JP3569295B2 - Method for producing nitrogen oxide absorbent - Google Patents

Description

[0001]
[Industrial applications]
The present invention is a nitrogen oxide absorbent that absorbs nitrogen oxides in a high-temperature gas such as a combustion gas,In particular, it relates to a method for manufacturing the same.
[0002]
[Prior art]
When the fuel is burned at a high temperature, even in the case of a clean fuel containing almost no nitrogen compounds, for example, natural gas, LP gas, kerosene, etc., nitrogen and oxygen in the air used for combustion react at a high temperature. Therefore, nitrogen oxides are generated. It is known that the generation amount increases as the combustion temperature increases. The removal of nitrogen oxides from high-temperature combustion gas has been technically established as the "ammonia-added catalytic reduction method", and many practical plants are in operation. That is, in this method, a catalyst layer prepared by supporting an oxide such as vanadium, nickel, chromium, iron, or copper on a catalyst carrier formed using titanium oxide or alumina is coated with a substantially same amount of ammonia as nitrogen oxide. The nitrogen oxides can be converted into harmless nitrogen by the following reaction by passing the combustion gas to which is added.
[0003]
2NO + 2NH₃+1/2 O₂→ 2N₂+ 3H₂O
Here, the reaction temperature is usually 300 to 400 ° C., and the space velocity is 10,000 to 20,000 h for a gas containing no soot or dust.^-15,000 to 6,000 h for heavy oil combustion gas^-13,000 to 5,000 h for coal combustion gas^-1It is about.
[0004]
[Problems to be solved by the invention]
However, the above-mentioned conventional method consumes a large amount of expensive ammonia, and also requires control of the amount of added ammonia in accordance with fluctuations in the amount of generated nitrogen oxides that change in response to fluctuations in the combustion state. Is complicated.
[0005]
By the way, recently, yttrium-barium-copper oxide superconductor material (YBa)₂Cu₃O_{7- δ}) Has the property of absorbing nitrogen oxides in a high-temperature (about 300 ° C.) gas containing oxygen and nitrogen oxides (Surface Science, 9 (7), p489, (1988)). ), Magazine "catalyst" 33 (2), p347, (1991)). However, when the present inventor conducted an experiment for confirming this fact, it was found that the hydration decomposition product of this superconductor material also had a property of efficiently absorbing nitrogen oxides. Therefore, when the cause of nitrogen oxide absorption was investigated, it was found that a mixture of an alkaline earth element oxide or hydroxide and a transition element oxide effectively absorbed nitrogen oxides. .
[0006]
The present invention has been made based on the above-described clarified facts, and it is possible to remove and recover nitrogen oxides in a high-temperature gas without consuming expensive ammonia, and to perform nitrogen oxide absorption that can be relatively easily regenerated. Agent,In particular, it aims at providing a manufacturing method thereof.
[0007]
[Means for Solving the Problems]
To solve the above problems,Nitrogen oxide absorbent produced by the nitrogen oxide absorbent production method according to the present invention,(1) A nitrogen oxide absorbent for absorbing nitrogen oxides in a high-temperature gas containing oxygen and nitrogen oxides, which is a mixture of an alkaline earth element oxide or hydroxide and a transition element oxide. And a material comprising:
[0008]
In the configuration 1, as the alkaline earth element, Ba, Ca, Sr, or the like is preferable, but Be, Mg, Ra, or the like can also be used. BaO, CaO and SrO are preferable as oxides of alkaline earth elements, and Ba (OH) is preferable as hydroxide.₂, Ca (OH)₂, Sr (OH)₂Etc. are preferred. Further, as the transition element, Cu, Ni, Co, Fe or the like is preferable, and as the oxide of the transition element, CuO, NiO, Co₂O₃, Fe₂O₃Etc. are preferred. Among them, particularly remarkable absorption effects were observed when Ba and Sr were used as alkaline earth elements and Cu and Fe were used as transition elements.
[0009]
Therefore, as an aspect of this configuration 1,
(2) In the nitrogen oxide absorbent of constitution 1,
The alkaline earth element is barium (Ba) and / or strontium (Sr), and the transition element is copper (Cu) and / or iron (Fe).
[0010]
Further, the nitrogen oxide absorbent of the constitution 1 can be produced by the production method of the following constitutions 3 and 4.
