Hydrotalcite-like derived oxide modified charcoal catalyst, preparation method and application thereof in deacidification of industrial flue gas

Abstract

The invention provides a hydrotalcite-like derived oxide modified charcoal catalyst, a preparation method and application of the hydrotalcite-like derived oxide modified charcoal catalyst in deacidification of industrial flue gas, and relates to the field of industrial flue gas. The preparation method of the catalyst comprises the following steps: performing oxygen-limited stepped carbonization and KOH activation treatment on agricultural biomass wastes to obtain a biochar precursor; then in-situ synthesizing layered double hydroxides on the surface of the biochar precursor through a high shear force field of a colloid mill reactor; and finally, carrying out nitrogen-containing atmosphere gradient pyrolysis and microwave plasma surface modification to prepare the biochar catalyst. According to the invention, the problems of uneven dispersion of LDHs and poor water interference resistance of a traditional biochar catalyst are solved; the removal efficiency of SO2 and HCl in industrial flue gas deacidification is greater than or equal to 95%, the adsorption capacity of CO2 is greater than or equal to 2.5 mmol / g, the removal efficiency of HF is greater than or equal to 90%, and the adsorbent is suitable for various industrial flue gas treatment scenes.

Description

Technical Field

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

[0002] The synergistic removal of acidic gases such as SO2, CO2, HCl, and HF in industrial flue gas is an important challenge in the field of air pollution control. Traditional wet desulfurization and deacidification technologies (such as the limestone-gypsum method) have disadvantages such as equipment corrosion and difficult wastewater treatment, while dry adsorption technologies (such as activated carbon and metal oxide adsorbents) generally face problems such as low adsorption capacity and poor water resistance, directly resulting in unstable activity and effective service life of the catalyst, and it is difficult to meet the increasingly strict environmental protection requirements. In recent years, catalysts in the field of flue gas deacidification have been widely studied and applied, and the development of highly efficient catalysts with strong water resistance has become the key to solving the problem of industrial flue gas deacidification.

[0003] Currently, globally, the quantity of agricultural biomass waste generated annually is huge. However, the existing treatment methods still mainly rely on extensive incineration, which not only emits pollutants such as PM2.5, but also causes serious waste of biomass resources. In recent years, preparing functional biochar (BC) from agricultural biomass waste based on pyrolysis conversion technology has become a breakthrough point for treating pollution with waste. By precisely regulating the surface chemical properties and pore structure of biochar, its technical economy in the collaborative treatment of industrial flue gas can be significantly improved.

[0004] However, there are still the following technical bottlenecks in the preparation and application fields of existing functional biochar materials: Conventional biochar preparation mostly uses one-step high-temperature carbonization (>600°C). Although it can form abundant pores, it destroys the natural oxygen-containing functional groups (such as phenolic hydroxyl groups and lactone groups) of biomass due to excessive carbonization, resulting in insufficient physical adsorption sites for acidic gases and causing an imbalance between the pores and surface functions of biochar; Hydrotalcite (Layered Double Hydroxides, abbreviated as LDHs) can be used to remove acidic gases due to its adjustable layer composition and rich basic sites. However, for the LDHs / biochar composite material synthesized by the traditional impregnation-precipitation method, due to the uneven surface charge distribution of biochar, LDHs are prone to agglomeration, resulting in a low exposure rate of active sites; In addition, the high-humidity environment of industrial flue gas will cause the hydration swelling of the LDHs layer, which will further lead to the entrapment and inactivation of active sites, reducing the activity and stability of the catalyst.

[0005] In view of the above problems, through the process innovation of "oxygen-limited carbonization - shear force field synthesis - gradient pyrolysis", the present invention develops a hydrotalcite-derived oxide modified biochar catalyst with efficient deacidification and anti-water interference functions. The technical breakthrough points are as follows: ① Retain the natural functional groups of biomass through oxygen-limited stepwise carbonization, combine with the directional activation of KOH to construct a through-type hierarchical pore structure, and synchronously optimize gas mass transfer and adsorption site density; ② Utilize the high shear force field of a colloid mill to promote the instantaneous nucleation and oriented growth of LDHs on the biochar surface, thereby obtaining thin-layer and highly dispersed LDHs layers, breaking through the disadvantages of poor dispersion and easy agglomeration of LDHs caused by the traditional impregnation-precipitation method; ③ Through gradient pyrolysis in a nitrogen-containing atmosphere and microwave plasma modification, construct a ternary synergistic interface of "metal oxide nanoparticles - oxygen-containing functional groups - siloxane hydrophobic layer" on the biochar surface, realizing the unified adsorption-catalytic synergistic removal of acidic gases and anti-water interference ability. Summary of the Invention

[0006] To solve the technical problems existing in the prior art, the present invention provides a hydrotalcite-derived oxide modified biochar catalyst, a preparation method thereof, and its application in industrial flue gas deacidification, so as to solve the problems of imbalance between the pores and surface functions of biochar, agglomeration of LDHs on the biochar surface, and poor anti-water performance of the catalyst, resulting in poor activity and stability of the catalyst.

