WO1998001217A1

WO1998001217A1 - Method and equipment for decomposing fluorocarbons

Info

Publication number: WO1998001217A1
Application number: PCT/JP1996/001857
Authority: WO
Inventors: Chiaki Izumikawa; Kazumasa Tezuka; Kazuto Ito; Hitoshi Atobe; Toraichi Kaneko
Original assignee: Dowa Mining Co., Ltd.; Dowa Iron Powder Co. Ltd.; Showa Denko K.K.
Priority date: 1996-07-04
Filing date: 1996-07-04
Publication date: 1998-01-15

Abstract

A method for decomposing fluorocarbons by bringing perfluorocarbon or hydrofluorocarbon gas into contact with a reactant comprising a solid carbonaceous materials and an alkaline earth metal compound at a temperature of 300 °C or above in the presence of 20 vol.% or less (exclusive of 0 %) oxygen gas.

Description

Description Decomposition method and equipment for fluorocarbons

The present invention relates to a method for efficiently decomposing fluorocarbons, especially perfluorocarbon or hydrofluorocarbon having about 1 to 5 carbon atoms, and a simple apparatus therefor.

Background art

Japanese Unexamined Patent Publication No. Hei 6-293350 discloses that magnets are heated by applying a microwave to the inside of the applicator, and the fluorocarbon is decomposed by contacting the gas with the heated magnets. A method for doing so is disclosed. Japanese Unexamined Patent Application Publication No. Hei 7-244255 discloses that a mixture of a carbonaceous material and an oxide or salt of an alkaline earth metal is irradiated with a microphone mouth wave to generate heat, and the heat is generated. Disclosed is a method for decomposing alpha by contacting fluorocarbon gas with the mixture. Purpose of the invention

Since the chlorofluorocarbon decomposition method described in the above-mentioned publications all uses a microphone mouth wave, an expensive microphone mouth wave generator is required, and the reaction vessel is limited to a heat-resistant material through which the microphone mouth wave is well transmitted. Problem. Some heat-resistant materials that allow microwaves to penetrate well are ceramic materials, but many of these materials react with fluorine to deteriorate the material. Therefore, there was still another problem in performing industrially inexpensive and stable CFC decomposition. ₍ Therefore, as a technology for decomposing CFCs without using microwaves, the same applicant has 7-year patent application No. 28619 (not disclosed) in a non-oxidizing atmosphere In this paper, we proposed a phantom decomposition method in which fluorocarbon gas is brought into contact with a material containing a heated carbonaceous material and an alkaline earth metal compound to cause a reaction. According to this prior application method, there is an advantage that the front can be decomposed even by using an ordinary heating furnace using an electric heater, and as described in this specification, R-113 etc. Can be efficiently decomposed.

According to subsequent studies, not all types of fluorocarbons can be decomposed by this prior application method, and perfluorocarbons and hide ports not described in the prior application specification can be decomposed. It was found that the decomposition efficiency was not always good for fluorocarbons such as fluorocarbons which do not have chlorine groups.

Accordingly, an object of the present invention is to develop an industrial method for efficiently decomposing carbon fluorides having no chlorine group, such as perfluorocarbon and hide-mouth fluorocarbon. Disclosure of the invention

The above-mentioned problem is that the gas of perfluorocarbon or hydrofluorocarbon is added to a reactant composed of a carbonaceous solid material and an alkaline earth metal compound at a temperature of 300 or more and at a temperature of 200 or more. It was found that the solution can be achieved by contacting in the presence of gaseous oxygen of vol.% or less (not including 0%). More specifically, a gas to be treated containing perfluorocarbon or fluorocarbon is continuously placed in a reaction vessel that is fully immersed in a reaction (1) consisting of a carbonaceous solid material and an alkaline earth metal compound. The exhaust gas after the reaction is continuously or intermittently discharged from the reaction vessel while being transported intermittently or intermittently, so that the oxygen concentration in the gas to be treated becomes 20 vol.% Or less. Oxygen into the gas to be treated before entering the reaction vessel (1), and transferring the heat required to decompose the perfluorocarbon or the hydrofluorocarbon from the outside of the reaction vessel to the reaction zone, or Inside the container It was found that the carbon fluoride gas could be efficiently decomposed by transmitting it from the side to the reaction zone.

In the method of the present invention, CO may coexist in the exhaust gas. In this case, preferably provided a step of oxidizing the C 0 in the exhaust gas to the C 0 _2. Further, in the method of the present invention, as a material constituting the reaction vessel, a heat-resistant alloy or a corrosion-resistant alloy such as stainless steel or a nickel-based alloy can be used. If the material is resistant to fluorine or hydrogen fluoride, the ceramic can be used. Boxes (for example, ceramics using aluminum fluoride) can also be used. Then, this reactor is installed in a furnace that can maintain the temperature of the furnace atmosphere at a required temperature, and the heat in the furnace can be transferred to the reactants in the container through the container wall.

