Method for catalytic degradation of dioxin in household garbage incineration fly ash at low temperature

Abstract

This invention belongs to the field of hazardous waste treatment and environmental catalysis technology, and discloses a method for low-temperature catalytic degradation of dioxins in municipal solid waste incineration fly ash. By combining fly ash pretreatment, medium-temperature thermal treatment, and low-temperature catalytic degradation, dioxins in fly ash are efficiently removed with high removal efficiency. A regenerable honeycomb composite catalyst was prepared, using nano-titanium dioxide as a carrier, loaded with vanadium-molybdenum active components, and treated with silane functional groups and zirconium-based premixes. This catalyst not only achieves efficient catalytic degradation of dioxins in a medium-low temperature environment, but also effectively inhibits the adsorption and deposition of toxic byproducts such as dust, tar, organic matter, and sulfur, significantly reducing the risk of catalyst poisoning, extending catalyst lifespan, enabling multiple regeneration cycles, and greatly reducing operating costs.

Description

Technical Field

[0001] This invention belongs to the field of hazardous waste treatment and environmental catalysis technology, specifically relating to a method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration, and particularly to a method for low-temperature degradation of dioxins in fly ash. Background Technology

[0002] Fly ash, the precipitate from flue gas purification systems and bottom ash settling at the bottom of flues and chimneys during municipal solid waste incineration, contributes to environmental pollution. Its pollution primarily stems from dioxins and heavy metals. Dioxins are among the most toxic compounds known, exhibiting teratogenic, carcinogenic, and mutagenic properties, as well as the ability to damage the human reproductive and immune systems. Studies show that dioxins in fly ash account for approximately 70% of dioxin emissions during incineration, with concentrations typically ranging from 500 to 5000 ng-TEQ / kg, far exceeding landfill and resource recovery limits.

[0003] Currently, the main technologies for dioxin treatment in fly ash include: 1) High-temperature melting / vitrification: Temperature 1200-1400℃, can completely decompose dioxins, but it has extremely high energy consumption, large equipment investment, high operating costs, and is prone to heavy metal volatilization and secondary pollution, thus limiting its large-scale application.

[0004] 2) Co-processing in cement kilns: Dioxins are decomposed at high temperatures in cement kilns, but the high chlorine content in fly ash easily corrodes equipment and affects clinker quality, limiting the amount that can be added and making it difficult to promote on a large scale.

[0005] 3) Low-temperature pyrolysis / desorption: Temperature 300-400℃, energy consumption is lower than melting, but the efficiency of simple pyrolysis is limited, high-chlorinated dioxins are not completely degraded and are prone to resynthesis, and the tail gas needs to be deeply treated.

[0006] 4) Catalytic degradation method: using metal oxides, noble metals, and molecular sieves as catalysts to achieve dioxin decomposition at medium and high temperatures.

[0007] Traditional catalysts suffer from problems such as poor low-temperature activity, weak resistance to chlorine poisoning, and susceptibility to interference from fly ash CaO / Cl⁻ / heavy metals. The reaction temperature often needs to be above 350℃, and they still have drawbacks such as high energy consumption, unstable efficiency, and short lifespan.

[0008] Chinese patent CN113814207B discloses a method for low-temperature degradation of dioxins in fly ash from municipal solid waste incineration in a pyrolysis furnace. The method uses nitrogen pyrolysis at a temperature of 350–400°C, but does not introduce a highly efficient catalytic system. The residence time is long and the efficiency is low. The dioxins generated may be resynthesized during the cooling process after high-temperature thermal decomposition. Furthermore, the flue gas generated in the pyrolysis furnace is treated in a spray tower after being adsorbed by activated carbon. The activated carbon only adsorbs the dioxins and does not actually degrade them, which poses a risk of secondary pollution.

[0009] Chinese patent CN112675917B discloses a method for preparing a sludge / fly ash-based low-temperature dioxin degradation catalyst. It utilizes heavy metals from fly ash and organic matter from sludge as raw materials for the preparation of functional materials. Through a thermal-acid method, proteins in the sludge are extracted and hydrolyzed to obtain amino acids of different types and single spatial configurations. The heavy metals in the fly ash are simultaneously converted into ionic states, forming coordination centers for metal-organic frameworks (MOFs). The different amino acids obtained through hydrolysis serve as mixed ligands for the MOFs, increasing structural diversity, while the single spatial configuration of the amino acids enhances structural stability. During the hydrothermal synthesis of MOFs, dioxins from the fly ash are encapsulated in multi-sized pores, achieving low-temperature catalytic degradation under visible / ultraviolet light conditions. This method has high requirements for the fly ash, the prepared catalyst cannot be regenerated and reused, and it relies on light / ultraviolet assistance, making it challenging to engineer.

[0010] In summary, the complete decomposition of dioxins using low-temperature catalytic degradation technology to generate non-toxic inorganic compounds such as CO2, H2O, and HCl for emission is currently a research hotspot and challenge in the field of pollution control. The industry urgently needs a low-temperature catalytic degradation technology for fly ash dioxins that is low-temperature, highly efficient, stable, highly resistant to interference, and renewable, to achieve safe, economical, and large-scale disposal. Summary of the Invention

[0011] In response to the current situation where dioxins in municipal solid waste incineration fly ash are difficult to degrade and the high energy consumption of high-temperature treatment of waste incineration fly ash, This invention employs a combination of fly ash pretreatment, medium-temperature heat treatment, and low-temperature catalytic degradation to efficiently remove dioxins from fly ash, achieving high removal efficiency.

[0012] The purpose of this invention is to provide a method for treating dioxins in fly ash from municipal solid waste incineration by medium- and low-temperature catalytic degradation, comprising the following steps: S001, Fly ash pretreatment: Dry fly ash is mixed with water, and soluble substances are dissolved in the water by physical or chemical methods. Solid particles in the fly ash are separated from liquid by filtration and centrifugation to obtain pretreated fly ash. The pretreated fly ash, retardant and bentonite are mixed evenly and then dried, crushed, granulated and screened to obtain granular material with a particle size of 2-5 mm. The inhibitor is urea phosphate, which is dissolved in deionized water to prepare a 5-10% urea phosphate solution; the mass ratio of inhibitor, bentonite and dry fly ash is 2-3:8-10:100. S002, Heat treatment: The above granular material is fed into the heat treatment device, the combustion fan is turned on to increase the furnace temperature and oxygen content, and promote the reaction; the fly ash particles are continuously heat treated at 400-600℃ for 50-100 minutes. During this process, the organochlorine source in fly ash is cut off, and the built-in urea phosphate inhibitor plays a synergistic role in effectively inhibiting the de novo synthesis of dioxins.

