A kind of low carbon dioxide adsorption heat activated carbon and preparation method thereof

Abstract

The present invention relates to a low-CO2 adsorption heat activated carbon and a preparation method thereof, and belongs to the field of activated carbon technology. In order to solve the problem that the existing activated carbon has a high CO2 adsorption heat, which leads to excessively high regeneration energy consumption, the present invention provides a low-CO2 adsorption heat activated carbon and a preparation method thereof. By subjecting the initial activated carbon to high-temperature pyrolysis or catalytic graphitization, pyrolysis activated carbon or catalytic graphitized activated carbon is obtained, thereby achieving effective removal of heteroatoms such as nitrogen and oxygen functional groups in the activated carbon, greatly reducing the CO2 adsorption heat of the activated carbon, thereby reducing regeneration energy consumption and improving the operating economy of the CO2 adsorption system. The activated carbon preparation method provided by the present invention can flexibly select experimental methods to obtain the required activated carbon according to the demand for CO2 adsorption capacity and the demand for reducing CO2 adsorption heat, and the activated carbon preparation process of this technical route is simple and low-cost, and has good application prospects and industrialization potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of activated carbon, and in particular relates to a low carbon dioxide adsorption heat activated carbon and a preparation method thereof. Background Art

[0002] The heat of adsorption of carbon dioxide refers to the heat released by the adsorption reaction between carbon dioxide and other substances under isothermal conditions. The heat of adsorption mainly comes from the interaction between CO2 molecules and the adsorbent surface, including van der Waals forces, electrostatic forces, and possible chemical bonds. When the heat of adsorption of CO2 is high, it means that the interaction between the CO2 molecules and the adsorbent is strong, so more energy is required to desorb the CO2 molecules from the adsorbent surface. This results in the need to provide higher temperatures or more energy to destroy the interaction between the CO2 molecules and the adsorbent during the regeneration process.

[0003] 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 the CO2 capture process. At present, commercial activated carbon with a well-developed pore structure (specific surface area> 600m2) can be obtained based on mature heat treatment methods. 2 ·g -1 However, activated carbon is usually limited by heat transfer during the CO2 capture process. The high adsorption heat leads to excessive regeneration energy consumption, which seriously affects the operating economy of the CO2 adsorption system and is not conducive to the large-scale application of CO2 capture. Summary of the Invention

[0004] In order to solve the problem that the existing activated carbon has high carbon dioxide adsorption heat which leads to high regeneration energy consumption, the present invention provides an activated carbon with low carbon dioxide adsorption heat and a preparation method thereof.

[0005] The technical solution of the present invention:

[0006] A method for preparing low carbon dioxide adsorption thermal activated carbon comprises the following steps:

[0007] Step 1: Using low-rank weakly sticky coal or non-sticky coal as raw material, crushing, acid-washing and drying it to obtain deashed coal particles, uniformly mixing the obtained deashed coal particles with an activator, and placing them in deionized water to obtain a mixed system I, and fully drying the solution in the mixed system I to obtain a solid mixture a, and using the obtained solid mixture a as a raw material to prepare initial activated carbon;

[0008] Step 2: Pyrolyze the initial activated carbon obtained in step 1 at 900-1600° C. under an inert atmosphere to obtain pyrolyzed activated carbon;

[0009] Alternatively, the initial activated carbon obtained in step 1 is uniformly mixed with the catalyst and then placed in deionized water to obtain a mixed system II, the solution in the mixed system II is fully dried to obtain a solid mixture b; the obtained solid mixture b is pyrolyzed at 900-1600° C. under an inert atmosphere to obtain a catalytic graphitization product; the obtained catalytic graphitization product is acid-washed to remove the catalyst to obtain a catalytically graphitized activated carbon.

[0010] Furthermore, the low-rank weakly caking coal or non-caking coal in step 1 includes one or a mixture of lignite, Zhundong sub-bituminous coal, Ningdong weakly caking or non-caking coal;

[0011] The size of the deashed coal particles is 1 μm to 10 mm, the reagent used for pickling is hydrochloric acid and / or hydrofluoric acid; the pickling temperature is 20 to 80° C., the pickling time is 10 to 24 hours; and the drying is performed at 60 to 150° C. for 6 to 24 hours.

[0012] Furthermore, the activator in step 1 is one or a mixture of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate or sodium bicarbonate; the mass ratio of the deashing coal particles to the activator is 1:0-2, and the temperature for fully drying the mixed system I is 80-150°C, and the drying time is 10-24 hours.

[0013] Furthermore, in step 1, the solid mixture a is used as a raw material to prepare the initial activated carbon by placing the solid mixture a in a horizontal tube furnace and introducing a flow rate of 0.1 to 10 L min -1 The inert gas is nitrogen, argon or helium or a mixture of the two or more, and the temperature is kept at 10℃·min -1 The heating rate is increased from room temperature to 700-900°C, and the activated product is obtained after constant temperature activation for 20-30 minutes. The activated product is naturally cooled to room temperature to obtain an activated product. The activated product is washed with dilute hydrochloric acid to remove the activator, and then washed with deionized water to neutrality, and dried at 80-150°C for 12-24 hours to obtain initial activated carbon.