Further, according to the present invention, as a device for suitably performing the above-mentioned decomposition method, a reaction vessel loaded with a reaction から composed of a carbonaceous solid material and an alkaline earth metal compound is provided. A gas inlet for gas to be treated provided in the reactor, a gas outlet provided for discharging gas after reaction from inside the reaction vessel, a furnace for accommodating the reaction vessel, and an atmosphere temperature in the furnace. A heat source for increasing the temperature to 300 or more, a pipe connecting the gas to be treated inlet and the gas containing carbon fluoride gas, and, if necessary, communicating with the gas outlet. Provided are an exhaust gas oxidizer connected to piping and a device for decomposing carbon fluorides consisting of As the reaction vessel, one composed of a heat-resistant alloy or a corrosion-resistant alloy as described above can be used. As a carbon fluoride-containing gas source, for example, a carbon fluoride-containing gas generated in a semiconductor manufacturing process and containing an appropriate amount of oxygen can be used. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is an equipment layout diagram showing an example of an apparatus for implementing the method of the present invention.

Fig. 2 shows another example of the exhaust gas path section of the device for implementing the method of the present invention. It is a device arrangement system diagram.

FIG. 3 is a device arrangement system diagram showing another example of the target gas introduction section for implementing the method of the present invention.

FIG. 4 is a schematic cross-sectional view of a reaction vessel part showing an example of heating a reaction vessel from inside the reaction vessel according to the method of the present invention.

FIG. 5 is a schematic sectional view of a reaction vessel part showing another example of heating a reactant from inside the reaction vessel according to the method of the present invention.

FIG. 6 is a diagram showing an example of performing heat exchange between the gas to be treated before entering the reaction vessel and the exhaust gas flowing out of the reaction vessel in carrying out the present invention.

Fig. 7 shows the inflow of CFC and the amount of CFC when the trifluorene (CFC) is decomposed in the case where the oxygen concentration in the gas to be treated is 0% and 10%. It is a figure showing the relation of the decomposition rate.

Figure 8 shows the flow rate of PFC and the decomposition rate of PFC when perfluoroethane (PFC) was decomposed when the oxygen concentration in the gas to be treated was 0% or 10%. FIG.

Figure 9 shows the difference in the decomposition rate of perfluoroethane (PFC) when the heating method for the reactants is electric heater heating and when microwave heating is used. Preferred embodiments of the invention

The present invention is a method for decomposing perfluoro-open carbon or hydrofluorocarbon having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms, wherein the decomposed fluorine is absorbed by a reactant and the decomposed carbon ( Furthermore, hydrogen) migrates into the exhaust gas. The perfluorocarbon or hydrofluorocarbon which can be suitably decomposed in the present invention is, for example, a substance which can be easily vaporized at room temperature (for example, a substance which is vaporized by accompanying an inert gas such as nitrogen gas). including) _{_{where, CF 4, C 2 F s}} , C 3 F 8, C - C 4 F 8 Etc., or a _{_{_{CHF 3. CH 2 FC 2 HFC}}} 2 H 2 F 4 , and the like. To carry out these decomposition reactions, a gas of perfluorocarbon or hydrofluorocarbon is added to a reactant composed of a carbonaceous solid material and an alkaline earth metal compound. It is important that the contact be made at a temperature of 0 ° C or higher and in the presence of 2 Ovol.% Or less (excluding 0%) of gaseous oxygen. Here, the carbonaceous solid material, one of the materials constituting the reactant, is one or two selected from the group consisting of coke powder, charcoal charcoal, coal, raw pitch, charcoal, activated carbon, and carbon black. The above can be used, and the form is preferably powdery. Alkaline earth metal compounds which are the other materials constituting the reactant include calcium, magnesium, rhodium or strontium oxide, calcium, magnesium, barium or strontium hydroxide, and One or two or more compounds selected from the group consisting of calcium carbonate, magnesium, barium and stomium carbonate or nitrate can be used, and preferably, calcium oxide is used. , Hydroxide, carbonate, or nitrate. Of these, quicklime, slaked lime, and limestone are advantageous because they are easy to handle.

These reactants can be used by directly charging a powdery or granular carbonaceous solid material and a powdery or granular alkaline earth metal compound in a reaction vessel. It is preferable that the solid material and the powdered alkaline earth metal compound are mixed and this mixture is granulated into granules of a size that is easy to handle. As a result, the carbon and the alkaline earth metal compound are brought close to each other, and the specific surface area (surface area per unit weight) of the reactant is increased, thereby increasing the chance of contact with the gas to be treated. it can. For granulation, water or an organic binder is used, and the granulated product is dried or fired to obtain a granulated product having sufficient strength and porosity. In the process of manufacturing such granulated products, the coal used as raw material Solid carbon and alkaline earth metal are present in the granulated product, even though they may change to a solid material or a powdered alkaline earth metal compound or its morphology and compound type or other. As long as the components are present in the required ratio, they can contribute to the decomposition reaction of the present invention.

For example, charcoal is used as a carbonaceous solid material, slaked lime is used as a raw earth metal compound, and these powders are blended in a required ratio. Water is added and kneaded. Particle size, eg 1 to 1 Omm, preferably! When the pellets are granulated to a size of ~ 5 mm and baked in a non-oxidizing atmosphere (for example, baked at 500 to 850 ° C), pellets are produced during the firing process. Most of the volatile components are removed, and slaked lime is completely transformed into oxidized calcium, so that highly pure pellets containing carbon (C) and calcium oxide (CaO) as main components can be obtained. The thus obtained reactant composed of C and Ca0 has sufficient strength and is a porous material having a large specific surface area, so that it can be suitably used for carrying out the method of the present invention.

