Macroscopic preparation of a class of covalent organic frameworks based on tetramethylpyrazine and their application in low hydrocarbon vocs gas adsorption and separation

Abstract

This invention utilizes inexpensive tetramethylpyrazine monomers as the connecting nodes in the construction of vinyl covalent organic frameworks (COFs). A series of tetramethylpyrazine-based COFs with good crystallinity, high specific surface area, and good chemical and thermal stability were successfully synthesized, and ionization of the materials was successfully achieved. The synthesis process avoided the use of highly toxic organic solvents, achieving a kilogram-scale production standard. This series of tetramethylpyrazine-based COFs can efficiently adsorb low-chain hydrocarbon VOCs and can obtain high-purity ethylene gas from light hydrocarbon ternary mixtures in a one-step process, showing broad application prospects in the adsorption and removal of VOCs in the petrochemical industry.

Description

Technical Field

[0001] This invention belongs to the field of porous organic materials, specifically relating to the large-scale preparation of a class of covalent organic framework materials based on tetramethylpyrazine and their application in the adsorption and separation of VOCs gases. Background Technology

[0002] Covalent organic frameworks (COFs) are a class of crystalline organic porous polymers composed of organic building blocks linked by dynamic covalent bonds. Due to their designable structure, high porosity, low density, and excellent chemical stability, COFs have wide applications in gas storage and separation, catalysis, sensing, energy storage, and optical devices. With the increasing diversity of COF types, various linkage mechanisms have been developed, including borate esters, triazines, imines, phenylhydrazones, keteneamines, polyimides, and vinyl groups. However, the development of COFs is severely hampered by the lack of efficient synthesis methods. Traditional solvothermal methods are unsuitable for practical industrial production due to their complex processes, high energy consumption, long reaction times, and limited scalability. Therefore, seeking simpler, faster, more energy-efficient, and environmentally friendly synthesis strategies is crucial for the industrial production of COFs.

[0003] In recent years, with the rapid development of industrialization, VOCs have become another major gaseous pollutant after particulate matter and sulfur dioxide. VOCs in the petrochemical industry mainly include combustion flue gas, process tail gas, hydrocarbon gases leaking from equipment, and odorous gases emitted from alkaline slag treatment units and wastewater treatment plants. Characteristic pollutants include alkanes, alkenes, cycloalkanes, alcohols, aromatic hydrocarbons, ethers and ketones, aldehydes, phenols, esters, halogenated hydrocarbons, and halides. Currently, VOCs waste gas treatment methods include scrubbing, catalytic combustion, regenerative thermal oxidation, activated carbon methods, purification and recovery methods, and biological methods. It has been proven that using physical adsorption technology to replace cumbersome traditional industrial methods can significantly reduce energy consumption. In this regard, porous adsorbents such as metal-organic frameworks (MOFs) and hydrogen-bonded organic frameworks (HOFs) have been developed for the adsorption and separation of VOCs gases. However, these materials generally suffer from poor chemical stability, high cost, and lack of product scalability, hindering their practical application. Therefore, the development of inexpensive materials with good VOCs adsorption and removal performance is urgently needed in industry.

[0004] On the one hand, this invention develops a class of inexpensive and stable vinyl COFs based on tetramethylpyrazine that can be prepared in large quantities by regulating and screening the organic building blocks used to construct COFs and by using a solvent-free synthesis method, and successfully achieves the ionization of tetramethylpyrazine-based COFs; on the other hand, this invention uses the prepared tetramethylpyrazine-based COFs as adsorbents to adsorb acetylene and ethane in VOCs gas, and achieves efficient separation of ethylene from acetylene and ethane in a one-step process. Summary of the Invention

[0005] The purpose of this invention is to design and synthesize a series of novel vinyl-linked COFs based on tetramethylpyrazine. These COFs have advantages such as low cost, high structural stability, and ease of large-scale production.

[0006] Another object of the present invention is to achieve the adsorption and removal of alkanes in VOCs gas by using tetramethylpyrazine-based COFs as adsorbents through a fixed-bed breakthrough experiment and adsorption separation. Other objects of the present invention will be clear to those skilled in the art from the foregoing and following description.

[0007] The first aspect of the present invention provides a method for synthesizing covalent organic framework materials based on tetramethylpyrazine and the ionization steps thereof, characterized in that the COFs materials are constructed in one step by means of vinyl covalent linkage.

[0008] Preferably, the synthesis method 1 involves directly adding the monomer tetramethylpyrazine, the aldehyde-containing di-linked monomer, and the catalyst into a reactor, and then performing melt polymerization under closed conditions to obtain COFs material, followed by cleaning and purification.

