Carbon-based catalyst for low-temperature catalytic oxidation of no and method for preparing the same

Abstract

The application belongs to the technical field of air pollution control, and particularly relates to a NO low-temperature catalytic oxidation carbon-based catalyst and a preparation method thereof. The preparation method comprises the following steps: (1) raw material superfine crushing pretreatment: pretreated soft manganese ore, low-rank coal powder and waste charcoal powder are solid-phase ball milled to 1000 meshes or more to obtain crushed raw materials; (2) supercritical treatment: alcohol and alkali are added to the crushed raw materials as catalysts to obtain a mixture, a surfactant is added to the mixture, then supercritical treatment is carried out, and then natural cooling is carried out, so that solid-liquid separation is carried out to obtain solid substances; (3) pyrolysis: the solid substances are placed in a sealed container, heated, and then constant-temperature heat treatment is carried out; (4) plasma modification: the solid substances after constant-temperature treatment are subjected to plasma modification, water washing and drying, and then the NO low-temperature catalytic oxidation carbon-based catalyst is obtained. The application can realize efficient catalytic oxidation and resource conversion of nitrogen oxides at a relatively low temperature.

Description

Technical Field

[0001] This invention belongs to the field of air pollution control technology, specifically relating to a carbon-based catalyst for low-temperature catalytic oxidation of NO and its preparation method. Background Technology

[0002] Coal-fired power plants, steel mills, and petrochemical industries generate large amounts of NO during the combustion of coal, oil, or natural gas. x Currently, most nitrogen oxide purification processes are performed after desulfurization. After semi-dry or wet desulfurization, the SO2 concentration in the flue gas is approximately 30-50 mg / m³. 3 The concentration range is determined, and then a denitrification process is carried out, mostly through NH3-SCR denitrification technology. For the steel sintering industry, on the one hand, it is necessary to burn part of the blast furnace gas to raise the flue gas temperature to above 200℃; on the other hand, it is necessary to continuously introduce the reducing agent NH3, using NH3 as a reducing agent to remove NO. x Catalytic conversion to N2 presents the problem of high overall operating costs and energy consumption. If the flue gas is not heated before undergoing a low-temperature NH3-SCR process, the catalyst's low-temperature catalytic performance will be poor, and the deposition of ammonium nitrate will pose significant safety hazards. Since NO constitutes the majority of nitrogen oxides, based on the above technical bottlenecks and difficulties, there is an urgent need to develop a non-ammonia-consuming NO catalytic oxidation technology. After NO is catalytically oxidized to NO2, it can be further utilized as a resource through absorption by alkaline substances.

[0003] Currently, catalysts used for the catalytic oxidation of NO mainly include activated carbon, molecular sieves, noble metals, and transition metal oxides. Among them, noble metal catalysts exhibit good catalytic activity, but their high cost limits their industrialization. To date, noble metal catalysts, especially Pt catalysts, are typical NO oxidation catalysts, demonstrating excellent catalytic performance. Due to their low cost, high catalytic activity, and stability, metal oxide catalysts have received increasing attention. Modifying noble metal or metal oxide catalysts by doping them with other metal oxides has been proven to improve catalytic activity, and this improvement can be attributed to synergistic effects. Carbon-based catalysts can be used for NO oxidation at room temperature, offering significant technological advantages. Ozone catalytic oxidation technology can rapidly and efficiently convert NO to NO2, but it suffers from drawbacks such as the generation of secondary ozone pollutants and high overall energy consumption.

[0004] In summary, to address the technical challenges of poor low-temperature catalytic activity and poor regeneration performance in existing NO catalytic oxidation, a regenerable low-temperature (<50℃) NO oxidation catalyst has been developed, which has great application prospects and practical value. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a carbon-based catalyst for the low-temperature catalytic oxidation of NO, which can achieve efficient catalytic oxidation and resource conversion of nitrogen oxides at relatively low temperatures. This invention also provides a method for its preparation.

