Preparation method and application of MOF (Metal Organic Framework) catalyst taking PET (Polyethylene Terephthalate) waste plastics as ligand source

Abstract

The invention discloses a preparation method and application of an MOF (Metal Organic Framework) catalyst taking PET (Polyethylene Terephthalate) waste plastics as a ligand source. The method comprises the following steps: depolymerizing PET to obtain terephthalic acid, taking the terephthalic acid as an organic framework for preparing MOF, adding a metal salt, an organic solvent, a regulator and the like into a reaction system, and reacting under the condition of heating or normal temperature. And after the reaction, centrifuging, washing, drying and the like are performed to finally obtain the MOF catalyst. The obtained catalyst has good thermal stability at the temperature of 400 DEG C or below, and has good performance of catalyzing olefin to be oxidized into epoxide. High-value conversion of volatile organic pollutants is achieved while PET is efficiently recycled, and environmental pollution is reduced. The preparation method provided by the invention not only is simple to operate and remarkable in cost benefit, but also can support gram-scale catalyst production, and is a method for effective recovery and resource utilization of waste plastics.

Description

Technical Field

[0001] The invention relates to the field of metal organic framework materials and catalytic oxidation, and in particular to a preparation method and application of a MOF catalyst using PET waste plastics as a ligand source. Background Art

[0002] While plastics bring convenience to our daily lives, they also bring a heavy burden to the environment due to their difficulty in degradation. With the increasing demand for plastics, the global annual production of plastics exceeds 35 billion tons, of which the annual production of PET plastics reaches about 400,000 tons. A large amount of waste plastics are often disposed of by landfill and incineration, and only 3% of waste plastics are recycled. At the same time, styrene, as a volatile organic compound, poses a serious threat to the ecological environment and can pollute water sources, soil, and the atmosphere.

[0003] In order to solve the environmental problems caused by a large amount of waste plastics, it is particularly important to recycle PET plastics reasonably and efficiently. Using waste PET as a ligand source to prepare metal organic framework (MOF) materials and apply them to adsorption, supercapacitors and other fields has been proven to be an effective strategy. CN115960366B discloses a method for preparing MOF materials using waste PET and stainless steel washing waste, and the PET fragments after acid hydrolysis are mixed with stainless steel pickling wastewater and then subjected to high temperature treatment. The resulting MOF material shows good performance in rhodamine adsorption. CN1177725155A discloses a method for preparing MOF adsorbents using PET waste plastics, which first depolymerizes PET to obtain terephthalic acid, and then uses a one-pot method to disperse metal ions into the resin pores using a complexing agent to prepare MOF-loaded resin composite adsorbents, which perform well in Congo red adsorption. Although there have been reports on the use of PET to prepare MOF materials, there is currently no report on the use of PET as an organic ligand source to prepare MOF catalysts and apply them to catalyze olefin epoxidation to convert them into high value-added chemicals. In view of this, it is of great significance to develop a method for preparing MOF catalysts using PET as an organic ligand source for catalyzing olefin epoxidation reactions, which will not only help to achieve pollution control, but also promote the high-value recycling of waste plastics. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a MOF catalyst by utilizing PET waste plastics as a source of organic ligands.

[0005] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0006] A method for preparing a MOF catalyst using PET waste plastic as a ligand source comprises the following steps:

[0007] S1. Add PET waste plastic, alkali and alcohol into a flask, condense and reflux at 180°C, add deionized water after cooling, and stir to obtain a mixed solution;

[0008] S2. The mixture was filtered, 1-10 mol / L H2SO4 solution was added dropwise to obtain a white precipitate, allowed to stand for 30 minutes, centrifuged to obtain a white product, washed and dried to obtain depolymerized terephthalic acid;

[0009] S3. The terephthalic acid obtained in S2 is mixed with a metal salt, N,N-dimethylformamide, a regulator and deionized water, and then transferred to a polytetrafluoroethylene-lined reactor to react at a certain temperature;

[0010] S4. After the reaction is completed, the mixture is cooled, and the MOF catalyst is obtained through centrifugal separation, washing, and drying.

