JP3607694B2 - Nitrogen oxide absorbent, its regeneration method and nitrogen oxide recovery method - Google Patents

Description

[0001]
[Industrial application fields]
The present inventionNitrogen oxide absorbent, its regeneration method and nitrogen oxide recovery methodAbout.
[0002]
[Prior art]
When fuel is burned at high temperatures, even if it is a clean fuel that contains almost no nitrogen compounds, such as natural gas, LP gas, kerosene, etc., nitrogen and oxygen in the air used for combustion react at high temperatures. As a result, nitrogen oxides are formed. It is known that the amount of generation increases as the combustion temperature increases. Removal of nitrogen oxides from high-temperature combustion gas has already been technically established as “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, copper, etc. on a catalyst carrier formed using titanium oxide or alumina has substantially the same amount of ammonia as nitrogen oxide. By passing the combustion gas to which is added, nitrogen oxides can be converted into harmless nitrogen by the following reaction.
[0003]
2NO + 2NH₃  +1/2 O₂  → 2N₂  + 3H₂  O Here, the reaction temperature is usually 300 to 400 ° C., and the space velocity is 10,000 to 20,000 h in a gas not containing soot and dust.^-15,000 to 6,000 h for heavy oil combustion gas^-13,000 to 5,000 hours for coal combustion gas^-1Degree.
[0004]
[Problems to be solved by the invention]
However, the above-described conventional method consumes a large amount of expensive ammonia, and it is necessary to adjust the amount of ammonia added in accordance with the variation in the amount of nitrogen oxide produced that varies according to the variation in the combustion state. There is a problem that is complicated.
[0005]
Incidentally, in recent years, yttrium-barium-copper oxide superconductor materials (YBa₂  Cu₃  O_{7- δ}) Have the property of absorbing nitrogen oxides in high temperature (about 300 ° C.) gas containing oxygen and nitrogen oxides (Journal “Surface Science” 9 (7), p489, (1988). ), Magazine "Catalyst" 33 (2), p347, (1991)). However, when the present inventor conducted an experiment to confirm this fact, it was found that the hydrated decomposition product of this superconductor material also has the property of efficiently absorbing nitrogen oxides. Therefore, when the cause of nitrogen oxide absorption was investigated, it was clarified that a mixture of an oxide or hydroxide of an alkaline earth element and an oxide of a transition element effectively absorbs the nitrogen oxide. .
[0006]
The present invention has been made on the basis of the above-mentioned elucidation facts. Nitrogen oxide absorption that can remove and recover nitrogen oxides in high-temperature gas without consuming expensive ammonia and that can be regenerated relatively easily. AgentAnd its regeneration method and nitrogen oxide recovery method,It is intended to provide.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the nitrogen oxide absorbent according to the present invention is:
(1)A nitrogen oxide absorbent that absorbs nitrogen oxide in a high-temperature gas containing oxygen and nitrogen oxide, and includes a mixture of an oxide or hydroxide of an alkaline earth element and an oxide of a transition element, The alkaline earth element is barium (Ba) and / or strontium (Sr), and the transition element is copper (Cu) and / or iron (Fe).The configuration is as follows.
[0008]
In this configuration 1, alkaline earth elements include Ba, Ca, Sr, etc.There isBe, Mg, Ra, etc.There is.In addition, as oxides of alkaline earth elements, BaO, CaO, SrOThere isAs the hydroxide, Ba (OH)₂ , Ca (OH)₂ , Sr (OH)₂ etcThere is.Transition elements such as Cu, Ni, Co, Fe, etc.There isExamples of transition element oxides include CuO, NiO, and Co.₂ O_Three , Fe₂ O_Three etcThere is.Of these, 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 Configuration 1, the alkaline earth element is barium (Ba) and / or strontium (Sr), and the transition element is copper (Cu) and / or iron (Fe). It was set as the characteristic characterized by this.
[0010]
Further, the nitrogen oxide absorbent of Configuration 1 isManufacturing method of (3) to (6) described nextCan be manufactured.