[0006] The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO according to the present invention includes the following steps:

[0007] (1) Pre-treatment of raw material ultrafine crushing: pre-treated soft manganese ore, low-rank coal powder and waste carbon powder are ball-milled to 1000 mesh or more to obtain crushed raw material; the pre-treated soft manganese ore is obtained by ultrasonic washing of the raw soft manganese ore in dilute hydrochloric acid and oxalic acid solutions respectively;

[0008] (2) Supercritical treatment: Methanol and sodium hydroxide are mixed and dissolved to obtain a mixed solution. The mixed solution is added to the crushed raw material to obtain a mixture. The surfactant is added to the mixture and then supercritical treatment is carried out. Then the mixture is cooled naturally. Here, alcohol and alkali are used as catalysts for the reaction. The solvent, alcohol and alkali are separated and recovered to obtain solid substances.

[0009] (3) Pyrolysis: After heating the solid material in a sealed container, heat it at a constant temperature.

[0010] (4) Plasma modification: The solid material after constant temperature treatment is subjected to plasma modification, water washing and drying to obtain the final product.

[0011] Preferably, in step (1), the mass ratio of pretreated soft manganese ore, low-rank coal powder, and waste carbon powder is (3~5):(20~30):(65~77).

[0012] Preferably, in step (1), the pretreated pyrolusite contains the following chemical components: MnO2 60wt.%~65wt.%, Fe2O3 20wt.%~25wt.%, with the remainder being impurity components. The ultrasonic washing conditions are: washing time 10~50min, washing temperature 30~80℃. The waste carbon powder is adsorption saturated carbon powder, more preferably one or more of water treatment saturated waste carbon powder, VOCs adsorption saturated waste carbon powder, and SO2 purification waste carbon powder.

[0013] Preferably, in step (1), the properties of the low-rank coal powder are: air-dried moisture content of 14.0%, air-dried ash content of 11.22%, volatile matter of 39%, and total sulfur content of 1.08%.

[0014] Preferably, in step (2), the alcohol in the catalyst is methanol, the alkali is sodium hydroxide, and the surfactant is N-methylpyrrolidone. The mass fractions of each component in the mixture are as follows: 42%~47% of the crushed raw material, 50% of the alcohol, and 3%~8% of the alkali.

[0015] Preferably, in step (2), the supercritical treatment temperature is 300~340℃, the time is 30~90min, and the atmosphere is nitrogen.

[0016] Preferably, in step (3), the temperature is increased from room temperature to 500~600℃ at a heating rate of 10℃ / min, and the heat treatment time is 6~9h.

[0017] Preferably, in step (4), the plasma treatment conditions are: oxygen concentration 1%~5%, treatment temperature 30~50℃, treatment time 30~60min, and power range 2~10kW.

[0018] Preferably, in step (4), the solid-liquid ratio of water washing is 1:10, and the product is dried at 150°C for 4 hours after water washing.

[0019] The present invention also provides a carbon-based catalyst for low-temperature catalytic oxidation of NO prepared by the above-described preparation method.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. The carbon-based catalyst prepared by the present invention using mechanochemical and supercritical hydrogenation coupling has a high specific surface area and a high proportion of microporous structure. The catalyst of the present invention can achieve efficient catalytic oxidation of nitrogen oxides at low temperatures. The carbon-based material can be recycled after washing and drying. It is suitable for different industries, such as low-temperature catalytic oxidation of nitrogen oxides and resource utilization of nitrates in glass, cement, coking and petrochemical industries.

[0022] 2. The catalyst of this invention can efficiently catalytically oxidize NO in flue gas to NO2 at low temperatures (<50℃), and the oxidized NO2 is converted to NO3 on the catalyst surface. - The form is fixed, and NO3 is fixed. - The carbon-based materials can be recovered and concentrated into the liquid phase through a weakly alkaline solution. The carbon-based materials can be recycled after simple drying, and the resource utilization of nitrates can be realized at the same time. In addition, this invention realizes the upgrading and utilization of low-rank pulverized coal and the resource recycling of waste carbon. It is of great significance for saving coal and biomass resources and the renewable utilization of carbon-based materials.

