A low-temperature SCR denitrification catalyst regeneration solution, its preparation method and application method

Abstract

This invention discloses a low-temperature SCR denitration catalyst regeneration solution, composed of the following components by weight: 7-8 parts oxalic acid; 0.3-1 parts citric acid; 5-7 parts ammonium metavanadate; 5-7 parts ammonium metatungstate; 2-3 parts ammonium paramolybdate; and 100 parts deionized water. This invention also proposes a method for preparing and using the low-temperature SCR denitration catalyst regeneration solution. This invention provides a low-temperature SCR denitration catalyst regeneration solution that improves the catalytic activity and denitration efficiency of the regenerated low-temperature catalyst by adjusting the proportions of the components in the catalyst regeneration solution.

Description

Technical Field

[0001] This invention relates to the field of catalyst regeneration technology, and more specifically, to a low-temperature SCR denitrification catalyst regeneration liquid, its preparation method, and its application method. Background Technology

[0002] Selective oxidation-reduction (SCR) denitrification uses a reducing agent to selectively reduce nitrogen oxides under the action of a catalyst, with the reaction products being water and nitrogen. SCR catalysts used in flue gas denitrification can be classified into high-temperature catalysts (345℃~590℃), medium-temperature catalysts (260℃~380℃), and low-temperature catalysts (80℃~300℃), each with a suitable reaction temperature. If the reaction temperature is too low, the catalyst activity will decrease, leading to a decline in denitrification efficiency, and continuous operation at low temperatures can cause permanent damage to the catalyst. If the reaction temperature is too high, NH3 is easily oxidized, increasing NOx formation and causing phase transitions in the catalyst material, leading to catalyst activity degradation. Therefore, different types of high, medium, and low-temperature catalysts require different types of regenerant solutions.

[0003] Catalyst deactivation can be categorized into two types: physical deactivation and chemical deactivation. Physical deactivation is primarily caused by physical changes in the catalyst's surface structure or alterations in its physical properties, rather than changes in the catalyst's active sites. Physical deactivation can be further classified into grinding, clogging, and sintering. Appropriate chemical formulations can be used to remove the covering and clogging substances, restoring activity; this is known as cleaning and regeneration.

[0004] Chemical deactivation, also known as chemical poisoning, mainly occurs when chemical components in fly ash adsorbed or absorbed by the catalyst react with the active sites of the catalyst, leading to passivation of the active sites and a decrease in catalyst activity. The working environment of denitrification catalysts is extremely harsh, and various factors can cause poisoning and deactivation. Common substances that can chemically poison catalysts include alkali (earth) metals and heavy metals. Reactivation and regeneration can be achieved by supplementing vanadium pentoxide and MoO3 or WO3 with appropriate chemical formulations.

[0005] Chinese invention patent CN101574671A discloses a regeneration solution for SCR denitrification catalyst. After preparing solution B sequentially, oxalic acid is added to adjust the pH value, and the solution is aged to obtain the catalyst regeneration solution. During the regeneration process, the catalyst needs to be impregnated twice and dried twice, with each impregnation lasting 5 hours. This not only results in a long overall catalytic regeneration cycle and low production efficiency, but also leads to low catalytic activity and denitrification efficiency of the regenerated low-temperature catalyst. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention proposes a low-temperature SCR denitrification catalyst regeneration solution, which improves the catalytic activity and denitrification efficiency of the regenerated low-temperature catalyst by adjusting the proportion of components in the catalyst regeneration solution.

[0007] The present invention also proposes a method for preparing a low-temperature SCR denitrification catalyst regeneration solution.

[0008] This invention also proposes a method for using a low-temperature SCR denitrification catalyst regeneration solution.

[0009] The technical solution adopted in this invention is: to provide a low-temperature SCR denitrification catalyst regeneration solution, which is composed of the following weight components:

[0010] 7-8 parts oxalic acid;

[0011] Citric acid 0.3-1 part;

[0012] Ammonium metavanadate 5-7 parts; when the amount of ammonium metavanadate is greater than 7 parts, it will not easily dissolve in the solution and will form a precipitate; when the amount is less than 5 parts, the content is too low to form a stable compound structure with ammonium metatungstate and oxalic acid, which is not conducive to the catalyst activity.

[0013] Ammonium metatungstate 5-7 parts; when the amount of ammonium metatungstate is greater than 7 parts or less than 5 parts, it will be detrimental to the formation of a stable compound structure with ammonium metavanadate and oxalic acid, which will be detrimental to the catalyst activity.

