A Zn-MOF microporous crystal material and its preparation method and application in gas separation

Abstract

The present invention relates to the technical field of three-dimensional porous framework crystal materials, and particularly relates to a Zn-MOF microporous crystal material, a preparation method thereof, and an application thereof in gas separation. The molecular formula is [Zn2(PMA)(TPB)] ·x H2O, where PMA is deprotonated 1,2,4,5-benzenetetracarboxylic acid, and TPB is 1,2,4,5-(4-pyridyl)benzene. The Zn-MOF microporous crystal material is formed by the coordination of Zn with the oxygen atoms of 1,2,4,5-benzenetetracarboxylic acid and the N atoms of 1,2,4,5-(4-pyridyl)benzene. The Zn-MOF microporous crystal material has a three-dimensional framework structure. The Zn-MOF microporous crystal material can be applied in the field of ethylene separation and purification.

Description

Technical Field

[0001] The invention relates to the technical field of three-dimensional porous framework crystal materials, and in particular to a Zn-MOF microporous crystal material and a preparation method thereof and application in gas separation. Background Art

[0002] Ethylene is an important light olefin and an important raw material in the chemical industry. It has a wide range of uses and is one of the main raw materials for the three major synthetic materials of plastics, synthetic rubber and synthetic fibers. When used, the purity of ethylene is usually required to reach more than 99.9%. However, in the process of producing ethylene (C2H4), impurity gases such as ethane (C2H6), acetylene (C2H2), and carbon dioxide are often produced. Therefore, in order to meet the requirements of downstream industries for olefin purity, these impurity gases must be removed. At present, cryogenic distillation is the main method for separating and purifying ethylene. This method has high energy consumption and large equipment investment. Therefore, how to achieve efficient separation and purification of ethylene under milder conditions is of great significance.

[0003] Metal-organic framework (MOF) is a new type of three-dimensional porous material obtained by self-assembly of organic ligands and metal ions or metal clusters. Compared with traditional porous materials (such as zeolites, activated carbon, etc.), MOF has the advantages of orderly pore structure, large specific surface area, and adjustable and modifiable structure. It is a porous material that has developed very rapidly in recent years. MOF has potential application value in the field of gas adsorption and separation. Although MOF materials have made some research progress in the field of selective separation and purification of olefins in recent years, current research mainly focuses on the separation of two-component mixed gases, and there are still few results on the one-step separation and purification of olefins in three-component mixed gases. Many MOF materials have disadvantages such as low adsorption capacity, low separation ratio, poor material stability and high synthesis cost, which seriously restricts the practical application of MOF materials. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of low adsorption capacity, poor separation selectivity and low water stability of MOF materials in the separation and purification of light olefins, which restrict their practical application, and provide a Zn-MOF microporous crystal material and a preparation method thereof and application in gas separation. The Zn-MOF microporous crystal material has high separation selectivity for mixed gases such as acetylene and ethylene, carbon dioxide gas and ethylene.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0006] A Zn-MOF microporous crystalline material, the molecular formula is [Zn2(PMA)(TPB)] xH2O, wherein PMA is deprotonated 1,2,4,5-pyromellitic acid, TPB is 1,2,4,5-(4-pyridyl)benzene, and the Zn-MOF microporous crystalline material is formed by the coordination of Zn with the oxygen atom of 1,2,4,5-pyromellitic acid and the N atom of 1,2,4,5-(4-pyridyl)benzene, and the Zn-MOF microporous crystalline material has a three-dimensional framework structure.

[0007] Furthermore, the crystal structure of the Zn-MOF microporous crystal material belongs to the triclinic system, the space group is P-1, the unit cell parameters are as follows: a=8.911 Å, b=9.646 Å, c=13.672 Å, α=69.77°, β=79.64°, γ=76.75°, and the unit cell volume is 1066.8 Å 3 .

[0008] Furthermore, in the three-dimensional framework of Zn-MOF, each Zn 2+ The four nitrogen atoms on each TPB ligand and the four Zn atoms on each TPB ligand form a tetrahedral coordination geometry. 2+ Coordination; Each PMA 4- and four Zn 2+ coordination;

[0009] Two adjacent PMAs 4- The ligands share two Zn 2+ A one-dimensional chain structure unit is formed by the above connection method, and four adjacent one-dimensional chain structure units are connected by TPB to form a three-dimensional framework structure by the above connection method.