[0007] To solve the above technical problems, the technical solutions adopted by the present invention are as follows: A preparation method of a hydrotalcite-derived oxide modified biochar catalyst, comprising the following steps: preparing a biochar precursor, preparing an LDHs / BC composite material, and preparing a catalyst; For the preparation of the biochar precursor, under nitrogen protection, the agricultural biomass waste is subjected to oxygen-limited stepwise carbonization treatment to obtain primary biochar; then the primary biochar is placed in a KOH solution, and under ultrasonic conditions, after heating and stirring at 60 - 90 °C, it is left to stand and age to obtain the biochar precursor; For the preparation of the LDHs / BC composite material, a mixed metal salt solution containing divalent metal ions and trivalent metal ions, an alkali solution, and formamide are simultaneously added to a colloid mill reactor loaded with the biochar precursor, and after shear reaction under the condition of a shear rate of 5000 - 15000 rpm, a crude product is obtained; the crude product is centrifuged, washed, and dried to obtain the LDHs / BC composite material; For the preparation of the catalyst, after the LDHs / BC composite material is gradient pyrolyzed in a nitrogen-containing mixed gas atmosphere, an LDOs / BC intermediate is obtained; then the LDOs / BC intermediate is placed in a microwave plasma reactor, using an Ar / O2 mixed gas as the working gas, and continuously introducing silane coupling agent vapor through a carrier gas, and performing microwave plasma treatment to prepare a hydrotalcite-derived oxide modified biochar catalyst.

[0008] Furthermore, among the precursors for preparing biochar, the agricultural biomass waste is at least one of the following: rice husk, straw, wood chips, Chinese medicine residues, and fruit shells; the particle size of the agricultural biomass waste is 0.15 - 0.85 mm; the oxygen-limited stepwise carbonization is to first carbonize at 300 - 400 °C for 30 - 50 min, and then carbonize at 500 - 800 °C for 1 - 3 h.

[0009] Preferably, in the precursors for preparing biochar, the concentration of the KOH solution is 0.5 - 3 mol / L; The ultrasonic frequency is 40 - 80 kHz, the stirring treatment time is 15 - 60 min, and the static aging time is 12 - 24 h; The volume-to-mass ratio of the primary biochar to the KOH solution is 5 - 10 mL:1 g.

[0010] Preferably, among the precursors for preparing the LDHs / BC composite material, the divalent metal ions are at least one of the following: Ca 2+ 、Mg 2+ 、Ni 2+ 、Zn 2+ ; the trivalent metal ions are at least one of the following: Al 3+ 、Fe 3+ 、Co 3+ ; In the mixed metal salt solution, the molar ratio of the divalent metal ions to the trivalent metal ions is 2 - 4:1; the total concentration of the metal ions in the mixed metal salt solution is 0.5 - 2.5 mol / L.

[0011] Preferably, in the precursors for preparing the LDHs / BC composite material, the alkali solution is an NaOH solution or ammonia water, and is used to adjust the pH value of the material system to 9 - 11; The addition amount of formamide is 5 - 15% of the total mass of the metal salts in the mixed metal salt solution; The mass-to-volume ratio of the biochar precursor to the mixed metal salt solution is 1 g:2 - 5 mL; The shear reaction temperature is 25 - 60 °C, and the shear reaction time is 2 - 10 min.

[0012] Preferably, in the precursors for preparing the catalyst, the nitrogen-containing mixed atmosphere is composed of nitrogen and ammonia, and the volume ratio of nitrogen to ammonia is 3 - 5:1; The gradient pyrolysis is to first pyrolyze at 300 - 400 °C for 0.5 - 1 h, and then pyrolyze at 600 - 800 °C for 2 - 4 h.

[0013] Preferably, in the precursors for preparing the catalyst, the volume percentage content of O2 in the Ar / O2 mixed gas is 10 - 20%, and the remaining amount 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%.

[0014] Preferably, in the preparation of the catalyst, the power of microwave plasma treatment is 300-800 W, the pressure of microwave plasma treatment is 50-200 Pa, and the time of microwave plasma treatment is 10-30 min.

[0015] The hydrotalcite-derived oxide-modified biochar catalyst is prepared by the aforementioned preparation method.

