Carbon molecular sieve porous carbon material and preparation method and application thereof

Abstract

The present application relates to the technical field of molecular sieve composite material, and specifically discloses a preparation method of carbon molecular sieve porous carbon material, comprising the following steps: S1, using soft carbon precursor as raw material, mixing the soft carbon precursor with strong oxidizing acid for oxidation treatment to obtain pre-oxidized material; S2, mixing the pre-oxidized material with alkaline etching agent for activation and pore forming to obtain etched porous carbon; S3, high-temperature carbonization and shrinkage healing of the etched porous carbon to obtain carbon molecular sieve porous carbon material. The carbon molecular sieve porous carbon material prepared by the present application has micropore openings shrunk to the range close to the difference in CO2 / N2 kinetic size, the material has high adsorption capacity for CO2 and weak adsorption for N2, and is suitable for the fields of flue gas CO2 / N2 separation, industrial tail gas decarburization, CO2 removal in closed space and low-concentration CO2 enrichment.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve materials technology, specifically to a carbon molecular sieve porous carbon material, its preparation method, and its application. Background Technology

[0002] The main components of flue gas emitted by coal-fired power plants, steel, cement, chemical and coal chemical industries are nitrogen and carbon dioxide. How to capture carbon dioxide in flue gas with low energy consumption and how to achieve high selective separation of CO2 / N2 under low partial pressure and complex atmosphere are technical challenges that urgently need to be overcome in the field of carbon capture materials.

[0003] In existing technologies, adsorption separation methods have attracted widespread attention due to their simple equipment, low energy consumption, and convenient operation. Common adsorption materials include zeolites, metal-organic frameworks, amine-functionalized porous materials, and porous carbon materials. Among them, porous carbon materials have great application prospects in CO2 capture and CO2 / N2 separation due to their advantages such as good thermal stability, acid and alkali resistance, low cost, tunable pore structure, and easy large-scale preparation. The separation performance of carbon molecular sieves mainly stems from the molecular sieving effect of pore size and pore opening. Constructing a carbon molecular sieve structure that can accommodate CO2 in the pore body and restrict N2 entry through the pore opening is key to achieving efficient CO2 / N2 separation. However, since the kinetic diameter difference between carbon dioxide and nitrogen is extremely small, if the pore opening of the carbon molecular sieve is too large, N2 can enter the pores, resulting in decreased selectivity; if the pore opening is too small, CO2 diffusion is hindered, reducing adsorption capacity and rate. Therefore, preparing carbon molecular sieve materials with pore openings within a certain range and near-molecular-scale pore opening control capability is both a challenge and a key focus of research.

[0004] Chinese patent CN109179415A discloses a method for preparing coal-based carbon molecular sieves, utilizing coal-based activated carbon with a wide pore size distribution through methane deposition to adjust the pore size. However, the wide pore size distribution of coal-based activated carbon itself results in insufficient uniformity in the deposition and pore adjustment process. An earlier Chinese patent, CN1030030A, disclosed a coal-to-carbon molecular sieve technology, which, while using inexpensive raw materials, involves a complex process and high production costs. Furthermore, Chinese patent CN101596445A uses organic polymers as raw materials, preparing carbon molecular sieves through steps such as curing, dry distillation, molding, carbonization activation, and carbon deposition to adjust the pore size. While this technology can yield products with relatively stable performance, the raw material costs are high, and the process is complex, involving multiple heat treatment steps. The publication number CN102757064A provides a method for preparing carbon molecular sieves using petroleum coke with a fixed carbon content of ≥85wt% as raw material. Petroleum coke, as a representative of soft carbon precursors, has a low raw material cost, but its carbon skeleton rearrangement and self-healing ability are strong during high-temperature carbonization. The micropores obtained by activation are prone to excessive shrinkage or closure during subsequent heat treatment, resulting in a narrow pore structure control window.

