Preparation process of ultra-pure carbon dioxide

Abstract

The invention relates to the technical field of carbon dioxide extraction and purification, in particular to a preparation process of ultra-pure carbon dioxide. A preparation process of ultra-pure carbon dioxide comprises the following steps: transferring a liquid phase III into an absorption tower filled with a carbon dioxide adsorption material which is a methyl functionalized covalent organic framework material coated with a polar polymer, so as to obtain a carbon dioxide-rich adsorption material; and transferring the carbon dioxide-rich adsorption material into a desorption tower to obtain the ultra-pure carbon dioxide. According to the preparation process of the ultra-high-purity carbon dioxide, a low-temperature rectification method is adopted, washing, flash evaporation and a carbon dioxide adsorption material are cooperatively matched, and impurity components such as SO2, H2, CO, CH4, N2 and 02 in crude carbon dioxide feed gas are removed, so that the ultra-high-purity carbon dioxide is obtained.

Description

Technical Field

[0001] The present application relates to the technical field of carbon dioxide extraction and purification, and more specifically, to a process for preparing ultra-high-purity carbon dioxide. Background Art

[0002] Carbon dioxide is not only a basic chemical raw material with a wide range of sources, low cost and easy access, but also a recyclable and environmentally friendly product. It has good economic benefits and great significance for environmental protection in achieving low-carbon emission reduction. Therefore, it is widely used in the food industry, mechanical processing, oil extraction, chemical industry and other fields.

[0003] At present, conventional carbon dioxide purification and liquefaction processes usually use external cold sources, such as propylene refrigeration, ammonia refrigeration, and freon refrigeration. However, when the raw gas contains a large amount of impurities such as H2, CO, and CH4, due to the high partial pressure of CO2 in the gas phase, a lower temperature is often required, resulting in the defect of excessive energy consumption. Summary of the Invention

[0004] In order to improve the defect of high energy consumption in conventional carbon dioxide purification and liquefaction processes, the present application provides a process for preparing ultra-high purity carbon dioxide.

[0005] The present application provides a process for preparing ultra-high purity carbon dioxide, which adopts the following technical solution: A process for preparing ultra-high purity carbon dioxide comprises the following steps: S1. Exchanging heat with the purified carbon dioxide raw gas, and then performing gas-liquid separation of the raw gas to obtain a gas phase 1 and a liquid phase 1; S2, subjecting the liquid phase 1 to heat exchange and supercooling treatment, and then to expansion and cooling, and then entering the top of the flash tower for gas-liquid separation to obtain gas phase 2 and liquid phase 2; S3, heat exchange treatment is performed on the liquid phase 2 and the liquid phase 2 enters the reboiler at the bottom of the flash tower, and the heavy components in the liquid phase 2 are flash-evaporated and separated to obtain the liquid phase 3; S4, transfer the liquid phase 3 to the absorption tower, the absorption tower pressure is 0.6-1.0bar, the absorption tower temperature range is 0-25℃, the absorption tower is filled with carbon dioxide adsorption material, the carbon dioxide adsorption material is a methyl functionalized covalent organic framework material coated with a polar polymer, the liquid phase 3 flow rate is 8-12m 3 / h, to obtain carbon dioxide-rich adsorption material; S5. Transfer the carbon dioxide-rich adsorption material to a desorption tower with a pressure of 1.5-2.5 bar and a temperature of 100-120° C. for 4-8 hours to obtain ultra-high purity carbon dioxide.

[0006] The ultra-high-purity carbon dioxide preparation process of the present application adopts a low-temperature distillation method, coordinated with washing, flash evaporation and carbon dioxide adsorption materials, to remove impurity components such as sulfide, H2, CO, CH4, N2 and O2 in the crude carbon dioxide raw gas, thereby obtaining ultra-high-purity carbon dioxide.

