric acid are brought into countercurrent contact. Thus, the sulfurous acid gas 205 is removed from the crude sulfuric acid 203 to produce high-purity sulfuric acid 206. Examples of the gas inert to sulfuric acid include air and inert gases such as nitrogen and argon, and air is preferably used from the viewpoint of low cost.

  The stripping tower 110 is preferably filled with a packing material at the top. Existing materials such as Raschig rings, pole rings, and saddles can be used as the filler. Further, the material of the packing and the wall surface of the diffusion tower 110 is not particularly limited as long as it has corrosion resistance to sulfuric acid, and for example, fluororesin, ceramic, glass, and the like can be applied. From the viewpoint of minimizing the elution of impurities, a fluororesin is preferably used. The required filling height is preferably about 3 to 10 in terms of the number of theoretical plates.

  The stripping tower 110 is provided with a liquid reservoir 111 at the bottom. The liquid reservoir 111 preferably has a nozzle 114 on a relatively high wall surface. Further, a partition plate 113 is provided in the vicinity of the nozzle 114 where the sparger 112 is not disposed. The partition plate 113 is divided into a region where the sparger 112 exists and a region where the sparger does not exist. In the embodiment, the partition plate 113 and the nozzle 114 are provided at two locations.

  In the step (S20), first, a crude sulfuric acid supply step (S21) for supplying the crude sulfuric acid 203 from the upper part of the stripping tower 110 is performed.

  Specifically, in the crude sulfuric acid supply step (S21), as shown in FIG. 2, the crude sulfuric acid 203 obtained in the absorption step (S10) is supplied from the upper part of the stripping tower 110. At this time, it is preferable to supply the crude sulfuric acid 203 from the top of the stripping tower 110. Moreover, the supply flow rate of the crude sulfuric acid 203 can be, for example, 10 to 10,000 kg / h. Further, the temperature of the crude sulfuric acid 203 supplied to the stripping tower 110 is preferably 60 to 130 ° C, more preferably 80 to 120 ° C. By setting the temperature to 60 ° C. or higher, the effect of dissipation becomes more sufficient, and by setting the temperature to 80 ° C. or higher, the effect of dissipation becomes even more sufficient. By setting the temperature to 120 ° C. or less, the means for increasing the temperature of the crude sulfuric acid 203 obtained in the absorption tower 101 does not require a very large capacity, so that the economy is not deteriorated.

  A liquid reservoir 111 is provided at the bottom of the stripping tower 110. After the crude sulfuric acid 203 supplied from the upper part of the stripping tower 110 flows down the packed part, it flows into the liquid storage part 111 and stays there.

  Next, a gas supply step (S22) is performed in which the gas 204 is supplied to the liquid reservoir 111, and the crude sulfuric acid 203 and the gas 204 are brought into countercurrent contact with each other in the liquid reservoir 111. In the gas supply step (S22), the gas 204 is introduced into the liquid reservoir 111, brought into gas-liquid contact, and bubbled and dispersed in the crude sulfuric acid 203. Thereby, the sulfurous acid gas 205 in the crude sulfuric acid 203 is removed. Moreover, the supply flow rate of the gas 204 can be set to 0.2 to 1000 kg / h, for example.

  The flow rate (kg / h) of the crude sulfuric acid (L) 203 supplied in the crude sulfuric acid supply step (S21) and the flow rate (kg / h) of the gas (G) 204 supplied in the gas supply step (S22). The liquid ratio (L / G) is 10 to 50 kg / kg, preferably 10 to 40 kg / kg. This is because if the gas-liquid ratio (L / G) is smaller than 10 kg / kg, the amount of inert gas to be used is large and uneconomical, and the amount of impurities brought in increases. By setting it to 10 kg / kg or more, high-purity sulfuric acid having sufficient purity can be obtained economically. On the other hand, when the gas-liquid ratio (L / G) is larger than 50 kg / kg, the gas-liquid contact cannot be performed sufficiently. By setting it to 50 kg / kg or less, bubbling in the liquid reservoir 111 can be performed efficiently.

