CN103301831A - Catalyst for removing nitrogen oxide in emission exhaust and preparation method thereof - Google Patents

Abstract

The invention provides a catalyst for removing nitrogen oxide in emission exhaust and a preparation method thereof. The catalyst comprises a first component oxide, a second component oxide, a third component oxide and a molding auxiliary. The preparation method comprises the following steps of: burdening and mixing, kneading, pugging, extruding, drying and roasting. The catalyst provided by the invention can be used as a reducing agent for ammonia gas so as to selectively catalyze and reduce the nitrogen oxide discharged from a coal-fired power plant.

Description

Catalyst for removing nitrogen oxides in exhaust gas and preparation method thereof

technical field

The invention belongs to the field of catalysts, and in particular relates to a catalyst for removing nitrogen oxides in exhaust gas and a preparation method thereof. the

Background technique

In the process of thermal power generation, fossil fuel combustion emits a large amount of NO _x , causing serious environmental pollution. Among various nitrogen oxide removal methods, selective catalytic reduction (selective catalytic reduction, SCR) technology is the most important and most industrially applicable method for removing NO _x from various exhaust gases. In this method, under the action of a catalyst, NO _x is reduced to N ₂ by using NH ₃ as a reducing agent and then discharged into the atmosphere.

The widely used catalysts are V ₂ O ₅ -WO ₃ /TiO ₂ and V ₂ O ₅ -MoO ₃ /TiO ₂ catalysts. In order to achieve a certain denitrification activity, the vanadium content is between 0.8% and 2%.

The research on vanadium-based catalysts for SCR denitrification process is very mature and has been applied commercially on a large scale. Catalysts mainly have two configurations: honeycomb and plate. Under the conditions of stoichiometric ratio NO/NH ₃ =1.0-1.1, temperature range of 300-450°C, and reaction space velocity of 2000-5000hr ^-1 , the removal rate of NO _x can reach 80%-95%. Several major international SCR catalyst suppliers have applied for a large number of patents on vanadium-based catalysts in terms of catalyst formulation, catalyst configuration and catalyst molding methods, such as Mitsubishi (US4833133, US4891348, US5869419, US7256155), Babcock-Hitachi (US5348987, US6063342 , US6833117), Degussa (US5198403, US5300472), catalytic chemical synthesis (US4188365, CN03122008.8), Sakai Chemical (US4755500, US4892716), etc.

The main advantages of vanadium-based catalysts are its high activity and high sulfur resistance, but there are also outstanding problems, that is, vanadium compounds are highly toxic, and vanadium-based catalysts can be damaged during preparation, use, and improper disposal of deactivated catalysts. secondary pollution. Some developed countries and regions have begun to assess the impact of the loss of vanadium compounds on the environment and human body, and limit the scope of use of vanadium-based SCR catalysts. Therefore, there is a need for a new type of SCR catalyst that can be used to reduce flue gas _NOx emissions, has high activity, wide temperature window, and good thermal stability. It has good SCR activity at the flue gas temperature of coal-fired power plants, and does not contain Vanadium compounds.

Cerium oxides or composite oxides are used as oxygen storage materials due to their excellent redox properties, but their sulfur resistance is poor. SO ₂ in the reaction atmosphere reacts with cerium oxide to form cerium sulfate, which loses its redox capacity. The flue gas of coal-fired power plants contains 400-1300ppm SO ₂ , such a high concentration of SO ₂ will make the cerium-based materials lose their effect quickly. In the present invention, _TiO2 is used as a skeleton material, and it forms homogeneous mud with cerium compounds, and is molded by an extruder to obtain a honeycomb catalyst structure. Through the mixed extrusion of TiO ₂ and cerium compounds, etc., the overall extrusion molding of cerium compounds is realized, the original denitrification activity of cerium compounds is retained, and the shortcomings of poor sulfur resistance of cerium compounds are overcome. The catalyst has high SCR activity and good sulfur resistance stability in the flue gas temperature range of the power plant, and can be used in the SCR denitrification process of the flue gas of the coal-fired power plant.

