Modified catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of waste gas treatment and cement industry flue gas multi-pollutant cooperative control, in particular to a modified catalyst for denitration of cement kiln flue gas and cooperative catalytic oxidation of toluene as well as a preparation method and application of the modified catalyst. The invention provides an efficient and stable modified catalyst capable of simultaneously removing methylbenzene and NOx as well as a preparation method and application of the efficient and stable modified catalyst. The modified catalyst takes a pure silicon molecular sieve MCM-41 synthesized under an alkaline condition as a carrier and can be prepared by reducing and loading Cu < 2 + > and Ce < 3 + > on the surface of the carrier through Cu (NO3) 2 and Ce (NO3) 3. The modified catalyst provided by the invention is simple in preparation method, can be applied to flue gas purification of a cement kiln, can be used for synergistically catalyzing and oxidizing toluene while denitration is performed, is superior to a single waste gas treatment method in industrial production, can meet actual engineering requirements, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of waste gas treatment and coordinated control of multiple pollutants in cement industry flue gas, and in particular to a modified catalyst for denitration of cement kiln flue gas and coordinated catalytic oxidation of toluene, as well as a preparation method and application thereof. Background Art

[0002] Nitrogen monoxide (NO) is the main pollutant emitted by the cement industry. Large amounts of nitrogen oxides (NOx) emitted will form acid rain and photochemical smog, which seriously harm the ecological environment and human health. Currently, the denitrification technologies for cement kilns mainly include low-nitrogen combustion technology, selective catalytic reduction technology (SCR) and selective non-catalytic reduction (SNCR) technology.

[0003] With the development of co-treatment of waste in cement kilns, the composition of flue gas pollutants has become more complex. Co-treatment of solid waste such as urban domestic garbage will produce volatile organic compounds (VOCs). The composition of VOCs is complex. Benzene, toluene, ethylbenzene and xylene are typical gases. Among them, toluene is highly toxic and has a low boiling point. It can damage the human skin, respiratory system and nervous system, leading to various adverse reactions. After toluene gas enters the atmosphere, it will participate in photochemical reactions near the ground, causing damage to the ozone layer.

[0004] Toluene and NOx are both major sources of air pollution. In view of the co-existence of these two types of pollutants in the co-disposal of waste in cement kilns, the development of catalysts with high activity and high resistance is the key to achieving the simultaneous removal of toluene and NOx.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The present invention provides a modified catalyst for cement kiln flue gas denitration and synergistic catalytic oxidation of toluene, as well as a preparation method and application thereof, which can simultaneously solve the problem of difficult NOx removal and the problem of toluene pollutants generated by cement kiln synergistic disposal of solid wastes, and meet actual engineering needs.

[0007] Specifically, the technical solution of the present invention is as follows: In the first aspect, the present invention provides a modified catalyst, which is composed of a pure silicon molecular sieve MCM-41 carrier and metal ions loaded on the surface of the carrier; the metal ions are Cu in a mass ratio of 1-3:1-3 2+ and Ce 3+ ; The metal ion loading is 20%±5%.

[0008] The modified catalyst provided by the invention can remove toluene and NOx simultaneously, thus achieving low-cost emission reduction.

[0009] The present invention uses pure silicon molecular sieve MCM-41 carrier to load metal ion Cu 2+ and Ce 3+ . CeO2 has good Ce 3+ ↔Ce 4+ CeO2 has high solubility for transition metal Cu and can form CuCe solid solution oxide in a wide range of Cu content. 2+ and Ce 4+ The strong Lewis acidic sites that can be formed between Cu and Ce and the strong interaction between Cu and Ce can increase the number of unsaturated metal cations in Cu-Ce-MCM-41.

[0010] The present invention converts the metal ion Cu 2+ and Ce 3+ After the introduction of the porous framework of MCM-41 molecular sieve, the entry of metal ions fills the surface defects in the framework, increases the acid amount and acid strength of the molecular sieve, thereby increasing the Lewis acid sites of the catalyst, thereby promoting the oxidation of NO into NO2 and activation of toluene, enhancing the toluene-SCR activity of the catalyst, and finally further reducing NO2 into N2 and H2O, and oxidizing toluene into CO2 and H2O.

[0011] The modified catalyst provided by the present invention is very suitable for cement kiln flue gas denitration and coordinated catalytic oxidation of toluene. It can treat two harmful gases at the same time and has a high removal efficiency for both harmful gases.