[0011] Preferably, the base in step S1 is one or more of sodium hydroxide, potassium hydroxide, barium hydroxide, and calcium hydroxide; the alcohol is one or more of methanol, ethanol, ethylene glycol, 1,3-propylene glycol, glycerol, 1,4-butanediol, and phenylethyl alcohol.

[0012] Preferably, in step S1, the liquid-to-solid ratio of alcohol to PET waste plastic is 2-8:1 mL / g, the mass ratio of alkali to PET waste plastic is 0.2-2:1, and the condensation reflux time is 1-12 h.

[0013] Preferably, in step S3, the metal salt is one or more of chromium nitrate, chromium sulfate, cobalt chloride, cobalt sulfate, cobalt nitrate, cobalt acetylacetonate, cerium sulfate, ammonium cerium nitrate, zirconium nitrate, zirconium sulfate, zirconium chloride, ferric chloride, ferric sulfate, ferric nitrate, ferric acetylacetonate and hydrate.

[0014] Preferably, the molar ratio of the metal salt to terephthalic acid in step S3 is 0.2-2:1.

[0015] Preferably, the regulator in step S3 is one or more of hydrochloric acid, nitric acid and sulfuric acid.

[0016] Preferably, the volume ratio of N,N-dimethylformamide to deionized water in step S3 is 0-5:1.

[0017] Preferably, the reaction temperature in step S3 is 25-180° C., and the reaction time is 12-48 h.

[0018] The application of the MOF catalyst in catalyzing olefin epoxidation. The method for preparing epoxides by catalyzing olefins using the MOF catalyst comprises the following steps: adding the MOF catalyst to an organic solvent, then adding olefins and an oxidant, reacting at 60-100° C. for 2-8 hours to obtain epoxides; the olefins include styrene, propylene, n-butene, isobutylene, cyclohexene or cyclopropene; the oxidant is one or more of tert-butyl hydroperoxide, hydrogen peroxide and oxygen.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides a method for preparing MOF from waste PET. The method uses terephthalic acid obtained by depolymerization of PET as an organic ligand to prepare a MOF catalyst. The obtained catalyst has good thermal stability below 400°C and has good performance in catalyzing the epoxidation of olefins to epoxides. While efficiently recycling PET, high-value conversion of volatile organic pollutants is achieved, reducing environmental pollution. The preparation method provided by the present invention is not only simple to operate, but also cost-effective, and can support gram-scale catalyst production. It is a method for effectively recycling and resource utilization of waste plastics. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD patterns of the MOF catalysts prepared in Examples 1-4.

[0022] Figure 2 FTIR graph of the MOF catalyst prepared in Example 1-4.

[0023] Figure 3 This is the TG graph of the Co-MOF catalyst prepared in Example 1.

[0024] Figure 4 This is the TG graph of the Ce-MOF catalyst prepared in Example 2.

[0025] Figure 5 TG graph of the Cr-MOF catalyst prepared in Example 3.

[0026] Figure 6 This is the TG graph of the Zr-MOF catalyst prepared in Example 4. DETAILED DESCRIPTION

[0027] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0028] Example 1

[0029] A method for preparing a Co-MOF catalyst using PET waste plastic as an organic ligand source comprises the following steps:

[0030] S1. Add 5g of PET waste plastic into a 500mL round-bottom flask, add 6g of NaOH, 27.5mL of ethylene glycol, condense and reflux at 180℃ for 1h, add 150mL of deionized water after cooling, and stir evenly.

[0031] S2. Filter the mixed solution, add 5 mol / L H2SO4 solution dropwise to obtain a white precipitate, and let stand for 30 minutes. Centrifuge to obtain a white product, wash, and dry to obtain depolymerized terephthalic acid.

