JP4873147B2 - Fluorine-containing compound gas treatment apparatus and treatment method - Google Patents

Description

The present invention is a catalyst PFC using a (Per Fluoro Compounds: perfluoro-containing compound) to a gas treatment apparatus and a gas processing method for processing a fluorine-containing compound gas such as.

In semiconductor and liquid crystal manufacturing processes, for example, PFCs such as CF ₄ , C ₂ F ₆ , SF ₆ , and NF ₃ are often used as dry etching gases and cleaning gases for film forming apparatuses. However, since PFC has a much higher global warming potential than CO ₂ , there is a global demand for reducing PFC emissions.

  Therefore, various methods and apparatuses for decomposing PFC have been proposed and put into practical use.

  For example, Patent Document 1 discloses a decomposition apparatus for a fluorine compound gas used in a semiconductor etching process. This decomposition apparatus has a preheater into which a fluorine compound gas is introduced, and a reactor arranged in the subsequent stage of the preheater. A heater is disposed outside the preheater, and the fluorine compound gas introduced into the decomposition apparatus is first heated by the preheater. The reactor is filled with a catalyst containing aluminum atoms. The fluorine compound gas heated in the preheater is then decomposed by contacting the catalyst in the reactor, and the gas generated by the decomposition is discharged from the reactor.

Patent Document 2 discloses a decomposition apparatus in which a heater is installed inside a reactor containing a reactant used for decomposing a fluorine compound gas.
JP 2001-224926 A ([0038], FIG. 10) Japanese Patent Laid-Open No. 10-15349 ([0031], FIG. 4)

  When the fluorine compound gas is decomposed using a catalyst, the decomposition reaction rate of the gas is influenced by the temperature of the catalyst. In addition, since the decomposition reaction is usually an exothermic reaction or an endothermic reaction, a partial temperature deviation tends to occur due to heat transfer. Therefore, it is desirable to control the temperature of the catalyst as uniformly as possible in order to cause a stable decomposition reaction so that energy is not wasted.

  Focusing on the temperature of the catalyst, in the decomposition apparatus disclosed in Patent Document 1, the fluorine compound gas is heated from the outside of the preheater and supplied to the reactor. In this case, the fluorine compound gas is supplied to the reactor while being sufficiently heated by the preheater.

  However, a temperature distribution occurs in the fluorine compound gas so that the temperature is high in the vicinity of the outer wall of the preheater, but the temperature decreases as the distance from the outer wall increases. As a result of the introduction of the fluorine compound gas having a temperature distribution into the reactor, a temperature distribution also occurs in the catalyst in the reactor, and the overall energy efficiency decreases due to unevenness of the reaction. This becomes more prominent as the flow rate of the fluorine compound gas per unit time increases and as the cross-sectional dimension perpendicular to the flow direction of the fluorine compound gas in the preheater increases.

  In order to uniformly preheat the fluorine compound gas to a predetermined temperature, it may be possible to lengthen the preheating space or make the preheater a packed bed. However, in this case, the weight of the packing is increased and the volume of the decomposition apparatus is increased, so that there are the following problems.

  (1) The surface area of the decomposition apparatus increases and the required electric capacity increases.

  (2) The weight of the packing (the weight of the decomposition apparatus) increases, and the temperature raising time (start-up time) to a predetermined temperature increases.

  (3) When used for the treatment of exhaust gas in a semiconductor manufacturing process, the flow rate of the exhaust gas is not constant but fluctuates. Therefore, if the temperature distribution of the packed bed or the weight of the apparatus is large, temperature control becomes difficult.

  (4) As the temperature control method, a method of detecting the temperature of the packed bed and controlling the outer wall temperature in the vicinity of the heater mounting portion by a PID control method or the like is usually used. However, since there is a large thermal resistance between the packed bed and the outer wall, it is difficult to maintain the temperature optimally against the fluctuation, particularly in a semiconductor manufacturing process in which the gas flow rate fluctuates frequently.

  Since the decomposition apparatus disclosed in Patent Document 2 has a heater installed inside the reactor containing the reactant, it is possible to heat the catalyst layer with a compact design. However, in this case, the decomposition reaction of the fluorine compound gas occurs on the surface of the heater, and the function of the heater is impaired by the corrosive gas generated as a result. In order to maintain the function of the heater over a long period of time, it is necessary to frequently perform maintenance such as replacement and repair of the heater. Since the heater is installed inside the reactor, the maintenance work of the heater is particularly complicated.

  In Patent Document 2, the heater is covered with a corrosion-resistant and heat-resistant cover. However, this does not sufficiently exhibit the performance of the heater. Therefore, it is not very realistic to install a heater inside the reactor.

  The object of the present invention is to employ a heating method from the outside that facilitates maintenance of the heater, and is excellent in temperature response with high thermal efficiency, uniformly heating the catalyst, and stably treating the fluorine-containing compound gas. It is to provide a particularly compact gas processing apparatus and gas processing method that can be performed.

  The gas treatment device of the present invention is a gas treatment device that circulates a fluorine-containing compound gas through a catalyst layer for treatment, and comprises an outer tube, an inner tube positioned inside the outer tube, and a catalyst provided in the inner tube. And a heater attached to the outer tube. The outer tube is introduced with compound gas from one end and closed at the other end. The inner tube has a gas discharge part on one end side, and is located inside the outer tube with the other end and the outer peripheral surface facing the other end and the inner peripheral surface of the outer tube with a space therebetween. The catalyst layer is filled in the inner tube from the other end of the inner tube to an intermediate position toward one end. The heater surrounds the catalyst layer and is attached to the outer peripheral surface of the outer tube.

  In the gas processing apparatus of the present invention configured as described above, the compound gas introduced into the outer tube flows between the inner peripheral surface of the outer tube and the outer peripheral surface of the inner tube, and at the other end of the outer tube. It makes a U-turn and is sent into the inner pipe. During this time, the compound gas is preheated by heat exchange with the gas flowing in the inner tube and heat from a heater provided outside the outer tube. The compound gas sent into the inner pipe passes through the catalyst layer, is decomposed during that time, and is discharged from the gas discharge portion. On the other hand, the heater indirectly heats the catalyst layer in the inner tube through a gap formed between the inner peripheral surface of the outer tube and the outer peripheral surface of the inner tube. The heating of the catalyst layer by the heater is predominantly performed by radiant heat transfer. In this way, the catalyst layer is uniformly heated by the radiation heat transfer from the heater and the preheated gas passing through the outer tube.

