A rare earth cluster metal-organic framework material for propylene / propane gas separation and a preparation method thereof

Abstract

The application provides a rare earth cluster metal organic framework material for propylene / propane gas separation and a preparation method thereof. The chemical formula of the rare earth cluster metal organic framework material is RE a X b K2L c (H2O) d wherein RE is a rare earth metal element, X is halogen, and L is a tetracarboxylic acid organic ligand; wherein a is greater than 2, b is greater than or equal to 4, c is greater than or equal to 2, and d is greater than or equal to 2; and the structure center of the rare earth cluster metal organic framework material is a hexanuclear rare earth cluster. The application provides a rare earth cluster metal organic framework material with a specific structure, so that the material has a high adsorption separation ratio and a volume propylene adsorption amount, and can be used as a high-efficiency gas adsorbent for separating propylene and propane.

Description

Technical Field

[0001] This invention belongs to the field of metal-organic framework porous materials technology, specifically relating to a rare earth cluster-based metal-organic framework material for propylene / propane gas separation and its preparation method. Background Technology

[0002] Metal-organic frameworks (MOFs) are porous crystalline materials that self-assemble by using a metal as the crystal center and coordinating organic compounds as ligands, linked by coordinate bonds. Compared to traditional inorganic materials, MOFs possess characteristics such as regular pore structure, high porosity, large specific surface area, diverse and tunable structures and properties. These properties make them promising for applications in gas storage, gas separation, catalysis, luminescence, sensing, and biomedicine.

[0003] Propylene and propane are two common hydrocarbon compounds. Due to their very similar structures, their separation is currently the most difficult among hydrocarbon gases. The difficulty in separating propylene and propane mainly depends on the similarity of their physical properties. Their boiling points are very similar, and their kinetic radii are also similar, making them extremely difficult to separate.

[0004] In the petrochemical industry, propylene plays a crucial role in the manufacture of various consumer products. Currently, propylene is mainly produced through the thermal cracking or catalytic cracking of hydrocarbons, with propane as a co-product. Due to the very small difference in volatility between propylene and propane, cryogenic distillation separation is considered the most energy-intensive single distillation technique in commercial applications. Therefore, there is an urgent need to develop an alternative separation method with low energy input and low carbon emissions. In recent years, the adsorption and separation of gases using porous solid adsorbents under environmental conditions has emerged as a promising solution.

[0005] Existing technologies disclose that 4A and 5A zeolite molecular sieves can achieve the separation of propane and propylene by employing pore sizes similar to those of propane and propylene molecules. 4A zeolite molecular sieves can adsorb propylene but not propane; however, their adsorption kinetics for propylene are slow, limiting their applicability. In contrast, 5A zeolite molecular sieves can accommodate both propane and propylene and can thermodynamically separate these two gases, but their selectivity is very low, ~2. MOF materials, due to their highly tunable pore structure, have broad application prospects in gas adsorption and separation. Furthermore, MOF materials with targeted functional groups and / or pore sizes can be designed through topologically oriented pore size adjustment, which is crucial for achieving the desired performance.

[0006] Currently, many MOF materials have been applied to the adsorption and separation of propane / propylene gases, with some MOF materials exhibiting higher separation efficiencies than traditional adsorbents. These MOF materials can be mainly divided into two categories: the first category utilizes specific types of adsorption sites to selectively adsorb propylene, such as MOF-74 / CPO-27 materials, which have abundant unsaturated metal coordination sites in their channels, allowing them to selectively bind to propylene rather than propane; the second category selects MOF materials with optimal pore sizes as splitting agents, exhibiting kinetic separation or more ideal selective molecular repulsion, such as KAUST-7 materials and Co-gallate materials, which can selectively adsorb propylene but not propane due to limited diffusion areas, exhibiting behavior similar to 4A zeolite molecular sieves.

[0007] To date, MOF materials with unsaturated metal coordination centers typically exhibit limited selectivity when these sites are rapidly saturated. Conversely, a few MOF materials exhibiting selective molecular repulsion possess high selectivity, but due to their limited porosity, their native adsorption capacity is correspondingly low (typically <2 mmol / g).

