Carbon molecular sieve adsorbent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of adsorbent preparation, in particular to a carbon molecular sieve adsorbent and a preparation method and application thereof.The carbon molecular sieve adsorbent is provided with a modified surface containing Si-O-Si bonds and obtained through modification treatment of a modifier and is loaded with rare earth metal elements; the invention also provides a preparation method of the carbon molecular sieve adsorbent, the preparation method comprises the steps of hydrothermal synthesis, surface modification, roasting, ion exchange reaction, re-roasting and the like, the component proportion of the carbon molecular sieve, the modifier and the rare earth metal salt as well as the temperature and time of the preparation process are accurately controlled, so that the carbon molecular sieve has ordered linearly distributed micropores, and the carbon molecular sieve adsorbent has high adsorption capacity. The pore diameter is 0.2-0.36 nm, and the proportion of the micropore volume to the total pore volume is greater than or equal to 90%; the carbon molecular sieve adsorbent can be used for separating nitrogen from methane, and has the characteristics of excellent nitrogen selectivity and high adsorption capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorbent preparation and gas separation, and in particular to a carbon molecular sieve adsorbent and a preparation method and application thereof. Background Art

[0002] In the field of materials science, adsorbents are important materials that can adsorb gases or other substances onto their surfaces through physical or chemical effects. Carbon molecular sieves, as a commonly used adsorbent, have a highly ordered pore structure and can be used to separate, purify and dry various gases. However, when separating nitrogen and methane, existing carbon molecular sieve adsorbents have problems with low nitrogen selectivity and adsorption capacity. The disordered micro-mesopores are easily blocked by water and oily substances, which greatly weakens the adsorption capacity, resulting in a decrease in separation rate and difficulty in regeneration.

[0003] At present, pressure swing adsorption (PSA) is the most suitable technology for methane purification in natural gas for general application due to its low technical energy consumption and simple process. Its core is to develop efficient molecular sieve adsorbent materials. Molecular sieves have high thermal stability / hydrothermal stability and low cost. They have been widely used in the field of adsorption separation and have industrial advantages that are difficult to match with other materials. Since the main components of natural gas reservoirs are methane and a small amount of nitrogen (<5%). Therefore, constructing nitrogen selective adsorbents, preferentially adsorbing nitrogen, and directly purifying methane can improve the utilization rate of methane, and can also use the adsorption residual pressure to reduce the compression energy consumption of methane in the later liquefaction process. Due to the slight difference between the kinetic diameter of nitrogen and the kinetic diameter of methane, nitrogen / methane separation can be achieved through kinetic separation or size screening effect. Of course, due to the small difference, the efficiency of separation is not enough only by the difference in kinetic diameter. It is more effective to modify the carbon molecular sieve to make it have stronger nitrogen selective adsorption capacity.

[0004] At the same time, carbon molecular sieves have a strong affinity for water, oil and other molecules. Due to the use of compressors in pressure swing adsorption, water, oil vapor and other impurity gases are inevitably introduced into the raw gas. This leads to the blockage of the carbon molecular sieve pores, the gradual decrease in separation effect, and even the loss of its function. Carbon molecular sieve pressure swing adsorption relies on van der Waals force to separate methane gas and nitrogen. Therefore, the larger the specific surface area of ​​the molecular sieve, the more uniform the pore size distribution and the more micropores or sub-micropores, the greater the adsorption capacity. When the micropores of the molecular sieve are blocked by water and oily substances, the adsorption capacity of the molecular sieve is greatly weakened, and the separation rate will decrease.

[0005] Patent CN101596445A discloses a method for preparing a carbon molecular sieve adsorbent, which uses a high molecular polymer as a raw material, undergoes solidification, dry distillation, fine grinding, molding, carbonization activation and carbon deposition pore adjustment preparation processes, and prepares a carbon molecular sieve for low-concentration gas pressure swing adsorption separation of methane gas. The carbon molecular sieve has a high adsorption capacity for methane, a large selective adsorption coefficient, good strength, low cost, and no pollution. However, the adsorbent mainly adsorbs methane and needs to be desorbed to achieve the purpose of effective utilization of methane.

