CN101513612A - Catalyst for removing nitrogen oxide and organic pollutant discharged in burning and method for preparing same - Google Patents

Abstract

The catalyst for removing nitrogen oxides and organic pollutants emitted by incineration disclosed by the invention is a catalyst with carbon nanotubes and alumina as the carrier and manganese oxide as the active component. The active component in the catalyst accounts for the total mass of the catalyst 1 to 10% of that. Prepared by solvothermal method. The catalyst prepared by the present invention uses CNTs and Al ₂ O ₃ as the carrier at the same time for the first time, which not only ensures the large specific surface area of the catalyst, but also ensures the mechanical strength of the catalyst, and at the same time reduces the operating temperature of the selective catalytic reaction technology, so that at 150 ° C 94.2% chlorobenzene removal rate at 200°C and 88.8% NO _X removal rate at 200°C. The catalyst of the invention can be used for removing nitrogen oxide (NO _x ) and dioxin (Dioxin) persistent organic pollutants discharged from high-temperature processes such as coal-fired power plants, metallurgical industries, and garbage incineration.

Description

Catalyst for removing nitrogen oxides and organic pollutants emitted by incineration and preparation method thereof

technical field

The invention relates to a catalyst capable of removing nitrogen oxides (NO _x ) and dioxins (Dioxin) persistent organic pollutants discharged from high-temperature processes such as coal-fired power plants, metallurgical industries, and garbage incineration, and a preparation method thereof.

Background technique

With the improvement of my country's comprehensive national strength, people's living standards have been continuously improved at the same time, accompanied by a large amount of energy consumption and the deterioration of the environment. Among them, the emissions of nitrogen oxides (NO _x ) and dioxins (Dioxin) persistent organic pollutants emitted during high-temperature processes including coal-fired power plants, metallurgical industries, and waste incineration are two major factors of environmental pollution. For example, in 2000, the total amount of NO _X emitted into the atmosphere by China reached 15 million tons, far exceeding the amount of NO _X produced by natural processes such as natural lightning (estimated at 380,000 tons per year in China). The emission of PCDD/DFs in China in recent years is estimated at 9952.8g I-TEQ/year, of which the emission in the atmosphere is about 4160.6g I-TEQ/year, far exceeding the 24.4g I-TEQ/year of the United States and Japan 140g I-TEQ/year. Due to the relatively late start of China's environmental pollution control, the lack of corresponding control technology and the inability to achieve cheap and effective control are the key factors causing the massive discharge of pollutants.

As a coal-fired developing country, with the rapid development of China's economy, the environmental pollution caused by coal combustion is becoming more and more serious, especially the pollution of NO _X in the flue gas of coal combustion. The control of sulfur oxides has been obtained. After application promotion, it has become a problem that cannot be ignored. According to the statistics of the National Environmental Protection Agency and relevant research estimates, the emission of NO _X in China was about 9.1 million tons in 1990, about 10 million tons in 1995, and about 15 million tons in 2000, with an average per square meter per day. The amount of NO _X emitted per kilometer of land reaches an astonishing 4kg, and the emission in 2004 was about 16 million tons. By 2010, China's NO _X emissions will reach 21.94 million tons. According to the CHINA-MAP project funded by NASA, the pollutant emissions of 29 regions in China have been detected through the PAINS-ASIA model, and the results show that if not controlled, the NO _X emissions are expected to increase to 2660-2970 by 2020 tons. Among them, the annual NO _X emission of thermal power plant boilers increased from 1.207-1.506 million tons in 1987 to 8.5 million tons in 2005. In view of this, the State Environmental Protection Administration restricted the _NOx emissions of coal-fired power plant boilers in the middle and late 1990s. In 2003, China promulgated the "Emission Standards of Air Pollutants for Thermal Power Plants", which set the maximum concentration limit of NO _X emission in the flue gas of thermal power plants to 450mg/m ³ , which is stricter than the current emission standard of 650mg/m ³ (for the period III of 300MW unit).

