Macroscopic preparation of ligustrazine-based covalent organic framework material and application of ligustrazine-based covalent organic framework material in adsorption and separation of low-chain hydrocarbon VOCs gas

Abstract

According to the invention, a ligustrazine monomer with low price is used as a connection node for constructing a vinyl covalent organic framework material, a series of ligustrazine-based covalent organic framework materials with good crystallinity, high specific surface area, good chemical stability and good thermal stability are successfully synthesized, and ionization of the materials is successfully realized. In the synthesis process, the use of a highly toxic organic solvent is avoided, and the standard of kilogram-level preparation is reached. The ligustrazine-based COF can efficiently adsorb low-chain hydrocarbon VOCs, high-purity ethylene gas can be obtained from a light hydrocarbon ternary mixture through a one-step method, and the ligustrazine-based COF has wide application prospects in adsorption and removal of VOCs gas in the petrochemical industry.

Description

Technical Field

[0001] The present invention belongs to the field of porous organic materials, and specifically relates to the large-scale preparation of a type of covalent organic framework material based on ligustrazine and its application in the field of VOCs gas adsorption and separation. Background Art

[0002] Covalent organic frameworks (COFs) are a class of crystalline organic porous polymers connected by dynamic covalent bonds from organic building monomers. Due to their structural designability, high porosity, low density, and excellent chemical stability, COFs have been widely used in gas storage and separation, catalysis, sensing, energy storage, and optical devices. With the continuous enrichment of COFs, COFs have developed a variety of connection methods such as borate, triazine, imine, phenylhydrazone, ketoenamine, polyimide, and vinyl. However, the development of COFs has been seriously hindered by the lack of efficient synthesis methods. The traditional solvothermal method is not suitable for actual industrial production applications due to its complex process, high energy consumption, long reaction time, and limited scalability. Therefore, seeking simpler, faster, more energy-saving 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 gases in the petrochemical industry mainly include combustion flue gas, process tail gas, hydrocarbon gas leaked from equipment, odorous gas emitted from alkali slag treatment equipment, sewage treatment plants, etc. The characteristic pollutants are: alkanes, olefins, cycloalkanes, alcohols, aromatic hydrocarbons, ether ketones, aldehydes, phenols, esters, halogenated hydrocarbons, halides, etc. At present, the methods for treating VOCs waste gas include washing method, catalytic combustion method, regenerative thermal oxidation method, activated carbon method, purification and recovery method, biological method, etc. It has been proved that the use of physical adsorption technology instead of cumbersome traditional industrial methods can greatly 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 have problems such as poor chemical stability, high cost, and non-scalability of products, which hinder their practical application. Therefore, it is urgently needed in industry to develop low-cost materials with good VOCs gas adsorption and removal performance.

[0004] On the one hand, the present invention regulates and screens the organic building blocks for constructing COFs, and develops a class of cheap and stable vinyl COFs based on ligustrazine that can be prepared in large quantities through a solvent-free synthesis method, and successfully achieves the ionization of ligustrazine-based COFs; on the other hand, the present invention uses the prepared ligustrazine-based COFs as an adsorbent to adsorb acetylene and ethane in VOCs gas, and efficiently achieves the separation of ethylene from acetylene and ethane through a one-step method. Summary of the invention

[0005] The purpose of the present invention is to design and synthesize a series of novel vinyl-linked COFs based on ligustrazine, which have the advantages of low economic cost, high structural stability, easy scale-up production and the like.

[0006] Another object of the present invention is to use a fixed bed penetration experiment and an adsorption separation method to use ligustrazine-based COFs as an adsorbent to achieve adsorption and removal of alkanes in VOCs gas. Other objects of the present invention are clear to those skilled in the art from the above and following descriptions.

[0007] The first aspect of the present invention provides a synthesis method of a covalent organic framework material based on ligustrazine and an ionization step thereof, which is characterized in that the COFs material is constructed in one step by covalently linking vinyl groups.

[0008] Preferably, the synthesis method 1 is to directly add the monomer ligustrazine, the di-linked monomer containing an aldehyde group and the catalyst into a reactor, melt polymerize under closed conditions to obtain the COFs material, and then wash and purify it.

[0009] Preferably, the monomer 1 is ligustrazine.

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

[0011] Further preferably, the di-linked monomer containing an aldehyde functional group is a linear molecule.

