JP2006193347A - Method and apparatus for producing high purity alkali carbonate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for producing a high purity alkali carbonate, by which the alkali carbonate containing extremely low content of metal impurities can be obtained. <P>SOLUTION: Carbon dioxide gas containing high content of metal impurities is dissolved in any of an acidic solution, a neutral solution, or an aqueous solution of an alkali hydrogen carbonate, and carbon dioxide gas which is generated from the solution and contains low content of metal impurities is obtained. Further, sodium carbonate, containing low content of metal impurities, is obtained by dissolving the obtained carbon dioxide gas into a high concentration alkali hydroxide aqueous solution, e.g. a sodium hydroxide aqueous solution. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a high-purity alkali carbonate having a low metal impurity concentration and a production apparatus therefor.

  Conventionally, alkali carbonates such as sodium carbonate (Na2CO3) and potassium carbonate (K2CO3) are produced by the Leblanc soda method, the ammonia soda method and the electrolytic method. However, sodium carbonate produced by the above method has a high metal impurity concentration. By the way, in the field of semiconductor manufacturing, sodium carbonate or potassium carbonate has come to be used as a raw material for a chemical solution for cleaning a silicon wafer. However, if metal impurities adhere to the wafer, the characteristics of the semiconductor device are adversely affected. Alkali carbonate produced by the above method cannot be used.

  Therefore, in order to obtain a higher-purity alkali carbonate such as sodium carbonate, carbon dioxide gas (carbon dioxide (CO2)) is dissolved in a high-purity sodium hydroxide (NaOH) aqueous solution, for example, as shown in the following formula (1). In order to obtain high-purity sodium carbonate by the reaction of the following formula (1), the carbon dioxide gas usually used in the reaction is a trace amount, but contains metal impurities in the particle state. In order to remove this, for example, a filter or the like is used.

2NaOH + CO2 → Na2CO3 + H2O (1)
However, if the particle size of the metal impurities contained in the carbon dioxide gas is smaller than the mesh of the filter, it passes through the filter, so that the technique using the filter has a limit in removal capability.

  In recent years, since the line width of semiconductor device patterns has become finer, the permissible value of metal impurities in a chemical solution has been lowered, and an alkali carbonate having a lower metal impurity concentration is required.

  On the other hand, for example, Patent Document 1 describes a method for producing high-purity carbon dioxide in which unreacted methane uses a small amount of methane as a raw material, but does not focus on reducing the metal impurity concentration.

Japanese Patent Application No. 11-85272 (Claim 1, paragraphs 0002-0004)

  This invention is made | formed in view of this situation, The objective of this invention is the manufacturing method of the high purity alkali carbonate which can obtain the highly pure alkali carbonate, for example, sodium carbonate or potassium carbonate, with a very low metal impurity density | concentration. And an apparatus for manufacturing the same.

In the method for producing a high purity alkali carbonate of the present invention, carbon dioxide gas containing metal impurities is dissolved in any one of an acidic liquid, a neutral liquid, and an aqueous solution of alkali hydrogen carbonate, and the metal impurities are captured in the liquid. Collecting carbon dioxide gas having a lower metal impurity concentration than the carbon dioxide gas by being collected,
And a step of dissolving the carbon dioxide gas obtained in this step in an aqueous alkali hydroxide solution to obtain a high purity alkali carbonate. “Dissolve carbon dioxide in any one of an acidic liquid, a neutral liquid and an aqueous alkali hydrogen carbonate solution” means any one of an acidic liquid, a neutral liquid and an aqueous alkali hydrogen carbonate solution It is not limited to be dissolved in the solution, and when passing through any two of the liquids sequentially, it also includes the case of passing each of the three liquids in order. Examples of the acidic liquid include strong acids such as sulfuric acid and nitric acid, but sulfuric acid is particularly preferable because it has low volatility and does not accompany the vapor of the solution with carbon dioxide. The neutral liquid includes pure water, but may be an alkali salt such as sodium salt or potassium salt. In short, it is preferable that the above-mentioned liquid for collecting the metal component is one in which carbon dioxide gas is not absorbed or hardly absorbed, and the metal component is not contained in the vapor. If it is pure water, since the steam is water, it does not become an impurity in the alkali carbonate, but even if it is a solution containing components that become impurities in the alkali carbonate, it must be less volatile. From this point, sulfuric acid is preferable.

