JP2009172494A - Decomposition catalyst of nitrous oxide and decomposition/removal method of nitrous oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a decomposition catalyst of nitrous oxide which firstly is cost advantageous, secondly, can decompose away the nitrous oxide of low concentration contained in an exhaust gas, at a high SV value and thirdly can easily and certainly reduce and decompose the nitrous oxide, and a decomposition and removal method of the nitrous oxide. <P>SOLUTION: This decomposition/removal method of nitrous oxide uses a rhodium catalyst 2 as a decomposition catalyst and performs the reduction/decomposition of the nitrous oxide of low concentration in an exhaust gas 1 through the following process: that is, a bonding and activation energy as a barrier to the decomposition of the nitrous oxide, is cut to a low level, under a trandient electron donating action of a single unpaired electron in the orbit of an outermost "O" shell 5s of the atomic structure and the transient electron forced dispossession action of two positive holes in the orbit of the inside "N" shell 4d. Thus, the exhaust gas 1 containing the nitrous oxide is supplied at the SV value of 10,000 (1/h) to 30,000 (1/h), within the temperature range of about 350 to 550°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nitrous oxide decomposition catalyst and a method for decomposing and removing nitrous oxide. That is, the present invention relates to a decomposition catalyst that reduces and decomposes low-concentration nitrous oxide contained in exhaust gas into nitrogen and oxygen, and a decomposition and removal method.

《Technical background》
Nitrous oxide has been used for anesthesia, food, etc., but recently, as a causative substance of global warming gas and greenhouse gas, its reduction has been highlighted. ing.
In other words, when nitrous oxide is released into the atmosphere, it becomes a causative agent of global warming, and is said to have a warming effect of about 310 times that of carbon dioxide. Is done.

<Conventional technology>
By the way, as a generation source of such nitrous oxide, exhaust gas from a chemical factory or the like is typical. For example, nitrous oxide produced as a by-product is contained in the exhaust gas that has passed through the ammonia oxidation step.
Such decomposition and removal of nitrous oxide in exhaust gas is currently under investigation and development. Typically, there is a technology (thermal decomposition method) in which such exhaust gas is heated at a high temperature at the thermal decomposition temperature of nitrous oxide, and the contained nitrous oxide is reduced to nitrogen and oxygen and then thermally decomposed. .
On the other hand, a technology (catalytic decomposition method) for reducing and decomposing nitrous oxide into nitrogen and oxygen by applying such exhaust gas with alumina, zeolite, zinc oxide, etc. to the exhaust gas with a catalyst has been developed. Yes.

《Information on prior art documents》
Examples of such prior art include those shown in the following patent documents. First, the pyrolysis method is as follows.
JP 2003-120919 A JP 61-259740 A JP, 2000-325743, A Next, the catalytic decomposition method is as follows. Japanese Patent Laid-Open No. 5-4027 JP-A-55-31463 Japanese Patent Laid-Open No. 10-80633 JP 2006-272239 A JP 2007-185574 A

<Conventional technology of pyrolysis method>
First, a representative example of the prior art of the pyrolysis method will be examined. First, regarding the thermal decomposition temperature of nitrous oxide, Patent Document 1 starts at about 800 ° C., Patent Document 2 has 1,000 ° C. to 1,300 ° C., and Patent Document 3 has 800 ° C. to 1 ° C. 200 ° C. That is, according to Patent Document 1, 800 ° C. or higher, and according to Patent Documents 2 and 3, about 800 ° C. to 1,300 ° C. are thermal decomposition temperatures of nitrous oxide for stable and practical implementation. .
And in such a thermal decomposition method in which thermal decomposition is performed by high-temperature heating and no catalyst is used, the nitrous oxide to be decomposed has a very high concentration. In Patent Document 1, 9% to 10% (mol), in Patent Document 2, 46% to 51% (volume), and in Patent Document 3, 10% to 12% (volume). In addition, patent document 2 makes object the exhaust gas from the process which oxidizes the mixture of cyclohexanol and cyclohexane with nitric acid, and manufactures adipic acid, and its processing gas.
Thus, the pyrolysis method was extremely effective at high concentrations, based on the characteristic that nitrous oxide has flame retardant properties. However, for example, application at a low concentration of about 50 ppm to 10,000 ppm (volume basis) has not been established technically.
For example, in order to raise the exhaust gas containing a low concentration of nitrous oxide to about 800 ° C. to 1,200 ° C., which is the thermal decomposition temperature of nitrous oxide, a large amount of fuel such as LNG or heavy oil is used. In addition, it is necessary to raise the overall temperature of the exhaust gas to the above thermal decomposition temperature of nitrous oxide, resulting in excessive energy loss, increasing heating equipment costs and fuel costs, etc. . Furthermore, when fuel containing hydrocarbons is used, it has been pointed out that carbon dioxide, which causes global warming, is emitted as the fuel burns.

<Conventional technology of catalytic decomposition>
Next, a representative example of the prior art of the catalytic decomposition method will be examined. First, in patent document 4, the contained nitrous oxide is decomposed | disassembled about the exhaust gas from the process which oxidizes the mixture of cyclohexanol and cyclohexane with nitric acid, and manufactures adipic acid using a cupric oxide catalyst.
The concentration of nitrous oxide in the exhaust gas is as high as 51% (volume), the reaction temperature is 400 ° C to 600 ° C, and the decomposition rate is 90% to 95%. The SV value is as low as 900 (1 / h), and the equipment scale of the apparatus is large. Further, since the concentration is high, even if the decomposition rate is 95%, exhaust gas containing 2% or more of nitrous oxide is discharged.
In Patent Document 5, nitrous oxide contained in the exhaust gas of excess anesthetic gas is decomposed using a catalyst such as platinum, palladium, rhodium, iridium, and ruthenium.
The nitrous oxide concentration in the exhaust gas is as extremely high as 50% to 75% (volume), and when the SV value is estimated in view of the catalyst contact time being 0.2 s or more, the SV value is 18, 000 (1 / h) or less. If this is applied to a low concentration of nitrous oxide, the degree of contact between the nitrous oxide and the catalyst is lowered, so that the SV value must be greatly reduced in order to secure the contact time with the catalyst.