[0013] S003, Low-temperature catalytic degradation: The heat-treated fly ash and gas mixture is cooled to 200°C and transported to the catalytic reactor after passing through a cooling tower and gravity dust collector. Under the action of the catalyst, a catalytic degradation reaction is carried out to completely remove residual dioxins. The core component of the catalytic reactor is the composite catalyst bed, which is composed of a regenerable honeycomb composite catalyst. The catalyst is a composite catalyst with vanadium-molybdenum active components loaded on nano-titanium dioxide as a support, and is prepared by processing with silane functional body and zirconium-based premix.

[0014] The catalytic temperature is 280–310℃, and the catalytic time is 5–10 minutes.

[0015] S004, Exhaust Gas Treatment and Emission: Gravity dust collectors separate and collect fly ash, which can be recycled as a resource-based raw material; the flue gas after catalytic degradation enters the post-treatment process, and after cooling, it meets environmental protection standards and can be directly discharged into the atmosphere, or sent to subsequent systems for further deep treatment.

[0016] Conventional catalysts are prone to corrosion and failure under long-term exposure to harmful gases such as Cl and S, as well as solid particles generated from combustion. Therefore, in order to prepare a composite catalyst with regenerable and highly efficient catalytic capabilities, the composite catalyst is a composite catalyst with active components loaded on nano-titanium dioxide as a carrier, specifically: S01, prepare a mixed solution of ammonium metavanadate and oxalic acid dihydrate in a molar ratio of 1:2, impregnate the nano-titanium dioxide carrier with ultrasound, remove moisture, dry, and calcine. S02, ammonium molybdate tetrahydrate was dissolved in deionized water to obtain a 5% ammonium molybdate solution; the support obtained in S01 was impregnated with ultrasonication, then the moisture was removed, dried, and calcined to obtain a composite catalyst with nano-titanium dioxide as the support and loaded with active components.

[0017] The ultrasonic power is 200-300W, the soaking time is 8-10 hours, and the substrate is dried in an oven at 105℃ for 12 hours; the calcination temperature is 400-500℃, and the calcination time is 3-5 hours; the liquid-solid ratio is 1.2-1.5:1, which just completely submerges the carrier.

[0018] The preparation method of the aforementioned nano-titanium dioxide carrier is specifically as follows: Nano-TiO2 was dried in an oven at 105℃ for 30 minutes to remove moisture. Nano-TiO2 powder, carboxymethyl cellulose, 1mm chopped glass fibers, and glycerin were then added sequentially to a mixer and mixed thoroughly. During mixing, ammonia and lactic acid were added as needed to control the pH value to 7.8–8.2, and a suitable amount of deionized water was added to adjust the adhesion and facilitate molding. After mixing, dispersed, soft, and resilient clay granules were obtained. These granules were then placed in a clay kneading machine to obtain cylindrical clay lumps with regular shapes. The lumps were sealed with plastic wrap and aged in a cool place for 24 hours. During aging, the moisture in the clay moved under capillary action, evenly penetrating all parts of the clay lumps and improving its malleability. Finally, the clay was placed in a honeycomb mold and extruded into the desired honeycomb shape using an extruder. The lumps were then dried at 80℃, calcined at 120℃ for 1 hour, calcined at 300℃ for 1 hour, and held at 500℃ for 2 hours to obtain the nano-titanium dioxide carrier.

[0019] To address the issues of catalyst regeneration and poisoning, the composite catalyst undergoes further surface treatment, specifically: S1, (N,N-dimethylaminopropyl)trimethoxysilane and 1,3-propanesulfonate lactone are dissolved in anhydrous acetone, protected by nitrogen, and stirred at 25-35°C for 7-9 hours to form a suspension containing a white solid precipitate. S2, the suspension is filtered to obtain a white solid, washed 2 to 3 times with anhydrous acetone, and then dried under vacuum at 50 to 60°C for 12 to 14 hours to obtain the final product, a white powder, which is the zwitterionic silane functional body. The zwitterionic silane functional body is then dissolved in anhydrous ethanol to obtain a zwitterionic silane functional body solution. S3 involves immersing a composite catalyst loaded with active components, using nano-titanium dioxide as a carrier, in a zwitterionic silane functional body solution and then ultrasonically treating it for 15–30 minutes. S4, zirconium n-propoxide and bis[ 3 - (triethoxysilane)[Propylamine] was added dropwise to glacial acetic acid and stirred at room temperature for 1-2 hours until a homogeneous zirconium-based premix was formed. The zirconium-based premix was then poured into a zirconium-based silane functionalized solution. The solution was then sonicated for 5-8 minutes to completely disperse the silane functionalized and premixed components. The solution was then shaken at room temperature for 2-3 hours. After the reaction was completed, the solution was washed 2-3 times with anhydrous ethanol to remove loosely bound particles on the surface of the support. Finally, the solution was dried in an oven at 100°C for 5-8 hours to obtain a surface-treated, regenerable honeycomb composite catalyst.

[0020] The mass ratio of (N,N-dimethylaminopropyl)trimethoxysilane to 1,3-propanesulfonate lactone is 2-3:1-2.

