Molded selenium-based adsorbent, preparation and application of molded selenium-based adsorbent in efficient demercuration of flue gas

Abstract

The invention relates to a formed selenium-based adsorbent, preparation and application of the formed selenium-based adsorbent in efficient demercuration of flue gas, and belongs to the technical field of flue gas mercury pollution prevention and control. The preparation method comprises the following steps: firstly preparing a spherical porous adsorbent carrier with a high specific surface area, then preparing a high-valence selenide solution based on an in-situ reduction method, putting the carrier into the solution, and modifying the surface of the carrier; and directly performing in-situ reduction on the high-valence selenium with uniformly distributed pores by using a reducing agent, anchoring the reduced elemental nano-selenium on the surface of the spherical carrier, and drying to form the spherical selenium-loaded adsorbent with fully exposed selenium active sites and uniform loading, and the adsorbent can be applied to fixed bed filler type mercury removal. The prepared adsorbent has excellent selectivity on mercury in complex flue gas, the mercury removal efficiency is up to 90% or above, the adsorption capacity is up to 101.04 mg / g, and the adsorption capacity is 300 times that of a traditional mercury removal material activated carbon.

Description

Technical Field

[0001] The invention belongs to the technical field of flue gas mercury pollution prevention and control, and specifically relates to a shaped selenium-based adsorbent, and its preparation and application in efficient mercury removal from flue gas. Background Art

[0002] Mercury and its compounds are highly toxic, can be transmitted over long distances, and can accumulate in organisms for a long time. Coal combustion has become the second largest source of mercury pollution in the world. Mercury in coal flue gas mainly exists in three forms: gaseous elemental mercury (Hg 0 ), oxidized mercury (Hg 2+ ) and particulate mercury (Hg p ). Due to Hg 0 It is chemically stable, insoluble in water and not easy to precipitate, so it is difficult to remove it with the existing pollutant control devices in coal-fired power plants. Therefore, flue gas mercury removal technology is a hot topic in the field of coal-fired flue gas purification. The existing demercuration technology mainly uses the powder adsorbent injection method, but this technology has many defects: the flue gas flow rate is fast, and the short residence time of the powder adsorbent and mercury is difficult to ensure a high demercuration efficiency due to the limited mass transfer coefficient; the adsorbent is removed by the electrostatic precipitator (ESP) after demercuration, resulting in the adsorbent being unable to be recovered, and the mercury-containing adsorbent is not easy to separate after mixing with fly ash, which will cause the risk of secondary release of mercury. In contrast, the fixed bed packing adsorbent can ensure that the adsorbent is fully in contact with the flue gas in a static state, thereby increasing the residence time of the mercury-containing gas and the adsorbent. At the same time, the mercury-containing adsorbent can be centrally processed, which is convenient for the subsequent recovery and utilization of mercury.

[0003] However, powdered adsorbents as fixed bed fillers have high bed pressure drop due to their small particle size and low bed porosity, making industrial applications difficult. In addition, the mass transfer efficiency of mercury between active components will also be significantly reduced, thus affecting the flue gas mercury removal efficiency.

[0004] Molded filler-type mercury removal adsorbents can solve the problem of high pressure drop, but the mercury removal effect of existing molded mercury adsorbents is still not ideal. This is mainly because the number of active sites on the molded adsorbent carrier is limited, making it difficult to maintain high mercury removal efficiency. Existing mercury adsorbents are generally prepared by traditional impregnation methods, but this method results in a small number of active sites and uneven distribution.

[0005] At present, the mercury removal capacity of most adsorbents is still at a low level, and is not suitable for environments with high mercury concentrations and complex flue gas compositions such as smelting and incineration. Therefore, it is urgent to develop a mercury removal adsorbent with high adsorption capacity and high adsorption rate to effectively meet various flue gas mercury removal needs. Summary of the invention

[0006] The present invention aims to solve the problems of existing mercury removal adsorbents, such as short contact time with mercury, low utilization rate of active components, difficulty in handling mercury-containing adsorbents, and low void ratio and high bed pressure drop in fixed beds of existing nano adsorbents, and provides a method for preparing a shaped selenium-based adsorbent for efficiently removing mercury from flue gas and its application.

[0007] According to a first aspect of the present invention, there is provided a method for preparing a shaped selenium-based adsorbent, comprising the following steps:

[0008] (1) mixing a carrier raw material and a binder, and then adding water to form a viscous mixture; the carrier raw material is silicon dioxide, aluminum oxide, zinc oxide or zeolite, and the binder is microcrystalline cellulose, polyurethane, cellulose ether or modified starch;

[0009] (2) adding the mixture obtained in step (1) into an extruder, extruding it into a strip bundle, and then putting the strip bundle material into a spheronizer for spheronization to finally obtain a spherical molding carrier wet material; and then drying it to obtain a porous spherical carrier;

[0010] (3) preparing a selenide solution, wherein the selenide contains oxygen, and then placing the porous spherical carrier obtained in step (2) in the selenide solution, and uniformly depositing the ions containing the selenium element in the selenide solution on the surface of the porous spherical carrier by ultrasound; the selenide solution is a selenate solution, a selenite solution, a selenium dioxide solution, a selenic acid solution or a selenous acid solution;

[0011] (4) adding a reducing agent, wherein the reducing agent is used to directly reduce the selenium-containing ions on the surface of the porous spherical carrier into active nano-selenium in situ and anchor them between the pores of the porous spherical carrier, and then ageing and drying to obtain a shaped selenium-based adsorbent.