In Patent Document 6, nitrous oxide is decomposed at a temperature of 250 ° C. to 600 ° C. using a composite metal oxide catalyst for exhaust gas containing nitrous oxide at a low concentration of about 950 ppm. When the SV value is estimated from the filling amount, it is a low level of about 5,300 (1 / h).
In Patent Document 7, for nitrous oxide contained in exhaust gas, a composite metal catalyst using rubidium, iridium, palladium, platinum, ruthenium or the like is supported on a porous support made of composite metal containing alumina, and the temperature is increased. Decomposes at 300 ° C to 500 ° C. The embodiment is directed to exhaust gas containing nitrous oxide having a low concentration of about 400 ppm, and its SV value is about 4,000 (1 / h) to 8,000 (1 / h). And low level.
Patent Document 8 proposes to use a metal in the fifth or sixth period of Group 8 of the periodic table as a decomposition catalyst for nitrous oxide. In that embodiment, exhaust gas after denitration is targeted, the contained nitrous oxide is at a low concentration of 1,000 ppm, platinum is selectively adopted as a supported catalyst, and the temperature is 300 ° C. to 400 ° C. Although nitrous oxide is decomposed, evaluation of the effect of rhodium catalyst, SV value, etc. is not disclosed.

About the problem
As described above, a large number of thermal decomposition methods and catalytic decomposition methods have been developed for exhaust gas containing a high concentration of nitrous oxide, and in particular, the results of the thermal decomposition method have been proven in practical use.
However, regarding exhaust gas containing a low concentration of nitrous oxide, neither thermal decomposition method nor catalytic decomposition method has been established. Specifically:

First, as described above, when the thermal decomposition method is applied when the concentration of nitrous oxide is low, the energy loss becomes excessive, the heating equipment cost and the fuel cost increase, and the practical use and industrialization are reduced. It is a difficult situation. In addition, the problem of carbon dioxide emission also occurs.
Secondly, as described above, the catalytic decomposition method requires a low SV value in order to achieve a high decomposition rate of nitrous oxide. Therefore, if the nitrous oxide is applied at a low concentration, the equipment becomes enormous, and practical use and industrialization are considered difficult.
In particular, the exhaust gas containing a low concentration of nitrous oxide is typically exhaust gas that has passed through an ammonia oxidation step, and is industrially discharged in large quantities. For example, the exhaust gas from the caprolactam production process and the exhaust gas from the nitric acid production process contain a low concentration of nitrous oxide, and the gas flow rate is large.
In view of such circumstances, regarding the catalytic decomposition method, a decomposition catalyst for industrially reducing low concentration nitrous oxide, that is, low concentration nitrous oxide is decomposed and removed under a high SV value. The appearance of a cracking catalyst that has been eagerly desired.
Thirdly, the conventional catalytic decomposition method has also been pointed out that the performance deteriorates due to the contained substances in the exhaust gas.
In other words, this type of exhaust gas often contains moisture (water vapor or water droplets), nitrogen oxides, sulfur dioxide, etc., but these contained substances act as components that interfere with the decomposition of nitrous oxide. In many cases, however, the reduction and decomposition of nitrous oxide does not proceed smoothly.
This was particularly noticeable when moisture and nitrogen oxides were contained. Furthermore, it was pointed out that nitrogen oxides, which are harmful substances, are produced as a by-product of reduction and decomposition.

<< About the present invention >>
The nitrous oxide decomposition catalyst and the method for decomposing and removing nitrous oxide according to the present invention have been developed in order to solve the above-described problems of the prior art.
The present invention is capable of decomposing and removing low-concentration nitrous oxide, firstly in terms of cost, secondly, under a high SV value, and thirdly, easily and reliably reduced. An object of the present invention is to propose a nitrous oxide decomposition catalyst that can be decomposed and removed, and a method for decomposing and removing nitrous oxide.

<About Claim>
The technical means of the present invention for solving such a problem is as follows. First, claim 1 is as follows. The nitrous oxide decomposition catalyst according to claim 1 is a nitrous oxide decomposition catalyst contained in exhaust gas, and rhodium is used.
The exhaust gas is supplied at a temperature lower than the thermal decomposition temperature of nitrous oxide while the concentration of nitrous oxide is 50 ppm to 10,000 ppm on a volume basis. The rhodium catalyst has a transient electron donating action of one unpaired electron in the outermost shell O shell 5s orbit of atomic structure, and a transient of two electron vacancies or holes in its inner N shell 4d orbit. It is characterized by reducing and decomposing nitrous oxide into nitrogen and oxygen based on the electron-storing action.
About Claim 2, it is as follows. The nitrous oxide decomposition catalyst according to claim 2 is the nitrous oxide decomposition catalyst according to claim 1, wherein the exhaust gas comprises exhaust gas that has undergone an ammonia oxidation step and contains nitrous oxide by-produced by oxidation of the ammonia. It is characterized by that.
About Claim 3, it is as follows. The nitrous oxide decomposition catalyst according to claim 3 is the nitrous oxide decomposition catalyst according to claim 1 or 2, wherein the exhaust gas absorbs a gas containing nitrogen oxide obtained through the ammonia oxidation step with sulfuric acid. It consists of exhaust gas from the step of obtaining nitrosylsulfuric acid and contains nitrous oxide.
About Claim 4, it is as follows. The nitrous oxide decomposition catalyst according to claim 4 is the nitrous oxide decomposition catalyst according to claim 1, wherein the exhaust gas is an exhaust gas from the step of oxidizing cyclohexanol and / or cyclohexane with nitric acid and contains nitrous oxide. It is characterized by this.
About Claim 5, it is as follows. The nitrous oxide decomposition catalyst according to claim 5 is the nitrous oxide decomposition catalyst according to claim 1, 2, 3, or 4, wherein the exhaust gas is obtained by subjecting nitrogen oxides contained in the gas to a selective reduction method using ammonia. It consists of exhaust gas that has been denitrated and contains nitrous oxide.
About Claim 6, it is as follows. The catalyst for decomposing nitrous oxide as claimed in claim 6, in claim 1, 2, 3, 4, or 5, wherein the rhodium catalyst is carried on the loading amount 50 g / ft ³ or more to 100 g / ft ³ carriers below, The exhaust gas is supplied at an SV value of 10,000 (1 / h) or more to 30,000 (1 / h) or less.

