Use of magnetic core-shell particles in pet degradation

Abstract

The application discloses application of Fe3O4@ZIF-8 magnetic core-shell particles in PET degradation, wherein superparamagnetic nano Fe3O4 is prepared by a hydrothermal method, and Fe3O4@ZIF-8 magnetic core-shell particles are synthesized by adopting a sodium polystyrene sulfonate (PSS) surface modification method. The Fe3O4@ZIF-8 magnetic core-shell particles provided by the application have superhigh porosity and easily obtained nano-pores, the catalyst is used in a glycol alcoholysis reaction of PET, and the catalyst can effectively reduce the introduction of impurities in a reaction system and improve product purity. Meanwhile, the superhigh pores of the catalyst have very strong adsorption performance, and the catalyst can greatly improve the whiteness of product bis-hydroxyethyl terephthalate (BHET). In addition, the catalyst has excellent recycling performance, and can keep original catalytic activity after multiple recycling.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling, specifically relating to the application of Fe3O4@ZIF-8 magnetic core-shell particles in PET degradation. Background Technology

[0002] Currently, the main methods for recycling waste polyethylene terephthalate (PET) are physical and chemical methods. Physical recycling methods are mostly "downgrading recycling," resulting in low-value recycled PET that can generally only be recycled once or twice. Chemical recycling methods degrade PET into monomers or oligomers, eliminating the limitations of raw materials for PET recycling. The resulting products are of high quality, have wide applications, and are not limited by downgrading or the number of recycling cycles. Currently, the main chemical recycling methods for PET include hydrolysis, methanol alcoholysis, ethylene glycol alcoholysis, and other chemical depolymerization methods.

[0003] Nano-Fe3O4, due to its high specific surface area, tunable pore size, and rich structure and composition, has been widely used in energy storage, gas-liquid phase separation, catalysis, optics, and magnetism. Currently, using magnetic nano-oxides as catalysts and achieving efficient and reusable catalysts through magnetic separation is a research hotspot in PET alcoholysis. Leian Bartolome et al. prepared superparamagnetic γ-Fe2O3 via co-precipitation and calcination. These magnetic nanoparticles achieved a BHET yield of over 90% at 300℃ and m(catalyst / PET) = 0.05, and over 80% at 255℃ and m(catalyst / PET) = 0.1. This demonstrates that magnetic nanomaterials, as magnetically separable catalysts, have great application potential in chemical catalysis.

[0004] However, metal oxide catalysts also have limitations, such as easy aggregation, easy oxidation, high required degradation temperature, poor catalytic efficiency, and low recovery rate for some catalysts. ZIFs are a novel type of MOF material with a tetrahedral three-dimensional network structure. They can be prepared using any metal as the metal source, and the pore size and coordination mode of the prepared metal framework can be adjusted. Moreover, most of the active sites are exposed, making loading more convenient. Coating ZIFs onto the surface of magnetic Fe3O4 nanoparticles forms a stable bimetallic core-shell morphology, which not only provides twice the number of coordination sites between metal ions and oxygen atoms, but also gives the catalyst excellent chemical stability and adsorption performance. Summary of the Invention

