JPH054027A - Treatment of exhaust gaseous dinitrogen monoxide - Google Patents

Abstract

PURPOSE:To allow the efficient and economical recovery of decomposition heat by continuously decomposing the exhaust gases contg. the dinitrogen monoxide byproduced in the process for producing adipic acid by nitric acid oxidation of cyclohexanol or cyclohexanone or a mixture composed thereof to nitrogen and oxygen in the presence of a cuprous oxide catalyst. CONSTITUTION:The exhaust gases 4 contg. the dinitrogen monoxide byproduced in the process for producing the adipic acid by the nitric acid oxidation of the cyclohexanol or cyclohexanone or the mixture composed thereof are supplied to an exchanger 14 for preheating the supplied gases. The oxidized exhaust gases 5 preheated up to a prescribed temp. are introduced into a reactor 15 packed with the cuprous oxide catalyst where the gases are continuously decomposed to the nitrogen and the oxygen. The greater part of the decomposition heat is absorbed to hot water 10 and 11 circulating between the outside of the reactor and a steam drum 17. The hot water is evaporated by the steam drum and the heat thereof is reutilized as steam 12. The treated gases 6 after the decomposing reaction preheat the oxidized exhaust gases 4 in the previous heat exchanger 14, by which these gases themselves are subjected to heat removal.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the production of adipic acid by oxidizing cyclohexanol or cyclohexanone or a mixture thereof with nitric acid to produce dinitrogen monoxide (hereinafter referred to as N ₂ O) which is a by-product. The purpose is to pass exhaust gas containing gas (hereinafter referred to as the oxidation exhaust gas) through a catalyst layer to continuously decompose the main component N ₂ O into nitrogen and oxygen, and effectively recover the heat generated at the time of decomposition. And a method for treating exhausted N ₂ O gas.

[0002]

BACKGROUND OF THE INVENTION When adipic acid is oxidized by nitric acid, the by-product gas is generally dinitrogen monoxide (N).
₂ O), nitric oxide (NO), nitrogen dioxide (NO ₂ ), carbon dioxide, and nitrogen. Of these, nitric oxide is oxidized to nitrogen dioxide, which is an atmospheric pollutant that dissolves in water and exhibits acidity, and is called NOx along with other nitrogen oxides that are in chemical equilibrium with both. In the adipic acid production process, in order to prevent air pollution, it is generally known that nitric oxide is converted into nitrogen dioxide by air oxidation and is recovered as nitric acid by absorption reaction with water together with byproduct nitrogen dioxide.

On the other hand, N ₂ O, unlike other NOx, is chemically stable, does not show acidity, and is not an air pollutant. For this reason, it is generally released to the atmosphere together with excess air required for oxidation. However, N ₂ O is considered to be a greenhouse gas that leads to global warming together with carbon dioxide and the like. The main sources of N ₂ O are from soil and ocean natural biometabolism (ATOMOSP).
HERIC OZONE, 1985). Therefore, N ₂ O emitted from adipic acid plants around the world is considered to be 5% or less of the total amount of emission on the earth. However, considering that the ozone layer may be destroyed and the release location can be specified, it is desirable to decompose into a gas that does not affect the environment.

Decomposition of N ₂ O into oxygen and nitrogen by an oxide catalyst is an important field of catalytic research and has been known for a long time (Yasukazu Saito, Catalyst, Vol. 1, No. 2, 1).
29 (1959)). Recently, it is also known to decompose N ₂ O in laughing gas for anesthesia (Japanese Patent Publication 61-50650 and others). The handling gas in this case is N ₂ O
It is a mixed gas of oxygen and oxygen, and is intended for a relatively small amount of treatment, and there is no mention of decomposition of N ₂ O by-produced from the adipic acid production process.

[0005]

SUMMARY OF THE INVENTION Therefore, the first object of the present invention is to provide a catalyst having a long life so that it can be used for a long time with respect to exhaust gas containing N ₂ O by-produced from the adipic acid production process. Is provided. A second object of the present invention is to provide a technique capable of completely decomposing N ₂ O in the oxidizing exhaust gas and recovering the obtained decomposition heat efficiently and economically.

[0006]

SUMMARY OF THE INVENTION The inventors of the present invention have proposed a catalyst, which has been considered to have higher activity than before, and other catalysts by using a flow-type decomposition reactor to remove N _An attempt was made to decompose the ₂ O. It was found that each of the catalysts showed a higher decomposition rate of N ₂ O as the reaction temperature was raised, and the catalytic activity was improved, and the initial activity to N ₂ O was recognized.