About Claim 7, it is as follows. The method for decomposing and removing nitrous oxide according to claim 7 is a method for decomposing and removing low-concentration nitrous oxide contained in exhaust gas, and rhodium is used as a catalyst.
The exhaust gas has an SV value of 10,000 (1 / h) or more to 30,000 (1 / h) or less at a temperature range of 350 ° C. or more and less than 550 ° C. in the blower unit and the heating unit. The rhodium catalyst is supplied and brought into contact with the rhodium catalyst.
Thus, the transient electron donating action of one unpaired electron in the outermost shell O-shell 5s orbit of the atomic structure of the rhodium catalyst, and the transient of two electron vacancies or holes in the inner N-shell 4d orbital. It is characterized in that nitrous oxide is reduced, decomposed, and removed to nitrogen and oxygen by reducing the binding and activation energy, which are decomposition barriers, based on the active electron-storing action.
About Claim 8, it is as follows. In the method for decomposing and removing nitrous oxide according to claim 8, in claim 7, the exhaust gas comprises exhaust gas that has undergone an ammonia oxidation step, and contains nitrous oxide by-produced by oxidation of the ammonia. The concentration of nitrous oxide contained is 50 ppm to 10,000 ppm on a volume basis.

《Action etc.》
Since the present invention comprises such means, the following is achieved.
(1) Rhodium is used as the decomposition catalyst.
(2) Exhaust gas that has passed through the oxidation process of ammonia and other exhaust gas containing nitrous oxide produced as a by-product at a low concentration of 50 ppm to 10,000 ppm on a volume basis are supplied to the rhodium catalyst. The
(3) This exhaust gas is supplied at an SV value of 10,000 (1 / h) to 30,000 (1 / h) in a temperature range of 350 ° C. to 550 ° C. below the thermal decomposition temperature of nitrous oxide. Is done.
(4) a rhodium catalyst is loaded in a loading amount ^{50g / ft 3 ~100g / ft 3} , 1 unpaired electron of outermost O-shell 5s orbital of the atomic structure is, the transient electron donating effect In addition, the two holes in the inner N-shell 4d orbital have a transient electron-storing action.
(5) Therefore, nitrous oxide contained in the exhaust gas is first reduced in its binding and activation energy based on the transient electron-storing action of the holes in the rhodium catalyst, and the oxidation is promoted transiently. Thus, nitrogen is liberated and oxygen atoms are adsorbed on the rhodium catalyst.
The adsorbed oxygen atoms are reduced in binding and activation energy based on the transient electron donating action of the unpaired electrons of the rhodium catalyst, the reduction is promoted transiently, and the adsorption is released. And released from the rhodium catalyst.
(6) In this way, nitrous oxide is reduced, decomposed and removed into nitrogen and oxygen by the catalytic activity of the rhodium catalyst.

(7) According to the present invention, first, low concentration nitrous oxide is reduced, decomposed and removed to nitrogen and oxygen at a temperature lower than the thermal decomposition temperature. That is, the binding energy and the activation energy, which have been energy barriers for nitrous oxide decomposition, are lowered, and thus reduced, decomposed and removed at a low temperature of, for example, about 350 ° C. to 550 ° C. without heating at a high temperature.
Second, low concentration nitrous oxide is reduced, decomposed and removed to nitrogen and oxygen under high SV values. That is, the low concentration of nitrous oxide contained in the exhaust gas due to the transitional electron donating and electron trapping actions of the rhodium catalyst reduces the binding and activation energy, resulting in an SV value of 10,000 (1 / h ) To 30,000 (1 / h), it is reduced, decomposed and removed at a high decomposition rate.
Third, for the same reason, even if the exhaust gas contains moisture, nitrogen oxides, oxygen, sulfur dioxide, etc. together with nitrous oxide, nitrous oxide is reduced, decomposed and removed without interference. . Moreover, these can be realized easily and simply by providing a rhodium catalyst in the exhaust gas exhaust line.
(8) The nitrous oxide decomposition catalyst and the nitrous oxide decomposition and removal method of the present invention exhibit the following effects.

<< First effect >>
First, low-concentration nitrous oxide can be reduced, decomposed, and removed into nitrogen and oxygen at a temperature lower than its thermal decomposition temperature, which is excellent in terms of various costs.
That is, the nitrous oxide decomposition catalyst and the method for decomposing and removing nitrous oxide according to the present invention are the above-described conventional example of nitrous oxide contained in exhaust gas at a low concentration of about 50 ppm to 10,000 ppm. Thus, reduction, decomposition, and removal can be performed at a temperature of about 350 ° C. to 550 ° C. without heating at a high temperature of about 800 ° C. to 1,200 ° C., for example.
As in the case of this type of conventional thermal decomposition method described above, when applied to a low concentration, the heating equipment cost for high-temperature heating and the fuel cost are increased, the energy loss is not excessive, and the cost is reduced. It opens the way to practical use. In addition, the installation space is excellent because the equipment is made compact. In addition, carbon dioxide (causal agent for global warming) is not discharged as the fuel burns.

<< Second effect >>
Second, low nitrous oxide can be reduced, decomposed and removed under high SV values.
That is, low concentrations of decomposition catalysts, and the decomposition of nitrous oxide, the removal method, based on the supported amount 50g ^/ ft ³ ~100g / ft 3 of high rhodium catalyst catalytic activity, in the exhaust gas of nitrous oxide of the present invention Nitrous oxide can be reduced, decomposed and removed at a high decomposition rate.
In the catalytic decomposition method of this kind of conventional example described above, the SV value is at most about 8,000 (1 / h), but in the present invention, 10,000 (1 / h) to 30,000 ( The exhaust gas containing a low concentration of nitrous oxide can be treated under a high SV value of 1 / h), that is, under a high flow rate and a large flow rate. For example, the exhaust gas from the caprolactam production process and the exhaust gas from the nitric acid production process contain a low concentration of nitrous oxide and the gas flow is large, but it does not increase the scale of the equipment. However, large-scale processing and large-capacity processing are possible, and the efficiency, economy, practicality, industriality, etc. are excellent.
As a result, nitrous oxide, which is increasingly requested to be reduced as a causative substance of global warming, can be reduced, and a clean exhaust gas can be released into the atmosphere.

