Preparation method and application of deep coal rock gas methane adsorbent based on graphene and MOF composite material

Abstract

The application discloses a preparation method and application of a deep coal rock gas methane adsorbent based on a graphene and MOF composite material, and belongs to the technical field of deep coal rock gas methane adsorption and purification. The preparation method is as follows: graphene material after pretreatment is prepared; cadmium nitrate, 3-amino-4-pyridine carboxylic acid and solvent B are mixed until completely dissolved to prepare a mixture; the mixture is placed in a set temperature to generate a coordination reaction, and then is cooled and crystallized; the crystal is washed and dried to prepare Cd-MOF; the graphene material after pretreatment and the Cd-MOF are added into solvent A, and then additives and a crosslinking agent are added and stirred to react, so that the composite material is prepared; a binder is added into the composite material, and then tabletting is carried out to prepare a shaped composite material; and the shaped composite material is subjected to high-temperature activation treatment in a protective atmosphere, so that the deep coal rock gas methane adsorbent is prepared. The graphene and the MOF are synthesized into the composite material, and the advantages of the two are complementary.

Description

Technical Field

[0001] This invention belongs to the field of deep coalbed methane adsorption and purification technology, specifically relating to a method for preparing and applying a deep coalbed methane adsorbent based on graphene and MOF composite materials. Background Technology

[0002] Deep coalbed methane is an important energy gas produced during coal pyrolysis and gasification. Its main component, methane, is a highly efficient and clean energy source with significant economic value. However, the separation and recovery of methane from deep coalbed methane has always been a key issue restricting its efficient utilization. Traditional methane adsorbents have many shortcomings in terms of performance, cost, and environmental friendliness, making it difficult to meet the growing industrial demands.

[0003] Currently, the commonly used method for methane separation from deep coalbed methane is adsorption. Traditional adsorbents such as activated carbon and molecular sieves have some limitations in the adsorption and separation of methane from deep coalbed methane. Activated carbon has a wide pore size distribution that is difficult to precisely control, resulting in limited adsorption selectivity for methane. In complex gas environments, it is difficult to efficiently separate and enrich methane. Zeolite molecular sieves have a regular pore structure and uniform pore size, enabling them to sieve different gases according to molecular size. They exhibit some adsorption selectivity for methane, but their chemical activity is relatively low, which is insufficient in promoting the desorption kinetics of methane, and the desorption process consumes a large amount of energy.

[0004] Metal-organic frameworks (MOFs) possess precisely tunable pore structures and offer advantages such as high specific surface area, abundant chemical functionality, and a large number of active sites. However, MOF materials also suffer from drawbacks such as low mechanical strength, poor stability, and generally poor conductivity. Graphene materials exhibit high specific surface area, strong adsorption properties, and good chemical stability and conductivity, but their tendency to aggregate reduces their specific surface area and effective active sites, thus affecting their adsorption of methane. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing and applying a deep coalbed methane adsorbent based on a graphene-MOF composite material. By synthesizing graphene and MOF into a composite material, the advantages of both materials are complemented. The high specific surface area, good conductivity, and structural stability of graphene can compensate for the insufficient conductivity and poor stability of MOF; while the abundant active sites and precisely tunable pore structure of MOF can solve the defects of single adsorption sites and limited adsorption selectivity of nano-carbon materials. This composite material combines the excellent properties of both, and in the methane desorption process, it can achieve a faster desorption rate, higher desorption efficiency, and more stable desorption performance through a synergistic effect.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a method for preparing a deep coalbed methane adsorbent based on graphene and MOF composite materials, comprising the following steps: Graphene was dispersed in solvent A to prepare a dispersion; then an acidifying agent was added to the dispersion, and the mixture was heated and stirred to carry out an acidification reaction. The mixture was then centrifuged, washed and dried in sequence to obtain the pretreated graphene material. Cadmium nitrate, 3-amino-4-pyridinecarboxylic acid, and solvent B were mixed until completely dissolved to obtain a mixture. The mixture was placed at a set temperature to undergo a coordination reaction, followed by cooling and crystallization. The crystals were washed and then dried to obtain Cd-MOF. Pretreated graphene and Cd-MOF were added to solvent A, followed by the addition of additives and crosslinking agents and stirring to obtain a composite material. A binder was added to the composite material, and then it was pressed into tablets to obtain a molded composite material. The molded composite material was then subjected to high-temperature activation treatment under a protective atmosphere to obtain a deep coal gas methane adsorbent.