  In order not to obstruct the flow of the compound gas between the outer tube and the inner tube, and to effectively exhibit the radiant heat transfer of the catalyst layer by the heater, the superficial gas flow velocity in the catalyst layer is set to U1, It is preferable that the clearance between the inner peripheral surface of the outer tube and the outer peripheral surface of the inner tube is defined so that U2 / U1 is 0.5 or more and 50 or less when the gas flow rate in the tube is U2.

  Further, the outer pipe has a gas introduction part for introducing the compound gas into the outer pipe, and the gas introduction part forms a swirling flow along the circumferential direction of the outer pipe with the compound gas introduced into the outer pipe. It is preferable that it is comprised so that it may flow. Thereby, the compound gas is sufficiently heated until the compound gas is introduced into the catalyst layer.

  Furthermore, the gas treatment apparatus of the present invention is preferably used when the compound gas is a gas containing PFC. In this case, the catalyst contained in the catalyst layer is a catalyst suitable for decomposing PFC. Although the corrosive gas is generated by decomposing the PFC, the outer tube is not in contact with the corrosive gas generated by the decomposition of the PFC in the gas processing apparatus of the present invention. Therefore, the outer tube can be made of a stainless material. Moreover, when the gas processing apparatus of this invention is used for decomposition | disassembly of PFC, it may have further the secondary gas processing part which processes the corrosive gas produced | generated by decomposition | disassembly of PFC. The secondary gas processing section is preferably integrated with the inner pipe so that the gas discharged from the gas discharge section of the inner pipe is directly introduced.

  The gas processing method of the present invention is a gas processing method of processing by flowing a fluorine-containing compound gas through a catalyst layer, and using the gas processing device of the present invention described above, the heater of the gas processing device is driven. While heating the catalyst layer, the compound gas is introduced into the outer tube from one end of the outer tube of the processing apparatus, and the introduced compound gas is discharged from the gas discharge unit of the inner tube. In the gas treatment method described above, the compound gas introduced into the outer tube flows from one end side to the other end side of the outer tube in the outer tube, and is sent to the inner tube on the other end side to heat the catalyst layer. It is decomposed by passing. The processing gas generated by the decomposition is discharged from the gas discharge unit.

  Thus, in the gas treatment method of the present invention, the above-described gas treatment apparatus of the present invention is used, so that the catalyst layer is heated uniformly.

  In the gas treatment method of the present invention, it is preferable that a swirl flow along the circumferential direction of the outer tube is generated in the compound gas introduced into the outer tube.

  According to the present invention, while the catalyst layer is heated from the outside, it has high thermal efficiency and excellent temperature responsiveness. Therefore, the catalyst layer can be heated uniformly, and the treatment of the compound gas is stable and It can be done efficiently.

  Next, embodiments of the present invention will be described with reference to the drawings.

  Referring to FIG. 1, a gas processing apparatus 1 according to an embodiment of the present invention that decomposes a fluorine-containing compound gas using a catalyst is schematically shown. The gas processing apparatus 1 is used, for example, for decomposing gas discharged from a dry etching apparatus used for manufacturing a semiconductor. In the semiconductor etching process, a gas containing PFC is used as an etching gas. The gas processing apparatus 1 decomposes the PFC. Below, the gas processing apparatus 1 shown in FIG. 1 is demonstrated in detail.

  The gas processing apparatus 1 is supplied with a gas containing PFC, hydrolyzes and discharges PFC contained in the supplied gas, and an acidic gas contained in the gas discharged from the PFC reaction unit 10 And a secondary gas processing unit 18 for detoxifying and discharging the gas. In this embodiment, the PFC reaction unit 10 and the secondary gas processing unit 18 are connected by a conduit 19.

  The PFC reaction unit 10 includes an outer tube 11 and an inner tube 12. The outer tube 11 is a cylindrical member, and one end thereof (the lower end in FIG. 1) is closed. Connected to the upper end of the outer tube 11 is a gas introduction tube 15 for introducing a gas containing PFC into the outer tube 11 together with water.

  The inner tube 12 is a cylindrical member having an outer diameter smaller than the inner diameter of the outer tube 11, and is inserted into the outer tube 11 with its upper end protruding from the outer tube 11. At the upper end of the outer tube 11, the outer tube 11 and the inner tube 12 are airtightly joined by, for example, welding or the like so as to close a gap with the inner tube 12. A gas discharge pipe 16 is connected to the upper end portion of the inner pipe 12. The gas discharge pipe 16 is connected to a conduit 19. A breathable plate 14 is attached to the lower end of the inner tube 12. The air permeable plate 14 can be configured by, for example, a punching plate or a mesh member in which a large number of through holes are formed.

  The inner tube 12 is inserted into the outer tube 11 to a position where the air permeable plate 14 is opposed to the bottom surface of the outer tube 11 with a space therebetween, so that the side on which the air permeable plate 14 is attached It is supported in the position. That is, the inner tube 12 is supported in a posture in which the air permeable plate 14 serves as a bottom wall.

  The central axis of the inner tube 12 coincides with the central axis of the outer tube 11. Therefore, inside the outer tube 11, the outer surface of the inner tube 12 is opposed to the inner surface of the outer tube 11 across the entire circumference in the circumferential direction of the inner tube 12.

  A catalyst is accommodated in the inner tube 12. The catalyst is supported on the gas permeable plate 14 and filled in a portion from the gas permeable plate 14 to a height H1 in the middle of the inner tube 12 in the axial direction. As a result, the catalyst layer 13 is formed in the lower portion of the inner tube 12. The catalyst is not particularly limited as long as it is suitable for decomposing PFC. For example, an alumina-based catalyst can be used. In order to hold the catalyst housed in the inner tube 12 from above, another breathable plate (not shown) may be provided inside the inner tube 12 so as to cover the catalyst layer 13.

