Preparation method of low-temperature microporous ZSM-5 molecular sieve denitration catalyst

Abstract

The application discloses a preparation method of a low-temperature microporous ZSM-5 molecular sieve denitration catalyst, and is characterized in that the method comprises the following steps: (1) mixing fly ash with dilute acid, dissolving and filtering to obtain iron-removed fly ash and an iron-containing liquid; (2) mixing the iron-removed fly ash with concentrated acid to perform acid dissolution and aluminum extraction, and filtering to obtain an aluminum-containing filtrate and a silicon-containing filter cake; (3) mixing the silicon-containing filter cake with an alkali solution to perform alkali dissolution and silicon extraction, and then filtering to obtain a silicon-containing filtrate; (4) mixing the aluminum-containing filtrate with the silicon-containing filtrate, and performing hydrothermal crystallization under an alkaline condition; (5) filtering, washing, drying and calcining the mixture obtained in the step (4) to obtain ZSM-5 molecular sieve; and (6) impregnating the ZSM-5 molecular sieve with a manganese-containing solution and the iron-containing liquid, and drying and calcining to obtain a denitration catalyst. The application uses fly ash as a raw material to prepare the molecular sieve denitration catalyst, can solve the problems of fly ash piling up and causing environmental problems, and can be used for tail gas denitration of a coal-fired power plant, so that the effect of treating waste with waste is achieved.

Description

Technical Field

[0001] This invention relates to the field of flue gas denitrification technology, specifically providing a method for preparing a ZSM-5 molecular sieve denitrification catalyst and the resulting catalyst. Background Technology

[0002] Fly ash is a byproduct of high-temperature combustion in coal-fired power plants. Currently, China is the world's largest producer and consumer of coal. With increasing coal consumption, fly ash emitted from coal-fired power plants has become one of the largest industrial solid wastes. Fly ash itself is a potential "urban mineral," with its chemical composition mainly including SiO2, Al2O3, Fe2O3, CaO, MgO, K2O, Na2O, P2O5, TiO2, MnO, and SO3. The mass fraction of SiO2 is approximately 35.6%–57.2%, and the mass fraction of Al2O3 is approximately 18.8%–55.0%, making it a typical aluminosilicate mineral. Currently, the comprehensive utilization of fly ash in China is mainly concentrated in industries such as cement, concrete, wall materials, agriculture, and roadbed construction. While these industries can absorb a portion of fly ash, their added value is low. Therefore, achieving high-value-added utilization of fly ash has become a research hotspot in recent years.

[0003] On the other hand, in addition to fly ash, coal combustion also produces particulate matter, nitrogen oxides, carbon oxides, and sulfur dioxide from power plant flue gas. Nitrogen oxides (NOx) x The main forms of N₂O are N₂O, NO, N₂O₃, NO₂, N₂O₄, and N₂O₅, with NO being the most prevalent, accounting for approximately [a certain percentage] of the total N₂O. x NO accounts for over 90% of the total, followed by NO2. In the atmosphere, NO is oxidized to NO2, and under ultraviolet radiation, NO2 reacts with CHx in flue gas to form photochemical smog, which is 4-5 times more toxic than NO and is extremely harmful to most human organs as well as plants and animals. Although N2O is present in relatively low amounts, it is a precursor to near-surface atmospheric ozone pollution, secondary fine particulate matter pollution, and eutrophication of surface water, making the resulting environmental problems a hot topic in air pollution. In 2003, my country's NO... x Emissions exceeded 16 million tons, reaching 21.94 million tons by 2012, making it the world's number one NO. x Emitting countries. At current pollutant emission levels, by 2020, NO... x Emissions will reach 30 million tons. Currently, my country's NO emissions... x Rapidly increasing emissions have exacerbated regional acid rain, even partially offsetting my country's significant efforts in SO2 control. Statistics show that my country's NO... xIncreased emissions have led to a shift in acid rain pollution from sulfuric acid-based to a complex of sulfuric and nitric acids. The proportion of nitrate ions in acid rain has gradually increased from 10% in the 1980s to 30% in recent years. Meanwhile, NO... x It is also an important cause of regional fine particulate pollution and haze, due to the recent increase in NO... x Significant increases in emissions have led to a decline in atmospheric visibility and a rise in haze in my country. Therefore, controlling NOx emissions is crucial. x Emissions control has become a crucial task in air pollution control. Currently, the main industrially applied denitrification technology is selective catalytic reduction (SCR) denitrification, which uses NH3 as a reducing agent. The catalyst is the core of SCR denitrification technology. Currently, commercially available catalysts use V2O5+WO3(MoO3) / TiO2 (anatase) as the active component. The active temperature window of this catalyst is 300–400℃. In the high-temperature range, it is easily affected by SO2 and ash in the flue gas, which reduces the catalyst's lifespan. Therefore, high-efficiency, low-temperature SCR catalysts have become a research hotspot in recent years. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a low-temperature microporous ZSM-5 molecular sieve denitrification catalyst. The method uses fly ash, such as fly ash from coal-fired power plants, as a waste material to prepare the molecular sieve denitrification catalyst. This method can solve the problem of fly ash disposal and the environmental problems caused by it, make full use of the silicon, aluminum, and iron resources in fly ash, prepare a transition metal supported molecular sieve denitrification catalyst, and can be used for denitrification of tail gas from coal-fired power plants, achieving the effect of treating waste with waste.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a low-temperature microporous ZSM-5 molecular sieve denitration catalyst, the method comprising the following steps:

[0007] (1) After mixing fly ash with dilute acid to dissolve and remove iron, filter to obtain iron-removed fly ash as filter cake and iron-containing liquid as filtrate.

[0008] (2) Mix the iron-removing fly ash with concentrated acid, perform acid dissolution to extract aluminum, and then filter to obtain aluminum-containing filtrate and silicon-containing filter cake;

[0009] (3) The silicon-containing filter cake is mixed with an alkaline solution to extract silicon by alkaline dissolution, and then filtered to obtain a silicon-containing filtrate;

[0010] (4) Mix the aluminum-containing filtrate with the silicon-containing filtrate and carry out a hydrothermal crystallization reaction under alkaline conditions;

[0011] (5) Filter the mixture obtained after the reaction in step (4), and wash, dry and calcine the filtered colloid to obtain powdered fly ash-based ZSM-5 molecular sieve;

[0012] (6) The ZSM-5 molecular sieve obtained in step (5) is impregnated with a manganese-containing solution and an iron-containing liquid in step (1), and then dried and calcined to obtain a transition metal-supported ZSM-5 molecular sieve denitration catalyst.

[0013] The ZSM-5 molecular sieve denitrification catalyst has an iron content of 5-7.5%, such as 5.5%, 6% or 7%, and a manganese content of 5-7.5%, such as 5.5%, 6% or 7%.

[0014] In step (1) of this invention, iron in fly ash can be dissolved using dilute acid at room temperature (e.g., 10-40℃, for example, 20-25℃) to prepare an iron-containing liquid. In one embodiment, the dilute acid used is dilute HCl or dilute H2SO4, and the concentration of the dilute acid is 1-3 mol / L, for example, 1:2. The specific amount of dilute acid can be determined according to actual needs, for example, the mass ratio of fly ash to dilute acid can be 10:(5-10), for example, 10:7. In one embodiment, the mass ratio of fly ash to the molar mass of dilute acid is 10g:(0.01-0.03)mol, for example, 10g:0.02mol.

[0015] In one embodiment, the molar ratio of Fe3+ to Fe2+ in the iron-containing liquid is adjusted to (2-6):1, such as 3:1, 4:1, or 5:1. This can be achieved, for example, by adding an oxidizing or reducing agent to promote the activity of subsequently loaded manganese. In one embodiment, the Fe in the iron-containing liquid... 3+ The content is 200-400mg / ml, such as 235mg / ml, 260mg / ml, 300mg / ml, 350mg / ml or 380mg / ml, Fe 2+ The content is 50-100mg / ml, such as 67mg / ml, 70mg / ml, 80mg / ml or 90mg / ml.

[0016] In one embodiment, the residual iron content in the iron-removed fly ash does not exceed 4%, for example, 2-3%, such as 2.5%, meaning that the iron element has not been completely dissolved.

