JP2012245480A - Reproduction method for used denitration catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reproduction method easy to wash out impurities and unnecessary to re-activate active ingredients, in reproducing the catalyst to which aluminum sulfate is added as an active improver.SOLUTION: In a reproduction method for used denitration catalysts which contain titanium oxide, oxides of vanadium, oxides of tungsten or molybdenum, and aluminum sulfate as main ingredients, the reproduction method for used denitration catalysts is characterized by impregnating the used denitration catalyst with water in advance, heat-treating it at ≥50°C and ≤100°C to hydrolyse the aluminum sulfate in the catalyst, and then washing the catalyst with water.

Description

  The present invention relates to a method for regenerating a used denitration catalyst mainly composed of titanium oxide, and more particularly to a method for regenerating a used denitration catalyst that can regenerate a used catalyst at a lower cost by adding aluminum sulfate. .

Nitrogen oxides (NOx) in smoke emitted from power plants, various factories, automobiles, etc. are the causative substances of photochemical smog and acid rain. As an effective removal method, ammonia (NH ₃ ) is reduced. Selective catalytic reduction denitration using a catalyst as a catalyst is widely used mainly in coal-fired power plants. In particular, in coal-fired boiler denitration, various metals contained in coal, such as alkali metals such as Na and K, alkaline earth metals such as Ca and Sr, Fe and Cr, transitions from Group VI to Group VII Metal salts such as metals and oxides, oxides of Group VB elements such as phosphoric acid, arsenous acid, and arsenic acid adhere to the denitration catalyst and reduce its performance.

  In contrast, sulfuric acid, aluminum sulfate, manganese sulfate, and other sulfates are added to the catalyst, and the sulfate radicals are adsorbed on the titanium oxide surface. Catalysts aimed at suppressing adsorption of poison components are known (Patent Documents 1 and 2). Among them, a catalyst containing aluminum sulfate as an active component (Patent Document 2) is an excellent catalyst having improved durability by fixing alkali and alkaline earth metal ions as sulfates in the catalyst and detoxifying them.

  On the other hand, the consciousness that the manufacturer is responsible for the effective use of resources has become established, and it is the responsibility of the catalyst manufacturer to have a technique for regenerating used denitration catalysts or recovering valuable materials. For this reason, research has been advanced on various regeneration methods of denitration catalysts and recovery of valuable materials, and many inventions have been made. However, the cost of regeneration treatment or waste liquid treatment is higher than expected, and there are very few methods that are economically feasible. Many of the methods currently in practical use are a combination of chemical solution washing and additional treatment of active ingredients. .

JP 55-145532 A Japanese Unexamined Patent Publication No. 2000-24520

The above-described conventional reproduction technique has the following problems to be solved.
(1) In order to completely remove poisons such as alkalis, it is necessary to wash the spent catalyst under harsh conditions such as treatment with a strong acid with a high concentration, and the active ingredients are washed out accordingly, so after regeneration However, there is a problem that an expensive active ingredient is discarded as a cleaning waste liquid as well as a process for re-loading the lacking active ingredient.
(2) When the used catalyst is washed under mild conditions in order to minimize the amount of the active ingredient to be washed out, the removal of impurities and the removal of poisons filling the pores become insufficient. Although the amount of recharging of the catalyst decreases, sufficient activity recovery of the catalyst cannot be expected.

  The problem to be solved by the present invention is to provide a regeneration method that facilitates washing out impurities and does not require reactivation of active ingredients when regenerating a catalyst to which aluminum sulfate is added as an activity improver.

The above-mentioned subject is achieved by the following method.
In the method for regenerating a used denitration catalyst mainly composed of titanium oxide, oxide of vanadium, oxide of tungsten or molybdenum, and aluminum sulfate, the used denitration catalyst is impregnated with water in advance, and then 50 ° C. or more and 100 This is achieved by hydrolyzing the aluminum sulfate in the catalyst by heat treatment at a temperature below 0 ° C. and then washing the catalyst with water.

  According to the present invention, it is possible to regenerate a catalyst that has deteriorated in an actual machine with the same performance as the initial stage with a small number of man-hours, and to increase the number of times the catalyst is repeatedly used. Further, according to the present invention, since the outflow of useful active components in the catalyst can be suppressed, expensive resources are not wasted.

Explanatory drawing of the flow sheet of the regeneration method of the used denitration catalyst of this invention.

