Diatomite-based nitrogen oxide adsorbent and preparation method thereof

Abstract

The invention belongs to the technical field of adsorbents, and particularly relates to a diatomite-based nitrogen oxide adsorbent and a preparation method thereof. The preparation method comprises the following steps: carrying out ultrasonic treatment on diatomite and an alkaline aqueous solution to obtain diatomite A; performing acid treatment on the diatomite A to obtain diatomite B; calcining the diatomite B to obtain diatomite C; mixing the diatomite C, a surfactant and a dispersing agent, and performing primary treatment to obtain diatomite D; mixing the diatomite D with a silane coupling agent, and then performing secondary drying to obtain diatomite E; performing coating modification treatment on the diatomite E, a coating agent and a modifier to obtain diatomite F; and drying, roasting and grinding the diatomite F to obtain the diatomite-based nitrogen oxide adsorbent. The diatomite-based nitrogen oxide adsorbent prepared in the invention has high nitrogen oxide adsorption efficiency, and can accurately detect the carbon content in coal.

Description

Technical Field

[0001] This invention belongs to the field of adsorbent technology, specifically relating to a diatomaceous earth-based nitrogen oxide adsorbent and its preparation method. Background Technology

[0002] The hydrocarbon content in coal is crucial for determining its metamorphic degree and studying its properties. Most coals contain 45%–55% carbon and 4%–6% hydrogen, totaling approximately 60%. Carbon and hydrogen constitute important indicators of coal quality and provide fundamental data for carbon dioxide emission control, process selection, and implementation in power generation and chemical industries. Therefore, efficient and accurate determination of the hydrocarbon content in coal is of great guiding significance for carbon dioxide emission control, operational optimization, and carbon dioxide emission reduction implementation in power generation and chemical enterprises. During coal combustion, nitrogen produces a large amount of nitrogen oxides. Since nitrogen oxides can be simultaneously adsorbed by carbon dioxide adsorbents, their presence complicates the determination of hydrocarbon content. Chinese standards GB / T 476 and GB / T 30733 specify the use of the three-section furnace method, the electrogravimetric method, and the elemental analyzer method for determining the carbon and hydrogen content in coal. All of these methods involve the adsorption of nitrogen oxides. Different nitrogen oxide adsorption compositions directly affect the determination of hydrocarbon content.

[0003] Currently, lead dioxide or manganese dioxide adsorbents are commonly used for nitrogen oxides, but they also interfere with the adsorption of moisture and carbon dioxide, causing major errors in hydrocarbon determination. Many traditional adsorbent materials, such as unmodified activated carbon, molecular sieves, and ordinary silica gel, have limited adsorption capacity for NOx, especially nitrogen dioxide. When analyzing high-nitrogen coal samples or performing continuous measurements on multiple samples, the adsorbent easily reaches saturation (breakthrough), preventing the complete capture of NOx in subsequent gas streams and interfering with subsequent carbon dioxide determination. Furthermore, combustion gas contains not only the target NOx but also large amounts of carbon dioxide, water vapor, and potentially sulfur dioxide. Some existing adsorbents (such as ordinary activated carbon and certain metal oxides) also have some adsorption capacity for these gas components. Competition for adsorption of the target NOx significantly reduces the effective adsorption capacity for NOx; more seriously, if the adsorbent also adsorbs some carbon dioxide, it will directly lead to a lower final carbon content, and this interference is difficult to detect and correct. Therefore, the development of novel adsorbents for nitrogen oxides in coal is of great significance for improving the accurate determination of hydrocarbon content in coal.

[0004] Therefore, there is an urgent need for a method to prepare a nitrogen oxide adsorbent with high NOx adsorption capacity, excellent selectivity (especially inertness to carbon dioxide), good high temperature and high humidity stability, and rapid adsorption kinetics. Summary of the Invention

[0005] The purpose of this invention is to provide a diatomaceous earth-based nitrogen oxide adsorbent and its preparation method. The diatomaceous earth-based nitrogen oxide adsorbent prepared by this method has high selective adsorption capacity for nitrogen oxides.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing a diatomaceous earth-based nitrogen oxide adsorbent, comprising the following steps: (1) Alkali treatment: Diatomaceous earth is ultrasonically treated with an alkaline aqueous solution to obtain diatomaceous earth A; (2) Acid treatment: Diatomaceous earth A is acid treated to obtain diatomaceous earth B; (3) Calcination: Diatomite B is calcined to obtain diatomite C; (4) Surface activation treatment: Diatomaceous earth C, surfactant and dispersant are mixed, and then the first step is performed to obtain diatomaceous earth D; (5) Coupling agent modification: Diatomaceous earth D is mixed with silane coupling agent to obtain diatomaceous earth E after a second drying process; (6) Modification and coating: Diatomaceous earth E, coating agent and modifier are coated and modified to obtain diatomaceous earth F; (7) Drying and calcining: The diatomaceous earth F is dried, calcined, and ground into powder to obtain a diatomaceous earth-based nitrogen oxide adsorbent.