Dioxin (including Polychlorinated dibenzo-p-dioxins and Polychlorinated dibenzo-p-furans, also known as PCDD/DFs) is composed of 2 or 1 oxygen atom linking 2 There are 210 congeners (75 isomers/congeners of PCDDs and 135 isomers/congeners of PCDFs) of tricyclic aromatic organic compounds composed of chlorine-substituted benzene rings, collectively referred to as dioxins. Dioxins are a class of very stable lipophilic solid compounds with a high melting point and a decomposition temperature greater than 700°C. They are extremely difficult to dissolve in water but soluble in most organic solvents, so dioxins are easy to accumulate in organisms . Microbial degradation, hydrolysis and photolysis in nature have little effect on the molecular structure of dioxins and are difficult to degrade naturally. Some isomers in dioxins are highly toxic substances, and their acute toxicity is equivalent to 1000 times that of potassium cyanide. Some data on human toxicity and clinical manifestations of dioxins have been obtained from victims of occupational exposure and industrial accidents, such as skin acne, headache, deafness, depression, insomnia, etc., and may cause chromosomal damage, heart failure, cancer wait.

Selective catalytic reaction technology (SCR) is the most effective method for flue gas purification and control of NO _X and dioxin emissions in high temperature processes. The SCR device can be arranged directly after the boiler (high ash flue gas section), or after the electrostatic precipitator (low ash flue gas section) or after the flue gas desulfurization device (tail flue gas section). The advantage of the arrangement of the high ash section is that the flue gas from the economizer does not need to be reheated before entering the catalytic reactor. The disadvantage is that this section of flue gas contains all the fly ash and SO ₂ produced during the combustion process, which can reduce the activity of the catalyst , The problem of shortened lifespan. Although there is no influence of dust in the arrangement of low ash section, the existence of SO ₂ will cause the same problem. Compared with the first two arrangements in the tail flue gas section, the content of dust and SO ₂ in the flue gas entering the SCR device is very small, and the catalyst can operate in a clean environment, so the service life is prolonged (the high dust type is 5 about 10 years, and the tail flue gas type is about 10 years), and it is easy to arrange. However, since the current operating temperature of mature SCR commercial catalysts is generally 300-400°C, a large amount of flue gas needs to be heated, resulting in increased costs. The SCR of most coal-fired power plants in the world adopts the arrangement of high ash section, and the SCR devices that have been built or are under construction in my country also adopt the arrangement of high ash section. In order to develop low ash segment SCR system, the development of catalyst with low temperature activity is the key.

Contents of the invention

The object of the present invention is to provide a low-temperature active catalyst for removing nitrogen oxides and organic pollutants discharged from incineration and a preparation method thereof.

The catalyst for removing nitrogen oxides and organic pollutants emitted by incineration of the present invention is a catalyst with carbon nanotubes (CNTs) and aluminum oxide as a carrier and an active component with manganese oxides, and the active components in the catalyst account for 1-10% of the total mass. The oxides of manganese mentioned above are Mn ₂ O ₃ and MnO ₂ .

The preparation method of the catalyst for removing nitrogen oxides and organic pollutants discharged from incineration adopts a solvothermal method, comprising the following steps:

1) Ultrasonic disperse the CNTs purified by HNO ₃ in isopropanol, and then pour it into a container placed in a water bath at 50-100°C as the bottom solution;

2) Grind aluminum isopropoxide and add isopropanol, stir evenly and use as aluminum alcohol phase, the mass ratio of aluminum isopropoxide and isopropanol is 1:15-1:30; pour deionized water into isopropanol In the alcohol, add the peptizer ammonium bifluoride and the surfactant polyethylene glycol 1000 at the same time and stir evenly as the water phase. The mass ratio of deionized water, isopropanol, ammonium bifluoride and polyethylene glycol 1000 is 50:50～150 : 1～5: 1～5; the volume ratio of aluminum alcohol phase and water phase is 2: 1;