[0012] Preferably, the reducing agent is ascorbic acid, glutathione, sodium thiosulfate or sodium bisulfite.

[0013] Preferably, in step (3), the mass concentration of selenide in the selenide solution is 10%-30%.

[0014] Preferably, in step (1), the mass ratio of the carrier raw material, the binder and water is in the range of (2-5): (7-10): 20.

[0015] Preferably, in step (1), the carrier raw material is micron-sized powder.

[0016] Preferably, in step (4), after adding the reducing agent, the alkali solution is added.

[0017] According to another aspect of the present invention, a prepared shaped selenium-based adsorbent is provided.

[0018] Preferably, the loading amount of selenium in the shaped selenium-based adsorbent is 10%-30%.

[0019] According to another aspect of the present invention, there is provided the use of the shaped selenium-based adsorbent for flue gas mercury removal.

[0020] Preferably, the shaped selenium-based adsorbent is used as a fixed bed filler for flue gas mercury removal.

[0021] Preferably, the particle size of the shaped selenium-based adsorbent is 3 mm-5 mm.

[0022] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0023] (1) The adsorbent prepared by the present invention has excellent selectivity for mercury in complex flue gas. The adsorbent has the best mercury removal performance when the particle size is 3 mm, the selenium loading is 25%, and the reaction temperature is 150°C. The mercury removal efficiency is as high as over 90%, and the adsorption amount is as high as 101.04 mg / g, which is 300 times the adsorption capacity of activated carbon, a traditional mercury removal material.

[0024] (2) The present invention anchors the active substance elemental selenium on the surface of the porous carrier by an in-situ reduction method. Compared with the conventional impregnation method, the effective loading amount of selenium is increased by 50%.

[0025] (3) The adsorbent can be used in a fixed bed packing method, overcoming the shortcomings of excessive bed pressure drop caused by the accumulation of powdered adsorbent and the difficulty in maintaining sufficient residence time in the injection method, and has broad industrial application prospects.

[0026] (4) The present invention selects a low-cost, non-toxic carrier material and prepares a porous carrier material with a developed pore structure through a simple and operable extrusion spheronization method.

[0027] (5) The present invention has the characteristics of mild preparation conditions, low synthesis cost, and mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart for preparing a porous spherical carrier using silica in Example 1.

[0029] Figure 2 This is a flow chart for preparing a shaped selenium-based adsorbent prepared by the in-situ reduction method (a) mentioned in the example and the impregnation method mentioned in comparative example 1 (b).

[0030] Figure 3The BET test graphs of the silica-based porous carrier and the shaped selenium-based adsorbent prepared in Example 2. Both materials are type IV adsorbents with typical H1 hysteresis loops, and both are mesoporous materials with developed pore structures and high specific surface areas, which are 215.33 m 2 / g and 190.26m 2 / g, which has great potential for mercury adsorption.

[0031] Figure 4 The following are scanning electron microscope images (SEM) of the silica-based porous carrier and the spherical selenium-based adsorbent prepared in Example 2. The surface of the porous carrier is irregularly flaky. The spherical selenium-based adsorbent has many short rod branches distributed on the surface, which indicates that the elemental selenium is successfully distributed on the carrier surface in the form of rods, the surface of the material becomes rough, and the pore structure is more complex, which is conducive to the subsequent removal of Hg. 0 adsorption.

[0032] Figure 5 It is a fixed bed reaction platform for the flue gas mercury adsorption experiment in the embodiment.

[0033] Figure 6 It is a mercury desorption reaction platform of the mercury-containing adsorbent in the embodiment.

[0034] Figure 7 The mercury removal efficiency of the M-Se / SiO2 shaped selenium-based adsorbent prepared by the in-situ reduction method in Examples 2 to 6 and Comparative Example 1 is 50.10% when the selenium is loaded on the porous spherical carrier. With the increase of the selenium loading, the mercury removal efficiency is finally increased to 92.5%. This is because the increase of active sites promotes the removal of Hg 0 However, as the selenium loading increased, the mercury removal efficiency decreased. This is because excessive selenium would affect the uniformity of the adsorbent surface structure and thus hinder the mercury removal from the adsorbent. 0 In addition, the mercury removal efficiency of the formed selenium-based adsorbent using the impregnation method is only 52.3%, because this method does not effectively load selenium.

[0035] Figure 8 The figure is a graph of mercury removal efficiency of shaped selenium-based adsorbents with different particle sizes mentioned in Examples 1, 2, 8, and 9. The particle size of the adsorbent is 50 μm, and the mercury removal efficiency is 95.1%. When the size of the adsorbent is increased to 1 mm and 3 mm, Hg 0The removal efficiency of mercury dropped to 93.2% and 92.5%, respectively. However, when the particle size reached 5 mm, the mercury removal efficiency dropped to 89.0%, because the adsorbent with larger particle size was filled in the quartz reactor with larger gaps, resulting in a shorter residence time of mercury-containing gas, which had a negative impact on the adsorption of mercury. If the particle size of the adsorbent is smaller, good mercury removal can be achieved. However, in a fixed bed reactor, the smaller the particle size (50 μm, 1 mm), the greater the gas resistance flowing through the reactor, which has an adverse effect on the operation of the equipment.

