Cobalt-based metal organic framework material, preparation method thereof and application of cobalt-based metal organic framework material in separation of propylene and ethylene

Abstract

The invention belongs to the technical field of gas adsorption separation, and particularly relates to a cobalt-based metal organic framework material, a preparation method thereof and application of the cobalt-based metal organic framework material in propylene-ethylene separation. The cobalt-based metal organic framework material provided by the invention can preferentially adsorb propylene in a mixture of propylene and ethylene, separation can be carried out at normal temperature and normal pressure, and the cobalt-based metal organic framework material has relatively low energy consumption and good safety, so that the economic benefit and the energy efficiency are improved to the maximum extent. The cobalt-based metal organic framework material provided by the invention has a relatively high specific surface area, can show a relatively high selective separation effect on propylene-ethylene mixed gas separation at normal temperature and normal pressure, and has a good application prospect. The cobalt-based metal organic framework material provided by the invention can selectively adsorb propylene and is suitable for separating propylene from ethylene.

Description

Technical Field

[0001] The invention belongs to the technical field of gas adsorption separation, and in particular relates to a cobalt-based metal organic framework material and a preparation method thereof and application thereof in propylene and ethylene separation. Background Art

[0002] Ethylene (C2H4) and propylene (C3H6) are the most important basic raw materials in the petrochemical industry and are key raw materials for the production of plastics, fibers, rubber, cosmetics and medicines. In traditional industrial production, olefins containing 2 to 4 carbon atoms are produced by steam cracking naphtha extracted from crude oil, which is highly dependent on crude oil. The sharp fluctuations in crude oil prices and the decline in reserves have had a huge impact on the production of C2H4 and C3H6. In recent years, the methanol to olefins (MTO) process is an important and advanced method for producing C2H4 using coal and natural gas. The reaction products are mainly C3H6 (~21wt%) and C2H4 (~51wt%). Therefore, purification of MTO products to obtain high-purity C3H6 and C2H4 is crucial for downstream applications and the chemical manufacturing industry.

[0003] Since the molecular size and physicochemical properties of polymer-grade C3H6 and C2H4 are very similar, the separation of the two is very challenging. The commonly used separation method mainly relies on high-pressure and low-temperature distillation, which consumes a lot of energy and does not meet the requirements of green chemistry. Summary of the invention

[0004] The purpose of the present invention is to provide a cobalt-based metal organic framework material and a preparation method thereof and application in propylene and ethylene separation. The cobalt-based metal organic framework material provided by the present invention can selectively adsorb propylene with low energy consumption.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a cobalt-based metal organic framework material, comprising a coordination metal and an organic ligand, wherein the coordination metal is Co 2+ , the organic ligand is 4,4'-(2,6-pyrazinediyl)dibenzoic acid.

[0007] Preferably, the cobalt-based metal organic framework material is a (3,9)-connected three-dimensional framework structure: each Co 2+ The coordination mode is hexacoordinated, coordinated with one μ3-OH and the oxygen atoms of the carboxylic acid groups of four different organic ligands, and the remaining coordination site is occupied by one N atom in the pyrazine ring of the organic ligand.

[0008] Preferably, the cobalt-based metal organic framework material has a trinuclear cobalt cluster structural unit, which forms a nine-connected saturated coordination mode, each trinuclear cobalt cluster structural unit is connected to 9 organic ligands, and each organic ligand is connected to 3 trinuclear cobalt cluster structural units.

[0009] Preferably, the topology type of the cobalt-based metal organic framework material is xmz topology.

[0010] Preferably, the specific surface area of ​​the cobalt-based metal organic framework material is 600 to 900 m 2 / g, the actual pore volume is 0.30~0.50cm 3 / g, and the porosity is 50-70%.

[0011] The present invention also provides a method for preparing the cobalt-based metal organic framework material described in the above scheme, comprising the following steps:

[0012] Cobalt salt, organic ligand, fluoroboric acid and solvent are mixed to carry out solvothermal reaction, wherein the organic ligand is 4,4'-(2,6-pyrazinediyl)dibenzoic acid, to obtain a cobalt-based metal organic framework material.

