JP2010179249A - Apparatus and method for decomposing perfluoro compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for decomposing perfluoro compounds, in which the HF corrosion of a member of a cooling unit, which is used for cooling a high-temperature gas containing HF of high concentration, is alleviated and to provide a method for decomposing perfluoro compounds by using the apparatus for decomposing perfluoro compounds. <P>SOLUTION: The apparatus for decomposing perfluoro compounds is provided with: a decomposition unit for decomposing the perfluoro compounds in the gas to be treated; the cooling unit for wetly cooling the gas generated by decomposing the perfluoro compounds; and an acidic gas removal unit for removing an acidic gas which is generated by decomposing the perfluoro compounds and contains HF. A HF neutralizing agent is added to the cooling unit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a perfluoro compound decomposition treatment apparatus and a decomposition treatment method for decomposing exhaust gas containing a fluorine compound such as perfluoro compound discharged from a semiconductor or liquid crystal manufacturing factory.

In a semiconductor or liquid crystal manufacturing process, a fluorine compound gas, particularly a perfluoro compound (hereinafter referred to as PFC) is usually used for etching or cleaning. Examples of PFC include CF ₄ , C ₂ F ₆ , C ₃ F ₈ , CHF ₃ , C ₄ F ₈ , SF ₆ and NF ₃ . PFC is a global warming gas with infrared absorption several thousand to several tens of thousands times that of carbon dioxide (CO ₂ ), and its emission was restricted worldwide by the Kyoto Protocol issued in February 2005. In the etching or cleaning process, only a part of the introduced PFC is used, and most of the PFC is discharged as exhaust gas. Thus, the PFC discharged to the atmosphere needs to be exhausted after being removed or decomposed.

  As a PFC treatment method, a catalyst method, a combustion method, a plasma method, and the like are known. In any PFC decomposition method, acidic gases such as SOx, NOx, and HF are generated after PFC decomposition. These acid gases must be removed before the exhaust gas is released into the atmosphere. In any of the above methods, PFC is decomposed at a high temperature of 700 ° C. or higher. Therefore, the exhaust gas temperature after PFC decomposition is also high, and it is necessary to cool it before releasing into the atmosphere. As the acid gas removal after the PFC decomposition and the exhaust gas cooling method, as disclosed in Patent Document 1, a wet removal apparatus is generally used.

  In the method of Patent Document 1, since a large amount of water is required for acid gas removal and gas cooling, a large amount of waste liquid is generated after the treatment. For this reason, a large amount of cost is required for waste liquid treatment, and at the same time, the risk of environmental pollution is high. Therefore, from the viewpoint of zero emission, there is an increasing need to reduce the amount of waste liquid from the PFC decomposition apparatus.

  As a high-temperature gas waste heat method of 500 ° C. or higher, the amount of industrial water necessary for cooling and the amount of waste water generated after gas cooling can be greatly reduced by using only the latent heat of vaporization of water (Patent Document 2). ). However, the method using only the latent heat of vaporization takes longer to cool the gas than the scrubber type cooling method using latent heat of vaporization and sensible heat. Therefore, the apparatus has a high temperature region of 500 ° C or higher and 100 ° C or lower. The low temperature region is mixed.

  Moreover, in the case where acidic gas such as HF is mixed in the exhaust gas at a high concentration (1 vol% or more) handled in the present invention, acid resistance is required for the members of the cooling device. Therefore, in order to apply a cooling device that uses only latent heat of vaporization, such as a cooling tower, to a system containing a high concentration of acid gas, the selection of the member becomes an important factor, and the specifications required for the member As mentioned above, it has acid resistance in a wide temperature range, particularly in a low temperature range of 200 ° C. or less where water condensation is a concern.

JP 2006-75743 A JP-A-11-37449

  An object of the present invention is to provide a perfluoro compound decomposition treatment apparatus and a treatment method using the same, which can reduce HF corrosion of apparatus members in a high-temperature gas cooling apparatus containing a high concentration of HF.