[0011]
(3) A method for producing a nitrogen oxide absorbent of constitution 1, wherein a molding agent is added to a mixture of an alkaline earth element oxide or hydroxide powder and a transition element oxide powder. A nitrogen oxide absorbent comprising a material containing a mixture of an oxide or hydroxide of an alkaline earth element and an oxide of a transition element by firing at a temperature of 300 to 600 ° C. after moldingGet.
(4) A method for producing a nitrogen oxide absorbent according to constitution 1, wherein an aqueous solution containing an alkaline earth element salt and a transition element salt is impregnated in a carrier material such as aluminum oxide, titanium oxide, or silicon oxide. And 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 by firing at a temperature of 300 to 600 ° C.Get.
[0012]
further,Configuration 1The nitrogen oxide absorbent ofManufacturing method (5) described nextCan be manufactured by.
[0013]
(5)Configuration 1A method for producing a nitrogen oxide absorbent according to claim 1, wherein 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 is inert. Solid nitrogen oxide absorbent comprising a mixture of barium and / or strontium oxide and copper and / or iron oxide after nitrate decomposition at a temperature of 400 to 600 ° C. in an atmosphereGet.
[0014]
Manufacturing method of (3) mentioned aboveIn the above, as the forming agent, for example, aluminum oxide, titanium oxide, silicon oxide, bentonite or the like in a sol or gel form can be used. In addition, as the alkaline earth element salts in Configuration 4, Ba (NO_Three )₂ Nitrates such as BaCl₂ As the transition element salts, Cu (NO) can be used._Three )₂ Nitrates such as CuCl₂ Such as chloride or CuSO_FourSulfates, etc. can be used. Further, as the support material, a molded body such as aluminum oxide, titanium oxide, silicon oxide or the like is used. here,Manufacturing method of (3) (4) mentioned aboveThe firing temperature was set to 300 to 600 ° C. because the firing was not sufficiently performed at a temperature lower than 300 ° C., and thus the molded shape could not be maintained. This is because the surface area and porosity are reduced, and good performance as an absorbent cannot be obtained. Also,Configuration 4As the inert gas, 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 and solid nitrogen oxides composed of barium oxide and copper oxide An absorbent is obtained.
[0015]
Furthermore, the following using the nitrogen oxide absorbent of the above-mentioned constitution 1Configuration 2, 3According to the method for recovering nitrogen oxides, the high concentration of nitrogen oxides absorbed from the high temperature gas can be recovered efficiently.
[0016]
(6) A first step in which a high-temperature gas at 250 to 500 ° C. containing oxygen and nitrogen oxide is brought into contact with the nitrogen oxide absorbent of Configuration 1 to absorb the nitrogen oxide in the high-temperature gas, and the nitrogen oxidation A second step of bringing the nitrogen oxide absorbent that has absorbed the substance into contact with an inert gas at 300 to 600 ° C. to desorb and recover the absorbed nitrogen oxide.
[0017]
thisConfiguration 2For example, nitrogen gas can be used as the inert gas.
(7) Configuration 3Therefore, the recovered nitrogen oxide can be effectively used as a raw material for producing nitric acid, and the nitrogen oxide absorbent from which nitrogen oxide has been eliminated can be repeatedly used.
[0018]
Also,Configuration 2, 3When the nitrogen oxide recovery method is applied to recovering nitrogen oxides in high-temperature gas containing carbon dioxide in addition to oxygen and nitrogen oxides, the nitrogen oxide absorbent used in this method absorbs carbon dioxide. By doing so, the ability to absorb nitrogen oxides gradually deteriorates. But the nextConfiguration 4, 5According to the nitrogen oxide absorbent regeneration method according to, this can be regenerated.
[0019]
(8) Nitrogen oxide in high-temperature gas containing carbon dioxide in addition to oxygen and nitrogen oxideConfiguration 2A nitrogen oxide absorbent regeneration method for regenerating the nitrogen oxide absorbent used in the recovery by the nitrogen oxide recovery method of claim 1, wherein nitric acid is added to the nitrogen oxide absorbent that has absorbed the nitrogen oxide and carbon dioxide. After reacting to desorb carbon dioxide, it is brought into contact with an inert gas at 300 to 600 ° C. to regenerate the nitrogen oxide absorbent.Configuration 4.
