Flue gas cleaning sorbents and methods for making the same

Abstract

The application discloses a flue gas purification adsorbent and a preparation method thereof. The application adopts a novel in-situ nitrogen doping and Cu loading method, utilizes the synchronous heat decomposition of ammonium carbonate and Cu (II) dispersion, simultaneously performs in-situ nitrogen doping and Cu (II) reduction in the ammonia atmosphere generated by the decomposition of ammonium carbonate, prevents the consumption of a large amount of reducing gas in the traditional nitrogen doping and Cu (II) reduction process, reduces environmental pollution, and lowers the reaction temperature and time of nitrogen doping due to good dispersity. The composite flue gas purification adsorbent prepared by the method can diversify the functions of the adsorbent under the condition of meeting the energy saving and environmental protection requirements.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of adsorbent synthesis, and particularly relates to a flue gas purification activated carbon adsorbent and a preparation method thereof. BACKGROUND

[0002] As an important adsorption material, activated carbon is widely used in the field of chemical gas treatment. Its key development as an important adsorbent lies in its rich pore structure, wide pore size distribution, easily modified surface properties, and relatively low synthesis cost. Under the background of the current national double carbon target and the increasingly stringent environmental protection indicators of industrial gas emissions, the treatment of flue gas from refineries has become a necessary process. The traditional flue gas from refineries mainly contains harmful gases such as carbon monoxide and sulfur dioxide after particle removal, and a large amount of carbon dioxide also needs to be captured and 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, etc. Among them, the material surface can be modified to a Lewis base environment rich in amine groups by amine functionalization or nitrogen doping of activated carbon materials, 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 internal structure, pores or surface of the adsorbent by ion exchange, thermal dispersion or impregnation method, and increase the adsorption performance of the adsorbent for carbon monoxide by means of π complexation adsorption between Cu(I) and carbon monoxide.

[0003] Traditional amine functionalization and nitrogen doping modification of activated carbon require a large amount of organic precursors and templates, and the process is complicated and easy to pollute. At the same time, it is difficult to avoid high-temperature and long-time activation process, which is not conducive to energy saving and environmental protection. In the preparation process of traditional activated carbon-based carbon monoxide adsorbents, Cu(II) is generally introduced by thermal dispersion, and then reduced and activated in a reducing atmosphere such as carbon monoxide and ammonia, which is a complicated process and consumes a large amount of toxic reducing gas. SUMMARY

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

[0005] According to a first aspect of the present application, the present application provides a preparation method of a flue gas purification adsorbent.

[0006] Specifically, the preparation method of the flue gas purification adsorbent comprises the following contents:

[0007] (1) providing a reactor: the reactor comprises a cylinder and heating facilities arranged outside the cylinder, the inside of the cylinder is provided with a first platform and a second platform arranged in an up-down direction, and the first platform is located above the second platform;

[0008] (2) taking 60-70 parts by weight of activated carbon raw powder, 10-20 parts by weight of ammonium carbonate and 10-20 parts by weight of copper chloride, mixing them thoroughly, and then laying them on the first platform of the reactor in step (1), and laying a mixture of sodium hydroxide and calcium chloride on the second platform;

[0009] (3) heating the materials in the reactor to realize one-step doping, thermal dispersion and reduction process;

[0010] (4) forming the activated carbon obtained in step (1) to obtain an activated carbon adsorbent.

[0011] Further, the first platform and the second platform are arranged on the first slide rail and the second slide rail respectively, and the first platform and the second platform can slide outward or inward along the slide rails, so as to facilitate the replacement of different batches of raw materials and lower adsorbents.

[0012] Further, the first platform and the second platform are of drawer type structure. The first slide rail and the second slide rail are fixed in the reactor through the first support and the second support below the first slide rail and the second slide rail.