[0014] Ammonium molybdate 2-3 parts; when the amount of ammonium molybdate is greater than 3 parts, it easily crystallizes with ammonium metavanadate and oxalic acid. Less than 2 parts, due to the low content, cannot form a stable compound structure with ammonium metatungstate and oxalic acid, which is detrimental to catalyst activity.

[0015] 100 parts deionized water; the amount of deionized water may be increased or decreased depending on the required solution concentration.

[0016] Compared with existing technologies, the above formulation has the following advantages:

[0017] 1. This invention provides a low-temperature SCR denitration catalyst regeneration solution. Citric acid is used to adjust the reducing power of oxalic acid. When oxalic acid dissolves ammonium metavanadate, both redox and coordination reactions occur. Adding an appropriate amount of citric acid can regulate the rates of both reactions. The added citric acid slows down the redox reaction and enhances the coordination reaction. In this formulation, ammonium metavanadate provides catalytically active sites, while ammonium metatungstate and ammonium molybdate provide acidic sites. The coordination structure formed between ammonium metavanadate and ammonium metatungstate via oxalic acid and citric acid, after calcination, forms a VOW-like structure on the TiO2 catalyst surface, exhibiting extremely strong NH3 adsorption capacity. This significantly enhances the catalytic rate in the low-temperature range, thereby improving the catalytic activity of the catalyst in this range. Compared to other formulations, this invention, by replacing some of the acidic sites of ammonium metatungstate with ammonium molybdate, gives the catalyst better water and sulfur resistance.

[0018] 2. The formulation components in this invention are simple, require no surfactants, have low production costs, and are suitable for large-scale application.

[0019] According to one embodiment of the present invention, it comprises the following components by weight:

[0020] 7 parts oxalic acid;

[0021] Citric acid 0.5 parts;

[0022] 5 parts of ammonium metavanadate;

[0023] 5 parts of ammonium metatungstate;

[0024] 2 parts of ammonium molybdate;

[0025] 100 portions of deionized water.

[0026] According to one embodiment of the present invention, it comprises the following weight components:

[0027] It consists of the following components by weight:

[0028] 8 parts oxalic acid;

[0029] 1 part citric acid;

[0030] 7 parts of ammonium metavanadate;

[0031] 6 parts of ammonium metatungstate;

[0032] 3 parts of ammonium molybdate;

[0033] 60 parts of deionized water.

[0034] A method for preparing a low-temperature SCR denitration catalyst regeneration solution includes the following steps:

[0035] (1) Dissolve the oxalic acid and citric acid in the formula in deionized water to prepare an acidic solution;

[0036] (2) Dissolve ammonium metatungstate and part of the ammonium metavanadate in the acidic solution prepared in step (1) and stir until the solution is stable. Then add the remaining ammonium metavanadate in the formula to obtain a mixed solution.

[0037] (3) Add the prescribed amount of ammonium molybdate to the mixed solution prepared in step (2), stir to dissolve, and then let it stand at 40°C for 3-6 hours.

[0038] Compared with existing technologies, the above preparation method has the following advantages:

[0039] (1) In the prior art, oxalic acid and citric acid are generally added last to adjust the pH value of the solution. In this invention, an acidic solution composed of oxalic acid and citric acid is prepared first, and then ammonium metatungstate, ammonium metavanadate, and ammonium paramolybdate are added to the acidic solution. The prior addition of oxalic acid and citric acid can accelerate the dissolution of ammonium metavanadate, shorten the preparation time of the regeneration solution, and the acid and citric acid participate in the reaction to form a stable active precursor compound in advance, thereby improving the activity of the catalyst and the denitrification efficiency at 180°C.

[0040] (2) In the prior art, ammonium metavanadate is generally added at once. In this application, ammonium metavanadate is added in steps to balance the ratio of redox reaction products and coordination reaction products in the solution, thereby improving the activity and denitrification efficiency of the catalyst at 180°C.

[0041] According to one embodiment of the present invention, in step (2), the stirring is carried out by constant temperature stirring, and the conditions are: stirring time of 1-4 hours and stirring temperature of 40°C.

[0042] According to one embodiment of the present invention, in step (2), a portion of the ammonium metavanadate accounts for 80%-90% of the ammonium metavanadate in the formulation.

[0043] A method for using a low-temperature SCR denitrification catalyst regeneration solution includes the following steps:

[0044] S1. Pretreatment of the catalyst;

[0045] S2. Place the pretreated catalyst into the regeneration solution and ultrasonically impregnate for 5-15 minutes.

