SCR (Selective Catalytic Reduction) industrial flue gas denitration method

Abstract

The invention provides an SCR (Selective Catalytic Reduction) industrial flue gas denitration method, which belongs to the technical field of flue gas treatment, and comprises the following steps: introducing industrial flue gas, and cooling in two stages; then spraying a reducing agent; the method comprises the steps that flue gas is subjected to a contact reaction with a rare-earth-based ultralow-temperature denitration catalyst, La-Ce-Pr ternary co-doping serves as a main active component of the catalyst, the catalyst is loaded on a TiO2-Al2O3 composite carrier subjected to plasma activation treatment, and the surface of the carrier is provided with a La-O-Ce-Pr active cluster of a core-shell structure. According to the denitration method disclosed by the invention, efficient denitration can be realized under the ultralow-temperature condition of 80-180 DEG C by cooling in two stages, optimizing a reducing agent atomization technology and adopting a novel rare-earth-based ultralow-temperature denitration catalyst, so that the problems of high high-temperature energy consumption, easiness in catalyst deactivation and the like in a traditional SCR technology are solved; the denitration efficiency and the catalyst stability are obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of flue gas treatment technology, and specifically relates to an SCR industrial flue gas denitrification method. Background Art

[0002] Nitrogen oxides in industrial flue gas are one of the main sources of air pollution. Their emission not only causes environmental problems such as acid rain and photochemical smog, but also causes serious harm to human health. Selective catalytic reduction (SCR) technology is currently the most widely used flue gas denitrification method. It converts NO into x It reacts with reducing agents (such as ammonia or urea) to be converted into harmless nitrogen and water. However, traditional SCR technology still has many limitations in practical applications. First, traditional catalysts (such as V2O5-WO3 / TiO2) usually require high temperature conditions of 300-400°C to exert their optimal activity, which not only increases energy consumption, but also limits its application in low-temperature flue gas treatment. Secondly, under high temperature conditions, the catalyst is easily deactivated due to sintering, poisoning or loss of active components, resulting in increased operating costs. In addition, the injection method and atomization effect of the reducing agent have a significant impact on the denitrification efficiency. Traditional ammonia injection technology often has problems such as uneven mixing and ammonia escape, which further reduces the denitrification efficiency and may cause secondary pollution.

[0003] In summary, the existing SCR technology has obvious shortcomings in terms of high energy consumption, catalyst deactivation, and low reducing agent utilization efficiency. It is urgent to develop an SCR denitrification method that can operate efficiently and stably under ultra-low temperature conditions.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The first purpose of the present invention is to provide an SCR industrial flue gas denitrification method, which achieves efficient denitrification under ultra-low temperature conditions of 80-180°C by cooling in two stages, optimizing the reducing agent atomization technology and adopting a new rare earth-based ultra-low temperature denitrification catalyst. It solves the problems of high high temperature energy consumption and easy catalyst deactivation in traditional SCR technology, and significantly improves the denitrification efficiency and catalyst stability.

[0006] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0007] An SCR industrial flue gas denitrification method comprises the following steps:

[0008] After the industrial flue gas is introduced, the temperature is lowered to 80-180℃ in two stages;

[0009] Then, a reducing agent is sprayed in, wherein the reducing agent is at least one of ammonia gas, urea solution or ammonium salt solution, and the reducing agent is atomized by pneumatic atomization technology during the spraying, and the atomized particle size is ≤20 μm;

[0010] The flue gas is then contacted with a rare earth-based ultra-low temperature denitration catalyst for reaction. The rare earth-based ultra-low temperature denitration catalyst has La-Ce-Pr ternary co-doping as a main active component and is supported on a plasma-activated TiO2-Al2O3 composite support, wherein the molar ratio of Pr, Ce and La is 1:2:1, and the surface of the TiO2-Al2O3 composite support has La-O-Ce-Pr active clusters with a core-shell structure, wherein the shell layer of the core-shell structure is CeO2 and the core layer is La-Pr oxide;

[0011] The purified flue gas after the reaction is discharged after dust removal.

[0012] The SCR industrial flue gas denitrification method provided by the present invention achieves efficient denitrification under ultra-low temperature conditions of 80-180°C through the synergistic effect of a series of technical means. It mainly forms a complete and efficient low-energy denitrification system through the combination of staged cooling, reducing agent atomization optimization and new rare earth-based catalysts. First, the present invention accurately controls the industrial flue gas from a high temperature state to an ultra-low temperature reaction range through two-stage cooling, which not only avoids the adverse effects of temperature changes on subsequent catalytic reactions caused by traditional single-stage cooling, but also creates an optimal temperature window for the activity of the catalyst. The selection of the temperature range of 80-180°C can not only ensure that the active sites of the rare earth-based catalyst are fully exposed, but also prevent the temperature from being too low to cause insufficient reaction kinetics or too high to cause catalyst sintering and deactivation.

[0013] In the reducing agent injection link, the present invention solves the pain points of uneven reducing agent distribution and high ammonia escape rate in traditional SCR technology through atomization technology requirements. By atomizing the reducing agent, the reducing agent particle size is controlled at the micron level, which greatly increases the contact area between the reducing agent and the flue gas, avoiding both the waste of reducing agent and the secondary pollution caused by unreacted ammonia. In addition, the synergistic effect of pneumatic atomization technology and subsequent catalytic reaction enables the ultra-fine atomized reducing agent to diffuse rapidly to the active sites on the catalyst surface, forming a homogeneous mixed system with the pre-cooled flue gas, laying a material foundation for efficient reaction under low temperature conditions.

[0014] The core point of the denitration method of the present invention is the use of a rare earth-based ultra-low temperature denitration catalyst, wherein the catalyst is co-doped with La-Ce-Pr as the active component, and its unique core-shell structure is stably loaded on a TiO2-Al2O3 composite carrier treated with plasma activation, wherein the molar ratio of Pr, Ce, and La of 1:2:1 optimizes the balance between oxygen vacancy concentration and acidic site distribution, and the high oxygen storage capacity of the CeO2 shell complements the strong acidity of the La-Pr core layer; and the plasma activation treatment significantly improves the surface energy of the TiO2-Al2O3 composite carrier, so that the active components can be highly dispersed in the form of "La-O-Ce-Pr" active clusters. This special structure can still maintain excellent redox performance at low temperatures; and the TiO2-Al2O3 composite carrier not only provides 150-300m 2 / g of high specific surface area, and the synergistic effect of the two phases also enhances the anti-sulfur and water resistance.

