Method for regenerating used denitration catalyst

Abstract

To provide a regeneration method of a used denitration catalyst.SOLUTION: A regeneration method of a used denitration catalyst includes a step for removing a catalyst poison such as arsenic from a used denitration catalyst 1 by bringing the used denitration catalyst into contact with a cleaning fluid 2 such as an aqueous solution of oxalic acid to dissolve the catalyst poison in the cleaning fluid, a step for removing the catalyst poison from the cleaning fluid by bringing the cleaning fluid, in which the catalyst poison is dissolved, into contact with an adsorbent-containing compact 3 made of titanium oxide, zeolite or the like housed in a fixed bed 4 to make the adsorbent-containing compact adsorb the catalyst poison, and a step for reusing the cleaning fluid rid of the catalyst poison for dissolving the catalyst poison and removing it from another used denitration catalyst.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] 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 a cleaning liquid and repeatedly using the cleaning liquid.

Background Art

[0002] Regenerating a used denitration catalyst and reusing it in a denitration apparatus has been studied. However, unless the cost required for regenerating a used denitration catalyst is lower than the cost required for manufacturing a new denitration catalyst, the industrial value of the regenerated denitration catalyst has to be said to be low. Various methods for regenerating used denitration catalysts have been studied so far.

[0003] For example, Patent Document 1 discloses a method for regenerating a used denitration catalyst mainly composed of titanium oxide, which comprises contacting the used denitration catalyst with a slurry in which titanium oxide particles are dispersed, draining the liquid, and subsequently performing a drying treatment.

[0004] Patent Document 2 discloses a method for regenerating a used denitration catalyst mainly composed of titanium oxide, which comprises contacting the used denitration catalyst with a slurry in which a zeolite represented by the empirical formula W m Z n O 2n ·NH2O (Z = Si + Al, N = variable, W = Ca, Ba, Sr) is dispersed, draining the liquid, and subsequently drying.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a method for inexpensively regenerating a used denitration catalyst by extending the life of a cleaning liquid and repeatedly using the cleaning liquid.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention has been completed including the following aspects.

[0008] 〔1〕Contact a used denitration catalyst with a cleaning liquid to dissolve and remove catalyst poisons from the used denitration catalyst into the cleaning liquid, contact the cleaning liquid in which the catalyst poisons are dissolved with a molded body containing an adsorbent contained in a fixed bed to adsorb the catalyst poisons on the molded body containing the adsorbent and remove the catalyst poisons from the cleaning liquid, Next, reuse the cleaning liquid from which the catalyst poisons have been removed by dissolving and removing the catalyst poisons from the used denitration catalyst. A method for regenerating a used denitration catalyst.

[0009] 〔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 denitration catalyst according to 〔1〕 or 〔2〕, wherein the molded body containing an adsorbent is a molded body containing titanium oxide or a molded body containing zeolite. 〔4〕The method for regenerating a used denitration 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.

[0010] 〔5〕The method for regenerating a used denitration catalyst according to any one of 〔1〕 to 〔4〕, wherein the form of the molded body containing an adsorbent is a Raschig ring, a Lessing ring, a Pall ring, a saddle, a Sulzer packing, beads, pellets, bars, plates, or cylinders.

Effects of the Invention

[0011] The regeneration method of the present invention has the following effects: (A) Since the removed catalyst poison or the adsorbent adsorbed with the catalyst poison hardly adheres to the denitration catalyst, even if the cleaning liquid is repeatedly used for regenerating the used denitration catalyst, the regeneration efficiency hardly decreases. (B) The adsorbent-containing molded body can be easily separated from the cleaning liquid. (C) Since the catalyst poison is concentrated and collected in the adsorbent-containing molded body, the disposal cost of the adsorbent-containing molded body adsorbed with the catalyst poison is lower than that of the disposal of the cleaning liquid in which the catalyst poison is dissolved. As a result, the regenerated catalyst can be supplied at low cost.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Embodiments for Carrying Out the Invention

[0013] The method for regenerating a used denitration catalyst of the present invention includes: (1) bringing the used denitration catalyst into contact with a cleaning liquid to dissolve and remove catalyst poisons from the used denitration catalyst into the cleaning liquid; (2) bringing the cleaning liquid in which the catalyst poisons are dissolved into contact with a molded body containing an adsorbent accommodated in a fixed bed to adsorb the catalyst poisons onto the molded body containing the adsorbent and remove the catalyst poisons from the cleaning liquid; and (3) then reusing the cleaning liquid from which the catalyst poisons have been removed to dissolve and remove the catalyst poisons from the used denitration catalyst.