[0008] Therefore, there is an urgent need in this field to develop a highly efficient gas adsorbent with high adsorption capacity and high selectivity. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a rare-earth cluster-based metal-organic framework material for propylene / propane gas separation and its preparation method. The present invention provides a rare-earth cluster-based metal-organic framework material with a specific structure, exhibiting a high adsorption-to-separation ratio and high volumetric propylene adsorption capacity, thereby enabling it to serve as a highly efficient gas adsorbent for separating propylene and propane.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a rare earth cluster-based metal-organic framework material, wherein the chemical formula of the rare earth cluster-based metal-organic framework material is RE. a X b K2L c (H2O) d In this context, RE represents rare earth metal elements, X represents halogens, and L represents tetracarboxylic acid organic ligands; where a is greater than 2, b is greater than or equal to 4, c is greater than or equal to 2, and d is greater than or equal to 2.

[0012] The structural center of the rare earth cluster-based metal-organic framework material is a hexanuclear rare earth cluster.

[0013] In this invention, a is greater than 2, for example, it can be 3, 4, 5, 6, 7, 8, etc.; b is greater than or equal to 4, for example, it can be 5, 6, 7, 8, 9, etc.; c is greater than or equal to 2, for example, it can be 3, 4, 5, 6, 7, 8, etc.; d is greater than or equal to 2, for example, it can be 3, 4, 5, 6, 7, 8, etc.

[0014] First, this invention modulates the specific structure of rare earth cluster-based metal-organic framework materials. Due to the introduction of tetracarboxylic acid organic ligands, the structure of rare earth cluster-based metal-organic framework materials has small windows and large pores. On the one hand, the small windows allow propylene to enter, which can ultimately be used to screen propane, thereby improving the adsorption selectivity of rare earth cluster-based metal-organic framework materials. On the other hand, the large pores are used to store a large amount of propylene, which ultimately improves the adsorption capacity of rare earth cluster-based metal-organic framework materials.

[0015] Preferably, the rare earth cluster-based metal-organic framework material has the chemical formula RE6X8K2L6(H2O)6.

[0016] In this invention, by controlling the synthesis of rare earth cluster-based metal-organic framework materials with the above-mentioned chemical formula, their separation performance for propylene and propane is further improved, as well as their volumetric adsorption capacity for propylene is increased.

[0017] Preferably, the rare earth metal element includes gadolinium and / or yttrium.

[0018] Preferably, the halogen includes fluorine.

[0019] Preferably, the tetracarboxylic acid organic ligand comprises 3,3',5,5'-biphenyltetracarboxylic acid.

[0020] In this invention, a specific type of ligand of 3,3',5,5'-biphenyltetracarboxylic acid is selected in order to precisely control the window size of the internal cavity so that propylene can pass through while propane is blocked.

[0021] In a second aspect, the present invention provides a method for preparing rare earth cluster-based metal-organic framework materials according to the first aspect, the method comprising the following steps:

[0022] A solution of a hexanuclear halogen-bridged rare earth cluster compound was mixed with a solution of a tetracarboxylic acid organic ligand, and the rare earth cluster-based metal-organic framework material was obtained after the reaction.

[0023] Preferably, the hexanuclear halogen-bridged rare earth cluster solution comprises a hexanuclear halogen-bridged rare earth cluster and a first solvent.

[0024] Preferably, the first solvent includes ethyl acetate.

[0025] Preferably, the concentration of the hexanuclear halogen-bridged rare earth cluster solution is 16-40 mg / mL, more preferably 25-30 mg / mL, and for example, it can be 16 mg / mL, 18 mg / mL, 20 mg / mL, 21 mg / mL, 22 mg / mL, 23 mg / mL, 24 mg / mL, 25 mg / mL, 26 mg / mL, 27 mg / mL, 28 mg / mL, 29 mg / mL, 30 mg / mL, 32 mg / mL, 35 mg / mL, 40 mg / mL, etc.