[0005] To address the shortcomings or deficiencies of existing technologies, this invention provides an application of Fe3O4@ZIF-8 magnetic core-shell particles in PET degradation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An application of Fe3O4@ZIF-8 magnetic core-shell particles in PET degradation, wherein the preparation of the Fe3O4@ZIF-8 magnetic core-shell particles includes the following steps: (1) Dissolve ferric chloride in ethylene glycol at room temperature by stirring to form a ferric chloride alcohol solution; (2) Sodium acetate was added to the obtained ferric chloride alcohol solution, and the resulting brown mixture was transferred into a hydrothermal synthesis reactor for reaction; (3) The black Fe3O4 magnetic particles obtained from the reaction were recovered by a magnet, and washed alternately with water and ethanol and dried. (4) Add sodium polystyrene sulfonate (PSS) to water and stir to dissolve, thus preparing a PSS solution; (5) Add a certain amount of Fe3O4 magnetic particles to the obtained PSS solution, stir at room temperature, and then use a magnet to recover the Fe3O4 magnetic particles and wash them with water to obtain the modified magnetic particles. (6) 2-Methylimidazole was mixed with anhydrous zinc acetate and methanol and subjected to a hydrothermal reaction to obtain the synthesis solution of ZIF-8. (7) The modified magnetic particles were added to the synthesis solution of ZIF-8. After mechanical stirring at a certain temperature for a certain time, the synthesized Fe3O4@ZIF-8 magnetic core-shell particles were separated from the reaction system using a magnet, washed with methanol and dried.

[0007] Furthermore, the stirring time in step (1) is 30 minutes.

[0008] Furthermore, the concentration of the ferric chloride alcohol solution obtained in step (1) is 5.4 g / 100 mL.

[0009] Furthermore, in step (2), the mass ratio of sodium acetate added to ferric chloride is 2:1.

[0010] Furthermore, the reaction in step (2) is carried out at a temperature of 200°C for 8 hours.

[0011] Furthermore, in step (3), the washing process involves alternating between water and ethanol three times.

[0012] Furthermore, the mass concentration of the PSS solution obtained in step (4) is 1.5%.

[0013] Furthermore, in step (5), the amount of Fe3O4 magnetic particles added is 2.5 mg / ml.

[0014] Furthermore, the stirring time in step (5) is 30 minutes.

[0015] Furthermore, the ZIF-8 synthesis solution described in step (6) consists of 1.2 g anhydrous zinc acetate, 2.6 g 2-methylimidazole and 80 mL methanol.

[0016] Furthermore, the hydrothermal reaction in step (6) is carried out at a temperature of 70°C for 10 minutes.

[0017] Furthermore, in step (7), the amount of modified magnetic particles added is 3 mg / mL.

[0018] Furthermore, the temperature of the mechanical stirring reaction in step (7) is 50°C and the time is 2 hours.

[0019] Furthermore, in step (7), the sample is washed three times with methanol.

[0020] Furthermore, the drying temperature in steps (3) and (7) is 60°C and the drying time is 12 hours.

[0021] Furthermore, the specific application method involves using ethylene glycol as a solvent and the Fe3O4@ZIF-8 magnetic core-shell particles as a catalyst to perform alcoholysis on PET.

[0022] Furthermore, in the alcoholysis, the amount of magnetic core-shell particles used is 0.3%-0.5% of the PET mass; the alcoholysis temperature is 180℃-210℃, and the time is 30min-60min.

[0023] The Fe3O4@ZIF-8 magnetic core-shell particles provided by this invention have ultra-high porosity and easily obtainable nanopores, which can provide more metal sites to bond with oxygen atoms in the polyethylene terephthalate (PET) structure. Moreover, their electron-withdrawing effect is stronger, making it easier for carbon atoms in the carbonyl group to be attacked by oxygen atoms in ethylene glycol to form a transition state, thereby generating the product dihydroxyethyl terephthalate (BHET) and enabling permanent recycling of PET.

[0024] Compared with the prior art, the significant advantages of the present invention are: 1. The magnetic nano-core-shell bimetallic organic framework Fe3O4@ZIFs catalyst used in this invention has higher catalytic activity than single metal catalysts, and its crystal structure is more stable and regular, with higher heat resistance.

[0025] 2. The nanocatalyst used in this invention has a large specific surface area and adjustable pore size. The catalytic activity can be improved by increasing the surface area of ​​the active sites. The high specific surface area and the combined effect of metal cations and carbonyl groups greatly improve the yield of BHET. The high specific surface area and high adsorption capacity can also improve the whiteness of the product.