[0013] Preferably, the molar ratio of the cobalt salt to the organic ligand is 1 to 3:1.

[0014] Preferably, the temperature of the solvent thermal reaction is 100-160° C., and the reaction time is 12-24 hours; and the solvent thermal reaction is carried out under closed conditions.

[0015] The present invention also provides the use of the cobalt-based metal organic framework material described in the above scheme or the cobalt-based metal organic framework material obtained by the preparation method described in the above scheme in propylene and ethylene separation.

[0016] Preferably, the cobalt-based metal organic framework material is activated before use, and the activation comprises the following steps: degassing and activating the cobalt-based metal organic framework material after solvent exchange.

[0017] The present invention provides a cobalt-based metal organic framework material. The cobalt-based metal organic framework material provided by the present invention can preferentially adsorb propylene in a mixture of propylene and ethylene, can be separated at room temperature and pressure, has low energy consumption and good safety, thereby maximizing economic benefits and energy efficiency. The cobalt-based metal organic framework material provided by the present invention has a high specific surface area, can show a high selective separation effect for separating propylene and ethylene mixed gas at room temperature and pressure, and has good application prospects.

[0018] The present invention also provides a method for preparing the cobalt-based metal organic framework material described in the above scheme. In the present invention, cobalt salt and 4,4'-(2,6-pyrazinediyl)dibenzoic acid are dissolved in a solvent for solvothermal reaction to obtain the cobalt-based metal organic framework material, which has simple steps and is easy to operate.

[0019] The present invention also provides the use of the cobalt-based metal organic framework material described in the above scheme or the cobalt-based metal organic framework material obtained by the preparation method described in the above scheme in propylene and ethylene separation. The cobalt-based metal organic framework material provided by the present invention can selectively adsorb propylene and is suitable for separation of propylene and ethylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 This is an optical microscope photograph of the cobalt-based metal organic framework material crystal in Example 1;

[0022] Figure 2 This is a microscopic crystal structure diagram of the cobalt-based metal organic framework material of Example 1;

[0023] Figure 3 The PXRD pattern of the synthesis and structural simulation of the cobalt-based metal organic framework material in Example 1;

[0024] Figure 4 The PXRD patterns of the cobalt-based metal organic framework material in Example 1 after being immersed in different solvents;

[0025] Figure 5 77K nitrogen adsorption isotherm of the cobalt-based metal organic framework material of Example 1;

[0026] Figure 6 is the adsorption isotherm of propylene and ethylene of the cobalt-based metal organic framework material of Example 1 at 298K;

[0027] Figure 7 This is the IAST separation coefficient curve of propylene / ethylene at different molar ratios of the cobalt-based metal organic framework material in Example 1 at 298K. DETAILED DESCRIPTION

[0028] The present invention provides a cobalt-based metal organic framework material, comprising a coordination metal and an organic ligand, wherein the coordination metal is Co 2+ , the organic ligand is 4,4'-(2,6-pyrazinediyl)dibenzoic acid.

[0029] In the present invention, the cobalt-based metal organic framework material is preferably a (3,9)-connected three-dimensional framework structure: each Co 2+ The coordination mode is hexacoordinated, coordinated with one μ3-OH and the oxygen atoms of the carboxylic acid groups of four different organic ligands, and the remaining coordination site is occupied by one N atom in the pyrazine ring of the organic ligand.

[0030] In the present invention, the cobalt-based metal organic framework material preferably has a trinuclear cobalt cluster structural unit, which forms a nine-connected saturated coordination mode, each trinuclear cobalt cluster structural unit is connected to 9 organic ligands, and each organic ligand is connected to 3 trinuclear cobalt cluster structural units.

[0031] In the present invention, the topology type of the cobalt-based metal organic framework material is preferably xmz topology.

[0032] In the present invention, the specific surface area of ​​the cobalt-based metal organic framework material is preferably 600 to 900 m 2 / g, specifically 750m 2 / g, and the actual pore volume is preferably 0.30 to 0.50 cm 3 / g, specifically 0.40cm 3 / g, and the porosity is preferably 50-70%, and specifically 60%.

