Composite oxide low-temperature denitration catalyst, and preparation method and application thereof

Abstract

The application belongs to the technical field of denitration, and particularly discloses a composite oxide low-temperature denitration catalyst, a preparation method and application thereof; the composite oxide low-temperature denitration catalyst with a nano-shell structure is prepared through layer-by-layer assembly; the catalyst can efficiently catalyze in-situ reduction of NO by CO at a relatively low temperature (250-500 DEG C), realizes synchronous removal of CO and NO in waste incineration flue gas, achieves the purpose of "waste treatment by waste", and the denitration rate is almost 100%.

Description

Technical Field

[0001] This invention relates to the field of denitrification technology, and in particular to a composite oxide low-temperature denitrification catalyst, its preparation method, and its application. Background Technology

[0002] Waste-to-energy incineration, as an economical and efficient solid waste treatment technology, features volume reduction, harmlessness, and resource recovery, and has gradually become one of the main methods for treating municipal solid waste. However, with the continuous increase in the processing capacity of waste-to-energy incineration plants, the emission of nitrogen oxides (NOx) in the flue gas has been increasing year by year. NOx in the flue gas from municipal solid waste incineration is mainly composed of NO, accounting for 95%.

[0003] Nitrogen oxides (NOx), as one of the major air pollutants, are a major contributor to a series of environmental problems, including acid rain, photochemical pollution, ozone layer depletion, and the greenhouse effect. Controlling NOx emissions has become a mandatory environmental requirement for waste-to-energy plants. Current denitrification technologies can be categorized into selective non-catalytic reduction (SNCR) and selective catalytic reduction (NH3-SCR) technologies, depending on whether a catalyst is used. Both technologies use NH3 as a reducing agent. This introduces an external reducing agent, increasing equipment investment and operating costs; furthermore, the escape of NH3 during operation can lead to new secondary pollution.

[0004] Patent application CN202311508800.X discloses an SCR denitrification system using CO as a reducing agent, its application, and an SCR denitrification method, belonging to the field of flue gas purification technology. The SCR denitrification system includes an SCR denitrification reactor, the interior of which comprises a reduction-storage double-layer catalyst, distributed in a multi-ringed pattern. It also discloses an SCR denitrification method using CO as a reducing agent, employing the aforementioned CO-based SCR denitrification system. This method and system can significantly improve the deactivation problem of CO-SCR denitrification catalysts and have broad application prospects in the field of industrial flue gas purification with high CO / NO ratios.

[0005] However, the denitrification rate of the aforementioned catalysts is poor, and sulfur dioxide in the flue gas from municipal solid waste incineration can easily poison the catalysts. Traditional catalysts also exhibit low NO conversion rates, high ammonia slip, and susceptibility to sulfur dioxide poisoning at low temperatures. Therefore, how to remove NOx from flue gas without altering the existing process, especially NOx removal from low-temperature flue gas containing a certain amount of sulfur, has become a bottleneck problem in current environmental pollutant control. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a composite oxide low-temperature denitrification catalyst, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention is implemented according to the following technical solution: One objective of this invention is to provide a method for preparing a composite oxide low-temperature denitration catalyst, comprising the following steps: S1. Take 0.86 mL of tetraethyl silicate, 4.3 mL of deionized water, 23 mL of anhydrous ethanol and 0.46 mL of ammonia water and mix them evenly. After stirring for 4 h, centrifuge and separate the precipitate. Wash the precipitate with anhydrous ethanol to obtain SiO2 nanospheres. Then disperse the obtained SiO2 nanospheres in 5 mL of anhydrous ethanol and sonicate for 15 min to obtain solution A. S2. Take 0.2 g of hydroxypropyl cellulose, 95 mL of anhydrous ethanol and 0.48 mL of deionized water and mix them evenly to prepare solution B. Pour the above solution A into solution B and disperse it by ultrasonication to prepare solution C. S3. Take 4 mL of tetrabutyl titanate and 18 mL of anhydrous ethanol and mix them evenly to prepare solution D; take 5 mL of anhydrous ethanol and 0.284 g of copper nitrate trihydrate and 0.41 g of chloroiridic acid and mix them evenly to prepare solution E; take solution D and solution E and add them dropwise to solution C, and react them at 85℃ and 900 r / min for 2 h. S4. After the reaction is complete, centrifuge to separate the precipitate, wash it with anhydrous ethanol, redisperse it in 20 mL of deionized water, add 4 mL of NaOH solution to the solution, and stir for 6 h. S5. The mixture obtained in step S4 above is centrifuged to separate the precipitate, and then the precipitate is washed with deionized water and anhydrous ethanol. After that, the washed precipitate is dispersed in deionized water, 1 mmol of hydrochloric acid is added, and the mixture is stirred for 30 min to acidify the sample. After acidification, the precipitate is separated by centrifugation, washed with deionized water and ethanol, vacuum dried for 12 h, and then calcined under a protective gas atmosphere to obtain the composite oxide low-temperature denitration catalyst.

[0008] Preferably, the concentration of the NaOH solution is 2.5 mol / L.

