Method for recovering physical and chemical properties of inferior waste PET bottle flakes
Through the forward and reverse catalytic reactions of titanium-based catalysts, the degradation and repolymerization of inferior waste PET bottle flakes are achieved, solving the problem of decreased physical and chemical properties and realizing efficient and green recycling.
Patent Information
- Application Number
- CN202410258775.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-03-07
- Publication Date
- 2025-09-09
AI Technical Summary
In the existing technology, the physical and chemical properties of inferior waste PET bottle flakes decrease during the physical recycling process, resulting in them being landfilled and incinerated, wasting resources and causing harm to the environment.
Titanium-based catalysts are used to carry out forward and reverse catalytic reactions under specific conditions to achieve the degradation of PET bottle flakes and the repolymerization of monomers, thereby restoring their physical and chemical properties.
Through degradation and repolymerization, the physical and chemical properties of inferior waste PET bottle flakes are restored, reducing the demand for new materials, improving resource utilization efficiency and reducing environmental pollution.
Smart Images
Figure CN120607699A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of plastic resource utilization, and in particular to a method for recycling inferior waste PET bottle flakes by using a titanium-based catalyst, thereby restoring their physical and chemical properties. Background Art
[0002] Polyethylene terephthalate (PET) bottle flakes are widely used in the outer packaging of soft drinks, dairy products, alcohol, cooking oil, condiments, etc. due to their superior mechanical properties, excellent tolerance, and low permeability to gas and water. By 2020, the demand for PET-based plastics has exceeded 400 million tons. Since most PET products are disposable consumer goods, their large-scale use releases excessive amounts of low-quality waste PET bottle flakes into the environment. Due to the non-biodegradable nature of PET bottle flakes during the human life cycle, the accumulation of low-quality waste PET bottle flakes in the environment poses a huge threat to soil, oceans, and organisms. Therefore, the recycling and utilization of low-quality waste PET bottle flakes has become a research hotspot in recent years.
[0003] The physical recycling of used PET bottle flakes generally involves four steps. First, used PET bottles are collected and sorted. At the recycling plant, they are categorized by color, shape, and other characteristics. The sorted PET bottles are then crushed and cleaned. These bottles are fed into a crusher, where they are broken into small particles, forming flakes. The flakes then undergo a cleaning process to remove dirt and impurities, ensuring they meet reuse standards. The cleaned flakes then enter a melting furnace, where they are heated to a high temperature and melted. The melted PET material passes through a special filter to remove further impurities, then is injected into water to form fine particles, known as pellets. Ultimately, these PET pellets can be recycled through processes such as injection molding, extrusion, and spinning to manufacture a variety of PET products, such as new PET bottles, fiber products, and plastic packaging.
[0004] During the physical recycling of used PET bottle flakes, the aforementioned steps are repeated over and over again. After long-term, repeated use, the physical and chemical properties of the PET bottle flakes deteriorate to a certain extent. This damage is inevitable with physical recycling methods, and the only option for these damaged, low-quality used PET bottle flakes is the most primitive landfill and incineration methods. This practice not only wastes resources but also causes significant harm to the environment.
[0005] The present invention provides a method for restoring the physical and chemical properties of low-quality waste PET bottle flakes. This method utilizes a titanium-based metal catalyst in the presence of a catalyst to reverse the forward and reverse catalytic reactions, thereby achieving degradation of the PET flakes and repolymerization of the monomers, thereby restoring the properties of the low-quality waste PET bottle flakes.
[0006] This method, while utilizing minimal catalyst usage, low energy consumption, and the repeated recycling of EG, not only achieves efficient degradation of low-quality waste PET bottle flakes but also restores their physical and chemical properties through repolymerization. This method, operating under mild industrial conditions and utilizing a green, efficient catalyst, restores the physical and chemical properties of low-quality waste PET bottle flakes, reducing the demand for new materials, improving resource utilization efficiency, and minimizing environmental pollution. It represents a green and environmentally friendly technology for recycling low-quality waste PET bottle flakes. Summary of the Invention
[0007] The purpose of the present invention is to provide a method for efficiently recycling low-quality waste PET bottle flakes, with low energy consumption and environmental friendliness, to overcome the shortcomings of the above-mentioned background technology.
