A cobalt-based porous aluminum catalyst for catalytic decomposition of N2O in tail gas of nitric acid production, and a preparation method and application thereof

Abstract

The present application belongs to the technical field of catalysts, and relates to a cobalt-based porous aluminum catalyst for catalytic decomposition of N2O in tail gas of nitric acid production as well as a preparation method and application thereof. The catalyst takes Al2O3 as a carrier, Co3O4 as an active component, and KF and K2O as additives. The preparation method comprises the following steps: dispersing a certain amount of cobalt salt, fluorine salt and pseudo-boehmite uniformly in deionized water to form a suspension, adjusting the pH of the suspension to a certain range by taking potassium salt as a precipitant to obtain a corresponding precipitate mixture, and then performing suction filtration and washing on the precipitate. The obtained filter cake is dried, calcined and formed to obtain the catalyst. The preparation method is simple and easy to realize industrial amplification. The prepared catalyst can realize direct catalytic decomposition of N2O at a lower temperature, has excellent resistance to O2, NO2 and water vapor, has a high crushing strength, and can be well applied to emission reduction of N2O in tail gas of nitric acid production.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts and relates to a cobalt-based porous aluminum catalyst for catalytic decomposition of N2O in tail gas from nitric acid production, and a preparation method and application thereof. Background Art

[0002] Nitrous oxide (N2O) is currently recognized as the third most potent greenhouse gas, with a warming potential 310 times that of carbon dioxide. It is also the primary contributor to ozone depletion in the stratosphere. Large amounts of N2O emissions are primarily generated by human activities, such as the industrial production of nitric and adipic acid, crop fertilization, and fossil fuel combustion. HNO3, a widely used chemical raw material, is not only used in the production of fertilizers, dyes, explosives, and rubber, but also serves as an oxidant in the production of various fatty acids.

[0003] As one of the most effective methods for eliminating N2O, direct catalytic decomposition has attracted considerable attention from both academia and industry in recent decades, with numerous research results published. Catalysts used for direct catalytic decomposition of N2O can be broadly categorized into three types: precious metal catalysts, metal oxide catalysts, and molecular sieve catalysts.

[0004] Chinese patent CN117563580A discloses a method for preparing a composite metal oxide catalyst for decomposing nitrous oxide. The active components of the composite metal oxide catalyst are Ca and Mg. When the N2O content is 4000ppm and the air velocity is controlled at 3000-7000h -1 Under the evaluation conditions, the catalyst can completely decompose N2O at 550°C. Although the catalyst is mainly composed of calcium and is relatively cheap, its actual industrial application requires high reaction temperatures and high energy consumption.

[0005] Chinese patent CN116371413A discloses a Co-based catalyst for the low-temperature and high-efficiency decomposition of nitrous oxide. The catalyst uses cesium-containing nitrate to modify Co3O4. The electron-donating effect of alkali metal cesium is used to reduce the activation energy of the reaction, promote the regeneration of active sites, and thus improve the N2O catalytic decomposition performance of the Co-based catalyst. When the N2O content is 800-1000ppm and the reaction space velocity is 30,000h -1 Under the evaluation conditions, the N2O conversion rate reached 91% at 350°C. However, due to the high price of the cesium element doped in the catalyst, it is not suitable for actual industrial application.

[0006] Chinese patent CN115335135A discloses a method for combined removal of NO from industrial waste gas. xand N2O. The method not only requires installing a large and complex reactor at the tail gas emission outlet, but also requires continuously adding a certain amount of NH3 as a reducing agent in the exhaust gas to catalytically decompose N2O with the aid of the reducing agent. The additional reducing agent not only significantly increases the cost of industrial application, but also has the risk of escaping unreacted NH3, causing secondary pollution.

[0007] Chinese patent CN201410174954.4 discloses a high-temperature catalyst for catalytic decomposition of N2O and a preparation method thereof. The catalyst disclosed in the patent uses an impregnation method to load active components on the outer surface of the carrier, which is easy to cause the active components to aggregate on the surface of the carrier at high temperatures. At the same time, in actual application, the scouring of high-speed gas flow of tail gas is easy to cause the loss of active components, thereby greatly reducing the service life of the catalyst.

