Biochar catalyst modified with hydrotalcite-like derivative oxide, preparation method and application thereof in industrial flue gas deacidification

Abstract

The present invention provides a biochar catalyst modified with a hydrotalcite-like derivative oxide, a preparation method, and its application in industrial flue gas deacidification, and relates to the field of industrial flue gas. The preparation method of the catalyst comprises the following steps: agricultural biomass waste is subjected to oxygen-limited stepwise carbonization and KOH activation treatment to obtain a biochar precursor; then, layered double hydroxides are synthesized in situ on the surface of the biochar precursor through the high shear force field of a colloid mill reactor; finally, a biochar catalyst is obtained through gradient pyrolysis in a nitrogen-containing atmosphere and microwave plasma surface modification. The present invention solves the problems of uneven LDHs dispersion and poor water interference resistance in traditional biochar catalysts; in the deacidification of industrial flue gas, the removal efficiency of SO2 and HCl is ≥95%, the adsorption capacity of CO2 is ≥2.5mmol / g, and the removal efficiency of HF is ≥90%, and it is suitable for a variety of industrial flue gas treatment scenarios.

Description

Technical Field

[0001] The present invention relates to the field of industrial flue gas, and in particular to a biochar catalyst modified with a hydrotalcite-like derivative oxide, a preparation method thereof, and application thereof in deacidification of industrial flue gas. Background Art

[0002] The synergistic removal of acidic gases such as SO2, CO2, HCl, and HF from industrial flue gas is a major challenge in air pollution control. Traditional wet desulfurization and deacidification technologies (such as the limestone-gypsum method) suffer from drawbacks such as equipment corrosion and difficulty in wastewater treatment. Dry adsorption technologies (such as activated carbon and metal oxide adsorbents) generally face problems such as low adsorption capacity and poor resistance to water interference. These directly lead to unstable catalyst activity and effective service life, making it difficult to meet increasingly stringent environmental protection requirements. In recent years, catalysts for flue gas deacidification have been widely researched and applied. The development of highly efficient catalysts with strong water interference resistance has become the key to solving the problem of industrial flue gas deacidification.

[0003] Globally, a massive amount of agricultural biomass waste is generated annually. However, the current treatment method still relies primarily on extensive incineration, which not only emits pollutants such as PM2.5 but also leads to a significant waste of biomass resources. In recent years, the production of functional biochar (BC) from agricultural biomass waste through pyrolysis conversion technology has become a breakthrough in waste-to-pollution treatment. By precisely manipulating the surface chemical properties and pore structure of biochar, its technical and economic feasibility in the coordinated treatment of industrial flue gases can be significantly improved.

[0004] However, the preparation and application of existing functionalized biochar materials still face the following technical bottlenecks: Conventional biochar preparation often uses a one-step high-temperature carbonization process (>600°C). Although this process can form abundant pores, excessive carbonization destroys the biomass's natural oxygen-containing functional groups (such as phenolic hydroxyl groups and lactone groups), resulting in insufficient physical adsorption sites for acidic gases and an imbalance between the biochar's pores and surface functionality. Layered double hydroxides (LDHs) can be used to remove acidic gases due to their adjustable layer composition and abundant alkaline sites. However, LDHs / biochar composites synthesized by the traditional impregnation-precipitation method are prone to agglomeration due to the uneven charge distribution on the biochar surface, resulting in low active site exposure. Furthermore, the high humidity of industrial flue gas causes hydration and expansion of the LDH layers, which in turn entraps and inactivates the active sites, reducing the activity and stability of the catalyst.

[0005] To address the above issues, the present invention has developed a hydrotalcite-derived oxide-modified biochar catalyst with efficient deacidification and water interference resistance through the process innovation of "oxygen-limited carbonization-shear field synthesis-gradient pyrolysis". Its technical breakthroughs are as follows: ① The natural functional groups of biomass are retained through oxygen-limited step-by-step carbonization, combined with KOH directional activation to construct through-type hierarchical channels, and simultaneously optimize gas mass transfer and adsorption site density; ② The high shear force field of the colloid mill is used to promote the instantaneous nucleation and oriented growth of LDHs on the biochar surface, thereby obtaining a thin layer, highly dispersed LDH layer, overcoming the disadvantages of the traditional impregnation-precipitation method that easily leads to poor LDH dispersion and easy agglomeration; ③ Through nitrogen atmosphere gradient pyrolysis and microwave plasma modification, a ternary synergistic interface of "metal oxide nanoparticles-oxygen-containing functional groups-siloxane hydrophobic layer" is constructed on the biochar surface, achieving the unification of adsorption-catalytic synergistic removal of acidic gases and water interference resistance. Summary of the Invention

[0006] In order to solve the technical problems existing in the prior art, the present invention provides a biochar catalyst modified with a hydrotalcite-like derivative oxide, a preparation method and its application in industrial flue gas deacidification, so as to solve the problems existing in the prior art such as the imbalance between biochar pores and surface functions, the agglomeration of LDHs on the biochar surface, and the poor catalyst activity and stability caused by the poor water resistance of the catalyst.