[0007] In one implementation process, the mass-to-volume ratio of graphene to solvent A in the dispersion is (0.01-0.03g):1mL; the volume ratio of the dispersion to the acidifying reagent is (4-5):1.

[0008] In one implementation process, solvent A is a mixed solution of N,N-dimethylformamide, ethanol, and acetonitrile; wherein the volume ratio of N,N-dimethylformamide, ethanol, and acetonitrile is 6:3:1.

[0009] In one implementation process, the acidifying agent is a mixture of concentrated sulfuric acid and hydrogen peroxide, and the volume ratio of concentrated sulfuric acid to hydrogen peroxide is (5-7):1; The heating and stirring time is 3-4 hours; the acidification reaction temperature is 70-80℃.

[0010] In one implementation process, the molar ratio of cadmium nitrate to 3-amino-4-pyridinecarboxylic acid is 1:(1-3); the ratio of cadmium nitrate to solvent B is 0.001 mol corresponding to 20-30 mL; The solvent B is composed of N,N-dimethylformamide, acetonitrile, and water, with a volume ratio of 6:3:1.

[0011] In one implementation process, the set temperature is 100℃, the coordination reaction time is 22-24h, and the cooling rate of the cooling crystallization is 13-15℃ / h.

[0012] In one implementation process, the mass ratio of the pretreated graphene material to Cd-MOF is 1:(0.5-1). The ratio of the total mass of the pretreated graphene material and Cd-MOF to the volume of solvent A is (0.01-0.05) g: 1 mL.

[0013] In one implementation process, the auxiliary agent is sodium dodecylbenzenesulfonate, the crosslinking agent is glutaraldehyde, and the binder is polyvinyl alcohol or sodium carboxymethyl cellulose; The amount of the additive is 1%-3% of the total mass of the pretreated graphene material and Cd-MOF; The amount of crosslinking agent used is 5%-10% of the total mass of the pretreated graphene material and Cd-MOF; The amount of adhesive used is 1%-3% of the mass of the composite material.

[0014] In one implementation process, the temperature of the stirring reaction is 40-50℃, and the stirring reaction time is 10-12h; The protective atmosphere is nitrogen, the temperature of the high-temperature activation treatment is 300-400℃, and the time of the high-temperature activation treatment is 3-4 hours.

[0015] The present invention also provides the application of the deep coal gas methane adsorbent prepared by the above-described method based on graphene and MOF composite materials in the methane adsorption process.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing a deep coalbed methane adsorbent based on a graphene-MOF composite material. By combining graphene and MOF, a novel composite material is prepared, fully leveraging the advantages of both and achieving synergy. Graphene, with its high specific surface area, excellent conductivity, and good structural stability, effectively improves the poor conductivity and instability of MOF materials. Meanwhile, the abundant active sites and precisely controllable pore structure of MOF materials can compensate for the limitations of graphene's single adsorption site and limited adsorption selectivity. During methane desorption, the two materials exhibit a significant synergistic effect, resulting in a faster desorption rate, enabling desorption operations to be completed in a shorter time; higher desorption efficiency, achieving highly efficient methane desorption; and more stable desorption performance, maintaining good performance even after multiple desorption cycles, providing a superior material choice for methane-related applications. The methane adsorbent prepared by this invention has advantages such as good methane adsorption selectivity, large specific surface area, high methane adsorption rate, good adsorption and separation effect, adjustable pore size, and high adsorption efficiency. It can realize the efficient desorption and utilization of methane and solve the problems existing in the desorption process of existing methane adsorbents.

[0017] Furthermore, pretreatment of graphene enhances its compatibility with other substances, allowing graphene sheets to disperse uniformly in solvents and forming better interfacial bonds with MOF materials. Simultaneously, acidification removes impurities from graphene, improving the consistency and repeatability of graphene material performance. Pretreated graphene is then combined with Cd-MOF to prepare a methane adsorbent. Compared to other traditional adsorbents, graphene possesses a huge specific surface area, while Cd-MOF has a rich and regular pore structure. The combination of these two materials produces a synergistic effect, providing more adsorption sites and significantly increasing the adsorption capacity and efficiency of methane.