[0009] Preferably, the protective gas is nitrogen.

[0010] Preferably, the calcination temperature is 650°C and the calcination time is 2 hours.

[0011] The second objective of this invention is to provide a low-temperature denitrification catalyst for composite oxides prepared by the above method.

[0012] The third objective of this invention is to provide an application of a composite oxide low-temperature denitrification catalyst in the simultaneous purification of CO and NO in flue gas from municipal solid waste incineration.

[0013] Compared with existing technologies, this invention has prepared a low-temperature denitrification catalyst with a nano-shell structure composite oxide through layer-by-layer assembly. This catalyst can efficiently catalyze the in-situ reduction of NO from CO at a relatively low temperature (250-500℃), achieving the simultaneous removal of CO and NO from the flue gas of municipal solid waste incineration, thus achieving the goal of "treating waste with waste", and the denitrification rate is almost 100%. Attached Figure Description

[0014] Figure 1 The image shows a scanning electron microscope (SEM) image of the nanoshell-structured composite oxide low-temperature denitration catalyst prepared in Example 1.

[0015] Figure 2 This is a flowchart of a fixed-bed reactor. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0017] Unless otherwise specified, all raw materials used in the following examples are commercially available. The following examples exemplify the preparation process of several composite oxide low-temperature denitration catalyst IrCuTiOx samples.

[0018] Example 1:

[0019] 1) Take 0.86 mL of tetraethyl silicate, 4.3 mL of deionized water, 23 mL of anhydrous ethanol and 0.46 mL of ammonia water and mix them evenly. After stirring for 4 h, centrifuge and separate the precipitate. Wash the precipitate with anhydrous ethanol to obtain SiO2 nanospheres. Then disperse the obtained SiO2 nanospheres in 5 mL of anhydrous ethanol and sonicate for 15 min to obtain solution A. 2) Mix 0.2 g of hydroxypropyl cellulose, 95 mL of anhydrous ethanol and 0.48 mL of deionized water evenly to prepare solution B. Pour the above solution A into solution B and disperse by ultrasonication to prepare solution C. 3) Take 4 mL of tetrabutyl titanate and 18 mL of anhydrous ethanol and mix them evenly to prepare solution D; take 5 mL of anhydrous ethanol and 0.284 g of copper nitrate trihydrate and 0.41 g of chloroiridic acid and mix them evenly to prepare solution E; take solution D and solution E and add them dropwise to solution C, and react them at 85℃ and 900 r / min for 2 h. 4) After the reaction is complete, centrifuge to separate the precipitate, wash it with anhydrous ethanol, redisperse it in 20 mL of deionized water, add 4 mL of 2.5 mol / L NaOH solution to the solution, and stir for 6 h. 5) The precipitate was separated by centrifugation and then washed with deionized water and anhydrous ethanol. The sample was then dispersed in deionized water, and 1 mmol of hydrochloric acid was added. The mixture was stirred for 30 min to acidify the sample. After acidification, the precipitate was separated by centrifugation, washed with deionized water and ethanol, vacuum dried for 12 h, and then calcined at 650 °C for 2 h under a nitrogen atmosphere to obtain denitrification catalyst sample 1. The electron micrograph of the prepared denitrification catalyst sample 1 is shown below. Figure 1 As shown, by Figure 1 It can be seen that the prepared catalyst has a nanoshell structure with an outer diameter of about 120 nm, an inner diameter of about 80 nm, and a wall thickness of 20 nm.

[0020] Comparative Example 1 1) Take 0.86 mL of tetraethyl silicate, 4.3 mL of deionized water, 23 mL of anhydrous ethanol and 0.46 mL of ammonia water and mix them evenly. After stirring for 4 h, centrifuge and separate the precipitate. Wash the precipitate with anhydrous ethanol to obtain SiO2 nanospheres. Then disperse the obtained SiO2 nanospheres in 5 mL of anhydrous ethanol and sonicate for 15 min to obtain solution A. 2) Mix 0.2 g of hydroxypropyl cellulose, 95 mL of anhydrous ethanol and 0.48 mL of deionized water evenly to prepare solution B. Pour the above solution A into solution B and disperse by ultrasonication to prepare solution C. 3) Take 4 mL of tetrabutyl titanate and 18 mL of anhydrous ethanol and mix them evenly to prepare solution D; take 5 mL of anhydrous ethanol and 0.284 g of copper nitrate trihydrate and mix them evenly to prepare solution E; take solution D and solution E and add them dropwise to solution C, and react them at 85℃ and 900 r / min for 2 h. 4) After the reaction is complete, centrifuge to separate the precipitate, wash it with anhydrous ethanol, redisperse it in 20 mL of deionized water, add 4 mL of 2.5 mol / L NaOH solution to the solution, and stir for 6 h. 5) After etching, the precipitate was separated by centrifugation and then washed with deionized water and anhydrous ethanol. The sample was then dispersed in deionized water, 1 mmol of hydrochloric acid was added, and the mixture was stirred for 30 min to acidify the sample. After acidification, the precipitate was separated by centrifugation, washed with deionized water and ethanol, vacuum dried for 12 h, and then calcined at 650 °C for 2 h under a nitrogen atmosphere to obtain denitrification catalyst sample 2.

