JP4452956B2 - Method for treating exhaust gas containing organosilicon - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for improving a method for treating exhaust gas containing organic silicon by high-temperature oxidation, and can be suitably applied particularly to high-temperature oxidation treatment of organic silicon-containing exhaust gas in semiconductor production or liquid crystal production. Is.
[0002]
[Prior art]
Conventionally, a high-temperature oxidation method, that is, a combustion method has been widely used as a treatment method for purifying harmful gases containing flammable harmful substances.
[0003]
Such a general high-temperature oxidation treatment method is, for example, according to the flow shown in FIG. 1, and harmful gas is sent to the heat receiving side of the heat exchanger 2 through the blower 1 and indirectly from the high-temperature exhaust gas after treatment. Then, the temperature is raised to a predetermined temperature by a burner 3 that is a heater, the flammable harmful substances are oxidatively decomposed in the high temperature reaction section 4, and the high temperature exhaust gas after treatment is supplied to the heat exchanger 2. Ventilated to the heat dissipation side and released to the atmosphere.
[0004]
In the above, the temperature at the time of oxidative decomposition is generally set to 750 ° C. or higher. Therefore, in the case where the harmful substance in the harmful gas is easily oxidized or the concentration of the harmful substance to be oxidized is low, etc. As a result, harmful substances are completely oxidized and discharged, and clogging on the heat radiation side of the heat exchanger 2 does not normally occur. Conventionally, nothing has been done as a countermeasure against clogging on the heat radiation side of the heat exchanger. It wasn't.
[0005]
However, some of the organic exhaust gas generated in the semiconductor manufacturing process and the liquid crystal manufacturing process may contain a relatively large amount of, for example, hexamethyldisilazane which is a kind of organic silicon. When high-temperature oxidation treatment is performed using the flow shown in -1, a large amount of solid matter adheres to and accumulates on the heat-transfer side heat transfer surface of the heat exchanger 2, and the heat exchanger is clogged in a very short time, and the amount of processing air As a result, there is a problem that sufficient processing cannot be performed.
[0006]
In addition, in the above, when a burner is used as a heater, the burner misfires and incomplete combustion occurs because a large amount of solid matter adheres to and accumulates on the burner metal part in contact with the exhaust gas. There was also a problem of falling into a dangerous state.
[0007]
Furthermore, it is not easy to completely remove the solid matter adhering to the heat transfer surface of the heat exchanger and the burner. In the worst case, it is necessary to replace the heat exchanger and the burner. Had to be expensive.
[0008]
[Problems to be solved by the invention]
The present invention aims to solve the above-mentioned problems, and is also clogged or incompletely burned even when exhaust gas containing a relatively large amount of organic silicon that is difficult to be oxidized is subjected to high-temperature oxidative decomposition treatment. The present invention provides an exhaust gas processing method that does not cause a large amount of repair costs.
[0009]
When examining the method for easily removing deposits generated during high-temperature oxidation treatment of exhaust gas containing organic silicon, the present inventors first analyzed the deposits, and as a result, some deposits were found. However, it has been found that silicon dioxide is essentially the main component.
[0010]
Furthermore, as a result of diligent research regarding the method for peeling and removing the above-mentioned deposit mainly composed of silicon dioxide, the present inventors have sprinkled water on the deposit of silicon dioxide that is not originally compatible with water. Surprisingly, it has been found that water penetrates into the deposit and destroys the shape of the deposit, and the water easily penetrates between the metal such as stainless steel and the deposit to cause the deposit to peel off easily. It was.
[0011]
As a result of further studies based on the above findings, the present inventors have reached the present invention.
[0012]
[Means for Solving the Problems]
That is, the present invention is an exhaust gas treatment method including a step of subjecting exhaust gas containing organic silicon to high-temperature oxidation treatment, and deposits mainly composed of oxides of organic silicon generated in the high-temperature oxidation treatment. An exhaust gas treatment method including a step of removing by water washing is provided.
[0013]
A preferred embodiment of the exhaust gas treatment method of the present invention includes a step of heat exchange treatment between the exhaust gas after the high temperature oxidation treatment and the exhaust gas before the high temperature oxidation treatment.
[0014]
In a preferred embodiment of the exhaust gas treatment method of the present invention, the organic silicon is an organic silicon having an alkylsilane group.
