KR101199477B1 - Method of regenerating SCR catalyst - Google Patents

Abstract

The present invention can be used by semi-permanently regenerating the catalyst having excellent mechanical strength and wear resistance by regenerating the waste catalyst in the acid solution, and then supported by a solution containing zirconium, thereby reducing the cost according to the purchase cost of the new catalyst Can be.

Description

Regeneration method of selective catalyst reduction catalyst {Method of regenerating SCR catalyst}

The present invention relates to a method for regenerating a selective reduction catalyst and to a selective reduction catalyst regenerated by the regeneration method.

Among the air pollutants, sulfur oxides and nitrogen oxides emitted from the combustion of fossil fuels such as natural gas, oil and coal cause acid rain and forest destruction, freon gas causes ozone layer destruction, and carbon dioxide, methane and nitrous oxide It is a huge threat to the global environment, causing warming problems. Among the gaseous nitrogen oxides present in the atmosphere, most of them produced by combustion are NO and NO ₂ , and these are commonly referred to collectively as nitrogen oxides (NOx). Of these, NO accounts for 90 to 95% of the total NOx emissions. However, NO is easily oxidized in the atmosphere to become NO ₂ , and during the process of becoming NO _{2, it} is decomposed into oxygen radicals to react with oxygen in the atmosphere to form ozone. The ozone is not only a causative agent of photochemical smog as a major factor of devastating respiratory diseases and forests, but an air pollutant which is a major cause of acid rain, and thus, efficient removal of nitrogen oxides is required.

Thus, various techniques for removing nitrogen oxides generated when using fossil fuels in fixed locations, such as thermal power plants and industrial boilers, have been studied. At present, the most widely used nitrogen oxide removal technology in thermal power plants and incinerators is a selective catalytic reduction (SCR) process in which ammonia is used as a reducing agent and the ammonia is reacted with nitrogen oxides on a catalyst to be decomposed and removed into harmless nitrogen and water. Most commercially available selective catalyst reduction catalysts (hereinafter referred to as SCR catalysts) are based on titanium dioxide (TiO2) as carriers, and the active materials are vanadium (1 to 3%), tungsten (10 to 20%) and extrusion molding. It can be prepared by supporting the organic and inorganic binder for.

Such selective catalyst reduction catalysts have a lifespan after approximately 2 to 5 years of deactivation due to poisoning by solid metals, alkaline earth metals and heavy metals contained in fly ash and deposition of solids as the operation time elapses.

Korean Patent Publication No. 10-2008-0024925 discloses a method for regenerating a honeycomb selective catalyst reduction catalyst by dipping it in distilled water, ultrasonic washing, washing and drying, and then recoating it with a catalyst. Korean Patent No. 10-0601035 proposes a method of removing and regenerating water after immersion in regenerated water at room temperature without containing chlorine and cleaning components in regenerating waste catalyst, and in Korean Patent No. 10-0673303 A catalyst performance evaluation process that analyzes the activator of the catalyst and evaluates the performance of the catalyst using an analyzer and thermal chemical regeneration of the target waste catalyst (alkaline solution such as nitric acid, sulfuric acid, potassium hydroxide, sodium hydroxide, etc.) It suggests how to play through. In addition, US Patent No. 6,395,665 proposes a method for cleaning a flue gas denitrification waste catalyst poisoned with a heavy metal such as As with a cleaning solution containing sulfuric acid or an aqueous ammonia solution.

However, the catalysts regenerated by the above methods increase the number of regenerations from the first regeneration, and thus the strength of the catalyst is weakened by continuous contact with water during the immersion and washing process of the regeneration process, and the dust is produced by operating for a long time in the SCR reactor of the power plant. Durability is gradually weakened by such abrasive materials, and after a maximum of two to three times of regeneration and use, they can no longer be regenerated and should be discarded and replaced with a new catalyst.

According to the present invention, the selective reduction spent catalyst is washed in an acid solution and then regenerated in a solution containing zirconium, thereby allowing semi-permanent regeneration of a catalyst having excellent mechanical strength and abrasion resistance. It is an object of the present invention to provide a method for regenerating a selective reduction spent catalyst which can reduce the amount of waste.