[0026] In this invention, the concentration of the hexanuclear halogen-bridged rare earth cluster solution is adjusted so that it can dissolve in the corresponding solvent. If the concentration is too low, it will affect the degree of reaction; otherwise, it will precipitate in excess, affecting the purity of the reactants.

[0027] Preferably, the tetracarboxylic acid organic ligand solution comprises a tetracarboxylic acid organic ligand potassium salt and a second solvent.

[0028] Preferably, the tetracarboxylic acid organic ligand potassium salt includes tetrapotassium 3,3',5,5'-biphenyltetracarboxylate, thereby achieving the effect of giving the rare earth cluster-based metal-organic framework material good adsorption performance.

[0029] Preferably, the second solvent comprises water.

[0030] Preferably, the concentration of the tetracarboxylic acid organic ligand solution is 5-15 mg / mL, more preferably 8-12 mg / mL, for example, it can be 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL, 10 mg / mL, 11 mg / mL, 12 mg / mL, 13 mg / mL, 14 mg / mL, 15 mg / mL, etc.

[0031] In this invention, the concentration of the organic ligand solution is controlled so that it can dissolve in the corresponding solvent. If the concentration is too low, it will affect the degree of reaction; otherwise, it will precipitate in excess, affecting the purity of the reactants.

[0032] Preferably, the volume ratio of the hexanuclear halogen-bridged rare earth cluster compound solution to the tetracarboxylic acid organic ligand solution is 1:(1-5), preferably 1:3, and for example, it can be 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, 1:3.2, 1:3.5, 1:3.8, 1:4, 1:4.2, 1:4.5, 1:4.8, 1:5, etc.

[0033] In this invention, when the hexanuclear halogen-bridged rare earth cluster solution is a hexanuclear halogen-bridged gadolinium cluster solution, the volume ratio of the hexanuclear halogen-bridged gadolinium cluster solution to the tetracarboxylic acid organic ligand solution is 1:(1-1.2), for example, it can be 1:1, 1:1.02, 1:1.05, 1:1.08, 1:1.1, 1:1.12, 1:1.15, 1:1.18, 1:1.2, etc.

[0034] In this invention, when the hexanuclear halogen-bridged rare earth cluster solution is a hexanuclear halogen-bridged yttrium cluster solution, the volume ratio of the hexanuclear halogen-bridged yttrium cluster solution to the tetracarboxylic acid organic ligand solution is 1:(3-5), for example, it can be 1:3, 1:3.2, 1:3.5, 1:3.8, 1:4, 1:4.2, 1:4.5, 1:4.8, 1:5, etc.

[0035] Preferably, the reaction temperature is 0-100℃, more preferably 40℃, and can be, for example, 0℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, etc.; the time is 10s-24h, for example, 10s, 20s, 50s, 60s, 1min, 10min, 30min, 50min, 1h, 5h, 10h, 12h, 15h, 18h, 20h, 22h, 24h, etc.

[0036] Preferably, the reaction is carried out under stirring.

[0037] Thirdly, the present invention provides a gas adsorbent for separating propylene and propane, said gas adsorbent comprising the rare earth cluster-based metal-organic framework material according to the first aspect.

[0038] The rare-earth cluster-based metal-organic framework material provided by this invention not only has a high adsorption-to-separation ratio (molecular sieve material, capable of adsorbing propylene but not propane), but also possesses the highest volumetric propylene adsorption capacity to date (94 cm⁻¹). 3 / cm 3 ).

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] This invention provides a rare-earth cluster-based metal-organic framework material. First, by controlling the specific structure of the rare-earth cluster-based metal-organic framework material, the introduction of a tetracarboxylic acid organic ligand results in a structure with small windows and large pores. On the one hand, the small windows allow propylene to enter, ultimately enabling the screening of propane, thereby improving the adsorption selectivity of the rare-earth cluster-based metal-organic framework material. On the other hand, the large pores are used to store a large amount of propylene, ultimately improving the adsorption capacity of the rare-earth cluster-based metal-organic framework material. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the pore structure of the rare earth cluster-based metal-organic framework material in this invention;

[0042] Figure 2 This is the PXRD diffraction pattern of the rare earth cluster-based metal-organic framework material in Example 1 of this invention;

[0043] Figure 3 The above are PXRD diffraction patterns of the rare earth cluster-based metal-organic framework material in Example 2 of this invention before and after soaking in water.

