A method for chemically preparing BHET powder from polyester bottle chips

Abstract

The present application belongs to the technical field of waste recycling, and particularly relates to a method for chemically preparing BHET powder from polyester bottle pieces, comprising the following steps: A, washing waste polyester bottle pieces, and obtaining brittle bottle pieces by high-temperature brittle treatment under the action of a brittle agent; B, crushing the brittle bottle pieces, and obtaining bottle piece powder after sieving and drying; C, adding ethylene glycol and an initiator to the bottle piece powder, and obtaining a reaction product by high-temperature reaction; and D, filtering the reaction product to remove impurities, and obtaining BHET powder by spray drying. The present application solves the problem that the existing PET polyester bottle recycling technology cannot completely depolymerize the polyester bottle pieces without producing side reactions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of waste recycling, and particularly relates to a method for chemically preparing BHET powder from polyester bottle pieces. BACKGROUND

[0002] In the field of polymer material application, with the increase of the use amount of polyethylene terephthalate (PET), the solid waste PET polyester discharged into the nature also increases sharply every year. However, because PET is difficult to degrade in the nature, illegal landfill or incineration treatment causes great pressure on the environment, and a large amount of waste PET needs to be recycled.

[0003] The recycling method of waste PET polyester material includes a physical method and a chemical method. The physical method mainly adopts mechanical processing to obtain low-value chemicals, and the economy is poor. At present, the waste PET polyester material is mainly recycled by the chemical method, that is, PET is depolymerized into monomers or other oligomers, and then is further processed and utilized. The functional materials developed based on PET depolymerization are various, such as polyurethane, PET-based copolyester, unsaturated polyester, various resins and additives, etc. Therefore, the demand for BHET powder is also increasing.

[0004] Strengthening the research on the recycling of waste PET polyester material, especially the recycling of PET polyester bottles, not only can solve the problem of solid PET waste, but also can improve the economic efficiency of the recycling of PET, so as to save high-cost fossil energy. However, if the PET polyester bottle is simply cut and then depolymerized, because the thickness of the PET polyester bottle is not uniform, there is a 6-fold to 10-fold difference in thickness at different positions of the bottle mouth, bottle body and bottle bottom. Artificial separation not only needs to consume a large amount of manpower and material resources, but also cannot guarantee the accuracy. Therefore, the bottle pieces are usually depolymerized together. However, at this time, the reaction time required by the bottle pieces with different thicknesses is actually different. If the depolymerization time is short, the thick bottle pieces cannot be completely depolymerized, which not only causes waste of resources, but also produces a large amount of incomplete depolymerization intermediate products. If the reaction time is prolonged, although the thick bottle pieces can be completely depolymerized, at this time, the thin bottle pieces will be over-reacted, resulting in an increase in by-products, which affects the yield and product quality.

[0005] How to effectively recycle and utilize the PET polyester bottle to make it completely depolymerized while avoiding the generation of by-products is a difficult problem to be solved. SUMMARY

[0006] The purpose of the present application is to solve the problem that the existing PET polyester bottle recycling technology cannot completely depolymerize the PET polyester bottle without generating side reactions, and to provide a method for chemically preparing BHET powder from polyester bottle pieces.

[0007] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0008] A method for chemically preparing BHET powder from polyester bottle flakes includes the following steps:

[0009] A. Wash the waste polyester bottle flakes and embrittle them at high temperature under the action of an embrittlement agent to obtain embrittled bottle flakes;

[0010] B. The brittle bottle flakes are crushed, sieved, and dried to obtain bottle flake powder;

[0011] C. Add ethylene glycol and initiator to the bottle flake powder, and react at high temperature to obtain the reaction product;

[0012] D. Filter the reaction product to remove impurities, and then spray dry it to obtain BHET powder.

[0013] Waste PET polyester bottle flakes are washed, treated with an embrittlement agent, then crushed into powder with a particle size of about 0.3 μm, sieved to remove impurities, dried, and then ethylene glycol and an initiator are added. The mixture is reacted at 160~240℃ for 0.5~2.5 h, impurities are filtered out, and the mixture is sprayed into powder to obtain BHET powder.