[0017] In step (2) of this invention, aluminum in fly ash is dissolved using concentrated acid to obtain an aluminum salt solution. Those skilled in the art will understand that during the acid dissolution process for aluminum extraction, other metallic elements in the fly ash, such as calcium and iron, will also partially dissolve. However, due to their low content, no significant negative impact has been observed in the hydrothermal synthesis of the molecular sieve in this invention. Furthermore, some of the Fe element may even enter the molecular sieve during subsequent hydrothermal synthesis, potentially inducing the formation of ZSM-5 molecular sieves at lower temperatures.

[0018] In one embodiment, the concentrated acid is concentrated HCl or H2SO4, and the concentration of the concentrated acid is 10-20 mol / L. The molar ratio of Al2O3 in the iron-containing fly ash to H+ in the acid solution is 1:6-10, for example, 1:7 or 1:8. In one embodiment, the acid-dissolution aluminum extraction reaction temperature is controlled at 100-150℃, and the reaction time is 1-3 hours to facilitate aluminum extraction.

[0019] In step (3) of this invention, silicon in the silica-containing filter cake is dissolved using an alkaline solution to generate soluble silicates, thereby obtaining a silica-containing filtrate through filtration. In one embodiment, the alkaline solution used is a sodium hydroxide or potassium hydroxide solution. During the alkaline dissolution reaction, the ratio of the dry weight of the silica-containing filter cake to the molar amount of hydroxide ions in the added alkali is 100g:(0.8-2)mol, for example, 100g:1mol, 100g:1.2mol, 100g:1.5mol, or 100g:1.8mol.

[0020] In one embodiment, the alkaline dissolution reaction temperature in step (3) is 90-100°C, such as 92°C, 95°C or 98°C, and the reaction time is 2-6h, such as 4h, so that silicon can be dissolved.

[0021] In step (4) of this invention, the aluminum-containing filtrate and the silicon-containing filtrate are mixed and subjected to a hydrothermal crystallization reaction under alkaline conditions, for example, by pouring the mixture into a stainless steel reactor lined with polytetrafluoroethylene. In one embodiment, the aluminum-containing filtrate and the silicon-containing filtrate are mixed at a Si:Al mass ratio of (40-100):1, for example, at 50:1, 60:1 or 80:1, and the pH of the system is adjusted to 10-12, for example, by using ammonia water or sodium hydroxide or potassium hydroxide solution. The crystallization reaction temperature is 80-130°C, for example, 100, 110 or 120°C, and the crystallization time is 24-72 hours, for example, 48 hours.

[0022] In step (5) of this invention, the mixture obtained after the reaction in step (4) is filtered, and the resulting colloid is washed, for example, with deionized water until neutral, and then dried, for example, in an oven. The drying temperature can be 90-100℃, such as 95℃, and the drying time can be 2-12h, such as 3h, which can be determined by those skilled in the art based on actual conditions. After drying, it is calcined to obtain powdered fly ash-based ZSM-5 molecular sieve. In one embodiment, the calcination temperature is 500-600℃, such as 550℃, the calcination time is 4-10h, such as 6h or 8h, and the heating rate is 3-7℃ / min, such as 5℃ / min. The ZSM-5 molecular sieve obtained by this invention has a microporous structure. In one embodiment, the micropore volume is 0.15-0.3cm³. 3 / g, specific surface area is 240-500m² 2 / g, for example 249-495m 2 / g, for example 260m 2 / g、300m 2 / g, 350m 2 / g、420m 2 / g or 480m 2 / g, with a pore size of 0.3-2nm, such as 0.31-1.96nm, for example 0.5, 1.0 or 1.5nm.

[0023] In step (6) of this invention, the prepared ZSM-5 molecular sieve is impregnated with a manganese-containing solution and the iron-containing liquid from step (1) to load the active component, and then dried to obtain the catalyst. In one embodiment, an iron-containing liquid and a manganese-containing solution are added to the ZSM-5 molecular sieve, and after magnetic stirring at 60°C for 24 hours, ethanol is added, stirred, evaporated to dryness, and calcined to obtain the Fe-Mn / ZSM-5 molecular sieve denitration catalyst. In one embodiment, the manganese-containing solution is a 0.01-0.1 mol / L, for example, a 0.02 mol / L Mn(NO3)2 solution. In one embodiment, the calcination temperature in step (6) is 500-600°C, for example, 550°C, the calcination time is 4-10 hours, for example, 6 hours or 8 hours, and the heating rate is 3-7°C / min, for example, 5°C / min.