However, in the continuous use for a long period of time, the effect of the composition of the oxidizing exhaust gas is exerted, and there are some cases where the activity is lowered during use despite the constant decomposition conditions. As a result of further research, it was found that cupric oxide showed a high decomposition rate for a long period of time and could be continuously decomposed into nitrogen and oxygen. That is, the present invention is a step of producing adipic acid by nitric acid oxidation of cyclohexanol or cyclohexanone or a mixture thereof, in which exhaust gas containing dinitrogen monoxide produced as a by-product is continuously converted into nitrogen gas in the presence of a cupric oxide catalyst. It is a method of treating exhausted nitrous oxide gas, characterized by decomposing it into oxygen.

Embodiments of the present invention will be described below. First, since the exhaust gas from the adipic acid production process contains NOx, which is the above-mentioned acidic gas, it is desirable to reduce the concentration as much as possible in consideration of corrosion due to this and supply it to the decomposition device. It is preferable that the total amount of nitric oxide and nitrogen dioxide in the oxidizing exhaust gas is adjusted to 1% or less by absorption of water and then the decomposition is carried out in a reactor filled with a catalyst.

The cupric oxide catalyst may be either alone or supported on a carrier, but it is desirable to support it in order to improve the heat resistant temperature. The carrier may be alumina, silica, titania, zeolite or any other type as long as it can withstand the use temperature, but alumina is preferable. The supported amount may be at least the amount capable of exhibiting the decomposition performance of N ₂ O,
It is preferred to have a loading of 1 to 10%.

In the present invention, a catalyst prepared by impregnating and supporting cupric oxide on a granular alumina carrier is filled in a tubular reaction tube so as to have a length of 50 mm or more.
If the gas flow rate (hereinafter referred to as SV) in the standard state relative to the superficial volume of the catalyst layer is too small, the amount of catalyst required for decomposition increases, and if it is too large, the decomposition rate of N ₂ O decreases and the reaction temperature does not rise. I can't. Therefore SV is preferably in between the ^100hr-1 of 10000hr ^-1.

On the other hand, the reaction temperature must be 400 ° C. or higher. The decomposition of N ₂ O can be performed by the formula (1)

[0012]

[Chemical 1]

This is an exothermic reaction. However, if the reaction temperature is raised too high only for the purpose of catalytic activity, the heat of reaction raises the temperature of the catalyst oxide and / or the carrier compound, which leads to deterioration of the catalyst such as a structural change, which is not preferable. Therefore, the reaction temperature is preferably within 400 to 600 ° C. Also, the reaction heat released in the above decomposition is relatively large, and the amount of heat can be recovered to generate steam, which can be used as a heat source.

An example in which a cupric oxide-alumina-supported catalyst is used for treating the oxidized exhaust gas from the adipic acid production step is shown below with reference to FIG. First, the nitrogen monoxide is oxidized by air to form nitrogen dioxide, and then the exhaust gas 1 from the adipic acid production process is supplied to the NOx absorption tower 13. Nitrogen dioxide in the gas is absorbed by the absorbed water 2 and the nitric acid solution 3
Is extracted from the bottom of the tower. From the top of the column, the oxidizing exhaust gas 4 containing N ₂ O as a main component is supplied to the heat exchanger 14 for preheating the supply gas at almost normal temperature and normal pressure.

The oxidation exhaust gas 5 preheated to a predetermined temperature
Are guided to the catalyst-filled reactor 15. The type of reactor is
Either a fixed bed or a fluidized bed may be used. In this example, an example of a fixed bed isothermal reactor is shown. Most of the decomposition heat is absorbed by the hot water 10 and 11 circulating between the outside of the reaction tube and the steam drum 17. Hot water evaporates in the steam drum and steam 1
The heat can be reused as 2. The evaporated water is always supplied from the water supply reserve tank 18 as boiler supply water 9.

In the case of adiabatic reaction with a fixed bed,
Since the reactor outlet temperature rises, it is desirable to dilute the oxidizing exhaust gas with air or the like and supply it to the reactor. The treated gas 6 containing nitrogen and oxygen as main components after the decomposition reaction is itself heat-removed by preheating the oxidizing exhaust gas 4 in the heat exchanger 14. The heat-treated processed gas 7 is
Further, it is preferable that the gas is cooled and / or diluted in a cooling heat exchanger or an atmosphere diluting device 16 and then discharged as a treated gas 8 close to the outside temperature to the atmosphere.

On the other hand, the temperature at which the decomposition reaction occurs and sufficient heat is obtained is 400 ° C. or higher. It is necessary to guide the oxidizing exhaust gas 4 to the introduction pipe 19 and warm it up to a predetermined temperature by the start-up preheater 20 at the time of start-up when the temperature of the reactor is low. This may be one that combusts a hydrocarbon or other combustible gas or liquid, but any type can be used as long as it can supply the necessary amount of heat.

