Flue gas purification adsorbent and preparation method thereof

Abstract

The invention discloses a flue gas purification adsorbent and a preparation method thereof. According to the invention, a novel in-situ nitrogen doping and Cu loading method is adopted, thermal decomposition of ammonium carbonate and dispersion of Cu (II) are carried out synchronously, and nitrogen doping and Cu (II) reduction are carried out in situ in an ammonia atmosphere generated by decomposition of ammonium carbonate, so that consumption of a large amount of reducing gas in the traditional nitrogen doping and Cu (II) reduction process is prevented, and environmental pollution is reduced; and due to good dispersibility, the reaction temperature and time of nitrogen doping are reduced. According to the composite flue gas purification adsorbent prepared by the method disclosed by the invention, the functions of the adsorbent can be diversified under the condition that the energy-saving and environment-friendly requirements are met to the greatest extent.

Description

Technical Field

[0001] The invention belongs to the field of adsorbent synthesis, and in particular relates to an activated carbon adsorbent for flue gas purification and a preparation method thereof. Background Art

[0002] As an important adsorption material, activated carbon is widely used in the field of chemical gas treatment. At the same time, its rich pore structure, wide pore size distribution, easily modified surface properties and relatively low synthesis cost have become the key to its development as an important adsorbent. In the context of the current national dual carbon development goals and the increasingly stringent environmental protection indicators for industrial gas emissions, the treatment of refinery flue gas has become a necessary process link. After the removal of particulate matter, the traditional refinery flue gas mainly contains harmful gases such as carbon monoxide and sulfur dioxide, which need to be removed. At the same time, it contains a large amount of carbon dioxide, which also needs to be captured, stored or reused. Traditional carbon dioxide and sulfur dioxide adsorbents can be divided into amine-functionalized or nitrogen-doped inorganic and organic materials, molecular sieves, MOFs and other materials. Among them, activated carbon materials can be modified to an amine-rich Lewis base environment through amine functionalization or nitrogen doping, which is conducive to the attachment of acidic gases such as carbon dioxide and sulfur dioxide. Traditional activated carbon adsorbents for carbon monoxide generally introduce Cu (I) into the adsorbent structure, pores or surface through ion exchange, thermal dispersion or impregnation, and use the π complex adsorption between Cu (I) and carbon monoxide to increase the adsorption performance of the adsorbent for carbon monoxide.

[0003] Traditional activated carbon amine functionalization and nitrogen doping modification require a large amount of organic precursors and templates, which are cumbersome and easy to cause pollution. At the same time, it is inevitable to have a high temperature and long activation process, which is not conducive to energy conservation and environmental protection. In the preparation process of traditional activated carbon-based carbon monoxide adsorbents, Cu (II) is generally introduced by thermal dispersion first, and then reduced and activated in a reducing atmosphere such as carbon monoxide and ammonia to obtain Cu (I). The process is cumbersome and consumes a large amount of toxic reducing gas. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a flue gas purification adsorbent and a preparation method thereof. A novel in-situ nitrogen doping and Cu loading method is adopted, wherein the thermal decomposition of ammonium carbonate and the dispersion of Cu (II) are carried out simultaneously, and nitrogen doping and Cu (II) reduction are carried out in situ in the ammonia atmosphere generated by the decomposition of ammonium carbonate, thereby preventing the large amount of reducing gas consumption in the traditional nitrogen doping and Cu (II) reduction process, reducing environmental pollution, and reducing the reaction temperature and time of nitrogen doping due to good dispersibility.

[0005] According to a first aspect of the present invention, the present invention provides a method for preparing a flue gas purification adsorbent.

[0006] Specifically, the preparation method of the flue gas purification adsorbent includes the following contents: (1) providing a reactor: the reactor comprising a cylinder and a heating facility provided outside the cylinder, wherein a first platform and a second platform arranged vertically are provided inside the cylinder, and the first platform is located above the second platform; (2) Take 60-70 parts by weight of activated carbon powder, 10-20 parts by weight of ammonium carbonate and 10-20 parts by weight of cupric chloride, mix them thoroughly, and spread them on the first platform of the reactor in step (1), and spread a mixture of sodium hydroxide and calcium chloride on the second platform; (3) Heating the materials in the reactor to achieve a one-step doping, thermal dispersion and reduction process; (4) The activated carbon obtained in step (1) is molded to obtain an activated carbon adsorbent.

[0007] Furthermore, the first platform and the second platform are respectively arranged on the first slide rail and the second slide rail, and the first platform and the second platform can slide outward or inward along the slide rail, so as to facilitate the replacement of different batches of raw materials and the lower layer adsorbent.

