JPS6012907B2 - Method for regenerating nitrogen oxide purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses nitrogen oxides (for example, nitrogen oxide N◯, nitrogen dioxide N02, etc., hereinafter abbreviated as N◯x).

) Relating to a method for regenerating a purification catalyst. To explain in detail, the present invention adds ammonia to NOx-containing gas, and
The present invention relates to a method for regenerating a catalyst for catalytically converting nitrogen into nitrogen and water. Exhaust gas from boilers, chemical industry plants, iron ore furnaces, glass melting furnaces, etc. contains NOx, and as a method to remove and purify this N○x, it is passed over a catalyst together with ammonia. A widely known method is to selectively convert NOx into harmless nitrogen and water by passing it through and carrying out a catalytic reaction.

The catalyst used in this method is a carrier such as alumina, silica, silica-alumina, or titanium oxide in which metal oxides such as copper, iron, vanadium, or tungsten are kept as active ingredients, or mixed and formed. There are known catalysts.

As long as these catalysts are used for clean exhaust gas from LNG-fired boilers and the like, stable N*x purification performance over a long period of time is recognized with almost no reduction in catalytic activity. However, many of the exhaust gases targeted for N○x purification contain sulfur oxides (for example, sulfur dioxide S02, sulfur trioxide S03, etc., hereinafter abbreviated as S○x), dust, etc. It can be seen that the activity of the above catalyst tends to decrease over time. The present inventors investigated in detail the causes of the decrease in the activity of the various catalysts mentioned above, and found that metal oxides in dust, S○x in scarlet gas, and substances added to exhaust gas form catalyst poisons. It has been discovered that ammonium sulfate, acidic ammonium sulfate, etc. are produced from the ammonia produced by dust, and metal oxides in dust adhere to the catalyst and reduce the specific surface area and pore volume of the catalyst. When targeting glass melting furnace exhaust gas, sodium,
Compounds of alkali metals such as potassium and compounds of alkali metals such as magnesium and calcium act chemically on the catalyst, and S○x, ammonium sulfate, and acidic ammonium sulfate combine with carrier components and catalyst components. It has been found that compounds or complexes such as sulfates and acidic sulfates are formed, resulting in a decrease in catalytic activity.

As a method for regenerating such a catalyst whose activity has decreased, there are known methods of physically removing adhering substances and methods of removing them by washing with water.

However, it has been found that it is difficult to remove the adhering substances to a state close to that of an unused catalyst using the former method, and that the latter method is by no means a good idea. That is,
The present inventors have found that when a catalyst whose activity has been reduced as described above is washed with water, the strength of the catalyst is significantly reduced. When examining the cause, it was found that sulfur compounds accumulate in the catalyst with decreased activity, and when washed with water, these become a strongly acidic aqueous solution inside the catalyst, dissolving the catalyst components and causing them to become water-soluble. It has been found that this is because the catalyst material that has changed into a sulfur-containing compound is also washed away during the cleaning treatment with an aqueous medium. Therefore, simply applying a cleaning method using an aqueous medium in a reactivation method for a catalyst that is composed of components that dissolve in a strongly acidic aqueous solution based on sulfur compounds accumulated inside the catalyst, or components that themselves transform into water-soluble sulfur-containing compounds. cannot be said to be sufficiently effective. Therefore, the present inventors conducted research with the aim of providing a method for regenerating a catalyst with decreased activity as an alternative to the above-mentioned known method. After heat-treating the catalyst with decreased activity in a hydrogen atmosphere, The present invention, which is characterized by washing with water, an ammonia solution, or an acidic solution, has been completed.

The first effect exhibited by the method of the present invention is that by treating a catalyst whose activity has decreased in a hydrogen atmosphere, sulfur compounds accumulated in the catalyst are removed and the activity is restored.

According to the method of the present invention, the effectiveness of treating the catalyst whose activity has been reduced at a temperature of 500° C. or lower, preferably 200 to 450° C. has been recognized.

The second effect exhibited by the method of the present invention is that the water-soluble compounds generated in the catalyst carrier and the active components of the catalyst are changed into soluble or insoluble substances by the treatment under a hydrogen atmosphere, and are used in the subsequent aqueous medium. This means that it can prevent elution during cleaning operations.