[0011]
(3) A method for producing a nitrogen oxide absorbent according to constitution 1, wherein
A molding agent is added to a mixture of the powder of the oxide or hydroxide of the alkaline earth element and the powder of the oxide of the transition element, and after molding, the mixture is calcined at a temperature of 300 to 600 ° C. A configuration characterized by obtaining a nitrogen oxide absorbent comprising a substance containing a mixture of an oxide or hydroxide of an element and an oxide of a transition element,
as well as,
(4) A method for producing a nitrogen oxide absorbent according to configuration 1, wherein
An aqueous solution containing salts of alkaline earth elements and salts of transition elements is impregnated into a carrier material such as aluminum oxide, titanium oxide, and silicon oxide, and then calcined at a temperature of 300 to 600 ° C. A nitrogen oxide absorbent comprising a substance containing a mixture of an oxide or hydroxide and an oxide of a transition element.
[0012]
Further, the nitrogen oxide absorbent of constitution 2 can be manufactured by the following production method of constitution 5.
[0013]
(5) The method for producing a nitrogen oxide absorbent according to configuration 2, wherein
Nitrate decomposition of a mixture of barium nitrate and / or strontium nitrate powder and at least one powder of copper oxide, iron oxide, copper nitrate and iron nitrate at 400 to 600 ° C. in an inert atmosphere And obtaining a solid nitrogen oxide absorbent containing a mixture of barium and / or strontium oxide and copper and / or iron oxide.
[0014]
In the above-described configuration 3, as the molding agent, for example, a sol-like or gel-like form of aluminum oxide, titanium oxide, silicon oxide, bentonite, or the like can be used. Further, as the salt of the alkaline earth element in the constitution 4, Ba (NO₃)₂Nitrate and BaCl₂And the like, and salts of the transition element include Cu (NO₃)₂Nitrates such as CuCl₂Chloride or CuSO₄And the like can be used. Further, as the carrier substance, a molded body of aluminum oxide, titanium oxide, silicon oxide, or the like is used. Here, in the constitutions 3 and 4, the firing temperature is set to 300 to 600 ° C. The firing is not sufficiently performed at a temperature lower than 300 ° C., so that the formed shape cannot be maintained and exceeds 600 ° C. This is because the surface area and porosity of the fired body decrease, and good performance as an absorbent cannot be obtained. Further, as the inert gas in Configuration 5, for example, nitrogen gas or the like can be used. When a mixture of barium nitrate powder and copper oxide or copper nitrate powder is exposed to an inert atmosphere at 400 to 600 ° C., barium nitrate is decomposed to absorb solid nitrogen oxide composed of barium oxide and copper oxide. Agent is obtained.
[0015]
Furthermore, according to the nitrogen oxide recovery method according to Configurations 6 and 7 using the nitrogen oxide absorbent of Configuration 1 described above, high-concentration nitrogen oxides absorbed from high-temperature gas can be efficiently recovered. .
[0016]
(6) a first step of bringing a high-temperature gas containing oxygen and nitrogen oxides at 250 to 500 ° C. into contact with the nitrogen oxide absorbent of Configuration 1 to absorb nitrogen oxides in the high-temperature gas;
A second step of contacting the nitrogen oxide absorbent that has absorbed the nitrogen oxides with an inert gas at 300 to 600 ° C. to desorb and recover the absorbed nitrogen oxides.
[0017]
As the inert gas in the structures 6 and 7, for example, nitrogen gas can be used. Here, according to Configuration 7, the recovered nitrogen oxide can be effectively used as a raw material for producing nitric acid, and the nitrogen oxide absorbent from which the nitrogen oxide has been desorbed can be repeatedly used.
[0018]
Further, when the nitrogen oxide recovery method according to any one of the constitutions 6 and 7 is applied to the case of recovering nitrogen oxide in a high-temperature gas containing carbon dioxide in addition to oxygen and nitrogen oxide, the nitrogen oxide absorption method used for this is used. As the agent absorbs carbon dioxide, its ability to absorb nitrogen oxides gradually degrades. However, according to the nitrogen oxide absorbent regenerating method according to the following constitutions 8 and 9, this can be regenerated.
[0019]
(8) Nitrogen oxide absorption that regenerates the nitrogen oxide absorbent used when nitrogen oxide in a high-temperature gas containing carbon dioxide in addition to oxygen and nitrogen oxide is recovered by the nitrogen oxide recovery method of Configuration 6. Agent regeneration method,
After nitric acid is reacted with the nitrogen oxide absorbent absorbing the nitrogen oxides and carbon dioxide to desorb carbon dioxide, the nitrogen oxide absorbent is brought into contact with an inert gas at 300 to 600 ° C. to regenerate the nitrogen oxide absorbent. Configuration characterized by
as well as,
(9) Nitrogen oxide absorption that regenerates the nitrogen oxide absorbent used when nitrogen oxide in a high-temperature gas containing carbon dioxide in addition to oxygen and nitrogen oxide is recovered by the nitrogen oxide recovery method of Configuration 6. Agent regeneration method,
After contacting a mixed gas of high-concentration nitrogen oxides at 300 to 500 ° C. and air with the nitrogen oxide absorbent that has absorbed the nitrogen oxides and carbon dioxide, the mixture is converted to an inert gas at 300 to 600 ° C. A configuration characterized by contacting and desorbing carbon dioxide to regenerate the nitrogen oxide absorbent.