[0018] Furthermore, compared to other products, the pore size and chemical environment of Cd-MOF in this invention can be precisely controlled, giving it a specific affinity and selectivity for methane molecules. The composite of graphene and Cd-MOF further optimizes the surface properties and pore structure of the adsorbent, enabling more effective recognition and adsorption of methane molecules, reducing interference from other gases, and improving the adsorption selectivity for methane. The two-dimensional structure of graphene facilitates molecular diffusion; when combined with Cd-MOF, it accelerates the diffusion rate of methane molecules within the adsorbent, allowing the adsorption process to quickly reach equilibrium and exhibiting faster adsorption kinetics. Simultaneously, the interfacial region formed between graphene and Cd-MOF provides additional diffusion channels and pathways for guest molecules, allowing adsorbed molecules to diffuse more rapidly from the interior of the composite material to the external environment during desorption, thereby improving desorption efficiency.

[0019] Furthermore, Cd-MOF itself possesses a certain degree of chemical stability, and the introduction of graphene can enhance the chemical stability of the composite material. The carbon atoms of graphene are tightly bound together by covalent bonds, forming a stable two-dimensional structure that can resist the erosion of some chemical substances, protecting Cd-MOF from external environmental influences and enabling the adsorbent to maintain stable adsorption performance in different chemical environments. Due to its unique structure and surface properties, methane molecules can desorb from the adsorbent surface under relatively low temperature or pressure changes, enabling the adsorbent to be recycled and reused. After multiple adsorption-desorption cycles, the structure and adsorption performance of the graphene-Cd-MOF composite material remain relatively stable, maintaining high adsorption capacity and selectivity.

[0020] In summary, the preparation method of the composite material methane adsorbent of the present invention is simple, has low raw material cost, is easy to control, and produces activated carbon with high specific surface area, high adsorption efficiency and rate, good stability, and easy recycling and reuse. It can produce efficient adsorption of methane gas through synergistic physical and chemical adsorption, resulting in excellent adsorption effect, long service life, and low methane purification cost. It effectively solves the technical problem of poor methane adsorption effect of activated carbon in the prior art and has strong practicality. Attached Figure Description

[0021] Figure 1 The image shows the adsorption isotherm at 273 K for the deep coal gas methane adsorbent based on graphene and MOF composite materials prepared in Example 3 of this invention. Detailed Implementation

[0022] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0024] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0025] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0026] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0027] This invention provides a method for preparing a deep coalbed methane adsorbent based on a graphene-MOF composite material, the preparation method comprising: Graphene was dispersed in a first organic solvent (solvent A) and ultrasonically treated to ensure full dispersion, thus obtaining a dispersion. An acidifying agent was added to the dispersion, and the mixture was heated and stirred to carry out an acidification reaction. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain the pretreated graphene material. Solvent B, consisting of cadmium nitrate, 3-amino-4-pyridinecarboxylic acid, N,N-dimethylformamide, acetonitrile, and water, was mixed and added to a sealed glass bottle. The mixture was then thoroughly shaken in an ultrasonic cleaner until completely dissolved. The dissolved mixture was placed in a 100°C oven for reaction, cooled to crystallize, washed, and dried to obtain Cd-MOF. The pretreated graphene material and Cd-MOF were added to a second organic solvent (another solvent, A) and ultrasonically treated. Then, additives and crosslinking agents were added, and the mixture was stirred to obtain a composite material. A binder was added to the composite material, and it was pressed into the desired shape and size. The molded composite material was then activated under nitrogen protection to obtain the final product.

[0028] The composite material for methane adsorbent obtained in this invention has advantages such as good methane adsorption selectivity, large specific surface area, high methane adsorption rate, good adsorption and separation effect, adjustable pore size, and high adsorption efficiency. It also exhibits good stability, is easy to recycle and reuse, and has good desorption efficiency. The hybrid material of this invention achieves highly efficient adsorption of methane gas through synergistic physical and chemical adsorption, effectively solving the technical problem of poor methane adsorption effect of activated carbon in the prior art, and has strong practicality.