《Third effect》
Thirdly, such reduction, decomposition and removal of nitrous oxide at a low concentration can be realized easily and reliably.
That is, in the nitrous oxide decomposition catalyst and the nitrous oxide decomposition / removal method of the present invention, nitrous oxide is reduced, decomposed and removed based on the high catalytic activity of the rhodium catalyst.
This type of exhaust gas often contains moisture (water vapor or water droplets), nitrogen oxides, sulfur dioxide, etc., but as in the above-described conventional catalytic decomposition method, There is no performance degradation due to substances contained in the exhaust gas, and in the present invention, decomposition and removal of nitrous oxide proceed smoothly with high performance and high efficiency as described above. Note that nitrogen oxides, which are harmful substances, are not generated as by-products.
As described above, the effects exerted by the present invention are remarkably large, such as all the problems existing in this type of conventional example are solved.

《About drawing》
The nitrous oxide decomposition catalyst and nitrous oxide decomposition and removal method of the present invention will be described in detail below based on the best mode for carrying out the invention shown in the drawings. 1 and 2 serve to explain the best mode for carrying out the present invention.
FIG. 1 (1) is an explanatory side sectional view of the decomposition processing apparatus and the like, and FIG. 1 (2) is a front sectional view showing an enlarged main part thereof. FIG. 2 is a block diagram of the embodiment.

About nitrous oxide
The present invention relates to a nitrous oxide decomposition catalyst and a method for decomposing and removing nitrous oxide. First, an outline of nitrous oxide will be described.
Nitrous oxide (N ₂ O) is also called dinitrogen monoxide, laughing gas, nitrogen oxide, etc., and its reduction has recently been requested as a causative substance of global warming. In particular, the exhaust gas 1 containing nitrous oxide is required to be reduced before being released into the atmosphere.
The source of nitrous oxide is a chemical manufacturing process, and a typical example is exhaust gas 1 via an ammonia oxidation process. Exhaust gas 1 containing a low concentration of nitrous oxide is industrially abundant. To be discharged. For example, in the production process of caprolactam or adipic acid, which is a raw material for nylon, and the production process of nitric acid, nitrous oxide is produced as a by-product and is contained in the exhaust gas 1 discharged.
The concentration of nitrous oxide in the exhaust gas 1 is a low concentration of about 50 ppm to 10,000 ppm on a volume basis. From the viewpoint of stably maintaining the decomposition rate of nitrous oxide, 500 ppm to 2, It can be said that about 000 ppm is more preferable (details will be described later). In the case of adipic acid, it is discharged at a high concentration, but the exhaust gas 1 after the primary treatment and a low concentration of nitrous oxide are the targets for decomposition and removal of the present invention.
Further, the exhaust gas 1 of the denitration apparatus that selectively reduces nitrogen oxides using ammonia also contains low-concentration nitrous oxide, but the exhaust gas 1 of each manufacturing process described above is also oxidized with nitrogen. In many cases, it is discharged after denitration treatment by a denitration apparatus.
Nitrous oxide is roughly like this.

<Exhaust gas 1>
Here, the exhaust gas 1 containing such a low concentration of nitrous oxide will be described in more detail. First, the ammonia oxidation process will be described. As the ammonia oxidation process, various processes for obtaining nitrogen oxides mainly composed of nitric oxide by oxidation of ammonia are conceivable, but nitrous oxide is by-produced during such oxidation of ammonia, and the exhaust gas thereof 1 contained.
For example, this type of ammonia oxidation step includes a step of oxidizing gaseous ammonia together with air and / or oxygen using a catalyst mainly composed of platinum, and the exhaust gas 1 contains nitrous oxide. Is contained at a low concentration of about 50 ppm to 10,000 ppm on a volume basis.
The temperature during oxidation of ammonia is preferably 700 ° C to 1,000 ° C. The pressure during oxidation of ammonia may be any of low pressure, medium pressure, and high pressure. For example, 101 (normal pressure) kPa to 303 kPa (absolute pressure) at low pressure, 304 kPa (absolute pressure) to 810 kPa (absolute pressure) at medium pressure. The high pressure is 811 kPa (absolute pressure) or more. The oxidation catalyst for ammonia may be any as long as nitrogen monoxide or the like is obtained upon oxidation of ammonia, but a catalyst containing platinum is typical.
The outline of the target exhaust gas 1 is as described above.

<< Each exhaust gas 1 >>
Various types of exhaust gas 1 through the above-described ammonia oxidation process, which is the subject of the present invention, can be considered, for example, nitric acid production process, hydroxylamine sulfate production process, nitrosylsulfuric acid production process, or chlorination. A typical example is exhaust gas 1 that passes through a manufacturing process of nitrosyl or the like. Furthermore, the exhaust gas 1 which processed the nitrogen oxide component in such an exhaust gas 1 with the denitration equipment is also considered.
Such exhaust gas 1 contains nitrous oxide at a low concentration of about 50 ppm to 10,000 ppm. Each such exhaust gas 1 will be described in further detail.

First, in the nitric acid production process, nitric acid is obtained by absorbing the gas that has passed through the ammonia oxidation process with water. In the process, the exhaust gas 1 containing nitrous oxide as an off-gas is discharged.
Next, the production process of hydroxylamine sulfate is as follows. That is, in one example of the production process of caprolactam (formal name: ε-caprolactam, structural formula: cyclic- (CH ₂ ) ₅ -NH-CO-), which is a raw material of nylon, in the production process of hydroxylamine sulfate First, the gas passed through the ammonia oxidation step is adjusted to a nitrose gas. Then, it is absorbed with an aqueous ammonium carbonate solution to synthesize ammonium nitrite, which is reduced with sulfur dioxide and then hydrolyzed to obtain hydroxylamine sulfate.
In such a process, the exhaust gas 1 containing nitrous oxide as an off gas is discharged.
On the other hand, hydroxylamine sulfate can also be obtained by reducing the gas passed through the ammonia oxidation step with hydrogen using a platinum catalyst in a sulfuric acid solution and / or a buffer solution of ammonium hydrogen sulfate and ammonium sulfate.
Even in such a process, the exhaust gas 1 containing nitrous oxide is discharged as off-gas.