  The residence time of the crude sulfuric acid 203 in the liquid reservoir 111 is 1 to 20 minutes, preferably 3 to 15 minutes, and more preferably 5 to 15 minutes. This is because if the residence time is shorter than 1 minute, the sulfurous acid gas 205 cannot be sufficiently removed from the crude sulfuric acid 203 retained in the liquid reservoir 111. By setting the residence time to 3 minutes or longer, the sulfurous acid gas 205 can be more sufficiently removed from the crude sulfuric acid 203. By setting the residence time to 5 minutes or longer, the sulfurous acid gas 205 can be more sufficiently removed from the crude sulfuric acid 203. On the other hand, if the residence time is longer than 20 minutes, the gas 204 supplied to the liquid reservoir 111 may not reach the entire liquid reservoir 111, and the production cost of the liquid reservoir 111 is increased. This is because it increases very much and becomes uneconomical. This is because by setting the residence time to 15 minutes or less, the gas 204 reaches the entire liquid reservoir 111 and is economically satisfactory.

  The temperature of the crude sulfuric acid 203 in the liquid reservoir 111 is 10 to 130 ° C, preferably 60 to 120 ° C. This is because if the temperature is lower than 10 ° C., the sulfurous acid gas 205 cannot be sufficiently removed from the crude sulfuric acid 203. On the other hand, when the temperature is higher than 60 ° C., the sulfurous acid gas 205 can be sufficiently removed from the crude sulfuric acid 203. This is because if the temperature is higher than 130 ° C., the material of the stripping tower 110 may be unbearable. By setting the temperature to 110 ° C. or lower, the problem on the material can be avoided.

  The method for dispersing the gas 204 into the crude sulfuric acid 203 is not particularly limited, and the gas 204 may be supplied using a single nozzle. From the viewpoint of increasing the mass transfer capacity coefficient by increasing the gas-liquid contact area. The sparger (perforated nozzle) 112 preferably includes a spout 112a composed of a group of small holes. The differential pressure at the sparger 112 is adjusted within an allowable range.

  The small holes of the sparger 112 are preferably 5 mm or less in diameter, and more preferably 3 mm or less in diameter. By setting it to 5 mm or less, each bubble of the gas 204 becomes smaller and the contact area of the gas and liquid is further increased, and by setting it to 3 mm or less, the contact area of the gas and liquid is further increased.

  The sparger 112 preferably ejects the gas 204 from the ejection port 112 a toward the bottom of the diffusion tower 110. In this case, the sparger 112 is arranged so that the height h of the jet port 112a from the tower bottom is 30% or less of the height H of the liquid reservoir 111 from the tower bottom. The height h of the spout 112a is preferably arranged to be 25% or less, more preferably 20% or less of the height H of the liquid reservoir 111. By setting the height h to 30% or less of the height H, the gas 204 can sufficiently come into contact with the crude sulfuric acid 203 in the liquid reservoir 111. By setting the height h to 25% or less of the height H, the gas-liquid contact becomes more sufficient, and by setting the height h to 20%, the gas-liquid contact becomes more sufficient. The height H from the bottom of the liquid reservoir 111 means the stationary height when the crude sulfuric acid 203 stays in the liquid reservoir 111. The height H in the embodiment corresponds to the height from the column bottom of the nozzle 114 because high purity sulfuric acid is discharged by the overflow means in the discharge step (S30) described later.

  Moreover, it is preferable that the sparger 112 is disposed so that the height h from the tower bottom of the spout 112a is 30 mm or more from the tower bottom. By setting the height h to 30 mm or more, it is possible to prevent the gas 204 from hitting the bottom of the stripping tower 110 and destroy the bubbles effective for gas-liquid contact, and to remove more sulfurous acid gas 205. In addition, when a nozzle for discharging high-purity sulfuric acid is arranged at the bottom of the stripping tower 110, it is possible to prevent the gas 204 from being mixed into the high-purity sulfuric acid extracted from the bottom of the tower. Can be further enhanced.