[0021] Zirconium n-propoxide and bis[ 3 - (triethoxysilane) The mass ratio of propylamine is 1:0.8 to 1.2; The mass ratio of zirconium propoxide functionalized silane, zirconium propoxide, and composite catalyst is 1.5–2.5:3–4:100; After a two-step treatment process involving zwitterionic silane functionalization and zirconium-based premix, the resulting surface-treated composite catalyst is a high-strength, high-activity, poison-resistant, and regenerable honeycomb composite catalyst. The zwitterionic silane forms a monolayer on the catalyst surface, providing anti-fouling and anti-poisoning properties without clogging pores or reducing activity. The zirconium-based premix forms a thin barrier layer, resisting sulfur, halogens, and dust, while not shielding active sites. Together, they form a thin layer containing Zr-O-Si and amino groups on the catalyst surface. This layer, combined with the zwitterionic silane, increases the surface hydroxyl groups and active sites. The resulting organic-inorganic hybrid film effectively solves the problem of catalyst poisoning in polluted environments. Furthermore, the introduction of zirconium improves the catalyst's thermal stability, further extending its lifespan.

[0022] Compared with existing technologies, the beneficial effects of this invention are as follows: 1) This invention employs a combination of fly ash pretreatment, medium-temperature heat treatment, and low-temperature catalytic degradation. First, the formation precursors of dioxins are reduced by using a retardant, which is beneficial for subsequent heat treatment and low-temperature catalytic oxidation. On the other hand, the combination of medium-temperature heat treatment and low-temperature catalytic oxidation is used to completely decompose dioxins and improve the catalytic degradation efficiency of dioxins.

[0023] 2) This invention provides a surface-treated, regenerable honeycomb composite catalyst with a high-strength support suitable for industrial applications. The honeycomb support, prepared by synergistic molding of nano-TiO2, carboxymethyl cellulose, chopped glass fiber, and glycerol, undergoes a process of mud preparation, aging, and gradient calcination. It exhibits uniform pore structure, high mechanical strength, and wear and impact resistance, and can be directly used in fixed-bed catalytic reactors, solving the problems of easy loss, high pressure drop, and difficulty in regeneration associated with traditional powder catalysts. Through stepwise impregnation with a mixture of ammonium metavanadate and ammonium molybdate solution, supplemented by ultrasonic-assisted dispersion, the vanadium and molybdenum active components achieve high dispersion and uniform loading on the TiO2 support surface. The catalyst retains high catalytic activity and high stability under medium- and low-temperature conditions, demonstrating excellent degradation and conversion capabilities for pollutants such as VOCs, dioxins, and nitrogen oxides.

[0024] 3) This invention provides a surface-treated, regenerable honeycomb composite catalyst that is high-strength, highly active, poison-resistant, and regenerable. Through surface treatment, the surface has a double-layer protection of zirconium-based zwitterionic functional groups and zirconium groups. On the one hand, this effectively inhibits the aggregation of active components on the catalyst surface, weakens the interaction between active components and the support, and increases the dispersion of the active phase on the catalyst surface. On the other hand, it helps improve the structural stability of the composite catalyst and extends its service life. It can effectively inhibit the adsorption and deposition of toxic byproducts such as dust, tar, organic matter, and sulfur / chlorine, significantly reducing the risk of catalyst contamination and poisoning, and extending its service life. Furthermore, after surface treatment, it has easy-to-clean properties; deactivated catalysts can regain catalytic activity through simple water washing, ethanol rinsing, or low-temperature drying, achieving multiple cycles of regeneration, significantly reducing usage costs, and solving the industry pain points of traditional catalysts being single-use, easily deactivated, and difficult to regenerate. Attached Figure Description

[0025] Figure 1 Electron micrograph of the surface-treated regenerable honeycomb composite catalyst prepared in Example 1; Figure 2 Electron micrograph of the nano-titanium dioxide carrier prepared in Example 1; Figure 3 Electron micrograph of the untreated regenerable honeycomb composite catalyst prepared in Comparative Example 1; Figure 4 A bar chart comparing the catalytic efficiency of the honeycomb composite catalysts prepared in Example 1 and Comparative Examples 1-4 after regeneration for dioxin removal. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0027] Example 1: A method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration, firstly, a nano-titanium dioxide carrier is prepared, specifically as follows: Powdered nano-TiO2 was dried in an oven at 105℃ for 30 minutes to remove moisture. 100 parts of nano-TiO2 powder, 8 parts of carboxymethyl cellulose, 5 parts of 1mm chopped glass fiber, and 6 parts of glycerol were added sequentially to a mixer and mixed evenly. During the mixing process, ammonia and lactic acid were added as needed to control the pH value to 8, and 33 parts of deionized water were added to adjust the adhesion. After mixing, dispersed, soft, and tough clay granules were obtained. The clay granules were placed in a clay kneading machine to obtain cylindrical clay lumps. The lumps were sealed with plastic wrap and aged in a cool place for 24 hours. Finally, they were placed in a honeycomb mold and extruded into the desired honeycomb shape using an extruder. The lumps were dried at 80℃, then calcined at 120℃ for 1 hour, calcined at 300℃ for 1 hour, and held at 500℃ for 2 hours to obtain the nano-titanium dioxide carrier.

[0028] Furthermore, a composite catalyst is prepared, specifically as follows: Ammonium metavanadate and oxalic acid dihydrate were prepared at a molar ratio of 1:2, and deionized water was added to obtain 150 parts of a mixed solution, with the mass concentration of ammonium metavanadate in the mixed solution being 2%. 100 parts of nano-titanium dioxide support were immersed in the mixed solution, just enough to completely submerge the support. After ultrasonic reaction for 10 hours, the solution was dried in an oven at 105℃ for 12 hours. After calcination at 500℃ for 4 hours, the solution was cooled and ready for use. Ammonium molybdate tetrahydrate was then dissolved in deionized water to prepare 150 parts of a 5% ammonium molybdate solution. The cooled support was then immersed in the ammonium molybdate solution and ultrasonicated for 10 hours, and then dried in an oven at 105℃ for 12 hours. After calcination at 500℃ for 4 hours, the solution was cooled and a composite catalyst with nano-titanium dioxide as the support and loaded with active components was obtained.

