JPH0468975B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for regenerating a denitrification catalyst, and particularly to a method for regenerating a used ammonia catalytic reduction denitrification catalyst without requiring extensive chemical treatment. (Prior Art) The ammonia (NH ₃ ) catalytic reduction denitrification method is widely used in large-capacity flue gas denitrification equipment such as boilers for thermal power generation because the equipment structure and operation are simple. These devices usually use several tens to ^hundreds of cubic meters of catalyst, and it is expected that the amount of spent catalyst that can no longer be used due to a decrease in catalytic activity will be enormous. For this reason, it has become an important issue both socially and economically to regenerate used catalysts through various treatments or recover valuables. Various methods for regenerating denitrification catalysts have been studied in the past, and these methods can be broadly classified into the following three types. (1) A method of rejuvenating the activity by washing with water, acidic solution, etc. to remove catalyst poisons (2) A method of removing acidic ammonium sulfate, which is the cause of decreased activity, by heating (3) Vanadium V Method of adding active ingredients such as compounds (problems to be solved by the invention) Among these, method (1) includes adding sodium (Na),
Although it is effective against poisoning by alkali metals such as potassium (K), it cannot restore the activity reduced by sintering due to heat. Furthermore, method (2) is ineffective against poisoning and sintering by Na and K. Furthermore, in (3), although the recovery of activity is remarkable, on the other hand, the oxidation activity of SO ₂ increases, which poses a big problem in practical use. As described above, each method has its advantages and disadvantages, and there are problems in adopting it as a general regeneration method for denitration catalysts whose activity is reduced due to a combination of various causes. The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide a method for regenerating ammonia catalytic reduction denitrification catalysts containing titanium, by which catalysts deteriorated due to any cause can be easily regenerated through simple treatment steps. Our goal is to provide the following. (Means for Solving the Problems) In short, the present invention combines titanium oxide (TiO ₂ ) and orthotitanic acid (TiO
(OH) ₄ ), metatitanic acid (TiO(OH) ₂ ), etc.
The TiO ₂ precursor contains one or more selected titanium compounds as TiO ₂ on the regenerated catalyst in excess of 70
By adding within % by weight, mixing in a dry or wet process, and then molding, the catalyst activity can be restored to a level equivalent to that of an unused catalyst. The reason why the catalyst activity is recovered by the present invention is as follows. In other words, according to the research conducted by the present inventors, the activity reduction phenomenon (deterioration) of the denitrification catalyst is caused by Na,
Alkali metal elements such as K are adsorbed to the adsorption sites of the reducing agent NH ₃ , acidic ammonium sulfate (NH ₄ HSO ₄ ) is deposited on the catalyst surface, and the NH ₃ adsorption sites are not used effectively, or sintering occurs. It is presumed that this is due to a decrease in the absolute amount of NH ₃ adsorption points, and that it is necessary to increase the number of NH ₃ adsorption points by some method in order to regenerate the catalyst. For this reason, various oxides were added to the titanium oxide/molybdenum oxide catalyst (Ti/Mo = 90/10 mol/mol) whose activity had decreased, and the denitrification activity and NH ₃ adsorption amount were measured. As shown, a remarkable decrease in the amount of NH ₃ adsorption and activity recovery was observed only in the case where TiO ₂ was added, which led to the realization of the regeneration method of the present invention. In the present invention, if the amount of TiO ₂ (or its precursor) added exceeds 70% by weight, no significant increase in activity can be expected and it is uneconomical. Note that the lower limit is not particularly limited, as long as it is at least an effective amount at which the effect is recognized. The regenerated catalyst used in the present invention may be any ammonia catalytic reduction denitrification catalyst containing at least titanium as a catalyst component, such as titanium oxide-molybdenum oxide, titanium oxide-vanadium oxide catalyst, and the like. Even if impurities are removed prior to the regeneration treatment of the present invention or supplementary regeneration treatment such as heating is added,
This is not outside the scope of the invention. Also,
In addition to adding TiO ₂ , it is also within the scope of the invention to add new active ingredients. Specifically, the present invention is carried out by the following processing steps. (a) A step of separating the spent catalyst into catalyst components and non-catalyst components according to the shape, (b) A step of finely pulverizing the catalyst component, (c) Adding titanium oxide (TiO ₂ ) to the obtained catalyst powder. , metatitanic acid (TiO(OH) ₂ ), forthotitanic acid (Ti(OH) ₄ ) and other titanium compounds in an amount of more than 0 and 70% by weight or less, preferably 10 to 50% by weight as TiO ₂ %, and then dry or wet mixing (kneading if necessary); (d) The mixture obtained in the above step is molded, dried, and fired in a conventional manner to form a catalyst molded body. Molding-activation process. Among these steps, the main focus of the present invention is to mix the spent catalyst shown in (c) with titanium oxide or its precursor at a certain ratio, and the final goal is to obtain the regenerated catalyst. If obtained, (a),
Steps (b) and (c) may be omitted or changed as appropriate. (Example) Hereinafter, the present invention will be explained in detail with reference to Examples. Examples 1 to 5 Titanium oxide/molybdenum oxide catalyst (Ti/Mo
= 90/10 atomic ratio) was crushed to 200 mesh or less and 90% or more, and 40g was added to titanium oxide powder (specific surface area 230m ² /g, containing 5% by weight of H ₂ SO ₄ ).
1g (Example 1), 4.4g (Example 2), 17.1g
(Example 3), 40g (Example 4) and 93.3g (Example 5) were added, and water was added and kneaded. After drying, the resulting paste was formed into pellets with a diameter of 5 mm and a length of 5 mm using a hydraulic press, and then baked at 450°C for 2 hours. Comparative Examples 1 and 2 The catalysts of Examples 1 to 5 and Comparative Examples 1 and 2 were added to the unused catalysts and the used catalysts of Examples 1 to 5 without adding titanium oxide powder.
It was crushed into ~20 meshes and the denitrification activity was measured under the following conditions. Space velocity SV: 60000h Gas composition: NO 200ppm NH ₃ 240ppm SO ₂ 500ppm CO ₂ 12% O ₂ 3% H ₂ O 12% N ₂ balance Reaction temperature: 350°C Also, the adsorption amount of NH ₃ under the same conditions as above is NH ₃
This was determined by analyzing the response characteristics of the NHx concentration at the catalyst bed outlet when injection was interrupted. those results first
Shown in the figure. From the results shown in Figure 1, Examples 1 to 5 in which titanium oxide was added had significantly increased activity, _NH3 adsorption amount, and denitrification rate (catalytic activity) compared to Comparative Example 2 in which titanium oxide was not added, and the amount of _TiO2 added was 10%. In the range of ~50% by weight,
It was found that the catalyst had the same activity as the unused catalyst (Comparative Example 1). Examples 6 and 7 In place of titanium oxide in Example 4, metatitanic acid (TiO(OH) ₂ ) slurry (Example 6) and orthotitanic acid (Ti(OH) ₄ ) slurry (Example 7) were used as TiO ₂ was added to give a total weight of 40 g, and a catalyst was prepared in the same manner. Example 8 A catalyst was prepared in the same manner as in Example 4, except that a dry mixing method using a V-type mixer was used instead of the kneading with water added in Example 4. Examples 9 and 10 Prior to the operation of Example 4, the spent catalyst was
The catalyst was prepared by adding a step of washing with 10 times the volume of water and 1N sulfuric acid to remove impurities and then drying. Example 11 Instead of the spent catalyst used in Example 4, a spent titanium oxide/vanadium oxide catalyst (Ti/V=
A catalyst was prepared in the same manner using 95/5 atomic ratio). Comparative Examples 3 and 4 Catalysts were prepared in the same manner as the unused catalyst used in Example 11 and the used catalyst used in Example 11, except that titanium oxide powder was not added. Table 1 shows the results of measuring the denitrification activity of each of the catalysts of Examples 6 to 11 and Comparative Examples 1 to 4 using a method similar to the method described above.

