Preparation method of nitrogen- and boron-modified coal-based activated carbon for carbon dioxide adsorption

Abstract

The present application discloses a preparation method of nitrogen- and boron-modified coal-based activated carbon for carbon dioxide adsorption, belonging to the technical field of the preparation of coal-based activated carbon. The preparation method mainly includes raw material pretreatment, carbonization treatment, activation treatment and nitrogen-boron modification treatment. By doping and modifying the coal-based activated carbon with nitrogen and boron elements during the preparation process of the activated carbon, the prepared coal-based activated carbon product has a rich pore structure, doped groups and a high specific surface area, and has a high CO2 adsorption selectivity, a large CO2 adsorption capacity and excellent adsorption performance. The raw materials required by this method are cheap and easy to obtain, the preparation process flow is simple, the activated carbon can be recycled after regeneration, the economic benefit is high, and the applicable range is wide.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of coal-based activated carbon, and particularly relates to a preparation method of nitrogen-boron modified coal-based activated carbon for carbon dioxide adsorption. Background Art

[0002] The emission of CO2 has caused large-scale global climate change, which has had a great impact on human life and has become one of the greatest challenges faced by mankind. CO2 capture methods include a series of methods such as absorption method, adsorption method, membrane separation method, cryogenic separation method, etc. In the adsorption method, due to the advantages of activated carbon such as large specific surface area, strong adsorption performance, cheap and easily available raw materials, and easy regeneration, it has been widely used in the adsorption and capture of CO2 to realize the resource utilization of CO2.

[0003] Activated carbon is a porous material mainly composed of carbon, with a highly developed pore structure, large specific surface area, strong adsorption performance, stable chemical properties, and characteristics such as acid resistance, alkali resistance, heat resistance, high mechanical strength, and easy regeneration. As an excellent adsorption material, it was mainly used in the early stage for deep purification such as air purification, high-purity domestic drinking water, industrial water and wastewater treatment, and dechlorination, decolorization and deodorization. With the continuous development of society, activated carbon has been widely used in various aspects of human production and life such as gas purification, water treatment, food, beverage, medicine, chemical industry, smelting, national defense and agriculture.

[0004] The activated carbon prepared by the current methods still has the characteristics of low CO2 adsorption capacity and poor selectivity. How to further increase the specific surface area of activated carbon, increase the number of nitrogen-containing and oxygen-containing functional groups in activated carbon, and enhance the adsorption capacity of activated carbon, especially the selectivity for CO2, is one of the important problems that need to be solved urgently. If activated carbon with both a high specific surface area and rich doping groups can be prepared, it is expected to significantly improve its adsorption performance for CO2. Chinese Patent CN202110373849.3 discloses a preparation method and application of a high specific surface area porous material. Coal or heavy organic matter is swollen with a solvent, a cross-linking agent is added, and under the catalysis of a Lewis acid, product A is obtained by reaction, and then it is washed with a solvent, filtered, and then dried to obtain a porous polymer; the porous polymer is subjected to activation treatment in an atmosphere of carbon dioxide, water vapor, air or a mixture thereof to obtain a porous carbon material. However, in its preparation process, the required activation time is relatively long, 1–10 h, while the present invention only needs 30–60 min to prepare an activated carbon material with high adsorption performance, greatly shortening the activation time and reducing the energy consumption. Summary of the Invention

[0005] Technical problems to be solved:

[0006] Aiming at the deficiencies of the prior art, the present application provides a preparation method of nitrogen and boron modified coal-based activated carbon for carbon dioxide adsorption, which solves the problems such as low CO2 adsorption capacity and poor adsorption effect existing at present.

[0007] Technical solution:

[0008] To achieve the above object, the present application is realized through the following technical solutions:

[0009] A preparation method of nitrogen and boron modified coal-based activated carbon for carbon dioxide adsorption, comprising the following steps:

[0010] Step A: Grind the raw coal sufficiently and screen it with a 200-mesh sieve. Take the undersize coal sample, dry it in an oven, and prepare a dry coal sample for later use.

[0011] Step B: Take 5 - 10 parts by mass of the activator and 5 - 10 parts by mass of the dry coal sample according to the mass ratio, place them in a beaker and mix evenly. Then add 30 - 50 parts by mass of distilled water, place it on a magnetic stirrer, stir well at room temperature for 4 - 8 h, and then dry it in an oven to prepare a mixed coal sample for later use.

