JP7701775B2 - Method for regenerating used denitrification catalyst - Google Patents

Description

The present invention relates to a method for regenerating a used denitration catalyst. More specifically, the present invention relates to a method for inexpensively regenerating a used denitration catalyst by extending the life of the cleaning solution and repeatedly using the cleaning solution.

Regenerating used denitration catalysts and reusing them in denitration equipment is being considered. However, unless the cost required to regenerate used denitration catalysts is lower than the cost required to manufacture new denitration catalysts, it must be said that the regenerated denitration catalysts have little industrial value. Various methods for regenerating used denitration catalysts have been considered.

For example, Patent Document 1 discloses a method for regenerating a used denitration catalyst, which is characterized by contacting a used denitration catalyst, the main component of which is titanium oxide, with a slurry in which titanium oxide particles are dispersed, draining the liquid, and then drying the catalyst.

Patent Document 2 discloses a method for regenerating a used denitration catalyst, which is characterized by contacting _a used denitration catalyst mainly composed of titanium oxide with a slurry in which a _zeolite having the rational formula _WmZnO2n.NH2O (Z=Si+Al, N=variable, W ₌ Ca, Ba, Sr) is dispersed, followed by draining and drying.

JP 2010-247125 A JP 2012-152672 A

The objective of the present invention is to provide a method for inexpensively regenerating used denitration catalysts by extending the life of the cleaning solution and repeatedly using the cleaning solution.

In order to solve the above problems, the present invention has been completed, which includes the following aspects:

[1] Contacting a used denitration catalyst with a cleaning solution to dissolve and remove catalyst poisons from the used denitration catalyst in the cleaning solution;
the cleaning liquid having the catalytic poison dissolved therein is brought into contact with the adsorbent-containing molded bodies contained in the fixed bed, so that the catalytic poison is adsorbed onto the adsorbent-containing molded bodies and the catalytic poison is removed from the cleaning liquid;
Then, the cleaning solution from which the catalytic poison has been removed is reused for dissolving and removing the catalytic poison from the used denitration catalyst.
A method for regenerating used denitrification catalysts.

[2] The method for regenerating a used denitration catalyst according to [1], wherein the catalyst poison is arsenic.
[3] The method for regenerating a used DeNOx catalyst according to [1] or [2], wherein the adsorbent-containing molded body is a molded body containing titanium oxide or a molded body containing zeolite.
[4] The method for regenerating a used DeNOx catalyst according to any one of [1] to [3], wherein the cleaning liquid is water, an acidic aqueous solution, an alkaline aqueous solution, or a manganese oxide suspension.

[5] A method for regenerating a used denitration catalyst according to any one of [1] to [4], in which the shape of the adsorbent-containing molded body is a Raschig ring, a Lessing ring, a Paul ring, a saddle, a Sulzer packing, a bead, a pellet, a bar, a plate, or a cylinder.

The regeneration method of the present invention has the following advantages: (A) the removed catalyst poison or the adsorbent that has adsorbed the catalyst poison is unlikely to adhere to the denitration catalyst, so that even if the cleaning solution is repeatedly used to regenerate the used denitration catalyst, the regeneration efficiency is unlikely to decrease; (B) the adsorbent-containing molded body can be easily separated from the cleaning solution; and (C) because the catalyst poison is concentrated and collected in the adsorbent-containing molded body, the disposal of the adsorbent-containing molded body with the adsorbed catalyst poison is less expensive than the disposal of the cleaning solution in which the catalyst poison is dissolved. As a result, the regenerated catalyst can be supplied at low cost.

FIG. 1 is a diagram showing an example of an apparatus used in the present invention. FIG. 1 is a diagram showing an example of an apparatus used in the present invention. FIG. 1 is a diagram showing an example of an apparatus used in the present invention. FIG. 13 is a diagram showing a structure in which a cleaning liquid is sucked in by creating negative pressure inside the fixed bed through bubbling. FIG. 1 is a diagram showing an example of an apparatus used in the present invention. FIG. 1 is a diagram showing an example of an apparatus used in the present invention. FIG. 1 is a diagram showing an example of an apparatus used in the present invention. FIG. 1 is a diagram showing an example of an apparatus used in the present invention. FIG. 1 is a diagram showing an example of an apparatus used in the present invention. FIG. 1 is a diagram showing an example of an apparatus used in the present invention. FIG. 1 is a diagram showing an example of an apparatus used in the present invention. FIG. 1 is a graph showing the change in As ₂ O ₃ concentration in a cleaning solution. FIG. 1 is a graph showing the change in the As ₂ O ₃ removal ability of a cleaning solution (the As ₂ O ₃ remaining rate in a catalyst).