[0036] Fig. 9 The figure shows the mercury removal efficiency of the shaped selenium-based adsorbent at different temperatures. 0 The adsorption performance was tested for 1 hour. When the reaction temperature increased from 90°C to 150°C, the mercury removal efficiency increased dramatically from 70.4% to 92.5%. The results show that increasing the temperature is beneficial to mercury removal because higher temperatures can 0 The mercury removal efficiency is improved by obtaining more kinetic energy between the active sites of Se and the molded selenium-based adsorbent. However, when the reaction temperature is increased from 150°C to 180°C, Hg 0 The removal efficiency dropped to 80.1%. When the reaction temperature was higher than 150°C, the elemental selenium on the selenium adsorbent was desorbed. Since selenium loaded on the surface of silica may have a certain adsorption energy, when the temperature of the demercuration experiment increased, the high temperature may destroy the chemical bond length, causing the elemental selenium to be released in the form of gas, resulting in a reduction in active sites and a reduction in the demercuration efficiency of the adsorbent.

[0037] Fig.10 The flow field prediction results of the shaped selenium-based adsorbents of different particle sizes mentioned in Example 1, Example 2, Example 8, and Example 9 were carried out by Fluent numerical simulation software. Particles with a diameter of 1 mm caused a significant temperature drop due to the influence on the temperature field; the temperature of the gas dropped sharply when flowing through the bed. The optimal reaction temperature for mercury adsorption is 150°C, and the obvious cooling zone observed in the temperature contour is not conducive to the removal of mercury. In contrast, particles with diameters of 3 mm and 5 mm have little effect on the temperature field. In addition, the pressure contour map shows that the pressure drops of the three particle sizes are 17.98Pa, 2Pa, and 1.68Pa, respectively, among which the pressure drop caused by 1mm particles is larger, and the pressure drop caused by 3mm and 5mm particles is negligible in the bed. In addition, 1mm particles exhibit a lower porosity, resulting in a significant reduction in the gas flow velocity through the bed. Appropriate superficial velocity is essential for effective mercury removal.

[0038] Fig.11The mercury saturation adsorption curve of the molded selenium-based adsorbent in Example 2 under nitrogen atmosphere. The figure below shows the breakthrough curves of the molded selenium-based adsorbent and commercial activated carbon at 150°C in a complex flue gas atmosphere, and its mercury adsorption capacity is as high as 101.04 mg / g. In contrast, the activated carbon quickly saturated and returned to the initial concentration in less than two hours, and the saturated adsorption capacity value was only 0.34 mg / g, indicating that the molded selenium-based adsorbent is an adsorbent with high mercury adsorption capacity and great application value.

[0039] Fig.12 It is the Hg-TPD curve of the mercury removal adsorbent in Example 2 of the present invention. The Hg-TPD test is used to identify the mercury species on the adsorbent after mercury removal and determine the mercury content by high temperature release measurement. After Hg is removed in N2 atmosphere, the Hg adsorbed by the adsorbent begins to decompose at 200-400℃ and reaches a peak at about 268℃. After 400℃, Hg 0 The concentration was below the detectable level, indicating that the sample had been completely decomposed, proving that the substance was mercury selenide. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0041] Figure 1 This is a flow chart for preparing a porous spherical carrier using silica in Example 1.

[0042] The present invention provides a method for preparing a shaped selenium-based adsorbent, the method comprising the following steps:

[0043] (1) Using the extrusion spheronization method to prepare spherical adsorbent carriers with well-developed pore structures;

[0044] (2) Based on the in-situ reduction method, a high-valent selenium ion solution is prepared, and a porous spherical carrier is placed in the solution to modify its surface;

[0045] (3) using a reducing agent to directly reduce the high-valent selenium evenly distributed in the pores in situ, so that the reduced elemental nano-selenium is anchored on the surface of the spherical carrier;

[0046] (4) Through water washing, centrifugation and drying, a selenium-based adsorbent with fully exposed selenium active sites and uniform loading is formed.

[0047] The present invention provides a method for preparing a shaped selenium-based adsorbent, which specifically comprises the following steps:

[0048] (1) One of silicon dioxide / alumina / zinc oxide / zeolite is used as a carrier raw material, and one of microcrystalline cellulose (MCC) / polyurethane / cellulose ether / modified starch is used as a binder. After they are fully mixed, deionized water is added and stirred to make the mixture viscous. The ratio of raw material: binder: water is preferably 5:7:20. The carrier raw material is at least micron-level powder.

[0049] (2) The product obtained in step (1) is extruded into a strip by an extruder (speed range is 500-1200 r / min), and then the strip product is moved to a spheronizer (speed range is 200-1000 r / min), wherein the speed setting of the spheronizer determines the size of the subsequent formed particles. The specific recommended parameters are shown in the following table:

[0050]

[0051] (3) The product obtained in step (2) is centrifuged and washed with water, and then dried at 100° C. for 12 hours to obtain a porous spherical carrier.

[0052] (4) Selenium oxygen compounds (including selenate, selenite, selenium dioxide, selenic acid, and selenous acid) are added into water and stirred until completely dissolved to obtain a saturated aqueous solution containing high-valent selenium ions.

[0053] (5) Under normal temperature conditions, the porous spherical carrier obtained in step (3) is immersed in the saturated solution in step (2), and ultrasonicated for 1-3 hours, and statically aged for 12-18 hours, so that the high-valent selenium ions are uniformly deposited on the surface of the porous spherical carrier; the loading amount of the selenium ions on the porous spherical carrier ranges from 10% to 30%.

[0054] (6) Using easily available reducing agents (ascorbic acid, glutathione, sodium thiosulfate, sodium bisulfite) as raw materials, adding them into water and stirring until completely dissolved to obtain a saturated aqueous solution.