Although the relative proportion of the carbonaceous solid material and the alkaline earth metal compound constituting the reactant depends on the type of these materials and compounds used, according to the experience of the present inventors, the weight ratio of the two materials is determined. Speaking of which, it is better to have the latter half more. In terms of the molar ratio of carbon (C) in the carbonaceous solid material to the oxide (MO) of alkaline earth metal (M) in the alkaline earth metal compound, the molar ratio of C / MO = 0.9 to 2,3, preferably 0.9 to 1.9, more preferably 4 to 1.9.

It is considered that perfluorocarbon or hydrofluorocarbon is a compound that is more stable than fluorofluorocarbon and hydrofluorocarbon, and is not easily decomposed. However, when perfluorocarbon or hydrofluorocarbon is brought into contact with the reactant according to the present invention at a temperature of 300 ° C. or more in the presence of oxygen, it can be decomposed efficiently. The lower limit of the required temperature is perfluorocarbon It depends on the type of bonfire or hydrofluor. If the required temperature is maintained, some decomposition occurs even in the absence of oxygen, but the decomposition efficiency is poor. On the other hand, in the case of chlorine-containing fluorocarbon gas such as fluorocarbons, the presence of oxygen does not significantly contribute to the decomposition even when the same reactant is used. There is a phenomenon in which decomposition proceeds more.

Therefore, in the method of the present invention, it is essential that an appropriate amount of oxygen gas is present in the gas to be treated, and the oxygen concentration is at least 5 vol. Good. However, 20 vol.? If the oxygen concentration is too high, the consumption of carbon in the reactant increases, and the effect of accelerating the decomposition reaction becomes saturated. Therefore, the oxygen concentration in the gas to be treated is 0.5 to 20 vol.%, Preferably 2 to 15 vol.%, And more preferably 5 to 10 vol.%. The reason why the decomposition of perfluorocarbon or hydrofluorcarbon proceeds efficiently due to the presence of this oxygen is not always clear at present. Air can be used as the oxygen source in the gas to be treated. Sometimes it may be a source of oxygen for oxygen C 0 _2.

In order to bring perfluorocarbon or hydrofluorocarbon (hereinafter abbreviated as PFC or HFC, or simply referred to as carbon fluoride) into contact with this reactant, an inert gas such as nitrogen gas is used. It is convenient to supply the reactants continuously or intermittently as a carrier. In this case, the carbon fluoride is diluted with an inert gas, which acts to carry away heat but does not substantially participate in the reaction. In the present specification, the term “oxygen concentration in the gas to be treated” means the oxygen concentration in the total gas containing such an inert carrier gas when the gas contains such an inert carrier gas.

FIG. 1 shows an example of an apparatus for implementing the method of the present invention. 1 in the figure is a metal reaction vessel (tube), which contains carbonaceous solid material and aluminum. Reactant 2 consisting of lithium earth metal compound is loaded. In the example shown in the figure, a reaction vessel 1 having a tubular shape is a vertical type, and a reactant 2 is mounted on a permeable floor 3 fixed in the vessel. As the metal tube of the reaction vessel 1, a tube made of stainless steel or nickel alloy can be used.

The reaction vessel 1 is set in a ripening furnace 4. The heating furnace 4 shown in the figure uses an electric heater 5 that uses a heating element that generates heat when energized as a heat source. The electric heater 5 raises the temperature of the furnace / atmosphere 6 to a required temperature. The heat in the furnace is transferred to the reactant 2 via the metal reaction vessel wall. The heat source is not limited to electric heaters as long as the temperature of furnace-atmosphere 6 can be raised to the required temperature. For example, high-temperature gas such as combustion exhaust gas can be used as the heat source.

In this way, the reaction vessel 1 installed in the heating furnace 4 is provided with the gas to be treated 7, and the gas to be treated 7 is connected by piping to the carbon fluoride vessel 8 containing PFC or HFC. Is done. The carbon fluoride container 8 can be indirectly heated by the heating means 9 if necessary, and this heating increases the gas pressure in the carbon fluoride container 8. The gas discharge pipe 10 from the container 8 is provided with a flow control valve 11. In the embodiment shown in Fig. 1, in addition to the carbon fluoride container 8, an oxygen gas cylinder 12 and a nitrogen gas cylinder 13 are separately provided. From these, oxygen gas and nitrogen gas are supplied to flow control valves 14 and 15, respectively. Oxygen gas is added to the carbon fluoride gas by leading it to the gas header 118 via the interposed gas discharge pipes 16 and 17 and leading the carbon fluoride to this header 118. At the same time, nitrogen gas as a carrier is mixed, and the gas to be treated mixed by the header 18 is sent to the gas to be treated inlet 7 of the reaction vessel 1 through the gas supply pipe 19. .

The present invention is not limited to this example, and a mixed gas obtained by premixing carbon fluoride, nitrogen and oxygen is prepared in one container, and this mixed gas is directly sent to the gas inlet 7 to be treated. Okay, put nitrogen gas in carbon fluoride container 8 The carbon fluoride is forcibly sent out of the container by this nitrogen gas. Oxygen gas may be added to the discharge line. In any case, the oxygen gas introduction pipe is connected to the vessel 8 itself or to the pipe from the vessel 8 to the gas guide 7 to be treated.