(9) Nitrogen oxide in high-temperature gas containing carbon dioxide in addition to oxygen and nitrogen oxideConfiguration 2The nitrogen oxide absorbent regeneration method for regenerating the nitrogen oxide absorbent used in the recovery by the nitrogen oxide recovery method of claim 1, wherein the nitrogen oxide absorbent that has absorbed the nitrogen oxide and carbon dioxide is 300 After contacting a gas mixture of high-concentration nitrogen oxide at ˜500 ° C. and air, it is brought into contact with an inert gas at 300-600 ° C. to desorb carbon dioxide to regenerate the nitrogen oxide absorbent. It was characterized byConfiguration 5.
[0020]
AboveConfiguration 4, 5As the inert gas, nitrogen gas or the like can be used.
[0021]
[Action]
By bringing the nitrogen oxide absorbent having the above-described configuration 1 into contact with a high-temperature gas containing oxygen and nitrogen oxide, the nitrogen oxide in the high-temperature gas can be effectively absorbed. This is because the oxide of the transition element catalyzes and the nitrogen oxide reacts with the alkaline earth oxide or hydroxide or the oxide of the transition element and is incorporated into the product. it is conceivable that. in this case,Configuration 1If 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, the nitrogen oxides are particularly excellent in absorption capacity. You can get something. The alkaline earth element absorption capacity is Ba = Sr> Ca, and the transition element oxide catalytic action is CuO = Fe.₂ O_Three > Co₂O_Three It has been confirmed that> NiO. Moreover, although the alkaline earth element oxide or hydroxide alone has a certain absorption ability, it has been confirmed that the absorption rate is extremely slow, so that it is not practical. In addition, substances containing alkaline earth element oxides or hydroxides and transition element oxides in some form, such as the above-mentioned oxide superconductors and hydrated decomposition products thereof, Has a certain absorptive capacity, but it has been confirmed that the absorptive capacity is small when compared with those composed mainly of a mixture of an oxide or hydroxide of an alkaline earth element and an oxide of a transition element. . This is considered to be because the amount of the mixture of the oxide or hydroxide of the alkaline earth element and the oxide of the transition element contained in these oxide superconductors is smaller than the total amount. .
[0022]
Also,(3) to (5) aboveAccording to this manufacturing method, a solid nitrogen oxide absorbent can be obtained.
[0023]
further,Configuration 2, 3According to this, nitrogen oxides absorbed by the nitrogen oxide absorbent of constitution 1 can be recovered in a high concentration state. This is because the nitrogen oxide absorbent that has absorbed nitrogen oxides is brought into contact with an inert gas having a temperature higher than the temperature of the high-temperature gas at the time of absorption, so that oxides of alkaline earth elements and nitrogen oxides It is considered that this reaction product is decomposed and nitrogen oxides incorporated into this product are eliminated. Further, since the reaction temperature and space velocity in this recovery method are almost the same as those in the conventional “ammonia-added catalytic reduction method”, the method of the present invention can be achieved by simply modifying a part of the apparatus for carrying out this conventional method. Can be implemented. Moreover,Configuration 3Therefore, the recovered nitrogen oxide can be effectively used as a raw material for nitric acid production, and the nitrogen oxide absorbent from which nitrogen oxide has been eliminated can be used repeatedly.
[0024]
Also,Configuration 4, 5According to the above, it is possible to regenerate the nitrogen oxide absorbent having a deteriorated ability to absorb nitrogen oxides by absorbing carbon dioxide in the high temperature gas. Here, when the nitrogen oxide absorbent absorbs carbon dioxide, the absorption ability of nitrogen oxide deteriorates because the reaction product of an alkaline earth oxide or the like reacts with carbon dioxide ( For example, CaCO_Three ) Increases, the alkaline earth metal oxides that can react with the nitrogen oxides are relatively reduced. Accordingly, if the reaction product of the alkaline earth element oxide or the like and carbon dioxide is decomposed back to the original alkaline earth element oxide or the like, the absorption capacity can be recovered and regenerated.Configuration 4Then, by reacting nitric acid with the reaction product of alkaline earth oxides and carbon dioxide to form nitrate and carbon dioxide, carbon dioxide is desorbed, and then the nitrate is deactivated at high temperature. It is decomposed by bringing it into contact with a gas and returned to the original oxide or the like of the alkaline earth element for regeneration. Also,Configuration 5Then, the above reaction product is decomposed by bringing a mixed gas of high-concentration nitrogen oxide at 300 to 500 ° C. and air into contact with a reaction product of an alkaline earth oxide or the like and carbon dioxide, thereby The carbon is desorbed and regenerated.