The method for regenerating a used denitration catalyst of the present invention includes (1) contacting the used denitration catalyst with a cleaning solution to dissolve and remove catalytic poisons from the used denitration catalyst in the cleaning solution, (2) contacting the cleaning solution with the dissolved catalytic poisons with an adsorbent-containing molded body contained in a fixed bed to adsorb the catalytic poisons to the adsorbent-containing molded body and remove the catalytic poisons from the cleaning solution, and (3) then reusing the cleaning solution from which the catalytic poisons have been removed for dissolving and removing the catalytic poisons from the used denitration catalyst.

The denitration catalyst that is the subject of the regeneration method of the present invention is not particularly limited as long as it is one that has been used in a denitration device. The denitration catalyst can be in the form of, for example, a honeycomb, a plate, a corrugated board, or the like. Examples of the active components of the denitration catalyst include those that contain oxides of titanium, oxides of molybdenum and/or tungsten, and oxides of vanadium (titanium-based catalysts); those that mainly contain aluminosilicates such as zeolite carrying metals such as Cu and Fe (zeolite-based catalysts); and those that are a mixture of titanium-based catalysts and zeolite-based catalysts. Of these, titanium-based catalysts are preferred.

Examples of titanium-based catalysts include Ti--V--W catalysts, Ti--V--Mo catalysts, and Ti--V--W--Mo catalysts.
The ratio of V element to Ti element is preferably 2 wt % or less, more preferably 1 wt % _or less, as a weight percentage of _V2O5 / _TiO2 . The ratio of Mo element and/or W element to Ti element is preferably 10 wt % or less, more preferably 5 wt % or less, as a weight percentage of ( _MoO3 + _WO3 )/ _TiO2 .

In preparing the catalyst, titanium oxide powder or a titanium oxide precursor can be used as the raw material for the titanium oxide. Examples of the titanium oxide precursor include titanium oxide slurry, titanium oxide sol, titanium sulfate, titanium tetrachloride, titanates, titanium alkoxides, etc. In the present invention, the raw material for the titanium oxide is preferably one that forms anatase type titanium oxide.
As the raw material of vanadium oxide, vanadium compounds such as vanadium pentoxide, ammonium metavanadate, and vanadyl sulfate can be used.
As the raw material of the oxide of tungsten, ammonium paratungstate, ammonium metatungstate, tungsten trioxide, tungsten chloride, etc. can be used.
As the raw material of the oxide of molybdenum, ammonium molybdate, molybdenum trioxide, etc. can be used.

The denitration catalyst used in the present invention may contain, as a promoter or additive, oxides of P, oxides of S, oxides of Al (e.g., alumina), oxides of Si (e.g., glass fiber), oxides of Zr (e.g., zirconia), gypsum (e.g., gypsum dihydrate), zeolite, etc. These can be used in the form of powder, sol, slurry, fiber, etc. when preparing the catalyst.

Examples of catalyst poisons that may adhere to used denitration catalysts include arsenic, phosphorus, and alkaline components. The regeneration method of the present invention is suitable for used denitration catalysts that have arsenic attached.

Examples of cleaning solutions used in the present invention include water (preferably soft water), acidic aqueous solutions, alkaline aqueous solutions, and manganese oxide suspensions. Of these, acidic aqueous solutions or alkaline aqueous solutions are preferred, and acidic aqueous solutions are more preferred. Examples of acidic aqueous solutions include aqueous solutions of organic acids such as oxalic acid and citric acid, aqueous solutions of mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and aqueous solutions of hydrogen halides such as hydrochloric acid and hydrofluoric acid. Examples of alkaline aqueous solutions include aqueous solutions of alkali metal hydroxides such as sodium hydroxide, ammonia water, and aqueous solutions of amines.

The method of contacting the used denitration catalyst with the cleaning liquid is not particularly limited. Examples include spraying, injection, and immersion. Of these, the immersion method is preferred. The used denitration catalyst 1 may be stored in a cage 7 and immersed in the cleaning liquid 2. The contact between the used denitration catalyst and the cleaning liquid can be carried out in two stages. In the first stage, the used denitration catalyst is contacted with a cleaning liquid consisting of water or the like. In the first stage, ash and the like are mainly removed. In the second stage, the used denitration catalyst is contacted with a cleaning liquid consisting of an acidic aqueous solution or the like. In the second stage, catalyst poisons such as arsenic are mainly removed.