[0009] Preferably, monomer 1 is tetramethylpyrazine.

[0010] Preferably, monomer 2 is a di-linked monomer containing an aldehyde functional group.

[0011] Further preferred, the di-linked monomers containing aldehyde functional groups are linear molecules.

[0012] In a preferred embodiment of the present invention, the aldehyde monomer is any one of terephthalaldehyde, 4,4'-biphenyldialdehyde, 1,4-bis(4-aldehydephenyl)benzene, 1,2-bis(4'-formylphenyl)acetylene, 4,4'-(1,3-butadiyne-1,4-diyl)bisbenzaldehyde, 2,5-dimethoxy-1,4-terephthalaldehyde, pyridine-2,5-dicarboxaldehyde, 2,5-dialdehydepyrazine, 2,2'-bipyridine-5,5'-dicarboxaldehyde, and 3,3'-bipyridine-6,6'-dicarboxaldehyde.

[0013] Preferably, the catalyst is a compound containing an anhydride functional group, a compound containing an acyl chloride functional group, or a compound containing a carboxylic acid functional group.

[0014] More preferably, the catalyst is one or more of the following: benzoic anhydride, sodium benzoate, benzoyl chloride, 4-trifluoromethylbenzoic anhydride, 4-methoxybenzoic anhydride, acetic anhydride, trifluoroacetic anhydride, benzoic acid, 4-fluorobenzoic acid, acetic acid, formic acid, and propionic acid.

[0015] Preferably, the monomer 3 is a straight-chain or branched alkyl monohalogen-substituted or dihalogen-substituted product.

[0016] Preferably, the resulting COFs are vinyl-linked COF blocks.

[0017] Preferably, the pore size of the COFs material is 0.8-5.0 nm.

[0018] Preferably, the molar ratio of organic monomer 1 to organic monomer 2 is 1:2.

[0019] Preferably, in the reaction system, the molar ratio of catalyst to organic monomer 2 is 1:1 to 8:1, more preferably 1:1 to 1:4.

[0020] Preferably, in the reaction system, the molar ratio of organic monomer 3 to organic monomer 1 is 1:4 to 4:1, and more preferably adjusted to 1:1 to 1:2.

[0021] Preferably, the pressure of the reaction system is 0-1 atm.

[0022] Preferably, the synthesis temperature is 160-200 ℃.

[0023] Preferably, the reaction time is 3-7 days, more preferably 5 days.

[0024] Preferably, the sealed reaction vessel is one of the following: a high-temperature and high-pressure resistant Pyrex tube, an ampoule requiring flame sealing, or a high-pressure reactor.

[0025] Preferably, the COFs material cleaning and purification steps are as follows: the obtained product is soaked in DMF or alkaline solution to remove unreacted monomers, then washed with THF or water to remove excess catalyst or alkali, and finally the obtained powder is heated and dried in a vacuum high-temperature oven at a temperature of 80-200 °C to obtain the final product.

[0026] Synthetic method 1 of this invention involves constructing vinyl COFs based on tetramethylpyrazine, the general formula of which can be expressed as:

[0027]

[0028] In the general formula: Organic monomer 1 is tetramethylpyrazine, i.e., 2,3,5,6-tetramethylpyrazine. Organic monomer 2 mainly includes any one of the following: terephthalaldehyde, 4,4'-biphenyldialdehyde, 1,4-bis(4-aldehydephenyl)benzene, 1,2-bis(4'-formylphenyl)acetylene, 4,4'-(1,3-butadiyne-1,4-diyl)bisbenzaldehyde, 2,5-dimethoxy-1,4-terephthalaldehyde, pyridine-2,5-dicarboxaldehyde, 2,5-dialdehydepyrazine, 2,2'-bipyridine-5,5'-dicarboxaldehyde, and 3,3'-bipyridine-6,6'-dicarboxaldehyde. Monomers 1 and 2 mentioned above can be combined arbitrarily, and the target COFs can be prepared under any of the catalyst conditions. The catalyst is one or more of the following: benzoic anhydride, sodium benzoate, benzoyl chloride, 4-trifluoromethylbenzoic anhydride, 4-methoxybenzoic anhydride, acetic anhydride, trifluoroacetic anhydride, benzoic acid, 4-fluorobenzoic acid, acetic acid, formic acid, and propionic acid.