[0029] In a first aspect, this invention provides a method for preparing a methane adsorbent for deep coalbed methane formation. This method is based on a graphene-MOF composite material, and the specific preparation method includes: (1) Graphene is dispersed in the first organic solvent (solvent A) and subjected to ultrasonic treatment to ensure full dispersion and obtain a dispersion; an acidifying agent is added to the dispersion, and the mixture is heated and stirred to carry out an acidification reaction. After the acidification reaction is completed, the mixture is centrifuged, washed, and dried to obtain the pretreated graphene material. (2) Add cadmium nitrate, 3-amino-4-pyridinecarboxylic acid, N,N-dimethylformamide, acetonitrile and water to a sealed glass bottle and shake it thoroughly in an ultrasonic cleaner until it is completely dissolved. Place the dissolved mixture in a 100°C oven to undergo a coordination reaction, cool it to crystallize, wash the crystals and dry them to obtain Cd-MOF. (3) The pretreated graphene material and Cd-MOF are placed in a second organic solvent (solvent A) and subjected to ultrasonic treatment. Then, additives and crosslinking agents are added and the mixture is stirred to obtain the composite material. (4) Add a binder to the composite material and press it into the required shape and size. Activate the molded composite material under nitrogen protection to obtain the final product.

[0030] The first organic solvent (solvent A) and the second organic solvent (another portion of solvent A) are the same. Both the first organic solvent (solvent A) and the second organic solvent (another portion of solvent A) are mixed solutions of N,N-dimethylformamide, ethanol and acetonitrile; wherein the mass ratio of N,N-dimethylformamide, ethanol and acetonitrile is 6:3:1.

[0031] In step (1), the mass-to-volume ratio of graphene to the first organic solvent (solvent A) is (0.01-0.03g):1mL; the volume ratio of dispersion to acidifying reagent is (4-5):1; the acidifying reagent is a mixture of concentrated sulfuric acid and hydrogen peroxide, and the volume ratio of the two is (5-7):1; the ultrasonic treatment time is 1-1.5h; the reaction temperature is 70-80℃, and the stirring time is 3-4h.

[0032] In step (2), the molar ratio of cadmium nitrate to 3-amino-4-pyridinecarboxylic acid is 1:(1-3), and the volume ratio of N,N-dimethylformamide, acetonitrile, and water in the solvent is 6:3:1. Solvent B consists of N,N-dimethylformamide, acetonitrile, and water, and the ratio of cadmium nitrate to solvent B is 0.001 mol corresponding to 20-30 mL. The coordination reaction takes 22-24 h; the cooling rate for crystallization is 13-15 °C / h.

[0033] In step (3): the mass ratio of pretreated graphene to Cd-MOF is 1:(0.5-1), and the total mass-volume ratio of the two to the second organic solvent (another solvent A) is (0.01-0.05 g):1 mL. The second organic solvent (another solvent A) is a mixed solution of N,N-dimethylformamide, ethanol and acetonitrile, with a ratio of 6:3:1; the ultrasonic treatment time in step (3) is 1-1.5 h.

[0034] In step (3), the auxiliary agent is sodium dodecylbenzenesulfonate (SDBS), and the crosslinking agent is glutaraldehyde; the amount of auxiliary agent is 1%-3% of the total mass of pretreated graphene and Cd-MOF, and the amount of crosslinking agent is 5%-10% of the total mass; the reaction temperature is 40-50℃, and the reaction time is 10-12 h.

[0035] The binder used in step (4) is polyvinyl alcohol or sodium carboxymethyl cellulose, and the amount of binder is 1%-3% of the mass of the composite material; the activation reaction temperature is 300℃-400℃, and the reaction time is 3-4h.

[0036] As a further explanation of the present invention, graphene partially coats Cd-MOF particles to a certain extent. SDBS molecules adsorbed on the surfaces of graphene and Cd-MOF form an adsorption layer of a certain thickness. When the particles approach each other, this adsorption layer creates steric hindrance, preventing further particle aggregation and thus maintaining their dispersed state. Under suitable reaction conditions, the two aldehyde groups of glutaraldehyde can undergo nucleophilic addition reactions with nucleophilic groups such as amino and hydroxyl groups on the surfaces of graphene and Cd-MOF. Through the above chemical reaction, covalent bonds are formed between glutaraldehyde and graphene and Cd-MOF. SDBS improves the dispersibility of graphene, enabling it to better contact Cd-MOF, and under the cross-linking effect of glutaraldehyde, graphene can surround Cd-MOF, forming a coating structure. This structure can protect the structural stability of Cd-MOF and also increase the specific surface area and adsorption sites of the composite material.