[0005] Therefore, existing methods for preparing carbon molecular sieve materials often suffer from problems such as difficulty in continuously adjusting pore size, complex processes, insufficient uniformity of deposition and sealing, or difficulty in simultaneously achieving adsorption capacity and selectivity. In particular, soft carbon precursors such as pitch and tar exhibit strong carbon framework rearrangement and self-healing capabilities during high-temperature carbonization, leading to excessive shrinkage or closure of the activated micropores during subsequent heat treatment, and narrow pore necks that hinder effective adsorption. How to utilize inexpensive soft carbon precursors such as pitch and tar to prepare carbon molecular sieve materials with pore sizes within a defined range and near-molecular-scale pore size control capabilities to achieve CO2 capture and efficient CO2 / N2 separation in flue gas remains a key technical problem that needs to be solved and urgently requires improvement. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a carbon molecular sieve porous carbon material, its preparation method and application, using inexpensive soft carbon precursor as raw material to prepare a carbon molecular sieve porous carbon material with high selective adsorption capacity for CO2 and weak adsorption capacity for N2.

[0007] The technical problem solved by this invention is achieved by the following technical solution: A method for preparing porous carbon molecular sieve materials includes the following steps: S1. Using soft carbon precursor as raw material, the soft carbon precursor is mixed with a strong oxidizing acid and subjected to oxidation treatment to obtain a pre-oxidized material. S2. The pre-oxidized material is mixed with an alkaline etchant to activate and create pores, thereby obtaining etched porous carbon; S3. The etched porous carbon is subjected to high-temperature carbonization and shrinkage healing to obtain carbon molecular sieve porous carbon material.

[0008] Furthermore, in step S1, the soft carbon precursor includes one or more of the following: coal tar pitch, petroleum pitch, mesophase pitch, coal tar, petroleum tar, heavy aromatic oil, and petroleum residue.

[0009] Furthermore, in step S1, the mass fraction of the strong oxidizing acid is 20-50%, and the strong oxidizing acid includes one or more of nitric acid, sulfuric acid, and fuming sulfuric acid.

[0010] Furthermore, in step S1, the liquid-to-solid ratio of the strong oxidizing acid to the soft carbon precursor is 10-20 mL / g, the oxidation treatment temperature is 60-90 °C, and the time is 4-8 h.

[0011] In this step, if the liquid-solid ratio of the strong oxidizing acid to the soft carbon precursor is too low, it can easily lead to insufficient contact between the soft carbon precursor and the oxidant. If it is too high, it will result in sample waste and increased costs. The oxidation temperature and time also play a role. If the oxidation temperature is too low or the treatment time is too short, it will lead to insufficient oxidation. If the oxidation temperature is too high or the treatment time is too long, it will lead to over-oxidation. Consequently, during the subsequent high-temperature carbonization shrinkage and healing stage, the pore structure cannot heal effectively, making it difficult to construct a porous structure with suitable pore necks, resulting in poor selective adsorption of the final product.

[0012] Furthermore, in step S2, the etched porous carbon is washed until neutral and then dried for later use.

[0013] Furthermore, in step S2, the mass ratio of the pre-oxidized material to the alkaline etchant is 1:0.5~1, the activation temperature is 600~800 ℃, and the activation time is 1~2 h. If there is too much alkaline etchant or the activation temperature is too high, it will also cause the subsequent neck of the hole to be difficult to heal effectively, resulting in poor product selectivity. Conversely, if there is too little etchant or the activation temperature is too low, it will lead to fewer pore structures and reduced adsorption capacity.

[0014] Preferably, in step S3, after activating the pore formation, the etched porous carbon is subjected to acid washing and water washing to remove inorganic salts and residual alkaline impurities.

[0015] Furthermore, the alkaline etching agent includes one or more of KOH, K2CO3, KCl, and ZnCl2.

