High-pore-volume nitrogen-doped activated carbon for capturing carbon dioxide and preparation method thereof

Abstract

The invention relates to high-pore-volume nitrogen-doped activated carbon for capturing carbon dioxide and a preparation method of the high-pore-volume nitrogen-doped activated carbon, and belongs to the technical field of activated carbon. In order to solve the problem that high nitrogen content and high pore volume of nitrogen-doped activated carbon are not matched, the invention provides a preparation method of high-pore-volume nitrogen-doped activated carbon for carbon dioxide capture. In the preparation process of the activated carbon, an activating medium composed of a carbon source and an activating agent and a nitrogen-containing precursor are respectively laid in different mutually isolated areas in a crucible, so that the carbon deposition effect of the nitrogen-containing precursor is weakened, the high pore volume of the activated carbon is maintained, the nitrogen content of the activated carbon is improved, and the high CO2 adsorption capacity and the high CO2 / N2 adsorption selectivity are obtained at the same time. When the high-pore-volume nitrogen-doped activated carbon prepared by the method is applied to the field of industrial CO2 trapping, high CO2 adsorption capacity can be obtained, and high CO2 purity in desorbed gas can be guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of activated carbon, and in particular relates to a high-pore volume nitrogen-doped activated carbon for carbon dioxide capture and a preparation method thereof. Background Art

[0002] Activated carbon has a well-developed pore structure, high specific surface area, good mechanical strength and chemical stability. It is an important industrial material and is widely used in CO2 capture. Currently, commercial activated carbon with a well-developed pore structure and a specific surface area of ​​> 600 m2 can be obtained based on mature heat treatment methods. 2 ·g -1 However, due to the complex composition of industrial emissions, including various components such as N2, O2, and H2O, the selectivity for CO2 during adsorption is relatively weak. Therefore, when activated carbon is used for CO2 capture, the purity of the resulting CO2 is often low, which is not conducive to the large-scale application and promotion of CO2 capture technology.

[0003] In addition to carbon, activated carbon usually contains heteroatoms such as O, H, N, and S. Among them, N doping is generally believed to help enhance the CO2 / N2 adsorption selectivity of activated carbon, thereby improving the CO2 capture capacity and capture purity of activated carbon. In the preparation process of activated carbon, nitrogen-containing precursors such as urea and melamine are usually used to dope nitrogen into activated carbon. However, since the decomposition of urea and melamine will produce carbon deposits, the nitrogen content of the prepared activated carbon is increased while the pore volume is greatly reduced. Therefore, improving the preparation method of nitrogen-doped activated carbon, while increasing the nitrogen content of activated carbon while maintaining its high pore volume, is of great significance to promoting the use of activated carbon for industrial CO2 capture. Summary of the Invention

[0004] In order to solve the problem of mismatch between high nitrogen content and high pore volume of nitrogen-doped activated carbon, the present invention provides a high pore volume nitrogen-doped activated carbon for carbon dioxide capture and a preparation method thereof.

[0005] The technical solution of the present invention:

[0006] A method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture comprises the following steps:

[0007] Step 1: Using low-rank weakly caking coal or non-caking coal as raw material, crushing and screening, acid washing to remove ash in the coal, and drying to obtain coal particles;

[0008] Step 2: uniformly mix the coal particles obtained in step 1 and the activator and place them in deionized water, fully dry the solution in the resulting mixed system, and place the dried mixture and the nitrogen-containing precursor in different isolated areas in the crucible;

[0009] Step 3: placing the crucible in a horizontal tube furnace for activation treatment to obtain an activated product;

[0010] Step 4: Wash the activated product to neutrality and dry it to obtain high-pore volume nitrogen-doped activated carbon.

[0011] Furthermore, the weakly caking coal or non-caking coal in step 1 is one or a mixture of lignite, Zhundong sub-bituminous coal, Ningdong weakly caking coal or non-caking coal.

[0012] Furthermore, the size of the crushing and screening in step 1 is 40-60 mesh, the reagent used for the pickling is hydrochloric acid and / or hydrofluoric acid; the washing temperature is 20-80°C, and the washing time is 10-24 hours; the drying temperature is 60-150°C, and the drying time is 6-24 hours.

[0013] Furthermore, the activator in step 2 is one or a combination of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate or sodium bicarbonate, and the mass ratio of the coal particles to the activator is 1:0.5~5.

[0014] Furthermore, the drying temperature in step 2 is 80-150° C., and the drying time is 10-24 h.