[0012] Preferably, the modified catalyst is made of pure silicon molecular sieve MCM-41 synthesized under alkaline conditions, and the loaded Cu is reduced by Cu(NO3)2 and Ce(NO3)3. 2+ 、Ce 3+ to the surface of the carrier.

[0013] In a second aspect, the present invention provides a method for preparing the modified catalyst, comprising: drying and calcining the pure silicon molecular sieve MCM-41 adsorbed with a metal ion solution.

[0014] Preferably, the drying temperature is 60±5°C and the drying time is 24±6h.

[0015] Preferably, the calcination temperature is 550±50° C. and the calcination time is 5±1 h.

[0016] In one optional more specific embodiment, the preparation method provided by the present invention comprises the following steps: S1, preparation of pure silicon molecular sieve MCM-41; S2, dispersing the prepared pure silicon molecular sieve MCM-41 into deionized water by ultrasonic dispersion to obtain a suspension; S3, containing Cu 2+ and Ce 3+ The solution is added dropwise to the suspension obtained in step S2 and stirred to obtain a suspension containing Cu 2+ 、Ce 3+ Suspension; S4. Filter the suspension obtained in step S3 after the reaction, wash, dry, and calcine in a muffle furnace in an air atmosphere to obtain the desired metal-loaded modified catalyst.

[0017] In a third aspect, the present invention provides the use of the modified catalyst, or the modified catalyst prepared by the preparation method, in cement kiln flue gas purification.

[0018] Toluene and nitrogen oxides are the main harmful gases in cement kiln flue gas. The modified catalyst of the present invention can be used for purifying cement kiln flue gas, and can catalyze and oxidize toluene for conversion while denitrifying.

[0019] In one optional more specific embodiment, the present invention provides a method for removing NO and toluene using the modified catalyst, comprising the following steps: First, catalytic oxidation of toluene is carried out in the secondary cyclone at the top of the decomposition furnace at a temperature of 300℃-600℃; then it enters the decomposition furnace to remove NO at a temperature of 750℃-1000℃; finally, it enters the rotary kiln with the raw material to participate in the cement clinker formation reaction. This method can solve the problem of flue gas treatment where toluene and NOx coexist, with high removal efficiency, simple process, and no waste catalyst generation.

[0020] In a fourth aspect, the present invention provides the modified catalyst, or the use of the modified catalyst prepared by the preparation method in the denitration and synergistic catalytic oxidation of toluene.

[0021] The present invention applies the modified catalyst or the modified catalyst prepared by the preparation method to the denitration of cement kiln flue gas purification by synergistic catalytic oxidation of toluene, which can simultaneously achieve the removal of toluene and nitrogen oxides, and the total removal rate of harmful gases is significantly improved compared with conventional methods: when the temperature condition is 550°C, the toluene removal rate is ≥85%; when the temperature condition is 600°C, the toluene removal rate is ≥90%. When the temperature condition is 800°C, the denitration rate is ≥45%.

[0022] Beneficial effects: The present invention provides a highly efficient and stable modified catalyst capable of removing toluene and NOx simultaneously, and a preparation method and application thereof. The modified catalyst uses pure silicon molecular sieve MCM-41 synthesized under alkaline conditions as a carrier, and can reduce the loaded Cu by Cu(NO3)2 and Ce(NO3)3. 2+ 、Ce 3+The modified catalyst provided by the invention has a simple preparation method, can be applied to cement kiln flue gas purification, can catalytically oxidize toluene while denitrifying, is superior to a single waste gas treatment method in industrial production, can meet actual engineering needs, and has good application prospects. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The endpoints and any values ​​of the ranges disclosed in this specification are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0025] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "specific implementations", or "some specific implementations" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0026] In the examples provided in this specification, if no specific techniques or conditions are specified, the techniques or conditions described in the literature in this field or the product instructions are used. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased through regular channels.

[0027] In the following examples, the modified catalyst Cu-Ce-MCM-41 was prepared according to the following method: S1. Preparation of pure silicon molecular sieve MCM-41: dissolve 2.4 g of hexadecyltrimethylammonium bromide in 120 ml of deionized water, and add 10.25 ml of ammonia water dropwise and stir; add tetraethyl orthosilicate dropwise to the prepared solution and stir for 3 hours to obtain a milky white suspension, pour the reacted suspension into a reactor and perform hydrothermal reaction at 110°C for 24 hours, after cooling, put it into a centrifuge and centrifuge it 3 times with deionized water and once with anhydrous ethanol, put the precipitate in the centrifuge tube into an oven and dry it at 60°C for 24 hours to obtain a white powder, and finally roast it in a muffle furnace at 550°C for 5 hours to obtain the desired porous carrier adsorbent.