[0007] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0008] A method for preparing a biochar catalyst modified with a hydrotalcite-like derivative oxide comprises the following steps: preparing a biochar precursor, preparing an LDHs / BC composite material, and preparing a catalyst;

[0009] The biochar precursor is prepared by subjecting agricultural biomass waste to oxygen-limited stepwise carbonization treatment under nitrogen protection to obtain primary biochar; the primary biochar is then placed in a KOH solution, heated and stirred at 60-90° C. under ultrasonic conditions, and then allowed to stand for aging to obtain a biochar precursor;

[0010] The LDHs / BC composite material is prepared by simultaneously adding a mixed metal salt solution containing divalent metal ions and trivalent metal ions, an alkali solution, and formamide to a colloid mill reactor loaded with a biochar precursor, and performing a shear reaction at a shear rate of 5000-15000 rpm to obtain a crude product; the crude product is centrifuged, washed, and dried to obtain the LDHs / BC composite material;

[0011] The catalyst is prepared by gradient pyrolysis of an LDHs / BC composite material in a nitrogen-containing mixed atmosphere to obtain an LDOs / BC intermediate; the LDOs / BC intermediate is then placed in a microwave plasma reactor, an Ar / O2 mixed gas is used as a working gas, and silane coupling agent vapor is continuously introduced through a carrier gas to perform microwave plasma treatment to obtain a biochar catalyst modified with a hydrotalcite-like oxide.

[0012] Furthermore, in the preparation of the biochar precursor, the agricultural biomass waste is at least one of the following: rice husks, straw, sawdust, Chinese medicine residue, and fruit shells; the particle size of the agricultural biomass waste is 0.15-0.85 mm; and the oxygen-limited stepwise carbonization is first carbonized at 300-400°C for 30-50 minutes, and then carbonized at 500-800°C for 1-3 hours.

[0013] Preferably, in the preparation of the biochar precursor, the concentration of the KOH solution is 0.5-3 mol / L;

[0014] The ultrasonic frequency is 40-80kHz, the stirring treatment time is 15-60min, and the static aging time is 12-24h;

[0015] The volume mass ratio of primary biochar to KOH solution is 5-10mL:1g.

[0016] Preferably, in the preparation of the LDHs / BC composite material, the divalent metal ion is at least one of the following: Ca 2+ Mg 2+ 、Ni 2+ 、Zn 2+ ; The trivalent metal ion is at least one of the following: Al 3+ 、Fe 3+ 、Co 3+ ;

[0017] The molar ratio of divalent metal ions to trivalent metal ions in the mixed metal salt solution is 2-4:1; and the total concentration of metal ions in the mixed metal salt solution is 0.5-2.5 mol / L.

[0018] Preferably, in the preparation of the LDHs / BC composite material, the alkali solution is NaOH solution or ammonia water, which is used to adjust the pH value of the material system to 9-11;

[0019] The amount of formamide added is 5-15% of the total mass of the metal salt in the mixed metal salt solution;

[0020] The mass volume ratio of biochar precursor to mixed metal salt solution is 1g:2-5mL;

[0021] The shearing reaction temperature is 25-60°C, and the shearing reaction time is 2-10 minutes.

[0022] Preferably, in the catalyst preparation, the nitrogen-containing mixed atmosphere consists of nitrogen and ammonia, and the volume ratio of nitrogen to ammonia is 3-5:1;

[0023] Gradient pyrolysis is first pyrolyzed at 300-400℃ for 0.5-1h, and then pyrolyzed at 600-800℃ for 2-4h.

[0024] Preferably, in the catalyst preparation, the volume percentage of O2 in the Ar / O2 mixed gas is 10-20%, and the remainder is argon; the flow rate of the Ar / O2 mixed gas is 20-50 mL / min;

[0025] The silane coupling agent is 3-aminopropyltriethoxysilane or hexamethyldisilazane; the carrier gas flow rate is 10-30 mL / min, and the volume concentration of the silane coupling agent vapor in the carrier gas is 5-20%.

[0026] Preferably, in the catalyst preparation, the power of the microwave plasma treatment is 300-800 W, the pressure of the microwave plasma treatment is 50-200 Pa, and the time of the microwave plasma treatment is 10-30 min.

[0027] The biochar catalyst modified with a hydrotalcite-like derived oxide is prepared by the aforementioned preparation method.

[0028] The application of the biochar catalyst modified with the hydrotalcite-like derivative oxide is to control the reaction pressure to be normal pressure-0.3 MPa, the reaction temperature to be 80-250° C., and the space velocity to be 300-5000 h -1 , using the biochar catalyst modified with the hydrotalcite-like oxide to remove acidic gases from flue gas with a moisture content of 5-15 vol%;

[0029] The acidic gases include SO2, CO2, HCl, and HF.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention's method for preparing a biochar catalyst modified with a hydrotalcite-like derivative oxide utilizes a process combining "oxygen-limited carbonization-shear field synthesis-gradient pyrolysis" and a synergistic strategy of multi-scale structural regulation and multifunctional interface integration to effectively overcome key technical bottlenecks in traditional biochar-based materials for acid gas removal, including imbalances in pore and surface functionality, poor dispersion of active sites, poor resistance to water interference, and poor catalytic activity and stability. These bottlenecks are specifically reflected in the following three aspects:

[0032] 1. Process improvements: a. Oxygen-limited step-wise carbonization combined with KOH chemical directional activation is used to construct a through-type microporous-mesoporous-macroporous hierarchical structure while retaining the natural oxygen-containing functional groups of the biomass. This resolves the contradiction between pore collapse and functional group destruction caused by traditional high-temperature carbonization, and simultaneously improves the specific surface area, gas mass transfer performance, and surface adsorption site density of the biochar; b. The high shear force field of the colloid mill reactor is used to simultaneously inject metal salt solution and alkaline solution. Through mechanical-chemical coupling, the LDHs are promoted to instantly nucleate and grow in an oriented manner on the biochar surface, forming a uniform nanosheet layer with a thickness of only 5-20nm. Compared with the traditional impregnation method, the dispersion uniformity of LDHs is improved and the interfacial bonding strength is enhanced, breaking through the disadvantages of the traditional impregnation-precipitation method that easily leads to poor dispersion and easy agglomeration of LDHs, and fundamentally avoiding the problem of active site agglomeration; c. Gradient pyrolysis is carried out in a nitrogen atmosphere to convert LDHs into highly dispersed metal oxide nanoparticles. At the same time, through microwave plasma modification, silane coupling agent vapor is synchronously introduced to construct a dense siloxane hydrophobic layer on the biochar surface, constructing a ternary synergistic interface of "metal oxide nanoparticles-oxygen-containing functional groups-siloxane hydrophobic layer", realizing the atomic-level interface fusion of the triple functions of "metal oxide catalytic activity-oxygen-containing functional group adsorption-hydrophobicity and moisture resistance", and thus realizing the unification of adsorption-catalytic synergistic removal of acidic gases in industrial flue gas and anti-water interference ability, further improving the catalytic activity and catalytic stability of the catalyst, and extending the effective service life of the catalyst.

[0033] 2. Performance improvement: The hierarchical pore structure forms a spatial coupling with the alkaline catalytic sites of highly dispersed metal oxide nanoparticles, significantly improving the removal efficiency of acidic gases such as SO2 and HCl compared to traditional biochar catalysts. The siloxane hydrophobic layer effectively blocks the competitive adsorption of water molecules in high-humidity flue gas. Compared with traditional biochar catalysts, the biochar catalyst of the present invention has significantly improved catalytic activity and stability for the removal of acidic gases in industrial flue gas at a humidity of 10-15 vol%, and has good resistance to water interference. The removal efficiency of SO2 and HCl in industrial flue gas is ≥95%, the adsorption capacity of CO2 is ≥2.5 mmol / g, and the removal efficiency of HF is ≥90%.

[0034] 3. In terms of green benefits: Using agricultural waste such as rice husks, straw, sawdust, and traditional Chinese medicine residues to replace commercial activated carbon reduces raw material costs and operating costs compared to traditional flue gas purification systems, further reducing the overall production costs of industries such as steel and waste incineration.

[0035] In summary, the preparation method of the biochar catalyst modified with hydrotalcite-like derivative oxides of the present invention effectively solves the long-standing pain point problem of efficiency, cost and water interference resistance in the field of industrial flue gas deacidification through the technical route of "waste resource utilization-precise regulation of interface functions-multi-mechanism synergistic deacidification". It has environmental benefits (reduction of acidic gas and solid waste emissions), economic benefits (low cost) and social benefits (agricultural waste management), and has broad industrialization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a process flow chart for preparing LDOs / BC catalyst according to an embodiment of the present invention.

[0037] Figure 2 This is a scanning electron microscope image of the LDOs / BC catalyst prepared in Example 2. DETAILED DESCRIPTION

[0038] In order to provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described. It should be noted that the following detailed description is illustrative and is intended to further illustrate the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0039] It should be noted that the terms used herein are intended only to describe specific embodiments and are not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," and the like are used to distinguish similar objects and are not used to describe a specific order or precedence. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0040] like Figure 1 As shown, an embodiment of the present invention provides a method for preparing a biochar catalyst modified with a hydrotalcite-like derivative oxide, comprising the following steps:

[0041] Step I. Preparation of biochar precursor

[0042] Agricultural biomass waste (such as rice husks, straw, sawdust, Chinese medicine residue, fruit shells, etc.) is crushed to 0.15-0.85mm and subjected to oxygen-limited step-by-step carbonization under nitrogen protection: first, the temperature is increased to 300-400℃ at 4-5℃ / min and kept warm for 30-50min, then the temperature is increased to 500-800℃ at 2-3℃ / min and kept warm for 1-3h to obtain primary biochar; then the primary biochar is immersed in 0.5-3mol / L KOH solution, treated for 15-60min under ultrasonic frequency of 40-80kHz, heating at 60-90℃ and stirring at 200-500rpm, and then aged for 12-24h to form a biochar precursor with a microporous-mesoporous-macroporous hierarchical structure.

[0043] The volume mass ratio of primary biochar to KOH solution is 5-10 mL:1 g.

[0044] Step II. Preparation of LDHs / BC composites

[0045] Containing divalent metal ions (Ca 2+ Mg 2+ 、Ni 2+ 、Zn 2+ etc.) and trivalent metal ions (Al 3+ 、Fe 3+ 、Co 3+ A mixed metal salt solution (metal molar ratio of 2:1-4:1, total concentration of 0.5-2.5 mol / L) containing 2,000 metals (such as 2,000 metals), alkali solution (0.05-0.5 mol / L NaOH solution or ammonia water), and formamide (5-15% of the total mass of the metal salts) were simultaneously added to a colloid mill reactor loaded with a biochar precursor. The reaction was carried out at a shear rate of 5000-15000 rpm, a temperature of 25-60°C, and a pH of 9.0-11.0 for 2-10 minutes to achieve in situ growth of layered double hydroxides (LDHs) on the biochar to obtain a crude product. The crude product was centrifuged, washed with ethanol / water, and vacuum dried to obtain an LDHs / BC composite material.

