Method for regenerating an alkaline earth metal-poisoned denitration catalyst

Abstract

This invention relates to the field of spent catalyst recycling technology, specifically to a method for regenerating alkaline earth metal poisoned denitration catalysts. The method includes: impregnating the alkaline earth metal poisoned denitration catalyst with a phosphoric acid solution, followed by drying and calcination to obtain a regenerated denitration catalyst. The method of this invention uses a one-step cleaning process with a phosphoric acid solution, without water washing or activation, and directly proceeds to drying and calcination, thus generating no wastewater.

Description

Technical Field

[0001] This invention relates to the field of spent catalyst recycling technology, specifically to a method for regenerating alkaline earth metal poisoned denitrification catalysts. Background Technology

[0002] In recent years, with increasingly stringent requirements for nitrogen oxide emissions, selective catalytic reduction (SCR) technology has become one of the most suitable denitrification strategies for low-concentration emission standards. SCR technology requires catalysts, and under flue gas conditions, prolonged operation can lead to a large amount of dust depositing on the catalyst surface, causing catalyst poisoning and deactivation, necessitating catalyst removal and disposal. This results in a large amount of spent denitrification catalysts needing disposal each year.

[0003] Generally, the deactivation of denitration catalysts is mainly caused by the deposition of components such as alkali metals and alkaline earth metals. In particular, alkaline earth metals, represented by calcium, have strong adhesion and are difficult to clean. Some studies have even reported that they can form stable inert compounds, such as CaWO4, with the active component WO3 in the denitration catalyst, leading to catalyst poisoning and failure.

[0004] Regeneration is an ideal method for disposing of spent denitrification catalysts and is widely used in the market. This method selectively cleans the poisoned components in the spent catalyst, thereby retaining the active components and restoring the catalyst's denitrification performance as much as possible. Currently, the main process for regenerating spent denitrification catalysts in the market is washing with a washing solution, followed by water washing, activation, drying, and calcination. For example, CN108906139A discloses a "method for regenerating a denitrification catalyst," which includes sequential washing steps with water, alkaline solution, and acid solution. Excess washing solution is used during washing, and acid activation and replenishment of active components are required after washing. This approach involves a long washing process, generating a large amount of acid and alkaline waste liquid that needs to be treated at each step. Another example is CN109317221A, which discloses a "method for regenerating deactivated denitrification catalysts," which includes three steps of soaking, one step of ultrasonic acid washing, and one step of impregnation. Each step also generates a large amount of waste liquid, and the process is also lengthy.

[0005] Because the poisoning components in denitrification catalysts are complex, especially those poisoned by alkaline earth metals such as calcium, cleaning is quite difficult. Therefore, existing cleaning technologies all involve lengthy cleaning processes. Furthermore, each cleaning step may leave residual components in the washing solution, often necessitating an additional water rinsing step, resulting in lengthy processes and large amounts of waste liquid. This leads to a series of problems in the current field of denitrification catalyst regeneration, including waste treatment and waste generation. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned problems in existing denitrification catalyst regeneration technology and to provide a regeneration method for alkaline earth metal poisoned denitrification catalysts. This method uses phosphoric acid solution for one-step cleaning, without water washing or activation, and directly dries and calcines, without generating wastewater.

[0007] To achieve the above objectives, the present invention provides a method for regenerating alkaline earth metal poisoned denitration catalysts. The method includes: impregnating the alkaline earth metal poisoned denitration catalysts with a phosphoric acid solution, followed by drying and calcination to obtain regenerated denitration catalysts.

[0008] Preferably, the concentration of the phosphoric acid solution is 1-80 wt%, more preferably 5-50 wt%.

[0009] Preferably, the soaking time is 0.5 hours or more.

[0010] Preferably, after impregnating the alkaline earth metal poisoned denitration catalyst with phosphoric acid solution, the impregnated product is directly dried and calcined in sequence to obtain a regenerated denitration catalyst; or, after impregnating the alkaline earth metal poisoned denitration catalyst with phosphoric acid solution, the solid phase of the impregnated product after solid-liquid separation is dried and calcined in sequence to obtain a regenerated denitration catalyst.

[0011] Preferably, the P2O5 loading in the regenerated denitrification catalyst is 1.0-5.0 wt%, more preferably 1.6-3.2 wt%.