[0026] 3. The magnetic nano-core-shell bimetallic organic framework Fe3O4@ZIFs catalyst retains the activity of solid catalysts while endowing them with certain magnetic properties, enabling them to achieve rapid separation and recovery under the action of an external magnetic field. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating the synthesis process of the Fe3O4@ZIF-8 magnetic core-shell particles of this invention.

[0028] Figure 2 SEM image of the prepared Fe3O4@ZIF-8 magnetic core-shell particles.

[0029] Figure 3 The IR spectrum of the prepared Fe3O4@ZIF-8 magnetic core-shell particles. Detailed Implementation

[0030] The present invention is illustrated by the following embodiments, but the present invention is not limited to the following embodiments. Any variations are included within the scope of the present invention without departing from the general spirit and intent.

[0031] A Fe3O4@ZIF-8 magnetic core-shell particle, the preparation of which includes the following steps: (1) Dissolve 2.7g of ferric chloride in 50mL of ethylene glycol at room temperature for 30min to form a ferric chloride alcohol solution; (2) Add 5.4 g of sodium acetate to the obtained ferric chloride alcohol solution, and transfer the resulting brown mixture into a hydrothermal synthesis reactor (the reactor is composed of a polytetrafluoroethylene liner and a stainless steel outer shell) and react at 200°C for 8 h. (3) The black Fe3O4 magnetic particles obtained from the reaction were recovered by a magnet and washed three times with water and ethanol alternately, and dried at 60℃ and -0.1MPa for 12h. (4) Add 1.5g of sodium polystyrene sulfonate (PSS) solid to 100mL of water and stir to dissolve, so as to prepare a PSS solution with a concentration of 1.5%; (5) Add 0.25g of Fe3O4 magnetic particles to the obtained PSS solution, stir at room temperature for 30min, then use a magnet to recover the Fe3O4 magnetic particles and wash with water to obtain the modified magnetic particles. (6) Mix 2.6g of 2-methylimidazole with 1.2g of anhydrous zinc acetate and 80mL of methanol, and react hydrothermally at 70℃ for 10min to obtain the synthesis solution of ZIF-8; (7) The modified magnetic particles were added to the ZIF-8 synthesis solution. After mechanical stirring at 50°C for 2 hours, the synthesized Fe3O4@ZIF-8 magnetic core-shell particles were separated from the reaction system using a magnet, washed with methanol, and dried at 60°C for 12 hours for later use. The SEM and IR images of the obtained Fe3O4@ZIF-8 magnetic core-shell particles are shown below. Figure 2 , 3 .

[0032] Example 1 Using PET granules as raw material, 2.0 g of PET, 7.0 g of ethylene glycol, and 0.01 g of Fe3O4@ZIF-8 magnetic core-shell particles were added sequentially to a 100 mL three-necked flask equipped with a thermometer, stirring rotor, and spherical condenser. The flask was then placed in a constant-temperature oil bath, and the reaction temperature was controlled at 180 °C. After reflux for 30 min, the unreacted PET raw material was separated by hot filtration, dried, and weighed. A certain amount of boiling water was then added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated, resulting in the precipitation of white needle-like crystals. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. The calculated degradation rate of PET was 27.2%, and the yield of monomeric BHET was 7.6%.

[0033] Example 2 Using PET granules as raw material, 2.0 g of PET, 7.0 g of ethylene glycol, and 0.01 g of Fe3O4@ZIF-8 magnetic core-shell particles were added sequentially to a 100 mL three-necked flask equipped with a thermometer, stirring rotor, and spherical condenser. The flask was then placed in a constant-temperature oil bath, and the reaction temperature was controlled at 195 °C. After reflux for 30 min, the unreacted PET raw material was separated by hot filtration, dried, and weighed. A certain amount of boiling water was then added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated, resulting in the precipitation of white needle-like crystals. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. The calculated degradation rate of PET was 30.8%, and the yield of monomeric BHET was 11.7%.