[0028] S2. Disperse the prepared pure silicon molecular sieve MCM-41 into deionized water by ultrasonic dispersion to obtain a suspension.

[0029] S3, containing Cu 2+ and Ce 3+ The solution is added dropwise to the suspension obtained in step S2 and stirred to obtain a solution containing Cu 2 + 、Ce 3+ The suspension contains Cu 2+ and Ce 3+ The specific solutions can be 0.018~0.054g / mL Cu(NO3)2 solution and 0.014~0.042g / mL Ce(NO3)3 solution.

[0030] Different embodiments adjust the mass ratio and loading amount of Cu and Ce by controlling the solution concentration and the solution drop amount. For example, in one embodiment, the specific steps of step S3 are: dissolve 0.9g of Cu(NO3)2 in 50mL of water, dissolve 2.1g of Ce(NO3)3 in 50mL of water, stir evenly, add dropwise to the suspension obtained in step S2 and stir; the drying temperature in step S4 is 60°C, the drying time is 24h; the roasting temperature is 550°C, and the roasting time is 5h.

[0031] S4. Filter the suspension obtained in step S3 after the reaction, wash, dry (60° C., 24 h), and calcine in a muffle furnace in an air atmosphere (550° C., 5 h) to obtain the desired metal-loaded modified catalyst.

[0032] Example 1

[0033] Cu:Ce=1:1 (mass ratio) and Cu-Ce-MCM-41 with a loading of 20% were ground to pass through a 60-mesh sieve to obtain a powder of 60-80 mesh.

[0034] 0.2g Cu-Ce-MCM-41 powder was added to a tube furnace with a diameter of 8mm. When the flue gas conditions were 500ppm toluene, 3% O2, N2 as the balance gas, the total gas flow rate was 300ml / min, and the temperature was 550℃, the toluene removal rate was 98.69%; when the temperature was 600℃, the toluene removal rate was 99.74%. When the flue gas conditions were 1000ppm toluene, 3% O2, N2 as the balance gas, the total gas flow rate was 450ml / min, and the temperature was 800℃, the denitrification rate was 62%.

[0035] Example 2

[0036] Cu:Ce=2:1 (mass ratio) and Cu-Ce-MCM-41 with a loading of 20% were ground to pass through a 60-mesh sieve to obtain a 60-80 mesh powder.

[0037] 0.2g Cu-Ce-MCM-41 powder was added to a tube furnace with a diameter of 8mm. When the flue gas conditions were 500ppm toluene, 3% O2, N2 as the balance gas, the total gas flow rate was 300ml / min, and the temperature was 550℃, the toluene removal rate was 90.19%; when the temperature was 600℃, the toluene removal rate was 96.23%. When the flue gas conditions were 1000ppm toluene, 3% O2, N2 as the balance gas, the total gas flow rate was 450ml / min, and the temperature was 800℃, the denitrification rate was 56.1%.

[0038] Example 3

[0039] Cu:Ce=3:1 (mass ratio) and Cu-Ce-MCM-41 with a loading of 20% were ground to pass through a 60-mesh sieve to obtain a powder of 60-80 mesh.

[0040] 0.2g Cu-Ce-MCM-41 powder was added to a tube furnace with a diameter of 8mm. When the flue gas conditions were 500ppm toluene, 3% O2, N2 as the balance gas, the total gas flow rate was 300ml / min, and the temperature was 550℃, the toluene removal rate was 92.69%; when the temperature was 600℃, the toluene removal rate was 97.76%. When the flue gas conditions were 1000ppm toluene, 3% O2, N2 as the balance gas, the total gas flow rate was 450ml / min, and the temperature was 800℃, the denitrification rate was 58%.

[0041] Example 4

[0042] Cu:Ce=1:2 (mass ratio) and Cu-Ce-MCM-41 with a loading of 20% were ground to pass through a 60-mesh sieve to obtain a 60-80 mesh powder.

[0043] 0.2g Cu-Ce-MCM-41 powder was added to a tube furnace with a diameter of 8mm. When the flue gas conditions were 500ppm toluene, 3% O2, N2 as the balance gas, the total gas flow rate was 300ml / min, and the temperature was 550℃, the toluene removal rate was 88.69%; when the temperature was 600℃, the toluene removal rate was 90.64%. When the flue gas conditions were 1000ppm toluene, 3% O2, N2 as the balance gas, the total gas flow rate was 450ml / min, and the temperature was 800℃, the denitrification rate was 47%.