[0014] Furthermore, the inert atmosphere in step 2 is introduced at a flow rate of 0.1 to 10 L min -1 The inert gas is used to maintain an inert atmosphere, wherein the inert gas is nitrogen, argon or helium or a mixture of the two. When the pyrolysis temperature is ≤ 1200 ° C, the temperature is set at 5 ° C·min -1 The heating rate is from room temperature to pyrolysis temperature. When the pyrolysis temperature is greater than 1200℃, the heating rate is first increased at 5℃·min -1 The heating rate was from room temperature to 1200℃, and then at 2℃·min -1 The heating rate is continued to rise from 1200° C. to the pyrolysis temperature, and the high-temperature pyrolysis time is 120 min.

[0015] Furthermore, the catalyst in step 2 is a mixture of one or more of FeCl3, CoCl2 or NiCl2; the mass ratio of the metal element to the activated carbon in the catalyst is 0.01 to 0.03:1, and the temperature for fully drying the mixed system II is 80 to 150°C, and the drying time is 10 to 24 hours.

[0016] Furthermore, the catalytic graphitization product in step 2 is washed with dilute hydrochloric acid to remove the catalyst, and then dried at 80-150° C. for 12-24 hours to obtain catalytic graphitized activated carbon.

[0017] The invention provides a method for preparing low-carbon dioxide adsorption heat activated carbon, and a method for preparing pyrolysis activated carbon or catalytic graphitization activated carbon.

[0018] Furthermore, the surface carbon content of the pyrolyzed activated carbon is 93.32~96.38at.%, the surface oxygen content is 3.25~6.17at.%, the surface nitrogen content is 0.37~1.94at.%, the CO2 adsorption capacity at 1 bar at 25°C is 2.56~3.27mmol / g, the CO2 adsorption capacity at 1 bar at 0°C is 4.35~5.82mmol / g, and the average value of isosteric adsorption heat is 27.1~31.7kJ / mol.

[0019] Furthermore, the surface carbon content of the catalytic graphitized activated carbon is 95.70~96.49at.%, the surface oxygen content is 3.00~3.80at.%, the surface nitrogen content is 0.31~0.73at.%, the CO2 adsorption capacity at 1 bar at 25°C is 2.09~2.55mmol / g, the CO2 adsorption capacity at 1 bar at 0°C is 3.36~4.44mmol / g, and the average value of the isosteric adsorption heat is 25.1~27.2kJ / mol.

[0020] Beneficial effects of the present invention:

[0021] The preparation method of low carbon dioxide adsorption heat activated carbon provided by the present invention achieves the effective removal of heteroatoms such as nitrogen and oxygen functional groups in the activated carbon through high-temperature pyrolysis and catalytic graphitization, thereby greatly reducing the CO2 adsorption heat of the activated carbon, thereby reducing the regeneration energy consumption of the activated carbon and improving the operating economy of the CO2 adsorption system.

[0022] The activated carbon preparation method provided by the present invention can flexibly select experimental methods to obtain the required activated carbon according to the requirements for CO2 adsorption capacity and the requirements for reducing CO2 adsorption heat. The activated carbon preparation process of this technical route is simple and low-cost, and has good application prospects and industrialization potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1Comparative graph of nitrogen adsorption isotherms of activated carbon prepared in Examples 1 to 6 and Comparative Example 1;

[0024] Figure 2 A comparison of nitrogen adsorption pore size distributions of activated carbons prepared in Examples 1 to 6 and Comparative Example 1;

[0025] Figure 3 Comparative diagram of X-ray photoelectron spectra of activated carbons prepared in Examples 1 to 6 and Comparative Example 1;

[0026] Figure 4 This is a comparison chart of the CO2 adsorption capacity of the activated carbon prepared in Examples 1 to 6 and Comparative Example 1 at 25°C;

[0027] Figure 5 A comparison chart of the CO2 adsorption capacity of activated carbon prepared in Examples 1 to 6 and Comparative Example 1 at 0°C;

[0028] Figure 6 Comparison of the CO2 isosteric adsorption heat of the activated carbons prepared in Examples 1 to 6 and Comparative Example 1;

[0029] Figure 7 A comparison chart of Raman test results of activated carbon prepared in Examples 1 to 6 and Comparative Example 1;

[0030] Figure 8 HRTEM images of activated carbons prepared in Examples 1 to 6 and Comparative Example 1, and lattice spacing images of activated carbons prepared in Examples 4 and 5, where a is AC; b is AC; c is AC1000; d is AC1300; e is AC1500; f is AC-Fe; g is AC-Co; h is AC-Ni; i is the lattice spacing of AC1500; j is the lattice spacing of AC-Fe; k is the lattice spacing of AC-Co; l is the lattice spacing of AC-Ni;

[0031] Figure 9 HRTEM images, lattice fringe size distributions, and lattice fringe orientation distributions of the activated carbons prepared in Examples 1 to 3 and Comparative Example 1, where columns (ad) are the original HRTEM images, binarized images, and skeletonized images of AC, AC1000, AC1300, and AC1500, respectively; columns (eh) are the lattice fringe size distributions of AC, AC1000, AC1300, and AC1500, respectively; and columns (il) are the lattice fringe orientation distributions of AC, AC1000, AC1300, and AC1500, respectively.