[0029] Finally, the composite catalyst is surface-treated to obtain a surface-treated, regenerable honeycomb composite catalyst, specifically as follows: 15 parts of (N,N-dimethylaminopropyl)trimethoxysilane and 5 parts of 1,3-propanesulfonate lactone were dissolved in 40 parts of anhydrous acetone. Under nitrogen protection, the mixture was stirred at 35°C for 7 hours to form a suspension containing a white solid precipitate. The suspension was filtered to obtain a white solid, which was washed 2-3 times with anhydrous acetone and then dried under vacuum at 60°C for 12 hours to obtain the final product, a white powder, which is the zwitterionic silane functional body. 3 parts of the zwitterionic silane functional body were then dissolved in 150 parts of anhydrous ethanol to obtain a zwitterionic silane functional body solution. One hundred parts of a composite catalyst loaded with active components using nano-titanium dioxide as a carrier were immersed in a zwitterionic silane functional body solution and ultrasonically treated for 15 to 30 minutes. 3 parts of zirconium n-propoxide and 2.4 parts of bis[ 3 - (triethoxysilane) [Propylamine] was added dropwise to 10 parts of glacial acetic acid, and the mixture was stirred at room temperature for 1-2 hours until a homogeneous premix was formed. The premix was then poured into a zwitterionic silane functionalized solution. The mixture was sonicated for 8 minutes to completely disperse the silane functionalized product and the premix. The mixture was then shaken at room temperature for 2 hours. After the reaction was complete, the mixture was washed 2-3 times with anhydrous ethanol to remove loosely bound particles from the support surface. Finally, it was dried in an oven at 100°C for 8 hours to obtain a surface-treated, regenerable honeycomb composite catalyst. The treated regenerable honeycomb composite catalyst was placed in the catalyst bed of a catalytic reactor.

[0030] To further catalyze the degradation of dioxins more thoroughly, fly ash pretreatment is performed: 100 parts of dry fly ash are mixed with water, and soluble substances are dissolved in the water by physical or chemical methods. Solid particles in the fly ash are separated from liquid by filtration and centrifugation to obtain pretreated fly ash; urea phosphate is dissolved in deionized water to prepare a 10% solution. After mixing 100 parts of pretreated fly ash, 20 parts of urea phosphate solution and 8 parts of bentonite evenly, the mixture is dried, crushed, granulated and screened to obtain granular material with an average particle size of 2.1 mm. The granular material is fed into the heat treatment device, the combustion fan is turned on to increase the furnace temperature, and the air is blown to increase the oxygen content in the furnace. The fly ash particles are continuously heat-treated at 500°C for 80 minutes. The heat-treated fly ash and gas mixture is cooled to 200°C after passing through a cooling tower and gravity dust collector and then transported to the catalytic reactor. Under the action of the catalyst, the catalytic degradation reaction is carried out in an environment of 300°C for 10 minutes. The gravity dust collector separates and collects fly ash, and tests its dioxin content. If it exceeds the standard, it re-enters the heat treatment stage. The flue gas after catalytic degradation enters the post-treatment stage, and after cooling, it meets environmental protection standards and is directly discharged into the atmosphere.

[0031] Example 2: A method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration, firstly, preparing a nano-titanium dioxide carrier, specifically: Powdered nano-TiO2 was dried in an oven at 105℃ for 30 minutes to remove moisture. 100 parts of nano-TiO2 powder, 10 parts of carboxymethyl cellulose, 4 parts of 1mm chopped glass fiber, and 7 parts of glycerol were added sequentially to a mixer and mixed evenly. During the mixing process, ammonia and lactic acid were added as needed to control the pH value to 8.1, and 36 parts of deionized water were added to adjust the adhesion. After mixing, dispersed, soft, and tough clay granules were obtained. The clay granules were placed in a clay kneading machine to obtain cylindrical clay lumps. The lumps were sealed with plastic wrap and aged in a cool place for 24 hours. Finally, they were placed in a honeycomb mold and extruded into the desired honeycomb shape using an extruder. They were dried at 80℃, then calcined at 120℃ for 1 hour, calcined at 300℃ for 1 hour, and held at 500℃ for 2 hours to obtain the nano-titanium dioxide carrier.

[0032] Furthermore, a composite catalyst is prepared, specifically as follows: Ammonium metavanadate and oxalic acid dihydrate were prepared at a molar ratio of 1:2, and deionized water was added to obtain 150 parts of a mixed solution, with the mass concentration of ammonium metavanadate in the mixed solution being 2%. 100 parts of nano-titanium dioxide support were immersed in the mixed solution, just enough to completely submerge the support. After ultrasonic reaction for 10 hours, the solution was dried in an oven at 105℃ for 12 hours. After calcination at 500℃ for 4 hours, the solution was cooled and set aside. Ammonium molybdate tetrahydrate was dissolved in deionized water to prepare 150 parts of a 5% ammonium molybdate solution. The cooled support was immersed in the ammonium molybdate solution and ultrasonicated for 10 hours. After drying in an oven at 105℃ for 12 hours, the solution was calcined at 500℃ for 4 hours. After cooling, a composite catalyst with nano-titanium dioxide as the support and loaded with active components was obtained.

[0033] Finally, the composite catalyst is surface-treated to obtain a surface-treated, regenerable honeycomb composite catalyst, specifically as follows: Ten parts of (N,N-dimethylaminopropyl)trimethoxysilane and five parts of 1,3-propanesulfonate lactone were dissolved in 30 parts of anhydrous acetone. Under nitrogen protection, the mixture was stirred at 25°C for 9 hours to form a suspension containing a white solid precipitate. The suspension was filtered to obtain a white solid, which was washed 2-3 times with anhydrous acetone and then dried under vacuum at 60°C for 12 hours to obtain the final product, a white powder, which is the zwitterionic silane functional body. Three parts of the zwitterionic silane functional body were then dissolved in 150 parts of anhydrous ethanol to obtain a zwitterionic silane functional body solution. One hundred parts of a composite catalyst loaded with active components using nano-titanium dioxide as a carrier were immersed in a zwitterionic silane functional body solution and ultrasonically treated for 20 minutes. Add 4 parts zirconium n-propoxide and 4 parts di[ 3 - (triethoxysilane) [Propylamine] was added dropwise to 20 parts of glacial acetic acid, and the mixture was stirred at room temperature for 2 hours until a homogeneous premix was formed. The premix was then poured into a zwitterionic silane functionalized solution. The mixture was then sonicated for 8 minutes to completely disperse the silane functionalized product and the premix. The mixture was then shaken at room temperature for 3 hours. After the reaction was complete, the mixture was washed 2-3 times with anhydrous ethanol to remove loosely bound particles from the support surface. Finally, it was dried in an oven at 100°C for 6 hours to obtain a surface-treated, regenerable honeycomb composite catalyst. The treated regenerable honeycomb composite catalyst was placed in the catalyst bed of a catalytic reactor.