[0023] 3. Compared with current precious metal catalysts and metal oxide NO oxidation catalysts, the present invention has a lower reaction temperature, higher NO low-temperature conversion rate, and the catalyst can be recycled and regenerated. Compared with ozone catalytic oxidation, the present invention does not generate secondary pollutant ozone, the mass transfer efficiency of NO and O2 catalytic oxidation is much higher than that of NO and O3 oxidation in the liquid phase, and the energy consumption is lower. Attached Figure Description

[0024] Figure 1 This is the pore size distribution curve of the catalyst obtained in Example 1 of the present invention;

[0025] Figure 2 This is the catalyst outlet concentration-reaction time relationship curve obtained in Example 1 of the present invention;

[0026] Figure 3 This is a test graph of the cyclic stability of the catalyst obtained in Example 1 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings and embodiments.

[0028] Unless otherwise specified, all raw materials used in the examples were commercially available.

[0029] Example 1

[0030] The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO includes the following steps:

[0031] (1) Pre-treatment of raw material ultrafine crushing: pre-treated soft manganese ore, low-rank coal powder and waste carbon powder are ball-milled to a mesh size of 1000 or more to obtain crushed raw material; the mass ratio of pre-treated soft manganese ore, low-rank coal powder and waste carbon powder is 4:26:70; the pre-treated soft manganese ore is obtained by ultrasonic washing of the raw soft manganese ore in dilute hydrochloric acid and oxalic acid solutions respectively. The ultrasonic washing conditions are: washing time is 10 min, washing temperature is 80℃, and the mass fraction of dilute hydrochloric acid and oxalic acid solutions is 6%; the pre-treated soft manganese ore includes the following chemical components: MnO2 60wt.%, Fe2O3 20wt.%, the rest are impurity components; the properties of low-rank coal powder are: air-dried basis moisture content is 14.0%, air-dried basis ash content is 11.22%, volatile matter is 39%, and total sulfur content is 1.08%; the waste carbon powder is water-treated saturated waste carbon;

[0032] (2) Supercritical treatment: Methanol and sodium hydroxide are mixed and dissolved to obtain a mixed solution. The mixed solution is added to the crushed raw material to obtain a mixture. The surfactant N-methylpyrrolidone is added to the mixture, and then supercritical treatment is carried out. Then the mixture is cooled naturally, and the solvent is recovered by solid-liquid separation to obtain a solid substance.

[0033] The mass fractions of each component in the mixture are as follows: crushed raw material 42%, methanol 50%, sodium hydroxide 8%, and N-methylpyrrolidone added at 20% of the volume of the mixed solution.

[0034] The supercritical treatment temperature was 300℃, the time was 30 min, and the atmosphere was nitrogen.

[0035] (3) Pyrolysis: The solid material is placed in a sealed container and heated from room temperature to 500℃ at a heating rate of 10℃ / min. The temperature is kept constant for 9 hours.

[0036] (4) Plasma modification: The solid material after constant temperature treatment is subjected to plasma modification, washed with water at a solid-liquid ratio of 1:10, and dried at 150℃ for 4 hours to obtain the final product. The plasma treatment conditions are: oxygen concentration 1%, treatment temperature 30℃, treatment time 60 min, and power range 2kW.

[0037] Example 2

[0038] The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO includes the following steps:

[0039] (1) Pre-treatment of raw material ultrafine crushing: pre-treated soft manganese ore, low-rank coal powder and waste carbon powder are ball-milled to a mesh size of 1000 or more to obtain crushed raw material; the mass ratio of pre-treated soft manganese ore, low-rank coal powder and waste carbon powder is 3:30:77; the pre-treated soft manganese ore is obtained by ultrasonic washing of the raw soft manganese ore in dilute hydrochloric acid and oxalic acid solutions respectively. The ultrasonic washing conditions are: washing time is 30 min, washing temperature is 50℃, and the mass fraction of dilute hydrochloric acid and oxalic acid solutions is 6%; the pre-treated soft manganese ore includes the following chemical components: MnO2 62wt.%, Fe2O3 22wt.%, the rest are impurity components; the properties of low-rank coal powder are: air-dried basis moisture content is 14.0%, air-dried basis ash content is 11.22%, volatile matter is 39%, and total sulfur content is 1.08%; the waste carbon powder is VOCs adsorption saturated waste carbon;

