Rare earth cluster-based metal organic framework material for propylene / propane gas separation and preparation method of rare earth cluster-based metal organic framework material

Abstract

The invention provides a rare earth cluster-based metal organic framework material for propylene / propane gas separation and a preparation method of the rare earth cluster-based metal organic framework material. The chemical formula of the rare earth cluster-based metal organic framework material is REaXbK2Lc (H2O) d, 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; the structure center of the rare earth cluster-based metal organic framework material is a six-core rare earth cluster. The invention provides the rare earth cluster-based metal organic framework material with a specific structure, so that the rare earth cluster-based metal organic framework material has high adsorption separation ratio and volume propylene adsorption capacity, and can be used as an efficient gas adsorbent for separating propylene and propane.

Description

Technical Field

[0001] The invention belongs to the technical field of metal organic framework porous materials, and in particular relates to a rare earth cluster-based metal organic framework material for propylene / propane gas separation and a preparation method thereof. Background Art

[0002] Metal-organic framework (MOF) is a porous crystalline material that is self-assembled by metal as the crystal center and coordinated organic compounds as ligands through coordination bonds. Compared with traditional inorganic materials, MOF materials have the characteristics of regular pore structure, high porosity, large specific surface area, diverse and adjustable structure and performance. These characteristics make it have important application prospects in the fields of gas storage, gas separation, catalysis, luminescence, sensing and biomedicine.

[0003] Propylene and propane are two common hydrocarbon compounds. Since they are very similar in structure, the screening of the two is the most difficult to implement among hydrocarbon gases. The difficulty of separating propylene and propane mainly depends on the similarity of their physical properties. The difference in boiling points between the two is small, and their kinetic radii are similar, which makes them extremely difficult to separate.

[0004] In the petrochemical industry, propylene plays a key role in the manufacture of a variety of consumer products. Currently, propylene is mainly produced by thermal or catalytic cracking of hydrocarbons, in which propane coexists as a by-product. Due to the small difference in volatility between propylene and propane, screening using cryogenic distillation separation technology is considered to be the most energy-intensive single distillation technology in commercial technology. 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 separation of gases under ambient conditions using porous solid adsorbents has become a very promising solution.

[0005] The prior art discloses that 4A zeolite molecular sieve and 5A zeolite molecular sieve can achieve separation between propane and propylene by adopting pore sizes similar to the molecular sizes of propane and propylene. 4A zeolite molecular sieve can adsorb propylene but not propane, however, its adsorption kinetics for propylene are slow, which limits the applicability of 4A zeolite molecular sieve. In contrast, 5A zeolite molecular sieve can accommodate two gases, propane and propylene, and can thermodynamically screen the two gases, but its own selectivity is very low, at ~2. MOF materials have broad application prospects in the field of gas adsorption and separation due to their highly adjustable pore structure. In addition, MOF materials with target functional groups and / or pore sizes can be designed by topologically oriented pore size adjustment, which is crucial to whether the expected performance can be achieved.

[0006] Nowadays, many MOF materials have been applied to the adsorption and separation of propane / propylene gas, and the separation efficiency of some MOF materials is higher than that of traditional adsorbents. These MOF materials can be mainly divided into two categories: the first category is to use a specific type of adsorption site to selectively adsorb propylene, such as MOF-74 / CPO-27 materials have abundant unsaturated metal coordination sites on their channels, which can selectively bind to propylene instead of propane; the second category is to select MOF materials with optimal pore size as splitting agents, showing kinetic separation or more ideal selective molecular exclusion, such as KAUST-7 materials and Co-gallate materials, which can selectively adsorb propylene, but do not adsorb propane due to limited diffusion area, and their behavior is similar to 4A zeolite molecular sieve.

[0007] To date, MOF materials with unsaturated metal coordination centers generally show limited selectivity as these sites are rapidly saturated. In contrast, the few MOF materials that exhibit selective molecular rejection have high selectivity but correspondingly low natural adsorption capacities (typically <2 mmol / g) due to their limited porosity.

[0008] Therefore, in the art, there is an urgent need to develop an efficient gas adsorbent with high adsorption capacity and high selectivity. Summary of the invention

[0009] In view of the shortcomings of the prior art, the object of the present invention is to provide a rare earth cluster-based metal organic framework material for propylene / propane gas separation and a preparation method thereof. The present invention provides a rare earth cluster-based metal organic framework material with a specific structure, which has a high adsorption separation ratio and a volume propylene adsorption amount, so that it can be used as an efficient gas adsorbent for separating propylene and propane.