[0033] The present invention also provides a method for preparing the cobalt-based metal organic framework material described in the above scheme, comprising the following steps:

[0034] Cobalt salt, organic ligand, fluoroboric acid and solvent are mixed (referred to as the first mixture) for solvothermal reaction, wherein the organic ligand includes 4,4'-(2,6-pyrazinediyl)dibenzoic acid to obtain a cobalt-based metal organic framework material.

[0035] In the present invention, the cobalt salt is preferably a soluble cobalt salt; the soluble cobalt salt preferably includes one or more of cobalt chloride, cobalt nitrate, cobalt acetate and cobalt sulfate; the cobalt nitrate is preferably hydrated cobalt nitrate; the hydrated cobalt nitrate is preferably cobalt nitrate hexahydrate.

[0036] In the present invention, the molar ratio of the cobalt salt to the organic ligand is preferably 1 to 3:1, specifically 2:1.

[0037] In the present invention, the solvent preferably includes an amide solvent and a low boiling point solvent; the amide solvent preferably includes one or more of N,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide and N,N-diethylformamide, more preferably N,N-dimethylacetamide; the boiling point of the low boiling point solvent is preferably 65-100°C, specifically 65°C; the low boiling point solvent preferably includes one or more of 1,4-dioxane, acetonitrile, methanol and ethanol, more preferably methanol; the volume ratio of the amide solvent to the low boiling point solvent is preferably 3-8:1, specifically 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1 or 8:1.

[0038] In the present invention, the ratio of the amount of the cobalt salt to the volume of the solvent is preferably (0.01-0.05) mmol:(2-3) mL, and specifically can be 0.04 mmol:2.3 mL.

[0039] In the present invention, the volume ratio of the amide solvent to fluoroboric acid is preferably 50 to 200:1, specifically 50:1, 75:1, 100:1, 125:1, 150:1, 175:1 or 200:1.

[0040] In the present invention, the first mixing is preferably: mixing the cobalt salt, the organic ligand and the amide solvent and then ultrasonicating to obtain a purple clear mixed solution, and mixing the mixed solution with fluoroboric acid and a low boiling point solvent.

[0041] In the present invention, the temperature of the solvent thermal reaction is preferably 100-160°C, specifically 120°C or 140°C, and the insulation reaction time is preferably 12-24h, specifically 14h or 20h; the solvent thermal reaction is preferably carried out in a closed condition.

[0042] In the present invention, after the solvothermal reaction, the obtained reaction product is preferably cooled and then washed and dried in sequence.

[0043] In the present invention, the final temperature of the cooling is preferably room temperature; the washing agent is preferably DMA; and the drying is preferably natural drying.

[0044] The present invention also provides the use of the cobalt-based metal organic framework material described in the above scheme or the cobalt-based metal organic framework material obtained by the preparation method described in the above scheme in propylene and ethylene separation.

[0045] In the present invention, the cobalt-based metal organic framework material is preferably activated before use, and the activation preferably comprises the following steps: degassing and activating the cobalt-based metal organic framework material after solvent exchange.

[0046] In the present invention, the solvent used for the solvent exchange preferably includes one or more of ethanol, methanol and dichloromethane; the temperature of the solvent exchange is preferably room temperature; the time of a single solvent exchange is preferably 1 to 3 hours, more preferably 2 hours, the frequency is preferably 4 to 8 times per day, and the total exchange time is preferably 3 to 4 days. The present invention exchanges free guest molecules (DMA, DMF, H2O, etc.) in the framework pores through solvent exchange, which is convenient for subsequent activation.

[0047] In the present invention, the degassing activation is preferably carried out under vacuum conditions; the temperature of the degassing activation is preferably 40-90°C, specifically 50°C, 60°C, 65°C, 70°C or 80°C, and the activation time is preferably 8-12h, specifically 10h.

[0048] In order to further illustrate the present invention, the scheme of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be understood as limiting the protection scope of the present invention.