[0015] In addition, the denitrification method of the present invention also forms a three-in-one technical closed loop of "temperature control-reducing agent optimization-catalytic reaction". The two-stage cooling creates an optimal working environment for the catalyst, pneumatic atomization ensures sufficient contact of the reactants, and the rare earth-based catalyst realizes the precise construction of low-temperature active sites at the atomic scale. This systematic design enables the denitrification efficiency to remain above 90% in the low-temperature range of 80-180°C, while the catalyst life is extended by more than 30%, far exceeding the performance indicators of traditional high-temperature SCR technology.

[0016] Preferably, as a further specific embodiment, the TiO2-Al2O3 composite support is prepared by a microemulsion-assisted coprecipitation method and then subjected to plasma activation treatment, wherein the microemulsion comprises a cyclohexane / n-butanol / water mixture system and 0.1-0.5 wt% of polyvinyl pyrrolidone is added;

[0017] The TiO2-Al2O3 composite support is immersed in a rare earth nitrate solution by microwave-photochemical synergistic impregnation method, and the impregnation is carried out for 30 minutes under the synchronous action of microwave and ultraviolet light, wherein the rare earth element accounts for 5-15% of the total mass of the catalyst;

[0018] After drying and calcination, it is doped with transition metal to obtain the product.

[0019] The present invention also provides a preparation method of the rare earth-based ultra-low temperature denitrification catalyst. By combining the two core processes of microemulsion-assisted coprecipitation and microwave-photochemical synergistic impregnation, a high-efficiency catalyst preparation system with a special core-shell structure active cluster is constructed. The method first adopts a microemulsion-assisted coprecipitation method to prepare a TiO2-Al2O3 composite carrier, and by combining a cyclohexane / n-butanol / water mixed microemulsion system with polyvinyl pyrrolidone, a uniform mixing of the carrier precursor on a molecular scale is achieved through the confinement effect of a microemulsion nanoreactor. The cyclohexane, The volume ratio of n-butanol and water is strictly controlled at 5:3:2, thus ensuring the formation of a stable reverse micro-micelle structure. The diameter of the water core is just in the range of 10-20nm, providing a size-controlled nano-reaction space for the subsequent co-precipitation of titanium-aluminum composite oxides. The addition of polyvinyl pyrrolidone further regulates the interfacial tension of the microemulsion, preventing particle agglomeration. At the same time, the carbonyl groups in its long-chain molecules can also coordinate with metal ions, guiding TiO2 and Al2O3 to achieve molecular-level compounding in a mass ratio of 3:1 to 1:1, ultimately forming a specific surface area of ​​150-300m 2 / g of highly dispersed carrier, this characteristic has a decisive influence on the loading density and dispersion of subsequent active components.

[0020] During the carrier synthesis process, the present invention also defines an alkaline environment with a co-precipitation pH value of 9-10. Within this pH range, Ti generated by the hydrolysis of tetrabutyl titanate 4+ Al provided by aluminum nitrate 3+ The invention can form hydroxide precipitation synchronously, avoiding the component segregation problem caused by the pH difference of metal ion precipitation in the traditional method. The invention also adds citric acid as a modifier in the mixed solution, so that the carboxyl groups contained in it chelate with metal ions to delay the precipitation rate and achieve uniform nucleation. It can also be used as a pore-forming agent to decompose and produce a mesoporous structure during the calcination stage. At the same time, the introduction of graphene quantum dots is achieved through its sp 2 The conductive network of the hybrid carbon skeleton significantly improves the electron transport capacity of the carrier, pre-constructing channels for the electron transfer process in subsequent catalytic reactions. The synergistic effect of these additives and the microemulsion system makes the final TiO2-Al2O3 composite carrier not only have a high specific surface area, but also have optimized pore structure and surface properties, laying an ideal foundation for the subsequent loading of active components.

[0021] In addition, the present invention also loads rare earth active components by adopting a microwave-photochemical synergistic impregnation method. This process breaks through the limitations of traditional impregnation methods in terms of component dispersion and bonding strength. Specifically, when the carrier after plasma activation treatment is immersed in a rare earth nitrate solution containing La, Ce, and Pr, microwave radiation and ultraviolet light are applied simultaneously, and deep impregnation can be completed within 30 minutes. The bulk heating characteristics of microwaves cause the solution in the carrier pores to heat up rapidly to generate local convection, greatly accelerating the diffusion rate of rare earth ions to the deep pores of the carrier; while ultraviolet light generates electron-hole pairs in the TiO2 carrier through photoexcitation, and the holes oxidize nitrates to release active oxygen species, which promotes the directional adsorption of rare earth ions on the carrier surface. In addition, the present invention also adds Ethylenediaminetetraacetic acid is used as a coordination regulator. The complex formed with rare earth ions undergoes gradual dissociation under the synergistic effect of microwave-photochemistry, achieving a gradient distribution of active components from the outer surface of the carrier to the inner pores. This "from the outside to the inside" loading method ensures the spatial uniformity of the active sites. After drying and calcining, the catalyst precursor obtained by this process will stably exist on the carrier surface in the form of La-O-Ce-Pr active clusters, among which Pr, Ce, and La maintain a precise molar ratio of 1:2:1. In the core-shell structure formed, the CeO2 shell provides abundant oxygen vacancies for NO activation, and the La-Pr core layer provides acidic sites to promote NH3 adsorption. The synergistic effect of the two realizes efficient SCR reaction under ultra-low temperature conditions.

[0022] Preferably, as a further specific embodiment, the titanium source in the TiO2-Al2O3 composite carrier is tetrabutyl titanate, and the aluminum source is aluminum nitrate.