[0032] Figure 10These are the HRTEM images, lattice fringe size distribution diagrams and lattice fringe orientation distribution diagrams of the activated carbon prepared in Examples 3 to 5, where ad are the original HRTEM images, binarized images and skeletonized images of AC1500, AC-Fe, AC-Co and AC-Ni, respectively; eh are the lattice fringe size distribution diagrams of AC1500, AC-Fe, AC-Co and AC-Ni, respectively; and il are the lattice fringe orientation distribution diagrams of AC1500, AC-Fe, AC-Co and AC-Ni, respectively. DETAILED DESCRIPTION

[0033] 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.

[0034] Example 1

[0035] This embodiment provides a method for preparing low carbon dioxide adsorption heat activated carbon, the specific steps are as follows:

[0036] Step 1: crush the Ningdong weakly sticky coal into coal particles of 0.25-0.425 mm, acid wash with a mixture of hydrochloric acid and hydrofluoric acid at 80° C. for 12 h, and dry at 80° C. for 24 h to obtain deashed coal particles;

[0037] 2.5 g of deashed coal particles and 2.5 g of potassium hydroxide were uniformly mixed and placed in deionized water to obtain a mixed system I. The mixed system I was dried at 90° C. for 24 h to obtain a solid mixture a.

[0038] The solid mixture a was placed in a horizontal tube furnace and introduced at a flow rate of 0.1 L min -1 The inert atmosphere was maintained by nitrogen at 10 °C·min -1 The temperature was raised from room temperature to 900 °C at a constant temperature for 20 min, and the activated product was obtained after natural cooling to room temperature. The activated product was washed with dilute hydrochloric acid to remove the potassium hydroxide activator, and then washed with deionized water until neutral. After drying at 90 °C for 24 h, the initial activated carbon was obtained, marked as AC.

[0039] Step 2: Place the initial activated carbon AC obtained in step 1 in a horizontal tube furnace and introduce a flow rate of 0.1 L min -1 The inert atmosphere was maintained by argon gas at 5 °C·min -1The temperature was raised from room temperature to 1000 °C at a constant temperature for 120 min and then naturally cooled to room temperature to obtain pyrolyzed activated carbon, which was labeled AC1000, where 1000 means the pyrolysis temperature was 1000 °C.

[0040] Example 2

[0041] This embodiment provides a method for preparing low carbon dioxide adsorption heat activated carbon, the specific steps are as follows:

[0042] Step 1: crush the Ningdong weakly sticky coal into coal particles of 0.25-0.425 mm, acid wash with a mixture of hydrochloric acid and hydrofluoric acid at 80° C. for 12 h, and dry at 80° C. for 24 h to obtain deashed coal particles;

[0043] 2.5 g of deashed coal particles and 2.5 g of potassium hydroxide were uniformly mixed and placed in deionized water to obtain a mixed system I. The mixed system I was dried at 90° C. for 24 h to obtain a solid mixture a.

[0044] The solid mixture a was placed in a horizontal tube furnace and introduced at a flow rate of 0.1 L min -1 The inert atmosphere was maintained by nitrogen at 10 °C·min -1 The temperature was raised from room temperature to 900 °C at a constant temperature for 20 min, and the activated product was obtained after natural cooling to room temperature. The activated product was washed with dilute hydrochloric acid to remove the potassium hydroxide activator, and then washed with deionized water until neutral. After drying at 90 °C for 24 h, the initial activated carbon was obtained, marked as AC.

[0045] Step 2: Place the initial activated carbon AC obtained in step 1 in a horizontal tube furnace and introduce a flow rate of 0.1 L min -1 The inert atmosphere was maintained by argon gas at 5 °C·min -1 The heating rate was from room temperature to 1200℃, and then at 2℃·min -1 The heating rate was increased from 1200°C to 1300°C and then pyrolyzed at a constant temperature for 120 min. After naturally cooling to room temperature, pyrolyzed activated carbon was obtained, which was marked as AC1300, where 1300 means the pyrolysis temperature is 1300°C.

[0046] Example 3

[0047] This embodiment provides a method for preparing low carbon dioxide adsorption heat activated carbon, the specific steps are as follows:

[0048] Step 1: crush the Ningdong weakly sticky coal into coal particles of 0.25-0.425 mm, acid wash with a mixture of hydrochloric acid and hydrofluoric acid at 80° C. for 12 h, and dry at 80° C. for 24 h to obtain deashed coal particles;

[0049] 2.5 g of deashed coal particles and 2.5 g of potassium hydroxide were uniformly mixed and placed in deionized water to obtain a mixed system I. The mixed system I was dried at 90° C. for 24 h to obtain a solid mixture a.

[0050] The solid mixture a was placed in a horizontal tube furnace and introduced at a flow rate of 0.1 L min -1 The inert atmosphere was maintained by nitrogen at 10 °C·min -1 The temperature was raised from room temperature to 900 °C at a constant temperature for 20 min, and the activated product was obtained after natural cooling to room temperature. The activated product was washed with dilute hydrochloric acid to remove the potassium hydroxide activator, and then washed with deionized water until neutral. After drying at 90 °C for 24 h, the initial activated carbon was obtained, marked as AC.

[0051] Step 2: Place the initial activated carbon AC obtained in step 1 in a horizontal tube furnace and introduce a flow rate of 0.1 L min -1 The inert atmosphere was maintained by argon gas at 5 °C·min -1 The heating rate was from room temperature to 1200℃, and then at 2℃·min -1 The heating rate was increased from 1200°C to 1500°C and then pyrolyzed at a constant temperature for 120 min. After naturally cooling to room temperature, pyrolyzed activated carbon was obtained, which was marked as AC1500, where 1500 means the pyrolysis temperature is 1500°C.