[0012] Step C: Place the dried mixed coal sample in a carbonization furnace for carbonization treatment to obtain a carbonized material for later use.

[0013] Step D: Place the carbonized material in an activation furnace for activation treatment to obtain activated carbon for later use.

[0014] Step E: Perform nitrogen modification treatment on the activated carbon: Take 5 - 15 parts by mass of the nitrogen source and 3 - 5 parts by mass of the activated carbon, place them in a beaker, add 50 - 100 parts by mass of distilled water, stir with a magnetic stirrer at room temperature for 16 - 24 h, then filter, and dry it in an oven to prepare nitrogen-modified activated carbon for later use.

[0015] Step F: Perform boron modification treatment on the nitrogen-modified activated carbon: Take 4 - 5 parts by mass of the boron source and 1 - 2 parts by mass of the nitrogen-modified activated carbon, place them in a beaker, add 50 - 100 parts by mass of distilled water, stir with a magnetic stirrer at room temperature for 2 - 4 h, then filter, and dry it in an oven to obtain the nitrogen and boron modified activated carbon product.

[0016] Preferably, the ash content A in the raw coal ad <5%, and the total sulfur content S t,d <0.5%.

[0017] Preferably, the activator is one or more of ZnCl2, KOH, and phosphoric acid.

[0018] Preferably, the stirring speed of the magnetic stirrer in Step B, Step E, and Step F is 300 - 500 r / min.

[0019] Preferably, the drying treatment temperature in steps A, B, E, and F is 60–80 °C, and the drying time is 4–6 h.

[0020] Preferably, the carbonization treatment conditions are a carbonization temperature of 600–700 °C, a heating rate of 15–20 °C / min, and a constant temperature time of 1–2 h.

[0021] Preferably, the activation treatment conditions are that the protective gas is nitrogen or argon, the activation temperature is 700–900 °C, the heating rate is 15–20 °C / min, and the activation time is 30–60 min.

[0022] Preferably, the nitrogen source is ammonium chloride and / or melamine.

[0023] Preferably, the boron source is borax and / or boric acid.

[0024] The principle of the present invention is as follows: In the process of preparing activated carbon, doping and modification of raw materials or activated carbon products can significantly improve the adsorption capacity of activated carbon. The doping elements are generally elements in the periodic table similar to carbon, which form a relatively stable structure by covalent bonding with the carbon skeleton. Nitrogen doping can change the arrangement of electrons in activated carbon, thereby increasing the conductivity of activated carbon, providing more active sites, increasing the number of doped groups in activated carbon, and further improving the adsorption performance of activated carbon. Boron doping will make the activated carbon have a higher degree of disordered graphitization, increase the number of micropores in the activated carbon, and further increase the specific surface area and adsorption capacity of the activated carbon material.

[0025] Beneficial effects:

[0026] The present application provides a preparation method of nitrogen-boron modified coal-based activated carbon for carbon dioxide adsorption, which has the following beneficial effects:

[0027] 1. Compared with the traditional preparation and modification methods of activated carbon, the coal-based activated carbon prepared by the present invention after nitrogen-boron modification has a rich pore structure and a relatively high specific surface area, a large CO2 adsorption capacity, and excellent adsorption performance.

[0028] 2. The specific surface area of the coal-based activated carbon prepared by the present invention can reach up to 1600 m 2 / g, while the specific surface area of currently commercially available activated carbon is mostly below 1200 m 2 / g.

[0029] 3. The CO2 saturated adsorption capacity of the coal-based activated carbon prepared by the present invention can reach up to 8.0 mmol / g, and the adsorption capacity of the existing technology is <5.0 mmol / g. Specific embodiments

[0030] To make the content of the present invention easy to understand, the following further illustrates the activated carbon preparation technology of the present invention in conjunction with embodiments, but the present invention is not limited thereto.

[0031] Example 1:

[0032] A preparation method of nitrogen-boron modified coal-based activated carbon for carbon dioxide adsorption, comprising the following steps:

[0033] Step A: Grind and screen the raw coal sufficiently to less than 200 mesh, and dry it in an oven at 70 °C for 4 h for later use.