  That is, the perfluoro compound decomposition treatment apparatus of the present invention includes a decomposition apparatus for decomposing perfluoro compound in a gas to be treated, a cooling apparatus for cooling the gas after decomposing the perfluoro compound by a wet method, An acid gas removing device for removing an acid gas containing HF generated after decomposing the perfluoro compound, and a perfluoro compound decomposing apparatus, wherein an HF neutralizing agent is added to the cooling device. And

  The perfluoro compound decomposition method of the present invention includes a decomposition step of decomposing the perfluoro compound in the gas to be treated, a cooling step of cooling the gas after decomposing the perfluoro compound by a wet method, An acid gas removing step of removing an acid gas containing HF generated after decomposing the perfluorocompound, wherein the HF neutralizing agent is added in the cooling step. To do.

  According to the present invention, the concentration of acidic gas in the exhaust gas after PFC decomposition can be reduced, and HF corrosion of the cooling device can be mitigated.

It is a system flow figure showing an example of the processing method of the present invention. It is a system configuration figure showing an example of a processing device of the present invention. It is the test equipment figure used for (Test example 1). It is the test equipment figure used for (Test example 2). It is a test result of (Test Example 2). It is a test result of (Test Example 2). It is a test result of (Test Example 2).

  Hereinafter, the present invention will be described in detail.

  FIG. 1 is a system flow showing an example of the processing method of the present invention. This system consists of a PFC decomposition process, a gas cooling process, and an acid gas removal process. The gas to be treated including PFC discharged from the semiconductor or liquid crystal manufacturing process is sent to the PFC decomposition step, where the PFC is decomposed and removed. The exhaust gas after PFC decomposition is sent to a gas cooling step, and a high temperature gas of 500 ° C. or higher is cooled. At that time, an HF neutralizing agent is added to the water sprayed in the gas cooling step. Finally, the exhaust gas is sent to the acid gas removal step, and the acid gas that has not been removed in the cooling step is neutralized and removed, rendered harmless, and then discharged to the atmosphere.

FIG. 2 is a system configuration diagram showing an example of the processing apparatus of the present invention. This system includes a wet removal device 200, a catalytic reaction vessel 210, a temperature reducing tower device 220, an acid gas removal device 230, an exhaust facility 240, and a neutralizing agent supply process 250. The PFC-containing gas is sent to the wet removal apparatus 200, and the acidic gas in the etching exhaust gas such as solids and SiF ₄ is removed. The gas discharged from the wet removal apparatus 200 is sent to the catalytic reaction tank 210, and the PFC in the gas to be treated is decomposed and removed. At that time, reaction water 30 and air 11 are supplied as reaction aids. When PFC is decomposed, acidic gases HF, SOx and NOx are generated. The gas after passing through the catalytic reactor 210 is as high as 400 to 700 ° C. Next, the gas after passing through the catalytic reaction vessel 210 is sent to the temperature reducing tower device 220 where it is cooled to about 200 ° C. At this time, the spray sprayed from the temperature reducing tower device 220 is supplied from the neutralizing agent supply step 250 and sprays water containing the HF neutralizing agent. The gas discharged from the temperature-decreasing tower device 220 is sent to the acid gas removing device 230, detoxified and then discharged.

  As the HF neutralizing agent sprayed from the temperature reducing tower device, alkali metal and alkaline earth metal hydroxides, carbonates and oxides, ammonia and urea can be used, but in the case of compounds having low water solubility, It is not possible to dissolve the amount of substance sufficient to remove HF, and if it is sprayed without being dissolved, it may cause clogging of the spray. Therefore, it is necessary to select a compound with as high a solubility as possible. preferable.

  Further, as the HF neutralizing agent, a compound having high reactivity with HF is desirable. The following shows the HF neutralization reaction when NaOH, ammonia, and urea are selected as the HF neutralizer, and the Gibbs energy (ΔG) of each reaction is added.

