Supported hybrid covalent organic framework adsorbent, preparation method thereof and application of adsorbent in ammonia gas adsorption separation

Abstract

The invention discloses a supported hybrid covalent organic framework adsorbent, a preparation method thereof and an application of ammonia gas adsorption separation, triamino compounds and diformyl compounds are used as composition modules, a series of covalent organic frameworks are formed by adjusting the variety and proportion of aldehyde compounds, and the proportion of metal halides of the covalent organic frameworks is adjusted, so that the supported hybrid covalent organic framework adsorbent is obtained. The metal halide is loaded to the hybrid covalent organic framework adsorbent to obtain the loaded hybrid covalent organic framework adsorbent, and the loaded hybrid covalent organic framework adsorbent prepared by the method has a porous structure and contains rich metal sites, so that the adsorption separation capacity of ammonia gas can be obviously improved; therefore, high-efficiency, high-capacity and selective reversible adsorption of ammonia gas is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthesis of supported adsorbents, and particularly relates to a supported hybrid covalent organic framework adsorbent, a preparation method thereof, and an application in ammonia adsorption and separation. Background Art

[0002] Ammonia (NH3), as one of the most important chemical raw materials, is widely used in fields such as agriculture, industry, and medicine, and is closely related to our lives. At the same time, NH3 has a high hydrogen content (17.7 wt%) and a high volumetric energy density (~ 0.105 kg / L), and is considered a potential hydrogen storage medium. In addition, the combustion of NH3 in a fuel cell only produces H2O and N2 as products, making NH3 an ideal carbon-free fuel for promoting carbon neutrality progress. On the other hand, NH3 is also considered one of the five major environmental pollutants. It can react with acidic gases such as NOx or SO2 to form PM2.5, and the alkalinity, toxicity, and corrosiveness of NH3 can also cause irreversible harm to human health. Therefore, it is very important to develop new adsorbents for efficient adsorption and separation of NH3.

[0003] Covalent organic frameworks (COFs) are a class of porous materials composed of organic molecular building blocks connected by all covalent bonds, with a high specific surface area and adjustable pore size, making them potential materials for NH3 adsorption. At present, there are few reports on the research of using COFs for ammonia adsorption. For example, Yaghi et al. studied and showed that a COF-10 linked by boron-oxygen covalent bonds can obtain an NH3 adsorption capacity of 15 mmol / g at 25 °C and 1 bar, which is higher than the NH3 adsorption capacities of molecular sieves MCM-41 and 13X under the same conditions (7.9 and 9 mmol / g, respectively). However, the above adsorption capacities still cannot meet scientific and technological applications (Nature Chemistry, 2010, 2: 235). Therefore, how to develop porous adsorbents based on COFs to be efficient and improve the NH3 adsorption capacity is an important issue.

[0004] The design idea of forming a new adsorbent by loading metal halides into the pores of COFs in a bidentate coordination form overcomes the above-mentioned deficiency of low NH3 adsorption amount of pure COFs. By adjusting the coordination group (methoxy-amine, hydroxy-amine), the coordination ability of the metal halide with the COF skeleton is adjusted, thereby regulating the interaction between the metal halide and NH3. Therefore, for efficient ammonia adsorption and separation, by adjusting the ligand structure, it is very meaningful to develop metal halide-loaded COF adsorbents to improve the NH3 adsorption and separation capacity. Summary of the Invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a supported hybrid covalent organic framework adsorbent, its preparation method, and its application in ammonia adsorption and separation. The supported hybrid covalent organic framework obtained in the present invention has the properties of porous materials, including high specific surface area, high total pore volume, and more exposed metal sites, significantly improving the adsorption capacity of NH3, thereby realizing the efficient, high-capacity, and selective adsorption of NH3.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows: A preparation method of a supported hybrid covalent organic framework adsorbent, comprising the following steps: 1) Preparation of hybrid covalent organic framework: Dissolve 1,3,5-tris(4-aminophenyl)benzene, 2,5-dihydroxyterephthalaldehyde, and 2,5-dimethoxyterephthalaldehyde in a mixed solvent of o-dichlorobenzene and n-butanol, then after degassing, add an acid catalyst and react at a certain temperature. After the reaction is completed, the product is washed with tetrahydrofuran and acetone and dried to obtain the hybrid covalent organic framework to be prepared; 2) Preparation of supported hybrid covalent organic framework adsorbent: Add the hybrid covalent organic framework obtained in step 1) to a methanol solution of metal halide, react at room temperature, and after the reaction is completed, dry by rotary evaporation to obtain the supported hybrid covalent organic framework adsorbent to be prepared.

