A method for preparing a methyl-functionalized metal-organic framework adsorbent and gas separation applications

Abstract

The application belongs to the technical field of new materials, and particularly relates to a methyl functionalized metal-organic framework material, a preparation method thereof and gas separation applications. The chemical general formula is [Zn2(DMA)4(H2TCPB-Me)2], wherein Zn2 is two divalent zinc ions, H2TCPB-Me is a 1,2,4,5-tetrakis(4-carboxylphenyl)-3,6-dimethyl ligand from which two protons are removed, and DMA is an N,N-dimethylacetamide solvent molecule. The Zn-MOF material structure belongs to a triclinic system, a P-1 space group, the cell parameter is a-axis length, an a-axis angle alpha=92.660(3)°, a beta=92.832(2)°, a gamma=104.788(3)°, and the cell volume is Z=2. The preparation method of the Zn-MOF material is that metal zinc salt and H4TCPB-Me are dissolved in a mixed solution of an organic solvent and water, and then 1:10 nitric acid is added; the sealed is placed in an 80-120 DEG C oven for 24-72 hours; and then naturally cooled to room temperature to obtain the Zn-MOF material. Due to the unique structure, the Zn-MOF material of the application can be applied to the fields of mixed gas C2H2 / CO2 and CO2 / CH4 separation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of new materials, and particularly relates to a methyl-functionalized metal-organic framework adsorbent material, a preparation method thereof, and a gas separation application. BACKGROUND

[0002] With the global emphasis on environmental protection and sustainable development, finding and promoting clean and efficient energy has become an urgent demand of the times. Methane (CH4) is an important component of natural gas, biogas, shale gas, and coalbed methane gas resources, and its development and utilization has attracted much attention. However, carbon dioxide gas is often mixed in during the extraction process, which reduces the combustion heat value and corrodes the gas pipeline, also limiting the range of utilization. Therefore, it is crucial to selectively capture CO2 and achieve efficient separation of CO2 / CH4. Acetylene (C2H2) is an important basic raw material in petrochemical industry, and its production and application play a crucial role in social development and technological progress, and have an immeasurable position. High-purity acetylene in industry is mainly obtained by cracking of carbon hydrocarbon compounds or partial combustion of methane, but the acetylene obtained by this method contains a large amount of carbon dioxide (CO2) impurity gas, which has a great influence on the quality of the final product in chemical engineering. Therefore, efficient separation of high-purity acetylene is of great significance to improve energy utilization efficiency and reduce production cost.

[0003] Current gas separation processes mainly include chemical absorption, low-temperature distillation, and solvent extraction, etc. These methods often have high energy consumption and adverse effects on the environment. For example, low-temperature distillation requires the mixed gas to be low-temperature condensed and liquefied, and then separated by distillation according to the evaporation temperature of different gases, which requires a large amount of energy to complete the separation process; and the solvent extraction method is relatively complicated, and may leave residual solvents, which poses potential risks to the environment and human health. Therefore, there is an urgent need for a low-energy, environmentally friendly separation and purification process and material.

[0004] Compared with traditional separation technologies, adsorption separation method can be carried out at normal temperature and pressure, with low cost and energy consumption, and good selectivity for target substances, which can achieve efficient separation; secondly, the adsorption method is simple to operate and low in cost. However, traditional adsorbents such as zeolites, molecular sieves, and activated carbon have small surface area and porosity, and their structures cannot be controlled, making it difficult to achieve gas separation. Metal-organic framework (MOF) is a crystalline material with periodic network structure formed by self-assembly of metal ions and organic ligands. MOF has strong application in gas adsorption, storage and separation, and selective gas adsorption due to its highly ordered pore structure, large specific surface area, adjustable and modifiable pore size, etc. It can be used as a low-energy, high-efficiency, and adaptable adsorbent. SUMMARY

[0005] The present application provides a Zn-MOF material

[0006] The technical scheme for solving the above technical problem is as follows: a Zn-MOF material, the chemical general formula of which is [Zn2(DMA)4(H2TCPB-Me)2], wherein Zn is a divalent zinc ion, H2TCPB-Me is a deprotonated 1,4-bis(4-carboxylphenyl)-3,6-dimethyl ligand, and DMA is N,N-dimethylacetamide. The crystal structure of the Zn-MOF material belongs to a triclinic system, a P-1 space group, the cell parameters of which are an axial length of a= 10. 104 1(3) A, an axial length of b= 12. 1 1 1(3) A, an axial length of c= 17. 1 1 1(3) A, an axial angle of a = 92.660(3) °, an axial angle of b = 92.832(2) °, an axial angle of g = 104.788(3) °, and a cell volume of V = 2 1 1 1(3) A3. The axial angle a = 92.660(3) °, the axial angle b = 92.832(2) °, the axial angle g = 104.788(3) °, and the cell volume is V = 2 1 1 1(3) A3. Z = 2.

