Size-controllable high-purity ZIF-8 material as well as preparation method and Cl capture application thereof

Abstract

The invention discloses a preparation method of a size-controllable high-purity ZIF-8 material, which comprises the following steps: 1) respectively dissolving an amine-containing organic ligand and a zinc salt in an alcohol solvent at room temperature to prepare a mixed solution of the amine-containing organic ligand and the zinc salt; 2) adding a deprotonation reagent and a template agent, stirring at low temperature for reaction, standing for aging, centrifugally collecting milk white precipitate, washing and drying to obtain a ZIF-8 precursor material; and 3) carrying out gradient calcination on the obtained ZIF-8 precursor material in an inert atmosphere to obtain high-purity ZIF-8 materials with different sizes. The ZIF-8 material is high in purity, controllable in size, rich in amino groups, good in heat stability and high in adsorption performance, low-temperature effective adsorption and fixation of chlorine elements can be achieved, the content of Cl pollutants in PVC pyrolysis products is effectively reduced, clean and high-quality high-value liquid and solid fuel products are obtained, and follow-up harmless utilization is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and in particular relates to a size-controllable high-purity ZIF-8 material, a preparation method thereof, and Cl capture application. Background Art

[0002] The total annual output of polyvinyl chloride (PVC) waste is growing rapidly, and its harmless treatment also poses huge challenges. The mass proportion of chlorine (Cl) elements in PVC is an average of 56wt%. Due to the instability of the carbon (C)-Cl structure in the PVC matrix, traditional treatment methods such as landfill and incineration will generate acidic hydrogen chloride (HCl). Excessive emissions will cause environmental pollution and equipment corrosion. When it comes into contact with oxygen (O), secondary chlorinated toxic carcinogenic products such as dioxins are generated, which affect the environment and human health. Compared with treatment technologies such as landfill and incineration, pyrolysis technology has great advantages in improving weight and volume reduction rates, reducing pollutant emissions and improving resource utilization. However, when treated through pyrolysis technology, halogenated pollutants such as HCl are easily generated at high temperatures, which will cause serious corrosion to equipment and pipelines, cause boiler contamination and slagging, and endanger industrial operation safety. Therefore, Cl pollutant absorption technology is one of the key technologies to promote the harmless thermal treatment of PVC.

[0003] Conventional Cl absorbents mainly include acidic metal oxides, alkaline zeolite molecular sieves, nano-based adsorbents, and biomass-based carbon materials. Currently, acidic metal oxides (CaO, ZnO, etc.) and alkaline zeolite molecular sieves (13X zeolite, ZSM-5) have been widely used in flue gas dehalogenation and other fields due to their low price and abundant raw material resources. However, metal oxides cannot achieve optimal Cl capture efficiency in the peak area of ​​Cl release from PVC thermal decomposition (240-400°C). Zeolite adsorbents lack sufficient adsorption sites, and Cl is easily re-released by external influences, resulting in ineffective capture. Traditional adsorbents have defects such as insufficient adsorption sites and poor low-temperature utilization. Therefore, in response to the above problems, finding a Cl capture agent that is more suitable for PVC pyrolysis to achieve harmless thermal treatment of PVC waste has become the core of technical research in this field. Summary of the Invention

[0004] The main purpose of the present invention is to provide a high-purity ZIF-8 material to address the problems and shortcomings of the low Cl element capture rate in the existing PVC heat treatment process. The material is applied to the Cl disposal of PVC heat treatment, which can significantly reduce the release of Cl pollutants during PVC pyrolysis and improve the quality of the pyrolysis products.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing a size-controllable high-purity ZIF-8 material comprises the following steps:

[0007] 1) dissolving an organic ligand and a zinc salt in an alcohol solvent at room temperature to obtain an organic ligand solution and a zinc salt solution, respectively;

[0008] 2) mixing the organic ligand solution and the zinc salt solution, adding a deprotonating agent and a template agent thereto, stirring the resulting mixed solution at low temperature for reaction, allowing it to stand for aging, collecting a milky white precipitate by centrifugation, washing it, and drying it to obtain a ZIF-8 precursor material;

[0009] 3) The obtained ZIF-8 precursor material is subjected to gradient calcination under an inert atmosphere to obtain high-purity ZIF-8 materials of different sizes.