[0046] Among them, the alkali solution is used to adjust the pH value of the material system to be within the range of 9-11.

[0047] The mass-to-volume ratio of biochar precursor to mixed metal salt solution is 1 g: (2-5) mL.

[0048] Step III. Preparation of LDOs / BC catalyst

[0049] The LDHs / BC composite material was gradient pyrolyzed in a nitrogen mixed atmosphere (N2:NH3 volume ratio of 3-5:1): the temperature was increased to 300-400℃ at 2-5℃ / min and kept for 0.5-1h, and then the temperature was continued to be increased to 600-800℃ and kept for 2-4h to obtain an LDOs / BC intermediate; then it was placed in a microwave plasma reaction chamber, and an Ar / O2 mixed gas (flow rate 20-50mL / min) was used as the working gas, and microwave plasma treatment was carried out at a power of 300-800W for 10-30min; at the same time, during the microwave plasma treatment process, silane coupling agent (APTES or HMDS) vapor was continuously introduced through the carrier gas (the silane coupling agent vapor concentration in the carrier gas was 5-20vol%, and the carrier gas flow rate was 10-30mL / min), and the cavity pressure of the reaction chamber was controlled at 50-200Pa (i.e., microwave plasma treatment pressure) to form a hydrophobic siloxane layer on the surface, and finally the LDOs / BC catalyst was prepared.

[0050] Among them, in the Ar / O2 mixed gas, the volume percentage content of O2 is 10-20%, and the rest is argon.

[0051] The embodiments of the present invention also provide a biochar catalyst modified with a hydrotalcite-like derivative oxide prepared by the aforementioned method.

[0052] The embodiment of the present invention also provides the use of the biochar catalyst modified with the hydrotalcite-like oxide in the deacidification of industrial flue gas. The biochar catalyst modified with the hydrotalcite-like oxide is used to remove acidic gases in industrial flue gas; the acidic gases include: SO2, CO2, HCl, and HF.

[0053] Specifically, the reaction pressure is normal pressure-0.3Mpa, the reaction temperature is 80-250°C, and the space velocity is 300-5000h -1 In a flue gas environment with a moisture content of 5-15 vol%, the biochar catalyst modified with the hydrotalcite-like oxide is used to remove acidic gases from industrial flue gas, with a removal efficiency of ≥95% for SO2 and HCl in the industrial flue gas, an adsorption capacity of ≥2.5 mmol / g for CO2, and a removal efficiency of ≥90% for HF.

[0054] The initial volume concentrations of CO2, SO2, HCl and HF in the industrial flue gas are 10-25%, 12-700 ppm, 10-200 ppm and 5-120 ppm respectively.

[0055] The present invention will be further described below with reference to some specific embodiments.

[0056] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0057] The deacidification performance evaluation method of the biochar catalyst modified with the hydrotalcite-like derivative oxide is as follows: the deacidification performance of the material is tested using a fixed bed reactor, and the temperature of the reactor is precisely controlled by a vertical tube furnace; the volume concentrations of CO2, SO2, HCl, and HF in the simulated gas are 10-25%, 12-700 ppm, 10-200 ppm, and 5-120 ppm, respectively; the volume concentration of O2 in the simulated gas is 6-18%, the volume concentration of H2O is 5-15%, and N2 is the balance gas; the deacidification reaction temperature is 80-250°C, the reaction pressure is normal pressure-0.3 MPa, and the space velocity is 300-5000 h -1 The catalyst's CO2 adsorption capacity was tested using a thermogravimetric analyzer, and the SO2, HCI, and HF contents in the flue gas before and after the reaction were measured using a Fourier transform infrared gas analyzer. Changes in the material's deacidification efficiency over time were observed. Specific evaluation indicators: CO2 adsorption capacity Q (mmol / g) and deacidification efficiency R (%) were calculated using the following formula:

[0058]

[0059] Where: C in : inlet volume concentration of SO2, HCl and HF (ppm);

[0060] C out : outlet volume concentration of SO2, HCl and HF (ppm);

[0061] Δm: increase in catalyst mass during adsorption (g);

[0062] m0: initial mass of catalyst (g).

[0063] Example 1

[0064] This embodiment provides a method for preparing a biochar catalyst modified with a hydrotalcite-like derivative oxide. The LDOs / BC catalyst is prepared using rice husk as a raw material. The specific steps are as follows:

[0065] Step I. Preparation of biochar precursor

[0066] 1) Raw Material Processing: Rice husks were crushed to a particle size of 0.3-0.6 mm and placed in a tubular furnace for oxygen-limited stepwise carbonization under nitrogen protection. The specific heating procedure was as follows: first, the temperature was raised to 350°C at a rate of 5°C / min and held for 30 minutes; then, the temperature was further increased to 700°C at a rate of 3°C / min and held for 2 hours to produce primary biochar.