[0007] The present application has the following beneficial effects:

[0008] 1. The synthesis method of the Zn-MOF material of the present application is simple in process and mild in conditions, and the yield reaches 25%-30%. After the reaction raw materials are dissolved, the required material can be obtained at about 100 DEG C. Among all the used raw materials, there is no toxic and harmful substance and catalyst, and no toxic and harmful substance is generated in the preparation process.

[0009] 2. The three three-dimensional topological networks of the Zn-MOF material of the present application are interpenetrated, and the thermal stability is excellent.

[0010] 3. The Zn-MOF material of the present application can be used for preparing an adsorption material to realize the adsorption and separation of various gases.

[0011] The crystal structure of the Zn-MOF material of the present application is tested at 150 K by a SuperNova micro-focus X-ray single crystal diffractometer of Agilent, and data reception is performed on an EosCCD. A graphite monochromator is used, and the wavelength (Cu K a) is The data analysis and absorption correction are performed by using a CrysAlisPro tool in a variable-angle scanning mode of w-2q. All structures are directly solved by using a SHELXS program packaged by SHELXTL, and structure refinement is performed by using a SHELXL full-matrix least square method. All non-hydrogen atoms are processed anisotropically, and hydrogen atoms of the organic ligand are generated by geometric symmetry. It is found that the structure of the Zn-MOF material of the present application belongs to a triclinic system, a P-1 space group, and the basic structural unit of the crystal is obtained by symmetry operation of an asymmetric unit

[0012] The asymmetric unit contains two deprotonated TCPB-Me ligands, two zinc ions, four N,N-dimethylacetamide molecules.

[0013] The zinc ions are connected to four oxygen atoms in a tetrahedral coordination mode, wherein the four oxygen atoms are from the oxygen atoms in the two carboxyl groups (Zn1: O1-C1-O2, O13-C37-O14; Zn2: O3-C36-O4, O9-C55-O10) of two different ligands (Zn1: O1, O14; Zn2: O4, O10) and two solvent N,N-dimethylacetamide molecules (Zn1: O17, O18; Zn2: O19, O20); each Zn atom center is combined with two oxygen atoms from two TCPB-Me ligands and two terminal N,N-dimethylacetamide to form a regular tetrahedron. Each TCPB-Me ligand is connected to two Zn atom centers through its two carboxyl oxygen atoms at the para position.

[0014] The crystal structure of the Zn-MOF material belongs to a triclinic system, a P-1 space group, and the cell parameters are an axial length of a= 13. 126 (3) A, an axial length of b= 13. 126 (3) A, an axial length of c= 20. 126 (3) A, an axial angle of α = 92. 660 (3) °, an axial angle of β = 92. 832 (2) °, an axial angle of γ = 104. 788 (3) °, and a cell volume of V = 3 030. 1 (2) A3. The axial angle α = 92. 660 (3) °, the axial angle β = 92. 832 (2) °, the axial angle γ = 104. 788 (3) °, and the cell volume is V = 3 030. 1 (2) A3. Z = 2.

[0015] The application further provides a preparation method of the Zn-MOF material, which comprises the following steps:

[0016] A. Dissolving H4TCPB-Me ligands and zinc nitrate hexahydrate in a solvent to obtain a uniform mixed solution, wherein the molar dosage ratio of the H4TCPB-Me ligands to the Zn (NO3) 2·6H2O is 1:1, and the concentration of the H4TCPB-Me ligands in the solution is 2.8333 mmol / L;

[0017] B. Adding 80 μL of 1:10 nitric acid.

[0018] C. Placing the mixed solution in step B in a glass bottle and incubating at 100 ℃ for 24-72 h to obtain the Zn-MOF material.

[0019] The application has the advantages that the preparation method is simple in conditions, fast in reaction, energy-saving and time-saving, and the preparation method of the Zn-MOF material is high in yield, low in ligand dosage and low in cost.

[0020] On the basis of the above technical scheme, the application can be further improved as follows:

[0021] In the application, further, the solvent is N,N-dimethylacetamide and water, and the volume ratio is 1:0.1-10.