[0007] [Alkali Treatment] The alkaline treatment used in this invention can remove some impurities (such as metal oxides and organic matter) from diatomaceous earth and initially open the pores, which is beneficial for subsequent modification.

[0008] Furthermore, the diatomaceous earth has an average particle size of 1-3 mm, a porosity of not less than 90%, and a specific surface area of ​​50 ± 10 m². 2 / g.

[0009] The diatomaceous earth used in this invention is commercially available, and this invention will not elaborate further on this.

[0010] Furthermore, by mass fraction, the alkaline aqueous solution contains: 8-15% alkaline hydroxide, 1-3% sodium hexametaphosphate (SHMP), and the balance being water.

[0011] In this invention, there are no special restrictions on the amount of diatomaceous earth and alkaline aqueous solution used; the diatomaceous earth can be completely immersed in the alkaline aqueous solution.

[0012] In this invention, 8-15% alkaline hydroxide is used to moderately dissolve part of the silicon framework, expand the original pores, unclog blocked channels, and initially improve the specific surface area and porosity. At the same time, it avoids excessive corrosion and damage to the diatomaceous earth framework structure by strong alkali. During the process of solvent extraction of impurities by alkaline hydroxide, sodium hexametaphosphate can generate electrostatic effect on the surface of diatomaceous earth to prevent the aggregation of diatomaceous earth particles. It can also chelate with metal impurities to prevent dissolved metal ions from reprecipitating back into the channels, ensuring unobstructed pores and significantly improving the subsequent purification effect.

[0013] Furthermore, the alkaline hydroxide is selected from NaOH and / or KOH, preferably NaOH.

[0014] Furthermore, the conditions for the ultrasonic treatment include: an ultrasonic frequency of 40-50 Hz and a treatment time of 1-2 hours.

[0015] In this invention, diatomaceous earth A can be obtained by ultrasonic treatment followed by filtration.

[0016] Furthermore, the alkali treatment step includes: selecting particles with an average particle size of 1-3 mm, a porosity of not less than 90%, and a specific surface area of ​​50 ± 10 m². 2 / g of diatomaceous earth was completely immersed in an alkaline aqueous solution (8-15% alkaline hydroxide, 1-3% sodium hexametaphosphate, water as the balance) and ultrasonically treated for 1 hour (ultrasonic frequency of 40-50Hz). After filtration, diatomaceous earth A was obtained.

[0017] [Acid Treatment] In this invention, the main function of acid treatment is acid purification, which can further dissolve carbonate impurities such as calcium and magnesium, purify the diatomaceous earth framework, increase surface hydroxyl groups, and enhance reactivity.

[0018] Furthermore, the acid treatment includes a first acid treatment and a second acid treatment, wherein the first acid treatment is carried out in the presence of an aqueous HF solution with a concentration of 0.1-0.3 mol / L, and the second acid treatment is carried out in the presence of an aqueous hydrochloric acid solution with a concentration of 4-5 mol / L.

[0019] This invention employs a two-step acid treatment. First, highly active Si-F bonds are generated through the reaction of HF diatomaceous earth, providing reaction sites for subsequent hydrochloric acid treatment and enhancing the surface Lewis acid. Then, hydrochloric acid further expands the pores and exposes more silanol groups, providing better anchoring points for subsequent modification treatment and increasing the overall performance of the adsorbent.

[0020] Furthermore, the treatment time for the first acid is 55-65 minutes.

[0021] Furthermore, the second acid treatment time is 5-6 hours. Furthermore, the acid treatment step includes: soaking diatomaceous earth A in an HF aqueous solution with a concentration of 0.1-0.3 mol / L for 55-65 min, then rinsing the soaked diatomaceous earth with secondary deionized water until the washing solution is neutral, to obtain diatomaceous earth A1; then soaking diatomaceous earth A1 in a hydrochloric acid aqueous solution with a concentration of 4-5 mol / L for 5-6 h, and finally rinsing the soaked diatomaceous earth with secondary deionized water until the washing solution is neutral, to obtain diatomaceous earth B.