[0067] 2) KOH activation: The primary biochar was mixed with a 2 mol / L KOH solution at a liquid-to-solid ratio of 8:1 (mL / g). The mixture was placed in an ultrasonic reactor and mechanically stirred at 300 rpm for 40 min at an ultrasonic frequency of 60 kHz and a temperature of 80°C. The mixture was then aged for 18 h to obtain a biochar precursor.

[0068] Step II. Preparation of LDHs / BC composites

[0069] 1) Prepare mixed metal salt solution: weigh Mg(NO3)2•6H2O and Al(NO3)3•9H2O, according to Mg 2+ With Al 3+ A mixed metal salt solution with a total concentration of 1.2 mol / L was prepared with a molar ratio of 3:1, and formamide was added thereto as an auxiliary agent at 10% of the total mass of the metal salts.

[0070] 2) Colloid Mill Reaction: The biochar precursor was loaded into a colloid mill reactor. The mixed metal salt solution and a 0.3 mol / L NaOH solution (alkaline solution) were pumped into the colloid mill at a mass-to-volume ratio of 1 g biochar to 5 mL. The pH of the reaction system was controlled at 10.5. The reaction was carried out at a shear rate of 10,000 rpm and a temperature of 45°C for 6 min to allow layered double hydroxides (LDHs) to grow in situ on the biochar surface, yielding a crude product.

[0071] 3) Post-treatment: The crude product was centrifuged and washed three times with anhydrous ethanol and three times with deionized water, and then dried in a vacuum drying oven at 60°C for 12 h to obtain the LDHs / BC composite material.

[0072] Step III. Preparation of LDOs / BC catalyst

[0073] 1) Gradient pyrolysis: The LDHs / BC composite material was placed in a tube furnace and subjected to gradient pyrolysis in a mixed atmosphere of N2 and NH3 with a volume ratio of 4:1. The specific procedure of the gradient pyrolysis was as follows: heating to 350°C at a rate of 3°C / min and holding for 0.8 h; then heating to 750°C and holding for 3 h to obtain the LDOs / BC intermediate.

[0074] 2) Microwave plasma modification: The LDOs / BC intermediate was placed in a microwave plasma reaction chamber, and a mixed gas of Ar and O2 (flow rate 35 mL / min) was introduced, and microwave plasma treatment was performed at a power of 600 W for 20 min. At the same time, during the microwave plasma treatment process, 3-aminopropyltriethoxysilane (APTES) vapor (concentration 12 vol%) was continuously introduced into the reaction chamber through nitrogen carrier gas (flow rate 20 mL / min), and the cavity pressure of the reaction chamber was controlled at 120 Pa (i.e., microwave plasma treatment pressure) to obtain the LDOs / BC catalyst.

[0075] Among them, in the Ar / O2 mixed gas, the volume percentage content of O2 is 15%, and the rest is argon.

[0076] This embodiment also provides a biochar catalyst modified with a hydrotalcite-like derivative oxide prepared by the aforementioned method.

[0077] This embodiment also provides the use of the hydrotalcite-like oxide-modified biochar catalyst in the deacidification of industrial flue gas. The hydrotalcite-like oxide-modified biochar catalyst is used to remove acidic gases from industrial flue gas; the acidic gases are SO2, CO2, HCl, and HF. Specifically, under the reaction pressure of atmospheric pressure, the reaction temperature of 180°C, and the space velocity of 500h -1 In a flue gas environment with a moisture content of 10 vol%, the biochar catalyst modified with the hydrotalcite-like oxide is used to remove acidic gases from the flue gas.

[0078] Performance test: Set the volume concentration of SO2 in the simulated industrial flue gas to 100ppm, the volume concentration of CO2 to 15%, the volume concentration of HCl to 50ppm, the volume concentration of HF to 25ppm, the volume concentration of O2 to 16%, and the moisture content to 10%. -1 Under the conditions, the deacidification performance of the biochar catalyst of this embodiment was evaluated using a fixed bed reactor: the SO2 removal efficiency was 98.3%, the HCl removal efficiency was 96.7%, the CO2 adsorption capacity was 2.8 mmol / g, and the HF removal efficiency was 93.5%.

[0079] Example 2

[0080] This embodiment provides a method for preparing a biochar catalyst modified with a hydrotalcite-like derivative oxide. The LDOs / BC catalyst is prepared using sawdust as a raw material. The specific steps are as follows:

[0081] Step I. Preparation of biochar precursor

[0082] 1) Raw Material Processing: Sawdust was crushed to a particle size of 0.2-0.5 mm and placed in a tubular furnace for oxygen-limited stepwise carbonization under nitrogen protection. The specific heating procedure was as follows: first, the temperature was raised to 400°C at a rate of 5°C / min and held for 30 minutes; then, the temperature was further raised to 600°C at a rate of 3°C / min and held for 3 hours to produce primary biochar.

[0083] 2) KOH activation: The primary biochar was mixed with a 1.5 mol / L KOH solution at a liquid-to-solid ratio of 6:1 (mL / g). The mixture was placed in an ultrasonic reactor and mechanically stirred at 400 rpm for 30 min at an ultrasonic frequency of 50 kHz and a temperature of 70°C. The mixture was then aged for 24 h to obtain a biochar precursor.

[0084] Step II. Preparation of LDHs / BC composites

[0085] 1) Prepare mixed metal salt solution: weigh Ni(NO3)2•6H2O and Fe(NO3)3•9H2O, and 2+ with Fe 3+ A mixed metal salt solution with a total concentration of 1.8 mol / L was prepared in a molar ratio of 2:1, and formamide was added thereto as an auxiliary agent at 8% of the total mass of the metal salts.