[0025]
【Example】
1. Examples and comparative examples of nitrogen oxide absorbent and its production method
Example 1-1
In this example, Ba (OH)₂  It is the example which comprised the powdery nitrogen oxide absorbent with the mixed powder of powder and CuO powder.
[0026]
Ba (OH) with a particle size of about 5-20 μm₂  And 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 produce a mixed powder. Obtained.
[0027]
The nitrogen oxide absorbent thus obtained was O₂  When the NO absorption amount and the initial absorption rate were measured with a thermobalance device after contacting with a high temperature gas having a concentration of 4%, NO concentration of 2000 ppm and a temperature of 350 ° C. for 300 minutes or more, the NO absorption amount was 8.2 mmol. The initial absorption rate showed a very high value of 0.040 mmol / g · min.
[0028]
In addition, the relationship between the contact time and the NO absorption amount in this case is shown by the plot points marked with ◯ in the graph of FIG. In FIG. 1, the horizontal axis represents the contact time (unit; minutes), and the vertical axis represents the absorption amount (unit; mmol / g).
[0029]
Example 1-2
In this example, Ba (OH)₂  A powdered nitrogen oxide absorbent having the same configuration as that of the first embodiment except that the mixing ratio of the powder and the CuO powder is 1: 1.
[0030]
When this NOx absorption amount and initial absorption rate were measured by contacting the nitrogen oxide absorbent with a high temperature gas similar to Example 1-1 and having a NO concentration of 1000 ppm, the NO absorption amount was The initial absorption rate showed a high value of 0.028 mmol / g · min. From the results of Examples 1-1 and 1-2, Ba (OH) compared to CuO powder as a catalyst.₂  It can be seen that the absorption capacity can be improved by increasing the proportion of the powder to some extent.
[0031]
Example 1-3
In this example, Ba (OH)₂  Y further to powder and CuO powder₂  O₃  Add the powder and change the mixing ratio₂  O₃  Powder: Ba (OH)₂  Powder: Nitrogen oxide absorbent in the form of CuO powder = 1: 2: 3.
[0032]
When this NOx absorption amount and initial absorption rate were measured by contacting the nitrogen oxide absorbent with a high temperature gas similar to Example 1-1 and having a NO concentration of 1000 ppm, the NO absorption amount was The initial absorption rate showed a relatively high value of 0.035 mmol / g · min. However, Y₂  O₃  The absorption capacity is slightly inferior to those of Examples 1-1 and 1-2 described above in which no powder is added. From this result, Y₂  O₃  It turns out that it is better not to add flour.
[0033]
Example 1-4
In this example, Ba (OH)₂  Powder and Fe₂  O₃  This is an example in which a powdered nitrogen oxide absorbent is composed of powder mixed with powder, and Fe instead of CuO powder.₂  O₃  Except for the point using powder, the configuration was the same as that of Example 1-1.
[0034]
When this NOx absorption amount and initial absorption rate were measured by contacting this nitrogen oxide absorbent with a high temperature gas similar to Example 1-1 and having a NO concentration of 2000 ppm, the NO absorption amount was Although it was 5.8 mmol / g and the initial absorption rate was as high as 0.038 mmol / g · min, it was slightly inferior to that of Example 1-1. From this result, it is understood that CuO powder is more effective as a catalyst than FeO.₂  O₃  You can see that it is better than 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 indicated by the plot points marked with ● in the graph of FIG.
[0035]
Reference Example 1-1
thisReference exampleIs Ba (OH)₂ Powder and Co₂ O_Three This is an example in which a powdered nitrogen oxide absorbent is composed of powder mixed with powder, and Co instead of CuO powder.₂ O_Three Except for the point using powder, the configuration was the same as that of Example 1-1.
[0036]
The nitrogen oxide absorbent was brought into contact with the same high-temperature gas as in Example 1-1 in the same manner, 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 more Co₂  O₃  You can see that it is a little better than the powder.