[0006] Patent CN109179369A discloses a method for preparing a phenolic resin-based carbon molecular sieve for adsorption and separation of methane and nitrogen. This method integrates carbonization and deposition pore adjustment during the preparation process, reduces energy loss, is more energy-efficient, and reduces the effect of heat on the change of matrix pore size during carbonization cooling and deposition heating. The pore size is relatively stable, the obtained matrix pore size is small, and the deposition time is reduced. After deposition, the sample has a nitrogen adsorption capacity of 6.5-7.5 ml / g and a methane adsorption capacity of 7-10 ml / g at 25 degrees Celsius / 1 atmosphere. Although the molecular sieve prepared by this method can be used for the kinetic separation of nitrogen and methane, the separation ratio is not high and nitrogen and methane cannot be effectively separated.

[0007] Patent CN110773120A obtains metal salt modified molecular sieve by impregnation modification of molecular sieve. The metal salt modified molecular sieve obtained by its preparation method can be used as a selective adsorbent for N2 / CH4, O2 / CH4 or (N2+O2) / CH4. Especially when separating N2 / CH4, the adsorption amount of methane is low. However, it cannot solve the problem that the adsorption capacity of the molecular sieve is greatly weakened when the micropores of the molecular sieve are blocked by water or oily substances. Summary of the invention

[0008] In view of the deficiencies in the prior art, the present invention provides a carbon molecular sieve adsorbent and a preparation method and application thereof. The carbon molecular sieve adsorbent has the characteristics of high selectivity and high nitrogen adsorption capacity for nitrogen and methane separation, while reducing the possibility of molecular sieve micropores being blocked by water and oily substances, thereby improving the regenerativeness of the carbon molecular sieve.

[0009] The present invention is achieved through the following technical solutions:

[0010] Provided is a carbon molecular sieve adsorbent, the carbon molecular sieve having a modified surface containing Si-O-Si bonds obtained by modification with a modifier, and loaded with rare earth metal elements;

[0011] Specifically, the micropores in the carbon molecular sieve are orderly linearly distributed, with a pore diameter of 0.2-0.36 nm, and the proportion of the micropore volume to the total pore volume is greater than or equal to 90%.

[0012] Specifically, the modifier includes one or a combination of two or more of hexamethylsilazane, trimethylchlorosilane, mercaptopropyltriethoxysilane or ethyl orthosilicate.

[0013] Specifically, the rare earth metal element comes from rare earth metal acetate or rare earth metal nitrate; the rare earth metal is one or more of ytterbium, lutetium, lanthanum, erbium, rubidium, yttrium or cerium; the concentration of the metal salt solution is 0.1-1.0 mol / L.

[0014] Specifically, the modification treatment includes: regulating the ratio of the three components of carbon molecular sieve, modifier, and rare earth metal salt, using a hydrothermal synthesis method to prepare a carbon molecular sieve precursor with a modified surface containing Si-O-Si bonds, and then using an ion exchange method to load rare earth metal elements on the active sites of the modified hydrophobic layer.

[0015] Specifically, the ratio of the carbon molecular sieve, the modifier and the rare earth metal salt is 10-40 g: 0.5-3 mol: 1-3.5 mol.

[0016] The present invention also provides a method for preparing the above carbon molecular sieve adsorbent, comprising the following steps:

[0017] (1) A carbon molecular sieve precursor containing Si-O-Si bonds was prepared by hydrothermal synthesis.

[0018] Specifically, the modifier and the organic solvent are mixed in a molar ratio of 1:1-5, deionized water is added, and the mixture is stirred evenly. Then, the mixture is placed in a high-pressure reactor and kept warm at a temperature of 145-155° C. for 24 hours. Finally, the carbon molecular sieve precursor is obtained by filtering, washing and drying.