NaOH + HF → NaF + H ₂ O ΔG = −196 kJ / mol (1)
NH ₃ + HF → NH ₄ F ΔG = −95 kJ / mol (2)
(NH ₂ ) ₂ CO + 2HF + H ₂ O → 2NH ₄ F + CO ₂ ΔG = 5 kJ / mol (3)

  It means that the reaction proceeds more easily as the Gibbs energy is more negative. As the HF neutralizing agent, a compound having a ΔG value smaller than −50 kJ / mol, such as ammonia, is preferable.

  In this embodiment, the acid gas removing device 230 is installed at the rear stage of the temperature reducing tower device 220. However, if the HF concentration in the gas can be removed by the HF neutralizing agent sprayed in the temperature reducing tower device 220, the acid gas removing device. 230 may not be installed. However, considering that the HF removal could not be completely performed by the temperature reducing tower device, it can be said that the installation on the acid gas removal device is a design on the safe side.

  In this embodiment, a packed tower type removal device is illustrated as a wet removal device, but there are a spray type, a shelf-type gas-liquid contact device, a scrubber, etc. as wet processing devices other than the packed tower type. In any case, it is desirable that gas-liquid contact is sufficient. Further, when the inner diameter of the apparatus is small, the gas linear velocity in the apparatus increases, and the amount of mist accompanying the gas increases. Therefore, it is desirable to design the gas flow rate in the apparatus to be 10 m / min or more and 18 m / min or less. In addition, tap water or circulating water in the apparatus can be used as the inflow water to the wet processing apparatus, but if only the circulating water is used, a large amount of solids and acidic components dissolved in the circulating water are discharged as mist. There is a possibility. Therefore, when installed in a packed tower or spray tower, tap water flows from the top nozzle and tap water also flows from the trays and scrubbers. It is desirable to reduce the concentration. Moreover, as inflow water, you may use alkaline aqueous solution etc. other than a tap water and circulating water.

  PFC is hydrolyzed on the catalyst. A typical PFC decomposition reaction is shown below.

CF ₄ + 2H ₂ O → CO ₂ + 4HF (4)
C ₂ F ₆ + 3H ₂ O → CO + CO ₂ + 6HF (5)
C ₄ F ₈ + 4H ₂ O → 4CO + 8HF (6)
CHF ₃ + H ₂ O → CO + 3HF (7)
SF ₆ + 3H ₂ O → SO ₃ + 6HF (8)
2NF ₃ + 3H ₂ O → NO + NO ₂ + 6HF (9)

In the reactions of the formulas (5), (6), and (7), CO is generated, but CO ₂ is obtained by supplying air as a reaction aid.

  The catalyst used for the decomposition of PFC is a catalyst for hydrolysis or oxidative decomposition, for example, selected from Al, Zn, Ni, Ti, Fe, Sn, Co, Zr, Ce, Si, W, Pt, and Pd. The catalyst contains at least one selected from the above. The catalyst component is included in the form of an oxide, metal, composite oxide or the like. In particular, a catalyst of Al and at least one selected from Ni, Zn, Ti, W, Co, and Pd is preferable because it has high PFC decomposition performance.

  PFC is treated by hydrolysis as shown in equations (1)-(6). If the amount of water to be supplied is small, the PFC decomposition reaction does not proceed, and the moisture to be condensed from the exhaust gas after PFC decomposition decreases, so that the gas cooling and acid gas removal performance is reduced. Further, when the amount of supplied water is large, both PFC decomposition and condensed water generation are preferable. However, when a large amount of water is contained, the temperature of the gas cannot be increased to a predetermined temperature. Therefore, the amount of water vapor added to the reaction tower during the hydrolysis of PFC is preferably 2 to 50 times the theoretical amount of water required for hydrolysis, usually 3 to 30 times.

  The hydrolysis temperature of PFC is preferably 500 to 850 ° C. When the PFC concentration is high, the reaction temperature should be raised, and when the PFC concentration is 1% or less, the reaction temperature should be lowered. When the reaction temperature is higher than 850 ° C., the catalyst tends to deteriorate and the reaction tower material also tends to corrode. Conversely, when the reaction temperature is lower than 500 ° C., the PFC decomposition rate decreases.