[0008] To achieve this object, the present invention adopts the following technical solutions:
[0009] A method for restoring the physical and chemical properties of inferior waste PET bottle flakes, comprising:
[0010] 1. Use tetrabutyl titanate or other titanium compounds as catalysts and ethylene glycol as the reaction solvent to degrade waste PET under reaction condition 1 to obtain a degradation liquid. Then, continue the PET polymerization reaction without separating the catalyst. Before the start of polymerization, replace the gas in the device in advance. First, use a vacuum pump to evacuate the device to -0.10MPa, check the device for leaks, then introduce inert gas until the device returns to normal pressure. Repeat the above operation three times to ensure that the device is filled with inert gas. Continue to pass inert gas under reaction condition 2 to allow the reaction to prepolymerize and remove excess EG. Then use a vacuum pump to evacuate the device to -0.08MPa and slowly condense to prevent EG from boiling and carrying out the material. Then use a vacuum pump to evacuate the device to -0.10MPa and stop when the reaction ends. Slowly cool to obtain PET with restored performance.
[0011] 2. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, wherein the waste PET is washed with clean water and has an ash content of less than 0.1%.
[0012] 3. The method of restoring the physical and chemical properties of low-quality waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that the titanium-based catalyst employed comprises tetrabutyl titanate, ethylene glycol dibutyl titanate, tetramethyl titanate, and isopropyl titanate. Dibutyl titanate must be compounded with an ethylene glycol solution before use. The compounding method comprises adding 1 mol of tetrabutyl titanate and 1 mol of ethylene glycol to a round-bottom flask, stirring at a reaction temperature of 130°C-140°C until the reaction is complete. The flask is then subjected to rotary evaporation at a reaction temperature of 40°C-60°C until no bubbles are generated, thereby obtaining the ethylene glycol dibutyl titanate catalyst.
[0013] 4. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that the amount of EG used in the alcoholysis is 2-5 times the mass of the inferior waste PET bottle flakes.
[0014] 5. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that the amount of the catalyst used in the glycolysis is 0.1%-0.5% of the mass of the PET bottle flakes.
[0015] 6. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that the temperature of reaction condition 1 is 180-200°C.
[0016] 7. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, wherein the reaction time of the ethylene glycol alcoholysis is 2-5 hours.
[0017] 8. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that the temperature of reaction condition 2 for PET polymerization is 260-300°C, preferably 260°C.
[0018] 9. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, wherein the prepolymerization time of the PET polymerization is 0.5-1.0 h.
[0019] 10. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, wherein the polycondensation time of the PET polymerization is maintained at a vacuum degree of -0.08 MPa for 0.5-1 h.
[0020] 11. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, wherein the polycondensation time of the PET polymerization is maintained at a vacuum degree of -0.10 MPa for 0.5-2.5 hours.
[0021] Invention Advantages
[0022] 1. This invention, for the first time, utilizes a titanium-based catalyst to chemically recycle low-quality waste PET bottle flakes and restore their physical and chemical properties. By using a titanium-based catalyst to degrade and repolymerize low-quality waste PET bottle flakes, the resulting PET bottle flakes not only have a higher molecular weight than low-quality waste PET bottle flakes, but also achieve a color that meets the standards of first-grade PET for bottles. The mild reaction conditions overcome the shortcomings of physical recycling of low-quality waste PET bottle flakes, which often involve high energy consumption during melt recasting and can easily cause irreversible performance damage to the PET bottle flakes.