Another method for producing the high-purity alkali carbonate of the present invention is to dissolve a carbon dioxide gas containing a metal impurity in an acidic liquid or a neutral liquid and collect the metal impurity in the liquid so that the carbon dioxide gas is collected. Obtaining carbon dioxide gas having a low metal impurity concentration;
Dissolving carbon dioxide purified in this step in an aqueous solution of alkali hydrogen carbonate, and collecting metal impurities in this solution to obtain carbon dioxide having a lower metal impurity concentration than the carbon dioxide;
And a step of dissolving the carbon dioxide gas obtained in this step in an aqueous alkali hydroxide solution to obtain a high purity alkali carbonate.

Moreover, the high purity alkali carbonate production apparatus of the present invention comprises a refining tank for storing any one of an acidic liquid, a neutral liquid and an aqueous alkali hydrogen carbonate solution,
Carbon dioxide supply means for supplying carbon dioxide containing metal impurities into the liquid in the refining tank,
A reaction tank for storing an alkali hydroxide aqueous solution;
A venting means provided to communicate the refining tank and the reaction tank, and for supplying carbon dioxide gas generated from the liquid in the refining tank to the liquid in the reaction tank to generate alkali carbonate; It is characterized by that.

Moreover, the other production apparatus of the high-purity alkali carbonate of the present invention includes a first refining tank for storing an acidic liquid or a neutral liquid,
Carbon dioxide supply means for supplying carbon dioxide containing metal impurities into the liquid of the first refining tank,
A second refining tank for storing an aqueous solution of alkali hydrogen carbonate;
A first refining tank is provided to communicate with the first refining tank, and a carbon dioxide gas generated from the liquid in the first refining tank is supplied to the liquid in the second refining tank. A ventilation means;
A reaction tank for storing an alkali hydroxide aqueous solution;
The second refining tank is provided so as to communicate with the reaction tank, and a second gas for generating an alkali carbonate by supplying carbon dioxide gas generated from the liquid in the second refining tank into the liquid in the reaction tank. And a ventilation means.

  According to the present invention, a metal contained in carbon dioxide is obtained by dissolving carbon dioxide (carbon dioxide) containing metal impurities in any one of an acidic liquid, a neutral liquid, and an aqueous alkali hydrogen carbonate solution. Impurities can be removed. When an acidic liquid or a neutral liquid is used, metal impurities in the carbon dioxide gas are transferred to the liquid, and as a result, metal impurities in the carbon dioxide gas are reduced. When a strong acid such as sulfuric acid or nitric acid is used as the acidic solution, the metal impurities become metal ions and dissolve in the acid. When alkali hydrogen carbonate is used, metal impurities are trapped as ions or hydroxides. By reacting the carbon dioxide gas purified in this way with alkali hydroxide, it is possible to obtain a high purity alkali carbonate having a very low metal impurity concentration, such as sodium carbonate or potassium carbonate.

  Further, by dissolving carbon dioxide containing metal impurities in an acidic liquid or neutral liquid, and further dissolving the carbon dioxide gas in an aqueous solution of alkali hydrogen carbonate, so to speak, two-stage refining treatment is carried out to further increase the metal impurities. A low concentration carbon dioxide gas can be obtained. Therefore, according to the present invention, the alkali carbonate can be suitably used as a raw material such as a cleaning liquid for silicon wafers, which is severe to metal contamination.

  Embodiments of the present invention will be described. FIG. 1 is a schematic configuration diagram showing an embodiment of an alkali carbonate production apparatus for carrying out the method of the present invention.

  In the figure, reference numeral 1 denotes a purification tank for purifying sodium carbonate, which is an alkali carbonate, and a predetermined amount of acidic solution is stored in the purification tank 1. A gas supply pipe 10 is inserted in the upper part of the refining tank 1, its tip is bent in an L shape, and a large number of gas discharge ports 11 are formed. The gas supply pipe 10 and the gas discharge port 11 constitute carbon dioxide supply means for supplying gas into the aqueous solution in the purification tank 1. An aqueous solution supply pipe 12 for supplying the acidic solution into the purification tank 1 is connected to the upper part of the purification tank 1, and a waste liquid discharge pipe 13 is connected to the lower part of the purification tank 1. Further, a gas supply pipe 15 is connected to the ceiling of the refining tank 1 via a mist separator 14. V1 to V3 are valves.

