A method for preparing an arsenic adsorbent for coal-fired flue gas

Abstract

This invention relates to a method for preparing an arsenic adsorbent for coal-fired flue gas. The steps include preparing nano-Fe2O3 by co-precipitation, preparing spherical adsorbent cores with a diameter of 20-30 mm by impregnation, and then uniformly spraying a mixed solution of potassium nitrate, lanthanum nitrate, and yttrium nitrate onto the surface of the spherical adsorbent. The adsorbent is then activated by drying and calcination to obtain the adsorbent. The arsenic removal adsorbent prepared by this invention can be applied to emission purification systems for arsenic-containing flue gas in various industries. It exhibits excellent arsenic adsorption efficiency, good resistance to sulfur and water, and high arsenic adsorption capacity, as well as superior mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, specifically relating to a method for preparing an arsenic adsorbent for coal-fired flue gas. Background Technology

[0002] Coal-fired power plants, non-ferrous metal smelting, waste incineration, and the petrochemical industry are the main sources of arsenic emissions into the atmosphere. These arsenic emissions tend to remain in the gaseous state and are highly volatile, persistent, and bioaccumulative in the environment, posing a threat to human health and the ecological environment and attracting great attention.

[0003] A more prominent problem with arsenic emissions is that they can poison SCR denitrification catalysts. SCR technology can remove most nitrogen oxides from flue gas and is widely used in the flue gas treatment of fossil fuel power plants and various boilers. However, once the flue gas contains trace amounts of arsenic, it will accumulate on the denitrification catalyst. When it reaches a certain concentration, the expensive denitrification catalyst will be poisoned and deactivated, and it will be difficult to regenerate.

[0004] Therefore, reducing arsenic emissions and minimizing the contact between arsenic-containing flue gas and catalysts has become a major challenge in flue gas emission treatment. Taking the thermal power industry, which has the highest atmospheric arsenic emissions, as an example, current arsenic pollution control in arsenic-containing coal combustion is divided into three aspects: pre-combustion pretreatment, in-process treatment, and post-combustion control. Pre-combustion pretreatment mainly refers to coal processing technologies, including coal preparation, power coal blending, briquettes, and coal-water slurry, which generally reduce arsenic pollution by improving coal combustion efficiency and reducing flue gas emissions. In-process treatment involves adding arsenic-fixing agents, such as kaolin, limestone, and bauxite, during combustion to fix arsenic in the coal residue, effectively controlling the emission of gaseous arsenic. Post-combustion arsenic removal mainly utilizes dust removal control units and hazardous gas control units in power plant air pollutant control equipment. These pollution control facilities can reduce arsenic emissions in flue gas during coal combustion to a certain extent, but they also have drawbacks. Dust removal control units require frequent bag replacement, and some hazardous gas control units can suffer from catalyst arsenic poisoning due to long-term arsenic accumulation.

[0005] The research and development of post-combustion arsenic removal technology has become a key focus in the environmental protection field. The development of sulfur- and water-resistant flue gas arsenic removal adsorbents has broad application prospects. Summary of the Invention

[0006] This invention aims to address the problem of high arsenic content in flue gas emitted from the thermal power and non-ferrous metal smelting industries, which can easily lead to catalyst poisoning, by providing a method for preparing an arsenic adsorbent for coal-fired flue gas.

[0007] This invention adopts the following technical solution: a method for preparing an arsenic adsorbent for coal-fired flue gas, comprising the following steps:

[0008] (1) Preparation of nano Fe2O3 powder: Ammonia water was slowly added dropwise to ferric nitrate solution under stirring, and the pH value of the mixed solution was controlled at 10-12. The solution was aged at room temperature for 10-18 hours and then filtered. The precipitate was washed with water and anhydrous ethanol until the washing solution was neutral. The precipitate was placed in a drying oven, dried and calcined, and then ground to obtain nano Fe2O3 powder.