[0022] In this invention, when performing the above-mentioned soaking, it is sufficient to immerse the corresponding solid material in an HF aqueous solution or a hydrochloric acid aqueous solution.

[0023] [Calcination] In this invention, calcination mainly serves as a physical purification process. This calcination can stabilize the structure of diatomaceous earth, remove residual organic matter and moisture, and enhance mechanical strength and thermal stability.

[0024] Furthermore, the calcination conditions include calcination at 400-450℃ for 1-2 hours.

[0025] Furthermore, the calcination step includes: calcining diatomaceous earth B at 400-450℃ for 1-2 hours to obtain diatomaceous earth C.

[0026] [Surface activation treatment] The surface activation treatment in this invention creates a monodisperse, low surface energy, and highly reactive interfacial environment for subsequent silane coupling agent anchoring and organic coating, fundamentally ensuring the selective adsorption capacity and color change reliability of the final adsorbent.

[0027] Furthermore, the surfactant is selected from polyoxyethylene fatty acid esters.

[0028] Furthermore, the polyoxyethylene fatty acid ester is selected from at least one of polyoxyethylene 40 stearate, polyoxyethylene 100 stearate and polyoxyethylene 8 laurate, preferably polyoxyethylene 40 stearate.

[0029] Furthermore, the dispersant is selected from polyethylene glycol.

[0030] Furthermore, the degree of polymerization of the polyethylene glycol is 500-4000, such as polyethylene glycol PEG500, polyethylene glycol PEG1000, polyethylene glycol PEG2000, polyethylene glycol PEG4000, preferably polyethylene glycol PEG4000.

[0031] Further, the mass ratio of the diatomaceous earth C, the surfactant, and the dispersant is (90-92):(5-6):(3-4).

[0032] There are no special restrictions on the mixing method of diatomaceous earth C, surfactant and dispersant, as long as they are mixed evenly. They can be mixed evenly under stirring conditions.

[0033] Furthermore, the conditions for the first drying include: a temperature of 105-120°C and a time of 1.5-2.5 hours.

[0034] Furthermore, the surface activation treatment step includes: thoroughly mixing diatomaceous earth C, polyoxyethylene 40 stearate and polyethylene glycol PEG4000 in a mass ratio of (90-92):(5-6):(3-4), and then drying at a constant temperature of 105-120℃ for 1.5-2.5h to obtain diatomaceous earth D.

[0035] [Coupling agent modification] The coupling agent modification in this invention can provide "anchor points" and reaction sites for subsequent organic coating, significantly altering surface properties.

[0036] Furthermore, the silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltris(2-methoxyethoxy)silane.

[0037] Furthermore, the silane coupling agent is a combination of γ-aminopropyltriethoxysilane and vinyltriethoxysilane, preferably with a mass ratio of γ-aminopropyltriethoxysilane to vinyltriethoxysilane of 1:1.

[0038] Furthermore, the mass ratio of the diatomaceous earth D to the silane coupling agent is (90-92):(8-10).

[0039] There are no special restrictions on the mixing conditions of diatomaceous earth D and silane coupling agent, as long as they are mixed evenly.

[0040] Furthermore, the conditions for the second drying include: a temperature of 105-120°C and a time of 1.5-2.5 hours.

[0041] Furthermore, the coupling agent modification step includes: thoroughly mixing diatomaceous earth D with a mass ratio of (90-92):(8-10) and a silane coupling agent (γ-aminopropyltriethoxysilane and vinyltriethoxysilane in a mass ratio of 1:1), and then drying at a constant temperature of 105-120℃ for 1.5-2.5h to obtain diatomaceous earth E.

[0042] [Modified Coating] Furthermore, the coating agent is selected from calcium stearate.

[0043] Furthermore, the modifier comprises a solution of hexadecyltrimethylammonium bromide and / or polyethyleneimine.

[0044] Furthermore, the modifier comprises hexadecyltrimethylammonium bromide and a polyethyleneimine solution, preferably with a mass ratio of hexadecyltrimethylammonium bromide to polyethyleneimine solution of 1:1.