[0019] Specifically, the organic solvent is selected from one or more of n-hexane, cyclohexane, n-heptane and toluene.

[0020] (2) The carbon molecular sieve precursor is calcined under a protective atmosphere, the calcination temperature and time are controlled, and the carbon molecular sieve is subjected to a first pore deposition to obtain a modified carbon molecular sieve.

[0021] Specifically, the calcination temperature is 540-560° C., and the calcination time is 1.5-4.5 hours.

[0022] (3) The modified carbon molecular sieve is mixed with a rare earth metal salt solution to carry out an ion exchange reaction to obtain a modified carbon molecular sieve loaded with rare earth metal elements.

[0023] Specifically, the loading amount of the rare earth metal element accounts for 5-15% of the mass of the modified carbon molecular sieve.

[0024] (4) The modified carbon molecular sieve loaded with rare earth metal elements is calcined under a protective atmosphere, the calcination temperature and time are controlled, and the carbon molecular sieve is subjected to a second pore deposition to obtain a carbon molecular sieve adsorbent.

[0025] Specifically, the calcination temperature is 600-900° C., and the calcination time is 0.5-2 hours.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] By subjecting the carbon molecular sieve to a specific modification treatment, an ordered Si-O-Si bond structure is formed on the surface of the carbon molecular sieve. This structure not only enhances the mechanical strength of the molecular sieve, but also significantly improves its adsorption performance for the target gas. The surface of the modified molecular sieve has a higher polarity, which is conducive to improving the loading capacity of rare earth metal elements. As active ingredients, rare earth metal elements occupy the main active sites in the carbon molecular sieve, which can greatly enhance the adsorption capacity of the carbon molecular sieve for nitrogen molecules, thereby improving the selectivity for nitrogen. In addition, the ordered linear micropore distribution ensures the precise screening of gas molecules by the molecular sieve, further enhancing its adsorption efficiency. This high-performance adsorbent has broad application prospects in the field of gas separation, and can achieve efficient and accurate capture of target gases, providing strong support for industrial production and environmental protection.

[0028] In the preparation method of the present invention, by accurately controlling the modification process, the conditions for loading rare earth metal elements, and the ratio of carbon molecular sieve, modifier and rare earth metal, the micropores in the carbon molecular sieve are orderly linearly distributed, and the pore size is uniformly distributed between 0.2-0.36nm. This unique pore structure enables the molecular sieve to have a large adsorption capacity while maintaining high selectivity. The proportion of micropore volume to total pore volume is greater than or equal to 90%, ensuring the effective utilization of the internal space of the molecular sieve and improving its gas adsorption capacity. In addition, the orderly linear micropores are also conducive to the diffusion and transmission of gas molecules inside the molecular sieve, reducing the mass transfer resistance during the adsorption process, and further improving the adsorption rate and efficiency.

[0029] In addition, the hydrophobic modified surface containing Si-O-Si bonds enables the carbon molecular sieve adsorbent of the present invention to exhibit good regeneration performance during use. When the adsorbent reaches a saturated state, it can be restored to its original adsorption capacity by simple heat treatment or other regeneration means. This excellent regeneration performance not only extends the service life of the adsorbent, but also reduces its use cost. In practical applications, effective utilization of resources and sustainable development of the environment can be achieved through regular regeneration and reuse. In addition, since the molecular sieve surface has been modified, its chemical stability and thermal stability have been significantly improved, and it can maintain stable adsorption performance under harsh working conditions, further broadening its scope of application.

[0030] In summary, the carbon molecular sieve adsorbent of the present invention shows significant beneficial effects in terms of adsorption performance, pore structure and regeneration performance, and provides a high-performance, low-cost adsorption material for the fields of industrial production and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for describing the embodiments are briefly introduced below.

[0032] Figure 1 Morphology of the carbon molecular sieve prepared in Example 2.