  As the acid gas removal device 230, general wet and dry removal devices can be used. Examples of wet methods include spray towers, packed towers, scrubbers, and shelf-type gas-liquid contact devices. Examples of the dry type include a fixed bed, a moving bed, and a fluidized bed type dry removal device using an acid gas neutralizer. Also, a bug filter method is good. Acid gas scavengers include alkali metal, alkaline earth metal basic salts such as calcium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, sodium bicarbonate, sodium carbonate, calcium carbonate, calcium oxide, or Basic substances such as ammonia and urea can be used.

  It is desirable to install the exhaust facility 240 at the subsequent stage of the acid gas removal device. When processing a large flow rate PFC, it is desirable to increase the linear velocity as much as possible. However, if the gas flow rate is increased in order to increase the linear velocity, the pressure loss in the apparatus increases. As the exhaust equipment, a general ejector and blower can be used, but any other method may be used as long as the apparatus system can be maintained at a negative pressure.

[Test Example 1]
This test example is the result of evaluating the HF removal effect when a neutralizing agent is added to the PFC decomposition exhaust gas. It was considered that the HF concentration in the gas was reduced by adding an HF neutralizing agent to the PFC decomposition exhaust gas, and as a result, corrosion of the member could be suppressed.

A schematic diagram of the test apparatus is shown in FIG. This test apparatus comprises a gas supply line, a neutralizer supply line, a reaction tube 100, a reaction water supply line, and an acid gas absorption tank 120. A PFC decomposition catalyst 104 is installed in the reaction tube. The supply gas is supplied from the upper part of the reaction tube, heated from the outside by the electric furnace 101, and flows into the catalyst layer. The composition of the supply gas was N ₂ : 1250 ml / min, Air: 125 ml / min, C ₂ F ₄ : 13 ml / min. Further, the reaction water necessary for the C ₂ F ₆ decomposition over the catalyst through the micro tube pump 110, and 25 times the supply of C ₂ F ₆ with a material volume ratio. Further, a neutralizing agent was added in order to remove HF generated after C ₂ F ₆ decomposition. The neutralizing agent was supplied to the lower part of the catalyst layer via the microtube pump 140. As the neutralizing agent, an aqueous solution of ammonia, urea and NaOH was used. The amount of neutralizing agent added was the same as the amount of HF produced by C ₂ F ₆ decomposition. A gas sample device 150 was installed at the bottom of the reaction tube so that exhaust gas could be collected in the tetra bag. The effect of adding the neutralizing agent was compared by the HF concentration in the gas collected from the gas sample device 150. The results are shown in Table 1. For neutralizing agent without the addition is HF was contained 5.7Vol% in the gas, the gas in HF concentration by adding neutralizing agent is reduced, ranking is without addition>Urea> NH ₃ > NaOH. Therefore, it was confirmed that the HF concentration in the gas was reduced by adding the neutralizing agent, and the usefulness of adding the neutralizing agent was confirmed.

  In this test example, despite the addition of the theoretical equivalent ratios in the formulas (1) to (3), HF could not be completely removed by any neutralizing agent. As this cause, the influence of the reaction rate of HF-neutralizing agent and the influence of insufficient mixing of HF-neutralizing agent are considered. As an evaluation of the influence of the reaction rate of the HF-neutralizing agent, when comparing the Gibbs energy (ΔG) value of the reactions (1) to (3) and the HF removal performance, there is a correlation between the HF removal performance and the magnitude of the ΔG value. It was confirmed that the neutralizing agent with a smaller ΔG value has higher HF removal performance. Therefore, as a selection index for the HF neutralizer, a compound having a smaller ΔG value in the reaction with HF is more preferable, and a compound having a smaller ΔG value than −50 kJ / mok is desirable. Any compound other than the three neutralizing agents mentioned in this example may be used as long as the ΔG value is smaller than −50 kJ / mol.

  Moreover, it is thought that it is necessary to improve the mixing state of HF-neutralizing agent because HF cannot be completely removed even with NaOH having the highest HF removal performance in this test example. When the neutralizer addition method is applied to an actual cooling tower, mixing is promoted by, for example, promoting gas convection diffusion by the swirl flow method or venturi structuring of the cooling tower body, and the reaction rate Is thought to improve. In addition, any structure that promotes gas mixing can be applied.