The adsorbent-containing compact used in the present invention is a compact containing a substance that adsorbs a catalyst poison such as arsenic, preferably a compact containing titanium oxide or a compact containing zeolite. The adsorbent-containing compact can be made into a shape that is efficient for solid-liquid contact. Examples of the shape of the adsorbent-containing compact include Raschig rings, Lessing rings, Pall rings, saddles, Sulzer packings, beads, pellets, bars, plates, and cylinders. The size of the adsorbent-containing compact is preferably a sieve with an opening of 0.84 mm, more preferably a sieve with an opening of 2 mm. There is no particular upper limit to the size of the adsorbent-containing compact as long as it fits within the fixed bed.
The plate-shaped adsorbent-containing compact may be one in which the adsorbent itself is molded into a plate shape, or one in which the adsorbent is attached to a plate-shaped substrate. Examples of the plate-shaped substrate include metal substrates such as metal lath and punched metal, ceramic substrates, and woven or nonwoven substrates made of fibers such as glass fiber. The cylindrical adsorbent-containing compact may be one in which the adsorbent itself is molded into a cylindrical shape, or one in which the adsorbent is attached to a cylindrical substrate. Examples of the cylindrical substrate include ceramic substrates.

The fixed bed is not particularly limited by its form, so long as it prevents the adsorbent-containing shaped bodies from moving due to the flow of the cleaning liquid. For example, the fixed bed may be a structure in which the adsorbent-containing shaped bodies are stored in an area partitioned by a mesh, net, nonwoven fabric, woven fabric, or the like, with openings large enough that the adsorbent-containing shaped bodies cannot pass through; a structure in which the adsorbent-containing shaped bodies are packed in a tower or tank; or a structure in which the adsorbent-containing shaped bodies, heavy enough not to move due to the flow of the cleaning liquid, are sunk to the bottom of a tank. In addition, in the present invention, the fixed bed may be a unit formed by placing multiple plate-shaped adsorbent-containing shaped bodies in a frame with gaps between the plate surfaces, or a unit formed by bundling multiple cylindrical adsorbent shaped bodies.

There are no limitations on the location of the fixed bed, so long as it can bring the cleaning liquid into contact with the adsorbent-containing compacts. Examples of locations where the fixed bed can be installed include the bottom of the cleaning tank (Figures 1 to 4), the wall of the cleaning tank (Figures 6 to 8), and outside the cleaning tank (Figures 9 to 11). The contact time can be set according to the degree of reduction of the catalytic poison in the catalyst.

In order to thin the boundary film on the surface of the denitrification catalyst and the surface of the adsorbent-containing molded body, it is preferable to stir the cleaning liquid. Stirring may be performed using a stirrer or by feeding in a gas such as air. It is preferable to keep the adsorbent-containing molded body from moving when stirring the cleaning liquid.

The following is an example of a device that can increase the contact efficiency between the cleaning liquid and the adsorbent-containing compacts.

The device shown in Figure 1 has a fixed bed 4 made of adsorbent-containing molded bodies (beads) 3 spread out at the bottom of the cleaning tank, and a bubbling pipe 6 is placed above it to supply air 5, allowing the cleaning solution 2 to be agitated by bubbling. The used denitration catalyst 1 is stored in a basket 7 with a hanging lug 8, and the basket 7 can be immersed in the cleaning solution 2.

The device shown in Figure 2 has a fixed bed 4 made of adsorbent-containing molded bodies (plates) 3' stacked flat with gaps between the plate surfaces at the bottom of the cleaning tank, and a bubbling pipe 6 placed above it to supply air 5, allowing the cleaning liquid 2 to be agitated by bubbling. The used denitration catalyst 1 is stored in a basket 7 with hanging lugs 8, and the basket 7 can be immersed in the cleaning liquid 2.

The device shown in Figure 3 has a fixed bed 4 at the bottom of the cleaning tank, which is made up of adsorbent-containing molded bodies (plates) 3' stored vertically in deep baskets 7 with gaps between the plate surfaces, and a bubbling pipe 6 placed underneath to supply air 5 and agitate the cleaning liquid 2 by bubbling. A used denitration catalyst 1 is stored in a shallow basket 7, and the basket 7 can be immersed in the cleaning liquid 2. When the catalyst has been regenerated, the regenerated catalyst can be removed by lifting up the shallow basket 7. Also, when the adsorption capacity of the adsorbent-containing molded bodies (plates) 3' has decreased, the used adsorbent-containing molded bodies (plates) 3' can be removed by lifting up the deep basket 7.