The manufacturing process for nitrosylsulfuric acid is as follows. That is, in another example of the production process of caprolactam, which is a raw material for nylon, in the production process of nitrosylsulfuric acid, first, the gas that has passed through the oxidation process of ammonia is adjusted to nitrose gas with air and / or oxygen.
Specifically, gaseous ammonia and air are mixed, the ammonia concentration is adjusted to 5% to 20% on a volume basis, a temperature of 700 ° C. to 1,000 ° C., and a pressure of 120 kPa using a platinum catalyst network. Oxidation is performed at (absolute pressure) to 200 kPa (absolute pressure) to obtain a gas containing nitric oxide. And it cools by heat exchange, introduce | transduces air, and adjusts to nitrose gas at the temperature of 50 to 200 degreeC. Then, the nitrose gas is absorbed with an aqueous sulfuric acid solution to obtain a liquid containing nitrosylsulfuric acid.
In this process, exhaust gas 1 containing 500 ppm to 2,000 ppm of nitrous oxide is discharged as an off-gas on a volume basis.
Nitrosyl chloride is produced by reacting this nitrosylsulfuric acid with hydrochloric acid, cyclohexanone oxime is obtained by reacting nitrosyl chloride with cyclohexane, and caprolactam is produced by Beckmann rearrangement.
About each exhaust gas 1, it is as above.

<About denitration treatment>
By the way, the exhaust gas 1 from each manufacturing process mentioned above contains nitrogen oxides. That is, this type of exhaust gas 1 typically contains 100 ppm to 3,000 ppm of nitric oxide and / or nitrogen dioxide on a volume basis.
On the other hand, in order to maintain the performance and extend the life of the rhodium catalyst 2 which is a decomposition catalyst for nitrous oxide, the content of nitrogen oxides is desirably 100 ppm or less on a volume basis. Therefore, this type of exhaust gas 1 is often supplied to the rhodium catalyst 2 after denitration treatment by a denitration apparatus in order to suppress the performance degradation and life reduction of the rhodium catalyst 2. That is, this type of exhaust gas 1 is subjected to denitration treatment at a temperature of 250 ° C. to 400 ° C. using a selective reduction catalyst using ammonia, so that the nitrogen oxide contained is 100 ppm or less on a volume basis.
In the exhaust gas 1 thus denitrated, nitrous oxide is contained in an amount of about 500 ppm to 2,000 ppm on a volume basis. The selective reduction catalyst for denitration treatment may be any as long as nitrogen oxides can be reduced. For example, a honeycomb-shaped catalyst in which vanadium pentoxide is supported using titanium oxide as a carrier is used.
In addition to the exhaust gases 1 described above, nitrous oxide is generally contained in the exhaust gas 1 discharged from the flue gas denitration apparatus. In other words, since nitrous oxide is by-produced in the process of reducing nitrogen oxide contained in general exhaust gas using ammonia, the exhaust gas 1 from a general exhaust gas denitration apparatus is also present. It can be considered as the object of the rhodium catalyst 2 of the invention.
The denitration process is as described above.

<< About the manufacturing process of adipic acid >>
Next, the production of nitrous oxide in the production process of adipic acid as a raw material for nylon will be described.
In a typical production process of adipic acid, cyclohexanol and / or cyclohexanone and nitric acid are reacted to produce adipic acid. At this time, nitrous oxide is produced as a by-product.
That is, when cyclohexanol obtained by first oxidizing air with cyclohexane is oxidized with nitric acid to produce adipic acid, nitrous oxide is produced as a by-product. In addition, nitrous oxide is also produced as a by-product when cyclohexanone obtained by further oxidizing air with cyclohexanol is oxidized with nitric acid to produce adipic acid.
Thus, nitrous oxide is produced in the production process of adipic acid, and the exhaust gas 1 contains nitrous oxide. The content of the nitrous oxide is 40% to 60% on a volume basis. % And high concentration. Therefore, the exhaust gas 1 after the primary treatment by a general thermal decomposition method or catalytic decomposition method, that is, the exhaust gas in which the contained nitrous oxide has a low concentration of about 50 ppm to 10,000 ppm by volume. 1 is the subject of the present invention.
The manufacturing process of adipic acid is as described above.

《Reaction formula etc.》
Here, with respect to each exhaust gas 1 described above, a supplementary explanation will be given regarding the chemical reaction formula of nitrous oxide byproduct.
First, in the oxidation process of ammonia (NH ₃ ), nitric oxide (NO) and nitrogen dioxide (NO ₂ ) are generated according to the following reaction formulas 1 and 2. And according to the following reaction formula 3, nitrous oxide (N ₂ O) is by-produced.

Next, in the nitric acid production process, nitric acid (HNO ₃ ) is produced in the following chemical formula 4 following the chemical formula 1 and chemical formula 2, and Nitric oxide (N ₂ O) is by-produced. The reaction formulas of the above chemical formula 1, chemical formula 2, and chemical formula 4 are summarized as the following chemical formula 5.

Next, in the production process of hydroxylamine sulfate, first, in the reaction formula of the following chemical formula 6, with nitric oxide (NO) and nitrogen dioxide (NO ₂ ), nitrose gas (dinitrogen trioxide, N ₂ O). ₃ ) is generated as an intermediate substance. Since the reaction formula of the chemical formula 6 is based on the chemical formula of the chemical formula 1 and the chemical formula 2, the nitrous oxide (N ₂ O) Will be by-produced. As described above, hydroxylamine sulfate (NH ₃ OH ₂ SO ₄ ) is generated based on the nitrose gas (N ₂ O ₃ ).

Next, in the production process of nitrosylsulfuric acid and nitrosyl chloride, first, the nitrose gas (N ₂ O ₃ ) is absorbed in an aqueous solution of sulfuric acid (H ₂ SO ₄ ) according to the reaction formula of the following chemical formula 7, and nitrosyl sulfuric acid (NS , NOHSO ₄ ) is produced, and then nitrosyl chloride (NOCl) is produced according to the reaction formula (8).
Since the reaction formula of the chemical formula 7 is based on the reaction formula of the chemical formula 6 and the chemical formulas of the chemical formula 1 and the chemical formula 2, the nitrous oxide (N ₂ O) is represented by the chemical formula of the chemical formula 3. Will be born.

