CN114260015A

CN114260015A - Flue gas denitration molded catalyst and preparation method and application thereof

Info

Publication number: CN114260015A
Application number: CN202111671007.2A
Authority: CN
Inventors: 罗光前; 赖言涛; 邹仁杰; 孙瑞泽; 李显; 姚洪
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2022-04-01

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a flue gas denitration molded catalyst, and a preparation method and application thereof. The invention comprises the following steps: (1) adding a binder, a pore-forming agent, a strength agent and a lubricant into the coal-fired fly ash, uniformly mixing, and then adding water for extrusion to obtain a carrier with a set shape; (3) dissolving manganese salt, cerium salt and nickel salt to obtain a mixed salt solution, and immersing a carrier into the mixed salt solution to load the manganese salt, the cerium salt and the nickel salt to obtain a precursor; (3) and calcining the precursor to obtain the flue gas denitration molded catalyst. The invention uses fly ash as a carrier to reduce the cost, and the denitration efficiency of the catalyst in the temperature range of 200 ℃ and 250 ℃ is more than 90% due to the compounding of Mn, Ce and Ni, so that the problems of blockage, poisoning and inactivation and the like of the catalyst caused by long-time operation of the catalyst under the high-temperature condition can be avoided, and the service life of the catalyst is prolonged.

Description

Flue gas denitration molded catalyst and preparation method and application thereof

Technical Field

The invention belongs to the technical field of catalysts, and particularly relates to a flue gas denitration molded catalyst, and a preparation method and application thereof.

Background

Nitrogen Oxides (NO)_x) Is one of toxic and harmful gases discharged in industrial fields such as boiler combustion, chemical engineering manufacturing and the like, and is a main reason for photochemical smog, ozone layer cavities, acid rain and the like. In industrial processes, combustion accounts for NO_xA significant portion of the emissions, with coal combustion accounting for 70%. The rapid development of the industry has led to an increasing emission of nitrogen oxides, which poses a great threat to the natural ecology and human health. Selective catalytic reduction (NH)₃SCR) is a mature and efficient denitration technology, and V-w (mo)/Ti catalysts are currently the most widely used commercial SCR catalysts, but are expensive, and furthermore, the active material V contains a high toxicity. Moreover, the working temperature range of the selective catalytic reduction is usually at 350 ℃ to 400 ℃, SO that the catalytic device is positioned at the upstream of an electrostatic precipitator (ESP) and a desulphurization device, and the flue gas contains a large amount of dust and SO simultaneously₂Gas, resulting in sintering, dust plugging and SO of the catalyst after long-term operation₂Poisoning and the like, and greatly shortens the service life of the catalyst. These problems are well solved by placing a catalytic device downstream of the electrostatic precipitator (ESP) or the desulfurization unit. However, since the flue gas temperature in the downstream equipment is significantly lower than the activation temperature of the commercial catalyst (V-W (Mo)/Ti), and the approach of reheating the tail flue gas to reach the activation temperature range of the commercial catalyst would add extra economic cost, high efficiency, low temperature (V-W (Mo)/Ti (Ti) was developed to overcome the above disadvantages<250 c), low cost catalysts would be desirable.

Nearly 6 hundred million tons of fly ash are reported to be generated in China every year, only less than 70 percent of the fly ash is recycled, the fly ash is mainly used for the production of cement, brick kilns and the like and the treatment of waste water, and the remaining large amount of fly ash is mostly buried to cause serious environmental pollution. The main components of the fly ash are SiO2, Fe2O3 and Al2O3, the phase compositions of the fly ash are mainly quartz and mullite, and the fly ash is a material with a porous structure, has higher specific surface area and good adsorption capacity, and can be used as an adsorbent and a good catalyst carrier. Therefore, the fly ash is used as the carrier of the denitration catalyst, so that the excessive accumulation of the fly ash in the whole world can be reduced, the problem of environmental pollution in the whole world is improved, and the cost of the catalyst is reduced. The purpose of treating wastes with processes of wastes against one another is achieved.

CN105727730A discloses a flue gas efficient desulfurization and denitration method and materials used in the same, and particularly discloses a method adopting extrusion molding, calcium hydroxide and the like are used as main materials, alumina sol is used as a binder and the like, and a molded catalyst prepared by the method has good denitration capability, but the catalyst has high raw material cost and poor economy, and is not suitable for large-scale use.