In the device shown in Figure 4, a fixed bed 4 filled with adsorbent-containing compacts (beads) 3 is placed at the bottom of the cleaning tank, and a bubbling pipe 6 equipped with a bubble nozzle mechanism 9 is placed below it to supply air 5. A bubble nozzle mechanism 9 as shown in Figure 5 is installed so as to penetrate the fixed bed 4, and the bubbling caused by this creates negative pressure inside the fixed bed, allowing the cleaning liquid 2 to be sucked into the fixed bed.

The device shown in Figure 6 has a fixed bed 4 packed with adsorbent-containing compacts (beads) 3 installed along the wall of the cleaning tank. A weir 7' separates the area for soaking the used denitration catalyst from the area of the fixed bed 4. The cleaning liquid is raised by bubbling in the center, and lowered along the wall. The device shown in Figure 7 is the same as the device shown in Figure 6, except that it has a fixed bed 4 made of adsorbent-containing compacts (plates) 3' stored vertically with gaps between the plate surfaces. The device shown in Figure 8 is the same as the device shown in Figure 6, except that it has a fixed bed 4 made of adsorbent-containing compacts (cylinders) 3" bundled and stored vertically.

The apparatus shown in FIG. 9 has a structure in which a fixed bed 4 filled with adsorbent-containing compacts (beads) 3 is installed outside the cleaning tank, and the cleaning liquid is circulated by a pump. The apparatus shown in FIG. 10 is the same as the apparatus shown in FIG. 9, except that a fixed bed 4 consisting of adsorbent-containing compacts (plates) 3' stored vertically with gaps between the plate surfaces is installed. The apparatus shown in FIG. 11 is the same as the apparatus shown in FIG. 9, except that a fixed bed 4 consisting of adsorbent-containing compacts (cylinders) 3" bundled and stored vertically is installed. In the apparatus shown in FIG. 10 or FIG. 11, the pressure loss of the fixed bed 4 is lower than that of the apparatus shown in FIG. 9, so that the cleaning liquid can be circulated even with a low-power pump.

After contacting the denitration catalyst with the cleaning solution, the liquid can be drained off and dried or calcined. The denitration catalyst after contacting the cleaning solution, or the denitration catalyst that has been dried or calcined thereafter, may have less than a specified amount of active components. In such cases, the active components can be replenished. To replenish the active components, for example, the catalyst is impregnated with a solution of a vanadium compound such as vanadyl sulfate (also known as vanadium(IV) oxysulfate) or ammonium metavanadate, or a tungsten or molybdenum compound such as ammonium tungstate or ammonium molybdate, and then drained off and dried or calcined. Calcination is preferably carried out at a temperature of 200 to 400°C.

Generally, the cleaning solution can be reused as long as the poison removing ability is maintained at a predetermined level. When the poison removing ability falls below a predetermined level, new cleaning solution is added or replaced. The used cleaning solution resulting from the replacement is disposed of.
In the present invention, the catalyst poison is removed from the cleaning liquid by the adsorbent-containing molded body. The cleaning liquid from which the catalyst poison has been removed has a higher catalyst poison removing ability than conventional cleaning liquids, and can be used repeatedly to regenerate a larger number of used DeNOx catalysts. As a result, the amount of used cleaning liquid disposed of is reduced compared to conventional methods. Disposal of the adsorbent-containing molded body that has adsorbed the catalyst poison is less expensive than disposal of the used cleaning liquid in which the catalyst poison is dissolved. As a result, the cost of regenerating the used DeNOx catalyst can be significantly reduced.

Next, we will explain the present invention in more detail by showing examples and comparative examples.

Example A cleaning tank as shown in Figure 1 was prepared. 100 ml of cleaning solution (aqueous solution of 5% oxalic acid) was stored in the cleaning tank. Titanium dioxide granules (sieve size 2 mm) were added to the cleaning solution at 10% by weight, and the granules were spread under the bulring pipe.
Regeneration treatment: The temperature of the cleaning solution was adjusted to 60°C. One used denitration catalyst ( _As2O3 content 0.79 _wt %, denitration rate 43.5%) was immersed in the cleaning tank. Air was fed in and the cleaning solution was stirred by bubbling. The titanium dioxide granules did not move even when stirred. The used denitration catalyst was a 100 mm x 100 mm plate made of SUS430 metal lath substrate coated with catalyst components (Ti/W/V atomic ratio = 96/5/1) mainly composed of oxides of titanium, tungsten and vanadium. One hour after the start of immersion, the denitration catalyst was taken out. The liquid was drained off and dried at 350°C to obtain a regenerated denitration catalyst.

