JPH0891811A - Device for purifying waste sulfuric acid and method thereof - Google Patents

Abstract

PURPOSE: To provide a device for purifying waste sulfuric acid which directly measures a concn. of a sulfuric acid in a distillation column and the concn. of a product sulfuric acid, efficiently purifies the waste sulfuric acid and produces a purified sulfuric acid constant in concn. CONSTITUTION: This device for purifying waste sulfuric acid consists of the distillation column 2 housing the waste sulfuric acid 6, a heating means 10 heating the waste sulfuric acid 6 housed in the distillation column 2 and a condenser 3 cooling and condensing a vapor of each component discharged from the distillation column 2 through a packed layer disposed on the distillation column 2, cooling part 47 cooling the waste sulfuric acid by discharging the waste sulfuric acid in the distillation column 2, a circulating pipeline 16 provided so as to return the waste sulfuric acid to the distillation column 2 via a waste sulfuric acid concn. measuring part 7 and a sulfuric acid concn., and measuring means 8 provided with a sulfuric acid concn. detector 50 at the waste sulfuric acid concn. measuring part 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for recovering and refining used waste sulfuric acid solution, and relates to a waste sulfuric acid refining apparatus and a refining control method capable of stably supplying reusable high-quality sulfuric acid. .

[0002]

2. Description of the Related Art In recent years, a large amount of sulfuric acid has been used in a wafer manufacturing process, an etching process, and a photoresist stripping process in a semiconductor manufacturing process. Sulfuric acid is mainly used in the wafer cleaning process, and a mixed acid of sulfuric acid and hydrofluoric acid or nitric acid is used in the etching process.
In the photoresist stripping process, a solution of sulfuric acid mixed with hydrogen peroxide as an oxidant or peroxydisulfuric acid generated by electrolyzing sulfuric acid is used.

In many cases, the waste sulfuric acid generated in these steps is either disposed of after being treated in a neutralization tank or is handed over to an industrial waste treatment company for treatment. It caused many problems in terms of impact and economy.
Therefore, in recent years, we have developed a waste sulfuric acid purification device that can collect and purify waste sulfuric acid that has been used in manufacturing processes such as semiconductor factories and can manufacture high-purity sulfuric acid that can be reused in the semiconductor manufacturing process described above. Is being promoted.

Conventionally, as this type of waste sulfuric acid refining apparatus,
It is equipped with a distillation column that stores waste sulfuric acid and heats it, and a condenser that cools and condenses and liquefies the vapor such as sulfuric acid vapor derived from this distillation column, at approximately 1 atm (760 Torr) or some. An atmospheric distillation unit operated at a high pressure and an exhaust device such as a vacuum pump for reducing the pressure inside the distillation system of the distillation column and the condenser are attached, and the reduced pressure distillation operates under a reduced pressure of several Torr to several tens Torr. The device is known. Since the atmospheric distillation unit is operated at about 1 atm (760 Torr), the boiling point of sulfuric acid is high, and the operating temperature is about 330 ° C or higher. Most of the atmospheric distillation methods employ a continuous method in which a fixed amount of waste sulfuric acid is continuously supplied to a distillation column for purification to continuously produce a fixed amount of product sulfuric acid. In such a continuous system, it can be operated steadily if the sulfuric acid concentration of the waste sulfuric acid supplied to the distillation column is stable, but it will start when the sulfuric acid concentration of the waste sulfuric acid fluctuates beyond a certain condition. There is a problem that the state becomes an unsteady state, and a product with stable quality cannot be obtained. Incidentally, if the sulfuric acid concentration of the waste sulfuric acid in the steady operation fluctuates by ± 2% or more with respect to the set value, the steady operation cannot be maintained and the unsteady state is assumed. On the other hand, since the vacuum distillation apparatus is operated under reduced pressure, the boiling point of sulfuric acid is lowered and the operating temperature is about 200 ° C. This vacuum distillation method employs a batch system (batch system) or a semi-batch system (semi-batch system). According to this method, the product sulfuric acid can be manufactured even if the sulfuric acid concentration in the waste sulfuric acid supplied changes.

By the way, in such a waste sulfuric acid refining treatment, the waste sulfuric acid in the distillation column is used as a standard for switching the heat treatment temperature of the waste sulfuric acid or for introducing the condensate into the product tank. It is necessary to accurately measure changes in the sulfuric acid concentration of the solution. However, it was impossible to directly measure the sulfuric acid concentration in the waste sulfuric acid because the waste sulfuric acid in the distillation column was in a boiling state, had a high temperature, and generated bubbles. Then, conventionally, in order to measure the sulfuric acid concentration of the waste sulfuric acid during distillation, the pressure of the vapor phase part of the distillation column and the temperature of the waste sulfuric acid solution in the column were measured, and the gas-liquid equilibrium was measured based on the measurement result. The sulfuric acid concentration of the waste sulfuric acid was estimated by performing calculation or using a chart as shown in FIG.

[0006]

However, in a waste sulfuric acid refining device for distilling waste sulfuric acid under a reduced pressure, a very small amount of air is mixed into the exhaust system of the device from the pipe connection parts and joint parts of each part. The pressure in the distillation column may change due to fluctuations in the exhaust volume of the vacuum pump of the exhaust means, and the method that estimates the sulfuric acid concentration in the distillation column as fluctuations in the vapor pressure or water vapor pressure of sulfuric acid causes errors in the actual sulfuric acid concentration and errors. Is likely to occur, and there is a time lag between the estimated time and the current operating time, making it difficult to perform the operation of the waste sulfuric acid purification device accurately and stably. It was not constant and it was not possible to recover a homogeneous product sulfuric acid.

A distillation apparatus for purifying waste sulfuric acid under atmospheric pressure,
For example, using two distillation columns, evaporate and evaporate the water in the first column, move the concentrated sulfuric acid solution remaining at the bottom to the second column, and heat it to a higher temperature to vaporize the sulfuric acid content and condense it. Even in a continuous atmospheric distillation apparatus that collects and recovers the product, if the sulfuric acid concentration in the waste sulfuric acid in the first tower fluctuates by about ± 2% or more than the set value, an unsteady state will result and product quality stable sulfuric acid will be produced. Since it is impossible to obtain, it is necessary to accurately monitor the concentration of waste sulfuric acid in the first column, and the conventional method for measuring the concentration of sulfuric acid described above cannot accurately monitor the concentration of sulfuric acid in waste sulfuric acid. It was difficult to obtain a stable and homogeneous product sulfuric acid.

The present invention has been made in view of the above circumstances, and directly measures the concentration of a sulfuric acid solution in a distillation column and the concentration of product sulfuric acid to efficiently purify waste sulfuric acid to produce purified sulfuric acid having a constant concentration. It is intended to provide a waste sulfuric acid refining apparatus and a refining method.

[0009]

A waste sulfuric acid refining apparatus according to the present invention comprises a distillation column containing waste sulfuric acid, heating means for heating the waste sulfuric acid contained in the distillation column, and an upper part of the distillation column. In a waste sulfuric acid refining device equipped with a condenser for cooling and condensing the vapor of each component derived from the distillation column via a packed bed arranged, the waste sulfuric acid in the distillation column is led out and the waste sulfuric acid is cooled. A circulation line provided so as to be returned to the inside of the distillation column through the cooling unit and the waste sulfuric acid concentration measuring unit, and the waste sulfuric acid concentration measuring unit is provided with a sulfuric acid concentration measuring means including a sulfuric acid concentration detector. It is characterized by that. The condenser may be provided with a condensate distributor for discharging condensed liquid to the outside of the condenser and supplying it to either a drain tank or a product tank.
Further, the sulfuric acid concentration measuring means may be provided with a pump for forcibly flowing the waste sulfuric acid derived from the distillation column through the circulation line. Further, the sulfuric acid concentration detector may be an ultrasonic densitometer that detects the sulfuric acid concentration by changing the propagation velocity of ultrasonic waves.

