JP3559076B2 - Sulfuric acid distillation apparatus and sulfuric acid distillation method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a sulfuric acid distillation apparatus that regenerates and uses sulfuric acid after washing treatment. Various substrates after surface treatment such as polishing are subjected to cleaning treatment such as degreasing and acid cleaning, and sulfuric acid (H ₂ SO ₄ ) is generally used for acid cleaning.
[0002]
For example, for silicon (Si) on which a semiconductor integrated circuit is formed, a single crystal ingot formed by a pulling method (Czochralski method) or the like is sliced to a thickness of about 500 μm, and then polished to form a smooth wafer. Then, cleaning is performed using an oxidizing agent obtained by adding hydrogen peroxide (H ₂ O ₂ ) to concentrated sulfuric acid, and a process of dissolving and removing contaminants and abrasives attached to the wafer surface is performed. I have.
[0003]
Sulfuric acid that has been treated in this way may be discarded as it is, but since it has a high concentration of sulfuric acid as the main component, it is subjected to distillation and regeneration to prevent pollution and economical aspects. I have.
[0004]
[Prior art]
FIG. 2 is a cross-sectional view showing the configuration of a conventional sulfuric acid distillation apparatus, which is composed of two parts, a low boiling point distillation column 1 and a high boiling point distillation column 2.
[0005]
Hereinafter, the case of the sulfuric acid waste liquid used for cleaning the Si wafer will be described. The sulfuric acid waste liquid is injected into the flask 2 through the inlet 3 provided in the flask 2 of the low boiling point distillation tower 1 through the first cock 4, The first distillation column 6 at the top of the first flask 2 is provided with a first condenser 7 for cooling, a first tray 8, and a first pan 5. An outlet tube 9 and a first receiver 10 are provided.
[0006]
Further, the high-boiling point distillation column 2 is connected to the low-boiling point distillation column 1 via a second cock 12 by a connecting pipe 13, and the second distillation column 14 is similarly connected to a second condenser 15 for cooling. A second tray 16, a second outlet pipe 17, and a second receiver 18 are provided.
[0007]
The second flask 19 has a discharge port 21 through a third cock 20, and is configured to be heated by a second heater 22.
Then, as a distillation procedure, first, the first cock 4 is opened, the sulfuric acid waste liquid 24 is injected from the injection port 3, and the cooling water 25 is supplied to the first condenser and circulated to 100 ° C. or higher. The water (low boiling point solution) contained in the sulfuric acid waste liquid 24 is distilled and collected in the first receiver 10 to be separated.
[0008]
After removing the water contained in the sulfuric acid waste liquid 24 in this way, the second cock 12 is opened, and the sulfuric acid waste liquid 24 is transferred from the first flask 2 to the second flask 19 by the connecting pipe 13. While the second condenser 15 is being cooled by the cooling water 27, the sulfuric acid waste liquid 24 is heated by the second heater 22 to a temperature (for example, 360 ° C.) higher than the boiling point of sulfuric acid, thereby distilling sulfuric acid. It is stored in the receiver 18 and separated.
[0009]
The high boiling point sulfate remains at the bottom of the second flask 19, which is separated from the outlet 21 by opening the third cock 20.
As described above, conventionally, the sulfuric acid waste liquid has been regenerated by the two-stage distillation method.
[0010]
[Problems to be solved by the invention]
As described above, a two-stage distillation method is used for the conventional regeneration of sulfuric acid waste liquid.
However, there is an economical problem such as using two heaters. Therefore, the problem is to regenerate sulfuric acid by single distillation.
[0011]
[Means for Solving the Problems]
The above-mentioned problem is that a sulfuric acid distillation region heats a container containing a sulfuric acid stock solution to be distilled to vaporize a stock solution component containing sulfuric acid,
Means for preventing the undiluted solution from being mixed into the distillation region by boiling the undiluted solution;
Means for liquefying the sulfuric acid vapor to obtain sulfuric acid of a target concentration, and means for refluxing sulfuric acid of a target concentration or less to a stock solution,
Further, at least a means for liquefying the low-boiling component in the source solution whose main component is water is a distillation region of the low-boiling component,
The problem can be solved by forming a sulfuric acid distillation apparatus by integrating a sulfuric acid distillation region and a distillation region with a component having a boiling point lower than that of sulfuric acid with a single distillation column.