[0010] In the above scheme, the organic ligand can be selected from one or more of a mixture of amine-containing reagents such as 2-methylimidazole and 2-amino-1-methylimidazole, N,N-dimethylformamide or acetamide.

[0011] In the above scheme, the zinc salt can be selected from one or more of zinc acetate, zinc nitrate, zinc sulfate, etc.

[0012] In the above scheme, the alcohol solvent can be methanol or ethanol.

[0013] In the above scheme, the molar ratio of the zinc salt to the organic ligand is 1:4-34.

[0014] In the above scheme, the zinc salt concentration in the mixed solution obtained in step 2) is 0.1 to 0.14 mol / L.

[0015] In the above scheme, the protonating agent is triethanolamine; and the template agent is polyethylene glycol.

[0016] In the above scheme, the low temperature is 5 to 10°C.

[0017] In the above scheme, the stirring reaction time is 1.5 to 2 hours.

[0018] In the above scheme, the temperature used for the static aging is 5 to 10° C. and the time is 20 to 24 hours.

[0019] In the above scheme, the washing step in step 2) is an alcohol wash (methanol, etc.), and the washing times are at least 3 to 5 times.

[0020] In the above scheme, the ZIF-8 precursor material obtained in step 2) is doped with a large amount of amino groups and has a particle size of 0.5-4 μm.

[0021] In the above solution, the inert atmosphere is nitrogen, helium or argon.

[0022] In the above scheme, the target calcination temperature of the gradient calcination is 300-400°C.

[0023] Furthermore, the temperature rise system adopted in the gradient calcination step includes: first heating to 90-105°C at a rate of 4-6°C / min and keeping warm for 15-30 minutes; then heating to 300-400°C at a rate of 10-15°C / min and keeping warm for 15-30 minutes.

[0024] Furthermore, the crystal size of ZIF-8 can be effectively controlled by adjusting the ratio of zinc salt and organic ligand and combining the introduction of triethanolamine and polyethylene glycol.

[0025] The size-controlled high-purity ZIF-8 material prepared according to the above scheme has an average particle size of 0.5-4 μm, a purity of up to 98.5-99.5%, and a pore volume of 0.663-0.681 cm 3 / g, average pore diameter of 1.16-1.42nm, specific surface area of ​​1500-1800m 2 / g.

[0026] The present invention also provides a method for capturing Cl using the high-purity ZIF-8 material, comprising the following steps:

[0027] (1) transporting the high-purity ZIF-8 material and PVC mixture to a pyrolysis reactor and introducing inert gas for co-pyrolysis;

[0028] (2) condensing the volatile matter obtained from the co-pyrolysis, collecting the liquid and gas separately, and obtaining high-value liquid fuel products and gas products;

[0029] (3) The carbon residue obtained by co-pyrolysis is subjected to solid-liquid separation to recover the metal substances, and the carbon residue after leaching is collected in a solid collection device, and the leachate is collected in a liquid collection device.

[0030] In the above scheme, the mass ratio of the high-purity ZIF-8 material to PVC is (0.5-2):1.

[0031] Preferably, the inert gas used in the co-pyrolysis is nitrogen, the temperature is 200-450° C., the heating rate is 8-12° C. / min, and the holding time is 25-35 min.

[0032] Furthermore, the flow rate of the inert atmosphere is 80-100 mL / min.

[0033] In the above scheme, the step of online recovery of metal substances from the carbon residue is: transporting the carbon residue after the reaction to a solid-liquid separation device, and washing and leaching it at 100-200°C for recovery.