CN109794248A discloses a low-cost flue gas denitration catalyst and its preparation and use methods, and specifically discloses that fly ash from coal burning is still used as the carrier of the catalyst, and Fe, Zn, and Cu are used as the active materials of the catalyst, however, the effect of expanding the surface area of fly ash by using a high-pressure reaction kettle and a steam activation method is very small in this technical scheme, and in addition, compared with the present invention, the patent mainly lacks a catalyst forming method, so there is still a certain distance from the actual industrial application of the catalyst.

In summary, the prior art still lacks of a flue gas denitration catalyst with high final economic benefit and low catalytic temperature.

Disclosure of Invention

Aiming at the defects or improvement requirements of the prior art, the invention provides a flue gas denitration formed catalyst, a preparation method and application thereof, aiming at reducing the cost by using fly ash as a carrier, wherein Mn has good low-temperature denitration performance, and researches show that adding a certain proportion of rare earth element Ce is beneficial to improving the structural stability and the dispersibility of manganese and improving the sulfur-resistant and water-resistant performance of the catalyst, and in addition, early tests show that when Mn and Ni form a composite structure, the low-temperature denitration performance of the catalyst is further beneficial to being improved, so that the catalyst with high efficiency, low temperature (<250 ℃) and low cost is finally obtained by selecting Mn, Ce and Ni as active components of the catalyst. The detailed technical scheme of the invention is as follows.

In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing a flue gas denitration catalyst, comprising the steps of:

(1) adding a binder, a pore-forming agent, a strength agent and a lubricant into the coal-fired fly ash, uniformly mixing, and then adding water for extrusion to obtain a carrier with a set shape;

(2) dissolving manganese salt, cerium salt and nickel salt to obtain a mixed salt solution, and immersing a carrier into the mixed salt solution to load the manganese salt, the cerium salt and the nickel salt to obtain a precursor;

(3) and calcining the precursor to obtain the flue gas denitration molded catalyst.

Preferably, the ratio of the amounts of the manganese salt, the cerium salt and the nickel salt is (1-5): (1-5): (1-5), preferably 1:1:1.

Preferably, in the step (2), the sum of the mass of the manganese salt, the mass of the cerium salt and the mass of the nickel salt is 5-30% of the mass of the carrier. The sum of the masses of the manganese salt, the cerium salt and the nickel salt means the mass when not supported on a carrier.

Preferably, the manganese salt is at least one of manganese nitrate, manganese chloride and manganese sulfate; the cerium salt is at least one of cerium nitrate, cerium chloride and cerium sulfate; the nickel salt is at least one of nickel nitrate, nickel chloride and nickel sulfate.

Preferably, the calcination in step (3) comprises a first calcination and a second calcination, wherein the temperature of the first calcination is 100-.

Preferably, the coal-fired fly ash in the step (1) is pretreated, the pretreatment comprises ultrasonic pickling, the temperature of the ultrasonic pickling is 50-100 ℃, the time is 1-2h, and the acid is preferably one of hydrochloric acid, nitric acid and carbon dioxide aqueous solution.

Preferably, the predetermined shape is one of a granular shape, a spherical shape, a cylindrical shape, a mesoporous shape, a clover shape and a clover shape.

Preferably, the binder comprises at least one of clay, kaolin, bentonite and pseudo-boehmite;

the pore-forming agent is starch or coconut shell activated carbon;

the strength agent is glass fiber or calcium sulfate whisker;

the lubricant is glycerol or ethanolamine.

According to another aspect of the invention, the flue gas denitration molded catalyst prepared by the preparation method is provided.

According to another aspect of the invention, the application of the flue gas denitration molded catalyst is to use NH₃For the use of the reducing agent for flue gas denitration, the catalytic temperature is preferably 150-250 ℃.