[0029] Synthesis method 2 of this invention is a one-pot synthesis method for ionic vinyl COFs based on tetramethylpyrazine, and the relevant general formula can be expressed as:

[0030]

[0031] In the general formula: Organic monomer 1 is tetramethylpyrazine, i.e., 2,3,5,6-tetramethylpyrazine. Organic monomer 2 mainly includes any one of the following: terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde, 1,4-bis(4-aldehydephenyl)benzene, 1,2-bis(4'-formylphenyl)acetylene, 4,4'-(1,3-butadiyne-1,4-diyl)bisbenzaldehyde, 2,5-dimethoxy-1,4-terephthalaldehyde, pyridine-2,5-dicarboxaldehyde, 2,5-dialdehydepyrazine, 2,2'-bipyridine-5,5'-dicarboxaldehyde, and 3,3'-bipyridine-6,6'-dicarboxaldehyde. Organic monomer 3 mainly includes, but is not limited to, one or more of the following: iodomethane, bromoethane, bromopropane, chloroethane, 1-bromobutane, 1,2-dibromoethane, 1,4-dibromobutane, 1-bromopentane, 1-bromohexane, and 1-bromoheptane. The catalyst is one or more of the following: benzoic anhydride, sodium benzoate, benzoyl chloride, 4-trifluoromethylbenzoic anhydride, 4-methoxybenzoic anhydride, acetic anhydride, trifluoroacetic anhydride, benzoic acid, 4-fluorobenzoic acid, acetic acid, formic acid, and propionic acid. Monomers 1, 2, and 3 mentioned above can be combined arbitrarily, and the target COFs can be prepared under any of the catalyst conditions.

[0032] Preferably, the VOCs gas mixture is acetylene / ethylene / ethane.

[0033] Preferably, the volume ratio of acetylene, ethylene, and ethane in the VOCs gas mixture is 1:1:1.

[0034] Preferably, the contact mode between the COFs adsorbent and the mixture containing acetylene / ethylene / ethane is any one of fixed bed adsorption, fluidized bed adsorption, or moving bed adsorption.

[0035] During the contact adsorption process, the acetylene and ethane components in the VOCs gas mixture have strong interactions with the main framework of the tetramethylpyrazine-based COF adsorbent, resulting in high adsorption capacity and slow diffusion within the pores. This allows them to be enriched in the fixed bed, thereby achieving the adsorption of acetylene and ethane from VOCs. On the other hand, the ethylene component in the VOCs gas mixture has weaker interactions with the adsorbent, resulting in a faster diffusion rate and lower adsorption capacity within the pores. This allows it to preferentially escape from the fixed bed, thus yielding high-purity ethylene from the VOCs gas mixture.

[0036] In a preferred embodiment, the COFs adsorbent is contacted with the three-component mixture containing acetylene / ethylene / ethane via fixed-bed adsorption. Under set temperature and pressure conditions, the mixed gas passes through the fixed-bed column loaded with COFs adsorbent at a set flow rate. Ethylene first penetrates the fixed-bed column, and high-purity ethylene gas with acetylene and ethane removed can be directly obtained at the outlet of the adsorption column.

[0037] Preferably, the flow rate of the mixed gas acetylene / ethylene / ethane is set to one of 1 ml / min, 2 ml / min, and 3 ml / min.

[0038] Preferably, the pressure of the adsorption column is 0-10 bar.

[0039] Preferably, the adsorption temperature is 20 ℃-100 ℃.

[0040] Compared with existing inventions, this invention has the following innovations:

[0041] 1. For the first time, low-cost tetramethylpyrazine was used as a building block for vinyl COFs, successfully achieving kilogram-scale production and significantly reducing material costs. The solvent-free synthesis strategy avoids the use of highly toxic solvents and catalysts, making the synthesis more environmentally friendly, reducing energy consumption in the production process, improving the crystallinity and specific surface area of ​​the COFs, and possessing broader applicability. 2. For the first time, a novel method is provided for using tetramethylpyrazine-based vinyl COFs to adsorb acetylene and ethane gases from a VOCs alkane tricomponent mixture, and to separate and purify ethylene in one step. Compared to other adsorbents for ethylene adsorption, this method eliminates the energy consumption problem generated during ethylene desorption and obtains ethylene gas with higher purity. Attached Figure Description

[0042] Figure 1 This invention relates to a monomeric structural formula for constructing covalent organic framework materials.

[0043] Figure 2 : A schematic diagram of the synthetic route for the covalent organic framework material prepared in this invention.

[0044] Figure 3 Powder diffraction pattern of a representative covalent organic framework material prepared in this invention.

[0045] Figure 4 Infrared spectrum of a representative covalent organic framework material prepared in this invention.

[0046] Figure 5 : 77K nitrogen isothermal adsorption-desorption curve of the representative covalent organic framework material prepared by this invention.