[0014] The denitration catalyst targeted by the regeneration method of the present invention is not particularly limited as long as it has been used in a denitration apparatus. The denitration catalyst can have a shape such as a honeycomb, a plate, or a corrugated board, for example. As the active component of the denitration catalyst, those containing titanium oxide, molybdenum and / or tungsten oxide, and vanadium oxide (titanium-based catalyst); those mainly containing aluminosilicates such as zeolite on which metals such as Cu and Fe are supported (zeolite-based catalyst); those formed by mixing a titanium-based catalyst and a zeolite-based catalyst, etc. can be mentioned. Among these, the titanium-based catalyst is preferred.

[0015] Examples of the titanium-based catalyst include Ti-V-W catalyst, Ti-V-Mo catalyst, Ti-V-W-Mo catalyst, etc. The ratio of the V element to the Ti element is preferably 2% by weight or less, more preferably 1% by weight or less, as the weight percentage of V2O5 / TiO2. The ratio of the Mo element and / or W element to the Ti element is preferably 10% by weight or less, more preferably 5% by weight or less, as the weight percentage of (MoO3 + WO3) / TiO2.

[0016] In the preparation of 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, titanate, and titanium alkoxide. In the present invention, those that form anatase-type titanium oxide are preferably used as the raw material for the titanium oxide. As the raw material for the vanadium oxide, vanadium compounds such as vanadium pentoxide, ammonium metavanadate, and vanadyl sulfate can be used. As the raw material for the tungsten oxide, ammonium paratungstate, ammonium metatungstate, tungsten trioxide, tungsten chloride, etc. can be used. As the raw material for the molybdenum oxide, ammonium molybdate, molybdenum trioxide, etc. can be used.

[0017] The denitration catalyst used in the present invention may contain, as a promoter or an additive, oxides of P, S, Al (e.g., alumina), Si (e.g., glass fiber), Zr (e.g., zirconia), gypsum (e.g., dihydrate gypsum, etc.), zeolite, etc. These can be used in the form of powder, sol, slurry, fiber, etc. during the catalyst preparation.

[0018] Examples of the catalyst poison adhering to the used denitration catalyst include arsenic, phosphorus, and alkaline components. The regeneration method of the present invention is suitable for the used denitration catalyst adhered with arsenic.

[0019] Examples of the cleaning liquid used in the present invention include water (preferably soft water), acidic aqueous solutions, alkaline aqueous solutions, manganese oxide suspensions, and the like. Among 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, aqueous ammonia, and aqueous solutions of amines.

[0020] The method of bringing the used denitration catalyst into contact with the cleaning liquid is not particularly limited. For example, spraying methods, injection methods, immersion methods, and the like can be mentioned. Among these, the immersion method is preferred. The used denitration catalyst 1 may be stored in a basket 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 steps. In the first step, the used denitration catalyst is brought into contact with a cleaning liquid composed of water or the like. In the first step, ash and the like are mainly removed. In the second step, the used denitration catalyst is brought into contact with a cleaning liquid composed of an acidic aqueous solution or the like. In the second step, catalyst poisons such as arsenic are mainly removed.

[0021] The adsorbent-containing molded body used in the present invention is a molded body containing a substance that adsorbs catalyst poisons such as arsenic, preferably a molded body containing titanium oxide or a molded body containing zeolite. The adsorbent-containing molded body can be formed into a shape with good efficiency of solid-liquid contact. Examples of the shape of the adsorbent-containing molded body include Raschig rings, Lessing rings, Pall rings, saddles, Sulzer packings, beads, pellets, bars, plates, cylinders (cylinders), and the like. The size of the adsorbent-containing molded body is preferably the oversize on a sieve with an opening of 0.84 mm, more preferably the oversize on a sieve with an opening of 2 mm. The upper limit of the size of the adsorbent-containing molded body is not particularly limited as long as it can be accommodated in a fixed bed. The plate-shaped adsorbent-containing molded body may be formed by molding the adsorbent itself into a plate shape, or may be formed by attaching the adsorbent 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 non-woven substrates made of fibers such as glass fiber. The cylindrical adsorbent-containing molded body may be formed by molding the adsorbent itself into a cylindrical shape, or may be formed by attaching the adsorbent to a cylindrical substrate. Examples of the cylindrical substrate include those made of a ceramic substrate and the like.