[0055] (7) The porous spherical carrier in step (5) is completely immersed in the saturated solution in step (6), and the reducing agent molecules in the solution quickly reduce the high-valent selenium ions on the surface of the carrier to elemental selenium and evenly load it between the pores. During this period, 1-5% sodium hydroxide solution is added to adjust it to weak alkalinity. After standing at room temperature for 2-8 hours, centrifugal washing is performed to remove excess metal ion impurities, and then drying is performed for 6-12 hours to obtain a molded selenium-based adsorbent. The molar ratio of high-valent selenium ions to reducing agent is 1:2, and the drying temperature is 60-80°C.

[0056] Furthermore, the purpose of adding sodium hydroxide solution to adjust to weak alkalinity is because high-valent selenium ions undergo ionization and hydrolysis reactions in aqueous solution. In an acidic environment, the generation of selenious acid (H2SeO3) will hinder the reduction process of sodium selenite. Under alkaline conditions, sodium hydroxide can neutralize selenious acid to generate selenate, thereby avoiding the inhibition of the reduction reaction by the accumulation of selenious acid.

[0057] The following are specific examples and comparative examples.

[0058] Example 1

[0059] The ratio of silicon dioxide: cellulose: water was set to 5:7:20. After the raw materials were mixed, the speed of the extruder was set to 500 r / min, and the speed of the spheronizer was set to 500 r / min to obtain a porous spherical carrier with a particle size of 1 mm.

[0060] A solution of selenious acid with a concentration of 20% was placed in a 50 ml beaker, followed by the addition of 10 ml of deionized water, and stirred with a magnetic stirrer for 20 min until the powder was completely dissolved.

[0061] 1 g of the shaped adsorbent carrier was added into a beaker and immersed in the selenious acid solution at 25 °C for 2 h.

[0062] 4 g of ascorbic acid was added to the solution of step (3), and the color of the adsorbent carrier was observed to change from colorless to red. 1% NaOH solution was added to make it weakly alkaline, and the mixture was allowed to stand for 12 h.

[0063] The solution was filtered, and the wet shaped selenium-loaded adsorbent was collected for centrifugal washing. The centrifugal speed was 7000 r / min, the centrifugal time was 10 min, the first three washings were washed with deionized water, and the last three washings were washed with anhydrous ethanol. The shaped selenium-based adsorbent was dried in an oven at 80°C for 6 h.

[0064] The above samples were placed in a reaction system and a mercury removal experiment was carried out under a N2 atmosphere, wherein the amount of adsorbent was 50 mg, the total gas flow rate was 1 L / min, the mercury removal reaction was carried out at 150°C, and the reaction time was 2 h. Finally, the mercury removal efficiency of the flue gas from the coal-fired power plant was obtained through data analysis and calculation.

[0065] Example 2

[0066] The ratio of silicon dioxide: cellulose: water was set to 5:7:20. After the raw materials were mixed, the speed of the extruder was set to 600 r / min, and the speed of the spheronizer was set to 500 r / min to obtain a porous spherical carrier with a particle size of 3 mm.

[0067] Sodium selenite solution with a concentration of 20% was placed in a 50 ml beaker, followed by the addition of 10 ml of deionized water, and stirred with a magnetic stirrer for 20 min until the powder was completely dissolved.

[0068] 1 g of the shaped adsorbent carrier was added into a beaker and immersed in the sodium selenite solution at 25 °C for 2 h.

[0069] 4 g of glutathione was added to the solution of step (3). The color of the adsorbent carrier was observed to change from colorless to red. 1% NaOH solution was added to make it weakly alkaline and allowed to stand for 12 h.

[0070] The solution was filtered, and the wet shaped selenium-loaded adsorbent was collected for centrifugal washing. The centrifugal speed was 7000 r / min, the centrifugal time was 10 min, the first three washings were washed with deionized water, and the last three washings were washed with anhydrous ethanol. The shaped selenium-based adsorbent was dried in an oven at 80°C for 6 h.

[0071] The above sample was placed in a reaction system, and a mercury removal experiment was carried out under a N2 atmosphere, wherein the amount of the adsorbent was 50 mg, the total gas flow rate was 1 L / min, the demercuration reaction was carried out at 150°C, and the reaction time was 2 hours. Finally, the demercuration efficiency of the flue gas of the coal-fired power plant was obtained by data analysis and calculation. At the same time, a comprehensive comparison was made with the existing selenium-based adsorbent to highlight the excellent demercuration performance of the molded selenium-loaded adsorbent prepared by the present invention.

[0072] Table 1 Mercury adsorption performance of different mercury adsorbents

[0073]

[0074]

[0075] Figure 3 The BET test graphs of the silica-based porous carrier and the shaped selenium-based adsorbent prepared in Example 2. Both materials are type IV adsorbents with typical H1 hysteresis loops, and both are mesoporous materials with developed pore structures and high specific surface areas, which are 215.33 m 2 / g and 190.26m 2 / g, which has great potential for mercury adsorption.

[0076] Figure 4 The following are scanning electron microscope images (SEM) of the silica-based porous carrier and the spherical selenium-based adsorbent prepared in Example 2. The surface of the porous carrier is irregularly flaky. The spherical selenium-based adsorbent has many short rod branches distributed on the surface, which indicates that the elemental selenium is successfully distributed on the carrier surface in the form of rods, the surface of the material becomes rough, and the pore structure is more complex, which is conducive to the subsequent removal of Hg. 0 adsorption.