[0033] Figure 2 The surface of the carbon molecular sieve prepared in Example 2.

[0034] Figure 3 Cross section of the carbon molecular sieve prepared in Example 2. DETAILED DESCRIPTION

[0035] The technical scheme of the present invention is described in detail below through embodiments. The described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments described in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0036] Preparation Example

[0037] Weigh 100g of coconut shell activated carbon, ball mill to obtain a powder with a particle size of about 10-100 microns, stir it with 10g coal tar (10wt%) until it is evenly mixed, use an extruder to extrude to obtain particles with a length of about 20mm and a diameter of about 5mm, and dry and solidify it under natural conditions; put the above particles into a high-temperature converter, continuously introduce 250mL / min of inert gas, increase the temperature to 850℃ at a heating rate of 10℃ / min and keep it for 240min, then stop heating, wait for the temperature to naturally drop to room temperature, take it out to obtain a carbon molecular sieve.

[0038] Example 1

[0039] Take 10 g of carbon molecular sieve, mix 0.5 mol of the modifier with an equal molar amount of cyclohexane, add an appropriate amount of deionized water, stir evenly to form a uniform mixture.

[0040] The mixture was placed in a high-pressure reactor and kept at 150° C. for 24 hours to perform a hydrothermal synthesis reaction.

[0041] After the reaction is completed, the modified carbon molecular sieve precursor is obtained by filtering, washing and drying.

[0042] The precursor was calcined at 550° C. for 4 hours under a nitrogen protective atmosphere to obtain a modified carbon molecular sieve.

[0043] The modified carbon molecular sieve is mixed with 1 mol of lanthanum salt solution, and an ion exchange reaction is performed to load the rare earth metal element on the carbon molecular sieve, thereby obtaining a modified carbon molecular sieve loaded with the rare earth metal element.

[0044] After the ion exchange reaction is completed, the modified carbon molecular sieve loaded with rare earth metal elements is calcined at 700° C. for 2 hours under a nitrogen protective atmosphere to obtain a final carbon molecular sieve adsorbent.

[0045] Example 2

[0046] Mix 20 g of carbon molecular sieve, 2 mol of modifier and 1.5 times the molar amount of cyclohexane, add an appropriate amount of deionized water, and stir evenly.

[0047] The mixture was placed in an autoclave and kept at 145°C for 24 hours.

[0048] After the reaction is completed, the carbon molecular sieve precursor is obtained by filtering, washing and drying.

[0049] The precursor was calcined at 540° C. for 4.5 hours under a nitrogen atmosphere.

[0050] The modified carbon molecular sieve is mixed with 2 mol of lanthanum salt solution, and an ion exchange reaction is performed to obtain a modified carbon molecular sieve loaded with rare earth metal elements.

[0051] After the ion exchange reaction is completed, the modified carbon molecular sieve loaded with rare earth metal elements is calcined at 800° C. for 2 hours under a nitrogen protective atmosphere to obtain a final carbon molecular sieve adsorbent.

[0052] Example 3

[0053] Mix 40 g of carbon molecular sieve, 3 mol of modifier and 2 times the molar amount of cyclohexane, add an appropriate amount of deionized water, and stir evenly.

[0054] The mixture was placed in an autoclave and kept at 155°C for 24 hours.

[0055] After the reaction is completed, the carbon molecular sieve precursor is obtained by filtering, washing and drying.

[0056] The precursor was calcined at 560° C. for 3.5 hours under a nitrogen atmosphere.

[0057] The modified carbon molecular sieve is mixed with 3.5 mol of lanthanum salt solution, and an ion exchange reaction is performed to obtain a modified carbon molecular sieve loaded with rare earth metal elements.

[0058] After the ion exchange reaction is completed, the modified carbon molecular sieve loaded with rare earth metal elements is calcined at 700° C. for 2 hours under a nitrogen protective atmosphere to obtain a final carbon molecular sieve adsorbent.

