Cobalt-based porous aluminum catalyst for catalytic decomposition of N2O in nitric acid production tail gas as well as preparation method and application of cobalt-based porous aluminum catalyst

Abstract

The invention belongs to the technical field of catalysts and relates to a cobalt-based porous aluminum catalyst for catalytic decomposition of N2O in nitric acid production tail gas as well as a preparation method and application of the cobalt-based porous aluminum catalyst. The catalyst takes Al2O3 as a carrier, Co3O4 as an active component and KF and K2O as auxiliaries, and the preparation method comprises the following steps: firstly, uniformly dispersing a certain amount of cobalt salt, villiaumite and pseudo-boehmite in deionized water to form a turbid liquid, regulating the pH value of the turbid liquid to a certain range by taking potassium salt as a precipitant to obtain a corresponding precipitate mixture, and then carrying out suction filtration and washing on the precipitate. And drying, roasting and forming the obtained filter cake to obtain the catalyst. The preparation method is simple, and industrial amplification is easy to realize. The prepared catalyst can realize direct catalytic decomposition of N2O at a low temperature, has excellent O2 resistance, NO2 resistance and water vapor resistance, has high crushing strength, and can be well applied to emission reduction of N2O in nitric acid production tail gas.

Description

Technical Field

[0001] The 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 largest greenhouse gas, with an atmospheric warming potential 310 times that of carbon dioxide. It is also the main substance that depletes ozone in the stratosphere. Large amounts of N2O emissions are mainly generated by human production activities, such as industrial production of nitric acid and adipic acid, crop fertilization, and fossil fuel combustion. HNO3, as a widely used chemical raw material, can not only be used in the production of fertilizers, dyes, explosives, and rubber manufacturing, but can also be used as an oxidant in the production of a variety of fatty acids. my country is one of the countries with the largest nitric acid production capacity in the world. Nitric acid companies produce a large amount of harmful nitrogen oxides (NO x , N2O). In order to meet the challenges of global climate change, protect the ecological environment, and achieve sustainable development of human society, it is crucial and urgent to adopt appropriate technical means to effectively reduce N2O emissions.

[0003] As one of the most effective methods for eliminating N2O, direct catalytic decomposition has attracted the attention of academia and industry in recent decades, and a large number of research results on direct catalytic decomposition of N2O have been widely reported. Catalysts used for direct catalytic decomposition of N2O can be roughly divided into three categories: 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 achieve complete decomposition of N2O at 550°C. Although the main component of the catalyst is Ca and the cost is relatively low, the reaction temperature required in actual industrial applications is high and the energy consumption is large.

[0005] Chinese patent CN116371413A discloses a Co-based catalyst for decomposing nitrous oxide at low temperature and high efficiency. The catalyst uses cesium-containing nitrate to modify Co3O4, and utilizes the electron-donating effect of alkali metal cesium 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 30000h -1Under the evaluation conditions, the conversion rate of N2O reached 91% at 350°C. However, due to the high price of cesium doped in the catalyst, it is not suitable for actual industrial application.

[0006] Chinese patent CN115335135A discloses a method for combined removal of NO in industrial waste gas. x The method not only requires the installation of a large and complex reactor at the exhaust outlet, but also requires the continuous addition of a certain amount of NH3 as a reducing agent to the exhaust gas to catalytically decompose N2O with the assistance of the reducing agent. The additional reducing agent not only greatly increases the cost of industrial application, but also has the risk of escaping of incompletely reacted NH3, causing secondary pollution.

[0007] Chinese patent CN201410174954.4 discloses a catalyst for high-temperature catalytic decomposition of N2O and its preparation method. The catalyst described in the patent uses an impregnation method to load the active components on the outer surface of the carrier, which easily leads to the aggregation of the active components on the surface of the carrier at high temperatures; at the same time, in actual applications, the flushing of the high-space-speed airflow of the exhaust gas can easily cause the loss of active components, thereby greatly reducing the service life of the catalyst.