[0044] Figure 4 The adsorption curves of carbon dioxide at 195K and nitrogen at 77K for the rare earth cluster-based metal-organic framework material in Example 1 of this invention are shown.

[0045] Figure 5 The adsorption curves of carbon dioxide at 195K and nitrogen at 77K for the rare earth cluster-based metal-organic framework material in Example 2 of this invention are shown.

[0046] Figure 6 This is a comparison chart of the adsorption amounts of propylene and propane in the rare earth cluster-based metal-organic framework material in Example 1 of this invention at 298K.

[0047] Figure 7 This is a comparison chart of the adsorption amounts of propylene and propane in the rare earth cluster-based metal-organic framework material at 298K in Example 2 of this invention.

[0048] Figure 8 This is the breakthrough curve of the rare earth cluster-based metal-organic framework material in Example 1 of the present invention against a propylene-propane mixture with a concentration ratio of 1:1 at 298K. Detailed Implementation

[0049] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0050] The preparation method of the hexanuclear fluorine-bridged rare earth clusters in the embodiments and comparative examples of this invention refers to the preparation method in CN111292909A, and includes the following exemplary steps:

[0051] A rare earth metal source is uniformly dispersed in an organic solvent, and then a fluorine source is added to the organic solvent containing the rare earth metal to obtain reaction system A. Reaction system A is subjected to a thermal reaction in an organic solvent at 80–160 °C for 24–72 h. After the thermal reaction, the supernatant of reaction system A is filtered, crystallized at low temperature, and washed to obtain a hexanuclear fluorine-bridged rare earth cluster.

[0052] The rare earth metal source is a rare earth metal salt, rare earth metal oxide, or rare earth metal element; the fluorine source is hydrofluoric acid, metal fluoride, or ammonium fluoride; the mass ratio of the rare earth metal source to the fluorine source is (20-5):1; the organic solvent is dimethylformamide, methanol, acetonitrile, dimethyl sulfoxide, ethanol, or ethyl acetate.

[0053] Example 1

[0054] This embodiment provides a rare earth cluster-based metal-organic framework material with the chemical formula Gd6F8K2L6(H2O)6, where L is a 3,3',5,5'-biphenyltetracarboxylic acid organic ligand.

[0055] This embodiment also provides a method for preparing the above-mentioned rare earth cluster-based metal-organic framework material, which includes the following steps: dissolving 30 mg of hexanuclear fluorine-bridged rare earth cluster compound in 3 mL of ethyl acetate to obtain a hexanuclear fluorine-bridged rare earth cluster compound solution;

[0056] Dissolve 23 mg of tetrapotassium 3,3',5,5'-biphenyltetracarboxylate in 3 mL of water to obtain a tetracarboxylic acid organic ligand solution;

[0057] A solution of a hexanuclear fluorine-bridged rare earth cluster compound (volume ratio 1:3) was mixed with a tetracarboxylic acid organic ligand solution at 40 °C, and the reaction was carried out for 12 h to obtain the structure shown below. Figure 1 The rare earth cluster-based metal-organic framework material shown.

[0058] from Figure 2 It can be seen that the rare earth cluster-based metal-organic framework material in Example 1 is basically consistent with the simulation results.

[0059] Example 2

[0060] This embodiment provides a rare earth cluster-based metal-organic framework material with the chemical formula Y6F8K2L6(H2O)6, where L is a 3,3',5,5'-biphenyltetracarboxylic acid organic ligand.