[0020]
As the inert gas in the above configurations 8 and 9, nitrogen gas or the like can be used.
[0021]
[Action]
By bringing the nitrogen oxide absorbent of the above configuration 1 into contact with a high-temperature gas containing oxygen and nitrogen oxides, the nitrogen oxides in the high-temperature gas can be effectively absorbed. This is because the oxide of the transition element acts as a catalyst, and the nitrogen oxide reacts with the oxide of the alkaline earth element or the hydroxide or the oxide of the transition element and is taken into the product. it is conceivable that. In this case, if barium (Ba) and / or strontium (Sr) is used as the alkaline earth element and copper (Cu) and / or iron (Fe) is used as the transition element as in the configuration 2, especially nitrogen oxide It is possible to obtain a material having excellent absorption capacity. In addition, the absorption capacity of the alkaline earth element is Ba = Sr> Ca, and the catalytic action of the transition element oxide is CuO = Fe₂O₃> Co₂O₃> NiO. Further, it has been confirmed that although an oxide or hydroxide of an alkaline earth element alone has a certain absorption capacity, the absorption rate is extremely low, so that it is not practical. Further, a substance containing an oxide of an alkaline earth element or an oxide of a hydroxide and a transition element in any form, for example, a substance such as the above-described oxide superconductor and a hydrate decomposition product thereof Has a certain absorption capacity, but it has been confirmed that its absorption capacity is small as compared with those having a mixture of an alkaline earth element oxide or hydroxide and a transition element oxide as a main component. . This is considered to be because the amount of the mixed amount of the oxide or hydroxide of the alkaline earth element and the oxide of the transition element contained in these oxide superconductors and the like is smaller than the total amount. .
[0022]
Further, according to the production methods of Configurations 3 to 5, a solid nitrogen oxide absorbent can be obtained.
[0023]
Further, according to the configurations 6 and 7, the nitrogen oxides absorbed by the nitrogen oxide absorbent of the configuration 1 can be recovered in a high concentration state. This is because by contacting the nitrogen oxide absorbent that has absorbed the nitrogen oxides with an inert gas at a temperature higher than the temperature of the high-temperature gas at the time of absorption, the oxides of the alkaline earth element and the like and the nitrogen oxides It is considered that this is because the reaction product of the above is decomposed and nitrogen oxides taken in the product are eliminated. In addition, the reaction temperature and space velocity in this recovery method are almost the same as those in the conventional "ammonia-added catalytic reduction method", so it is only necessary to remodel a part of the equipment for implementing this conventional method.Nitrogen oxide recoveryCan be implemented. Moreover, according to the configuration 7, the recovered nitrogen oxide can be effectively used as a raw material for producing nitric acid, and the nitrogen oxide absorbent from which the nitrogen oxide has been desorbed can be repeatedly used.
[0024]
Further, according to the constitutions 8 and 9, it is possible to regenerate the nitrogen oxide absorbent whose ability to absorb carbon dioxide in the high-temperature gas and to absorb nitrogen oxides is deteriorated. Here, the absorption ability of nitrogen oxides is deteriorated by the absorption of carbon dioxide by the nitrogen oxide absorbent because a reaction product (e.g., an oxide of an alkaline earth element or the like) reacts with carbon dioxide. For example, CaCO₃It is considered that the increase in the amount of) relatively decreases the amount of alkaline earth metal oxides and the like that can react with nitrogen oxides. Therefore, if the reaction product between the alkaline earth element oxide and the like and carbon dioxide is decomposed and returned to the original alkaline earth element oxide and the like, the absorption capacity can be restored and the regeneration can be performed. In the structure 8, carbon dioxide is desorbed by reacting nitric acid with a reaction product of an oxide of an alkaline earth element or the like and carbon dioxide to generate nitrate and carbon dioxide. By contacting with an inert gas, it is decomposed and returned to the original alkaline earth element oxide or the like for regeneration. Further, in the configuration 9, the reaction product of an oxide of an alkaline earth element and the like and carbon dioxide is brought into contact with a mixed gas of a high-concentration nitrogen oxide at 300 to 500 ° C. and air to decompose the reaction product. Thus, carbon dioxide is desorbed and regenerated.
[0025]
【Example】
1.Examples of the nitrogen oxide absorbent produced in the present invention, and comparative examples
Example 1-1
This embodiment is an example in which a powdery nitrogen oxide absorbent is composed of a mixed powder of Ba (OH) 2 powder and CuO powder.