[0052] Example 4

[0053] This embodiment provides a method for preparing low carbon dioxide adsorption heat activated carbon, the specific steps are as follows:

[0054] Step 1: crush the Ningdong weakly sticky coal into coal particles of 0.25-0.425 mm, acid wash with a mixture of hydrochloric acid and hydrofluoric acid at 80° C. for 12 h, and dry at 80° C. for 24 h to obtain deashed coal particles;

[0055] 2.5 g of deashed coal particles and 2.5 g of potassium hydroxide were uniformly mixed and placed in deionized water to obtain a mixed system I. The mixed system I was dried at 90° C. for 24 h to obtain a solid mixture a.

[0056] The solid mixture a was placed in a horizontal tube furnace and introduced at a flow rate of 0.1 L min -1 The inert atmosphere was maintained by nitrogen at 10 °C·min -1 The temperature was raised from room temperature to 900 °C at a constant temperature for 20 min, and the activated product was obtained after natural cooling to room temperature. The activated product was washed with dilute hydrochloric acid to remove the potassium hydroxide activator, and then washed with deionized water until neutral. After drying at 90 °C for 24 h, the initial activated carbon was obtained, marked as AC.

[0057] Step 2: 2 g of the initial activated carbon AC obtained in step 1 was uniformly mixed with 0.58 g of FeCl3 and placed in deionized water to obtain a mixed system II. The mixed system II was placed at 90°C and dried for 24 hours to obtain a solid mixture b. The mass of Fe in the solid mixture b was ensured to be 20% of the mass of the initial activated carbon.

[0058] The obtained solid mixture b was placed in a horizontal tube furnace and introduced at a flow rate of 0.1 L min -1 The inert atmosphere was maintained by argon gas at 5 °C·min -1 The heating rate was from room temperature to 1200℃, and then at 2℃·min -1 The heating rate was increased from 1200°C to 1500°C, and then the mixture was pyrolyzed at a constant temperature for 120 minutes. After naturally cooling to room temperature, a catalytic graphitization product was obtained. The catalyst was washed away from the obtained catalytic graphitization product with dilute hydrochloric acid, and the product was dried at 90°C for 24 hours to obtain catalytic graphitized activated carbon, which was labeled as AC-Fe, where Fe refers to an Fe-based catalyst.

[0059] Example 5

[0060] This embodiment provides a method for preparing low carbon dioxide adsorption heat activated carbon, the specific steps are as follows:

[0061] Step 1: crush the Ningdong weakly sticky coal into coal particles of 0.25-0.425 mm, acid wash with a mixture of hydrochloric acid and hydrofluoric acid at 80° C. for 12 h, and dry at 80° C. for 24 h to obtain deashed coal particles;

[0062] 2.5 g of deashed coal particles and 2.5 g of potassium hydroxide were uniformly mixed and placed in deionized water to obtain a mixed system I. The mixed system I was dried at 90° C. for 24 h to obtain a solid mixture a.

[0063] The solid mixture a was placed in a horizontal tube furnace and introduced at a flow rate of 0.1 L min -1 The inert atmosphere was maintained by nitrogen at 10 °C·min -1 The temperature was raised from room temperature to 900 °C at a constant temperature for 20 min, and the activated product was obtained after natural cooling to room temperature. The activated product was washed with dilute hydrochloric acid to remove the potassium hydroxide activator, and then washed with deionized water until neutral. After drying at 90 °C for 24 h, the initial activated carbon was obtained, marked as AC.

[0064] Step 2: 2 g of the initial activated carbon AC obtained in step 1 was uniformly mixed with 0.81 g of CoCl2·6H2O and placed in deionized water to obtain a mixed system II. The mixed system II was dried at 90°C for 24 h to obtain a solid mixture b, ensuring that the mass of Co in the solid mixture b was 20% of the mass of the initial activated carbon;

[0065] The obtained solid mixture b was placed in a horizontal tube furnace and introduced at a flow rate of 0.1 L min -1 The inert atmosphere was maintained by argon gas at 5 °C·min -1 The heating rate was from room temperature to 1200℃, and then at 2℃·min -1 The temperature was raised from 1200°C to 1500°C and then pyrolyzed at a constant temperature for 120 min. After naturally cooling to room temperature, a catalytic graphitization product was obtained. The catalyst was washed away from the obtained catalytic graphitization product with dilute hydrochloric acid and dried at 90°C for 24 h to obtain catalytic graphitized activated carbon, which was labeled as AC-Co, where Co refers to a Co-based catalyst.

[0066] Example 6

[0067] This embodiment provides a method for preparing low carbon dioxide adsorption heat activated carbon, the specific steps are as follows:

[0068] Step 1: crush the Ningdong weakly sticky coal into coal particles of 0.25-0.425 mm, acid wash with a mixture of hydrochloric acid and hydrofluoric acid at 80° C. for 12 h, and dry at 80° C. for 24 h to obtain deashed coal particles;

[0069] 2.5 g of deashed coal particles and 2.5 g of potassium hydroxide were uniformly mixed and placed in deionized water to obtain a mixed system I. The mixed system I was dried at 90° C. for 24 h to obtain a solid mixture a.