[0023] The present invention further defines the raw material system for the preparation of TiO2-Al2O3 composite carriers. By selecting specific titanium and aluminum sources and combining the synergistic modification of citric acid and graphene quantum dots, a highly specific carrier synthesis raw material system is constructed, wherein the titanium source is tetrabutyl titanate rather than conventional titanyl sulfate or titanium tetrachloride. This selection is based on the unique behavior of tetrabutyl titanate in the microemulsion system. Its alkoxy structure can achieve controllable hydrolysis under alkaline hydrolysis conditions, avoiding the problem of particle coarsening caused by instantaneous precipitation. At the same time, n-butanol as a hydrolysis by-product is compatible with the n-butanol component in the microemulsion system and will not destroy the phase equilibrium of the microemulsion. The matching aluminum source is aluminum nitrate rather than aluminum chloride or aluminum isopropoxide, mainly considering that nitrate ions can be completely decomposed without residue during the subsequent roasting process, and Al 3+ The stable existence form in aqueous microemulsion is beneficial to the interaction with Ti 4+ of co-precipitation.

[0024] In addition, the citric acid added in the present invention is not a simple pH adjustment, but has more important functions. First, the carboxyl group it has can react with Ti 4+ 、Al 3+ The formation of soluble complexes slows down the precipitation rate and separates the nucleation and growth processes, thereby obtaining composite oxides with uniform particle size distribution; secondly, the thermal decomposition of citric acid in the subsequent calcination process will produce CO2 and H2O, forming a mesoporous structure in the carrier. This dual-mode pore system (micropore + mesopore) not only increases the specific surface area but also optimizes the mass transfer efficiency; finally, the residual citrate forms a carboxylic acid terminal on the carrier surface, providing a specific anchoring site for the subsequent loading of rare earth active components; and the introduction of graphene quantum dots solves the problem of poor electronic conductivity of traditional TiO2-Al2O3 carriers. The quantum dots with a diameter of less than 5nm are firmly bonded to the hydroxyl groups on the surface of the carrier through the esterification reaction of the edge carboxyl groups, forming an electron transport network throughout the carrier, which can significantly accelerate the Ce in the subsequent SCR reaction. 3+ / Ce 4+ With Pr 3+ / Pr 4+ redox cycles between.

[0025] Preferably, as a further specific embodiment, 0.05-0.1 mol / L of citric acid and 0.01-0.05 wt% of graphene quantum dots are further added to the microemulsion.

[0026] Preferably, as a further specific embodiment, the volume ratio of cyclohexane, n-butanol and water in the microemulsion is 5:3:2, and the coprecipitation pH value is 9-10.

[0027] The present invention also precisely defines the compositional ratios of the microemulsion system. By controlling the volume ratio of cyclohexane, n-butanol, and water within a specific range of 5:3:2 and maintaining a coprecipitation pH of 9-10, a thermodynamically stable microemulsion environment with ideal nanoreactor properties is constructed. The 50% cyclohexane content ensures macroscopic fluidity for industrial operation while providing sufficient organic medium space for reverse micelle formation. The 30% n-butanol cosurfactant, due to its longer carbon chain in the molecular structure, enables a more stable interfacial film with cyclohexane, while the presence of hydroxyl groups maintains the necessary hydrophilicity. This amphiphilic balance ensures the microemulsion remains stable over a wide temperature range. The 20% water content ensures that the core diameter of the reverse micelles formed is within the range of 10-15 nm, providing a suitably sized nanoreaction space for the coprecipitation of the TiO2-Al2O3 precursor.

[0028] The weak alkaline condition of the coprecipitation pH value of 9-10, on the one hand, promotes the gradual hydrolysis of the alkoxy groups of tetrabutyl titanate rather than explosive dissociation, thus avoiding the coarsening of particles caused by local oversaturation; on the other hand, it makes Al 3+ Converted to Al(OH)4 - The form carries the same negative charge as the partially hydrolyzed Ti-OH species, and maintains a uniform dispersion state in the water core of the microemulsion through electrostatic repulsion, ultimately achieving co-precipitation at the molecular level. Moreover, the pH window is just above the isoelectric point of polyvinyl pyrrolidone, which enables the polyvinyl pyrrolidone molecules to maintain an extended conformation and give full play to the steric hindrance effect, thereby preventing the agglomeration of the primary nanoparticles.

[0029] Preferably, as a further specific embodiment, the concentration of the rare earth nitrate solution is 0.5-1.5 mol / L, and 0.1-0.3 mol / L of ethylenediaminetetraacetic acid is added to the rare earth nitrate solution.

[0030] The present invention also makes key restrictions on the composition of the rare earth nitrate impregnation solution. By precisely controlling the concentration of the rare earth nitrate solution in the range of 0.5-1.5 mol / L and adding 0.1-0.3 mol / L of ethylenediaminetetraacetic acid, an impregnation system with high loading efficiency and uniform distribution of active components is constructed. Through the precise regulation of the rare earth ion complexation balance, the controllable construction of active sites on the carrier surface is achieved. When the concentration is lower than 0.5 mol / L, it is difficult to achieve the target loading amount of 5-15% within 30 minutes of microwave-photochemical synergistic impregnation, while exceeding 1.5 mol / L will lead to excessive deposition on the outer surface of the carrier to form block aggregates, destroying the formation of the core-shell structure.

[0031] The limited amount of EDTA added ensures that it neither completely complexes all rare earth ions (resulting in insufficient loading) nor regulates the deposition kinetics of the active components through a dynamic complexation-dissociation equilibrium. Under the synergistic effect of microwave-photochemistry, the dissociation rate of the EDTA-RAE complex and the re-adsorption rate of the hydroxyl groups on the support surface achieve a delicate balance: microwave heating causes some of the complex to dissociate and release free rare earth ions. These ions are oxidized by the TiO2 surface holes excited by ultraviolet light, forming MO-Ti (M=La, Ce, Pr) bonds with the hydroxyl groups on the support surface. At the same time, the undissociated EDTA-RAE complex continues to diffuse into the deep pores of the support, forming a gradient loading effect from the surface to the inside. This "competitive complexation" mechanism ensures that the rare earth active components in the final catalyst are not only evenly distributed on the outer surface, but also exhibit an ideal decreasing concentration gradient in the internal pores of the support. More importantly, the introduction of EDTA effectively suppresses the Pr 3+ The oxidation tendency during the impregnation process ensures the accuracy of the 1:2:1 molar ratio of Pr, Ce and La.