The second effect is necessary because the dust components accumulated on the deteriorated catalyst, which are useless or poisonous to the catalyst, must be sufficiently removed by washing with water or the like. The third effect exhibited by the method of the present invention is that by washing the catalyst treated under a hydrogen atmosphere with an aqueous medium such as water, ammonia solution, or an acidic solution, the dust accumulated on the catalyst is removed and the catalytic activity is restored. It is a point.

The cleaning effect varies depending on the dust accumulated on the catalyst, and sufficient effects can be recognized by appropriately selecting washing with water, washing with an ammonia solution, or washing with an acidic solution. The catalyst regeneration method of the present invention is particularly applicable to catalysts that have deteriorated by being used for denitrification of exhaust gas that contains alkali metal compounds as dust components other than sulfur oxides, such as exhaust gas from competitive furnaces and glass melting furnaces. A remarkable effect was observed.

In the method of the present invention, when the treatment is carried out in a hydrogen atmosphere, it is suitable to carry out the hydrogen treatment in a gas phase, but it is also possible to carry out the hydrogen treatment in a suitable solvent.

The processing temperature is 50 to 500oo, but if it is less than 200qo, there are disadvantages such as slow reduction rate or poor reduction efficiency, and if it is high temperature above 450qo, there will be economic loss due to temperature rise, so Preferably 200
A range of ˜450oo is chosen.

When hydrogen is used in a gas phase, it is usually diluted with nitrogen, but hydrogen alone can also be used as a gas, as well as carbon monoxide,
It can also be used after being diluted with carbon dioxide gas, water vapor, etc.
The amount of hydrogen used varies depending on the state of deterioration of the catalyst. Although the effect is greater if a sufficient amount of hydrogen is used, it is not economical, and it is preferable to determine the amount of hydrogen based on the amount of sulfur accumulated in the catalyst whose activity has decreased. That is, it is preferable to use hydrogen in an amount of 0.5 to 90 times, particularly preferably 2 to 25 times, the amount of sulfur in the catalyst with reduced activity. There are no particular restrictions on the processing pressure, but
It is usually effective under normal pressure. When using a moving bed reactor, the treatment method is to place the catalyst with reduced activity extracted from the reaction system into a separately provided heating furnace into which hydrogen-containing gas can be introduced, and to raise the salt content. , a conventional reduction furnace is suitable in this case. However, it is possible to adopt industrially a method of regenerating the catalyst by supplying a hydrogen-containing gas instead of the N○x-containing gas while the reactor is still filled with the N○x purification catalyst. Coal gas, water gas, generator gas, oil cracking gas, etc., which are supplied in large quantities as raw materials for city gas, etc., can also be used as the hydrogen-containing gas in the method of the present invention. Of course, it is preferable that these gases be used after being desulfurized. Regarding the mechanism of treatment with hydrogen, it was confirmed that the sulfur content accumulated in the catalyst becomes sulfur dioxide, hydrogen sulfide, etc. and is removed from the catalyst. To regenerate a catalyst that has a large amount of highly toxic dust attached to it, such as one used for Akatsuki feeder gas, it is necessary to clean the catalyst after heat treatment in a hydrogen atmosphere. Water, an ammonia solution, or an acidic solution can be appropriately used as the cleaning liquid.

The choice of cleaning fluid depends on the catalyst active components and the type of dust on the catalyst. For example, when removing an alkali metal compound adhering to the catalyst, it is preferable to wash with an acidic solution, but sufficient washing with water or an ammonia solution can also be effective. The ammonia solution used in the present invention has a pH of 8 to 13, and an aqueous ammonia solution is usually used.

Further, the acidic solution used in the present invention has a pH of 2 to 6, and usually a dilute aqueous solution of nitric acid is used. Moreover, the cleaning liquid can also be used in combination with the above solutions. There are no particular restrictions on the temperature and pressure of the cleaning solution during cleaning, but the treatment can usually be carried out at a temperature of 10 to 80 o'clock and normal pressure.

The cleaning method of the present invention includes a method in which a catalyst with decreased activity is placed on the belt or in a container and a cleaning solution is poured onto the catalyst, or a catalyst with decreased activity is immersed in a container containing the cleaning solution. It can be crushed and treated with a static layer or under-washing treatment.

The effectiveness of cleaning can be determined by analyzing the concentration of dust metal compounds in the cleaning solution using atomic absorption spectroscopy or the like and determining the rate of decrease in the concentration.