[0032] S3. Weigh 2 g of terephthalic acid obtained in step S2, 1.56 g of cobalt chloride, 30 mL of N,N-dimethylformamide, and 15 mL of deionized water, mix and stir, then transfer to a polytetrafluoroethylene-lined reactor and react at 180°C for 24 h.

[0033] S4. After cooling, centrifugation, washing and drying were performed to obtain 1.77 g of Co-MOF catalyst.

[0034] The XRD pattern of the prepared Co-MOF catalyst is shown in Figure 1 The FTIR image of the prepared Co-MOF catalyst is shown in Figure 2 The TG diagram of the prepared Co-MOF catalyst is shown in Figure 3 shown. Figure 1 The appearance of the 9.0° diffraction characteristic peak and Figure 2 The appearance of the Co-O front in the sample indicates the successful synthesis of Co-MOF. Figure 3 The TG graphs show that Co-MOF has very good thermal stability below 400 °C.

[0035] Example 2

[0036] A method for preparing a Ce-MOF catalyst using PET waste plastic as an organic ligand source comprises the following steps:

[0037] S1. Add 5g of PET waste plastic into a 500mL round-bottom flask, add 6g of NaOH, 27.5mL of ethylene glycol, condense and reflux at 180℃ for 4h, then add 150mL of deionized water after cooling and stir evenly.

[0038] S2. Filter the mixed solution, add 5 mol / L H2SO4 solution dropwise to obtain a white precipitate, and let stand for 30 minutes. Centrifuge to obtain a white product, wash, and dry to obtain depolymerized terephthalic acid.

[0039] S3. Weigh 0.17 g of terephthalic acid obtained in step S2 and add it to a beaker containing 7.30 g of N,N-dimethylformamide to obtain solution A. Meanwhile, dissolve 0.82 g of cerium ammonium nitrate in a glass beaker containing 1.8 mL of deionized water and stir for 30 minutes to obtain solution B. Add solution B dropwise into solution A, and stir the mixed solution at room temperature for 24 hours.

[0040] S4. After centrifugation, washing and drying, 0.4 g of Ce-MOF catalyst was obtained.

[0041] The XRD pattern of the prepared Ce-MOF catalyst is shown in Figure 1 The FTIR image of the prepared Ce-MOF catalyst is shown in Figure 2 The TG diagram of the prepared Ce-MOF catalyst is shown in Figure 4 shown. Figure 1 The appearance of the 7.1° and 8.2° diffraction characteristic peaks and Figure 2 The appearance of Ce-O front in the sample indicates the successful synthesis of Ce-MOF. Figure 4 The TG graph shows that Ce-MOF has good thermal stability below 300°C.

[0042] Example 3

[0043] A method for preparing a Cr-MOF catalyst using PET waste plastic as an organic ligand source comprises the following steps:

[0044] S1. Add 5g of PET waste plastic into a 500mL round-bottom flask, add 6g of NaOH, 27.5mL of ethylene glycol, condense and reflux at 180℃ for 4h, then add 150mL of deionized water after cooling and stir evenly.

[0045] S2. The mixed solution was filtered, 5 mol / L H2SO4 solution was added dropwise to obtain a white precipitate, which was allowed to stand for 30 minutes and centrifuged to obtain a white product, which was washed and dried to obtain depolymerized terephthalic acid.

[0046] S3. Weigh 0.83 g of terephthalic acid obtained in step S2, 2.01 g of chromium nitrate nonahydrate, and 30 mL of deionized water, then add 0.25 mL of nitric acid dropwise while stirring, mix well, transfer to a polytetrafluoroethylene-lined reactor, and react at 160°C for 24 h.

[0047] S4. After cooling, centrifugation, washing and drying were performed to obtain 0.42 g of Cr-MOF catalyst.