3) Drop the aluminum alcohol phase and the water phase into the bottom solution of step 1), control the flow rate of the water phase to 0.5-1ml/s, and the flow rate of the aluminum alcohol phase to 1-2ml/s, and continue stirring for 1-2ml/s after the titration is completed. 3h;

4) Dissolve manganese acetate tetrahydrate in isopropanol, prepare manganese acetate tetrahydrate isopropanol solution with a concentration of 0.01g/ml～0.02g/ml, and then pour manganese acetate tetrahydrate isopropanol solution into step 3 ) in the mixed solution, the volume ratio of manganese acetate tetrahydrate isopropanol solution to the mixed solution is 1:3～1:6, after stirring evenly, pour it into a hydrothermal kettle and seal it, heat up to 150～300°C, and keep it warm for 1～5h , cooled, washed with ethanol by centrifugation, and dried at 50-120°C to obtain a catalyst.

The beneficial effect of the present invention is that: in the gas-solid heterogeneous catalytic reaction, the gaseous substance is firstly adsorbed on the surface of the catalyst, and then the catalytic process is completed. Generally speaking, under the same conditions, the larger the surface area of the catalyst, the stronger its catalytic ability . In the present invention, carbon nanotubes and aluminum oxide are used as carriers, and the specific surface area test shows that the specific surface area of the catalyst is ^240m2 /g. Carbon nanotubes have the characteristics of large specific surface area and strong adsorption capacity for organic gases such as dioxins. And after activation by acid pretreatment, the acid sites on its surface are increased, and the adsorption capacity of NH ₃ reducing agent on its surface is obviously increased. However, Al ₂ O ₃ has strong thermal stability and high mechanical strength, which can effectively resist the impact of air flow and maintain the structure of the catalyst. The manganese-based catalyst has excellent low-temperature SCR characteristics, presents a variety of oxide states, and presents different performances, and has strong anti-toxicity ability to sulfur dioxide and water vapor in flue gas. The catalyst of the invention can be used for removing nitrogen oxide (NO _x ) and dioxin (Dioxin) persistent organic pollutants discharged from high-temperature processes such as coal-fired power plants, metallurgical industries, and garbage incineration.

The catalyst prepared by the present invention uses CNTs and Al ₂ O ₃ as the carrier at the same time for the first time, which not only ensures the large specific surface area of the catalyst but also ensures the mechanical strength of the catalyst, and at the same time reduces the operating temperature of the SCR, making it reach 94.2% at 150°C The removal rate of _{chlorobenzene} reaches 88.8% at 200°C.

Description of drawings

Fig. 1 is the X-ray diffraction (XRD) of catalyst;

Fig. 2 is the scanning electron micrograph (SEM) of catalyst;

Fig. 3 is the transmission electron microscope figure (TEM) of catalyst;

Detailed ways

Example 1:

Put the carbon nanotubes in 60% nitric acid solution, heat under reflux for 2h, then wash with deionized water until neutral, and dry at 80°C, put 0.1g of the CNTs purified by the above HNO ₃ in isopropanol After ultrasonication for 30 minutes, pour it into a three-necked flask placed in a water bath at 70°C as the base solution; grind 3g of aluminum isopropoxide and add it to 60ml of isopropanol for ultrasonication for 30 minutes, then pour it into a dropping bottle as the aluminum alcohol phase. Pour deionized water into 20ml of isopropanol, add 0.2g of peptizer ammonium bifluoride and 0.2g of surfactant polyethylene glycol 1000 until completely dissolved, and pour into another drop bottle as the water phase; insert the drop bottle into three ports On the side of the flask, when the bottom liquid is stirred, open the valve of the dropping bottle, control the flow of the water phase to 0.5ml/s, and the flow of the aluminum alcohol phase to 1ml/s, and continue to stir for 1.5h after the titration; Dissolve manganese acetate hydrate in 20ml isopropanol to obtain manganese acetate tetrahydrate isopropanol solution, then pour it into a three-neck flask and continue stirring for 30 minutes, then pour it into a hydrothermal kettle to seal, put it in an oven, heat up to 270°C, and keep it warm for 4.5h , cooling with the furnace. The sample was taken out and washed three times by centrifugation with ethanol, and dried in an oven at 80° C. for 2 hours to obtain a catalyst.