  As the acidic solution, for example, a strong acid such as sulfuric acid or nitric acid is used. In order to suppress the vapor of the solution from being accompanied by carbon dioxide gas, a solution having as little volatility as possible is preferable, and sulfuric acid is particularly preferable. Further, a neutral solution such as pure water may be used instead of the acidic solution.

  A reaction tank 2 for reacting the purified carbon dioxide gas is provided at the subsequent stage of the purification tank 1. The reaction tank 2 contains a predetermined amount of an aqueous alkali hydroxide solution. As the alkali hydroxide aqueous solution, sodium hydroxide (NaOH) is used because it is a step of producing sodium carbonate in this example. The concentration of the aqueous sodium hydroxide solution is adjusted to 27% by weight, for example. The tip of the gas supply pipe 15 described above is inserted into the upper part of the reaction tank 2, and the tip is bent into an L shape and a number of gas discharge ports 16 are formed. Is done. That is, the gas supply pipe 15 communicates the gas phase part of the refining tank 1 and the liquid phase part of the reaction tank 2, and constitutes a gas discharge port 16 and a ventilation means for supplying carbon dioxide gas into the aqueous solution of the reaction tank 2. Is done. An aqueous solution supply pipe 21 for supplying the alkaline aqueous solution into the reaction tank 2 and a gas discharge pipe 22 for discharging the carbon dioxide gas in the reaction tank 2 are connected to the upper part of the reaction tank 2. An aqueous solution discharge pipe 23 is connected to the lower part of the reaction tank 2. Further, the reaction tank 2 is connected to the suction filtration means 3 through the aqueous solution discharge pipe 23. V4 and V5 are valves.

  Next, the manufacturing method of the high purity alkali carbonate implemented with the said apparatus is demonstrated. In the present invention, high-purity alkali carbonate means that metal impurities are lower than carbon dioxide gas as a raw material, and does not limit the range of metal impurity concentration. For example, the metal impurity concentration is 10 ppb or less. . In the following description, it is assumed that an acid solution such as sulfuric acid is stored in the purification tank 1 and an aqueous sodium hydroxide solution is stored in the reaction tank 2. First, carbon dioxide gas (carbon dioxide (CO2)) as a raw material is supplied into a refining tank 1 containing sulfuric acid through a gas supply pipe 10. Carbon dioxide generated from dry ice, an incinerator, or the like is used as the carbon dioxide gas as the raw material. For this reason, the carbon dioxide gas used in the present invention contains a metal impurity although it is a very small amount in a general sense.

  The carbon dioxide gas is discharged from the gas discharge ports 11 formed at the tip of the gas supply pipe 10 and diffused into the sulfuric acid by bubbling. Carbon dioxide gas is generated from the surface of sulfuric acid because the carbon dioxide gas has the property of shifting from the liquid phase portion to the gas phase portion without being dissolved in the acidic solution. At this time, the metal impurities in the particle state contained in the carbon dioxide gas are dissolved in the sulfuric acid and changed in form as metal ions and collected in the liquid. Therefore, the gas phase portion of the refining tank 1 has an extremely high concentration of metal impurities. It will be filled with low carbon dioxide. The carbon dioxide gas released to the gas phase part in the purification tank 1 is sent to the gas supply pipe 15 after the alkali mist is removed by the mist separator 14 installed on the ceiling part of the purification tank 1.

  Then, purified carbon dioxide gas (low metal impurity concentration) is supplied into the reaction tank 2 containing a predetermined amount of sodium hydroxide aqueous solution through the gas supply pipe 15, and the carbon dioxide gas is supplied to the gas supply pipe 15. The gas is discharged from the gas discharge ports 16 formed at the tip of the gas and diffused into the aqueous sodium hydroxide solution by bubbling. Then, the reaction shown in the following formula (2) occurs in the reaction tank 2, and sodium carbonate (Na2CO3) having a low metal impurity concentration is precipitated and precipitated. Further, the carbon dioxide gas reacted in the aqueous solution is discharged outward through the gas discharge pipe 22. The carbon dioxide gas may be supplied into the refining tank 1 through the gas supply pipe 10.

