Synergistic catalytic recovery method of CF4 and SO2

Abstract

The invention discloses a concerted catalysis recovery method of CF4 and SO2, and belongs to the technical field of waste gas treatment. The method comprises the following steps: preparing a Ga / theta-Al2O3 co-catalyst, firstly, carrying out aluminum isopropoxide hydrolysis, hydrothermal treatment and calcination to obtain theta-Al2O3 nanosheets, and then impregnating a Ga component and roasting to obtain the co-catalyst; the method comprises the following steps: mixing a gas containing CF4 and SO2 with a carrier gas, introducing the mixture into a fixed bed reactor filled with the co-catalyst, and introducing water vapor to carry out a synergistic catalytic reaction; after the tail gas is absorbed by alkali liquor, the pH is adjusted, a precipitator is added for precipitation, and BaSO4 and BaFCl are recovered. The acidity of the carrier is regulated and controlled through Ga, protons are induced to overflow, synergistic interaction of CF4 hydrolysis and SO2 oxidation is achieved, by-products are recycled, and the process is simple and efficient.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of industrial waste gas pollution control and resource utilization, and particularly relates to a method for synergistically catalytic recovery of CF4 and SO2. BACKGROUND

[0002] The electrolytic aluminum industry not only emits a large amount of CO2 in the production process, but also emits CF4 with extremely high greenhouse effect and SO2 with acidic corrosiveness. According to the production of 3850 million tons of electrolytic aluminum in China in 2021, about 2 kg of CF4 will be produced per ton of electrolytic aluminum, and at least 76,000 tons of CF4 will be emitted annually. The global warming potential of CF4 is about 7390 times that of CO2, and the natural decomposition time of CF4 in the atmosphere is as long as 5x10 4 The C-F bond energy in the CF4 molecule is high, and traditional pyrolysis methods require harsh conditions, while catalytic hydrolysis can decompose CF4 into CO2 and HF at a lower temperature, so it is considered an effective means to treat CF4. On the other hand, SO2 is an acidic gas produced in the electrolytic aluminum production process, which has serious harm to the environment, and usually needs to be treated by catalytic oxidation or absorption process.

[0003] The existing technology mainly focuses on the independent treatment of single pollutants, and corresponding treatment processes are developed for the removal of perfluorocarbons (such as CF4) or sulfur dioxide (SO2) in electrolytic aluminum flue gas. For example, Chinese invention patent CN114797449A reports a fixed-bed catalytic decomposition technology based on θ-Al2O3 nanosheet catalyst, which can realize efficient decomposition of CF4, and combines chemical precipitation method to recycle the by-product HF to generate cryolite (Na3AlF6) and calcium fluoride (CaF2). This method shows certain potential in CF4 degradation and fluorine resource recycling. However, this technology system only targets the treatment of fluorine-containing gas, and does not consider the complex working conditions of SO2 and CF4 coexisting in actual electrolytic aluminum flue gas, and lacks research and process integration of multi-pollutant synergistic conversion mechanism.

[0004] In actual industrial emissions, CF4 and SO2 often exist simultaneously in high-temperature flue gas systems. If a step-by-step treatment strategy is adopted, multiple independent treatment units need to be configured, resulting in a long process flow, increased equipment investment, significant exergy loss in heat transfer and utilization, low heat recovery efficiency, and high overall energy consumption. In addition, the operating conditions (such as temperature window, gas residence time, catalyst tolerance, etc.) between different purification units may not match, easily causing secondary pollution or catalyst deactivation. Therefore, the existing technology faces key bottlenecks such as poor synergy, low energy utilization rate, and high operating cost when dealing with complex mixed pollutants. It is urgent to develop an integrated catalytic treatment technology that can realize the simultaneous and efficient conversion of CF4 and SO2, with the characteristics of simultaneous removal of pollutants and gradient utilization of reaction heat, to improve the process economy and environmental sustainability, and meet the urgent needs of the electrolytic aluminum industry for green and low-carbon treatment technology. SUMMARY

[0005] The purpose of the embodiments of the present application is to provide a method for the synergistic catalytic recovery of CF4 and SO2 to solve the problems of long process flow, low energy utilization rate, high operating cost, and easy secondary pollution or catalyst deactivation in the existing step-by-step treatment process of CF4 and SO2.

[0006] To solve the above technical problems, the technical solution adopted by the present application is a method for the synergistic catalytic recovery of CF4 and SO2, comprising the following steps: S1, preparing a Ga / θ-Al2O3 co-catalyst; S2, mixing the CF4 and SO2-containing gas to be treated with a carrier gas and passing it into a fixed bed reactor packed with the Ga / θ-Al2O3 co-catalyst, while supplying water vapor into the fixed bed reactor through a water vapor generator, controlling the reaction conditions to carry out the synergistic catalytic reaction of CF4 hydrolysis and SO2 oxidation; S3, passing the tail gas produced by the synergistic catalytic reaction into a lye absorption bottle to absorb F - and SO4 2- in the tail gas, adjusting the pH value of the solution after absorption, adding a precipitating agent and controlling the temperature to carry out a precipitation reaction, centrifugally separating to obtain a precipitate product, and realizing the recovery of fluorine-containing and sulfur-containing by-products.