[0045] The polyethyleneimine solution is a solution formed by dissolving polyethyleneimine in water. Further, the mass concentration of the polyethyleneimine solution is 30-50%, preferably 30%.

[0046] The polyethyleneimine solution in this invention can be obtained commercially, for example, purchased from Shanghai Youen Chemical Co., Ltd., model number polyethyleneimine UN-1369.

[0047] Furthermore, the average molecular weight of the polyethyleneimine in the polyethyleneimine solution is 6000-12000, preferably 10000.

[0048] In this invention, the long alkyl chain of calcium stearate can form a nanoscale Ca-O-Si cross-linked network during subsequent drying and calcination, increasing the water contact angle of the final adsorbent, effectively and completely blocking the penetration of water molecules and weakening the physical adsorption of carbon dioxide. At the same time, the quaternary ammonium cation of hexadecyltrimethylammonium bromide is further anchored to the negative potential site on the diatomaceous earth surface, which can better capture nitrogen oxides. In addition, the hyperbranched amine group of polyethyleneimine and the quaternary ammonium group in hexadecyltrimethylammonium bromide form a stable covalent structure. Its amine group can reduce nitrogen dioxide to generate azo compounds to achieve chemical fixation, and avoid contact with carbon dioxide due to the steric hindrance of the hydrophobic layer.

[0049] Furthermore, the modifier also contains cerium nitrate.

[0050] Furthermore, the mass ratio of cerium nitrate to hexadecyltrimethylammonium bromide is (0.5-0.8):1, preferably (0.65-0.7):1.

[0051] In this invention, it was found that adding cerium nitrate can significantly increase the adsorption capacity of the final adsorbent for nitrogen oxides, especially when testing the hydrocarbon content in high-carbon coal (e.g., anthracite), exhibiting better accuracy. It is also highly sensitive to errors in carbon dioxide adsorption. The adsorption capacity decay is presumably due to the insufficient oxidizing capacity of hexadecyltrimethylammonium bromide and polyethyleneimine for nitric oxide. This invention introduces cerium nitrate, which preferentially loads onto the sites of polyethyleneimine, introducing a trivalent / tetravalent cerium redox cycle onto the adsorbent to further increase the adsorption capacity for nitric oxide. Furthermore, the final calcination to form cerium dioxide enhances the cross-linking of the framework.

[0052] Furthermore, the mass ratio of the diatomaceous earth E, the coating agent and the modifier is (88-90):(5-6):(5-6).

[0053] Furthermore, the conditions for the coating modification treatment include: grinding at a speed of 20,000-35,000 r / min for 1-2 min, preferably at a speed of 28,000 r / min for 1-2 min.

[0054] Furthermore, the modified coating step includes: grinding diatomaceous earth E, calcium stearate and modifier in a mass ratio of (88-90):(5-6):(5-6) at a speed of 28000 r / min for 1-2 min to obtain diatomaceous earth F.

[0055] [Drying and calcining] Furthermore, the drying and calcination conditions include: heating to 400-450°C at a rate of 10-20°C / min at room temperature, and holding for 10-20 min.

[0056] In this invention, there are no special limitations on the grinding conditions. Generally, the average particle size of the powder prepared is controlled at 50-60 mesh in a high-precision grinding mill.

[0057] Furthermore, the drying and calcining conditions also include: drying and calcining in a mixed gas of nitrogen and HF, preferably with a volume ratio of nitrogen to HF of 1:0.3.

[0058] In this invention, drying and roasting in nitrogen and HF gases can better increase the adsorbent's resistance to water vapor interference. For example, when testing the hydrocarbon content of lignite with high moisture content, it has better accuracy. This is presumably because the presence of HF can better form a monomolecular fluorocarbon barrier, destroy the hydrogen bond network of water molecules, and increase its contact angle.

[0059] Further, the drying and calcination step includes: heating diatomaceous earth F to 400-450℃ at a rate of 10-20℃ / min in a mixed atmosphere of nitrogen and HF gas with a volume ratio of 1:0.3, holding for 10-20min, then cooling to room temperature, and grinding the powder to an average particle size of 50-60 mesh using a high-precision grinding mill to obtain a diatomaceous earth-based nitrogen oxide adsorbent.

[0060] In a second aspect, the present invention provides a diatomaceous earth-based nitrogen oxide adsorbent, which is prepared by the preparation method of the diatomaceous earth-based nitrogen oxide adsorbent described in the first aspect of the present invention.