[0008] In summary, the current N2O decomposition catalysts still have many problems such as catalytic activity, stability, and resistance to impurity gases, which need to be improved, complex preparation processes, and high costs for industrial applications. Therefore, developing a high-performance, low-cost catalyst for catalytic decomposition of N2O at low temperatures is of great practical significance for achieving N2O emission reduction in nitric acid production tail gas and protecting the human living environment. Summary of the invention

[0009] In view of this, the purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide an easy-to-implement and efficient catalyst preparation method. This method is different from the conventional research ideas of loading active components by selecting a carrier combined with an impregnation method, or modifying by a single metal additive. Instead, on the one hand, the active components are modified by co-doping with metals and non-metals, and on the other hand, a high-performance Co-FK / Al2O3 catalyst is prepared through a relatively simple process by combining catalyst preparation and molding.

[0010] To achieve the above object, the technical solution of the present invention is as follows:

[0011] On one hand, the present invention provides a cobalt-based porous aluminum catalyst for catalytic decomposition of N2O in tail gas from nitric acid production, wherein 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%.

[0012] Another aspect of the present invention provides a method for preparing the cobalt-based porous aluminum catalyst as described above, comprising the following steps:

[0013] Step 1: dispersing pseudo-boehmite in deionized water and stirring thoroughly to obtain a pseudo-boehmite dispersion;

[0014] Step 2: Adding cobalt salt and fluoride salt to the pseudo-boehmite dispersion to obtain a suspension;

[0015] Step 3: at a certain temperature, adding a potassium salt aqueous solution dropwise into the suspension to perform a precipitation reaction, while fully stirring, and stopping the addition of the potassium salt solution and stirring when the mixed solution reaches a specific pH value;

[0016] Step 4: Filter and wash the mixed solution, and control the pH of the filtrate;

[0017] Step 5: Drying, calcining and molding the obtained filter cake to obtain the catalyst.

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

[0019] Furthermore, 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.

[0020] Furthermore, 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.

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

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

[0023] Furthermore, in step 5, the drying temperature is 80-180° C., and the time is 6-24 hours; the roasting temperature is 300-700° C., and the time is 0.5-5 hours.

[0024] Furthermore, the molding process in step 5 is compression molding or extrusion molding using a tablet press or an extruder.

[0025] Another aspect of the present invention provides the use of the cobalt-based porous aluminum catalyst as described above or the cobalt-based porous aluminum catalyst prepared by the preparation method as described above in reducing N2O emissions from tail gas in nitric acid production.

[0026] Compared with the prior art, the present invention 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 with F, K non-metallic elements and metal elements.

[0028] (2) The catalyst perfectly combines preparation and molding, successfully integrating the active components into the Al2O3 carrier at the right time, greatly simplifying the catalyst preparation process, reducing the catalyst preparation cost, and having good industrial application prospects.

[0029] (3) The catalyst can achieve efficient N2O emission reduction under conditions of high water vapor, O2 and certain NO2 concentrations, exhibits strong resistance to impurity gases, and has high crushing strength, and can be well applied to the reduction of N2O emissions in the tail gas of nitric acid production. DETAILED DESCRIPTION

[0030] In order to facilitate the understanding of the present invention, the present invention will be described more fully below. However, the present invention can be implemented 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 understanding of the disclosure of the present invention more thorough and comprehensive.

[0031] The reagents used in the examples of the present invention were all from Sinopharm Chemical Reagent Co., Ltd. and were of analytical grade.

[0032] In the embodiment of the present invention, the evaluation device uses an American Agilent 7820A chromatograph to perform quantitative analysis on N2O in the tail gas.

[0033] In the embodiment of the present invention, the tablet forming device adopts the TDP-5 single punch tablet press of Shanghai Tianfeng Pharmaceutical Equipment Co., Ltd.

[0034] In the embodiment of the present invention, the extrusion forming device adopts the ZYDJ-30 single screw extruder of Zibo Yuecheng Machinery Co., Ltd.

[0035] Example 1

[0036] Catalyst preparation

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

[0038] Catalyst Evaluation

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

[0040] Example 2

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

[0042] Example 3

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

[0044] Example 4

[0045] The pH value of the catalyst was adjusted to 8.5 by dropping potassium carbonate solution in Example 1, and the other preparation steps and evaluation conditions remained unchanged. The mass percentages of the components in the catalyst were: Co3O4: 57%, KF: 1%, K2O: 1%, 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 other preparation steps and evaluation conditions remained unchanged. The mass percentages of the components in the catalyst were: Co3O4: 57%, KF: 1.5%, K2O: 1.5%, Al2O3: 40%. The catalyst evaluation results are shown in Table 1.