[0048] The XRD pattern of the prepared Cr-MOF catalyst is shown in Figure 1 The FTIR image of the prepared Cr-MOF catalyst is shown in Figure 2The TG diagram of the prepared Cr-MOF catalyst is shown in Figure 5 shown. Figure 1 The appearance of 3.3° and 9.0° diffraction peaks and Figure 2 The appearance of Cr-O front indicates the successful synthesis of Cr-MOF. Figure 5 The TG graph shows that Cr-MOF has good thermal stability below 400 °C.

[0049] Example 4

[0050] A method for preparing a Zr-MOF catalyst using PET waste plastic as an organic ligand source comprises the following steps:

[0051] S1. Add 5g of PET waste plastic into a 500mL round-bottom flask, add 6g of NaOH, 27.5mL of ethylene glycol, condense and reflux at 180℃ for 4h, then add 150mL of deionized water after cooling and stir evenly.

[0052] S2. Filter the mixed solution, add 5 mol / L H2SO4 solution dropwise to obtain a white precipitate, and let stand for 30 minutes. Centrifuge to obtain a white product, wash, and dry to obtain depolymerized terephthalic acid.

[0053] S3. Weigh 1.26 g of terephthalic acid obtained in step S2, 0.88 g of zirconium chloride, and 30 mL of N,N-dimethylformamide containing 2 mL of hydrochloric acid, mix and stir, and transfer to a polytetrafluoroethylene-lined reactor and react at 180°C for 24 h.

[0054] S4. After cooling, centrifugation, washing and drying were performed to obtain 1.36 g of Zr-MOF catalyst.

[0055] The XRD pattern of the prepared Zr-MOF catalyst is shown in Figure 1 The FTIR image of the prepared Zr-MOF catalyst is shown in Figure 2 The TG diagram of the prepared Zr-MOF catalyst is shown in Figure 6 shown. Figure 1 The appearance of the 7.3° and 8.5° diffraction characteristic peaks and Figure 2 The appearance of Zr-O front indicates the successful synthesis of Zr-MOF. Figure 6 The TG graph shows that Zr-MOF has good thermal stability below 500°C.

[0056] Example 5

[0057] The application of catalytic styrene oxidation comprises the following steps:

[0058] 0.6 g of styrene, 8 mL of acetonitrile, 30 mg of the Co-MOF catalyst described in Example 1, 3.1 mL of tert-butyl hydroperoxide, and 50 mg of biphenyl as an internal standard were added to a 35 mL thick-walled pressure-resistant tube, and the reaction was carried out at 100 ° C for 8 hours. The reaction results were analyzed by gas chromatography and the products were quantified by the internal standard method. The results showed that the conversion rate of styrene reached 99% and the yield of styrene oxide reached 46%. It shows that the Co-MOF catalyst of the present invention has a good performance in catalyzing the oxidation of styrene to generate styrene oxide.

[0059] Example 6

[0060] The application of catalytic styrene oxidation comprises the following steps:

[0061] 0.6 g of styrene, 8 mL of acetonitrile, 30 mg of the Ce-MOF catalyst described in Example 2, 2 mL of tert-butyl hydroperoxide, and 50 mg of biphenyl as an internal standard were added to a 35 mL thick-walled pressure-resistant tube, and the reaction was carried out at 80° C. for 6 h. The reaction results were analyzed by gas chromatography, and the products were quantified by the internal standard method. The results showed that the conversion rate of styrene reached 68%, and the yield of styrene oxide reached 27%.

[0062] Example 7

[0063] The application of catalytic styrene oxidation comprises the following steps:

[0064] 0.6 g of styrene, 8 mL of acetonitrile, 30 mg of the Cr-MOF catalyst described in Example 3, 2 mL of tert-butyl hydroperoxide, and 50 mg of biphenyl as an internal standard were added to a 35 mL thick-walled pressure-resistant tube, and the reaction was carried out at 80° C. for 6 h. The reaction results were analyzed by gas chromatography, and the products were quantified by the internal standard method. The results showed that the conversion rate of styrene reached 61%, and the yield of styrene oxide reached 21%.

