Carbon-based catalyst for NO low-temperature catalytic oxidation and preparation method thereof

Abstract

The invention belongs to the technical field of air pollution control, and particularly relates to a carbon-based catalyst for NO low-temperature catalytic oxidation and a preparation method thereof. Comprising the following steps: (1) raw material ultrafine crushing pretreatment: carrying out solid-phase ball milling on pretreated pyrolusite, low-rank coal powder and waste carbon powder to 1000 meshes or above to obtain crushed raw materials; (2) supercritical treatment: adding alcohol and alkali into the crushed raw materials as catalysts to obtain a mixture, adding a surfactant into the mixture, then carrying out supercritical treatment, then naturally cooling, and carrying out solid-liquid separation to obtain a solid substance; (3) pyrolysis: putting the solid substance into a closed container, heating, and carrying out constant-temperature heat treatment; and (4) plasma modification: carrying out plasma modification on the solid substance subjected to constant-temperature treatment, washing with water, and drying. According to the invention, efficient catalytic oxidation and resource conversion of nitrogen oxides can be realized at a relatively low temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of air pollution control, and in particular relates to a carbon-based catalyst for the low-temperature catalytic oxidation of NO and a preparation method thereof. Background Art

[0002] Coal-fired power plants, steel and petrochemical industries produce a large amount of NO during the combustion of coal, oil or gas. x The current nitrogen oxide purification process is mostly placed in the process after desulfurization. The SO2 concentration in the flue gas after semi-dry or wet desulfurization is about 30~50mg / m 3 The concentration range is then reduced, and the denitrification process is mostly carried out 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 increase the flue gas temperature to above 200℃, and on the other hand, it is necessary to continuously introduce the reducing agent NH3 to use NH3 as a reducing agent to reduce NO x Catalytic conversion to N2 results in high overall operating costs and energy consumption. If the flue gas is directly subjected to the low-temperature NH3-SCR process without heating, the catalyst's low-temperature catalytic performance will be poor, and ammonium nitrate deposition will also pose a significant safety hazard. Because NO accounts for the vast majority of nitrogen oxides, the aforementioned technical bottlenecks and difficulties necessitate the development of a non-ammonia-consuming NO catalytic oxidation technology. After catalytic oxidation of NO to NO2, it can be further recycled through absorption by alkaline substances.

[0003] Currently, the catalysts used for NO catalytic oxidation mainly include activated carbon, molecular sieves, precious metals, and transition metal oxides. Among them, precious metals have good catalytic activity, but their high cost limits their industrialization. So far, precious metal catalysts, especially Pt catalysts, are typical NO oxidation catalysts, showing excellent catalytic performance. Metal oxide catalysts have received increasing attention due to their low cost, high catalytic activity and stability. Modification of precious metal or metal oxide catalysts by doping with other metal oxides has been shown to improve catalytic activity, and the improvement in catalytic activity can be attributed to synergistic effects. Carbon-based catalysts can be used for NO oxidation at room temperature and have good technical advantages. Ozone catalytic oxidation technology can quickly and efficiently convert NO to NO2, but it has disadvantages such as the production of secondary ozone pollutants and high overall energy consumption.

[0004] In summary, in order to address the technical difficulties of poor low-temperature catalytic activity and poor recycling regeneration performance of existing NO catalytic oxidation, a regenerative low-temperature (<50°C) NO oxidation catalyst has been developed, which will have good application prospects and practical value. Summary of the Invention

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

[0006] The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO according to the present invention comprises the following steps: (1) Raw material ultrafine crushing pretreatment: solid phase ball milling of pretreated pyrolusite, low-rank coal powder and waste carbon powder to a size of 1000 mesh or more to obtain crushed raw materials; pretreated pyrolusite is obtained by ultrasonically washing the raw pyrolusite in dilute hydrochloric acid and oxalic acid solutions respectively; (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, a surfactant is added to the mixture, and then supercritical treatment is performed, and then the temperature is naturally lowered. Here, alcohol and alkali serve as catalysts for the reaction, and solid-liquid separation is performed to recover the solvent, alcohol, and alkali to obtain a solid substance; (3) Pyrolysis: placing the solid material in a sealed container and heating it up, then heat treating it at a constant temperature; (4) Plasma modification: The solid material after constant temperature treatment is subjected to plasma modification, water washing, and drying.

