TWI879750B - Method for decomposing hydrogen peroxide and device used therein - Google Patents

Abstract

The problem to be solved by the present invention is to economically and effectively treat hydrogen peroxide in wastewater containing sulfuric acid and hydrogen peroxide. As a solution, the following technology is provided. A method for decomposing hydrogen peroxide, wherein the hydrogen peroxide is hydrogen peroxide in wastewater containing sulfuric acid and hydrogen peroxide; and the method comprises the following steps: adding a vanadium sulfate solution to the wastewater and stirring it; leaving the wastewater to stand for a certain period of time after reaching a peak temperature; and cooling it after standing. A decomposition device can decompose hydrogen peroxide in wastewater containing sulfuric acid and hydrogen peroxide, and the device has one or more decomposition tanks capable of performing decomposition reaction; the decomposition tanks are composed of the following structures: an input opening for inputting wastewater and/or vanadium sulfate into the decomposition tank; a stirring means for stirring the wastewater during the decomposition reaction in the decomposition tank; a discharge opening for discharging oxygen generated by the decomposition reaction; a thermometer for measuring the peak temperature of the wastewater during the decomposition reaction; and a cooling means for cooling the wastewater after the decomposition reaction.

Description

Method for decomposing hydrogen peroxide and device using the same

The present invention relates to a method for decomposing hydrogen peroxide and a device using the method. The hydrogen peroxide is hydrogen peroxide in waste liquid, which is discharged from the manufacturing steps of semiconductors and contains sulfuric acid and hydrogen peroxide.

In the wafer cleaning step of the semiconductor manufacturing process, SPM (Sulfuric acid Hydrogen Peroxide Mixture) containing sulfuric acid and hydrogen peroxide is used as a cleaning solution. In this step, after using SPM, hydrogen peroxide is added to SPM to restore its oxidizing power and reuse it as a cleaning solution. However, during the repeated reuse process, the content of water derived from hydrogen peroxide increases, which reduces the concentration of sulfuric acid in SPM, causing the cleaning power to decline, so appropriate liquid exchange is required. The SPM waste liquid discharged during the liquid exchange contains hydrogen peroxide. When the hydrogen peroxide exceeds a certain concentration, it cannot be transported as industrial waste (Patent Document 1). As means for decomposing and treating hydrogen peroxide in the sulfuric acid waste liquid containing hydrogen peroxide, the following methods have been proposed: thermal decomposition of hydrogen peroxide using large-scale equipment (Patent Document 1); a method of decomposing hydrogen peroxide with particularly low concentration using vanadium metal or vanadium compound as a catalyst (Patent Document 2), etc. [Prior Art Document] (Patent Document)

Patent document 1: Japanese Patent Publication No. 2013-208602. Patent document 2: Japanese Patent Publication No. 2002-001358.

[Problem to be solved by the invention] However, when the inventors used vanadium sulfate as a catalyst to decompose hydrogen peroxide in sulfuric acid waste liquid, in order to confirm whether the hydrogen peroxide in the sulfuric acid waste liquid had been decomposed to a specific concentration, they had to use an expensive concentration meter that was resistant to sulfuric acid, which was a problem of wasting money and labor. That is, the problem to be solved by the present invention is to economically and effectively treat hydrogen peroxide in waste liquid containing sulfuric acid and hydrogen peroxide. [Technical means for solving the problem]

In the process of conducting research to solve the above problems, the inventors found that hydrogen peroxide in wastewater containing sulfuric acid and hydrogen peroxide can be treated economically and effectively by a method comprising the following steps, and the present invention was completed as a result of further continuous research. The steps are: adding a vanadium sulfate solution to the wastewater and stirring it; leaving the wastewater to stand for a certain period of time after reaching a peak temperature; and cooling it after standing.