[0023] 2. The present invention adopts a titanium-based catalyst and realizes the degradation of PET and the repolymerization of monomers by adjusting the forward catalytic and reverse catalytic reactions of the catalyst, thereby restoring the performance of inferior waste PET.
[0024] 3. This invention uses a green and efficient catalyst to restore the physical and chemical properties of low-quality waste PET bottle flakes, reducing the demand for new materials, improving resource utilization efficiency, and reducing environmental pollution. This represents a green and environmentally friendly technology for recycling low-quality waste PET bottle flakes. Therefore, using a titanium-based catalyst to degrade and repolymerize low-quality waste PET bottle flakes restores their physical and chemical properties, achieving green and efficient recycling of low-quality waste PET bottle flakes. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 This is a flow chart of the present invention specifically implementing the use of titanium-based catalysts to restore the physical and chemical properties of inferior waste PET bottle flakes.
[0026] Figure 2 This is a GPC spectrum of the PET bottle flakes in the second embodiment of the present invention. DETAILED DESCRIPTION
[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods. These embodiments are not intended to limit the present invention.
[0028] Example 1
[0029] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.05% of ethylene glycol dibutyl titanate was added as a catalyst, and the amount of EG was 90g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 11798.
[0030] Example 2
[0031] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 90g. The reaction temperature was controlled at 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled at 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 20172.
[0032] Example 3
[0033] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% tetrabutyl titanate was added as a catalyst, and the amount of EG was 90g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 17618.
[0034] Example 4
[0035] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of tetramethyl titanate was added as a catalyst, and the amount of EG was 90g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 8223.
[0036] Example 5
[0037] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% isopropyl titanate was added as a catalyst, and the amount of EG was 90g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 2370.
[0038] Example 6
[0039] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.15% of ethylene glycol dibutyl titanate was added as a catalyst, and the amount of EG was 90g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 11984.
[0040] Example 7
[0041] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.2% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 90g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The device was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 18905.
[0042] Example 8
[0043] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.25% of ethylene glycol dibutyl titanate was added as a catalyst, and the amount of EG was 90g. The reaction temperature was controlled to 190℃, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260℃, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 11978.
[0044] Example 9
[0045] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 120g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 18227.
[0046] Example 10
[0047] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 150g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The device was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 16974.
[0048] Example 11
[0049] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 90g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The device was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 0.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 5986.
[0050] Example 12
[0051] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 90g. The reaction temperature was controlled at 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled at 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The device was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.0h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 11533.
[0052] Example 13
[0053] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 90g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The device was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 2.0h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 11029.
[0054] Example 14
[0055] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 90g. The reaction temperature was controlled at 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled at 260°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The device was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 2.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 10315.
[0056] Example 15
[0057] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 90g. The reaction temperature was controlled at 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled at 270°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The device was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 16974.
[0058] Example 16
[0059] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 90g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 280°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 19300.
[0060] Example 17
[0061] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 90g. The reaction temperature was controlled to 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled to 290°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 18636.
[0062] Example 18
[0063] 30g of low-quality waste PET bottle flakes were added to a 250mL three-necked flask, and 0.1% of ethylene glycol dibutyl titanate was added as a catalyst, with an EG dosage of 90g. The reaction temperature was controlled at 190°C, the reaction time was 5h, and the solution became clear and transparent. The device was then replaced with inert gas. The reaction temperature was controlled at 300°C, the prepolymerization time was 1h, and inert gas was continuously introduced. The device was then evacuated to -0.08MPa using a vacuum pump and slowly polycondensed for 1h. The vacuum was then continued to be evacuated to -0.10MPa and rapidly polycondensed for 1.5h. After replacing the vacuum with inert gas, the product was slowly cooled and the resulting PET bottle flakes were analyzed using GPC. The analysis results showed that the molecular weight of the resulting PET bottle flakes was 17618.