In another embodiment of the waste sulfuric acid refining apparatus according to the present invention, a distillation column containing waste sulfuric acid, a heating means for heating the waste sulfuric acid contained in the distillation column, and a distillation column are provided above the distillation column. In a waste sulfuric acid refining device equipped with a condenser for cooling and condensing the vapor of each component derived from the distillation column via a packed bed, a waste sulfuric acid in the distillation column is derived, and cooling for cooling the waste sulfuric acid. Concentration measuring means having a circulation pipe provided so as to be returned to the inside of the distillation column through a waste water concentration measuring unit and a sulfuric acid concentration measuring unit, and a sulfuric acid concentration measuring means in the waste sulfuric acid concentration measuring unit, and the condenser. Based on the sulfuric acid concentration of the waste sulfuric acid measured by the sulfuric acid concentration measuring means, and a condensate distribution device that is provided in the condenser and draws the condensed liquid out of the condenser to supply the condensed liquid to either the drain tank or the product tank. To control the heating of waste sulfuric acid of the above heating means With adjusting the temperature of the waste sulfuric acid inner it is characterized in that a control means for controlling switching the supply direction of the condensate of the condensate distribution apparatus. Further, the sulfuric acid concentration measuring means may be provided with a pump for forcibly flowing the waste sulfuric acid derived from the distillation column through the circulation line. Further, the sulfuric acid concentration detector may be an ultrasonic densitometer that detects the sulfuric acid concentration by changing the propagation velocity of ultrasonic waves.

These spent sulfuric acid refining apparatuses may be provided with an exhaust device for reducing the pressure inside the distillation column and inside the condenser. Further, in the waste sulfuric acid refining apparatus, it is desirable that at least each part of the distillation column above the packed bed, the condenser, and the pipe line connecting them are made of quartz glass.

In the method for purifying waste sulfuric acid according to the present invention, waste sulfuric acid contained in a distillation column having a heating means is heated, and a gas phase discharged from the distillation column is cooled in a condenser to be condensed and liquefied. In the waste sulfuric acid refining method for producing purified sulfuric acid from this condensate, a waste sulfuric acid concentration measuring unit provided with a cooling unit for discharging the waste sulfuric acid in the distillation column and cooling the waste sulfuric acid and a sulfuric acid concentration detector is provided. The waste sulfuric acid is circulated through a circulation pipe provided so as to be returned to the distillation column, and the sulfuric acid concentration of the waste sulfuric acid is measured by the waste sulfuric acid concentration measuring unit. It is input to the control means and compared with a preset sulfuric acid concentration of waste sulfuric acid, and when the measured sulfuric acid concentration becomes equal to the preset sulfuric acid concentration, the temperature of the waste sulfuric acid is set to a preset value. The heating means so that the sulfuric acid distillation temperature is reached Controlling the heating temperature of waste sulfuric acid according to the above, and feeding the condensate liquefied by the condenser to the outside of the condenser and supplying it to either the drain tank or the product tank. Is characterized by switching control. In this method, when measuring the sulfuric acid concentration of the waste sulfuric acid in the liquid phase, the waste sulfuric acid derived from the distillation column is cooled through the circulation pipe, The sulfuric acid concentration may be measured. Further, as the sulfuric acid concentration detector, an ultrasonic densitometer that detects the sulfuric acid concentration by a change in the propagation velocity of ultrasonic waves may be used. Further, in this waste sulfuric acid purification method, the waste sulfuric acid may be purified under reduced pressure.

[0013]

The waste sulfuric acid refining apparatus of the present invention is provided so as to lead out the waste sulfuric acid in the distillation column and return it to the distillation column through the cooling section for cooling the waste sulfuric acid and the waste sulfuric acid concentration measuring section. By providing a sulfuric acid concentration measuring means having a circulation conduit and a sulfuric acid concentration detector in the waste sulfuric acid concentration measuring unit,
The sulfuric acid concentration of waste sulfuric acid in the distillation column can be directly measured, and the accurate sulfuric acid concentration can be measured without changing the measured value due to the pressure fluctuation in the system.

According to another aspect of the present invention, in the waste sulfuric acid refining apparatus, the waste sulfuric acid in the distillation column is led out and returned to the distillation column through a cooling unit for cooling the waste sulfuric acid and a waste sulfuric acid concentration measuring unit. A circulation conduit provided so as to provide a sulfuric acid concentration measuring means including a sulfuric acid concentration detector in the waste sulfuric acid concentration measuring unit,
A condensate distributor provided in the condenser for discharging condensed liquid to the outside of the condenser and supplying it to either a drain tank or a product tank, and sulfuric acid of waste sulfuric acid measured by the sulfuric acid concentration measuring means. Based on the concentration, the heating means controls the heating of the waste sulfuric acid to adjust the temperature of the waste sulfuric acid in the distillation column, and a control means for switching and controlling the supply direction of the condensate of the condensate distributor. According to the configuration, the sulfuric acid concentration of the waste sulfuric acid in the distillation column is accurately measured, the measured value is compared with the preset sulfuric acid concentration of the waste sulfuric acid, and the measured sulfuric acid concentration is preset as described above. The heating temperature of the waste sulfuric acid by the heating means is controlled so that the temperature of the waste sulfuric acid becomes equal to the preset waste sulfuric acid distillation temperature when it becomes equal to the sulfuric acid concentration, and the condensate liquefied by the condenser is Out of the condenser Te controls switching the supply direction of the condensate of the condensate distribution apparatus supplies to one of the drain tank and a product tank. As a result, the sulfuric acid concentration of the waste sulfuric acid in the distillation column can be directly measured, and the accurate sulfuric acid concentration can be measured without the measured value fluctuating due to the pressure fluctuation in the system. By inputting to the control means and controlling the heating temperature of the waste sulfuric acid by the heating means and the supply direction of the condensate of the condensate distributor, it is possible to produce a high-concentration sulfuric acid having a constant concentration at all times.

According to the present invention, a condensate distribution device for discharging the condensed liquid to the outside of the condenser and supplying it to either the drain tank or the product tank is provided. Even during distillation, the product sulfuric acid can be obtained without mixing the initial fraction containing a large amount of water with the product sulfuric acid fraction. Further, the sulfuric acid concentration measuring means, a cooling unit for cooling the waste sulfuric acid derived from the distillation column through the circulation pipe and sending it to the waste sulfuric acid concentration measuring unit, and the waste sulfuric acid in the distillation column in the circulation pipe. By providing a pump for forced circulation, the waste sulfuric acid in the distillation column is forced to flow, and is supplied to the waste sulfuric acid concentration measuring unit while being cooled to a temperature suitable for measurement. The concentration measurement accuracy can be improved. In addition, the sulfuric acid concentration detector uses an ultrasonic densitometer that detects the concentration of sulfuric acid based on changes in the propagation velocity of ultrasonic waves, so that the sulfuric acid concentration can be accurately measured in a short time simply by contacting the sensor with waste sulfuric acid. Can be measured. Furthermore, if at least each part of the distillation column upper part, the condenser and the pipe connecting them are made of quartz glass, the sulfuric acid vapor will come into contact with the distillation column upper part, the condenser and the pipe connecting them in the vacuum distillation. It is possible to prevent impurities from being eluted from the respective parts, and to obtain highly purified purified sulfuric acid having a low content of impurities.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a waste sulfuric acid refining apparatus according to the present invention. This waste sulfuric acid refining apparatus 1 includes a distillation column 2, a condenser 3 connected to the distillation column 2, and the condenser. 3, a condensate distribution device 4 connected to the condenser 3, an exhaust device 5 connected to the condenser 3 to exhaust the inside of the distillation system, and a tank 7 for measuring the waste sulfuric acid 6 in the distillation column 2 (waste sulfuric acid concentration measuring section) The sulfuric acid concentration measuring means 8 for measuring the sulfuric acid concentration in a liquid phase state, and the waste sulfuric acid in the distillation column 2 based on the sulfuric acid concentration measuring result of the waste sulfuric acid 6 measured by the sulfuric acid concentration measuring means 8. The control unit 9 controls the heating temperature of 6 and the supply direction of the condensate of the condensate distributor 4.