[0013] Further, the mixing in step (2) adopts a conventional method in the art, for example, a stirrer can be selected to complete the mixing. 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 high speed greater than 300 rpm is used for dispersion, the activated carbon raw powder particles will generate excessive heat due to friction, and part of the ammonium carbonate will be easily decomposed by heat, which will affect the subsequent process. In this case, the mixing and stirring process can be divided into 2-3 sections, and each section is separated by 10-15 seconds.

[0014] Further, the amount of substance of the mixture of sodium hydroxide and calcium chloride to ammonium carbonate is 1:1-1.5:1; and the amount of substance of sodium hydroxide to calcium chloride is 0.5:1-1:1.

[0015] Further, the reactor is a horizontal columnar reactor, preferably a closed cavity structure. One end of the reactor is provided with a flip door; the other end is a closed end and is provided with an exhaust port, which is communicated with the absorption liquid in the tail gas absorption tank through a pipeline. The inner layer material of the reactor is stainless steel.

[0016] Further, the flip door can be opened by 180° with the hinge on one side of the door as the rotating shaft. A pressure sensor is arranged on the closed end of the reactor, and a pair of safety valve groups (one open and one standby) are arranged on 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 gas not involved in the reaction into the ammonia gas absorption tank. Thanks to the extremely high solubility of ammonia gas, the water filled in the absorption tank can be used.

[0017] Further, the heating rate in step (3) is generally 5-15℃ / min. During the heating period, the ammonium carbonate on the first platform gradually decomposes to produce ammonia and carbon dioxide gas; the carbon dioxide gas is diffused and adsorbed by the mixture of sodium hydroxide and calcium chloride on the second platform, and the ammonia gas stays in the reactor to reduce Cu (II) to Cu (I) in situ, while part of the ammonia gas is loaded on the surface and inside the pores of the activated carbon at high temperature to realize nitrogen doping. At the same time of the reduction of Cu (II), the high temperature environment also helps the thermal dispersion of Cu species, which are uniformly dispersed on the surface and inside part of the pores of the activated carbon. After heating, the above three steps are all completed.

[0018] Further, the termination temperature of the heating in step (3) is 250-350℃, and the temperature is maintained for 1-1.5 hours. The gas atmosphere is the ammonia atmosphere produced by the thermal decomposition of ammonium carbonate.

[0019] Further, the molding in step (4) can adopt the conventional method in the field. For example, the Cu (I) loaded and nitrogen-doped activated carbon obtained in step (3) can be mixed uniformly with a binder such as carboxymethyl cellulose, and the uniformly mixed material is poured into a hydraulic machine mold to be molded under a certain temperature and pressure for a certain time. The pressure of the hydraulic molding is generally 7-10 MPa, the molding temperature is 100-150℃, and the maintenance time is 15-25 minutes.

[0020] According to the second aspect of the present application, the present application also provides a flue gas purification adsorbent obtained by the above-mentioned preparation method.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] 1. The present application innovatively introduces a one-step heating method, which utilizes the thermal decomposition of ammonium carbonate to produce ammonia, reduces Cu species in situ, modifies activated carbon by nitrogen doping, and disperses Cu (II) species in the same heating step, thereby preparing a flue gas purification adsorbent. Compared with the preparation process of traditional CO adsorbents, carbon capture adsorbents and SO2 adsorbents, the present application reduces the energy required for a large amount of heating and activation and the consumption of reducing gas, shortens the preparation time, greatly simplifies the preparation process, and avoids energy consumption and waste.

[0023] 2. This invention innovatively integrates CO adsorbent, carbon capture adsorbent, and SO2 adsorbent into one unit. Based on the rich pore structure and pore size distribution of activated carbon and the presence of competing adsorption sites, it has good adsorption capacity for all three gases and has good application prospects in flue gas carbon capture and purification as well as pressure swing adsorption processes. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the reactor used in this invention.

[0025] In the diagram, the numbers correspond to: 1-Safety valve assembly, 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

[0026] The flue gas purification adsorbent and its preparation method of the present invention will be described in more detail below with reference to specific embodiments.