Contents of the invention

The object of the present invention is to provide a catalyst for removing nitrogen oxides in exhaust gas and a preparation method thereof for the deficiencies of the prior art. the

The invention provides a catalyst for removing nitrogen oxides in exhaust gas. The catalyst composition includes a first component oxide, a second component oxide, a third component oxide, and a forming aid;

The first component oxide is the base material, selected from titanium oxide TiO ₂ , and its weight percentage is 45-85% of the weight of the catalyst. ;

The second component oxide is selected from one or a combination of oxides of cerium CeO ₂ , zirconium oxide ZrO ₂ , and lanthanum, and its weight percentage is 6-50% of the weight of the catalyst;

The third component oxide is selected from one or a combination of tungsten oxide WO ₃ and molybdenum oxide, and its weight percentage is 5-10% of the weight of the catalyst;

The forming auxiliary agent is clay, and the weight percent content of the added amount thereof is 5%-30%. the

The invention provides a catalyst for removing nitrogen oxides in exhaust gas, and the catalyst has a honeycomb structure. the

In the catalyst for removing nitrogen oxides in exhaust gas provided by the present invention, the second component oxides are oxides of cerium (CeO ₂ ) and oxides of zirconium (ZrO ₂ ), and CeO ₂ and ZrO ₂ are in the form of a solid solution. The form exists in the catalyst, and the molar ratio of CeO ₂ and ZrO ₂ is 4:1～1:1.

In the catalyst for removing nitrogen oxides in exhaust gas provided by the invention, the second component oxides are cerium oxides and zirconium oxides, and the weight percentage of cerium oxides is 4 to 35% of the weight of the catalyst. %, the weight percentage of zirconium oxide is 2-15% of the weight of the catalyst. the

The present invention also provides a preparation method for a catalyst for removing nitrogen oxides in exhaust gas, specifically comprising the following steps:

(1) Ingredients and Mixing

Mix the raw materials that make up the catalyst evenly according to the proportion; in some embodiments, choose a solution containing cerium nitrate or zirconium nitrate to add to the dry powder mixture containing titanium dioxide and ammonium paratungstate and mix evenly together;

(2) kneading

Put the prepared mixture into the kneader for kneading, seal the kneaded catalyst mud with a plastic film and stale to ensure that the moisture in the mud will not evaporate, and the stale time is 24 to 48 hours;

Put the prepared mixture into the kneader for kneading. To obtain a catalyst sludge suitable for extrusion requires mixing the above described components with a suitable liquid medium. The liquid phase medium is composed of water and extrusion aids, which can provide the moldability of the catalyst sludge and the necessary green strength after molding. During the kneading process, different inorganic binders, organic plasticizers, lubricants, surfactants and viscosity-adjusting substances are added to the catalyst sludge to achieve viscosity control of the mixture and increase the plasticity of the catalyst sludge. Suitable inorganic binders are silica-containing materials, preferred inorganic binders include activated clays, kaolin and silica sols. These silicon-containing substances are added to make the catalyst structure obtained by firing contain silicon oxide binder, and its weight percentage content is 3-15%. Organic plasticizers are mainly cellulose ethers or their derivatives. In the present invention, methyl cellulose is used as an organic plasticizing agent to shape the green body, and the addition amount is usually 3-8%. In the kneading process, glass fiber is also added to further improve the strength of the green body, and the addition amount is 3-6%. The kneading time is 3-6 hours, and finally the catalyst sludge with a water content of 15-22% is obtained. Seal the kneaded catalyst mud with a plastic film for aging to ensure that the moisture in the mud will not evaporate. The aging time is 24 to 48 hours;

(3) Practicing mud

Add the kneaded catalyst mud that has been stale for a period of time into the vacuum mud refining machine, turn on the mud refining machine and vacuum pump to carry out vacuum mud refining, the vacuum degree is maintained at -0.08 ~ -0.095Mpa, and the catalyst mud is repeated 5 to 10 times After vacuum refining, a catalyst mud section with a smooth surface, good viscosity, and a diameter of 50 mm is formed. After the catalyst mud section is sealed, it continues to decay for 24 to 48 hours;

(4) extrusion

Take a piece of stale catalyst mud and put it into the material cylinder of the extruder to extrude through a porous die to form a honeycomb structure;