[0032] Preferably, as a further specific embodiment, the mass ratio of TiO2 to Al2O3 in the TiO2-Al2O3 composite carrier is 1:1-3:1, and the specific surface area is 150-300m 2 / g.

[0033] The present invention also makes key restrictions on the composition and physical properties of the TiO2-Al2O3 composite carrier, by precisely controlling the mass ratio of TiO2 to Al2O3 in the range of 1:1 to 3:1 and ensuring that the specific surface area reaches 150-300m 2 / g technical indicators, a composite carrier system with excellent surface properties and structural stability was constructed. Through the synergistic effect of titanium and aluminum components and the fine control of pore structure, it provides an ideal loading platform for rare earth active components. The TiO2 / Al2O3 mass ratio range of 1:1 to 3:1 has been systematically verified by experiments. When the TiO2 ratio is too high, although it can provide more surface acid sites, the thermal stability of the carrier will be significantly reduced. During the calcination process, crystal phase transformation is likely to occur, resulting in a sharp decrease in specific surface area. If the Al2O3 ratio is too high, the redox properties of the carrier surface will be weakened, which is not conducive to the subsequent Ce 3+ / Ce 4+ With Pr 3+ / Pr 4+ The electron transfer between redox pairs; the high specific surface area limitation not only provides sufficient loading sites for rare earth active components, but more importantly, forms rich surface defects and lattice distortions. These structural features will be converted into specific oxygen vacancy concentrations and surface energy distributions during the subsequent plasma activation treatment, becoming the preferred anchoring sites for the core-shell structure La-O-Ce-Pr active clusters.

[0034] Preferably, as a further specific embodiment, the transition metals are Mn and Ce, wherein Mn exists in the form of Mn3O4, and the doping amount is 2-3% of the total mass of the catalyst; Ce exists in the form of CeO2, and the doping amount is 1-2% of the total mass of the catalyst.

[0035] In addition, the present invention further introduces the doping of transition metal elements on the basis of rare earth-based ultra-low temperature denitrification catalysts, and forms a single atomic layer active site on the carrier surface through atomic layer deposition technology. This method pushes the performance boundary of the catalyst to a new height. Although rare earth elements provide excellent low-temperature activity and anti-poisoning ability, there are still kinetic limitations in specific reaction steps such as NH3 oxidation and NO dissociation. The introduction of specific transition metals can just make up for this deficiency. At the same time, atomic layer deposition technology realizes the single atomic layer dispersion of transition metals on the carrier surface through self-limiting surface reactions. Compared with traditional impregnation or mechanical mixing methods, it can not only accurately control the doping amount (avoiding mutual shielding of active sites caused by excessive doping), but more importantly, it ensures atomic-level contact between transition metals and rare earth active clusters, forming a composite active center with a synergistic effect; and its The single atomic layer active sites formed by atomic layer deposition technology are essentially a highly dispersed metal-oxygen-metal (MO-M') bridge bond structure constructed on the surface of the TiO2-Al2O3 carrier, where M represents the transition metal and M' represents the Ti or Al on the carrier surface. This special structure ensures the dispersion of the single atomic layer of the transition metal, maximizing the atomic utilization rate. In addition, the MO-Ti / Al bonding formed by the transition metal and the carrier stabilizes the valence state of the transition metal, preventing it from migrating and agglomerating during the reaction. In addition, this single atomic layer structure forms a spatially complementary distribution with the core-shell structure La-O-Ce-Pr active cluster. The transition metal sites are mainly located in the lattice defects on the carrier surface, while the rare earth active clusters are preferentially distributed in the mesoporous channels. The two are electronically coupled through the oxygen vacancy network on the carrier surface, forming a multi-dimensional catalytic reaction channel.

[0036] The present invention also makes precise restrictions on the specific selection and existence form of transition metal elements. By doping Mn and Ce in specific proportions and existing in the specific chemical forms of Mn3O4 and CeO2, a composite active system with multi-valent synergy and optimized redox properties is constructed. The technical essence of this system lies in the functional enhancement and stability improvement of catalytic active sites at the atomic scale through the precise coordination and electronic coupling of transition metals and rare earth elements. Mn is limited to existing in the form of Mn3O4 and the doping amount is 2-3% of the total mass of the catalyst. As a mixed-valence oxide, Mn3O4 has a unique electronic structure that can provide flexible electron transfer channels in the SCR reaction. When Mn exists in this form, its d electron orbital can form effective electronic coupling with the 4f orbital of the rare earth element Pr, significantly promoting the activation and dissociation of NO molecules under low temperature conditions. The doping amount of 2-3% ensures a sufficient Mn active site density while avoiding the problem of rare earth active site coverage caused by excessive Mn.

[0037] At the same time, the present invention also limits Ce to exist in the form of CeO2 and the doping amount is 1-2% of the total mass of the catalyst, and introduces CeO2 through atomic layer deposition technology, so that it is distributed on the grain boundaries and defect positions of the carrier surface, forming a "point-surface" combined composite cerium oxide system with the CeO2 shell in the main rare earth active cluster. This special distribution produces a triple synergistic effect: first, the surface-deposited CeO2 nano-islands act as an electron buffer pool, which can quickly regulate the Ce 3+ / Ce 4+ With Pr 3+ / Pr 4+ The electron balance between them enables the catalyst to maintain stable redox performance under fluctuating working conditions; secondly, the additional CeO2 fills the oxygen vacancy gradient on the support surface, forming a continuous oxygen ion transport network, and the 1-2% Ce doping amount not only supplements the loss of Ce in the main active cluster due to sintering, but also does not destroy the original 1:2:1 molar ratio balance of Pr, Ce, and La. Therefore, the present invention constructs a dynamically stable active site network. Under reaction conditions, the Mn3O4 single atomic layer and the CeO2 nano-island are connected by surface oxygen bridges to form an active interface of Mn-O-Ce, and this interface generates long-range electronic interactions with the adjacent La-O-Ce-Pr core-shell structure active clusters through the Ti-O bond network on the support surface. This multi-level structural design enables the catalyst surface to have three types of active centers at the same time: NO dissociation center provided by Mn3O4, oxygen activation center provided by CeO2, and NH3 adsorption activation center provided by rare earth active clusters. The three realize the relay conversion of reactant molecules through the mediation of surface oxygen vacancies.