[Action]
The principle of the present invention will be described below.
In a catalyst using aluminum sulfate as an activity improver, since aluminum sulfate is soluble, it elutes during the washing operation as it is, and it is necessary to add the reduced amount by impregnation or the like.

  Therefore, the present inventors paid attention to the fact that when aluminum sulfate is heated to 50 ° C. or higher, it gradually hydrolyzes according to Equation 1, and skillfully utilizes this to add water to the used denitration catalyst containing aluminum sulfate. After the impregnation, it was found that the spent denitration catalyst can be easily regenerated by hydrolyzing aluminum sulfate by heating to 50 ° C. or higher and then washing with water, and the present invention has been achieved.

Al ₂ (SO ₄ ) ₃ + 3H ₂ O → Al (OH) ₃ + 3H + + SO ₄ ^2- (1)
That is, by impregnating a used catalyst with water in advance and further heating the aluminum sulfate to a hydrolysis temperature (50 ° C.) or higher and 100 ° C. or lower to promote the hydrolysis of aluminum sulfate, the sulfuric acid is eluted as ions. However, aluminum can be insolubilized in the catalyst as aluminum hydroxide, while elution of alkali is promoted by hydrogen ions generated by hydrolysis.

Furthermore, in this operation, the sulfate radicals are eluted in the cleaning solution, so that the sulfate radicals in the catalyst are reduced. However, since the sulfate radicals are exposed to the exhaust gas, SO _{3 in} the exhaust gas is supplied into the catalyst. As a result, the aluminum remaining in the catalyst by hydrolysis of aluminum sulfate becomes a sulfate radical retaining material, so that only the sulfate radical necessary as an activity improving material can be retained in the catalyst, and the catalyst has an activity enhancement effect again. be able to. Therefore, it is not necessary to re-impregnate aluminum sulfate for regeneration, and furthermore, the elution of active ingredients is suppressed at the hydrogen ion concentration produced by hydrolysis of aluminum sulfate, so that active ingredients such as V and Mo are re-supported. Therefore, the spent catalyst can be regenerated by simple operation.

  The method for regenerating a used denitration catalyst of the present invention will be specifically described with reference to the flow sheet of FIG. In this method, water is impregnated with a spent catalyst 1 comprising a composition containing titanium oxide, an oxide of V, an oxide of W or Mo, and aluminum sulfate, and a liquid draining step of draining water after impregnation. 3. It consists of a holding step 4, a washing step 5, a draining step 6, and a drying step 7 for holding the catalyst after draining at 50 ° C. or more and 100 ° C. or less for a certain time. The water impregnation step 2 may be a method of immersing a used catalyst in a tank filled with water, leaving it for about several minutes to 30 minutes, then pulling it up and draining it, or spraying the catalyst with water. Further, when the water absorption rate of the catalyst is measured in step 2 and only water corresponding thereto is impregnated, the subsequent liquid draining step 3 can be omitted. The holding time in the holding step 4 is not particularly limited, but is 30 minutes or longer, preferably 1 hour or longer. If the holding time is too short, hydrolysis of aluminum sulfate in the catalyst becomes insufficient, and the object of the present invention may not be achieved. In addition, when the environmental humidity is low, moisture evaporates from the catalyst, so that a high result (80 degrees or higher) in the holding process gives a good result.

Hereinafter, the present invention will be described in detail using specific examples.
[Catalyst Preparation Example 1]
Titanium oxide (made by Ishihara Sangyo Co., Ltd., specific surface area 100 m ² / g) 1200 kg, molybdenum trioxide 21.6 kg, ammonium metavanadate 35.1 kg, aluminum sulfate 13-14 hydrate (Al ₂ (SO4) ₃ containing 56-59% ) 89.9 kg, silica sol (manufactured by Nissan Chemical Industries, trade name OS sol, containing 20 wt% as SiO ₂ ) 129.7 kg, and water are mixed in a kneader for 60 minutes, then silica alumina ceramic fiber (manufactured by NICHIAS) While gradually adding kg, the mixture was kneaded for 30 minutes to obtain a catalyst paste having a moisture content of 27%.