  On the other hand, an electrothermal heater 17 is provided outside the outer tube 11 for preheating the gas introduced into the outer tube 11 and for heating the catalyst accommodated in the inner tube 12. Yes. The heater 17 is annular, surrounds the outer peripheral surface of the outer tube 11 over the entire circumference, and is installed in close contact with the outer peripheral surface of the outer tube 11. Further, the relationship between the dimension of the heater 17 in the axial direction of the outer tube 11 and the height H1 of the catalyst layer 13 is fluid depending on the design, but the outer tube 11 so that the heater 17 surrounds the catalyst layer 13. The dimension of the heater 17 is approximately equal to or higher than the height H1 of the catalyst layer 13 (preferably 1.2 to 2.0 times) so that the heater 17 is installed at a position corresponding to the catalyst layer 13 in the axial direction. It is preferable that

The type of the heater 17 is not particularly limited as long as the catalyst can be heated to a temperature suitable for PFC decomposition. For example, when decomposing CF ₄ which is a kind of PFC, if the catalyst is heated to 400 to 900 ° C., particularly about 700 ° C. or more, a decomposition rate of almost 100% can be obtained. Therefore, as the heater 17, a heater having a capability of generating heat up to about 800 ° C. can be preferably used.

  Moreover, although the annular | circular shaped heater 17 was shown here as a form of the heater 17, if it is comprised so that the outer peripheral surface of the outer tube | pipe 11 can be heated over a perimeter, arbitrary forms are employ | adopted. Can do. For example, a configuration in which a plurality of rod-shaped heaters are arranged on the outer peripheral surface of the outer tube 11 along the circumferential direction, or a configuration in which a flexible planar heater is wound on the outer peripheral surface of the outer tube 11. Can be mentioned.

In the PFC reaction unit 10, HF (hydrogen fluoride) is generated by the decomposition of the PFC. For example, the decomposition reaction formula of CF ₄ is as follows.
CF ₄ + 2H ₂ O → CO ₂ + 4HF (Scheme 1)

HF produced by the decomposition of PFC is acidic and corrosive. The secondary gas processing unit 18 is a so-called scrubber that removes HF generated in the PFC reaction unit 10 by neutralization or the like. The secondary gas processing unit 18 includes a reaction vessel 18a that stores a processing agent 18b that reacts with HF to remove HF. An example of the treating agent is Ca (OH) ₂ . In this case, the decomposition reaction formula of HF is as follows.
2HF + Ca (OH) ₂ → CaF ₂ + 2H ₂ O (Reaction Formula 2)

Next, the PFC processing method using the above-described gas processing apparatus 1 will be described taking as an example the case where CF ₄ is decomposed as PFC.

A gas containing N ₂ as a main component and containing CF ₄ in a proportion of 1 to 3 vol% is introduced into the PFC reaction unit 10 together with water at normal temperature and normal pressure from the gas introduction pipe 15. The gas introduced from the gas introduction pipe 15 flows as a whole flow between the outer pipe 11 and the inner pipe 12 to the bottom of the outer pipe 11, where it U-turns and passes through the inner pipe from the breathable plate 14. 12, enters the inner pipe 12 and rises through the gas discharge pipe 16.

Inside the inner pipe 12, the gas first passes through the catalyst layer 13, and then reaches the gas discharge pipe 16 through the space above the catalyst layer 13. Meanwhile, outside of the outer tube 1 1 and the heater 17 is energized, the heater 17, the catalyst layer 13 is indirectly heated through the space between the outer tube 11 and inner tube 12. More specifically, the heat from the heater 17 is mainly radiant heat, from the inner wall of the outer tube 11 to the outer wall of the inner tube 12 via a space between the inner peripheral surface of the outer tube 11 and the outer peripheral surface of the inner tube 12. It is transmitted to. As a result, the catalyst in the catalyst layer 13 is heated.

  At a temperature of about 700 ° C., which is the object of this embodiment, the amount of heat transferred by radiation reaches 10 times the amount of heat transferred by convection. Therefore, heat transfer from the heater 17 to the catalyst is dominated by radiation rather than conduction and convection. Unlike the direct heating by the heater, the heating by radiation enables heating with less unevenness. The heater 17 also heats the gas flowing between the outer tube 11 and the inner tube 12, and the heated gas is sent into the catalyst layer 13 through the breathable plate 14.

In this way, the catalyst is controlled at about 700 ° C., so that when the gas passes through the catalyst layer 13, CF ₄ contained in the gas reacts with water and is decomposed into CO ₂ and HF (reaction formula) 1). The gas in which CF ₄ is decomposed flows toward the gas discharge pipe 16 in the space above the catalyst layer 13.

In order to cause the decomposition reaction of CF ₄ stably and efficiently, it is important to make the temperature of the catalyst in the catalyst layer 13 as uniform as possible, in other words, to make the temperature distribution of the catalyst layer 13 as small as possible. is there.

  As described above, the gas introduced from the gas introduction pipe 15 into the outer pipe 11 is heated by the heater 17 when passing through the portion of the outer pipe 11 to which the heater 17 is attached. In addition, the gas passes through the gap between the outer tube 11 and the inner tube 12, and the distance from the heater 17 is not large, so the gas is heated efficiently and uniformly. The gas heated by the heater 17 is introduced into the catalyst layer 13 from the breathable plate 14.

  Further, prior to heating by the heater 17, the gas introduced into the outer pipe 11 from the gas introduction pipe 15 first exchanges heat between the inner pipe 12 and the exhaust gas directed from the catalyst layer 13 to the gas discharge pipe 16. Preheated by Since the exhaust heat is effectively used, the heating by the heater 17 can be further reduced. By this heat exchange, the gas in the inner pipe 12 is cooled to a temperature of about 200 ° C. in the process until it passes through the catalyst layer 13 and is discharged from the gas discharge pipe 16.

  As described above, in the present embodiment, the PFC reaction unit 10 has a double tube structure including the outer tube 11 having the heater 17 installed on the outer wall surface and the inner tube 12 having the catalyst layer 13 provided. The gas introduced into the tube 11 is U-turned at the end in the outer tube 11 and enters the inner tube 12, passes through the catalyst layer 13 in the inner tube 12, and is discharged. Thus, the catalyst layer 13 is centered from the portion in contact with the inner pipe 12 by a synergistic effect of the preheating of the gas that effectively uses the exhaust heat and the heating of the catalyst layer 13 by the radiant heat from the heater 17. The entire part is heated to a substantially uniform temperature.