[0024] In one embodiment, the total amount of Fe / Mn active components supported on the molecular sieve denitration catalyst in step (6) accounts for 10%-15% of the catalyst mass, for example, 12%; in another embodiment, the mass ratio of the two can be 1.5:1 to 1:1.5, for example, 1:1 or 1:1.2.

[0025] In one embodiment of the present invention, the fly ash used contains 4-10% iron, 19-35% aluminum, and 40-60% silicon.

[0026] In this invention, unless otherwise specified, the content of each metal element in fly ash is calculated based on its oxide; the content or percentage is mass content or mass percentage.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. This invention utilizes fly ash, a solid waste emitted from coal-fired boilers, to synthesize a molecular sieve denitrification catalyst. The preparation method is simple to operate, low in cost, and has a high utilization rate of raw materials. It can convert aluminum and silicon elements in fly ash into effective components in molecular sieves, and iron in the iron-containing liquid fly ash is loaded onto the molecular sieve as an active component, so that aluminum, iron, and silicon elements are fully utilized, achieving the purpose of solid waste resource utilization and increasing the added value of fly ash.

[0029] 2. ZSM-5 molecular sieves can be synthesized directly by hydrothermal crystallization using aluminum-containing filtrate and silicon-containing filtrate, eliminating the need for template agents, reducing costs, and facilitating industrial production.

[0030] 3. The denitrification catalyst of this invention is safe and non-toxic. Compared with existing denitrification catalysts, this catalyst has higher low-temperature denitrification efficiency, and can reduce NO in the gas within the low-temperature range of 100-300℃. x The concentration decreased by 90%-98%. Attached Figure Description

[0031] Figure 1 Process flow diagram for transition metal-supported fly ash-based ZSM-5 molecular sieve low-temperature denitrification catalyst;

[0032] Figure 2 The XRD pattern of ZSM-5 molecular sieve in Example 1 shows that all the diffraction peaks basically correspond to the standard diffraction peaks of ZSM-5 molecular sieve, and the crystallization is good with virtually no diffraction peaks of other impurities.

[0033] Figure 3 The image shows the SEM image of the ZSM-5 molecular sieve in Example 1. It can be seen that the molecular sieve has a needle-like morphology with a radius of 9-30 nm.

[0034] Figure 4 The XPS image of the transition metal supported fly ash-based ZSM-5 molecular sieve low-temperature denitrification catalyst in Example 1 shows that the active component Fe in the catalyst exists in the trivalent form, while Mn exists in the form of both tetravalent and trivalent forms.

[0035] Figure 5 The diagram shows the denitrification efficiency of the transition metal-supported fly ash-based ZSM-5 molecular sieve low-temperature denitrification catalyst in Example 1. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments and accompanying drawings. However, the present invention is not limited to the listed embodiments, but should also include equivalent improvements and modifications to the technical solutions defined in the appended claims of the present invention.

[0037] In the following examples / comparative examples, the relevant parameters are characterized using the following methods:

[0038] (1) The crystal structure of the prepared ZSM-5 molecular sieve was confirmed by XRD analysis using the D8 ADVANCE from Bruker GmbH, Germany, with a scan rate of 5° / min to 50° / min.

[0039] (2) The morphology of the prepared ZSM-5 molecular sieve was determined by SEM using a Nova NanoSEM450 scanning electron microscope from FEI Company in the Czech Republic.

[0040] (3) The surface elemental composition of the ZSM-5 molecular sieve denitration catalyst was determined by X-ray photoelectron spectroscopy using an ESCALAB 250Xi X-ray photoelectron spectrometer from Thermo Scientific, UK.