Figure 1 is the X-ray diffraction (XRD) of the prepared catalyst; Figure 2 is the scanning electron microscope (SEM) of the prepared catalyst; Figure 3 is the transmission electron microscope (TEM) of the prepared catalyst.

Get 5ml of the catalyst of the present invention and place it in a stainless steel pipe fixed-bed reactor with an inner diameter of 1 cm. The catalytic test utilizes a certain flow rate of Ar to blow the insulated liquid chlorobenzene to form chlorobenzene vapor with a concentration of 25 ppm. Air is used as the balance gas, the purity of all gases is 99.999%, and the space velocity of the total air flow is 28800h ^-1 . Reactants and reaction products were analyzed using an online chromatographic instrument equipped with a flame ionization thermal conductivity detector (FID). The reaction starts at 100°C and is heated every 50°C until 300°C. The catalyst at a given temperature is kept warm for 2.5 hours, and the average value of the chromatographic data measured within 30 minutes after being in a steady state is used as the concentration of chlorobenzene before and after the reaction at this temperature to obtain the efficiency of dechlorinated benzene. The removal rate of chlorobenzene at 100°C is 83.9%. The removal rate of chlorobenzene at 150°C is 94.2%. The removal rate of chlorobenzene at 200°C is 97.8%. The removal rate of chlorobenzene at 250°C is 96.8%. The removal rate of chlorobenzene at 300°C is 99.5%.

Example 2:

Put the carbon nanotubes in 60% nitric acid solution, heat under reflux for 2h, then wash with deionized water until neutral, and dry at 80°C, put 0.1g of the CNTs purified by the above HNO ₃ in isopropanol After ultrasonication for 30 minutes, pour it into a three-necked flask placed in a water bath at 70°C as the base liquid; grind 2g of aluminum isopropoxide and add it to 50ml of isopropanol for ultrasonication for 30 minutes, then pour it into a dropping bottle as the aluminum alcohol phase. Pour deionized water into 19ml of isopropanol, add 0.15g of peptizer ammonium bifluoride and 0.15g of surfactant polyethylene glycol 1000 at the same time until completely dissolved, pour into another drop bottle as the water phase; insert the drop bottle into three ports On the side of the flask, when the bottom liquid is stirred, open the valve of the dropping bottle, control the flow rate of the water phase to 0.5ml/s, and the flow rate of the aluminum alcohol phase to 1ml/s, and continue to stir for 1.5h after the titration; Dissolve manganese acetate hydrate in 18ml isopropanol to obtain manganese acetate tetrahydrate isopropanol solution, then pour it into a three-neck flask and continue stirring for 30 minutes, then pour it into a hydrothermal kettle to seal, put it in an oven, heat up to 270°C, and keep it warm for 4.5h , cooling with the furnace. The sample was taken out and washed three times by centrifugation with ethanol, and dried in an oven at 80° C. for 2 hours to obtain a catalyst.

Get 5ml catalyst of the present invention to be placed in the stainless steel tube fixed-bed reactor that internal diameter is 1cm, nitrogen is as carrier gas, and flow rate is 1L/min, and oxygen 50ml/min, volume fraction after He gas dilution is 0.40vol%NO/He and The flow rate of 0.40vol% NH ₃ /He is 1.5ml/min, and the total volume space velocity is 15000h-1. The denitrification rate of the catalyst is obtained by measuring the concentration of NO _x at the inlet and outlet of the fixed bed reactor by flue gas analyzer. The denitrification rate is 67.7% at 100°C. The denitrification rate is 77.5% at 150°C. The denitrification rate is 88.8% at 200°C. The denitrification rate is 78.4% at 250°C. The denitrification rate is 68.4% at 300°C.