[0007] Preferably, in step (1), the mass ratio of pretreated pyrolusite, low-rank coal powder, and waste carbon powder is (3-5): (20-30): (65-77).

[0008] Preferably, in step (1), the pretreated pyrolusite contains the following chemical components: MnO2 60wt.%~65wt.%, Fe2O3 20wt.%~25wt.%, and the rest are impurity components, and the ultrasonic washing conditions are: washing time is 10~50min, and washing temperature is 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.

[0009] Preferably, in step (1), the properties of the low-rank coal powder are: air-dried basis moisture content is 14.0%, air-dried basis ash content is 11.22%, volatile matter content is 39%, and total sulfur content is 1.08%.

[0010] Preferably, in step (2), the alcohol in the catalyst is methanol, the base is sodium hydroxide, and the surfactant is N-methylpyrrolidone, and the mass fractions of the components of the mixture are as follows: 42% to 47% of crushed raw materials, 50% of alcohol, and 3% to 8% of base.

[0011] Preferably, in step (2), the supercritical treatment temperature is 300-340°C, the time is 30-90 minutes, and the atmosphere is nitrogen.

[0012] Preferably, in step (3), the temperature is raised from room temperature to 500-600°C at a heating rate of 10°C / min, and the heat treatment time is 6-9h.

[0013] Preferably, in step (4), the plasma treatment conditions are: oxygen concentration 1% to 5%, treatment temperature 30 to 50° C., treatment time 30 to 60 min, and power range: 2 to 10 kW.

[0014] Preferably, 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 h.

[0015] The present invention also provides a carbon-based catalyst for low-temperature catalytic oxidation of NO prepared by the above preparation method.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The carbon-based catalyst prepared by mechanochemistry and supercritical hydrogenation coupling in the present invention 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 a relatively low temperature. The carbon-based material can be recycled after washing and drying, and is suitable for different industries, such as the low-temperature catalytic oxidation of nitrogen oxides and the resource utilization of nitrates in the glass, cement, coking, and petrochemical industries.

[0017] 2. The catalyst of the present invention can catalyze and oxidize NO in flue gas to NO2 at low temperature (<50℃). At the same time, the oxidized NO2 is converted to NO3 on the catalyst surface. - Fixed in the form of NO3 - The carbon-based materials can be recovered and concentrated into the liquid phase through a weak 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, the present invention realizes the quality improvement of low-grade pulverized coal and the resource recycling of waste carbon, which is of great significance for saving coal resources and biomass resources and the renewable utilization of carbon-based materials.

[0018] 3. Compared with existing noble metal catalysts and metal oxide NO oxidation catalysts, the present invention has a low reaction temperature, a high low-temperature NO conversion rate, and the catalyst can be recycled; compared with the ozone catalytic oxidation method, the present invention does not produce the secondary pollutant ozone, the mass transfer efficiency of the catalytic oxidation of NO and O2 is much higher than the oxidation of NO and O3 in the liquid phase, and the energy consumption is lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the pore size distribution curve of the catalyst obtained in Example 1 of the present invention; Figure 2 This is the catalyst outlet concentration-reaction time relationship curve obtained in Example 1 of the present invention; Figure 3This is a test chart of the cyclic stability of the catalyst obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments.

