JP2012210599A - Regeneration method of used denitration catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To promote the regeneration use of a used denitration catalyst in which the transportation of a washing liquid, the waste liquid treatment after the use, and the handling of the washing liquid are easy, the decrease of the mechanical strength by the elution and washing of an active constituent is not caused, and a catalyst poison component that adsorbs to the used catalyst is efficiently removed by a few treatment steps.SOLUTION: The regeneration method of a used denitration catalyst includes: a washing step in which a used denitration catalyst including titanium oxide (TiO) is immersed in a washing liquid, and a catalyst poison component in the catalyst is removed; or a step in which the used denitration catalyst after the washing step is impregnated into a solution including at least one of a catalytically active component compound chosen from vanadium (V), molybdenum (Mo), and tungsten (W), and the regeneration method of a used denitration catalyst uses an aqueous solution of aluminum sulfate as the washing liquid.

Description

  The present invention relates to a method for regenerating a spent denitration catalyst containing titanium oxide as a main component, and in particular, in cleaning with a chemical solution, phosphorus, alkali metal, alkaline earth accumulated in the catalyst without eluting active components in the catalyst. The present invention relates to the above regeneration method capable of efficiently removing only catalyst poison components such as metals.

  A so-called flue gas denitration device that uses ammonia or urea as a reducing agent and purifies nitrogen oxides in exhaust gas with a titanium oxide catalyst is widely used around the world, mainly in the treatment of boiler exhaust gas. More than 30 years have passed since the development of the titanium oxide-based catalyst used in Japan, and the regeneration of the used catalyst tends to gradually increase.

  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 on various regeneration methods of spent catalysts and recovery of valuable materials has been advanced, and many inventions have been made (for example, Patent Documents 1 to 3). However, the actual situation is that there are very few methods that are economically feasible because the cost of regeneration treatment or waste liquid treatment is higher than expected.

  Many of the methods that are currently in practical use are methods that combine chemical cleaning with mineral acids and organic acids and additional treatment of active ingredients, and enormous costs are required for transporting these acid solutions and processing waste liquids. The catalyst regeneration process is limited to the minimum necessary.

JP 55-145532 A Japanese Unexamined Patent Publication No. 2000-24520 JP 2004-267897 A

The above catalyst regeneration method is an economical method with relatively few operation steps, but has the following major drawbacks. That is, TiO _{2 as} a catalyst component is converted into metal ions of various metals (alkali metals such as Na and K, alkaline earth metals such as Ca and Sr, Group VI to Group VII transition metals such as Fe and Cr). In addition, the oxoacid ions of Group VB elements such as phosphoric acid, arsenous acid, and arsenic acid are strongly adsorbed, and a very large amount of acid or chemical solution is required for their removal. For this reason, enormous costs are incurred for transportation of these cleaning solutions and waste liquid treatment after use, and handling of these strong acid solutions requires great care.

In addition, these ions are negligibly removed to the liquid phase by a single acid wash. For this reason, when it is attempted to increase the removal rate, it is necessary to repeatedly wash in a strongly acidic solution. However, the following adverse effects are caused and it is difficult to achieve economically. Therefore, a spent catalyst having a large amount of the above components can only be put up with a low performance recovery rate or give up the regeneration treatment.
(1) Since active components such as vanadium, tungsten, and molybdenum in the catalyst are eluted every time the cleaning is repeated, a large amount of active components are required in the activation treatment step after the cleaning.
(2) Since binder components such as silica and alumina are also eluted, a decrease in the mechanical strength of the catalyst is inevitable, and an additional step of adding a binder is necessary.

  The problem to be solved by the present invention is to eliminate the above-mentioned problems of the prior art, facilitate the transport of the cleaning liquid, the waste liquid treatment after use, the handling of the cleaning liquid, and the mechanical strength due to the elution and cleaning of the active ingredients. In other words, the catalyst poison component adsorbed on the used catalyst is efficiently removed with a small number of processing steps, and the recycling of the used denitration catalyst is promoted.

In order to achieve the above object, the invention claimed in the present application is as follows.
(1) A cleaning step in which a used denitration catalyst containing titanium oxide (TiO ₂ ) is immersed in a cleaning solution to remove catalyst poison components in the catalyst, or vanadium (V), molybdenum (Mo) and A method for regenerating a spent denitration catalyst comprising a step of impregnating a solution containing one or more catalytically active component compounds selected from tungsten (W), wherein the cleaning liquid is an aqueous solution of aluminum sulfate. A method for regenerating spent denitration catalyst.
(2) The method for regenerating a used denitration catalyst according to (1), wherein the concentration of aluminum sulfate in the cleaning liquid exceeds 0 as Al ₂ (SO ₄ ) ₃ and is 5 wt%.