Next, in the production method of adipic acid, for example, cyclohexanol (C ₆ H ₁₁ OH) obtained by subjecting cyclohexane (C ₆ H ₁₂ ) to air oxidation according to the following reaction formulas 9 and 10; When cyclohexanone (C ₆ H ₁₀ O) obtained by further air oxidation is oxidized with sulfuric acid (HNO ₃ ), adipic acid (HOOC— (CH ₂ ) ₄ —COOH) is produced. , Nitrous oxide (N ₂ O) is by-produced

<About decomposition catalyst>
Next, the nitrous oxide decomposition catalyst will be described. As described above, nitrous oxide (N ₂ O) contained in the exhaust gas 1 is reduced, decomposed, and removed into nitrogen (N ₂ ) and oxygen (O ₂ ) by the rhodium catalyst 2.
First, the rhodium catalyst 2 is used alone, or is a platinum (Pt) catalyst, palladium (Pd), which is a metal of the fifth or sixth group of the eighth group of the periodic table capable of exhibiting the same action. ) Used in combination with a catalyst.
In the rhodium (Rh) of the rhodium catalyst 2, that is, rhodium in the fifth period of the eighth group of the periodic table, first, one unpaired electron exists in the 5s orbit of the outermost shell O shell of the atomic structure. ing. Therefore, in the reaction process, self becomes Rh ⁺ transiently, and this unpaired electron transiently donates an electron to the reaction partner (reaction target molecule), lowers the binding energy and activation energy of the reaction partner, and becomes donor-like Acts as an electron and transiently promotes the other party's reduction reaction.
At the same time, the rhodium (Rh) of the rhodium catalyst 2 has eight counter electrons in the 4d orbit of the N shell inside the outermost shell O shell of the atomic structure. Since there are up to 10 counter electrons in the N-shell 4d orbital, there are two electron vacancies, ie holes (hole ⁺ ) lacking electrons. In the reaction process, these two holes transiently take away electrons from the reaction partner in order to fill the electron deficiency, and transiently promote the oxidation reaction of the partner.
The catalytic action, catalytic activity, and decomposition action of rhodium are due to such transient electron donating action and reduction promoting ability of unpaired electrons, and transient electron desorption action and oxidation promoting ability of holes.
The cracking catalyst is like this.

<Reduction, decomposition, removal, etc. of nitrous oxide>
Next, reduction, decomposition, removal and the like of nitrous oxide will be described. The rhodium catalyst 2 lowers the binding and activation energy, which is a decomposition barrier of nitrous oxide, based on such a transient electron donating action and a transient electron depriving action.
Therefore, nitrous oxide is reduced, decomposed, and removed into nitrogen and oxygen by the following reaction formulas 11 and 12 under a high SV value at a temperature lower than the thermal decomposition temperature. In chemical formula 12, 1/2 O ₂ is oxygen in the air.

In the example shown in FIG. 1, the rhodium catalyst 2 is attached and supported on the porous carrier 4 of the decomposition treatment apparatus 3 that is a catalytic converter. That is, the decomposition treatment apparatus 3 is connected to the exhaust pipe 5 for the exhaust gas 1, and the porous carrier 4 that is a carrier base is inserted into the outer cylinder 6. As the porous carrier 4, for example, a honeycomb core made of an aggregate of a large number of hollow columnar cell spaces 8 partitioned by cell walls 7, made of ferritic stainless steel, alumina, other metal, or ceramics. Is used.
The porous carrier 4 has its axis oriented in the flow direction of the exhaust gas 1, and the rhodium catalyst 2 is adhered and supported on the cell wall 7 by coating or the like. The exhaust gas 1 is supplied to the cell space 8. And pass. The amount of supported rhodium catalyst 2, for example 50 g / ft ³ or more to 100 g / ft ³ or less (1,765g / ^{m 3} or more ~3,531g / ^{m 3} or less) has a degree. In addition, when it is less than 50 g / ft ³ , the reduction and decomposition rate of nitrous oxide is reduced or insufficient, and when it exceeds 100 g / ft ³ , the carrying efficiency (coating efficiency) is lowered.
And exhaust gas 1 is 350 degreeC-550 degreeC below the thermal decomposition temperature of nitrous oxide in ventilation parts 9, such as a fan and a blower, and heating parts 10, such as a heater, a burner, a heating furnace, and a heat exchanger. The temperature is less than (eg, 400 ° C. or more and 500 ° C. or less) and is supplied to the decomposition processing apparatus 3. In addition, if it is less than 350 degreeC, the reduction | restoration and decomposition | disassembly of nitrous oxide will fall or lack, and if it is 550 degreeC or more, it will reach thermal decomposition temperature.

Further, the SV value (space velocity) between the exhaust gas 1 containing nitrous oxide and the rhodium catalyst 2 of the decomposition treatment device 3 is 10,000 (1 / h) or more to 30,000 (1 / h) or less. The exhaust gas 1 is supplied to and passed through the decomposition treatment apparatus 3 on which the rhodium catalyst 2 is adhered and supported at the flow rate. By the way, if it is less than 10,000 (1 / h), the speed and efficiency of reduction and decomposition of nitrous oxide are poor, and if it exceeds 30,000 (1 / h), reduction and decomposition of nitrous oxide are reduced and insufficient. To do.
First, the gas flow rate of the exhaust gas 1 is a normal (standard state) gas flow rate. Loading amount of the porous carrier 4 rhodium catalyst 2 is a従Gai generally denoted example ^{50g / ft 3 ~100g / ft 3} , is caused to adhere it to the outer surface of the open pores of the porous carrier 4 catalyst When expressed in terms of the amount of rhodium catalyst 2 contained in the layer (coating layer), 100 g / ft ³ corresponds to 1 wt% to 4 wt%, for example, 100 g / ft ³ is 2.45 wt%.
Second, the relationship between the temperature range and the SV value is relative. Within the above range, the higher the temperature and the lower the SV value, the more reliable the reduction, decomposition and removal of nitrous oxide. Nearly 100% can be implemented. On the other hand, nitrous oxide can be reduced, decomposed and removed within the above-mentioned range even if the temperature is low and the SV value is high, and there is a possibility that the nitrous oxide can be carried out with a necessary minimum level of about 30%.
Thirdly, in the illustrated example of FIG. 1, the exhaust gas 1 is supplied to the decomposition processing apparatus 3 after passing through the blower unit 9 and the heating unit 10. It is also conceivable to attach the air blowing unit 9 and the heating unit 10 to the above.
Reduction, decomposition, removal, etc. of nitrous oxide are performed in this way.

<About the action>
The nitrous oxide decomposition catalyst and the nitrous oxide decomposition and removal method of the present invention are configured as described above. Therefore, it becomes as follows.
(1) The sub catalyst for decomposing nitrogen oxides is made of rhodium, the porous carrier 4 rhodium catalyst 2 decomposition treating apparatus 3, which is attached carried, supported ^amount, a 50g / ft ³ ~100g / ft 3 ing. A platinum catalyst or a palladium catalyst can be used in combination with the rhodium catalyst 2.