[0034] Step B: Take 6 g of KOH and 8 g of dried coal sample and place them in a beaker for uniform mixing, then add 40 mL of distilled water, place it on a magnetic stirrer, and stir thoroughly at a speed of 300 r / min at room temperature for 4 h, and then dry it in an oven at 70 °C for 4 h for later use.

[0035] Step C: Place the dried mixed coal sample in a carbonization furnace for carbonization treatment, with a carbonization temperature of 600 °C, a heating rate of 15 °C / min, and a constant temperature time of 1 h to obtain carbonized material for later use.

[0036] Step D: Place the carbonized material in an activation furnace for activation treatment under a nitrogen atmosphere, with an activation temperature of 750 °C, a heating rate of 15 °C / min, and an activation time of 30 min to obtain an activated carbon product for later use.

[0037] Step E: Conduct nitrogen modification treatment on the activated carbon. Take 10 g of ammonium chloride and 3 g of the activated carbon product and place them in a beaker, add 60 g of distilled water, and stir thoroughly at a speed of 300 r / min at room temperature for 16 h using a magnetic stirrer, then filter, and dry it in an oven at 70 °C for 4 h to obtain nitrogen-modified activated carbon for later use.

[0038] Step F: Conduct boron modification treatment on the activated carbon. Take 4 g of borax and 1 g of the nitrogen-modified activated carbon product and place them in a beaker, add 60 g of distilled water, stir at a speed of 300 r / min at room temperature for 2 h using a magnetic stirrer, then filter, and dry it in an oven at 70 °C for 4 h to obtain a nitrogen-boron modified activated carbon product. Mark it as A1, and conduct specific surface area and carbon dioxide adsorption tests on the activated carbon product. The test results are shown in Table 1.

[0039] Example 2:

[0040] A preparation method of nitrogen-boron modified coal-based activated carbon for carbon dioxide adsorption, comprising the following steps:

[0041] Step A: Grind and screen the raw coal sufficiently to less than 200 mesh, and dry it in an oven at 80 °C for 5 h for later use.

[0042] Step B: Take 8 g of KOH and 8 g of dry coal sample, place them in a beaker and mix evenly. Then add 50 mL of distilled water, place it on a magnetic stirrer, and stir thoroughly at a speed of 400 r / min at room temperature for 6 h. Then dry it in an oven at 60 °C for 5 h for later use;

[0043] Step C: Place the dried mixed coal sample in a carbonization furnace for carbonization treatment. The carbonization temperature is 650 °C, the heating rate is 20 °C / min, and the constant temperature time is 1.5 h to obtain the carbonized material for later use;

[0044] Step D: Place the carbonized material in an activation furnace for activation treatment under a nitrogen atmosphere. The activation temperature is 850 °C, the heating rate is 20 °C / min, and the activation time is 45 min to obtain the activated carbon product for later use;

[0045] Step E: Conduct nitrogen modification treatment on the activated carbon. Take 15 g of ammonium chloride and 5 g of the activated carbon product, place them in a beaker, add 100 g of distilled water, and stir thoroughly at a speed of 400 r / min at room temperature for 20 h. Then filter, and dry it in an oven at 60 °C for 5 h to obtain the nitrogen-modified activated carbon for later use;

[0046] Step F: Conduct boron modification treatment on the activated carbon. Take 5 g of borax and 2 g of the nitrogen-modified activated carbon product, place them in a beaker, add 100 g of distilled water, stir at a speed of 400 r / min at room temperature for 4 h, then filter, and dry it in an oven at 60 °C for 5 h to obtain the nitrogen-boron modified activated carbon product. Mark it as A2, and conduct specific surface area and carbon dioxide adsorption tests on the activated carbon product. The test results are shown in Table 1.

[0047] Comparative Example 1:

[0048] No nitrogen and boron modification treatments were carried out, and other steps were the same as in Example 1.