The invention has the following beneficial effects:

(1) the invention uses fly ash as a carrier to reduce the cost, Mn has good low-temperature denitration performance, Ce is favorable for improving the structural stability and the dispersibility of manganese and improving the sulfur-resistant and water-resistant performance of the catalyst, Mn and Ni form a composite structure and are favorable for further improving the low-temperature denitration performance of the catalyst, and Mn, Ce and Ni ensure that the denitration efficiency of the catalyst reaches more than 90 percent in the low-temperature 200-plus 250 ℃ temperature range, so the catalytic device can be arranged behind a dust removal and desulfurization device, can avoid the problems that the catalyst faces blockage, poisoning and inactivation and the like due to long-time operation under the high-temperature condition, and can further prolong the service life of the catalyst.

(2) The catalyst has good sulfur-resistant and water-resistant performances, and the denitration efficiency is still over 80% when the concentration of SO2 is 100ppm and the concentration of H2O is 10 Vol.%.

(3) The catalyst of the invention has high flue gas treatment capacity and airspeedIs 4000h^-1-8000h^-1The denitration efficiency is higher and reaches more than 80% in the range, so that the denitration catalyst can be applied to most of flue gas treatment scenes.

(4) The catalyst of the invention adopts the fly ash of the fire coal as the raw material and adopts low-cost pretreatment means such as: the CO2 water washing pretreatment enriches the pore structure of the coal fly ash, increases the specific surface area of the coal fly ash, further obtains a good catalyst carrier, greatly reduces the raw material cost of the catalyst, and realizes the purpose of treating waste by waste. In addition, other components of the catalyst are non-toxic and do not bring secondary pollution.

(5) The catalyst of the invention adopts some lower cost forming agents such as: the raw materials such as clay (binder), starch (pore-forming agent) and the like are low in cost and easy to obtain, and the raw material cost of the catalyst is greatly reduced.

(6) The formed catalyst prepared by the invention has more practical engineering value compared with the powder catalyst in most patents or articles, and has good mechanical strength and very convenient transportation and storage. .

Drawings

FIG. 1 is a graph showing denitration curves at 80 to 320 ℃ for catalysts of example 1, example 7, example 8 and example 9.

FIG. 2 is a graph showing denitration curves at 80 to 320 ℃ for the shaped catalysts prepared in examples 1 to 3.

Fig. 3 is a graph of the denitration profiles of the formed catalysts prepared in examples 1-3 at 200 ℃ and an atmosphere of 10 vol.% H2O and 100ppm SO 2.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

Examples

The fly ash of the invention is fly ash of coal in a Chongqing Luohu thermal power plant, and the components are shown in Table 1.

TABLE 1 fly ash ingredient table for coal

The coal fly ash was subjected to ultrasonic pickling, and the structural change after pickling was as shown in table 2. The nitric acid ultrasonic pickling is carried out for 2 hours by using 5 percent nitric acid ultrasonic pickling. The treatment was carried out using an aqueous solution of carbon dioxide, specifically with a flow of CO2 of 0.2L/min, water/ash of 50ml/g, a CO2 wash time of 2h, and a wash temperature of 50 ℃.

TABLE 2 post-pickling structural table of fly ash of coal

Sample (I)	S_BET(m²/g)	Pore volume (10)^-2cm³/g)	Average pore diameter (nm)
				Raw fly ash	2.41	0.67	11.07
CO2 water-washed fly ash	87.54	10.49	4.80
				Nitric acid ultrasonic pickling fly ash	122.77	14.41	4.69

From tables 1-2, it is evident that Si, Al, Na, Ca, Mg, Fe are the main elements in the fly ash, and most of the alkali metals (Na, K), alkaline earth metals (Ca, Mg) and S elements in the fly ash are removed after nitric acid ultrasonic pickling, and the main components of the fly ash, namely SiO2 and Al2O3, are found to be good carriers for the catalyst by XRD test on the fly ash. Meanwhile, the specific surface area of the coal-fired fly ash subjected to nitric acid ultrasonic pickling is obviously improved, and the pore structure of the catalyst carrier is greatly enriched.