[0007] Further, S101, dissolving aluminum isopropoxide in isopropyl alcohol liquid to form a mixed liquid, adding deionized water to the mixed liquid for hydrolysis, transferring to a reaction kettle after stirring, and carrying out hydrothermal reaction, cooling, washing, centrifuging and drying treatment after the reaction is completed to obtain a white precursor powder; S102, placing the white precursor powder in a crucible, controlling the heating rate to carry out calcination, and obtaining a θ-Al2O3 nanosheet carrier; S103. Ga components are loaded onto the θ-Al2O3 nanosheet support by impregnation, followed by ultrasonic dispersion, drying and calcination to obtain the Ga / θ-Al2O3 cocatalyst.

[0008] Furthermore, in step S101, the ratio of aluminum isopropoxide to liquid isopropanol is 8~12g:100mL; the mass ratio of aluminum isopropoxide to deionized water is 10:8~12; the temperature of the hydrothermal reaction is 100℃~120℃, and the reaction time is 0.5~2h.

[0009] Furthermore, in step S102, the heating rate of calcination is 1~5℃ / min, the calcination temperature is 850℃~950℃, and the calcination time is 3~5h.

[0010] Furthermore, in step S103, the impregnation solution used to load the Ga component is a Ga(NO3)3 solution, wherein the molar fraction of Ga in the Ga(NO3)3 solution is 5% to 30%; the calcination temperature is 600℃ to 700℃, and the calcination time is 2 to 4 hours.

[0011] Furthermore, in step S2, the fixed-bed reactor is a corrosion-resistant quartz fixed-bed reactor with a height of 310 mm, an outer diameter of 20 mm, and an inner diameter of 17 mm; the loading amount of the Ga / θ-Al2O3 co-catalyst is 2.0 g.

[0012] Furthermore, in step S2, the concentration of CF4 in the gas to be treated is 500~3000ppm, and the concentration of SO2 is 500~20000ppm; the carrier gas is air, and the total gas flow rate after mixing the gas to be treated and the carrier gas is 30~40mL·min. -1 The corresponding mass hourly space velocity is 950~1050 mL·g -1 ·h -1 .

[0013] Furthermore, in step S2, the water vapor supply rate is 0.006~0.01 mL·min. -1 The temperature of the synergistic catalytic reaction is 450~600℃.

[0014] Furthermore, in step S2, an air supply system, a preheating zone, and a steam generator are sequentially installed upstream of the fixed-bed reactor. The preheating zone preheats the mixed gas to be treated and the carrier gas to 140~160℃. Downstream of the fixed-bed reactor, an absorption bottle, a drying tube, and a gas analyzer are sequentially connected.

[0015] Furthermore, in step S3, the alkaline solution is NaOH solution; the pH of the solution after absorption is adjusted to 5-7; the precipitant is BaCl2; the temperature of the precipitation reaction is 55-65℃; and the precipitation products are BaSO4 and BaFCl.

[0016] Compared with existing technologies, the beneficial effects of this invention include the following: Firstly, it achieves synergistic promotion to significantly improve conversion efficiency. The H protons generated during SO2 oxidation can escape and migrate through the Ga / θ-Al2O3 catalyst, thereby promoting the activation of CF bonds in CF4. At the same time, the hydroxyl groups generated by CF4 hydrolysis can accelerate the further oxidation of SO2, enabling the efficient and simultaneous removal of the two pollutants in the same device. Experiments have verified that under 550℃ conditions, the conversion rates of both CF4 and SO2 can stably reach over 95%, which is significantly better than the technical effect of treating them separately. Secondly, it has the outstanding advantages of low energy consumption and simple process. A single fixed-bed reactor can simultaneously treat the two pollutants, eliminating the need for traditional desulfurization and CF4 decomposition. The Ga / θ-Al2O3 catalyst prepared by hydrothermal and impregnation methods is not only inexpensive and has mild preparation conditions, but also has an excellent service life, capable of stable operation for more than 2500 hours. Compared with the existing θ-Al2O3 catalysts that require a reaction temperature of 750℃ and a stable operating time of 350 hours to treat CF4, this invention significantly reduces the reaction temperature and significantly extends the catalyst's service life, making it more suitable for continuous production. Thirdly, it can realize the resource utilization of by-products. By precisely controlling the pH value of the absorbent and adding specific precipitants, the fluorine-containing and sulfur-containing by-products generated by the reaction can be directionally converted into high-quality chemical raw materials such as BaSO4 and BaFCl, successfully achieving the organic unity of electrolytic aluminum flue gas pollution control and resource recycling. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a diagram showing the synergistic effect of the Ga / θ-Al2O3 catalyst of this invention on the decomposition of CF4 under different SO2 concentrations. Figure 2 This is a diagram showing the effect of the Ga / θ-Al2O3 catalyst of this invention on the synergistic treatment of CF4 decomposition under oxygen-free conditions; Figure 3This is a diagram showing the CF4 decomposition effect of the Ga / θ-Al2O3 catalyst of the present invention during long-term synergistic treatment of 2500ppmCF4 and 5000ppmSO2. Figure 4 This is a graph showing the SO2 conversion effect of the Ga / θ-Al2O3 catalyst of the present invention during long-term synergistic treatment of 2500ppmCF4 and 5000ppmSO2. Figure 5 These are the in-situ infrared spectra of the Ga / θ-Al2O3 catalyst of this invention under different pollutant reaction conditions; Figure 6 This describes the regeneration of active sites in the Ga / θ-Al2O3 catalyst of this invention under different pollutant reaction conditions; Figure 7 This invention relates to the resource recovery and absorption of SO4 in the absorbent liquid. 2- The obtained XRD pattern of BaSO4 and digital photographs of the samples; Figure 8 The F in the resource recovery and absorption liquid of this invention - The obtained XRD pattern of BaFCl and digital photographs of the sample. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This embodiment provides a synergistic catalytic recovery method for CF4 and SO2. Specifically, by controlling the composition design of the catalyst and optimizing the reaction process parameters, the reaction coupling between the hydrolysis and decomposition of carbon tetrafluoride (CF4) and the oxidation of sulfur dioxide (SO2) is promoted, achieving synergistic activation and efficient conversion of the two in the catalytic system. Based on this, the fluorine-containing (such as HF or fluorides) and sulfur-containing (such as SO3, H2SO4, or sulfates) products generated during the reaction are further targeted and recycled, thereby constructing an integrated catalytic purification technology that combines the synergistic removal of pollutants with the potential for regenerating valuable chemicals.