2NaOH + CO2 → Na2CO3 + H2O (2)
And the valve | bulb V5 is opened, the slurry which is a deposit is extracted, and it sends to the suction filtration means 3, and the sodium carbonate which is solid content is isolate | separated from a mother liquid here, The highly pure sodium carbonate with a very low metal impurity concentration is obtained.

  According to the above-described embodiment, by dissolving carbon dioxide (carbon dioxide) containing metal impurities in sulfuric acid, metal impurities contained in carbon dioxide can be removed, and the carbon dioxide can be removed at a high concentration. By dissolving in a sodium hydroxide aqueous solution, a solid content of high purity sodium carbonate having a very low metal impurity concentration can be obtained. Therefore, this aqueous solution of sodium carbonate can be suitably used as an etching solution (cleaning solution) for the silicon wafer.

  In FIG. 1, a predetermined amount of, for example, 51% by weight potassium hydroxide aqueous solution is stored in the reaction tank 2 in place of the sodium hydroxide aqueous solution, and purified carbon dioxide gas is dissolved in the potassium hydroxide aqueous solution. ) Reaction occurs, and high purity potassium carbonate having a low metal impurity concentration is precipitated.

2KOH + CO2 → K2CO3 + H2O (3)
Therefore, the same effect as described above can be obtained with this potassium carbonate.

  Further, even if pure water is used instead of sulfuric acid in the reaction tank 1 in FIG. 1, the metal impurities in the particle state contained in the carbon dioxide gas can be collected in the liquid. Low-purity sodium carbonate or potassium carbonate can be obtained.

  Another embodiment of the present invention will be described. The embodiment described here is the same as the embodiment described above except that carbon dioxide, which is a raw material containing metal impurities, is dissolved in an aqueous solution of alkali hydrogen carbonate, for example, an aqueous solution of sodium bicarbonate (NaHCO3). Produces highly pure alkali carbonate with extremely low concentration. Therefore, in FIG. 2, the same reference numerals are given to portions having the same configuration as that of the above-described embodiment. In the following description, the refining tank 1 stores a predetermined amount of, for example, 5 to 8% by weight of sodium bicarbonate aqueous solution maintained at 60 ° C. or less, preferably 30 ° C. or less. It is assumed that a predetermined amount of aqueous sodium hydroxide solution is stored.

  When carbon dioxide containing metal impurities is dissolved in the sodium hydrogen carbonate aqueous solution in the refining tank 1, the metal impurities in the particle state contained in the carbon dioxide are trapped as hydroxides or metal ions. The oxide accumulates at the bottom of the purification tank 1 as a precipitate. The gas phase portion of the refining tank 1 is filled with carbon dioxide gas from which impurities have been removed. In this case, a small amount of water accompanies the carbon dioxide gas.

  Thus, even when carbon dioxide containing metal impurities is dissolved in an aqueous sodium hydrogen carbonate solution, the metal impurities contained in the carbon dioxide gas can be removed. Similarly to the above, high-purity sodium carbonate having an extremely low metal impurity concentration can be obtained. Can get. In FIG. 2, an aqueous solution of potassium bicarbonate is stored in the purification tank 1, and a predetermined amount of an aqueous potassium hydroxide solution is stored in the reaction tank 2 instead of the aqueous sodium hydroxide solution, and the purified carbon dioxide gas is stored in water. When dissolved in an aqueous potassium oxide solution, the reaction shown in the above formula (3) occurs, and high purity potassium carbonate having a low metal impurity concentration is deposited.

  Still another embodiment of the present invention will be described. FIG. 3 shows an apparatus for producing an alkali carbonate in this embodiment. In FIG. 3, 4 is a first refining tank. A predetermined amount of acidic solution or neutral solution is stored in the first purification tank 4. A gas supply pipe 40 is inserted into the upper part of the first refining tank 4, and its distal end is bent in an L shape and has a large number of gas discharge ports 41, which is configured as an air diffuser structure. The gas supply pipe 40 and the gas discharge port 41 constitute carbon dioxide supply means for supplying gas into the liquid in the first purification tank 4. Further, an aqueous solution supply pipe 42 for supplying the acidic solution or pure water into the first purification tank 4 is connected to the upper part of the first purification tank 4, and the lower part of the first purification tank 4. Is connected to a waste liquid discharge pipe 43. Further, a gas supply pipe 45 is connected to the ceiling of the first refining tank 4 via a mist separator 44. V6 to V8 are valves.