[0077] Figure 5 It is a fixed bed reaction platform for the flue gas mercury adsorption experiment in the embodiment. Figure 6 It is a mercury desorption reaction platform of the mercury-containing adsorbent in the embodiment.

[0078] Example 3

[0079] The ratio of silicon dioxide: cellulose: water was set to 5:7:20. After the raw materials were mixed, the speed of the extruder was set to 600 r / min, and the speed of the spheronizer was set to 500 r / min to obtain a porous spherical carrier with a particle size of 3 mm.

[0080] Sodium selenite solution with a concentration of 10% was placed in a 50 ml beaker, followed by addition of 10 ml of deionized water, and stirred with a magnetic stirrer for 20 min until the powder was completely dissolved.

[0081] 1 g of the shaped adsorbent carrier was added into a beaker and immersed in the sodium selenite solution at 25 °C for 2 h.

[0082] 2 g of glutathione was added to the solution of step (3). The color of the adsorbent carrier was observed to change from colorless to red. 1% NaOH solution was added to make it weakly alkaline and allowed to stand for 12 h.

[0083] The solution was filtered, and the wet shaped selenium-loaded adsorbent was collected for centrifugal washing. The centrifugal speed was 7000 r / min, the centrifugal time was 10 min, the first three washings were washed with deionized water, and the last three washings were washed with anhydrous ethanol. The shaped selenium-based adsorbent was dried in an oven at 80°C for 6 h.

[0084] The above samples were placed in a reaction system and a mercury removal experiment was carried out under a N2 atmosphere, wherein the amount of adsorbent was 50 mg, the total gas flow rate was 1 L / min, the mercury removal reaction was carried out at 150°C, and the reaction time was 2 h. Finally, the mercury removal efficiency of the flue gas from the coal-fired power plant was obtained through data analysis and calculation.

[0085] Example 4

[0086] The ratio of silicon dioxide: cellulose: water was set to 5:7:20. After the raw materials were mixed, the speed of the extruder was set to 600 r / min, and the speed of the spheronizer was set to 500 r / min to obtain a porous spherical carrier with a particle size of 3 mm.

[0087] Sodium selenite solution with a concentration of 15% was placed in a 50 ml beaker, followed by the addition of 10 ml of deionized water, and stirred with a magnetic stirrer for 20 min until the powder was completely dissolved.

[0088] 1 g of the shaped adsorbent carrier was added into a beaker and immersed in the sodium selenite solution at 25 °C for 2 h.

[0089] 3 g of glutathione was added to the solution of step (3). The color of the adsorbent carrier was observed to change from colorless to red. 1% NaOH solution was added to make it weakly alkaline and allowed to stand for 12 h.

[0090] The solution was filtered, and the wet shaped selenium-loaded adsorbent was collected for centrifugal washing. The centrifugal speed was 7000 r / min, the centrifugal time was 10 min, the first three washings were washed with deionized water, and the last three washings were washed with anhydrous ethanol. The shaped selenium-based adsorbent was dried in an oven at 80°C for 6 h.

[0091] The above samples were placed in a reaction system and a mercury removal experiment was carried out under a N2 atmosphere, wherein the amount of adsorbent was 50 mg, the total gas flow rate was 1 L / min, the mercury removal reaction was carried out at 150°C, and the reaction time was 2 h. Finally, the mercury removal efficiency of the flue gas from the coal-fired power plant was obtained through data analysis and calculation.

[0092] Example 5

[0093] The ratio of silicon dioxide: cellulose: water was set to 5:7:20. After the raw materials were mixed, the speed of the extruder was set to 600 r / min, and the speed of the spheronizer was set to 500 r / min to obtain a porous spherical carrier with a particle size of 3 mm.

[0094] Sodium selenite solution with a concentration of 25% was placed in a 50 ml beaker, followed by addition of 10 ml of deionized water, and stirred with a magnetic stirrer for 20 min until the powder was completely dissolved.

[0095] 1 g of the shaped adsorbent carrier was added into a beaker and immersed in the sodium selenite solution at 25 °C for 2 h.

[0096] 5 g of glutathione was added to the solution of step (3). The color of the adsorbent carrier was observed to change from colorless to red. 1% NaOH solution was added to make it weakly alkaline and allowed to stand for 12 h.

[0097] The solution was filtered, and the wet shaped selenium-loaded adsorbent was collected for centrifugal washing. The centrifugal speed was 7000 r / min, the centrifugal time was 10 min, the first three washings were washed with deionized water, and the last three washings were washed with anhydrous ethanol. The shaped selenium-based adsorbent was dried in an oven at 80°C for 6 h.

[0098] The above samples were placed in a reaction system and a mercury removal experiment was carried out under a N2 atmosphere, wherein the amount of adsorbent was 50 mg, the total gas flow rate was 1 L / min, the mercury removal reaction was carried out at 150°C, and the reaction time was 2 h. Finally, the mercury removal efficiency of the flue gas from the coal-fired power plant was obtained through data analysis and calculation.

[0099] Example 6

[0100] The ratio of silicon dioxide: cellulose: water was set to 5:7:20. After the raw materials were mixed, the speed of the extruder was set to 600 r / min, and the speed of the spheronizer was set to 500 r / min to obtain a porous spherical carrier with a particle size of 3 mm.

[0101] Sodium selenite solution with a concentration of 30% was placed in a 50 ml beaker, followed by addition of 10 ml of deionized water, and stirred with a magnetic stirrer for 20 min until the powder was completely dissolved.