[0010] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[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 , wherein RE is a rare earth metal element, X is a 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;

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

[0013] In the present 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] Firstly, the present invention regulates the specific structure of the rare earth cluster-based metal-organic framework material. Due to the introduction of tetracarboxylic acid organic ligands, the structure of the rare earth cluster-based metal-organic framework material has small windows and large pores. On the one hand, the small windows allow propylene to enter and can eventually be used to screen 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, thereby ultimately improving the adsorption capacity of the rare earth cluster-based metal-organic framework material.

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

[0016] In the present invention, the rare earth cluster-based metal organic framework material with the above chemical formula structure is synthesized by regulation, so as to further improve its separation performance for propylene and propane, and to increase its volume adsorption capacity for propylene.

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

[0018] Preferably, the halogen comprises fluorine.

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

[0020] In the present 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 pores so as to allow propylene to pass through while blocking propane.

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

[0022] The hexanuclear halogen bridged rare earth cluster solution is mixed with the tetracarboxylic acid organic ligand solution, and the rare earth cluster-based metal organic framework material is obtained after 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 comprises ethyl acetate.

[0025] Preferably, the concentration of the hexanuclear halogen-bridged rare earth cluster solution is 16-40 mg / mL, preferably 25-30 mg / mL, 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 the present invention, the concentration of the hexanuclear halogen-bridged rare earth cluster solution is regulated so that it can be dissolved in the corresponding solvent. Too low a concentration will affect the degree of reaction, whereas excessive precipitation will occur, 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, so as to achieve the effect of making the rare earth cluster-based metal organic framework material have 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, 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 the present invention, the concentration of the organic ligand solution is regulated so that it can be dissolved in the corresponding solvent. Too low a concentration will affect the degree of reaction, whereas excessive precipitation will occur, affecting the purity of the reactants.

[0032] Preferably, the volume ratio of the hexanuclear halogen-bridged rare earth cluster solution to the tetracarboxylic acid organic ligand solution is 1:(1-5), preferably 1:3, 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 the present 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 the present 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°C, preferably 40°C, for example, it can be 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc.; the reaction time is 10s-24h, for example, it can be 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] In a third aspect, the present invention provides a gas adsorbent for separating propylene and propane, wherein the gas adsorbent for separating propylene and propane comprises the rare earth cluster-based metal organic framework material according to the first aspect.

[0038] The rare earth cluster metal organic framework material provided by the present invention not only has a high adsorption separation ratio (molecular sieve material, can adsorb propylene, but not propane), but also has the highest volumetric propylene adsorption capacity to date (single 94cm 3 / cm 3 ).

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

[0040] The present invention provides a rare earth cluster-based metal organic framework material. Firstly, the present invention adjusts the specific structure of the rare earth cluster-based metal organic framework material. Due to the introduction of tetracarboxylic acid organic ligands, the structure of the rare earth cluster-based metal organic framework material has a small window and a large cavity. On the one hand, the small window allows propylene to enter, and can eventually be used to screen propane, thereby improving the adsorption selectivity of the rare earth cluster-based metal organic framework material; on the other hand, the large cavity is used to store a large amount of propylene, thereby finally improving the adsorption capacity of the rare earth cluster-based metal organic framework material. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0042] Figure 2 The PXRD diffraction pattern of the rare earth cluster metal organic framework material in Example 1 of the present invention;

[0043] Figure 3 The PXRD diffraction patterns of the rare earth cluster metal organic framework material before and after soaking in water in Example 2 of the present invention;

[0044] Figure 4 195K carbon dioxide and 77K nitrogen adsorption curves of the rare earth cluster metal organic framework material in Example 1 of the present invention;

[0045] Figure 5 195K carbon dioxide and 77K nitrogen adsorption curves of the rare earth cluster metal organic framework material in Example 2 of the present invention;

[0046] Figure 6 This is a comparison chart of the adsorption of propylene and propane by the rare earth cluster metal organic framework material at 298K in Example 1 of the present invention;

[0047] Figure 7 This is a comparison chart of the adsorption of propylene and propane by the rare earth cluster metal organic framework material at 298K in Example 2 of the present invention;

[0048] Figure 8 This is the breakthrough curve of the rare earth cluster metal organic framework material in Example 1 of the present invention for a propylene-propane mixed gas with a concentration ratio of 1:1 at a temperature of 298K. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is further described below by combining the accompanying drawings and specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0050] The preparation method of the hexanuclear fluorine-bridged rare earth cluster in the examples and comparative examples of the present invention refers to the preparation method in CN111292909A, and exemplarily includes the following steps:

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

[0052] The rare earth metal source is a rare earth metal salt, a rare earth metal oxide or a rare earth metal element; the fluorine source is hydrofluoric acid, a metal fluoride or an 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. The chemical formula of the rare earth cluster-based metal organic framework material is Gd6F8K2L6(H2O)6, and L is a 3,3',5,5'-biphenyltetracarboxylic acid organic ligand.