[0022] The beneficial effect of the further scheme is that the solvent composed of N,N-dimethylacetamide and water is easy to obtain, low in price, and less polluting, and the prepared Zn-MOF material has better crystallinity.

[0023] In the application, further, the molar ratio of the H4TCPB ligand to the zinc nitrate hexahydrate is 1:1, and the concentration of the H4TCPB ligand in the solution is 2.8333 mmol / L.

[0024] The beneficial effect of the further scheme is that the determined concentration and molar ratio make the Zn-MOF material have better crystal morphology, and the reaction is more smooth.

[0025] The application further provides application of the Zn-MOF material in the field of low-carbon hydrocarbon gas separation, the Zn-MOF material is subjected to adsorption test on single components CO2, C2H2 and CH4 gas, and differential C2H2 / CO2 and CO2 / CH4 adsorption amounts are obtained for gas separation.

[0026] The beneficial effect of the application is that the Zn-MOF material is applied to the field of C2H2 / CO2 and CO2 / CH4 gas separation, so that the function of the Zn-MOF material is more comprehensive. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a structure diagram of an asymmetric structure unit of the Zn-MOF material of the application;

[0028] Figure 2 It is a structure diagram of the Zn-MOF material of the application: (a) coordination environment of zinc ions; (b) S-shaped chains arranged in parallel in a layer; (c) two connection modes between chains; (d) pores;

[0029] Figure 3 It is an XRD spectrum diagram of testing and simulation of the Zn-MOF material of the application, the abscissa is a Bragg diffraction angle, and the ordinate is a diffraction intensity;

[0030] Figure 4 It is a thermogravimetric curve diagram of the Zn-MOF material of the application, the abscissa is a temperature, and the ordinate is a weight loss percentage;

[0031] Figure 5 It is an infrared spectrum diagram of the Zn-MOF material of the application, the abscissa is a wave number, and the ordinate is a light transmittance;

[0032] Figure 6 It is an N2 adsorption isotherm diagram of the Zn-MOF material of the application at 77K, the abscissa is a pressure, and the ordinate is an adsorption amount;

[0033] Figure 7 The pore size distribution curve of the Zn-MOF material of the present application, the abscissa is the pore size, and the ordinate is the pore size distribution;

[0034] Figure 8 The adsorption isotherm graph of the Zn-MOF material of the present application at 273K for CO2, CH4 and C2H2, the abscissa is the pressure, and the ordinate is the adsorption amount;

[0035] Figure 9 The adsorption isotherm graph of the Zn-MOF material of the present application at 298K for CO2, CH4 and C2H2, the abscissa is the pressure, and the ordinate is the adsorption amount;

[0036] Figure 10 The adsorption enthalpy graph of the Zn-MOF material of the present application for CO2, CH4 and C2H2, the abscissa is the adsorption amount, and the ordinate is the adsorption enthalpy;

[0037] Figure 11 The adsorption selectivity graph of the Zn-MOF material of the present application for C2H2 / CO2 and CO2 / CH4 mixed gas at 273K and 298K, respectively, the abscissa is the pressure, and the ordinate is the common logarithm of selectivity; DETAILED DESCRIPTION

[0038] The principles and features of the present application will be described in detail below with reference to the embodiments, which are only used to explain the present application and not to limit the scope of the present application.

[0039] Example 1

[0040] A method for preparing a Zn-MOF material, specifically comprising the following steps:

[0041] A. 0.0100 g, 0.0170 mmol of 1,2,4,5-tetrakis(4-carboxyphenyl)-3,6-dimethylbenzene (H4TCPB-Me) ligand and 0.0050 g, 0.0168 mmol of zinc nitrate hexahydrate are accurately weighed with an analytical balance in a reaction container, 6 mL of a mixed solvent of N,N-dimethylacetamide and water is added to the reaction container under room temperature conditions, the volume ratio of N,N-dimethylacetamide to water is 1:1; and 80 μL of 1:10 nitric acid is further added;

[0042] B. The mixed solution in step A is placed in a glass bottle and incubated in a constant temperature blast oven at 100°C for 24-72 h to obtain a colorless crystal-shaped Zn-MOF material.