(2) Then, the exhaust gas 1 containing a low concentration of nitrous oxide is supplied to the rhodium catalyst 2 of the decomposition treatment apparatus 3 and passes therethrough.
Exhaust gas 1 is typically exhaust gas 1 that has undergone an ammonia oxidation step, but also contains nitrous oxide produced as a by-product at a low concentration of about 50 ppm to 10,000 ppm on a volume basis. The exhaust gas 1 thus supplied is supplied to the rhodium catalyst 2 of the decomposition treatment apparatus 3 and passes therethrough.

  (3) Further, the exhaust gas 1 has an SV value of 10,000 (1 / h) to 30,000 (1 / h) in a temperature range of 350 ° C. to 550 ° C. which is lower than the thermal decomposition temperature of nitrous oxide. , Supplied to and passed through the rhodium catalyst 2 of the decomposition treatment apparatus 3.

(4) a rhodium catalyst 2, in a loading amount ^{50g / ft 3 ~100g / ft 3} , is supported on the porous carrier 4. In the rhodium catalyst 2, one unpaired electron e ^{− in} the outermost shell O-shell 5s orbit of atomic structure has a transient electron donating action, and two electron vacancies in the inner N-shell 4d orbital. Hole (hole ⁺ ) having a transient electron-storing action.

(5) Therefore, nitrous oxide in the exhaust gas 1 is first interfered with the holes of the rhodium catalyst 2. Based on the transient electron-storing action, the binding energy and activation energy are lowered, the oxidation reaction is transiently promoted, so that nitrogen N ₂ is liberated and oxygen O atoms are adsorbed on the rhodium catalyst 2. Is done.
That is, nitrous oxide (molecular formula: N ₂ O structural formula: N = N = O) as a reaction target molecule has a double bond (=) between nitrogen (N) and oxygen (O) in the structural formula as σ It consists of an electronic bond and a π electron bond. First, the π-electron bond, which has a weaker binding force than the σ-electron bond, is interfered by one hole of the rhodium catalyst 2 and is transiently pulled to the hole side. The electronic bond is first broken. Next, the remaining single bond, that is, the σ electron bond, whose bond energy is lowered by that amount, is also broken by the interference with the remaining holes.
In this way, nitrous oxide breaks both the double bonds between nitrogen and oxygen in the structural formula, so that nitrogen is liberated and oxygen atoms (O) are adsorbed on the rhodium catalyst 2 ( hole ⁺ -O-hole ⁺ ). The activation energy which is a decomposition reaction barrier of nitrous oxide is lowered by interference with the holes of the rhodium catalyst 2, and thus nitrogen is liberated.
Thereafter, the oxygen atoms adsorbed on the rhodium catalyst 2 in this manner are subjected to interference of unpaired electrons of the rhodium catalyst 2. Then, based on the transient electron donating action, the binding energy and the activation energy are lowered, and the reduction reaction is transiently promoted. As a result, the holes and electrons are combined, and the oxygen atoms (O) are released from the adsorption and restraint by the holes to be diatomicized to become oxygen molecules (O ₂ ) and are released from the rhodium catalyst 2.

(6) In this way, the nitrous oxide, which is the reaction target molecule, has its binding energy and activation energy, which are the decomposition reaction barrier, lowered by the catalytic activity of the rhodium catalyst 2, so that it is less than its thermal decomposition temperature. It is reduced and decomposed into nitrogen and oxygen at temperature and under a high SV value.
That is, nitrous oxide is lowered by the action of unpaired electrons and holes of the rhodium catalyst 2 in the energy barrier that has been a reaction barrier of the reaction path of the reaction formula. That is, the binding energy and activation energy required for the reaction are greatly reduced. Accordingly, for example, reduction and decomposition reactions are established at a lower temperature of 350 ° C. to 550 ° C. or less, regardless of the thermal decomposition reaction of about 800 ° C. to 1,200 ° C. Moreover, even if exhaust gas 1 is supplied at a high flow rate and high flow rate under an SV value of 10,000 (1 / h) to 30,000 (1 / h), a reduction and decomposition reaction is established. Become.

(7) Therefore, according to the nitrous oxide decomposition catalyst and the method for decomposing and removing nitrous oxide according to the present invention, the following first, second and third are obtained.
First, low-concentration nitrous oxide is reduced and decomposed into nitrogen and oxygen at a temperature below its thermal decomposition temperature.
That is, due to the catalytic activity of the rhodium catalyst 2, low-concentration nitrous oxide is reduced, decomposed, and removed at a relatively low temperature of, for example, about 350 ° C. to 550 ° C. without requiring high-temperature heating. .

Second, low concentration nitrous oxide is easily reduced, decomposed and removed to nitrogen and oxygen by the high catalytic activity of the rhodium catalyst 2.
Therefore, even when the SV value between the exhaust gas 1 and the rhodium catalyst 2 is 10,000 (1 / h) to 30,000 (1 / h), it is reduced and decomposed into nitrogen and oxygen at a high decomposition rate. , Will be removed.

Thirdly, the exhaust gas 1 often contains moisture, nitrogen oxides, oxygen, sulfur dioxide, and other substances, but the rhodium catalyst 2 is used for the same reason as described above. It will surely promote the reduction and decomposition of nitrous oxide without being disturbed by these substances.
Further, such reduction, decomposition and removal of nitrous oxide can be realized simply and easily by simply attaching a decomposition treatment device 3 filled with the rhodium catalyst 2 to the exhaust pipe 5 of the exhaust gas 1.

