JP2012139665A - NOx REMOVAL CATALYST AND METHOD OF REGENERATING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a NOx removal catalyst and methods of manufacturing and regenerating the NOx removal catalyst, which can easily wash out impurities adhered to the catalyst and facilitate reactivation.SOLUTION: The NOx removal catalyst is a catalyst for reducing and removing nitrogen oxide in an exhaust gas by using ammonia and urea as a reducing agent, and is mainly composed of a composition containing an oxide of titanium (Ti), an oxide of molybdenum (Mo) and/or tungsten (W), an oxide of vanadium (V) and aluminum sulfate (Al(SO)). In the composition, (1) >0 atom% and ≤3 atom% of Mo or W with respect to Ti atoms is included and (2) the content of the aluminum sulfate is 1.5-7 wt.% with respect to TiO.

Description

  The present invention relates to a denitration catalyst containing titanium oxide as a main component and a regeneration method thereof, and more particularly, to a denitration catalyst that is easy to wash out impurities and that can be easily reactivated, a manufacturing method thereof, and a regeneration method.

  Denitration catalysts with titanium oxide as the main component and ammonia or urea as a reducing agent are highly active and excellent in durability, so they are widely used for flue gas treatment in boilers and other countries at home and abroad, becoming the mainstream of denitration catalysts. (Patent Document 1).

  On the other hand, in recent years, the need to regenerate and reuse the denitration catalyst has been increasing due to increasing awareness of effective use of resources and protection of resources. The denitration catalyst, when used for a long period of time in an actual machine, is attached by heat sintering, adhesion of catalyst poisons (alkaline metals such as Na and K, alkaline earth metals such as Ca and Sr), carbonates and sulfates, etc. The activity decreases due to pore clogging and the like due to sulfation of active ingredients Mo and V. Many of the denitration catalyst regeneration methods that are currently in practical use are washed out from the pores by washing the sulfate radicals and poisonous substances adhering to the catalyst with an acid or chemical solution to compensate for the reduced catalytic activity. The mainstream is a method of impregnating a solution containing active ingredients such as Mo, V and the like (Patent Documents 2, 3, and 4).

JP 50-128681 JP 55-145532 A Japanese Unexamined Patent Publication No. 2000-24520 JP 2004-267897 A

In the conventional catalyst described above, the active component is treated with a complexing agent such as strong acid, oxalic acid, or citric acid to recover the activity of the catalyst that has deteriorated due to adhesion of poisons or pore clogging due to sulfation of the active component. However, these methods have the following problems.
(1) In order to completely remove poisons such as alkalis, it is necessary to wash under harsh conditions such as treatment with a strong acid of high concentration, and along with that, expensive active ingredients are washed out and discarded as washing waste liquid In addition to the above problems, the bond between particles is loosened under severe conditions, and the strength of the catalyst is lowered. For this reason, it is necessary to restore the activity by impregnating a large amount of a new active ingredient and a strength improver. However, since the pores are blocked accordingly, the activity and strength are in a trade-off relationship. It is difficult to make it high.
(2) Washing under mild conditions to minimize the amount of active ingredient that is washed out will result in insufficient removal of impurities and poisons filling the pores, and the amount of active ingredient that is recharged However, it is not possible to expect a sufficient recovery of activity.

  In view of the above problems, an object of the present invention is to provide a denitration catalyst that is easy to wash out impurities adhering to the catalyst and that can be easily reactivated, a method for producing the same, and a method for regenerating the same.