[0012] Preferably, the impregnation is performed by stirring or by standing.

[0013] Preferably, the drying temperature is 30-180℃.

[0014] Preferably, the roasting temperature is 500-700℃ and the roasting time is 2-8h.

[0015] Preferably, the alkaline earth metal poisoning denitration catalyst is surface de-dust removed before impregnation.

[0016] More preferably, the method for removing dust from the surface includes high-pressure air blowing and / or water washing.

[0017] Preferably, the alkaline earth metal content in the alkaline earth metal poisoning denitrification catalyst is 0.1 wt% or more.

[0018] A second aspect of the present invention provides a regenerated denitrification catalyst obtained using the regeneration method of the present invention described above.

[0019] Through the above technical solution, the regeneration method of the alkaline earth metal poisoned denitrification catalyst of the present invention directly shortens the existing waste denitrification catalyst regeneration and cleaning process by phosphate impregnation and cleaning, and achieves zero wastewater discharge.

[0020] The regenerated denitrification catalyst showed good activity recovery within the temperature range of 200-600℃, and its performance was essentially close to that of the fresh catalyst. Within this temperature range, the difference in nitrogen oxide conversion rate compared to the fresh catalyst was less than 10%. Furthermore, at a lower temperature of 200℃, the nitrogen oxide conversion rate could reach over 85% of that of the fresh denitrification catalyst. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The first aspect of the present invention provides a method for regenerating an alkaline earth metal poisoned denitration catalyst, the method comprising: impregnating the alkaline earth metal poisoned denitration catalyst with a phosphoric acid solution, followed by drying and calcining, to obtain a regenerated denitration catalyst.

[0023] In this invention, the alkaline earth metal poisoning denitration catalyst is not particularly limited, and its components may include TiO2, V2O5, WO3, etc. Specifically, it may contain V2O5 and / or WO3 as the main component. The content of V2O5 and / or WO3 may be, for example, 1-10 wt%, preferably 1-5 wt%.

[0024] In this invention, the alkaline earth metal content in the alkaline earth metal poisoning denitration catalyst is, for example, 0.1 wt% or more, specifically 0.5-3 wt%. The specific alkaline earth metal can be Ca, Mg, etc.

[0025] In the method of the present invention, the alkaline earth metal poisoned denitration catalyst can be impregnated with phosphoric acid solution, and the impregnated product can be directly dried and calcined in sequence to obtain a regenerated denitration catalyst; or, the alkaline earth metal poisoned denitration catalyst can be impregnated with phosphoric acid solution, and the solid phase of the impregnated product after solid-liquid separation can be dried and calcined in sequence to obtain a regenerated denitration catalyst.

[0026] As described above, the drying process of the present invention can be performed directly on the impregnated product; alternatively, the impregnated product can be separated into solid and liquid phases, with the solid phase used for drying and the liquid phase recycled for the regeneration method of the present invention after appropriate replenishment of phosphoric acid. When the impregnated product is dried directly, all the phosphorus in the phosphoric acid solution enters the regenerated denitrification catalyst, which is preferable from the perspective of conveniently controlling the phosphorus content of the final regenerated denitrification catalyst. However, from the perspective of operating cost and economy, it is preferable to dry the solid phase of the impregnated product after solid-liquid separation.

[0027] According to the regeneration method of the present invention, the phosphorus content in the regenerated denitrification catalyst can be adjusted by regulating the concentration of the phosphoric acid solution. From the perspective of improving the nitrogen oxide conversion rate of the regenerated denitrification catalyst, preferably, the P2O5 loading in the regenerated denitrification catalyst is 1.0-5.0 wt%, more preferably 1.6-3.2 wt%. By controlling the nitrogen oxide concentration of the regenerated denitrification catalyst to the above-mentioned concentration, its nitrogen oxide conversion rate, especially the nitrogen oxide conversion rate at low temperatures, can be further improved.

[0028] Regarding the concentration of phosphoric acid solution, when the impregnated product is directly dried and calcined sequentially, the amount of phosphoric acid to be added can be calculated using the target phosphorus content of the regenerated denitrification catalyst. However, when the solid phase of the impregnated product is dried and calcined sequentially after solid-liquid separation, the phosphoric acid contained in the liquid phase removed during solid-liquid separation needs to be further considered. In this case, the concentration of phosphoric acid solution is controlled by calculating the final phosphorus concentration of the regenerated denitrification catalyst and the weight of the solution separated during solid-liquid separation.