[0015]
In a preferred embodiment of the exhaust gas treatment method of the present invention, the organic silicon oxide is substantially silicon dioxide.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The exhaust gas treatment method of the present invention can be applied to any exhaust gas as long as it contains organic silicon. For example, alcohols, ketones, aliphatic carbonization having a concentration of several thousand ppm or less. The present invention can be suitably applied to exhaust gas containing organic solvents such as hydrogen and aromatic hydrocarbons.
[0017]
The exhaust gas is not limited to the so-called exhaust gas discharged from the exhaust systems of various factories. For example, the exhaust gas containing a low-concentration organic solvent is treated with an adsorption concentrator. As a matter of course, the concentrated gas and the like obtained by the above process include a gas that is not called exhaust gas.
[0018]
The above-described adsorption-type concentrator is as shown in FIG. 3, for example. Exhaust gas containing a low-concentration organic solvent is passed through the adsorption portion of the honeycomb-shaped adsorbent that rotates continuously, purified, and adsorbed. The organic solvent adsorbed on the adsorbent is desorbed by a small amount of high-temperature desorption air that is vented to the desorption portion of the body. Thereby, the adsorbent is continuously regenerated, and the concentrated gas containing the organic solvent is taken out from the adsorption type concentrator. Organic silicon having a relatively low boiling point, such as hexamethyldisilazane or its decomposition product, trimethylsilanol, is concentrated by this adsorption type concentrator. That is, it exists in a relatively high concentration in the concentrated gas, and when this concentrated gas is processed by the high-temperature oxidation method, a large amount of deposits, which are organic silicon oxides mainly composed of silicon dioxide, may be generated. In many cases, the exhaust gas treatment method of the present invention exhibits excellent effects.
[0019]
The exhaust gas treatment method of the present invention can be more suitably applied when the organic silicon contained in the exhaust gas is an organic silicon having an alkylsilane group.
[0020]
Here, the organic silicon having an alkylsilane group means organic silicon having a siloxane bond, a silazane bond, a silanol bond, or the like.
[0021]
Hexamethyldisilazane and its hydrolysis product, trimethylsilanol, are especially used in semiconductor manufacturing processes, liquid crystal manufacturing processes, etc., or are abundantly generated organic silicon, and exhaust gas containing them is oxidized at high temperature. When treated, clogging in the heat exchanger occurs remarkably, and these organic silicons are substances that are extremely difficult to remove from the exhaust gas before the high temperature oxidation treatment. The exhaust gas treatment method of the present invention can be applied particularly preferably when the contained exhaust gas is to be treated.
[0022]
The deposit which is an oxide of organic silicon in the exhaust gas treatment method of the present invention is mainly composed of silicon dioxide.
[0023]
In addition to silicon dioxide, the deposit contains incompletely combusted soot, organic silicon to be treated, chemical changes thereof, and other components in exhaust gas, etc., but silicon dioxide is the main component. As long as the present invention is applicable.
[0024]
The typical shape of the deposit is a solid material in which fine particles are compressed, and such deposit adheres to the inner walls of various pipes, instruments, fixtures, and equipment, and depending on the compressed air and brushing, Often difficult to remove.
[0025]
The high-temperature oxidation treatment in the exhaust gas treatment method of the present invention is not particularly limited as long as it is a treatment method for obtaining a harmless exhaust gas by oxidizing and decomposing a harmful organic solvent contained in the exhaust gas at a high temperature. Any method may be used.
[0026]
In the exhaust gas treatment method of the present invention, the high-temperature oxidation treatment is performed at a high-temperature oxidation treatment temperature, that is, a temperature in the high-temperature reaction part is 750 ° C. or higher, and the residence time of the exhaust gas in this reaction part is 0.5 seconds or more. The high temperature oxidation treatment is preferably performed under conditions of 1.0 second or longer.
[0027]
The heat exchanger used for the heat exchange treatment between the exhaust gas after the high temperature oxidation treatment and the exhaust gas before the high temperature oxidation treatment in the exhaust gas treatment method of the present invention is not particularly limited, for example A flat plate flow heat exchanger (Fig. 4), a multi-tube heat exchanger (Fig. 5) and the like are preferably used.
[0028]
In the present invention, it is more preferable to use a heat exchanger having a structure in which the deposits adhering to the heat exchanger heat-dissipation side heat transfer surface can be easily sprinkled and removed. The distance between the surfaces is relatively wide, and it is particularly preferable because it has a structure in which the deposit can be easily removed by watering.
[0029]
The material of the heat transfer surface of the heat exchanger is preferably made of stainless steel. This is because the stainless steel is not only excellent in heat resistance but also highly effective in preventing corrosion due to water spray.