That is, the present invention relates to the following technology. [1] A method for decomposing hydrogen peroxide, wherein the hydrogen peroxide is hydrogen peroxide in a waste liquid containing sulfuric acid and hydrogen peroxide; and the method comprises the following steps: a step of adding a vanadium sulfate solution to the waste liquid and stirring it; a step of standing the waste liquid for a certain period of time after it reaches a peak temperature; and, a step of cooling after standing. [2] The method as described in [1] above, wherein the waste liquid is a mixed solution of sulfuric acid and hydrogen peroxide (SPM), and the mixed solution of sulfuric acid and hydrogen peroxide is used for semiconductor wafer cleaning. [3] The method as described in [1] or [2] above, wherein the hydrogen peroxide content in the waste liquid is 1.6 to 10.0 wt%.

[4] The method as described in any one of [1] to [3] above, wherein the waste liquid is distributed into a volume of 40 liters. [5] The method as described in any one of [1] to [4] above, wherein the amount of the vanadium sulfate solution added to 1 liter of the waste liquid is 0.05 to 0.25 g. [6] The method as described in any one of [1] to [5] above, wherein the peak temperature is 40 to 130°C.

[7] The method as described in any one of [1] to [6] above, wherein the stirring is performed by air bubbling. [8] The method as described in any one of [1] to [7] above, wherein the standing time after reaching the peak temperature for the decomposition of the waste liquid containing 1.6 to 10.0 wt % of hydrogen peroxide is 5 minutes or more. [9] A regeneration method for regenerating waste liquid containing sulfuric acid and hydrogen peroxide into industrial sulfuric acid, the regeneration method using the method as described in any one of [1] to [8] above.

[10] A decomposition device capable of decomposing hydrogen peroxide in wastewater containing sulfuric acid and hydrogen peroxide, the device comprising one or more decomposition tanks capable of carrying out a decomposition reaction; the decomposition tanks comprising the following structures: an inlet opening for inletting wastewater and/or vanadium sulfate into the decomposition tank; a stirring means for stirring the wastewater during the decomposition reaction in the decomposition tank; a discharge opening for discharging oxygen generated by the decomposition reaction; a thermometer for measuring the peak temperature of the wastewater during the decomposition reaction; and a cooling means for cooling the wastewater after the decomposition reaction.

[11] The device as described in [10] above, wherein the amount of waste liquid introduced into the decomposition tank is less than 80% of the capacity of the decomposition tank. [12] The device as described in [10] or [11] above, wherein the cooling means is external cooling by cold water. [13] The device as described in any one of [10] to [12] above, wherein the device is automated. [Effect of the invention]

Since the method of the present invention does not require large-scale equipment, an expensive hydrogen peroxide concentration meter, or time-based concentration measurement using the hydrogen peroxide concentration meter, it is possible to economically and effectively decompose hydrogen peroxide in wastewater containing sulfuric acid and hydrogen peroxide. In addition, since the method of the present invention treats the wastewater in the state of raw liquid without neutralizing or diluting the wastewater, the amount of solution generated after treatment can be suppressed. Furthermore, the method of the present invention can safely treat the wastewater even when the hydrogen peroxide concentration is high by distributing the wastewater into a certain amount and using a plurality of decomposition tanks for treatment. Furthermore, the device of the present invention can automatically implement the above method and can simply and accurately perform continuous hydrogen peroxide decomposition treatment.

The present invention is described in detail below based on suitable embodiments of the present invention. The present invention relates to a method for decomposing hydrogen peroxide, wherein the hydrogen peroxide is hydrogen peroxide in a waste liquid containing sulfuric acid and hydrogen peroxide, and the method comprises the following steps: adding a vanadium sulfate solution to the waste liquid and stirring it; leaving the waste liquid to stand for a certain period of time after reaching a peak temperature; and cooling the waste liquid after standing.

Furthermore, the present invention also relates to a decomposition device that uses the above method and can decompose hydrogen peroxide in wastewater containing sulfuric acid and hydrogen peroxide. The device has one or more decomposition tanks that can perform decomposition reactions. Furthermore, the decomposition tank has the following structure: an opening for feeding, which is used to feed wastewater and/or vanadium sulfate into the decomposition tank; a stirring means, which stirs the wastewater during the decomposition reaction in the decomposition tank; a discharge opening, which is used to discharge oxygen generated by the decomposition reaction; a thermometer, which measures the peak temperature of the wastewater during the decomposition reaction; and a cooling means, which cools the wastewater after the decomposition reaction.