Example 3:

Put the carbon nanotubes in 60% nitric acid solution, heat under reflux for 2h, then wash with deionized water until neutral, and dry at 80°C, put 0.1g of the CNTs purified by the above HNO ₃ in isopropanol After ultrasonication for 30 minutes, pour it into a three-necked flask placed in a water bath at 70°C as the base solution; grind 2.2g of aluminum isopropoxide and add it to 56ml of isopropanol for ultrasonication for 30 minutes, then pour it into a dropping bottle as the aluminum alcohol phase. Pour 8ml of deionized water into 20ml of isopropanol, add 0.18g of peptizer ammonium bifluoride and 0.18g of surfactant polyethylene glycol 1000 until completely dissolved, and pour into another drop bottle as the water phase; insert the drop bottle into On the side of the three-necked flask, when the bottom liquid is stirred, open the valve of the dropping bottle, control the flow rate of the water phase to 0.5ml/s, and the flow rate of the aluminum alcohol phase to 1ml/s, and continue to stir for 1.5h after the titration is completed; 0.32g Dissolve manganese acetate tetrahydrate in 30ml of isopropanol to obtain manganese acetate tetrahydrate isopropanol solution, then pour it into a three-necked flask and continue stirring for 30 minutes, then pour it into a hydrothermal kettle to seal, put it in an oven, heat up to 270°C, and keep it warm for 4.5 h, cooling with the furnace. The sample was taken out and washed three times by centrifugation with ethanol, and dried in an oven at 80° C. for 2 hours to obtain a catalyst.

Claims (3)

1. remove the nitrogen oxide of discharged in burning and the catalyst of organic pollution for one kind, it is characterized in that this catalyst is a carrier with CNT and aluminium oxide, oxide with manganese is the catalyst of active component, and active component accounts for 1～10% of catalyst gross mass in the catalyst.

2. the nitrogen oxide of removal discharged in burning according to claim 1 and the catalyst of organic pollution, the oxide that it is characterized in that manganese is Mn ₂O ₃And MnO ₂

3. the Preparation of catalysts method of the nitrogen oxide of removal discharged in burning according to claim 1 and organic pollution is characterized in that may further comprise the steps:

1) will be through HNO ₃CNTs behind the purifying is ultrasonic to be dispersed in the isopropyl alcohol, pour into then place 50～100 ℃ of water-baths container as end liquid;

2) aluminium isopropoxide is ground the back and add isopropyl alcohol, the back that stirs is as the aluminium alcoholates phase, and the mass ratio of aluminium isopropoxide and isopropyl alcohol is 1: 15～1: 30; Deionized water is poured in the isopropyl alcohol, add peptizing agent ammonium acid fluoride and surfactant polyethylene 1000 simultaneously and stir the back as water, the mass ratio of deionized water, isopropyl alcohol, ammonium acid fluoride and cetomacrogol 1000 is 50: 50～150: 1～5: 1～5; The volume ratio of aluminium alcoholates phase and water is 2: 1;

3) aluminium alcoholates phase and water are splashed in the end liquid of step 1), the flow of control water is 0.5～1ml/s, and the flow of aluminium alcoholates phase is 1～2ml/s, continues to stir 1～3h after titration finishes;

4) four hydration manganese acetates are dissolved in the isopropyl alcohol, configuration concentration is the four hydration manganese acetate aqueous isopropanols of 0.01g/ml～0.02g/ml, then four hydration manganese acetate aqueous isopropanols are poured in the mixed liquor of step 3), the volume ratio of four hydration manganese acetate aqueous isopropanols and mixed liquor is 1: 3～1: 6, and the hot still sealing of falling back stirs, be warming up to 150～300 ℃, insulation 1～5h, the ethanol centrifuge washing is used in cooling, 50～120 ℃ of dryings, obtain catalyst.

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