[0016] For the application of the hydrotalcite-derived oxide-modified biochar catalyst, the reaction pressure is controlled at atmospheric pressure - 0.3 Mpa, the reaction temperature is 80-250 °C, and the space velocity is 300-5000 h -1 , and the hydrotalcite-derived oxide-modified biochar catalyst is used to remove acidic gases in the flue gas with a moisture content of 5-15 vol%; The acidic gases include: SO2, CO2, HCl, HF.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method of the hydrotalcite-derived oxide-modified biochar catalyst of the present invention, through the process cooperation of "oxygen-limited carbonization - shear force field synthesis - gradient pyrolysis", and the synergistic strategy of multi-scale structure regulation and multi-functional interface integration, effectively overcomes the key technical bottlenecks existing in the traditional biochar-based materials in the removal of acidic gases, such as the imbalance between pores and surface functions, poor dispersion of active sites, poor water resistance interference performance, poor catalyst activity and stability, etc., which are specifically reflected in the following three aspects: 1. In terms of process improvement: a. By adopting oxygen-limited stepwise carbonization combined with KOH chemical orientation activation, while retaining the natural oxygen-containing functional groups of biomass, a through-hole microporous-mesoporous-macroporous hierarchical structure is constructed, solving the contradiction between pore collapse and functional group destruction caused by traditional high-temperature carbonization, and simultaneously improving the specific surface area, gas mass transfer performance and surface adsorption site density of biochar; b. Using the high shear force field of a colloid mill reactor to simultaneously inject metal salt solution and alkali solution, through the mechanical-chemical coupling effect, LDHs are induced to instantaneously nucleate and grow in an oriented manner on the surface of biochar, forming uniform nanosheets with a thickness of only 5-20 nm. Compared with the traditional impregnation method, the dispersion uniformity of LDHs is improved, and the interfacial bonding strength is increased, breaking through the disadvantages of poor dispersion and easy agglomeration of LDHs easily caused by the traditional impregnation-precipitation method, and fundamentally avoiding the problem of active site agglomeration; c. Under a nitrogen-containing atmosphere, gradient pyrolysis is carried out to convert LDHs into highly dispersed metal oxide nanoparticles. At the same time, through microwave plasma modification, silane coupling agent vapor is introduced synchronously to construct a dense siloxane hydrophobic layer on the surface of biochar, 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 - hydrophobic moisture resistance", and further realizing the unity of the adsorption-catalytic synergistic removal of acidic gases in industrial flue gas and the water resistance interference ability, further improving the catalytic activity and catalytic stability of the catalyst, and prolonging the effective service life of the catalyst.

[0018] 2. In terms of performance improvement: The hierarchical pore structure forms a spatial coupling with the basic catalytic sites of highly dispersed metal oxide nanoparticles, significantly improving the removal efficiency of acidic gases such as SO2 and HCl compared with traditional biochar catalysts; the siloxane hydrophobic layer effectively blocks the competitive adsorption of water molecules in high-humidity flue gas. The biochar catalyst of the present invention has significantly improved catalytic activity and stability for the removal of acidic gases in industrial flue gas and good water resistance interference ability at a humidity of 10-15 vol%; the removal efficiency of SO2 and HCl in industrial flue gas is ≥95%, the adsorption capacity for CO2 is ≥2.5 mmol / g, and the removal efficiency for HF is ≥90%.

[0019] 3. In terms of green benefits: Using agricultural waste such as rice husks, straws, wood chips, and Chinese medicine residues to replace commercial activated carbon reduces the raw material cost, and the operating cost is lower than that of the traditional flue gas purification system, further reducing the comprehensive production cost of industries such as steel and waste incineration.

[0020] In summary, the preparation method of the hydrotalcite-derived oxide modified biochar catalyst of the present invention effectively solves the long-existing pain points in the field of industrial flue gas deacidification, namely the difficulty in balancing efficiency, cost, and water interference resistance, through the technical route of "waste resource utilization - precise regulation of interfacial functions - multi-mechanism synergistic deacidification". It combines environmental benefits (emission reduction of acidic gases and solid waste), economic benefits (low cost), and social benefits (treatment of agricultural waste), and has broad industrialization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a process flow chart for preparing the LDOs / BC catalyst in the embodiment of the present invention.

[0022] Figure 2 It is a scanning electron microscope image of the LDOs / BC catalyst prepared in Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described. It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0024] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, "first", "second", etc. are used to distinguish similar objects and are not used to describe a specific order or sequence. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] As Figure 1 shown, the embodiment of the present invention provides a preparation method of a hydrotalcite-derived oxide modified biochar catalyst, which comprises the following steps: Step I. Preparation of biochar precursor Agricultural biomass waste (such as rice husks, straws, wood chips, Chinese medicine residues, fruit shells, etc.) is crushed to 0.15 - 0.85 mm, and under nitrogen protection, oxygen-limited stepwise carbonization is carried out: first, it is heated at 4 - 5 °C / min to 300 - 400 °C and kept warm for 30 - 50 min, then heated at 2 - 3 °C / min to 500 - 800 °C and kept warm for 1 - 3 h to obtain primary biochar; subsequently, the primary biochar is impregnated in 0.5 - 3 mol / L KOH solution, and treated under ultrasonic with a frequency of 40 - 80 kHz, heating at 60 - 90 °C and stirring at 200 - 500 rpm for 15 - 60 min, and then left to stand and age for 12 - 24 h to form a biochar precursor with a hierarchical structure of micropores - mesopores - macropores.

[0026] Among them, the volume - mass ratio of the primary biochar to the KOH solution is 5 - 10 mL:1 g.

[0027] Step II. Preparation of LDHs / BC composite A mixed metal salt solution containing divalent metal ions (Ca 2+ , Mg 2+ , Ni 2+ , Zn 2+ , etc.) and trivalent metal ions (Al 3+ , Fe 3+ , Co 3+ , etc.) (metal molar ratio 2:1 - 4:1, total concentration 0.5 - 2.5 mol / L), an alkali solution (NaOH solution or ammonia water with a concentration of 0.05 - 0.5 mol / L), and formamide (5 - 15% of the total mass of the metal salt) are simultaneously added to a colloid mill reactor loaded with the biochar precursor, and reacted under a shear rate of 5000 - 15000 rpm, a temperature of 25 - 60 °C, and a pH of 9.0 - 11.0 for 2 - 10 min to achieve in - situ growth of layered double - metal hydroxides (LDHs) on the biochar, obtaining a crude product; after the crude product is centrifuged, washed with ethanol / water, and vacuum - dried, an LDHs / BC composite is obtained.