[0064] Example 19
[0065] HPLC was used to analyze the PET conversion rate and degradation product yield under the optimal conditions described in Example 2. Specifically, 1.0 g of the degradation solution was diluted to 80 g with acetonitrile. 0.2 g of the diluted solution was then diluted to 10 g with methanol. The solution was filtered through an organic filter and the degradation product content was measured using HPLC. The analysis showed a 100% PET conversion rate and an 84.59% degradation product yield.
[0066] Example 20
[0067] The PET bottle flakes obtained under the optimal conditions in Example 2 were crushed into pellets using a pulverizer. The a, b, and L values of the resulting PET bottle flakes were measured using a YS6060 desktop spectrophotometer. The analysis results showed that the chromaticity values of the PET bottle flakes were: a = -1.23, b = 5.59, and L = 93.73, meeting the colorimetric standards for first-grade PET bottles.
[0068] Example 21
[0069] The PET bottle flakes obtained under the optimal conditions in Example 2 were crushed into particles using a pulverizer and digested with concentrated nitric acid. The solution was then diluted and subjected to ICP testing to measure the amount of metal ion leaching from the PET bottle flakes. The analysis results showed that the Sb and Ti levels leached under strong acid conditions were both less than 120 ppm, meeting the standard requirements for food-grade PET bottles.
Claims
1. A method for restoring the physical and chemical properties of inferior waste PET bottle flakes, characterized in that: The specific steps are as follows: using tetrabutyl titanate or other titanium compounds as catalysts and ethylene glycol as reaction solvent to degrade waste PET under reaction condition 1 to obtain a degradation liquid, and then continuing the PET polymerization reaction without separating the catalyst. Before the start of polymerization, the device is gas-replaced in advance. First, use a vacuum pump to evacuate the device to -0.10MPa, check whether the device is leaking, and then pass in inert gas until the device returns to normal pressure. Repeat the above operation three times to ensure that the device is full of inert gas. Continue to pass inert gas under reaction condition 2 to pre-polymerize the reaction and remove excess EG. Then use a vacuum pump to evacuate the device to -0.08MPa and slowly condense to prevent EG from boiling and bringing out the material. Then use a vacuum pump to evacuate the device to -0.10MPa, stop when the reaction ends, and slowly cool to obtain PET with restored performance.
2. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that: The waste PET is washed with clean water and the ash content is less than 0.1%.
3. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that: The titanium catalysts used include tetrabutyl titanate, ethylene glycol dibutyl titanate, tetramethyl titanate, and isopropyl titanate. Dibutyl titanate needs to be compounded with an ethylene glycol solution. The compounding method involves adding 1 mol of tetrabutyl titanate and 1 mol of ethylene glycol to a round-bottom flask and stirring at a reaction temperature of 130°C-140°C until the reaction is complete. Then, rotary evaporation is performed at a reaction temperature of 40°C-60°C until no bubbles are generated, resulting in the ethylene glycol dibutyl titanate catalyst.
4. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that: The amount of EG used in ethylene glycol hydrolysis is 2-5 times the mass of low-quality waste PET bottle flakes.
5. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that: The amount of catalyst used for glycol hydrolysis is 0.1%-0.5% of the mass of the PET bottle flakes.
6. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that: The temperature of reaction condition 1 is 180-200°C.
7. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that: The reaction time of ethylene glycol alcoholysis is 2-5h.
8. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that: The temperature of reaction condition 2 for PET polymerization is 260-300°C, with 260°C being preferred.
9. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium catalyst according to claim 1, characterized in that: The prepolymerization time for PET polymerization is 0.5-1.0h.
10. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that: The polycondensation time of PET polymerization is maintained at a vacuum degree of -0.08 MPa for 0.5-1 h.
11. The method for restoring the physical and chemical properties of inferior waste PET bottle flakes using a titanium-based catalyst according to claim 1, characterized in that: The polycondensation time of PET polymerization is maintained at a vacuum degree of -0.10 MPa for 0.5-2.5 h.