By controlling the entire catalyst layer 13 at a substantially uniform temperature, the CF ₄ decomposition reaction using the catalyst can be performed stably and efficiently. Moreover, since the heater 17 is disposed outside the outer tube 11, the heater 17 is not exposed to the corrosive gas generated by the CF ₄ decomposition reaction, and the maintenance of the heater 17 is easy.

  Moreover, since the catalyst layer 13 is heated uniformly, the PFC reaction part 10, especially the catalyst layer 13, can be comprised with a larger diameter than before. Accordingly, if the amount of the catalyst is the same as the conventional one, the height of the catalyst layer 13 can be made lower than the conventional one, and the overall height of the PFC reaction unit 10 can be designed to be lower and more compact.

  Focusing on heat transfer, the PFC reaction unit 10 can be broadly divided into a heat exchange section A and a heating section B. The heat exchange section A is a section corresponding to a portion where the heater 17 is not attached among the portions where the outer tube 11 is doubled with the inner tube 12. Heat exchange is performed between the flowing gas and the gas flowing in the inner pipe 12. The heating section B is a section corresponding to a portion where the heater 17 is attached among the portions where the outer tube 11 is doubled with the inner tube 12. In the heating region B, gas and catalyst are transferred by the heater 17. Heated. In order to promote heat transfer in the heat exchange section A, in the heat exchange section A, it is preferable that the inner tube 12 is filled with a filler 13a. As the filler 13a, for example, an alumina sphere can be used.

  In order to sufficiently preheat the gas introduced from the gas introduction pipe 15 into the outer pipe 11, the height of the heat exchange section A (the axial length of the outer pipe 11) is the height of the catalyst layer 13 ( In this embodiment, it is preferably 0.5 times or more of the height H1 of the heating section B). Although there is no upper limit to the height of the heat exchange section A, in reality, it is limited by the height of the room where the gas treatment device is installed, and is set to a value that is, for example, three times or less the height of the catalyst layer 13. .

The PFC reaction unit 10, by the decomposition of CF _4, HF is generated corrosive gases. Therefore, it is desirable that at least the inner surface of the inner tube 12 exposed to HF is made of a corrosion-resistant material such as Inconel. On the other hand, since the outer tube 11 does not come into contact with HF produced by the decomposition reaction of CF ₄ , any material such as a stainless material can be used as long as the mechanical strength and heat resistance required for the outer tube 11 can be secured. Can be configured.

Thus, the range of material selection of the outer tube 11 can be expanded by making the PFC reaction part 10 into a double tube structure. On the other hand, in the case of a conventional single tube structure, the entire structure must be made of a corrosion resistant material. However, also in this embodiment, when the gas introduced into the outer tube 11 contains a corrosive gas, it is desirable that the outer tube 11 is also made of a corrosion-resistant material. In addition, since the PFC reaction unit 10 has a double tube structure, even if the inner tube 12 is damaged by the gas generated by the decomposition reaction of CF ₄ , the generated gas immediately passes through the PFC reaction unit 10. It can be prevented from leaking outside.

The gas containing HF generated by the decomposition of CF ₄ is discharged from the PFC reaction unit 10 through the gas discharge pipe 16 and introduced into the secondary gas processing unit 18 through the conduit 19. HF contained in the gas introduced into the secondary gas processing unit 18 is removed by neutralization or adsorption by the processing agent 18b accommodated in the reaction vessel 18a (see, for example, Reaction Formula 2), and clean gas And is discharged from the secondary gas processing unit 18.

As a gas processing method in the secondary gas processing unit 18, either a dry method or a wet method can be applied. In the case of the dry method, iron oxide (Fe ₂ O ₃ ), calcium hydroxide (Ca (OH) ₂ ) described above, or the like can be used as the treating agent 18b. In the case of the wet type, for example, alkaline water can be used as the treating agent 18b.

  Here, since the gas discharged from the PFC reaction unit 10 is an acidic gas containing HF and water, the gas is further cooled in the process of passing through the conduit 19 and reaching the secondary gas processing unit 18. 19 may condense. This also causes the conduit 19 to corrode. Therefore, in this embodiment, by introducing air for gas dilution from the vicinity of the gas discharge pipe 16 into the inner pipe 12, the concentration of the acid gas flowing in the conduit 19 is lowered, and the acid in the conduit 19 is reduced. Condensation is suppressed.

  In the PFC reaction unit 10 of the present embodiment described above, the gap C between the outer tube 11 and the inner tube 12 is appropriately set from the viewpoint of pressure loss of the gas flowing in the outer tube 11 and the viewpoint of radiant heat transfer by the heater 17. It is preferable to set to.

  The gap C considering these two viewpoints can be determined based on the respective gas flow rates in the outer tube 11 and the inner tube 12. For example, the gas flow rate in the inner tube 12 is U1, and the gas flow rate in the outer tube 11 is U2. Here, since the inner pipe 12 has the catalyst layer 13, the gas flow rate U1 in the inner pipe 12 is the gas flow rate at a predetermined temperature and pressure in an empty state where the catalyst layer 13 does not exist. The actual flow rate is defined by the superficial gas flow rate divided by the cross-sectional area of the inner pipe 12. Further, as shown in FIG. 2, the outer diameter of the inner tube 12 is D1, the thickness of the tube wall of the inner tube 12 is t, and the inner diameter of the outer tube 11 is D2.

  In a general single-tube PFC cracking apparatus, the inner diameter of a pipe having a catalyst layer is a gas to be processed per unit time so that the superficial gas flow rate in the pipe is in the range of 0.01 to 3 m / s. It is determined according to the amount. In the present embodiment, the superficial gas flow velocity U1 in the catalyst layer 13 in the inner pipe 12 corresponds to this. If the amount of gas to be processed per unit time and the superficial gas flow velocity U1 are determined, the inner diameter (= D1-2t) of the inner pipe 12 is determined. The thickness t of the tube wall of the inner tube 12 can be set to, for example, about 1 to 5 mm based on the material of the inner tube 12, the mechanical strength necessary for the inner tube 12, and the like.