[0047] Figure 6 : A schematic diagram illustrating the kilogram-scale preparation of a representative covalent organic framework material prepared in this invention.

[0048] Figure 7 Powder diffraction patterns of kilogram-scale preparations of representative covalent organic framework materials prepared in this invention.

[0049] Figure 8 The single-component adsorption curves of the representative covalent organic framework material prepared in this invention at 298K for acetylene, ethylene, ethane, and carbon dioxide are shown.

[0050] Figure 9 The penetration test diagram of the representative covalent organic framework material prepared by this invention at 298K in an acetylene / ethylene / ethane mixed gas. Detailed Implementation

[0051] Unless otherwise stated in the context of this application, the technical terms and abbreviations used herein have their conventional meanings as known to those skilled in the art; unless otherwise stated, the raw material compounds used in the following examples are all commercially available. Example 1 is a method for synthesizing the material, Example 2 is a method for synthesizing the material at the kilogram-scale, and Examples 3 and 4 are tests of the adsorption and separation of acetylene / ethylene / ethane gases by representative materials.

[0052] The specific implementation method for the synthesis and related performance characterization of vinyl-linked covalent organic framework materials based on tetramethylpyrazine, as mentioned in this invention, is as follows. Conversely, the following examples are only for further explanation and illustration of this invention and should not be considered as limiting the scope of the invention.

[0053] Example 1:

[0054] According to the above general formula, weigh out 2,3,5,6-tetramethylpyrazine (0.2 mmol, 27.2 mg) and terephthalaldehyde (0.4 mmol, 53.6 mg), 4,4'-biphenyldicarboxaldehyde (0.4 mmol, 84.1 mg), 1,4-bis(4-aldehydephenyl)benzene (0.4 mmol, 114.5 mg), 1,2-bis(4'-formylphenyl)acetylene (0.4 mmol, 93.7 mg), 4,4'-(1,3-butyrynyl-1,4-diyl)bisbenzaldehyde (0.4 mmol, 103.3 mg), 2,5-dimethoxy-1,4-terephthalaldehyde (0.4 mmol, 77.7 mg), pyridine-2,5-dicarboxaldehyde (0.4 mmol, 54.0 mg), and 2,5-dialdehydepyrazine (0.4 mmol, 53.6 mg). One of the following: 54.4 mg of benzoic anhydride, 2,2'-bipyridine-5,5'-dicarboxaldehyde (0.4 mmol, 84.8 mg), 3,3'-bipyridine-6,6'-dicarboxaldehyde (0.4 mmol, 84.8 mg), and one of the following: benzoic anhydride (0.4 mmol, 90.5 mg), 4-trifluoromethylbenzoic anhydride (0.4 mmol, 144.8 mg), acetic anhydride (0.5 mmol, 51.0 mg), benzoic acid (0.8 mmol, 97.7 mg), 4-fluorobenzoic acid (0.8 mmol, 115.3 mg), or propionic acid (0.6 mmol, 44.4 mg), was carefully placed into a high-temperature, high-pressure resistant thick-walled glass tube. After evacuating to a pressure of 0.15 mmHg, the tube was removed from the vacuum line and sealed with a flame generated by an oxyhydrogen generator to isolate it from air. The sealed glass tube was placed in an oven at 180 °C and reacted for 5 days. A red solid powder was obtained after the reaction. This powder was then soaked in DMF and CH3OH, followed by Soxhlet extraction in THF for 48 h to obtain a red bulk material with a yield of approximately 71%-83%. Figure 3 As shown, the powder X-ray diffraction pattern indicates that the synthesized COFs material has high crystallinity. Figure 4 Infrared spectroscopy further confirmed that the material is a vinyl-linked COF material, with 1626 cm⁻¹... -1 The peak corresponds to the stretching vibration of the carbon-carbon double bond. Figure 5 The image shows the nitrogen isotherm adsorption-desorption curve of this material at 77 K, with a BET surface area of ​​660 m². 2 / g, Figure 6 This is a schematic diagram illustrating the preparation of this material at the kilogram level, with a single batch yielding nearly 1.2 kg. Figure 7 The image shows the X-ray diffraction pattern of powder prepared at the kilogram scale for this material. Figure 8The image shows the single-component adsorption curve of this material measured at 298 K. Figure 9 The three-component breakthrough curve of this material was measured at a ratio of acetylene / ethylene / ethane = 1 / 1 / 1.