[0007] The carbon dioxide adsorption material is a methyl-functionalized covalent organic framework (COF) coated with a polar polymer. COFs offer low density, high specific surface area, and easily adjustable pore size and structure. Combined with the introduction of methyl groups, the COFs enable more efficient gas capture and adsorption. Furthermore, the polar polymer coating further filters impurities such as N2 and O2, enabling the methyl-functionalized COFs to adsorb CO2 as purely as possible, further improving the purity of ultra-high-purity CO2.

[0008] Preferably, the preparation method of the carbon dioxide adsorbent material is: dissolving polyacrylic acid in N,N-dimethylformamide, stirring and dissolving at 40-60°C, removing bubbles by ultrasound, then adding a methyl-functionalized covalent organic framework material and tumbling, and after a polymer film is evenly attached to the surface of the methyl-functionalized covalent organic framework material, taking it out and drying it at room temperature for 24-48 hours, and finally vacuum drying to obtain the carbon dioxide adsorbent material.

[0009] Preferably, the concentration of the polyacrylic acid-N,N-dimethylformamide solution is 15-20 wt %.

[0010] Preferably, the mass ratio of the polyacrylic acid-N,N-dimethylformamide solution to the methyl functionalized covalent organic framework material is 1:(4-6).

[0011] Preferably, the preparation method of the methyl-functionalized covalent organic framework material comprises the following steps: A1. Mix dimethyl 2,5-dimethyl terephthalate and hydrazine hydrate, heat under reflux for 20-30 hours, cool to room temperature, remove the solvent by rotary evaporation, and dry in vacuo to obtain 2,5-dimethyl terephthalic acid hydrazide; A2. Mix 2,5-dimethylterephthaloyl hydrazide, 2,4,6-tris(4-formaldehydephenyl)-1,3,5-triazine, o-dichlorobenzene and n-butanol, and then sonicate for 10-20 minutes. Then transfer the solution to a quartz tube, add acetic acid dropwise, evacuate under freezing conditions, pass nitrogen, and cycle 2-4 times. Seal with a flame under vacuum conditions. After the temperature rises to room temperature, react at 100-140°C for 70-80 hours, then cool and filter, wash with acetone and ether, and finally extract with tetrahydrofuran and acetone for 20-30 hours. Dry under vacuum at 70-90°C overnight to obtain a methyl-functionalized covalent organic framework material.

[0012] Preferably, in A1, the molar ratio of dimethyl 2,5-dimethylterephthalate to hydrazine hydrate is 1:(2-3).

[0013] Preferably, the steps of A2 are as follows: 0.02-0.04 mmol 2,5-dimethylterephthaloyl hydrazide, 0.01-0.03 mmol 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 0.2-0.4 ml o-dichlorobenzene and 0.1-0.3 ml n-butanol were mixed and then ultrasonicated for 10-20 minutes. The solution was then transferred to a quartz tube and 40-60 μL of 6 mol / L acetic acid was added dropwise. The tube was vacuumed and purged with nitrogen under freezing conditions for 2-4 cycles. The tube was flame-sealed under vacuum conditions. After the temperature reached room temperature, the tube was reacted at 100-140°C for 70-80 hours. The tube was then cooled, filtered, washed with acetone and ether, and finally stripped with tetrahydrofuran and acetone for 20-30 hours. The tube was then vacuum-dried at 70-90°C overnight to obtain a methyl-functionalized covalent organic framework material.

[0014] Preferably, the steps of A2 are as follows: 0.02-0.04 mmol 2,5-dimethylterephthaloyl hydrazide, 0.01-0.03 mmol 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 0.2-0.4 ml o-dichlorobenzene, 0.1-0.3 ml n-butanol and 2-4 mg metal oxide were mixed, followed by ultrasonication for 10-20 min; the solution was then transferred to a quartz tube, 40-60 μL of 6 mol / L acetic acid was added dropwise, vacuumed under freezing conditions, vented with nitrogen, and cycled 2-4 times, with flame sealing under vacuum conditions. After the temperature reached room temperature, the reaction was carried out at 100-140°C for 70-80 h, followed by cooling, filtration, and washing with acetone and ether. Finally, the solution was extracted with tetrahydrofuran and acetone for 20-30 h, and vacuum dried at 70-90°C overnight to obtain a methyl-functionalized covalent organic framework material; The metal oxide is one of nickel oxide and palladium oxide or a mixture of the two.