On the other hand, an exhaust gas pipe 21 is connected to the gas outlet 20 of the reaction vessel 1, and the exhaust gas pipe 21 is connected to a halogen absorption bin 22. A gas discharge pipe 23 is attached to this bin 22. Have been. A sampling pipe 24 is attached to the exhaust gas pipe 21, and the gas sampled by the sampling pipe 4 is sent to the gas separator 25.

Figure 2 shows an example in which an exhaust gas oxidizer 26 is connected to the exhaust gas pipe 21 of the exhaust gas coming out of the reaction vessel 1. It is those substantially entire amount of the exhaust gas passing through the exhaust gas oxidizing apparatus 2 6 Yoko was made to pass through the catalyst layer 2 7, promoting the oxidation reaction from C 0 to C 0 ₂ in the catalyst layer 2 7 Oxidizing catalyst is installed. As this catalyst, a catalyst in which a noble metal catalyst such as platinum or palladium is supported on a heat-resistant carrier, or a hopcalite catalyst can be used. Further, an oxygen introduction pipe 28 for adding oxygen to the exhaust gas before entering the exhaust gas oxidizing apparatus 26 is connected, and a flow control valve 29 of the oxygen introduction pipe 28 causes a flow from the oxygen source 30 to be stopped. Adjust the amount of oxygen added to the exhaust gas. A line 35 for introducing nitrogen gas 34 is provided in the exhaust gas line 21 upstream of the position where oxygen is introduced, and nitrogen gas 34 is mixed in the exhaust gas from this line 35. by the so as to introduce a C 0 concentration lower to whether we oxygen in the exhaust gas, even if the C 0 concentration in the exhaust gas was high summer, such as burns C 0 or C 0 ₂ oxygen introduction position The phenomenon can be suppressed. Air can be used as the oxygen source 30 added to the exhaust gas. The exhaust gas that has passed through the exhaust gas oxidizer 26 is sent to the halogen absorption bin 2 along the same route as in Fig. 1.

In the apparatus shown in Fig. 1 and Fig. 2, The temperature of the atmosphere inside the furnace 4 is transmitted through the vessel wall. As shown in the figure, the temperature of the reaction zone continues to be detected by the temperature sensor 32 by the temperature sensor (thermocouple) 31 inserted near the center of the reaction cell 2 as shown in the figure. The amount of heat supplied from the heat source 5 is controlled so that the temperature is maintained. In addition, heating furnace

The temperature of the furnace atmosphere 6 in 4 is also detected by the temperature sensor 33, and the temperature of the heating furnace itself is appropriately controlled based on the detected value.

Thus, the PFC or HFC in the gas to be treated is almost completely (

At a decomposition rate of nearly 100%), and the decomposed fluorine reacts with the alkaline earth metal in the reactant to form an alkaline earth metal fluoride. Fluorine no longer remains. Moreover it or be oxidized by the exhaust gas oxidizing apparatus 2 6 all C 0 in the exhaust gas to the C 0 _2. Fig. 3 shows an example in which used PFC or HFC used in the semiconductor manufacturing process is decomposed according to the present invention. Spent PFC or HFC from the semiconductor manufacturing process is usually extracted as carbon fluoride containing oxygen and nitrogen. This oxygen-containing carbon fluoride 37 is generally sent via a line 38 to a routine treatment step 36. To apply the present invention, the carbon fluoride supply pipe 38 is connected to the gas inlet 7 of the reaction vessel 1. In the illustrated example, a branch pipe 40 is attached from the supply pipe 38 via a three-way valve 39, and this branch pipe 40 is connected to the gas inlet 7 to be processed. A nitrogen gas supply pipe 41 is connected to the branch pipe 40 so that nitrogen gas can be sent from the nitrogen gas source 42 into the branch pipe 40 at a variable flow rate. As a result, when the three-way valve 39 is switched, even if the source gas is difficult to flow toward the branch pipe 40, the source gas is supplied by supplying a necessary amount of nitrogen gas from the nitrogen gas source 42. It can be conveyed toward the processing gas inlet 7 at substantially the same flow rate. The used PFC or HFC is usually extracted as a gas containing oxygen and nitrogen, and the oxygen content in the used gas does not usually exceed 20% by volume. Therefore, the method of the present invention is very advantageous for the decomposition of used PFC or HFC discharged in the semiconductor manufacturing process.

FIGS. 4 and 5 show an example of the present invention in which a heating source is installed inside the reaction vessel 1 so that ripening is transmitted to the reactant 2 from inside the vessel. In both figures, reference numeral 44 denotes a heat-resistant furnace material surrounding the reaction vessel 1, reference numeral 7 denotes an inlet for the gas to be treated into the vessel, and reference numeral 20 denotes a gas outlet from the vessel.

In the case of Fig. 4, a heating element 43, which generates heat when energized, is arranged inside a layer of the reactant 2, and the heating element 43 is covered with a corrosion-resistant heat-resistant cover. According to this example, since heat is transferred from the inside of the packed bed of the reactant 2, the heating rate for raising the reactant to the desired temperature can be increased, and the heat loss is reduced.