[0086] 2) Colloid Mill Reaction: The biochar precursor was loaded into a colloid mill reactor. The mixed metal salt solution and a 0.3 mol / L NaOH solution (alkaline solution) were pumped into the colloid mill at a mass-to-volume ratio of 1 g biochar to 4 mL. The pH of the reaction system was controlled at 9.8. The reaction was carried out at a shear rate of 8000 rpm and a temperature of 50°C for 8 min to allow layered double hydroxides (LDHs) to grow in situ on the biochar surface, yielding a crude product.

[0087] 3) Post-treatment: The crude product was centrifuged and washed three times with anhydrous ethanol and three times with deionized water, and then dried in a vacuum drying oven at 60°C for 12 h to obtain the LDHs / BC composite material.

[0088] Step III. Preparation of LDOs / BC catalyst

[0089] 1) Gradient Pyrolysis: The LDHs / BC composite was placed in a tube furnace and subjected to gradient pyrolysis in a mixed atmosphere of N₂ and NH₃ (volume ratio: 5:1). The gradient pyrolysis procedure was as follows: heating to 350°C at a rate of 2°C / min, holding for 0.5 h, then continuing to 650°C and holding for 4 h to obtain the LDOs / BC intermediate.

[0090] 2) Microwave plasma modification: The LDOs / BC intermediate was placed in a microwave plasma reaction chamber, and a mixed gas of Ar and O2 (flow rate 35 mL / min) was introduced, and microwave plasma treatment was performed at a power of 450 W for 25 min. At the same time, hexamethyldisilazane (HMDS) vapor (concentration 15 vol%) was continuously introduced into the reaction chamber through nitrogen carrier gas (flow rate 20 mL / min), and the cavity pressure of the reaction chamber was controlled at 150 Pa (i.e., microwave plasma treatment pressure) to form a hydrophobic siloxane layer on the surface of the biochar to obtain the LDOs / BC catalyst.

[0091] Among them, in the Ar / O2 mixed gas, the volume percentage content of O2 is 15%, and the rest is argon.

[0092] This embodiment also provides a biochar catalyst modified with a hydrotalcite-like derivative oxide prepared by the aforementioned method, the scanning electron microscope image of which is shown in FIG. Figure 2 shown.

[0093] This embodiment also provides the application of the biochar catalyst modified with the hydrotalcite-like oxide in the deacidification of industrial flue gas. The biochar catalyst modified with the hydrotalcite-like oxide is used to remove acidic gases from industrial flue gas; the acidic gases are SO2, CO2, HCl, and HF. Specifically, the reaction pressure is atmospheric pressure, the reaction temperature is 200°C, and the space velocity is 1000h -1 In a flue gas environment with a moisture content of 12 vol%, the biochar catalyst modified with the hydrotalcite-like oxide is used to remove acidic gases from the flue gas.

[0094] Performance test: Set the volume concentration of SO2 in the simulated industrial flue gas to 200ppm, the volume concentration of CO2 to 20%, the volume concentration of HCl to 50ppm, the volume concentration of HF to 25ppm, the volume concentration of O2 to 16%, the moisture content to 12%, and the pressure to 0.1MPa, the temperature to 200℃, and the air velocity to 1000h -1 Under the above conditions, the performance of the biochar catalyst of this embodiment was evaluated using a fixed bed reactor: the SO2 removal efficiency was 95.6%, the HCl removal efficiency was 95.1%, the CO2 adsorption capacity was 2.6 mmol / g, and the HF removal efficiency was 91.3%.

[0095] Example 3

[0096] This embodiment provides a method for preparing a biochar catalyst modified with a hydrotalcite-like derivative oxide. The LDOs / BC catalyst is prepared using Chinese medicinal residue as a raw material. The specific steps are as follows:

[0097] Step I. Preparation of biochar precursor

[0098] 1) Raw Material Processing: Dried traditional Chinese medicine residue (including astragalus and licorice) was ground to a particle size of 0.4-0.7 mm and placed in a tube furnace for oxygen-limited stepwise carbonization under nitrogen protection. The specific heating program was as follows: first, the temperature was raised to 380°C at a rate of 5°C / min and held for 30 minutes; then, the temperature was further increased to 650°C at a rate of 3°C / min and held for 2.5 hours to produce primary biochar.

[0099] 2) KOH activation: The primary biochar was mixed with a 2.5 mol / L KOH solution at a liquid-to-solid ratio of 7:1 (mL / g). The mixture was placed in an ultrasonic reactor and mechanically stirred at 400 rpm for 50 min at an ultrasonic frequency of 70 kHz and a temperature of 75°C. The mixture was then aged for 20 h to obtain a biochar precursor.

[0100] Step II. Preparation of LDHs / BC composites

[0101] 1) Prepare mixed metal salt solution: weigh calcium chloride and aluminum chloride, according to Ca 2+ With Al 3+ A mixed metal salt solution with a total concentration of 1.5 mol / L was prepared at a molar ratio of 2.5:1, and formamide was added thereto as an auxiliary agent at a concentration of 12% of the total mass of the metal salts.