The gas flow rate U2 in the outer tube 11 is determined so that U2 / U1 is preferably 0.5 to 50, more preferably 1 to 20. U2 / U1 is equal to the cross-sectional area inside the inner pipe 12 / the cross-sectional area of the gas flow part of the outer pipe 11 (the part excluding the inner pipe 12).
U2 / U1 = (D1-2t) ² / (D2 ² -D1 ² ) (Formula 3)
Can be expressed as

If U2 / U1, D1, and t are determined, the inner diameter D2 of the outer tube 11 can be determined from Equation 3. Since the inner diameter D2 of the outer tube 11 and the outer diameter D1 of the inner tube 12 are determined as described above, the gap C between the outer tube 11 and the inner tube 12 is
C = (D2-D1) / 2 (Formula 4)
It becomes.

  As can be seen from Equation 3, if the difference between D2 and D1, that is, the gap C between the inner peripheral surface of the outer tube 11 and the outer peripheral surface of the inner tube 12 is increased, the value of U2 / U1 is decreased, and the gap C is decreased. Then, the value of U2 / U1 becomes large. If the gap C is large and U2 / U1 is less than 1, particularly less than 0.5, the amount of radiant heat transferred from the heater 17 to the catalyst layer 13 may decrease, and the catalyst layer 13 may not be heated uniformly. . On the other hand, when the gap C is small and U2 / U1 exceeds 20, particularly 50, the pressure loss of the gas flowing through the outer tube 11 increases.

  Therefore, as described above, the gap C is defined so that U2 / U1 is preferably 0.5 or more and 50 or less, more preferably 1 or more and 20 or less, and particularly preferably 2 or more and 16 or less. In view of the flow of the catalyst and the heating of the catalyst layer 13.

  It should be noted that the U-turn portion of the gas flow, that is, the distance between the other closed end of the outer tube 11 and the other end of the inner tube 12 facing this is set so that the gas flow velocity is U2 or less. Is preferred.

  Regarding the heating of the gas in the outer tube 11, the gas introduced into the outer tube 11 from the gas introduction tube 15 is introduced into the inner tube 12 through the gas permeable plate 14 until the heat exchange section. Preheated in A and further heated in heating section B. In order for the gas to be sufficiently heated in these sections, it is important to prevent gas drift in the outer tube 11.

  Therefore, in the present embodiment, the gas is introduced into the outer tube 11 so that the gas forms a swirling flow along the inner peripheral surface of the outer tube 11 in the outer tube 11. In this way, by causing a swirling flow of gas in the outer tube 11, it is possible to prevent gas drift until the gas introduced into the outer tube 11 reaches the breathable plate 14, Heat transfer from the outer tube 11 to the inner tube 12 can be performed more uniformly over the entire circumference of the inner tube 12.

  Various methods are conceivable as a method for generating a swirl flow in the gas in the outer tube 11. For example, if the gas is introduced in the configuration shown in FIGS. 3 and 4, it can be realized with a simple configuration.

  In the example shown in FIG. 3, the distal end surface of the gas introduction tube 15 is closed, and the distal end portion is inserted into the outer tube 11 so as to be parallel to the radial direction of the outer tube 11 and connected to the outer tube 11. ing. An opening 15 a is formed in a region including a portion facing the circumferential direction of the outer tube 11 on the peripheral surface of the gas introducing tube 15 at the distal end portion that has entered the outer tube 11 of the gas introducing tube 15. The gas sent to the gas introduction pipe 15 is ejected into the outer pipe 11 from the opening 15a, and thereby, a swirl flow along the inner peripheral surface of the outer pipe 11 can be generated in the outer pipe 11.

  Although FIG. 3 shows an example in which the gas introduction pipe 15 is entered in parallel with the radial direction of the outer pipe 11, the present invention is not limited to this, and when the gas introduction pipe 15 is entered in parallel with the axial direction of the outer pipe 11, The structure of this example can also be applied when the gas introduction pipe 15 is connected in parallel with a plane passing through the central axis.

  In the example shown in FIG. 4, the gas inlet tube 15 ′ having an opening 15 a ′ on the distal end surface is caused to enter the outer tube 11 by causing the distal end portion to enter the outer tube 11 so as to be parallel to the tangential direction of the outer tube 11. It is connected. Even with such a configuration, the opening 15 a ′ from which the gas is ejected faces the circumferential direction of the outer tube 11, so that a swirl flow along the inner circumferential surface of the outer tube 11 can be generated.

  Next, another embodiment of the present invention will be described with reference to FIG.

  The gas processing apparatus shown in FIG. 5 has a structure in which a PFC reaction unit 20 and a secondary gas processing unit 25 are integrated.

  As in the above-described embodiment, the PFC reaction unit 20 includes an outer tube 21, an inner tube 22 disposed inside the outer tube 21, a catalyst layer 23 provided inside the inner tube 22, and an outer side of the outer tube 21. The heater 24 is disposed. The outer tube 21 and the inner tube 22 are formed so that the lower end portions are expanded in a flange shape, and in this portion formed in the flange shape, a gas containing PFC to be processed is introduced into the outer tube 21. The gas introduction pipe 26 is connected. The gas introduction pipe 26 has a structure for generating a swirling flow in the outer pipe 21 as in the above-described embodiment.

  The outer tube 21 is closed at the upper end surface, and the peripheral portion of the outer tube 21 is connected to the peripheral portion of the inner tube 22 in a flange shape over the entire periphery. Yes. Furthermore, the upper end of the inner tube 22 is disposed at a distance from the upper surface of the outer tube 21.

  The catalyst layer 23 is located on the upper part of the inner tube 22. Therefore, a breathable plate 22a similar to the above-described embodiment that supports the catalyst contained in the catalyst layer 23 is provided in the axially intermediate portion of the inner tube 22. An air permeable plate 22b is also provided at the upper end of the inner tube 22 so that the catalyst in the catalyst layer 23 does not accidentally spill out to the outer tube 21 side. Furthermore, in the inner pipe 22, the filling material 23a is filled in the heat exchange section A.

  The heater 24 is disposed at a position corresponding to the catalyst layer 23 in the transverse direction of the outer tube 21 and the inner tube 22. Similarly to the above-described embodiment, the heater 24 is configured to be able to heat the outer peripheral surface of the outer tube 21 over the entire periphery, and is installed in close contact with the outer peripheral surface of the outer tube 21.

  The secondary gas processing unit 25 is disposed below the PFC reaction unit 20, and the inside thereof communicates directly with the inside of the inner tube 22 through the lower end opening of the inner tube 22. A processing agent for neutralizing or adsorbing and removing HF is housed in the secondary gas processing unit 25 as in the above-described embodiment. In addition, a gas discharge pipe 27 for discharging the gas from which HF has been removed by the processing agent is connected to the lower part of the secondary gas processing unit 25.