The above-mentioned subject is achieved by the following method.
(1) A catalyst for reducing and removing nitrogen oxides in exhaust gas using ammonia or urea as a reducing agent, titanium (Ti) oxide, molybdenum (Mo) and / or tungsten (W) oxide, vanadium (V) The main component is a composition comprising oxide and aluminum sulfate (Al ₂ (SO ₄ ) ₃ ), and the composition is (1) Mo or W exceeds 0 with respect to Ti atoms and is 3 atomic% or less. (2) A denitration catalyst characterized in that the content of aluminum sulfate is 1.5 to 7 wt% with respect to TiO ₂ .
(2) A method for producing a catalyst for reducing and removing nitrogen oxides in exhaust gas using ammonia or urea as a reducing agent, and oxidizing titanium (Ti) oxide, molybdenum (Mo) and / or tungsten (W). The composition is composed of an oxide, vanadium (V) oxide, and aluminum sulfate (Al ₂ (SO ₄ ) ₃ ), and the composition is (1) Mo or W exceeds 0 with respect to Ti atoms. atomic% or less, (2), characterized in that the content of aluminum sulfate is mixed with the compound or a precursor thereof so as to TiO ₂ in 1.5～7Wt%, after forming a predetermined catalyst shape, drying or baking The method for producing a denitration catalyst according to (1).
(3) The method according to (2), wherein the maximum history temperature of the drying or baking is 450 ° C. or less.
(4) The denitration catalyst described in (1) used in the exhaust gas discharged from the combustion apparatus is immersed in water or an acidic aqueous solution to remove the deposits on the catalyst, and at the same time, the components in the catalyst An elution and removal of at least a part of the aluminum sulfate is impregnated with an aqueous solution containing aluminum sulfate and vanadyl sulfate, followed by draining and drying. Playback method.

  According to the present invention, a catalyst deteriorated in an actual machine can be regenerated with the same performance and strength as the initial stage, and the number of repeated uses of the catalyst can be significantly increased.

The inventors took the following measures based on the inventive idea of producing a catalyst that is easy to wash out impurities adhering to the catalyst and easy to re-activate in consideration of regeneration from the time of production of a new catalyst.
(1) Mo oxide is adsorbed as molybdic acid, and it is adsorbed only to those that strongly adsorb Mo compounds among the adsorption points that activate the catalyst. It was difficult to elute.
(2) In place of the Mo compound, aluminum sulfate was used as an activator, and in order to facilitate elution during regeneration, firing was performed under temperature conditions in which aluminum sulfate was not decomposed.

  By taking such a measure, for example, potassium ions that have penetrated into the catalyst are deteriorated by being adsorbed to Ti as shown in Formula 1 in the case of the conventional catalyst, as shown in Formula 2. Thus, the alkali metal is not adsorbed on Ti but reacts with the sulfate radical, so that the deterioration is reduced and the water is easily eluted as sulfate.

Ti-MO ₄ -Ti-OH + K ⁺ → Ti-MO ₄ -Ti-OK + H ⁺ ... (1) M = Mo, W, V, etc.
Ti-SO ₄ -Al + K ⁺ → Ti-SO ₄ -K + Al ₃ ⁺ (2)

Furthermore, after the catalyst is regenerated, aluminum sulfate and deposits are removed by washing, and then the catalyst is regenerated by impregnating with aluminum sulfate and vanadyl sulfate, whereby high activity as in the initial stage can be obtained again. Moreover, since aluminum sulfate has a binder effect, it can also compensate for the strength reduction accompanying the increase in pore volume after washing.

As the aluminum sulfate used in the denitration catalyst of the present invention, industrial aluminum sulfate (Al ₂ (SO ₄ ) ₃ · 13 to 14H ₂ O) having crystal water can be used. The addition amount is preferably more than 1.5 wt% and 7 wt% or less with respect to titanium oxide as anhydrous aluminum sulfate (Al ₂ (SO ₄ ) ₄ ). If the amount added is too small, the toxicity resistance is low, and after the catalyst becomes a used catalyst, the recovery of the pore volume after regeneration by washing is small, and the activity improving effect by the subsequent activation operation becomes small. On the other hand, when the amount added is large, for example, when water is added until aluminum sulfate is dissolved during the production of the catalyst, pasting may become difficult. Ti raw materials include dried hydrous titanium oxide and titanium oxide sols, TiO ₂ -SiO ₂ composite oxides, Mo and W raw materials include ammonium molybdate, meta or ammonium paratungstate, trioxide Molybdenum can be used. At this time, the addition amount of Mo and W is preferably more than 0 and not more than 3 atomic% with respect to Ti. If the amount is more than this, the amount of elution at the time of washing increases.