[0021] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0022] Example 1 The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO comprises the following steps: (1) Raw material ultrafine crushing pretreatment: pretreated pyrolusite, low-rank coal powder and waste carbon powder are solid-phase ball-milled to above 1000 mesh to obtain crushed raw materials; wherein, the mass ratio of pretreated pyrolusite, low-rank coal powder and waste carbon powder is 4:26:70; pretreated pyrolusite is obtained by ultrasonically washing the raw pyrolusite in dilute hydrochloric acid and oxalic acid solutions respectively, and the ultrasonic washing conditions are: washing time is 10 min, washing temperature is 80 ° C, and the mass fraction of dilute hydrochloric acid and oxalic acid solutions is 6%; pretreated pyrolusite includes the following chemical components: MnO2 60wt.%, Fe2O3 20wt.%, and 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%; waste carbon powder is water-treated saturated waste carbon; (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, a surfactant N-methylpyrrolidone is added to the mixture, and then supercritical treatment is performed, and then the temperature is naturally lowered, and the solid-liquid separation is performed to recover the solvent to obtain a solid material; The mass fractions of the components of the mixture are as follows: crushed raw materials 42%, methanol 50%, sodium hydroxide 8%, and N-methylpyrrolidone added in an amount of 20% of the volume of the mixed solution; The supercritical treatment temperature was 300 °C, the time was 30 min, and the atmosphere was nitrogen; (3) Pyrolysis: Place the solid material in a sealed container and heat it from room temperature to 500°C at a heating rate of 10°C / min for 9 hours. (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°C for 4 hours. The plasma treatment conditions are: oxygen concentration 1%, treatment temperature 30°C, treatment time 60 minutes, and power range: 2kW.

[0023] Example 2 The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO comprises the following steps: (1) Raw material ultrafine crushing pretreatment: pretreated pyrolusite, low-rank coal powder and waste carbon powder are solid-phase ball-milled to above 1000 mesh to obtain crushed raw materials; wherein, the mass ratio of pretreated pyrolusite, low-rank coal powder and waste carbon powder is 3:30:77; pretreated pyrolusite is obtained by ultrasonically washing the raw pyrolusite in dilute hydrochloric acid and oxalic acid solutions respectively, and the ultrasonic washing conditions are: washing time is 30 min, washing temperature is 50 ° C, and the mass fraction of dilute hydrochloric acid and oxalic acid solutions is 6%; pretreated pyrolusite includes the following chemical components: MnO2 62wt.%, Fe2O3 22wt.%, and 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%; waste carbon powder is VOCs adsorption saturated waste carbon; (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, a surfactant N-methylpyrrolidone is added to the mixture, and then supercritical treatment is performed, and then the temperature is naturally lowered, and the solid-liquid separation is performed to recover the solvent to obtain a solid material; The mass fractions of the components of the mixture are as follows: 47% of crushed raw materials, 50% of methanol, 3% of sodium hydroxide, and the amount of N-methylpyrrolidone added is 40% of the volume of the mixed solution; The supercritical treatment temperature was 320 °C, the time was 60 min, and the atmosphere was nitrogen; (3) Pyrolysis: The solid material was placed in a sealed container and heated from room temperature to 550°C at a rate of 10°C / min for 7 h. (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°C for 4 hours. The plasma treatment conditions are: oxygen concentration 3%, treatment temperature 30°C, treatment time 30 minutes, and power: 10kW.