[0015] Preferably, the metal oxide is a mixture of nickel oxide and palladium oxide, and the mass ratio of nickel oxide to palladium oxide is (1-2):1.

[0016] Nickel oxide can react with sulfides in the carbon dioxide feed gas, while palladium oxide can remove methane from the carbon dioxide feed gas. Therefore, when nickel oxide and palladium oxide are doped into the methyl-functionalized covalent organic framework material, the final carbon dioxide obtained will have a higher purity.

[0017] In summary, this application has the following beneficial effects: 1. The ultra-high purity carbon dioxide preparation process of the present application adopts a cryogenic distillation method, coordinated with washing, flash evaporation and carbon dioxide adsorption materials, to remove impurities such as sulfide, H2, CO, CH4, N2 and O2 in the crude carbon dioxide feed gas, thereby obtaining ultra-high purity carbon dioxide.

[0018] 2. The carbon dioxide adsorption material is a methyl-functionalized covalent organic framework material coated with a polar polymer. The covalent organic framework material has the characteristics of low density, high specific surface area, easy adjustment of pore size and structure, etc., and the introduction of methyl groups enables the covalent organic framework to more fully capture and adsorb gases. In addition, the coating of the polar polymer can further filter impurity components such as N2 and O2, enabling the methyl-functionalized covalent organic framework material to adsorb carbon dioxide as purely as possible, thereby further improving the purity of ultra-high-purity carbon dioxide.

[0019] 3. Nickel oxide can react with sulfides in the carbon dioxide feed gas, while palladium oxide can remove methane from the carbon dioxide feed gas. Therefore, when nickel oxide and palladium oxide are doped into the methyl-functionalized covalent organic framework material, the carbon dioxide finally obtained will have a higher purity. DETAILED DESCRIPTION

[0020] The present application is further described in detail below in conjunction with Examples 1 to 8 and Comparative Examples 1 to 2.

[0021] raw material

[0022] Polyacrylic acid CAS: 9003-01-4; N,N-dimethylformamide CAS: 68-12-2; Dimethyl 2,5-dimethylterephthalate CAS: 54100-53-7; Hydrazine hydrate CAS: 7803-57-8; 2,4,6-Tris(4-formylphenyl)-1,3,5-triazine CAS: 443922-06-3; o-Dichlorobenzene CAS: 95-50-1; n-Butanol CAS: 71-36-3; Acetone CAS: 67-64-1; Diethyl ether CAS: 60-29-7; Tetrahydrofuran CAS: 109-99-9; Acetone CAS: 67-64-1; Nickel oxide CAS: 1313-99-1; Palladium oxide CAS: 1314-08-5. Example 1

[0023] A process for preparing ultra-high purity carbon dioxide comprises the following steps: S1. Exchanging heat with the purified carbon dioxide raw gas, and then performing gas-liquid separation of the raw gas to obtain a gas phase 1 and a liquid phase 1; S2, the liquid phase one is subjected to heat exchange subcooling treatment, and then is subjected to expansion cooling, and then is subjected to gas-liquid separation at the top of a flash tower to obtain a gas phase two and a liquid phase two; S3, the liquid phase two is subjected to heat exchange treatment and enters a reboiler at the bottom of the flash tower, and after the heavy components in the liquid phase two are subjected to flash separation, a liquid phase three is obtained; The specific steps and the use equipment of S1-S3 are shown in Example 3 of the granted announcement CN115501632B.