[0061] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: The diatomaceous earth-based nitrogen oxide adsorbent prepared by the method of this invention has excellent properties such as three-dimensional network structure, high porosity, large specific surface area, high adsorption efficiency, and real-time color change. It overcomes the defects of traditional lead dioxide and manganese dioxide adsorbents, such as low adsorption efficiency, many limiting conditions, and great influence on hydrocarbon adsorption. It has a good effect on nitrogen oxide adsorption in the determination of hydrocarbon content in coal and can accurately detect the carbon content in coal. Detailed Implementation

[0062] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] In the following embodiments: The diatomaceous earth has an average particle size of 2 mm, a porosity of not less than 96%, and a specific surface area of ​​50 m². 2 / g The polyethyleneimine solution was purchased from Shanghai Youen Chemical Co., Ltd., model number UN-1369, with a mass concentration of 30% and an average molecular weight of 10,000 for the polyethyleneimine in the solution.

[0064] Example 1 This embodiment provides a modified preparation of a diatomaceous earth-based nitrogen oxide adsorbent, comprising the following steps: (1) Alkali treatment: Diatomite was completely immersed in an alkaline aqueous solution (10% alkaline hydroxide, 2% sodium hexametaphosphate (SHMP), water balance) and ultrasonically treated for 1 hour (ultrasonic frequency of 50Hz), and then filtered to obtain diatomite A. (2) Acid treatment: Diatomite A was soaked in 0.3 mol / L HF aqueous solution for 60 min, and then rinsed with secondary deionized water until the washing solution was neutral to obtain diatomite A1; then diatomite A1 was soaked in 5 mol / L hydrochloric acid aqueous solution for 5 h, and finally rinsed with secondary deionized water until the washing solution was neutral to obtain diatomite B; (3) Calcination: Diatomite B was calcined at 450℃ for 2 hours to obtain diatomite C; (4) Surface activation treatment: Diatomaceous earth C, polyoxyethylene 40 stearate and polyethylene glycol PEG4000 in a mass ratio of 92:4:4 were thoroughly mixed and then dried at 110℃ for 2h to obtain diatomaceous earth D. (5) Coupling agent modification: Diatomaceous earth D with a mass ratio of 92:8 and silane coupling agent (γ-aminopropyltriethoxysilane and vinyltriethoxysilane with a mass ratio of 1:1) are thoroughly mixed and then dried at 110℃ for 2h to obtain diatomaceous earth E. (6) Modification and coating: Diatomaceous earth E, calcium stearate and modifier (hexadecyltrimethylammonium bromide and polyethyleneimine solution with a mass ratio of 88:6:6) are ground at 28000 r / min for 2 min to obtain diatomaceous earth F; (7) Drying and calcining: Diatomite F is heated to 450°C at a rate of 15°C / min in a mixed atmosphere of nitrogen and HF gas with a volume ratio of 1:0.3, held for 10 min, and then cooled to room temperature. The powder is then ground to an average particle size of 60 mesh using a high-precision grinding mill to obtain diatomite-based nitrogen oxide adsorbent.

[0065] Example 2 This embodiment provides a modified preparation of a diatomaceous earth-based nitrogen oxide adsorbent, comprising the following steps: (1) Alkali treatment: Diatomite was completely immersed in an alkaline aqueous solution (10% alkaline hydroxide, 2% sodium hexametaphosphate (SHMP), water balance) and ultrasonically treated for 1 hour (ultrasonic frequency of 50Hz), and then filtered to obtain diatomite A. (2) Acid treatment: Diatomite A was soaked in 0.3 mol / L HF aqueous solution for 60 min, and then rinsed with secondary deionized water until the washing solution was neutral to obtain diatomite A1; then diatomite A1 was soaked in 4.5 mol / L hydrochloric acid aqueous solution for 5.5 h, and finally rinsed with secondary deionized water until the washing solution was neutral to obtain diatomite B; (3) Calcination: Diatomaceous earth B was calcined at 450℃ for 1.5h to obtain diatomaceous earth C; (4) Surface activation treatment: Diatomaceous earth C, polyoxyethylene 40 stearate and polyethylene glycol PEG4000 in a mass ratio of 90:6:4 were thoroughly mixed and then dried at 110℃ for 2h to obtain diatomaceous earth D. (5) Coupling agent modification: Diatomaceous earth D with a mass ratio of 90:10 and silane coupling agent (γ-aminopropyltriethoxysilane and vinyltriethoxysilane with a mass ratio of 1:1) are thoroughly mixed and then dried at 110℃ for 2h to obtain diatomaceous earth E. (6) Modification and coating: Diatomaceous earth E, calcium stearate and modifier (hexadecyltrimethylammonium bromide and polyethyleneimine solution with a mass ratio of 90:5:5) are ground at 28000 r / min for 2 min to obtain diatomaceous earth F; (7) Drying and calcining: Diatomite F is heated to 400°C at a rate of 20°C / min in a mixed atmosphere of nitrogen and HF with a volume ratio of 1:0.3, held for 20 min, and then cooled to room temperature. The powder is then ground to an average particle size of 60 mesh using a high-precision grinding mill to obtain diatomite-based nitrogen oxide adsorbent.