[0037] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0038] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0039] Example 1 (1) 10 g of graphene was dispersed in 1000 mL of a first organic solvent consisting of N,N-dimethylformamide, ethanol, and acetonitrile, and ultrasonically treated for 1.5 h to ensure complete dispersion and obtain a dispersion. 25 mL of a concentrated sulfuric acid-hydrogen peroxide mixture was added to 100 mL of the dispersion, with a volume ratio of concentrated sulfuric acid to hydrogen peroxide of 5:1. The mixture was stirred at 80 °C for 4 h to carry out an acidification reaction. After the acidification reaction was completed, the mixture was centrifuged and washed, and dried at 50 °C for 4 h to obtain the pretreated graphene material. (2) 2.36 g cadmium nitrate, 1.38 g 3-amino-4-pyridinecarboxylic acid, 120 mL N,N-dimethylformamide, 60 mL g acetonitrile and 20 mL deionized water were mixed and added to a sealed glass bottle. The mixture was shaken thoroughly in an ultrasonic cleaner until completely dissolved. The dissolved mixture was placed in a 100℃ oven and reacted for 24 h. The mixture was cooled and crystallized at a cooling rate of 13℃ / h. The crystals were washed and dried to obtain Cd-MOF. (3) 4 g of pretreated graphene and 2 g of Cd-MOF were mixed and added to a second organic solvent of 600 mL N,N-dimethylformamide, ethanol and acetonitrile, and ultrasonically treated for 1.5 h. Then 0.18 g of dodecylbenzenesulfonic acid as an auxiliary agent and 0.6 g of glutaraldehyde as a crosslinking agent were added, and the mixture was stirred at 50 °C for 12 h to obtain the composite material; (4) Add 0.15 g of polyvinyl alcohol as a binder to 5 g of composite material, and press it into the required shape and size. Activate the molded composite material at 400°C for 4 h under nitrogen protection to obtain the final product.

[0040] Example 2 (1) 30 g of graphene was dispersed in 1000 mL of a first organic solvent consisting of N,N-dimethylformamide, ethanol, and acetonitrile, and ultrasonically treated for 1.5 h to ensure complete dispersion and obtain a dispersion. 20 mL of a concentrated sulfuric acid-hydrogen peroxide mixture was added to 100 mL of the dispersion, with a volume ratio of concentrated sulfuric acid to hydrogen peroxide of 5:1. The mixture was stirred at 80 °C for 4 h to carry out an acidification reaction. After the acidification reaction was completed, the mixture was centrifuged and washed, and dried at 50 °C for 4 h to obtain the pretreated graphene material. (2) 2.36 g cadmium nitrate, 2.76 g 3-amino-4-pyridinecarboxylic acid, 120 mL N,N-dimethylformamide, 60 mL g acetonitrile and 20 mL deionized water were mixed and added to a sealed glass bottle. The mixture was shaken thoroughly in an ultrasonic cleaner until completely dissolved. The dissolved mixture was placed in a 100℃ oven and reacted for 24 h. The mixture was cooled and crystallized at a cooling rate of 13℃ / h. The crystals were washed and dried to obtain Cd-MOF. (3) 4 g of pretreated graphene and 4 g of Cd-MOF were mixed and added to a second organic solvent of 600 mL N,N-dimethylformamide, ethanol and acetonitrile, and ultrasonically treated for 1 h. Then 0.18 g of dodecylbenzenesulfonic acid as an auxiliary agent and 0.6 g of glutaraldehyde as a crosslinking agent were added, and the mixture was stirred at 50 °C for 12 h to obtain the composite material; (4) Add 0.15 g of polyvinyl alcohol as a binder to 5 g of composite material, and press it into the required shape and size. Activate the molded composite material at 400°C for 4 h under nitrogen protection to obtain the final product.