[0027] like Figure 1 As shown, the reactor used in this invention includes a cylindrical body and a heater 7 disposed outside the cylindrical body. Inside the cylindrical body are a first platform 5 and a second platform 6 arranged vertically, with the first platform 5 located above the second platform 6. The first and second platforms have a drawer-type structure and are respectively mounted on a first slide rail 9 and a second slide rail 6. The first and second slide rails are fixed inside the reactor by a first support 10 and a second support 10. A pressure sensor 2 is provided at the closed end of the reactor, and a flip-top door 8 is provided at the open end. The reactor also has an exhaust port, which is connected to the absorbent liquid 4 in the tail gas absorption tank 3 via a pipeline. A pressure sensor 2 and a safety valve assembly 1 are also provided at the closed end of the reactor tail to maintain the reactor operating within a safe pressure range.

[0028] Examples 1-6

[0029] Examples 1-6 provide activated carbon, ammonium carbonate and copper chloride powders with different weight ratios, and the heat treatment conditions in the reactor are adjusted accordingly, as shown in Table 1 below.

[0030] Table 1

[0031] 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 Copper chloride 15 15 15 20 20 10 Heat treatment temperature / °C 250 350 300 300 350 300 Heat treatment time / h 1 1.5 1 1 1.5 1

[0032] The preparation methods of the adsorbents in Examples 1-6 are as follows:

[0033] Take the active carbon raw powder, ammonium carbonate powder and copper chloride powder of the corresponding mass number in Table 1, add them into a mixing stirrer, the stirring speed is 300 rpm, and the stirring time is 50 seconds. Put the completely mixed solid mixture into the first platform (drawer) of the horizontal column reactor shown in the drawing and evenly lay it, and put the mixed solid powder of calcium chloride and sodium hydroxide with a total mass and a 1:1 ammonium carbonate into the second platform (drawer) of the lower layer of the reactor, and the mass ratio of the two in the mixed powder is also 1:1.

[0034] After the materials are placed, close the reactor door; turn on the reactor heater, set the heating rate to 10℃ / min, heat to the corresponding heat treatment temperature in Table 1, and keep for the corresponding heat treatment time. After heating is completed, take out the mixed solid in the upper drawer and place it in a dry environment for standby use after natural cooling.

[0035] Take 80 parts by weight of the active carbon powder with Cu(I) loaded reduction and N doping as described above and 10 parts by weight of sodium carboxymethyl cellulose, mix them thoroughly, add the uniformly mixed powder into 10 parts by weight of water, stir them uniformly, pour them into a hydraulic machine, and finally obtain the molded active carbon adsorbent.

[0036] Comparative Examples 1-3

[0037] The preparation of the adsorbent is the same as in Examples 1-6, except that different weight fractions of components are added in Comparative Examples 1-3.

[0038] Comparative Example 4

[0039] The preparation of the adsorbent is carried out by a conventional method. First, take the corresponding mass of active carbon and ammonium carbonate powder, mix them thoroughly, add them into the first platform (drawer) of the reactor for treatment for the corresponding time and temperature, and obtain the nitrogen-doped active carbon powder. Mix the powder with the corresponding mass of copper chloride powder, and after the temperature drops to room temperature, transfer the powder into a tube furnace for heat treatment under CO atmosphere for the corresponding time and temperature, and obtain the active carbon powder loaded with Cu(I) and nitrogen doping. The molding method is the same as in Examples 1-6.

[0040] The raw material ratio and heat treatment conditions of Comparative Examples 1-4 are listed in Table 2.

[0041] Table 2

[0042] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Activated carbon 100 80 80 60 Ammonium carbonate 0 20 0 20 Copper chloride 0 0 20 20 Heat treatment temperature / °C - 300 300 300 Heat treatment time / h - 1 1 1

[0043] Adsorbent performance test: the evaluation methods used in Examples 1-6 and Comparative Examples 1-4 are the same. Among them, the adsorption performance is tested by a Micromatics HPVA high-pressure adsorption instrument, the pretreatment condition is to keep 5 bar at 150℃ for 4 hours under CO atmosphere, then vacuum and drop to room temperature, and the corresponding adsorption isotherms are obtained by testing three kinds of gases respectively, and the adsorption amount at 1 bar is listed in Table 3.