The decomposition reaction of hydrogen _peroxide performed in the decomposition tank of the present invention by contacting vanadium sulfate with wastewater is as follows: _H2O2 → _H2O +(1/2) _O2 (Formula 1) In the reaction of Formula 1, vanadium sulfate acts as a catalyst in the decomposition reaction of hydrogen peroxide, and vanadium sulfate itself does not react. The decomposition reaction is an exothermic reaction.

The present invention is to sequentially put waste liquid and vanadium sulfate solution into a decomposition tank from an opening for input, and stir them by means of a stirring means.

The waste liquid used in the present invention contains sulfuric acid and hydrogen peroxide. The concentration of sulfuric acid is not particularly limited, and is, for example, about 70% by weight. The concentration of hydrogen peroxide is also not particularly limited, and is preferably 10.0% by weight or less, more preferably 7.0% by weight or less, further preferably 1.6 to 10.0% by weight, and particularly preferably 1.6 to 7.0% by weight. The waste liquid may contain components other than sulfuric acid and hydrogen peroxide.

The type of waste liquid is not particularly limited as long as it contains sulfuric acid and hydrogen peroxide. Examples of the waste liquid treated by the present invention include SPM waste liquid used for semiconductor wafer cleaning, chemical polishing liquid, etc., and preferably SPM waste liquid used for semiconductor wafer cleaning. When the waste liquid is SPM waste liquid used for semiconductor wafer cleaning, the daily waste liquid generation amount is not particularly limited, for example, 1000 to 4000 liters. When a large amount of waste liquid is treated using one decomposition tank, especially when the hydrogen peroxide in the waste liquid is at a high concentration, the decomposition reaction will proceed violently, so there is a concern that danger may occur during the waste liquid treatment operation. Therefore, from the perspective of safe treatment, it is better to allocate a certain amount of waste liquid and use multiple decomposition tanks to treat hydrogen peroxide in the waste liquid, although there is no special restriction, for example, it can be allocated to a capacity of 40 liters. By allocating a certain amount of waste liquid for treatment, even if the hydrogen peroxide is at a high concentration, it can still be safely treated. In addition, because the decomposition reactions in each decomposition tank are independent of each other, even if one of the decomposition tanks is dangerous, it will not affect other decomposition tanks, so the dangers associated with the waste liquid treatment operation can be minimized.

The vanadium sulfate solution used in the present invention is not particularly limited as long as it can decompose hydrogen peroxide in the waste liquid. The amount of vanadium sulfate solution used is not particularly limited, but is preferably 0.05 to 0.25 g per 1 liter of waste liquid to be treated. If it exceeds 0.25 g, the decomposition of hydrogen peroxide will be excessively promoted, and there is a concern that it will be dangerous during the waste liquid treatment operation. On the other hand, if it is less than 0.05 g, the decomposition reaction of hydrogen peroxide will not proceed sufficiently.

The material of the decomposition tank used in the present invention is not particularly limited as long as it is resistant to strong acid. For example, it can be made of metal lined with resin, metal lined with glass, and fluororesin, etc., preferably metal lined with glass. The shape of the decomposition tank is not particularly limited as long as it does not hinder the decomposition of hydrogen peroxide in the waste liquid containing sulfuric acid and hydrogen peroxide. For example, cylindrical, box-shaped, etc. can be listed. From the perspective of ease of stirring, cylindrical is preferred. The size of the decomposition tank is not particularly limited as long as it can safely decompose hydrogen peroxide in the waste liquid containing sulfuric acid and hydrogen peroxide. For example, φ300mm×H700mm and a capacity conversion of about 50 liters can be listed. The amount of waste liquid put into the decomposition tank is not particularly limited as long as it can be safely treated. It is preferably less than 80% of the capacity of the decomposition tank, for example, 40 liters. The openings for the waste liquid and the vanadium sulfate solution can be the same or different. The openings can be opened and closed.