[0015] Furthermore, the nitrogen-containing precursor in step 2 is one or a mixture of urea, melamine or ethylenediamine, and the mass ratio of the coal particles to the nitrogen-containing precursor in the mixture powder is 1:0.5-5.

[0016] Furthermore, the activation treatment in step 3 is carried out under an inert atmosphere at a temperature of 2-10 °C·min -1 The heating rate is raised to 700~1600 ℃ and kept warm for 5~360 min; the carrier gas of the inert atmosphere is one or a mixture of nitrogen, argon or helium, and the volume flow ratio of the carrier gas is 0.1~10 L·min -1 .

[0017] Furthermore, the washing to neutrality in step 4 is to first wash away the activator in the activated product with dilute hydrochloric acid, detect whether the activator is completely washed away with a pH reagent, and then wash it to neutrality with deionized water; the drying temperature is 80~150℃, and the drying time is 12~24 hours.

[0018] A high-pore volume nitrogen-doped activated carbon prepared according to the preparation method provided by the present invention, wherein the high-pore volume nitrogen-doped activated carbon has a specific surface area of ​​1532 m 2 ·g -1 The micropore volume is 0.60 cm 3 ·g -1The total pore volume is 0.68 cm 3 ·g -1 , the micropore ratio is 88.5%.

[0019] Furthermore, the high-pore volume nitrogen-doped activated carbon has a surface carbon content of 86.0 at.%, a surface oxygen content of 8.7 at.%, a surface nitrogen content of 5.3 at.%, a CO2 adsorption capacity of 3.66 mmol / g at 1 bar at 25°C, and a N2 adsorption capacity of 0.39 mmol / g.

[0020] Beneficial effects of the present invention:

[0021] This invention provides a method for preparing activated carbon with both high pore volume and high nitrogen content. This method improves the activated carbon's CO2 adsorption capacity while ensuring the purity of the CO2 in the desorbed gas. By separating the activation medium (carbon source and activator) from the nitrogen-containing precursor, the carbon deposition effect of the nitrogen-containing precursor is reduced. This method increases the nitrogen content while maintaining the activated carbon's high pore volume, thereby achieving both high CO2 adsorption capacity and high CO2 / N2 adsorption selectivity. Furthermore, when applied to industrial CO2 capture, the resulting activated carbon exhibits the advantages of both high CO2 adsorption capacity and high CO2 purity in the desorbed gas. Because this preparation method is based on the established industrial carbonization-activation process, it does not require modification of existing equipment and therefore has promising application prospects and industrial potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the sample laying method in a tube furnace according to Example 1 and Comparative Example 2 of the present invention, a is Comparative Example 2, and b is Example 1;

[0023] Figure 2 The nitrogen adsorption isotherms of the high-pore volume nitrogen-doped activated carbon obtained in Example 1 of the present invention and Comparative Examples 1 and 2 are shown;

[0024] Figure 3 The pore size distribution curves of high-pore volume nitrogen-doped activated carbon obtained in Example 1 of the present invention and Comparative Examples 1 and 2 are shown;

[0025] Figure 4 Graph showing the CO2 adsorption capacity of high-porous volume nitrogen-doped activated carbon obtained in Example 1 of the present invention and Comparative Examples 1 and 2 at 25°C;

[0026] Figure 5 2 is a graph of CO2 / N2 selectivity of high pore volume nitrogen-doped activated carbon obtained in Example 1 of the present invention and Comparative Examples 1 and 2 at different CO2 concentrations at 1 bar. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below with reference to the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be included in the scope of protection of the present invention. The process equipment or devices not specifically noted in the following examples are all conventional equipment or devices in the art. Unless otherwise specified, the raw materials used in the examples of the present invention can be obtained commercially; unless otherwise specified, the technical means used in the examples of the present invention are all conventional means well known to those skilled in the art.

[0028] Example 1

[0029] This embodiment provides a method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture, comprising the following steps:

[0030] Step 1: Using Ningdong coal as raw material, crushing it into 40-60 mesh coal particles, and acid washing with a mixture of hydrochloric acid and hydrofluoric acid at 80°C for 12 hours to obtain coal particles;

[0031] Step 2: Take 3 g of the coal particles obtained in step 1, mix them evenly with 3 g of potassium hydroxide, place them in deionized water, and dry them at 90°C for 24 hours to fully dry the solution in the obtained mixed system. Then, the dried mixture and 3 g of melamine are placed in different isolated areas in a nickel crucible;

[0032] Step 3: Place the crucible with the sample in a horizontal tube furnace and heat at 100 mL min -1 Nitrogen was used as carrier gas at 10 ℃·min -1 The temperature was raised from room temperature to the activation temperature of 800 °C for 10 min, and then naturally cooled to room temperature to obtain the activated product.