[0026]
Ba (OH) having a particle size of about 5 to 20 μm₂And a CuO powder having a particle size of about 5 to 20 μm are uniformly stirred and mixed at a weight ratio of about 4: 1 to prepare a mixed powder, and a powdery nitrogen oxide absorbent is used. Obtained.
[0027]
The nitrogen oxide absorbent thus obtained is₂The sample was brought into contact with a high-temperature gas having a concentration of 4% and a NO concentration of 2000 ppm and a temperature of 350 ° C. for 300 minutes or more, and its NO absorption amount and initial absorption speed were measured by a thermobalance device. The NO absorption amount was 8.2 mmol. / G 2, and the initial absorption rate showed an extremely high value of 0.040 mmol / g · min.
[0028]
Note that the relationship between the contact time and the NO absorption amount in this case is shown by plotted points marked with ○ in the graph of FIG. In FIG. 1, the horizontal axis represents the contact time (unit: minute), and the vertical axis represents the absorption amount (unit: mmol / g).
[0029]
Example 1-2
This embodiment uses Ba (OH)₂Except that the mixing ratio of the powder and the CuO powder was set to 1: 1, the powdered nitrogen oxide absorbent had the same structure as that of the first embodiment.
[0030]
This nitrogen oxide absorbent was similarly contacted with a high-temperature gas having a NO concentration of 1000 ppm, which was the same high-temperature gas as in Example 1-1, and the NO absorption amount and the initial absorption rate were measured. 5.8 mmol / g, and the initial absorption rate showed a high value of 0.028 mmol / g · min. From the results of Examples 1-1 and 1-2, compared to CuO powder as a catalyst, Ba (OH)₂It can be seen that increasing the proportion of the powder to a certain extent is superior to the absorption capacity.
[0031]
Example 1-3
This embodiment uses Ba (OH)₂Powder and CuO powder with Y₂O₃Powder and add these mix proportions to Y₂O₃Powder: Ba (OH)₂Powder: CuO powder = 1: 2: 3 is a powdery nitrogen oxide absorbent.
[0032]
This nitrogen oxide absorbent was similarly contacted with a high-temperature gas having a NO concentration of 1000 ppm, which was the same high-temperature gas as in Example 1-1, and the NO absorption amount and the initial absorption rate were measured. 3.8 mmol / g, and the initial absorption rate showed a relatively high value of 0.035 mmol / g · min. Where Y₂O₃The absorption capacity is slightly inferior to those of Examples 1-1 and 1-2 without adding powder. From this result, Y₂O₃It turns out that it is better not to add powder.
[0033]
Example 1-4
This embodiment uses Ba (OH)₂Powder and Fe₂O₃This is an example in which a powdery nitrogen oxide absorbent is constituted by a powder mixture with powder, and FeO is used instead of CuO powder.₂O₃Except for using the powder, the other configuration was the same as that of Example 1-1.
[0034]
This nitrogen oxide absorbent was similarly contacted with a high-temperature gas having the same concentration as in Example 1-1 and a NO concentration of 2000 ppm, and the NO absorption amount and the initial absorption rate were measured. It was 5.8 mmol / g, and the initial absorption rate showed a high value of 0.038 mmol / g · min, but it was slightly inferior to that of Example 1-1. From these results, it can be seen that CuO powder is more effective as a catalyst₂O₃You can see that it is superior to powder. In this case, the relationship between the contact time (horizontal axis: unit; minute) and the NO absorption amount (vertical axis: unit; mmol / g) is shown by plotted points in the graph of FIG.
[0035]
Example 1-5
This embodiment uses Ba (OH)₂Powder and Co₂O₃This is an example in which a powdery nitrogen oxide absorbent is composed of a mixed powder with powder, and CoO powder is used instead of CuO powder.₂O₃Except for using the powder, the other configuration was the same as that of Example 1-1.
[0036]
The nitrogen oxide absorbent was similarly brought into contact with the same high-temperature gas as in Example 1-1, and the NO absorption amount and the initial absorption rate were measured. The NO absorption amount was 5.3 mmol / g. Although the absorption rate showed a high value of 0.039 mmol / g · min, it was slightly inferior to Examples 1-4. From this result, the action as a catalyst is Fe₂O₃Powder is Co₂O₃It turns out that it is slightly better than powder.
[0037]
Example 1-6
This embodiment uses Ba (OH)₂This is an example in which a powdery nitrogen oxide absorbent is composed of a mixed powder of powder and NiO powder, and is the same as Example 1-1 except that NiO powder is used instead of CuO powder. Configuration.