[0007] Further, in step 1), the molar ratio of the feed of 1,3,5-tris(4-aminophenyl)benzene to the sum of the feeds of 2,5-dihydroxyterephthalaldehyde and 2,5-dimethoxyterephthalaldehyde is 1:0.8 - 1.2; the reaction temperature is 80 - 120 °C, and the reaction time is 48 - 72 h.

[0008] Further, in step 1), the volume ratio of o-dichlorobenzene to n-butanol is 1:1; the molar ratio of the acid catalyst to 1,3,5-tris(4-aminophenyl)benzene is 0.01 - 0.1:1; the acid catalyst is one of hydrochloric acid, acetic acid, phosphoric acid, and nitric acid.

[0009] Further, in step 2), the mass ratio of the metal halide to the total mass of the metal halide hybrid covalent organic framework is 1 - 99%, methanol is used as the solvent of the metal halide, and the mass-to-volume ratio of the metal halide to methanol is 1:20 - 30, with the mass unit being g and the volume unit being mL.

[0010] Further, in step 2), the metal halide is one of lithium chloride, calcium chloride, magnesium chloride, calcium bromide, cobalt chloride, nickel chloride, strontium chloride, tin chloride, lithium bromide, and manganese chloride.

[0011] The present invention provides a supported hybrid covalent organic framework adsorbent prepared by the above method.

[0012] Furthermore, the typical chemical structural formula of the supported adsorbent is shown in Formula I below: Formula I.

[0013] The present invention provides an application of a supported hybrid covalent organic framework adsorbent, and the application is to use the obtained supported hybrid covalent organic framework adsorbent for the adsorption and separation of ammonia.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The present invention uses covalent organic framework as the main body. By adjusting the structural units and their ratios of the covalent organic framework, a series of nitrogen atom-oxygen atom chelating sites are formed. By adjusting the types of metal halides, a class of metal halide-supported covalent organic framework adsorbent materials is obtained. The supported covalent organic framework adsorbent prepared by the present invention has rich and adjustable metal ion sites, has a good adsorption capacity for NH3, and can significantly improve the NH3 adsorption capacity; 2) When the proportion of 2,5-dihydroxyterephthalaldehyde (DHTA) reaches 100% in the present invention, the formed metal halide-supported covalent organic framework adsorbent can adsorb 57 mmol / g of NH3 at 25 °C and 1 bar; 3) The NH3 cyclic adsorption stability of the metal halide-supported covalent organic framework adsorbent material of the present invention is good; 4) The supported hybrid covalent organic framework adsorbent prepared by the present invention has the advantages of large NH3 adsorption capacity and good regeneration performance, and has broad market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Scanning electron microscope photograph of 74.6% LiCl@[OH]-TD-COF, a covalent organic framework supported by lithium chloride of the present invention; 100% ; Figure 2 Dispersive mapping energy spectrum of 74.6% LiCl@[OH]-TD-COF, a covalent organic framework supported by lithium chloride of the present invention; 100% ; Figure 3 Thermogravimetric curve of 74.6% LiCl@[OH]-TD-COF, a covalent organic framework supported by lithium chloride of the present invention; 100% ; Figure 4 Nitrogen adsorption curve and pore size distribution of [OH]-TD-COF, a covalent organic framework supported by lithium chloride of the present invention, under 77K; 25% ; Figure 5 Nitrogen adsorption curve and pore size distribution of [OH]-TD-COF, a covalent organic framework of the present invention, under 77K; 100%-TD-COF and Lithium Chloride-Loaded Covalent Organic Framework 74.6%LiCl@[OH] 100% -FTIR Characterization of -TD-COF before and after Adsorbing NH3 Detailed Implementation Modes

[0016] The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the scope protected by the present invention is not limited to the described scope. Example 1

[0017] 1) Synthesis of 74.6%LiCl@[OH] 100% -TD-COF Dissolve 0.1 mmol of 1,3,5-tris(4-aminophenyl)benzene (TAPB) and a total of 0.1 mmol of 2,5-dihydroxyterephthalaldehyde (DHTA) and 2,5-dimethoxyterephthalaldehyde (DMPA) with different molar ratios (0:100, 25:75, 50:50, 75:25, 100:0) in an equal volume mixture of orthodichlorobenzene and n-butanol. Add 0.0012 mol of acetic acid as a catalyst and react at 120 °C for 72 h. Then collect the precipitate, wash it with tetrahydrofuran and acetone, and dry it to obtain the covalent organic framework material [OH] x% [OCH3] (100-x)% -TD-COF; Add the above-prepared COFs into methanol solutions containing different masses of LiCl and react at room temperature for 24 h. The product after rotary evaporation and drying is the LiCl-loaded hybrid covalent organic framework material to be prepared.