[0049] Step A: Grind and screen the raw coal thoroughly to less than 200 mesh, and dry it in an oven at 70 °C for 4 h for later use;

[0050] Step B: Take 6 g of KOH and 8 g of dry coal sample, place them in a beaker and mix evenly. Then add 40 mL of distilled water, place it on a magnetic stirrer, and stir thoroughly at a speed of 300 r / min at room temperature for 4 h. Then dry it in an oven at 70 °C for 4 h for later use;

[0051] Step C: Place the dried mixed coal sample in a carbonization furnace for carbonization treatment. The carbonization temperature is 600 °C, the heating rate is 15 °C / min, and the constant temperature time is 1 h to obtain the carbonized material for later use;

[0052] Step D: Place the carbonized material in an activation furnace and conduct activation treatment under a nitrogen atmosphere. The activation temperature is 750 °C, the heating rate is 15 °C / min, and the activation time is 30 min to obtain an activated carbon product, labeled as B1. Conduct specific surface area and carbon dioxide adsorption tests on the activated carbon product, and the test results are shown in Table 1.

[0053] Comparative Example 2:

[0054] Only conduct nitrogen modification treatment, and the other steps are the same as in Example 1.

[0055] Step A: Grind and screen the raw coal sufficiently to less than 200 mesh, dry it in an oven at 70 °C for 4 h, and then set it aside for use.

[0056] Step B: Take 6 g of KOH and 8 g of the dried coal sample, place them in a beaker and mix evenly, then add 40 mL of distilled water, place it on a magnetic stirrer, and stir thoroughly at a speed of 300 r / min at room temperature for 4 h. Then dry it in an oven at 70 °C for 4 h and set it aside for use.

[0057] Step C: Place the dried mixed coal sample in a carbonization furnace for carbonization treatment. The carbonization temperature is 600 °C, the heating rate is 15 °C / min, and the constant temperature time is 1 h to obtain a carbonized material for standby.

[0058] Step D: Place the carbonized material in an activation furnace and conduct activation treatment under a nitrogen atmosphere. The activation temperature is 750 °C, the heating rate is 15 °C / min, and the activation time is 30 min to obtain an activated carbon product for standby.

[0059] Step E: Conduct nitrogen modification treatment on the activated carbon. Take 10 g of ammonium chloride and 3 g of the activated carbon product, place them in a beaker, add 60 g of distilled water, stir thoroughly at a speed of 300 r / min at room temperature for 16 h using a magnetic stirrer, then filter, and dry it in an oven at 70 °C for 4 h to obtain a nitrogen-modified activated carbon product, labeled as B2. Conduct specific surface area and carbon dioxide adsorption tests on the activated carbon product, and the test results are shown in Table 1.

[0060] Comparative Example 3:

[0061] Only conduct boron modification treatment, and the other steps are the same as in Example 1.

[0062] Step A: Grind and screen the raw coal sufficiently to less than 200 mesh, dry it in an oven at 70 °C for 4 h, and then set it aside for use.

[0063] Step B: Take 6 g of KOH and 8 g of the dried coal sample, place them in a beaker and mix evenly, then add 40 mL of distilled water, place it on a magnetic stirrer, and stir thoroughly at a speed of 300 r / min at room temperature for 4 h. Then dry it in an oven at 70 °C for 4 h and set it aside for use.

[0064] Step C: Place the dried mixed coal sample in a carbonization furnace for carbonization treatment at a carbonization temperature of 600 °C, a heating rate of 15 °C / min, and a constant temperature time of 1 h to obtain carbonized material for standby;

[0065] Step D: Place the carbonized material in an activation furnace for activation treatment under a nitrogen atmosphere at an activation temperature of 750 °C, a heating rate of 15 °C / min, and an activation time of 30 min to obtain activated carbon products for standby;

[0066] Step E: Conduct boron modification treatment on the activated carbon. Take 4 g of borax and 1 g of the activated carbon product and place them in a beaker. Add 60 g of distilled water and stir with a magnetic stirrer at a rotation speed of 300 r / min at room temperature for 2 h, then filter and dry in an oven at 70 °C for 4 h to obtain boron-modified activated carbon products. Labeled as B3, conduct specific surface area and carbon dioxide adsorption tests on the activated carbon products, and the test results are shown in Table 1.