[0041] In the following examples / comparative examples, the fly ash used is fly ash from a coal-fired power plant, and its composition is as follows:

[0042] Table 1 Chemical composition of fly ash (wt%)

[0043] <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[TiO2]]> CaO MgO <![CDATA[Fe2O3]]> FeO <![CDATA[K2O]]> <![CDATA[Na2O]]> LOI <![CDATA[P2O5]]> sum 45.90 42.11 1.59 2.44 2.09 2.20 1.03 0.52 0.12 0.24 0.46 99.44

[0044] Example 1

[0045] A method for preparing a low-temperature microporous ZSM-5 molecular sieve denitration catalyst is as follows:

[0046] 1. First, mix fly ash and dilute hydrochloric acid and dissolve at room temperature. Filter the mixture. The filtrate is an iron-containing liquid and the filter cake is iron-removed fly ash. The concentration of dilute hydrochloric acid is 2 mol / L, and the mass ratio of fly ash to dilute acid is 10:7.3. Stir the mixture for 2 hours.

[0047] 2. Then, the iron-removing fly ash and concentrated hydrochloric acid are mixed for acid leaching and aluminum extraction, and filtered to obtain an aluminum-containing filtrate and a silica-containing filter cake; wherein, the concentration of concentrated HCl is 12 mol / L, the molar ratio of Al2O3 in the iron-removing fly ash to H+ in the acid solution is 1:7, the acid leaching and aluminum extraction temperature is 140℃, and the reaction time is 1.5 hours.

[0048] 3. The silica-containing filter cake and alkaline solution are mixed and dissolved, then filtered to obtain a silica-containing filtrate; wherein the alkaline solution is a sodium hydroxide solution, and the mass ratio of silica-containing filter cake to sodium hydroxide is 1:0.48; the reaction temperature is 95℃, and the reaction time is 4h;

[0049] 4. Next, the aluminum-containing filtrate and the silicon-containing filtrate are mixed, the pH of the system is adjusted to alkaline, and after being mixed evenly, hydrothermal crystallization is performed; wherein, the aluminum-containing filtrate and the silicon-aluminum liquid are mixed at a Si:Al ratio of 50:1, the pH of the system is adjusted to 10, and the mixture is poured into a stainless steel reactor lined with polytetrafluoroethylene and crystallized at 110℃ for 48 hours.

[0050] 5. Then, the mixture obtained in step (4) is filtered, washed, dried, and cooled to obtain powdered fly ash-based ZSM-5 molecular sieve;

[0051] 6. Finally, the iron-containing liquid (Fe) from step (1) is added to the ZSM-5 molecular sieve obtained in step (5). 3+ with Fe 2+ The Fe-Mn / ZSM-5 molecular sieve denitration catalyst was obtained by impregnating a 0.02 mol / L manganese nitrate solution with a molar ratio of approximately 3:1 at 60°C and magnetically stirring for 24 h. Ethanol was then added and stirred until the mixture was evaporated to dryness. The catalyst was then calcined at 550°C for 5 h at a heating rate of 5°C / min to obtain the catalyst. The total amount of active components supported on the molecular sieve accounted for 12% of the catalyst mass, and the mass ratio of iron to manganese was 1:1.5.

[0052] Testing revealed that the ZSM-5 molecular sieve obtained in step (4) possesses a microporous structure with a pore volume of 0.26 cm³. 3 / g, specific surface area is 486m² 2 / g, with a pore size of 1.38nm.

[0053] Example 2

[0054] 1. First, mix fly ash and dilute hydrochloric acid and dissolve at room temperature. Filter the mixture. The filtrate is an iron-containing liquid and the filter cake is iron-removed fly ash. The concentration of dilute hydrochloric acid is 1 mol / L, and the mass ratio of fly ash to dilute acid is 10:5. Stir the mixture for 2 hours.

[0055] 2. Then, the iron-removing fly ash and concentrated hydrochloric acid are mixed for acid leaching and aluminum extraction, and filtered to obtain aluminum-containing filtrate and silica-containing filter cake; wherein, the concentration of concentrated HCl is 10 mol / L, the molar ratio of Al2O3 in the iron-removing fly ash to H+ in the acid solution is 1:6, the acid leaching and aluminum extraction temperature is 100℃, and the reaction time is 1 hour.