(5) dry

Place the extruded honeycomb body in the air for 24-72 hours and then dry it in a drying oven at 120°C for 5-10 hours to evaporate the water and then shape it to obtain an extruded honeycomb catalyst dry body;

(6) Roasting

The dried catalyst body is placed in a muffle furnace for calcination; the heating temperature range for calcination is between 500-700° C., and the residence time during the calcination process is 2-4 hours. the

The catalyst provided by the invention can be used for ammonia gas as a reducing agent to selectively catalyze and reduce nitrogen oxides discharged from coal-fired power plants. the

The beneficial effects of the present invention are as follows: (1) The selected raw material is domestic ordinary micron TiO ₂ , the source of the raw material is convenient, the price is low, and no pretreatment is required, and the preparation process is simple; (2) The catalyst does not contain vanadium, and the environment is non-toxic friendly.

Description of drawings

Fig. 1 has shown that the hole number prepared by embodiment 1 is that on the extruded honeycomb denitrification catalyst of 25, the NOx conversion rate varies with the inlet gas temperature curve;

Fig. 2 has shown the NOx conversion ratio curve with inlet gas temperature on the extruded honeycomb denitration catalyst of different hole numbers prepared by embodiment 2;

Fig. 3 shows that the number of holes prepared by embodiment 3 is the curve of change of NOx conversion rate with inlet gas temperature on the extruded honeycomb denitration catalyst of 25;

Fig. 4 has shown that the number of holes prepared by embodiment 4 is the curve of change of NOx conversion ratio with inlet gas temperature on the extruded honeycomb denitration catalyst of 25;

Fig. 5 shows that the number of holes prepared by embodiment 5 is 9 Extrusion-type honeycomb denitration catalysts NOx conversion rate varies with the inlet gas temperature curve;

Fig. 6 shows the variation curve of NOx conversion rate with inlet gas temperature on the extruded honeycomb denitration catalyst with 9 pores prepared according to Example 6. the

Detailed ways

The following examples will further illustrate the present invention, but do not limit the present invention thereby. the

Example 1

Commercial metatitanic acid was calcined at 500°C for 4 hours to obtain titanium dioxide. The average particle size was 1.6 μm measured by laser particle size analyzer, and the specific surface area was 70m ² /g by BET analysis. Mix 882g of the above-mentioned titanium dioxide, 56g of cerium-zirconium composite oxide powder with a cerium-zirconium molar ratio of 4:1 prepared by homogeneous precipitation method, and 97.7g of ammonium paratungstate, and then add it into the kneader. Take 50mL of 25% ammonia water and 300mL of deionized water to make a solution, add it into the kneader and start kneading. 54.5 g of kaolin, 23 g of methylcellulose, 32.5 g of glass fiber and 25 g of glycerin were also added during the kneading process. Knead for a period of time until the material is uniform and the water content is appropriate to obtain catalyst sludge. After the catalyst mud is stale for 24 to 48 hours, vacuum mud refining is started. After the drilled mud is placed for 24 hours, it is extruded by a hydraulic piston extruder through a porous die to form a honeycomb structure. Three kinds of molds with different cell densities were selected to obtain honeycomb bodies with the following specifications (see Table 1):

Table 1 Structural parameters of three kinds of honeycomb catalyst structures

The extruded honeycomb body was placed in air for 48 hours, dried in a drying oven at 120° C. for 5 hours, and then calcined in a muffle furnace at 500° C. for 2 hours to obtain a honeycomb catalyst for denitrification. the

The denitrification activity test method of the prepared catalyst is as follows: the extruded monolithic honeycomb catalyst is cut into small pieces of 3.6 cm, placed in a fixed bed reactor, and the reaction atmosphere simulates the flue gas composition, wherein NO: 550ppm, NH ₃ : 550ppm, O ₂ : 5%, CO ₂ : 10%, SO ₂ : 1450ppm (if added), H ₂ O is pumped into the evaporator to be evaporated and then mixed with the raw material gas, and the pump flow rate is controlled so that the water vapor concentration is 10%. The feed gas flow rate was adjusted so that the dry basis space velocity of the reaction was 5000 hr ^-1 . The concentration of NO at the inlet and outlet is detected separately, so as to calculate the conversion rate of NO and obtain the denitrification efficiency of the catalyst. Attached Figure 1 shows the denitrification efficiency of the catalyst structure with 25 pores in the range of 280-400°C. It can be seen that in the temperature range of 340-360°C, the conversion rate of NO on the catalyst remains above 96%, which has a great Good denitrification activity.

