JPS6347497B2 - - Google Patents

Description

[Detailed Description of the Invention] <<Industrial Application Field>> The present invention relates to a method for removing toxic gas by dry processing waste gas containing halogen-based toxic gas, including: (1) waste gas and a solid processing agent; (2) Reduce the moisture in the solid processing agent to improve the removal efficiency of toxic gases and reliably reduce the concentration of toxic gases in the waste gas to below the safe permissible limit. To provide a product that can suppress the generation of highly acidic gas due to reaction with a chemical and prevent deterioration of processing equipment due to corrosion.

<<Prior Art>> At present, halogen-based gases are widely used not only for semiconductor applications such as dry etching and doping, but also for optical fibers, excimer lasers, and the like.

However, this halogen-based gas is highly toxic, so after use, it must be diluted with an inert gas or gaseous fluoride, and the halogen-based waste gas must be diluted to a safe low concentration of toxic gases. need to be processed.

As a dry treatment method for waste gas containing halogen-based toxic gases, for example, a method of treating _F2- containing waste gas with soda lime, activated alumina, etc. at room temperature is known. Japanese Patent Publication No. 54-35191 states that _2- containing waste gas is treated with carbonate lime or slaked lime, and Japanese Patent Publication No. 1987-92 states that HF-containing waste gas is treated with activated alumina. Treatment with granular calcined dolomite is disclosed in JP-A-59-150526.

≪Problems to be solved by the invention≫ Therefore, as an example, when examining the conventional method of treating waste gas containing F ₂ gas at room temperature using soda lime, it is found that the concentration of F ₂ gas in the waste gas is relatively high. In the case of high concentration, _F2 gas can be removed to below the allowable concentration; (1) In the case of low concentration, _F2 gas cannot be removed sufficiently as the dilution gas increases, and the removal efficiency is low. (2) The actual situation is that the equipment has progressed to corrosion and cannot withstand long-term treatment.

≪Means for solving the problems≫ The present inventors have identified (1) among the factors that affect the efficiency of dry processing:
Processing temperature is extremely important, and gas flow rate and gas concentration are almost unrelated. (2) Moisture contained in the solid processing agent, that is, free water,
Crystal water has the effect of reducing the contact area in the toxic gas removal reaction, thereby reducing the removal efficiency (3) The above water in the solid processing agent reacts with the halogen gas to form a highly acidic gas , for example, HCl,
We have newly discovered that HF is generated and promotes corrosion of equipment, and based on this discovery, we have completed the present invention.

That is, the present invention provides a dry treatment method for halogen-based waste gas in which waste gas containing halogen-based toxic gas is passed through a processing device filled with a solid processing agent to reduce the concentration of the toxic gas. After dehydrating and drying the soda lime in advance,
This method is characterized by bringing waste gas containing halogen gas into contact with the soda lime at 200 to 300°C.

The waste gas to be treated by the present invention includes Cl ₂ , HCl,
Chlorine-based toxic gases such as BCl ₃ , SiCl ₄ , SiH ₂ Cl ₂ or F ₂ , HF, BF ₃ , SiF ₄ , GeF ₄ , MoF ₆ , WF ₆
It contains at least one type of fluorine-based toxic gas such as.

Soda lime, which serves as a solid treatment agent, is in the form of granules or powder.

The soda lime is subjected to dehydration and drying treatment in advance as a pretreatment when it is brought into contact with waste gas.
This process can be done by vacuum drying at room temperature, but
It is preferable to heat and dry for about 5 hours.

In addition, as mentioned above, the waste gas is the toxic halogen gas emitted from semiconductor factories, etc., and is converted into N ₂ , CO ₂ , He,
Inert gas such as Ar, Ne or CF ₄ , C ₂ F ₆ , SF ₆
It is diluted with a gaseous fluoride such as.

In the removal process, the waste gas may be heated in advance and passed through the reaction tube, or a heater may be set in the reaction tube to heat it to a predetermined temperature.

If the temperature of the removal treatment is lower than 200°C, the removal efficiency will decrease, and if it is higher than 300°C, the running cost will increase, so a temperature of 200 to 300°C is preferable.

≪Operation≫ First, the soda lime is subjected to a pretreatment of dehydration and drying, so that the moisture contained inside, mainly free water, can be lowered in advance. Since the temperature is kept at a high temperature of ~300℃, residual moisture in soda lime, mainly crystallization water, can be liberated and evaporated.

Therefore, the surface of soda lime can be prevented from being covered with moisture, and a large surface area of soda lime that can come into contact with waste gas can be secured.

In addition, as mentioned above, at the stage where the waste gas comes into contact with soda lime, most of the moisture in the soda lime is removed, so harmful gases in the waste gas, for example,
Cl ₂ , F _2, etc. react with this moisture and become highly acidic.
It also eliminates the generation of HCl and HF gases that corrode processing equipment.

≪Effects of the invention≫ (1) Since a large surface area of soda lime that can come into contact with waste gas can be secured, the removal efficiency of harmful gases is increased, and even in the case of waste gas containing a low concentration of harmful gases, this can be sufficiently tolerated. Can be removed to a concentration below the limit.