The distillation column 2 is a container made of a material which is unlikely to be corroded by the waste sulfuric acid 6 and sulfuric acid vapor generated during distillation, and is a container having a pressure resistance capable of being operated under a reduced pressure condition, and preferably a thick wall. A container made of glass or ceramics, more preferably quartz glass or borosilicate glass is used. A heater 10 for heating is provided at the bottom of the distillation column 2.
Is provided. A mantle heater is preferably used as the heating heater 10. The heating heater 10 controls the heating temperature according to a control signal from the control means 9. A packing layer 11 filled with a packing material such as Raschig ring for improving the separation of the low boiling point component (mainly water) vapor generated in the initial stage of distillation from the sulfuric acid vapor is provided in the upper part of the distillation column 2. There is.

The distillation column 2 is provided with a waste sulfuric acid supply pipe 12 for introducing the waste sulfuric acid 6 into the column and a drain pipe 13 for discharging the waste sulfuric acid from the bottom of the distillation column 2. These waste sulfuric acid supply pipe 12 and drain pipe 13 have valves 14 and 15 respectively.
Is intervening. The drain pipe 13 is branched on the way to the valve 15, and the branched pipe serves as a circulation pipe line 16 of the sulfuric acid concentration measuring means 8.

At the upper part of the distillation column 2, there is provided a pipe 17 for guiding the vapor generated in the column into the condenser 3. Condenser 3
Is a container made of a material that is unlikely to be corroded by sulfuric acid vapor, and having a pressure resistance capable of being operated in a reduced pressure state inside, preferably made of thick glass or ceramics, more preferably quartz glass or borosilicate glass. It is a container. Inside the condenser 3, there is provided a cooling flexible pipe 18 for circulating cooling water to cool, condense and liquefy the steam introduced into the condenser 3. At the bottom of the condenser 3, a pipe 19 for leading the condensed liquid from the inside of the condenser 3 to the condensate distribution device 4 and a pipe 20 connected to the exhaust device 5 are attached.

The condensate distributor 4 is provided with a product tank 21.
A drain tank 22, a pipe 19 connecting the condenser 3 and the product tank 21, a first switching valve 23 interposed in the pipe 19, a first switching valve 23 of the pipe 19 and the condenser 3 19b which is branched between and connected to the drain tank 22
And a second switching valve 25 interposed in the pipe 19b. A valve 26 is provided at the bottom of the product tank 21.
A product sulfuric acid discharge pipe 27 having a valve is attached, and a drain pipe 29 having a valve 28 is attached to the bottom of the drain tank 22. In the condensate distribution device 4, the condensate drawn out from the bottom of the condenser 3 through the pipe 19 by the opening / closing switching operation of the first and second switching valves 23, 25 is supplied to either the drain tank 22 or the product tank 21. It is possible to switch the supply direction of the condensate to be introduced into the crab. The control means 9 is used to switch between opening and closing the first and second switching valves 23 and 25.
Signal.

The exhaust device 5 includes a vacuum pump 30, and a pipe 20 disposed between the vacuum pump 30 and the condenser 3.
Mist separator 32 and sulfuric acid removing cylinder 31 interposed in
And is configured. The mist separator 32 is filled with a filter made of a material resistant to concentrated sulfuric acid such as glass wool, and the cooling pipe 3 for cooling the gas phase introduced through the pipe 20 again to liquefy the low boiling point component in the gas phase.
3 are provided. The sulfuric acid removing cylinder 31 is filled with an alkaline absorbent such as soda lime. Further, at the bottom of the mist separator 32, a discharge pipe 35 having a valve 34 for discharging the liquid accumulated inside is attached.

The product tank 21 is provided with a pipe 37 connected to the mist separator 32 via a valve 36, and the drain tank 22 is joined with the pipe 37 via a valve 38 to join the mist separator 32. A connected tube 39 is provided. And product tank 21 and drain tank 22
Is connected to the mist separator 32 through these valves 36 and 38 and pipes 37 and 39, so that the same reduced pressure state as the inside of the condenser 3 and the distillation column 2 which are also connected to the mist separator 32 by the pipe 20 can be achieved. It has become. In this embodiment, the product sulfuric acid 40 can be withdrawn from the product tank 21 or the low boiling point condensate can be withdrawn from the drain tank 22 while the interiors of the distillation column 2 and the condenser 3 are kept under reduced pressure. , A pipe 37 that connects the product tank 22 and the mist separator 32, and a pipe 43 that opens to the atmosphere through a valve 41 and a filter 42 are provided, and a pipe 39 that connects the drain tank 22 and the mist separator 32. A pipe 45 that joins the pipe 43 through the valve 44 and reaches the filter 42 is provided.

The sulfuric acid concentration measuring means 8 is branched in the middle of a drain pipe 13 extending from the bottom of the distillation column 2, the waste sulfuric acid 6 is led out from the distillation column 2 through the drain pipe 13, and passed through the measuring tank 7 to the distillation column. The circulation pipe 16 arranged so as to be returned to the inside of the container 2, the measurement tank 7 provided in the middle of the circulation pipe 16 for storing a predetermined amount of waste sulfuric acid 6, and the measurement tank 7 Valve 4 interposed in the upstream circulation line 16
6 and the circulation line 1 between the valve 46 and the measuring tank 7.
6, a cooler 47 interposed therebetween, a liquid feed pump 48 interposed in the circulation pipe line 16 on the downstream side of the measurement tank 7, and a liquid phase (waste sulfuric acid) inside the measurement tank 7 And a sulfuric acid concentration measuring instrument 50 having a sensor unit 49.

As the sulfuric acid concentration measuring instrument 50, an ultrasonic densitometer for detecting the sulfuric acid concentration by changing the propagation velocity of ultrasonic waves is preferably used. The method for measuring the sulfuric acid concentration in the waste sulfuric acid 6 is to measure the sulfuric acid concentration by grasping the change in electrical conductivity, the change in physical properties (specific gravity, viscosity, etc.), the change in absorbance, etc. in addition to the change in the propagation velocity of the ultrasonic waves. A densitometer of the detecting type may be used.