[0037]
Reference Example 1-2
thisReference exampleIs Ba (OH)₂ This is an example in which a powdered nitrogen oxide absorbent is composed of a mixed powder of powder and NiO powder, and the structure other than that using NiO powder instead of CuO powder is the same as in Example 1-1. The configuration.
[0038]
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. As a result, the NO absorption amount was 2.5 mmol / g. The absorption rate is 0.015 mmol / g · min.1-4, Reference Example 1-1Although it is a low value compared with the above, it was found that the material itself is inexpensive, and is a value that is sufficiently practical for industrial use. From this result, the action of NiO as a catalyst is Co₂ O_Three It turns out that it is inferior to powder.
[0039]
Reference Example 1-3
thisReference exampleIs Ca (OH)₂ This is an example in which a powdered nitrogen oxide absorbent is composed of mixed powder of powder and CuO powder, and Ba (OH)₂ Ca (OH) instead of powder₂ Except for the point using powder, the configuration was the same as that of Example 1-1.
[0040]
When this NOx absorption amount and initial absorption rate were measured by contacting this nitrogen oxide absorbent with a high temperature gas similar to Example 1-1 and having a NO concentration of 2000 ppm, the NO absorption amount was 1.3 mMol / g and the initial absorption rate is 0.034 mMol / g · min, which is a lower value compared to Examples 1-1 to 1-4, but the material itself is inexpensive. Therefore, it was found that the value is sufficiently practical for industrial use. From this result, Ca (OH)₂  Ba (OH) than when using₂  It can be seen that the absorption capacity is better when using. In this case, the relationship between the contact time (horizontal axis: units; minutes) and the NO absorption amount (vertical axis: units; mmol / g) is shown by the plot points marked with Δ in the graph of FIG.
[0041]
Example 1-5
This example is an example in which a powdered nitrogen oxide absorbent is composed of a mixed powder of BaO powder and CuO powder, and Ba (OH)₂ Except for the point that BaO powder was used instead of the powder, and the mixing ratio of BaO powder and CuO powder was 3.5: 1, the same configuration as in Example 1-1 was used.
[0042]
When this NOx absorption amount and initial absorption rate were measured by contacting this nitrogen oxide absorbent with a high temperature gas similar to Example 1-1 and having a NO concentration of 2000 ppm, the NO absorption amount was It was 3.8 mmol / g, and the initial absorption rate was 0.031 mmol / g · min. In this case, the relationship between the contact time (horizontal axis: units; minutes) and the NO absorption amount (vertical axis: units; mmol / g) is indicated by the plot points marked with ▲ in the graph of FIG.
[0043]
Example 1-6
In this example, Ba (OH)₂ Except for the point that SrO powder was used instead of powder, the same configuration as in Example 1-1 was used.
[0044]
The nitrogen oxide absorbent was brought into contact with the same high temperature gas as in Example 1-1 in the same manner, and the NO absorption amount and the initial absorption rate were measured. The NO absorption amount was 8.4 mmol / g. The absorption rate was as high as 0.035 mmol / g · min, almost the same value as in Example 1-1. From this result, Ba (OH)₂  It can be seen that the powder and the SrO powder have substantially the same absorption capacity.
[0045]
Example 1-7
In this example, Ba (OH)₂ This is an example in which a solid nitrogen oxide absorbent is composed of a mixture of CuO and CuO.
[0046]
Ba (OH) with a particle size of about 5-20 μm₂  And 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 the medium was added to the mixed powder to form a paste. Next, this paste-like material was filled into a large number of through-holes having a diameter of 5 mm formed on an aluminum plate having a thickness of 5 mm, and was left to dry for several to tens of hours. Thereafter, a large number of 5 mmφ × 5 mm cylindrical molded bodies thus obtained were fired at 500 ° C. for about 3 hours in an air atmosphere to obtain a large number of solid nitrogen oxide absorbents.
[0048]
When this NOx absorption amount and initial absorption rate were measured by contacting this nitrogen oxide absorbent with a high temperature gas similar to Example 1-1 and having a NO concentration of 2000 ppm, the NO absorption amount was The initial absorption rate was a high value of 0.035 mmol / g · min.