[0040] (2) Supercritical treatment: Methanol and sodium hydroxide are mixed and dissolved to obtain a mixed solution. The mixed solution is added to the crushed raw material to obtain a mixture. The surfactant N-methylpyrrolidone is added to the mixture, and then supercritical treatment is carried out. Then the mixture is cooled naturally, and the solvent is recovered by solid-liquid separation to obtain a solid substance.

[0041] The mass fractions of the mixture are as follows: crushed raw material 47%, methanol 50%, sodium hydroxide 3%, and N-methylpyrrolidone added at 40% of the volume of the mixed solution.

[0042] The supercritical treatment temperature was 320℃, the time was 60 min, and the atmosphere was nitrogen.

[0043] (3) Pyrolysis: The solid material is placed in a sealed container and heated from room temperature to 550°C at a heating rate of 10°C / min. The temperature is kept constant for 7 hours.

[0044] (4) Plasma modification: The solid material after constant temperature treatment is subjected to plasma modification, washed with water at a solid-liquid ratio of 1:10, and dried at 150℃ for 4 hours to obtain the final product. The plasma treatment conditions are: oxygen concentration 3%, treatment temperature 30℃, treatment time 30 min, and power 10kW.

[0045] Example 3

[0046] The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO includes the following steps:

[0047] (1) Pre-treatment of raw material ultrafine crushing: pre-treated soft manganese ore, low-rank coal powder and waste carbon powder are ball-milled to a mesh size of 1000 or more to obtain crushed raw material; the mass ratio of pre-treated soft manganese ore, low-rank coal powder and waste carbon powder is 5:20:65; the pre-treated soft manganese ore is obtained by ultrasonic washing of the raw soft manganese ore in dilute hydrochloric acid and oxalic acid solutions respectively. The ultrasonic washing conditions are: washing time is 50 min, washing temperature is 30℃, and the mass fraction of dilute hydrochloric acid and oxalic acid solutions is 6%; the pre-treated soft manganese ore includes the following chemical components: MnO2 65wt.%, Fe2O3 25wt.%, the rest are impurity components; the properties of low-rank coal powder are: air-dried basis moisture content is 14.0%, air-dried basis ash content is 11.22%, volatile matter is 39%, and total sulfur content is 1.08%; the waste carbon powder is SO2 purified waste carbon powder;

[0048] (2) Supercritical treatment: Methanol and sodium hydroxide are mixed and dissolved to obtain a mixed solution. The mixed solution is added to the crushed raw material to obtain a mixture. The surfactant N-methylpyrrolidone is added to the mixture, and then supercritical treatment is carried out. Then the mixture is cooled naturally, and the solvent is recovered by solid-liquid separation to obtain a solid substance.

[0049] The mass fractions of each component in the mixture are as follows: crushed raw material 45%, methanol 50%, sodium hydroxide 5%, and N-methylpyrrolidone added at 20% of the volume of the mixed solution;

[0050] The supercritical treatment temperature was 340℃, the time was 90 min, and the atmosphere was nitrogen.

[0051] (3) Pyrolysis: The solid material is placed in a sealed container and heated from room temperature to 600℃ at a heating rate of 10℃ / min. The temperature is kept constant for 6 hours.

[0052] (4) Plasma modification: The solid material after constant temperature treatment is subjected to plasma modification, washed with water at a solid-liquid ratio of 1:10, and dried at 150℃ for 4 hours to obtain the final product. The plasma treatment conditions are: oxygen concentration 5%, treatment temperature 50℃, treatment time 60 min, and power 2kW.