[0102] 1 g of the shaped adsorbent carrier was added into a beaker and immersed in the sodium selenite solution at 25 °C for 2 h.

[0103] 6 g of glutathione was added to the solution of step (3). The color of the adsorbent carrier was observed to change from colorless to red. 1% NaOH solution was added to make it weakly alkaline and allowed to stand for 12 h.

[0104] The solution was filtered, and the wet shaped selenium-loaded adsorbent was collected for centrifugal washing. The centrifugal speed was 7000 r / min, the centrifugal time was 10 min, the first three washings were washed with deionized water, and the last three washings were washed with anhydrous ethanol. The shaped selenium-based adsorbent was dried in an oven at 80°C for 6 h.

[0105] The above samples were placed in a reaction system and a mercury removal experiment was carried out under a N2 atmosphere, wherein the amount of adsorbent was 50 mg, the total gas flow rate was 1 L / min, the mercury removal reaction was carried out at 150°C, and the reaction time was 2 h. Finally, the mercury removal efficiency of the flue gas from the coal-fired power plant was obtained through data analysis and calculation.

[0106] Example 7

[0107] In order to further clarify the preparation effects of in-situ and impregnation methods on selenium-based adsorbents, the selenium element ratio of the formed selenium-based adsorbent was tested by inductively coupled plasma optical emission spectrometry (ICP-OES). When the theoretical selenium loading was 20%, the selenium loading of the adsorbent prepared by in-situ reduction was 19.5%, while the selenium loading of the adsorbent prepared by ordinary impregnation was only 9.81%, which indicates that selenium was not effectively loaded.

[0108] Example 8

[0109] The ratio of silicon dioxide: cellulose: water was set to 5:7:20. After the raw materials were mixed, the speed of the extruder was set to 900 r / min, and the speed of the spheronizer was set to 700 r / min to obtain a porous spherical carrier with a particle size of 5 mm.

[0110] 20% selenic acid was placed in a 50 ml beaker, followed by addition of 10 ml of deionized water, and stirred with a magnetic stirrer for 20 min until the powder was completely dissolved.

[0111] 1 g of the shaped adsorbent carrier was added into a beaker and immersed in the selenic acid solution at 25 °C for 2 h.

[0112] 4 g of sodium thiosulfate was added to the solution of step (3). The color of the adsorbent carrier was observed to change from colorless to red. 1% NaOH solution was added to make it weakly alkaline and allowed to stand for 12 h.

[0113] The solution was filtered, and the wet shaped selenium-loaded adsorbent was collected for centrifugal washing. The centrifugal speed was 7000 r / min, the centrifugal time was 10 min, the first three washings were washed with deionized water, and the last three washings were washed with anhydrous ethanol. The shaped adsorbent was dried in an oven at 80°C for 6 h to obtain the shaped adsorbent.

[0114] The above samples were placed in a reaction system and a mercury removal experiment was carried out under a N2 atmosphere, wherein the amount of adsorbent was 50 mg, the total gas flow rate was 1 L / min, the mercury removal reaction was carried out at 150°C, and the reaction time was 2 h. Finally, the mercury removal efficiency of the flue gas from the coal-fired power plant was obtained through data analysis and calculation.

[0115] Example 9

[0116] The ratio of silicon dioxide: cellulose: water was set to 5:7:20. After the raw materials were mixed, the speed of the extruder was set to 1000 r / min, and the speed of the spheronizer was set to 900 r / min to obtain a porous spherical carrier with a particle size of 7 mm.

[0117] 20% selenium dioxide was placed in a 50 ml beaker, followed by addition of 10 ml of deionized water, and stirred with a magnetic stirrer for 20 min until the powder was completely dissolved.

[0118] 1 g of the shaped adsorbent carrier was added into a beaker and immersed in the selenium dioxide solution at 25 °C for 2 h.

[0119] 4 g of sodium bisulfite was added to the solution of step (3). The color of the adsorbent carrier was observed to change from colorless to red. 1% NaOH solution was added to make it weakly alkaline and allowed to stand for 12 h.

[0120] The solution was filtered, and the wet shaped selenium-loaded adsorbent was collected for centrifugal washing at a speed of 7000 r / min and a centrifugal time of 10 min. Deionized water was used for the first three washes and anhydrous ethanol was used for the last three washes. The final shaped adsorbent was obtained by drying in an oven at 80°C for 6 h.

[0121] The above samples were placed in a reaction system and a mercury removal experiment was carried out under a N2 atmosphere, wherein the amount of adsorbent was 50 mg, the total gas flow rate was 1 L / min, the mercury removal reaction was carried out at 150°C, and the reaction time was 2 h. Finally, the mercury removal efficiency of the flue gas from the coal-fired power plant was obtained through data analysis and calculation.

[0122] Example 10

[0123] The ratio of alumina: cellulose: water was set to 5:7:20. After the raw materials were mixed, the speed of the extruder was set to 600 r / min, and the speed of the spheronizer was set to 500 r / min to obtain a porous spherical carrier with a particle size of 3 mm.

[0124] 20% sodium selenite was placed in a 50 ml beaker, followed by addition of 10 ml of deionized water, and stirred with a magnetic stirrer for 20 min until the powder was completely dissolved.

[0125] 1 g of the shaped adsorbent carrier was added into a beaker and immersed in the sodium selenite solution at 25 °C for 2 h.

[0126] When 0.2 mol of glutathione is added to the solution of step (3), the color of the adsorbent carrier is observed to change from colorless to red. A 1% NaOH solution is added to make it weakly alkaline and the solution is allowed to stand for 12 h.