  It is also within the scope of the present invention to add raw materials that are usually added to a denitration catalyst, such as a binder such as silica sol and a strength member such as inorganic fibers, in addition to the raw materials to be active ingredients. Silica sol has the effect of improving strength, while reducing the pore volume. Further, since silica sol cannot be eluted with water or a weak acid chemical, it hinders increase in pore volume after regeneration. However, conventionally, since the strength was insufficient, the amount of silica sol added could not be reduced. However, in the present invention, since aluminum sulfate has a binder effect, the amount of binder such as silica sol added is minimized. It is also possible to reduce it. The addition amount of silica is 8 wt% or less, preferably 4 wt% or less, based on the total weight of titanium oxide and the oxide of the active component, and is preferable because the pore recovery is good.

  Any method for adding these active ingredients may be used, but a method of kneading or kneading with a kneader in the presence of water is economical and excellent.

  Next, a method for regenerating the catalyst of the present invention used in an actual machine will be specifically described. In the present invention, water or water to which 0.1 to 10 wt% of basic substances such as water, acids such as oxalic acid, citric acid and other organic acids, and ammonia and amines can be used as the cleaning solution for the used catalyst. After adding the spent catalyst while warming the solution of 3 to 20 times the catalyst weight to room temperature or a temperature of 100 ° C. or less, hold the solution for 0.5 to 24 hours while moving the solution with a stirrer or pump, Catalyst poison and aluminum sulfate are eluted from the catalyst. After a predetermined time has elapsed, the catalyst is taken out and dried. Further, in the regeneration method of the present invention, the catalyst after the washing treatment is impregnated in a solution to which aluminum sulfate and vanadyl sulfate are added as active component liquids and then dried. By performing this operation, the reproduction process is completed. At this time, aluminum sulfate plays a role of a sulfate radical retainer in the catalyst. The amount of aluminum sulfate added is preferably in the range of more than 1 in the cleaning solution and 20 wt%. If it is less than this, it is difficult to obtain high activity after regeneration. Moreover, when more than this, a pore will become small and activity will fall. A binder such as silica sol may be added to the impregnating solution. However, since aluminum sulfate plays a role of increasing the strength, the amount of the binder added can be reduced.

Hereinafter, the present invention will be described in detail using specific examples.
[Example 1]
1,200 kg of titanium oxide (made by Ishihara Sangyo Co., Ltd., specific surface area 100 m ² / g), 21.6 kg of molybdenum trioxide, 35.1 kg of ammonium metavanadate, aluminum sulfate 13-14 hydrate (Al ₂ (SO ₄ ) ₃ as 56-59% 89.9kg, silica sol (manufactured by Nissan Chemical Co., Ltd., trade name OS sol, 20wt% as SiO ₂ ) 129.7kg, and water are mixed in a kneader for 60 minutes, and then silica-alumina ceramic fiber (manufactured by NICHIAS) While gradually adding 194.5 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 0.2 mm thick SUS430 steel plate and sandwiched between two sheets of plain paper for PPC (Oostrich). 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 a 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.
[Example 2]
A catalyst was obtained in the same manner as in Example 1 except that the calcination temperature in Example 1 was changed to 400 ° C.
[Examples 3 and 4]
The catalyst was obtained in the same manner as in Example 1 except that the amount of aluminum sulfate added in Example 1 was changed to 31.3 kg and 146.1 kg, respectively. The addition amount of aluminum sulfate is 1.5 wt% and 7 wt%, respectively, with respect to the titanium oxide weight.
[Examples 5 and 6]
A catalyst was obtained in the same manner as in Example 1 except that the amount of molybdenum trioxide added in Example 1 was changed to 10.8 kg and 64.9 kg, respectively. The composition of the catalyst is Ti / Mo / V = 100 / 0.5 / 2 and 100/3/2, respectively, in atomic ratio.
[Example 7]
A catalyst was obtained in the same manner as in Example 1 except that the molybdenum trioxide of Example 1 was replaced with an equimolar amount of ammonium metatungstate. The composition of this catalyst is Ti / W / V = 100/1/2 in atomic ratio.