The present invention comprises the steps of (A) washing the spent catalyst containing the poisoning substance with an acid solution; And

(B) a method for regenerating a selective reduction catalyst comprising the step of supporting the washed waste catalyst in a solution containing zirconium.

In the present invention, the selective reduction catalyst refers to a catalyst used in a selective catalytic reduction (SCR) process used to remove nitrogen oxides (NOx) emitted from a thermal power plant.

Hereinafter, the regeneration method of the selective reduction catalyst according to the present invention will be described in detail.

The form of the selective reduction catalyst according to the present invention may have a variety of forms such as honeycomb (honeycomb), spherical, particulate, flat, tubular or rim type, depending on the use environment, preferably can provide a large surface area It may have a honeycomb form.

In general, the selective reduction catalyst of the present invention may be one in which an active ingredient including a metal oxide is supported on a carrier.

As the carrier, for example, one or more selected from the group consisting of titanium dioxide (TiO ₂ ), alumina (Al ₂ O ₃ ), and silica (SiO ₂ ) may be used. Preferably, titanium dioxide may be used. have.

In addition, the metal oxide included in the active ingredient may be used at least one selected from the group consisting of vanadium oxide, manganese oxide, barium oxide, molybdenum oxide and tungsten oxide, preferably vanadium pentoxide (V ₂ O ₅ ) and trioxide Tungsten (WO ₃ ) may be used.

In the case of vanadium pentoxide (V ₂ O ₅ ), the catalytic activity of converting NOx to N ₂ by a redox cycle increases the activity of the catalyst, and in the case of tungsten trioxide (WO ₃ ), the thermal stability of the catalyst It serves to increase the number of acid sites of the catalyst and to stabilize the Bronsted acidity. In addition, it serves to prevent oxidation of NH ₃ by increasing resistance to chemical poisoning of the catalyst by alkali metal oxide, etc., and the crystal structure of the carrier (ex, TiO ₂ ) is rutile in anatase type. It is to prevent deformation into).

In the present invention, the content of the metal oxide is not particularly limited, and may include 0.1 to 10 parts by weight, preferably 0.1 to 1 part by weight based on the selective reduction catalyst. When the content of the metal oxide is less than 0.1 parts by weight, there is a fear that the denitrification performance is lowered, and when it exceeds 10 parts by weight, the economic effect may be lowered.

In the selective reduction catalyst of the present invention, the method of supporting the active ingredient containing the metal oxide on the carrier is not particularly limited, and may be supported using general catalyst preparation methods such as deposition, injection, and adsorption of metal oxide. It is possible to use more effective adsorption methods for NOx removal by increasing the dispersion of the material.

The selective reduction catalyst is used to remove nitrogen oxide (NOx) discharged from the SCR process, etc., the mechanical strength and durability is weakened as it is used for a long time. In the present invention, the catalyst discarded after being used in an SCR process is referred to as a waste catalyst.

Regeneration of the spent catalyst may comprise (A) washing the spent catalyst containing the poisonous substance with an acid solution; And

(B) can be regenerated by a method comprising the step of supporting the washed waste catalyst in a solution containing zirconium.

The method for regenerating the selective reduction catalyst of the present invention may further comprise physically removing the solids deposited on the spent catalyst prior to the step of washing with the acid solution.

Since solid matters such as fly ash are deposited in the waste catalyst of the present invention, such solids may be removed through the physical removal. The physical removal may be performed using a vacuum cleaner or a blower.

Step (A) of the present invention is a step of washing the waste catalyst containing the poisoning substance with an acid solution, wherein the poisoning substance is at least one selected from the group consisting of sulfur, phosphorus, alkali metals, alkaline earth metals and heavy metals, etc. Can be mentioned.

The type of acid solution used in the present invention is not particularly limited, and one or more selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, and formic acid may be used, and preferably sulfuric acid (H ₂ SO ₄ ) may be used. have.

In addition, the concentration of the acid solution is not particularly limited and may be 0.05 to 1 M. When the concentration is less than 0.05 M, the cleaning power may be lowered. When the concentration is higher than 1 M, excessive acidity may dissolve not only the poisoning substance but also the active ingredient in the catalyst, thereby lowering the activity of the regenerated catalyst.