[0065] Example 8

[0066] The application of catalytic styrene oxidation comprises the following steps:

[0067] 0.6 g of styrene, 8 mL of acetonitrile, 30 mg of the Zr-MOF catalyst described in Example 4, 2 mL of tert-butyl hydroperoxide, and 50 mg of biphenyl as an internal standard were added to a 35 mL thick-walled pressure-resistant tube, and the reaction was carried out at 80° C. for 6 h. The reaction results were analyzed by gas chromatography, and the products were quantified by the internal standard method. The results showed that the conversion rate of styrene reached 18%, and the yield of styrene oxide reached 5%.

Claims

1. A method for preparing a MOF catalyst using PET waste plastic as a ligand source, characterized in that: The steps include: S1. Add PET waste plastic, alkali and alcohol into a flask, condense and reflux at 180°C, add deionized water after cooling, and stir to obtain a mixed solution; S2. The mixture was filtered, 1-10 mol / L H2SO4 solution was added dropwise to obtain a white precipitate, allowed to stand for 30 minutes, centrifuged to obtain a white product, washed and dried to obtain depolymerized terephthalic acid; S3. The terephthalic acid obtained in S2 is mixed with a metal salt, N,N-dimethylformamide, a regulator and deionized water, and then transferred to a polytetrafluoroethylene-lined reactor to react at a certain temperature; S4. After the reaction is completed, the mixture is cooled, and the MOF catalyst is obtained through centrifugal separation, washing, and drying.

2. The method for preparing the MOF catalyst according to claim 1, characterized in that: The alkali in step S1 is one or more of sodium hydroxide, potassium hydroxide, barium hydroxide, and calcium hydroxide; The alcohol is one or more of methanol, ethanol, ethylene glycol, 1,3-propylene glycol, glycerol, 1,4-butanediol, and phenylethyl alcohol.

3. The method for preparing the MOF catalyst according to claim 1, characterized in that: In step S1, the liquid-to-solid ratio of alcohol to PET waste plastic is 2-8:1 mL / g, the mass ratio of alkali to PET waste plastic is 0.2-2:1, and the condensation reflux time is 1-12 h.

4. The method for preparing the MOF catalyst according to claim 1, characterized in that: In step S3, the metal salt is one or more of chromium nitrate, chromium sulfate, cobalt chloride, cobalt sulfate, cobalt nitrate, cobalt acetylacetonate, cerium sulfate, cerium ammonium nitrate, zirconium nitrate, zirconium sulfate, zirconium chloride, ferric chloride, ferric sulfate, ferric nitrate, ferric acetylacetonate and hydrate.

5. The method for preparing the MOF catalyst according to claim 1, characterized in that: The molar ratio of the metal salt to terephthalic acid in step S3 is 0.2-2:

1.

6. The method for preparing the MOF catalyst according to claim 1, characterized in that: The regulator in step S3 is one or more of hydrochloric acid, nitric acid and sulfuric acid.

7. The method for preparing the MOF catalyst according to claim 1, characterized in that: The volume ratio of N,N-dimethylformamide to deionized water in step S3 is 0-5:

1.

8. The method for preparing the MOF catalyst according to claim 1, characterized in that: The reaction temperature in step S3 is 25-180° C., and the reaction time is 12-48 h.

9. Use of the MOF catalyst according to claim 1 in catalyzing olefin epoxidation.

10. A method for preparing epoxide from olefins using the MOF catalyst according to claim 1, characterized in that: The steps include: The MOF catalyst is added to an organic solvent, and then an olefin and an oxidant are added, and the reaction is carried out at 60-100° C. for 2-8 hours to obtain an epoxide; the olefin includes styrene, propylene, n-butene, isobutylene, cyclohexene or cyclopropene; the oxidant is one or more of tert-butyl hydroperoxide, hydrogen peroxide, and oxygen.

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