[0022] The fixed bed is not particularly limited by its form as long as the adsorbent-containing molded body is prevented from moving by the flow of the cleaning liquid. For example, a structure in which the adsorbent-containing molded body is stored in a place partitioned by a perforated plate, a net, a non-woven fabric, a woven fabric, etc. with an opening that the adsorbent-containing molded body cannot pass through, a structure in which the tower or tank is filled with the adsorbent-containing molded body, and a structure in which the adsorbent-containing molded body having a weight that cannot be moved by the flow of the cleaning liquid is sunk to the bottom of the tank can be cited. Further, in the present invention, as the fixed bed, a unitized one in which a plurality of plate-shaped adsorbent-containing molded bodies are placed in a frame with a gap between the plate surfaces, a unitized one in which a plurality of cylindrical adsorbent molded bodies are bundled, etc. can be used.

[0023] The fixed bed is not limited by its installation location as long as the cleaning liquid and the adsorbent-containing molded body can be brought into contact. Examples of the installation location of the fixed bed include, for example, the bottom in the cleaning tank (Figs. 1 to 4), the vicinity of the wall in the cleaning tank (Figs. 6 to 8), outside the cleaning tank (Figs. 9 to 11), etc. The contact time can be set according to the degree of reduction of the catalyst poison in the catalyst.

[0024] In order to thin the boundary film on the surface of the denitration catalyst and the surface of the adsorbent-containing molded body, it is preferable to stir the cleaning liquid. The stirring may be performed by a stirrer, or may be performed by sending in a gas such as air. It is preferable to prevent the adsorbent-containing molded body from moving when the cleaning liquid is stirred.

[0025] Examples of devices that can enhance the contact efficiency between the cleaning liquid and the adsorbent-containing molded body are shown below.

[0026] The device shown in Fig. 1 installs a fixed bed 4 formed by spreading adsorbent-containing molded bodies (beads) 3 at the bottom in the cleaning tank, arranges a bubbling pipe 6 thereon to supply air 5, and enables the cleaning liquid 2 to be stirred by bubbling. The used denitration catalyst 1 is stored in a basket 7 with a hanging lug 8, and the entire basket 7 can be immersed in the cleaning liquid 2.

[0027] The device shown in Fig. 2 installs a fixed bed 4 formed by stacking adsorbent-containing molded bodies (plates) 3' with gaps between the plate surfaces horizontally at the bottom in the cleaning tank, arranges a bubbling pipe 6 thereon to supply air 5, and enables the cleaning liquid 2 to be stirred by bubbling. The used denitration catalyst 1 is stored in a basket 7 with a hanging lug 8, and the entire basket 7 can be immersed in the cleaning liquid 2.

[0028] The device shown in Fig. 3 installs a fixed bed 4 formed by storing adsorbent-containing molded bodies (plates) 3' with gaps between the plate surfaces vertically in a deep basket 7 at the bottom in the cleaning tank, arranges a bubbling pipe 6 below it to supply air 5, and enables the cleaning liquid 2 to be stirred by bubbling. The used denitration catalyst 1 is stored in a shallow basket 7, and the entire basket 7 can be immersed in the cleaning liquid 2. When the catalyst is regenerated, the regenerated catalyst can be taken out by pulling up the shallow basket 7. Also, when the adsorption capacity of the adsorbent-containing molded body (plate) 3' decreases, the used adsorbent-containing molded body (plate) 3' can be taken out by pulling up the deep basket 7.