Example 2

Commercial metatitanic acid was calcined at 500°C for 4 hours to obtain titanium dioxide. The average particle size was 1.6 μm measured by laser particle size analyzer, and the specific surface area was 70m ² /g by BET analysis. Mix 882g of the above-mentioned titanium dioxide, 112g of cerium-zirconium composite oxide powder with a cerium-zirconium molar ratio of 4:1 prepared by homogeneous precipitation method, and 97.7g of ammonium paratungstate, and then add them into the kneader. Get 50mL of 25% ammonia water and 300mL of deionized water to make a solution, add it into the kneader and start kneading. 54.5 g of kaolin, 23 g of methylcellulose, 32.5 g of glass fiber and 25 g of glycerin were also added during the kneading process. Knead for a period of time until the material is uniform and the water content is appropriate to obtain catalyst sludge. After the catalyst mud is stale for 24 to 48 hours, vacuum mud refining is started. After the drilled mud is placed for 24 hours, it is extruded by a hydraulic piston extruder through a porous die to form a honeycomb structure. Three kinds of molds with different cell densities were selected to obtain honeycomb bodies with the following specifications (see Table 1):

The extruded honeycomb body was placed in air for 48 hours, dried in a drying oven at 120° C. for 5 hours, and then calcined in a muffle furnace at 500° C. for 2 hours to obtain a honeycomb catalyst for denitrification. the

The activity evaluation of the catalyst is the same as in Example 1. Three extruded catalysts with different pore densities were cut into 3.6cm segments and placed in a fixed-bed reactor to evaluate the denitrification efficiency of these three catalysts in the range of 280-400°C. The results are shown in Figure 2. the

Example 3

Commercial metatitanic acid was calcined at 500°C for 4 hours to obtain titanium dioxide. The average particle size was 1.6 μm measured by laser particle size analyzer, and the specific surface area was 70m ² /g by BET analysis. Mix 792g of the above-mentioned titanium dioxide, 90g of cerium oxide powder prepared by the solution combustion synthesis method, and 97.7g of ammonium paratungstate and add them into the kneader. Take 50mL of 25% ammonia water and 300mL of deionized water to make a solution, add it into the kneader and start kneading. 54.5 g of kaolin, 23 g of methylcellulose, 32.5 g of glass fiber and 25 g of glycerin were also added during the kneading process. Knead for a period of time until the material is uniform and the water content is appropriate to obtain catalyst sludge. After the catalyst mud is stale for 24 to 48 hours, vacuum mud refining is started. After the drilled mud is placed for 24 hours, it is extruded by a hydraulic piston extruder through a porous die to form a honeycomb structure. Three kinds of molds with different cell densities were selected to obtain honeycomb bodies with the following specifications (see Table 1):

The extruded honeycomb body was placed in the air for 48 hours, dried in a drying oven at 120°C for 5 hours, and then calcined in a muffle furnace at 500°C for 2 hours to obtain a honeycomb catalyst for denitrification. the

Catalyst activity evaluation is the same as in Example 1. The catalyst structure with 25 holes was cut into 3.6 cm segments and loaded into a fixed bed reactor, and the denitration rate of the catalyst was evaluated at different temperature points, and the results are shown in Figure 3. the