[0049] Example 1

[0050] This embodiment provides a cobalt-based metal organic framework material, wherein the organic ligand of the cobalt-based metal organic framework material is 4,4'-(2,6-pyrazinediyl)dibenzoic acid, and the structural formula of the organic ligand is as follows:

[0051]

[0052] 33 mg of cobalt nitrate hexahydrate and 18 mg of organic ligand 4,4'-(2,6-pyrazinediyl)dibenzoic acid were weighed and placed in a 20 mL glass vial, followed by the addition of 3.50 mL of N,N-dimethylacetamide, and the glass vial containing the mixture was ultrasonically treated to obtain a clear purple solution, and then 0.50 mL of methanol and 60 μL of fluoroboric acid were added. The obtained mixed solution was ultrasonically mixed evenly, covered and sealed, and placed in a 120°C oven for solvothermal reaction under the naturally generated pressure of the glass vial for 22 hours. After cooling to room temperature, light orange-red transparent cubic crystals were collected, and the obtained crystals were washed with DMA and then dried in air to obtain a cobalt-based metal organic framework material.

[0053] Example 2

[0054] Weigh 22 mg of cobalt nitrate hexahydrate and 12 mg of organic ligand 4,4'-(2,6-pyrazinediyl)dibenzoic acid into a 20 mL glass vial, then add 2.00 mL of N,N-dimethylacetamide, and ultrasonically treat the glass vial containing the above mixture to obtain a clear purple solution. Then add 90 μL of fluoroboric acid, and ultrasonically mix the obtained mixed solution evenly. The solution is sealed with a cover and placed in an oven at 120°C to react for 24 hours. After cooling to room temperature, light orange-red transparent cubic crystals are collected, and the obtained crystals are washed with DMA and then dried in air to obtain a cobalt-based metal organic framework material.

[0055] The cobalt-based metal organic framework material prepared in this example was observed by electron microscope, and the results were as follows: Figure 1 As shown, the crystal structure of the cobalt-based metal organic framework material prepared in this embodiment is as follows Figure 2 As shown. Figure 1 and Figure 2 It can be seen that the cobalt-based metal organic framework material provided by the present invention has a distorted cubic cage structure and a trinuclear cobalt cluster structural unit, and exhibits good stability and high propylene / ethylene separation performance.

[0056] Test Example 1

[0057] The powder of the cobalt-based metal organic framework material prepared in Example 1 was characterized by XRD. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the powder XRD pattern of the cobalt-based metal organic framework material prepared in the present invention is basically consistent with the diffraction peak position of the XRD pattern obtained by single crystal structure simulation, indicating that the compounds prepared in the present invention are all pure phases.

[0058] The chemical stability test of the cobalt-based metal organic framework material prepared in Example 1 was carried out by immersing it in MeCN, MeOH, EtOH, CH3COCH3 or CH2C12 solvents respectively. The test results are as follows: Figure 4 As shown. Figure 4 It can be seen that the diffraction peak positions of the XRD patterns of the cobalt-based metal-organic framework materials after immersion for 3 days remain basically the same, proving that the crystal structure of the cobalt-based metal-organic framework materials can still exist stably in low-boiling point organic solvents.

[0059] Test Example 2

[0060] 100 mg of the cobalt-based metal-organic framework material prepared in Example 1 was washed three times with N,N-dimethylacetamide, and the free guest molecules in the pores were exchanged with ethanol solvent, and mixed with ethanol solvent to perform solvent exchange. The frequency of solvent exchange was 3 hours each time, 4 exchanges per day, and the exchange time was 3 days to obtain a pretreated cobalt-based metal-organic framework material. The crystals were then vacuumed at 65°C for 10 hours to remove the free ethanol molecules in the pores to obtain a fully activated cobalt-based metal-organic framework material, and further performance tests were performed.

[0061] The specific surface area of ​​the cobalt-based metal organic framework material prepared in Example 1 was tested, and specifically a 77K nitrogen isothermal adsorption test was performed. The results are as follows: Figure 5 As shown. Figure 5 It can be seen that the nitrogen adsorption curve is a typical type I curve, and its maximum nitrogen adsorption capacity is 260cm 3 / g, BET specific surface area is 750m 2 / g.