[0038]
When the nitrogen oxide absorbent was brought into contact with the same high-temperature gas as in Example 1-1 and the NO absorption amount and the initial absorption rate were measured, the NO absorption amount was 2.5 mmol / g. The absorption rate is 0.015 mmol / g · min, which is a low value as compared with Examples 1-1 to 1-5. However, since the material itself is inexpensive, it is a value enough to withstand practical use for industrial use. I found it. From this result, the action of NiO as a catalyst is Co₂O₃It turns out that it is inferior to powder.
[0039]
Example 1-7
This embodiment uses Ca (OH)₂This is an example in which a powdery nitrogen oxide absorbent is composed of a mixed powder of powder and CuO powder, and Ba (OH)₂Ca (OH) instead of powder₂Except for using the powder, the other configuration was the same as that of Example 1-1.
[0040]
When this nitrogen oxide absorbent was similarly contacted with a high-temperature gas having the same concentration as in Example 1-1 and a NO concentration of 2000 ppm, and the NO absorption amount and the initial absorption rate were measured, the NO absorption amount was 1.3 mmol / g and the initial absorption rate is 0.034 mmol / g · min, which is a low value as compared with Examples 1-1 to 1-4, but the material itself is inexpensive. Therefore, it was found that the value was sufficiently practical for industrial use. Also, from the results, Ca (OH)₂Ba (OH) than when using₂It can be seen that the use of is superior to the absorption capacity. In this case, the relationship between the contact time (horizontal axis: unit; minute) and the NO absorption amount (vertical axis: unit; mmol / g) is shown by plotted points in the graph of FIG.
[0041]
Examples 1-8
This embodiment is an example in which a powdery nitrogen oxide absorbent is composed of a mixed powder of BaO powder and CuO powder, and Ba (OH)₂Except for using BaO powder instead of powder and using a 3.5: 1 mixing ratio between BaO powder and CuO powder, the other configuration was the same as that of Example 1-1.
[0042]
This nitrogen oxide absorbent was similarly contacted with a high-temperature gas having the same concentration as in Example 1-1 and a NO concentration of 2000 ppm, and the NO absorption amount and the initial absorption rate were measured. It was 3.8 mmol / g and the initial absorption rate was 0.031 mmol / g · min, which proved to be a value sufficient for practical use. In this case, the relationship between the contact time (horizontal axis: unit; minute) and the NO absorption amount (vertical axis: unit; mmol / g) is shown by plotted points in the graph of FIG.
[0043]
Examples 1-9
This embodiment uses Ba (OH)₂Except for using SrO powder instead of powder, the other configuration was the same as that of Example 1-1.
[0044]
This nitrogen oxide absorbent was similarly brought into contact with the same high-temperature gas as in Example 1-1, and the NO absorption amount and the initial absorption rate were measured. The NO absorption amount was 8.4 mmol / g. The absorption rate showed an extremely high value of 0.035 mmol / g · min, which is almost the same as that of Example 1-1. From this result, Ba (OH)₂It can be seen that the powder and the SrO powder have substantially the same absorption capacity.
[0045]
Examples 1-10
This embodiment uses Ba (OH)₂This is an example in which a mixture of Cu and CuO constitutes a solid nitrogen oxide absorbent.
[0046]
Ba (OH) having a particle size of about 5 to 20 μm₂And a powder of CuO having a particle size of about 5 to 20 μm were uniformly stirred and mixed at a weight ratio of about 4: 1 to prepare a mixed powder.
[0047]
Next, an aluminum oxide sol in which about 10% of aluminum oxide was dispersed in a medium was added to the mixed powder to form a paste. Next, this paste was filled in a large number of through-holes having a diameter of 5 mm formed in an aluminum plate having a thickness of 5 mm, and left to dry for several to ten and several hours. Thereafter, a large number of 5 mmφ × 5 mm columnar molded bodies thus obtained were calcined at 500 ° C. for about 3 hours in an air atmosphere to obtain a large number of solid nitrogen oxide absorbents.
[0048]
This nitrogen oxide absorbent was similarly contacted with a high-temperature gas having the same concentration as in Example 1-1 and a NO concentration of 2000 ppm, and the NO absorption amount and the initial absorption rate were measured. 6.2 mmol / g, and the initial absorption rate showed a high value of 0.035 mmol / g · min.
[0049]
Example 1-11
This embodiment is an example in which a solid nitrogen oxide absorbent is constituted by a mixed compact of BaO and CuO obtained by the impregnation method. Ba (NO) was added to the aluminum oxide molded body which had been adjusted to a 5 mmφ × 5 mm cylindrical shape in advance.₃)₂And Cu (NO₃)₂After impregnating with a mixed aqueous solution of the above, calcining was performed in the same manner to obtain a similar solid nitrogen oxide absorbent.