[0008] In summary, the current N2O decomposition catalyst still has problems such as the need to improve catalytic activity, stability, and resistance to impurity gases, complex preparation process, and high industrial application cost. Therefore, developing a high-performance and low-cost catalyst for catalytic decomposition of N2O at low temperatures has very important practical significance for realizing the emission reduction of N2O in tail gas of nitric acid production and protecting the human living environment. SUMMARY

[0009] Therefore, the purpose of the present application is to overcome the shortcomings of the prior art and provide an easy-to-implement and efficient catalyst preparation method. Unlike the conventional research approach of loading active components by selecting a carrier combined with an impregnation method or modifying by a single metal additive, the present application modifies the active components by co-doping with metals and non-metals, and starts from the combination of catalyst preparation and molding, to prepare a high-performance Co-F-K / Al2O3 catalyst through a relatively simple process.

[0010] To achieve the above-mentioned purpose, the technical solutions of the present application are as follows:

[0011] In one aspect, the present application provides a cobalt-based-porous aluminum catalyst for catalytic decomposition of N2O in tail gas of nitric acid production. The catalyst uses Al2O3 as a carrier, Co3O4 as an active component, and KF and K2O as additives. The mass percentage of each component in the catalyst is as follows: Co3O4: 43.0% to 60.0%, KF: 1.0% to 5.0%, K2O: 0.5% to 2.0%, and Al2O3: 33.0% to 50.0%.

[0012] In another aspect, the present application provides a preparation method of the cobalt-based-porous aluminum catalyst as described above, which includes the following steps:

[0013] Step 1: disperse pseudo-boehmite in deionized water and fully stir to obtain a pseudo-boehmite dispersion liquid;

[0014] Step 2: add a cobalt salt and a fluorine salt to the pseudo-boehmite dispersion liquid to obtain a suspension liquid;

[0015] Step 3: at a certain temperature, dropwise add an aqueous potassium salt solution to the suspension liquid to perform a precipitation reaction, while fully stirring, and stop dropping the potassium salt solution and stirring when the mixture reaches a specific pH value;

[0016] Step 4: perform suction filtration and washing on the mixture, and control the pH of the filtrate;

[0017] Step 5: dry, calcine, and shape the obtained filter cake to obtain the catalyst.

[0018] Further, the pseudo-boehmite in Step 1 is one or more of hydrated aluminum oxide [Al2O3·nH2O] n = 0.08-0.62, and the mass ratio of deionized water to pseudo-boehmite in the pseudo-boehmite dispersion liquid is 10-25:1.

[0019] Further, the cobalt salt in Step 2 is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt acetate, and cobalt oxalate, the fluorine salt is one or more of sodium fluoride, potassium fluoride, ammonium fluoride, and ammonium hydrogen fluoride, and the molar ratio of the cobalt salt to the fluorine salt is 5-8:1.

[0020] Further, the potassium salt in Step 3 is one or more of potassium carbonate, potassium bicarbonate, and potassium hydroxide, and the molar concentration of the potassium salt is 0.5-1.5 mol / L.

[0021] Further, the certain temperature in Step 3 is 20-80°C, the stirring rate is 300-700 r / min, and the specific pH is 8.5-11.5.

[0022] Further, the pH of the filtrate in Step 4 is controlled to be 7-8.

[0023] Further, the drying temperature in Step 5 is 80-180°C, and the time is 6-24 h; the calcination temperature is 300-700°C, and the time is 0.5-5 h.

[0024] Further, the shaping process in Step 5 is compression shaping or extrusion shaping using a tablet press or an extruder.

[0025] The application further provides an application of the cobalt-based-porous aluminum catalyst as described above or prepared by the preparation method as described above in N2O emission reduction of tail gas in nitric acid production.

[0026] Compared with the prior art, the application has the following beneficial effects:

[0027] (1) Compared with traditional single metal oxide catalysts and composite metal oxide catalysts, the catalytic decomposition temperature of N2O is greatly reduced by co-doping of F, K non-metal elements and metal elements.