[0059] Example 4

[0060] Mix 20 g of carbon molecular sieve, 2 mol of modifier and 1.5 times the molar amount of cyclohexane, add an appropriate amount of deionized water, and stir evenly.

[0061] The mixture was placed in an autoclave and kept at 145°C for 24 hours.

[0062] After the reaction is completed, the carbon molecular sieve precursor is obtained by filtering, washing and drying.

[0063] The precursor was calcined at 540° C. for 1.5 hours under a nitrogen atmosphere.

[0064] The modified carbon molecular sieve is mixed with 2 mol of lanthanum salt solution, and an ion exchange reaction is performed to obtain a modified carbon molecular sieve loaded with rare earth metal elements.

[0065] After the ion exchange reaction is completed, the modified carbon molecular sieve loaded with rare earth metal elements is calcined at 800° C. for 2 hours under a nitrogen protective atmosphere to obtain a final carbon molecular sieve adsorbent.

[0066] Example 5

[0067] Mix 20 g of carbon molecular sieve, 2 mol of modifier and 1.5 times the molar amount of cyclohexane, add an appropriate amount of deionized water, and stir evenly.

[0068] The mixture was placed in an autoclave and kept at 145°C for 24 hours.

[0069] After the reaction is completed, the carbon molecular sieve precursor is obtained by filtering, washing and drying.

[0070] The precursor was calcined at 540° C. for 4.5 hours under a nitrogen atmosphere.

[0071] The modified carbon molecular sieve is mixed with 2 mol of lanthanum salt solution, and an ion exchange reaction is performed to obtain a modified carbon molecular sieve loaded with rare earth metal elements.

[0072] After the ion exchange reaction is completed, the modified carbon molecular sieve loaded with rare earth metal elements is calcined at 800° C. for 0.5 hours under a nitrogen protective atmosphere to obtain a final carbon molecular sieve adsorbent.

[0073] Comparative Example 1:

[0074] The carbon molecular sieve adsorbent was prepared by a conventional two-step activation method without doping with rare earth metal elements or surface modification. The remaining preparation conditions were the same as those in Example 1, but the ion exchange reaction and surface modification steps were omitted.

[0075] Add 20g of carbon molecular sieve to an appropriate amount of deionized water and stir evenly.

[0076] The mixture was placed in an autoclave and kept at 145°C for 24 hours.

[0077] After the reaction is completed, the carbon molecular sieve precursor is obtained by filtering, washing and drying.

[0078] The precursor was calcined at 540° C. for 4.5 hours under a nitrogen atmosphere.

[0079] Then calcined at 800°C for 2 hours.

[0080] Comparative Example 2

[0081] Mix 20 g of carbon molecular sieve, 2 mol of modifier and 1.5 times the molar amount of cyclohexane, add an appropriate amount of deionized water, and stir evenly.

[0082] The mixture was placed in an autoclave and kept at 145°C for 24 hours.

[0083] After the reaction is completed, the carbon molecular sieve precursor is obtained by filtering, washing and drying.

[0084] The precursor was calcined at 540° C. for 4.5 hours under a nitrogen atmosphere.

[0085] The modified carbon molecular sieve was calcined at 800° C. for 2 hours under a nitrogen protective atmosphere.

[0086] Comparative Example 3

[0087] Add 20g of carbon molecular sieve to an appropriate amount of deionized water and stir evenly.

[0088] The mixture was placed in an autoclave and kept at 145°C for 24 hours.

[0089] After the reaction is completed, the carbon molecular sieve precursor is obtained by filtering, washing and drying.

[0090] The precursor was calcined at 540° C. for 4.5 hours under a nitrogen atmosphere.

[0091] The carbon molecular sieve is mixed with 2 mol of lanthanum salt solution to carry out ion exchange reaction.

[0092] After the ion exchange reaction is completed, the carbon molecular sieve loaded with rare earth metal elements is calcined at 800° C. for 2 hours under a nitrogen protective atmosphere.