[0127] The solution was filtered, and the wet shaped selenium-loaded adsorbent was collected for centrifugal washing. The centrifugal speed was 7000 r / min, the centrifugal time was 10 min, the first three washings were washed with deionized water, and the last three washings were washed with anhydrous ethanol. The shaped adsorbent was dried in an oven at 80°C for 6 h to obtain the shaped adsorbent.

[0128] The above samples were placed in a reaction system and a mercury removal experiment was carried out under a N2 atmosphere, wherein the amount of adsorbent was 50 mg, the total gas flow rate was 1 L / min, the mercury removal reaction was carried out at 150°C, and the reaction time was 2 h. Finally, the mercury removal efficiency of the flue gas from the coal-fired power plant was obtained through data analysis and calculation.

[0129] Embodiment 11

[0130] The ratio of zeolite: cellulose: water was set to 5:7:20. After the raw materials were mixed, the speed of the extruder was set to 600 r / min, and the speed of the spheronizer was set to 500 r / min to obtain a porous spherical carrier with a particle size of 3 mm.

[0131] 20% sodium selenite was placed in a 50 ml beaker, followed by addition of 10 ml of deionized water, and stirred with a magnetic stirrer for 20 min until the powder was completely dissolved.

[0132] 1 g of the shaped adsorbent carrier was added into a beaker and immersed in the sodium selenite solution at 25 °C for 2 h.

[0133] 4 g of glutathione was added to the solution of step (3). The color of the adsorbent carrier was observed to change from colorless to red. 1% NaOH solution was added to make it weakly alkaline and allowed to stand for 12 h.

[0134] The solution was filtered, and the wet shaped selenium-loaded adsorbent was collected for centrifugal washing. The centrifugal speed was 7000 r / min, the centrifugal time was 10 min, the first three washings were washed with deionized water, and the last three washings were washed with anhydrous ethanol. The shaped adsorbent was dried in an oven at 80°C for 6 h to obtain the shaped adsorbent.

[0135] The above samples were placed in a reaction system and a mercury removal experiment was carried out under a N2 atmosphere, wherein the amount of adsorbent was 50 mg, the total gas flow rate was 1 L / min, the mercury removal reaction was carried out at 150°C, and the reaction time was 2 h. Finally, the mercury removal efficiency of the flue gas from the coal-fired power plant was obtained through data analysis and calculation.

[0136] Comparative Example 1

[0137] According to the method of Example 2, the difference is that the method is an impregnation method, firstly, the nano selenium is reduced and then the carrier is placed in a selenium-containing solution, the method is as follows: 20% of selenous acid is placed in 10ml of deionized water to obtain a selenous acid solution, and then 4g of a reducing agent ascorbic acid is added to reduce the elemental selenium. Then the shaped adsorbent carrier is placed in the selenium-containing solution, and allowed to stand for 12h, the solution is filtered, and the shaped selenium-loaded adsorbent is collected for centrifugal washing treatment, the centrifugal speed is 7000r / min, the centrifugal time is 10min, the first three washings are washed with deionized water, and the last three washings are washed with anhydrous ethanol, and the shaped adsorbent is dried in an oven at 80°C for 6h to obtain the shaped adsorbent.

[0138] Figure 2 This is a flow chart for preparing a shaped selenium-based adsorbent prepared by the in-situ reduction method (a) mentioned in the example and the impregnation method mentioned in comparative example 1 (b).

[0139] Figure 7 The mercury removal efficiency of the M-Se / SiO2 shaped selenium-based adsorbent prepared by the in-situ reduction method in Examples 2 to 6 and Comparative Example 1 is 50.10% when the selenium is loaded on the porous spherical carrier. With the increase of the selenium loading, the mercury removal efficiency is finally increased to 92.5%. This is because the increase of active sites promotes the removal of Hg 0 However, as the selenium loading increased, the mercury removal efficiency decreased. This is because excessive selenium would affect the uniformity of the adsorbent surface structure and thus hinder the mercury removal from the adsorbent. 0In addition, the mercury removal efficiency of the formed selenium-based adsorbent using the impregnation method is only 52.3%, because this method does not effectively load selenium.

[0140] Figure 8 The figure is a graph of mercury removal efficiency of shaped selenium-based adsorbents with different particle sizes mentioned in Examples 1, 2, 8, and 9. The particle size of the adsorbent is 50 μm, and the mercury removal efficiency is 95.1%. When the size of the adsorbent is increased to 1 mm and 3 mm, Hg 0 The removal efficiency of mercury dropped to 93.2% and 92.5%, respectively. However, when the particle size reached 5 mm, the mercury removal efficiency dropped to 89.0%, because the adsorbent with larger particle size was filled in the quartz reactor with larger gaps, resulting in a shorter residence time of mercury-containing gas, which had a negative impact on the adsorption of mercury. If the particle size of the adsorbent is smaller, good mercury removal can be achieved. However, in a fixed bed reactor, the smaller the particle size (50 μm, 1 mm), the greater the gas resistance flowing through the reactor, which has an adverse effect on the operation of the equipment.