[0028] (2) The catalyst perfectly combines preparation and molding, successfully fuses the active component in the Al2O3 carrier at the right time point, greatly simplifies the catalyst preparation process, reduces the catalyst preparation cost, and has good industrial application prospect.

[0029] (3) The catalyst can realize efficient emission reduction of N2O under the conditions of high water vapor, O2 and certain NO2 concentration, has strong anti-impurity gas ability, and has high crushing strength, and can be well applied to the emission reduction of N2O in the tail gas of nitric acid production. DETAILED DESCRIPTION

[0030] In order to facilitate the understanding of the present application, the present application will be described more fully below. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0031] The reagents used in the embodiments of the present application are all from National Pharmaceutical Chemical Reagent Co., Ltd., and are of analytical purity.

[0032] The evaluation device in the embodiments of the present application uses a U.S. Agilent 7820A chromatograph to quantitatively analyze N2O in the tail gas.

[0033] The tablet molding device in the embodiments of the present application uses a TDP-5 single punch tablet press of Shanghai Tianfeng Pharmaceutical Equipment Co., Ltd.

[0034] The extrusion molding device in the embodiments of the present application uses a ZYDJ-30 single screw extruder of Zibo Yuesheng Machinery Co., Ltd.

[0035] Example 1

[0036] Preparation of the catalyst

[0037] First, 2.10 g of pseudo-boehmite ([Al2O3-nH2O]n=0.2) was dispersed in 50 mL of deionized water, and 15.42 g of cobalt nitrate and 0.25 g of ammonium fluoride were dissolved in the above solution. Under vigorous stirring (500 r / min) at 30°C, 0.5 mol / L potassium carbonate solution was added dropwise to adjust the pH to 9. The reaction liquid was filtered, washed, and the pH of the filtrate was controlled to 7. The filter cake was dried at 100°C for 6 h and calcined at 400°C for 3 h (heating rate 4°C / min). Graphite powder with a mass of 2 wt.% of the catalyst was added, mixed thoroughly, and then put into a single-punch tablet machine to form tablets to obtain the catalyst Co-F-K / Al2O3. The mass percentage of each component in the catalyst was: Co3O4: 57%, KF: 1.5%, K2O: 1.5%, and Al2O3: 40%.

[0038] Evaluation of the catalyst

[0039] The above catalyst was sieved and then tested for catalytic performance. The catalyst evaluation conditions were: the raw material gas contained 3000 ppm N2O, the rest was nitrogen, and the space velocity was 10000 h -1 The evaluation device was heated at a rate of 2°C / min, and sampling and online analysis were performed every 10 min. The catalyst evaluation results are shown in Table 1.

[0040] Example 2

[0041] In Example 1, the mass of pseudo-boehmite ([Al2O3-nH2O]n=0.2) was changed to 4.90 g, and the rest of the preparation steps and evaluation conditions were unchanged. The mass percentage of each component in the catalyst was: Co3O4: 47%, KF: 1.5%, K2O: 1.5%, and Al2O3: 50%. The catalyst evaluation results are shown in Table 1.

[0042] Example 3

[0043] In Example 1, the mass of ammonium fluoride was changed to 0.39 g, and the rest of the preparation steps and evaluation conditions were unchanged. The mass percentage of each component in the catalyst was: Co3O4: 57%, KF: 2%, K2O: 1%, and Al2O3: 40%. The catalyst evaluation results are shown in Table 1.

[0044] Example 4

[0045] In Example 1, the pH adjusted by adding potassium carbonate solution was changed to 8.5, and the rest of the preparation steps and evaluation conditions were unchanged. The mass percentage of each component in the catalyst was: Co3O4: 57%, KF: 1%, K2O: 1%, and Al2O3: 41%. The catalyst evaluation results are shown in Table 1.

[0046] Example 5

[0047] The calcination temperature in Example 1 was changed to 600°C. The rest of the preparation steps and evaluation conditions were unchanged. The mass percentage of each component in the catalyst was: Co304: 57%, KF: 1.5%, K2O: 1.5%, Al203: 40%. The catalyst evaluation results are shown in Table 1.