The stirring means used in the present invention is not particularly limited as long as it can effectively contact the waste liquid with the vanadium sulfate solution and promote the decomposition reaction of the hydrogen peroxide in the waste liquid. Examples thereof include a stirrer and air bubbling. Since the waste liquid contains sulfuric acid, when a metal stirring means is used, there is a concern that the sulfuric acid may cause the metal to dissolve or corrode. Therefore, from the perspective of not using metal, air bubbling is preferred. When air bubbling is used as a stirring means, the air circulation rate is not particularly limited as long as it can effectively contact the waste liquid with the vanadium sulfate solution and promote the decomposition reaction of the hydrogen peroxide in the waste liquid, and it is a circulation rate that can be safely implemented. Furthermore, if air bubbling is performed continuously, there is a concern that the decomposition reaction may become violent, so it is better to perform it intermittently.

The oxygen generated by the decomposition reaction can be discharged through the discharge opening. The discharge opening for discharging the oxygen can be the same as or different from the discharge opening for introducing the waste liquid and/or the vanadium sulfate solution.

The present invention measures the peak temperature of the waste liquid in the decomposition reaction by a thermometer and then leaves it alone for a certain period of time. The peak temperature of the waste liquid measured in the present invention indicates the maximum temperature of the waste liquid. The waste liquid is heated by the heat generated by the decomposition reaction of hydrogen peroxide. When the temperature of the waste liquid begins to drop, the temperature before the start of the drop is regarded as the maximum temperature of the waste liquid.

The means for measuring the temperature of the waste liquid used in the present invention is not particularly limited, and preferably a thermocouple detector coated with a fluorine resin or the like is used. The peak temperature is positively correlated with the hydrogen peroxide concentration in the waste liquid, for example, when the hydrogen peroxide concentration is 2.0 to 8.0 wt%, it is 40 to 130°C. From the perspective of safely carrying out the decomposition reaction, the peak temperature is preferably below 80°C.

Even in the standing step, the decomposition reaction of hydrogen peroxide continues. Based on the experimentally known relationship between the peak temperature and the standing time to reduce the hydrogen peroxide concentration to a specific concentration, the hydrogen peroxide can be reduced to a specific concentration by standing alone. This step eliminates the need for an expensive concentration meter for continuously measuring the hydrogen peroxide concentration in the waste liquid, and enables the decomposition reaction of hydrogen peroxide to be controlled economically and effectively. In one embodiment, when the hydrogen peroxide concentration in the waste liquid is 1.6 to 10.0% by weight, the standing time is more than 5 minutes.

The present invention will be cooled by cooling means after standing still. The cooling used in the present invention is implemented after standing still, and its main function is to completely terminate the decomposition reaction and reduce the temperature of the waste liquid to a safe temperature. During the standing still period, the decomposition reaction will continue, so if cooling is performed during the standing still period, it may cause the decomposition reaction to end before reaching a specific hydrogen peroxide concentration. Therefore, cooling is not performed during the standing still period, but starts after the standing still is completed.

The cooling means used in the present invention is not particularly limited as long as it can reduce the waste liquid after the decomposition reaction of hydrogen peroxide has been completed to a safe temperature without changing the composition of the waste liquid. Preferably, it is external cooling by cold water. Furthermore, when external cooling is performed by cold water, the decomposition tank can have a double tank structure in a manner that the cooling water can flow through the outer casing of the decomposition tank. In addition, if a glass lining is used on the inner side of the decomposition layer, the cooling efficiency can be improved and it is preferred. The concentration of hydrogen peroxide in the liquid obtained after the method of the present invention is preferably less than 0.5% by weight, and more preferably less than 0.1% by weight.

Furthermore, the present invention relates to a regeneration method, which uses the method of the present invention to regenerate industrial sulfuric acid from waste liquid containing sulfuric acid and hydrogen peroxide.

The method of the present invention, in one aspect, can be implemented using an automated device of the present invention. [Example]

Next, the method for decomposing hydrogen peroxide of the present invention and the device using the method are further described in detail by the following examples and comparative examples, but the present invention is not limited thereto.