[0050]
When this nitrogen oxide absorbent was similarly contacted with a high-temperature gas having the same concentration as in Example 1-1 and a NO concentration of 2000 ppm, and the NO absorption amount and the initial absorption rate were measured, the NO absorption amount was It was 6.5 mmol / g and the initial absorption rate was 0.036 mmol / g · min, indicating a high value.
[0051]
Examples 1-12
In this embodiment, Ba (NO₃)₂Powder and Cu (NO₃)₂A homogeneous mixture with the above powder was decomposed into nitrates at a temperature of 400 to 600 ° C. in a nitrogen gas atmosphere to obtain a solid nitrogen oxide absorbent composed of BaO and CuO.
[0052]
When this nitrogen oxide absorbent was similarly contacted with a high-temperature gas having the same concentration as in Example 1-1 and a NO concentration of 2000 ppm, and the NO absorption amount and the initial absorption rate were measured, the NO absorption amount was 4.2 mmol / g, and the initial absorption rate showed a high value of 0.044 mmol / g · min.
[0053]
Comparative Example 1
This comparative example is based on the yttrium-barium-copper oxide superconductor material (YBa).₂Cu₃O_{7- δ}) Powder. The powder of this oxide superconductor material is₂When the NO absorption amount and the initial absorption rate were measured by contacting with a high-temperature gas having a concentration of 2%, a NO concentration of 2000 ppm, and a temperature of 330 ° C. for 300 minutes or more, the NO absorption amount was 1.4 mmol / g. , And the initial absorption rate was 0.05 mmol / g · min, indicating a tentative absorption capacity. However, the material itself is expensive and cannot be said to be practical for industrial use. After the NO-absorbed material was regenerated by a regenerating method described below, the sample was brought into contact with a high-temperature gas at 415 ° C. (the composition was the same as above) and the absorption was measured again. g and the initial absorption rate was 0.05 mmol / g · min. When the regeneration treatment was performed again, the same high-temperature gas as described above was contacted except that the NO concentration was 4000 ppm, and the absorption was measured. The NO absorption amount was 0.84 mmol / g. Was 0.12 mmol / g · min, and it was recognized that the absorption capacity tended to gradually decrease with each regeneration.
[0054]
Comparative Example 2
This comparative example is based on the yttrium-barium-copper oxide superconductor material (YBa).₂Cu₃O_{7- δ})), Left at room temperature for 30 minutes, and dried at 110 ° C. to obtain YBa.₂Cu₃O_{7- δ}Is a hydration degradation product of It should be noted that this hydration decomposition product contains a plurality of types of compositions, and it is presumed that these also contain Ba hydroxide. However, accurate analysis of all the compositions has not yet been carried out. Not done. This hydration degradation product is₂When the NO absorption amount and the initial absorption rate were measured by contacting a high-temperature gas having a concentration of 2%, a NO concentration of 2000 ppm, and a temperature of 325 ° C. for 300 minutes or more, the NO absorption amount was 4.6 mmol / g. , The initial absorption rate was 0.045 mmol / g · min, indicating a considerably high absorption capacity. However, the material itself is expensive and cannot be said to be practical for industrial use. After the NO-absorbed material was regenerated by a regenerating method described below, the sample was brought into contact with the same high-temperature gas as described above, the temperature of which was changed to 390 ° C., and the absorption was measured again. g and the initial absorption rate was 0.045 mmol / g · min.
[0055]
Comparative Example 3
This comparative example is based on commercially available Ba (OH)₂Powder alone.
[0056]
This Ba (OH)₂Powder, O₂When the NO absorption amount and the initial absorption rate were measured by contacting with a high-temperature gas having a concentration of 4% and a NO concentration of 1000 ppm and a temperature of 350 ° C. for 300 minutes or more, the NO absorption amount was 2.8 mmol / g or less. Yes, the initial absorption rate was 0.013 mmol / g · min. Although this comparative example had a certain absorption capacity, it was found that the absorption rate was extremely low, so that it was not practical.
[0057]
Comparative Example 4
This comparative example is based on YBa₂Cu₃O_{7- δ}Which is one of the hydration products of₂BaCuO₅It is. When the absorption capacity was measured in the same manner as in Comparative Example 3, it was found that it had no absorption capacity.
[0058]
Comparative Example 5
In this comparative example, Y₂O₃Powder and Ba (OH)₂Is a mixed powder obtained by uniformly mixing the powder with the powder at a weight ratio of 1: 4. When the absorption capacity was measured in the same manner as in Comparative Examples 3 and 4, the NO absorption was 0.37 mmol / g or less, and the initial absorption rate was 0.005 mmol / g · min. It turned out to be poor.