[0009] (2) Preparation of spherical adsorbent core: The nano Fe2O3 obtained in step (1) and ammonium heptamolybdate and cerium nitrate hexahydrate are added to a formamide aqueous solution and ultrasonically prepared into a sol; under stirring conditions, γ-Al2O3, CaSO4 and hydroxyethyl cellulose are sequentially impregnated with the sol to obtain mud; spherical adsorbent cores with a diameter of 20~30mm are obtained by particle forming process;

[0010] (3) Preparation of spherical adsorbent surface agent: A mixed solution of potassium nitrate, lanthanum nitrate and yttrium nitrate is uniformly sprayed onto the surface of the spherical adsorbent obtained in step (2) and dried at 105°C;

[0011] (4) Calcination activation: The spherical adsorbent sprayed in step (3) is calcined and activated at 500~600℃ for 4~6h in an air atmosphere to obtain a sulfur-resistant and water-resistant flue gas arsenic removal adsorbent.

[0012] Furthermore, in step (1), the precipitate is dried at 100-105℃ for 4-6 hours and calcined in air at 450-550℃ for 4-6 hours.

[0013] Furthermore, in step (2), the temperature of the ultrasonic treatment stage is 50~80℃, the power of the ultrasonic treatment stage is 150~250W, and the ultrasonic treatment stage time is 3~6h.

[0014] Furthermore, in step (2), the volume ratio of sol to added powder is 0.8-1.

[0015] Furthermore, in step (2), the amount of hydroxyethyl cellulose added is 6-9% of the mass of CaSO4.

[0016] Furthermore, in step (3), the amount of spherical adsorbent surface agent sprayed is 1-5% of the mass of the spherical adsorbent core.

[0017] Furthermore, the specific surface area of ​​the adsorbent is 100~180m². 2 / g, pore volume 0.30~1.10cm³ 3 / g.

[0018] The components of a coal-fired flue gas arsenic adsorbent, by mass percentage, are: Fe2O3 15~20%, MoO3 12~18%, CaSO4 15~20%, Al2O3 19~28%, CeO2 19~28%, K2O 1~2%, La2O3 0.5~1%, Y2O3 0.5~1%.

[0019] The advantages of this invention are as follows:

[0020] (1) The adsorbent γ-Al2O3 and CeO2 composite carrier prepared in this invention is used as the core and nano Fe2O3 is used as the adsorption center. The carrier has a high specific surface area and high pore volume, which can better disperse nano Fe2O3, thereby increasing the effective contact area between the adsorption center and the arsenic-containing flue gas, so that it can better exert its adsorption efficiency.

[0021] (2) The core of the adsorbent prepared by the present invention is supplemented with MoO3 and CaSO4 as auxiliary agents, which not only greatly improves the mechanical strength of the core, but also has good anti-sulfur and anti-water function, preventing sulfur adsorption in flue gas and clogging of micropores.

[0022] (3) The adsorbent prepared by the present invention uses K2O, La2O3 and Y2O3 as the spray coating. The spray coating can reduce the adsorption of sulfur and water by the core of the adsorbent. Among them, La2O3 and Y2O3 are rare earth metal oxides with good adsorption capacity for arsenic, which can enhance the adsorbent's ability to capture arsenic. Attached Figure Description

[0023] Figure 1 The surface microstructures of the embodiments and comparative examples of the present invention are shown under a scanning electron microscope.

[0024] Figure 2 The figures show the arsenic adsorption efficiency of simulated arsenic-containing flue gas under experimental conditions in the embodiments and comparative examples of the present invention. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be further described below in conjunction with specific examples.

[0026] Example 1: A method for preparing a sulfur- and water-resistant flue gas arsenic removal adsorbent, the steps of which are as follows:

[0027] (1) Under stirring conditions, 1 mol / L ammonia water was slowly added dropwise to 5 mol / L ferric nitrate solution until the pH value was 12. After aging at room temperature for 18 h, the precipitate was separated by filtration. The precipitate was washed with water and anhydrous ethanol and then dried in a drying oven at 105 °C. The dried precipitate was calcined at 500 °C in air atmosphere for 4 h and then ground to obtain nano Fe2O3 powder.