[0008] Furthermore, the first platform and the second platform are drawer-type structures. The first slide rail and the second slide rail are fixed in the reactor through the first support and the second support.

[0009] Furthermore, the mixing in step (2) is performed by conventional methods in the art, such as by using a stirrer. The stirring speed of the mixing stirrer is generally 200-400 rpm, and the stirring time is 40-60 seconds. It should be noted that if a high speed of more than 300 rpm is used for dispersion, the friction between the activated carbon raw powder particles will generate excessive heat, and some ammonium carbonate will be easily decomposed by heat, affecting the subsequent process. In this case, the mixing and stirring process can be divided into 2-3 sections, each with an interval of 10-15 seconds.

[0010] Furthermore, the amount of the mixture of sodium hydroxide and calcium chloride to ammonium carbonate is 1:1-1.5:1; the amount of the mixture of sodium hydroxide and calcium chloride is 0.5:1-1:1.

[0011] Furthermore, the reactor is a horizontal columnar reactor, preferably a closed cavity structure. One end of the reactor is open and provided with a flip door; the other end is a closed end and provided with an exhaust port, which is connected to the absorption liquid in the tail gas absorption tank through a pipeline. The inner layer material of the reactor is stainless steel.

[0012] Furthermore, the flip door can be opened 180 degrees with the fixed hinge on one side of the door as the rotation axis. A pressure sensor is set at the closed end of the reactor, and a pair of safety valve groups (one open and one standby) are also set at the upper part of the closed end. When the pressure sensor shows that the pressure in the reactor is higher than the critical pressure, the safety valve opens and releases the ammonia that has not participated in the reaction into the ammonia absorption tank. Thanks to the extremely high solubility of ammonia, the absorption tank can be filled with water.

[0013] Furthermore, the heating rate in step (3) is generally 5-15°C / minute. During the heating period, the ammonium carbonate on the first platform gradually decomposes to produce ammonia and carbon dioxide gas; the carbon dioxide gas diffuses and is adsorbed by the sodium hydroxide and calcium chloride mixture on the second platform, and the ammonia stays in the reactor to reduce Cu (II) to Cu (I) in situ. At the same time, part of the ammonia loads the nitrogen-containing groups on the surface and inside the pores of the activated carbon at high temperature to achieve nitrogen doping. While Cu (II) is reduced, the high temperature environment also helps the thermal dispersion of the Cu species, making it evenly dispersed on the surface of the activated carbon and inside some pores. After the heating is completed, the above three steps are all completed.

[0014] Furthermore, the temperature at which the temperature is raised in step (3) is terminated is 250-350°C, and the temperature is maintained for 1-1.5 hours. The gas atmosphere is an ammonia atmosphere generated by thermal decomposition of ammonium carbonate.

[0015] Furthermore, the molding described in step (4) can be carried out by conventional methods in the art. For example, the Cu (I) loading and nitrogen-doped activated carbon completed in step (3) can be added to a binder such as carboxymethyl cellulose and mixed evenly, and the evenly kneaded material can be poured into a hydraulic press mold and molded at a certain temperature and pressure for a certain time. The pressure of hydraulic molding is generally 7-10MPa, the molding temperature is 100-150°C, and it is maintained for 15-25 minutes.

[0016] According to a second aspect of the present invention, the present invention also provides a flue gas purification adsorbent, which is obtained by the above-mentioned preparation method.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention innovatively introduces a one-step heating method, which utilizes the thermal decomposition of ammonium carbonate to generate ammonia, completes the in-situ reduction of Cu species, the nitrogen doping modification of activated carbon, and the thermal dispersion of Cu (II) species in the same heating step, and then produces a flue gas purification adsorbent. Compared with the preparation process of traditional CO adsorbents, carbon capture adsorbents and SO2 adsorbents, it reduces a lot of energy required for heating activation and the consumption of reducing gas, shortens the preparation time, greatly simplifies the preparation process, and avoids energy consumption and waste.

[0018] 2. The present invention innovatively integrates CO adsorbent, carbon capture adsorbent and SO2 adsorbent into one. Based on the rich pore structure and pore size distribution of activated carbon and in the presence of competitive adsorption, it has good adsorption capacity for the three gases and has good application prospects in flue gas carbon capture and purification and pressure swing adsorption process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of the reactor used in the present invention.

[0020] In the figure, the digital marks correspond to: 1-safety valve group, 2-pressure sensor, 3-exhaust gas absorption tank, 4-water, 5-first platform, 6-second platform, 7-heater, 8-flip door, 9-first slide rail / second slide rail, 10-first support / second support. Implementation

[0021] The flue gas purification adsorbent and the preparation method thereof of the present invention are described in more detail below in conjunction with specific embodiments.