  Further, a second purification tank 5 for further purifying the purified carbon dioxide gas is provided at the subsequent stage of the first purification tank 1. The second refining tank 5 contains a predetermined amount of alkali hydrogen carbonate aqueous solution. The tip of the gas supply pipe 45 described above is inserted into the upper part of the second refining tank 5, the tip is bent in an L shape, and a number of gas discharge ports 46 are formed. Configured as a structure. That is, the gas supply pipe 45 communicates the gas phase portion of the first refining tank 4 and the liquid phase portion of the second refining tank 5 together with the gas discharge port 46 in the liquid of the second refining tank 5. A first ventilation means for supplying carbon dioxide gas is configured. An aqueous solution supply pipe 51 for supplying the alkaline aqueous solution into the second purification tank 5 is connected to the upper part of the second purification tank 5, and an aqueous solution is connected to the lower part of the second purification tank 5. A discharge pipe 52 is connected. Further, a gas supply pipe 54 is connected to the ceiling of the second refining tank 5 via a mist separator 53. V9 and V10 are valves.

  Further, a reaction tank 6 for reacting the purified carbon dioxide gas is provided at the subsequent stage of the second purification tank 5. A predetermined amount of an aqueous alkali hydroxide solution is contained in the reaction vessel 6. The tip of the gas supply pipe 54 described above is inserted into the upper part of the reaction tank 6, and the tip is bent into an L shape and a number of gas discharge ports 55 are formed. Is done. That is, the gas supply pipe 54 communicates the gas phase part of the second purification tank 5 and the liquid phase part of the reaction tank 6, and supplies the carbon dioxide gas into the liquid of the reaction tank 6 together with the gas discharge port 55. Two ventilation means are configured. Further, an aqueous solution supply pipe 61 for supplying the alkaline aqueous solution into the reaction tank 6 and a gas discharge pipe 62 for discharging carbon dioxide in the reaction tank 6 are connected to the upper part of the reaction tank 6. An aqueous solution discharge pipe 63 is connected to the lower part of the reaction tank 6. Further, the reaction tank 6 is connected to the suction filtration means 7 through the aqueous solution discharge pipe 63. V11 and V12 are valves.

  About the manufacturing method of the high purity alkali carbonate implemented with the said apparatus, it consists of the manufacturing method which combined two embodiment mentioned above. When a sodium hydrogen carbonate aqueous solution is stored in the second refining tank 5 and a sodium hydroxide aqueous solution is stored in the reaction tank 6, high-purity sodium carbonate having a very low metal impurity concentration can be obtained. become. Alternatively, when a potassium hydrogen carbonate aqueous solution is stored in the second purification tank 5 and a potassium hydroxide aqueous solution is stored in the reaction tank 6, high purity potassium carbonate having a very low metal impurity concentration can be obtained. Become.

  In the apparatus having such a configuration, carbon dioxide gas containing metal impurities is dissolved in, for example, sulfuric acid in the first refining tank 4, and further, carbon dioxide gas generated from the liquid is dissolved in an aqueous solution of alkali hydrogen carbonate in the second refining tank 5. Therefore, a carbon dioxide gas having a lower metal impurity concentration can be obtained. As a result, a higher purity alkali carbonate having a very low metal impurity concentration can be obtained. Further, the same effect as described above can be obtained by storing an aqueous solution of alkali hydrogen carbonate in the first refining tank 4 and storing sulfuric acid in the second refining tank 5, for example.

  In the above-described embodiment, when a neutral solution excluding an acidic solution or pure water is used in the previous stage, entrainment of vapor is inevitable even if the volatility of the solution is small. When carbon dioxide gas is dissolved in an aqueous alkali hydroxide solution, the accompanying acid component, for example, is taken into the alkali carbonate and becomes an impurity. It is preferable that an acidic solution such as sulfuric acid is placed in the first purification tank 4 and an aqueous solution of alkali hydrogen carbonate is placed in the second purification tank 5.