In the case of Fig. 5, the inside of the reaction vessel 1 is divided into a packed bed of the reactant 2 and a heating bed, and the gas to be treated introduced into the vessel 1 passes through the heating bed and then to the packed bed of the reactant. It is made to flow. In the heating layer, a heating element 46 that generates heat when energized is attached to the container lid 45. The gas to be treated is given heat when passing through the heating layer and is also transferred to the reactant 2. In this example, since the electric heater is placed in the container, there is an advantage that the heat utilization efficiency is high and the heat generating body 46 does not contact the reactant or the gas after the reaction, so that the deterioration is small.

Fig. 6 shows an example of the present invention in which a heat exchanger 48 for exchanging heat between the gas to be treated before being introduced into the reaction vessel 1 having a heating source and the exhaust gas discharged from the reaction vessel 2 is arranged. It is a thing. By arranging this heat exchanger 48, the sensible heat of the exhaust gas is imparted to the gas to be treated, so that the maturation can be recovered, so that the heat consumption of the heating source can be reduced. In the case of the above-described apparatus of the present invention, when the charged reactants are exhausted, the decomposition reaction 1 is terminated. The end point of the reaction can be known from the time when the detection of carbon fluorides or other fluorine compounds in the exhaust gas has started. When the reaction is completed, the operation of the equipment is stopped, and the reaction is started by adding a new reactant. This allows the decomposition of carbon fluorides sequentially using the same equipment. In order to make this batch system continuous, multiple similar units were installed side by side, and while one unit was operating, the reactants in the other unit were replaced, and one unit stopped. Sometimes, a double-tower switching system in which the gas flow path is switched to the other device can be adopted. In addition, if a continuous or intermittent supply of the reactant into the reaction vessel and a continuous or intermittent discharge of the used reactant from the reaction vessel are used, the same device can be operated continuously for a long time. it can.

Fig. 7 shows that, as in the comparative example described later, trichloro-trifluorethane (CFC) containing chlorine as a constituent was converted to a concentration of 10 vol.% Of CFC and a gas flow rate of 0.15 liter. Torno content, molar ratio of CZC a0 in the reactant: 1.6 7. Maximum temperature of the reactant: 800 ° C, when the oxygen concentration in the gas to be treated is 0% and 1 ()% This shows the relationship between the inflow of CFC and the CFC decomposition rate during the decomposition treatment of. Here, the decomposition rate of CFC is as described below, and the inflow of CFC is the integrated amount (g) of CFC that has flowed into the reaction vessel until the indicated decomposition rate. From the results shown in Fig. 7, it can be seen that in the decomposition treatment of chlorofluorocarbon containing chlorine as a component, the decomposition rate drops sharply if the target gas contains oxygen.

On the other hand, Fig. 8 shows that, as in Example 1 described later, perfluoroethane (PFC) was mixed with PFC concentration: 10 vo%, gas flow rate: 0.15 liter / min, and C Assuming that the Ca ratio is 1.67 and the maximum temperature of the reactant is 800, the PFC is decomposed when the oxygen concentration in the gas to be treated is 0% and 10%. The relationship between the inflow of PFC and the decomposition rate of PFC was shown. Things. In other words, the reaction conditions in Fig. 8 are the same as those in Fig. 7, except that trichloro-trifluorene is replaced by perfluorene as the gas to be decomposed. In Fig. 8, contrary to the one in Fig. 7, it is clear that the decomposition rate drops sharply if the gas to be treated does not contain oxygen.

Fig. 9 shows the difference in the decomposition rate of perfluoroethane (PFC) when the heating method is electric heater heating as in the example and when the heating method is microphone mouth wave separately. It is. In each case, the reaction conditions were as follows: concentration of carbon fluoride: 1 Ovol.%, Gas flow rate: 0.15 liter Z, oxygen concentration: 10 vol.%, CZC of reactant The molar ratio of a0 is set to 1.67. Microwave o-wave heating is performed by forming the reaction tube of the later-described embodiment from a ceramic material having microphone mouth-wave transmission, and applying this to an microwave oven. The reactor had the same capacity as the example described later, except that it was installed inside the reactor.

As can be seen from the results in Fig. 9, in the case of electric heater heating, the maximum temperature of the reactants in the reaction tube was maintained at 800 ° C throughout, and until the cumulative inflow of PFC became about 40 g. The decomposition rate was close to 100%, and when the flow rate was about 55 g, the decomposition rate was reduced to 95%. On the other hand, in the case of microphone mouth-wave heating, the decomposition rate began to drop when the integrated inflow of PFC was about 20 g, and the temperature of the reactant could not be maintained at 800 ° C. The agent temperature also dropped sharply. In other words, when the cumulative inflow of PFC was 29 g, the decomposition rate was 95%, and the temperature of the reactant was 600 ° C. Thereafter, both values dropped sharply, and the decomposition treatment became ineffective. This is because, in the case of microwave heating, if the gas to be treated contains oxygen, the reactant (particularly carbon) is oxidized, and the microwave cannot maintain the reactant temperature at the intended temperature for a long time. It is presumed to be. Example

(Example 1)