[0049]
Example 1-8
In this example, a solid nitrogen oxide absorbent was constituted by a mixed molded body of BaO and CuO obtained by an impregnation method. Ba (NO) is applied to an aluminum oxide molded body that has been previously adjusted to a cylindrical shape of 5 mmφ × 5 mm._Three )₂ And Cu (NO_Three )₂ After impregnating the mixed aqueous solution, the same calcination was performed to obtain a similar solid nitrogen oxide absorbent.
[0050]
When this NOx absorption amount and initial absorption rate were measured by contacting this nitrogen oxide absorbent with a high temperature gas similar to Example 1-1 and having a NO concentration of 2000 ppm, 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]
Example 1-9
In this embodiment, Ba (NO_Three )₂ Powder and Cu (NO_Three )₂ Nitrate decomposition of the uniform mixture with the powder was performed 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 NOx absorption amount and initial absorption rate were measured by contacting this nitrogen oxide absorbent with a high temperature gas similar to Example 1-1 and having a NO concentration of 2000 ppm, the NO absorption amount was The initial absorption rate showed a high value of 0.044 mmol / g · min.
[0053]
Comparative Example 1
This comparative example is an yttrium-barium-copper oxide superconductor material (YBa₂Cu₃  O_{7- δ}) Powder. This oxide superconductor material powder was changed to O₂  When the NO absorption amount and the initial absorption rate were measured by contacting a high temperature gas having a concentration of 2%, 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. The initial absorption rate was 0.05 mmol / g · min, indicating a temporary absorption capacity. However, the material itself is expensive and cannot be said to be practical for industrial use. When the NO absorption was regenerated by a regeneration method described later and then contacted with a high temperature gas at 415 ° C. (composition is the same as above), the absorption measurement was performed again. As a result, the NO absorption amount was 1.2 mmol / g, and the initial absorption rate was 0.05 mmol / g · min. Further, when the regeneration treatment was performed again and the absorption was measured by contacting with the same high temperature gas as above except that the NO concentration was 4000 ppm, the NO absorption amount was 0.84 mmol / g, and the initial absorption rate. Was 0.12 mmol / g · min, and it was recognized that the absorption capacity gradually decreased with each regeneration.
[0054]
Comparative Example 2
This comparative example is an yttrium-barium-copper oxide superconductor material (YBa₂Cu₃  O_{7- δ}YBa obtained by adding water to the solution and leaving it at room temperature for 30 minutes, followed by drying at 110 ° C.₂  Cu₃  O_{7- δ}This is a hydration decomposition product. The hydrated decomposition product includes a plurality of types of compositions, and it is estimated that Ba hydroxide is also included therein. However, accurate analysis of all the compositions has not been performed yet. I have not been told. This hydrated decomposition product is converted to O₂  When the NO absorption amount and the initial absorption rate were measured by contacting with a high temperature gas having a concentration of 2%, 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 is not practical for industrial use. In addition, when what absorbed NO was regenerated by the regeneration method described later and then contacted with the same high-temperature gas as described above except that only the temperature was changed to 390 ° C., the absorption measurement was performed again. g, and the initial absorption rate was 0.045 mmol / g · min.
[0055]
Comparative Example 3
This comparative example is commercially available Ba (OH)₂  Powder alone.
[0056]
This Ba (OH)₂  O powder₂  When the NO absorption amount and the initial absorption rate were measured by contacting a high temperature gas having a concentration of 4%, 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. 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 slow, so that it was not practical.
[0057]
Comparative Example 4
This comparative example is YBa₂  Cu₃  O_7-One of the hydration products of δ, whose composition has been elucidated₂  BaCuO₅  It is. When the absorption capacity measurement similar to the said comparative example 3 was performed, it turned out that it has no absorption capacity at all.
[0058]
Comparative Example 5
This comparative example is Y₂  O₃  Powder and Ba (OH)₂  The mixed powder is uniformly mixed 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 amount was 0.37 mmol / g or less, and the initial absorption rate was 0.005 mmol / g · min. It was found to be poor.