[0041] Example 3 (1) 10 g of graphene was dispersed in 1000 mL of a first organic solvent consisting of N,N-dimethylformamide, ethanol, and acetonitrile, and ultrasonically treated for 1 h to ensure complete dispersion, thus obtaining a dispersion. 25 mL of a concentrated sulfuric acid-hydrogen peroxide mixture was added to 100 mL of the dispersion, with a volume ratio of concentrated sulfuric acid to hydrogen peroxide of 5:1. The mixture was stirred at 80 °C for 3 h to carry out an acidification reaction. After the acidification reaction was completed, the mixture was centrifuged and washed, and then dried at 50 °C for 4 h to obtain the pretreated graphene material. (2) 2.36 g cadmium nitrate, 4.14 g 3-amino-4-pyridinecarboxylic acid, 120 mL N,N-dimethylformamide, 60 mL g acetonitrile and 20 mL deionized water were mixed and added to a sealed glass bottle. The mixture was shaken thoroughly in an ultrasonic cleaner until completely dissolved. The dissolved mixture was placed in a 100℃ oven and reacted for 24 h. The mixture was cooled and crystallized at a cooling rate of 13℃ / h. The crystals were washed and dried to obtain Cd-MOF. (3) 4 g of pretreated graphene and 4 g of Cd-MOF were mixed and added to 480 mL of a second organic solvent consisting of N,N-dimethylformamide, ethanol, and acetonitrile, and ultrasonically treated for 1.5 h. Then 0.18 g of dodecylbenzenesulfonic acid was added as an auxiliary agent and 0.6 g of glutaraldehyde as a crosslinking agent, and the mixture was stirred at 40 °C for 10 h to obtain the composite material. (4) Add 0.15 g of sodium carboxymethyl cellulose as a binder to 5 g of composite material, and press it into the required shape and size by compression. Activate the molded composite material at 300°C for 4 h under nitrogen protection to obtain the final product.

[0042] Example 4 (1) 30 g of graphene was dispersed in 1000 mL of a first organic solvent consisting of N,N-dimethylformamide, ethanol, and acetonitrile, and ultrasonically treated for 1 h to ensure complete dispersion, thus obtaining a dispersion. 25 mL of a concentrated sulfuric acid-hydrogen peroxide mixture was added to 100 mL of the dispersion, with a volume ratio of concentrated sulfuric acid to hydrogen peroxide of 5:1. The mixture was stirred at 70 °C for 3 h to carry out an acidification reaction. After the acidification reaction was completed, the mixture was centrifuged and washed, and then dried at 50 °C for 4 h to obtain the pretreated graphene material. (2) 2.36 g cadmium nitrate, 2.76 g 3-amino-4-pyridinecarboxylic acid, 120 mL N,N-dimethylformamide, 60 mL g acetonitrile and 20 mL deionized water were mixed and added to a sealed glass bottle. The mixture was thoroughly shaken in an ultrasonic cleaner until completely dissolved. The dissolved mixture was placed in a 100℃ oven and reacted for 22 h. The mixture was cooled and crystallized at a cooling rate of 15℃ / h. The crystals were washed and dried to obtain Cd-MOF. (3) 4 g of pretreated graphene and 3 g of Cd-MOF were mixed and added to 360 mL of a second organic solvent consisting of N,N-dimethylformamide, ethanol, and acetonitrile, and ultrasonically treated for 1 h. Then 0.18 g of dodecylbenzenesulfonic acid was added as an auxiliary agent and 0.3 g of glutaraldehyde as a crosslinking agent, and the mixture was stirred at 50 °C for 12 h to obtain the composite material. (4) Add 0.05 g of sodium carboxymethyl cellulose as a binder to 5 g of composite material, and press it into the required shape and size by compression. Activate the molded composite material at 300°C for 4 h under nitrogen protection to obtain the final product.