[0046] S3. After draining the catalyst impregnated in step S2, dry and calcine it to obtain the regenerated catalyst product.

[0047] Compared with existing technologies, the above-described method of use has the following advantages:

[0048] (1) Compared with the prior art of directly immersing the catalyst in the regeneration solution, the present invention treats the regeneration solution with ultrasound during impregnation. The adsorption rate of the active component depends on the pH value of the solution when the catalyst support surface is at the same potential. The pH of the solution at the TiO2 isopotential is approximately between 6 and 7, so the pH of the active solution is generally adjusted to between 6 and 7. The present invention uses ultrasonic impregnation. The cavitation effect generated by ultrasound in the solution effectively improves the diffusion rate of the active precursor compound in the catalyst pores, while balancing the adsorption rate on the catalyst surface, thereby eliminating the need for pH adjustment and saving production time.

[0049] According to one embodiment of the present invention, the ultrasonic impregnation power is 300-500W and the frequency is 40-60kHz.

[0050] According to one embodiment of the present invention, in step S3, the drying temperature is 100-150℃ and the drying time is 180 min; the calcination temperature is 350-550℃ and the calcination time is 180-360 min.

[0051] According to one embodiment of the present invention, in step S1, the pretreatment of the catalyst includes the following steps: first, immersing the catalyst in deionized water and sonicating for 5-10 minutes until the deionized water fills the pores of the catalyst, then taking out the catalyst and drying it at 100-110°C until the water content is 10%-15%. Detailed Implementation

[0052] The embodiments of the present invention are described in detail below. In this description, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0053] All raw materials used in this embodiment are commercially available. The deactivated catalysts in this embodiment are all Ti-VW honeycomb catalyst samples (150*150*1000mm) from a waste incineration plant that has been in operation for 10,000 hours, with V2O5 and WO3 contents decreasing from 1.6% and 6.2% to 1.1% and 5.3% respectively; and the denitrification rate decreasing from 91% to 42.1% (based on sampling and testing).

[0054] In this embodiment, the denitrification efficiency and catalyst activity at 180℃ were tested according to the provisions of DL / T1286-2013 "Technical Specification for Testing Flue Gas Denitrification Catalysts in Thermal Power Plants" and GB / T 38219-2019 "Technical Specification for Testing Flue Gas Denitrification Catalysts". The flue gas conditions for testing are shown in the table below:

[0055] Example of flue gas conditions

[0056] parameter unit numerical values Remark Ugs m / s 2.1 wet base AV <![CDATA[M 3 / h / m 2 ]]> 11.4 wet base <![CDATA[O2]]> % 4.6 dry base <![CDATA[H2O]]> % 9.9 NO mL / L 170 <![CDATA[Dry basis, 3.0% O2]]> <![CDATA[SO2]]> mL / L 45 <![CDATA[Dry basis, 3.0% O2]]> temperature ˚C 180 Example

[0057] The preparation method of the low-temperature SCR denitration catalyst regeneration solution in this embodiment includes the following steps:

[0058] (1) Dissolve 7 parts by weight of oxalic acid and 0.5 parts by weight of citric acid in 100 parts by weight of deionized water to prepare an acidic solution;

[0059] (2) Dissolve 5 parts by weight of ammonium metatungstate and 4.5 parts by weight of ammonium metavanadate in the acidic solution prepared in step (1) and stir until the solution is stable. Then add 0.5 parts by weight of ammonium metavanadate to obtain a mixed solution.

[0060] (3) Add 2 parts by weight of ammonium molybdate to the mixed solution prepared in step (2), stir to dissolve, and then let it stand at 40°C for 4 hours to obtain the finished regenerated solution.

[0061] Specifically, in step (2), the stirring is carried out under constant temperature conditions: stirring time of 1 hour and stirring temperature of 40℃.

[0062] Example 2

[0063] The preparation method of the low-temperature SCR denitration catalyst regeneration solution in this embodiment includes the following steps:

[0064] (1) Dissolve 8 parts by weight of oxalic acid and 1 part by weight of citric acid in 60 parts by weight of deionized water to prepare an acidic solution;

[0065] (2) Dissolve 6 parts by weight of ammonium metatungstate and 6 parts by weight of ammonium metavanadate in the acidic solution prepared in step (1) and stir until the solution is stable. Then add 1 part by weight of ammonium metavanadate to obtain a mixed solution.

[0066] (3) Add 3 parts by weight of ammonium molybdate to the mixed solution prepared in step (2), stir to dissolve, and then keep it at 40°C for 6 hours to obtain the finished regenerated solution.