[0016] Furthermore, in step S4, the high-temperature carbonization shrinkage healing is carried out under the protection of an inert gas. During the treatment, the temperature is increased at a rate of 1~10℃ / min to 900~1100℃, and then held for 1~5 h. Preferably, the inert gas is N2 or Ar. During the high-temperature treatment, the micropores formed by alkaline etching shrink and partially heal, forming a carbon molecular sieve pore structure with an aperture size of 0.33~0.45 nm. In this step, if the temperature rises too quickly, the carbon structure migration and rearrangement during carbonization will be insufficient, and the pore neck will be difficult to heal effectively. If the temperature is too high, the pore neck will be over-closed, reducing the adsorption capacity of the pore structure. If the temperature is too low, the pore structure will not heal effectively, resulting in both N2 and CO2 being able to enter but poor selective adsorption.

[0017] A porous carbon molecular sieve material is prepared by any of the methods described above, wherein the porous carbon molecular sieve material has selective adsorption capacity for CO2.

[0018] The aforementioned porous carbon molecular sieve material is used in CO2 / N2 separation, flue gas CO2 capture, industrial tail gas decarbonization, closed space CO2 removal, or low-concentration CO2 enrichment.

[0019] Beneficial Effects: The carbon molecular sieve porous carbon material, its preparation method, and its application described in this invention are as follows: The carbon molecular sieve porous carbon material is prepared using soft carbon precursors such as pitch and tar as raw materials. Nitric acid, sulfuric acid, or a mixture thereof are used to controllably oxidize the precursors, transforming them from soft carbon precursors into hard carbonized precursors with limited carbon skeleton rearrangement capabilities. Subsequently, through pre-carbonization, alkaline etching for pore formation, and high-temperature shrinkage and healing processes, the micropore openings formed by etching undergo controllable shrinkage and partial healing. The pore size is larger than that of CO2 but smaller than that of N2, thereby achieving excellent selectivity.

[0020] In this invention, the degree of oxidation of the soft carbon precursor, pre-carbonization treatment, and activation pore formation jointly determine the self-healing ability of the carbon skeleton during high-temperature carbonization. If the initial oxidation degree is low, or if sufficient and effective pore formation is not performed, the carbon skeleton rearrangement and self-healing ability are strong, and the pore openings are prone to over-healing, leading to a decrease in CO2 adsorption capacity. If the oxidation degree is too high, pore formation is excessive, the carbon skeleton is over-crosslinked, or the structure is broken after etching, increasing the proportion of open pores and raising N2 adsorption, resulting in poor selectivity. Therefore, this invention, through the scientific configuration of each process and parameter, enables the final porous carbon molecular sieve material to acquire a moderate self-healing ability, shrinking the micropore openings to a range close to the CO2 / N2 kinetic size difference, thereby achieving highly selective CO2 adsorption.

[0021] In this invention, the orifice size is adjusted by combining various processes and parameters, and the final material has a high adsorption capacity for CO2 and a weak adsorption capacity for N2. It is suitable for applications such as CO2 / N2 separation in flue gas, decarbonization of industrial tail gas, CO2 removal in confined spaces, and enrichment of low-concentration CO2.

[0022] The raw materials for this invention are widely available and inexpensive. The orifice control parameters are clearly defined and the nodes are controllable, making it suitable for continuous processing and production, and it has a promising future for industrial applications. Attached Figure Description

[0023] Figure 1 This is a SEM image of the porous carbon molecular sieve material in Example 1 of the present invention.

[0024] Figure 2 The image shows the SEM image of the porous carbon material in Example 4, which is a carbon molecular sieve.

[0025] Figure 3 The image shows the SEM image of the porous carbon molecular sieve material in Comparative Example 5.

[0026] Figure 4 Comparison diagram of CO2 adsorption-desorption isotherms of porous carbon materials using carbon molecular sieves in Example 1, Comparative Example 4, and Comparative Example 5.