[0010] Furthermore, in the three-dimensional framework of Zn-MOF, there are one-dimensional channels of 4.9×6.4 Å along the a-axis and 5.0×6.8 Å along the b-axis.

[0011] The present invention also provides a method for preparing the Zn-MOF microporous crystalline material, comprising the following steps:

[0012] The inorganic salt of Zn, 1,2,4,5-pyromellitic acid and 1,2,4,5-(4-pyridyl)benzene are uniformly dispersed in a deionized water solvent system for hydrothermal reaction synthesis. After the reaction is completed, the reaction product is post-treated to obtain the target product.

[0013] Furthermore, the inorganic salt of Zn is one of nitrate, halide or acetate of Zn, and acetate is preferred.

[0014] Further, the molar ratio of the inorganic salt of Zn, 1,2,4,5-pyromellitic acid and 1,2,4,5-(4-pyridyl)benzene is 2:1:1.

[0015] Furthermore, the amount of deionized water used was limited to 5 mL of deionized water per 0.2 mmol of Zn inorganic salt.

[0016] Furthermore, the temperature of the hydrothermal synthesis was 140°C and the reaction time was 72 hours.

[0017] Furthermore, the uniform dispersion refers to ultrasonically oscillating the reactants in an ultrasonic oscillator for 5-10 minutes at room temperature.

[0018] Furthermore, the post-treatment operation is as follows: after the reaction is completed, the mother liquor is removed, deionized water is added thereto, and a solid product is obtained by filtering, and the obtained solid product is washed with deionized water for 3-5 times, and the product is obtained after drying.

[0019] More specifically, the specific operation of the drying is: first place it at room temperature for 5 hours, then place it in a 50°C oven for 10 hours, and then transfer it to a 120°C vacuum drying oven for further drying for 48 hours to remove the solvent water molecules in the pores and activate the Zn-MOF material for adsorbing gases such as ethylene, ethane, acetylene and carbon dioxide.

[0020] The present invention also provides application of the Zn-MOF microporous crystal material in ethylene separation and purification.

[0021] Beneficial technical effects of the present invention:

[0022] The present invention provides a flexible Zn-MOF material with molecular sieving function, which is a microporous material with high crystallinity, high purity and three-dimensional framework structure, and has good air stability and thermal stability. It can not only realize the separation of acetylene and ethylene two-component mixed gas, but also can separate and purify ethylene in a three-component mixed gas of acetylene, carbon dioxide and ethylene in one step. In addition, the Zn-MOF material is prepared in a pure water solvent system, avoiding the use of a large amount of organic solvents, which not only saves costs but also is beneficial to the protection of the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The coordination structure diagram of Zn ions in the Zn-MOF synthesized in Example 1-3;

[0024] Figure 2 This is a diagram of the one-dimensional chain structure unit of ZnPMA extending along the a-axis of Zn-MOF;

[0025] Figure 3 Schematic diagram of the coordination structure between the ligand TPB and Zn ions in Zn-MOF;

[0026] Figure 4 It is the stacking diagram of Zn-MOF projected along the b-axis direction;

[0027] Figure 5 This is the pore distribution diagram along the b-axis in Zn-MOF;

[0028] Figure 6 This is the pore distribution diagram along the a-axis in Zn-MOF;

[0029] Figure 7 is the powder X-ray diffraction pattern of Zn-MOF material;

[0030] Figure 8 This is the thermogravimetric analysis diagram of Zn-MOF material;

[0031] Fig. 9 This is the CO2 adsorption isotherm curve of Zn-MOF material at 195K;

[0032] Fig.10 This is the adsorption isotherm diagram of C2H2, C2H4, and CO2 of Zn-MOF material at 273K;

[0033] Fig.11 This is the adsorption isotherm diagram of C2H2, C2H4, and CO2 of Zn-MOF material at 298K;

[0034] Fig.12 This is a statistical chart of the calculation results of the adsorption selectivity of Zn-MOF materials for a 1:1 two-component mixed gas of C2H2:C2H4 at 298K predicted by IAST theory;

[0035] Fig.13 This is a statistical chart of the calculated results of the adsorption selectivity of Zn-MOF material for a 1:1 binary gas mixture of CO2:C2H4 at 298K predicted by the IAST theory. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and examples, which do not limit the present invention in any form. In the following examples, except for deionized water which is homemade, all other raw materials used are commercially available.