Example 4

Commercial metatitanic acid was calcined at 500°C for 4 hours to obtain titanium dioxide. The average particle size was 1.6 μm measured by laser particle size analyzer, and the specific surface area was 70m ² /g by BET analysis. 882g of the above-mentioned titanium dioxide and 97.7g of ammonium paratungstate were mixed evenly and added to the kneader. Take 111.3 g of cerium nitrate and add 300 mL of deionized water to prepare a cerium nitrate solution and add it to a kneader to start kneading. 54.5 g of kaolin, 23 g of methylcellulose, 32.5 g of glass fiber and 25 g of glycerin were also added during the kneading process. Knead for a period of time until the material is uniform and the water content is appropriate to obtain catalyst sludge. After the catalyst mud is stale for 24 to 48 hours, vacuum mud refining is started. After the drilled mud is placed for 24 hours, it is extruded by a hydraulic piston extruder through a porous die to form a honeycomb structure. Three kinds of molds with different cell densities were selected to obtain honeycomb bodies with the following specifications (see Table 1):

The extruded honeycomb body was placed in air for 48 hours, dried in a drying oven at 120° C. for 5 hours, and then calcined in a muffle furnace at 500° C. for 2 hours to obtain a honeycomb catalyst for denitrification. the

The activity evaluation of the catalyst is the same as in Example 1. The catalyst structure with 25 holes was cut into 3.6 cm segments and put into a fixed bed reactor, and the denitration rate of the catalyst was evaluated at different temperature points, and the results are shown in Figure 4. After testing the denitrification activity at different temperature points, the catalyst bed was kept at 360°C. At this time, 1450ppm _SO2 was added to investigate its sulfur resistance. The results showed that in the 70-hour sulfur resistance test, the denitrification activity of the catalyst was It has been maintained at 97%, indicating that the catalyst has good sulfur tolerance.

Example 5

Commercial metatitanic acid was calcined at 500°C for 4 hours to obtain titanium dioxide. The average particle size was 1.6 μm measured by laser particle size analyzer, and the specific surface area was 70m ² /g by BET analysis. Mix 706g of the above-mentioned titanium dioxide, 176g of cerium oxide powder prepared by the solution combustion synthesis method, and 97.7g of ammonium paratungstate and add them into the kneader. Take 50mL of 25% ammonia water and 300mL of deionized water to make a solution, add it into the kneader and start kneading. 54.5 g of kaolin, 23 g of methylcellulose, 32.5 g of glass fiber and 25 g of glycerin were also added during the kneading process. Knead for a period of time until the material is uniform and the water content is appropriate to obtain catalyst sludge. After the catalyst mud is stale for 24 to 48 hours, vacuum mud refining is started. After the drilled mud is placed for 24 hours, it is extruded by a hydraulic piston extruder through a porous die to form a honeycomb structure. Three kinds of molds with different cell densities were selected to obtain honeycomb bodies with the following specifications (see Table 1):

The extruded honeycomb body was placed in air for 48 hours, dried in a drying oven at 120°C for 5 hours, and then calcined in a muffle furnace at 600°C for 2 hours to obtain a honeycomb catalyst for denitrification. the

The activity evaluation of the catalyst is the same as in Example 1. The catalyst structure with 9 holes was cut into small pieces of 3.6 cm and put into the reactor, and the denitration rate of the catalyst was evaluated at different temperature points, and the results are shown in Figure 5. After testing the denitrification activity at different temperature points, the catalyst bed was kept at 360°C. At this time, 1450ppm _SO2 was added to investigate its sulfur resistance. The results showed that in the 100-hour sulfur resistance test, the denitrification activity of the catalyst It has been maintained at 95%, indicating that the catalyst has good sulfur tolerance. In the sulfur resistance test, the oxidation rate of SO ₂ to SO ₃ was determined by solution absorption method to be 0.5%.

Example 6

Commercial metatitanic acid was calcined at 500°C for 4 hours to obtain titanium dioxide. The average particle size was 1.6 μm measured by laser particle size analyzer, and the specific surface area was 70m ² /g by BET analysis. 484g of the above-mentioned titanium dioxide, 180g of cerium oxide powder prepared by the solution combustion synthesis method, and 97.7g of ammonium paratungstate were mixed evenly and added to the kneader. Take 50mL of 25% ammonia water and 300mL of deionized water to make a solution, add it into the kneader and start kneading. 218 g of kaolin, 23 g of methylcellulose, 32.5 g of glass fiber and 25 g of glycerin were also added during the kneading process. Knead for a period of time until the material is uniform and the water content is appropriate to obtain catalyst sludge. After the catalyst mud is stale for 24 to 48 hours, vacuum mud refining is started. After the drilled mud is placed for 24 hours, it is extruded by a hydraulic piston extruder through a porous die to form a honeycomb structure. Three kinds of molds with different cell densities were selected to obtain honeycomb bodies with the following specifications (see Table 1):