[0067] Table 1 Treatment methods and performance test data of activated carbon products in examples and comparative examples

[0068] Sample Treatment method <![CDATA[Specific surface area / (m 2 ·g -1 )]]> <![CDATA[Carbon dioxide adsorption capacity / (mmol·g -1 )]]> A1 Nitrogen and boron modification 1361 5.5 A2 Nitrogen and boron modification 1527 6.2 B1 Unmodified 846 2.1 B2 Nitrogen modification 1129 3.6 B3 Boron modification 1218 3.9

[0069] It can be seen from the examples, comparative examples and the results in Table 1 that compared with the activated carbon without modification treatment or only single-element modification treatment, after nitrogen and boron modification treatment, its specific surface area and carbon dioxide adsorption capacity have been significantly improved, indicating that the dual-element doping modification effect is better than the single-element doping modification. The doping of nitrogen and boron can effectively enrich the pore structure of the activated carbon, increase the specific surface area of the activated carbon, and thus increase the carbon dioxide adsorption capacity of the activated carbon.

[0070] The above is a detailed description of the present invention in combination with examples, but the implementation mode of the present invention is not limited by the above examples. Those skilled in the art, based on the inspiration of the present invention, should be within the protection scope of the present invention for improvements, replacements, and modifications made without departing from the core guiding ideology of the present invention.

Claims

1. A preparation method of nitrogen and boron modified coal-based activated carbon for carbon dioxide adsorption, characterized in that, The following steps are involved: Step A, grinding the raw coal fully and sieving it with a 200-mesh sieve, taking the coal sample under the sieve and drying it in an oven to obtain a dry coal sample for later use; Step B, taking 5-10 parts by weight of the activator and 5-10 parts by weight of the dry coal sample in a beaker and mixing them evenly, then adding 30-50 parts by weight of distilled water, placing the mixture on a magnetic stirrer, stirring the mixture at room temperature for 4-8 hours, and then drying the mixture in an oven to obtain a mixed coal sample for later use; Step C, placing the dried mixed coal sample in a carbonization furnace for carbonization treatment to obtain a carbonized material for standby use; Step D, placing the carbonized material in an activation furnace for activation treatment to obtain activated carbon for standby use; Step E, performing nitrogen modification treatment on the activated carbon: 5-15 parts by weight of nitrogen source and 3-5 parts by weight of activated carbon are placed in a beaker, 50-100 parts by weight of distilled water are added, and the mixture is stirred at room temperature for 16-24 hours using a magnetic stirrer, filtered, and dried in an oven to obtain nitrogen-modified activated carbon for later use; Step F, performing boron modification treatment on the nitrogen-modified activated carbon: 4-5 parts by mass of a boron source and 1-2 parts by mass of the nitrogen-modified activated carbon are placed in a beaker, 50-100 parts by mass of distilled water are added, and the mixture is stirred at room temperature for 2-4 hours using a magnetic stirrer, filtered, and dried in an oven to obtain a nitrogen-boron-modified activated carbon product; The activation treatment conditions are as follows: the protective gas is nitrogen or argon, the activation temperature is 700-900°C, the heating rate is 15-20°C / min, and the activation time is 30-60min.

2. The preparation method of nitrogen and boron modified coal-based activated carbon for carbon dioxide adsorption according to claim 1, characterized in that: The ash content A in the raw coal ad < 5%, and the total sulfur content S t,d < 0.5%.

3. The preparation method of nitrogen and boron modified coal-based activated carbon for carbon dioxide adsorption according to claim 1, characterized in that: The activator is one or more of ZnCl2, KOH and phosphoric acid.

4. The preparation method of nitrogen and boron modified coal-based activated carbon for carbon dioxide adsorption according to claim 1, characterized in that: In step B, step E and step F, the stirring speed of the magnetic stirrer is 300-500 r / min.

5. The preparation method of nitrogen and boron modified coal-based activated carbon for carbon dioxide adsorption according to claim 1, characterized in that: The drying treatment temperature of step A, step B, step E and step F is 60-80° C., and the drying time is 4-6 hours.

6. The preparation method of nitrogen and boron modified coal-based activated carbon for carbon dioxide adsorption according to claim 1, characterized in that: The carbonization treatment conditions are as follows: a carbonization temperature of 600-700°C, a heating rate of 15-20°C / min, and a constant temperature time of 1-2h.

7. The preparation method of nitrogen and boron modified coal-based activated carbon for carbon dioxide adsorption according to claim 1, characterized in that: The nitrogen source is ammonium chloride and / or melamine.

8. The preparation method of nitrogen and boron modified coal-based activated carbon for carbon dioxide adsorption according to claim 1, characterized in that: The boron source is borax and / or boric acid.