(2) Even if waste gas comes into contact with soda lime, the generation of highly acidic gas can be prevented, eliminating corrosion of the processing equipment and preventing deterioration, thereby enabling long-term use of the equipment. do.

≪Example≫ Using the following experimental equipment, the pretreatment for dehydrating and drying soda lime was performed and was not performed, and the temperature when bringing the waste gas into contact with soda lime,
Experiments were conducted to determine the rate of removal of harmful gases from waste gas when the gas flow rate and type of waste gas were varied.

As shown in Fig. 1, the experimental apparatus consists of a reaction column 1,
Consisting of a dilution gas supply source 2, a halogen gas supply source 3 to be treated, a raw material gas supply line 4, and a gas chlorine line 5, the reaction tube 1 is a cylindrical body made of SUS316 with a length of 495 mm and an inner diameter of 53 mm, near the center. This is a vertical fixed bed type reactor filled with granular soda lime 20 and having an intake chamber 7 and a clean air chamber 8 formed at both ends through filters 6, respectively.

Gas supply lines 10 and 11 are led out in parallel from the dilution gas supply source 2 and the halogen-based gas supply source 3, and a variable flow rate valve, a flow meter, etc. are interposed in these lines, and then a single raw material gas supply line 4 is connected. are integrated and connected through the intake chamber 7 of the reaction tube 1, so that an inert gas such as a halogen gas diluted with _N2 gas (hereinafter referred to as raw material waste gas) can be supplied to the reaction tube 2. .

In addition, a gas chlorine line 5 is installed in the clean air chamber 8 of the reaction tube 1.
A gas chromatograph 12 and a flow meter 14 are connected to the gas chromatograph line 5, and the flow rate of the raw material waste gas permeating into the clean air chamber 4 through the soda lime layer 20 and the concentration of halogen-based gas in the gas are measured respectively. ,
calculate.

Incidentally, reference numeral 15 is a heater for heating the reaction tube 1.

Experimental example 1 A reaction tube was filled with 600g of granulated soda lime that had been heated and vacuum dried at 300℃ for 5 hours, and the reaction tube was heated to 300℃.
Cl 2 gas heated to ℃ and diluted to 14% with N ₂ gas is continuously flowed into the reaction column at a flow rate of 0.6 m/min, and the concentration of Cl ₂ gas in the waste gas is _0.5 ppm (ACGIH TLV
The amount of raw material waste gas supplied was measured until reaching the voluntary standards (see the voluntary standards by the Institute of Health and Welfare, Inc.).

In addition, in a comparative example, 600 g of soda lime was filled into the reaction column without dehydration and drying, and then
The same treatment as above was performed.

The amount of raw material waste gas supplied is 1 kg of soda lime.
The reconverted numerical values are shown when used (the same applies to the following experimental examples).

FIG. 2 is a chart showing the results, and shows that the supply amount of the present invention is approximately six times that of the comparative example, and it can be seen that the influence of pretreatment on removal efficiency is unexpectedly large.

Experimental example 2 Pretreatment was performed in the same manner as in experimental example 1, and the gas flow rate was
Set at 0.5 m/min and diluted to 2% with _N2 gas.
Using BCl ₃ gas as raw material waste gas, the temperature of the reaction column is
The amount of raw material waste gas supplied was measured at four stages: 150°C, 200°C, 250°C, and 300°C.

FIG. 3 is a chart showing the results, and it can be seen that the amount of raw material waste gas supplied increases as the processing temperature increases.

Looking at the change in the supply amount of raw material waste gas from 150°C to 300°C, the processing capacity gradually increases from 200°C to 250°C to 300°C, but shows a rapid increase from 150°C to 200°C.

Therefore, the processing capacity is still not substantially sufficient at 150°C, and the processing temperature should be set at 200°C or higher.

Incidentally, if the treatment temperature is higher than 300° C., the running cost increases as described above, which is not economically preferable.

Experimental Example 3 Pretreatment was performed in the same manner as in Experimental Example 1, the temperature of the reaction column was set at 300°C, and Cl ₂ diluted to 14% with N ₂ gas was used.
Gas is used as raw material waste gas, 0.2m/min, 0.6m/mi
The gas flow rate was varied in three stages of n and 1.0 m/min, and the gas was supplied to the reaction column, and the amount of raw material waste gas supplied at each flow rate was measured.

Figure 4 is a chart showing the results, and shows that the feed rate of raw material waste gas hardly changes depending on the gas flow rate, and in actual waste gas treatment, the amount of treatment per unit time and the dilution concentration of raw material waste gas are It can be seen that even if the gas flow rate is changed to match the size of the gas, the waste gas treatment capacity remains the same.

Experimental example 4 The pretreatment and gas flow rate were set to 0.5 m/min, and the temperature of the reaction tube was set to 300℃, and the amount supplied to the clean air chamber was determined by changing the type of raw material waste gas flowing into the reaction tube. It was measured.