[0034] Furthermore, the Cl capture method of the present invention can achieve a Cl capture efficiency of more than 80%, and the metal Zn2+ The recovery rate reaches more than 90%.

[0035] This invention provides a rapid synthesis method for a high-purity, size-controllable ZIF-8 metal-organic framework (MOF) material. By carefully controlling the ratio of zinc salts and organic ligands, combined with a low-temperature synthesis method, the introduction of amine-containing reagents and auxiliary reagents, and a staged calcination process, the resulting material contains a high concentration of amino groups and achieves controllable crystal size. Compared to traditional Cl adsorbents, the high-purity ZIF-8 material described in this invention possesses a large number of amino groups, a more developed pore structure, and significantly increased pore size and specific surface area. This allows volatiles to more easily enter the absorbent pores, resulting in more complete contact with the absorbent, effectively promoting the absorption of pollutants such as Cl.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1) The present invention provides a method for preparing a high-purity ZIF-8 material that is safe, controllable, simple in process, reproducible, size-controllable, and rich in amino groups;

[0038] 2) Utilizing the thermal stability and high adsorption performance of the high-purity ZIF-8 material of the present invention, effective adsorption and fixation of chlorine at low temperatures can be achieved;

[0039] 3) The high-purity ZIF-8 material described in the present invention can effectively reduce the Cl pollutant content in PVC pyrolysis products, obtain clean and high-quality high-value liquid and solid fuel products, and promote subsequent harmless utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the SEM image of the ZIF-8 material obtained in Example 1;

[0041] Figure 2 This is the SEM image of the ZIF-8 material obtained in Example 2;

[0042] Figure 3 This is the SEM image of the ZIF-8 material obtained in Example 3;

[0043] Figure 4 Flow chart of the Cl capture application method of the ZIF-8 adsorbent provided in the embodiment;

[0044] Figure 5 A schematic diagram of a Cl capture application method device using a ZIF-8 adsorbent provided in an embodiment;

[0045] In the formula, 1-feeder, 2-air inlet, 3-pyrolysis reaction chamber, 4-feed controller, 5-solid purifier, 6-solid washing chamber, 7-washing liquid storage chamber, 8-gas-liquid collection chamber, 9-liquid condensation chamber, 10-gas collection chamber. DETAILED DESCRIPTION

[0046] The following is a detailed description of the technical solutions used in the present invention through specific implementation examples. The description is only a part of the present invention and does not represent all embodiments. Unless otherwise specified, the experimental methods used in the present invention are conventional methods, and the instruments and equipment used are commercial products in the field of this technology.

[0047] In the following examples, the Cl capture device used is shown in Figure 5 It includes a mixed pyrolysis device, a gas and liquid product collection device, and a solid purification and collection device. Reference numerals 1 represent a feeder, 2 a gas inlet, 3 a pyrolysis reaction chamber, 4 a feed controller, 5 a solid purifier, 6 a solid washing chamber, 7 a washing liquid storage chamber, 8 a gas and liquid collection chamber, 9 a liquid condensation chamber, and 10 a gas collection chamber. After the mixture reacts in the mixed pyrolysis device, the pyrolysis solid carbon residue is collected by the solid purifier, while the gas and liquid products are collected by the gas and liquid collection devices.

[0048] Example 1

[0049] A high-purity ZIF-8 material, the preparation method of which comprises the following steps:

[0050] 1) Dissolve 29.6 g of 2-methylimidazole, 29.6 g of 2-amino-1-methylimidazole, and 4.92 g of Zn(OAC)2·2H2O (the molar ratio of 2-methylimidazole to 2-amino-1-methylimidazole to Zn(OAC)2·2H2O is 16:12:1) in 160 mL of methanol to obtain an organic ligand solution and a zinc salt solution;

[0051] 2) After mixing the obtained organic ligand solution and zinc salt solution, add 10g of triethanolamine and 5g of polyethylene glycol at 5°C.