[0059]
Comparative Example 6
This comparative example is an yttrium-barium-copper oxide superconductor material (YBa₂Cu₃  O_{7- δ})₂  O₃  The pellets were formed, dried and fired (400 ° C.) by adding the sol.
[0060]
This comparative example is₂  When the NO absorption amount and the initial absorption rate were measured by contacting with a high temperature gas having a concentration of 2%, 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. The initial absorption rate was 0.02 mmol / g · min. This comparative example was found to have poor practicality because of its extremely low absorption capacity.
[0061]
Comparative Example 7
This comparative example is Ba (OH)₂  Cr as catalyst for powder 4₂  O₃  It is a mixed powder obtained by adding powder 1 and mixing.
[0062]
When this mixed powder was subjected to nitrogen oxide absorption capacity measurement, it was found that it had no absorption capacity at all. From this result, Cr₂  O₃  It can be seen that the powder has no catalytic action.
[0063]
2. Example of nitrogen oxide recovery method
Example 2
In this example, the nitrogen oxide in the high temperature gas is absorbed using the nitrogen oxide absorbent of each of the above examples, and then the absorbed nitrogen oxide is desorbed and recovered as a high concentration nitrogen oxide. This is a nitrogen oxide recovery method. This method was performed according to the following procedure.
[0064]
Nitrogen oxide absorbent, O₂  Nitrogen oxide in the high-temperature gas was absorbed by contacting with a high-temperature gas having a concentration of 4%, NO concentration of 1000 ppm and a temperature of 350 ° C. for 300 minutes or more. Next, the nitrogen oxide absorbent that absorbed nitrogen oxide was brought into contact with 400 ° C. high-temperature nitrogen gas. As a result, it was possible to recover a gas containing high-concentration nitrogen oxides exceeding 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 can be obtained if the flow rate of nitrogen gas is reduced or the temperature is increased.
[0065]
In addition, if the gas containing high concentration nitrogen oxides (NO etc.) collect | recovered in this way is transferred to a nitric acid manufacturing system etc., it can utilize effectively as raw materials for nitric acid manufacture. That is, for example, when a system for performing the nitrogen oxide recovery method according to this embodiment is installed as a NOx removal system in combustion gas such as thermal power generation, and a nitric acid production system is coupled to this system, the removed NOx is immediately It can be effectively used as a raw material for nitric acid production. In addition, if the nitrogen oxide absorbent after desorbing the nitrogen oxide is transferred again to the nitrogen oxide absorption step, the nitrogen oxide absorbent can be repeatedly used.
[0066]
3. Examples of nitrogen oxide absorbent regeneration methods
In this example, the nitrogen oxide recovery method of Example 2 was applied to the case of recovering nitrogen oxides in a high-temperature gas containing carbon dioxide in addition to oxygen and nitrogen oxides. It is an Example of the nitrogen oxide absorbent regeneration method which reproduces | regenerates this, when an oxide absorbent absorbs a carbon dioxide and the capability to absorb nitrogen oxide deteriorates. Hereinafter, a wet method (Example 3-1) by adding nitric acid and a dry method (Example 3-2) by contact with a mixed gas of high-concentration nitrogen oxide and air 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 oxide in a high-temperature gas containing 2% of carbon dioxide five times by the method of Example 2, Nitrogen oxide absorption capacity was reduced to about 30% compared to the initial capacity.
[0068]
Nitric acid water was added to the nitrogen oxide absorbent. The amount added was approximately 0 to 20% more than the equivalent amount of carbonate produced in the nitrogen oxide. Next, after completion of the reaction due to the addition of nitric acid, it was calcined in 450 ° C. nitrogen gas 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 capacity was almost completely restored to the initial state and 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, and air was added to 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 capacity was almost completely restored to the initial state and regenerated.
[0070]
As described above, the embodiment described in detail has the following advantages.
[0071]
a. Nitrogen oxide can be absorbed and removed without consuming expensive ammonia in the application temperature range of the “ammonia addition 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 “ammonia addition selective catalytic reduction method”.
[0073]
c. The absorbent after absorption of nitrogen oxides can easily desorb and absorb high-concentration nitrogen oxides by circulating an inert gas containing no nitrogen oxide and oxygen at the same temperature as the absorption temperature or at a temperature of 50 ° C. The agent can be regenerated.