[0070] The solid mixture a was placed in a horizontal tube furnace and introduced at a flow rate of 0.1 L min -1 The inert atmosphere was maintained by nitrogen at 10 °C·min -1 The temperature was raised from room temperature to 900 °C at a constant temperature for 20 min, and the activated product was obtained after natural cooling to room temperature. The activated product was washed with dilute hydrochloric acid to remove the potassium hydroxide activator, and then washed with deionized water until neutral. After drying at 90 °C for 24 h, the initial activated carbon was obtained, marked as AC.

[0071] Step 2: 2 g of the initial activated carbon AC obtained in step 1 was uniformly mixed with 0.81 g of NiCl2·6H2O and placed in deionized water to obtain a mixed system II. The mixed system II was dried at 90°C for 24 h to obtain a solid mixture b, ensuring that the mass of Ni in the solid mixture b was 20% of the mass of the initial activated carbon;

[0072] The obtained solid mixture b was placed in a horizontal tube furnace and introduced at a flow rate of 0.1 L min -1 The inert atmosphere was maintained by argon gas at 5 °C·min -1 The heating rate was from room temperature to 1200℃, and then at 2℃·min -1The temperature was raised from 1200°C to 1500°C and then pyrolyzed at a constant temperature for 120 min. After naturally cooling to room temperature, a catalytic graphitization product was obtained. The catalyst was washed away from the obtained catalytic graphitization product with dilute hydrochloric acid and dried at 90°C for 24 h to obtain catalytic graphitized activated carbon, which was labeled as AC-Ni, where Ni refers to a Ni-based catalyst.

[0073] Comparative Example 1

[0074] This comparative example provides a method for preparing initial activated carbon, and the specific steps are as follows:

[0075] Step 1: crush the Ningdong weakly sticky coal into coal particles of 0.25-0.425 mm, acid wash with a mixture of hydrochloric acid and hydrofluoric acid at 80° C. for 12 h, and dry at 80° C. for 24 h to obtain deashed coal particles;

[0076] 2.5 g of deashed coal particles and 2.5 g of potassium hydroxide were uniformly mixed and placed in deionized water to obtain a mixed system I. The mixed system I was dried at 90° C. for 24 h to obtain a solid mixture a.

[0077] The solid mixture a was placed in a horizontal tube furnace and introduced at a flow rate of 0.1 L min -1 The inert atmosphere was maintained by nitrogen at 10 °C·min -1 The temperature was raised from room temperature to 900 °C at a constant temperature for 20 min, and the activated product was obtained after natural cooling to room temperature. The activated product was washed with dilute hydrochloric acid to remove the potassium hydroxide activator, and then washed with deionized water until neutral. After drying at 90 °C for 24 h, the initial activated carbon was obtained, marked as AC.

[0078] The activated carbon prepared in Examples 1 to 6 and Comparative Example 1 was subjected to nitrogen adsorption test, and the adsorption-desorption isotherms and pore size distribution results were as follows: Figure 1 、 2 The pore structure of activated carbon under different process conditions is shown in Table 1.

[0079] Table 1

[0080]

[0081] Figure 1 As shown in Table 1, the specific surface area of ​​AC is 1365m 2 ·g -1 , the pore volume is 0.79cm 3 ·g -1 . Figure 2 The results showed that the activated carbon produced was mainly micropores, with a distribution range of micropores between 0.4 and 0.8 nm. After high-temperature pyrolysis and catalytic graphitization, the pore volume and micropore ratio of the activated carbon decreased.

[0082] The activated carbons prepared in Examples 1 to 6 and Comparative Example 1 were subjected to X-ray photoelectron spectroscopy testing. The results are as follows: Figure 3 The element content of activated carbon and CO2 adsorption performance at 1 bar under different process conditions are shown in Table 2.

[0083] Table 2

[0084]

[0085] The surface oxygen and nitrogen contents of AC were measured to be 19.41 at.% and 0.83 at.%, respectively. After high-temperature pyrolysis and catalytic graphitization, the contents of oxygen and nitrogen functional groups on the activated carbon surface were significantly reduced, indicating that the high-temperature pyrolysis and catalytic graphitization processes effectively removed heteroatoms from the activated carbon.

[0086] The CO2 adsorption test results of the activated carbon prepared in Examples 1 to 6 and Comparative Example 1 are as follows: Figure 4 and Figure 5 As shown in the figure, the CO2 adsorption capacity of activated carbon varies depending on the pore volume.

[0087] Figure 6 Comparison of the CO2 isosteric adsorption heat of the activated carbon prepared in Examples 1 to 6 and Comparative Example 1; Figure 6 As shown in the figure, due to the difference in physical and chemical structure, the isosteric heat of adsorption of activated carbon is greatly reduced after high-temperature pyrolysis and catalytic graphitization. Taking the average value of the isosteric heat of adsorption, it can be found that the adsorption heat of activated carbon can be reduced by 22.4% after high-temperature pyrolysis and catalytic graphitization.

[0088] Figure 7 The Raman test results of the activated carbon prepared in Examples 1 to 6 and Comparative Example 1 are compared. By comparing the heteroatom content, it can be seen that in addition to the heteroatom content, the higher the graphitization degree of the activated carbon, the more Raman shift is about 2700 cm -1 The higher the 2d peak intensity at , the lower the isosteric adsorption heat.