[0034] To further catalyze the degradation of dioxins more thoroughly, the fly ash is pretreated as follows: 100 parts of dry fly ash are mixed with water, and soluble substances are dissolved in the water using physical or chemical methods. Solid particles in the fly ash are separated from the liquid using filtration and centrifugation to obtain pretreated fly ash. Urea phosphate is dissolved in deionized water to prepare a 10% solution. After the pretreated fly ash, 30 parts of urea phosphate solution and 9 parts of bentonite were mixed evenly, the mixture was dried, crushed, granulated and screened to obtain granular material with a particle size of 2.3 mm. The granular material is fed into the heat treatment device, the combustion fan is turned on to increase the furnace temperature, and the air is blown to increase the oxygen content in the furnace. The fly ash particles are continuously heat-treated at 600°C for 50 minutes. The heat-treated fly ash and gas mixture is cooled to 200°C after passing through a cooling tower and gravity dust collector and then transported to the catalytic reactor. Under the action of the catalyst, the catalytic degradation reaction is carried out in an environment of 310°C for 5 minutes. The gravity dust collector separates and collects fly ash, tests its dioxin content, and if it meets the standards, it is treated for resource recovery. The flue gas after catalytic degradation enters the post-treatment process, and after cooling, it meets environmental protection standards and can be directly discharged into the atmosphere.

[0035] Example 3: A method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration, firstly, preparing a nano-titanium dioxide carrier, specifically: Powdered nano-TiO2 was dried in an oven at 105℃ for 30 minutes to remove moisture. 100 parts of nano-TiO2 powder, 9 parts of carboxymethyl cellulose, 6 parts of 1mm chopped glass fiber, and 8 parts of glycerol were added sequentially to a mixer and mixed thoroughly. During mixing, ammonia and lactic acid were added as needed to control the pH at 7.8, and 39 parts of deionized water were added to adjust the binding properties. After mixing, dispersed, soft, and resilient clay granules were obtained. These granules were placed in a clay mortar to obtain cylindrical clay lumps. The lumps were sealed with plastic wrap and aged in a cool place for 24 hours. Finally, they were placed in a honeycomb mold and extruded into the desired honeycomb shape using an extruder. The lumps were dried at 80℃, then calcined at 120℃ for 1 hour, calcined at 300℃ for 1 hour, and held at 500℃ for 2 hours to obtain the nano-titanium dioxide carrier.

[0036] Furthermore, a composite catalyst is prepared, specifically as follows: Ammonium metavanadate and oxalic acid dihydrate were prepared at a molar ratio of 1:2, and deionized water was added to obtain 150 parts of a mixed solution, with the mass concentration of ammonium metavanadate in the mixed solution being 2%. 100 parts of nano-titanium dioxide support were immersed in the mixed solution, just enough to completely submerge the support. After ultrasonic reaction for 10 hours, the solution was dried in an oven at 105℃ for 12 hours. After calcination at 500℃ for 4 hours, the solution was cooled and set aside. Ammonium molybdate tetrahydrate was dissolved in deionized water to prepare 150 parts of a 5% ammonium molybdate solution. The cooled support was immersed in the ammonium molybdate solution and ultrasonicated for 10 hours. After drying in an oven at 105℃ for 12 hours, the solution was calcined at 500℃ for 4 hours. After cooling, a composite catalyst with nano-titanium dioxide as the support and loaded with active components was obtained.

[0037] Finally, the composite catalyst is surface-treated to obtain a surface-treated, regenerable honeycomb composite catalyst, specifically as follows: 15 parts of (N,N-dimethylaminopropyl)trimethoxysilane and 10 parts of 1,3-propanesulfonate lactone were dissolved in 50 parts of anhydrous acetone. Under nitrogen protection, the mixture was stirred at 30°C for 8 hours to form a suspension containing a white solid precipitate. The suspension was filtered to obtain a white solid, which was washed 2-3 times with anhydrous acetone and then dried under vacuum at 60°C for 12 hours to obtain the final product, a white powder, which is the zwitterionic silane functional body. 3.7 parts of the zwitterionic silane functional body were then dissolved in 150 parts of anhydrous ethanol to obtain a zwitterionic silane functional body solution. One hundred parts of a composite catalyst loaded with active components using nano-titanium dioxide as a carrier were immersed in a zwitterionic silane functional body solution and ultrasonically treated for 20 minutes. 4 parts of zirconium n-propoxide and 4.5 parts of bis[ 3 - (triethoxysilane)[Propylamine] was added dropwise to 15 parts of glacial acetic acid, and the mixture was stirred at room temperature for 2 hours until a homogeneous zirconium-based premix was formed. The premix was then poured into a zwitterionic silane functionalized solution. The mixture was then sonicated for 8 minutes to completely disperse the silane functionalized product and the premix. The mixture was then shaken at room temperature for 2 hours. After the reaction was complete, the mixture was washed 2-3 times with anhydrous ethanol to remove loosely bound particles from the support surface. Finally, it was dried in an oven at 100°C for 8 hours to obtain a surface-treated, regenerable honeycomb composite catalyst. The treated regenerable honeycomb composite catalyst was placed in the catalyst bed of a catalytic reactor.

[0038] To further catalyze the degradation of dioxins more thoroughly, the fly ash is pretreated as follows: 100 parts of dry fly ash are mixed with water, and soluble substances are dissolved in the water using physical or chemical methods. Solid particles in the fly ash are separated from the liquid using filtration and centrifugation to obtain pretreated fly ash. Urea phosphate is dissolved in deionized water to prepare a 10% solution. After the pretreated fly ash, 20 parts of urea phosphate solution and 8 parts of bentonite were mixed evenly, the mixture was dried, crushed, granulated and screened to obtain granular material with a particle size of 2.3 mm. The granular material is fed into the heat treatment device, the combustion fan is turned on to increase the furnace temperature, and the oxygen content in the furnace is increased by blowing air. The fly ash particles are continuously heat-treated at 500°C for 80 minutes. The heat-treated fly ash and gas mixture is cooled to 200°C by a cooling tower and gravity dust collector and then transported to the catalytic reactor. Under the action of the catalyst, the catalytic degradation reaction is carried out in an environment of 280°C for 10 minutes. The gravity dust collector separates and collects fly ash, tests its dioxin content, and if it meets the standards, it is treated for resource recovery. The flue gas after catalytic degradation enters the post-treatment process, and after cooling, it meets environmental protection standards and can be directly discharged into the atmosphere.