Further, it is preferable to dry the treated catalyst after the washing treatment at a temperature of 20 mm or less. The N*x purification performance of the regenerated catalyst obtained by the above method is significantly increased compared to the catalyst whose activity has decreased, and has recovered to the same level or higher than that of the unused catalyst.

Furthermore, the crushing strength of the catalyst was hardly reduced by this regeneration treatment. The present invention will be explained in more detail below using Examples, but the present invention is not limited to these Examples.

Example 1 Using an electrostatic precipitator, ammonia (N) was added to iron ore sintering furnace exhaust gas whose dust content was adjusted to 409'N, and the mixture was supplied to a reactor for purification of N○x.

The average exhaust gas composition is NO x 180 m, S○ x 25 m
, oxygen 1 string volume %, carbon monoxide 0. insect volume %, carbon dioxide gas 8 volume %, water vapor 10 volume %, remaining nitrogen, NH3
NH3 is added so that /N○x=1.2 (molar ratio).

The catalyst packed in the reactor has a weight composition ratio of V as an oxide.
205:Ti02=10:90 (weight ratio) was extrusion molded, and this was fired in air at 400 oo for 10 hours.

The reactor is a cylindrical one supported by a wire mesh, filled with the above catalyst particles, and into which the above exhaust gas is fed at a space velocity of 800 r-
1 (STP), the gas inlet temperature is extended at a temperature of 260q0.
It was subjected to an activity test for 50 cycles.

During this period, the catalyst was fluidized with exhaust gas once a day to prevent clogging of the catalyst layer by dust. To see the changes in the catalyst over time,
The activity, physical properties of the catalyst, and compounds accumulated on the catalyst were measured, and the results shown in Table 1 were obtained.

For activity, the purification rate of N○x was measured using an N○x meter (Chemilumi type), and for analysis of the catalyst, the specific surface area was measured using BET.
Compounds accumulated on the catalyst were measured by crab light X-ray analysis. Then, about 1k9 of the catalyst with reduced activity was placed in a reduction furnace, and after replacing with nitrogen gas, nitrogen gas containing 5% by volume of hydrogen was flowed at a flow rate of 35 SO/min (STP) and treated at 40,000 for 3 hours.

Next, add the hydrogen-treated catalyst to a container containing two bottles of hot water, leave it at 6,000 ℃ for 2 hours, and drain the washing water.

After repeating this operation four times, the treated catalyst was heated to 120°C.
The field was dried for one hour. At this time, the concentrations of vanadium, titanium, potassium, etc. in the cleaning solution were measured by source absorption spectrometry, and the results shown in Table 2 were obtained. The strength of the catalyst regenerated in this way is the same as that of an unused catalyst, and the NOx
The purification performance and physical properties were also restored to almost the same state as shown in Table 1.

Table 1 Unused catalyst Used for 1,500 hours Regenerated catalyst N○x purification rate (%) 93
73 93 Specific surface area (ga/even)
35 18 3
5 Sulfur in catalyst (weight miscellaneous) 0.08
4.80 0.12 Potassium in catalyst (weight) −
1.75 0.08 Table 2 (Elemental phosphorus/light) 1st 2nd 3rd 4th Vanadium 0.033 0.039 0.047 0
．． 047 Titanium 0.007 0.007 0.0
06 0.001 potassium 4.87 1.84
0.72 0.19 Comparative Example 1 The catalyst with reduced activity shown in Example 1 was washed with water in the same manner as in Example 1 without being subjected to hydrogen treatment.

The concentration of elements dissolved in the cleaning solution was measured in the same manner as in Example 1, and the results shown in Table 3 were obtained. The water washing treatment cracked the catalyst and weakened its strength.

It can be seen that the catalyst component was released into the cleaning solution, and the method of the present invention, which involves hydrogen treatment and then washing with water, is superior. No.
3 Table (Elemental phosphorus/female) 1st 2nd 3rd 4th Vanadium 4.74 2.60 1.18
0.66 Titanium 2.32 2.18
1.82 1.18 1st 2nd 3rd 4th Potassium 4.72 2.05 0.66 0
．． 16 Example 2 As a catalyst for purification of NOx, TAJ02.
Using titanium phosphate with a composition of P205, a catalyst with a composition of V2Q: titanium phosphate = 30:70 (weight ratio) was heated at a space velocity of 700 skin r-1 (STP) and a gas inlet temperature of 280.
qo, except that the usage time was increased to 150 hours.
We obtained the results shown in the table.