[0028] (2) Take 150g of nano Fe2O3 obtained in step (1), 147.13g of ammonium heptamolybdate, and 700.62g of cerium nitrate hexahydrate and add them to a 5% formamide aqueous solution. Set the ultrasonic oscillator to a water temperature of 80℃, an ultrasonic power of 250W, and an ultrasonic duration of 6h to make a sol. Mix the obtained sol with 280g of γ-Al2O3, 150g of CaSO4, and 13g of hydroxyethyl cellulose powder at a volume ratio of 0.8:1 and stir for 2h to obtain mud.

[0029] (3) The mud obtained in step (2) is aged for 24 hours, extruded into long strips by a three-dimensional hydraulic press, cut and placed into an austenitic mold and heated at 200°C for 6 hours to complete the molding, and a spherical adsorbent core with a diameter of 20 mm is obtained.

[0030] (4) Spray a mixed solution of 10.73g potassium nitrate, 13.29g lanthanum nitrate hexahydrate and 16.96g yttrium nitrate hexahydrate, with a total solute mass concentration of 10%, onto the spherical adsorbent core obtained in step (3), and dry it at 105°C;

[0031] (5) The spherical adsorbent obtained in step (4) is activated by calcination at 500°C for 4 hours in air atmosphere to obtain a sulfur-resistant and water-resistant flue gas arsenic removal adsorbent. The weight percentage of each component in the adsorbent is: Fe2O3 15%, MoO3 12%, CaSO4 15%, Al2O3 28%, CeO2 28%, K2O 1%, La2O3 0.5%, Y2O3 0.5%. Example 2:

[0032] A method for preparing a sulfur- and water-resistant flue gas arsenic removal adsorbent includes the following steps:

[0033] (1) Under stirring conditions, 1 mol / L ammonia water was slowly added dropwise to 5 mol / L ferric nitrate solution until the pH value was 11. After aging at room temperature for 14 h, the precipitate was separated by filtration. The precipitate was washed with water and anhydrous ethanol and then dried in a drying oven at 105 °C. The dried precipitate was calcined at 550 °C in air atmosphere for 4 h and then ground to obtain nano Fe2O3 powder.

[0034] (2) Take 185g of nano Fe2O3, 190.04g of ammonium heptamolybdate, and 550.47g of cerium nitrate hexahydrate obtained in step (1) and add them to a 5% formamide aqueous solution. Set the ultrasonic oscillator to a water temperature of 50℃, an ultrasonic power of 150W, and an ultrasonic duration of 4h to prepare a sol. The obtained sol is then mixed with 220g of γ-Al2O3, 185g of CaSO4, and 16g of hydroxyethyl cellulose powder and impregnated and stirred in equal volume. After stirring for 2h, mud is obtained.

[0035] (3) The mud obtained in step (2) is aged for 24 hours, extruded into long strips by a three-dimensional hydraulic press, cut and placed into an austenitic mold and heated at 200°C for 6 hours to complete the molding, and a spherical adsorbent core with a diameter of 30 mm is obtained.

[0036] (4) Spray a mixed solution consisting of 16.01g potassium nitrate, 26.58g lanthanum nitrate hexahydrate and 33.92g yttrium nitrate hexahydrate, with a total solute mass concentration of 10%, onto the spherical adsorbent core obtained in step (3), and dry it at 105°C;

[0037] (5) The spherical adsorbent obtained in step (4) is activated by calcination at 550°C for 4 hours in air atmosphere to obtain a sulfur-resistant and water-resistant flue gas arsenic removal adsorbent. The weight percentage of each component in the adsorbent is: Fe2O3 18.5%, MoO3 15.5%, CaSO4 18.5%, Al2O3 22%, CeO2 22%, K2O 1.5%, La2O3 1%, Y2O3 1%.

[0038] Example 3:

[0039] A method for preparing a sulfur- and water-resistant flue gas arsenic removal adsorbent includes the following steps:

[0040] (1) Under stirring conditions, 1 mol / L ammonia water was slowly added dropwise to 5 mol / L ferric nitrate solution until the pH value was 10. After aging at room temperature for 10 h, the precipitate was separated by filtration. The precipitate was washed with water and anhydrous ethanol and then dried in a drying oven at 105 °C. The dried precipitate was calcined at 450 °C in air atmosphere for 4 h and then ground to obtain nano Fe2O3 powder.