[0093] Performance Testing

[0094] Test Example 1

[0095] The volumes of nitrogen and methane adsorbed by the carbon molecular sieve adsorbents prepared in the examples and comparative examples within 15 minutes were measured using a static adsorption device, and the adsorption capacities of nitrogen and methane and the nitrogen / methane separation coefficient were calculated.

[0096] The performance tests were performed on the adsorption materials prepared in Examples 1-5 and Comparative Examples 1-3, and the test results are shown in the following table:

[0097] Table 1 Static adsorption test results of carbon molecular sieves for nitrogen and methane in the examples and comparative examples

[0098] It can be seen from the test data in the above table that the carbon molecular sieve prepared in the embodiment not only meets the industry standards, but also performs well in the nitrogen adsorption capacity and adsorption selectivity performance tests, exceeding the existing material standards.

[0099] Test Example 2

[0100] The adsorption of the sample on a mixture of 70% methane and 30% nitrogen by volume was determined using a dynamic adsorption device. An infrared analyzer was used as a detector to detect the change in the volume fraction of methane at the outlet in real time, and the best methane purification result was obtained in about 5 minutes.

[0101] Table 2 Dynamic adsorption test results of carbon molecular sieve for 30% nitrogen and 70% methane in the examples and comparative examples

[0102] The data show that under the dynamic adsorption environment, the sample maintains high selectivity and high adsorption capacity for nitrogen, showing excellent nitrogen-methane separation performance, while the adsorbents prepared in Comparative Examples 1-3 show poor selectivity.

[0103] Regeneration performance test:

[0104] The regeneration performance test of the carbon molecular sieve adsorbent in the present invention comprises the following steps:

[0105] The carbon molecular sieve adsorbent samples that have been subjected to the adsorption test in Example 2 and Comparative Example 2 are placed in a closed container, and a vacuum pump is used to perform a vacuum regeneration treatment for 10 minutes to completely desorb the gas adsorbed in the sample. Then, a static adsorption device is used again to measure the volumes of nitrogen and methane adsorbed by the above samples within 15 minutes, and the adsorption capacities of nitrogen and methane and the nitrogen / methane separation coefficient are calculated; this is repeated twice, and the carbon molecular sieves in Example 2 are numbered as regenerated samples S1 and S2, and the carbon molecular sieves in Comparative Example 3 are numbered as regenerated samples D1 and D2, and the results are shown in Table 3.

[0106] Table 3 Static adsorption test results after regeneration of carbon molecular sieve in Example 2

[0107] The data show that after the modified and rare earth metal element-loaded carbon molecular sieve in Example 2 was regenerated, the sample still maintained high selectivity and high adsorption capacity, while the regenerated sample of the unmodified carbon molecular sieve in Comparative Example 3 showed obvious attenuation. Therefore, it can be concluded that the Si-O-Si bond modification of the carbon molecular sieve improves the regenerability of the carbon molecular sieve.

[0108] The carbon molecular sieve provided by the present invention and its preparation method and application, through a specific modification treatment, an ordered Si-O-Si bond structure is formed on the surface of the carbon molecular sieve. This structure not only enhances the mechanical strength of the molecular sieve, but also significantly improves its adsorption performance for the target gas. The surface of the modified molecular sieve has a higher polarity, which is conducive to improving the loading capacity of rare earth metal elements, and rare earth metal elements, as active ingredients, occupy the main active sites in the carbon molecular sieve, which can greatly enhance the adsorption of nitrogen molecules by the carbon molecular sieve, thereby improving the selectivity for specific gases. The carbon molecular sieves prepared in Examples 1-5 show very excellent nitrogen adsorption capacity and selectivity, and are suitable for the field of methane nitrogen separation. The results of Comparative Examples 1-3 further demonstrate the important role of accurately controlling the modification treatment conditions and loading rare earth metal elements in improving the adsorption capacity and selectivity of carbon molecular sieves.