Approximately 1k9 of the catalyst with reduced activity was placed in a reduction furnace, replaced with nitrogen gas, and nitrogen gas containing 2% by volume of hydrogen was flowed at a flow rate of 10 som/min (STP), and treated at 370 qo for 4 hours.

Next, wash with 2 sleeves of 0.3% nitric acid solution at 60°C for 3 times.
I went around.

The concentration of elements dissolved in the cleaning solution was measured in the same manner as in Example 1, and the results shown in Table 5 were obtained. Both the strength and activity of the regenerated catalyst had been restored to almost the same state as the catalyst using clay.

Table 4 Unused catalyst Used for 1,500 hours
Regenerated catalyst NOX purification rate (high) 92
82 92 Specific surface area (material/
Evening) 16 11
16 Sulfur in catalyst (by weight) 0
．． 02 3.76 0
．． 08 Potassium in catalyst (weight*)
1.40 0.04th
5 Table (Evening of the Elements/cZ) 1st 2nd 3rd
Vanadium 0.13 0.11
0.14 Titanium 0.014 0.005
0.002 Potassium 3-24
2.19 1.17 Comparative Example 2 The catalyst with reduced activity shown in Example 2 was washed with an aqueous nitric acid solution in the same manner as in Example 2 without being subjected to hydrogen treatment.

The concentration of elements dissolved in the cleaning solution was measured in the same manner as in Example 1, and the results shown in Table 6 were obtained.

The catalyst cracked and its strength weakened due to treatment with nitric acid aqueous solution.

The catalyst component was eluted into the cleaning solution, indicating that the method of the present invention, which involves hydrogen treatment and then cleaning with a nitric acid aqueous solution, is superior. Table 6 (Element phosphorus/female) 1st 2nd 3rd Vanadium 7.10 5.79
3.81 Titanium 0.85 0.
75 0.34 Potassium 2.75
1.88 1.10 ☆Example As a catalyst for 3N○x purification, y-alumina morsel was treated with titanium tetrachloride, and y
A titanium-treated y-alumina carrier with -N203:Ti02=70:20 (weight ratio) was used, and this carrier was immersed in an aqueous ammonium vanadate solution, and the rest was carried out in the same manner as in Example 1. =10:20
:70 (weight ratio).

This catalyst was subjected to the N○x purification reaction in the same manner as in Example 1 except that the space velocity was 500 dish r-1 (STP) and the total usage time was 150 field hours.The results are shown in Table 7. I got it.

Hydrogen treatment was carried out through the catalyst with reduced activity by flowing nitrogen gas containing 5% by volume of hydrogen at 65 SO/min (STP) for 4 hours at a temperature of 350 qo.

Next, washing treatment was performed three times at 25° C. with 2.3% ammonia aqueous solution.

The concentration of elements dissolved in the cleaning solution was measured in the same manner as in Example 1, and the results shown in Table 8 were obtained. The regenerated catalyst had recovered to almost the same strength and activity as the unused catalyst.

Table 7 Unused catalyst Used for 1,500 hours
Regenerated catalyst NOX purification rate (omitted) 93
66 90 Specific surface area (de/y) 78 42
75 Sulfur in catalyst (wt%) 0
．． 01 7.84
0.83 Potassium in catalyst (by weight)
0.78 0.
03 Table 8 (Elements/Metals) 1st 2nd 3rd Vanadium 0.084 0.103
0.102 Titanium 0.008 0.00
5 0.001 potassium 1.72 1.
14 0.69 Comparative Example 3 The catalyst with reduced activity shown in Example 3 was treated with an ammonia aqueous solution in exactly the same manner as in Example 3 without being subjected to hydrogen treatment, and the results shown in Table 9 were obtained.

As a result of the water washing treatment, the strength of the catalyst was similar to that of Comparative Example 1, and the cracking strength of the catalyst was weakened. Table 9 (Evening of the Elements/Iso) 1st 2nd 3rd Vanadium 3.46 1.80
0.94 Titanium 1.36 1.29
1.11 Potassium 1.58 1.2
4 0.56 Example 4N○x purification catalyst V
205:Ti02:Si02i15:72:13 N
○x It was subjected to a purification reaction, and the results shown in Table 10 were obtained.