[0041] (2) Take 200g of nano Fe2O3 obtained in step (1), 220.69g of ammonium heptamolybdate, and 475.41g of cerium nitrate hexahydrate and add them to a 5% formamide aqueous solution. Set the ultrasonic oscillator to a water temperature of 50℃, an ultrasonic power of 250W, and an ultrasonic duration of 6h to make a sol. The obtained sol is mixed with 190g of γ-Al2O3, 200g of CaSO4 and 16g of hydroxyethyl cellulose powder and impregnated and stirred in equal volume. After stirring for 2h, mud is obtained.

[0042] (3) The mud obtained in step (2) is aged for 24 hours, extruded into long strips by a three-dimensional hydraulic press, cut and placed into an austenitic mold and heated at 200°C for 6 hours to complete the molding, and a spherical adsorbent core with a diameter of 30 mm is obtained.

[0043] (4) Spray a mixed solution consisting of 21.46g potassium nitrate, 26.58g lanthanum nitrate hexahydrate and 33.92g yttrium nitrate hexahydrate, with a total solute mass concentration of 10%, onto the spherical adsorbent core obtained in step (3), and dry it at 105°C;

[0044] (5) The spherical adsorbent obtained in step (4) is activated by calcination at 600°C for 6 hours in air atmosphere to obtain a sulfur-resistant and water-resistant flue gas arsenic removal adsorbent. The weight percentage of each component in the adsorbent is: Fe2O3 20%, MoO3 18%, CaSO4 20%, Al2O3 19%, CeO2 19%, K2O 2%, La2O3 1%, Y2O3 1%.

[0045] Comparative Example 1:

[0046] Same as Example 1, but ordinary Fe2O3 powder was used instead of nano Fe2O3 powder for preparation.

[0047] The weight percentages of each component in the obtained adsorbent are: Fe2O3 15%, MoO3 12%, CaSO4 15%, Al2O3 28%, CeO2 28%, K2O 1%, La2O3 0.5%, Y2O3 0.5%.

[0048] Comparative Example 2:

[0049] Same as in Example 1, but without adding ammonium heptamolybdate, and with the addition of cerium nitrate and γ-Al2O3 to balance the mass.

[0050] Comparative Example 3:

[0051] Similar to Example 1, the adsorbent was obtained by direct calcination activation without spraying a mixed solution of potassium nitrate, lanthanum nitrate, and yttrium nitrate.

[0052] The weight percentages of each component in the obtained adsorbent are: Fe2O3 15.3%, MoO3 12.2%, CaSO4 15.3%, Al2O3 28.6%, CeO2 28.6%.

[0053] The adsorbents prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to BET surface area testing, and their surface physical properties, such as surface area and micropore volume, were measured. The BET test results are shown in Table 1.

[0054] Table 1 BET Test Results

[0055]

[0056] The surface microstructure of the adsorbents prepared in Examples 1-3 and Comparative Examples 1-3 was observed using scanning electron microscopy. The SEM images are shown below. Figure 1 As shown.

[0057] The adsorbents prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to arsenic adsorption experiments. A fixed-bed evaluation method was used, with an adsorption temperature of 300℃. The simulated flue gas was As(g) 10ppb, NO 500ppm, SO2 500ppm, H2O 5%, O2 5%, with equilibrium N2 and a space velocity of 2000h⁻¹. -1 The adsorption efficiency was analyzed online using gas chromatography-mass spectrometry. The arsenic adsorption efficiency was as follows: Figure 2 As shown.

[0058] The arsenic adsorption capacity of the samples from Examples 1-3 and Comparative Examples 1-3 that showed complete adsorption was analyzed by X-ray fluorescence spectroscopy. The arsenic adsorption capacity is shown in Table 2.

[0059] Table 2 Arsenic Adsorption Capacity

[0060]

[0061] Combination Figure 1 As shown in Table 1, the pore structure in the SEM images of Comparative Examples 1, 2, and 3 does not significantly improve the surface area, and the micropore volume is not high. The adsorbent prepared by the method of this invention has a larger specific surface area and micropore volume, and its gas adsorption capacity is stronger and its theoretical adsorption capacity is higher.