The method of the present invention was carried out using an apparatus having the same principle as that shown in FIG. In other words, along the axis of a tubular furnace (electrical capacity 20 KW) equipped with a heating element (using a Kanthal alloy) that generates heat when energized, an austenitic system with an inner diameter of 28 mm and a length of 100 Omm was used. A reaction tube made of stainless steel (SUS304) was penetrated, and 100 g of a granular reactant prepared using charcoal and slaked lime as raw materials was charged into the furnace center of the reaction tube. This reactant was prepared by mixing charcoal with a particle size of 250 m or less and slaked lime with a particle size of 250 or less at a weight ratio of 1: 3, mixing with a Henschel mixer, adding water, and granulating. After drying at 110 ° C for 4 hours, heat-treating at 800 ° C for 8 hours in a nitrogen atmosphere, and dehydrating and firing. It is a pelletized pellet. The raw material used was charcoal with a fixed carbon content of 78%, volatile matter of 9%, ash content of 3% and water content of 10%, and slaked lime used as a raw material of JIS 9001 standard. Analysis of the produced pellets revealed that the reactant pellets were composed mainly of carbon (C) and calcium oxide (Ca〇), and the molar ratio of CZC a0 was 1.67. A thermocouple was placed at the center of the reactant and the temperature of the reactant was measured during the reaction.

Using the per full O b ethane (C ₂ F _e) as fluorocarbon subjected to decomposition, as shown in Figure 1, with the addition of oxygen gas to the path one Furuoroetan, the nitrogen gas as a wire carrier Rya Led to the reaction tube. At that time, the flow rate of the gas to be treated was fixed at 0.15 liters, and five tests (Να1 to 5) were performed with only the amount of oxygen gas added. In each case, the amount of carbon fluoride in the gas to be treated was kept constant at 10 vol.%. In each case, the introduction of the gas to be treated was performed after the energization of the heating element was started and the temperature at the center of the reactant reached 800 ° C. Responsive During this time, the capacity of the tubular furnace was adjusted so that the temperature measured by a thermocouple inserted at the center of the reactant (the part of the bulk of the reactant where the temperature became high) was maintained at 800 ° C. Controlled. This temperature maintained during the reaction is hereinafter referred to as "reactant maximum temperature".

A part of the exhaust gas discharged from the reaction tube continues to be sampled as shown in Fig. 1 and led to the gas analyzer, and the rest goes out of the system after passing the caustic soda solution through the separated fluorine absorption bottle. Discharged. Analysis of exhaust gas, containing Murrell fluorocarbon in the exhaust gas, and other fluorine compounds, 0 _2. N _2, was performed on C_〇 _2, CO. Fluorocarbon, for _{_{0 2, N 2. C 0}} 2 uses Gasukuroma preparative graphics, using C 0 gas detecting tube for C_〇, and for other fluorine compounds of that were using ion chroma Togurafi .

Table 1 shows the reaction conditions and reaction results of each test (Na 1 to 5). In Table 1, the decomposition rate after 30 minutes, the amount of decomposition of carbon fluoride, and the Ca〇 consumption rate of the reactant shown in the column of reaction results were determined as follows.

[Decomposition rate% after 30 minutes]

The amount of carbon fluoride remaining in the exhaust gas was measured from the exhaust gas sample 30 minutes after the start of the reaction, and the amount of carbon fluoride in the exhaust gas with respect to the amount of carbon fluoride in the gas to be treated was 100 minutes. Expressed as a percentage.

[Decomposition amount of carbon fluoride (g)]

This is the amount of carbon fluoride decomposed by the end of the reaction. The end point of the reaction was the time when the decomposition rate dropped to 95%. Actually, the decomposition rate every 30 minutes was calculated from the exhaust gas analysis value every 30 minutes, and the value obtained by multiplying the amount of carbon fluoride that flowed in each 30 minutes by the decomposition rate at that time was used for that 30 minutes. The amount of decomposition of carbon fluoride (g) was defined as the integrated value of the amount of decomposition from the start of the reaction until the decomposition rate decreased to 95%.

[C a 0 consumption rate of reactant%]

As a percentage of the amount of C a 0 in the reactants consumed up to the reaction end point is there. Flip assumed to occur in the generation of consumed Haji 3 ₂ 30, from the integrated value of the amount of fluorine fluoride in the carbon decomposed by the reaction end point, the accumulated value of the full Tsu quantal detected in the exhaust gas, C The integrated value of the amount of fluorine fixed to a was determined, and the amount of C a 0 consumed up to the end of the reaction was calculated.

From the results in Table 1, it can be seen that at では α1 where the oxygen concentration in the gas to be treated is 0%, the decomposition rate after 30 minutes has reached almost 100%, or the decomposition of carbon fluoride decomposed by the end of the reaction. Although the amount was 13 g, as the oxygen concentration increased as in Nos. 2 to 4, the decomposition rate after 30 minutes also reached 100% and decomposed by the end of the reaction. It can be seen that the decomposition amount of carbon fluoride has increased to 3-5. When the oxygen concentration is further increased as in No. 5, the amount of decomposition of carbon fluoride up to the end of the reaction slightly decreases. In addition, as can be seen from the measurements of Να3 and の 0, the amount of C0 in the exhaust gas of No. 4 with the larger amount of added oxygen was larger than that of Να3.