[0052] After stirring for 2 h and aging at 5°C for 24 h, the mixture was centrifuged at 8000 rpm for 15 min, and the precipitate was collected after washing to obtain the ZIF-8 precursor material;

[0053] 3) The prepared ZIF-8 material was first heated from room temperature to 100°C at a heating rate of 5°C / min in a nitrogen atmosphere, kept warm for 15 minutes, and then continued to be heated to 300°C at a heating rate of 15°C / min, kept warm for 30 minutes, and then naturally cooled to room temperature to obtain the high-purity ZIF-8 material.

[0054] The average particle size of the ZIF-8 material prepared in this embodiment was 0.5 μm (see Figure 1 ), the pore volume is 0.666cm 3 / g, average pore diameter of 1.16nm, specific surface area of ​​1550m 2 / g, purity is 99.5%.

[0055] Application Examples

[0056] The high-purity ZIF-8 material obtained in this example is used as a Cl capture adsorbent for PVC. The specific application steps are as follows:

[0057] (1) The obtained high-purity ZIF-8 material was mixed with PVC in a mass ratio of 1:1; the obtained mixture was transported to a pyrolysis reactor, the reaction atmosphere was regulated to be high-purity N2, the flow rate was 100 mL / min, and the co-pyrolysis reaction was carried out at 300°C, wherein the heating rate was 10°C / min and the holding time was 30 min;

[0058] (2) condensing the volatile matter after de-Clming to obtain a high-value liquid fuel product, and collecting the uncondensed gas;

[0059] (3) The carbon residue after the reaction was washed in a water bath at 150°C, and the solid carbon residue and the washing liquid were collected by filtration.

[0060] After testing, the above method of the present invention is used, the capture efficiency of Cl reaches 90%; after the residual carbon is washed and leached, the metal Zn 2+ The recovery rate reached 98%.

[0061] Example 2

[0062] A high-purity ZIF-8 material, whose preparation method and application method are roughly the same as those in Example 1, except that: in step (1), 14.8 g of 2-methylimidazole, 14.8 g of 2-amino-1-methylimidazole and 4.92 g of Zn(OAC)2·2H2O (the molar ratio of 2-methylimidazole to 2-amino-1-methylimidazole and Zn(OAC)2·2H2O is 8:6:1) are respectively dissolved in 160 mL of methanol solution.

[0063] The average particle size of the ZIF-8 adsorbent prepared in this embodiment was 1.3 μm (see Figure 2 ), the pore volume is 0.674 cm 3 / g, average pore diameter of 1.25nm, specific surface area of ​​1650m 2 / g, purity is 99.1%.

[0064] The Cl capture efficiency reached 86%, and after the residual carbon was washed and leached, the metal Zn 2+ The recovery rate reached 95%.

[0065] Example 3

[0066] A high-purity ZIF-8 material, whose preparation method and application method are roughly the same as those in Example 1, except that: in step (1), 3.6 g of 2-MeIM and 3.6 g of 2-amino-1-methylimidazole and 4.92 g of Zn(OAC)2·2H2O (the molar ratio of 2-methylimidazole and 2-amino-1-methylimidazole to Zn(OAC)2·2H2O is 2:1.5:1) are respectively dissolved in 160 mL of methanol solution.

[0067] The average particle size of the ZIF-8 adsorbent prepared in this embodiment is 4 μm (see Figure 3 ), the pore volume is 0.681cm 3 / g, pore diameter of 1.42nm, specific surface area of ​​1800m 2 / g, purity is 98.8%. The Cl capture efficiency reaches 83%, and after the residual carbon is washed and leached, the metal Zn 2+ The recovery rate reached 91%.

[0068] Example 4

[0069] A high-purity ZIF-8 material, the application method of which is substantially the same as that of Example 1, except that:

[0070] In step (1), the obtained mixture is transported to a pyrolysis reactor, the reaction atmosphere is regulated to be high-purity N2 with a flow rate of 100 mL / min, and a co-pyrolysis reaction is carried out at 250°C.