[0037] Example 1 Preparation of Zn-MOF microporous crystalline material

[0038] Zn(NO3)2·6H2O (0.2mmol), H4PMA ligand (0.1mmol), and TPB (0.1mmol) were mixed in a 20mL polytetrafluoroethylene liner; 5mL of deionized water was added thereto and stirred thoroughly at room temperature to fully mix the reactants; the liner was then sealed into a stainless steel reactor, and the reaction apparatus was placed in a heating device at 140°C for 72 hours, then naturally cooled to room temperature, the reaction apparatus was opened, the mother liquor was removed, deionized water was added for filtration to obtain a solid product, the obtained solid product was then washed with deionized water for 3-5 times, and the product Zn-MOF was obtained after drying.

[0039] Example 2 Preparation of Zn-MOF microporous crystalline material

[0040] The difference between Example 2 and Example 1 is that the zinc salt is Zn(CH3COO)2, and the other conditions are exactly the same as those in Example 1.

[0041] Example 3 Preparation of Zn-MOF microporous crystalline material

[0042] The difference between Example 3 and Example 1 is that the zinc salt is ZnCl2, and the other conditions are exactly the same as those in Example 1.

[0043] (1) Structural characterization of Zn-MOF materials

[0044] The crystal structures obtained in Examples 1-3 are the same. The single crystal diffraction data of Zn-MOF were collected on a Bruker Apex II diffractometer at room temperature. The X-ray used was MoKα ray ( λ = 0.71073Å), the crystal structure was solved by direct method after data reduction, and the structure was refined by SHELXL program. The hydrogen on carbon atoms was obtained by theoretical hydrogenation. The refinement parameters are shown in Table 1.

[0045] Table 1 Main crystallographic data of Zn-MOF

[0046] .

[0047] like Figure 1 As shown, in the Zn-MOF structure, each Zn 2+ It is coordinated with two carboxyl O atoms from two different PMA ligands and two N atoms from two TPB neutral ligands to form a tetrahedral coordination geometry.

[0048] like Figure 2 As shown, in the three-dimensional framework of Zn-MOF, each PMA 4- and four Zn 2+ Coordination; two adjacent PMA 4- The ligands share two Zn2+ , forming a one-dimensional chain structure unit through the above connection method; four adjacent one-dimensional chain structure units are connected by TPB ligands (see Figure 3 ), forming the final three-dimensional interpenetrating frame structure, see Figure 4 The framework structure has a diameter of 4.9×6.4 Å along the a-axis direction. Figure 5 ) and a one-dimensional pore with 5.0 × 6.8 Å along the b-axis ( Figure 6 as shown).

[0049] (2) Characterization of the physical phase and stability of Zn-MOF materials

[0050] Figure 7 This is a comparison chart between the powder X-ray diffraction (XRD) spectrum of Zn-MOF and the theoretical simulation XRD. It can be seen from the figure that the synthesized Zn-MOF material has good crystallinity and high purity.

[0051] In order to determine the thermal stability of the Zn-MOF material synthesized in Example 1, a thermal stability test was performed using thermogravimetric analysis (TG). The sample was heated from room temperature to 700°C at a heating rate of 5°C / min. The results are as follows: Figure 8 The sample lost all the solvent water molecules in the pores before 120°C, and then a platform appeared until the framework began to collapse at 290°C, indicating that the synthesized Zn-MOF material has good thermal stability.

[0052] (3) Specific surface area and pore size test of Zn-MOF materials

[0053] In order to test the specific surface area and pore size of the Zn-MOF material prepared in Example 1, the sample was first dried by placing it at room temperature for 5 hours, then drying it in a 50°C oven for 10 hours, and then transferring it to a 120°C vacuum drying oven for further drying for 48 hours to remove the solvent water molecules in the pores.

[0054] Then the samples were subjected to isothermal adsorption test of CO2 at 195K. The test results are shown in Fig. 9 As shown, the specific surface area of ​​the Zn-MOF material is 319 m 2 / g, pore size is 0.52nm.