[0028] Among them, the alkali solution is used to adjust the pH value of the material system within the range of 9 - 11.

[0029] The mass - volume ratio of the biochar precursor to the mixed metal salt solution is 1 g:(2 - 5) mL.

[0030] Step III. Preparation of LDOs / BC catalyst The LDHs / BC composite material was pyrolyzed stepwise in a nitrogen-containing mixed atmosphere (with a volume ratio of N2:NH3 of 3 - 5:1): heated at 2 - 5 °C / min to 300 - 400 °C and held for 0.5 - 1 h, then further heated to 600 - 800 °C and held for 2 - 4 h to obtain the LDOs / BC intermediate; subsequently, it was placed in a microwave plasma reaction chamber, and a mixture of Ar / O2 (flow rate 20 - 50 mL / min) was used as the working gas, and microwave plasma treatment was carried out at a power of 300 - 800 W for 10 - 30 min; meanwhile, during the microwave plasma treatment, silane coupling agent (APTES or HMDS) vapor was continuously introduced through a carrier gas (the concentration of silane coupling agent vapor in the carrier gas was 5 - 20 vol%, and the carrier gas flow rate was 10 - 30 mL / min), and the chamber pressure of the reaction chamber was controlled to be 50 - 200 Pa (i.e., the microwave plasma treatment pressure) to form a hydrophobic siloxane layer on the surface, and finally the LDOs / BC catalyst was prepared.

[0031] Among them, in the Ar / O2 mixture gas, the volume percentage content of O2 is 10 - 20%, and the remaining amount is argon.

[0032] The embodiment of the present invention also provides a biochar catalyst modified with a hydrotalcite-like derived oxide prepared by the aforementioned method.

[0033] The embodiment of the present invention also provides the application of the biochar catalyst modified with the hydrotalcite-like derived oxide in the deacidification of industrial flue gas. The biochar catalyst modified with the hydrotalcite-like derived oxide is used to remove acidic gases in industrial flue gas; the acidic gases include: SO2, CO2, HCl, HF.

[0034] Specifically, in a flue gas environment with a reaction pressure of atmospheric pressure - 0.3 Mpa, a reaction temperature of 80 - 250 °C, an airspeed of 300 - 5000 h -1 , and a moisture content of 5 - 15 vol%, the biochar catalyst modified with the hydrotalcite-like derived oxide is used to remove acidic gases in industrial flue gas. The removal efficiency of SO2 and HCl in industrial flue gas is ≥95%, the adsorption capacity for CO2 is ≥2.5 mmol / g, and the removal efficiency for HF is ≥90%.

[0035] Among them, 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.

[0036] The following combines some specific embodiments to further illustrate the present invention.

[0037] For those without specific experimental procedures or conditions in each embodiment, the operations or conditions of the conventional experimental procedures described in the literature in this field can be followed. For reagents or instruments without indicating the manufacturer, they are all commercially available conventional reagent products.

[0038] The method for evaluating the acid removal performance of the hydrotalcite-derived oxide modified biochar catalyst: The fixed-bed reactor is used to test the acid removal performance of the material, 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%, N2 is the balance gas, the acid removal reaction temperature is 80-250 °C, the reaction pressure is atmospheric pressure - 0.3 Mpa, and the space velocity is 300-5000 h -1 . The thermogravimetric analyzer is used to test the CO2 adsorption capacity of the catalyst, and the Fourier transform infrared gas analyzer is used to detect the contents of SO2, HCI, and HF in the flue gas before and after the reaction, and observe the change of the acid removal efficiency of the material with time. Specific evaluation indicators: The calculation formulas for the CO2 adsorption capacity Q (mmol / g) and the acid removal efficiency R (%) are as follows:

[0039] Where: C in : The inlet volume concentration (ppm) of SO2, HCI, and HF; C out : The outlet volume concentration (ppm) of SO2, HCI, and HF; Δm: The increase in the mass of the catalyst during the adsorption process (g); m0: The initial mass of the catalyst (g).

[0040] Example 1 This example provides a preparation method of a hydrotalcite-derived oxide modified biochar catalyst. Rice husk is used as the raw material to prepare the LDOs / BC catalyst. The specific steps are as follows: Step I. Preparation of the biochar precursor 1) Raw material treatment: The rice husk is crushed to a particle size of 0.3-0.6 mm and placed in a tube furnace for oxygen-limited stepwise carbonization treatment under nitrogen protection. The specific heating program is as follows: First, heat up to 350 °C at a rate of 5 °C / min and hold for 30 min; then continue to heat up to 700 °C at a rate of 3 °C / min and hold for 2 h to obtain the primary biochar.