[0012]
[Action]
The present invention provides a method of regenerating a sulfuric acid waste liquid by a simple distillation method by providing a sulfuric acid distillation area near a flask containing the sulfuric acid waste liquid, while providing a distillation area for low-boiling components (water) at a distance from the flask. It realizes one distillation.
[0013]
Here, sulfuric acid is a strong acid that decomposes at 340 ° C., but does not show a constant boiling point because it is an azeotrope. For example, the concentration of commercially available concentrated sulfuric acid is 97%, and when heated, it is reduced from about 290 ° C. It decomposes by releasing sulfur trioxide (SO ₃ ), and has a property that the boiling point increases from 315 ° C. to 338 ° C. and the concentration increases to 98.3%.
[0014]
Thus sulfuric acid is composed of _SO 3 -H ₂ O _{system, H 2 SO 4 -H 2 O} ( boiling point 290 ° _C.) in addition to _H 2 SO ₄ is in this system, _{H 2} SO 4 -2H ₂ O (boiling point 167 ° C.) is present and each is distilled at that temperature. Therefore, in order to obtain concentrated H ₂ SO ₄ , it is necessary to heat to at least 300 ° C. or higher.
[0015]
However, in this heating process, hydrates such as H ₂ SO ₄ —H ₂ O and H ₂ SO ₄ -2H ₂ O are distilled. Therefore, when trying to obtain a H ₂ SO ₄ composition, It is necessary to keep other hydrates from going to the distillate receiver and to proceed with the dehydration of this hydrate and eventually to H ₂ SO ₄ for distillation.
[0016]
When the sulfuric acid waste liquid is heated to 300 ° C. or higher, the waste liquid may be scattered to the distillation region due to boiling and mixed into the distillate, and it is necessary to form a single distillation column in consideration of these.
[0017]
【Example】
FIG. 1 is a sectional view of a single distillation type sulfuric acid distillation apparatus according to the present invention.
That is, the sulfuric acid distillation apparatus is made entirely of quartz, the distillation flask 30 has a distillation column 31, an inlet 32 for supplying the sulfuric acid waste liquid 24, and a reflux pipe 33 for refluxing the sulfuric acid hydrate. It is configured.
[0018]
Here, the distillation column 31 includes a sulfuric acid distillation region 34 and a low-boiling-point component distillation region 35, and the sulfuric acid distillation region includes a first condenser 36, a first thermometer 37, and a second thermometer 38, Measure the steam temperature during sulfuric acid distillation.
[0019]
A first tray 40 is provided below the first condenser 36, and a sulfuric acid receiver 42 is provided through a first outlet pipe 41. In addition, a first cock 43 is provided in the middle of the first outlet pipe 41, and a second cock 44 is provided in the return pipe 33.
[0020]
Next, there is a second condenser 45 in the low boiling point distillation region 35, and a second receiver 46 below the second condenser 45.
Further, a discharge port 49 for taking out a waste liquid through the third cock 48 is provided below the flask 30, and a heater 50 is provided so as to cover a lower portion of the flask 30.
[0021]
Note that a porous filter 52 is provided below the sulfuric acid distillation region 34 of the distillation tower 31 to prevent splashes of boiling sulfuric acid waste liquid from entering the sulfuric acid distillation region 34 and accumulating in the first tray 40.
[0022]
Here, the operation procedure of this distillation apparatus is as follows. After opening the fourth cock 51 connected to the inlet 32 and injecting the sulfuric acid waste liquid 24 into the flask 30, the fourth cock 51 is closed, and the heater 50 is energized. To heat the waste liquid 24.
[0023]
A refrigerant having a temperature equal to or higher than the boiling point of water and equal to or lower than the boiling point of sulfuric acid dihydrate (167 ° C.) is circulated through the first condenser 36 in the sulfuric acid distillation area 34. In addition, water is circulated through the second condenser 45 in the low-boiling-point distillation area 35.