[0022] like Figure 1 As shown, the reactor used in the present invention includes a cylinder and a heater 7 arranged outside the cylinder. A first platform 5 and a second platform 6 arranged up and down are provided inside the cylinder, and the first platform 5 is located above the second platform 6. The first platform and the second platform are drawer-type structures, which are respectively arranged on the first slide rail 9 and the second slide rail 9, and the first slide rail and the second slide rail are fixed to the inside of the reactor by the first support 10 and the second support 10. A pressure sensor 2 is provided at the closed end of the reactor, and a flip door 8 is provided at the other end opening. The reactor is also provided with an exhaust port, which is connected to the absorption liquid 4 in the tail gas absorption tank 3 through a pipeline. A pressure sensor 2 and a safety valve group 1 are also provided at the closed end of the tail of the reactor, which can maintain the reactor operating within a safe pressure range.

[0023] Examples 1-6 Examples 1-6 respectively provide activated carbon, ammonium carbonate and copper chloride powder in different weight proportions, and make certain adjustments to the heat treatment conditions in the reactor, as shown in Table 1 below.

[0024] Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Activated carbon 70 70 70 60 60 80 Ammonium carbonate 15 15 15 20 20 10 Cupric chloride 15 15 15 20 20 10 Heat treatment temperature / ℃ 250 350 300 300 350 300 Heat treatment time / h 1 1.5 1 1 1.5 1 The preparation method of the adsorbent in Examples 1-6 is: Take the activated carbon raw powder, ammonium carbonate powder and cupric chloride powder of the corresponding mass number in Table 1, add them into the mixing agitator, stir at 300rpm, and stir for 50 seconds. Put the completely mixed solid mixture into the first platform (drawer) of the horizontal column reactor shown in the attached figure and spread it evenly, put the mixed solid powder of calcium chloride and sodium hydroxide in the second platform (drawer) of the lower layer of the reactor with the amount of total substance and ammonium carbonate in a ratio of 1:1, and the amount ratio of the two substances in the mixed powder is also 1:1.

[0025] After the materials are placed, close the reactor door; turn on the reactor heater, set the heating rate to 10°C / min, heat to the corresponding heat treatment temperature in Table 1, and maintain the corresponding heat treatment time. After heating is completed and the temperature drops naturally, take out the mixed solids in the upper drawer and place them in a dry environment for later use.

[0026] Take 80 parts by weight of the above activated carbon powder that has completed Cu (I) loading reduction and N doping and 10 parts by weight of sodium carboxymethyl cellulose, mix them thoroughly, add 10 parts by weight of water to the evenly mixed powder, stir evenly, pour into a hydraulic press to form, and finally obtain a molded activated carbon adsorbent.

[0027] Comparative Examples 1-3 The preparation of the adsorbent is the same as that of Examples 1-6, except that different weight portions of components are added in Comparative Examples 1-3.

[0028] Comparative Example 4 The adsorbent was prepared by a conventional method. First, corresponding parts by mass of activated carbon and ammonium carbonate powder were weighed, fully mixed, and added to the first platform (drawer) of the reactor for treatment at a corresponding time and temperature to obtain nitrogen-doped activated carbon powder; the above powder was fully mixed with corresponding parts by mass of copper chloride powder, and when the temperature dropped to room temperature, the powder was transferred and placed in a tubular furnace for heat treatment under a CO atmosphere for a corresponding time and temperature to obtain Cu (I)-loaded and nitrogen-doped activated carbon powder. The molding method was the same as that of Examples 1-6.

[0029] The raw material ratios and heat treatment conditions of Comparative Examples 1-4 are listed in Table 2.

[0030] Table 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Activated carbon 100 80 80 60 Ammonium carbonate 0 20 0 20 Cupric chloride 0 0 20 20 Heat treatment temperature / ℃ - 300 300 300 Heat treatment time / h - 1 1 1 Adsorbent performance test: The evaluation methods used in Examples 1-6 and Comparative Examples 1-4 are the same. The adsorption performance is tested by a Micromatics HPVA high pressure adsorption instrument. The pretreatment conditions are 5 bar and 150°C for 4 hours under a CO atmosphere, followed by vacuuming and cooling to room temperature. The three gases are tested separately to obtain the corresponding adsorption isotherms, and the adsorption amount at 1 bar is listed in Table 3.