[0062] Test Example 3

[0063] The cobalt-based metal organic framework material prepared in Example 1 has permanent pores and a stable structure. The cobalt-based metal organic framework material activated in Test Example 2 was subjected to an isothermal adsorption test of propylene and ethylene at 298K. The results are as follows: Figure 6 As shown. Figure 6 It can be seen that the cobalt-based metal organic framework material of the present invention has an adsorption capacity of 77.0 cm-1 of propylene at 298 K and 1 bar. 3 / g, and the adsorption capacity of ethylene is 32.0 cm 3 / g.

[0064] The IAST model was used to calculate the selectivity of propylene and ethylene two-component gases. The results are as follows: Figure 7 As shown. Figure 7 It can be seen that under the conditions of 298K and 1 bar, the cobalt-based metal organic framework material prepared in Example 1 has selectivities of 8.3, 9.0 and 9.7 for C3H6 / C2H4 two-component gases with molar ratios of 0.5 / 0.5, 0.2 / 0.5 and 0.1 / 0.9, respectively, and has good selectivity.

[0065] It can be seen from the above examples that the cobalt-based metal organic framework material provided by the present invention has the ability to selectively adsorb propylene in a mixture of propylene and ethylene, obtains polymer-grade ethylene by separation, and obtains high-purity propylene by desorption, and has good application prospects.

[0066] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A cobalt-based metal organic framework material, characterized in that: It includes a coordination metal and an organic ligand, wherein the coordination metal is Co 2+ , the organic ligand is 4,4'-(2,6-pyrazinediyl)dibenzoic acid.

2. The cobalt-based metal organic framework material according to claim 1, characterized in that The cobalt-based metal organic framework material is a (3,9)-connected three-dimensional framework structure: each Co 2+ The coordination mode is hexacoordinated, coordinated with one μ3-OH and the oxygen atoms of the carboxylic acid groups of four different organic ligands, and the remaining coordination site is occupied by one N atom in the pyrazine ring of the organic ligand.

3. The cobalt-based metal organic framework material according to claim 1 or 2, characterized in that: The cobalt-based metal organic framework material has a trinuclear cobalt cluster structural unit, which forms a nine-connected saturated coordination mode, each trinuclear cobalt cluster structural unit is connected to 9 organic ligands, and each organic ligand is connected to 3 trinuclear cobalt cluster structural units.

4. The cobalt-based metal organic framework material according to claim 1 or 2, characterized in that The topology type of the cobalt-based metal organic framework material is xmz topology.

5. The cobalt-based metal organic framework material according to claim 1 or 2, characterized in that: The specific surface area of ​​the cobalt-based metal organic framework material is 600 to 900 m 2 / g, the actual pore volume is 0.30~0.50cm 3 / g, and the porosity is 50-70%.

6. The method for preparing the cobalt-based metal organic framework material according to any one of claims 1 to 5, characterized in that: The following steps are involved: Cobalt salt, organic ligand, fluoroboric acid and solvent are mixed to carry out solvothermal reaction, wherein the organic ligand is 4,4'-(2,6-pyrazinediyl)dibenzoic acid, to obtain a cobalt-based metal organic framework material.

7. The preparation method according to claim 6, characterized in that: The molar ratio of the cobalt salt to the organic ligand is 1 to 3:

1.

8. The preparation method according to claim 6 or 7, characterized in that: The temperature of the solvent thermal reaction is 100-160° C., and the reaction time is 12-24 hours; the solvent thermal reaction is carried out under closed conditions.

9. Use of the cobalt-based metal organic framework material according to any one of claims 1 to 5 or the cobalt-based metal organic framework material obtained by the preparation method according to any one of claims 6 to 8 in propylene and ethylene separation.

10. The use according to claim 9, characterized in that: The cobalt-based metal organic framework material is activated before use, and the activation comprises the following steps: degassing and activating the cobalt-based metal organic framework material after solvent exchange.

Images