[0056] 3. The silica-containing filter cake and alkaline solution are mixed and dissolved, then filtered to obtain a silica-containing filtrate; wherein the alkaline solution is a sodium hydroxide solution, and the mass ratio of silica-containing filter cake to sodium hydroxide is 1:0.48; the reaction temperature is 95℃, and the reaction time is 4h;

[0057] 4. Next, the aluminum-containing filtrate and the silicon-containing filtrate are mixed, the pH of the system is adjusted to alkaline, and after being mixed evenly, hydrothermal crystallization is performed; wherein, the aluminum-containing filtrate and the silicon-aluminum liquid are mixed at a Si:Al ratio of 60:1, the pH of the system is adjusted to 11, and the mixture is poured into a stainless steel reactor lined with polytetrafluoroethylene and crystallized at 110℃ for 48 hours.

[0058] 5. Then, the mixture obtained in step (4) is filtered, washed, dried, and cooled to obtain powdered fly ash-based ZSM-5 molecular sieve;

[0059] 6. Finally, the iron-containing liquid (Fe) from step (1) is added to the ZSM-5 molecular sieve obtained in step (5). 3+ with Fe 2+ The Fe-Mn / ZSM-5 molecular sieve denitration catalyst was obtained by impregnating a 0.02 mol / L manganese nitrate solution with a molar ratio of approximately 4:1 at 60°C and magnetically stirring for 24 h. Ethanol was then added and stirred until the mixture was evaporated to dryness. The catalyst was then calcined at 550°C for 5 h at a heating rate of 5°C / min to obtain the catalyst. The total amount of the supported active components accounted for 10% of the catalyst mass, and the mass ratio of iron to manganese was 1:1.2.

[0060] Testing revealed that the ZSM-5 molecular sieve obtained in step (4) possesses a microporous structure with a pore volume of 0.15 cm³. 3 / g, with a specific surface area of ​​249m² 2 / g, with a pore size of 0.31nm.

[0061] Example 3

[0062] 1. First, mix fly ash and dilute hydrochloric acid and dissolve at room temperature. Filter the mixture. The filtrate is an iron-containing liquid and the filter cake is iron-removed fly ash. The concentration of dilute hydrochloric acid is 3 mol / L, and the mass ratio of fly ash to dilute acid is 10:10. Stir the mixture for 2 hours.

[0063] 2. Then, the iron-removing fly ash and concentrated hydrochloric acid are mixed for acid leaching and aluminum extraction, and filtered to obtain aluminum-containing filtrate and silica-containing filter cake; wherein, the concentration of concentrated HCl is 20 mol / L, the molar ratio of Al2O3 in the iron-removing fly ash to H+ in the acid solution is 1:10, the acid leaching and aluminum extraction temperature is 150℃, and the reaction time is 3 hours.

[0064] 3. The silica-containing filter cake and alkaline solution are mixed and dissolved, then filtered to obtain a silica-containing filtrate; wherein the alkaline solution is a sodium hydroxide solution, and the mass ratio of silica-containing filter cake to sodium hydroxide is 1:0.48; the reaction temperature is 95℃, and the reaction time is 4h;

[0065] 4. Next, the aluminum-containing filtrate and the silicon-containing filtrate are mixed, the pH of the system is adjusted to alkaline, and after being mixed evenly, hydrothermal crystallization is carried out; wherein, the aluminum-containing filtrate and the silicon-aluminum liquid are mixed at a Si:Al ratio of 80:10, the pH of the system is adjusted to 12, and poured into a stainless steel reactor lined with polytetrafluoroethylene, and crystallized at 110℃ for 48h.

[0066] 5. Then, the mixture obtained in step (4) is filtered, washed, dried, and cooled to obtain powdered fly ash-based ZSM-5 molecular sieve;

[0067] 6. Finally, the iron-containing liquid (Fe) from step (1) is added to the ZSM-5 molecular sieve obtained in step (5). 3+ with Fe 2+ The Fe-Mn / ZSM-5 molecular sieve denitration catalyst was obtained by impregnating a 0.02 mol / L manganese nitrate solution with a molar ratio of approximately 5:1 at 60°C with magnetic stirring for 24 h, adding ethanol and stirring until dry, and calcining at 550°C for 5 h at a heating rate of 5°C / min. The total amount of the supported active component accounted for 15% of the catalyst mass, and the mass ratio of iron to manganese was 1:1.