[0021] In some specific embodiments, the synergistic catalytic recovery method of CF4 and SO2 includes the following steps: S1. Preparation of a co-catalyst for CF4 and SO2; S101. Dissolve aluminum isopropoxide in liquid isopropanol and stir to form a transparent mixture; wherein the ratio of aluminum isopropoxide to liquid isopropanol is 8~12:100ml; add deionized water at a mass ratio of aluminum isopropoxide to deionized water of 10:8~12 to promote hydrolysis, stir and transfer to a reaction vessel lined with polytetrafluoroethylene, and perform hydrothermal reaction at 100℃–120℃ for 0.5–2h, cool, wash, centrifuge and dry to obtain a white precursor powder.

[0022] S102. The precursor is placed in a crucible, and the heating rate is controlled at 1–5 °C / min. It is then calcined at 850 °C–950 °C for 3–5 h to obtain θ-Al₂O₃ nanosheet support. Due to its high specific surface area and abundant Lewis acid sites, θ-Al₂O₃ nanosheets are beneficial for the high dispersion of active components and the adsorption and activation of reactant molecules, making them suitable for the catalytic hydrolysis of CF₄.

[0023] S103. Introducing metal additives using an impregnation method. S1031. θ-Al2O3 nanosheets were impregnated with a Ga(NO3)3 solution with a molar fraction of 5%–30%, ultrasonically dispersed, rotary dried, and then calcined at 600℃–700℃ for 2–4 h to obtain Ga / θ-Al2O3. The introduction of Ga can regulate the acidity of the support surface and induce a proton overflow effect, promoting the synergistic process of CF4 decomposition and SO2 oxidation.

[0024] In this embodiment, the amount of Ga ions is a key process parameter affecting proton overflow efficiency and catalytic performance. Specifically, if the amount of Ga ions is too high, it can easily lead to Ga ion aggregation and precipitation of the Ga2O3 phase, resulting in reduced dispersion of the Ga active component. This not only weakens the regulatory effect of Ga ions but also significantly inhibits proton overflow efficiency. If the amount of Ga ions is too low, its ability to regulate the active sites on the catalyst surface is insufficient, failing to fully activate the proton transport channels, making it difficult to achieve the optimal proton overflow efficiency.

[0025] In this embodiment, the amount of Ga ions is a key process parameter affecting proton overflow efficiency and catalytic performance. Specifically, if the amount of Ga ions is too high, it can easily lead to Ga ion aggregation and precipitation of the Ga2O3 phase, resulting in reduced dispersion of the Ga active component. This not only weakens the regulatory effect of Ga ions but also significantly inhibits proton overflow efficiency. If the amount of Ga ions is too low, its ability to regulate the active sites on the catalyst surface is insufficient, failing to fully activate the proton transport channels, making it difficult to achieve the optimal proton overflow efficiency.

[0026] S2, Preparation and mixing of reaction gases S201. A corrosion-resistant quartz fixed-bed reactor is used. The reactor height is 310 mm, the outer diameter is 20 mm, the inner diameter is 17 mm, and the loading is 2.0 g of Ga / θ-Al2O3 catalyst. A gas supply system, a preheating zone, and a water vapor generator are sequentially installed upstream of the reactor, while an absorption bottle, a drying tube, and a gas analyzer are sequentially connected downstream. In this embodiment, a preheating zone is set up to preheat the reaction gas to 140~160℃ to ensure that the reaction gas reaches the preset reaction temperature when entering the reaction vessel, thereby ensuring the efficiency and effect of the catalytic reaction. In this embodiment, water vapor contained in the reaction gas can easily damage the gas analyzer if it enters the gas analyzer. To avoid this risk, a drying tube is installed in the flow path of the reaction gas into the gas analyzer. The reaction gas is dried through the drying tube before being introduced into the gas analyzer.