[0033] Step 4: The activator in the activated product was washed away with dilute hydrochloric acid. A pH test was used to verify complete removal of the activator, followed by washing with deionized water until neutral. After drying at 90°C for 24 hours, a high-pore volume nitrogen-doped activated carbon, designated AC-1-S, was obtained. Here, 1 refers to the mass ratio of melamine to coal particles, and S refers to the separation of melamine and the activation medium (coal and activator) into different regions of the nickel crucible.

[0034] Example 2

[0035] This embodiment provides a method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture, comprising the following steps:

[0036] Step 1: Using Ningdong coal as raw material, crushing it into 40-60 mesh coal particles, and acid washing with a mixture of hydrochloric acid and hydrofluoric acid at 70°C for 16 hours to obtain coal particles;

[0037] Step 2: Take 3 g of the coal particles obtained in step 1, mix them evenly with 3 g of potassium hydroxide, place them in deionized water, and dry them at 110°C for 20 hours to fully dry the solution in the resulting mixed system. Then, the dried mixture and 3 g of melamine are placed in different isolated areas in a nickel crucible;

[0038] Step 3: Place the crucible with the sample in a horizontal tube furnace and heat at 100 mL min -1 Nitrogen was used as carrier gas at 10 ℃·min -1 The temperature was raised from room temperature to the activation temperature of 1000 °C for 10 min, and then naturally cooled to room temperature to obtain the activated product.

[0039] Step 4: Wash the activator in the activated product with dilute hydrochloric acid, use a pH reagent to detect whether the activator is completely washed away, and then wash it with deionized water until it is neutral; after drying at 90° C. for 24 h, a high-pore volume nitrogen-doped activated carbon is obtained.

[0040] Example 3

[0041] This embodiment provides a method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture, comprising the following steps:

[0042] Step 1: Using Ningdong coal as raw material, crushing it into 40-60 mesh coal particles, and acid washing with a mixture of hydrochloric acid and hydrofluoric acid at 60°C for 20 hours to obtain coal particles;

[0043] Step 2: Take 3 g of the coal particles obtained in step 1, mix them evenly with 3 g of potassium hydroxide, place them in deionized water, and dry them at 130°C for 15 hours to fully dry the solution in the resulting mixed system. Then, the dried mixture and 3 g of melamine are placed in different isolated areas in a nickel crucible;

[0044] Step 3: Place the crucible with the sample in a horizontal tube furnace and heat at 100 mL min -1 Nitrogen was used as carrier gas at 10 ℃·min -1 The temperature was raised from room temperature to the activation temperature of 1200 °C for 10 min, and then naturally cooled to room temperature to obtain the activated product.

[0045] Step 4: Wash the activator in the activated product with dilute hydrochloric acid, use a pH reagent to detect whether the activator is completely washed away, and then wash it with deionized water until it is neutral; after drying at 90° C. for 24 h, a high-pore volume nitrogen-doped activated carbon is obtained.

[0046] Example 4

[0047] This embodiment provides a method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture, comprising the following steps:

[0048] Step 1: Using Ningdong coal as raw material, crushing it into 40-60 mesh coal particles, and acid washing with a mixture of hydrochloric acid and hydrofluoric acid at 50°C for 24 hours to obtain coal particles;

[0049] Step 2: Take 3 g of the coal particles obtained in step 1, mix them evenly with 3 g of potassium hydroxide, place them in deionized water, and dry them at 150°C for 10 hours to fully dry the solution in the resulting mixed system. Then, the dried mixture and 3 g of melamine are placed in different isolated areas in a nickel crucible;

[0050] Step 3: Place the crucible with the sample in a horizontal tube furnace and heat at 100 mL min -1 Nitrogen was used as carrier gas at 10 ℃·min -1 The heating rate was increased from room temperature to the activation temperature of 1400 °C for 10 min, and then naturally cooled to room temperature to obtain the activated product.

[0051] Step 4: Wash the activator in the activated product with dilute hydrochloric acid, use a pH reagent to detect whether the activator is completely washed away, and then wash it with deionized water until it is neutral; after drying at 90° C. for 24 h, a high-pore volume nitrogen-doped activated carbon is obtained.