[Test Example 2]
This test example is a result of evaluating the HF resistance of a metal by installing a metal test piece in PFC decomposition exhaust gas and conducting a continuous test for 300 h under two conditions with and without a neutralizing agent.

  A schematic diagram of the test apparatus is shown in FIG. This test apparatus includes a gas supply line, a reaction tube 100, a reaction water supply line, and an acid gas absorption tank 120. A PFC decomposition catalyst 104 is installed in the reaction tube. The gas supply conditions are the same as in Test Example 1. Further, five types of metal test pieces 130 were installed in the lower stage of the PFC decomposition catalyst 104. Three metal test pieces of the same type were installed in series, and the corrosion temperature was inclined. The corrosion temperature was 200 ° C, 400 ° C, and 600 ° C from the low temperature side. In addition, as metal test piece types used in this test, Fe-based alloys SUS304, SUS310S, and Ni-based alloys Inconel 600 (made by Special Metal), Incoloy 800 (made by Special Metal), Hastelloy C-276 ( 5 types) (manufactured by Haynes). Table 2 shows the composition of the metal test piece used in this test. Moreover, this test example was implemented by two conditions with or without a neutralizing agent, and the corrosion behavior of the metal test piece by the presence or absence of a neutralizing agent was evaluated. A 300 h continuous test was performed under the above conditions, the weight of the metal test piece was measured, and the corrosion thickness was estimated from the obtained weight.

  The change in weight of each test piece after the 300 h continuous test is shown in FIGS. Depending on the type of test piece, the weight after the continuous test increased from the initial weight, but this was assumed to be due to the formation of an oxide film or the like. That is, it was determined that no metal loss due to corrosion occurred, and the weight reduction rate in this case was expressed as 0.0%. Regarding the weight change before and after the test, Inconel 600, Incoloy 825 and Hastelloy C-276 have high HF resistance in the temperature range of 200 to 600 ° C. regardless of the presence or absence of the neutralizing agent, and the weight reduction rate is 0.0%. Met. However, in SUS304 and SUS310S, it has been found that the weight reduction rate increases as the temperature decreases regardless of the presence or absence of the neutralizing agent. However, in terms of the effect of adding the neutralizing agent, the weight reduction rate was reduced under the condition where the neutralizing agent was added, and the effect of inhibiting corrosion due to the addition of the neutralizing agent was recognized.

  As a result of observing the cross-sectional state of the Inconel 600 and the SUS304 specimen with the SEM, it was confirmed that a Cr oxide film was formed on the base material on the surface of the Inconel 600 specimen. It was not confirmed on the surface, but it was confirmed that the corrosion inside the material had progressed. Since similar film formation was confirmed for Ni-based alloys other than Inconel 600, it was speculated that the high corrosion resistance of Ni-based alloys was due to the formation of Cr oxide films. Therefore, the knowledge which can suppress corrosion by the production | generation of the Cr oxide film on a metal test piece was acquired.

It is desirable to perform a heat treatment in advance before processing the member to form a chromium oxide film. As an example of the film forming method, for example, there is a method in which about 3 vol% of H ₂ O ₂ is added to an Ar gas stream, and this gas stream is treated at 800 ° C. for 24 hours. However, methods other than the above can be applied as long as they can form a chromium oxide film.

  An effective condition for the thickness of the chromium oxide film formed on the Ni-based alloy is 0.3 μm or more. If the amount of Cr in the material is small, a film having a sufficient thickness cannot be formed.

  Next, the corrosion thickness after one year of operation was estimated from the results of the 300 h continuous test. The estimation conditions were that the temperature was 200 ° C. where the corrosion was most advanced, and the corrosion was a uniform corrosion. In addition, it is known that the corrosion rate of many materials changes with time, and the corrosion progresses at a relatively high rate in the early stage of corrosion, and the corrosion rate decreases gradually or in a very short time depending on the formed film. Yes. However, in this example, in order to make a strict evaluation on the safety side, the corrosion rate was maintained at a constant value, and the amount of corrosion was estimated to increase in proportion to time. The following formula (10) was used for the estimation of the corrosion thickness.