[0027] S202. The pretreated electrolytic aluminum flue gas containing CF4 and SO2 is mixed with air in a certain proportion; under preferred conditions, the CF4 concentration is 500–3000 ppm, the SO2 concentration is 500–20000 ppm, and the total gas flow rate is 30–40 mL·min. -1 The corresponding mass hourly space velocity is approximately 1000 ± 50 mL·g. -1 ·h -1 In this embodiment, if the CF4 concentration is too high, the active sites on the catalyst surface will be over-occupied, resulting in a decrease in the effective treatment efficiency of the active sites per unit time, and thus significantly reducing the decomposition efficiency of CF4. If the SO2 concentration is too high, a large amount of sulfur and oxygen species will be deposited on the catalyst surface and accumulate. These species will block the active sites on the catalyst surface and inhibit the occurrence of the proton overflow effect, ultimately leading to a simultaneous decline in the decomposition of CF4 and the removal of SO2.

[0028] S203, through a water vapor generator at a rate of 0.006–0.01 mL / min -1 The reactor is supplied with steam at a certain influent rate, and the reactor temperature is controlled at 450–600℃. The reaction system is kept rich in oxygen (air is used as the carrier gas). The steam provides protons and hydroxyl groups for the hydrolysis of CF4, and the protons generated during the SO2 oxidation process can escape to assist in the activation of CF4, forming a synergistic effect.

[0029] In this embodiment, the steam rate is a key process parameter affecting the efficiency of CF4 and SO2 treatment: if the steam rate is too high, the excess steam will dilute the concentration of CF4 and SO2 in the reaction system, resulting in a decrease in the collision probability between the reactant gas molecules and the active sites on the catalyst surface per unit volume, thereby causing a simultaneous decrease in the efficiency of CF4 decomposition and SO2 removal; if the steam rate is too low, the supply of H2O as a proton source will be insufficient, which will directly inhibit the proton overflow efficiency, resulting in the catalyst active sites not being fully activated, and ultimately significantly inhibiting the CF4 decomposition and SO2 removal effects.

[0030] S204. Under the above conditions, a concerted reaction takes place. The levels of CF4, SO2, CO2, and SO42 before and after the reaction are monitored by gas chromatography and ion chromatography. 2- F - Calculate the pollutant conversion rate at equal concentrations. The CF4 conversion rate is:

[0031] SO2 conversion rate:

[0032] In this embodiment, the H protons generated during SO2 oxidation migrate out through the Ga / θ-Al2O3 catalyst, promoting the activation of C–F bonds in CF4. Simultaneously, the hydroxyl groups generated from CF4 hydrolysis accelerate further SO2 oxidation, enabling efficient removal of both pollutants in the same apparatus. Experiments show that in this embodiment, the conversion rates of both CF4 and SO2 can stably reach over 95% at 550℃, significantly higher than when treated separately.

[0033] S3, Recycling By-products The exhaust gas is passed through an absorption bottle into an alkaline absorption bottle (NaOH solution) to generate F. - and SO4 2- Adjust the pH of the solution to 5–7, add reagents such as BaCl2, stir, and precipitate BaSO4 and BaFCl at a constant temperature of 55–65℃. The precipitate obtained by centrifugation can be dried and used as an industrial raw material or medical contrast agent, realizing the resource utilization of sulfur- and fluorine-containing by-products.

[0034] Example 1 10.0 g of aluminum isopropoxide was added to 100 mL of isopropanol liquid and stirred at 500 rpm for 12 h. 10 mL of deionized water was added to the mixture, and stirring was continued for 10 min. The mixture was then transferred to a 150 mL polytetrafluoroethylene-lined reactor and reacted in an oven at 110 °C for 1 h. The resulting mixture was cooled, washed, centrifuged, and dried at 80 °C to obtain a white precursor powder. This precursor was heated to 600 °C at 5 °C / min, then to 900 °C at 1 °C / min and held for 4 h to obtain θ-Al₂O₃ nanosheets. Subsequently, 10 g of θ-Al₂O₃ nanosheets were dispersed in 400 mL of deionized water and sonicated for 30 min. Ga(NO₃)₃ with a molar ratio (Ga / Al) of 30% was added to the solution, and stirring was continued for 30 min. The solvent was removed by rotary evaporation, and the solution was calcined at 650 °C for 4 h to obtain the Ga / θ-Al₂O₃ catalyst.

[0035] Example 2 8.0 g of aluminum isopropoxide was added to 100 mL of isopropanol and stirred at 500 rpm for 12 h. 6.4 mL of deionized water (aluminum isopropoxide to deionized water mass ratio 10:8) was added to the mixture, and stirring was continued for 10 min. The mixture was then transferred to a 150 mL polytetrafluoroethylene-lined reactor and reacted in an oven at 100 °C for 0.5 h. The resulting mixture was cooled, washed, centrifuged, and dried at 80 °C to obtain a white precursor powder. This precursor was heated to 900 °C at a rate of 1 °C / min and held for 3 h to obtain θ-Al₂O₃ nanosheets. Subsequently, 10 g of θ-Al₂O₃ nanosheets were dispersed in 400 mL of deionized water and sonicated for 30 min. Ga(NO₃)₃ with a molar ratio (Ga / Al) of 5% was added to the solution, and stirring was continued for 30 min. The solvent was removed by rotary evaporation, and the solution was calcined at 600 °C for 2 h to obtain the Ga / θ-Al₂O₃ catalyst.