  The shape of the sparger 112 is not particularly limited to the above, but it is preferable to arrange the sparger 112 in the widest possible range of the horizontal section of the liquid reservoir 111, for example, in order to eliminate the non-contact portion of the gas and liquid as much as possible. . For example, a sparger having a small hole in a pipe formed in a cross shape, a U-shape, a ring shape, or a double ring shape can be preferably applied.

  Next, a discharging step (S30) for discharging the high purity sulfuric acid 206 from the nozzle 114 is performed. In the discharging step (S30), the high-purity sulfuric acid 206 from which the sulfurous acid gas 205 has been removed from the crude sulfuric acid 203 is discharged from the nozzle 114 and transported to the tank 120. In this case, the high-purity sulfuric acid 206 in the region where the sparger 112 separated by the partition plate 113 does not exist is overflowed from the nozzle 114 and discharged to the tank 120.

  In the discharge step (S30), the high-purity sulfuric acid 206 is not particularly limited as long as the high-purity sulfuric acid 206 can be discharged from the diffusion tower 110 to the tank 120. For example, the high-purity sulfuric acid 206 can be discharged by a pump, but it is preferable that the high-purity sulfuric acid 206 is discharged from the nozzle 114 by overflowing. This is because it is not necessary to increase unnecessary devices by adopting the overflow means. Further, when the high purity sulfuric acid 206 is discharged from the nozzle 114, it is preferable that the nozzle 114 is installed on the wall surface of the liquid reservoir 111 and a cover is installed so that bubbles are not mixed.

  By performing the above steps (S10, S20, S30), the sulfurous acid gas 205 can be removed from the crude sulfuric acid 203 to produce high-purity sulfuric acid. The high-purity sulfuric acid obtained by the method for producing high-purity sulfuric acid in the embodiment of the present invention can contain a sulfurous acid gas concentration of 1 ppm by weight or less. Therefore, it can be optimally used as a cleaning solution for silicon wafers used in semiconductor factories.

  As a means for transporting the crude sulfuric acid 203 from the absorption tower 101 to the stripping tower 110, for example, a circulation pump 130 may be used as shown in FIG. When the crude sulfuric acid 203 is transported by the circulation pump 130, for example, the temperature of the crude sulfuric acid 203 at the inlet of the circulation pump 130 is preferably 0 to 30 ° C, and more preferably 20 to 30 ° C. By setting the temperature of the crude sulfuric acid 203 at the inlet of the circulation pump 130 to 0 ° C. or higher, the viscosity does not increase and the transportation efficiency does not decrease. On the other hand, by setting the temperature of the crude sulfuric acid 203 at the inlet of the circulation pump 130 to 30 ° C. or less, it is possible to prevent the metal components constituting the circulation pump 130 from being dissolved into the crude sulfuric acid 203. As a method for controlling the temperature in this way, for example, the cooler 131 can be installed at the inlet of the circulation pump 130. In addition, FIG. 3 is another figure explaining the manufacturing method of the high purity sulfuric acid in embodiment of this invention.

  Further, in order to set the temperature of the crude sulfuric acid 203 supplied in the crude sulfuric acid supply step (S21) to the temperature described above, for example, a method of heating the crude sulfuric acid 203 with a heater such as steam or an electric heater, FIG. As shown in FIG. 4, there is a method of exchanging heat between the crude sulfuric acid 203 at the outlet of the absorption tower 101 and the crude sulfuric acid 203 at the outlet of the circulation pump 130 by the heat exchanger 132. From the viewpoint of cost reduction, it is preferable to adopt a method in which heat is exchanged by the heat exchanger 132. In addition, FIG. 4 is another figure explaining the manufacturing method of the high purity sulfuric acid in embodiment of this invention.

  As described above, according to the method for producing high-purity sulfuric acid in the embodiment of the present invention, the crude sulfuric acid 203 is supplied from the upper part of the stripping tower 110 with the crude sulfuric acid 203 (S21), and the gas 204 is stored in the liquid reservoir. And a gas supply step (22) in which the crude sulfuric acid 203 and the gas 204 are counter-contacted in the reservoir 111. Therefore, the sulfurous acid gas 205 can be efficiently removed from the crude sulfuric acid 203 with a smaller amount of gas 204. Moreover, the high-purity sulfuric acid 206 obtained has a low sulfurous acid gas concentration and is of high quality.