[0048] Example 6

[0049] The forming method in Example 1 was changed to extrusion forming. The specific steps were as follows: 100 g of the catalyst prepared according to Example 1 was added with 1.5 g of sesbania powder and stirred uniformly. After uniform mixing, 50 mL of a 5.0% citric acid aqueous solution was added, and the kneaded mud was put into an extruder for forming. The rest of the preparation steps and evaluation conditions were unchanged. The mass percentage of each component in the catalyst was: Co304: 57%, KF: 1.5%, K2O: 1.5%, Al203: 40%. The catalyst evaluation results are shown in Table 1.

[0050] Example 7

[0051] 5 vol.% H2O, 5 vol.% O2, and 200 ppm NO2 were introduced into the raw material gas. The catalyst prepared according to Example 1 was subjected to water vapor resistance, oxygen resistance, and nitrogen dioxide resistance performance tests. The test results are shown in Table 1.

[0052] Example 8

[0053] 5 vol.% H2O, 5 vol.% O2, and 200 ppm NO2 were introduced into the raw material gas. The reaction furnace temperature was kept constant at 320°C. The catalyst prepared according to Example 1 was subjected to stability tests. The test results are shown in Table 2.

[0054] Comparative Example 1

[0055] 11.85 g of cobalt carbonate was weighed, dried at 80°C for 6 h, and calcined at 400°C for 4 h. The obtained catalyst was tabletted and formed, and after screening, the catalyst was evaluated under the same conditions as in Example 1. The catalyst evaluation results are shown in Table 1.

[0056] Comparative Example 2

[0057] 15.42 g of cobalt nitrate and 0.25 g of ammonium fluoride were dissolved in 50 mL of deionized water, and under intense stirring (500 r / min) at 30°C, 0.5 mol / L ammonium carbonate solution was added dropwise to adjust the pH to 9. The reaction liquid was subjected to suction filtration, washed, and the filtrate pH was controlled to 7. The filter cake was dried at 100°C for 6 h, and the dried solid was calcined in a muffle furnace at 400°C for 3 h (heating rate 4°C / min) to obtain a catalyst. The obtained catalyst was tabletted and formed, and after screening, the catalyst was evaluated under the same conditions as in Example 1. The catalyst evaluation results are shown in Table 1.

[0058] Comparative Example 3

[0059] Take 15.42 g of cobalt nitrate and dissolve in 50 mL of deionized water, under the condition of 30℃ and 500 r / min stirring, add 0.5 mol / L potassium carbonate solution drop by drop to adjust pH to 9. After reaction, the liquid is filtered, washed, and the filtrate pH is controlled to 7. The filter cake is dried at 100℃ for 6 h, and the dried solid is calcined in a muffle furnace at 400℃ for 3 h (heating rate 4℃ / min) to obtain the catalyst. The obtained catalyst is pressed into a tablet, and the catalyst evaluation conditions are the same as in Example 1. The catalyst evaluation results are shown in Table 1.

[0060] Comparative Example 4

[0061] Take 15.42 g of cobalt nitrate and 0.25 g of ammonium fluoride and dissolve in 50 mL of deionized water, under the condition of 30℃ and 500 r / min stirring, add 0.5 mol / L potassium carbonate solution drop by drop to adjust pH to 9. After reaction, the liquid is filtered, washed, and the filtrate pH is controlled to 7. The filter cake is dried at 100℃ for 6 h, and the dried solid is calcined in a muffle furnace at 400℃ for 2 h (heating rate 4℃ / min) to obtain the catalyst. Take 4.9 g of pseudo-boehmite and mix well, then calcine at 400℃ for 1 h (heating rate 4℃ / min), and the obtained catalyst is pressed into a tablet, screened, and then evaluated. The catalyst evaluation conditions are the same as in Example 1. The catalyst evaluation results are shown in Table 1.

[0062] Table 1 - Activity test results

[0063]

[0064] Table 2 - Stability test results

[0065]

[0066] The above description is only to better explain the embodiments of the present application, and is not a limitation thereof. Any modification or equivalent replacement within the spirit and scope of the present application is included in the scope of the present application.