The control means 9 includes the sulfuric acid concentration measuring instrument 5
Data of the measured value of the sulfuric acid concentration in the waste sulfuric acid 6 sent from 0 is input, and the input measured value is compared with the stored sulfuric acid concentration value (referred to as a reference value). When it becomes equal to the reference value, the heating heater 10 is controlled to raise or lower the heating temperature of the waste sulfuric acid, and at the same time, the first switching valve 23 and the second switching valve 25 of the condensate distribution device 4 are connected. It is designed to control the switching of opening and closing. It is desirable that these switching valves 23, 25 be constructed by using solenoid valves that can be easily opened and closed by an electric signal. Further, in order to make the operating condition of the waste sulfuric acid refining device 1 more suitable, the thermometer 51 capable of measuring the liquid temperature of the waste sulfuric acid 6 in the distillation column 2 and the gas phase pressure in the distillation column 2 can be measured. And a proper pressure gauge 52 are provided, and these measured data are input to the control means 9 to be compared with the proper liquid temperature range and the proper pressure range stored in advance, and the liquid temperature of the waste sulfuric acid 6 and the inside of the distillation column 2 are compared. The heating temperature of the heater 10 for heating and the evacuation speed of the vacuum pump 30 may be controlled so that the pressure in the range is within an appropriate range.

The waste sulfuric acid refining apparatus 1 is operated as follows. First, a desired amount of waste sulfuric acid 6 to be purified is introduced into the distillation column 2 through the waste sulfuric acid supply pipe 12. The concentration of the waste sulfuric acid 6 is about 60 to 90 wt%, the impurities are mostly water, and some metal components and the like are included. Then valve 3
6. The valve 38 is opened, the other valves are closed, the vacuum pump 30 of the exhaust device 5 is driven, and the entire system of the refining device 1 is switched to 20.
The pressure is reduced to less than Torr, preferably about 10 Torr. While maintaining this pressure, the heater 10 for heating is operated to heat the waste sulfuric acid 6 in the distillation column 2. Then, when the waste sulfuric acid 6 is heated to about 130 ° C., the evaporation of water in the waste sulfuric acid 6 becomes severe. The vaporized water vapor passes through the packed bed 11 arranged at the upper part of the distillation column 2 to suppress the amount of entrained sulfuric acid as much as possible, and then is introduced into the condenser 3 through the pipe 17. The water vapor introduced into the condenser 3 comes into contact with the cooling flexible pipe 18 arranged therein, is cooled and condensed, and a liquid containing a large amount of water is stored at the bottom of the condenser 3. Therefore, the valve 25 is opened, and the condensed liquid containing a large amount of water stored in the bottom of the condenser 3 is stored in the drain tank 22 through the pipe 19b. Then, the heating temperature of the waste sulfuric acid 6 in the distillation column 2 is gradually increased to about 190 ° C. As a result, impurities having a boiling point lower than that of sulfuric acid in the waste sulfuric acid 6 are vaporized and introduced into the condenser 3, and are cooled and condensed inside the condenser 3 to form a condensate, which is passed from the bottom of the condenser 3 through the pipe 19b and the valve 25. Further, it is accommodated in the drain tank 22. During this time, the sulfuric acid concentration of the waste sulfuric acid 6 in the distillation column 2 increases.

The sulfuric acid concentration of the waste sulfuric acid 6 is measured one by one by the sulfuric acid concentration measuring means 8. To measure the sulfuric acid concentration of the waste sulfuric acid 6 by the sulfuric acid concentration measuring means 8, the valve 46 of the circulation conduit 16 is opened, the cooler 47 and the liquid feed pump 48 are driven, and the waste sulfuric acid 6 in the distillation column 2 is circulated. It is introduced into the pipe line 16, cooled and stored in the measurement tank 7, and the waste sulfuric acid 6 in the measurement tank 7 is returned to the distillation column 2 through the circulation pipe line 16. The sulfuric acid concentration of the waste sulfuric acid 6 is directly measured by the sulfuric acid concentration meter 50 having the sensor portion 49 arranged in the liquid phase.

When the sulfuric acid concentration of the waste sulfuric acid 6 in the distillation column 2 reaches a predetermined concentration, for example 96 wt% or more, the waste sulfuric acid 6 is further added.
Is heated to 200 ° C or higher, preferably 200 to 210 ° C. As a result, sulfuric acid begins to vaporize in the distillation column 2. The vaporized sulfuric acid is introduced into the condenser 3, cooled, condensed, and becomes a high-concentration (96 wt% or more) sulfuric acid liquid, which flows down to the bottom of the condenser 3.

At the initial stage of the condensation of sulfuric acid, since the sulfuric acid condensed in the condenser 3 flows down, impurities such as water attached to the inner wall of the condenser 3 are entrained, so that the sulfuric acid concentration is higher than the target value. Is also declining. Therefore, the temperature of the waste sulfuric acid 6 in the distillation column 2 is raised and vaporization of the sulfuric acid is started, and then the condensed sulfuric acid is allowed to flow down for a while, and the second switching valve 25 and the pipe 1 are connected.
A cleaning operation of introducing the drain tank 22 through 9b is performed, then the second switching valve 25 is closed, and the first switching valve 2 is closed.
By opening No. 3, the sulfuric acid condensed in the condenser 3 is introduced into the product tank 21 through the pipe 24. The time for the above washing operation is appropriately set according to the production rate of sulfuric acid, the flow path length of the condenser 3 and the like, but is preferably about 60 to 180 seconds from the start of vaporization of sulfuric acid. If the cleaning time is shorter than the above range, impurities such as water in the condenser 3 and the pipe 19 are not sufficiently removed, and the concentration of the product sulfuric acid 40 flowing down into the product tank 21 is lowered. On the other hand, if the washing time is longer than the above range, the recovery rate of the sulfuric acid 40 as a product is lowered, which is not preferable.

Fine particles (mist) of sulfuric acid may be entrained in the gas phase discharged from the condenser 3 through the pipe 20. A mist separator 32 provided between the condenser 3 and the vacuum pump 30 in order to prevent the vacuum pump 30 from being corroded by the sulfuric acid content and being discharged to the outside air.
The gas phase discharged from the condenser 3 is further cooled, and the mist is collected by passing through a filter, and then the alkaline agent and the gas phase are contacted in the sulfuric acid removal cylinder 31 to completely remove the sulfuric acid content. After that, the vacuum pump 30 is inserted.

When the distillation treatment is continued and the waste sulfuric acid 6 in the distillation column 2 decreases and the residual liquid disappears, the heating of the heating heater 10 is temporarily stopped and the first switching valve 23 is closed. As a result, the valve 14 is opened, the waste sulfuric acid to be purified is introduced into the distillation column 2 through the waste sulfuric acid supply pipe 12, and the above-mentioned distillation treatment step is repeated.

When impurities in waste sulfuric acid such as metal salts are accumulated as a residue at the bottom of the distillation column 2 by continuing this waste sulfuric acid refining treatment, the valve 15 is opened to remove the residue. Discharge to the outside. In addition, the product sulfuric acid 4 in the product tank 21
In order to extract 0, the first switching valve 23 and the valve 36 are closed, and the valve 41 is opened to introduce the atmosphere into the product tank 21 through the filter 42 and the pipe 43. After making the pressure equal to the atmospheric pressure, the valve 26 is opened, and the product sulfuric acid 40 is passed through the product sulfuric acid extracting pipe 27.
To the outside. Further, in order to extract the condensate in the drain tank 22, the second switching valve 25 and the valve 38 are closed and the valve 44 is opened to introduce the atmosphere into the drain tank 22 through the filter 42 and the pipe 45. After making the internal pressure of the drain tank 22 equal to the atmospheric pressure by the valve 2
8 is opened, and the condensate in the drain tank 22 is extracted through the discharge pipe 29.

The product sulfuric acid 40 extracted from the product tank 21 is supplied to a production line using sulfuric acid such as a semiconductor factory for reuse.