[0141] Fig. 9 The figure shows the mercury removal efficiency of the shaped selenium-based adsorbent at different temperatures. 0 The adsorption performance was tested for 1 hour. When the reaction temperature increased from 90°C to 150°C, the mercury removal efficiency increased dramatically from 70.4% to 92.5%. The results show that increasing the temperature is beneficial to mercury removal because higher temperatures can 0 The mercury removal efficiency is improved by obtaining more kinetic energy between the active sites of Se and the molded selenium-based adsorbent. However, when the reaction temperature is increased from 150°C to 180°C, Hg 0 The removal efficiency dropped to 80.1%. When the reaction temperature was higher than 150°C, the elemental selenium on the selenium adsorbent was desorbed. Since selenium loaded on the surface of silica may have a certain adsorption energy, when the temperature of the demercuration experiment increased, the high temperature may destroy the chemical bond length, causing the elemental selenium to be released in the form of gas, resulting in a reduction in active sites and a reduction in the demercuration efficiency of the adsorbent.

[0142] Fig.10The flow field prediction results of the shaped selenium-based adsorbents of different particle sizes mentioned in Example 1, Example 2, Example 8, and Example 9 were carried out by Fluent numerical simulation software. Particles with a diameter of 1 mm caused a significant temperature drop due to the influence on the temperature field; the temperature of the gas dropped sharply when flowing through the bed. The optimal reaction temperature for mercury adsorption is 150°C, and the obvious cooling zone observed in the temperature contour is not conducive to the removal of mercury. In contrast, particles with diameters of 3 mm and 5 mm have little effect on the temperature field. In addition, the pressure contour map shows that the pressure drops of the three particle sizes are 17.98Pa, 2Pa, and 1.68Pa, respectively, among which the pressure drop caused by 1mm particles is larger, and the pressure drop caused by 3mm and 5mm particles is negligible in the bed. In addition, 1mm particles exhibit a lower porosity, resulting in a significant reduction in the gas flow velocity through the bed. Appropriate superficial velocity is essential for effective mercury removal.

[0143] Fig.11 The mercury saturation adsorption curve of the molded selenium-based adsorbent in Example 2 under nitrogen atmosphere. The figure below shows the breakthrough curves of the molded selenium-based adsorbent and commercial activated carbon at 150°C in a complex flue gas atmosphere, and its mercury adsorption capacity is as high as 101.04 mg / g. In contrast, the activated carbon quickly saturated and returned to the initial concentration in less than two hours, and the saturated adsorption capacity value was only 0.34 mg / g, indicating that the molded selenium-based adsorbent is an adsorbent with high mercury adsorption capacity and great application value.

[0144] Fig.12 It is the Hg-TPD curve of the mercury removal adsorbent in Example 2 of the present invention. The Hg-TPD test is used to identify the mercury species on the adsorbent after mercury removal and determine the mercury content by high temperature release measurement. After Hg is removed in N2 atmosphere, the Hg adsorbed by the adsorbent begins to decompose at 200-400℃ and reaches a peak at about 268℃. After 400℃, Hg 0 The concentration was below the detectable level, indicating that the sample had been completely decomposed, proving that the substance was mercury selenide.

[0145] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a shaped selenium-based adsorbent, characterized in that: The following steps are involved: (1) mixing a carrier raw material and a binder, and then adding water to form a viscous mixture; the carrier raw material is silicon dioxide, aluminum oxide, zinc oxide or zeolite, and the binder is microcrystalline cellulose, polyurethane, cellulose ether or modified starch; (2) adding the mixture obtained in step (1) into an extruder, extruding it into a strip bundle, and then putting the strip bundle material into a spheronizer for spheronization to finally obtain a spherical molding carrier wet material; and then drying it to obtain a porous spherical carrier; (3) preparing a selenide solution, wherein the selenide contains oxygen, and then placing the porous spherical carrier obtained in step (2) in the selenide solution, and uniformly depositing the ions containing the selenium element in the selenide solution on the surface of the porous spherical carrier by ultrasound; the selenide solution is a selenate solution, a selenite solution, a selenium dioxide solution, a selenic acid solution or a selenous acid solution; (4) adding a reducing agent, wherein the reducing agent is used to directly reduce the selenium-containing ions on the surface of the porous spherical carrier into active nano-selenium in situ and anchor them between the pores of the porous spherical carrier, and then ageing and drying to obtain a shaped selenium-based adsorbent.

2. The method for preparing a shaped selenium-based adsorbent according to claim 1, characterized in that: The reducing agent is ascorbic acid, glutathione, sodium thiosulfate or sodium bisulfite.

3. The method for preparing a shaped selenium-based adsorbent according to claim 1, characterized in that: In step (3), the mass concentration of selenide in the selenide solution is 10%-30%.

4. The method for preparing a shaped selenium-based adsorbent according to claim 1, characterized in that: In step (1), the mass ratio of the carrier raw material, the binder and water is in the range of (2-5): (7-10):

20.

5. The method for preparing a shaped selenium-based adsorbent according to claim 1, characterized in that: In step (1), the carrier raw material is micron-sized powder.

6. The method for preparing a shaped selenium-based adsorbent according to claim 1, characterized in that: In step (4), after adding the reducing agent, the alkali solution is added.

7. A shaped selenium-based adsorbent prepared by the method of any one of claims 1 to 6.

8. The shaped selenium-based adsorbent according to claim 7, characterized in that: The loading amount of selenium in the molded selenium-based adsorbent is 10%-30%.

9. Use of the shaped selenium-based adsorbent according to claim 7 or 8 for removing mercury from flue gas.

10. The use according to claim 9, characterized in that The shaped selenium-based adsorbent is used as a fixed bed filler for flue gas mercury removal; Preferably, the particle size of the shaped selenium-based adsorbent is 3 mm-5 mm.

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