  In the gas processing apparatus shown in FIG. 5, the gas introduced at normal temperature and normal pressure from the gas introduction pipe 26 flows up spirally through the gap between the outer pipe 21 and the inner pipe 22 and rises at the top of the outer pipe 21. Make a U-turn and enter the inner tube 22. During this time, the gas is preheated by heat exchange with the gas in the inner pipe 22 in the heat exchange section A and heated by the heater 24 in the heating section B.

  The gas that has entered the inner tube 22 comes into contact with the catalyst in the catalyst layer 23, and the PFC is decomposed. The catalyst in the catalyst layer 23 is heated not only by the gas heated through the outer tube 21 but also by heat transfer mainly composed of radiation by the heater 24, as in the above-described embodiment. Heated uniformly. As a result, the PFC can be decomposed stably and efficiently.

  The gas obtained by decomposing PFC in the catalyst layer 23 is directly introduced into the secondary gas processing unit 25 while being cooled by heat exchange with the gas flowing in the outer pipe 21 in the heat exchange section A. The gas introduced into the secondary gas processing unit 25 is cleaned by removing HF, and is discharged from the gas discharge pipe 27.

  The most characteristic point of this embodiment is that the PFC reaction unit 20 and the secondary gas processing unit 25 are integrated, and the gas from the PFC reaction unit 20 is directly introduced into the secondary gas processing unit 25. Thereby, the piping which connects the PFC reaction part 20 and the secondary gas processing part 25 becomes unnecessary. Further, since the piping is not necessary, there is no risk of condensation of the acidic gas due to a temperature drop in the piping, and therefore it is not necessary to introduce dilution air into the piping. As described above, the configuration of the gas processing apparatus can be further simplified.

  Next, still another embodiment of the present invention will be described with reference to FIG.

  The gas processing apparatus shown in FIG. 6 has a structure in which the PFC reaction unit 30 and the secondary gas processing unit 35 are integrated, and this point is the same as that shown in FIG. However, in this embodiment, the shapes of the outer tube 31 and the inner tube 32 are different from the structure shown in FIG.

  The outer tube 31 and the inner tube 32 are formed in a stepped cylindrical shape whose upper diameter is smaller than the lower diameter, and the inner wall of the inner tube 32 is a part of the bottom wall of the outer tube 31. As shown, it is arranged inside the outer tube 31.

  In the upper portion of the small diameter of the gas processing apparatus, the upper surface of the outer tube 31 is closed, and the upper end of the inner tube 32 is located at a distance from the closed upper surface of the outer tube 31. A catalyst layer 33 is arranged on the upper part of the inner pipe 32 with its upper and lower ends held by a gas permeable plate, and below it is filled with a packing material 33a. A heater 34 is installed in close contact with the outer peripheral surface of the outer tube 31 at a position corresponding to the catalyst layer 33 in the transverse direction of the outer tube 31 and the inner tube 32.

  On the other hand, a gas introduction pipe 36 for introducing a gas containing PFC to be processed is connected to the outer pipe 31 in the gap between the outer pipe 31 and the inner pipe 32 at the lower portion of the large diameter of the gas processing apparatus. ing. The gas introduction pipe 36 also has a structure for generating a swirling flow in the outer pipe 31 as in the above-described embodiment. A treatment agent for removing HF generated by the decomposition of PFC in the catalyst layer 33 is accommodated in the inner pipe 32. Further, a gas discharge pipe 37 for discharging the gas from which HF has been removed by the processing agent is connected to the lower end of the inner pipe 32.

  In this embodiment, the gas containing PFC introduced from the gas introduction pipe 36 at normal temperature and normal pressure first flows toward the upper part while swirling the outer periphery of the portion containing the processing agent at the lower part of the large diameter. In the meantime, it is preheated by heat exchange with the gas flowing through the portion in which the treatment agent is stored. Conversely, the gas flowing through the portion of the inner pipe 32 in which the processing agent is stored is cooled by heat exchange with the gas introduced from the gas introduction pipe 36. Other gas flows, decomposition reactions, and the like are the same as those of the gas processing apparatus shown in FIG.

  As described above, this embodiment can be considered to have a configuration in which the treatment agent is accommodated in the inner tube 32 at the lower part of the double tube structure having the outer tube 31 and the inner tube 32. According to this idea, in the double-pipe structure of this embodiment, it can be said that the portion in which the processing agent is stored is the secondary gas processing unit 35 and the remaining portion is the PFC reaction unit 30.

  Alternatively, in the present embodiment, the secondary gas processing unit 35 also has a double pipe structure surrounded by the outer wall and the inner wall, and the outer wall and the inner wall are respectively continuous with the outer tube 31 and the inner tube 32 of the PFC reaction unit 30. Therefore, it can be considered that the space between the outer wall and the inner wall is a gas flow path for supplying gas to the PFC reaction unit 30.

  6A and 6B, the gas processing apparatus shown in FIG. 6 can preheat the introduced gas and cool the discharged gas without increasing the overall size as much as the gas processing apparatus shown in FIG. Can be performed more effectively.

  The present invention has been described with reference to some typical embodiments. The present invention is not limited to these embodiments, and can be appropriately changed within the scope of the technical idea of the present invention.

  For example, in the above-described embodiments, the vertical direction of the PFC reaction unit is specified and described. However, the PFC reaction unit shown in FIGS. 1, 5 and 6 may be turned upside down. Furthermore, it is also possible to install the PFC reaction unit in a posture inclined with respect to the vertical direction.

  In each of the above-described embodiments, the outer tube and the inner tube are cylindrical, and the cross-sectional area is uniform at an arbitrary position in the axial direction. However, the outer tube and the inner tube do not need to have a cylindrical shape with a uniform cross-sectional area, and may have a frustum shape, for example. Furthermore, the cross-sectional shapes of the outer tube and the inner tube do not need to be circular, and can be any shape such as a triangle, a quadrangle, a pentagon or more polygon, or an ellipse or an oval. However, when a swirling flow is generated between the outer tube and the inner tube, the swirling flow is easily generated by making the outer tube and the inner tube cylindrical.