Examples 1 and 2 of the present invention will be described below. FIG. 2 is a block diagram of the first and second embodiments.
In the decomposition test apparatus 3 for field tests of Examples 1 and 2, the rhodium catalyst 2 is attached and supported on the cell wall 7 of the porous carrier 4. The structure of the porous carrier 4 is as follows.
・ Structure: Ceramic honeycomb core ・ Shape: Circular pillar ・ Direct diameter: 25.4mm
・ Length: 50.8mm
-Number of cell spaces 8: 200 / in ² (31 / cm ² )
In Examples 1 and 2, the test gas of the exhaust gas 1 was supplied to and passed through the rhodium catalyst 2 of the decomposition treatment apparatus 3. In the figure, 11 is a humidity control unit, 12 is a flow meter, and the composition of the test gas is as follows.
・ N ₂ O: 0.1% by volume (1,000 ppm)
・ O ₂ : 3% by volume
H ₂ O: 4% by volume
・ N ₂ : Balance

First, Example 1 is as follows.
Example 1 relates to the relationship between the SV value and temperature, and the decomposition rate. That is, in Example 1, first, the amount of rhodium catalyst 2 attached to the porous carrier 4 was set to 100 g / ft ³ (3,531 g / m ³ ). The SV value was changed to 10,000 (1 / h) and 20,000 (1 / h).
At the same time, for both SV values, the temperature of the exhaust gas 1 (reaction temperature) is changed to a temperature of 500 ° C., 450 ° C., 400 ° C., etc., so that the decomposition rate of nitrous oxide (reduction rate, The removal rate was measured in wt%.
As a result, the following data in Table 1 was obtained.

The results of the examples are as shown in Table 1, confirming the effects of the present invention.
That is, when the SV value was 10,000 (1 / h), a decomposition rate of 79% was obtained even at a temperature of 400 ° C., and a decomposition rate of 100% was obtained at 500 ° C.
Even when the SV value was 20,000 (1 / h), a decomposition rate of 98% was obtained when the temperature was 500 ° C., and a decomposition rate of 39% was obtained even at 400 ° C.
In Example 1, such data was obtained.

Next, Example 2 is as follows.
Example 2 relates to the relationship between the amount of rhodium catalyst attached and supported and the decomposition rate. That is, in Example 2, first, the SV value was set to 10,000 (1 / h), and the test gas temperature (reaction temperature) was set to 500 ° C.
The amount of rhodium catalyst 2 attached to the porous carrier 4 is 20 g / ft ³ (706 g / m ³ ), 40 g / ft ³ (1,412 g / m ³ ), 100 g / ft ³ (3,531 g / m). ³ ) The setting was changed to, for example, and the decomposition rate (reduction rate, removal rate) of nitrous oxide was measured in wt% for each.
As a result, the following data in Table 2 was obtained.

The results of Example 2 are as shown in Table 2, and the effects of the present invention were confirmed.
That is, even when the adhesion loading amount of the rhodium catalyst 2 is 20 g / ft ³ (706 g / m ³ ), a decomposition rate of 53% is obtained, and at 100 g / ft ³ (3,531 g / m ³ ), 100%. Was obtained (same as in the above-mentioned example).
In Example 2, such data was obtained.

The nitrous oxide decomposition catalyst according to the present invention is used for explaining the best mode for carrying out the invention. (1) FIG. 1 is a side sectional explanatory view of a decomposition treatment apparatus and the like. (2) FIG. It is the front sectional view which expanded the principal part. FIG. 2 is a block diagram of an embodiment for explaining the best mode for carrying out the invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas 2 Rhodium catalyst 3 Decomposition processing apparatus 4 Porous support 5 Exhaust pipe 6 Outer cylinder 7 Cell wall 8 Cell space 9 Blower part 10 Heating part 11 Humidity control part 12 Flowmeter

Claims (8)

It is a decomposition catalyst of low concentration nitrous oxide contained in exhaust gas, and rhodium is used,
The exhaust gas has a concentration of nitrous oxide of 50 ppm to 10,000 ppm on a volume basis, and is supplied at a temperature lower than the thermal decomposition temperature of nitrous oxide.
The rhodium catalyst has a transient electron donating action of one unpaired electron in the outermost shell O shell 5s orbit of atomic structure, and a transient of two electron vacancies or holes in its inner N shell 4d orbit. A nitrous oxide decomposition catalyst characterized by reducing and decomposing nitrous oxide into nitrogen and oxygen based on an electron-storing action.   The nitrous oxide decomposition catalyst according to claim 1, wherein the exhaust gas comprises exhaust gas that has undergone an ammonia oxidation step, and contains nitrous oxide by-produced by oxidation of the ammonia, A nitrous oxide decomposition catalyst characterized by the above.   3. The nitrous oxide decomposition catalyst according to claim 1, wherein the exhaust gas absorbs a nitrogen-containing gas obtained through the ammonia oxidation step with sulfuric acid, thereby converting nitrosylsulfuric acid. A nitrous oxide decomposition catalyst comprising exhaust gas from the step of obtaining and containing nitrous oxide.   The nitrous oxide decomposition catalyst according to claim 1, wherein the exhaust gas is an exhaust gas from the step of oxidizing cyclohexanol and / or cyclohexane with nitric acid, and contains nitrous oxide. A featured nitrous oxide decomposition catalyst.   The nitrous oxide decomposition catalyst according to claim 1, 2, 3, or 4, wherein the exhaust gas is obtained by denitrating nitrogen oxides contained in the gas by a selective reduction method using ammonia. A nitrous oxide decomposition catalyst comprising exhaust gas and containing nitrous oxide. According to claim 1, 2, 3, 4, or catalyst for decomposing nitrous oxide as described in 5, the rhodium catalyst is carried on the loading amount 50 g / ft ³ or more to 100 g / ft ³ carriers below, the exhaust gas Is supplied at an SV value of 10,000 (1 / h) or more to 30,000 (1 / h) or less, a nitrous oxide decomposition catalyst. A method for decomposing and removing low concentration nitrous oxide contained in exhaust gas, using rhodium as a catalyst,
The exhaust gas has an SV value of 10,000 (1 / h) or more to 30,000 (1 / h) or less at a temperature range of 350 ° C. to less than 550 ° C. Fed to and contacted with the rhodium catalyst;
Thus, the transient electron donating action of one unpaired electron in the outermost shell O-shell 5s orbit of the atomic structure of the rhodium catalyst, and the transient of two electron vacancies or holes in the inner N-shell 4d orbital. Based on the dynamic electron seizure effect,
A method for decomposing and removing nitrous oxide, characterized in that the bond and activation energy of nitrous oxide are reduced, reduced, decomposed and removed into nitrogen and oxygen by reducing activation energy.   8. The method for decomposing and removing nitrous oxide according to claim 7, wherein the exhaust gas comprises exhaust gas that has undergone an ammonia oxidation step, and contains nitrous oxide by-produced by oxidation of the ammonia. A method for decomposing and removing nitrous oxide, characterized in that the concentration of contained nitrous oxide is 50 ppm to 10,000 ppm on a volume basis.

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