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

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

[0014] Further preferably, the catalyst is one or more of 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 monohalogen substituted or dihalogen substituted product of a linear or branched alkyl group.

[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 the catalyst to the 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 the organic monomer 3 to the organic monomer 1 is 1:4 to 4:1, 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°C.

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

[0024] Preferably, the sealed reaction container is one of a Pyrex tube resistant to high temperature and pressure, an ampoule bottle requiring flame sealing, and a high-pressure reactor.

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

[0026] The synthesis method 1 of the present invention is to construct vinyl COFs based on ligustrazine, and the relevant general formula can be expressed as:

[0027] In the general formula: organic monomer 1 is ligustrazine, i.e., 2,3,5,6-tetramethylpyrazine. Organic monomer 2 mainly includes: terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde, 1,4-di(4-formylphenyl)benzene, 1,2-di(4'-formylphenyl)acetylene, 4,4'-(1,3-butadiyne-1,4-diyl)dibenzaldehyde, 2,5-dimethoxy-1,4-terephthalaldehyde, pyridine-2,5-dicarboxaldehyde, 2,5-dicarboxylic pyrazine, 2,2'-bipyridine-5,5'-dicarboxaldehyde, 3,3'-bipyridine-6,6'-dicarboxaldehyde. The above-mentioned monomers 1 and 2 can be combined arbitrarily, and the target COFs can be prepared under any one of the conditions of the catalyst. The catalyst is one or more of 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.

[0028] The synthesis method 2 of the present invention is a one-pot method for synthesizing ionic vinyl COFs based on ligustrazine, and the relevant general formula can be expressed as:

[0029] In the general formula: organic monomer 1 is ligustrazine, i.e. 2,3,5,6-tetramethylpyrazine. Organic monomer 2 mainly includes: any one of terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde, 1,4-di(4-formylphenyl)benzene, 1,2-di(4'-formylphenyl)acetylene, 4,4'-(1,3-butadiyne-1,4-diyl)bisbenzaldehyde, 2,5-dimethoxy-1,4-terephthalaldehyde, pyridine-2,5-dicarboxaldehyde, 2,5-dicarboxylic pyrazine, 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 iodomethane, ethyl bromide, propyl bromide, ethyl chloride, 1-bromobutane, 1,2-dibromoethane, 1,4-dibromobutane, 1-bromopentane, 1-bromohexane, 1-bromoheptane, etc. The catalyst is one or more of 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, propionic acid. The above-mentioned monomer 1, monomer 2 and monomer 3 can be combined at will, and the target COFs can be prepared under any one of the conditions of the catalyst.

[0030] Preferably, the VOCs gas mixture is acetylene / ethylene / ethane.

[0031] Preferably, the volume ratio of acetylene, ethylene and ethane in the VOCs gas mixture is 1:1:1.

[0032] Preferably, the contacting mode of the COFs adsorbent and the three-component mixture containing acetylene / ethylene / ethane is any one of fixed bed adsorption, fluidized bed adsorption and moving bed adsorption.

[0033] During the contact adsorption process, the acetylene and ethane components in the VOCs gas mixture have a strong interaction with the main frame of the COF adsorbent based on ligustrazine, have a high adsorption capacity, and diffuse relatively slowly in the pores, so they can be enriched in the fixed bed, thereby achieving the adsorption of acetylene and ethane in VOCs; on the other hand, the ethylene component in the VOCs gas mixture has a weak interaction with the adsorbent, has a fast diffusion rate in the pores, has a low adsorption capacity, and can escape from the fixed bed preferentially, thereby obtaining high-purity ethylene from the VOCs gas mixture.

[0034] In a preferred example, the contact mode between the COFs adsorbent and the three-component mixture containing acetylene / ethylene / ethane is fixed bed adsorption. Under the set temperature and pressure conditions, the mixed gas passes through the fixed bed column loaded with the COFs adsorbent at a set flow rate. Ethylene first penetrates the fixed bed column, and high-purity ethylene gas from which acetylene and ethane are removed can be directly obtained at the outlet of the adsorption column.

[0035] 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.

[0036] Preferably, the pressure of the adsorption column is 0-10 bar.

[0037] Preferably, the adsorption temperature is 20°C-100°C.