  The gap between the outer pipe and the inner pipe is also uniform if the outer pipe and the inner pipe are similar, but the outer pipe and the inner pipe have different shapes, and the gap between the two is the same. May be different in the axial direction.

  As another additional configuration, a temperature sensor (not shown) may be installed inside the catalyst layer, and the heater may be controlled according to the temperature detected by the temperature sensor. Furthermore, it is also preferable to provide a nozzle (not shown) for filling the inner tube with a catalyst in the outer tube.

  The gas to be processed has been described by taking the gas containing PFC as an example in the above-described embodiment. In the present invention, any gas containing fluorine is not limited to PFC, but monofluoromethane, difluoromethane, trifluoromethane, tetrafluoromethane, monochlorotrifluoromethane, dichlorodifluoromethane, trichloromonofluoromethane, hexafluoroethane, Fluorocarbons such as monochloropentafluoromethane, hexafluoroethane, tetrafluoroethylene, dichlorotetrafluoroethane, trichlorotrifluoroethane, octafluoropropane, hexafluoropropene, octafluorobutane, hexafluorobutene, octafluoropentene, difluorocarbonyl Nitrogen fluorides such as trifluoroammonia; Sulfur fluorides such as sulfur hexafluoride and difluorosulfoxide; Tetrafluor Silicon fluoride such as silane; and fluorinated oxygen such as difluoromethyl ether can be applied to the processing of various gases. As for the catalyst, a known catalyst can be used corresponding to the gas to be treated.

  Thus, by appropriately combining the gas to be treated and the catalyst, the gas treatment apparatus of the present invention can be used not only for the decomposition of the gas but also for the production of the compound.

  In the above-described embodiment, the reaction unit (for example, the PFC reaction unit 10) is provided in the former stage, and the secondary gas processing unit (for example, the second gas removal unit for removing HF) that further processes the gas generated in the reaction unit in the subsequent stage. A configuration having a secondary gas processing section 18) is shown. However, if the gas generated in the former reaction section can be released into the atmosphere as it is, the latter secondary gas processing section is not necessary.

  Next, specific examples of the present invention will be described together with comparative examples.

Example 1
In this example, CF ₄ was decomposed using the gas processing apparatus 1 having the configuration shown in FIG. The inner tube 12 was made of Inconel and had an inner diameter of 150 mm and a tube wall thickness of 4.0 mm. The outer tube 11 was made of stainless steel, had an inner diameter of 188 mm, and a height from the bottom surface to the gas introduction tube 15 of 500 mm. Therefore, the size of the gap C between the outer tube 11 and the inner tube 12 was 15 mm.

  A ceramic fiber heater (model number: VS-08A18T, output: 3.9 kW) manufactured by Sakaguchi Electric Heat Co., Ltd. was used as the heater 17 attached to the outside of the outer tube 11. The heater 17 was controlled so that the temperature of the wall surface of the outer tube 11 at the portion where the heater 17 was installed was 710 ° C. In addition, the temperature at the center of the catalyst layer 13 was also measured.

The catalyst layer 13 was filled with 6.8 L (liter) of an alumina catalyst. Therefore, the height of the packed bed 13 was about 380 mm. In addition, in order to promote heat transfer of the introduced gas, heat exchange section A was filled with 1.8 liters (height 100 mm) of alumina spheres (3.4 mmφ) as filler 13a. From the gas introduction pipe 15, an N ₂ -based gas containing CF ₄ at a ratio of 1% by volume was introduced at a flow rate of 43 L / min. Therefore, the space velocity SV expressed by “flow rate of gas to be treated / catalyst volume” was 375 / hr. Note that water and air were also introduced from the gas introduction pipe 15 together with the CF ₄ decomposition reaction. The ratios of water and air introduced together with the processing gas to the processing gas were 20% and 17%, respectively.

(Example 2)
CF ₄ was decomposed under the same conditions as in Example 1 except that the space velocity SV was 750 / hr (process gas flow rate = 85 L / min).

(Example 3)
CF ₄ was decomposed under the same conditions as in Example 1 except that the space velocity SV was 1500 / hr (processing gas flow rate = 170 L / min).

(Comparative Example 1)
In this example, CF ₄ was decomposed using a conventional catalytic reactor having a single-tube cylindrical reactor. The reactor was made of Inconel, the inner diameter was 150 mm, the tube wall thickness was 4.0 mm, and the height from the lower end to the gas inlet was 800 mm. The catalyst layer was filled with 6.8 L of alumina catalyst at a height of about 380 mm. The stage before the catalyst layer was filled with alumina spheres at a height of 400 mm as a preheating filler.

  A ceramic electric tubular furnace (model number: ARF-200-800) manufactured by Asahi Rika Seisakusho Co., Ltd. was used as a heater for preheating gas installed on the outer wall of the reactor. The heater was controlled so that the temperature of the wall of the reactor at the portion where the heater was installed was 740 ° C. In addition, the temperature at the center of the catalyst layer was also measured.

  The components of the gas to be treated were the same as those in Example 1. However, the space velocity SV was 169 / hr (processing gas flow rate = 19 L / min).

(Comparative Example 2)
CF ₄ was decomposed under the same conditions as in Comparative Example 1 except that the space velocity SV was 255 / hr (processing gas flow rate = 29 L / min).

(Comparative Example 3)
CF ₄ was decomposed under the same conditions as in Comparative Example 1 except that the space velocity SV was 341 / hr (process gas flow rate = 39 L / min).

(Comparative Example 4)
CF ₄ was decomposed under the same conditions as in Comparative Example 1 except that the space velocity SV was 429 / hr (processing gas flow rate = 49 L / min).

(Comparative Example 5)
CF ₄ was decomposed under the same conditions as in Comparative Example 1 except that the space velocity SV was 524 / hr (process gas flow rate = 59 L / min).

(Comparative Example 6)
CF ₄ was decomposed under the same conditions as in Comparative Example 1 except that the space velocity SV was 618 / hr (processing gas flow rate = 70 L / min).

(result)
Table 1 shows the measurement results of the temperature at the center of the catalyst layer for Examples 1 to 3 and Comparative Examples 1 to 6. Moreover, the graph of the relationship between the temperature of the catalyst layer center part and space velocity SV is shown in FIG.