[0036] Example 3 12.0 g of aluminum isopropoxide was added to 100 mL of isopropanol liquid and stirred at 500 rpm for 12 h. 14.4 mL of deionized water (aluminum isopropoxide to deionized water mass ratio 10:12) was added to the mixture, and stirring was continued for 10 min. The mixture was then transferred to a 150 mL polytetrafluoroethylene-lined reactor and reacted in an oven at 120 °C for 2 h. The resulting mixture was cooled, washed, centrifuged, and dried at 80 °C to obtain a white precursor powder. This precursor was heated to 950 °C at 5 °C / min and held for 5 h to obtain θ-Al₂O₃ nanosheets. Subsequently, 10 g of θ-Al₂O₃ nanosheets were dispersed in 400 mL of deionized water and sonicated for 30 min. Ga(NO₃)₃ with a molar ratio (Ga / Al) of 15% was added to the above solution, and stirring was continued for 30 min. The solvent was removed by rotary evaporation, and the solution was calcined at 700 °C for 3 h to obtain the Ga / θ-Al₂O₃ catalyst.

[0037] Example 4 9.0 g of aluminum isopropoxide was added to 100 mL of isopropanol and stirred at 500 rpm for 12 h. 8.1 mL of deionized water (aluminum isopropoxide to deionized water mass ratio 10:9) was added to the mixture, and stirring was continued for 10 min. The mixture was then transferred to a 150 mL polytetrafluoroethylene-lined reactor and reacted in an oven at 105 °C for 1.25 h. The resulting mixture was cooled, washed, centrifuged, and dried at 80 °C to obtain a white precursor powder. This precursor was heated to 880 °C at a rate of 3 °C / min and held for 3.5 h to obtain θ-Al₂O₃ nanosheets. Subsequently, 10 g of θ-θ-Al₂O₃ nanosheets were dispersed in 400 mL of deionized water and sonicated for 30 min. Ga(NO₃)₃ with a molar ratio (Ga / Al) of 20% was added to the solution, and stirring was continued for 30 min. The solvent was removed by rotary evaporation, and the solution was calcined at 650 °C for 3 h to obtain the Ga / θ-Al₂O₃ catalyst.

[0038] Comparative Example 1 (Aluminum isopropoxide dosage exceeded the range) 13.0 g of aluminum isopropoxide was added to 100 mL of isopropanol liquid and stirred at 500 rpm for 12 h. 10 mL of deionized water was added to the mixture, and stirring was continued for 10 min. The mixture was then transferred to a 150 mL polytetrafluoroethylene-lined reactor and reacted in an oven at 110 °C for 1 h. The resulting mixture was cooled, washed, centrifuged, and dried at 80 °C to obtain a white precursor powder. This precursor was heated to 600 °C at 5 °C / min, then to 900 °C at 1 °C / min and held for 4 h to obtain θ-Al₂O₃ nanosheets. Subsequently, 10 g of θ-Al₂O₃ nanosheets were dispersed in 400 mL of deionized water and sonicated for 30 min. Ga(NO₃)₃ with a molar ratio (Ga / Al) of 30% was added to the solution, and stirring was continued for 30 min. The solvent was removed by rotary evaporation, and the solution was calcined at 650 °C for 4 h to obtain the Ga / θ-Al₂O₃ catalyst. Due to the excessive use of aluminum isopropoxide, the synthesized θ-Al2O3 nanosheets had uneven geometry and larger size, resulting in uneven Ga doping distribution on the prepared Ga / θ-Al2O3 catalyst.

[0039] Comparative Example 2 (Hydrothermal reaction temperature out of range) 10.0 g of aluminum isopropoxide was added to 100 mL of isopropanol liquid and stirred at 500 rpm for 12 h. 10 mL of deionized water was added to the mixture, and stirring was continued for 10 min. The mixture was then transferred to a 150 mL polytetrafluoroethylene-lined reactor and reacted at 125 °C for 1 h. The resulting mixture was cooled, washed, centrifuged, and dried at 80 °C to obtain a white precursor powder. This precursor was heated to 600 °C at 5 °C / min, then to 900 °C at 1 °C / min and held for 4 h to obtain θ-Al₂O₃ nanosheets. Subsequently, 10 g of θ-Al₂O₃ nanosheets were dispersed in 400 mL of deionized water and sonicated for 30 min. Ga(NO₃)₃ with a molar ratio (Ga / Al) of 30% was added to the solution, and stirring was continued for 30 min. The solvent was removed by rotary evaporation, and the solution was calcined at 650 °C for 4 h to obtain the Ga / θ-Al₂O₃ catalyst. Because the hydrothermal reaction temperature was outside the range, the θ-Al2O3 nanosheets underwent excessive nucleation, resulting in the formation of a large number of irregular θ-Al2O3 bulks, which led to the failure to prepare the Ga / θ-Al2O3 catalyst.