[0043] As Figure 1 and Figure 2The colorless crystal-like Zn-MOF material was tested at 150 K by SuperNova micro-focus X-ray single crystal diffractometer of Agilent Company, and data reception was carried out on Eos CCD. The graphite monochromator was used, and λ(Cu Kα) was The data analysis and absorption correction were carried out by using CrysAlisPro tool in the ω-2θ variable-angle scanning mode. All structures were directly solved by using SHELXS program packaged by SHELXTL, and structure refinement was carried out by using SHELXL full-matrix least squares method. All non-hydrogen atoms were processed anisotropically, and hydrogen atoms of the organic ligand were generated by geometric symmetry. The crystal data shown in Table 1, the typical bond length data of the crystal shown in Table 2, and the typical bond angle data of the crystal shown in Table 3 were obtained.

[0044] Table 1: Crystal data

[0045]

[0046]

[0047] Table 2: Typical bond length data of the crystal (unit: )

[0048]

[0049]

[0050] Table 3: Typical bond angle data of the crystal (unit: °)

[0051]

[0052]

[0053] In combination with the crystal data in Table 1, Table 2 and Table 3, the following related characterization of the Zn-MOF material was obtained:

[0054] The asymmetric unit is composed of 2 TCPB-Me ligands with two protons removed, 2 zinc ions, and 4 N,N-dimethylacetamide molecules.

[0055] The zinc ion is connected to four oxygen atoms in a four-coordinated mode, and the four oxygen atoms are oxygen atoms (Zn1: O1, O14; Zn2: O4, O10) from two carboxyl groups (Zn1: O1-C1-O2, O13-C37-O14; Zn2: O3-C36-O4, O9-C55-O10) of different two ligands and two solvent molecules N,N-dimethylacetamide molecules (Zn1: O17, O18; Zn2: O19, O20).

[0056] The carboxylate groups (O1-C1-O2, O13-C37-O14; O3-C36-O4, O9-C55-O10) in the ligand adopt a monodentate bridging mode to connect adjacent Zn atoms, eventually forming a [Zn(DMA)2][COO]2 structure. The carboxyl groups in TCPB-Me lose two protons and adopt a monodentate bridging to connect adjacent Zn atoms, forming a one-dimensional S-shaped chain. These chains are arranged in parallel in the corresponding layer, and adjacent layers are arranged in anti-S shape in parallel.

[0057] The Zn-MOF material structure of the application belongs to triclinic system, P-1 space group, and the cell parameters are axis length Axis angle α = 92.660 (3) °, β = 92.832 (2) °, γ = 104.788 (3) °, and the cell volume is Z = 2.

[0058] As shown in Figure 3 , the colorless crystal Zn-MOF material is tested by a powder X-ray diffractometer, and the Bragg diffraction angle is 3-50 °, and the diffraction intensity is measured every 0.01 °. The Zn-MOF material shows a diffraction pattern as shown in the figure. From the diffraction pattern in the figure, it can be seen that the collected Zn-MOF material has good phase purity.

[0059] As shown in Figure 4 , the colorless crystal Zn-MOF material is analyzed by thermogravimetric curve, and the thermogravimetric test is carried out on a Mettler simultaneous thermogravimetric analyzer, the machine model is RGA / DSC-1, the reaction gas and the protective gas are both nitrogen, the flow rates are 25 mL / min respectively, the running time is 50 minutes, the temperature rising rate is 10 ℃ / min, and the test temperature range is 30-900 ℃. From Figure 4 the thermogravimetric curve, it can be seen that the Zn-MOF material can be stable to about 489 ℃; the complex loses the solvent in the channel before 92 ℃, the weight loss from 92 ℃ to 400 ℃ is to lose the coordinated solvent, and the weight loss from 400 ℃ to 489 ℃ is the collapse of the framework. It shows that the Zn-MOF material of the application has good stability and can be decomposed at high temperature.

[0060] As shown in Figure 5 , the colorless crystal aluminum-based complex is detected by infrared spectrum, and the infrared test adopts KBr tabletting method, and the Nicolet 330 FTIR spectrometer is used to collect the infrared spectrum of the region of 4000-400 cm -1 . From Figure 5 , it can be seen that the absorption peak of the complex near 1600 cm -1 can be attributed to the benzene ring skeleton stretching vibration peak in the ligand, and the absorption peak near 1400 cm -1The absorption peaks in the vicinity can be attributed to the symmetric stretching vibration peaks of deprotonated carboxylate, located at 1300-400 cm -1 The absorption peaks in the region are fingerprint characteristic peaks of the Zn-MOF material.