A hydrogen peroxide decomposition device 1 (manufactured by Kanto Engineering Co., Ltd.) having the structure of FIG. 1 is prepared to treat 2,800 liters of waste liquid containing sulfuric acid and hydrogen peroxide (70% by weight sulfuric acid and less than 7% by weight hydrogen peroxide) per day. The waste liquid is discharged from the wafer cleaning step of self-manufacturing semiconductors and includes 6 decomposition tanks. The hydrogen peroxide decomposition device can be stored in a PVC (polyvinyl chloride) resin box with an outer diameter of approximately D1200mm×W3000mm×H2000mm, and the capacity of each decomposition tank is 23 liters. The processing time of one batch of one decomposition tank is set to 1 hour, and all six decomposition tanks are set to automatic continuous operation. The automatic processing flow of one batch of one decomposition tank is as follows. When the device starts to operate automatically, waste liquid is added from the wastewater treatment tank, and 3g of vanadium sulfate is added from the decomposition tank. In the decomposition tank, air bubbling is performed intermittently, and after the temperature is measured to be 40°C, the air bubbling is completely stopped. After the peak temperature is measured, the decomposition tank is allowed to stand for 15 minutes. After standing, cooling water is circulated to cool the outside of the decomposition tank until the liquid temperature in the decomposition tank reaches 35°C. After cooling, the decomposed waste liquid containing vanadium sulfate is discharged from the decomposition tank and stored in a holding tank. In addition, cooling water is also discharged separately. The hydrogen peroxide concentration of the decomposed waste liquid is less than 0.1% by weight. Using six tanks to carry out the above operation, approximately 3,000 liters of treatment can be completed in 24 hours.

1: Hydrogen peroxide decomposition device 2: Decomposition tank 3: Opening for input 4: Stirring means 5: Opening for discharge 6: Thermometer 7: Cooling means

FIG. 1 shows the structure of the decomposition tank of the hydrogen peroxide decomposition device of the present invention.

2 Domestic storage information (please note in the order of storage institution, date, and number) None 3 Foreign storage information (please note in the order of storage country, institution, date, and number) None

1: Hydrogen peroxide decomposition device

2: Decomposition tank

3: Opening for input

4: Stirring method

5: Opening for discharge

6: Thermometer

7: Cooling measures

Claims (8)

A method for decomposing hydrogen peroxide, wherein the hydrogen peroxide is hydrogen peroxide in a waste liquid containing sulfuric acid and hydrogen peroxide; and the method comprises the following steps: adding a vanadium sulfate solution to the waste liquid and stirring it; leaving the waste liquid to stand for a certain time after reaching a peak temperature; and cooling it after standing; the peak temperature is the maximum temperature of the waste liquid heated by the heat generated by the decomposition reaction of hydrogen peroxide, and the maximum temperature of the waste liquid is the temperature before the temperature of the waste liquid starts to drop. For the decomposition of the waste liquid containing 1.6-10.0% by weight of hydrogen peroxide, the standing time after reaching the peak temperature is more than 5 minutes. The method as described in claim 1, wherein the waste liquid is a mixture of sulfuric acid and hydrogen peroxide, and the mixture of sulfuric acid and hydrogen peroxide is used for cleaning semiconductor wafers. The method as described in claim 1 or 2, wherein the hydrogen peroxide in the waste liquid is 1.6 to 10.0% by weight. A method as claimed in claim 1 or 2, wherein the waste liquid is dispensed into 40 liter volumes. The method as described in claim 1 or 2, wherein the amount of vanadium sulfate solution added to 1 liter of waste liquid is 0.05-0.25 g. The method as described in claim 1 or 2, wherein the peak temperature is 40~130℃. A method as described in claim 1 or 2, wherein the stirring is performed by air bubbling. A regeneration method for regenerating waste liquid containing sulfuric acid and hydrogen peroxide into industrial sulfuric acid, wherein the regeneration method uses the method described in any one of claim items 1 to 7.