[0027] Figure 5Comparison diagram of N2 adsorption-desorption isotherms of porous carbon materials in carbon molecular sieves in Example 1, Comparative Example 4, and Comparative Example 5. Detailed Implementation

[0028] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0029] Example 1

[0030] A method for preparing porous carbon molecular sieve materials includes the following steps: S1. Take 10 g of coal tar pitch and add it to 150 mL of 40 wt% nitric acid. Stir and oxidize at 80 °C for 6 h to obtain the pre-oxidized material. S2. Mix the pre-oxidized material with KOH at a mass ratio of 1:1 and activate it at 650 °C for 1 h to activate and create pores, thereby obtaining etched porous carbon. S3. The etched porous carbon was washed sequentially with 1 M hydrochloric acid, washed with water until neutral, and dried. Then, it was heated to 900 °C at a rate of 2 °C / min under Ar atmosphere and held for 3 h to obtain carbon molecular sieve porous carbon material.

[0031] The SEM image of the porous carbon molecular sieve material prepared in this embodiment is shown below. Figure 1 As shown, the product particles have an irregular shape and a relatively irregular surface.

[0032] Example 2

[0033] In this embodiment, in step S1, the strong oxidizing acid is a mixture of nitric acid and sulfuric acid with a volume ratio of 3:1 and a total acid mass fraction of 40 wt%. In step S3, the high-temperature carbonization temperature is adjusted to 1000℃, and the rest is the same as in embodiment 1.

[0034] Example 3

[0035] In this embodiment, in step S1, the soft carbon precursor is petroleum tar, the oxidant is 40 wt% sulfuric acid, and in step S3, the high-temperature carbonization temperature is adjusted to 1100℃. The rest is the same as in Example 1.

[0036] Example 4

[0037] In this embodiment, the nitric acid concentration in step S1 is adjusted to 20 wt%, and the rest is the same as in Example 1.

[0038] Example 5

[0039] In this embodiment, the nitric acid concentration in step S1 is adjusted to 50 wt%, and the rest is the same as in Example 1.

[0040] Example 6

[0041] In this embodiment, the nitric acid oxidation temperature in step S1 is adjusted to 60°C, and the mass ratio of the pre-oxidized material to KOH in step S2 is adjusted to 1:0.75. The rest is the same as in Example 1.

[0042] Example 7

[0043] In this embodiment, the nitric acid oxidation temperature in step S1 is adjusted to 90°C, and the mass ratio of the pre-oxidized material to KOH in step S2 is adjusted to 1:0.5. The rest is the same as in Example 1.

[0044] Compare with Example 1 In this comparative example, no oxidation treatment is performed in step S1. The coal tar pitch is directly mixed with the etchant for activation treatment, and the rest is the same as in Example 1.

[0045] Compare with Example 2 In this comparative example, no activation and pore-forming treatment is performed in step S2. The pre-oxidized material is directly heated to 900 °C at 2 °C / min under Ar atmosphere and held for 3 h. The rest is the same as in Example 1.

[0046] Compare with Example 3 In this comparative example, the high-temperature carbonization shrinkage healing process is not performed in step S3, and the etched porous carbon obtained in step S3 is the product.

[0047] Compare with Example 4 In this comparative example, the concentration of nitric acid in step S1 is 5 wt%, and the rest is the same as in Example 1.

[0048] The SEM image of the porous carbon molecular sieve material prepared in this comparative example is shown below. Figure 2 As shown, the overall particles of the product have an irregular shape, while the surface is relatively regular. This is mainly due to the low degree of oxidation, which allows the carbon skeleton to retain a high degree of self-healing ability, which is also reflected in the morphology of the product surface.

[0049] Compare with Example 5 In this comparative example, the concentration of nitric acid in step S1 was 60 wt%, and the rest was the same as in Example 1. The SEM image of the porous carbon molecular sieve material prepared in this example is shown below. Figure 3 As shown, the product particles exhibit an irregular shape with numerous pores on the surface. This is mainly due to the excessive oxidation level, which hinders self-healing during the high-temperature carbonization stage, preventing the pores from closing effectively.