[0024]
In such a state, when the temperature of the sulfuric acid waste liquid 24 reaches 100 ° C., the low-boiling component, that is, water starts to boil, and the steam passes through the filter 52 and the first condenser 36 and reaches the low-boiling component distillation region 35. The water is cooled in the second condenser 45 and becomes water and accumulates in the second receiver 46.
[0025]
Next, when free water evaporates and disappears in the sulfuric acid waste liquid 24, the liquid temperature rises to 167 ° C. and evaporation of sulfuric acid dihydrate (H ₂ SO ₄ -2H ₂ O) starts. As a refrigerant flowing through the first condenser 36, for example, a fluorine-based inert organic solvent having a boiling point of 215 ° C. (product name: Fluorinert FC-70, manufactured by 3M Company) is kept at 150 ° C. and circulated. Is distilled and accumulates in the first tray 40, but is returned to the flask 30 by closing the first cock 43 in the first outlet pipe 41 and opening the second cock 44 in the reflux pipe 33. This is repeated, but the steam temperature of the dihydrated sulfuric acid and the steam temperature after the distillation are measured by the first thermometer 37 and the second thermometer 38 in advance.
[0026]
Here, since water is gradually removed in the process of repeating the reflux, the equilibrium of the sulfated dihydrate is displaced to change to the sulfated monohydrate (H ₂ SO ₄ —H ₂ O). The temperature rises to 290 ° C., and evaporation of the sulfuric acid monohydrate starts, and is cooled by the first condenser 36 and accumulated in the first pan 40. However, the first cock 43 is closed and the second The cock 44 is opened, and the sulfuric acid monohydrate is refluxed to the flask 30.
[0027]
When the reflux is continued in this manner, the equilibrium of the sulfuric acid monohydrate gradually shifts, and the temperature of the sulfuric acid waste liquid 24 rises. When the temperature measured by the first thermometer exceeds 300 ° C., the steam is converted into sulfuric anhydride. Therefore, the first cock 43 is opened, the second cock 44 is closed, and the sulfuric acid is accumulated in the sulfuric acid receiver 42 through the first outlet pipe 41.
[0028]
When the distillation is continued in this way, since the sulfate remaining at the bottom of the flask 30 is a high-boiling sulfate, the third cock 48 is periodically opened and removed from the outlet 49.
[0029]
By taking such a method, regeneration of concentrated sulfuric acid is possible.
[0030]
【The invention's effect】
By implementing the present invention, concentrated sulfuric acid can be regenerated with less power than before and used repeatedly.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a configuration of a sulfuric acid distillation apparatus according to the present invention.
FIG. 2 is a cross-sectional view showing a configuration of a conventional sulfuric acid distillation apparatus.
[Explanation of symbols]
24 Sulfuric acid waste liquid 30 Flask 31 Distillation tower 33 Reflux pipe 34 Sulfuric acid distillation area 35 Low boiling point component distillation area 36 First condenser 37 First thermometer 38 Second thermometer 40 First pan 41 First outlet pipe 42 Sulfuric acid receiver 43 First cock 44 Second cock

Claims (2)

A device that obtains sulfuric acid by distilling sulfuric acid waste liquid,
A sulfuric acid distillation region and a distillation region of a component having a lower boiling point than the sulfuric acid are formed integrally by a single distillation column, and the sulfuric acid distillation region is
Means for heating the container containing the undiluted solution to evaporate the undiluted component containing sulfuric acid;
Means for preventing undiluted components from being mixed into the distillation zone by boiling the undiluted solution;
Means for liquefying the sulfuric acid vapor to obtain sulfuric acid of a target concentration, and for refluxing sulfuric acid of a target concentration or less to a stock solution
And the distillation region of low-boiling components is
Means for distilling low-boiling components in a source liquid mainly composed of water. A step of heating the undiluted solution to distill a low-boiling component containing water as a main component,
After the sulfuric acid hydrate evaporating from the undiluted solution is distilled by a refrigerant maintained at a temperature equal to or lower than the boiling point of sulfuric acid dihydrate, the sulfuric acid hydrate is refluxed to the undiluted solution to increase the sulfuric acid concentration. Process and
A sulfuric acid distillation method comprising:

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