[0039] Comparative Example 1: The composite catalyst was not surface-treated and was directly loaded onto the catalyst bed of the vanadium-molybdenum catalytic reactor. Other aspects were the same as in Example 1. Comparative Example 2: When surface-treating the composite catalyst, 15 parts of zirconium n-propoxide and 12 parts of bis[ 3 - (triethoxy) silicon The zirconium-based premix obtained by reacting propylamine is otherwise the same as in Example 1; Comparative Example 3: When the composite catalyst was surface-treated, only a zirconium-based premix was used for treatment, and no zwitterionic silane functional body was used for treatment. Other aspects were the same as in Example 1. Comparative Example 4: Commercially available vanadium-molybdenum honeycomb composite catalyst supported on titanium dioxide; Comparative Example 5: A commercially available vanadium-tungsten honeycomb composite catalyst supported on titanium dioxide.

[0040] Experimental data and results analysis

[0041] 1. Catalyst surface morphology analysis

[0042] The morphology of the composite catalyst surface was characterized using a Hitachi SU-8010 field emission scanning electron microscope, with an accelerating voltage of 15 kV, a probe current of 10 nA, a resolution of 1.5 nm, and a magnification of 20,000. Electron microscopy images of the surface-treated regenerable honeycomb composite catalyst and the prepared nano-titanium dioxide support obtained in Example 1 are shown below. Figure 1-2 ; and an electron micrograph of the untreated, regenerable honeycomb composite catalyst prepared in Example 1 is shown in Figure 1. Figure 3 ; After being magnified 20,000 times by a scanning electron microscope, Figure 2 It can be seen that the surface morphology of the nano-titanium dioxide raw material is relatively loose, with uniform surface dispersion and micropores; the surface morphology of the vanadium-molybdenum catalyst after surface treatment in Example 1 is also observed. Figure 1 Upon observation, no aggregation was observed, and the active material was uniformly distributed. The electron micrograph of the composite catalyst in Comparative Example 1 is shown below. Figure 3 As can be seen, the active materials exhibit agglomeration and uneven distribution. This is because during surface treatment, the functional groups in the zwitterionic silane functional group can make vanadium and molybdenum more evenly dispersed, and also increase the number of active sites, making it easier to adsorb large hydrophobic molecules such as dioxins, thereby improving catalytic efficiency.

[0043] 2. Performance characterization of catalysts

[0044] Static nitrogen adsorption is a commonly used method for determining specific surface area. Its principle involves observing the adsorption and desorption of nitrogen gas by the sample under vacuum conditions, and then using a mathematical model to calculate the specific surface area and pore size distribution of the sample. The total specific surface area of ​​the adsorbent material is also calculated. In a JW-BK200C specific surface area and pore size analyzer, the catalyst was first degassed under vacuum at 200°C for 8 hours, and then the catalyst samples from Examples 1-3 and Comparative Examples 1-5 were tested at liquid nitrogen temperature, as shown in Table 1.

[0045] Table 1. Record of specific surface area and pore size of catalysts

[0046] Pores can be classified into micropores (<2nm), mesopores (2-50nm), and macropores (>50nm). Mesoporous and microporous structures are beneficial for the adsorption of various gaseous pollutants. Dioxin molecules have a size of 1.40nm. The closer the catalyst pore size is to the size of the pollutant molecule, the easier it is for stable adsorption to occur. Catalysis of pollutants involves first adsorbing the pollutant molecules onto the active sites on the catalyst surface, and then catalytically oxidizing them using adsorbed oxygen on the catalyst surface and lattice oxygen in the bulk. Table 1 shows that the surface-treated regenerable honeycomb composite catalysts in Examples 1-3 have a smaller specific surface area than Comparative Example 1, but smaller pore sizes than Comparative Examples 1 and 3-5. Therefore, after dual surface treatment with zwitterionic silane functional groups and zirconium-based premixes, a larger specific surface area and smaller pore size are achieved, providing more active sites for the catalytic reaction and resulting in better catalytic performance. This is because the stable structure formed after surface treatment of the zirconium-based premix improves thermal stability, prevents high-temperature crystal transformation, and enhances the catalyst's resistance to sulfur and wear. The coating film formed by this process reduces the specific surface area. Furthermore, the pretreatment with zirconium-based silane functionalized bodies makes the pores less prone to clogging, and the surface changes from hydrophilic to amphiphilic, which increases the specific surface area. Therefore, in Comparative Example 2, increasing the amount of zirconium propoxide in the zirconium-based premix significantly reduces both the specific surface area and the pore size.

[0047] 3. Catalytic degradation efficiency of dioxins

[0048] The equipment used to detect the dioxin content in the gas before and after catalytic degradation was a high-resolution chromatography / high-resolution mass spectrometry system. The chromatographic column used was a DB-5MS, 60m × 0.25mm (inner diameter) × 0.25μm (film thickness); the injection port temperature was 270℃; the carrier gas was He; the flow rate was 1.2mL / min; the autosampler injection capacity was 1μL; the column temperature program was as follows: first, hold at 150℃ for 1 minute, then increase the temperature to 190℃ at a rate of 25℃ / min, then increase the temperature to 280℃ at a rate of 3℃ / min, and finally hold at 280℃ for 20 minutes.

[0049] The catalysts from Examples 1-2 and Comparative Examples 1-5 were installed in the catalyst bed of a catalytic reactor, with a flue gas space velocity of 7000 h⁻¹. -1 The flue gas temperature was 200℃. After the start of operation, the inlet and outlet gas samples were collected and analyzed after 24 hours of stabilization. The catalyst bed temperature was set to 280℃ and the catalytic treatment time was 5 minutes. The results are shown in Table 2.