[0050] Compare with Example 6 In this embodiment, the temperature for high-temperature carbonization shrinkage healing in step S3 is 1300 ℃, and the rest is the same as in embodiment 1.

[0051] Compare with Example 7 In this embodiment, the temperature for high-temperature carbonization shrinkage healing in step S3 is 800 ℃, and the rest is the same as in embodiment 1.

[0052] Compare with Example 8 In this embodiment, in step S3, the mass ratio of the pre-oxidized material to KOH is 1:2, and the rest is the same as in embodiment 1.

[0053] Compare with Example 9 In this embodiment, in step S2, the mass ratio of the pre-oxidized material to KOH is 1:0.25, and the rest is the same as in embodiment 1.

[0054] All reagents used in the examples and comparative examples were commercially available products. The porous carbon molecular sieve materials prepared in the examples and comparative examples were analyzed for N2 adsorption, CO2 adsorption, specific surface area, micropore volume, and pore size. The porous carbon molecular sieve materials obtained in the examples and comparative examples were uniformly sieved to 40–60 mesh, and 1.00 g of each was packed into a quartz fixed-bed adsorption column with an inner diameter of 10 mm and a length of 200 mm. The adsorbent bed was fixed at both ends with quartz wool. The test method was set according to HG / T2691-2024 "Method for Determination of Dynamic Carbon Dioxide Adsorption by Molecular Sieves" and combined with the CO2 / N2 separation application conditions of this invention. A breakthrough test was conducted using simulated flue gas with a CO2 / N2 volume ratio of 15 / 85, at a test temperature of 25 ℃ and a total flow rate of 30 mL / min. The results are shown in Table 1.

[0055] All gas adsorption tests were conducted after the samples were degassed under vacuum at 200 °C for 8 h. CO2 adsorption was measured at 25 °C and 1 bar, and N2 adsorption was measured at 25 °C and 1 bar. CO2 / N2 selectivity was calculated using IAST under a mixed gas condition with a CO2 / N2 volume ratio of 15 / 85.

[0056] Table 1. Statistical analysis of structural parameters and CO2 / N2 separation performance of porous carbon molecular sieve materials.

[0057] As shown in Table 1, the materials prepared using the technical solutions of this invention in Examples 1-7 have high micropore volume and limited pore size, exhibiting high CO2 adsorption and low N2 adsorption with a large difference, demonstrating excellent CO2 / N2 selectivity. In contrast, Comparative Examples 1 and 2 did not undergo precursor oxidation or activation etching treatment, resulting in excessively strong self-healing ability of the carbon framework or ineffective pore formation, leading to insufficient adsorption of both N2 and CO2. Comparative Example 3 did not undergo high-temperature shrinkage healing, resulting in a high proportion of open pores and enhanced adsorption of both CO2 and N2, but with insufficient selectivity. Comparative Examples 4 and 5 show that controlling the concentration of strong oxidizing acid is crucial. Comparative Examples 6 and 7 show that high-temperature carbonization shrinkage healing requires a specific temperature range to obtain high-performance products. Excessive temperature leads to over-healing, preventing effective entry of N2 and CO2 into the pore structure, while insufficient temperature restricts pore structure healing, allowing large amounts of N2 and CO2 to enter, resulting in poor selectivity. Comparing Examples 8 and 9, it can be seen that improper setting of the etchant ratio is not conducive to the formation of the target hole structure.

[0058] Combination Figure 4 and Figure 5 It can be seen that, compared with Example 1, Comparative Example 4 has too low an oxidation degree, and the pores are excessively closed during the high-temperature carbonization shrinkage healing stage. The specific surface area under CO2 adsorption-desorption test is significantly reduced, and the pore structure under N2 test is also very small. On the other hand, Comparative Example 5 is excessively oxidized, and the pore healing ability during the high-temperature carbonization shrinkage healing stage is significantly limited, resulting in an excessively wide pore neck. The pore structure under CO2 test is not significantly increased, and it also has a high specific surface area under N2 test, ultimately resulting in poor selectivity for adsorption between CO2 and N2.