[0061] As shown in Figure 6 , the colorless crystal Zn-MOF material was tested by the ASAP2020 instrument of Micromeritics, USA. The zinc-based complex showed the adsorption isotherm of single-component N2 at 77K as shown in the figure, which was type II isotherm with a very small desorption hysteresis. From the isotherm, the single-point BET specific surface area of the Zn-MOF material at P / P0=0.2 was 38.804 m 2 / g, and the BET specific surface area was 37.619 m 2 / g. The total pore volume at P / P0=0.99 was 0.073 cm 3 / g; the t-plot micropore volume was 0. The pore size distribution calculated from the N2 adsorption isotherm is shown in Figure 7 .

[0062] As shown in Figure 8 and Figure 9 , the colorless crystal Zn-MOF material was tested by the ASAP2020 instrument of Micromeritics, USA. The zinc-based complex showed the adsorption isotherm of single-component CO2, C2H2 and CH4 gas as shown in the figure. The adsorption amounts of CO2, C2H2 and CH4 at 273K were 22.5 cm 3 / g, 28.8 cm 3 / g and 9.4 cm 3 / g, respectively, and the adsorption amounts of CO2, C2H2 and CH4 at 298K were 18.4 cm 3 / g, 25.7 cm 3 / g and 5.7 cm 3 / g, respectively. Therefore, from the differentiated adsorption amounts in the figure, it can be seen that the Zn-MOF material can be applied in the field of gas separation of C2H2 / CO2, CO2 / CH4.

[0063] As shown in Figure 10 , the CO2, C2H2 and CH4 adsorption isotherms were used to calculate the adsorption enthalpy using the virial formula, and the relationship curves of the adsorption enthalpy and the adsorption amount of CO2, C2H2 and CH4 were obtained. From the figure, it can be seen that the maximum adsorption enthalpy of the Zn-MOF material for CO2, C2H2 and CH4 was 29.69 kJ / mol, 47.57 kJ / mol and 20.82 kJ / mol, respectively.

[0064] As shown in Figure 11As shown, the adsorption selectivity of the Zn-MOF material for CO2, C2H2 and CH4 is analyzed using ideal adsorbed solution theory, and a selectivity-pressure curve is obtained as shown in the figure. As can be seen from the figure, the Zn-MOF material has high adsorption selectivity for C2H2 / CO2 and CO2 / CH4.

[0065] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A Zn-MOF material, characterized in that: The general chemical formula is [Zn2(DMA)4(H2TCPB-Me)2], where Zn is a divalent zinc ion, H2TCPB-Me is a 1,2,4,5-tetra(4-carboxyphenyl)-3,6-xylene ligand with two protons removed, and DMA is an N,N-dimethylacetamide solvent molecule. Each Zn atom center coordinates with two oxygen atoms from the TCPB ligand and two oxygen atoms from the N,N-dimethylacetamide solvent molecule, forming a regular tetrahedron. Each TCPB-Me ligand is connected to two Zn atom centers through its two carboxyl oxygen atoms. The Zn-MOF material structure belongs to the triclinic crystal system, space group P-1, and its unit cell parameter is the axis length. The axial angles α = 92.660(3)°, β = 92.832(2)°, γ = 104.788(3)°, and the unit cell volume is... Z = 2.

2. A method for preparing the Zn-MOF material as described in claim 1, characterized in that, Includes the following steps: A. H4TCPB-Me ligand and zinc nitrate hexahydrate are dissolved in a solvent to obtain a homogeneous mixed solution. The molar ratio of H4TCPB-Me ligand to zinc nitrate hexahydrate is 1:1, and the concentration of H4TCPB-Me ligand in the solution is 2.8333 mmol / L. B. Add 80 μL of 1:10 nitric acid to step A; C. Place the mixed solution described in step B in a glass bottle and keep it at 100°C for 24–72 h to obtain the Zn-MOF material.

3. The method for preparing the zinc-based complex according to claim 2, characterized in that, The solvent is composed of N,N-dimethylacetamide and water, wherein the volume ratio of N,N-dimethylacetamide to water is 1:

1.

4. The method for preparing Zn-MOF material according to any one of claims 2 or 3, characterized in that, The molar ratio of the H4TCPB-Me ligand to the zinc nitrate hexahydrate is 1:1, and the concentration of the H4TCPB-Me ligand is 2.8333 mmol / L.

5. An application of the Zn-MOF material as described in claim 1 in the field of mixed gas separation, characterized in that, The Zn-MOF material was tested for adsorption of single-component CO2, C2H2, and CH4 gases, and the results showed significant differences in the adsorption amounts of C2H2 / CO2 and CO2 / CH4, which can be used for gas separation.

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