The extruded honeycomb body was placed in air for 48 hours, dried in a drying oven at 120° C. for 5 hours, and then calcined in a muffle furnace at 500° C. for 2 hours to obtain a honeycomb catalyst for denitrification. the

The activity evaluation of the catalyst is the same as in Example 1. The catalyst structure with 9 holes was cut into small pieces of 3.6 cm and put into the reactor, and the denitration rate of the catalyst was evaluated at different temperature points, and the results are shown in Figure 6. the

The above description is used to illustrate the principles and functions of the present invention, but not to limit the present invention. Any person skilled in the art can modify and change the above-mentioned embodiments without departing from the idea and spirit of the present invention. Therefore, the protection scope of the present invention should be determined by the listed claims. the

Claims (9)

1. A catalyst for removing nitrogen oxides in exhaust gas, characterized in that: the catalyst composition includes a first component oxide, a second component oxide, a third component oxide, and a forming aid; The first component oxide is a matrix material selected from titanium oxides; The second component oxide is selected from one or a combination of oxides of cerium, zirconium, and lanthanum; The third component oxide is selected from one or a combination of tungsten oxides, molybdenum oxides; The forming aid is clay. 2. The catalyst for removing nitrogen oxides in exhaust gas according to claim 1, characterized in that: the catalyst has a honeycomb structure. 3. The catalyst for removing nitrogen oxides in exhaust gas according to claim 1, characterized in that: the first component oxide is a matrix material, and its content is 45-85% of the weight of the catalyst. 4. The catalyst for removing nitrogen oxides in exhaust gas according to claim 1, characterized in that: the content of the second component oxide is 6-50% of the weight of the catalyst. 5. The catalyst for removing nitrogen oxides in exhaust gas according to claim 1, characterized in that: the content of the third component oxide is 5-10% of the weight of the catalyst. 6. The catalyst for removing nitrogen oxides in exhaust gas according to claim 1, characterized in that: the clay is added in an amount of 5-30% of the weight of the catalyst. 7. According to the catalyst for removing nitrogen oxides in exhaust gas according to claim 1, it is characterized in that: said second component oxide is oxide of cerium and oxide of zirconium, and the content of oxide of cerium is catalyst The content of the zirconium oxide is 2-15% of the weight of the catalyst. 8. the preparation method of the described catalyst of claim 1 is characterized in that: specifically comprise the following steps: (1) Ingredients and Mixing Mix the raw materials forming the catalyst evenly according to the proportion; (2) kneading Put the prepared mixture into the kneader for kneading, seal the kneaded catalyst mud with a plastic film and stale to ensure that the moisture in the mud will not evaporate, and the stale time is 24 to 48 hours; (3) Practicing mud Add the kneaded catalyst mud that has been stale for a period of time into the vacuum mud refining machine, turn on the mud refining machine and vacuum pump to carry out vacuum mud refining, the vacuum degree is maintained at -0.08 ~ -0.095Mpa, and the catalyst mud is repeated 5 to 10 times After vacuum refining, a catalyst mud section with a smooth surface, good viscosity, and a diameter of 50 mm is formed. After the catalyst mud section is sealed, it continues to stale for 24 to 48 hours; (4) extrusion Take a piece of stale catalyst mud and put it into the material cylinder of the extruder to extrude through a porous die to form a honeycomb structure; (5) dry Place the extruded honeycomb body in the air for 24-72 hours and then dry it in a drying oven at 120°C for 5-10 hours to evaporate the water and then shape it to obtain an extruded honeycomb catalyst dry body; (6) Roasting The dried catalyst body is placed in a muffle furnace for calcination; the heating temperature range for calcination is between 500-700° C., and the residence time during the calcination process is 2-4 hours. 9. The catalyst according to claim 1 can be used for ammonia as a reducing agent, and selectively catalytically reduces nitrogen oxides emitted by coal-fired power plants.

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