[0040] Comparative Example 3 (calcination temperature out of range) 10.0 g of aluminum isopropoxide was added to 100 mL of isopropanol liquid and stirred at 500 rpm for 12 h. 10 mL of deionized water was added to the mixture, and stirring was continued for 10 min. The mixture was then transferred to a 150 mL polytetrafluoroethylene-lined reactor and reacted in an oven at 110 °C for 1 h. The resulting mixture was cooled, washed, centrifuged, and dried at 80 °C to obtain a white precursor powder. This precursor was heated to 600 °C at 5 °C / min, then to 960 °C at 1 °C / min and held for 4 h to obtain θ-Al₂O₃ nanosheets. Subsequently, 10 g of θ-Al₂O₃ nanosheets were dispersed in 400 mL of deionized water and sonicated for 30 min. Ga(NO₃)₃ with a molar ratio (Ga / Al) of 30% was added to the solution, and stirring was continued for 30 min. The solvent was removed by rotary evaporation, and the solution was calcined at 650 °C for 4 h to obtain the Ga / θ-Al₂O₃ catalyst. Due to the calcination temperature being outside the range, inert α-Al2O3 appeared in the synthesized θ-Al2O3 nanosheets, resulting in an impure phase in the prepared Ga / θ-Al2O3 catalyst.

[0041] Comparative Example 4 (Ga(NO3)3 molar ratio out of range) 10.0 g of aluminum isopropoxide was added to 100 mL of isopropanol liquid and stirred at 500 rpm for 12 h. 10 mL of deionized water was added to the mixture, and stirring was continued for 10 min. The mixture was then transferred to a 150 mL polytetrafluoroethylene-lined reactor and reacted in an oven at 110 °C for 1 h. The resulting mixture was cooled, washed, centrifuged, and dried at 80 °C to obtain a white precursor powder. This precursor was heated to 600 °C at 5 °C / min, then to 900 °C at 1 °C / min and held for 4 h to obtain θ-Al₂O₃ nanosheets. Subsequently, 10 g of θ-Al₂O₃ nanosheets were dispersed in 400 mL of deionized water and sonicated for 30 min. Ga(NO₃)₃ with a molar ratio (Ga / Al) of 32% was added to the solution, and stirring was continued for 30 min. The solvent was removed by rotary evaporation, and the solution was calcined at 650 °C for 4 h to obtain the Ga / θ-Al₂O₃ catalyst. Because the molar ratio of Ga(NO3)3 was out of range, the amount of Ga modification was too large and could not be uniformly doped into the θ-Al2O3 nanosheets, resulting in the precipitation of Ga2O3 nanoparticles, which led to the failure to prepare the Ga / θ-Al2O3 catalyst.

[0042] Comparative Example 5 (roasting temperature out of range) 10.0 g of aluminum isopropoxide was added to 100 mL of isopropanol and stirred at 500 rpm for 12 h. 10 mL of deionized water was added to the mixture, and stirring was continued for 10 min. The mixture was then transferred to a 150 mL polytetrafluoroethylene-lined reactor and reacted at 110 °C for 1 h. The resulting mixture was cooled, washed, centrifuged, and dried at 80 °C to obtain a white precursor powder. This precursor was heated to 600 °C at 5 °C / min, then to 900 °C at 1 °C / min and held for 4 h to obtain θ-Al₂O₃ nanosheets. Subsequently, 10 g of θ-Al₂O₃ nanosheets were dispersed in 400 mL of deionized water and sonicated for 30 min. Ga(NO₃)₃ with a molar ratio (Ga / Al) of 30% was added to the solution, and stirring was continued for 30 min. The solvent was removed by rotary evaporation, and the solution was calcined at 710 °C for 4 h to obtain the Ga / θ-Al₂O₃ catalyst. The calcination temperature was outside the specified range, resulting in a smaller specific surface area and insufficient exposed active sites in the prepared Ga / θ-Al2O3 catalyst, leading to poor catalytic performance.

[0043] Example 5 Two g of the Ga / θ-Al₂O₃ catalyst prepared in Example 1 was packed into a quartz tube in a fixed-bed reactor. Simulated aluminum electrolysis flue gas (2500 ppm CF₄, 0-20000 ppm SO₂, the remainder being air) was introduced at a rate of 33.3 mL / min. -1 The flow rate is introduced into the reactor, and simultaneously passed through a steam generator at a rate of 0.008 mL / min. -1Water vapor was introduced at a controlled rate to maintain the reaction temperature at 550℃. The reaction tail gas was analyzed by gas chromatography. Figure 1 It can be seen that when CF4 is hydrolyzed by catalysis alone, the decomposition rate of CF4 is about 60%; when different concentrations of SO2 gas are introduced for synergistic treatment, the decomposition rate of CF4 is significantly increased to over 90%, and when the SO2 concentration is 5000 ppm, the decomposition rate of CF4 reaches 99%.