In the series of distillation operations described above, the sulfuric acid concentration measuring means 8 measures the sulfuric acid concentration of the waste sulfuric acid 6 in the distillation column 2 one by one, and the measured value obtained by the sulfuric acid concentration measuring instrument 50 is controlled by the controlling means. 9 and compares it with the sulfuric acid concentration value (reference value) that has been set and stored in advance, and when the measured value becomes equal to the reference value, the heating heater 10 is controlled to control the heating temperature of the waste sulfuric acid. And a first cleaning valve 23 and a second switching valve 23 of the condensate distribution device 4 after a cleaning operation for elevating the water content and adhering the water adhering to the inner wall of the condenser 3 with the condensed sulfuric acid for a predetermined time. The opening and closing switching with 25 is controlled. As a result, high-concentration sulfuric acid is vaporized from the distillation column 2, condensed in the condenser 3, and water and the like adhering to the inner wall of the condenser 3 is drained off. Sulfuric acid is introduced, and as a result, a high-concentration product sulfuric acid 40 is obtained, and even when the distillation operation is repeated, variations in the concentration of the obtained product sulfuric acid 40 are reduced.

Further, in order to make the operating condition of the waste sulfuric acid refining apparatus 1 more suitable, a thermometer 51 capable of measuring the liquid temperature of the waste sulfuric acid 6 in the distillation column 2 and the pressure of the gas phase in the distillation column 2 And a pressure gauge 52 capable of measuring, respectively, inputting these measurement data into the control means 9 and comparing them with the previously stored proper liquid temperature range and proper pressure range, and the liquid temperature of the waste sulfuric acid 6 and the distillation. The heating temperature of the heater 10 for heating and the exhaust speed of the vacuum pump 30 are controlled so that the pressure in the tower 2 falls within an appropriate range.

The waste sulfuric acid refining apparatus according to this embodiment is provided with the sulfuric acid concentration measuring means 8 for measuring the sulfuric acid concentration of the waste sulfuric acid 6 in the distillation column 2, whereby the waste sulfuric acid in the distillation column 2 is The sulfuric acid concentration of 6 can be measured directly and accurately, and by inputting the measured value into the control means 9 and comparing it with the sulfuric acid concentration value (reference value) set and stored in advance. Since the operation of the apparatus is controlled, it is possible to obtain product sulfuric acid having a higher purity and a stable quality than ever before. In addition, the measurement of the sulfuric acid concentration and the control of the operating state enable automatic operation of the apparatus. Further, the distillation column 2 is measured by the sulfuric acid concentration measuring means 8.
Since the sulfuric acid concentration of the waste sulfuric acid 6 in the inside can be measured directly and accurately, the complicated vapor-liquid equilibrium calculation using the pressure and the liquid temperature in the conventional distillation column 2 becomes unnecessary, and the working efficiency is improved. Quality control can be performed with a stable sulfuric acid concentration in the product sulfuric acid, improving reliability.

In the above-mentioned embodiment, the sulfuric acid refining apparatus of the one-column type vacuum distillation was described, but in addition to this, it can be applied to the two-column type waste sulfuric acid refining apparatus and the continuous type apparatus of the atmospheric distillation method. Needless to say. Further, in this embodiment, the product tank 21 in the condensate distribution device 4 is
Although the first switching valve 23 and the second switching valve 25 are provided on the upstream side of the drain tank 22 and the drain tank 22, a three-way switching valve is used instead of these two switching valves 23, 25. The distribution of the condensate may be switched by the switching operation of the switching valve. Further, by arranging the ultrasonic type sulfuric acid concentration measuring instrument 50 in the product tank 21 and monitoring the concentration of the product sulfuric acid in the product tank 21, the quality control of the product sulfuric acid can be performed finely.

(Experimental Example 1) Waste sulfuric acid was purified by a vacuum distillation method using the apparatus of the present invention of the system shown in FIG. The specifications of the device used are as follows. Distillation column 2: Quartz glass, lower flask volume 20 liters, condenser 3: hard borosilicate glass, water-cooled, product tank 21: hard borosilicate glass, volume 10 liters, measurement tank 7: hard borosilicate Glass, volume 3 liters, vacuum pump 30: dry pump, maximum pumping speed 300
Liter / min. Using a device constructed by connecting these with a hard borosilicate glass tube, the whole system is kept at 15 Torr, and about 80w per time
Waste sulfuric acid having a sulfuric acid concentration of t% was supplied to a 10 liter distillation column, and was discarded by an ultrasonic liquid concentration meter (FUD- / MODEL-10-online manufactured by Fuji Kogyo Co., Ltd.) provided in a concentration measurement tank. While monitoring the sulfuric acid concentration in the sulfuric acid, (a) when the concentration of the waste sulfuric acid is 96 wt% or less, the heating heater is used to maintain the heating temperature of the waste sulfuric acid at 190 ° C., and the condensate at the bottom of the condenser is also heated. The second switching valve 2
Discharge to drain tank 22 from 5. (B) When the concentration of waste sulfuric acid reaches 96 wt% or more, the waste sulfuric acid is heated by a heater for heating so as to raise the heating temperature to about 200 to 210 ° C., and after washing for about 120 seconds, condensation on the bottom of the condenser is performed. The second switching valve 25 was closed and the first switching valve 23 was opened so as to send the liquid to the product tank 21, and the condensate containing high-concentration sulfuric acid was stored in the product tank 21. During this period, the sulfuric acid concentration of the purified sulfuric acid stored in the product tank was measured 12 times at intervals of 2 hours by the titration method and the ultrasonic sulfuric acid concentration meter. Table 1 shows the results.

[0039]

[Table 1]

Comparative Example In order to compare with the above-mentioned device of the present invention, a device of the same standard as the above-mentioned device of the present invention was constructed without using the sulfuric acid concentration measuring means 8 and the control means, and the waste sulfuric acid heating of the distillation column was performed. Temperature 19
Switching from 0 ° C. to 200 to 210 ° C., and switching of the first and second switching valves 23 and 25 in the condensate distribution device (above (a) and (b)), the waste sulfuric acid concentration as a guide The change is that the value obtained from the temperature-pressure-concentration chart shown in FIG. 2 is used as the concentration of waste sulfuric acid by using the values of the pressure and temperature in the distillation column measured by the pressure gauge 52 and the thermometer 51, respectively. The above (a) and (b) were switched and operated. Then, as in the previous method, the sulfuric acid concentration of the purified sulfuric acid stored in the product tank was measured 12 times at intervals of 2 hours by the titration method and the ultrasonic type sulfuric acid concentration meter. The results are shown in Table 2.

[0041]

[Table 2]

As is clear from the measurement results shown in Tables 1 and 2, when the waste sulfuric acid is purified by the apparatus of the present invention, the purified sulfuric acid in the product tank has an average of 12 measurements. The value was about 96 wt%, and the standard deviation was 0.095% (measured by the titration method), which was extremely small. On the other hand, the average value in the comparative device does not reach 96 wt%, and the standard deviation is 3.4 to 4 compared with the device of the present invention.
The concentration of sulfuric acid obtained by the device of the present invention is 5.2 times as large as
It can be seen that the variation is much smaller than the concentration of sulfuric acid obtained by the comparative example device (that is, the conventional device), and it can be seen that the product sulfuric acid of stable quality can be recovered by the device of the present invention. This is because in the conventional device, in the distillation process, the sulfuric acid concentration of waste sulfuric acid, which is the standard for switching from the process of collecting the condensate containing water and impurities to the drain tank to the process of collecting sulfuric acid to the product tank, can be estimated. It is considered that slight air intrusion into the apparatus and measurement error of the thermometer and the pressure gauge cause an error in the sulfuric acid concentration estimated value, and the switching timing does not match. On the other hand, in the device of the present invention, the sulfuric acid concentration of the waste sulfuric acid in the distillation column can be directly measured, so that the measurement error in the conventional device is eliminated or becomes extremely small, and the condensate containing water and impurities is drained. It has become possible to switch from the process of collecting in the tank to the process of collecting sulfuric acid in the product tank at ideal timing. Further, as shown in Table 1 and Table 2, the sulfuric acid concentration of the recovered sulfuric acid was measured by the titration method and the ultrasonic type sulfuric acid concentration meter each time, but there was almost no difference between these values. Therefore, it was confirmed that the sulfuric acid concentration can be accurately measured using the ultrasonic type sulfuric acid concentration meter.