[0029] The device shown in Fig. 4 installs a fixed bed 4 formed by filling adsorbent-containing molded bodies (beads) 3 at the bottom in the cleaning tank, arranges a bubbling pipe 6 equipped with a bubble nozzle mechanism 9 below it to supply air 5. The bubble nozzle mechanism 9 as shown in Fig. 5 is installed so as to penetrate the fixed bed 4, and by bubbling with this, a negative pressure can be created inside the fixed bed, and the cleaning liquid 2 can be sucked into the fixed bed.

[0030] The apparatus shown in Fig. 6 is provided with a fixed bed 4 filled with an adsorbent-containing molded body (beads) 3 at the side wall inside the washing tank. The used denitration catalyst is separated by a weir 7' into a region where it is immersed and the region of the fixed bed 4. It has a structure in which the cleaning liquid is raised by bubbling at the central part and the cleaning liquid is lowered at the side wall. The apparatus shown in Fig. 7 is the same as the apparatus shown in Fig. 6 except that a fixed bed 4 formed by vertically storing an adsorbent-containing molded body (plate) 3' with a gap between the plate surfaces is provided. The apparatus shown in Fig. 8 is the same as the apparatus shown in Fig. 6 except that a fixed bed 4 formed by vertically storing a bundled adsorbent-containing molded body (cylinder) 3'' is provided.

[0031] Also, the apparatus shown in Fig. 9 has a structure in which a fixed bed 4 filled with an adsorbent-containing molded body (beads) 3 is installed outside the washing 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 formed by vertically storing an adsorbent-containing molded body (plate) 3' with a gap between the plate surfaces is provided. The apparatus shown in Fig. 11 is the same as the apparatus shown in Fig. 9 except that a fixed bed 4 formed by vertically storing a bundled adsorbent-containing molded body (cylinder) 3'' is provided. In the apparatus shown in Fig. 10 or Fig. 11, since the pressure loss of the fixed bed 4 is lower than that of the apparatus shown in Fig. 9, the cleaning liquid can be circulated even with a pump having low power.

[0032] The denitration catalyst after being brought into contact with the cleaning liquid can be drained and dried or calcined. The denitration catalyst after being brought into contact with the cleaning liquid, or the denitration catalyst dried or calcined thereafter may have an active ingredient content below a predetermined amount. In such a case, the active ingredient can be replenished. The replenishment of the active ingredient is carried out, for example, by impregnating 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, draining, and then drying or calcining. The calcination is preferably carried out at a temperature of 200 to 400 °C.

[0033] Generally, the cleaning liquid can be repeatedly used while maintaining a predetermined level of catalyst poison removal ability. When the catalyst poison removal ability drops below the predetermined level, fresh cleaning liquid is added or replaced. The used cleaning liquid generated by the replacement is discarded. In the present invention, catalyst poisons are removed from the cleaning liquid by the adsorbent-containing molded body. Since the cleaning liquid from which the catalyst poisons have been removed has a higher catalyst poison removal ability than conventional cleaning liquids, it can be repeatedly used for the regeneration of a larger amount of used denitration catalysts. As a result, the amount of discarded used cleaning liquid is reduced compared to the prior art. The disposal of the adsorbent-containing molded body that has adsorbed the catalyst poison is less expensive than the disposal of the used cleaning liquid in which the catalyst poison is dissolved. These factors can significantly reduce the cost of regenerating used denitration catalysts.

[0034] Next, examples and comparative examples are shown to more specifically explain the present invention.

[0035] Examples A cleaning tank as shown in FIG. 1 was prepared. 100 ml of a cleaning liquid (an aqueous solution of 5% oxalic acid) was stored in the cleaning tank. 10% by weight of titanium dioxide granules (oversize on a 2 mm sieve) were added to the cleaning liquid and spread under the barring pipe. Regeneration treatment: The temperature of the cleaning liquid was adjusted to 60°C. One used denitration catalyst (As2O3 content 0.79% by weight, denitration rate 43.5%) was immersed in the cleaning tank. Air was fed in and the cleaning liquid was stirred by bubbling. The titanium dioxide granules did not move even with stirring. The used denitration catalyst is a 100 mm × 100 mm plate-shaped one formed by applying a catalyst component mainly composed of oxides of titanium, tungsten, and vanadium (Ti / W / V atomic ratio = 96 / 5 / 1) to a SUS430 metal lath substrate. One hour after the start of immersion, the denitration catalyst was taken out. It was drained and dried at 350°C to obtain a regenerated denitration catalyst.