In addition, the acid solution in the present invention may further include one or more selected from the group consisting of vanadium, tungsten, barium, manganese, molybdenum and oxides thereof in order to improve the activity of the spent catalyst.

In the present invention, the washing may be performed for 30 to 120 minutes.

Step (B) of the present invention is a step of supporting a spent catalyst washed with an acid solution in a solution containing zirconium.

The solution used in this step is not particularly limited, and water may be preferably used.

In this step, the concentration of zirconium in the solution may be 0.5 to 5 M.

In addition, step (B) of the present invention can be carried out for 30 to 120 minutes.

By this step, the zirconium in the solution is supported on the catalyst, thereby generating a matrix in the catalyst carrier, thereby greatly improving the mechanical strength and durability with the performance recovery of the catalyst.

The method for regenerating the selective reduction catalyst of the present invention may further comprise drying and calcining the spent catalyst after performing step (B). Through the firing step, it is possible to improve the mechanical strength of the spent catalyst and to remove foreign substances remaining in the spent catalyst.

Drying in this step may be performed for 1 to 3 hours at a temperature of 150 to 250 ℃. If the temperature is less than 150 ° C., excessive drying time may be required, and if it exceeds 250 ° C., internal deformation of the catalyst may occur. It is possible to prevent the phenomenon that the efficiency of the catalyst is reduced due to undrying or excessive drying at a temperature in the above range.

In addition, the firing may be performed for 1 to 3 hours at a temperature of 400 to 600 ℃. If the firing temperature is less than 150 ° C., excessive firing time may be required. If the firing temperature is higher than 600 ° C., internal deformation of the catalyst may occur.

The present invention also relates to a selective reduction catalyst regenerated by the above-mentioned regeneration method of the selective reduction catalyst.

The carrier of the regenerated catalyst is formed of a matrix of zirconium. The content of zirconium contained in the catalyst is not particularly limited, and may be 0.1 to 5.0 parts by weight, preferably 0.5 to 2.0 parts by weight. If the content is less than 0.1 part by weight, there is a fear that the effect of improving the mechanical strength and durability is insignificant, and when the content is more than 5.0 parts by weight, the additional effect is insignificant, and thus the economic effect may be lowered.

The invention also relates to a process for removing nitrogen oxides comprising contacting the regenerated selected reduction catalyst with exhaust gas under a reducing agent.

Removal of nitrogen oxides in the present invention can be carried out using a selective catalytic reduction process.

The selective catalytic reduction (SCR) process may be performed in the presence of one or more reducing agents selected from the group consisting of ammonia (NH 3), urea, hydrocarbons, and the like, and preferably, ammonia may be used as the reducing agent. Nitrogen oxides can be removed by using the catalyst according to the invention.

The recycled waste catalyst used and contaminated by the selective catalyst reduction process can be regenerated (secondary regeneration) by the following method.

Secondary regeneration of the spent catalyst is not particularly limited, and the regeneration method described above, that is, (A) washing the spent catalyst containing the poisoning substance with an acid solution; And

(B) immersing the washed waste catalyst in a solution containing zirconium.

Prior to the washing with the acid solution, the method may further include physically removing the solids deposited on the spent catalyst, and may further include drying and calcining the washed waste catalyst.

In the case of the regenerated catalyst loaded with zirconium, it is not affected by the mechanical strength and the wear resistance even when used in the SCR process. Therefore, in the second regeneration of the present invention, step (B), that is, the step of supporting the spent catalyst in the solution containing zirconium may not be performed.

The selective reduction catalyst secondary regenerated by the above method can be reused in the SCR process for removal of nitrogen oxides, and the waste catalyst coated with contaminants after the process can be regenerated tertiarily by the above method. That is, the waste catalyst can be continuously used after regeneration by the above method.

According to the present invention, the spent catalyst is washed in an acid solution and then regenerated in a zirconium-containing solution. Thus, the catalyst having excellent mechanical strength and abrasion resistance can be semi-permanently recycled, thereby reducing the cost according to the purchase cost of the new catalyst. It is economically valuable.

Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples, but the scope of the present invention is not limited by the following examples.