[Comparative Example 1]
A catalyst was obtained in the same manner as in Example 1 except that aluminum sulfate was not added.
[Reference Example 1]
A catalyst was obtained in the same manner as in Example 1 except that the calcination temperature was changed to 500 ° C. in Example 1.
[Comparative Example 2]
A catalyst was obtained in the same manner as in Example 1 except that the amount of molybdenum trioxide added was 108.1 kg in Example 1. The composition of this catalyst is Ti / Mo / V = 100/5/2 in atomic ratio.

[Reproduction example 1]
In order to confirm the effect of the combination of the catalyst of the present invention and its regeneration method, the following tests were conducted.
(1) Exhaust gas exposure test The catalysts of Examples 1 to 7, Comparative Examples 1 and 2 and Reference Example 1 (referred to as the initial catalyst) were cut into 100 mm squares, and the exhaust gas generated from the propane combustion furnace was subjected to 5000 conditions under the conditions shown in Table 1. Exposed to time and used as an exposed catalyst.
(2) Cleaning test The exposed catalyst 100 mm square −1 sheet was dried at 150 ° C., weighed, placed in a petri dish containing 100 ml of 1N oxalic acid, and held at 60 ° C. for 6 hours while shaking the solution. Thereafter, the catalyst was taken out, dried and then dried at 150 ° C. and then at 350 ° C. The weight after drying was measured to obtain a washed catalyst. The amounts of Al and SO ₄ in the washed catalyst were quantified using a fluorescent X-ray analyzer.
(3) Activation test Separately, 180 ml of pure water, 17.4 g of aluminum sulfate 13-14 hydrate (containing 56-59% as Al ₂ (SO ₄ ) ₃ ), vanadyl sulfate (containing 70% as VOSO ₄ ) ) 3.3 g was dissolved to prepare an activator.

  Put the activator in a petri dish, immerse the washed catalyst in this for about 30 seconds, impregnate with aluminum sulfate and vanadyl sulfate, pull up the catalyst from the liquid, drain and dry at 120 ° C and 350 ° C and calcinate to activate A catalyst was obtained.

[Comparative playback example 1]
In the catalyst of Example 1, a catalyst was obtained in the same manner as in Regeneration Test Example 1 except that aluminum sulfate was not added in the activation test of (3) of Regeneration Test Example 1.
[Test Example 1]
In the regeneration example 1 and the comparative regeneration example 1, each pore volume in the initial catalyst, the deteriorated catalyst, the washed catalyst, and the activation catalyst was measured using a pore volume measuring device by mercury porosimetry.

  For Examples 1 to 7, Comparative Example 1, and Reference Example 1, the pore volume after each processing step is summarized in Table 2. In Examples, Comparative Examples, and Reference Examples, the catalyst volume of any of Examples, Comparative Examples, and Reference Examples is the same as that of the initial catalyst, but the pore volume is not significantly different. Decreases. At this point, there is no difference between the examples, comparative examples, and reference examples.