[0038] Preferably, as a further specific embodiment, the injection amount of the reducing agent is proportional to the NO in the flue gas. X The molar ratio is 0.8-1.2:1.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention provides an SCR industrial flue gas denitrification method, which achieves efficient denitrification under ultra-low temperature conditions of 80-180°C by cooling in two stages, optimizing the reducing agent atomization technology, and adopting a new rare earth-based ultra-low temperature denitrification catalyst. This solves the problems of high energy consumption at high temperature and easy deactivation of catalysts in traditional SCR technology, and significantly improves the denitrification efficiency and catalyst stability. DETAILED DESCRIPTION

[0041] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the embodiments described below are part of the embodiments of the present invention, not all of them, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] In order to more clearly illustrate the technical solutions of the present invention, specific embodiments are provided below for illustration.

[0043] Example 1

[0044] The specific steps of an SCR industrial flue gas denitrification method of the present invention are as follows:

[0045] Step 1: Flue gas cooling

[0046] Flue gas source: Flue gas emitted from coal-fired boilers or industrial furnaces;

[0047] Industrial flue gas (initial temperature 350°C) is introduced and two-stage cooling is adopted:

[0048] The first stage: cooling to 200℃ through waste heat recovery device;

[0049] The second stage: cooling to 80℃ through indirect water cooling device;

[0050] Step 2: Injection of reducing agent

[0051] Spray urea solution (concentration 10%), use pneumatic atomization technology, control the atomization particle size to 20μm, the reducing agent and NO in the flue gas X The molar ratio is 0.8:1;

[0052] Step 3: Catalytic reaction

[0053] The flue gas is passed through a reactor filled with a rare earth-based ultra-low temperature denitrification catalyst. The catalyst preparation method is as follows:

[0054] 3.1 Preparation of TiO2-Al2O3 composite support

[0055] (1) Raw material preparation

[0056] Titanium source: tetrabutyl titanate, purity ≥99%;

[0057] Aluminum source: aluminum nitrate, purity ≥99%;

[0058] Microemulsion system:

[0059] Cyclohexane: 50 mL (volume ratio 5);

[0060] n-Butanol: 30 mL (volume ratio 3);

[0061] Deionized water: 20 mL (volume ratio 2);

[0062] Polyvinylpyrrolidone: 0.1 g (0.1 wt%);

[0063] additive:

[0064] Citric acid: 0.05 mol / L (final concentration);

[0065] Graphene quantum dots: 0.01 wt% (ultrasonic dispersion in water);

[0066] (2) Microemulsion-assisted coprecipitation

[0067] Microemulsion preparation:

[0068] Cyclohexane, n-butanol, and polyvinyl pyrrolidone were mixed and magnetically stirred for 30 min to form a homogeneous oil phase;

[0069] Then, citric acid and graphene quantum dots were added to the water to form an aqueous phase, and then the aqueous phase was slowly added to the oil phase and stirred for 1 h to form a transparent microemulsion.

[0070] Coprecipitation reaction:

[0071] Tetrabutyl titanate and aluminum nitrate were dissolved in the microemulsion, and ammonia water was added dropwise to adjust the pH to 9.0;

[0072] The reaction was continued at 40 °C for 4 h to produce Ti(OH)4 and Al(OH)3 coprecipitates;

[0073] Aging and washing:

[0074] The precipitate was aged in the microemulsion for 12 h, centrifuged, and washed three times with ethanol to remove residual organic matter;

[0075] Drying and calcination: vacuum drying at 60 °C for 12 h, followed by calcination in a muffle furnace at 500 °C for 4 h (heating rate 2 °C / min) to obtain a TiO2-Al2O3 composite support (mass ratio 1:1, specific surface area 150 m 2 / g);

[0076] 3.2 Rare earth active component loading (La-Ce-Pr ternary doping)

[0077] (1) Plasma activation treatment of carrier

[0078] The support was placed in a plasma reactor, purged with argon (50 sccm), and treated at 300 W power for 30 min to enhance the surface hydroxyl density and defect sites;

[0079] (2) Microwave-photochemical synergistic impregnation

[0080] Preparation of rare earth nitrate solution:

[0081] Lanthanum nitrate, cerium nitrate, and praseodymium nitrate were mixed in a molar ratio of 1:2:1 to a total concentration of 0.5 mol / L, and 0.1 mol / L ethylenediaminetetraacetic acid was added to obtain a rare earth nitrate solution;

[0082] Impregnation process:

[0083] The carrier is immersed in a rare earth nitrate solution and placed in a microwave-ultraviolet coordinated reactor;

[0084] Microwave power 300W (80℃), UV wavelength 254nm (intensity 50mW / cm 2 ), synchronous action for 30 min;

[0085] Centrifuge and dry at 60°C for 12 h;

[0086] (3) Calcination

[0087] Calcination at 550°C (heating rate 1°C / min) for 5 h formed La-O-Ce-Pr active clusters with a core-shell structure, thereby obtaining a crude catalyst, in which rare earth elements accounted for 5% of the total mass of the catalyst;

[0088] 3. Transition metal doping

[0089] The crude catalyst is placed in a hot-wall ALD reactor to introduce transition metals;

[0090] (1) Atomic layer deposition (ALD) process

[0091] Equipment: Hot-wall ALD reactor, substrate temperature 200°C;

[0092] Precursor:

[0093] Mn source: dimethyl manganese, pulse time 0.1s;

[0094] Ce source: tetrakis(dimethylamino)cerium, pulse time 0.2s;

[0095] Oxidant: ozone, pulse time 0.5s;

[0096] Sedimentation cycle:

[0097] Mn3O4: 50 cycles (controlled doping amount 2wt%);

[0098] CeO2: 30 cycles (controlled doping amount 1wt%);

[0099] (2) Post-processing

[0100] Annealing at 400℃ in nitrogen for 2h stabilizes the crystal structure of Mn3O4 and CeO2 to obtain a rare earth-based ultra-low temperature denitrification catalyst.