[0061] This embodiment also provides a method for preparing the above-mentioned rare earth cluster-based metal-organic framework material, which includes the following steps:

[0062] 30 mg of hexanuclear fluorine-bridged rare earth cluster compound was dissolved in 3 mL of ethyl acetate to obtain a hexanuclear fluorine-bridged rare earth cluster compound solution;

[0063] Dissolve 69 mg of tetrapotassium 3,3',5,5'-biphenyltetracarboxylate in 9 mL of water to obtain a tetracarboxylic acid organic ligand solution;

[0064] A solution of hexanuclear fluorine-bridged rare earth cluster compound with a tetracarboxylic acid organic ligand in a volume ratio of 1:3 was mixed at 40°C and reacted for 12 h to obtain the rare earth cluster-based metal-organic framework material.

[0065] from Figure 3 It can be seen that the rare earth cluster-based metal-organic framework material in Example 2 is basically consistent with the simulation results.

[0066] Example 3

[0067] The difference between this embodiment and Example 1 is that the concentration of the hexanuclear fluorine-bridged rare earth cluster compound solution is 25 mg / mL, while all other aspects are the same as in Example 1.

[0068] Example 4

[0069] The difference between this embodiment and Example 1 is that the concentration of the hexanuclear fluorine-bridged rare earth cluster compound solution is 30 mg / mL, while all other aspects are the same as in Example 1.

[0070] Example 5

[0071] The difference between this embodiment and Example 1 is that the concentration of the hexanuclear fluorine-bridged rare earth cluster compound solution is 15 mg / mL, while all other aspects are the same as in Example 1.

[0072] Example 6

[0073] The difference between this embodiment and Example 1 is that the tetracarboxylic acid organic ligand is replaced with dipotassium terephthalate, while all other aspects are the same as in Example 1.

[0074] Example 7

[0075] The difference between this embodiment and Example 1 is that the volume ratio of the hexanuclear fluorine-bridged rare earth cluster compound solution to the tetracarboxylic acid organic ligand solution is 1:0.5, while all other aspects are the same as in Example 1.

[0076] Example 8

[0077] The difference between this embodiment and Example 1 is that the volume ratio of the hexanuclear fluorine-bridged rare earth cluster compound solution to the tetracarboxylic acid organic ligand solution is 1:5, while all other aspects are the same as in Example 1.

[0078] Example 9

[0079] The difference between this embodiment and Embodiment 2 is that the volume ratio of the hexanuclear fluorine-bridged rare earth cluster solution to the tetracarboxylic acid organic ligand solution is 1:1, while all other aspects are the same as in Embodiment 2.

[0080] Example 10

[0081] The difference between this embodiment and Embodiment 2 is that the volume ratio of the hexanuclear fluorine-bridged rare earth cluster compound solution to the tetracarboxylic acid organic ligand solution is 1:8, while all other aspects are the same as in Embodiment 2.

[0082] Comparative Example 1

[0083] This comparative example provides a rare-earth cluster-based metal-organic framework material with the chemical formula Gd6F8L. 12 (H2O)6.

[0084] Comparative Example 2

[0085] This comparative example provides a rare-earth cluster-based metal-organic framework material with the chemical formula Y6F8L. 12 (H2O)6.

[0086] Comparative Example 3

[0087] This comparative example provides a rare-earth cluster-based metal-organic framework material with the chemical formula Gd6F8L. 12 (DMF)6.

[0088] Comparative Example 4

[0089] This comparative example provides a rare-earth cluster-based metal-organic framework material with the chemical formula Y6F8L. 12 (DMF)6.

[0090] Test conditions

[0091] In the embodiments and comparative examples of the present invention, the crystal structure of the prepared rare earth cluster-based metal-organic framework material was determined by powder X-ray diffraction, and the porous structure and adsorption performance of the prepared rare earth cluster-based metal-organic framework material were characterized by BET specific surface area method, carbon dioxide adsorption at 195 K and nitrogen adsorption at 77 K.

[0092] from Figures 4-5 It can be seen that the rare earth cluster-based metal-organic framework material provided by this invention has a strong adsorption effect on carbon dioxide with a small kinetic radius, but hardly adsorbs nitrogen.