[0024] Example 3 The method for preparing the carbon-based catalyst for low-temperature catalytic oxidation of NO comprises the following steps: (1) Raw material ultrafine crushing pretreatment: pretreated pyrolusite, low-rank coal powder and waste carbon powder are solid-phase ball-milled to above 1000 mesh to obtain crushed raw materials; wherein, the mass ratio of pretreated pyrolusite, low-rank coal powder and waste carbon powder is 5:20:65; pretreated pyrolusite is obtained by ultrasonically washing the raw pyrolusite in dilute hydrochloric acid and oxalic acid solutions respectively, and the ultrasonic washing conditions are: washing time is 50 min, washing temperature is 30 ° C, and the mass fraction of dilute hydrochloric acid and oxalic acid solutions is 6%; pretreated pyrolusite includes the following chemical components: MnO2 65wt.%, Fe2O3 25wt.%, and 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%; waste carbon powder is SO2 purified waste carbon powder; (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, a surfactant N-methylpyrrolidone is added to the mixture, and then supercritical treatment is performed, and then the temperature is naturally lowered, and the solid-liquid separation is performed to recover the solvent to obtain a solid material; The mass fractions of the components of the mixture are as follows: 45% of crushed raw materials, 50% of methanol, 5% of sodium hydroxide, and N-methylpyrrolidone added in an amount of 20% of the volume of the mixed solution; The supercritical treatment temperature was 340 °C, the time was 90 min, and the atmosphere was nitrogen; (3) Pyrolysis: Place the solid material in a sealed container and heat it from room temperature to 600°C at a heating rate of 10°C / min for 6 hours. (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°C for 4 hours. The plasma treatment conditions are: oxygen concentration 5%, treatment temperature 50°C, treatment time 60 minutes, and power: 2kW.

[0025] The catalyst obtained in Example 1 was subjected to adsorption-desorption test to obtain a pore size distribution curve as shown in FIG. Figure 1 As shown, Figure 1 It shows that the pore size distribution of the catalyst of the present invention is concentrated, with the pore size mostly ranging from 2 to 5 nm, and the material is mainly mesoporous, which is conducive to adsorption; The catalyst obtained in Example 1 was subjected to a NO purification test and a NO cycle test (five cycles) under the following test conditions: NO, 400 ppm; O2, 10 wt.%; GHSV, 300 h -1 ; relative humidity, 90%; temperature, 48℃; gas volume flow rate 1L / min, the outlet concentration-reaction time relationship curve is shown in Figure 2 After five cycles, the obtained NO cumulative penetration capacity changes with the number of reactions. Figure 3.

[0026] Depend on Figure 2 It can be seen that the catalyst of the present invention has high catalytic activity and a long overall life cycle, which can reach more than 380 hours.

[0027] Depend on Figure 3 It can be seen that the values ​​of the NO cumulative breakthrough capacity are close at different cycle numbers, indicating that the NO purification ability of the catalyst has not been significantly attenuated during multiple cycles, which demonstrates the excellent cyclic stability of the catalyst of the present invention.

Claims

1. A method for preparing a carbon-based catalyst for low-temperature catalytic oxidation of NO, characterized in that: The steps include: (1) Ultrafine crushing pretreatment of raw materials: solid-phase ball milling of pretreated pyrolusite, low-grade coal powder and waste carbon powder to a size of more than 1000 mesh to obtain crushed raw materials; The pretreated pyrolusite is prepared by ultrasonically washing the raw pyrolusite in dilute hydrochloric acid and oxalic acid solutions respectively; (2) Supercritical treatment: alcohol and alkali are added to the crushed raw materials to obtain a mixture, a surfactant is added to the mixture, and then supercritical treatment is performed, followed by natural cooling, and solid-liquid separation to obtain a solid material; (3) Pyrolysis: placing the solid material in a sealed container and heating it up, then heat treating it at a constant temperature; (4) Plasma modification: The solid material after constant temperature treatment is subjected to plasma modification, water washing, and drying.

2. The method for preparing a 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 pyrolusite, low-rank coal powder, and waste carbon powder is (3-5): (20-30): (65-77).

3. The method for preparing a 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 rest are impurity components; ultrasonic washing conditions: washing time is 10~50min, and washing temperature is 30~80℃.

4. The method for preparing a 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, the base is sodium hydroxide, and the surfactant is N-methylpyrrolidone. The mass fractions of the components of the mixture are as follows: 42% to 47% of crushed raw materials, 50% of alcohol, and 3% to 8% of base.

5. The method for preparing a 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°C, the time is 30-90 minutes, and the atmosphere is nitrogen.

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

7. The method for preparing a 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°C, treatment time 30~60min, power range: 2~10kW.

8. The method for preparing a 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 claims 1-8.

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