[0050] Table 2. Record of catalytic degradation efficiency of dioxins

[0051] As shown in Table 2, the composite catalysts of Examples 1-3 achieved a dioxin conversion rate of over 99% after treatment at 280°C for 5 minutes, meeting the EU requirement of less than 0.1 ng TEQ / m³ for dioxins. 3 The emission standards were met. Comparative Examples 1-2 and 4 all showed catalytic efficiencies exceeding 90%. However, in Comparative Example 2, the increased zirconium concentration resulted in an excessively thick film layer, hindering the active sites of the catalyst layer and significantly reducing the catalytic rate. The 5-minute treatment time was insufficient for the catalytic reaction, leading to a significant decrease in catalytic efficiency. Comparative Example 5 used a vanadium-tungsten catalytic system, which has high temperature requirements; the reaction temperature of 280℃ did not reach the system's optimal reaction temperature, resulting in a significant decrease in catalytic efficiency.

[0052] 4. Catalytic effect of composite catalysts under harsh conditions

[0053] To compare the durability, resistance to poisoning, sulfur, and dust of the composite catalysts in Examples 1-3 and Comparative Examples 1-5, 200 mg / Nm³ of nitrogen oxides were introduced before they entered the catalytic reactor. 3 sulfur dioxide pollutants and 5g / Nm 3 The fly ash has a flue gas space velocity of 7000 h⁻¹. -1 The flue gas temperature was 200℃. Inlet and outlet gas samples were collected and analyzed after 24 hours, one week, and one month of operation. The catalyst bed temperature was set to 280℃ and the catalytic treatment time was 5 minutes. The results are shown in Table 3.

[0054] Table 3. Degradation catalytic efficiency (%) of composite catalysts under harsh conditions

[0055] Catalysts are frequently exposed to challenging high-sulfur and dusty environments. These conditions lead to irreversible damage to the catalyst's surface microstructure and chemical composition, affecting its initial catalytic efficiency and sulfur and dust resistance. Table 3 shows that dual surface treatment with zirconium-based premixes and zirconium functional groups provides more active sites for the catalytic reaction, resulting in better catalytic performance. Furthermore, the excellent chemical and mechanical stability formed after surface treatment, primarily due to the formation of stable RO-R' bonds (where R or R' represents Zr or Si) through condensation hydrolysis, significantly improves the catalyst's sulfur resistance and abrasion resistance. Therefore, even after one month of operation in dusty and high-sulfur environments, it still maintains approximately 90% catalytic efficiency. Comparative Example 5 exhibited significantly less reduction in catalytic efficiency compared to other comparative examples in environments where the temperature was below its optimal catalytic effect. This was primarily because the mechanical strength of the vanadium-tungsten composite catalyst was significantly higher than that of the vanadium-molybdenum system. Consequently, the catalyst experienced less wear under high dust impact, resulting in a smaller reduction in catalytic efficiency. Comparative Example 2, on the other hand, was limited in its catalytic efficiency due to its high zirconium concentration. However, the slight wear of the zirconium protective layer under high dust impact actually improved its catalytic efficiency in harsh environments.

[0056] 5. Regeneration of composite catalysts

[0057] The composite catalysts used in Example 1 and Comparative Example 1 were cleaned and regenerated, and then cleaned and regenerated again every 6 months under normal operating conditions. Table 3 shows the dioxin removal effect after 5 regenerations in Example 1 and 60 days of operation. As can be seen from Table 3, the repair effect after cleaning and regeneration is not much different from the initial effect. This is because the surface-treated regenerable honeycomb composite catalyst in the examples, after being treated with zirconium-based and zwitterionic silane functional groups, has good anti-fly ash adhesion, good anti-alkali metal and anti-tar effects due to the protection of the silane functional groups. In addition, because it is hydrophobic and does not clog pores, its adsorption of hydrophobic macromolecules such as dioxins is enhanced, resulting in good regeneration effect and long life. Figure 4 This is a bar chart comparing the dioxin removal effects of Example 1 and Comparative Examples 1-4 after initial use and 5 regenerations. It can be seen more intuitively that the composite catalyst prepared in the examples has a significantly better regeneration effect and dioxin catalytic effect than the comparative examples.

[0058] Table 4. Catalytic efficiency of dioxin regeneration using composite catalysts

[0059] 6. Detection of treated fly ash and purified gas.

[0060] The fly ash before treatment and the fly ash in the gravity dust collector were collected, and the changes in dioxin concentration before and after treatment were detected, as shown in Table 5; after 3 months of operation of each embodiment and comparative example, the pre-emission test was carried out, as shown in Table 6.

[0061] Table 5. Record of Dioxin Concentration in Fly Ash

[0062] Table 6. Detection Records of the Purified Gas

[0063] As shown in Tables 1-6, the surface-treated, regenerable honeycomb composite catalysts prepared in Examples 1-3 exhibit significantly improved catalytic degradation efficiency for dioxins compared to the control group. Furthermore, they demonstrate good resistance to poisoning, sulfur, and dust, significantly reducing the risk of catalyst contamination and extending their service life. The surface-treated catalysts are also easy to clean; deactivated catalysts can be restored to catalytic activity through simple water washing, ethanol rinsing, or low-temperature drying, enabling multiple regeneration cycles and significantly reducing operating costs. The heat-treated and purified fly ash meets standards and can be recycled. The catalytically purified gas meets emission standards and can be directly emitted.

[0064] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Equal modifications and variations made by those skilled in the art to the technical solution of the present invention, as long as they do not depart from the overall concept of the present invention, shall still fall within the scope of the present invention.