[0052] Comparative Example 1

[0053] This comparative example provides a method for preparing activated carbon without nitrogen doping, comprising the following steps:

[0054] Step 1: Using Ningdong coal as raw material, crushing it into 40-60 mesh coal particles, and acid washing with a mixture of hydrochloric acid and hydrofluoric acid at 80°C for 12 hours to obtain coal particles;

[0055] Step 2: Take 3 g of the coal particles obtained in step 1, mix them evenly with 3 g of potassium hydroxide, place them in deionized water, and dry them at 90°C for 24 hours to fully dry the solution in the obtained mixed system. Then, place the dried mixture in a nickel crucible;

[0056] Step 3: Place the crucible with the sample in a horizontal tube furnace and heat at 100 mL min -1 Nitrogen was used as carrier gas at 10 ℃·min -1 The temperature was raised from room temperature to the activation temperature of 800 °C for 10 min, and then naturally cooled to room temperature to obtain the activated product.

[0057] Step 4: Wash the activated carbon with dilute hydrochloric acid to remove the activator. Check with a pH tester to ensure complete removal of the activator. Wash the activated carbon with deionized water until neutral. Dry the activated carbon at 90°C for 24 hours to obtain nitrogen-free activated carbon, designated AC-0. Here, 0 refers to the mass ratio of melamine to deashed coal particles.

[0058] Comparative Example 2

[0059] This comparative example provides a method for preparing nitrogen-doped activated carbon, comprising the following steps:

[0060] Step 1: Using Ningdong coal as raw material, crushing it into 40-60 mesh coal particles, and acid washing with a mixture of hydrochloric acid and hydrofluoric acid at 80°C for 12 hours to obtain coal particles;

[0061] Step 2: Take 3 g of the coal particles obtained in step 1, mix them evenly with 3 g of potassium hydroxide and 3 g of melamine, place them in deionized water, and dry them at 90°C for 24 hours to fully dry the solution in the obtained mixed system. Then, spread the dried mixture in a nickel crucible;

[0062] Step 3: Place the crucible with the sample in a horizontal tube furnace and heat at 100 mL min -1 Nitrogen was used as carrier gas at 10 ℃·min -1 The temperature was raised from room temperature to the activation temperature of 800 °C for 10 min, and then naturally cooled to room temperature to obtain the activated product.

[0063] Step 4: Wash the activated product with dilute hydrochloric acid to remove the activator. Complete removal of the activator was checked with a pH tester, and then the product was washed with deionized water until neutral. After drying at 90°C for 24 hours, a high-pore volume nitrogen-doped activated carbon, designated AC-1-B, was obtained. Here, 1 refers to the mass ratio of melamine to coal particles, and S refers to the mixture of melamine and the activation medium (coal and activator) before being placed in a nickel crucible.

[0064] The activated carbon prepared in Example 1, Comparative Example 1 and Comparative Example 2 was subjected to nitrogen adsorption test, and the obtained adsorption-desorption isotherms and pore size distribution results were as follows: Figure 2 、 3 As shown in Table 1, the pore structure of activated carbon under different process conditions is shown in Table 1.

[0065] Table 1

[0066]

[0067] Figure 2 As shown in Table 1, the specific surface area of ​​AC-0 is 1005 m 2 ·g -1 , the pore volume is 0.58 cm 3·g -1 . Figure 3 The results show that the activated carbon prepared is mainly microporous, with a distribution range of micropores in the range of 0.4-0.8 nm. In contrast, when the nitrogen-containing precursor is mixed with the carbon source and the activator and heated, the specific surface area of ​​the obtained activated carbon (AC-1-B) decreases to 873 m 2 ·g -1 , the pore volume is reduced to 0.50 cm 3 ·g -1 When the nitrogen-containing precursor is placed separately from the carbon source and the activator and heated, depending on the amount of nitrogen-containing precursor added, the carbon deposition effect is avoided, the nitrogen source decomposes and NH3 is introduced, achieving deep activation of the carbon source. The specific surface area of ​​the obtained activated carbon (AC-1-S) increases to 1532 m 2 ·g -1 , the pore volume becomes 0.68 cm 3 ·g -1 This shows that after separation and placement, the activated carbon produced can ensure that the pore volume of the activated carbon remains unchanged or even increase the pore volume of the activated carbon.

[0068] The prepared activated carbon was subjected to X-ray photoelectron spectroscopy test, and the results are shown in Table 2.

[0069] Table 2

[0070]

[0071] The surface oxygen and nitrogen contents of AC-0 were measured to be 6.9 at.% and 4.0 at.%, respectively. After nitrogen doping, the surface oxygen and nitrogen contents of AC-1-S were 8.7 at.% and 5.3 at.%, respectively, and those of AC-1-B were 7.5 at.% and 9.1 at.%, respectively. This indicates that the addition of a nitrogen source significantly increases the surface nitrogen content of activated carbon. However, due to insufficient and uneven mixing, the effect of separating the nitrogen source on the increase in nitrogen functional groups is slightly weaker.