[0041] 2) KOH activation: Mix the primary biochar with a KOH solution at a concentration of 2 mol / L according to a liquid-solid ratio of 8:1 (mL / g), place it in an ultrasonic reactor, and under the conditions of an ultrasonic frequency of 60 kHz and a temperature of 80 °C, carry out mechanical stirring at 300 rpm for 40 min, and then let it stand and age for 18 h to obtain a biochar precursor.

[0042] Step II. Preparation of LDHs / BC composite 1) Prepare a mixed metal salt solution: Weigh Mg(NO3)2•6H2O and Al(NO3)3•9H2O, and prepare a mixed metal salt solution with a total concentration of 1.2 mol / L according to a molar ratio of Mg 2+ to Al 3+ of 3:1, and add formamide accounting for 10% of the total mass of the metal salts as an auxiliary agent.

[0043] 2) Colloid mill reaction: Load the biochar precursor into a colloid mill reactor, and at the same time, pump in the above volume of the mixed metal salt solution and a NaOH solution (alkali solution) with a concentration of 0.3 mol / L according to a mass-volume ratio of biochar to the mixed metal salt solution of 1 g:5 mL, and control the pH of the reaction system to be 10.5; React for 6 min under the conditions of a shear rate of 10000 rpm and a temperature of 45 °C to enable the in-situ growth of layered double metal hydroxide (LDHs) on the surface of the biochar to obtain a crude product.

[0044] 3) Post-treatment: After the crude product is centrifuged, wash it 3 times with anhydrous ethanol and deionized water in turn, and then dry it in a vacuum drying oven at 60 °C for 12 h to obtain the LDHs / BC composite.

[0045] Step III. Preparation of LDOs / BC catalyst 1) Gradient pyrolysis: Place the LDHs / BC composite in a tubular furnace and carry out gradient pyrolysis under a mixed atmosphere with a volume ratio of N2 to NH3 of 4:1; The specific gradient pyrolysis procedure is: Heat up to 350 °C at a rate of 3 °C / min and hold for 0.8 h; Continue to heat up to 750 °C and hold for 3 h to obtain an LDOs / BC intermediate.

[0046] 2) Microwave plasma modification: Put the LDOs / BC intermediate into a microwave plasma reaction chamber, introduce a mixed gas of Ar and O2 (flow rate 35 mL / min), and carry out microwave plasma treatment at a power of 600 W for 20 min; At the same time, during the microwave plasma treatment process, continuously introduce 3-aminopropyltriethoxysilane (APTES) vapor (concentration 12 vol%) into the reaction chamber through a nitrogen carrier gas (flow rate 20 mL / min), and control the chamber pressure of the reaction chamber to be 120 Pa (i.e., the microwave plasma treatment pressure) to obtain the LDOs / BC catalyst.

[0047] Among them, in the Ar / O2 mixed gas, the volume percentage content of O2 is 15%, and the remaining amount is argon.

[0048] This example also provides a biochar catalyst modified with a hydrotalcite-derived oxide prepared by the aforementioned method.

[0049] This example also provides the application of the biochar catalyst modified with the hydrotalcite-derived oxide in the deacidification of industrial flue gas. The biochar catalyst modified with the hydrotalcite-derived oxide is used to remove acidic gases in industrial flue gas; the acidic gases are SO2, CO2, HCl, and HF. Specifically, under the conditions of atmospheric pressure, a reaction temperature of 180 °C, and a space velocity of 500 h -1 , in a flue gas environment with a moisture content of 10 vol%, the acidic gases in the flue gas are removed using the biochar catalyst modified with the hydrotalcite-derived oxide.

[0050] Performance test: Set the volume concentration of SO2 in the simulated industrial flue gas to 100 ppm, the volume concentration of CO2 to 15%, the volume concentration of HCl to 50 ppm, the volume concentration of HF to 25 ppm, the volume concentration of O2 to 16%, and the moisture content to 10%. Under the conditions of atmospheric pressure, a temperature of 180 °C, and a space velocity of 500 h -1 , use a fixed-bed reactor to evaluate the deacidification performance of the biochar catalyst in this example: the SO2 removal efficiency is 98.3%, the HCl removal efficiency is 96.7%, the CO2 adsorption capacity is 2.8 mmol / g, and the HF removal efficiency is 93.5%.

[0051] Example 2 This example provides a preparation method of a biochar catalyst modified with a hydrotalcite-derived oxide. Wood chips are used as raw materials to prepare the LDOs / BC catalyst. The specific steps are as follows: Step I. Preparation of biochar precursor 1) Raw material treatment: Crush the wood chips to a particle size of 0.2 - 0.5 mm, place them in a tubular furnace, and perform oxygen-limited stepwise carbonization treatment under nitrogen protection. The specific heating program is as follows: First, heat up to 400 °C at a rate of 5 °C / min and hold for 30 min; then continue to heat up to 600 °C at a rate of 3 °C / min and hold for 3 h to obtain primary biochar.

[0052] 2) KOH activation: Mix the primary biochar with a KOH solution with a concentration of 1.5 mol / L at a liquid-solid ratio of 6:1 (mL / g), place it in an ultrasonic reactor, and perform mechanical stirring at a frequency of 50 kHz and a temperature of 70 °C for 30 min at 400 rpm, and then let it stand and age for 24 h to obtain a biochar precursor.