[0109] The present invention provides a carbon molecular sieve adsorbent and a preparation method and application thereof, wherein particular emphasis is placed on specific parameters such as the modification treatment of the carbon molecular sieve, the loading of rare earth metal elements, the ratio of each key component, the parameters of the preparation steps and the preparation method. By precisely controlling these parameters, the present invention can prepare a carbon molecular sieve adsorbent material with excellent nitrogen selectivity and high adsorption capacity. The above specific embodiments are only exemplary embodiments of the present invention and are not intended to limit the scope of protection thereof. Any modification, substitution or equivalent transformation based on the spirit and principles of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A carbon molecular sieve adsorbent, characterized in that: The carbon molecular sieve has a modified surface containing Si-O-Si bonds obtained by modification with a modifier and is loaded with rare earth metal elements; the micropores in the carbon molecular sieve are orderly linearly distributed, the pore diameter is 0.2-0.36nm, and the proportion of micropore volume to total pore volume is greater than or equal to 90%.

2. The carbon molecular sieve adsorbent according to claim 1, characterized in that: The modifier includes one or a combination of two or more of hexamethylsilazane, trimethylchlorosilane, mercaptopropyltriethoxysilane or ethyl orthosilicate.

3. The carbon molecular sieve adsorbent according to claim 1, characterized in that: The rare earth metal element comes from rare earth metal acetate or rare earth metal nitrate; the rare earth metal is one or more of ytterbium, lutetium, lanthanum, erbium, rubidium, yttrium or cerium; the concentration of the metal salt solution is 0.1-1.0 mol / L.

4. The carbon molecular sieve adsorbent according to claim 1, characterized in that: The modification treatment includes: regulating the ratio of the carbon molecular sieve, the modifier and the rare earth metal salt, preparing a carbon molecular sieve precursor with a modified surface containing Si-O-Si bonds by a hydrothermal synthesis method, and then loading rare earth metal elements on the active sites of the modified surface by an ion exchange method.

5. The carbon molecular sieve adsorbent according to claim 4, characterized in that: The ratio of the carbon molecular sieve, the modifier and the rare earth metal salt is 10-40g: 0.5-3mol: 1-3.5mol.

6. A method for preparing the carbon molecular sieve adsorbent according to claim 1, characterized in that: The following steps are involved: (1) preparing a carbon molecular sieve precursor containing Si-O-Si bonds by a hydrothermal synthesis method; (2) calcining the carbon molecular sieve precursor under a protective atmosphere, controlling the calcination temperature and time, and performing a first pore deposition on the carbon molecular sieve to obtain a modified carbon molecular sieve; (3) Mixing the modified carbon molecular sieve with a rare earth metal salt solution to carry out an ion exchange reaction to obtain a modified carbon molecular sieve loaded with rare earth metal elements; (4) calcining the modified carbon molecular sieve loaded with rare earth metal elements under a protective atmosphere, controlling the calcination temperature and time, and performing a second pore deposition on the carbon molecular sieve to obtain a carbon molecular sieve adsorbent.

7. The preparation method according to claim 6, characterized in that: Step (1) The hydrothermal synthesis method comprises mixing a modifier and an organic solvent in a molar ratio of 1:1-5, adding deionized water, stirring evenly, and then placing the mixture in a high-pressure reactor, keeping the mixture at a temperature of 145-155° C. for 24 hours, and finally obtaining a carbon molecular sieve precursor by filtering, washing and drying.

8. The preparation method according to claim 7, characterized in that: The organic solvent is selected from one or more of n-hexane, cyclohexane, n-heptane and toluene.

9. The preparation method according to claim 6, characterized in that: The loading amount of the rare earth metal element in step (3) accounts for 5-15% of the mass of the modified carbon molecular sieve.

10. Use of the carbon molecular sieve adsorbent according to any one of claims 1 to 5 in separation of nitrogen and methane mixed gas.

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