[0102] 2) Colloid Mill Reaction: The biochar precursor was loaded into a colloid mill reactor. The mixed metal salt solution and a 0.3 mol / L NaOH solution (alkaline solution) were simultaneously pumped into the biochar at a mass-to-volume ratio of 1 g:2 mL. The pH of the reaction system was controlled to 10.2. The reaction was carried out at a shear rate of 12,000 rpm and a temperature of 50°C for 5 min to allow layered double hydroxides (LDHs) to grow in situ on the biochar surface, obtaining a crude product.

[0103] 3) Post-treatment: The crude product was centrifuged and washed three times with anhydrous ethanol and three times with deionized water, and then dried in a vacuum drying oven at 60°C for 12 h to obtain the LDHs / BC composite material.

[0104] Step III. Preparation of LDOs / BC catalyst

[0105] 1) Gradient Pyrolysis: The LDHs / BC composite was placed in a tube furnace and subjected to gradient pyrolysis in a mixed atmosphere of N₂ and NH₃ (volume ratio) 5:1. The gradient pyrolysis procedure was as follows: heating to 380°C at a rate of 4°C / min, holding for 1 hour, then continuing to 700°C and holding for 3.5 hours to obtain the LDOs / BC intermediate.

[0106] 2) Microwave plasma modification: The LDOs / BC intermediate was placed in a microwave plasma reaction chamber, and a mixed gas of Ar and O2 (flow rate 35 mL / min) was introduced, and microwave plasma treatment was performed at a power of 700 W for 15 min. At the same time, during the microwave plasma treatment, hexamethyldisilazane (HMDS) vapor (concentration 18 vol%) was continuously introduced into the reaction chamber through argon carrier gas (flow rate 25 mL / min), and the cavity pressure of the reaction chamber was controlled to 150 Pa (i.e., microwave plasma treatment pressure). A hydrophobic siloxane layer was formed on the surface of the biochar to obtain the LDOs / BC catalyst.

[0107] Among them, in the Ar / O2 mixed gas, the volume percentage content of O2 is 15%, and the rest is argon.

[0108] This embodiment also provides a biochar catalyst modified with a hydrotalcite-like derivative oxide prepared by the aforementioned method.

[0109] This embodiment also provides the application of the biochar catalyst modified with the hydrotalcite-like oxide in the deacidification of industrial flue gas. The biochar catalyst modified with the hydrotalcite-like oxide is used to remove acidic gases from industrial flue gas; the acidic gases are SO2, CO2, HCl, and HF. Specifically, at a reaction pressure of 0.15 MPa, a reaction temperature of 200°C, and a space velocity of 3000 h -1 In a flue gas environment with a moisture content of 12 vol%, the biochar catalyst modified with the hydrotalcite-like oxide is used to remove acidic gases from the flue gas.

[0110] Performance test: Set the volume concentration of SO2 in the simulated industrial flue gas to 50ppm, the volume concentration of CO2 to 25%, the volume concentration of HCl to 50ppm, the volume concentration of HF to 50ppm, the volume concentration of O2 to 18%, the moisture content to 12%, at a pressure of 0.15MPa, a temperature of 200℃, and an air velocity of 3000h -1 Under the above conditions, the performance of the biochar catalyst of this embodiment was evaluated using a fixed bed reactor: the SO2 removal efficiency was 97.5%, the HCl removal efficiency was 97.1%, the CO2 adsorption capacity was 2.7 mmol / g, and the HF removal efficiency was 94.2%.

[0111] Comparative Example 1

[0112] Comparative Example 1 adopts the technical solution of Example 1, except that, in step II. Preparation of LDHs / BC composite material, the colloid mill reaction is omitted and modified to stir the biochar precursor and LDHs precursor solution (mixed metal salt solution, alkali solution, formamide) at 500 rpm for 1 h to obtain a crude product.

[0113] Under the same test conditions as in Example 1, the deacidification performance of the biochar catalyst of Comparative Example 1 was tested, and its SO2 removal efficiency was 82.4%, HCl removal efficiency was 68.3%, CO2 adsorption capacity was 1.2 mmol / g, and HF removal efficiency was 65.9%.

[0114] Comparative Example 2

[0115] Comparative Example 2 adopts the technical solution of Example 1, except that, in step III. preparing the LDOs / BC catalyst, the microwave plasma and silane coupling agent treatment are omitted, and the material after gradient pyrolysis is directly used as the biochar catalyst of Comparative Example 2.

[0116] Under the same test conditions as in Example 1, the deacidification performance of the biochar catalyst of Comparative Example 2 was tested, and its SO2 removal efficiency was 87.6%, HCl removal efficiency was 73.2%, CO2 adsorption capacity was 1.5 mmol / g, and HF removal efficiency was 70.1%.

[0117] Comparative Example 3

[0118] Comparative Example 3 adopts the technical solution of Example 3, except that, in step I. preparing the biochar precursor, the KOH activation treatment is omitted, and the primary biochar without KOH activation is directly used in the subsequent step II. preparing the LDHs / BC composite material.

[0119] Under the same test conditions as in Example 3, the deacidification performance of the biochar catalyst of Comparative Example 3 was tested, and its SO2 removal efficiency was 76.8%, HCl removal efficiency was 64.7%, CO2 adsorption capacity was 0.9 mmol / g, and HF removal efficiency was 61.8%.