[0029] The concentration of the phosphoric acid solution used can be, for example, 1-80 wt%, preferably 5-50 wt%. Furthermore, the weight ratio of water to alkaline earth metal poisoning denitrification catalyst in the phosphoric acid solution can preferably be, for example, 5-20:1, preferably 8-15:1.

[0030] According to the present invention, the impregnation can be carried out by stirred impregnation or static impregnation. To ensure sufficient reaction between the phosphoric acid solution and the alkaline earth metal poisoned denitration catalyst, it is preferable that the impregnation involves sufficient contact between the two; therefore, stirred impregnation is preferred. Furthermore, from the perspective of uniformly impregnating the alkaline earth metal poisoned denitration catalyst with the phosphoric acid solution, the impregnation time is preferably 0.5 h or more, preferably 0.5-10 h, and more preferably 1-3 h.

[0031] According to the present invention, the final regenerated denitration catalyst is obtained by drying and calcining the above-described impregnation product. The conditions and equipment for the drying and calcination are not particularly limited, and any conditions and equipment commonly used in the art for preparing denitration catalysts can be used.

[0032] According to a preferred embodiment of the present invention, the drying temperature can be 30-180°C, preferably 80-150°C. Furthermore, the drying time is only required to ensure the catalyst is thoroughly dried; for example, the drying time can be 0.5-500 hours, preferably 5-100 hours.

[0033] According to a preferred embodiment of the present invention, the calcination temperature is 400-700℃ and the calcination time is 2-8h; more preferably, the calcination temperature is 500-600℃ and the calcination time is 3-5h.

[0034] According to a preferred embodiment of the present invention, the method may further include: performing surface descaling on the alkaline earth metal poisoned denitration catalyst before impregnating it. This surface descaling removes surface impurities from the alkaline earth metal poisoned denitration catalyst, improving the performance of the regenerated catalyst. The surface descaling method is not particularly limited and may include, for example, high-pressure air blowing and / or water washing.

[0035] A second aspect of the present invention provides a regenerated denitrification catalyst obtained by the regeneration method of the present invention described above.

[0036] The regenerated denitrification catalyst of the present invention exhibits excellent nitrogen oxide conversion. The activity of the regenerated denitrification catalyst can be well recovered in the temperature range of 250-550°C. Under the conditions of 450°C and 60,000 mL / (g·h) space velocity, the difference in nitrogen oxide conversion compared with the fresh catalyst does not exceed 10%, preferably less than 8%. Furthermore, at a lower temperature of 200°C, the nitrogen oxide conversion can also reach more than 85% of that of the fresh denitrification catalyst.

[0037] The present invention will be described in detail below through examples.

[0038] Comparative Example 1

[0039] Fresh denitrification catalyst was prepared as a comparative example.

[0040] The raw material addition was calculated based on 1.0 wt% V₂O₅, 3.0 wt% WO₃, and the balance TiO₂. During preparation, ammonium metavanadate, ammonium metatungstate, and titanium dioxide were added to 50 mL of aqueous solution according to the above proportions and stirred. The solution was then heated to 100 °C until the solvent evaporated completely. Finally, the solution was calcined at 500 °C for 3 hours to obtain a fresh denitrification catalyst.

[0041] Comparative Example 2

[0042] Prepare a denitrification catalyst containing 1.9 wt% CaO poisoning.

[0043] The preparation process of the fresh catalyst was the same as in Comparative Example 1, with the amount of calcium added calculated based on the 1.9 wt% CaO dosage in the finished product. During preparation, calcium hydroxide and the fresh catalyst as described in Comparative Example 1 were added to 50 mL of water in the above proportions, with a water-to-catalyst weight ratio of 10:1, and the mixture was stirred. Subsequently, the mixture was heated at 100°C until the solvent evaporated completely. Finally, it was calcined at 500°C for 3 hours to obtain a denitrification catalyst containing 1.9 wt% CaO poisoning.

[0044] Example 1

[0045] The denitrification catalyst containing 1.9 wt% CaO from Comparative Example 2 was used for treatment. This catalyst contained 1.0 wt% V₂O₅, 3.0 wt% WO₃, 1.9 wt% CaO, and the balance was TiO₂.