[0053] Step II. Preparation of LDHs / BC composite material 1) Preparation of mixed metal salt solution: Weigh Ni(NO3)2•6H2O and Fe(NO3)3•9H2O, and prepare a mixed metal salt solution with a total concentration of 1.8 mol / L according to the molar ratio of Ni 2+ to Fe 3+ of 2:1. Then add formamide accounting for 8% of the total mass of the metal salts as an auxiliary agent.

[0054] 2) Colloid mill reaction: Load the biochar precursor into the colloid mill reactor. At the same time, pump in the above volume of the mixed metal salt solution and a NaOH solution (alkali solution) with a concentration of 0.3 mol / L according to the mass-volume ratio of biochar to the mixed metal salt solution of 1 g:4 mL, and control the pH of the reaction system to be 9.8. React for 8 min under the conditions of a shear rate of 8000 rpm and a temperature of 50 °C to enable the in-situ growth of layered double metal hydroxide (LDHs) on the surface of the biochar, obtaining a crude product.

[0055] 3) Post-treatment: After centrifugal separation of the crude product, wash it 3 times with anhydrous ethanol and deionized water in sequence, and then dry it in a vacuum drying oven at 60 °C for 12 h to obtain the LDHs / BC composite material.

[0056] Step III. Preparation of LDOs / BC catalyst 1) Gradient pyrolysis: Place the LDHs / BC composite material in a tube furnace and carry out gradient pyrolysis under a mixed atmosphere with a volume ratio of N2 to NH3 of 5:1. The specific gradient pyrolysis procedure is as follows: Heat up to 350 °C at a rate of 2 °C / min and hold for 0.5 h; then continue to heat up to 650 °C and hold for 4 h to obtain the LDOs / BC intermediate.

[0057] 2) Microwave plasma modification: Put the LDOs / BC intermediate into the microwave plasma reaction chamber, introduce a mixed gas of Ar and O2 (flow rate 35 mL / min), and carry out microwave plasma treatment for 25 min at a power of 450 W. At the same time, continuously introduce hexamethyldisilazane (HMDS) vapor (concentration 15 vol%) into the reaction chamber through a nitrogen carrier gas (flow rate 20 mL / min), control the chamber pressure of the reaction chamber to be 150 Pa (i.e., the microwave plasma treatment pressure), and form a hydrophobic siloxane layer on the surface of the biochar to obtain the LDOs / BC catalyst.

[0058] Among them, in the Ar / O2 mixed gas, the volume percentage content of O2 is 15%, and the remaining amount is argon.

[0059] This example also provides a biochar catalyst modified by a hydrotalcite-derived oxide prepared by the aforementioned method, and the scanning electron micrograph is as Figure 2 shown.

[0060] This embodiment also provides the application of the hydrotalcite-derived oxide modified biochar catalyst in the deacidification of industrial flue gas. The hydrotalcite-derived oxide modified biochar catalyst is used to remove acidic gases in industrial flue gas; the acidic gases are SO2, CO2, HCl, and HF. Specifically, under the conditions of atmospheric pressure, a reaction temperature of 200 °C, and a space velocity of 1000 h -1 , in a flue gas environment with a moisture content of 12 vol%, the hydrotalcite-derived oxide modified biochar catalyst is used to remove acidic gases in the flue gas.

[0061] Performance test: Set the volume concentration of SO2 in the simulated industrial flue gas to 200 ppm, the volume concentration of CO2 to 20%, the volume concentration of HCl to 50 ppm, the volume concentration of HF to 25 ppm, the volume concentration of O2 to 16%, and the moisture content to 12%. Under the conditions of a pressure of 0.1 MPa, a temperature of 200 °C, and a space velocity of 1000 h -1 , use a fixed-bed reactor to evaluate the performance of the biochar catalyst in this embodiment: the SO2 removal efficiency is 95.6%, the HCl removal efficiency is 95.1%, the CO2 adsorption capacity is 2.6 mmol / g, and the HF removal efficiency is 91.3%.

[0062] Example 3 This embodiment provides a preparation method of a hydrotalcite-derived oxide modified biochar catalyst. The LDOs / BC catalyst is prepared using Chinese medicine residues as raw materials. The specific steps are as follows: Step I. Preparation of biochar precursor 1) Raw material treatment: Crush the dried Chinese medicine residues (herbal residues containing astragalus and licorice) to a particle size of 0.4 - 0.7 mm, place them in a tubular furnace, and carry out oxygen-limited stepwise carbonization treatment under nitrogen protection. The specific heating program is as follows: First, heat up to 380 °C at a rate of 5 °C / min and hold for 30 min; then continue to heat up to 650 °C at a rate of 3 °C / min and hold for 2.5 h to obtain primary biochar.

[0063] 2) KOH activation: Mix the primary biochar with a 2.5 mol / L KOH solution at a liquid-solid ratio of 7:1 (mL / g), place it in an ultrasonic reactor, and under the conditions of an ultrasonic frequency of 70 kHz and a temperature of 75 °C, carry out mechanical stirring at 400 rpm for 50 min, and then stand for aging for 20 h to obtain the biochar precursor.