[0034] Example 3 Using PET granules as raw material, 2.0 g of PET, 7.0 g of ethylene glycol, and 0.01 g of Fe3O4@ZIF-8 magnetic core-shell particles were added sequentially to a 100 mL three-necked flask equipped with a thermometer, stirring rotor, and spherical condenser. The flask was then placed in a constant-temperature oil bath, and the reaction temperature was controlled at 200 °C. After reflux for 30 min, the unreacted PET raw material was separated by hot filtration, dried, and weighed. A certain amount of boiling water was then added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated, resulting in the precipitation of white needle-like crystals. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. The calculated degradation rate of PET was 36.5%, and the yield of monomeric BHET was 19.5%.

[0035] Example 4 Using PET granules as raw material, 2.0 g of PET, 7.0 g of ethylene glycol, and 0.01 g of Fe3O4@ZIF-8 magnetic core-shell particles were added sequentially to a 100 mL three-necked flask equipped with a thermometer, stirring rotor, and spherical condenser. The flask was then placed in a constant-temperature oil bath, and the reaction temperature was controlled at 205 °C. After reflux for 30 min, the unreacted PET raw material was separated by hot filtration, dried, and weighed. A certain amount of boiling water was then added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated, resulting in the precipitation of white needle-like crystals. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. The calculated degradation rate of PET was 50.7%, and the yield of monomeric BHET was 32.0%.

[0036] Example 5 Using PET granules as raw material, 2.0 g of PET, 7.0 g of ethylene glycol, and 0.01 g of Fe3O4@ZIF-8 magnetic core-shell particles were added sequentially to a 100 mL three-necked flask equipped with a thermometer, stirring rotor, and spherical condenser. The flask was then placed in a constant-temperature oil bath, and the reaction temperature was controlled at 210 °C. After reflux for 30 min, the unreacted PET raw material was separated by hot filtration, dried, and weighed. A certain amount of boiling water was then added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated, resulting in the precipitation of white needle-like crystals. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. The degradation rate of PET was calculated to be 98.8%, and the yield of monomeric BHET was 64.3%.

[0037] Example 6 Using PET granules as raw material, 2.0 g of PET, 7.0 g of ethylene glycol, and 0.01 g of Fe3O4@ZIF-8 magnetic core-shell particles were added sequentially to a 100 mL three-necked flask equipped with a thermometer, stirring rotor, and spherical condenser. The flask was then placed in a constant-temperature oil bath, and the reaction temperature was controlled at 205 °C. After reflux for 40 min, the unreacted PET raw material was separated by hot filtration, dried, and weighed. A certain amount of boiling water was then added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated, resulting in the precipitation of white needle-like crystals. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. The calculated degradation rate of PET was 74.2%, and the yield of monomeric BHET was 50.6%.

[0038] Example 7 Using PET granules as raw material, 2.0 g of PET, 7.0 g of ethylene glycol, and 0.01 g of Fe3O4@ZIF-8 magnetic core-shell particles were added sequentially to a 100 mL three-necked flask equipped with a thermometer, stirring rotor, and spherical condenser. The flask was then placed in a constant-temperature oil bath, and the reaction temperature was controlled at 205 °C. After reflux for 50 min, the unreacted PET raw material was separated by hot filtration, dried, and weighed. A certain amount of boiling water was then added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated, resulting in the precipitation of white needle-like crystals. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. The calculated degradation rate of PET was 84.7%, and the yield of monomeric BHET was 52.0%.

[0039] Example 8 Using PET granules as raw material, 2.0 g of PET, 7.0 g of ethylene glycol, and 0.01 g of Fe3O4@ZIF-8 magnetic core-shell particles were added sequentially to a 100 mL three-necked flask equipped with a thermometer, stirring rotor, and spherical condenser. The flask was then placed in a constant-temperature oil bath, and the reaction temperature was controlled at 205 °C. After reflux for 60 min, the unreacted PET raw material was separated by hot filtration, dried, and weighed. A certain amount of boiling water was then added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated, resulting in the precipitation of white needle-like crystals. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. The degradation rate of PET was calculated to be 99.1%, and the yield of monomeric BHET was 45.3%.