[0036] Without replacing the cleaning liquid, the regeneration treatment of another used denitration catalyst (As₂O₃ content: 0.79% by weight, denitration rate: 43.5%) was further carried out 9 times. The As₂O₃ concentration in the cleaning liquid was measured at the end of each regeneration treatment. The results are shown in Fig. 12. The denitration rates and As₂O₃ contents of 10 regenerated denitration catalysts obtained from 10 regeneration treatments were measured respectively. The average denitration rate was 56.5%. 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 Fig. 13. "Ave." in Fig. 13 represents the average value.

[0037] Comparative Example The regeneration treatment was carried out 7 times in the same manner as in the example except that titanium dioxide granules (oversize material with a mesh opening of 2 mm) were not added to the cleaning liquid. The As₂O₃ concentration in the cleaning liquid was measured at the end of each regeneration treatment. The results are shown in Fig. 12. The denitration rates and As₂O₃ contents of 7 regenerated denitration catalysts obtained from 7 regeneration treatments were measured respectively. 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 Fig. 13.

[0038] As shown in Fig. 12, in the comparative example, the As₂O₃ concentration in the cleaning liquid increases with the increase in the number of uses, while in the example, even when the number of uses increases or the As₂O₃ concentration in the cleaning liquid is high, it is about 200 ppm. Also, as shown in Fig. 13, in the comparative example, it is difficult for the As₂O₃ residual rate in the catalyst to decrease from around the 5th time, while in the example, the As₂O₃ residual rate in the catalyst is low up to the 10th time. From these facts, according to the method of the present invention, since the catalyst poison washed out by the regeneration treatment does not remain much in the cleaning liquid, it is less likely that the catalyst poison returns from the cleaning liquid to the denitration catalyst in the next regeneration treatment. Also, according to the method of the present invention, even with the same number of uses of the cleaning liquid, less arsenic remains in the denitration catalyst, that is, the catalyst removal ability is maintained high, and the average denitration rate of the regenerated catalyst is high.

Explanation of Symbols

[0039] 1: Used denitration catalyst 2: Cleaning liquid 3: Adsorbent-containing molded body (beads) 3’: Adsorbent-containing molded body (plate) 3”: Adsorbent-containing molded body (cylinder) 4: Fixed bed 5: Air 6: Bubbling pipe 7: Basket 7’: Weir 7”: Sieve plate 8: Hanging lug 9: Bubble nozzle

Claims

1. Stirring of the cleaning liquid by bubbling, Removal of catalyst poisons from the used denitration catalyst, Removal of catalyst poisons from the cleaning liquid, and Reuse of the cleaning liquid from which the catalyst poisons have been removed for the removal of catalyst poisons from the used denitration catalyst including performing, The stirring of the cleaning liquid by bubbling causes a flow in the cleaning liquid, The removal of catalyst poisons from the used denitration catalyst consists of bringing the flowing cleaning liquid into contact with the used denitration catalyst and dissolving the catalyst poisons adhering to the used denitration catalyst in the cleaning liquid, The removal of catalyst poisons from the cleaning liquid consists of bringing the flowing cleaning liquid by the above stirring into contact with the adsorbent-containing molded body and adsorbing the catalyst poisons dissolved in the cleaning liquid in the removal of catalyst poisons from the used denitration catalyst onto the adsorbent-containing molded body, The adsorbent-containing molded body is a molded body containing titanium oxide or a molded body containing zeolite and is housed in a fixed bed so as not to move by the flow of the cleaning liquid generated by the above stirring, The used denitration catalyst has the shape of a honeycomb, plate or corrugated board and is separated from the adsorbent-containing molded body, A method for regenerating a used denitration catalyst.

2. The method for regenerating a used denitration catalyst according to claim 1, wherein the catalyst poison is arsenic.

3. The method for regenerating a used denitration 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.

4. 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, Lessing ring, Pall ring, saddle, Sulzer packing, bead, pellet, bar, plate, or cylinder.

Images