[0068] Testing revealed that the ZSM-5 molecular sieve obtained in step (4) possesses a microporous structure with a pore volume of 0.3 cm³. 3 / g, specific surface area is 495m² 2 / g, with a pore size of 1.96nm.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that hydrogen peroxide is added to the iron-containing liquid obtained in step (1) to convert ferrous ions into ferric ions; and the Mn in the obtained catalyst is tetravalent.

[0071] Comparative Example 2

[0072] The difference from Example 2 is that the process of dissolving iron with dilute acid in step (1) is omitted, and the molecular sieve obtained in the last step (5) is only impregnated in a 0.02 mol / L manganese nitrate solution. After impregnation, it is stirred and evaporated to dryness at 60°C for 24 hours. Then, it is calcined at 550°C for 5 hours at a heating rate of 5°C / min to obtain the Mn / ZSM-5 molecular sieve denitration catalyst.

[0073] Comparative Example 3

[0074] The difference from Example 3 is that ZSM-5 molecular sieve is synthesized using purely chemical reagents instead of fly ash.

[0075] Preparation of seed crystals:

[0076] (1) Dissolve and mix 710.3g H2O, 13.8g NaOH and 117.0g TPAOH solution thoroughly until homogeneous.

[0077] (2) 158.9g of silicic acid was gradually added to the above solution in batches under stirring. After shaking for 1 hour at room temperature, the solution was aged at 100℃ for 16 hours.

[0078] Synthesis of ZSM-5 molecular sieve:

[0079] (3) Mix 867.8g H2O, 8.8g NaOH and 10.3g sodium aluminate thoroughly to dissolve them.

[0080] (4) Add 113.1g of silicic acid gradually in batches to solution (3) while stirring thoroughly and shake vigorously at room temperature for 1 hour.

[0081] (5) Add 50g of the colloidal seed crystals obtained in step (2) to (4) and shake for another 1h. Then place the material in a 50ml stainless steel reactor, crystallize at 180℃ for 40h, filter, wash thoroughly with deionized water, and dry at 105℃ for 24h.

[0082] (6) The ZSM-5 molecular sieve obtained in step (5) was added to a 0.02 mol / L ferric nitrate solution and a 0.02 mol / L manganese nitrate solution, and impregnated by magnetic stirring at 60 °C for 24 h. Ethanol was added and stirred until dry. The mixture was then calcined at 550 °C for 5 h at a heating rate of 5 °C / min to obtain the Fe-Mn / ZSM-5 molecular sieve denitration catalyst. The total amount of active components accounted for 15% of the catalyst mass.

[0083] Catalyst denitration tests in Examples 1-4 and Comparative Examples 1-3:

[0084] Test method: Industrial waste gas containing nitrogen oxides and a mixture of ammonia, oxygen, and nitrogen are contacted with the aforementioned ZSM-5 molecular sieve denitrification catalyst to carry out a denitrification reaction. The reaction temperature can be 100-450℃. The volume concentration of nitrogen oxides (NO) can be 100-1000 ppm. Based on the total volume of the mixed gas, the amount of oxygen can be 3-5% by volume, and the amount of nitrogen can be 95-97% by volume. The molar ratio of ammonia to the nitrogen oxides (NO) is (1-3):1. The volume hourly space velocity (VHSV) of the total feed of industrial waste gas and ammonia is 3000-150000 h⁻¹. -1 .

[0085] The test results are shown in Table 2:

[0086]

[0087]

[0088] All devices or components involved in this invention can be existing processing facilities, devices, or components with corresponding functions in the art, and will not be described in detail. Anything not specifically described herein is understood or known to those skilled in the art based on their prior knowledge, and will not be described in detail here.

[0089] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are within the spirit and scope of the present invention.