[0059]
Comparative Example 6
This comparative example is based on the yttrium-barium-copper oxide superconductor material (YBa).₂Cu₃O_{7- δ}Al)₂O₃The pellets are formed, dried and fired (400 ° C.) by adding the sol.
[0060]
This comparative example is referred to as O₂When the NO absorption amount and the initial absorption rate were measured by contacting a high-temperature gas having a concentration of 2%, a NO concentration of 2000 ppm, and a temperature of 350 ° C. for 300 minutes or more, the NO absorption amount was 0.35 mmol / g. And the initial absorption rate was 0.02 mmol / g · min. This comparative example was found to be poor in practicality due to extremely low absorption capacity.
[0061]
Comparative Example 7
This comparative example is composed of Ba (OH)₂Cr as a catalyst in powder 4₂O₃This is a mixed powder obtained by adding powder 1 and mixing.
[0062]
When the mixed powder was measured for nitrogen oxide absorption capacity, it was found that the powder had no absorption capacity. From these results, it can be seen that Cr₂O₃It turns out that the powder has no action as a catalyst.
[0063]
2. Example of nitrogen oxide recovery method
In this embodiment, after absorbing the nitrogen oxides in the high-temperature gas using the nitrogen oxide absorbent of each of the above-described embodiments, the absorbed nitrogen oxides are desorbed and recovered as high-concentration nitrogen oxides. Nitrogen oxide recovery method. This method was performed in the following procedure.
[0064]
Nitrogen oxide absorbent, O₂The nitrogen oxides in the high-temperature gas were absorbed by contacting with a high-temperature gas having a concentration of 4%, a NO concentration of 1000 ppm, and a temperature of 350 ° C. for 300 minutes or more. Next, the nitrogen oxide absorbent having absorbed the nitrogen oxides was brought into contact with a high-temperature nitrogen gas at 400 ° C. As a result, it was possible to recover a gas containing a high concentration of nitrogen oxides that was equal to or higher than the measurement upper limit (2000 ppm) of the NO analyzer used for the measurement. In this case, it was also confirmed that a higher concentration of nitrogen oxides could be obtained by reducing the flow rate of the nitrogen gas or increasing the temperature.
[0065]
If the gas containing high-concentration nitrogen oxides (NO and the like) thus recovered is transferred to a nitric acid production system or the like, it can be effectively used as a raw material for nitric acid production or the like. That is, for example, when a system for carrying out the nitrogen oxide recovery method according to this embodiment is installed as a system for removing NOx in combustion gas such as thermal power generation and a nitric acid production system is connected to this system, the removed NOx is immediately It can be effectively used as a raw material for nitric acid production. Further, if the nitrogen oxide absorbent after the nitrogen oxides are desorbed is transferred to the nitrogen oxide absorbing step again, the nitrogen oxide absorbent can be repeatedly used.
[0066]
3. Example of nitrogen oxide absorbent regenerating method
This embodiment applies the nitrogen oxide recovery method of Embodiment 2 to the case of recovering nitrogen oxides in a high-temperature gas containing carbon dioxide in addition to oxygen and nitrogen oxides. This is an embodiment of a nitrogen oxide absorbent regenerating method for regenerating when the ability of the oxide absorbent to absorb carbon dioxide and absorb nitrogen oxides deteriorates. Hereinafter, a wet method by adding nitric acid water (Example 3-1) and a dry method by contacting a mixed gas of high-concentration nitrogen oxide and air (Example 3-2) will be described.
[0067]
Example 3-1
The nitrogen oxide absorbent regenerated in this example is a nitrogen oxide absorbent obtained by repeating the recovery of nitrogen oxides in a high-temperature gas containing 2% of carbon dioxide five times by the method of Example 2, The one whose nitrogen oxide absorption capacity was reduced to about 30% compared to the initial capacity was used.
[0068]
A nitric acid solution was added to the nitrogen oxide absorbent. The amount to be added was approximately 0 to 20% excess of the equivalent of the carbonate generated in the nitrogen oxide. Next, after completion of the reaction by the addition of nitric acid aqueous solution, this was baked in a nitrogen gas at 450 ° C. for 100 minutes. As a result, carbon dioxide contained as a product in the nitrogen oxide absorbent was completely removed, and the nitrogen oxide absorption ability was almost completely restored to the initial state, and the nitrogen oxide absorbent was regenerated.