[0024] S4, the liquid phase three is transferred to an absorption tower, the pressure of the absorption tower is 1 bar, the temperature of the absorption tower ranges from 25℃ to 30℃, the absorption tower is filled with carbon dioxide adsorption material, the carbon dioxide adsorption material is a polar polymer-coated methyl-functionalized covalent organic framework material, the flow rate of the liquid phase three is 10 m 3 / h, and a carbon dioxide-rich adsorption material is obtained. The preparation method of the carbon dioxide adsorption material is as follows: Polyacrylic acid is dissolved in N,N-dimethylformamide, stirring and dissolving at 50℃, ultrasonic removal of bubbles, then adding methyl-functionalized covalent organic framework material for tumbling, when the surface of the methyl-functionalized covalent organic framework material is uniformly attached with a polymer film, it is taken out and air-dried at room temperature for 48h, and finally vacuum dried to obtain the carbon dioxide adsorption material.

[0025] The concentration of the polyacrylic acid-N,N-dimethylformamide solution is 20wt%, and the mass ratio of the polyacrylic acid-N,N-dimethylformamide solution to the methyl-functionalized covalent organic framework material is 1:5.

[0026] The preparation method of the methyl-functionalized covalent organic framework material includes the following steps: A1, 2,5-dimethyl terephthalate is mixed with hydrazine hydrate, the molar ratio of 2,5-dimethyl terephthalate to hydrazine hydrate is 1:2.5, heated to reflux for 24h, cooled to room temperature, removed the solvent by rotary evaporation, and vacuum dried to obtain 2,5-dimethyl terephthalic hydrazide; A2, 0.03mmol 2,5-dimethyl terephthalic hydrazide, 0.02mmol 2,4,6-tris(4-formaldehyde phenyl)-1,3,5-triazine, 0.3ml o-dichlorobenzene and 0.2ml n-butanol are mixed, and then ultrasonic for 15min; then the solution is transferred to a quartz tube, 50μL of 6mol / L acetic acid is added dropwise, vacuum is pumped under refrigeration, nitrogen is introduced, and the cycle is repeated for 3 times, vacuum is applied, and flame sealing is performed, after the temperature rises to room temperature, 120℃ reaction is carried out for 72h, then cooled and filtered, washed with acetone and diethyl ether, finally, eluted with tetrahydrofuran and acetone for 24h, and vacuum dried at 80℃ overnight to obtain the methyl-functionalized covalent organic framework material.

[0027] S5. The carbon dioxide-rich adsorption material is transferred to a desorption tower. The desorption tower pressure is 2.5 bar, the desorption tower temperature is 120° C., and desorption is performed for 8 hours to obtain ultra-high purity carbon dioxide.

[0028] Example 2-Example 3 The difference from Example 1 is that the mass ratio of the polyacrylic acid-N,N-dimethylformamide solution to the methyl-functionalized covalent organic framework material is different, as shown in Table 1.

[0029] Table 1 Mass ratio of each component of carbon dioxide adsorption material of Example 1 to Example 3 Example 4

[0030] The difference from Example 1 is that the methyl-functionalized covalent organic framework material is also loaded with metal oxides; The preparation method of the methyl functionalized covalent organic framework material comprises the following steps: A1. Mix dimethyl 2,5-dimethyl terephthalate and hydrazine hydrate in a molar ratio of 1:2.5, heat under reflux for 24 hours, cool to room temperature, remove the solvent by rotary evaporation, and dry in vacuo to obtain 2,5-dimethyl terephthalic acid hydrazide; A2. 0.03 mmol of 2,5-dimethylterephthaloyl hydrazide, 0.02 mmol of 2,4,6-tris(4-formaldehydephenyl)-1,3,5-triazine, 0.3 ml of o-dichlorobenzene, 0.2 ml of n-butanol, and 3 mg of metal oxide were mixed, followed by ultrasonication for 15 min. The solution was then transferred to a quartz tube, 50 μL of 6 mol / L acetic acid was added dropwise, and vacuum was evacuated and nitrogen was passed through under freezing conditions for three cycles. The vacuum was flame-sealed, and after the temperature was raised to room temperature, the reaction was carried out at 120°C for 72 h. The reaction was then cooled, filtered, and washed with acetone and ether. Finally, the reaction was extracted with tetrahydrofuran and acetone for 24 h, and dried under vacuum at 80°C overnight to obtain a methyl-functionalized covalent organic framework material. The metal oxide is a mixture of nickel oxide and palladium oxide, and the mass ratio of nickel oxide to palladium oxide is 3:2. Example 5

[0031] The difference from Example 4 is that the metal oxide is only nickel oxide. Example 6

[0032] The difference from Example 4 is that the metal oxide is only palladium oxide.