[0064] Step II. Preparation of LDHs / BC composite material 1) Prepare a mixed metal salt solution: Weigh calcium chloride and aluminum chloride, according to Ca 2+ and Al 3+Prepare a mixed metal salt solution with a total concentration of 1.5 mol / L at a molar ratio of 2.5:1, and add formamide accounting for 12% of the total mass of the metal salts as an auxiliary agent thereto.

[0065] 2) Colloid mill reaction: Load the biochar precursor into a colloid mill reactor. Synchronously, pump the above-mentioned mixed metal salt solution and a NaOH solution (alkali solution) with a concentration of 0.3 mol / L into the reactor according to the mass-volume ratio of biochar to the mixed metal salt solution being 1 g:2 mL, and control the pH of the reaction system to be 10.2; React for 5 min under the conditions of a shear rate of 12000 rpm and a temperature of 50 °C to enable the in-situ growth of layered double metal hydroxides (LDHs) on the biochar surface and obtain a crude product.

[0066] 3) Post-treatment: After the crude product is centrifuged and separated, wash it 3 times each with absolute ethanol and deionized water, and then dry it in a vacuum drying oven at 60 °C for 12 h to obtain the LDHs / BC composite material.

[0067] Step III. Prepare the LDOs / BC catalyst 1) Gradient pyrolysis: Place the LDHs / BC composite material in a tubular furnace and perform gradient pyrolysis under a mixed atmosphere with a volume ratio of N2 to NH3 being 5:1. The specific gradient pyrolysis procedure is as follows: Heat up to 380 °C at a rate of 4 °C / min and hold for 1 h; Continue to heat up to 700 °C and hold for 3.5 h to obtain the LDOs / BC intermediate.

[0068] 2) Microwave plasma modification: Place the LDOs / BC intermediate in a microwave plasma reaction chamber, introduce a mixed gas of Ar and O2 (flow rate 35 mL / min), and perform microwave plasma treatment for 15 min at a power of 700 W; At the same time, during the microwave plasma treatment, continuously introduce hexamethyldisilazane (HMDS) vapor (concentration 18 vol%) into the reaction chamber through an argon carrier gas (flow rate 25 mL / min), and control the chamber pressure of the reaction chamber to be 150 Pa (i.e., the microwave plasma treatment pressure); Form a hydrophobic siloxane layer on the biochar surface to obtain the LDOs / BC catalyst.

[0069] Among them, in the Ar / O2 mixed gas, the volume percentage content of O2 is 15%, and the remaining amount is argon.

[0070] This example also provides a biochar catalyst modified with a hydrotalcite-derived oxide prepared by the foregoing method.

[0071] This embodiment also provides the application of the hydrotalcite-derived oxide-modified biochar catalyst in the deacidification of industrial flue gas. The hydrotalcite-derived oxide-modified biochar catalyst is used to remove acidic gases in industrial flue gas; the acidic gases are SO2, CO2, HCl, and HF. Specifically, in a flue gas environment with a reaction pressure of 0.15 MPa, a reaction temperature of 200 °C, a space velocity of 3000 h -1 , and a moisture content of 12 vol%, the acidic gases in the flue gas are removed using the hydrotalcite-derived oxide-modified biochar catalyst.

[0072] Performance test: Set the volume concentration of SO2 in the simulated industrial flue gas to 50 ppm, the volume concentration of CO2 to 25%, the volume concentration of HCl to 50 ppm, the volume concentration of HF to 50 ppm, the volume concentration of O2 to 18%, and the moisture content to 12%. Under the conditions of a pressure of 0.15 MPa, a temperature of 200 °C, and a space velocity of 3000 h -1 , use a fixed-bed reactor to evaluate the performance of the biochar catalyst of this embodiment: the SO2 removal efficiency is 97.5%, the HCl removal efficiency is 97.1%, the CO2 adsorption capacity is 2.7 mmol / g, and the HF removal efficiency is 94.2%.

[0073] Comparative Example 1 Comparative Example 1 adopts the technical solution of Example 1. The difference is that in step II. for preparing the LDHs / BC composite material, the colloid mill reaction is omitted and modified to stir the biochar precursor with the LDHs precursor solution (mixed metal salt solution, alkali solution, formamide) at 500 rpm for 1 h to obtain a crude product.

[0074] Under the same test conditions as in Example 1, the deacidification performance of the biochar catalyst of Comparative Example 1 is tested. Its SO2 removal efficiency is 82.4%, the HCl removal efficiency is 68.3%, the CO2 adsorption capacity is 1.2 mmol / g, and the HF removal efficiency is 65.9%.

[0075] Comparative Example 2 Comparative Example 2 adopts the technical solution of Example 1. The difference is that in step III. for 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.

[0076] Under the same test conditions as in Example 1, the deacidification performance of the biochar catalyst of Comparative Example 2 is tested. Its SO2 removal efficiency is 87.6%, the HCl removal efficiency is 73.2%, the CO2 adsorption capacity is 1.5 mmol / g, and the HF removal efficiency is 70.1%.