[0067] Comparative Examples 1-6

[0068] The preparation steps of the low-temperature SCR denitration catalyst regeneration liquid in this comparative example are the same as those in Example 1, but the components are different, as detailed in the table below:

[0069] Comparative Example 7

[0070] The preparation method of the low-temperature SCR denitration catalyst regeneration solution in this comparative example includes the following steps:

[0071] (1) Dissolve 7 parts by weight of oxalic acid and 0.5 parts by weight of citric acid in 100 parts by weight of deionized water to prepare an acidic solution;

[0072] (2) Dissolve 5 parts by weight of ammonium metatungstate and 5 parts by weight of ammonium metavanadate in the acidic solution prepared in step (1) and stir to dissolve, so as to obtain a mixed solution;

[0073] (3) Add 2 parts by weight of ammonium molybdate to the mixed solution prepared in step (2), stir to dissolve, and then let it stand at 40°C for 4 hours to obtain the finished regenerated solution.

[0074] Specifically, in step (2), the stirring is carried out under constant temperature conditions: stirring time of 1 hour and stirring temperature of 40℃.

[0075] Comparative Example 8

[0076] The preparation method of the low-temperature SCR denitration catalyst regeneration solution in this comparative example includes the following steps:

[0077] (1) Dissolve 5 parts by weight of ammonium metatungstate and 5 parts by weight of ammonium metavanadate in 100 parts of deionized water and stir the solution until the solution is stable to obtain solution A.

[0078] (2) Add 2 parts by weight of ammonium molybdate to the A solution prepared in step (1), stir and dissolve to obtain solution B;

[0079] (3) Add 7 parts by weight of oxalic acid and 0.5 parts by weight of citric acid to the B solution prepared in step (2) to obtain the finished regenerated solution.

[0080] Specifically, in step (2), the stirring is carried out under constant temperature conditions: stirring time of 1 hour and stirring temperature of 40℃.

[0081] Experimental Examples 1-2

[0082] The method of using the low-temperature SCR denitrification catalyst regeneration solution in this experimental example includes the following steps:

[0083] S1. Pretreatment of the catalyst;

[0084] S2. Place the pretreated catalyst into the regeneration solution and ultrasonically impregnate for 5-15 minutes.

[0085] S3. After draining the catalyst impregnated in step S2, dry and calcine it to obtain the regenerated catalyst product.

[0086] Specifically, in step S2, the ultrasonic impregnation power is 300-500W and the frequency is 40-60kHz.

[0087] Specifically, in step S3, the drying temperature is 100-150℃ and the drying time is 180 min; the calcination temperature is 350-550℃ and the calcination time is 180-360 min.

[0088] Specifically, in step S1, the pretreatment of the catalyst includes the following steps: first, immerse the catalyst in deionized water and sonicate for 5-10 minutes until the deionized water fills the pores of the catalyst, then take out the catalyst and dry it at 100-110℃ until the water content is 10%-15%.

[0089] Following the above-described method, the regenerated catalyst was prepared by treating the catalyst with the regeneration solutions from Examples 1-2, where Example 1 corresponds to Example 1 and Example 2 corresponds to Example 2. The small-scale test results of the regenerated catalyst are as follows:

[0090] Experimental Example 3-10

[0091] In this experimental example, following the usage method of the low-temperature SCR denitration catalyst regeneration solution in Experimental Example 1, the deactivated catalyst was regenerated using the regeneration solutions prepared in Comparative Examples 1-7. Comparative Examples 1-8 correspond sequentially to Experimental Examples 3-10. The small-scale test results of the regenerated catalyst are as follows:

[0092] Comparing Experiment 1 with 3-8, it can be shown that when the amount of ammonium metavanadate, ammonium metatungstate, or ammonium paramolybdate exceeds the formulation amount, the catalyst activity and denitrification efficiency of the regenerated catalyst are reduced under low temperature conditions (180℃).

[0093] Comparing Experiment 1 with 9-10, it can be shown that adding ammonium metavanadate all at once or adding citric acid and oxalic acid at the end in the preparation method of low-temperature SCR denitrification catalyst regeneration liquid results in a decrease in both catalyst activity and denitrification efficiency of the regenerated catalyst under low-temperature conditions (180℃).

[0094] Experimental Control Examples 1-2

[0095] The method of using the low-temperature SCR denitrification catalyst regeneration solution in the control example of this experiment includes the following steps:

[0096] S1. Pretreatment of the catalyst;

[0097] S2. Place the pretreated catalyst into the regeneration solution and soak for 5 hours;

[0098] S3. After draining the catalyst impregnated in step S2, dry and calcine it to obtain the regenerated catalyst product.