[0021] NO and CO removal rates were evaluated using a fixed-bed reactor consisting of a quartz tube reactor, a temperature control system, and a gas path regulation system. The detailed flow chart of the reaction system and the specific gas path are as follows: Figure 2As shown in the diagram. Each reactant gas, after being regulated by a pressure regulator and flow meter, enters the mixer at a set flow rate, where it is thoroughly mixed before entering the reactor. After the reaction, the gas is split into two streams: one stream enters a flue gas analyzer (Testo 350, Germany) for online analysis of its composition, and the other stream is discharged. The composition and content of the reacted gas are analyzed online using a flue gas analyzer (Testo 350, Germany). The technical specifications of the flue gas analyzer used are shown in Table 1.

[0022] Table 1. Main Technical Specifications of Testo 350 Multi-Component Flue Gas Analyzer ; Denitrification catalyst sample 1 and denitrification catalyst sample 2 were pressed into tablets and sieved to obtain 40-60 mesh catalysts. 0.5 g of the catalyst was weighed and added to the reactor. CO was first introduced to raise the reactor temperature to 500℃ and hold for 2 hours to pretreat the catalyst. After pretreatment, heating was stopped, and the reaction temperature was allowed to drop below 100℃. Simulated gas was obtained by adjusting the flow rates of each gas stream using a flow meter: 500 ppm NO, 5000 ppm CO, 0.25% O2. The background gas was nitrogen, and the reaction space velocity was 60000 h⁻¹. -1 Start the program to raise the temperature to 250℃ and 500℃ respectively at 10℃ / min, keep the temperature constant for 30min, and read the NO and CO concentrations at the reactor outlet; calculate the denitrification rate according to the following formula (1).

[0023] η NO =(C in -C out ) / C in × 100% (1) NO and CO undergo a redox reaction under the action of a catalyst, converting into N2 and CO2; the denitrification rates are shown in Table 2.

[0024] Table 2 ; As shown in Table 2, the composite oxide low-temperature denitrification catalyst prepared by this invention can catalyze the in-situ reduction of NO from CO at a relatively low temperature (250-500℃), achieving simultaneous removal of CO and NO, thus achieving the goal of "treating waste with waste", and the denitrification rate is almost 100%.

[0025] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite oxide low-temperature denitration catalyst, characterized in that, Includes the following steps: S1. Take 0.86 mL of tetraethyl silicate, 4.3 mL of deionized water, 23 mL of anhydrous ethanol and 0.46 mL of ammonia water and mix them evenly. After stirring for 4 h, centrifuge and separate the precipitate. Wash the precipitate with anhydrous ethanol to obtain SiO2 nanospheres. Then disperse the obtained SiO2 nanospheres in 5 mL of anhydrous ethanol and sonicate for 15 min to obtain solution A. S2. Take 0.2 g of hydroxypropyl cellulose, 95 mL of anhydrous ethanol and 0.48 mL of deionized water and mix them evenly to prepare solution B. Pour the above solution A into solution B and disperse it by ultrasonication to prepare solution C. S3. Take 4 mL of tetrabutyl titanate and 18 mL of anhydrous ethanol and mix them evenly to prepare solution D; take 5 mL of anhydrous ethanol and 0.284 g of copper nitrate trihydrate and 0.41 g of chloroiridic acid and mix them evenly to prepare solution E; take solution D and solution E and add them dropwise to solution C, and react them at 85℃ and 900 r / min for 2 h. S4. After the reaction is complete, centrifuge to separate the precipitate, wash it with anhydrous ethanol, redisperse it in 20 mL of deionized water, add 4 mL of NaOH solution to the solution, and stir for 6 h. S5. The mixture obtained in step S4 above is used to separate the precipitate using a centrifuge, and then the precipitate is washed with deionized water and anhydrous ethanol. The washed precipitate was then dispersed in deionized water, 1 mmol of hydrochloric acid was added, and the mixture was stirred for 30 min to acidify the sample. After acidification, the precipitate was separated by centrifugation, washed with deionized water and ethanol, vacuum dried for 12 h, and then calcined under a protective gas atmosphere to obtain the composite oxide low-temperature denitration catalyst.

2. The preparation method of the composite oxide low-temperature denitration catalyst according to claim 1, characterized in that: The concentration of the NaOH solution is 2.5 mol / L.

3. The preparation method of the composite oxide low-temperature denitration catalyst according to claim 1, characterized in that: The protective gas is nitrogen.

4. The preparation method of the composite oxide low-temperature denitration catalyst according to claim 1, characterized in that: The calcination temperature is 650℃ and the calcination time is 2 hours.

5. A composite oxide low-temperature denitrification catalyst prepared by the method according to any one of claims 1-4.

6. The application of the composite oxide low-temperature denitrification catalyst as described in claim 5 in the simultaneous purification of CO and NO in flue gas from municipal solid waste incineration.

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