表１および図７のグラフより、実施例１〜３は、空間速度ＳＶによらず触媒層中心部での温度がほぼ一定に加熱されていることがわかる。それに対して比較例１〜６では、空間速度ＳＶが大きくなればなるほど、すなわち処理ガスの流量が増加すればするほど、触媒層中心部での温度が著しく低下することがわかる。

From the graph of Table 1 and FIG. 7, it can be seen that in Examples 1 to 3, the temperature at the center of the catalyst layer is heated almost uniformly regardless of the space velocity SV. On the other hand, in Comparative Examples 1-6, it turns out that the temperature in a catalyst layer center part falls remarkably, so that the space velocity SV becomes large, ie, the flow volume of process gas increases.

Table 2 shows the CF ₄ concentration (before reaction, after reaction, and after 1 hour), reaction rate, and reaction rate for Examples 1 to 3. The concentration of CF ₄ was measured with an FT-IR (Fourier transform infrared) spectrometer (model number: FT-730G, cell optical path length: 10 m, resolution: 2 cm ⁻¹ ) manufactured by Horiba, Ltd. The reaction rate was determined by the following formula.
The reaction rate (%) = {- CF ₄ components / supplied gas (CF ₄ components supplied in the gas CF ₄ components in discharged gas)} × 100

表２より、空間速度ＳＶが大きくなるほど反応率が低下する傾向が見られるものの、ＳＶ＝１５００／ｈｒであっても８５％以上の反応率を達成できることがわかる。表には示していないが、比較例については、空間速度ＳＶが２００／ｈｒを越えると（比較例２〜６）、ＣＦ₄の反応率は６０％以下に低下するという結果が得られた。

Table 2 shows that although the reaction rate tends to decrease as the space velocity SV increases, a reaction rate of 85% or more can be achieved even when SV = 1500 / hr. Although not shown in the table, for the comparative example, when the space velocity SV exceeded 200 / hr (Comparative Examples 2 to 6), the result was that the reaction rate of CF ₄ was reduced to 60% or less.

  The time until the temperature of the central portion of the catalyst layer reaches a constant temperature (start-up time) was within 1 hour in each of Examples 1 to 3, but 2 to 3 hours in Comparative Examples 1 to 6. Cost.

  From the above, in Examples 1 to 3, the catalyst in the catalyst layer can be uniformly heated even if the flow rate of the gas to be processed is increased, and thus stable treatment is possible.

It is a figure which shows typically the structure of the gas processing apparatus by one Embodiment of this invention. It is sectional drawing of the outer tube | pipe and inner tube | pipe of the PFC reaction part shown in FIG. It is a cross-sectional view of a PFC reaction section at a portion where a gas introduction pipe is connected, showing an example of a structure for generating a swirl flow in the outer pipe. It is a cross-sectional view of the PFC reaction part in the part where the gas introduction pipe is connected, showing another example of a structure for generating a swirl flow in the outer pipe. It is a figure which shows typically the structure of the gas treatment apparatus by other embodiment of this invention. It is a figure which shows typically the structure of the gas treatment apparatus by further another embodiment of this invention. It is a graph which shows the relationship between space velocity SV and catalyst layer center part temperature in Examples 1-3 and Comparative Examples 1-6.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas processing apparatus 10,20,30 PFC reaction part 11,21,31 Outer pipe 12,22,32 Inner pipe 13,23,33 Catalyst layer 15,26,36 Gas introduction pipe 16,27,37 Gas exhaust pipe 17 , 24, 34 Heater 18, 25, 35 Secondary gas processing section 19 Conduit

Claims (10)

A gas processing apparatus for processing by passing a fluorine-containing compound gas through a catalyst layer,
An outer tube in which the compound gas is introduced from one end and the other end is closed;
An inner tube located on the inner side of the outer tube, having a gas discharge part on one end side, with the other end and the outer peripheral surface facing the other end and the inner peripheral surface of the outer tube with a gap, respectively;
A catalyst layer filled in the inner tube from the other end of the inner tube to an intermediate position toward one end;
A heater surrounding the catalyst layer and attached to the outer peripheral surface of the outer tube;
A gas processing apparatus.   When the superficial gas flow rate in the catalyst layer is U1, and the gas flow rate in the outer pipe is U2, the inner peripheral surface of the outer pipe and the inner pipe are adjusted so that U2 / U1 is 0.5 to 50. The gas processing apparatus according to claim 1, wherein a gap with an outer peripheral surface of the pipe is defined.   The outer pipe has a gas introduction part for introducing the fluorine-containing compound gas into the outer pipe, and the gas introduction part is configured so that the fluorine-containing compound gas introduced into the outer pipe is in the circumferential direction of the outer pipe. The gas processing apparatus according to claim 1, wherein the gas processing apparatus is configured to flow while forming a swirling flow along the line.   The gas introduction part is formed with an opening facing the circumferential direction of the outer pipe, and the gas introduction pipe attached to the outer pipe so that the opening is located in a space between the outer pipe and the inner pipe The gas processing apparatus according to claim 3, comprising:   The gas treatment according to any one of claims 1 to 4, wherein the fluorine-containing compound gas is a gas containing PFC, and the catalyst contained in the catalyst layer is a catalyst suitable for decomposing the PFC. apparatus.   The gas processing apparatus according to claim 5, wherein the outer tube is made of a stainless material.   The gas processing apparatus according to claim 5, further comprising a secondary gas processing unit that processes a corrosive gas generated by decomposition of the PFC.   The gas processing apparatus according to claim 7, wherein the secondary gas processing unit is integrated with the inner pipe so that the gas discharged from the gas discharge unit of the inner pipe is directly introduced. A gas treatment method for treating a fluorine-containing compound gas by passing it through a catalyst layer,
Using the processing apparatus of claim 1,
While heating the catalyst layer by driving the heater of the processing apparatus, the fluorine-containing compound gas is introduced into the outer pipe from one end of the outer pipe of the processing apparatus,
The fluorine-containing compound gas is allowed to flow from one end side to the other end side of the outer tube in the outer tube, and is sent to the inner tube on the other end side, passing through the heated catalyst layer, and A gas treatment method comprising decomposing a contained compound gas and discharging a processing gas from a gas discharge portion of the inner pipe.   The gas processing method according to claim 9, wherein the fluorine-containing compound gas introduced into the outer tube includes generating a swirling flow along the circumferential direction of the outer tube in the outer tube.

Images