The raw material waste gas is F ₂ , HF, BF ₃ , SiF ₄ , GeF ₄ ,
_WF6 , _MoF6 , _Cl2 , HCl, _{BCl3 , SiCl2} , _SiH2Cl2
Each of these was diluted to 2% with N ₂ gas as a single type of gas.

Figure 5 is a diagram showing the results, and shows that if soda lime is used as a solid treatment agent, the soda lime is pretreated by dehydration and drying, and the removal treatment is performed at 300℃, the harmful gases can be reduced to below the allowable concentration. It can be seen that the supply amount of raw material waste gas that can be continuously processed exceeds 700 liters, including all types of toxic halogen gases.

In particular, when the toxic gas is HF, _F2 or HCl, the amount of waste gas supplied is greater than 10,000 liters.

Therefore, by employing the treatment method of the present invention, raw material waste gas can be efficiently removed to a safe low concentration regardless of the type of toxic halogen gas.

Experimental Example 5 A reaction tube was filled with soda lime that had been dehydrated and dried at 300°C for 5 hours, heated to 300°C, and N ₂
SiF ₄ gas diluted to 5% with gas was supplied to the reaction column until the concentration of SiF ₄ gas in the clean air chamber reached the allowable concentration.

In addition, as a comparative example, soda lime that had been dehydrated and dried at 150°C for 5 hours was filled into the reaction tube, and the reaction tube was opened.
After heating to 150°C, the same treatment as above was used.

As a result, no abnormality was observed inside the reaction column when pretreatment and removal treatment were performed at 300℃, but when pretreatment and removal treatment were performed at 150℃, there was no abnormality observed inside the reaction column. Occurrence of white powdery deposits was observed.

FIG. 6 is an X-ray diffraction diagram of the deposit (Cu is used as a target), and according to the diagram, remarkable absorption peaks are observed at diffraction angles of 18 degrees, 22 degrees, and 34 degrees.

On the other hand, using Cu as the target, _FeSiF6・
When performing an X-ray diffraction experiment on 6H ₂ O, the diffraction angle was 18.5 degrees,
Since clear absorption peaks appear at 21.3 degrees and 33.9 degrees, the deposits can be fixed on FeSiF ₆ 6H ₂ O.

From this, it can be estimated that the following reaction will proceed when the temperature conditions for the pretreatment and removal treatment are as low as 150°C.

SiF ₄ +2H ₂ O→SiO ₂ +4HF ...(1) Fe+2HF→FeF ₂ +H ₂ ...(2) FeF ₂ +SiF ₄ +6H ₂ O→ FeSiF ₆・6H ₂ O ...(3) That is, heating of soda lime If this is not carried out sufficiently, a considerable proportion of moisture, specifically free water and crystallized water, will remain in the soda lime, and this moisture will react with SiF ₄ in the raw material waste gas to produce HF. (See reaction formula (1)), Fe, which is the material of the processing equipment, is
is corroded and becomes iron fluoride (see reaction formula (2)),
It is thought that a deposit called FeSiF ₆ .6H ₂ O was then formed with SiF ₄ (see reaction formula (3)).

Therefore, the occurrence of such deposits containing FeSiF ₆ .6H ₂ O as a component is evidence that corrosion of the processing equipment is proceeding above all else.

On the other hand, pre-treatment is performed and removal treatment is carried out at 300℃.
It can be seen that if the treatment is carried out at a high temperature of 1, no occurrence of the deposits is observed, and therefore corrosion of the processing equipment can be prevented.

[Brief explanation of the drawing]

Figure 1 is a schematic explanatory diagram of the experimental equipment for the method of the present invention, Figure 2 is a chart showing the difference in removal processing capacity depending on the presence or absence of pretreatment, and Figure 3 is the removal processing capacity when the removal processing temperature is changed. Figure 4 is a diagram showing the removal capacity when changing the gas flow rate, Figure 5 is a diagram showing the removal capacity when the type of raw material waste gas is changed, and Figure 6 is a graph showing the experimental results. It is an X-ray diffraction diagram of the deposit obtained in . DESCRIPTION OF SYMBOLS 1... Reaction column, 2... Dilution gas supply source, 3... Halogen gas supply source, 4... Raw material gas supply line, 20
...soda lime.

Claims (1)

[Scope of Claims] 1. In a dry treatment method for halogen-based waste gas in which waste gas containing halogen-based toxic gas is passed through a processing device filled with a solid processing agent to reduce the concentration of the toxic gas, A dry treatment method for halogen-based waste gas, which comprises using soda lime, dehydrating and drying the soda lime in advance, and then bringing the waste gas containing halogen-based gas into contact with the soda lime at 200 to 300°C. 2. The method for dry treatment of halogen-based waste gas according to claim 1, characterized in that soda lime is dehydrated and dried at 300°C. 3 Halogen-based toxic gases include Cl ₂ , HCl, BCl ₃ ,
_SiCl4 , _SiH2Cl2 , F2 _, HF, _BF3 , _SiF4 , _{GeF4 ,}
The method for dry treatment of halogen-based waste gas according to claim 1 or 2, characterized in that the method is at least one of MoF ₆ and WF ₆ .