[Example]
In this example, the effect of the method for producing high-purity sulfuric acid of the present invention was examined. First, high purity sulfuric acid of each of Example 1 and Comparative Example 1 was produced by the following method.

(Method for producing high-purity sulfuric acid in Example 1)
In Example 1, high-purity sulfuric acid was basically manufactured according to the method for manufacturing high-purity sulfuric acid in the embodiment. Specifically, in the absorption step (S10), anhydrous sulfuric acid was absorbed into ultrapure water to obtain crude sulfuric acid containing 8 ppm by weight of sulfurous acid gas. The concentration of crude sulfuric acid was 96% by weight. Next, in the crude sulfuric acid supply step (S21), crude sulfuric acid heated to about 70 ° C. was supplied from the top of the stripping tower at 1055 kg / h. The upper part of the stripping tower has a tower diameter of 250 mm and was filled with a nominal 1 inch PTFE Raschig ring at a height of 4050 mm. Under the packed bed, a liquid reservoir having a tower diameter of 500 mm and a height of 800 mm was provided. The sparger was arranged so as to correspond to a position 120 mm from the bottom of the stripping tower, that is, a position 15% of the height of the liquid reservoir. As the sparger, a sparger having a small hole having an inner diameter of 3 mm and a spout formed of a group of 100 small holes was used. In order to supply gas to the sparger, one nozzle with an inner diameter of about 40 mm is installed at the approximate center of the bottom of the stripping tower, and air is supplied as a gas to be supplied to the sparger at a flow rate of 40 Nm ³ / h. did. On the wall surface, a nozzle having an inner diameter of about 40 mm was provided at a height of 500 mm from the bottom of the stripping tower. The cover was installed so that air might not be caught in the nozzle. The high purity sulfuric acid in Example 1 was obtained by making it overflow from this nozzle.

  In the method for producing high-purity sulfuric acid in Example 1, the gas-liquid ratio (L / G) between the flow rate of the crude sulfuric acid supplied in the crude sulfuric acid supply step (S21) and the flow rate of the gas supplied in the gas supply step (S22). ) Was 21.9 kg / kg, the residence time of the crude sulfuric acid in the liquid reservoir was about 10 minutes, and the temperature of the crude sulfuric acid in the liquid reservoir was 65 ° C.

(Method for producing high-purity sulfuric acid in Comparative Example 1)
Comparative Example 1 is basically the same as Example 1, except that Comparative Example 1 is different only in that no liquid reservoir is provided in the stripping tower. That is, a packed tower having a tower diameter of 250 mm and packed with a nominal 1 inch PTFE-made lahiscil ring at a height of 4050 m was used. 844 kg / h of 96 wt% sulfuric acid containing 5 ppm by weight of sulfurous acid gas was supplied from the top of the column, and dry air of 80 Nm ³ / h was supplied from the bottom.

  In the method for producing high-purity sulfuric acid in Comparative Example 1, the gas-liquid ratio (L / G) between the flow rate of the crude sulfuric acid supplied in the crude sulfuric acid supply step and the flow rate of the gas supplied in the gas supply step is 8.9 kg / kg, and the temperature of the crude sulfuric acid in the liquid reservoir was 72 ° C. In Comparative Example 1, more than twice the amount of air used in Example 1 was used.

(Evaluation methods)
About the obtained high purity sulfuric acid, the sulfurous acid gas concentration and the removal rate of sulfurous acid gas were measured, respectively. As a measuring method, a redox titration method using potassium permanganate was used. The concentration of the sulfurous acid gas remaining in the high purity sulfuric acid was set to 1 ppm by weight or less.