[0046] An aqueous solution of H3PO4 was prepared, wherein H3PO4 was added at a ratio of 1.0 wt% P2O5 to the final catalyst (i.e., the total weight of the final regenerated catalyst is the sum of the weight of the CaO-poisoned denitration catalyst and the weight of H3PO4 as P2O5), and the weight ratio of water to the CaO-poisoned denitration catalyst was 10:1. The phosphoric acid solution was thoroughly soaked and mixed with the denitration catalyst. After 1 hour, the solution was evaporated to dryness at 100°C until all water was evaporated. The impregnated catalyst was then calcined at 500°C for 3 hours to obtain the phosphoric acid regenerated catalyst.

[0047] Example 2

[0048] The CaO-poisoned denitrification catalyst was regenerated according to the method in Example 1, except that H3PO4 was added at a ratio of 1.6 wt% P2O5.

[0049] Example 3

[0050] The CaO-poisoned denitrification catalyst was regenerated according to the method in Example 1, except that H3PO4 was added at a ratio of 3.2 wt% P2O5.

[0051] Example 4

[0052] The CaO-poisoned denitrification catalyst was regenerated according to the method in Example 1, except that H3PO4 was added at a ratio of 4.6 wt% P2O5.

[0053] Test Case

[0054] The denitrification performance of the phosphoric acid regenerated catalyst of the above embodiments, the fresh catalyst of Comparative Example 1, and the CaO poisoned denitrification catalyst of Comparative Example 2 were evaluated. The flue gas composition was controlled as 500 ppm NO, 550 ppm NH3, 2 vol% O2, with N2 as the balance gas and a space velocity of 60000 mL / (g·h).

[0055] The results of catalyst performance evaluation are shown in Table 1, and the phosphorus and calcium contents in the catalyst are shown in Table 2.

[0056] Table 1

[0057]

[0058] Table 2

[0059]

[0060] As can be seen from the results in Tables 1 and 2, the method of the present invention for regenerating CaO-poisoned denitrification catalyst can significantly improve the nitrogen oxide conversion rate of the catalyst.

[0061] Furthermore, a comparison of the results from Examples 1-4 shows that when the P2O5 content in the final phosphoric acid regeneration catalyst is 1.6-3.2 wt%, the conversion rate of nitrogen oxides in the phosphoric acid regeneration catalyst at low temperatures can be further improved.

[0062] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for regenerating an alkaline earth metal poisoned denitration catalyst, characterized in that, The method includes: impregnating an alkaline earth metal poisoned denitration catalyst with a phosphoric acid solution, followed by direct drying and calcination of the impregnated product to obtain a regenerated denitration catalyst. The P2O5 loading in the regenerated denitrification catalyst is 1.0-5.0 wt%.

2. The regeneration method according to claim 1, wherein, The concentration of the phosphoric acid solution is 1-80 wt%.

3. The regeneration method according to claim 1, wherein, The concentration of the phosphoric acid solution is 5-50 wt%.

4. The regeneration method according to claim 1, wherein, The soaking time is more than 0.5 hours.

5. The regeneration method according to claim 1, wherein, The P2O5 loading in the regenerated denitrification catalyst is 1.6-3.2 wt%.

6. The regeneration method according to any one of claims 1-4, wherein, The impregnation is performed by either stirring or static impregnation.

7. The regeneration method according to any one of claims 1-4, wherein, The drying temperature is 30-180℃.

8. The regeneration method according to any one of claims 1-4, wherein, The roasting temperature is 400-700℃, and the roasting time is 2-8 hours.

9. The regeneration method according to any one of claims 1-4, wherein, Before impregnating the alkaline earth metal poisoning denitration catalyst, the surface of the alkaline earth metal poisoning denitration catalyst is de-dusted.

10. The regeneration method according to claim 9, wherein, The surface dust removal methods include high-pressure air blowing and / or water washing.

11. The regeneration method according to any one of claims 1-4, wherein, The alkaline earth metal content in the denitrification catalyst poisoned by alkaline earth metal is above 0.1 wt%.

12. A regenerated denitrification catalyst obtained by any one of the regeneration methods of claims 1-11.

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