Example 1

As the waste catalyst used in the regeneration method of the waste catalyst, a honeycomb type catalyst prepared by supporting V ₂ O ₅ and WO ₃ on a titanium oxide support was operated at a domestic SCR flue gas denitrification facility for more than 14000 hours to denitrification efficiency. The catalyst lowered to about 60% (350% C, 80% new catalyst) was used.

The spent catalyst was formed in the form of a module having a width of 20 mm x 20 mm x 100 mm in height, washed and washed with a 0.1 M sulfuric acid solution in a washing tank, and then additionally supported by a solution containing zirconium to 0.5 weight of zirconium in the catalyst. After loading, it was reused after drying for 2 hours at 250 ° C and firing for 2 hours at 500 ° C. Zirconium was supported only during the first regeneration and did not carry zirconium during the second to third regeneration, and was used after repeating the above regeneration process.

Examples 2-4

The spent catalyst was regenerated in the same manner as in Example 1, except that 1.0 part by weight, 1.5 parts by weight and 2.0 parts by weight of zirconium were supported in the catalyst.

Comparative Example 1

The waste catalyst was regenerated in the same manner as in Example 1 except that no zirconium was used.

Experimental Example 1. Measurement of nitrogen oxide removal rate

Examples 1 to 4, Comparative Example 1, a new catalyst and a spent catalyst were attached to a honeycomb catalytic reactor to measure NOx removal activity. The reaction conditions were similar to those of the combustion exhaust gases at 350 ° C reaction temperature, 20000hr-1 space velocity and 1.0 NH3 / NOx molar ratio (oxygen concentration 3.5%, nitrogen oxide 350 ppm, sulfur dioxide 400 ppm, ammonia). The denitrification rate was measured after passing through 350 ppm and nitrogen, which is a balance gas.

The measured denitrification rate is shown in Table 1 below.

NOx removal rate (%) Before regeneration 1 play 2 plays 3 plays New catalyst 80 - - - Waste catalyst 60 - - - Comparative Example 1 (0.1MH ₂ SO ₄ ) 78 72 68 Example 1 (0.1MH ₂ SO ₄ + 0.5 parts by weight Zr) 79 79 78 Example 2 (0.1MH ₂ SO ₄ + 1.0 parts by weight Zr) 78 78 78 Example 3 (0.1MH ₂ SO ₄ + 1.5 parts by weight Zr) 80 80 79 Example 4 (0.1MH ₂ SO ₄ + 2.0 parts by weight Zr) 79 79 79

As shown in Table 1, the catalyst regenerated with only 0.1 M sulfuric acid showed a similar denitrification rate to the new catalyst when used after one regeneration, but the denitrification rate gradually decreased as the number of regenerations increased. However, in the case of the catalysts of Examples 1 to 4 further supporting zirconium, the denitrification rate does not decrease even if regeneration is continued three or more times, and shows a similar denitrification rate to the new catalyst.

Experimental Example 2 Measurement of Mechanical Strength of Catalyst

Examples 1 to 4, Comparative Example 1, the new catalyst and the spent catalyst were processed into a tetrahedral form having a size of 20 mm x 20 mm x 20 mm to measure mechanical strength. The strength was measured by measuring the axial and lateral strength of the catalyst using an Instron strength measuring instrument (Instron Universal Testing Instrument Model 4201, Instron).

The measured axial strength and side strength are shown in Tables 2 and 3 below.

Axial Strength (kg / cm ² ) Before regeneration 1 play 2 plays 3 plays New catalyst 18 - - - Waste catalyst 17 - - - Comparative Example 1 (0.1MH ₂ SO ₄ ) 16 13 9 Example 1 (0.1MH ₂ SO ₄ + 0.5 parts by weight Zr) 19 19 18 Example 2 (0.1MH ₂ SO ₄ + 1.0 parts by weight Zr) 21 21 20 Example 3 (0.1MH ₂ SO ₄ + 1.5 parts by weight Zr) 25 24 24 Example 4 (0.1MH ₂ SO ₄ + 2.0 parts by weight Zr) 23 22 22