[0093] Depend on Figures 6-7 As shown, the rare-earth cluster-based metal-organic framework materials provided by this invention all exhibit excellent propylene and propane molecular sieving performance and have extremely high sieving ratios. Figure 7 For example, in Example 2, the material can adsorb 66.4 cm³ of [material name missing] at 25 degrees Celsius and 1 atmosphere. 3 / g of propylene, while propane under these conditions can only adsorb 0.3cm. 3 / g.

[0094] from Figure 8 It can be seen that when the rare earth cluster-based metal-organic framework material in Example 1 was subjected to a breakthrough test at 298K on a propylene-propane mixture with a concentration ratio of 1:1, propane broke through from the beginning, while propylene only began to break through after nearly 30 minutes. This indicates that the rare earth cluster-based metal-organic framework material provided by the present invention can preferentially adsorb propylene in the mixed gas.

[0095] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A rare-earth cluster-based metal-organic framework material, characterized in that, The chemical formula of the rare earth cluster-based metal-organic framework material is RE6X8K2L6(H2O)6, where RE is a rare earth metal element, X is a halogen, and L is a tetracarboxylic acid organic ligand. The tetracarboxylic acid organic ligand is 3,3',5,5'-biphenyltetracarboxylic acid; The structural center of the rare earth cluster-based metal-organic framework material is a hexanuclear rare earth cluster.

2. The rare earth cluster-based metal-organic framework material according to claim 1, characterized in that, The rare earth metal elements include gadolinium and / or yttrium.

3. The rare earth cluster-based metal-organic framework material according to claim 1, characterized in that, The halogens include fluorine.

4. A method for preparing rare earth cluster-based metal-organic framework materials according to any one of claims 1-3, characterized in that, The method includes the following steps: A solution of a hexanuclear halogen-bridged rare earth cluster compound was mixed with a solution of a tetracarboxylic acid organic ligand, and the rare earth cluster-based metal-organic framework material was obtained after the reaction.

5. The method according to claim 4, characterized in that, The hexanuclear halogen-bridged rare earth cluster solution comprises a hexanuclear halogen-bridged rare earth cluster and a first solvent.

6. The method according to claim 5, characterized in that, The first solvent includes ethyl acetate.

7. The method according to claim 4, characterized in that, The concentration of the hexanuclear halogen-bridged rare earth cluster solution is 16-40 mg / mL.

8. The method according to claim 7, characterized in that, The concentration of the hexanuclear halogen-bridged rare earth cluster solution is 25-30 mg / mL.

9. The method according to claim 4, characterized in that, The tetracarboxylic acid organic ligand solution comprises a tetracarboxylic acid organic ligand potassium salt and a second solvent.

10. The method according to claim 9, characterized in that, The tetracarboxylic acid organic ligand potassium salt includes tetrapotassium 3,3',5,5'-biphenyltetracarboxylate.

11. The method according to claim 9, characterized in that, The second solvent includes water.

12. The method according to claim 4, characterized in that, The concentration of the tetracarboxylic acid organic ligand solution is 5-15 mg / mL.

13. The method according to claim 12, characterized in that, The concentration of the tetracarboxylic acid organic ligand solution is 8-12 mg / mL.

14. The method according to claim 4, characterized in that, The volume ratio of the hexanuclear halogen-bridged rare earth cluster solution to the tetracarboxylic acid organic ligand solution is 1:(1-5).

15. The method according to claim 14, characterized in that, The volume ratio of the hexanuclear halogen-bridged rare earth cluster solution to the tetracarboxylic acid organic ligand solution is 1:

3.

16. The method according to claim 4, characterized in that, The reaction temperature is 0-100℃.

17. The method according to claim 16, characterized in that, The reaction was carried out at a temperature of 40°C.

18. The method according to claim 4, characterized in that, The reaction time is 10s-24h.

19. The method according to claim 4, characterized in that, The reaction was carried out under stirring.

20. A gas adsorbent for separating propylene and propane, characterized in that, The gas adsorbent for separating propylene and propane includes the rare earth cluster-based metal-organic framework material according to any one of claims 1-3.

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