[0077] Comparative Example 3 Comparative Example 3 adopted the technical solution of Example 3, the difference being that in Step I. Preparation of the biochar precursor, the KOH activation treatment was omitted, and the primary biochar without KOH activation was directly used in the subsequent Step II. Preparation of the LDHs / BC composite material.

[0078] Under the same test conditions as in Example 3, the acid removal performance of the biochar catalyst of Comparative Example 3 was tested. Its SO2 removal efficiency was 76.8%, the HCl removal efficiency was 64.7%, the CO2 adsorption capacity was 0.9 mmol / g, and the HF removal efficiency was 61.8%.

[0079] Through the comprehensive comparison of Examples 1-3 and Comparative Examples 1-3, it is shown that: 1) The process synergy of the preparation method of the present invention: The colloid mill process improves the HCl / HF removal efficiency by ≥25%, and the plasma modification improves the HF stability in a humid environment by ≥20%; 2) The technical indivisibility of the preparation method of the present invention: The absence of any key step (such as KOH activation, plasma modification) will lead to the simultaneous deterioration of the multi-component removal performance of the biochar catalyst for flue gas.

[0080] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Preparation method of a biochar catalyst modified by a hydrotalcite-derived oxide, characterized in that, It includes the following steps: Prepare a biochar precursor, prepare an LDHs / BC composite material, and prepare a catalyst; For the preparation of the biochar precursor, under nitrogen protection, the agricultural biomass waste is subjected to oxygen-limited stepwise carbonization treatment to obtain primary biochar; Then the primary biochar is placed in a KOH solution, and under ultrasonic conditions, after heating and stirring at 60 - 90 °C, it is left to stand and age to obtain the biochar precursor; For the preparation of the LDHs / BC composite material, a mixed metal salt solution containing divalent metal ions and trivalent metal ions, an alkali solution, and formamide are simultaneously added to a colloid mill reactor loaded with the biochar precursor. Under the condition of a shear rate of 5000 - 15000 rpm, after shear reaction, a crude product is obtained; the crude product is centrifuged, washed, and dried to obtain the LDHs / BC composite material; For the preparation of the catalyst, after the LDHs / BC composite material is pyrolyzed step by step in a nitrogen-containing mixed atmosphere environment, an LDOs / BC intermediate is obtained; Then the LDOs / BC intermediate is placed in a microwave plasma reactor, using an Ar / O2 mixed gas as the working gas, and the silane coupling agent vapor is continuously introduced through a carrier gas for microwave plasma treatment to prepare a biochar catalyst modified with a hydrotalcite-like derived oxide.

2. The preparation method of the hydrotalcite-like derived oxide modified biochar catalyst 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 husk, straw, wood chips, traditional Chinese medicine residues, fruit shells; the particle size of the agricultural biomass waste is 0.15 - 0.85 mm; the oxygen-limited stepwise carbonization is to first carbonize at 300 - 400 °C for 30 - 50 min, and then carbonize at 500 - 800 °C for 1 - 3 h.

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

4. The preparation method of the hydrotalcite-like derived oxide modified biochar catalyst according to claim 1, characterized in that, 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; the total concentration of metal ions in the mixed metal salt solution is 0.5 - 2.5 mol / L.

5. The preparation method of the hydrotalcite-like derived oxide modified biochar catalyst according to claim 1, characterized in that, In the preparation of the LDHs / BC composite material, the alkali solution is a NaOH solution or ammonia water, used to adjust the pH value of the material system to 9 - 11; The addition amount of formamide is 5 - 15% of the total mass of the metal salt in the mixed metal salt solution; The mass-volume ratio of the biochar precursor to the mixed metal salt solution is 1 g:2 - 5 mL; The shear reaction temperature is 25 - 60 °C, and the shear reaction time is 2 - 10 min.

6. The preparation method of the hydrotalcite-like derived oxide modified biochar catalyst according to claim 1, characterized in that, In the preparation of the catalyst, the nitrogen-containing mixed atmosphere is composed of nitrogen and ammonia, and the volume ratio of nitrogen to ammonia is 3 - 5:1; The stepwise pyrolysis is to first pyrolyze at 300 - 400 °C for 0.5 - 1 h, and then pyrolyze at 600 - 800 °C for 2 - 4 h.

7. The preparation method of the hydrotalcite-like derived oxide modified biochar catalyst according to claim 1, characterized in that, In the preparation of the catalyst, the volume percentage content of O2 in the Ar / O2 mixed gas is 10 - 20%, and the remaining amount 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 preparation method of the hydrotalcite-like derived oxide modified biochar catalyst according to claim 1, characterized in that, In the preparation of the catalyst, 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.

9. Hydrotalcite-derived oxide-modified biochar catalyst, characterized in that, It is prepared by using the preparation method according to any one of claims 1 - 8.

10. Use of the hydrotalcite-derived oxide-modified biochar catalyst according to claim 9, characterized in that, The reaction pressure is controlled at atmospheric pressure - 0.3 Mpa, the reaction temperature is 80 - 250 °C, and the space velocity is 300 - 5000 h -1 , and the biochar catalyst modified by the hydrotalcite-like derived oxide is used to remove acidic gases in flue gas with a moisture content of 5 - 15 vol%; The acidic gases include: SO2, CO2, HCl, HF.

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