  According to the present invention, it is possible to easily and inexpensively remove only the catalyst poison component, which has been difficult with the prior art. As a result, the regeneration market of the denitration catalyst is activated, which can greatly contribute to resource recycling.

[Principle / Action]
The conventional catalyst regeneration method of cleaning spent denitration catalyst with mineral acid or organic acid and removing catalyst poison components such as P, K, and arsenic accumulated in the catalyst is This is done by increasing the acidity or repeatedly washing. However, if the catalyst is treated under such conditions, elution of active components contributing to the denitration reaction such as tungsten (W), molybdenum (Mo), and vanadium (V), which are active components in the catalyst, is promoted. In addition, recovery of denitration performance cannot be expected only by washing treatment, and an activation treatment step for adding an active ingredient is necessary. In addition, alumina (Al ₂ O ₃ ) and silica (SiO ₂ ), which act as a binder between titania (TiO ₂ ) particles, which are the main components of the catalyst, are also eluted, reducing the mechanical strength of the catalyst, In some cases, not only activation processing but also processing for imparting strength is required. Thus, with the conventional catalyst regeneration technology, it is difficult to remove only the catalyst poison component while retaining the active component and the binder in the catalyst.

In view of the above-mentioned problems of the prior art, the inventors of the present application can efficiently remove the catalytic poison component adsorbed on TiO ₂ with a small number of processing steps without causing a decrease in mechanical strength due to elution and washing of the active component. As a result, it was found that by washing a used denitration catalyst in an aqueous solution of aluminum sulfate for a certain period of time, only the catalyst poison component in the catalyst can be efficiently removed.

In the method of the present invention, it is desirable that the catalyst is washed with an aqueous aluminum sulfate solution containing Al ₂ (SO ₄ ) ₃ of more than 0 and not more than 5 wt%, and in particular, the pH of the washing solution is preferably about 2 to 3. This PH is slightly higher than the PH of the cleaning liquid used in the conventional cleaning process. With such a PH, only the catalyst poison component can be removed without eluting the active component in the catalyst. In addition, since Al ions are present in the cleaning liquid, the elution of Al in the catalyst is suppressed by the coexisting ion effect, and at the same time, Al ions in the cleaning liquid are adsorbed in the catalyst pores, thereby suppressing a decrease in catalyst strength Has an effect. That is, it is possible to simultaneously remove the catalyst poison component and reinforce the strength of the catalyst by a single washing process.

Further, the sulfate ions in the cleaning solution are adsorbed on TiO ₂ in the catalyst, thereby activating the adsorption point of ammonia contributing to the denitration reaction. Normally, when a denitration catalyst is used in an exhaust gas at 350 to 400 ° C., excess sulfate radicals contained in the catalyst are easily detached from TiO ₂ by heat, but the catalyst treated by the method of the present invention. Since Al ions are supported in the catalyst, the Al ions fix the sulfate radicals on TiO ₂ and exhibit the effect of suppressing desorption due to heat. As a result, the degree of recovery of the denitration performance of the catalyst can be further increased.

Hereinafter, a specific example is shown and the effect of this invention is demonstrated in detail.
[Example 1]
As a coal exhaust gas denitration catalyst, a SUS430 metal lath substrate coated with a denitration catalyst component (Ti / W / V atomic ratio = 93/5/2) mainly composed of oxides of titanium, tungsten and vanadium is used. After 10,000 hours of use, it was cut into 100 mm squares and used as a catalyst to be treated.
On the other hand, 5 g of aluminum sulfate (manufactured by Kishida Chemical Co.) as Al ₂ (SO ₄ ) ₃ was dissolved in 95 g of pure water to prepare a 5 wt% aluminum sulfate aqueous solution.
This aqueous solution was transferred to a petri dish, and after adding one 100 mm square of catalyst to be treated, the solution was kept at 60 ° C. for 30 minutes while shaking the solution. Thereafter, the catalyst was taken out and thoroughly drained, and then dried at 150 ° C. for 1 hour and further at 350 ° C. for 1 hour.