(Other Embodiments) Next, another embodiment of the waste sulfuric acid refining apparatus of the present invention will be described. The waste sulfuric acid refining apparatus in this example is configured with the same components as the apparatus 1 in the previous example shown in FIG. 1, and the packed bed 11 of the distillation column 2 is constructed.
It is characterized in that the upper part, the condenser 3 and the conduit 17 connecting them are made of quartz glass.

Since the atmospheric distillation apparatus is operated at 1 atm or higher, the boiling point of sulfuric acid is not high, and the material of the apparatus is limited to quartz glass. However, this quartz glass is eluted in the distillation column due to corrosion by sulfuric acid and a high temperature of 330 ° C., and a large temperature difference is always generated on the glass surface in the condenser, so Si is eluted from the inner surface of the condenser. As a result,
The product sulfuric acid was contaminated with tens to hundreds of ppb of Si, and it was impossible to purify it to ultra-high purity sulfuric acid having a metal impurity concentration of 0.1 ppb or less. On the other hand, like the waste sulfuric acid refining apparatus of the present embodiment, in a vacuum distillation apparatus that is equipped with an exhaust device 5 and purifies the waste sulfuric acid under a reduced pressure condition in the system, the boiling point of sulfuric acid is 200.degree. The operating temperature is lower than that of the atmospheric distillation apparatus. However, in the conventional vacuum distillation apparatus, hard borosilicate glass (trade name: Pyrex glass) is generally used as the main material, and even if it is operated at a lower temperature than the atmospheric distillation apparatus as described above. , S which is a component in the glass
About several ppb of i, Na, and B were found in the product sulfuric acid, and it was not possible to reach the product sulfuric acid concentration where the impurity concentration was 1 ppb or less.

In this embodiment, the upper part of the packed bed 11 of the distillation column 2, the condenser 3 and the pipe 17 connecting them are made of quartz glass, and the waste sulfuric acid is purified by vacuum distillation. As is clear from the results of Experimental Example 2 below, 0.1 pp for all metallic impurities was obtained by a vacuum distillation type waste sulfuric acid refining apparatus made of quartz glass.
It is possible to obtain high-purity purified sulfuric acid of level b. In addition,
The portion formed of quartz glass is at least the distillation column 2
It is sufficient that the upper part of the packed bed 11 and the condenser 3 and the conduit 17 connecting them are included, and the entire apparatus including these parts may be formed of quartz glass. Hereinafter, experimental examples for demonstrating the effect of the present embodiment will be described.

(Experimental Example 2) Experiment: Comparative Experiment As a test for demonstrating the effectiveness of a vacuum distillation system in which the apparatus material is quartz glass, (A) a vacuum distillation method in which the apparatus material is quartz glass Waste sulfuric acid refining apparatus (configuration is the same as the apparatus of FIG. 1) (B) Vacuum distillation type waste sulfuric acid refining apparatus whose apparatus material is hard borosilicate glass (configuration is the same as the apparatus of FIG. 1) (C) The waste sulfuric acid refining treatment was carried out using three types of equipment, that is, an atmospheric distillation type waste sulfuric acid refining apparatus whose apparatus material is quartz glass (a vacuum distillation apparatus of FIG. 1 from which a vacuum exhaust apparatus and a mist separator are omitted). The outline specifications of the device used are as follows.・ Treatment rate (product sulfuric acid treatment rate) 50 ml / min ・ Recovery rate 95% ・ Sulfuric acid concentration Inlet: 90 wt% Outlet: 96 wt% ・ Power consumption (equipment power) maximum 15 kW ・ Vacuum system: Dry pump Ultimate vacuum: 10 Torr ・Raw material Sulfuric acid a) 90 wt% sulfuric acid solution b) Sulfuric acid / hydrogen peroxide aqueous solution (H ₂ SO ₄ 90 wt%, H ₂ O ₂ 3 wt%)

Of these apparatuses, two kinds of experiments (A) and (B) were conducted in the same manner as the apparatus having the constitution shown in FIG. 1, and the waste sulfuric acid refining apparatus by the atmospheric distillation method shown in (C) was the apparatus shown in FIG. Then, the vacuum pump 30 and the mist separator 32 were removed, and the operation was performed under normal pressure. Table 3 shows the metal analysis results in sulfuric acid as a product obtained by the purification treatment of the 90 wt% sulfuric acid solution performed by the devices (A) to (C). The metal components were analyzed by ICP emission analysis.

[0048]

[Table 3]

From the results of Table 3, it is understood that the product sulfuric acid obtained by the vacuum distillation waste sulfuric acid refining apparatus made of quartz glass: apparatus (A) can achieve the level of 0.1 ppb for all metal impurities. Hard borosilicate glass vacuum distillation waste sulfuric acid refining apparatus: It is understood that Na, Si, and B, which are constituent elements of the hard borosilicate glass, were detected in the product sulfuric acid obtained by the apparatus (B). A level of 0.1 ppb could be achieved for the other components. On the other hand, 230 ppb of Si, which is a constituent material of quartz glass, was detected in the product sulfuric acid obtained by the apparatus (C) for waste sulfuric acid refining apparatus of quartz glass, which is of atmospheric distillation type. Other metal impurities could reach the level of 0.1 ppb as in the devices (A) and (B). From this result, regardless of the material of the equipment and the operation method (reduced pressure and normal pressure), the purification of the waste sulfuric acid by the distillation method completely eliminated the metallic impurities other than the material (glass) components (Na, Si, B) of the equipment. It was confirmed that they could be separated. Further, when comparing the elution amounts of Si, which is the glass component of the equipment material, the waste sulfuric acid refining treatment method by the depressurization method is obviously advantageous, and the highest purity product sulfuric acid was obtained from the equipment (A). Therefore, it can be seen that the waste sulfuric acid refining device made of quartz glass is most effective. Next, depending on the boiling temperature (about 200 ° C. for vacuum distillation and about 330 ° C. for atmospheric distillation) for performing waste sulfuric acid distillation purification, the materials of the distillation column 2, that is, quartz glass and hard borosilicate glass Experiment 2 examined how much the constituent elements would elute.

Experiment The apparatus used in this experiment was the above-mentioned apparatus (A): reduced pressure quartz glass apparatus (boiling temperature of about 200 ° C.) apparatus (B): reduced pressure Pyrex apparatus (boiling temperature of about 200 ° C.) apparatus (C): A refining treatment experiment was performed using the system shown in Fig. 1 using an atmospheric pressure quartz glass device (boiling temperature about 330 ° C), and then the metal components contained in the sulfuric acid concentrated in the distillation column were analyzed by IPC emission spectrometry. Was analyzed. The components to be analyzed are Na, B, and Si, which are constituent components of glass, and Li, which is a standard substance. The waste sulfuric acid solution used in this experiment was used as an internal standard for analytical values in sulfuric acid for electronic industry manufactured by Kanto Chemical Co., Inc.
Was added (46 ppb), all other metal components were 1
It was prepared below ppb. Table 4 shows the metal concentration in the used sulfuric acid solution used.