(Example 2)

The same tests as in Example 1 (Nos. 6 to 9) were performed, except that the oxygen concentration in the gas to be treated was kept constant at 5 vol.% And the reactants were used with different molar ratios of CZCaO. . The molar ratio of CZC a0 in the reactant was determined by analyzing the pellets produced in the same manner as in Example 1 by changing the blending amounts of charcoal and slaked lime. The amount was measured and determined from these measurements. The test results are also shown in Table 1. This result indicates that the amount of decomposition of perfluoroethane up to the end of the reaction is affected by the molar ratio of C7Ca0. In this example, it can be seen that the best results were obtained when the molar ratio of C / Ca0 was about 1.7.

(Example 3)

The same test as in Example 1 was conducted except that perfluoromethane was used instead of perfluoroethane. At that time, the oxygen concentration was changed to 0% (No. 10) and 10% (No. 11). Table 1 shows the test results. It can also be seen that the amount of decomposition up to the end of the reaction was significantly increased by the addition of oxygen.

(Example 4)

The same test as in Example 1 was performed except that trifluoromethane (CHF ₃ ) was used instead of perfluoroethane. At that time, the concentration of carbon fluoride and the concentration of oxygen were both constant at 5 vol.%, The gas flow rate was 0.12 liter Z, and the reactant was C / C a0 mole = 1.6. The maximum temperature of the reactants was changed (Να12 to 17) using the sample No. 7 (Fig. 7). The results are shown in Table 1. The maximum reaction temperature was 40 (decomposition rate after 30 minutes was lower than TC, whereas almost 100% was degraded at 400 ° C or higher. [Comparative Example]

Trichlorotrifluoroethane containing chlorine as a constituent was subjected to the same decomposition treatment as in Example 1. Table 1 also shows the reaction conditions and the reaction results. In this case, the amount of decomposition increased when oxygen was not present in the gas to be treated (Comparative Example No. 1), and the amount of decomposition was rather reduced when oxygen was present (Comparative Example 2).

(Example 5)

Tests in Examples 1 and 2 パー Perfluorobenzene was decomposed under the same reaction conditions as α3. At that time, nitrogen was added to the exhaust gas (CO concentration: 20%) as shown in Fig. 2. After adding oxygen, the mixture was guided to an exhaust gas oxidation unit 26 and passed through a catalyst layer 27 (Test No. 18). The amount of nitrogen added was 5.0 liters Z, the amount of oxygen added was 1.5 liters / minute, and the catalyst was a commercial product containing 0.5% platinum supported on alumina (manufactured by Nikki Chemical Co., Ltd.). It was used. The results are shown in Table 1, and the C0 concentration in the exhaust gas was 0%.

(Example 6)

The same reaction conditions as in Test No. 3 of Example 1 except that the reaction temperature was set to 700 In this case, perfluoroethane was decomposed (Test # α19). The reaction results are shown in Table 1. The results were slightly inferior to those of Να3 at 800 ° C. However, sufficient decomposition was performed.

(Example 7)

The same test as in Example 4 was carried out except that 1,1,1,2 tetrafluoroethane (C ₂ H ₂ F ₄ ) was used instead of trifluoromethane (C HF ₃ ) (Test # α20) . At that time, the maximum temperature of the reactant was set to 35 (TC. The results are shown in Table 1. The decomposition rate was close to 100% even at 350 ° C.

¾ 1

Test reaction condition Reaction result

So-called experiment

種類 Kind of α-carbon fluoride ¾ ^ Oxygen concentration of carbon C / CaO reaction of reactant ¾ ^ After 30 minutes; [Molar ratio of degas exhaust gas vol.% Vol.%, Decomposition rate% rfk (g ) coi degree ¾

1 74 years old [) e emissions _{C z F, 10 () 0.15} 1.67 800 99.9 13 22

2 Same as above 1 Same as above Same as above 99.9 31 53

(1)

3 Same as above Same as above Same as above 99.9 51 88 20

4 Same as above 10 Same as above Same as above 99.9 52 90 30

5 Same as above 20 Same as above Same as above 99.9 31 53

6 Perfluoroethane C ₂ F (j 10 5 0.15 0.78 800 97.3 13 20

7 [5j [, 5 "J] — Same as above 1.17 Same as above 99.9 39 63

Example

(2) (3) ί ^ Ι [51 G Same as above 1. G 99.9 51 88 20

8 f5l [[Hi 回同同 same as above 2.06 [1] above 99.9 39 72

9 [s Ji J J I IJ Ditto 99 6 26 53

Example 1 π u 0.15 QQ 13

(3)