【table】

[Table] From the results in Table 1, (a) metatitanic acid and orthotitanic acid can be used in addition to TiO ₂ as the TiO ₂ raw material, and (b) treatments such as water washing and pickling are carried out prior to the treatment of the present invention. (iii) The method of the present invention is extremely effective in restoring the activity of not only titanium oxide/molybdenum oxide catalysts but also other denitrification catalysts such as titanium oxide/vanadium oxide catalysts. is clear. (Effects of the Invention) According to the present invention, by adding titanium oxide or its precursor to the regenerated catalyst, the adsorption amount of NH ₃ can be increased and the activity can be restored. It has a remarkable effect on degraded catalysts that have been affected by a combination of various factors that reduce NH ₃ adsorption, such as sintering. Furthermore, since it does not involve any process that requires special chemical treatment or wastewater treatment, it is possible to obtain a catalyst with performance comparable to that of an unused catalyst using extremely simple equipment.
In particular, it is extremely advantageous in practice because it can be used in conjunction with ordinary catalyst manufacturing equipment, except for the step of pulverizing the spent catalyst.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the amount of TiO ₂ added, the amount of NH ₃ adsorption, and the denitrification rate for the regenerated catalyst given in the example of the present invention, and FIG.
FIG. 2 is an explanatory diagram comparing the effect of adding TiO ₂ with other additives.

Claims (1)

[Claims] 1. In a method for regenerating an ammonia catalytic reduction denitrification catalyst containing titanium, one or more titanium compounds selected from titanium oxide (TiO ₂ ) or a TiO ₂ precursor are used as TiO ₂ in the catalyst to be regenerated. A method for regenerating a denitrification catalyst, characterized by adding and mixing more than 0 to 70% by weight with respect to the regenerated catalyst. 2. The method for regenerating a denitrification catalyst according to claim 1, wherein the catalyst to be regenerated is washed with water or dilute sulfuric acid in advance. 3. The method for regenerating a denitration catalyst according to claim 1 or 2, wherein the titanium compound is added by dry mixing or kneading with water.