[0014] By brittle-crushing the flakes into powder, not only can the depolymerization time and degree of depolymerization of each part be uniform, but the reaction time can also be effectively shortened, and the amount of ethylene glycol and initiator used can be reduced, which is in line with the principles of green chemistry.

[0015] Polyester bottle flakes typically become brittle at low temperatures, but this process is energy-intensive, requiring liquid nitrogen to lower the temperature to below -100°C, making it economically unviable and difficult to promote. Furthermore, the cleanliness of the bottles is critical during the low-temperature embrittlement process; any impurities will affect subsequent reactions.

[0016] The high-temperature embrittlement process of this invention is actually a depolymerization process. Traditional depolymerization processes involve the addition of catalysts, resulting in rapid processes where the PET molecular weight becomes extremely small, leading to liquefaction. In contrast, the high-temperature embrittlement process of this invention is a slow and controllable depolymerization process driven solely by an embrittlement agent. During this process, the chain length within the PET gradually shortens, but does not become extremely small, thus maintaining the shape of the bottle flake. In other words, the high-temperature embrittlement process of this invention shortens the long chains within the PET, and short-chain PET is brittle.

[0017] Preferably, in step A, the high-temperature embrittlement includes: causing the embrittlement agent to form high-temperature steam at a high temperature, and spraying the waste polyester bottle flakes with the high-temperature steam to cause them to become embrittled.

[0018] This invention, developed through long-term research, creatively achieves the embrittlement of polyester bottle flakes at high temperatures. The high-temperature steam alters the internal structure while simultaneously providing effective and deep cleaning of the bottle flake's outer surface. Therefore, the process of this invention does not require sophisticated pretreatment of the bottle flakes; simple cleaning suffices.

[0019] Preferably, in step A, the waste polyester bottle flakes are placed in a pipe, and the high-temperature steam is continuously injected from the pipe to impact the waste polyester bottle flakes, causing them to become brittle.

[0020] Preferably, the pipe has a height of 40cm and a pipe opening diameter of 15cm.

[0021] Preferably, in step A, the high-temperature embrittlement temperature is 160~230℃, and the processing time is 0.5~1.5h.

[0022] Preferably, in step A, the embrittlement agent includes one or more of water and alcohols. In step C, the initiator includes one or more of potassium salts, calcium salts, sodium salts, magnesium salts, zinc salts, ammonium salts, and iron salts.

[0023] The initiator is an initiator well known to those skilled in the art, and may be selected from one or more alkali metals and metal salts.

[0024] Preferably, in step B, the sieve used for sieving is 20-100 mesh; in step C, the amount of ethylene glycol added is 0.1-1 times the mass of the bottle flake powder, and the amount of initiator added is 0.1-1.5% of the mass of the bottle flake powder; in step D, the filter used for filtration and impurity removal includes a 0.5μm filter.

[0025] Preferably, in step B, the sieve used for sieving is 40-60 mesh; in step C, the amount of ethylene glycol added is 0.5 times the mass of the bottle flake powder, and the amount of initiator added is 0.3% of the mass of the bottle flake powder.

[0026] Preferably, in step B, the pulverization includes crushing; in step C, the temperature of the high-temperature reaction is 160~240℃ and the time is 0.5~2.5h.

[0027] Preferably, in step B, the sieving includes a vibrating screen; in step C, the temperature of the high-temperature reaction is 190~200℃.

[0028] A BHET powder product obtained by the above-mentioned method for chemically preparing BHET powder from polyester bottle flakes.