[0038] Compared with the prior art inventions, the present invention has the following innovations: 1. For the first time, low-cost ligustrazine was used as a building block of vinyl COFs, and kilogram-level large-scale production was successfully achieved, greatly reducing material costs. Through the strategy of solvent-free synthesis, the use of highly toxic solvents and catalysts was avoided, making material synthesis more environmentally friendly, reducing energy consumption in the production process, improving the crystallinity and specific surface area of ​​COFs, and having a relatively wide range of universality. 2. For the first time, a new method for using ligustrazine-based vinyl COFs to adsorb acetylene and ethane gases from a three-component mixture of VOCs alkanes, and separating and purifying ethylene in one step was provided. Compared with other adsorbents that adsorb ethylene, this method can save the energy consumption problem generated during the desorption of ethylene and obtain ethylene gas with higher purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 : The present invention is used to construct the monomer structure formula of the covalent organic framework material.

[0040] Figure 2 : Schematic diagram of the synthesis route of the covalent organic framework material prepared by the present invention.

[0041] Figure 3 : Powder diffraction pattern of a representative covalent organic framework material prepared in the present invention.

[0042] Figure 4 : Infrared spectrum of a representative covalent organic framework material prepared by the present invention.

[0043] Figure 5 : 77K nitrogen isothermal adsorption-desorption curve of the representative covalent organic framework material prepared by the present invention.

[0044] Figure 6 : Schematic diagram of the kilogram-scale preparation of representative covalent organic framework materials prepared by the present invention.

[0045] Figure 7 : Powder diffraction pattern of kilogram-scale preparation of a representative covalent organic framework material prepared by the present invention.

[0046] Figure 8 : Single component adsorption curves of acetylene, ethylene, ethane and carbon dioxide at 298K for the representative covalent organic framework material prepared by the present invention.

[0047] Fig. 9 : Penetration test diagram of acetylene / ethylene / ethane mixed gas at 298K for the representative covalent organic framework material prepared by the present invention. DETAILED DESCRIPTION

[0048] Unless otherwise specified in the context of this application, the technical terms and abbreviations used in this application have the conventional meanings known to those skilled in the art; unless otherwise specified, the raw material compounds used in the following examples are commercially available. Example 1 is a synthesis method of the material, Example 2 is a synthesis method for kilogram-scale preparation of the material, and Examples 3 and 4 are tests of representative materials for adsorption and separation of acetylene / ethylene / ethane gases.

[0049] According to the present invention, the synthesis of vinyl-linked covalent organic framework materials based on ligustrazine and related performance characterization tests are described in detail below. On the contrary, the following examples are only used to further explain and invent the present invention and should not be considered to limit the scope of the present invention.

[0050] Embodiment 1: According to the above general formula, 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-formylphenyl)benzene (0.4 mmol, 114.5 mg), 1,2-bis(4'-formylphenyl)acetylene (0.4 mmol, 93.7 mg), 4,4'-(1,3-butadiyn-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), 2,5-diformylpyrazine (0.4 mmol, 1 Carefully place one of 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) in a high temperature and high pressure resistant thick wall glass tube. After evacuating the tube to a pressure of 0.15 mmHg, remove it from the vacuum line and seal the glass tube with the flame generated by the hydrogen and oxygen generator to isolate it from the air. The sealed glass tube was placed in an oven at 180°C for 5 days. After the reaction, a red solid powder was obtained. After soaking it in DMF and CH3OH, Soxhlet extraction was performed in THF for 48 hours to obtain a red bulk material with a yield of about 71%-83%. Figure 3 As shown in Figure 2, the powder X-ray diffraction pattern shows that the synthesized COFs material has high crystallinity. Figure 4 Infrared spectroscopy test further proved that the material is a vinyl-linked COFs material, among which the 1626 cm -1 The peak corresponding to the stretching vibration of the carbon-carbon double bond, Figure 5 is the nitrogen isothermal adsorption-desorption curve of the material at 77 K. Its BET surface area is 660 m 2 / g, Figure 6 This is a schematic diagram of the kilogram-scale preparation of this material, which can reach nearly 1.2 kg in a single batch. Figure 7 This is the X-ray diffraction pattern of the powder prepared at the kilogram level for this material. Figure 8is the single component adsorption curve of the material measured at 298 K. Fig. 9 This is the three-component penetration curve of the material measured at the ratio of acetylene / ethylene / ethane = 1 / 1 / 1.