  In the above, the carbon dioxide gas discharged from the reaction tank 2 or the reaction tank 6 is returned to the refining tank 1 (example in FIGS. 1 and 2) or the first refining tank 4 (example in FIG. 3) which is the previous stage of the processing system. You may make it make it. FIG. 4 is a diagram showing such an example, and a configuration in which carbon dioxide gas discharged from the subsequent stage of the processing system 100 that generates sodium carbonate or potassium carbonate is returned to the gas supply pipe 10 and supplied to the front stage of the processing system 100. Show. In the figure, P is a pump, V13 is a valve, and 101 is a check valve.

It is a schematic block diagram which shows one form of the apparatus which manufactures the highly pure alkali carbonate with a very low metal impurity concentration which implements the method of this invention. It is a schematic block diagram which shows one form of the apparatus which manufactures the highly pure alkali carbonate with a very low metal impurity concentration which implements the method of this invention. It is a schematic block diagram which shows one form of the apparatus which manufactures the highly pure alkali carbonate with a very low metal impurity concentration which implements the method of this invention. In the apparatus which manufactures the alkali carbonate of this invention, it is a schematic block diagram which shows the example which returns the carbon dioxide gas discharged | emitted from the reaction tank to the refinement | purification tank which is the front | former stage of a processing system.

Explanation of symbols

1 Purification tank 10 Gas supply pipe 11 Gas discharge port 15 Gas supply pipe 16 Gas discharge port 2 Reaction tank 22 Gas discharge pipe 3 Suction filtration means 4 First purification tank 5 Second purification tank 6 Reaction tank 7 Suction filtration means V1 ~ V13 Valve

Claims (4)

Carbon dioxide containing metal impurities is dissolved in any one of an acidic liquid, a neutral liquid, and an aqueous alkali hydrogen carbonate solution, and the metal impurities are collected in the liquid so that the metal impurities are more than the carbon dioxide. Obtaining a low concentration of carbon dioxide;
And a step of dissolving the carbon dioxide gas obtained in this step in an aqueous alkali hydroxide solution to obtain a high-purity alkali carbonate, and a method for producing a high-purity alkali carbonate. Dissolving carbon dioxide containing metal impurities in an acidic liquid or neutral liquid, and collecting carbon impurities in the liquid to obtain carbon dioxide having a lower metal impurity concentration than the carbon dioxide;
Dissolving carbon dioxide purified in this step in an aqueous solution of alkali hydrogen carbonate, and collecting metal impurities in this solution to obtain carbon dioxide having a lower metal impurity concentration than the carbon dioxide;
And a step of dissolving the carbon dioxide gas obtained in this step in an aqueous alkali hydroxide solution to obtain a high-purity alkali carbonate, and a method for producing a high-purity alkali carbonate. A refining tank for storing one of an acidic liquid, a neutral liquid, and an aqueous solution of alkali hydrogen carbonate;
Carbon dioxide supply means for supplying carbon dioxide containing metal impurities into the liquid in the refining tank,
A reaction tank for storing an alkali hydroxide aqueous solution;
A venting means provided to communicate the refining tank and the reaction tank, and for supplying carbon dioxide gas generated from the liquid in the refining tank to the liquid in the reaction tank to generate alkali carbonate; An apparatus for producing high-purity alkali carbonate characterized by the above. A first refining tank for storing acidic or neutral liquid;
Carbon dioxide supply means for supplying carbon dioxide containing metal impurities into the liquid of the first refining tank,
A second refining tank for storing an aqueous solution of alkali hydrogen carbonate;
A first refining tank is provided to communicate with the first refining tank, and a carbon dioxide gas generated from the liquid in the first refining tank is supplied to the liquid in the second refining tank. A ventilation means;
A reaction tank for storing an alkali hydroxide aqueous solution;
The second refining tank is provided so as to communicate with the reaction tank, and a second gas for generating an alkali carbonate by supplying carbon dioxide gas generated from the liquid in the second refining tank into the liquid in the reaction tank. A high-purity alkali carbonate producing apparatus, comprising:

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