Claims

1. A method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration, characterized in that, The method for low-temperature catalytic degradation of dioxins in municipal solid waste incineration fly ash includes the following steps: S001, Fly ash pretreatment: Dry fly ash is mixed with water, and soluble substances are dissolved in the water by physical or chemical methods. Solid particles in the fly ash are separated from liquid by filtration and centrifugation to obtain pretreated fly ash. The pretreated fly ash, retardant and bentonite are mixed evenly and then dried, crushed, granulated and screened to obtain granular material with a particle size of 2-5 mm. S002, Heat treatment: The granular material is fed into the heat treatment device, the combustion fan is turned on to increase the furnace temperature and oxygen content, and the reaction is promoted. The fly ash particles are continuously heat treated at 400-600℃ for 50-100 minutes. S003, Low-temperature catalytic degradation: The heat-treated fly ash and gas mixture is cooled to 200°C and transported to the catalytic reactor after passing through a cooling tower and gravity dust collector. Under the action of a catalyst, a catalytic degradation reaction is carried out. The core component of the catalytic reactor is the catalyst bed, which is composed of a regenerable honeycomb composite catalyst. The catalyst is a composite catalyst with active components loaded on nano-titanium dioxide as a support. The regenerable honeycomb composite catalyst is prepared by treating the composite catalyst with silane functional body and zirconium-based premix. S004, Exhaust Gas Treatment and Emission: Gravity dust collectors separate and collect fly ash. The flue gas after catalytic degradation enters the post-treatment system and is then cooled. If it meets environmental protection standards, it can be directly discharged into the atmosphere or sent to a subsequent system for further deep treatment.

2. The method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration according to claim 1, characterized in that, The retardant is urea phosphate, which is dissolved in deionized water to prepare a 5-10% urea phosphate solution; the mass ratio of retardant, bentonite and dry fly ash is 2-3:8-10:100; the catalytic temperature of the catalytic reactor is 280-310℃, and the catalytic time is 5-10 minutes.

3. The method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration according to claim 1, characterized in that, The preparation method of composite catalysts loaded with active components using nano-titanium dioxide as a support is as follows: S01, prepare a mixed solution of ammonium metavanadate and oxalic acid dihydrate in a molar ratio of 1:2, impregnate the nano-titanium dioxide carrier with ultrasound, remove moisture, dry, and calcine. S02, ammonium molybdate tetrahydrate was dissolved in deionized water to obtain an ammonium molybdate solution; the support obtained in S01 was impregnated with ultrasonication, then the water was removed, dried, and calcined to obtain a composite catalyst with nano-titanium dioxide as the support and loaded with active components. The ultrasonic power is 200-300W, the soaking time is 8-10 hours, and the drying time is 12 hours in an oven at 105℃; the calcination temperature is 400-500℃, and the calcination time is 3-5 hours; the liquid-solid ratio is 1.2-1.5:1, which just completely submerges the carrier.

4. The method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration according to claim 3, characterized in that, The preparation method of the nano-titanium dioxide carrier is as follows: Nano-TiO2 is dried in an oven at 105℃ for 30 minutes to remove moisture; nano-TiO2 powder, carboxymethyl cellulose, 1mm chopped glass fibers, and glycerol are sequentially added to a mixer and mixed evenly; during the mixing process, ammonia and lactic acid are added to control the pH value to 7.8–8.2, and deionized water is added to adjust the adhesion; after mixing, dispersed, soft, and resilient clay granules are obtained; the clay granules are placed in a clay kneading machine to obtain cylindrical clay lumps; sealed with plastic wrap and aged in a cool place for 24 hours; finally, placed in a honeycomb mold and extruded into the desired honeycomb shape using an extruder, dried at 80℃, then calcined at 120℃ for 1 hour, calcined at 300℃ for 1 hour, and held at 500℃ for 2 hours to obtain the nano-titanium dioxide carrier.

5. The method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration according to claim 4, characterized in that, The mass ratio of nano-TiO2 dry powder, carboxymethyl cellulose, 1mm short-cut glass fiber filaments and glycerol is 100:8~10:4~6:6~8.

6. The method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration according to claim 1, characterized in that, The composite catalyst is surface-treated to obtain a surface-treated, regenerable honeycomb composite catalyst, specifically as follows: S1, (N,N-dimethylaminopropyl)trimethoxysilane and 1,3-propanesulfonate lactone are dissolved in anhydrous acetone, protected by nitrogen, and stirred at 25-35°C for 7-9 hours to form a suspension containing a white solid precipitate. S2, the suspension is filtered to obtain a white solid, washed 2 to 3 times with anhydrous acetone, and then dried under vacuum at 50 to 60°C for 12 to 14 hours to obtain the final product, a white powder, which is the zwitterionic silane functional body. The zwitterionic silane functional body is then dissolved in anhydrous ethanol to obtain a zwitterionic silane functional body solution. S3 involves immersing a composite catalyst loaded with active components, using nano-titanium dioxide as a carrier, in a zwitterionic silane functional body solution and then ultrasonically treating it for 15–30 minutes. S4, zirconium n-propoxide and bis[ 3 - (triethoxysilane) [Propylamine] was added dropwise to glacial acetic acid and stirred at room temperature for 1-2 hours until a homogeneous zirconium-based premix was formed. The zirconium-based premix was then poured into a zirconium-based silane functionalized solution. The solution was then sonicated for 5-8 minutes to completely disperse the silane functionalized and zirconium-based premix. The solution was then shaken at room temperature for 2-3 hours. After the reaction was completed, the solution was washed 2-3 times with anhydrous ethanol to remove loosely bound particles on the surface of the support. Finally, the solution was dried in an oven at 100°C for 5-8 hours to obtain a surface-treated, regenerable honeycomb composite catalyst.

7. The method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration according to claim 6, characterized in that, The mass ratio of (N,N-dimethylaminopropyl)trimethoxysilane and 1,3-propanesulfonate lactone is 2-3:1-2; zirconium n-propoxide and bis[ 3 - (triethoxysilane) The mass ratio of propylamine is 1:0.8 to 1.2; the mass ratio of zirconium propoxide functionalized silane, zirconium propoxide and composite catalyst is 1.5 to 2.5:3 to 4:

100.

8. The method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration according to claim 1, characterized in that, The regenerable honeycomb composite catalyst exhibits high catalytic activity and high stability under medium and low temperature conditions, and can be recycled after cleaning.

9. The method for low-temperature catalytic degradation of dioxins in fly ash from municipal solid waste incineration as described in any one of claims 1 to 8, applied to the removal of dioxins from fly ash from municipal solid waste incineration.

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