[0033] Example 7-Example 8 The difference from Example 4 is that the mass ratio of nickel oxide to palladium oxide is different, as shown in Table 2.

[0034] Table 2 Mass ratio of nickel oxide to palladium oxide in Example 4 and Example 7-Example 8

[0035] Comparative Example 1 A process for preparing ultra-high purity carbon dioxide comprises the following steps: S1. Exchanging heat with the purified carbon dioxide raw gas, and then performing gas-liquid separation of the raw gas to obtain a gas phase 1 and a liquid phase 1; S2, subjecting the liquid phase 1 to heat exchange and supercooling treatment, and then to expansion and cooling, and then entering the top of the flash tower for gas-liquid separation to obtain gas phase 2 and liquid phase 2; S3, heat exchange treatment is performed on the liquid phase 2 and the liquid phase 2 enters the reboiler at the bottom of the flash tower, and the heavy components in the liquid phase 2 are flash-evaporated and separated to obtain the liquid phase 3; For the specific steps of S1-S3 and the equipment used, please refer to Example 3 of the authorization announcement number CN115501632B.

[0036] Comparative Example 2 The difference from Example 1 is that the carbon dioxide adsorption material is a covalent organic framework material with only methyl functionalization.

[0037] Performance testing

[0038] 1. Carbon dioxide concentration test The product concentrations of Examples 1 to 8 and Comparative Examples 1 to 2 were tested with reference to GB / T 2023938-2009, and the test data are shown in Table 3.

[0039] Table 3 Test data table of Example 1-Example 8 and Comparative Example 1-Comparative Example 2

[0040] Referring to Example 1 and Comparative Examples 1-2 and in combination with Table 3, it can be seen that the carbon dioxide concentration in Comparative Example 2 is significantly increased compared to Comparative Example 1, which shows that the operation of adding methyl-functionalized covalent organic framework materials in the absorption tower can effectively increase the concentration of carbon dioxide products.

[0041] The reason is that covalent organic framework materials have the characteristics of low density, high specific surface area, easy adjustment of pore size and structure, and the introduction of methyl groups, which enables the covalent organic framework to more fully capture and adsorb carbon dioxide, further increasing the concentration of carbon dioxide products by removing impurity gases.

[0042] Compared with Comparative Example 2, the carbon dioxide concentration in Example 1 is further increased, which shows that coating the surface of the methyl-functionalized covalent organic framework material with a polar polymer can further increase the concentration of the carbon dioxide product.

[0043] The reason is that the coating of polar polymers can further filter impurity components such as N2 and O2, prompting the methyl-functionalized covalent organic framework material to adsorb carbon dioxide as purely as possible, thereby further improving the purity of carbon dioxide.

[0044] Referring to Examples 1 to 3 and in combination with Table 3, it can be seen that the carbon dioxide concentrations of Examples 2 and 3 are reduced to a certain extent compared to Example 1. This indicates that when the mass ratio of the polyacrylic acid-N,N-dimethylformamide solution and the methyl-functionalized covalent organic framework material is adopted in Example 1, the prepared product will have a higher concentration of carbon dioxide.

[0045] The reason for this may be that when the proportion of the polyacrylic acid-N,N-dimethylformamide solution is too small, the thickness of the polar polymer coating is insufficient, making it difficult for the polar polymer to filter out impurities such as N2 and O2, resulting in a lower carbon dioxide concentration in the product. However, when the proportion of the polyacrylic acid-N,N-dimethylformamide solution is too large, the polar polymer coating may also block carbon dioxide, resulting in a slightly lower carbon dioxide concentration in the product.