Claims

1. A method for preparing a low-temperature microporous ZSM-5 molecular sieve denitration catalyst, characterized in that, The preparation method includes the following steps: (1) After mixing fly ash with dilute acid to dissolve and remove iron, filter to obtain iron-removed fly ash as filter cake and iron-containing liquid as filtrate; (2) Mix the iron-removing fly ash with concentrated acid, perform acid dissolution to extract aluminum, and then filter to obtain aluminum-containing filtrate and silicon-containing filter cake; (3) The silicon-containing filter cake is mixed with an alkaline solution to extract silicon by alkaline dissolution, and then filtered to obtain a silicon-containing filtrate; (4) Mix the aluminum-containing filtrate with the silicon-containing filtrate and carry out a hydrothermal crystallization reaction under alkaline conditions; (5) Filter the mixture obtained after the reaction in step (4), and wash, dry and calcine the colloid obtained by filtration to obtain powdered fly ash-based ZSM-5 molecular sieve; (6) Impregnate the manganese-containing solution and the iron-containing liquid from step (1) with the ZSM-5 molecular sieve obtained in step (5), and then dry and calcine to obtain the transition metal-supported ZSM-5 molecular sieve denitration catalyst; wherein, the iron-containing liquid contains Fe 3+ with Fe 2+ The molar ratio is (2-6):1; The ZSM-5 molecular sieve denitration catalyst contains 5-7.5% iron and 5-7.5% manganese. In step (4), the aluminum-containing filtrate and the silicon-containing filtrate are mixed at a Si:Al mass ratio of (40-100):1, and the pH value of the system is adjusted to 10-12. The crystallization reaction temperature is 80-150℃ and the crystallization time is 24-72h.

2. The preparation method according to claim 1, characterized in that, The dilute acid added in step (1) is dilute HCl or dilute H2SO4, and the concentration of the dilute acid is 1-3 mol / L.

3. The preparation method according to claim 2, characterized in that, The ratio of the mass of fly ash to the molar mass of dilute acid is 10 g : (0.01-0.03) mol.

4. The preparation method according to claim 3, characterized in that, The iron content in the iron-removing fly ash is 2-3% by mass.

5. The preparation method according to any one of claims 1-4, characterized in that, The concentrated acid mentioned in step (2) is concentrated HCl or H2SO4, and the concentration of the concentrated acid is 10-20 mol / L. This is to remove Al2O3 from the iron-containing fly ash and H2SO4 from the concentrated acid. + The molar ratio is 1:6-10.

6. The preparation method according to claim 5, characterized in that, The acid dissolution reaction temperature is 100-150℃, and the reaction time is 1-3 hours.

7. The preparation method according to any one of claims 1-4 and 6, characterized in that, The alkaline solution in step (3) is a sodium hydroxide or potassium hydroxide solution, wherein the ratio of the mass of the silica filter cake on a dry basis to the molar amount of hydroxide ions in the added alkaline solution is 100g:(0.8-2)mol.

8. The preparation method according to claim 7, characterized in that, In step (3), the alkaline dissolution reaction temperature is 90-100℃ and the reaction time is 2-6h.

9. The preparation method according to any one of claims 1-4, 6 and 8, characterized in that, In steps (5) and (6), the calcination temperature is 500-600℃, the calcination time is 4-10h, and the heating rate is 3-7℃ / min.

10. The preparation method according to claim 7, characterized in that, In step (6), iron-containing liquid and manganese-containing solution are added to ZSM-5 molecular sieve, and the mixture is magnetically stirred at 50-70℃ for 12-48 hours. Then, ethanol is added, stirred, evaporated to dryness, and calcined to obtain Fe-Mn / ZSM-5 molecular sieve denitration catalyst. In the obtained catalyst, manganese exists in both tetravalent and trivalent forms, and Mn... 4+ / Mn 3+ The ratio is (1.5-1.2):

1.

11. The preparation method according to claim 10, characterized in that, The manganese-containing solution is a 0.01-0.1 mol / L Mn(NO3)2 solution.

12. The preparation method according to any one of claims 1-4, 6, 8 and 10-11, characterized in that, The ZSM-5 molecular sieve obtained in step (5) has a microporous structure with a pore volume of 0.15-0.3 cm³. 3 / g, specific surface area is 249-495m² 2 / g, with a pore size of 0.31-1.96nm.

13. The preparation method according to claim 12, characterized in that, In step (6), the total amount of active components supported on the molecular sieve denitration catalyst accounts for 10%-15% of the catalyst mass; the mass ratio of iron to manganese is 1.5:1-1:1.5.

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