[0031] Table 3 Adsorption capacity of adsorbents for different components (unit: mL / g) CO adsorption <![CDATA[CO2 adsorption capacity]]> <![CDATA[SO2 adsorption capacity]]> Example 1 43.7 28.2 34.6 Example 2 43.3 26.6 33.1 Example 3 47.3 30.7 36.4 Example 4 47.9 31.3 37.3 Example 5 45.0 28.2 35.0 Example 6 46.2 29.2 35.5 Comparative Example 1 41.1 24.5 31.3 Comparative Example 2 40.5 33.5 38.8 Comparative Example 3 48.7 23.1 30.2 Comparative Example 4 46.4 30.1 35.6 It can be seen from Table 3 that the different proportions of ammonium carbonate and copper chloride added in Examples 1-6 and the different heating treatment conditions have a great influence on the adsorption performance of the adsorbent. Mild heat treatment conditions will lead to uneven thermal dispersion of Cu (I) and incomplete doping of N elements, resulting in a decrease in the adsorption of the three gases. Excessive heat treatment conditions will cause the Cu element to be excessively reduced to copper by ammonia produced by thermal decomposition of ammonium carbonate, blocking the macropores of the activated carbon, causing the slit pores inside the macropores to lose their adsorption capacity and the adsorption performance to decrease. At the same time, under appropriate heat treatment conditions and within the recommended addition range, the addition of ammonium carbonate and copper chloride contributes to more Cu (I) and N element loading and doping and better gas adsorption performance.

[0032] It can be seen from Comparative Example 1 that the adsorption capacity of the activated carbon without adding any elements for the three gases is greatly reduced; it can be seen from Comparative Example 2 that the activated carbon in situ nitrogen doped with only ammonium carbonate has a greater affinity for the acidic gases CO2 and SO2, but poor adsorption of CO; it can be seen from Comparative Example 3 that although the activated carbon with only cupric chloride added was only subjected to in situ thermal dispersion without ammonia atmosphere reduction, it still showed a strong adsorption capacity for CO after the CO atmosphere reduction in the sample chamber before the molded adsorbent test, but poor adsorption for the other two gases; it can be seen from Comparative Example 4 that the activated carbon obtained by the conventional distribution method of first nitrogen doping and then Cu element loading reduction has a slightly decreased adsorption performance compared with Example 4 with exactly the same conditions. At the same time, due to the two-step loading operation, the total time is more than doubled, and the process energy consumption and gas emissions are relatively large.

Claims

1. A method for preparing a flue gas purification adsorbent, characterized in that: Includes the following: (1) providing a reactor: the reactor comprising a cylinder and a heating facility provided outside the cylinder, wherein a first platform and a second platform arranged vertically are provided inside the cylinder, and the first platform is located above the second platform; (2) Take 60-70 parts by weight of activated carbon powder, 10-20 parts by weight of ammonium carbonate and 10-20 parts by weight of cupric chloride, mix them thoroughly, and spread them on the first platform of the reactor in step (1), and spread a mixture of sodium hydroxide and calcium chloride on the second platform; (3) Heating the materials in the reactor to achieve a one-step doping, thermal dispersion and reduction process; (4) The activated carbon obtained in step (1) is molded to obtain an activated carbon adsorbent.

2. The preparation method according to claim 1, characterized in that: The first platform and the second platform are respectively arranged on the first slide rail and the second slide rail, and the first platform and the second platform can slide outward or inward along the slide rail.

3. The preparation method according to claim 1, characterized in that: The mixing in step (2) is performed by a stirrer, the stirring speed of the mixing stirrer is 200-400 rpm, and the stirring time is 40-60 seconds.

4. The preparation method according to claim 3, characterized in that: In step (2), the stirring speed of the mixing stirrer is greater than 300 rpm, and the mixing stirring is divided into 2-3 stages, with an interval of 10-15 seconds between each stage.

5. The preparation method according to claim 1, characterized in that: In step (2), the amount of the mixture of sodium hydroxide and calcium chloride to ammonium carbonate is 1:1-1.5:1, and the amount of the mixture of sodium hydroxide and calcium chloride is 0.5:1-1:

1.

6. The preparation method according to claim 1, characterized in that: The heating rate in step (3) is 5-15°C / min.

7. The preparation method according to claim 1, characterized in that: The termination temperature of the heating in step (3) is 250-350°C, and the temperature is maintained for 1-1.5 hours.

8. The preparation method according to claim 1, characterized in that: The molding process described in step (4) is as follows: adding a binder to the Cu (I)-loaded and nitrogen-doped activated carbon obtained in step (3) and kneading them uniformly, pouring the kneaded material into a hydraulic press mold, and molding it under a certain temperature and pressure.

9. The preparation method according to claim 8, characterized in that: The pressure of hydraulic forming is 7-10MPa, the forming temperature is 100-150℃, and it is maintained for 15-25 minutes.

10. The flue gas purification adsorbent obtained by the preparation method according to any one of claims 1 to 9.

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