Claims

1. A cobalt-based porous aluminum catalyst for catalytic decomposition of N2O in tail gas from nitric acid production, characterized in that: The catalyst uses Al2O3 as a carrier, Co3O4 as an active component, and KF and K2O as additives. The mass percentages of the components in the catalyst are: Co3O4: 43.0% to 60.0%, KF: 1.0% to 5.0%, K2O: 0.5% to 2.0%, and Al2O3: 33.0% to 50.0%. The preparation method of the catalyst comprises the following steps: Step 1: dispersing pseudo-boehmite in deionized water and stirring thoroughly to obtain a pseudo-boehmite dispersion; Step 2: adding cobalt salt and fluoride salt to the pseudo-boehmite dispersion to obtain a suspension; Step 3: At a certain temperature, add the potassium salt aqueous solution dropwise to the suspension to carry out precipitation reaction while stirring thoroughly. Stop adding the potassium salt solution and stirring when the mixed solution reaches a specific pH value; the specific pH value is 8.5-11.5; Step 4: Filter and wash the mixed solution, and control the pH of the filtrate; Step 5: Drying, calcining and shaping the obtained filter cake to obtain the catalyst.

2. A method for preparing the cobalt-based porous aluminum catalyst according to claim 1, characterized in that: The steps include: Step 1: dispersing pseudo-boehmite in deionized water and stirring thoroughly to obtain a pseudo-boehmite dispersion; Step 2: adding cobalt salt and fluoride salt to the pseudo-boehmite dispersion to obtain a suspension; Step 3: At a certain temperature, add the potassium salt aqueous solution dropwise to the suspension to carry out precipitation reaction while stirring thoroughly. Stop adding the potassium salt solution and stirring when the mixed solution reaches a specific pH value; the specific pH value is 8.5-11.5; Step 4: Filter and wash the mixed solution, and control the pH of the filtrate; Step 5: Drying, calcining and shaping the obtained filter cake to obtain the catalyst.

3. The method for preparing the cobalt-based porous aluminum catalyst according to claim 2, wherein: In step 1, the pseudo-boehmite is one or more hydrated aluminum oxides [Al2O3·nH2O] with n=0.08-0.62, and the mass ratio of deionized water to pseudo-boehmite in the pseudo-boehmite dispersion is 10-25:

1.

4. The method for preparing a cobalt-based porous aluminum catalyst according to claim 2, wherein: In step 2, the cobalt salt is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt acetate and cobalt oxalate, the fluoride salt is one or more of sodium fluoride, potassium fluoride, ammonium fluoride and ammonium bifluoride, and the molar ratio of the cobalt salt to the fluoride salt is 5 to 8:

1.

5. The method for preparing the cobalt-based porous aluminum catalyst according to claim 2, wherein: In step 3, the potassium salt is one or more of potassium carbonate, potassium bicarbonate, and potassium hydroxide, and the molar concentration of the potassium salt is 0.5 to 1.5 mol / L.

6. The method for preparing a cobalt-based porous aluminum catalyst according to claim 2, wherein: In step 3, the predetermined temperature is 20-80° C., and the stirring speed is 300-700 r / min.

7. The method for preparing a cobalt-based porous aluminum catalyst according to claim 2, wherein: In step 4, the pH of the filtrate is controlled to be 7-8.

8. The method for preparing a cobalt-based porous aluminum catalyst according to claim 2, wherein: In step 5, the drying temperature is 80-180 °C and the time is 6-24 h; the roasting temperature is 300-700 °C and the time is 0.5-5 h.

9. The method for preparing a cobalt-based porous aluminum catalyst according to claim 2, wherein: The molding process in step 5 is compression molding or extrusion molding using a tablet press or an extruder.

10. Use of the cobalt-based porous aluminum catalyst according to claim 1 or the cobalt-based porous aluminum catalyst prepared by the preparation method according to any one of claims 2 to 9 in reducing N2O emissions from tail gas in nitric acid production.

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