[0053] The catalyst obtained in Example 1 was subjected to adsorption-desorption tests, and the pore size distribution curve was obtained as follows: Figure 1 As shown, Figure 1 This indicates that the catalyst of the present invention has a concentrated pore size distribution, with most pore sizes ranging from 2 to 5 nm, and the material is mainly mesoporous, which is beneficial for adsorption.

[0054] The catalyst obtained in Example 1 was subjected to NO purification and NO cycling tests (five cycles) under the following conditions: NO, 400 ppm; O2, 10 wt.%; GHSV, 300 h. -1 Relative humidity: 90%; Temperature: 48℃; Gas volumetric flow rate: 1 L / min. The outlet concentration-reaction time relationship curve is shown below. Figure 2 After five cycles, the bar chart showing the change in cumulative NO breakthrough capacity with the number of reactions is shown below. Figure 3 .

[0055] Depend on Figure 2 It can be seen that the catalyst of this invention has high catalytic activity and a long overall life cycle, which can reach more than 380 hours.

[0056] Depend on Figure 3 It can be seen that the cumulative NO penetration capacity values ​​are similar under different cycles, indicating that the catalyst's NO purification capacity does not significantly decrease during multiple cycles, which demonstrates the excellent cycle stability of the catalyst of this invention.

Claims

1. A method for preparing a carbon-based catalyst for the low-temperature catalytic oxidation of NO, characterized in that, Includes the following steps: (1) Pre-treatment of raw material ultrafine crushing: pre-treated soft manganese ore, low-rank coal powder and waste carbon powder are ball-milled to 1000 mesh or more to obtain crushed raw material; Pretreated pyrolusite is obtained by ultrasonically washing the raw pyrolusite ore in dilute hydrochloric acid and oxalic acid solutions, respectively. (2) Supercritical treatment: alcohol and alkali are added to the crushed raw material to obtain a mixture, surfactant is added to the mixture, and then supercritical treatment is carried out. After natural cooling, solid substances are obtained after solid-liquid separation. (3) Pyrolysis: After heating the solid material in a sealed container, heat it at a constant temperature. (4) Plasma modification: The solid material after constant temperature treatment is subjected to plasma modification, water washing and drying to obtain the product; The surfactant is N-methylpyrrolidone; the low temperature is <50℃.

2. The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO according to claim 1, characterized in that, In step (1), the mass ratio of pretreated soft manganese ore, low-rank coal powder, and waste carbon powder is (3~5):(20~30):(65~77).

3. The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO according to claim 1, characterized in that, In step (1), the pretreated pyrolusite contains the following chemical components: MnO2 60wt.%~65wt.%, Fe2O3 20wt.%~25wt.%, and the remainder are impurity components; ultrasonic washing conditions: washing time is 10~50min, and washing temperature is 30~80℃.

4. The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO according to claim 1, characterized in that, In step (2), the alcohol in the catalyst is methanol and the alkali is sodium hydroxide. The mass fractions of each component in the mixture are as follows: crushed raw material 42%~47%, alcohol 50%, alkali 3%~8%.

5. The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO according to claim 1, characterized in that, In step (2), the supercritical treatment temperature is 300~340℃, the time is 30~90min, and the atmosphere is nitrogen.

6. The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO according to claim 1, characterized in that, In step (3), the temperature is increased from room temperature to 500~600℃ at a heating rate of 10℃ / min, and the heat treatment time is 6~9h.

7. The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO according to claim 1, characterized in that, In step (4), the plasma treatment conditions are: oxygen concentration 1%~5%, treatment temperature 30~50℃, treatment time 30~60min, and power range 2~10kW.

8. The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO according to claim 1, characterized in that, In step (4), the solid-liquid ratio of water washing is 1:10, and after water washing, the product is dried at 150°C for 4 hours.

9. A carbon-based catalyst for low-temperature catalytic oxidation of NO prepared by the preparation method according to any one of claims 1-8.

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