The obtained paste is placed on a 0.7 mm thick base material obtained by metallizing a SUS430 steel plate with a thickness of 0.2 mm and sandwiched between two sheets of plain paper for PPC. The catalyst was applied through a pressure roller so as to fill the mesh of the metal lath substrate, dried, and calcined at 450 ° C. for 2 hours to obtain an initial catalyst.
The composition of this catalyst is Ti / Mo / V = 100/1/2 in atomic ratio, and the amount of aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) added is 4 wt% with respect to the titanium oxide weight.
[Catalyst Preparation Example 2]
An initial catalyst was obtained in the same manner except that the molybdenum trioxide of Catalyst Preparation Example 1 was changed to equimolar ammonium tungstate. The composition of this catalyst is Ti / W / V = 100/1/2 in atomic ratio, and the amount of aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) added is 4 wt% with respect to the titanium oxide weight.

[Comparative Catalyst Preparation Example 1]
A catalyst was prepared in the same manner except that the aluminum sulfate of Catalyst Preparation Example 1 was not added.
[Deterioration test]
The catalysts of Catalyst Preparation Examples 1 and 2 and Comparative Catalyst Preparation Example 1 (assumed as initial catalyst) were cut into 100 mm squares, impregnated with potassium sulfate aqueous solution so as to be 0.2% as K ₂ O, dried, and then at 400 ° C. Firing was performed for 2 hours to obtain a deteriorated catalyst.

[Example 1]
As a regeneration test, 100 mm square −1 sheet of the catalyst preparation example 1 after the deterioration test was put in a petri dish containing 40 ml of pure water, and after a few minutes, the catalyst was taken out and drained. The obtained catalyst was kept for 1 hour in a sealed container heated to 50 ° C. Thereafter, the catalyst taken out from the container was placed in a petri dish containing 100 ml of water and held for 0.5 to 2 hours with occasional shaking. After draining, the catalyst was dried at 150 ° C. and then at 350 ° C.
[Example 2]
A regeneration test was conducted in the same manner as in Example 1 except that the catalyst was changed to Catalyst Preparation Example 2.

[Comparative Example 1]
As a comparative regeneration test, the 100 mm square of the catalyst after the deterioration test of Catalyst Preparation Example 1 was placed in a petri dish containing 100 ml of 1N oxalic acid and held for 0.5 to 2 hours with occasional shaking, and after draining 150 C. followed by drying at 350.degree.
[Comparative Example 2]
A regeneration test was conducted in the same manner as in Example 1 except that the deterioration catalyst in Comparative Catalyst Preparation Example 1 was used as the deterioration catalyst.
[Test Example 1]
The amount of V and K in the catalyst after Examples 1 and 2 and Comparative Examples 1 and 2 and the amounts of V and K in the catalyst before and after each deterioration test were measured using a fluorescent X-ray apparatus, and the residual ratio with respect to the initial stage Calculated as The results are shown in Table 1.

In Examples 1 and 2, the amount of K ₂ O after the regeneration test is reduced, but V remains. It can be seen that the amount of V remains in the catalyst while K of the catalyst poison is eluted in the regeneration method of this example. On the other hand, in Comparative Example 1 washed with oxalic acid, the elution of K is the same as in Examples 1 and 2, but it can be seen that V is eluted simultaneously with K. Further, in Comparative Example 2 in which the same regeneration method as that of Example 1 was carried out using a catalyst containing no aluminum sulfate, no K elution was observed. From this, it is clear that the method of the present invention is an excellent method for promoting K elution and suppressing V elution in a catalyst containing aluminum sulfate.
[Test Example 2]
The catalyst after regeneration treatment in Examples 1 and 2 and Comparative Examples 1 and 2 and the catalyst before and after each deterioration test were each cut to 100 × 20 mm and filled into a reaction tube in a flow system. The denitration rate was measured. The results are shown in Table 3.

  It can be seen that the catalyst subjected to the regeneration test of the example has a denitration rate substantially equal to that before the deterioration test. On the other hand, the catalyst of the comparative example has lower denitration performance than before the deterioration test. From this, it can be seen that the catalyst regeneration method of the present invention is highly effective.

1 Used catalyst 2 Water impregnation process 3 Liquid draining process 4 Holding process (50-100 ° C)
5 Washing process 6 Liquid draining process 7 Drying process

Claims (1)

In the method for regenerating a used denitration catalyst mainly composed of titanium oxide, oxide of vanadium, oxide of tungsten or molybdenum, and aluminum sulfate, the used denitration catalyst is impregnated with water in advance, and then 50 ° C. or more and 100 A method for regenerating a spent denitration catalyst, wherein the catalyst is washed with water after hydrolysis of aluminum sulfate in the catalyst by heat treatment at a temperature not higher than ° C.

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