[0043] Example 5 (1) 20 g of graphene was dispersed in 1000 mL of a first organic solvent consisting of N,N-dimethylformamide, ethanol, and acetonitrile, and ultrasonically treated for 1.5 h to ensure complete dispersion and obtain a dispersion. 20 mL of a concentrated sulfuric acid-hydrogen peroxide mixture was added to 100 mL of the dispersion, with a volume ratio of concentrated sulfuric acid to hydrogen peroxide of 6:1. The mixture was stirred at 70 °C for 4 h to carry out an acidification reaction. After the acidification reaction was completed, the mixture was centrifuged and washed, and dried at 50 °C for 4 h to obtain the pretreated graphene material. (2) 2.36 g cadmium nitrate, 2.76 g 3-amino-4-pyridinecarboxylic acid, 120 mL N,N-dimethylformamide, 60 mL g acetonitrile and 20 mL deionized water were mixed and added to a sealed glass bottle. The mixture was thoroughly shaken in an ultrasonic cleaner until completely dissolved. The dissolved mixture was placed in a 100℃ oven and reacted for 22 h. The mixture was cooled and crystallized at a cooling rate of 15℃ / h. The crystals were washed and dried to obtain Cd-MOF. (3) 4 g of pretreated graphene and 2 g of Cd-MOF were mixed and added to 240 mL of an organic solvent containing N,N-dimethylformamide, ethanol, and acetonitrile, and ultrasonically treated for 1.5 h. Then 0.15 g of dodecylbenzenesulfonic acid was added as an auxiliary agent and 0.3 g of glutaraldehyde as a crosslinking agent, and the mixture was stirred at 40 °C for 10 h to obtain the composite material; (4) Add 0.05 g of polyvinyl alcohol as a binder to 5 g of composite material, and press it into the required shape and size. Activate the molded composite material at 400°C for 3 h under nitrogen protection to obtain the final product.

[0044] Example 6 (1) 20 g of graphene was dispersed in 1000 mL of a first organic solvent consisting of N,N-dimethylformamide, ethanol, and acetonitrile, and ultrasonically treated for 1 h to ensure complete dispersion, thus obtaining a dispersion. 20 mL of a concentrated sulfuric acid-hydrogen peroxide mixture was added to 100 mL of the dispersion, with a volume ratio of concentrated sulfuric acid to hydrogen peroxide of 7:1. The mixture was stirred at 70 °C for 4 h to carry out an acidification reaction. After the acidification reaction was completed, the mixture was centrifuged and washed, and then dried at 50 °C for 4 h to obtain the pretreated graphene material. (2) 2.36 g cadmium nitrate, 1.38 g 3-amino-4-pyridinecarboxylic acid, 120 mL N,N-dimethylformamide, 60 mL g acetonitrile and 20 mL deionized water were mixed and added to a sealed glass bottle. The mixture was shaken thoroughly in an ultrasonic cleaner until completely dissolved. The dissolved mixture was placed in a 100℃ oven and reacted for 23 h. The mixture was cooled and crystallized at a cooling rate of 14℃ / h. The crystals were washed and dried to obtain Cd-MOF. (3) 4 g of pretreated graphene and 2 g of Cd-MOF were mixed and added to 120 mL of an organic solvent consisting of N,N-dimethylformamide, ethanol, and acetonitrile, and ultrasonically treated for 1.5 h. Then 0.12 g of dodecylbenzenesulfonic acid was added as an auxiliary agent and 0.6 g of glutaraldehyde as a crosslinking agent, and the mixture was stirred at 50 °C for 10 h to obtain the composite material. (4) Add 0.1 g of sodium carboxymethyl cellulose as a binder to 5 g of composite material, and press it into the required shape and size by compression. Activate the molded composite material at 400°C for 3 h under nitrogen protection to obtain the final product.

[0045] To characterize the effects of different synthesis conditions on the dynamic adsorption capacity and specific surface area of ​​the methane adsorbent, the dynamic adsorption capacity, specific surface area, and micropore volume of the adsorbents synthesized in Examples 1-6 were tested, and the stability of the methane adsorbent was investigated through a cycle-desorption cycle experiment. The results are shown in Table 1.

[0046] Table 1 Performance Tests of Methane Adsorbent

[0047] The research results show that the composite methane adsorbent exhibits extremely high adsorption capacity. Under standard temperature and pressure conditions, the dynamic adsorption capacity of the methane adsorbent prepared by this product can reach a maximum of 82.8 mL / g, which is higher than the average level of similar adsorbents on the market. It also demonstrates excellent selectivity for methane in complex gas mixtures. The adsorbent exhibits excellent desorption performance; after multiple cycle-desorption experiments, the adsorption efficiency can still reach up to 90.1%, and the desorption efficiency can reach up to 94.6%. This allows the adsorbent to quickly and effectively release the adsorbed methane after completing its adsorption task, facilitating methane recovery and providing favorable conditions for the adsorbent's recycling. It possesses a large specific surface area, reaching up to 1823.8 m² / g, and contains numerous regular micropores and mesopores, providing abundant adsorption sites for methane adsorption. Furthermore, this composite methane adsorbent is environmentally friendly during production and use, containing no harmful substances and causing no pollution. After disposal, it is also easy to handle and can be recycled through simple regeneration or recovery processes, meeting the requirements of modern green and environmentally friendly development.