Side Strength (kg / cm ² ) Before regeneration 1 play 2 plays 3 plays New catalyst 9 - - - Waste catalyst 9 - - - Comparative Example 1 (0.1MH ₂ SO ₄ ) 8 5 3 Example 1 (0.1MH ₂ SO ₄ + 0.5 parts by weight Zr) 10 10 9 Example 2 (0.1MH ₂ SO ₄ + 1.0 parts by weight Zr) 12 12 12 Example 3 (0.1MH ₂ SO ₄ + 1.5 parts by weight Zr) 14 13 13 Example 4 (0.1MH ₂ SO ₄ + 2.0 parts by weight Zr) 13 13 13

As shown in Table 2 and Table 3, in the case of a catalyst regenerated with only 0.1 M sulfuric acid, the mechanical strength (axial strength and lateral strength) gradually decreased as the number of regeneration was increased. However, in the case of the catalysts of Examples 1 to 4 further supporting zirconium, the axial and lateral strengths were rather increased compared to the new catalyst.

Experimental Example 3. Measurement of Wear of Catalyst

Examples 1 to 4 and Comparative Example 1, the new catalyst and the spent catalyst were installed in the SCR reactor sample port of the coal-fired power plant to measure the wear resistance after the actual operation for 2000 hours.

The measured wear resistance is shown in Table 4.

Wear rate (%) Before regeneration 1 play 2 plays 3 plays New catalyst 0 - - - Waste catalyst 4 - - - Comparative Example 1 (0.1MH ₂ SO ₄ ) 8 15 22 Example 1 (0.1MH ₂ SO ₄ + 0.5 parts by weight Zr) 6 7 9 Example 2 (0.1MH ₂ SO ₄ + 1.0 parts by weight Zr) 5 5 6 Example 3 (0.1MH ₂ SO ₄ + 1.5 parts by weight Zr) 4 5 5 Example 4 (0.1MH ₂ SO ₄ + 2.0 parts by weight Zr) 4 6 6

As shown in Table 4, the catalyst prepared by Comparative Example 1 increased the wear rate as the number of regenerations increased, but the wear rate of the catalysts of Examples 1 to 4 was almost unchanged.

Claims (18)

(A) washing the spent catalyst containing the poisonous substance with an acid solution; And
(B) reclaiming the washed waste catalyst in a solution containing zirconium having a concentration of 0.5 to 5 M.
The method of claim 1,
The selective reduction catalyst is a regeneration method of a selective reduction catalyst carrying an active ingredient containing a metal oxide on a carrier.
The method of claim 2,
And the carrier is at least one selected from the group consisting of titanium dioxide, alumina and silica.
The method of claim 2,
A method for regenerating a selective reduction catalyst wherein the carrier is titanium dioxide.
The method of claim 2,
The metal oxide is at least one selected from the group consisting of vanadium oxide, manganese oxide, barium oxide, molybdenum oxide and tungsten oxide.
The method of claim 2,
The metal oxide is vanadium pentoxide (V ₂ O ₅ ) and tungsten trioxide (WO ₃ ) regeneration method of the selective reduction catalyst.
The method of claim 1,
The poisoning substance is sulfur, phosphorus, alkali metal, alkaline earth metal or heavy metal.
The method of claim 1,
And physically removing the solids deposited on the spent catalyst before step (A).
The method of claim 1,
The acid solution is at least one selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, oxalic acid and formic acid.
The method of claim 1,
A method for regenerating a selective reduction catalyst wherein the concentration of the acid component in the acid solution is 0.05 to 1 M.
delete The method of claim 1,
After performing step (B), further comprising drying and calcining the spent catalyst.
13. The method of claim 12,
Drying is carried out at 150 to 250 ° C. for 1 to 3 hours.
13. The method of claim 12,
Firing is a regeneration method of the selective reduction catalyst is carried out at 400 to 600 ℃ for 1 to 3 hours.
A selective reduction catalyst which is regenerated by the regeneration method according to claim 1 and comprising 0.5 parts by weight to 2.0 parts by weight of zirconium.
delete A method of removing nitrogen oxides comprising contacting the selective reduction catalyst according to claim 15 with the exhaust gas in the presence of a reducing agent.
18. A secondary regeneration method of a selective reduction catalyst which regenerates the waste catalyst contaminated by the nitrogen oxide removal method according to claim 17 by the method according to claim 1.