[0044] Example 6 Two g of the Ga / θ-Al₂O₃ catalyst prepared in Example 1 was packed into a quartz tube in a fixed-bed reactor. Simulated aluminum electrolysis flue gas (2500 ppm CF₄, 5000 ppm SO₂, the remainder being air or Ar) was introduced at a rate of 33.3 mL / min. -1 The flow rate is introduced into the reactor, and simultaneously passed through a steam generator at a rate of 0.008 mL / min. -1 Water vapor was introduced at a controlled rate to maintain the reaction temperature at 550℃. The reaction tail gas was analyzed by gas chromatography. Figure 2 It can be seen that when CF4 is hydrolyzed by catalysis alone, the decomposition rate of CF4 is about 60%; when the SO2 concentration is 5000ppm, the decomposition rate of CF4 reaches 99%; when the remainder is Ar gas, that is, no oxygen is present in the reaction process, the introduction of SO2 gas cannot promote the decomposition of CF4.

[0045] Example 7 Two g of the Ga / θ-Al₂O₃ catalyst prepared in Example 1 was packed into a quartz tube in a fixed-bed reactor. Simulated aluminum electrolysis flue gas (2500 ppm CF₄, 5000 ppm SO₂, the remainder being air) was introduced at a rate of 33.3 mL / min. -1 The flow rate is introduced into the reactor, and simultaneously passed through a steam generator at a rate of 0.008 mL / min. -1 Water vapor was introduced at a controlled rate to maintain the reaction temperature at 550℃. The reaction tail gas was analyzed by gas chromatography. Figure 3 and Figure 4 As can be seen, the decomposition or conversion rates of CF4 and SO2 reached approximately 99% and 98%, respectively, and there was no significant inactivation after continuous operation for more than 2,500 hours.

[0046] Example 8 50 mg of the Ga / θ-Al2O3 catalyst prepared in Example 1 was packed into an in-situ infrared thermocatalytic cell, and the catalyst was subjected to an in-situ in-situ infrared thermocatalytic reaction at 33.3 mL / min under the condition of air as a protective gas. -1 Pretreatment was performed at 550℃ for 60 min under controlled flow conditions. After acquiring background spectra using an infrared spectroscopy instrument, 2500 ppm CF4 gas was introduced, and signal changes on the catalyst surface were monitored. Figure 5 It can be seen that it is between 2600-3500cm -1 Within a range, only at 3400cm-1 A relatively weak H proton signal was observed at the location.

[0047] Example 9 50 mg of the Ga / θ-Al2O3 catalyst prepared in Example 1 was packed into an in-situ infrared thermocatalytic cell, and the catalyst was subjected to an in-situ in-situ infrared thermocatalytic reaction at 33.3 mL / min under the condition of air as a protective gas. -1 Pretreatment was performed at 550℃ for 60 min under controlled flow conditions. After acquiring background spectra using an infrared spectroscopy instrument, 5000 ppm SO2 gas was introduced, and signal changes on the catalyst surface were monitored. Figure 5 It can be seen that it is between 2600-3500cm -1 Within the range, only 3200-3500cm -1 A relatively weak H proton signal was observed within the range.

[0048] Example 10 50 mg of the Ga / θ-Al2O3 catalyst prepared in Example 1 was packed into an in-situ infrared thermocatalytic cell, and the catalyst was subjected to an in-situ in-situ infrared thermocatalytic reaction at 33.3 mL / min under the condition of air as a protective gas. -1 Pretreatment was performed at 550℃ for 60 min under controlled flow conditions. After acquiring background spectra using an infrared spectroscopy instrument, 2500 ppm CF4 + 5000 ppm SO2 gas was introduced, and signal changes on the catalyst surface were monitored. Figure 5 It can be seen that it is between 2600-3500cm -1 Within the range of 2700-3500cm -1 The observation of a very strong H proton signal within the range indicates that there is a significantly enhanced H proton supply during the CF4 and SO2 co-processing process, which is the reason for the significant increase in decomposition and conversion rates during the co-processing process.

[0049] Example 11 50 mg of the Ga / θ-Al2O3 catalyst prepared in Example 1 was packed into an in-situ infrared thermocatalytic cell, and the catalyst was subjected to an in-situ in-situ infrared thermocatalytic reaction at 33.3 mL / min under the condition of air as a protective gas. -1 Pretreatment was performed at 550℃ for 60 min under controlled flow conditions. After acquiring background spectra using an infrared spectroscopy instrument, 2500 ppm CF4 + 5000 ppm SO2 gas was first introduced, followed by water vapor, and the regeneration of active sites on the catalyst surface was monitored. Figure 6 As can be seen, when CF4 and SO2 are treated synergistically, the regeneration rate of active sites on the catalyst can reach 100%, which proves the super stability of the catalyst when CF4 and SO2 are treated synergistically.

[0050] Example 12 50 mg of the Ga / θ-Al2O3 catalyst prepared in Example 1 was packed into an in-situ infrared thermocatalytic cell, and the catalyst was subjected to an in-situ in-situ infrared thermocatalytic reaction at 33.3 mL / min under the condition of air as a protective gas. -1 Pretreatment was performed at 550℃ for 60 min under controlled flow conditions. After acquiring background spectra using an infrared spectroscopy instrument, 2500 ppm CF4 gas was first introduced, followed by water vapor, to monitor the regeneration of active sites on the catalyst surface. Figure 6 As can be seen, when treated with CF4 alone, the regeneration rate of active sites on the catalyst only reaches 49%.