[0072] like Figure 4 、 Figure 5 As shown in Table 2, the CO2 adsorption experiment shows that the CO2 adsorption capacity of activated carbon varies depending on the pore volume. Due to the reduction of micropore volume and increase of micropore size caused by the introduction of nitrogen source, the CO2 adsorption capacity of activated carbon at 25 ℃ and 1 bar decreased after nitrogen doping. However, due to the increase in micropore volume, the CO2 adsorption capacity of AC-1-S only decreased slightly to 3.66 mmol / g, while the CO2 adsorption capacity of AC-1-B decreased significantly to 3.39 mmol / g. In addition, as Figure 5As shown in the figure, the CO2 / N2 adsorption selectivity of activated carbon increases due to the increased nitrogen content. AC-1-B also exhibits a higher CO2 / N2 adsorption selectivity due to its higher nitrogen content. However, compared to AC-0, AC-1-S maintains a high CO2 adsorption capacity while increasing its CO2 adsorption selectivity by 8-20% due to its 32.5% higher surface nitrogen content.

Claims

1. A method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture, characterized in that: The steps include: Step 1: Using low-rank weakly caking coal or non-caking coal as raw material, crushing and screening, acid washing to remove ash in the coal, and drying to obtain coal particles; Step 2: uniformly mix the coal particles obtained in step 1 and the activator and place them in deionized water, fully dry the solution in the resulting mixed system, and place the dried mixture and the nitrogen-containing precursor in different isolated areas in the crucible; Step 3: placing the crucible in a horizontal tube furnace for activation treatment to obtain an activated product; Step 4: Wash the activated product to neutrality and dry it to obtain high-pore volume nitrogen-doped activated carbon.

2. The method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture according to claim 1, characterized in that: The weakly caking coal or non-caking coal in step 1 is one or a mixture of lignite, Zhundong sub-bituminous coal, Ningdong weakly caking coal or non-caking coal.

3. The method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture according to claim 1 or 2, characterized in that: The size of the crushing and screening in step 1 is 40-60 mesh, and the reagent used for the pickling is hydrochloric acid and / or hydrofluoric acid; the washing temperature is 20-80°C, and the washing time is 10-24 hours; the drying temperature is 60-150°C, and the drying time is 6-24 hours.

4. The method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture according to claim 3, characterized in that: In step 2, the activator is one or a combination of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate or sodium bicarbonate, and the mass ratio of the coal particles to the activator is 1:0.5~5.

5. The method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture according to claim 4, characterized in that: The drying temperature in step 2 is 80-150°C and the drying time is 10-24 hours.

6. The method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture according to claim 5, characterized in that: In step 2, the nitrogen-containing precursor is one or a mixture of urea, melamine or ethylenediamine, and the mass ratio of the coal particles to the nitrogen-containing precursor in the mixture powder is 1:0.5-5.

7. The method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture according to claim 6, characterized in that: The activation treatment in step 3 is carried out under an inert atmosphere at 2-10 ℃·min -1 The heating rate is raised to 700~1600 ℃ and kept warm for 5~360 min; the carrier gas of the inert atmosphere is one or a mixture of nitrogen, argon or helium, and the volume flow ratio of the carrier gas is 0.1~10 L·min -1 .

8. The method for preparing high-pore volume nitrogen-doped activated carbon for carbon dioxide capture according to claim 7, characterized in that: The washing to neutrality in step 4 is to first wash away the activator in the activated product with dilute hydrochloric acid, detect whether the activator is completely washed away with a pH reagent, and then wash it to neutrality with deionized water; the drying temperature is 80~150℃, and the drying time is 12~24 hours.

9. A high-pore volume nitrogen-doped activated carbon prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The specific surface area of ​​the high pore volume nitrogen-doped activated carbon is 1532 m 2 ·g -1 The micropore volume is 0.60 cm 3 ·g -1 The total pore volume is 0.68 cm 3 ·g -1 , the micropore ratio is 88.5%.

10. The high-pore volume nitrogen-doped activated carbon according to claim 9, characterized in that The high-pore volume nitrogen-doped activated carbon has a surface carbon content of 86.0 at.%, a surface oxygen content of 8.7 at.%, and a surface nitrogen content of 5.3 at.%. The CO2 adsorption capacity at 1 bar at 25°C is 3.66 mmol / g, and the N2 adsorption capacity is 0.39 mmol / g.

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