Another used denitration catalyst ( _As2O3 content 0.79 _wt %, denitration rate 43.5%) was regenerated 9 times without replacing the cleaning solution. _{The As2O3} concentration in the cleaning solution was measured at the end of each regeneration process. The results are shown in Figure 12. The denitration rate and _As2O3 content of 10 regenerated denitration catalysts obtained by 10 regeneration processes were measured. The average denitration rate was 56.5%. The ratio of _{the As2O3} content in the catalyst after the regeneration process _{to the As2O3} content in the catalyst before cleaning ( _As2O3 residual rate) was calculated. The results are shown in Figure 13. "Ave. _" in Figure 13 represents the average value.

Comparative Example The regeneration treatment was carried out seven times in the same manner as in the Example, except that titanium dioxide granules (those on a 2 mm mesh sieve) were not added to the cleaning solution. _{The As2O3 concentration} in the cleaning solution was measured at the end of each regeneration treatment. The results are shown in Figure 12. The denitration rate and _As2O3 content _of seven regenerated denitration catalysts obtained in seven regeneration treatments were measured. The average denitration rate was _52.3 %. The ratio of the _As2O3 content in the catalyst after the regeneration treatment _{to the As2O3} content in the catalyst before cleaning ( _As2O3 residual rate) was calculated. The results are shown in Figure 13.

As shown in Fig. 12, in the comparative example, _{the As2O3} concentration in the cleaning solution increases with the number of uses, but in the examples, even if the number of uses increases, _{the As2O3} concentration in the cleaning solution is at most about 200 ppm. Also, as shown in Fig. 13, in the comparative example, the _As2O3 residual rate in the catalyst is difficult to decrease from about the fifth use, but in the examples, the _As2O3 residual rate in the catalyst is low up to _{the tenth} use.
For these reasons, according to the method of the present invention, the catalyst poison washed out by the regeneration process does not remain in the cleaning solution in large amounts, so that the catalyst poison is unlikely to return from the cleaning solution to the DeNOx catalyst in the next regeneration process. Furthermore, according to the method of the present invention, even with the same number of uses of the cleaning solution, less arsenic remains in the DeNOx catalyst, i.e., the catalyst removal ability is maintained at a high level, and the average deNOx rate of the regenerated catalyst is high.

1: Spent denitrification catalyst
2: Cleaning solution
3: Adsorbent-containing compacts (beads)
3': Adsorbent-containing molded body (plate)
3": Adsorbent-containing compact (cylinder)
4: Fixed floor
5. Air
6: Bubbling pipe
7. Basket
7': Weir
7": Perforated plate
8: Hanging rug
9. Bubble nozzle

Claims (4)

Agitation of the cleaning solution by bubbling,
Removal of catalyst poisons from spent denitration catalysts;
Removing catalytic poisons from the cleaning solution; and reusing the cleaning solution from which the catalytic poisons have been removed for removing catalytic poisons from a used denitration catalyst;
The stirring of the cleaning solution by bubbling creates a flow in the cleaning solution,
The removal of catalytic poisons from the used denitration catalyst comprises contacting a flowing cleaning solution with the used denitration catalyst and dissolving catalytic poisons adhering to the used denitration catalyst in the cleaning solution;
The removal of the catalytic poison from the cleaning liquid comprises bringing the cleaning liquid flowing by the above stirring into contact with an adsorbent-containing shaped body, and causing the adsorbent-containing shaped body to adsorb the catalytic poison dissolved in the cleaning liquid in the removal of the catalytic poison from the used DeNOx catalyst,
the adsorbent-containing molded body is a molded body containing titanium oxide or a molded body containing zeolite, and is contained within the fixed bed so as not to be moved by the flow of the cleaning liquid generated by the stirring ;
The used denitration catalyst is in the form of a honeycomb, a plate or a corrugated board and is separated from the adsorbent-containing molded body;
A method for regenerating used denitrification catalysts. The method for regenerating a used denitration catalyst according to claim 1, wherein the catalyst poison is arsenic. The method for regenerating a used denitrification catalyst according to claim 1 or 2, wherein the cleaning liquid is water, an acidic aqueous solution, an alkaline aqueous solution, or a manganese oxide suspension. The method for regenerating a used denitration catalyst according to any one of claims 1 to 3, wherein the shape of the adsorbent-containing molded body is a Raschig ring, a Lessing ring, a Pall ring, a saddle, a Sulzer packing, a bead, a pellet, a bar, a plate, or a cylinder.

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