[0051] Example 13 The exhaust gas generated in Example 4 was passed into 500 mL of alkaline absorbent solution (10 g / L NaOH) for absorption. The resulting absorbent solution was analyzed by ion chromatography, and the F content in the solution was... - Content is 25g / L -1 SO4 2- Content is 10gL -1 First, dilute hydrochloric acid was added to the solution to control the pH to the range of 5-7. Then, BaCl2 (stoichiometric ratio 1:1) was added, and the mixture was stirred continuously for 30 minutes. After centrifugation, a white precipitate (BaSO4) was obtained. The remaining solution was heated to 60°C in a water bath, and excess BaCl2 was added. The subsequent white precipitate was BaFCl. The white crystals were identified by XRD as pure phase BaSO4 and BaFCl (e.g., BaFCl). Figure 7 and Figure 8 (As shown), it can be used as an industrial raw material or a medical contrast agent.

[0052] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for the synergistic catalytic recovery of CF4 and SO2, characterized in that, Includes the following steps: S1. Preparation of Ga / θ-Al2O3 cocatalyst; S2. The gas to be treated containing CF4 and SO2 is mixed with the carrier gas and then introduced into a fixed-bed reactor filled with the Ga / θ-Al2O3 cocatalyst. At the same time, water vapor is supplied to the fixed-bed reactor through a water vapor generator to control the reaction conditions for the synergistic catalytic reaction of CF4 hydrolysis and SO2 oxidation. S3. Pass the tail gas generated by the synergistic catalytic reaction into an alkaline absorption bottle to absorb the F in the tail gas. - and SO4 2- The pH of the solution after absorption is adjusted, a precipitant is added and the temperature is controlled to carry out the precipitation reaction. The precipitate is obtained by centrifugation, thus realizing the recovery of fluorine- and sulfur-containing byproducts.

2. The method for synergistic catalytic recovery of CF4 and SO2 according to claim 1, characterized in that, S101. Dissolve aluminum isopropoxide in liquid isopropanol and stir to form a mixture. Add deionized water to the mixture for hydrolysis. After stirring, transfer the mixture to a reaction vessel for hydrothermal reaction. After the reaction is completed, cool, wash, centrifuge and dry to obtain white precursor powder. S102. Place the white precursor powder in a crucible and calcine it by controlling the heating rate to obtain θ-Al2O3 nanosheet carrier. S103. Ga components are loaded onto the θ-Al2O3 nanosheet support by impregnation, followed by ultrasonic dispersion, drying and calcination to obtain the Ga / θ-Al2O3 cocatalyst.

3. The method for synergistic catalytic recovery of CF4 and SO2 according to claim 2, characterized in that, In step S101, the ratio of aluminum isopropoxide to liquid isopropanol is 8~12g:100mL; the mass ratio of aluminum isopropoxide to deionized water is 10:8~12; the temperature of the hydrothermal reaction is 100℃~120℃, and the reaction time is 0.5~2h.

4. The method for synergistic catalytic recovery of CF4 and SO2 according to claim 2, characterized in that, In step S102, the heating rate of calcination is 1~5℃ / min, the calcination temperature is 850℃~950℃, and the calcination time is 3~5h.

5. The method for synergistic catalytic recovery of CF4 and SO2 according to claim 2, characterized in that, In step S103, the impregnation solution used to load the Ga component is a Ga(NO3)3 solution, wherein the molar fraction of Ga in the Ga(NO3)3 solution is 5% to 30%; the calcination temperature is 600℃ to 700℃, and the calcination time is 2 to 4 hours.

6. The method for synergistic catalytic recovery of CF4 and SO2 according to claim 1, characterized in that, In step S2, the fixed-bed reactor is a corrosion-resistant quartz fixed-bed reactor with a height of 310 mm, an outer diameter of 20 mm, and an inner diameter of 17 mm; the loading amount of the Ga / θ-Al2O3 co-catalyst is 2.0 g.

7. The method for synergistic catalytic recovery of CF4 and SO2 according to claim 1, characterized in that, In step S2, the concentration of CF4 in the gas to be treated is 500~3000ppm, and the concentration of SO2 is 500~20000ppm; the carrier gas is air, and the total gas flow rate after mixing the gas to be treated and the carrier gas is 30~40mL·min. -1 The corresponding mass hourly space velocity is 950~1050 mL·g -1 ·h -1 .

8. The method for synergistic catalytic recovery of CF4 and SO2 according to claim 1, characterized in that, In step S2, the water vapor supply rate is 0.006~0.01 mL·min. -1 The temperature of the synergistic catalytic reaction is 450~600℃.

9. The method for synergistic catalytic recovery of CF4 and SO2 according to claim 1, characterized in that, In step S2, an air supply system, a preheating zone, and a water vapor generator are sequentially installed upstream of the fixed bed reactor. The preheating zone preheats the mixed gas to be treated and the carrier gas to 140~160℃. An absorption bottle, a drying tube, and a gas analyzer are sequentially connected downstream of the fixed bed reactor.

10. The method for synergistic catalytic recovery of CF4 and SO2 according to claim 1, characterized in that, In step S3, the alkaline solution is NaOH solution; the pH of the solution after absorption is adjusted to 5-7; the precipitant is BaCl2; the precipitation reaction temperature is 55-65℃; and the precipitation products are BaSO4 and BaFCl.

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