[0044] Table 3 Adsorption capacity of different components (unit: mL / g)

[0045] CO adsorption capacity CO2adsorption capacity SO2adsorption 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

[0046] As can be seen from Table 3, the different proportions of ammonium carbonate and copper chloride added in Examples 1-6 and different heating treatment conditions have a greater impact on the adsorption performance of the adsorbent. Mild heat treatment conditions can cause uneven thermal dispersion of Cu(I) and incomplete doping of N elements, resulting in a decrease in the adsorption capacity of the three gases. Excessive heat treatment conditions can cause Cu elements to be over-reduced to form elemental copper by ammonia gas produced by the thermal decomposition of ammonium carbonate, blocking the large pores of activated carbon, resulting in the loss of adsorption capacity of the internal slit pores of the large pores and a decrease in adsorption performance. At the same time, within the recommended addition range under suitable heat treatment conditions, the addition of ammonium carbonate and copper chloride helps to load more Cu(I) and N elements and better gas adsorption performance.

[0047] As can be seen from Comparative Example 1, the adsorption capacity of activated carbon without adding any elements is greatly reduced for the three gases. As can be seen from Comparative Example 2, activated carbon with only ammonium carbonate added for in-situ nitrogen doping has a greater affinity for acidic gases CO2 and SO2, but has poor adsorption for CO. As can be seen from Comparative Example 3, activated carbon with only copper chloride added, which only undergoes in-situ thermal dispersion without reduction in an ammonia atmosphere, still exhibits strong adsorption capacity for CO after reduction in a CO atmosphere in the sample room before the adsorbent test, but has poor adsorption for the other two gases. As can be seen from Comparative Example 4, the activated carbon obtained by the conventional distribution method of first nitrogen doping and then Cu element loading and reduction has slightly decreased adsorption performance compared with Example 4 under the same conditions, and the total time is more than doubled due to two-step loading operations, and the process energy consumption and gas emissions are large.

Claims

1. A method for preparing a flue gas purification adsorbent, characterized in that, Includes the following: (1) Provide a reactor: the reactor includes a cylinder and a heating facility located outside the cylinder, and the cylinder is provided with a first platform and a second platform arranged vertically inside the cylinder, with the first platform 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 copper chloride, mix them thoroughly, and spread them evenly on the first platform of the reactor described in step (1). Spread the mixture of sodium hydroxide and calcium chloride evenly on the second platform. (3) The material in the reactor is heated to achieve one-step doping, thermal dispersion and reduction process; the heating is terminated at 250-350℃ and held at this temperature for 1-1.5 hours. (4) The activated carbon obtained in step (3) is shaped to obtain activated carbon adsorbent.

2. The preparation method according to claim 1, characterized in that, The first platform and the second platform are respectively mounted 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 done using a mixer with a mixing speed of 200-400 rpm and a mixing time of 40-60 seconds.

4. The preparation method according to claim 3, characterized in that, In step (2), the mixing speed of the mixer is greater than 300 rpm, and the mixing is carried out in 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 ratio of sodium hydroxide and calcium chloride mixture to ammonium carbonate is 1:1 to 1.5:1, and the ratio of sodium hydroxide to calcium chloride is 0.5:1 to 1:

1.

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

7. The preparation method according to claim 1, characterized in that, The molding process described in step (4) is as follows: Cu(I) loaded and nitrogen-doped activated carbon obtained in step (3) is added to the binder and kneaded evenly. The evenly kneaded material is poured into the hydraulic press mold and molded under a certain temperature and pressure.

8. The preparation method according to claim 7, characterized in that, The hydraulic forming pressure is 7-10 MPa, the forming temperature is 100-150℃, and the holding time is 15-25 minutes.

9. The flue gas purification adsorbent obtained by any of the preparation methods described in claims 1-8.

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