[0062] Combination Figure 2 As shown in Table 2, the arsenic adsorption efficiency and capacity of the adsorbent prepared by the method of the present invention are better than those of the adsorbents obtained in Comparative Examples 1, 2 and 3. Under experimental conditions, the examples can achieve an adsorption efficiency of 89% and an adsorption capacity of 54 mg / g.

[0063] As shown in Comparative Example 1, nano Fe2O3, as the main active ingredient, cannot be replaced by ordinary Fe2O3; in Comparative Example 2, MoO3, as an additive to enhance the adsorbent's resistance to sulfur and water, can effectively delay the decrease in adsorption efficiency, increase adsorption capacity, and prevent adsorbent deactivation; in Comparative Example 3, the K2O, La2O3, and Y2O3 coatings can effectively improve the adsorbent's ability to capture arsenic.

[0064] In summary, the arsenic adsorbent proposed in this invention has the advantages of high adsorption efficiency, good sulfur and water resistance, and large adsorption capacity. It can be used for arsenic adsorption and purification under complex flue gas conditions and has broad application prospects.

Claims

1. A method for preparing an arsenic adsorbent for coal-fired flue gas, characterized in that: Includes the following steps: (1) Preparation of nano Fe2O3 powder: Ammonia water was slowly added dropwise to ferric nitrate solution under stirring, and the pH value of the mixed solution was controlled at 10-12. The solution was aged at room temperature for 10-18 hours and then filtered. The precipitate was washed with water and anhydrous ethanol in turn until the washing solution was neutral. The precipitate was placed in a drying oven to dry and calcine. After grinding, nano Fe2O3 powder was obtained. (2) Preparation of spherical adsorbent core: The nano Fe2O3 obtained in step (1) and ammonium heptamolybdate and cerium nitrate hexahydrate were added to a 5% formamide aqueous solution and ultrasonically prepared into a sol; γ-Al2O3, CaSO4 and hydroxyethyl cellulose were impregnated with the above sol under stirring conditions to obtain mud. Through a particle forming process, spherical adsorbent cores with a diameter of 20~30mm are obtained; (3) Preparation of spherical adsorbent surface agent: A mixed solution of potassium nitrate, lanthanum nitrate and yttrium nitrate is uniformly sprayed onto the surface of the spherical adsorbent obtained in step (2) and dried at 100~105℃; (4) Calcination activation: The spherical adsorbent sprayed in step (3) is calcined and activated at 500~600℃ for 4~6h in an air atmosphere to obtain a sulfur-resistant and water-resistant flue gas arsenic removal adsorbent.

2. The method for preparing the arsenic adsorbent for coal-fired flue gas as described in claim 1, characterized in that: In step (1), the precipitate is dried at 100~105℃ for 4~6h and calcined in air at 450~550℃ for 4~6h.

3. The method for preparing the arsenic adsorbent for coal-fired flue gas as described in claim 1, characterized in that: In step (2), the temperature of the ultrasonic treatment stage is 50~80℃, the power of the ultrasonic treatment stage is 150~250W, and the ultrasonic treatment time is 3~6h.

4. The method for preparing the arsenic adsorbent for coal-fired flue gas as described in claim 1, characterized in that: In step (2), the amount of hydroxyethyl cellulose added is 6-9% of the mass of CaSO4.

5. The method for preparing the arsenic adsorbent for coal-fired flue gas as described in claim 1, characterized in that: In step (3), the amount of coating on the surface of the spherical adsorbent is 1-5% of the mass of the core of the spherical adsorbent.

6. The method for preparing the arsenic adsorbent for coal-fired flue gas as described in claim 1, characterized in that: The specific surface area of ​​the adsorbent is 100~180m². 2 / g, pore volume 0.30~1.10cm³ 3 / g.

7. The method for preparing the arsenic adsorbent for coal-fired flue gas as described in claim 1, characterized in that: The mass percentages of each component in the prepared coal-fired flue gas arsenic adsorbent are as follows: Fe2O3 15~20%, MoO3 12~18%, CaSO4 15~20%, Al2O3 19~28%, CeO2 19~28%, K2O 1~2%, La2O3 0.5~1%, Y2O3 0.5~1%.

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