However, when these exposed catalysts were compared before and after the cleaning test (2), the comparative catalyst had no change in the pore volume before and after the test, but both the catalyst of the example and the reference example were small. It can be seen that the pore volume is increased from the initial stage, and in particular, the increase is large in the examples. Furthermore, when compared after the activation test of (3), it can be seen that the pore volume of the catalyst of Comparative Example 1 has decreased after activation.
[Test Example 2]
In Examples 1, 5, 6 and Comparative Example 2, the amount of Mo in the initial catalyst and the catalyst after washing in regeneration example 1 was measured using a fluorescent X-ray apparatus. The amount of Mo after washing with respect to the initial stage was calculated as the Mo remaining rate. The results are shown in Table 3. In Examples 1, 5, and 6, the Mo residual ratio is almost 100%, and it can be seen that Mo is not eluted by washing. On the other hand, in Comparative Example 2, it is about 58%, and Mo is eluted. From this, the outflow of Mo by washing can be suppressed within the range of addition of Mo of the present invention.
[Test Example 3]
In Examples 1 to 7, Comparative Examples 1 and 2 and Reference Example 1, the initial catalyst, the exposed catalyst and the activation catalyst obtained in Regeneration Example 1 were each cut to 100 × 20 mm and filled into a reaction tube in a flow system, The denitration rate was measured under the conditions shown in Table 4. The results are shown in Table 5.

It can be seen that the catalyst of the example has almost the same denitration rate as the initial stage after activation. On the other hand, all of the catalysts of the comparative examples have low denitration performance. From this, it can be seen that when the catalyst (Example) comprising the method of the present invention is combined with the regeneration method of the present invention (Regeneration Example 1), a high effect can be obtained.
[Test Example 4]
For the initial catalyst of Example 1, regeneration test example 1 and comparative regeneration test example 1 (3) after the activation test, a grid with an average particle diameter of 70 mm was dropped from a height of 500 mm onto a catalyst inclined at 45 degrees. A grid wear test was performed to measure the amount of wear, and the strength was compared. The results are shown in Table 6.

  Compared to regeneration example 1 (with aluminum sulfate added), the wear strength of the catalyst regenerated in comparative regeneration example 1 is lower. From this result, it is understood that a high wear strength can be obtained by combining the catalyst of the present invention with the regeneration test of the present invention.

Claims (4)

A catalyst that reduces and removes nitrogen oxides in exhaust gas using ammonia or urea as a reducing agent. Titanium (Ti) oxide, molybdenum (Mo) and / or tungsten (W) oxide, vanadium (V) The composition is mainly composed of an oxide and aluminum sulfate (Al ₂ (SO ₄ ) ₃ ), and the composition is (1) Mo or W exceeds 0 with respect to Ti atoms and is 3 atomic% or less, (2 ) denitration catalyst content of aluminum sulfate is characterized in that it is a 1.5～7Wt% to TiO _2. A method for producing a catalyst for reducing and removing nitrogen oxides in exhaust gas using ammonia or urea as a reducing agent, comprising titanium (Ti) oxide, molybdenum (Mo) and / or tungsten (W) oxide, vanadium (V) The main component is a composition comprising oxide and aluminum sulfate (Al ₂ (SO ₄ ) ₃ ), and the composition is (1) Mo or W exceeds 0 with respect to Ti atoms and is 3 atomic% or less. (2) The above compound or a precursor thereof is mixed so that the content of aluminum sulfate is 1.5 to 7 wt% with respect to TiO ₂ , molded into a predetermined catalyst shape, and then dried or calcined. Item 2. A method for producing a denitration catalyst according to Item 1. The method according to claim 2, wherein the maximum history temperature of the drying or baking is 450 ° C or lower. The denitration catalyst according to claim 1 used in exhaust gas discharged from a combustion device is immersed in water or an acidic aqueous solution to remove the deposits on the catalyst, and at the same time, sulfuric acid which is a component in the catalyst A method for regenerating a denitration catalyst, wherein at least a part of aluminum is eluted and removed, and the washed catalyst is impregnated with an aqueous solution containing aluminum sulfate and vanadyl sulfate, followed by draining and drying.