Example 1

(1) Adding 5% nitric acid into coal-fired fly ash, performing ultrasonic pickling for 2 hours, wherein the acid to ash ratio is 10ml/g, the pickling temperature is 50 ℃, washing with water to be neutral after pickling, drying, taking 69g of coal-fired fly ash, adding 5g of clay, 2g of starch, 3g of glass fiber, 1g of glycerol and 20g of water, stirring and mixing uniformly, putting into a kneader for 2 hours, uniformly dispersing and kneading, standing for 4 hours after kneading, adding a spiral extruder for extrusion molding, respectively extruding cylindrical molding particles with the equivalent diameter of 5mm and the length of 15mm, and drying by adopting a sectional drying mode of 50 ℃ (4 hours) +100 ℃ (4 hours) to obtain a carrier;

(2) dissolving 3.59g of manganese nitrate, 6.54g of cerium nitrate and 3.67g of nickel nitrate to obtain a mixed salt solution, wherein the quantity ratio of manganese, cerium and nickel is 1:1:1, the content of active components such as manganese, cerium, nickel and the like accounts for 20 wt% of the total mass of the fly ash, and immersing a carrier into the mixed salt solution to load manganese salt, cerium salt and nickel salt to obtain a precursor;

(3) the precursor is dried in a segmented way at 250 ℃ (4h) +500 ℃ (4h)Calcining at a heating rate of 5 ℃/min to obtain the flue gas denitration molded catalyst, and recording the Mn as the Mn₁Ce₁Ni₁。

Example 2

The difference between this example and example 1 is that the shape of the carrier is different, specifically, it is a round hole shape, with an outer diameter of 5mm and an inner diameter of 1.5 mm.

Example 3

This example differs from example 1 in that the shape of the support is different, in particular a clover shape, with an equivalent diameter of 5mm

Example 4

This example differs from example 1 in that the pretreatment method of the fly ash of coal combustion differs, and the treatment is carried out using an aqueous solution of carbon dioxide, specifically CO₂The flow rate is 0.2L/min, the ratio of water to ash is 50ml/g, and CO₂The washing time is 2h, and the washing temperature is 50 ℃.

Example 5

This example differs from example 2 in that the pretreatment method of the fly ash from coal combustion differs, and the treatment is carried out using an aqueous solution of carbon dioxide, specifically CO₂The flow rate is 0.2L/min, the ratio of water to ash is 50ml/g, and CO₂The washing time is 2h, and the washing temperature is 50 ℃.

Example 6

This example differs from example 3 in that the pretreatment method of the fly ash of coal combustion differs, and the treatment is carried out using an aqueous solution of carbon dioxide, specifically CO₂The flow rate is 0.2L/min, the ratio of water to ash is 50ml/g, and CO₂The washing time is 2h, and the washing temperature is 50 ℃.

Example 7

This example differs from example 1 in that the ratio of the amounts of manganese, cerium and nickel species is 1:1:0.5, noted as Mn₁Ce₁Ni_0.5。

Example 8

This example differs from example 1 in that the ratio of the amounts of manganese, cerium and nickel species is 1:1:1.5, noted as Mn₁Ce₁Ni_1.5。

Example 9

This example differs from example 1 in that the ratio of the amounts of manganese, cerium and nickel species is 1:1:2, noted as Mn₁Ce₁Ni₂。

Test examples

And (4) testing mechanical properties by using a universal pressure tester. The compression strength test method is that the formed catalyst is vertically placed on a test platform, the pressurizing speed is 2mm/min, the catalyst is applied with vertical pressure, and the maximum pressure which can be borne by the formed catalyst sample on a unit area before the formed catalyst sample is damaged is the axial compression strength of the formed catalyst sample, and is expressed by MPa.

And (4) testing the denitration performance. The experimental conditions are as follows: the temperature is 80-320 ℃, N₂Balance gas, 6 Vol.% O₂，500ppm NO，500ppm NH₃,GHSV＝6000h^-1。

And (5) testing the sulfur resistance and water resistance. The experimental conditions are as follows: at a temperature of 200 ℃ N₂Balance gas, 6 Vol.% O₂，500ppm NO，500ppm NH₃,SO₂＝100ppm、H₂O＝10Vol.％、GHSV＝6000h^-1。

The test results are shown in table 3.

Table 3 table of test results of examples

The catalysts of example 1, example 7, example 8 and example 9 were subjected to XPS test, and the test results are shown in table 4.