[0048] like Figure 1 As shown, the methane adsorbent for deep coalbed methane prepared in Example 3 exhibits a continuously increasing adsorption capacity for methane at 273 K with increasing absolute pressure. Within a lower pressure range, the adsorption capacity increases rapidly with increasing pressure, but the rate of increase gradually slows down as the pressure further increases. This is because the adsorption sites on the adsorbent surface are gradually occupied, reaching near saturation, and further increases in pressure no longer significantly improve the adsorption capacity.

[0049] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a deep coalbed methane adsorbent based on graphene and MOF composite materials, characterized in that, Includes the following steps: Graphene was dispersed in solvent A to prepare a dispersion; then an acidifying agent was added to the dispersion, and the mixture was heated and stirred to carry out an acidification reaction. The mixture was then centrifuged, washed, and dried sequentially to obtain pretreated graphene material. The acidifying agent was a mixture of concentrated sulfuric acid and hydrogen peroxide, with a volume ratio of (5-7):

1. Solvent A was a mixed solution of N,N-dimethylformamide, ethanol, and acetonitrile, with a volume ratio of 6:3:

1. Cadmium nitrate, 3-amino-4-pyridinecarboxylic acid, and solvent B are mixed until completely dissolved to obtain a mixture. The mixture is placed at a set temperature to undergo a coordination reaction, followed by cooling and crystallization. The crystals are washed and then dried to obtain Cd-MOF. The set temperature is 100℃, the coordination reaction time is 22-24h, and the cooling rate for crystallization is 13-15℃ / h. Pretreated graphene material and Cd-MOF were added to solvent A, followed by the addition of additives and crosslinking agents and stirring to obtain a composite material. A binder was added to the composite material, and then the mixture was pressed into tablets to obtain a molded composite material. The molded composite material was then subjected to high-temperature activation treatment under a protective atmosphere to obtain a deep coal gas methane adsorbent. The additive was sodium dodecylbenzene sulfonate, and the crosslinking agent was glutaraldehyde. The temperature of the stirring reaction is 40-50℃, and the stirring reaction time is 10-12h; The protective atmosphere is nitrogen, the temperature of the high-temperature activation treatment is 300-400℃, and the time of the high-temperature activation treatment is 3-4 hours.

2. The preparation method of the deep coal gas methane adsorbent based on graphene and MOF composite materials according to claim 1, characterized in that, The mass-to-volume ratio of graphene to solvent A in the dispersion is (0.01-0.03g):1mL; the volume ratio of the dispersion to the acidifying reagent is (4-5):

1.

3. The preparation method of the deep coal gas methane adsorbent based on graphene and MOF composite materials according to claim 1, characterized in that, The heating and stirring time is 3-4 hours; the acidification reaction temperature is 70-80℃.

4. The preparation method of the deep coal gas methane adsorbent based on graphene and MOF composite materials according to claim 1, characterized in that, The molar ratio of cadmium nitrate to 3-amino-4-pyridinecarboxylic acid is 1:(1-3); the ratio of cadmium nitrate to solvent B is 0.001 mol corresponding to 20-30 mL; The solvent B is composed of N,N-dimethylformamide, acetonitrile, and water, with a volume ratio of 6:3:

1.

5. The method for preparing a deep coalbed methane adsorbent based on graphene and MOF composite materials according to claim 1, characterized in that, The mass ratio of the pretreated graphene material to Cd-MOF is 1:(0.5-1). The ratio of the total mass of the pretreated graphene material and Cd-MOF to the volume of solvent A is (0.01-0.05) g: 1 mL.

6. The method for preparing a deep coalbed methane adsorbent based on graphene and MOF composite materials according to claim 1, characterized in that, The adhesive is polyvinyl alcohol or sodium carboxymethyl cellulose; The amount of the additive is 1%-3% of the total mass of the pretreated graphene material and Cd-MOF; The amount of crosslinking agent used is 5%-10% of the total mass of the pretreated graphene material and Cd-MOF; The amount of adhesive used is 1%-3% of the mass of the composite material.

7. The application of the deep coal gas methane adsorbent based on graphene and MOF composite material prepared by the method of any one of claims 1 to 6 in the methane adsorption process.

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