[0048] Example 6

[0049] The molding method in Example 1 is changed to extrusion molding, and the specific steps are as follows: prepare 100g of catalyst according to Example 1, add 1.5g of sesbania powder and stir evenly. After mixing evenly, add 50mL of citric acid aqueous solution with a mass fraction of 5.0%, knead into a mud ball and put it into an extruder for molding. The remaining preparation steps and evaluation conditions remain unchanged. The mass percentages of each component in the catalyst are: Co3O4: 57%, KF: 1.5%, K2O: 1.5%, Al2O3: 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 gas, and the catalyst prepared in Example 1 was tested for its resistance to water vapor, oxygen, and nitrogen dioxide. 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 gas, and the temperature of the reactor was kept constant at 320° C. The catalyst prepared in Example 1 was tested for stability. 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 formed into tablets, sieved, and evaluated. The catalyst evaluation conditions were the same as those in Example 1. The catalyst evaluation results are shown in Table 1.

[0056] Comparative Example 2

[0057] Weigh 15.42g of cobalt nitrate and 0.25g of ammonium fluoride and dissolve them in 50mL of deionized water. Under vigorous stirring at 30°C (500r / min), add 0.5mol / L of ammonium carbonate solution drop by drop to adjust the pH to 9. The liquid after the reaction is filtered and washed, and the pH of the filtrate is controlled to 7. The filter cake is dried at 100°C for 6h, and the dried solid is placed in a muffle furnace at 400°C for 3h (heating rate 4°C / min) to obtain a catalyst. The obtained catalyst is formed into sheets and evaluated after screening. The catalyst evaluation conditions are the same as those in Example 1. The catalyst evaluation results are shown in Table 1.

[0058] Comparative Example 3

[0059] Weigh 15.42g of cobalt nitrate and dissolve it in 50mL of deionized water. Under vigorous stirring at 30°C (500r / min), add 0.5mol / L potassium carbonate solution drop by drop to adjust the pH to 9. The liquid after the reaction is filtered and washed, and the pH of the filtrate is controlled to 7. The filter cake is dried at 100°C for 6h, and the dried solid is placed in a muffle furnace at 400°C for 3h (heating rate 4°C / min) to obtain a catalyst. The obtained catalyst is pressed into tablets, 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] Weigh 15.42g of cobalt nitrate and 0.25g of ammonium fluoride and dissolve them in 50mL of deionized water. Under vigorous stirring at 30°C (500r / min), add 0.5mol / L potassium carbonate solution drop by drop to adjust the pH to 9. The liquid after the reaction is filtered and washed, and the pH of the filtrate is controlled to 7. The filter cake is dried at 100°C for 6h, and the dried solid is placed in a muffle furnace and roasted at 400°C for 2h (heating rate 4°C / min) to obtain a catalyst. Weigh 4.9g of pseudo-boehmite and mix it thoroughly, then roast it again at 400°C for 1h (heating rate 4°C / min), and the obtained catalyst is formed into sheets, sieved and 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 for better explaining the embodiments of the present invention, and is not intended to limit the present invention. Any modification or equivalent substitution that does not depart from the spirit and scope of the present invention shall fall within the scope of the present invention.

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%.

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, adding a potassium salt aqueous solution dropwise into the suspension to perform a precipitation reaction, while fully stirring, and stopping the addition of the potassium salt solution and stirring when the mixed solution reaches a specific pH value; Step 4: Filter and wash the mixed solution, and control the pH of the filtrate; Step 5: Drying, calcining and molding the obtained filter cake to obtain the catalyst.

3. The method for preparing a cobalt-based porous aluminum catalyst according to claim 2, characterized in that: In the step 1, the pseudo-boehmite is one or more hydrated aluminum oxides [Al2O3·nH2O]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, characterized in that: 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, characterized in that: 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, characterized in that: In step 3, the certain temperature is 20-80° C., the stirring rate is 300-700 r / min, and the specific pH is 8.5-11.

5.

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

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