[0071] The test showed that the ZIF-8 adsorbent prepared in this embodiment has a Cl capture efficiency of 82%. After the residual carbon is washed and leached, the metal Zn 2+ The recovery rate reached 97%.

[0072] Example 5

[0073] A high-purity ZIF-8 material, whose preparation method and application method are roughly the same as those in Example 1, except that:

[0074] In step 3), the temperature is first increased from room temperature to 100°C at a heating rate of 5°C / min, kept at this temperature for 15 minutes, and then continued to be increased to 400°C at a heating rate of 15°C / min, kept at this temperature for 30 minutes, and then naturally cooled to room temperature to obtain the high-purity ZIF-8 material.

[0075] In step (1), the obtained mixture is transported to a pyrolysis reactor, the reaction atmosphere is regulated to be high-purity N2 with a flow rate of 100 mL / min, and a co-pyrolysis reaction is carried out at 350°C.

[0076] The test showed that the ZIF-8 adsorbent prepared in this embodiment has a Cl capture efficiency of 84%. After the residual carbon is washed and leached, the metal Zn2+ The recovery rate reached 96%.

[0077] Example 6

[0078] A high-purity ZIF-8 material, whose preparation method and application method are roughly the same as those in Example 1, except that:

[0079] 29.6 g of 2-methylimidazole, 29.6 g of N,N-dimethylformamide, and 4.92 g of Zn(OAC)2·2H2O (the molar ratio of 2-methylimidazole to 2-amino-1-methylimidazole and Zn(OAC)2·2H2O is 16:18:1) were dissolved in 160 mL of methanol solution to obtain an organic ligand solution and a zinc salt solution.

[0080] The average particle size of the ZIF-8 material prepared in this embodiment was 0.8 μm (see Figure 1 ), the pore volume is 0.679 cm 3 / g, average pore diameter of 1.19nm, specific surface area of ​​1600m 2 / g, purity is 97.7%. Cl capture efficiency reaches 88.5%, and after the residual carbon is washed and leached, the metal Zn 2+ The recovery rate reached 97.6%.

[0081] Comparative Example 1

[0082] A ZIF-8 material, whose preparation method and application method are roughly the same as those in Example 1, except that: the prepared ZIF-8 material is directly heated from room temperature to 300°C at a heating rate of 10°C / min in a nitrogen atmosphere, kept warm for 30 minutes, and then naturally cooled to room temperature.

[0083] The average particle size of the ZIF-8 material prepared in this embodiment was 0.7 μm (see Figure 1 ), the pore volume is 0.673 cm 3 / g, average pore diameter of 1.18nm, specific surface area of ​​1530m 2 / g, with a purity of 86.7%. The Cl capture efficiency reached 75.5%, and after the residual carbon was washed and leached, the metal Zn 2+ The recovery rate reached 90.5%.

[0084] Comparative Example 2

[0085] A ZIF-8 material, whose preparation method and application method are roughly the same as those in Example 1, except that: after the obtained organic ligand solution and zinc salt solution are mixed, they are directly stirred at 5°C for 2 hours, aged at 5°C for 24 hours, centrifuged at 8000 rpm for 15 minutes, washed, and then the precipitate is collected to obtain the ZIF-8 material.

[0086] The average particle size of the ZIF-8 material prepared in this embodiment was 0.9 μm (see Figure 1 ), the pore volume is 0.653 cm 3 / g, average pore diameter of 1.19nm, specific surface area of ​​1500m 2 / g, with a purity of 81.2%.

[0087] The Cl capture efficiency reached 68.8%, and after the residual carbon was washed and leached, the metal Zn 2+ The recovery rate reached 89.5%.

[0088] Comparative Example 3

[0089] A ZIF-8 material, whose preparation method and application method are roughly the same as those in Example 1, except that:

[0090] After mixing the obtained organic ligand solution and zinc salt solution, 10 g of triethanolamine and 5 g of polyethylene glycol were added and stirred at room temperature (25°C) for 2 hours. After aging reaction at room temperature for 24 hours, the mixture was centrifuged at 8000 rpm for 15 minutes, washed and the precipitate was collected to obtain ZIF-8 material.