11 fHl J-t in l Γ l ⁿ ! L .J-t gg 9 Q

12 1 ・ Rifle 1tan CHF ₃ 5 5 fi 1.67 300 34.3

13 Same as above Same as above Same as above 350 56.9

14 Same as above Same as above Same as above 385 85.6

鰂

15 (g. L 1 = 1 J J inn Rfi

16 Same as above Same as above Same as above 410 99.7 60 94

IT Same as above Same as above Same as above 450 99.9 61 95

1 222- ke B-112- l 10 0 0.15 1.67 860 99.9 55 70

i Tan C ₂ C1 ₃ F ₃

Hiko example

2 Same as above 10 Same as above Same as above 99, 9 13 16

Out

(5) 18 bar - 71 αιί emissions _{C 2 F, i 10 5 0.15} 1. C7 800 9D.9 51 83 0

(6) 19 '1-7 | 0? C Fu 10 5 0.15 1.67 700 89.5

Implementation 1.1.1.2

(7) 20 IJC ₂ H ₂ F, 5 5 0.12 1.67 350 96.8 56 82

As described above, according to the present invention, perfluorocarbon or hydrofluorocarbon can be completely decomposed by a simple treatment method, and the decomposed fluorine can be fixed as a harmless substance. For this reason, the method for decomposing carbon fluorides of the present invention is simple because of the simplicity of the decomposer, the high efficiency of decomposition, the ease of post-treatment of decomposition products, and the low cost of the reactants. It has an effect that is not available in particular, and can make a great contribution to the decomposition of used perfluorocarbon or hydrofluorocarbon generated in the semiconductor manufacturing process.

Claims

The scope of the claims

1. A gas of perfluorocarbon or hydrofluorocarbon is added to a reactant composed of a carbonaceous solid material and an alkaline earth metal compound at a temperature of 300 ° C or more and 20 vol. A method for decomposing carbon fluorides, comprising contacting in the presence of gaseous oxygen of not more than 0% (excluding 0%).

2. Continuously or intermittently feed gas to be treated containing perfluorocarbon or hydrofluorocarbon into a reaction vessel into which a reaction (2) consisting of a carbonaceous solid material and an alkaline earth metal compound is loaded. And the exhaust gas after the reaction is continuously or intermittently discharged from the reaction vessel. At that time, the exhaust gas is introduced into the reaction vessel so that the oxygen concentration in the gas to be treated becomes 20 vol. To include oxygen in the previous gas to be treated, and to transfer the heat necessary to decompose the perfluorocarbon or fluorocarbon at the outside of the reaction vessel to the reaction zone or from the inside of the reaction vessel; A method for decomposing carbon fluorides, which is transmitted to the reaction zone.

3. To continuously or intermittently transport the gas to be treated, including perfluoro-α-carbon and hydrofluorocarbon, into a reaction vessel equipped with a reaction composed of a carbonaceous solid material and an alkaline earth metal compound. After the reaction, the exhaust gas is discharged continuously or intermittently from the reaction vessel. In this case, the exhaust gas before entering the reaction vessel is controlled so that the oxygen concentration in the gas to be treated becomes 20 vol.% Or less. The process gas contains oxygen, and the heat required to decompose the perfluorocarbon or hydrofluorocarbon is transferred from the outside of the reaction vessel to the reaction zone or from the inside of the reaction vessel to the reaction zone. be transmitted to, and C_〇 in the exhaust gas be oxidized to C_〇 _2, force, decomposition of Ranaru fluorinated carbons.

4. The method for decomposing carbon fluorides according to claim 2, wherein the heat transmitted to the reaction zone is generated by an electric heater using a heating element that generates heat when energized.

5. The reactants are placed in a metal or ceramic reaction vessel. 3. The method for decomposing carbon fluorides according to claim 2.

6. Perfluorocarbon or Hydrofluorcarbon has a low carbon number

3. The method for decomposing carbon fluorides according to claim 1 or 2, which is 1 to 5 carbon fluorides.

7. The carbonaceous solid material is one or more selected from the group consisting of coke powder, charcoal, coal, raw pitch, charcoal, activated carbon, and carbon black. The alkaline earth metal compounds are calcium, magnesium, 3. The method for decomposing carbon fluoride according to claim 1, which is an oxide, hydroxide, carbonate or nitrate of barium or strontium.

8. The carbon fluoride according to claim 1, wherein the reactant is a granular material obtained by mixing a powdery carbonaceous solid material and a powdery alkaline earth metal compound, and granulating the mixture. Classification method.

9. The method for decomposing carbon fluorides according to claim 3, wherein the oxidation treatment is performed using an oxidation catalyst or a reactant.

10. A reaction vessel equipped with a reactant composed of a carbonaceous solid material and an alkaline earth metal compound, a gas inlet to be treated provided in the reaction vessel, and the reaction vessel A gas outlet provided to discharge the gas after the reaction from the inside, a furnace accommodating the reaction vessel, a heat source for increasing the ambient temperature in the two furnaces to 300 or more, An apparatus for decomposing carbon fluorides, comprising: a pipe connecting the gas to be treated inlet and a carbon fluoride-containing gas source.

1 1. A reaction vessel equipped with a reaction vessel composed of a carbonaceous solid material and an alkaline earth metal compound, a gas inlet to be treated provided in the reaction vessel, A gas outlet provided to discharge the gas after the reaction, a furnace for accommodating the reaction vessel, a heat source for increasing the ambient temperature of the furnace to 300 or more, An apparatus for decomposing carbon fluorides, comprising: a pipe connecting the port to a carbon fluoride-containing gas source; and an exhaust gas oxidizer connected to the pipe so as to communicate with the gas outlet.

1 2. Gas sources containing carbon fluoride are generated in the semiconductor manufacturing process. An apparatus for decomposing carbon fluorides according to claim 10 or 11