[0046] With reference to Example 1 and Example 4 and in combination with Table 3, it can be seen that the carbon dioxide concentration in Example 4 is significantly increased compared to that in Example 1, which indicates that the addition of metal oxides can further increase the carbon dioxide concentration of the product.

[0047] With reference to Examples 4 to 6 and in combination with Table 3, it can be seen that the carbon dioxide concentrations of Examples 5 to 6 are slightly lower than those of Example 4. This indicates that, compared with the use of nickel oxide or palladium oxide alone, the products prepared by combining nickel oxide and palladium oxide will have a higher carbon dioxide concentration.

[0048] The reason is that nickel oxide can react with sulfides in the carbon dioxide raw gas, while palladium oxide can remove methane from the carbon dioxide raw gas. Therefore, when nickel oxide and palladium oxide are doped into the methyl-functionalized covalent organic framework material, the final carbon dioxide obtained will have a higher purity.

[0049] That is to say, the preparation process of the ultra-high purity carbon dioxide in the embodiment removes the impurity components such as sulfides, H2, CO, CH4, N2 and O2 in the raw carbon dioxide gas by using the method of low-temperature rectification, cooperating with washing, flashing and carbon dioxide adsorption material, so as to obtain the ultra-high purity carbon dioxide.

[0050] It can be seen from the comparison between the examples 4 and 7-8 and in combination with the table 3 that the carbon dioxide concentration of the examples 7-8 is slightly decreased compared with the example 4, which indicates that when the mass ratio of the nickel oxide and the palladium oxide is used as in the example 4, the product prepared will have a higher carbon dioxide concentration.

[0051] The specific embodiment is only an explanation of the present application, which is not a limitation of the present application, and the person skilled in the art can make a modification of the present embodiment without creative contribution according to the need after reading the present specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A process for preparing ultra-high purity carbon dioxide, characterized in that: The following steps are involved: S1. Exchanging heat with the purified carbon dioxide raw gas, and then performing gas-liquid separation of the raw gas to obtain a gas phase 1 and a liquid phase 1; S2, subjecting the liquid phase 1 to heat exchange and supercooling treatment, and then to expansion and cooling, and then entering the top of the flash tower for gas-liquid separation to obtain gas phase 2 and liquid phase 2; S3, heat exchange treatment is performed on the liquid phase 2 and the liquid phase 2 enters the reboiler at the bottom of the flash tower, and the heavy components in the liquid phase 2 are flash-evaporated and separated to obtain the liquid phase 3; S4, transfer the liquid phase 3 to the absorption tower, the absorption tower pressure is 0.6-1.0bar, the absorption tower temperature range is 0-25℃, the absorption tower is filled with carbon dioxide adsorption material, the carbon dioxide adsorption material is a methyl functionalized covalent organic framework material coated with a polar polymer, the liquid phase 3 flow rate is 8-12m 3 / h, to obtain carbon dioxide-rich adsorption material; S5. Transfer the carbon dioxide-rich adsorption material to a desorption tower with a pressure of 1.5-2.5 bar and a temperature of 100-120° C. for 4-8 hours to obtain ultra-high purity carbon dioxide.

2. The process for preparing ultra-high purity carbon dioxide according to claim 1, characterized in that: The preparation method of the carbon dioxide adsorption material is: Dissolve polyacrylic acid in N,N-dimethylformamide, stir and dissolve at 40-60°C, remove bubbles with ultrasound, then add methyl-functionalized covalent organic framework material and tumble. When a polymer film is evenly attached to the surface of the methyl-functionalized covalent organic framework material, take it out and dry it at room temperature for 24-48 hours, and finally vacuum dry it to obtain a carbon dioxide adsorption material.