[0089] Figure 8 HRTEM images of activated carbons prepared in Examples 1 to 6 and Comparative Example 1, and lattice spacing images of activated carbons prepared in Examples 4 and 5, where a is AC; b is AC; c is AC1000; d is AC1300; e is AC1500; f is AC-Fe; g is AC-Co; h is AC-Ni; i is the lattice spacing of AC1500; j is the lattice spacing of AC-Fe; k is the lattice spacing of AC-Co; l is the lattice spacing of AC-Ni;

[0090] like Figure 8As shown in a, macropores of hundreds of nanometers can be observed on the surface of activated carbon particles AC. In addition, increasing the magnification, it can be observed that the AC carbon plane is composed of short-range disordered microcrystals, which is a typical amorphous carbon structure, such as Figure 8 As shown in b. After high temperature pyrolysis treatment, Figure 8 As shown in Figure c, the microcrystalline structure of the AC1000 surface changes little. When the pyrolysis temperature is increased to 1300℃ and 1500℃, the growth of the microcrystalline size on the surface of the activated carbon can be clearly observed. Microcrystalline structures tens of nanometers long can be observed on the surface of the activated carbon, and the microcrystalline size of AC1500 is larger than that of AC1300, indicating that increasing the pyrolysis temperature is conducive to the increase of the microcrystalline size in the activated carbon. After catalytic graphitization treatment, it can be found that the length and width of the microcrystalline of AC-Fe, AC-Co and AC-Ni are further increased compared with AC1500, as shown in Figure d. Figure 8 fh. In addition, from Figure 8 As shown in Figure 1, catalytic graphitization reduces the activated carbon crystallite spacing and increases the degree of graphitization. Compared to AC1500, large activated carbon crystallites grow around Fe, Co, and Ni nanoparticles after catalytic graphitization. HRTEM images reveal that the large crystallites produced by catalytic graphitization are located around the metal nanoparticles, while areas away from the nanoparticles still exhibit an amorphous carbon structure.

[0091] In order to quantitatively reveal the effects of high-temperature pyrolysis and catalytic graphitization on the activated carbon microstructure, the size and orientation of the lattice fringes in the HRTEM image are counted. The image is processed by Fourier transform, smoothing filter, inverse Fourier transform, binarization and skeletonization to obtain the size distribution and orientation distribution information of the activated carbon microstructure, such as Figure 9 and Figure 10 The microcrystalline structural parameters of activated carbon are shown in Table 3. To avoid interference from image noise in the extracted information, since the minimum size of the lattice fringe (1×1) is 0.28nm, the lattice fringe parameters with a length of less than 0.3nm were removed to improve accuracy. In addition, considering that the lattice fringe size is concentrated in the range of 0.3 to 3.3nm (microcrystalline size 1×1 to 8×8, accounting for more than 98%), the statistical analysis mainly focuses on the lattice fringes within 0.3 to 3.3nm.

[0092] Figure 9 HRTEM images, lattice fringe size distributions, and lattice fringe orientation distributions of the activated carbons prepared in Examples 1 to 3 and Comparative Example 1, where columns (ad) are the original HRTEM images, binarized images, and skeletonized images of AC, AC1000, AC1300, and AC1500, respectively; columns (eh) are the lattice fringe size distributions of AC, AC1000, AC1300, and AC1500, respectively; and columns (il) are the lattice fringe orientation distributions of AC, AC1000, AC1300, and AC1500, respectively.

[0093] Figure 10 These are the HRTEM images, lattice fringe size distribution diagrams and lattice fringe orientation distribution diagrams of the activated carbon prepared in Examples 3 to 5, where ad are the original HRTEM images, binarized images and skeletonized images of AC1500, AC-Fe, AC-Co and AC-Ni, respectively; eh are the lattice fringe size distribution diagrams of AC1500, AC-Fe, AC-Co and AC-Ni, respectively; and il are the lattice fringe orientation distribution diagrams of AC1500, AC-Fe, AC-Co and AC-Ni, respectively.

[0094] Figure 9 The ad shows the original HRTEM image and its binarized and skeletonized images. It can be found that after binarization and skeletonization, the lattice fringes in the image are distinguished from the background, thereby achieving the extraction and statistics of the lattice fringes. By counting the lattice fringes size, it can be found that the proportion of lattice fringes in activated carbon decreases exponentially with the increase of the lattice fringes size, such as Figure 9 eh. Furthermore, after high-temperature pyrolysis, the proportion of lattice fringes sized 0.3-0.8 nm in the activated carbon decreased. Compared to AC (56%), the proportion of lattice fringes sized 0.3-0.8 nm in AC1000, AC1300, and AC1500 decreased to 44%, 41%, and 38%, respectively. This indicates that increasing the pyrolysis temperature increases the proportion of large crystallites in the activated carbon and the degree of graphitization, which is consistent with the results revealed by Raman and XRD.