[0101] Step 4: Clean up the emissions

[0102] After the reaction, the flue gas is discharged through dust removal treatment, and the NO in the tail gas is detected. X The emission concentration and ammonia concentration showed a denitrification efficiency of 92.4%, NO X The emission concentration is 38.6 mg / m3 and the ammonia concentration is 3.2 ppm.

[0103] Example 2

[0104] The specific steps of an SCR industrial flue gas denitrification method of the present invention are as follows:

[0105] Step 1: Flue gas cooling

[0106] Flue gas source: Flue gas emitted from coal-fired boilers or industrial furnaces;

[0107] Industrial flue gas (initial temperature 450°C) is introduced and two-stage cooling is adopted:

[0108] The first stage: cooling to 250℃ through waste heat recovery device;

[0109] The second stage: cooling to 180℃ through indirect water cooling device;

[0110] Step 2: Injection of reducing agent

[0111] Ammonium salt solution (concentration 10%) was sprayed, and the atomized particle size was controlled to be 10 μm using pneumatic atomization technology. The reducing agent and NO in the flue gas were X The molar ratio is 1.2:1;

[0112] Step 3: Catalytic reaction

[0113] The flue gas is passed through a reactor filled with a rare earth-based ultra-low temperature denitrification catalyst. The catalyst preparation method is as follows:

[0114] 3.1 Preparation of TiO2-Al2O3 composite support

[0115] (1) Raw material preparation

[0116] Titanium source: tetrabutyl titanate, purity ≥99%;

[0117] Aluminum source: aluminum nitrate, purity ≥99%;

[0118] Microemulsion system:

[0119] Cyclohexane: 50 mL (volume ratio 5);

[0120] n-Butanol: 30 mL (volume ratio 3);

[0121] Deionized water: 20 mL (volume ratio 2);

[0122] Polyvinylpyrrolidone: 0.5 g (0.5 wt %);

[0123] additive:

[0124] Citric acid: 0.1 mol / L (final concentration);

[0125] Graphene quantum dots: 0.05 wt% (ultrasonic dispersion in water);

[0126] (2) Microemulsion-assisted coprecipitation

[0127] Microemulsion preparation:

[0128] Cyclohexane, n-butanol, and polyvinyl pyrrolidone were mixed and magnetically stirred for 30 min to form a homogeneous oil phase;

[0129] Then, citric acid and graphene quantum dots were added to the water to form an aqueous phase, and then the aqueous phase was slowly added to the oil phase and stirred for 1 h to form a transparent microemulsion.

[0130] Coprecipitation reaction:

[0131] Tetrabutyl titanate and aluminum nitrate were dissolved in the microemulsion, and ammonia water was added dropwise to adjust the pH to 10.0;

[0132] The reaction was continued at 40 °C for 4 h to produce Ti(OH)4 and Al(OH)3 coprecipitates;

[0133] Aging and washing:

[0134] The precipitate was aged in the microemulsion for 12 h, centrifuged, and washed three times with ethanol to remove residual organic matter;

[0135] Drying and calcination: vacuum drying at 60 °C for 12 h, followed by calcination in a muffle furnace at 500 °C for 4 h (heating rate 2 °C / min) to obtain a TiO2-Al2O3 composite support (mass ratio 3:1, specific surface area 300 m 2 / g);

[0136] 3.2 Rare earth active component loading (La-Ce-Pr ternary doping)

[0137] (1) Plasma activation treatment of carrier

[0138] The support was placed in a plasma reactor, purged with argon (50 sccm), and treated at 300 W power for 30 min to enhance the surface hydroxyl density and defect sites;

[0139] (2) Microwave-photochemical synergistic impregnation

[0140] Preparation of rare earth nitrate solution:

[0141] Lanthanum nitrate, cerium nitrate, and praseodymium nitrate were mixed in a molar ratio of 1:2:1 to a total concentration of 0.5 mol / L, and 0.1 mol / L ethylenediaminetetraacetic acid was added to obtain a rare earth nitrate solution;

[0142] Impregnation process:

[0143] The carrier is immersed in a rare earth nitrate solution and placed in a microwave-ultraviolet coordinated reactor;

[0144] Microwave power 300W (80℃), UV wavelength 254nm (intensity 50mW / cm 2 ), synchronous action for 30 min;

[0145] Centrifuge and dry at 60°C for 12 h;

[0146] (3) Calcination

[0147] Calcination at 550°C (heating rate 1°C / min) for 5 h formed La-O-Ce-Pr active clusters with a core-shell structure, thereby obtaining a crude catalyst, in which rare earth elements accounted for 15% of the total mass of the catalyst;

[0148] 3. Transition metal doping

[0149] The crude catalyst is placed in a hot-wall ALD reactor to introduce transition metals;

[0150] (1) Atomic layer deposition (ALD) process

[0151] Equipment: Hot-wall ALD reactor, substrate temperature 200°C;

[0152] Precursor:

[0153] Mn source: dimethyl manganese, pulse time 0.1s;

[0154] Ce source: tetrakis(dimethylamino)cerium, pulse time 0.2s;

[0155] Oxidant: ozone, pulse time 0.5s;

[0156] Sedimentation cycle:

[0157] Mn3O4: 60 cycles (controlled doping amount 3wt%);

[0158] CeO2: 40 cycles (controlled doping amount 2wt%);

[0159] (2) Post-processing

[0160] Annealing at 400℃ in nitrogen for 2h stabilizes the crystal structure of Mn3O4 and CeO2 to obtain a rare earth-based ultra-low temperature denitrification catalyst.

[0161] Step 4: Clean up the emissions

[0162] After the reaction, the flue gas is discharged through dust removal treatment, and the NO in the tail gas is detected. X The emission concentration and ammonia concentration showed a denitrification efficiency of 94.7%, NO x The emission concentration is 25.8 mg / m 3 , the ammonia concentration is 2.7ppm.