3. The process for preparing ultra-high purity carbon dioxide according to claim 2, wherein: The concentration of the polyacrylic acid-N,N-dimethylformamide solution is 15-20 wt %.

4. The process for preparing ultra-high purity carbon dioxide according to claim 2, wherein: The mass ratio of the polyacrylic acid-N, N-dimethylformamide solution to the methyl functionalized covalent organic framework material is 1:(4-6).

5. The process for preparing ultra-high purity carbon dioxide according to claim 1, characterized in that: The preparation method of the methyl functionalized covalent organic framework material comprises the following steps: A1. Mix dimethyl 2,5-dimethyl terephthalate and hydrazine hydrate, heat under reflux for 20-30 hours, cool to room temperature, remove the solvent by rotary evaporation, and dry in vacuo to obtain 2,5-dimethyl terephthalic acid hydrazide; A2. Mix 2,5-dimethylterephthaloyl hydrazide, 2,4,6-tris(4-formaldehydephenyl)-1,3,5-triazine, o-dichlorobenzene and n-butanol, and then sonicate for 10-20 minutes. Then transfer the solution to a quartz tube, add acetic acid dropwise, evacuate under freezing conditions, pass nitrogen, and cycle 2-4 times. Seal with a flame under vacuum conditions. After the temperature rises to room temperature, react at 100-140°C for 70-80 hours, then cool and filter, wash with acetone and ether, and finally extract with tetrahydrofuran and acetone for 20-30 hours. Dry under vacuum at 70-90°C overnight to obtain a methyl-functionalized covalent organic framework material.

6. The process for preparing ultra-high purity carbon dioxide according to claim 5, characterized in that: In A1, the molar ratio of dimethyl 2,5-dimethylterephthalate to hydrazine hydrate is 1:(2-3).

7. The process for preparing ultra-high purity carbon dioxide according to claim 5, characterized in that: The steps of A2 are as follows: 0.02-0.04 mmol 2,5-dimethylterephthaloyl hydrazide, 0.01-0.03 mmol 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 0.2-0.4 ml o-dichlorobenzene and 0.1-0.3 ml n-butanol were mixed and then ultrasonicated for 10-20 minutes. The solution was then transferred to a quartz tube and 40-60 μL of 6 mol / L acetic acid was added dropwise. The tube was vacuumed and purged with nitrogen under freezing conditions for 2-4 cycles. The tube was flame-sealed under vacuum conditions. After the temperature reached room temperature, the tube was reacted at 100-140°C for 70-80 hours. The tube was then cooled, filtered, washed with acetone and ether, and finally stripped with tetrahydrofuran and acetone for 20-30 hours. The tube was then vacuum-dried at 70-90°C overnight to obtain a methyl-functionalized covalent organic framework material.

8. The process for preparing ultra-high purity carbon dioxide according to claim 5, characterized in that: The steps of A2 are as follows: 0.02-0.04 mmol 2,5-dimethylterephthaloyl hydrazide, 0.01-0.03 mmol 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 0.2-0.4 ml o-dichlorobenzene, 0.1-0.3 ml n-butanol and 2-4 mg metal oxide were mixed, followed by ultrasonication for 10-20 min; the solution was then transferred to a quartz tube, 40-60 μL of 6 mol / L acetic acid was added dropwise, vacuumed under freezing conditions, vented with nitrogen, and cycled 2-4 times, with flame sealing under vacuum conditions. After the temperature reached room temperature, the reaction was carried out at 100-140°C for 70-80 h, followed by cooling, filtration, and washing with acetone and ether. Finally, the solution was extracted with tetrahydrofuran and acetone for 20-30 h, and vacuum dried at 70-90°C overnight to obtain a methyl-functionalized covalent organic framework material; The metal oxide is one of nickel oxide and palladium oxide or a mixture of the two.

9. The process for preparing ultra-high purity carbon dioxide according to claim 8, characterized in that: The metal oxide is a mixture of nickel oxide and palladium oxide, and the mass ratio of nickel oxide to palladium oxide is (1-2):1.

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