[0051]

[Table 4]

60 kg of the above sulfuric acid solution was purified by distillation, and the above-mentioned metal components contained in 6 kg of sulfuric acid remaining in the distillation column were analyzed. The results of this analysis are shown in Table 5. In addition, a value obtained by dividing each analysis value by the value of Li as a standard substance is shown, and this value was obtained in order to ignore the influence of the elution amount of the metal component from the glass due to the difference in the concentration rate.

[0053]

[Table 5]

From the results of this experiment, a large amount of Si was stored in the distillation column of the atmospheric pressure type waste sulfuric acid refining apparatus made of quartz glass in the apparatus (C).
It can be seen that is being eluted. And the elution amount of Si of this device (C) is hard borosilicate glass (Pyrex)
14.5 times as much as the amount of Si eluted in the distillation column of the decompression-type waste sulfuric acid refining device (B) made by quartz production, and 57.2 times as much as the amount of Si eluted in the distillation column of the decompression-type waste sulfuric acid purification device (A) made of quartz glass It was found that Si was eluted. This is atmospheric distillation about 330
It is presumed that it is performed at a high temperature of ℃. It was also clarified that metal components other than Si were completely separated by distillation. Further, in an experiment using a waste sulfuric acid refining apparatus [apparatus (B)] made of hard borosilicate glass (Pyrex), it was shown that Na and B are eluted as well as Si is eluted. It was found that the quartz glass vacuum distillation type waste sulfuric acid refining apparatus (A) has the least elution of metal components. From this, in the waste sulfuric acid refining method of the atmospheric pressure distillation method made of quartz glass, since the processing temperature becomes high, a large amount of quartz glass is eluted from the inside of the distillation column, so the wall thickness of the distillation column is inevitably reduced. It has also become apparent that there is a drawback that the replacement cycle of the distillation column is shortened.

From the above experiments and experiments, the following facts were found in the waste sulfuric acid distillation purification apparatus. (1) In comparison with the depressurization method and the atmospheric pressure method, it was found that the atmospheric pressure method had an extremely large amount of Si as a glass component element mixed in the refined product. It is considered that Si elution is promoted by the high boiling temperature. (2) In the comparison of the case where the material of the distillation column is quartz glass and the case of Pyrex glass when the depressurization method is adopted, Pyrex glass has a glass component element S in the sulfuric acid product.
It was found that a large amount of i, B, Na was mixed. (3) It was found that the metal component contained in the waste sulfuric acid supplied to the distillation column was not contained in the refined product by distillation, but was almost separated and remained in the distillation column. (4) From the above, the mixing of the glass component elements contained in the refined product is caused by heating the sulfuric acid vapor vaporized by boiling to a high temperature in the upper part of the distillation column (above the packed bed) and further to the condenser. Therefore, it is determined that the glass component element is dissolved and accompanied. Therefore, it is desirable to use quartz glass with less elution in this portion. For this reason, as a purification distillation apparatus for waste sulfuric acid, a vacuum distillation apparatus is used to prevent metal components from being mixed in the product.The distillation column communicates with the upper part and at least a packed bed disposed in the middle of the distillation column. It was decided to use quartz glass for the condenser and the conduit connecting these.

Experiment The apparatus used in this experiment was the same as that of the apparatus of FIG. 1, and the upper part of the packed bed 11 of the distillation column 2 of the apparatus, the pipe 17 and the material of the condenser 3 were made of quartz glass. It is made of hard borosilicate glass. Then, an experiment was conducted by adopting a reduced pressure method as the treatment.

When the product sulfuric acid obtained by purifying the waste sulfuric acid by the above-mentioned apparatus was analyzed in the same manner as in the experiment, Na and Si, which are the constituent materials of the glass, could reach the level of 0.1 wtppb at 0.5 wtppb or less. It was possible to obtain the same result as the sulfuric acid refined by the waste sulfuric acid refining apparatus made entirely of quartz glass in the apparatus (A). This is shown in Table 6.

[0058]

[Table 6]

As described above, in the vacuum distillation type waste sulfuric acid refining apparatus of the present invention, if at least the upper part of the packed bed of the distillation column, the condenser and the pipes connecting them are made of quartz glass, metal impurities in the sulfuric acid product It is possible to suppress all the components to the 0.1 ppb level. Further, if the waste sulfuric acid is refined using the apparatus of the present invention, the cost of the apparatus itself will be significantly reduced as compared with the vacuum distillation type waste sulfuric acid refining apparatus which is entirely made of quartz glass.

Experiment Next, an experiment for using the device of the present invention will be described. Hydrogen peroxide is added to concentrated sulfuric acid in order to remove organic substances in wafer cleaning and photoresist stripping processes, and hydrogen peroxide is added to sulfuric acid that is treated with a sulfuric acid solution heated to 100 ° C. or higher, An SPM cleaning method is used in which treatment is performed with a sulfuric acid solution heated to a high temperature of 100 ° C. or higher. The concentration of waste sulfuric acid after being used in this SPM cleaning method is a mixed solution of sulfuric acid 60 to 80%, hydrogen peroxide 0.1 to 5.0%, and water. Since the oxidation effect is increased by adding hydrogen peroxide to sulfuric acid, it is considered that the amount of metal components eluted from the inner surface of the glass is increased. Therefore, an experiment for confirming the influence of metal elution from the inner surface of the glass was conducted. The waste sulfuric acid solution used in this experiment was prepared by adding hydrogen peroxide and ultrapure water to special reagent grade sulfuric acid to prepare a solution containing 90 wt% sulfuric acid and 3 wt% hydrogen peroxide. Vacuum distillation of the above waste sulfuric acid solution in which the upper part of the packed bed 11 of the distillation column 2 shown in FIG. 1, the condenser 3 and the conduit 17 connecting them are made of quartz glass, and the other parts are made of hard borosilicate glass. The product sulfuric acid was obtained using the waste sulfuric acid refining device of the method. Table 7 shows the analysis results of the product sulfuric acid.

[0061]

[Table 7]

From the above experimental results, if the waste sulfuric acid solution used in the SPM cleaning method is purified by the vacuum distillation system in the distillation purification apparatus using quartz glass as the main part in this example,
It was confirmed that even if a few percent of hydrogen peroxide was mixed in the raw material sulfuric acid, the product sulfuric acid could be purified to high-purity purified sulfuric acid having an impurity concentration of 0.1 ppb level. That is,
When purifying a waste sulfuric acid solution containing about 3% of hydrogen peroxide discharged by the SPM cleaning method, a high-purity product sulfuric acid can be obtained by the distillation purification apparatus of the present embodiment according to the vacuum distillation method. It was found that the effect of the addition and addition of S on the purified product sulfuric acid is small.