[0066] Example 3 This embodiment provides a modified preparation of a diatomaceous earth-based nitrogen oxide adsorbent, comprising the following steps: (1) Alkali treatment: Diatomite was completely immersed in an alkaline aqueous solution (10% alkaline hydroxide, 2% sodium hexametaphosphate (SHMP), water balance) and ultrasonically treated for 1 hour (ultrasonic frequency of 40Hz), and then filtered to obtain diatomite A. (2) Acid treatment: Diatomite A was soaked in 0.2 mol / L HF aqueous solution for 65 min, and then rinsed with secondary deionized water until the washing solution was neutral to obtain diatomite A1; then diatomite A1 was soaked in 4.5 mol / L hydrochloric acid aqueous solution for 5.5 h, and finally rinsed with secondary deionized water until the washing solution was neutral to obtain diatomite B; (3) Calcination: Diatomaceous earth B was calcined at 450℃ for 1.5h to obtain diatomaceous earth C; (4) Surface activation treatment: Diatomaceous earth C, polyoxyethylene 40 stearate and polyethylene glycol PEG4000 in a mass ratio of 91:5:4 were thoroughly mixed and then dried at 110℃ for 2h to obtain diatomaceous earth D. (5) Coupling agent modification: Diatomaceous earth D with a mass ratio of 91:9 and silane coupling agent (γ-aminopropyltriethoxysilane and vinyltriethoxysilane with a mass ratio of 1:1) are thoroughly mixed and then dried at 110℃ for 2h to obtain diatomaceous earth E. (6) Modification and coating: Diatomaceous earth E, calcium stearate and modifier (hexadecyltrimethylammonium bromide and polyethyleneimine solution with a mass ratio of 89:5:6) are ground at 28000 r / min for 2 min to obtain diatomaceous earth F; (7) Drying and calcining: Diatomite F is heated to 420°C at a rate of 20°C / min in a mixed atmosphere of nitrogen and HF with a volume ratio of 1:0.3, held for 15 min, and then cooled to room temperature. The powder is then ground to an average particle size of 60 mesh using a high-precision grinding mill to obtain diatomite-based nitrogen oxide adsorbent.

[0067] Example 4 The method of Example 1 differs in that: The modifier is a mixture of hexadecyltrimethylammonium bromide, polyethyleneimine solution, and cerium nitrate in a mass ratio of 1:1:0.65.

[0068] The rest of the preparation process was the same as in Example 1, and the final diatomaceous earth-based nitrogen oxide adsorbent was obtained.

[0069] Example 5 The method according to Example 2 differs in that: The modifier is a mixture of hexadecyltrimethylammonium bromide, polyethyleneimine solution, and cerium nitrate in a mass ratio of 1:1:0.7.

[0070] The rest of the preparation process was the same as in Example 2, and the final diatomaceous earth-based nitrogen oxide adsorbent was obtained.

[0071] Comparative Example 1 The method of Example 1 differs in that: Replace all the modifiers with calcium stearate, i.e., the modification coating in step (6): grind diatomaceous earth E and calcium stearate in a mass ratio of 90:10 at a speed of 28000 r / min for 2 min to obtain diatomaceous earth F.

[0072] The rest of the preparation process was the same as in Example 1, and the final diatomaceous earth-based nitrogen oxide adsorbent was obtained.

[0073] Comparative Example 2 The method of Example 1 differs in that: Replace all calcium stearate with the modifier, i.e., no modification coating in step (6): grind diatomaceous earth E with a mass ratio of 90:10 and the modifier (a solution of hexadecyltrimethylammonium bromide and polyethyleneimine with a mass ratio of 1:1) at a speed of 28000 r / min for 2 min to obtain diatomaceous earth F.