[0095] As shown in Table 3, the average size of the lattice fringes (L avg ) and median size (L med ) can be used to reveal the effects of high-temperature pyrolysis and catalytic graphitization on the microcrystalline structure of activated carbon. After high-temperature pyrolysis, the average size of the lattice fringes in activated carbon increased. Compared with AC (0.90±0.57nm), the average size of the lattice fringes in AC1000, AC1300 and AC1500 increased to 1.06±0.68nm, 1.17±0.75nm and 1.23±0.77nm. This shows that as the pyrolysis temperature increases, the crystallite size in activated carbon increases, the degree of graphitization of activated carbon increases, and the median size of the lattice fringes further confirms this conclusion. In addition, the directional distribution of the lattice fringes in the HRTEM image was statistically analyzed, and the maximum value of the orientation distribution was set to 90°, as shown in Figure 2. Figure 9As shown in Table 3, the lattice fringes of activated carbon exhibit minimal changes in their directional distribution after high-temperature pyrolysis. Further statistical analysis of the proportion of lattice fringes within a 60° range reveals that after high-temperature pyrolysis, the lattice fringes of activated carbon are concentrated within the range of 80° to 140° or 60° to 120°. Furthermore, the proportion of lattice fringes with directional distribution within this range for AC, AC1000, AC1300, and AC1500 is 43.5%, 44.9%, 34.1%, and 39.2%, respectively, indicating that high-temperature pyrolysis has minimal effect on the lattice fringes' directional distribution.

[0096] Table 3

[0097] Sample <![CDATA[L avg (nm)]]> <![CDATA[L med (nm)]]> Directional angle (°) Directional ratio (%) AC 0.90±0.57 0.72 80～140 43.5 AC1000 1.06±0.68 0.89 60～120 44.9 AC1300 1.17±0.75 0.93 80～140 34.1 AC1500 1.23±0.77 1.01 60～120 39.2 AC-Fe 1.29±0.82 1.07 60～120 41.8 AC-Co 1.30±0.80 1.10 80～140 34.5 AC-Ni 1.29±0.79 1.09 60～120 36.6

[0098] After high-temperature pyrolysis treatment, it can be found that the proportion of large-sized microcrystals in activated carbon increases, the average size and median size of the lattice fringes in activated carbon increase, and the graphitization degree of activated carbon is significantly improved. However, after high-temperature pyrolysis, the directional distribution of the lattice fringes in activated carbon changes little. Compared with high-temperature pyrolysis, catalytic graphitization treatment can be performed on activated carbon and the size and directional distribution of its lattice fringes can be statistically analyzed to reveal the influence of catalytic graphitization on the graphitization degree of activated carbon, such as Figure 10 and shown in Table 3.

[0099] After catalytic graphitization, it can be found that the proportion of lattice fringes of 0.3-0.8 nm in activated carbon is further reduced. Compared with AC1500 (38%), the content of lattice fringes of 0.3-0.8 nm in AC-Fe, AC-Co and AC-Ni is reduced to 37%, 36% and 35%, respectively. Figure 10 This indicates that after catalytic graphitization, the proportion of large-sized microcrystals in the activated carbon is increased, the graphitization degree of the activated carbon is improved, and the graphitization effect is Ni>Co>Fe, which is consistent with the results revealed by Raman and XRD.

[0100] In addition, after catalytic graphitization, the average size of the lattice fringes in the activated carbon (L avg ) and median size (L med) further increased, as shown in Table 3. After catalytic graphitization treatment, the average size of the lattice fringes in the activated carbon increased and then remained stable. Compared with AC1500 (1.23±0.77nm), the average size of the lattice fringes in AC-Fe, AC-Co and AC-Ni increased to 1.29±0.82nm, 1.30±0.80nm and 1.29±0.79nm, indicating that catalysts such as Fe, Co and Ni promote the graphitization of activated carbon, and the median size of the lattice fringes further confirms this conclusion. Compared with AC1500, it can be found that the average size (1.29~1.30nm) and median size (1.07~1.10nm) of the lattice fringes in AC-Fe, AC-Co and AC-Ni are comparable, indicating that the growth of the crystallite size in the activated carbon is approaching the limit. In addition, the directional distribution of the lattice fringes in the HRTEM images was statistically analyzed, as shown in Figure 3. Figure 10 il. It can be found that catalytic graphitization has little effect on the directional distribution of the activated carbon lattice fringes, as shown in Table 3. After catalytic graphitization, the activated carbon lattice fringes are concentrated in the range of 80-140° or 60-120°. The proportion of lattice fringes with directional distribution within this range is 39.2%, 41.8%, 34.5%, and 36.6% for AC1500, AC-Fe, AC-Co, and AC-Ni, respectively, indicating that catalytic graphitization has little effect on the directional distribution of the lattice fringes.

[0101] In summary, the trend of the adsorption heat change shows that the adsorption heat decreases monotonically with the increase of the adsorption amount. This shows that as CO2 changes from single-layer adsorption to multi-layer adsorption, its adsorption heat decreases. The oxygen / nitrogen functional groups have the effect of enhancing the adsorption potential (adsorption heat) during the CO2 adsorption process. Therefore, after the functional groups are removed by high-temperature pyrolysis, the CO2 adsorption heat of the activated carbon decreases. After the pyrolysis temperature reaches 1500°C, the nitrogen / oxygen functional group content of the activated carbon has actually decreased to a stable level. At this time, it can be considered that the degree of graphitization of the activated carbon dominates the reduction in the adsorption heat of CO2. After high-temperature pyrolysis and catalytic graphitization, the edges of the activated carbon crystallites are cross-linked and condensed, which increases the crystallite size, reduces the number of edge sites, and heals the defect structure, which promotes the reduction of the adsorption heat of CO2 by the activated carbon.