[0018]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

[0019]

Example 1 A commercially available carrier alumina was impregnated with an aqueous solution of cupric nitrate having a predetermined concentration under stirring for 1.5 hours or more, and then draining was performed so as to prevent pooling and uneven loading. Next, it was dried for 6 hours using hot air at 120 ° C. Further, the temperature of the electric furnace was gradually increased and firing was performed at 500 ° C. for 3 hours. The amount of copper carried in the baked product was 3% by weight in terms of cupric oxide.

Approximately 28 cm ³ of catalyst in a quartz tube with an inner diameter of 22 mm
The stuffed, the outer quartz tube heated at electric heater, the reaction temperature 495 ° C., in ^SV900hr-1, was carried out the decomposition of N ₂ O. As shown in FIG. 3, almost no decrease in the decomposition rate was observed.

[0021]

[Comparative Example] The initial activities of various catalysts were compared by using the exhaust gas having the composition shown in Table 1 produced as a by-product from the adipic acid production process.
A quartz tube having an inner diameter of 32 mm was filled with various catalysts so as to have a length of 100 mm to obtain a reaction tube. Enclose the area around this reaction tube in an electric furnace and fill the reaction tube with the oxidized exhaust gas by SV900hr ^-1.
It was heated to a predetermined temperature while flowing in. The gas at the inlet and outlet of the reaction tube was sampled, and the concentrations of N ₂ O, nitrogen, oxygen, and carbon dioxide were measured by gas chromatography, and N ₂ O
The decomposition rate was obtained. The results are shown in Table 2 with 50% and 90% N
₂ shows the temperature at which the decomposition rate of O was shown. In the table, JGC is manufactured by JGC Chemical Co., Ltd., Nikko is manufactured by Nikko Rica Co., Ltd., and Nissan is manufactured by Nissan Gardler Catalyst Co., Ltd. In addition, “not achieved” indicates that decomposition has occurred, but the predetermined decomposition rate has not been reached.

Among these, a palladium-supported alumina catalyst (JGC / K240) and a cupric oxide / zinc oxide mixture catalyst (JGC / N211), which are highly active even at low temperatures, were subjected to a long-term test. About 28 cm ³ of the catalyst was packed in a quartz tube having an inner diameter of 22 mm, and the outside of the quartz tube was heated by an electric heater. The reaction temperature was 430 ° C. in the case of palladium-supported alumina catalyst and 440 ° C. in the case of cupric oxide and zinc oxide catalysts. The oxidizing exhaust gas having the composition shown in Table 1 was flowed at SV900hr ^-1 for N
_The change with time of the decomposition rate of ₂ O was observed. As shown in FIG. 2, the activity of the catalyst decreased and the decomposition rate decreased.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

INDUSTRIAL APPLICABILITY According to the present invention, when cyclohexanol, cyclohexanone or a mixture thereof is oxidized with nitric acid to produce adipic acid, N ₂ O which is a main component of exhaust gas produced as a by-product is continuously mixed with nitrogen and oxygen. The heat generated during the decomposition can be effectively recovered.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a process for treating the oxidation exhaust gas and recovering the heat of reaction as described above according to the present invention.

FIG. 2 is a diagram showing a long-term change in the decomposition rate of N ₂ O in the oxidizing exhaust gas by the catalyst of Comparative Example.

FIG. 3 is a diagram showing a long-term change in the decomposition rate of N ₂ O in the oxidizing exhaust gas by the catalyst of Example.

[Explanation of symbols]

1 Exhaust gas from adipic acid manufacturing process 2 absorbed water 3 Nitric acid aqueous solution 4 The oxidative exhaust gas 5 Oxidized exhaust gas (preheated) 6 treated gas 7 Processed gas (heat removed) 8 Processed gas (cooled) 9 Boiler supply water 10 hot water (with reactor) 11 Hot water (reactor out) 12 steam 13 NOx absorption tower 14 Heat exchanger for preheating supply gas 15 Catalyst filling reactor 16 Cooling heat exchanger or air dilution device 17 Steam drum 18 Spare tank for water supply 19 Piping for introduction at startup 20 Start-up catalyst preheater

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display area C07C 55/14 6742-4H

Claims (2)

[Claims] 1. A process for producing adipic acid by nitric acid oxidation of cyclohexanol, cyclohexanone or a mixture thereof, wherein exhaust gas containing dinitrogen monoxide, which is a by-product, is continuously converted into nitrogen in the presence of a cupric oxide catalyst. A method for treating exhausted dinitrogen monoxide gas, which comprises decomposing it into oxygen and oxygen. 2. The exhausted dinitrogen monoxide gas is heated by a preheater and supplied to a decomposition device having the catalyst layer, and the heat generated during decomposition generates steam, and the gas after decomposition is used. The method for treating exhausted dinitrogen monoxide gas according to claim 1, wherein the preheater is heated.