[0163] Example 3

[0164] The specific steps of an SCR industrial flue gas denitrification method of the present invention are as follows:

[0165] Step 1: Flue gas cooling

[0166] Flue gas source: Flue gas emitted from coal-fired boilers or industrial furnaces;

[0167] Industrial flue gas (initial temperature 450°C) is introduced and two-stage cooling is adopted:

[0168] The first stage: cooling to 250℃ through waste heat recovery device;

[0169] The second stage: cooling to 130℃ through indirect water cooling device;

[0170] Step 2: Injection of reducing agent

[0171] Ammonium salt solution (concentration 10%) was sprayed, and the atomized particle size was controlled to be 10 μm using pneumatic atomization technology. The reducing agent and NO in the flue gas were X The molar ratio is 1:1;

[0172] Step 3: Catalytic reaction

[0173] The flue gas is passed through a reactor filled with a rare earth-based ultra-low temperature denitrification catalyst. The catalyst preparation method is as follows:

[0174] 3.1 Preparation of TiO2-Al2O3 composite support

[0175] (1) Raw material preparation

[0176] Titanium source: tetrabutyl titanate, purity ≥99%;

[0177] Aluminum source: aluminum nitrate, purity ≥99%;

[0178] Microemulsion system:

[0179] Cyclohexane: 50 mL (volume ratio 5);

[0180] n-Butanol: 30 mL (volume ratio 3);

[0181] Deionized water: 20 mL (volume ratio 2);

[0182] Polyvinylpyrrolidone: 0.3 g (0.3 wt%);

[0183] additive:

[0184] Citric acid: 0.06 mol / L (final concentration);

[0185] Graphene quantum dots: 0.03 wt% (ultrasonic dispersion in water);

[0186] (2) Microemulsion-assisted coprecipitation

[0187] Microemulsion preparation:

[0188] Cyclohexane, n-butanol, and polyvinyl pyrrolidone were mixed and magnetically stirred for 30 min to form a homogeneous oil phase;

[0189] Then, citric acid and graphene quantum dots were added to the water to form an aqueous phase, and then the aqueous phase was slowly added to the oil phase and stirred for 1 h to form a transparent microemulsion.

[0190] Coprecipitation reaction:

[0191] Tetrabutyl titanate and aluminum nitrate were dissolved in the microemulsion, and ammonia water was added dropwise to adjust the pH to 10.0;

[0192] The reaction was continued at 40 °C for 4 h to produce Ti(OH)4 and Al(OH)3 coprecipitates;

[0193] Aging and washing:

[0194] The precipitate was aged in the microemulsion for 12 h, centrifuged, and washed three times with ethanol to remove residual organic matter;

[0195] Drying and calcination: vacuum drying at 60 °C for 12 h, followed by calcination in a muffle furnace at 500 °C for 4 h (heating rate 2 °C / min) to obtain a TiO2-Al2O3 composite support (mass ratio 2:1, specific surface area 250 m 2 / g);

[0196] 3.2 Rare earth active component loading (La-Ce-Pr ternary doping)

[0197] (1) Plasma activation treatment of carrier

[0198] The support was placed in a plasma reactor, purged with argon (50 sccm), and treated at 300 W power for 30 min to enhance the surface hydroxyl density and defect sites;

[0199] (2) Microwave-photochemical synergistic impregnation

[0200] Preparation of rare earth nitrate solution:

[0201] Lanthanum nitrate, cerium nitrate, and praseodymium nitrate were mixed in a molar ratio of 1:2:1 to a total concentration of 1 mol / L, and 0.2 mol / L ethylenediaminetetraacetic acid was added to obtain a rare earth nitrate solution;

[0202] Impregnation process:

[0203] The carrier is immersed in a rare earth nitrate solution and placed in a microwave-ultraviolet coordinated reactor;

[0204] Microwave power 300W (80℃), UV wavelength 254nm (intensity 50mW / cm 2 ), synchronous action for 30 min;

[0205] Centrifuge and dry at 60°C for 12 h;

[0206] (3) Calcination

[0207] Calcination at 550°C (heating rate 1°C / min) for 5 h formed La-O-Ce-Pr active clusters with a core-shell structure, thereby obtaining a crude catalyst, in which rare earth elements accounted for 10% of the total mass of the catalyst;

[0208] 3. Transition metal doping

[0209] The crude catalyst is placed in a hot-wall ALD reactor to introduce transition metals;

[0210] (1) Atomic layer deposition (ALD) process

[0211] Equipment: Hot-wall ALD reactor, substrate temperature 200°C;

[0212] Precursor:

[0213] Mn source: dimethyl manganese, pulse time 0.1s;

[0214] Ce source: tetrakis(dimethylamino)cerium, pulse time 0.2s;

[0215] Oxidant: ozone, pulse time 0.5s;

[0216] Sedimentation cycle:

[0217] Mn3O4: 60 cycles (controlled doping amount 3wt%);

[0218] CeO2: 40 cycles (controlled doping amount 2wt%);

[0219] (2) Post-processing

[0220] Annealing at 400℃ in nitrogen for 2h stabilizes the crystal structure of Mn3O4 and CeO2 to obtain a rare earth-based ultra-low temperature denitrification catalyst.

[0221] Step 4: Clean up the emissions

[0222] After the reaction, the flue gas is discharged through dust removal treatment, and the NO in the tail gas is detected. x The emission concentration and ammonia concentration show a denitrification efficiency of 98.4%, NO x The emission concentration is 18.3 mg / m 3 , the ammonia concentration is 1.8ppm.

[0223] Comparative Example 1

[0224] The specific implementation method is consistent with Example 3, except that instead of using rare earth-based ultra-low temperature denitrification catalyst, a catalyst commonly used in SCR industrial flue gas denitrification on the market is used. Finally, the NO in the exhaust gas is detected. x The denitrification efficiency of the emission concentration and ammonia concentration is only 82.6%, and the NO x The emission concentration is 78.5mg / m 3 , ammonia escape is as high as 8.4ppm.