[0099] Specifically, in step S3, the drying temperature is 100-150℃ and the drying time is 180 min; the calcination temperature is 350-550℃ and the calcination time is 180-360 min.

[0100] Specifically, in step S1, the pretreatment of the catalyst includes the following steps: first, immerse the catalyst in deionized water and sonicate for 5-10 minutes until the deionized water fills the pores of the catalyst, then take out the catalyst and dry it at 100-110℃ until the water content is 10%-15%.

[0101] Following the above-described method, the catalyst was treated with the regeneration solutions from Examples 1-2 to obtain regenerated catalysts. Control Example 1 corresponds to Example 1, Control Example 2 corresponds to Example 2, Control Example 3 corresponds to Comparative Example 7, and Control Example 4 corresponds to Comparative Example 8. The small-scale test results of the regenerated catalysts are as follows:

[0102] In summary, by combining experimental examples 1-2 and comparative examples 1-2, it can be demonstrated that placing the pretreated catalyst into the regeneration solution for ultrasonic impregnation can not only shorten the impregnation time, but also improve the low-temperature denitrification efficiency and catalytic activity of the regenerated catalyst.

[0103] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A low-temperature SCR denitration catalyst regeneration solution, characterized in that, It consists of the following components by weight: 7-8 parts oxalic acid; Citric acid 0.3-1 part; 5-7 parts of ammonium metavanadate; 5-7 parts of ammonium metatungstate; 2-3 parts of ammonium molybdate; 50-100 parts deionized water.

2. The low-temperature SCR denitrification catalyst regeneration solution according to claim 1, characterized in that: It consists of the following components by weight: 7 parts oxalic acid; Citric acid 0.5 parts; 5 parts of ammonium metavanadate; 5 parts of ammonium metatungstate; 2 parts of ammonium molybdate; 100 portions of deionized water.

3. The low-temperature SCR denitrification catalyst regeneration solution according to claim 1, characterized in that: Composed of the following weight components composition: 8 parts oxalic acid; 1 part citric acid; 7 parts of ammonium metavanadate; 6 parts of ammonium metatungstate; 3 parts of ammonium molybdate; 60 parts of deionized water.

4. The method for preparing the low-temperature SCR denitrification catalyst regeneration liquid according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Dissolve the oxalic acid and citric acid in the formula in deionized water to prepare an acidic solution; (2) Dissolve ammonium metatungstate and part of the ammonium metavanadate in the acidic solution prepared in step (1) and stir until the solution is stable. Then add the remaining ammonium metavanadate in the formula to obtain a mixed solution. (3) Add the prescribed amount of ammonium molybdate to the mixed solution prepared in step (2), stir to dissolve, and then let it stand at 40°C for 3-6 hours.

5. The method for preparing a low-temperature SCR denitrification catalyst regeneration solution according to claim 4, characterized in that: In step (2), the stirring is carried out under constant temperature conditions: stirring time of 1-4 hours and stirring temperature of 40℃.

6. The method for preparing a low-temperature SCR denitrification catalyst regeneration solution according to claim 4, characterized in that: In step (2), a portion of the ammonium metavanadate accounts for 80%-90% of the total amount of ammonium metavanadate in the formula.

7. The method of using the low-temperature SCR denitrification catalyst regeneration solution as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Pretreatment of the catalyst; S2. Place the pretreated catalyst into the regeneration solution and ultrasonically impregnate for 5-15 minutes. S3. After draining the catalyst impregnated in step S2, dry and calcine it to obtain the regenerated catalyst product.

8. The method of using the low-temperature SCR denitrification catalyst regeneration solution according to claim 7, characterized in that, In step S2, the ultrasonic impregnation power is 300-500W and the frequency is 40-60kHz.

9. The method of using the low-temperature SCR denitrification catalyst regeneration solution according to claim 7, characterized in that, In step S3, the drying temperature is 100-150℃ and the drying time is 180 min; the calcination temperature is 350-550℃ and the calcination time is 180-360 min.

10. The method of using the low-temperature SCR denitrification catalyst regeneration solution according to claim 7, characterized in that, In step S1, the catalyst is pretreated. The steps include: first, immersing the catalyst in deionized water and sonicating for 5-10 minutes until the deionized water fills the pores of the catalyst; then, removing the catalyst and drying it at 100-110℃ until the water content is 10%-15%.