Claims

1. A method for preparing activated carbon with low carbon dioxide adsorption heat, characterized in that: The steps include: Step 1: Using low-rank weakly sticky coal or non-sticky coal as raw material, crushing, acid-washing and drying it to obtain deashed coal particles, uniformly mixing the obtained deashed coal particles with an activator and placing them in deionized water to obtain a mixed system I, fully drying the solution in the mixed system I to obtain a solid mixture a, and using the obtained solid mixture a as a raw material to prepare initial activated carbon, the solid mixture a is placed in a horizontal tube furnace and introduced at a flow rate of 0.1 to 10 L min -1 The inert gas is nitrogen, argon or helium or a mixture of the two or more, and the temperature is kept at 10 ℃·min -1 The temperature was raised from room temperature to 700-900℃ at a constant temperature for 20-30 min, and the activated product was obtained after natural cooling to room temperature. The activated product was washed with dilute hydrochloric acid to remove the activator, and then washed with deionized water until neutral, and dried at 80-150℃ for 12-24 h to obtain the initial activated carbon. Step 2: Pyrolyze the initial activated carbon obtained in step 1 at 900-1600° C. under an inert atmosphere to obtain pyrolyzed activated carbon; Alternatively, the initial activated carbon obtained in step 1 is uniformly mixed with the catalyst and then placed in deionized water to obtain a mixed system II, the solution in the mixed system II is fully dried to obtain a solid mixture b; the obtained solid mixture b is pyrolyzed at 900-1600°C under an inert atmosphere to obtain a catalytic graphitization product; the obtained catalytic graphitization product is acid-washed to remove the catalyst to obtain a catalytically graphitized activated carbon.

2. The method for preparing activated carbon with low carbon dioxide adsorption heat according to claim 1, characterized in that: The low-rank weakly caking coal or non-caking coal in step 1 includes one or a mixture of lignite, Zhundong sub-bituminous coal, Ningdong weakly caking or non-caking coal; The size of the deashed coal particles is 1 μm to 10 mm, the reagent used for the pickling is hydrochloric acid and / or hydrofluoric acid; the pickling temperature is 20 to 80°C, and the pickling time is 10 to 24 hours; the drying is performed at 60 to 150°C for 6 to 24 hours.

3. The method for preparing activated carbon with low carbon dioxide adsorption heat according to claim 2, characterized in that: In step 1, the activator is one or a mixture of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate or sodium bicarbonate; the mass ratio of the deashed coal particles to the activator is 1:0~2, and the temperature for fully drying the mixed system I is 80~150°C, and the drying time is 10~24 hours.

4. The method for preparing activated carbon with low carbon dioxide adsorption heat according to claim 3, characterized in that: The inert atmosphere in step 2 is introduced at a flow rate of 0.1 to 10 L min -1 The inert gas is used to maintain an inert atmosphere, wherein the inert gas is nitrogen, argon or helium or a mixture of the two. When the pyrolysis temperature is ≤ 1200 °C, the temperature is set at 5 °C·min -1 The heating rate was from room temperature to pyrolysis temperature. When the pyrolysis temperature was greater than 1200 °C, the heating rate was first increased at 5 °C·min -1 The heating rate was from room temperature to 1200 °C, and then at 2 °C·min -1 The heating rate continued to rise from 1200 °C to the pyrolysis temperature, and the pyrolysis time was 120 min.

5. The method for preparing activated carbon with low carbon dioxide adsorption heat according to claim 4, characterized in that: The catalyst in step 2 is one or a mixture of FeCl3, CoCl2 or NiCl2; the mass ratio of the metal element to the activated carbon in the catalyst is 0.01~0.03:1, and the temperature for fully drying the mixed system II is 80~150°C, and the drying time is 10~24 h.

6. The method for preparing activated carbon with low carbon dioxide adsorption heat according to claim 5, characterized in that: The catalytic graphitization product of step 2 is washed with dilute hydrochloric acid to remove the catalyst, and then dried at 80-150° C. for 12-24 h to obtain catalytic graphitized activated carbon.

7. Pyrolytic activated carbon or catalytic graphitized activated carbon prepared by the method for preparing low carbon dioxide adsorption thermal activated carbon according to any one of claims 1 to 6.

8. The pyrolytic activated carbon according to claim 7, characterized in that The pyrolyzed activated carbon has a surface carbon content of 93.32~96.38 at.%, a surface oxygen content of 3.25~6.17 at.%, a surface nitrogen content of 0.37~1.94 at.%, a CO2 adsorption capacity of 2.56~3.27 mmol / g at 25°C and 1 bar, a CO2 adsorption capacity of 4.35~5.82 mmol / g at 0°C and 1 bar, and an average isosteric heat of adsorption of 27.1~31.7 kJ / mol.

9. The catalytic graphitized activated carbon according to claim 8, characterized in that The catalytic graphitized activated carbon has a surface carbon content of 95.70-96.49 at.%, a surface oxygen content of 3.00-3.80 at.%, a surface nitrogen content of 0.31-0.73 at.%, a CO2 adsorption capacity of 2.09-2.55 mmol / g at 25°C and 1 bar, a CO2 adsorption capacity of 3.36-4.44 mmol / g at 0°C and 1 bar, and an average isosteric heat of adsorption of 25.1-27.2 kJ / mol.

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