[0063]

As described above, according to the present invention,
Since the sulfuric acid concentration measuring means for measuring the sulfuric acid concentration of the waste sulfuric acid in the distillation column is provided, the sulfuric acid concentration of the waste sulfuric acid in the distillation column can be directly and accurately measured. Further, by inputting the measured value to the control means and comparing it with the sulfuric acid concentration value (reference value) set and stored in advance, the control means for controlling the operation of the apparatus is provided. Therefore, it is possible to stably produce sulfuric acid, which is a product of higher purity and constant quality than before. In addition, the measurement of the sulfuric acid concentration and the control of the operating state enable automatic operation of the apparatus. Further, since the sulfuric acid concentration of the waste sulfuric acid in the distillation column can be directly and accurately measured by the sulfuric acid concentration measuring means, a complicated gas-liquid equilibrium calculation using the pressure and liquid temperature in the conventional distillation column is unnecessary, Work efficiency is improved. Further, when the sulfuric acid concentration is obtained by estimation, the timing of switching from the step of collecting the condensate containing water and impurities in the drain tank due to a measurement error due to pressure fluctuations to the step of collecting the sulfuric acid in the product tank is performed. On the other hand, in the present invention, by directly measuring the sulfuric acid concentration of the waste sulfuric acid, the measurement error is eliminated or becomes extremely small, and the sulfuric acid is collected in the product tank from the step of collecting the condensate containing water and impurities in the drain tank. It becomes possible to switch to the process to be performed at an ideal timing, the dispersion of the sulfuric acid concentration of the product sulfuric acid becomes extremely small even when the repeated operation is performed, and the recovery rate of sulfuric acid becomes good. Further, at least the upper part of the distillation column of the waste sulfuric acid refining device, the condenser, and each part of the pipe connecting them are made of quartz glass, and the refining process of the waste sulfuric acid is carried out by the vacuum distillation system by this device. Even if sulfuric acid vapor comes into contact with the upper part, the condenser, and the pipe connecting them, it is possible to prevent impurities from being eluted from the respective parts, and the content of the metallic element as an impurity is 0.1 ppb level of high purity. Purified sulfuric acid is obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a waste sulfuric acid refining apparatus of the present invention.

FIG. 2 is a graph illustrating a vapor-liquid equilibrium curve used for estimating a sulfuric acid concentration in conventional waste sulfuric acid refining.

[Explanation of symbols]

1 ... Waste sulfuric acid refining device, 2 ... Distillation tower, 3 ... Condenser,
4 ... Condensate distribution device, 5 ... Exhaust device, 6 ... Waste sulfuric acid, 7 ... Measuring tank (sulfuric acid concentration measuring section), 8 ... Sulfuric acid concentration measuring means, 9 ... Control means, 10 ... Heater for heating, 16 ... Circulation line, 21 ... Product tank, 22 ...
Drain tank, 40 ... Product sulfuric acid, 47 ... Cooler, 4
8 ... Liquid feed pump, 50 ... Sulfuric acid concentration meter.

Claims (14)

[Claims] 1. A distillation column containing waste sulfuric acid, a heating means for heating the waste sulfuric acid stored in the distillation column, and a packed bed disposed at the upper part of the distillation column, which is derived from the distillation column. In a waste sulfuric acid refining device equipped with a condenser for cooling and condensing vapor of each component, the waste sulfuric acid in the distillation column is led out, and the distillation column is passed through a cooling unit for cooling the waste sulfuric acid and a waste sulfuric acid concentration measuring unit. A waste sulfuric acid refining apparatus comprising: a circulation pipe provided so as to be returned to the inside; and a sulfuric acid concentration measuring means including a sulfuric acid concentration detector in the waste sulfuric acid concentration measuring unit. 2. The condenser is provided with a condensate distributor for discharging condensed liquid to the outside of the condenser and supplying the condensed liquid to either a drain tank or a product tank. Waste sulfuric acid refining equipment. 3. The waste sulfuric acid refining apparatus according to claim 1, wherein a pump for forcibly flowing the waste sulfuric acid is provided in the circulation pipe of the sulfuric acid concentration measuring means. 4. The waste sulfuric acid refining device according to claim 1, wherein the sulfuric acid concentration detector is an ultrasonic densitometer that detects the sulfuric acid concentration by a change in the propagation velocity of ultrasonic waves. 5. The waste sulfuric acid purification apparatus according to claim 1, further comprising an exhaust device for reducing the pressure inside the distillation column and the inside of the condenser. 6. The waste sulfuric acid refining apparatus according to claim 5, wherein at least each of the distillation column above the packed bed, the condenser, and the conduit connecting them are formed of quartz glass. 7. A distillation column containing waste sulfuric acid, a heating means for heating the waste sulfuric acid contained in the distillation column, and a packed bed disposed at the upper part of the distillation column, which is derived from the distillation column. In a waste sulfuric acid refining device equipped with a condenser for cooling and condensing vapor of each component, the waste sulfuric acid in the distillation column is led out, and the distillation column is passed through a cooling unit for cooling the waste sulfuric acid and a waste sulfuric acid concentration measuring unit. A circulation pipe provided to return the liquid inside, a sulfuric acid concentration measuring means provided with the sulfuric acid concentration detector in the waste sulfuric acid concentration measuring section, and a condenser provided in the condenser, and a condensed liquid is provided outside the condenser. The condensate distribution device that is supplied to either the drain tank or the product tank, and controls the heating of the waste sulfuric acid of the heating means based on the sulfuric acid concentration of the waste sulfuric acid measured by the sulfuric acid concentration measuring means. And adjust the temperature of the waste sulfuric acid in the distillation column, A waste sulfuric acid refining apparatus comprising: a control means for switching and controlling the supply direction of the condensate of the condensate distributor. 8. The waste sulfuric acid refining apparatus according to claim 7, wherein a pump for forcedly flowing the waste sulfuric acid is provided in the circulation line of the sulfuric acid concentration measuring means. 9. The waste sulfuric acid purification apparatus according to claim 7, wherein the sulfuric acid concentration detector is an ultrasonic densitometer that detects the sulfuric acid concentration by a change in the propagation velocity of ultrasonic waves. 10. The waste sulfuric acid refining device according to claim 7, further comprising an exhaust device for reducing the pressure inside the distillation column and the inside of the condenser. 11. The waste sulfuric acid refining apparatus according to claim 10, wherein at least the distillation column above the packed bed, the condenser, and the conduits connecting them are made of quartz glass. 12. Waste sulfuric acid contained in a distillation column having a heating means is heated, and a gas phase discharged from the distillation column is cooled in a condenser to be condensed and liquefied, and purified sulfuric acid is produced from the condensed liquid. In the method for purifying waste sulfuric acid, the waste sulfuric acid in the distillation column is returned to the distillation column through a cooling unit for cooling the waste sulfuric acid and a waste sulfuric acid concentration measuring unit provided with a sulfuric acid concentration detector. The waste sulfuric acid is circulated through a circulation pipe provided in the, and the sulfuric acid concentration of the waste sulfuric acid is measured by the waste sulfuric acid concentration measuring unit, and the measurement result of the sulfuric acid concentration of the waste sulfuric acid is input to the control means, Compared with the sulfuric acid concentration of the waste sulfuric acid that has been set, when the measured sulfuric acid concentration becomes equal to the preset sulfuric acid concentration, the temperature of the waste sulfuric acid is adjusted to the preset waste sulfuric acid distillation temperature. Controls the heating temperature of waste sulfuric acid by heating means Further, the condensate liquefied by the condenser is led out of the condenser and is supplied to either a drain tank or a product tank, and the condensate supply direction of the condensate distributor is switched and controlled. Waste sulfuric acid refining method. 13. The method for refining waste sulfuric acid according to claim 12, wherein the sulfuric acid concentration detector is an ultrasonic densitometer that detects the sulfuric acid concentration by a change in the propagation velocity of ultrasonic waves. 14. The method for purifying waste sulfuric acid according to claim 12, wherein the purification treatment of waste sulfuric acid is performed under reduced pressure.