The catalyst with reduced activity was subjected to hydrogen treatment by flowing coal gas containing about 50% hydrogen at a rate of 4 1/min (STP) for 3 hours at a temperature of 400°C.

The composition of the coal gas used was: Day 25 group volume%, CH43 volume%, C07 volume%, N25 volume%, C2 ratio 2 volume%.
, C2 day was 61% by volume, and C022% by volume. then 0
．． Washing treatment* was performed three times at 60°C using two 3% nitric acid aqueous solutions.

The concentration of elements dissolved in the cleaning solution was measured in the same manner as in Example 1, and the results shown in Table 11 were obtained. The regenerated catalyst is
Both the strength and activity of the catalyst had recovered to almost the same state as the unused catalyst.

Table 10 Unused catalyst Used for 1,500 hours
Regenerated catalyst NOx purification rate (omitted) 94
77 95 specific surface area (
evening) 95
46 95 Sulfur in catalyst (heavy)
0.07 4.42
0.08 Potassium in catalyst (weight)
−1.73
0.05 Table 11 (Elements/Female) 1st
2nd 3rd Vanadium 0.051 0.047 0.
058 Titanium 0.008 0.004
0.001 potassium 4.93 2.0
2 1-35. Example 5 Using titanium oxide with a high surface area as a catalyst for N○x purification, V2Q: Ti0
A catalyst having a composition of 2=15:85 (weight ratio) was subjected to an activity test and a regeneration treatment in the same manner as in Example 1.

The change over time and the concentration of elements dissolved in the cleaning solution were measured in the same manner as in Example 1, and the results shown in Tables 12 and 13 were obtained.

Table 12 Unused catalyst Used for 1,500 hours Regenerated catalyst N
○x Purification rate (grandchild) 94
78 94 Specific surface area (de/even)
110 51 11
0 Sulfur in catalyst (weight association) 0.13
5.25 0.21
Potassium in catalyst (weight*)
1.78 0.06th 13th
Table (Element Shun/Light) 1st 2nd 3rd 4th Vanadium 0.038 0.059 0.070
0.072 Titanium 0,007 0.007 0.
005 0,001 Chirikurium 5.19 2.02
0.76 0.22 Comparative Example 4 Approximately 1k9 of the catalyst with reduced activity shown in Example 1 was placed in a reduction furnace and subjected to hydrogen treatment in exactly the same manner as in Example 1, and then measured without water washing treatment. Results The results shown in Table 14 were obtained.

Table 14: Unused catalyst Used for 1,500 hours Hydrogen treatment catalyst N○x purification rate (%) 93
73 78 Specific surface area (Mi/Even)
35 18
31 Sulfur in catalyst (weight) 0.0
8 4.80 0.1
3 Potassium in catalyst (weight scale)
1.75 1.77 Example 6Mo
N○x with a composition of o3:Ti02=10:90 (weight ratio)
The purification catalyst was subjected to the NOx purification reaction in the same manner as in Example 1, except that the space velocity was 700 plate r-1 (STP), the gas inlet temperature was 280 pm, and the usage time was 1500 hours. I got the results showing this.

The regeneration treatment was carried out in the same manner as in Example 1, except that the catalyst whose activity had decreased was washed three times with water, and the results shown in Table 16 were obtained. Table 15 Unused catalyst Used for 1,500 hours Hydrogen treatment catalyst N○x purification rate (male) 88
77 87 specific surface area (kumi/evening)
45 35
42 Sulfur in catalyst (wt%)
0.03 4.50
0.10 Potassium in catalyst (weight density)
1.60 0.07 16th
Table (Elements/Metals) 1st 2nd 3rd Molybdenum 0.051 0.044 0.0
52 Titanium 0.007 0.006
0.003 potassium 5.33 1.30
0.30 Note that when the catalyst was washed with water after being used for 150 feeding hours without being subjected to hydrogen treatment, the catalyst cracked significantly and could no longer be used again.

Claims (1)

[Claims] 1. When regenerating a catalyst containing titanium and further containing vanadium or molybdenum for reducing nitrogen oxides in exhaust gas containing sulfur compounds and alkali metal compounds with ammonia and converting them into nitrogen and water, A method for regenerating a nitrogen oxide purifying catalyst, which comprises heat-treating a degraded catalyst in a hydrogen-containing gas atmosphere and then washing it with an aqueous medium.