[0055] This embodiment also provides a method for preparing the above rare earth cluster-based metal organic framework material, which comprises 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] The hexanuclear fluorine-bridged rare earth cluster solution and the tetracarboxylic acid organic ligand solution in a volume ratio of 1:3 were mixed at 40°C and reacted for 12 hours to obtain a structure such as Figure 1 The rare earth cluster-based metal-organic framework material is 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. The chemical formula of the rare earth cluster-based metal organic framework material is 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 rare earth cluster-based metal organic framework material, which comprises the following steps:

[0062] Dissolve 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;

[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 hexanuclear fluorine-bridged rare earth cluster solution and a tetracarboxylic acid organic ligand solution in a volume ratio of 1:3 were mixed at 40° C. and reacted for 12 hours 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 embodiment 1 is that the concentration of the hexanuclear fluorine-bridged rare earth cluster solution is 25 mg / mL, and the other aspects are the same as those of embodiment 1.

[0068] Example 4

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

[0070] Example 5

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

[0072] Example 6

[0073] The difference between this embodiment and embodiment 1 is that the tetracarboxylic acid organic ligand is replaced by dipotassium terephthalate, and the rest is the same as embodiment 1.

[0074] Example 7

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

[0076] Example 8

[0077] The difference between this embodiment and embodiment 1 is that the volume ratio of the hexanuclear fluorine-bridged rare earth cluster solution to the tetracarboxylic acid organic ligand solution is 1:5, and the other aspects are the same as those of embodiment 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, and the other aspects are the same as those of 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 solution to the tetracarboxylic acid organic ligand solution is 1:8, and the other aspects are the same as those of embodiment 2.

[0082] Comparative Example 1

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

[0084] Comparative Example 2

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

[0086] Comparative Example 3

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

[0088] Comparative Example 4

[0089] This comparative example provides a rare earth cluster metal organic framework material, the chemical formula of the rare earth cluster metal organic framework material is 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 is determined by powder X-ray diffraction method, and the porous structure and adsorption performance of the prepared rare earth cluster-based metal-organic framework material are characterized by BET specific surface area method, 195K carbon dioxide and 77K nitrogen adsorption method.

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

[0093] Depend on Figure 6-Figure 7 As shown, the rare earth cluster metal organic framework materials provided by the present invention have good propylene propane molecular sieving performance and have a very high sieving ratio. Figure 7 For example, the material of Example 2 can adsorb 66.4 cm at 25 degrees Celsius and 1 atmosphere. 3 / g of propylene, while propane 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 penetration test on a propylene-propane mixed gas with a concentration ratio of 1:1 at a temperature of 298K, propane penetrated from the beginning, while propylene only began to penetrate at nearly 30 minutes, indicating 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 illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by 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 metal organic framework material is RE a X b K2L c (H2O) d , wherein RE is a rare earth metal element, X is a 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; 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 chemical formula of the rare earth cluster-based metal organic framework material is RE6X8K2L6(H2O)6.

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

4. The rare earth cluster metal organic framework material according to any one of claims 1 to 3, characterized in that: The halogen includes fluorine.

5. The rare earth cluster-based metal organic framework material according to any one of claims 1 to 4, characterized in that: The tetracarboxylic acid organic ligand includes 3,3',5,5'-biphenyltetracarboxylic acid.

6. A method for preparing a rare earth cluster-based metal organic framework material according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: The hexanuclear halogen bridged rare earth cluster solution is mixed with the tetracarboxylic acid organic ligand solution, and the rare earth cluster-based metal organic framework material is obtained after reaction.

7. The method according to claim 6, characterized in that The hexanuclear halogen-bridged rare earth cluster solution comprises a hexanuclear halogen-bridged rare earth cluster and a first solvent; Preferably, the first solvent comprises ethyl acetate; Preferably, the concentration of the hexanuclear halogen-bridged rare earth cluster solution is 16-40 mg / mL, preferably 25-30 mg / mL.

8. The method according to claim 6 or 7, characterized in that: The tetracarboxylic acid organic ligand solution comprises a tetracarboxylic acid organic ligand potassium salt and a second solvent; Preferably, the tetracarboxylic acid organic ligand potassium salt includes tetrapotassium 3,3',5,5'-biphenyltetracarboxylate; Preferably, the second solvent comprises water; Preferably, the concentration of the tetracarboxylic acid organic ligand solution is 5-15 mg / mL, preferably 8-12 mg / mL.

9. The method according to any one of claims 6 to 8, 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), preferably 1:3; Preferably, the reaction temperature is 0-100°C, preferably 40°C, and the reaction time is 10s-24h; Preferably, the reaction is carried out under stirring.

10. A gas adsorbent for separating propylene and propane, characterized in that: The gas adsorbent for separating propylene and propane comprises the rare earth cluster-based metal organic framework material according to any one of claims 1-5.

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