[Example 2]
The catalyst was treated in the same manner as in Example 1 except that the concentration of the aluminum sulfate aqueous solution was changed to 2 wt%.
[Comparative Example 1]
The catalyst was treated in the same manner as in Example 1 except that the concentration of the aluminum sulfate aqueous solution was changed to 10 wt%.
[Comparative Example 2]
The catalyst was treated in the same manner as in Example 1 except that the aluminum sulfate aqueous solution in Example 1 was changed to a 1N sulfuric acid solution.

[Comparative Example 3]
The catalyst was treated in the same manner as in Example 1 except that the aluminum sulfate aqueous solution in Example 1 was changed to a 1N oxalic acid solution.
[Comparative Example 4]
In Example 1, the catalyst was similarly treated under the solution temperature condition of 20 ° C. without heating the aqueous aluminum sulfate solution.
[Examples 3 and 4]
In 180 ml of pure water, 5 g of ammonium metavanadate (NH ₄ VO ₃ ) and 5 g of molybdenum trioxide (MoO ₃ ) were dissolved to prepare a yellow-brown transparent Mo-V solution. This cleaning liquid is an aqueous solution of a complex oxoacid salt of Mo and V, which mainly contains a compound represented by the formula (NH ₄ ) ₃ Mo ₂ V ₃ O ₁₅ .

The catalyst treated in Examples 1 and 2 was immersed in this cleaning solution for 30 seconds, impregnated with Mo and V components, and the catalyst was removed from the solution. After draining, the catalyst was dried at 120 ° C for 1 hour and further dried at 350 ° C. did.
For the regenerated catalyst of Examples 1 to 4 and Comparative Examples 1 to 3, the contents of phosphorus (P) and potassium (K) as catalyst poison components in the catalyst component and vanadium (V) as the active component are fluorescent. Quantified by X-ray analysis. Further, as an index of the mechanical strength of the catalyst, the content of alumina (Al ₂ O ₃ ) in the catalyst was similarly quantified.

Separately from this, the denitration rate of the catalyst was measured under the conditions shown in Table 1.
The obtained results are summarized in Table 2. First, looking at the results of Comparative Example 2 cited as an example of the conventional method, it can be seen that 70 to 80% of P and K in the catalyst have been removed, and the denitration rate has also recovered. However, the Al ₂ O ₃ amount in the catalyst is reduced to about 10% and the V amount is reduced to about half. For this reason, due to a decrease in the binder effect of Al ₂ O ₃ and a lack of the absolute amount of V active components, there is a high possibility that wear due to dust will occur or the catalyst deterioration rate will increase when used again in exhaust gas. . In addition, when the activation process is performed after the cleaning process, it is necessary to carry a large amount of V, which is not economical.

In contrast, in the present invention, as shown in Examples 1 and 2, the decrease in V in the catalyst is small, but only the catalyst poison components such as P and K are decreased, and the denitration rate is greatly recovered. I understand. Furthermore, the amount of Al ₂ O ₃ in the catalyst is sufficiently secured. Therefore, if this method is used, it is possible to regenerate the spent catalyst by an easy operation of only the washing treatment without reducing the mechanical strength. Furthermore, the cleaning liquid used in the present invention can be easily transported since a solid powder of aluminum sulfate can be dissolved in water on site in comparison with a mineral acid or an organic acid that has been conventionally subjected to regeneration treatment. Moreover, if the used aluminum sulfate waste liquid is neutralized, phosphorus, potassium, arsenic, etc. eluted in the cleaning liquid can be precipitated and removed together with aluminum, and can be discarded after removing harmful components in the waste liquid. it can. In addition, even when the activation treatment is performed after the cleaning treatment to improve the denitration performance, the denitration performance can be improved with a small amount of the active component, so that it can be said to be an excellent catalyst regeneration method.

Claims (2)

A cleaning step of immersing a used denitration catalyst containing titanium oxide (TiO ₂ ) in a cleaning solution to remove catalyst poison components in the catalyst, or vanadium (V), molybdenum (Mo) and tungsten (W after the cleaning step) A method for regenerating a spent denitration catalyst comprising a step of impregnating a solution containing at least one catalytically active component compound selected from the group consisting of an aqueous solution of aluminum sulfate as the cleaning liquid How to play. The method for regenerating a spent denitration catalyst according to claim 1, wherein the concentration of aluminum sulfate in the cleaning liquid is more than 0 and 5 wt% as Al ₂ (SO ₄ ) ₃ .