(Evaluation results)
The concentration of sulfurous acid gas in the high-purity sulfuric acid in Example 1 was 0.6 ppm by weight, which was significantly below the target value while reducing the amount of gas used. The removal rate of sulfurous acid gas was as high as 92%. On the other hand, the concentration of sulfurous acid gas in the high-purity sulfuric acid in Comparative Example 1 was 1.3 ppm, which was higher than the target value, despite using more than twice the amount of air used in Example 1. . Further, the removal rate of sulfurous acid gas was 74%, which was lower than that of Example 1.

  As described above, according to the embodiment, by providing the crude sulfuric acid supply step (S21) and the gas supply step (S22), the amount of air used for removing sulfurous acid gas can be reduced. It was found that high-quality high-purity sulfuric acid can be produced by efficiently removing the sulfurous acid gas.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

  The high-purity sulfuric acid produced by the method for producing high-purity sulfuric acid of the present invention can be contained in a sulfurous acid gas concentration of 1 ppm by weight or less, so that it is optimally used as a cleaning solution for silicon wafers used in semiconductor factories. be able to.

It is a flowchart which shows the manufacturing method of the high purity sulfuric acid in embodiment of this invention. It is a figure explaining the manufacturing method of the high purity sulfuric acid in embodiment of this invention. It is another figure explaining the manufacturing method of the high purity sulfuric acid in embodiment of this invention. It is another figure explaining the manufacturing method of the high purity sulfuric acid in embodiment of this invention. It is a schematic diagram which shows the conventional stripping tower.

Explanation of symbols

  101 absorption tower, 110 diffusion tower, 111 liquid reservoir, 112 sparger, 112a spout, 113 partition plate, 114 nozzle, 120 tank, 130 circulation pump, 131 cooler, 132 heat exchanger, 201 water and / or dilute Sulfuric acid, 202 sulfuric anhydride, 203 crude sulfuric acid, 204 gas, 205 sulfurous acid gas, 206 high purity sulfuric acid, H, h height.

Claims (6)

In a stripping tower having a liquid reservoir at the bottom, the sulfurous acid gas concentration is reduced by removing the sulfurous acid gas from the crude sulfuric acid by bringing the crude sulfuric acid containing sulfurous acid gas into contact with a gas inert to sulfuric acid in countercurrent contact. A method for producing high-purity sulfuric acid of 1 ppm by weight or less ,
A crude sulfuric acid supply step of supplying the crude sulfuric acid from an upper portion of the stripping tower;
A gas supply step of supplying the gas to the liquid reservoir and bringing the crude sulfuric acid and the gas into countercurrent contact with each other in the liquid reservoir ;
A method for producing high-purity sulfuric acid, wherein the residence time of the crude sulfuric acid in the liquid reservoir is 1 to 20 minutes . A gas-liquid ratio (L) between the flow rate (kg / h) of the crude sulfuric acid (L) supplied in the crude sulfuric acid supply step and the flow rate (kg / h) of the gas (G) supplied in the gas supply step. / G) is 10-50 kg / kg , The temperature of the said crude sulfuric acid in the said liquid reservoir part is 10-130 degreeC, The manufacturing method of the high purity sulfuric acid of Claim 1 characterized by the above-mentioned.   The method for producing high-purity sulfuric acid according to claim 1 or 2, wherein the gas supply step is performed by a sparger including a spout composed of a small hole group having a diameter of 5 mm or less. The sparger spouts the gas from the spout toward the bottom of the stripping tower,
The sparger is arranged such that the height of the jet outlet from the tower bottom is 30% or less of the height of the liquid reservoir from the tower bottom. A method for producing high-purity sulfuric acid as described in 1. The sparger spouts the gas from the spout toward the bottom of the stripping tower,
The method for producing high-purity sulfuric acid according to claim 3, wherein the sparger is arranged such that a height of the jet outlet from the tower bottom is 30 mm or more from the tower bottom. The liquid reservoir has a nozzle on a relatively high wall surface;
A discharge step of discharging high-purity sulfuric acid from the nozzle ,
The method for producing high-purity sulfuric acid according to any one of claims 1 to 5, wherein the relatively high position is a position where the high-purity sulfuric acid can be discharged from the nozzle by overflow means .

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