[0074]
d. The regenerated nitrogen oxide absorbent can be reused in the absorption process.
[0075]
e. The recovered high-concentration nitrogen oxide (mainly nitrogen oxide) can be used as a raw material for chemical industry such as nitric acid production.
[0076]
f. Absorbent whose absorption capacity has been reduced by absorbing carbon dioxide in the combustion gas or carbon dioxide in the air is a mixed gas of high-concentration nitrogen oxide and air recovered by wet treatment using nitric acid or by desorption. Can be easily reproduced.
[0077]
g. The nitrogen oxide absorbent of this example is very easy to prepare because it can be, for example, a mixed powder obtained by physical operation of fine powder of barium hydroxide or barium oxide and fine powder of copper oxide.
[0078]
h. If a pellet-like absorbent is required for industrial use, a clay such as aluminum oxide, titanium oxide, silicon oxide or bentonite, which is usually used for catalyst preparation, is added to the absorbent in the form of a sol or gel. Can be easily prepared.
[0079]
【The invention's effect】
【The invention's effect】
As described above in detail, the nitrogen oxide absorbent according to the present inventionAnd its regeneration method and nitrogen oxide recovery methodNitrogen oxide absorbent,A mixture of an oxide or hydroxide of an alkaline earth element and an oxide of a transition element, wherein the alkaline earth element is barium (Ba) and / or strontium (Sr), and the transition element is copper (Cu) And / or iron (Fe)A nitrogen oxide absorbent that can efficiently remove and recover nitrogen oxides in a high-temperature gas without consuming expensive ammonia, and a method for producing the same, a regeneration method thereof, and a method for recovering nitrogen oxides are obtained. It is what.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing nitrogen oxide absorption capacity of an embodiment of the present invention.

Claims (5)

  A nitrogen oxide absorbent that absorbs nitrogen oxide in a high-temperature gas containing oxygen and nitrogen oxide, and includes a mixture of an oxide or hydroxide of an alkaline earth element and an oxide of a transition element, A nitrogen oxide absorbent, wherein the alkaline earth element is barium (Ba) and / or strontium (Sr), and the transition element is copper (Cu) and / or iron (Fe). A first step of contacting a nitrogen oxide absorbent according to claim 1 with a high-temperature gas containing oxygen and nitrogen oxide at 250 to 500 ° C to absorb the nitrogen oxide in the high-temperature gas, and the nitrogen oxidation A second step of bringing the nitrogen oxide absorbent that has absorbed the substance into contact with an inert gas at 300 to 600 ° C. to desorb and recover the absorbed nitrogen oxide. The nitrogen oxide recovery method according to claim 2 , wherein the nitrogen oxide recovered in the second step is transferred to a nitric acid production system and used as a raw material for nitric acid production, and the nitrogen oxide is released from the nitrogen oxide. A method for recovering nitrogen oxides, wherein the absorbent is transferred to the first step and used as a nitrogen oxide absorbent in the first step. The nitrogen oxide absorption which regenerates the nitrogen oxide absorbent used when the nitrogen oxide in the high temperature gas containing carbon dioxide in addition to oxygen and nitrogen oxide is recovered by the nitrogen oxide recovery method according to claim 2 In this method, the nitrogen oxide and the nitrogen oxide absorbent that has absorbed carbon dioxide are reacted with nitric acid to desorb carbon dioxide, and then contacted with an inert gas at 300 to 600 ° C. A method for regenerating a nitrogen oxide absorbent, characterized by regenerating the nitrogen oxide absorbent. The nitrogen oxide absorption which regenerates the nitrogen oxide absorbent used when the nitrogen oxide in the high temperature gas containing carbon dioxide in addition to oxygen and nitrogen oxide is recovered by the nitrogen oxide recovery method according to claim 2 It is an agent regeneration method, and after making the mixed gas of 300-500 degreeC high concentration nitrogen oxide and air contact the nitrogen oxide absorber which absorbed the said nitrogen oxide and carbon dioxide, 300-600 A nitrogen oxide absorbent regeneration method, wherein the nitrogen oxide absorbent is regenerated by contacting with an inert gas at ° C to desorb carbon dioxide.

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