[0120] A comprehensive comparison of Examples 1-3 with Comparative Examples 1-3 shows that:

[0121] 1) Process synergy of the preparation method of the present invention: the colloid mill process improves the HCl / HF removal efficiency by ≥25%, and plasma modification improves the HF stability in a humid environment by ≥20%;

[0122] 2) The technical indivisibility of the preparation method of the present invention: the absence of any key step (such as KOH activation and plasma modification) will lead to the simultaneous degradation of the biochar catalyst's performance in removing multiple components from flue gas.

[0123] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a biochar catalyst modified with a hydrotalcite-like derivative oxide for removing acidic gases from industrial flue gas, characterized in that: The following steps are involved: Preparation of biochar precursors, preparation of LDHs / BC composite materials, and preparation of catalysts; The biochar precursor is prepared by subjecting agricultural biomass waste to oxygen-limited stepwise carbonization treatment under nitrogen protection to obtain primary biochar; Then, the primary biochar is placed in a KOH solution, heated and stirred at 60-90°C under ultrasonic conditions, and then allowed to stand for aging to obtain a biochar precursor; The LDHs / BC composite material is prepared by simultaneously adding a mixed metal salt solution containing divalent metal ions and trivalent metal ions, an alkali solution, and formamide to a colloid mill reactor loaded with a biochar precursor, and performing a shear reaction at a shear rate of 5000-15000 rpm to obtain a crude product; the crude product is centrifuged, washed, and dried to obtain the LDHs / BC composite material; In the preparation of the catalyst, the LDHs / BC composite material is subjected to gradient pyrolysis in a nitrogen-containing mixed atmosphere to obtain an LDOs / BC intermediate; The LDOs / BC intermediate was then placed in a microwave plasma reactor, with Ar / O2 mixed gas as the working gas, and silane coupling agent vapor was continuously introduced through the carrier gas for microwave plasma treatment to obtain a hydrotalcite-derived oxide-modified biochar catalyst for removing acidic gases from industrial flue gas.

2. The method according to claim 1, characterized in that In the preparation of the biochar precursor, the agricultural biomass waste is at least one of the following: rice husks, straw, sawdust, traditional Chinese medicine residue, and fruit shells; the particle size of the agricultural biomass waste is 0.15-0.85 mm; and the oxygen-limited stepwise carbonization is first carbonized at 300-400° C. for 30-50 minutes and then carbonized at 500-800° C. for 1-3 hours.

3. The method according to claim 1, characterized in that In the preparation of the biochar precursor, the concentration of the KOH solution is 0.5-3 mol / L; The ultrasonic frequency is 40-80kHz, the stirring treatment time is 15-60min, and the static aging time is 12-24h; The volume mass ratio of primary biochar to KOH solution is 5-10mL:1g.

4. The method according to claim 1, wherein In the preparation of the LDHs / BC composite material, the divalent metal ion is at least one of the following: Ca 2+ Mg 2+ 、Ni 2+ 、Zn 2+ ; The trivalent metal ion is at least one of the following: Al 3+ 、Fe 3+ 、Co 3+ ; The molar ratio of divalent metal ions to trivalent metal ions in the mixed metal salt solution is 2-4:1; and the total concentration of metal ions in the mixed metal salt solution is 0.5-2.5 mol / L.

5. The method according to claim 1, wherein In the preparation of the LDHs / BC composite material, the alkali solution is NaOH solution or ammonia water, which is used to adjust the pH value of the material system to 9-11; The amount of formamide added is 5-15% of the total mass of the metal salt in the mixed metal salt solution; The mass volume ratio of biochar precursor to mixed metal salt solution is 1g:2-5mL; The shearing reaction temperature is 25-60°C, and the shearing reaction time is 2-10 minutes.

6. The method according to claim 1, characterized in that In the catalyst preparation, the nitrogen-containing mixed atmosphere is composed of nitrogen and ammonia, and the volume ratio of nitrogen to ammonia is 3-5:1; Gradient pyrolysis is first pyrolysis at 300-400℃ for 0.5-1h, and then pyrolysis at 600-800℃ for 2-4h.

7. The method according to claim 1, characterized in that In the catalyst preparation, the volume percentage of O2 in the Ar / O2 mixed gas is 10-20%, and the remainder is argon; the flow rate of the Ar / O2 mixed gas is 20-50 mL / min; The silane coupling agent is 3-aminopropyltriethoxysilane or hexamethyldisilazane; The carrier gas flow rate is 10-30 mL / min, and the volume concentration of the silane coupling agent vapor in the carrier gas is 5-20%.

8. The method according to claim 1, characterized in that In the catalyst preparation, the power of the microwave plasma treatment is 300-800W, the pressure of the microwave plasma treatment is 50-200Pa, and the time of the microwave plasma treatment is 10-30min.

9. A biochar catalyst modified with a hydrotalcite-like derivative oxide for removing acidic gases from industrial flue gas, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. The use of a biochar catalyst modified with a hydrotalcite-like derivative oxide for removing acidic gases from industrial flue gas according to claim 9, characterized in that: Control the reaction pressure to be normal pressure-0.3Mpa, the reaction temperature to be 80-250℃, and the space velocity to be 300-5000h -1 , using the biochar catalyst modified with the hydrotalcite-like oxide to remove acidic gases from flue gas with a moisture content of 5-15 vol%; The acidic gases include SO2, CO2, HCl, and HF.

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