[0051] Embodiment 2: According to the above general formula, low-priced ligustrazine and terephthalaldehyde monomers were selected as raw materials for kilogram-scale production. Ligustrazine (5 mol, 680 g), terephthalaldehyde (10.0 mol, 1340 g), and benzoic anhydride (10.0 mol, 2262.3 g) were carefully loaded into a 2L NSG fast-opening magnetic stirring reactor, and the pressure in the reactor was evacuated to 0.15 mmHg. The temperature program was set to maintain 130 °C for 5 h at a heating rate of 5 °C / min to complete the pre-condensation process, and then the temperature was raised to 180 °C for 5 days. After the reaction, a red reaction block was obtained, which was crushed by a pulverizer 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 demonstrated kilogram-scale synthesis of COF powders, such as Figure 7 As shown, the powder X-ray diffraction pattern shows that the COFs material prepared on a kilogram scale does not lose its crystallinity.

[0052] Example 3: Weigh about 200 mg of the prepared fresh COF sample and activate it at 120°C for 12 h in the activation station of the gas adsorption instrument. Finally, the single-component adsorption curves of the material for acetylene, ethylene, ethane, and carbon dioxide were measured at 298 K. Figure 8 As shown, the adsorption trend of the material for the three gases is acetylene>ethane>ethylene>carbon dioxide.

[0053] Example 4: The COF prepared in Example 1 was ground into a uniform powder, 2.0 g of the sample was weighed and loaded into an adsorption column with an inner diameter of 5.0 mm and a length of 500 mm. At room temperature of 25 °C, a mixed gas of acetylene / ethane / ethylene was passed into the adsorption column at a flow rate of 1 ml / min. Fig. 9 As shown, the penetration test results indicate that COF materials can achieve highly selective separation of acetylene / ethylene / ethane ternary gas mixture and obtain high-purity ethylene.

[0054] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention in any form. Any researcher and technician familiar with the field, without departing from the scope of the technical solution of the present invention, using the above content to make non-innovative changes and modifications to the technical solution of the present invention, such as only changing the addition ratio of raw materials and reagents, reaction time and operation process, etc., should be included in the protection scope of the present invention.

Claims

1. A method for preparing a type of covalent organic framework material (COFs) based on vinyl linkage of ligustrazine, characterized in that: The covalent organic framework material is prepared by a solvent-free method, and then low-chain hydrocarbon VOCs gas adsorption and separation are achieved.

2. The synthesis method as claimed in claim 1 mainly comprises two kinds, respectively comprising the following steps: Synthesis method 1 is completed under the following reaction steps, mainly comprising: (1) Adding organic monomer 1 and organic monomer 2 to a reactor, adding a catalyst to react; (2) After the reaction is completed, washing and purification are performed to obtain a COF product based on ligustrazine. Synthesis method 2 is completed under the following reaction steps, mainly including: (1) Adding organic monomer 1, organic monomer 2 and organic monomer 3 to a reactor, adding a catalyst to react; (2) After the reaction is completed, washing and purification are performed to obtain an ionized COF product based on ligustrazine.

3. The synthesis method as claimed in claim 1 or 2, wherein the raw materials used are as follows: The organic monomer 1 is ligustrazine, i.e., 2,3,5,6-tetramethylpyrazine. The organic monomer 2 is a di-linked monomer containing an aldehyde functional group. The organic monomer 3 is a monohalogen substituted product or a dihalogen substituted product of a linear or branched alkyl group. 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.

4. The preparation method according to claim 1 or 2, characterized in that: The cleaning and purification conditions are: 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 80-200°C to obtain the final product.

5. The cleaned and purified material as claimed in claim 4, wherein the pore size is between 0.8 nm and 5.0 nm.

6. Use of the covalent organic framework material prepared as claimed in claims 2 and 3, characterized in that: The covalent organic framework material is used as an adsorbent to adsorb low-chain hydrocarbon VOCs gases, and can preferentially adsorb acetylene and ethane, thereby achieving the separation of ethylene from acetylene and ethane to obtain polymerization-grade ethylene.

7. The use as claimed in claim 6, wherein the specific application method is: The covalent organic framework material is ground into powder of uniform size and loaded into an adsorption column. Under the temperature condition of 20-100° C., a mixed gas of acetylene / ethane / ethylene is passed into the adsorption column to achieve adsorption of light hydrocarbon gas and finally obtain high-purity ethylene.

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