[0069]
Example 3-2
The same deteriorated nitrogen oxide absorbent as in Example 3-1 was added to the high-concentration nitrogen oxide recovered in Example 2 by adding air at 400 ° C. containing 5% nitrogen oxide and 5% oxygen. For 120 minutes. Thereby, the carbonate in the nitrogen oxide absorbent was changed to nitrate. Next, this was contacted with nitrogen gas at 450 ° C. for 100 minutes. As a result, carbon dioxide contained as a product in the nitrogen oxide absorbent was completely removed, and the nitrogen oxide absorption ability was almost completely restored to the initial state, and the nitrogen oxide absorbent was regenerated.
[0070]
According to the embodiment described in detail above, there are the following advantages.
[0071]
a. Nitrogen oxides can be absorbed and removed without consuming expensive ammonia in the application temperature range of the "ammonia-added selective catalytic reduction method", which is currently in practical use.
[0072]
b. Since the absorption capacity (absorption amount and absorption rate) of the nitrogen oxide absorbent of this example is large, the required amount of the absorbent is almost the same as the amount of catalyst in the "selective catalytic reduction method with ammonia addition".
[0073]
c. After absorbing the nitrogen oxides, the absorbent is easily desorbed and absorbs high-concentration nitrogen oxides by flowing an inert gas containing no nitrogen oxides and oxygen at the same temperature as the absorption temperature to 50 ° C. The agent can be regenerated.
[0074]
d. The regenerated nitrogen oxide absorbent can be reused in the absorption step.
[0075]
e. The recovered high-concentration nitrogen oxides (mainly nitrogen oxide) can be used as raw materials for chemical industry such as nitric acid production.
[0076]
f. Absorbents that absorb carbon dioxide in combustion gas or carbon dioxide in air and have reduced absorption capacity are mixed gas of high-concentration nitrogen oxides and air collected in wet treatment method by adding nitric acid water or in desorption process. Can be easily reproduced.
[0077]
g. The nitrogen oxide absorbent of this embodiment may be, for example, a mixed powder obtained by a physical operation of barium hydroxide or barium oxide fine powder and copper oxide fine powder, and is therefore extremely easy to prepare.
[0078]
h. If an absorbent in the form of pellets is required for industrial use, clays such as aluminum oxide, titanium oxide, silicon oxide or bentonite which are usually used for catalyst preparation are added to the above absorbent in the form of a sol or gel. It can be easily prepared by molding.
[0079]
【The invention's effect】
As detailed above,According to the method for producing a nitrogen oxide absorbent according to the present invention, the nitrogen oxide absorbent is composed of a substance containing a mixture of an oxide or hydroxide of an alkaline earth element and an oxide of a transition element. By doing so, it is possible to manufacture a nitrogen oxide absorbent capable of efficiently removing and recovering nitrogen oxides in a high-temperature gas without consuming expensive ammonia.
[Brief description of the drawings]
FIG. 1 is a view showing a nitrogen oxide absorbing capacity of an embodiment of the present invention.

Claims (3)

Absorbs nitrogen oxides in high-temperature gas containing oxygen and nitrogen oxides, a nitrogen oxide absorbent comprising a substance containing a mixture of an oxide or hydroxide of an alkaline earth element and an oxide of a transition element A manufacturing method,
A molding agent is added to a mixture of an alkaline earth element oxide or hydroxide powder and a transition element oxide powder, and after molding, the mixture is fired at a temperature of 300 to 600 ° C. A method for producing a nitrogen oxide absorbent, characterized by obtaining a nitrogen oxide absorbent. Absorbs nitrogen oxides in high-temperature gas containing oxygen and nitrogen oxides, a nitrogen oxide absorbent comprising a substance containing a mixture of an oxide or hydroxide of an alkaline earth element and an oxide of a transition element A manufacturing method,
An aqueous solution containing a salt of an alkaline earth element and a salt of a transition element is impregnated into a carrier material of any of aluminum oxide, titanium oxide and silicon oxide, and then calcined at a temperature of 300 to 600 ° C. A method for producing a nitrogen oxide absorbent, characterized by obtaining a nitrogen oxide absorbent. Absorbs nitrogen oxides in high-temperature gas containing oxygen and nitrogen oxides, a nitrogen oxide absorbent comprising a substance containing a mixture of an oxide or hydroxide of an alkaline earth element and an oxide of a transition element A manufacturing method,
The alkaline earth element is barium (Ba) and / or strontium (Sr), the transition element is copper (Cu) and / or iron (Fe);
Nitrate decomposition of a mixture of barium nitrate and / or strontium nitrate powder and at least one powder of copper oxide, iron oxide, copper nitrate and iron nitrate in an inert atmosphere at a temperature of 400 to 600 ° C. And obtaining a solid nitrogen oxide absorbent containing a mixture of barium and / or strontium oxide and copper and / or iron oxide.

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