[0225] Comparative Example 2

[0226] The specific implementation method is consistent with Example 3. The difference is that the main active component of the rare earth-based ultra-low temperature denitrification catalyst is adjusted to be La-Ce binary doped, and the NO in the exhaust gas is finally detected. x The emission concentration and ammonia concentration resulted in a denitrification efficiency of 89.2%, and NO X Emission is 42.6mg / m 3 , ammonia escape 4.7ppm.

[0227] Therefore, it can be seen from the above denitration results that the denitration method provided by the present invention achieves efficient denitration under ultra-low temperature conditions of 80-180°C, significantly improving the denitration efficiency and catalyst stability. When the traditional industrial flue gas denitration catalyst is used in Comparative Example 1, under the same operating conditions, the traditional catalyst is significantly less active under low temperature conditions and requires high temperatures above 350°C to achieve a denitration efficiency of 82.6%, and the ammonia escape rate remains high. When the active component in the rare earth-based ultra-low temperature denitration catalyst is adjusted to La-Ce binary doping in Comparative Example 2, its denitration efficiency is reduced to 89.2%, NO X Emission is 42.6mg / m 3, ammonia escape 4.7ppm, although better than the traditional catalyst, but compared with the performance of the ternary doping system of Example 3 is significantly different, especially at a low temperature of 130 ° C, the reaction kinetics slowed down significantly, indicating that the introduction of Pr has an irreplaceable role in the regulation of oxygen vacancies in the core-shell structure active clusters. Therefore, it can be seen from the above data that the solution provided by the present invention has outstanding creative advantages over traditional SCR technology. Traditional SCR technology relies on V2O5-WO3 / TiO2 catalysts and needs to operate at high temperatures of 300-400 ° C. Not only is the energy consumption high, but the catalyst is easily deactivated due to sintering, poisoning or loss of active components. The present invention, through the synergistic effect of the La-Ce-Pr ternary co-doped core-shell structure active clusters and the plasma activated TiO2-Al2O3 composite carrier, can still maintain excellent redox performance at low temperatures, so that the denitrification efficiency is stabilized at more than 90% in the range of 80-180 ° C, NO X Emission concentration is less than 50mg / m 3 , ammonia slip is below 3.2ppm. Simultaneously, pneumatic atomization technology controls the reducing agent atomization particle size to ≤20μm, significantly improving the mixing uniformity of the reducing agent and flue gas and reducing ammonia slip. In comparison, traditional technologies have a denitrification efficiency of only approximately 85%, require high-temperature operation, consume high energy, and have poor stability. The systematic design of this invention achieves the goals of low-temperature, high-efficiency, low-energy, and long-life denitrification. It is particularly suitable for low-temperature flue gas treatment in industries such as steel and cement, providing a revolutionary solution for industrial denitrification.

[0228] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A SCR industrial flue gas denitrification method, characterized in that: The following steps are involved: After the industrial flue gas is introduced, the temperature is lowered to 80-180℃ in two stages; Then, a reducing agent is sprayed in, wherein the reducing agent is at least one of ammonia gas, urea solution or ammonium salt solution, and the reducing agent is atomized by pneumatic atomization technology during the spraying, and the atomized particle size is ≤20 μm; The flue gas is then contacted with a rare earth-based ultra-low temperature denitration catalyst for reaction. The rare earth-based ultra-low temperature denitration catalyst has La-Ce-Pr ternary co-doping as a main active component and is supported on a plasma-activated TiO2-Al2O3 composite support, wherein the molar ratio of Pr, Ce and La is 1:2:1, and the surface of the TiO2-Al2O3 composite support has La-O-Ce-Pr active clusters with a core-shell structure, wherein the shell layer of the core-shell structure is CeO2 and the core layer is La-Pr oxide; The purified flue gas after the reaction is discharged after dust removal.

2. The SCR industrial flue gas denitrification method according to claim 1, characterized in that: The preparation method of the rare earth-based ultra-low temperature denitration catalyst comprises: The TiO2-Al2O3 composite support is prepared by a microemulsion-assisted coprecipitation method and then subjected to plasma activation treatment. The microemulsion contains a cyclohexane / n-butanol / water mixture system and is added with 0.1-0.5wt% of polyvinyl pyrrolidone. The TiO2-Al2O3 composite support is immersed in a rare earth nitrate solution by microwave-photochemical synergistic impregnation method, and the impregnation is carried out for 30 minutes under the synchronous action of microwave and ultraviolet light, wherein the rare earth element accounts for 5-15% of the total mass of the catalyst; After drying and calcination, it is doped with transition metal to obtain the product.

3. The SCR industrial flue gas denitrification method according to claim 2, characterized in that: The titanium source in the TiO2-Al2O3 composite carrier is tetrabutyl titanate, and the aluminum source is aluminum nitrate.

4. The SCR industrial flue gas denitrification method according to claim 2, characterized in that: 0.05-0.1 mol / L of citric acid and 0.01-0.05 wt% of graphene quantum dots are also added to the microemulsion.

5. The SCR industrial flue gas denitrification method according to claim 2, characterized in that: The volume ratio of cyclohexane, n-butanol and water in the microemulsion is 5:3:2, and the coprecipitation pH value is 9-10.

6. The SCR industrial flue gas denitrification method according to claim 2, characterized in that: The concentration of the rare earth nitrate solution is 0.5-1.5 mol / L, and 0.1-0.3 mol / L of ethylenediaminetetraacetic acid is added to the rare earth nitrate solution.

7. The SCR industrial flue gas denitrification method according to claim 2, characterized in that: The mass ratio of TiO2 to Al2O3 in the TiO2-Al2O3 composite carrier is 3:1-1:1, and the specific surface area is 150-300m 2 / g.

8. The SCR industrial flue gas denitrification method according to claim 2, characterized in that: The transition metals are Mn and Ce, wherein Mn exists in the form of Mn3O4, and the doping amount is 2-3% of the total mass of the catalyst; Ce exists in the form of CeO2, and the doping amount is 1-2% of the total mass of the catalyst.

9. The SCR industrial flue gas denitrification method according to claim 1, characterized in that: The amount of the reducing agent injected is related to the NO X The molar ratio is 0.8-1.2:1.