Corrosion thickness (mm / year) = Specimen thickness (mm) x Weight loss (g / year)
/ Specimen weight (g) (10)

  Table 3 shows the estimation results of the corrosion thickness. The corrosion thicknesses of Inconel 600, Incoloy 825, and Hastelloy C-276 were estimated to be 0.00 mm / year regardless of the presence or absence of a neutralizing agent. However, SUS304 and SUS310S have corrosion thicknesses of 4.97 and 2.45 mm / year, respectively, even in the presence of the neutralizing agent, and were judged to be unsuitable as a temperature reducing tower material. The difference in the corrosion strength of the five materials examined this time was considered from the composition of the materials.

  FIG. 7 shows the relationship between the corrosion thickness of each material and the Cr / Ni ratio in the material. Here, the reason for paying attention to Cr and Ni is that the corrosion resistance tendency of the five materials examined this time is higher in corrosion resistance than Ni-based alloys, and it is the formation of Cr oxide film that contributes to corrosion resistance. This is because the knowledge was obtained. From FIG. 7, it was found that there was a correlation between the corrosion thickness of each material and the Cr / Ni ratio, and a material with a smaller Cr / Ni ratio has higher HF resistance.

  From this test example, it was found that a material satisfying the following index is effective as a HF-resistant material in a low temperature range.

  Among members exposed to corrosive gas containing HF, members exposed to the corrosive gas at a temperature of 200 to 600 ° C. are Cr 10 to 25 wt%, Fe 5 to 45 wt%, C 0.2 to 1.0 wt%, Mn 0.2. A Ni-based alloy containing ˜1.5 wt% is preferable, and a material formed from a member having a Cr / Ni composition ratio of 0.7 or less in the Ni-based alloy is preferable as the HF-resistant material.

  Further, it is desirable that the Ni-based alloy has a Ni content of 30 wt% or more and a Cr content of 10 to 25 wt% in a member having a Cr / Ni ratio of 0.7 or less. Inconel 600, Incoloy 800, and Hastelloy C-276 are preferable when judged by the members used in this test example, but incoloy 800 having a low content of molybdenum and carbon is particularly preferable. Further, the materials shown in this test example can be used as long as they meet the above index.

  According to the present invention, the high temperature range of 500 ° C. or more and the low temperature range of 200 ° C. or less are mixed, and the corrosion resistance of the member exposed to the HF corrosive environment can be improved.

100 reaction tube 101 electric furnace 103 alumina wool 105 glass wool 110 microtube pump 120 acid gas absorption 150 gas sample device 201 spray nozzle 213 PFC decomposition catalyst

Claims (5)

A decomposing apparatus for decomposing the perfluoro compound in the gas to be treated;
A cooling device for cooling the gas after decomposing the perfluoro compound by a wet method;
An acid gas removal device for removing acid gas containing HF generated after decomposing the perfluoro compound;
In a perfluoro compound decomposition treatment apparatus comprising:
In the cooling apparatus, an HF neutralizing agent is added.   The perfluoro compound decomposition treatment apparatus according to claim 1, wherein the cooling device is a gas temperature-decreasing tower using latent heat of vaporization of water.   3. The par according to claim 1, wherein the HF neutralizer contains one or more of alkali metal and alkaline earth metal hydroxides, carbonates and oxides, ammonia, and urea. Fluoro compound decomposition processing equipment.   4. The perfluoro compound decomposition treatment apparatus according to claim 1, wherein the decomposition apparatus is a perfluoro compound decomposition apparatus using a catalytic method. A decomposition step for decomposing the perfluoro compound in the gas to be treated;
A cooling step of cooling the gas after decomposing the perfluoro compound by a wet method;
An acid gas removing step for removing an acid gas containing HF generated after decomposing the perfluoro compound;
In a method for decomposing perfluorocompound having
In the cooling step, a HF neutralizing agent is added, and the method for decomposing a perfluoro compound.

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