[0055] Example 2:

[0056] Following the general formula described above, inexpensive tetramethylpyrazine and terephthalaldehyde monomers were selected as raw materials for kilogram-scale production. Tetramethylpyrazine (5 mol, 680 g), terephthalaldehyde (10.0 mol, 1340 g), and benzoic anhydride (10.0 mol, 2262.3 g) were carefully weighed and placed into a 2L NSG quick-opening magnetically stirred reactor. The reactor was evacuated until the internal pressure reached 0.15 mmHg. A heating program was set to maintain the temperature at 130 °C for 5 h at a heating rate of 5 °C / min to complete the pre-condensation process. Subsequently, the temperature was increased to 180 °C and reacted for 5 days. After the reaction, a red reaction mass was obtained. This mass was pulverized and washed with a large amount of DMF, CH3OH, THF solvents, and concentrated NaOH solution to obtain a red powder with a particle size distribution of 60-80 mesh, with a yield of 72%. Figure 6 Kilogram-scale synthesis of COF powders was demonstrated, such as Figure 7 As shown, the powder X-ray diffraction pattern indicates that the COFs materials prepared at the kilogram scale did not lose their crystallinity.

[0057] Example 3: Approximately 200 mg of the prepared fresh COF sample was weighed and activated at 120°C for 12 h in the activation station of a gas adsorption analyzer. Finally, the single-component adsorption curves for acetylene, ethylene, ethane, and carbon dioxide were measured at 298 K. (See figure). Figure 8 As shown, the adsorption trends of the material for the three gases are acetylene > ethane > ethylene > carbon dioxide.

[0058] Example 4: The COF prepared in Example 1 was ground into a uniform powder. 2.0 g of the sample was weighed and packed into an adsorption column with an inner diameter of 5.0 mm and a length of 500 mm. At room temperature (25 °C), a mixed gas of acetylene / ethane / ethylene was introduced into the adsorption column at a flow rate of 1 ml / min. Figure 9 As shown, the breakthrough test results indicate that the COF material can achieve highly selective separation of the ternary mixture of acetylene / ethylene / ethane and obtain high-purity ethylene.

[0059] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any non-innovative changes and modifications made by those skilled in the art to the technical solution of the present invention based on the above content without departing from the scope of the technical solution of the present invention, such as changing only the ratio of raw materials and reagents, reaction time, and operating procedures, should be included within the protection scope of the present invention.

Claims

1. Use of a class of ligand-free covalent organic frameworks based on tetramethylpyrazine with ethenyl linkages, characterized in that, Covalent organic framework material is used as adsorbent to adsorb low-chain hydrocarbon VOCs gas, adsorb acetylene and ethane, realize separation of ethylene and acetylene and ethane, and obtain polymerization-grade ethylene; wherein, the covalent organic framework material is prepared by a solvent-free method, and then low-chain hydrocarbon VOCs gas adsorption and separation are realized; The preparation method of the two kinds of covalent organic framework materials comprises the following steps: Synthesis method 1 is completed under the following reaction steps, comprising: (1) adding organic monomer 1 and organic monomer 2 into a reactor, and adding a catalyst for reaction; (2) after the reaction is completed, the product based on ligustrazine COF is obtained through cleaning and purification; Synthesis method 2 is completed under the following reaction steps, comprising: (1) adding organic monomer 1, organic monomer 2 and organic monomer 3 into a reactor, and adding a catalyst for reaction; (2) after the reaction is completed, the ionized COF product based on ligustrazine is obtained through cleaning and purification; The raw materials used in the preparation method of the covalent organic framework material are as follows: The organic monomer 1 is ligustrazine, i.e. 2,3,5,6-tetramethylpyrazine; the organic monomer 2 is a two-linking monomer containing an aldehyde group functional group; the organic monomer 3 is a single-halogen or double-halogen substituted straight-chain or branched alkyl; the catalyst is a compound containing an anhydride functional group, a compound containing an acyl chloride functional group or a compound containing a carboxylic acid functional group.

2. Use according to claim 1, characterized in that, The cleaning and purification conditions are as follows: The obtained product is soaked in DMF or NaOH aqueous solution to remove unreacted monomers, then washed with THF or water to remove excess catalyst, and finally the obtained powder is heated and dried in a vacuum high-temperature oven at a temperature of 80-200 ℃ to obtain the final product.

3. Use according to claim 2, characterized in that, The pore size of the material after cleaning and purification is between 0.8 nm and 5.0 nm.

4. The use according to claim 3, wherein the specific application method is as follows: The covalent organic framework material is ground into a uniform powder and loaded into an adsorption column, and under the temperature condition of 20-100 ℃, mixed gas acetylene / ethane / ethylene is introduced into the adsorption column, so that the adsorption of light hydrocarbon gas can be realized, and finally high-purity ethylene is obtained.

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