Table 4 XPS characterization results for different catalyst formulations

As can be seen from FIG. 1, in the temperature range of 80-260 ℃, when Mn: the molar ratio of Ce to Ni is 1:1:1, the maximum denitration performance of the catalyst reaches 98.4%, and XPS tests show that Mn in the catalyst is in the formula³⁺、Mn⁴⁺、O_αThe higher content of (A) leads the catalyst to have better low-temperature denitration performance, which is also related to the catalytic action of MnOx and the valence state thereof, which is MnO2 and is proved in various literatures>Mn2O3>MnO, i.e., the higher the valence state, the better and consistent the catalytic performance.

It can be seen from fig. 2 that the denitration performance of the molded round-hole catalyst is better than that of the cylindrical and cloverleaf catalysts, and the round-hole catalyst achieves 98.40% of the maximum denitration efficiency at 200 ℃, which is mainly due to the fact that the round-hole catalyst has larger contact area with gas than the cylindrical and cloverleaf catalysts.

The results of mechanical property tests on the three catalysts are shown in table 3, and the mechanical properties of the round-hole catalyst are lower than those of cylindrical and cloverleaf catalysts, but the axial compressive strength of the round-hole catalyst is 2.74Mpa, which also reaches the national standard (2Mpa), so that the denitration performance of the round-hole catalyst can be improved, and the cost of raw materials can be saved.

From fig. 3, it can be seen that, when the reaction is carried out under the atmosphere condition containing 10 vol.% of H2O and 100ppm of SO2 for 4 hours, the denitration efficiency is still about 80%, and moreover, after the H2O and the SO2 are cut off for 1 hour, the denitration performance is respectively restored to 89.40%, 91.51% and 90.89%, which indicates that the three catalysts have good sulfur-resistant and water-resistant performance.

Application examples

The coal-fired boiler of 20t/h of Hubei City east renewable resources science and technology development Limited company has the NOx concentration of 150ppm before desulfurization and the actual flue gas temperature of 140 ℃, and by adopting the round-hole-shaped catalyst, the denitration efficiency reaches 78.42(140 ℃), and if the flue gas temperature is heated to 200 ℃, the denitration efficiency reaches 97.8 percent. If the cylindrical catalyst is adopted, the denitration efficiency reaches 74.14 percent (140 ℃), and the denitration efficiency reaches 92.68 percent when the catalyst is heated to 200 ℃. If the clover-shaped catalyst is adopted, the denitration efficiency reaches 76.88(140 ℃), and the denitration efficiency reaches 94.46% when the catalyst is heated to 200 ℃.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. The preparation method of the flue gas denitration molded catalyst is characterized by comprising the following steps of:

2. The method according to claim 1, wherein the ratio of the amounts of the manganese salt, the cerium salt and the nickel salt is (1-5): (1-5): (1-5), preferably 1:1:1.

3. The method according to claim 2, wherein the sum of the mass of the manganese salt, the cerium salt and the nickel salt in step (2) is 5 to 30% of the mass of the support.

4. The production method according to claim 2 or 3, wherein the manganese salt is at least one of manganese nitrate, manganese chloride, and manganese sulfate; the cerium salt is at least one of cerium nitrate, cerium chloride and cerium sulfate; the nickel salt is at least one of nickel nitrate, nickel chloride and nickel sulfate.

5. The preparation method as claimed in claim 1, wherein the calcination in step (3) comprises a first calcination and a second calcination, wherein the temperature of the first calcination is 100-300 ℃ for 4-6h, and the temperature of the second calcination is 300-500 ℃ for 4-6 h.

6. The preparation method according to claim 1, wherein the coal fly ash is pretreated in the step (1), the pretreatment comprises ultrasonic acid washing, the temperature of the ultrasonic acid washing is 50-100 ℃, the time is 1-2h, and preferably, the acid is one of hydrochloric acid, nitric acid and carbon dioxide aqueous solution.

7. The method of claim 1, wherein the predetermined shape is one of granular, spherical, cylindrical, mesoporous, trilobed, and tetrafoil.

8. The method of claim 1, wherein the binder comprises at least one of clay, kaolin, bentonite, and pseudoboehmite;

the pore-forming agent is starch or coconut shell activated carbon;

the strength agent is glass fiber or calcium sulfate whisker;

the lubricant is glycerol or ethanolamine.

9. The flue gas denitration molded catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the flue gas denitration molded catalyst according to claim 9, wherein the application is to use NH₃For the use of the reducing agent for flue gas denitration, the catalytic temperature is preferably 150-250 ℃.