[0040] Example 9 Using PET granules as raw material, 2.0 g of PET, 7.0 g of ethylene glycol, and 0.006 g of Fe3O4@ZIF-8 magnetic core-shell particles were added sequentially to a 100 mL three-necked flask equipped with a thermometer, stirring rotor, and spherical condenser. The flask was then placed in a constant-temperature oil bath, and the reaction temperature was controlled at 205 °C. After reflux for 40 min, the unreacted PET raw material was separated by hot filtration, dried, and weighed. A certain amount of boiling water was then added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated, resulting in the precipitation of white needle-like crystals. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. The calculated degradation rate of PET was 67.7%, and the yield of monomeric BHET was 43.4%.

[0041] Example 10 Using PET granules as raw material, 2.0 g of PET, 7.0 g of ethylene glycol, and 0.014 g of Fe3O4@ZIF-8 magnetic core-shell particles were added sequentially to a 100 mL three-necked flask equipped with a thermometer, stirring rotor, and spherical condenser. The flask was then placed in a constant-temperature oil bath, and the reaction temperature was controlled at 205 °C. After reflux for 40 min, the unreacted PET raw material was separated by hot filtration, dried, and weighed. A certain amount of boiling water was then added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated, resulting in the precipitation of white needle-like crystals. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. The calculated degradation rate of PET was 81.3%, and the yield of monomeric BHET was 57.6%.

[0042] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. The application of Fe3O4@ZIF-8 magnetic core-shell particles in PET degradation, characterized in that: The preparation of the Fe3O4@ZIF-8 magnetic core-shell particles includes the following steps: (1) Dissolve ferric chloride in ethylene glycol at room temperature by stirring to form a ferric chloride alcohol solution; (2) Sodium acetate was added to the obtained ferric chloride alcohol solution, and the resulting brown mixture was transferred into a hydrothermal synthesis reactor for reaction; (3) The black Fe3O4 magnetic particles obtained from the reaction were recovered by a magnet, and washed with water and ethanol alternately and dried. (4) Add sodium polystyrene sulfonate to water and stir to dissolve it, so as to prepare a PSS solution with a mass concentration of 1.5%; (5) Add Fe3O4 magnetic particles to the obtained PSS solution at a rate of 2.5 mg / mL, stir for 30 min at room temperature, then use a magnet to recover the Fe3O4 magnetic particles and wash with water to obtain the modified magnetic particles. (6) Mix 2.6 g of 2-methylimidazole with 1.2 g of anhydrous zinc acetate and 80 mL of methanol, and react hydrothermally at 70 °C for 10 min to obtain the synthesis solution of ZIF-8. (7) The modified magnetic particles were added to the ZIF-8 synthesis solution at a rate of 3 mg / mL. After mechanically stirring the reaction at 50 °C for 2 h, the synthesized Fe3O4@ZIF-8 magnetic core-shell particles were separated from the reaction system using a magnet, washed with methanol and dried. The specific application method involves using ethylene glycol as a solvent and the Fe3O4@ZIF-8 magnetic core-shell particles as a catalyst to perform alcoholysis on PET; wherein the amount of magnetic core-shell particles used is 0.5% of the mass of PET; the alcoholysis temperature is 210℃ and the time is 30 min.

2. The application according to claim 1, characterized in that: The concentration of the ferric chloride alcohol solution obtained in step (1) is 5.4 g / 100 mL.

3. The application according to claim 1, characterized in that: In step (2), the mass ratio of sodium acetate to ferric chloride is 2:1; the reaction temperature is 200℃ and the reaction time is 8h.

Images