[0059] The above results indicate that the degree of oxidation of the soft carbon precursor, pre-carbonization treatment, and activation pore formation in this invention jointly determine the degree of self-healing of the carbon skeleton during the high-temperature carbonization process. Only through the synergistic effect of precursor oxidation, alkaline etching pore formation, and high-temperature shrinkage healing can a porous carbon material with high CO2 adsorption capacity and weak N2 adsorption be prepared.

[0060] The porous carbon molecular sieve products prepared in each embodiment can be used for CO2 / N2 gas separation, and are particularly suitable for flue gas from coal-fired power plants, tail gas from the steel and cement industries, tail gas from coal chemical plants, air purification in confined spaces, and enrichment of low-concentration CO2. This material can be recycled using fixed-bed pressure swing adsorption, temperature swing adsorption, vacuum pressure swing adsorption, or electrothermal regeneration adsorption.

[0061] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing porous carbon molecular sieve materials, characterized in that, Includes the following steps: S1. Using soft carbon precursor as raw material, the soft carbon precursor is mixed with a strong oxidizing acid and subjected to oxidation treatment to obtain a pre-oxidized material. S2. The pre-oxidized material is mixed with an alkaline etchant to activate and create pores, thereby obtaining etched porous carbon; S3. The etched porous carbon is subjected to high-temperature carbonization and shrinkage healing to obtain carbon molecular sieve porous carbon material.

2. The method for preparing porous carbon molecular sieve materials according to claim 1, characterized in that, In step S1, the soft carbon precursor includes one or more of the following: coal tar pitch, petroleum pitch, mesophase pitch, coal tar, petroleum tar, heavy aromatic oil, and petroleum residue.

3. The method for preparing porous carbon molecular sieve materials according to claim 1, characterized in that, In step S1, the mass fraction of the strong oxidizing acid is 20-50%, and the strong oxidizing acid includes one or more of nitric acid, sulfuric acid, and fuming sulfuric acid.

4. The method for preparing porous carbon molecular sieve materials according to claim 1, characterized in that, In step S1, the liquid-to-solid ratio of the strong oxidizing acid to the soft carbon precursor is 10-20 mL / g, the oxidation treatment temperature is 60-90 °C, and the time is 4-8 h.

5. The method for preparing porous carbon molecular sieve materials according to claim 1, characterized in that, In step S2, the etched porous carbon is washed until neutral and then dried for later use.

6. The method for preparing porous carbon molecular sieve materials according to claim 1, characterized in that, In step S2, the mass ratio of the pre-oxidized material to the alkaline etchant is 1:0.5~1, the activation temperature is 600~800 ℃, and the activation time is 1~2 h.

7. The method for preparing porous carbon molecular sieve materials according to claim 6, characterized in that, The alkaline etching agent includes one or more of KOH, K2CO3, KCl, and ZnCl2.

8. The method for preparing porous carbon molecular sieve materials according to claim 1, characterized in that, In step S4, the high-temperature carbonization shrinkage healing is carried out under the protection of an inert gas; during the treatment, the temperature is increased to 900~1100 ℃ at a rate of 1~10 ℃ / min and then held for 1~5 h.

9. A porous carbon molecular sieve material, characterized in that, The carbon molecular sieve porous carbon material prepared by any one of the methods described in claims 1 to 8 has a selective adsorption capacity for CO2.

10. The application of the porous carbon molecular sieve material as described in claim 9 in CO2 / N2 separation, flue gas CO2 capture, industrial tail gas decarbonization, closed space CO2 removal, or low-concentration CO2 enrichment.

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