[0018] For example, 0.746 g of LiCl is loaded on 0.254 g of [OH] 100% -TD-COF to obtain 74.6%LiCl@[OH] 100% -TD-COF.

[0019] 2) Material Characterization: From Figure 1 , the SEM image analysis of the sample 74.6%LiCl@[OH] 100% -TD-COF shows that the synthesized covalent organic framework has a rich pore structure.

[0020] From Figure 2 , the EDS mapping image analysis of the sample 74.6%LiCl@[OH] 100% -TD-COF shows that carbon, nitrogen, oxygen, and chlorine elements are evenly dispersed throughout the covalent organic framework, indicating that lithium chloride is evenly dispersed in the covalent organic framework.

[0021] From Figure 3 , the sample [OH]100% The thermogravimetric analysis (TGA) curve of -TD-COF shows that there is no significant weight loss of this covalent organic framework until 400 °C, indicating its excellent thermal stability and high decomposition temperature. Example 2

[0022] Nitrogen adsorption measurement: The adsorption device uses the BET method. First, the covalent organic framework 74.6% LiCl@[OH] synthesized in Example 1 100% -TD-COF is subjected to vacuum degassing activation treatment, and then the gas adsorption temperature is controlled at 77 K and the gas pressure is 0-100 kPa to measure the equilibrium adsorption capacity and record the data. The nitrogen adsorption results are as Figure 4 shown, and the BET specific surface area is converted to 110 m 2 g −1 , and the pore size distribution is 2 nm. Example 3

[0023] Measure the infrared spectra of [OH] 100% -TD-COF and the infrared spectra of 74.6% LiCl@[OH] 100% -TD-COF before and after adsorption under the conditions of 25 °C and 1 bar NH3. The results are as Figure 5 shown. It can be seen from the results that after the 74.6% LiCl@[OH] 100% -TD-COF material adsorbs ammonia, an obvious peak appears at 3366.9 cm -1 , which is due to the hydrogen bond vibration of N-H. Example 4

[0024] NH3 adsorption measurement: The adsorption device uses the dynamic adsorption weighing calculation method. First, the metal halide-loaded covalent organic framework adsorbent synthesized in Example 1 is activated and degassed by vacuum drying at 120 °C for 4 hours, and then 0.5 g is taken and placed in a dynamic adsorption tube for dynamic adsorption of NH3 experiment to measure the adsorption amount. The adsorption temperature is controlled at 25 °C, the partial pressure of NH3 is 1 bar, and the adsorption capacity at different times is weighed. When the mass no longer changes, the equilibrium adsorption capacity is obtained and the data is recorded. The equilibrium adsorption capacity is shown in Table 1. It shows that the adsorption capacity of [OH] 100% -TD-COF is higher than that of [OCH3] 100% -TD-COF; for different metal halide loadings, the adsorption capacity of 74.6% LiCl@[OH] 100% -TD-COF can reach 57 mmol / g.

[0025] Table 1 Influence of [OH] with different lithium chloride loadings x% [OCH3] (100-x)% -TD-COF on the ammonia adsorption capacity: Example 5

[0026] Determination of the NH3 adsorption capacity of 74.6% LiCl@[OH] 100% -TD-COF at different temperatures. The equilibrium adsorption capacities are shown in Table 2. It shows that as the temperature increases, the adsorption capacity decreases.

[0027] Table 2 Effect of temperature on the NH3 adsorption capacity of 74.6% LiCl@[OH] 100% -TD-COF Example 6

[0028] Determination of the NH3 adsorption capacity of 74.6% LiCl@[OH] 100% -TD-COF at different pressures. The equilibrium adsorption capacities are shown in Table 3. It shows that as the pressure increases, the adsorption capacity increases.