[0044] Example 5

[0045] Cu:Ce=1:3 (mass ratio) and Cu-Ce-MCM-41 with a loading of 20% were ground to pass through a 60-mesh sieve to obtain a powder of 60-80 mesh.

[0046] 0.2g Cu-Ce-MCM-41 powder was added to a tube furnace with a diameter of 8mm. When the flue gas conditions were 500ppm toluene, 3% O2, N2 as the balance gas, the total gas flow rate was 300ml / min, and the temperature was 550℃, the toluene removal rate was 85.69%; when the temperature was 600℃, the toluene removal rate was 93.74%. When the flue gas conditions were 1000ppm toluene, 3% O2, N2 as the balance gas, the total gas flow rate was 450ml / min, and the temperature was 800℃, the denitrification rate was 45%.

[0047] Comparative Example 1

[0048] When the flue gas conditions were 500ppm toluene, 3% O2, N2 as the balance gas, and the total gas flow rate was 300ml / min, 0.2g Cu-MCM-41 (20%) was added to a tube furnace with a diameter of 8mm. When the temperature condition was 550℃, the toluene removal rate was 67.2%; when the temperature condition was 600℃, the toluene removal rate was 79.64%. When the flue gas conditions were 1000ppm NO, 3% O2, N2 as the balance gas, the total gas flow rate was 450ml / min, and the temperature condition was 800℃, the denitrification rate was 40%.

[0049] Comparative Example 2

[0050] When the flue gas conditions were 500ppm toluene, 3% O2, N2 as the balance gas, and the total gas flow rate was 300ml / min, 0.2gCe-MCM-41 (20%) was added to a tube furnace with a diameter of 8mm. When the temperature condition was 550℃, the toluene removal rate was 58.53%; when the temperature condition was 600℃, the toluene removal rate was 75.67%. When the flue gas conditions were 1000ppm NO, 3% O2, N2 as the balance gas, the total gas flow rate was 450ml / min, and the temperature condition was 800℃, the denitrification rate was 38%.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified catalyst, characterized in that: It is composed of a pure silicon molecular sieve MCM-41 carrier and metal ions loaded on the surface of the carrier; the metal ions are Cu 2+ and Ce 3+ ; The metal ion loading is 20%±5%.

2. The modified catalyst according to claim 1, characterized in that: It is made of pure silicon molecular sieve MCM-41 synthesized under alkaline conditions, and loaded with Cu by reduction of Cu(NO3)2 and Ce(NO3)3. 2+ 、Ce 3+ to the surface of the carrier.

3. The method for preparing the modified catalyst according to claim 1 or 2, characterized in that: include: The pure silicon molecular sieve MCM-41 adsorbed with the metal ion solution is dried and calcined.

4. The method for preparing the modified catalyst according to claim 3, characterized in that: The drying temperature is 60±5℃ and the drying time is 24±6h.

5. The method for preparing the modified catalyst according to claim 3 or 4, characterized in that: The calcination temperature is 550±50℃ and the calcination time is 5±1h.

6. The method for preparing a modified catalyst according to any one of claims 3 to 5, characterized in that: The steps include: S1, preparation of pure silicon molecular sieve MCM-41; S2, dispersing the prepared pure silicon molecular sieve MCM-41 into deionized water by ultrasonic dispersion to obtain a suspension; S3, containing Cu 2+ and Ce 3+ The solution is added dropwise to the suspension obtained in step S2 and stirred to obtain a suspension containing Cu 2+ 、Ce 3+ Suspension; S4. Filter the suspension obtained in step S3 after the reaction, wash, dry, and calcine in a muffle furnace in an air atmosphere to obtain the desired metal-loaded modified catalyst.

7. Use of the modified catalyst according to claim 1 or 2, or the modified catalyst prepared by the preparation method according to any one of claims 3 to 6 in cement kiln flue gas purification.

8. Use of the modified catalyst according to claim 1 or 2, or the modified catalyst prepared by the preparation method according to any one of claims 3 to 6, in the denitration and synergistic catalytic oxidation of toluene.

9. The use according to claim 7 or 8, characterized in that: The toluene removal rate at a temperature of 550°C is ≥85%; and / or the toluene removal rate at a temperature of 600°C is ≥90%.

10. The use according to claim 7 or 8, characterized in that: The denitrification rate under the temperature condition of 800℃ is ≥45%.