[0074] The rest of the preparation process was the same as in Example 1, and the final diatomaceous earth-based nitrogen oxide adsorbent was obtained.

[0075] Comparative Example 3 The method of Example 1 differs in that: In step (7), during the drying and roasting process, the mixed atmosphere of nitrogen and HF gas with a volume ratio of 1:0.3 is replaced with a pure nitrogen atmosphere.

[0076] The rest of the preparation process was the same as in Example 1, and the final diatomaceous earth-based nitrogen oxide adsorbent was obtained.

[0077] Comparative Example 4 The method of Example 1 differs in that: In step (2), acid treatment: Diatomaceous earth A is soaked in HF aqueous solution with a concentration of 0.3 mol / L for 120 min, and then the soaked diatomaceous earth is rinsed with secondary deionized water until the washing solution is neutral to obtain diatomaceous earth B.

[0078] The rest of the preparation process was the same as in Example 1, and the final diatomaceous earth-based nitrogen oxide adsorbent was obtained.

[0079] Comparative Example 5 Acid treatment in step (2): Diatomaceous earth A was soaked in a 4.5 mol / L hydrochloric acid aqueous solution for 7 hours. Then, the soaked diatomaceous earth was rinsed with secondary deionized water until the washing solution was neutral to obtain diatomaceous earth B.

[0080] The rest of the preparation process was the same as in Example 1, and the final diatomaceous earth-based nitrogen oxide adsorbent was obtained.

[0081] Performance testing 1. Use a concentration of 500 mg / m³ 3 Nitrogen oxides were used for adsorption tests, with the remainder being nitrogen. The results of the saturated adsorption efficiency of the diatomaceous earth-based nitrogen oxide adsorbents in each embodiment and comparative example, tested by static adsorption method, are shown in Table 1.

[0082] 2. Test the carbon content in the known standard samples of lignite (52.3% C by mass) and anthracite (92.4% C by mass) respectively. Control group: Carbon content was tested using the three-section furnace method according to GB / T 476 standard, using lead dioxide / manganese dioxide adsorbent, and the operation was carried out according to national standard procedures.

[0083] Experimental group: Similar to the control group, except that the equipment and process were the same, but the lead dioxide / manganese dioxide adsorbent was replaced with the diatomaceous earth-based nitrogen oxide adsorbent used in the examples and comparative examples.

[0084] The test results are shown in Table 1.

[0085] Table 1 Test Results

[0086] The performance test results above show that the diatomaceous earth-based nitrogen oxide adsorbents prepared in Examples 1-5 have high nitrogen oxide adsorption efficiency and can accurately detect the carbon content in coal. This is presumably because the diatomaceous earth carrier has high purity, high specific surface area, and stable structure, and the chemically bonded functional groups on its surface exhibit excellent selectivity for nitrogen oxides. In particular, the diatomaceous earth-based nitrogen oxide adsorbents prepared when the modifier in Examples 3-4 contains cerium nitrate exhibit high nitrogen oxide adsorption efficiency. This is presumably because the invention introduces cerium nitrate, which preferentially loads onto the sites of polyethyleneimine, introduces a trivalent / tetravalent cerium redox cycle onto the adsorbent, further increasing the adsorption capacity for nitric oxide, and the final calcination to form cerium dioxide enhances the cross-linking of the framework.

[0087] The comparative examples, lacking the necessary technical solutions, showed significantly inferior performance compared to the examples. In Comparative Example 1, the modifier was entirely replaced with calcium stearate, and in Comparative Example 2, the modifier was entirely replaced with another modifier. The resulting diatomaceous earth-based nitrogen oxide adsorbent exhibited reduced adsorption efficiency and could not accurately detect the carbon content in coal. This further illustrates that the preparation method of this invention requires the synergistic effect of the coating agent calcium stearate and the modifier to achieve high selective adsorption of nitrogen oxides. In Comparative Example 3, replacing the nitrogen and HF gas mixture (volume ratio 1:0.3) with pure nitrogen during drying and roasting reduced the adsorption efficiency of the resulting diatomaceous earth-based nitrogen oxide adsorbent, making it unable to accurately detect the carbon content in coal, especially when detecting carbon content in lignite with high moisture content, where the deviation was even greater. In Comparative Example 4, only HF aqueous solution was used for acid treatment, and in Comparative Example 5, only hydrochloric acid aqueous solution was used for acid treatment. The resulting diatomaceous earth-based nitrogen oxide adsorbents exhibited reduced adsorption efficiency for nitrogen oxides and could not accurately detect the carbon content in coal.