[0091] The ZIF-8 absorbent prepared in this embodiment has an average particle size of 0.7 μm and a pore volume of 0.661 cm 3 / g, pore size of 1.15nm, specific surface area of ​​1510m 2 / g, with a purity of 85.2%.

[0092] The capture efficiency of Cl reaches 65%. After the residual carbon is washed and leached, the metal Zn 2+ The recovery rate reached 90%.

[0093] Finally, it should be noted that the technical solutions implemented above are examples, which are only used to illustrate the technical solutions of this article, and are not intended to limit them. For those skilled in the art, modifications and replacements can still be made based on the examples, which obviously fall within the scope of protection of the present invention. The present invention is not limited to the above-mentioned embodiments, but also has many other variations. Simple modifications and changes to the embodiments according to the technical essence of the present invention are all within the scope of protection of the present invention without departing from the technical solution ideas of the present invention.

Claims

1. A method for preparing a size-controllable high-purity ZIF-8 material, characterized in that: The steps include: 1) dissolving the amine-containing organic ligand and the zinc salt in an alcohol solvent at room temperature to prepare a mixed solution; 2) adding a deprotonating agent and a template agent to the obtained mixed solution, and then stirring and reacting at low temperature, standing for aging, collecting a milky white precipitate by centrifugation, washing, and drying to obtain a ZIF-8 precursor material; 3) The obtained ZIF-8 precursor material is subjected to gradient calcination under an inert atmosphere to obtain high-purity ZIF-8 materials of different sizes.

2. The preparation method according to claim 1, characterized in that The zinc salt is one or more of zinc acetate, zinc nitrate and zinc sulfate; the amine-containing organic ligand is a mixture of one or more of 2-amino-1-methylimidazole, N,N-dimethylformamide and acetamide and 2-methylimidazole.

3. The preparation method according to claim 1, characterized in that The molar ratio of the zinc salt to the organic ligand is 1:4-34.

4. The preparation method according to claim 1, characterized in that The protonating agent is triethanolamine; and the template agent is polyethylene glycol.

5. The preparation method according to claim 1, characterized in that The low temperature is 5-10°C; the stirring reaction time is 1.5-2h.

6. The preparation method according to claim 1, characterized in that The target calcination temperature of the gradient calcination is 300-400°C; the adopted heating system includes: first heating to 90-105°C at a rate of 4-6°C / min, keeping warm for 15-30 minutes; then heating to 300-400°C at a rate of 10-15°C / min, keeping warm for 15-30 minutes.

7. The high-purity ZIF-8 material prepared by the preparation method according to any one of claims 1 to 6, characterized in that: Its average particle size is 0.5-4 μm, the purity is as high as 98.5-99.5%, and the pore volume is 0.6-0.69 cm 3 / g, average pore diameter of 1.16-1.42nm, specific surface area of ​​1500-1800m 2 / g.

8. A method for Cl capture using the high-purity ZIF-8 material according to claim 7, characterized in that: The steps include: (1) transporting the high-purity ZIF-8 material and PVC mixture to a pyrolysis reactor and introducing inert gas for co-pyrolysis; (2) condensing the volatile matter obtained from the co-pyrolysis, and collecting the liquid and gas separately to obtain liquid fuel products and gas products; (3) The carbon residue obtained by co-pyrolysis is subjected to hot water leaching, solid-liquid separation, recovery of metal substances, and separate recovery of the carbon residue and liquid phase after leaching.

9. The method according to claim 8, characterized in that The mass ratio of the high-purity ZIF-8 material to PVC is (0.5-2):

1.

10. The method according to claim 8, characterized in that The inert gas used in the co-pyrolysis is nitrogen, the temperature is 200-450° C., the heating rate is 8-12° C. / min, and the holding time is 25-35 min.

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