[0030]
In the exhaust gas treatment method of the present invention, the method for water-washing the deposit containing organic silicon oxide as a main component is not particularly limited. For example, shower-like water is sprayed and applied to the deposit. A method or the like is preferably used. With this method, it is possible to pour water evenly on the sediment deposited on the heat radiation side of the heat exchanger.
[0031]
Hereinafter, the present invention will be described in detail with reference to the drawings.
[0032]
FIG. 2 shows an example of a flow using the processing method of the present invention. The gas to be treated is sent to the heat receiving side of the heat exchanger 2 through the blower 1, indirectly recovering heat from the treated high-temperature exhaust gas, and further heated to a predetermined temperature by the burner 3 as a heater. The The flammable harmful substances are oxidatively decomposed in the high temperature reaction section 4. The high-temperature exhaust gas after the treatment is vented to the heat radiating side of the heat exchanger 2 and released to the atmosphere. The heat exchanger 2 is provided with a watering line 5 for watering the heat radiating side. Moreover, the drain line 6 for discharging | emitting the washing waste water at the time of watering is attached to the heat exchanger heat radiation side.
[0033]
Deposits mainly composed of silicon dioxide adhere to and accumulate on the heat-transfer side heat transfer surface of the heat exchanger 2, clogging occurs on the heat-release side of the heat exchanger, the processing air volume is reduced, and normal high-temperature oxidation treatment is performed. When it is no longer performed, the temperature rise of the gas to be treated by the burner 3 is stopped, the heat exchanger is cooled, and then the blower 1 is stopped. Then, watering is performed from the watering line 5, and the solid substance mainly composed of silicon dioxide deposited on the heat exchanger is washed away. Washing wastewater containing solids mainly composed of silicon dioxide generated at this time is discharged out of the heat exchanger through the drainage line 6.
[0034]
【Example】
Example 1
High-temperature oxidation treatment was performed according to the flow sheet of FIG. 2 using the present invention with respect to exhaust gas of 20 cubic meters per minute containing about 10 ppm of hexamethyldisilazane and about 2000 ppm of an organic solvent mainly composed of isopropyl alcohol. As the heat exchanger 2, a flat plate flow heat exchanger made of stainless steel was used. The burner 3 used LPG as fuel. The temperature of the reaction part 4 was controlled to be 750 ° C.
[0035]
After 10 days of treatment, the treatment air volume decreased by about 10%. Therefore, the burner 3 was stopped and the high temperature oxidation treatment was stopped. The heat exchanger was cooled to about 40 ° C. over about 5 hours. Thereafter, the blower 1 was stopped and the heat exchanger 2 was inspected. As a result, it was confirmed that a large amount of white solid was adhered and deposited on the heat transfer surface heat radiation side of the heat exchanger 2. Therefore, when water was sprayed from the water sprinkling line 5 to the heat exchanger from the upstream side of the heat exchanger 2 side, the white solid adhered to and deposited on the heat exchanger heat sink side was almost completely. Stripped and removed. From the drainage line 6, wastewater in which a large amount of white powder of silicon dioxide was dispersed was discharged. In addition, since it was confirmed that white solid matter adhered to and accumulated in the metal part in contact with the exhaust gas of the burner 3, water was sprayed in the same manner as in the heat exchanger. The white solid that had adhered and deposited was almost completely peeled off. Then, the blower 1 and the burner 3 were restarted, the temperature of the reaction part 4 rose to 750 degreeC of steady process temperature, and the high temperature oxidation process was restarted. The processing air volume was restored to 20 cubic meters per minute, that is, the original air volume at which the processing was started.
[0036]
Analysis of the white solid adhered to and deposited on the heat exchanger 2 and the burner 3 revealed that the main component was silicon dioxide, and the ratio of silicon dioxide was 90% or more.
[0037]
(Comparative Example 1)
For the same exhaust gas as in Example 1, high-temperature oxidation treatment was performed according to the flow sheet of FIG. The temperatures of the heat exchanger 2, the burner 3, the fuel, and the reaction unit 4 were also the same as in Example 1.
[0038]
The butyl acetate removal efficiency at the beginning of the high-temperature oxidation treatment was extremely good at 99% or more. The pressure on the heat dissipation side of the heat exchanger 2 has not been monitored, and the clogging status on the heat exchanger heat dissipation side cannot be grasped. Sufficient oxidative decomposition treatment was not possible. Further, the processing air volume was also reduced to 50% or less at the start of the processing. For this reason, the burner 3 was stopped and the high temperature oxidation treatment was stopped.