[0029] Table 3 Effect of pressure on the NH3 adsorption capacity of 74.6% LiCl@[OH] 100% -TD-COF Example 7

[0030] Desorption determination of NH3: The adsorption device uses the dynamic adsorption weighing calculation method. First, the metal halide-supported covalent organic framework adsorbent synthesized in Example 1 is activated and degassed by vacuum drying at 120 °C for 4 hours, and then 0.5 g is taken and placed in a dynamic adsorption tube for the dynamic adsorption experiment of NH3 to measure the adsorption amount. The adsorption temperature is controlled at 25 °C, the partial pressure of NH3 is 1 bar, and the adsorption capacities at different times are weighed. When the mass no longer changes, the equilibrium adsorption capacity is obtained, and the data is recorded. The equilibrium adsorption capacities are shown in Table 4. It shows that the adsorption capacity of 100% -TD-COF is higher than that of [OCH3] 100% -TD-COF; for different metal halide loadings, the adsorption capacity of 74.6% LiCl@[OH] 100% -TD-COF can reach 57 mmol / g.

[0031] Table 4 Effect of desorption temperature on the NH3 desorption capacity of 74.6% LiCl@[OH] 100% -TD-COF Example 8

[0032] Adsorption-desorption cycle measurement of NH3: The adsorption-desorption device uses the breakthrough method. First, the covalent organic framework 74.6% LiCl@[OH] 100% -TD-COF synthesized in Example 1 was subjected to vacuum degassing activation treatment, and then the gas adsorption temperature was controlled at 298 K to measure the breakthrough adsorption capacity, and the data was recorded by a computer. Desorption was carried out at 353 K, indicating that desorption was difficult, while complete desorption could be achieved at 393 K. The results of the cyclic adsorption-desorption are shown in Table 5, indicating good cyclic adsorption stability.

[0033] Table 5 Ammonia cyclic adsorption capacity of 74.6% LiCl@[OH] 100% -TD-COF

Claims

1. A preparation method of a supported hybrid covalent organic framework adsorbent, characterized in that It includes the following steps: 1) Preparation of hybrid covalent organic framework: Dissolve 1,3,5-tris(4-aminophenyl)benzene, 2,5-dihydroxyterephthalaldehyde, and 2,5-dimethoxyterephthalaldehyde in a mixed solvent of orthodichlorobenzene and n-butanol. Then, after degassing, add an acid catalyst and react at a certain temperature. After the reaction, the product is washed with tetrahydrofuran and acetone and dried to obtain the hybrid covalent organic framework to be prepared. 2) Preparation of supported hybrid covalent organic framework adsorbent: Add the hybrid covalent organic framework obtained in step 1) to a methanol solution of metal halide and react at room temperature. After the reaction, it is dried by rotary evaporation to obtain the supported hybrid covalent organic framework adsorbent to be prepared.

2. The preparation method of a supported hybrid covalent organic framework adsorbent according to claim 1, wherein In step 1), the molar ratio of the feed amount of 1,3,5-tris(4-aminophenyl)benzene to the sum of the feed amounts of 2,5-dihydroxyterephthalaldehyde and 2,5-dimethoxyterephthalaldehyde is 1:0.8 - 1.2; the reaction temperature is 80 - 120 °C, and the reaction time is 48 - 72 h.

3. The preparation method of a supported hybrid covalent organic framework adsorbent according to claim 1, characterized in that In step 1), the volume ratio of orthodichlorobenzene to n-butanol is 1:1; the molar ratio of the acid catalyst to 1,3,5-tris(4-aminophenyl)benzene is 0.01 - 0.1:1; the acid catalyst is one of hydrochloric acid, acetic acid, phosphoric acid, and nitric acid.

4. The preparation method of a supported hybrid covalent organic framework adsorbent according to claim 1, characterized in that In step 2), the mass ratio of the metal halide to the total mass of the metal halide hybrid covalent organic framework is 1 - 99%. Methanol is used as the solvent for the metal halide, and the mass-to-volume ratio of the metal halide to methanol is 1:20 - 30, with the mass unit being g and the volume unit being mL.

5. The preparation method of a supported hybrid covalent organic framework adsorbent according to claim 4, characterized in that In step 2), the metal halide is one of lithium chloride, calcium chloride, magnesium chloride, calcium bromide, cobalt chloride, nickel chloride, strontium chloride, tin chloride, lithium bromide, and manganese chloride.

6. A supported hybrid covalent organic framework adsorbent prepared by the method according to any one of claims 1 - 5.

7. The supported hybrid covalent organic framework adsorbent according to claim 6, wherein The typical chemical structural formula of the supported adsorbent is shown as formula Ⅰ below: Formula Ⅰ.

8. Use of the supported hybrid covalent organic framework adsorbent as described in claim 6, characterized in that The application is to use the obtained supported hybrid covalent organic framework adsorbent for the adsorption and separation of ammonia.

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