[0088] The above experimental results further demonstrate the importance of the technical solution defined in this invention to its technical effect.

[0089] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for the preparation of a diatomaceous earth based nitrogen oxide adsorbent, characterized in that, The method comprises the following steps: (1) alkali treatment: ultrasonic treatment of diatomite with an alkaline aqueous solution to obtain diatomite A; (2) acid treatment: acid treatment of diatomite A to obtain diatomite B; (3) calcination: calcination of diatomite B to obtain diatomite C; (4) surface activation treatment: mixing of diatomite C, a surfactant and a dispersant, followed by first drying to obtain diatomite D; (5) coupling agent modification: mixing of diatomite D with a silane coupling agent to obtain, followed by second drying to obtain diatomite E; (6) modification coating: coating modification treatment of diatomite E, a coating agent and a modifier to obtain diatomite F; (7) drying and calcination: drying and calcination of diatomite F, followed by grinding to obtain diatomite-based nitrogen oxide adsorbent.

2. The method of claim 1, wherein the diatomaceous earth-based nitrogen oxide adsorbent is prepared by the steps of: The average particle size of the diatomite is 1-3 mm, the porosity is not less than 90%, the specific surface area is 50±10 m 2 / g; the alkaline aqueous solution contains 8-15% of alkaline hydroxide, 1-3% of sodium hexametaphosphate, and water in balance; the ultrasonic treatment conditions include an ultrasonic frequency of 40-50 Hz and a treatment time of 1-2 h.

3. The method of claim 1, wherein the diatomaceous earth-based nitrogen oxide adsorbent is prepared by the steps of: The acid treatment comprises first acid treatment and second acid treatment, the first acid treatment is carried out in the presence of an HF aqueous solution with a concentration of 0.1-0.3 mol / L, and the second acid treatment is carried out in the presence of an aqueous hydrochloric acid solution with a concentration of 4-5 mol / L.

4. The method of claim 1, wherein the diatomaceous earth-based nitrogen oxide adsorbent is prepared by the steps of: The calcination conditions comprise calcination at 400-450℃ for 1-2h.

5. The method of claim 1, wherein the diatomaceous earth-based nitrogen oxide adsorbent is prepared by the steps of: The surfactant is selected from polyoxyethylene fatty acid esters; the dispersant is selected from polyethylene glycol; the mass ratio of diatomite C, the surfactant and the dispersant is (90-92):(5-6):(3-4); the first drying conditions comprise a temperature of 105-120℃ and a time of 1.5-2.5h.

6. The method of claim 5, wherein the diatomaceous earth-based nitrogen oxide adsorbent is prepared by the steps of: The polyoxyethylene fatty acid ester is selected from at least one of polyoxyethylene 40 stearate, polyoxyethylene 100 stearate and polyoxyethylene 8 laurate, preferably polyoxyethylene 40 stearate; the polyethylene glycol has a degree of polymerization of 500-4000.

7. The method for preparing the diatomaceous earth-based nitrogen oxide adsorbent according to claim 1, characterized in that, The silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane and vinyltris(2-methoxyethoxy)silane; the mass ratio of diatomite D and the silane coupling agent is (90-92):(8-10); The coating agent is selected from calcium stearate; the modifier comprises hexadecyltrimethylammonium bromide and / or polyethyleneimine solution.

8. The method of claim 1, wherein the diatomaceous earth-based nitrogen oxide adsorbent is prepared by the steps of: The mass ratio of diatomite E, the coating agent and the modifier is (88-90):(5-6):(5-6); The coating modification treatment conditions comprise grinding at a rotation speed of 20000-35000 r / min for 1-2 min.

9. The method of making diatomite-based nitrogen oxide adsorbents according to any of claims 1-8, characterized in that, The drying and calcination conditions comprise heating at a rate of 10-20℃ / min to 400-450℃ at room temperature and staying for 10-20 min.

10. A diatomaceous earth based nitric oxide adsorbent, characterized in that, The diatomite-based nitrogen oxide adsorbent is prepared by the method for preparing diatomite-based nitrogen oxide adsorbent according to any one of claims 1-9.

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