[0039]
After that, the heat exchanger 2 was cooled to about 30 ° C., which is not problematic when a person enters the heat exchanger. The cooling took about 6 hours. Thereafter, the blower 1 was stopped, and a person entered the heat exchanger 2 and inspected. As a result, it was found that the heat radiation side was completely clogged. A black substance was deposited on the heat dissipation side of the heat exchanger. When this deposit was analyzed, it was found that these substances were a mixture of carbon caused by soot generated by incomplete combustion of the burner 3 and silicon dioxide which is an oxide of hexamethyldisilazane.
[0040]
(Comparative Example 2)
For the same exhaust gas as in Example 1, high-temperature oxidation treatment was performed according to the flow sheet of FIG. The temperatures of the heat exchanger 2, the burner 3, the fuel, and the reaction unit 4 were also the same as in Example 1.
[0041]
The butyl acetate removal efficiency at the beginning of the high-temperature oxidation treatment was extremely good at 99% or more. Although the pressure on the heat radiation side of the heat exchanger 2 was not monitored, from the result of Comparative Example 1, the burner 3 was stopped and the high-temperature oxidation treatment was stopped one week after the start of the treatment. After that, the heat exchanger 2 was cooled to about 30 ° C., which is not problematic when a person enters the heat exchanger. The cooling took about 6 hours.
[0042]
Thereafter, the blower 1 was stopped and a person entered the heat exchanger 2 and inspected. As a result, it was confirmed that white silicon dioxide was deposited on the heat transfer surface of the heat radiating section. This deposit was first removed with a brush, and then removed with compressed air. However, silicon dioxide is in close contact with the heat transfer surface of the heat exchanger 2, and it is impossible to completely remove the deposit. The time taken to remove the deposit was about 3 hours.
[0043]
Then, the blower 1 and the burner 3 were restarted, the temperature of the reaction part 4 rose to 750 degreeC of steady process temperature, and the high temperature oxidation process was restarted. The time from when the blower 1 was restarted until the temperature of the reaction section 4 reached a steady temperature was about 30 minutes.
[0044]
In removing the silicon dioxide deposited on the heat exchanger, it took about 9 hours and 30 minutes from the discontinuation of the high-temperature oxidation treatment to the resumption.
[0045]
It was also found that a large amount of white powder of silicon dioxide was mixed in the exhaust to the atmosphere for several minutes immediately after the blower 1 was started.
[0046]
Furthermore, when the high-temperature oxidation treatment was continued, when the high-temperature oxidation treatment was performed for about one week, the burner 3 frequently misfired, making it difficult to perform a sufficient high-temperature oxidation treatment. Further, the processing air volume was also reduced to 50% or less at the start of the processing.
[0047]
【The invention's effect】
As described above, according to the exhaust gas treatment method of the present invention, the deposit mainly composed of silicon dioxide generated when the exhaust gas containing organic silicon is subjected to high-temperature oxidation treatment is extremely short and extremely simple. Can be removed.
As described above, the exhaust gas treatment method of the present invention exhibits a great effect particularly in the industrial field of exhaust gas containing organic silicon, such as semiconductor manufacturing and liquid crystal manufacturing. Is great.
[Brief description of the drawings]
FIG. 1 is an example of a flow sheet of an exhaust gas treatment method using a conventional high-temperature oxidation treatment method.
FIG. 2 is an example of a flow sheet of an exhaust gas treatment method using the high temperature oxidation treatment method of the present invention.
FIG. 3 is an example of an adsorption type concentrator.
FIG. 4 is an example of a flat plate flow heat exchanger used in the present invention.
FIG. 5 is an example of a multi-tube heat exchanger used in the present invention.
[Explanation of symbols]
1 Blower 2 Heat Exchanger 3 Heater (Burner)
4 reaction section 5 sprinkling line 6 drainage line

Claims (1)

An exhaust gas treatment method comprising a step of subjecting an exhaust gas containing organic silicon having an alkylsilane group to a high temperature oxidation treatment, and a step of performing a heat exchange treatment between the exhaust gas after the high temperature oxidation treatment and the exhaust gas before the high temperature oxidation treatment A flat plate flow heat exchanger having a heat transfer surface made of stainless steel as a heat exchanger used in the heat exchange treatment, and a flat plate flat flow heat exchanger on the heat radiation side heat transfer in the high temperature oxidation treatment. An exhaust gas treatment method comprising a step of removing, by water cleaning, a deposit that is substantially composed of silicon dioxide, which is an oxide of organic silicon adhering to a surface .

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