[0055] Example 4 Gas adsorption and gas separation performance tests of Zn-MOF materials

[0056] In order to characterize the single-component adsorption performance of Zn-MOF prepared in Example 1 for C2H2, C2H4 and CO2 at 273K and 298K, the single-component adsorption isotherms of these gases at these two temperatures were tested. Fig.10It can be seen that at 273K and 1 bar, the adsorption capacity of Zn-MOF for C2H2 is 132.6 mL / g, the adsorption capacity for CO2 is 92.5 mL / g, and there is almost no adsorption for C2H4. Fig.11 It can be seen that at 298K and 1bar, the adsorption capacity of Zn-MOF for C2H2 is 114.8mL / g, the adsorption capacity for CO2 is 84.1mL / g, and there is almost no adsorption for C2H4.

[0057] In order to further determine the separation performance of the prepared Zn-MOF for C2H4 in C2H2 / C2H4 and CO2 / C2H4 mixed systems, the ideal adsorbed solution theory (IAST) was used to predict the separation selectivity of the two-component mixed gas of C2H2 / C2H4 and CO2 / C2H4 at a molar ratio of 1:1. Fig.12 The figure shows the separation ratio of a mixed gas with a volume ratio of C2H2 / C2H4 of 1:1. The separation ratio at room temperature and one atmosphere is 2.48×10 10 , Fig.13 The figure shows the separation ratio of a mixed gas with a volume ratio of CO2 / C2H4 of 1:1. The separation ratio at room temperature and one atmosphere is 1.96×10 72 , indicating that the synthesized Zn-MOF material has good separation performance for the above two mixed gases at room temperature.

Claims

1. A Zn-MOF microporous crystalline material, characterized in that: The molecular formula is [Zn2(PMA)(TPB)] x H2O, wherein PMA is deprotonated 1,2,4,5-pyromellitic acid, TPB is 1,2,4,5-(4-pyridyl)benzene, the Zn-MOF microporous crystalline material is formed by coordination of Zn with oxygen atoms of 1,2,4,5-pyromellitic acid and N atoms of 1,2,4,5-(4-pyridyl)benzene, and the Zn-MOF microporous crystalline material has a three-dimensional framework structure; In the three-dimensional framework of Zn-MOF, each Zn 2+ The four nitrogen atoms on each TPB ligand and the four Zn atoms on each TPB ligand form a tetrahedral coordination geometry. 2+ Coordination; Each PMA 4- and four Zn 2+ coordination; Two adjacent PMAs 4- The ligands share two Zn 2+ , a one-dimensional chain structure unit is formed by the above-mentioned linking method, four adjacent one-dimensional chain structure units are connected by TPB, and a three-dimensional framework structure is formed by the above-mentioned connection method; The crystal structure of the Zn-MOF microporous crystal material belongs to the triclinic system, the space group is P-1, the unit cell parameters are as follows: a=8.911 Å, b=9.646 Å, c=13.672 Å, α=69.77°, β=79.64°, γ=76.75°, and the unit cell volume is 1066.8 Å 3 .

2. The Zn-MOF microporous crystalline material according to claim 1, characterized in that: In the three-dimensional framework of Zn-MOF, there are one-dimensional channels of 4.9×6.4 Å along the a-axis and 5.0×6.8 Å along the b-axis.

3. A method for preparing the Zn-MOF microporous crystalline material according to any one of claims 1 to 2, characterized in that: The steps include: The inorganic salt of Zn, 1,2,4,5-pyromellitic acid and 1,2,4,5-(4-pyridyl)benzene are uniformly dispersed in a deionized water solvent system for hydrothermal reaction synthesis. After the reaction is completed, the reaction product is post-treated to obtain the target product.

4. The method for preparing the Zn-MOF microporous crystalline material according to claim 3, characterized in that: The inorganic salt of Zn is one of Zn nitrate, Zn halide or Zn acetate.

5. The method for preparing the Zn-MOF microporous crystalline material according to claim 3, characterized in that: The molar ratio of the inorganic salt of Zn, 1,2,4,5-pyromellitic acid and 1,2,4,5-(4-pyridyl)benzene is 2:1:1, and the amount of deionized water added is limited to 5 mL of deionized water per 0.2 mmol of the inorganic salt of Zn.

6. The method for preparing the Zn-MOF microporous crystalline material according to claim 3, characterized in that: The temperature of the hydrothermal synthesis was 140 °C and the reaction time was 72 h.

7. Use of the Zn-MOF microporous crystalline material as described in any one of claims 1 to 2 in the separation and purification of ethylene.

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