[0029] Compared with the prior art, implementing the present invention has the following beneficial effects:

[0030] This invention provides a method for chemically preparing BHET powder from polyester bottle flakes. It innovatively achieves embrittlement of the polyester bottle flakes at high temperatures. The high-temperature steam alters the internal structure while simultaneously providing effective and deep cleaning of the outer surface of the flakes. Therefore, the process of this invention does not require sophisticated pretreatment of the bottle flakes; simple cleaning suffices. Embrittling and crushing the bottle flakes into powder not only unifies the depolymerization time and degree of depolymerization in each component but also effectively shortens the reaction time, reduces the amount of ethylene glycol and initiator used, and conforms to green chemistry principles, making it promising for large-scale application. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0032] Example 1

[0033] Take 300g of waste PET polyester bottle flakes, clean them simply, and treat them in a cylinder 40cm high and 15cm in diameter at 200℃ with steam for 1 hour to shorten the long chains inside the PET and make it brittle. At the same time, the bottle flakes are deeply cleaned. After that, they are crushed into powder, separated by a 50-mesh vibrating screen, and 60g of ethylene glycol and 0.6g of zinc acetate are added. The mixture is reacted at 195℃ for 1 hour, filtered (0.5μm filter screen), and sprayed into powder to obtain BHET powder with a yield of 99.9% and a purity of 99.8%.

[0034] Example 2

[0035] Take 100g of waste PET polyester bottle flakes, clean them simply, and treat them in a cylinder 40cm high and 15cm in diameter at 230℃ under ethanol vapor for 0.5h to shorten the long chains inside the PET and make it brittle. At the same time, the bottle flakes are deeply cleaned during the process. After that, crush them into powder, separate them through a 20-mesh vibrating screen, add 10g of ethylene glycol and 0.1g of potassium acetate, react at 240℃ for 0.5h, filter (0.5μm filter screen), spray into powder, and obtain BHET powder with a yield of 99.3% and a purity of 99.8%.

[0036] Example 3

[0037] Take 500g of waste PET polyester bottle flakes, clean them simply, and treat them in a cylinder 40cm high and 15cm in diameter at 160℃ under methanol vapor for 1.5h to shorten the long chains inside the PET and make it brittle. At the same time, the bottle flakes are deeply cleaned during the process. After that, crush them into powder, separate them through a 100-mesh vibrating screen, add 500g of ethylene glycol and 7.5g of ammonium acetate, react at 160℃ for 2.5h, filter (0.5μm filter screen), spray into powder, and obtain BHET powder with a yield of 99.5% and a purity of 99.2%.

[0038] Comparative Example 1

[0039] Take 300g of waste PET polyester bottle flakes, add 900g of ethylene glycol and 0.9g of zinc acetate, react at 196℃ for 2h, filter (38μm filter screen), there are 45g of insoluble matter. After conventional crystallization and distillation purification, the yield is 70.6%, and 0.5% of diethylene glycol in the product is difficult to remove.

[0040] Comparative Example 2

[0041] Take 300g of waste PET polyester bottle flakes, add 900g of ethylene glycol and 0.9g of zinc acetate, react at 196℃ for 8h, filter (38μm filter screen), there are 6g of insoluble matter. After conventional crystallization and distillation purification, the yield is 83.3%, and 5% of diethylene glycol in the product is difficult to remove.

[0042] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for chemically preparing BHET powder from polyester bottle flakes, characterized in that, Includes the following steps: A. The waste polyester bottle flakes are washed and then embrittled at high temperature under the action of an embrittlement agent to obtain embrittled bottle flakes; the high temperature embrittlement temperature is 160~230℃ and the treatment time is 0.5~1.5h; the embrittlement agent includes one or more of water and alcohols; B. The brittle bottle flakes are crushed, sieved, and dried to obtain bottle flake powder; C. Ethylene glycol and an initiator are added to the bottle flake powder, and the mixture is reacted at high temperature to obtain the reaction product; the amount of ethylene glycol added is 0.1 to 1 times the mass of the bottle flake powder; the high temperature reaction is carried out at 160 to 240°C for 0.5 to 2.5 hours; the initiator includes one or more of potassium salt, calcium salt, sodium salt, magnesium salt, zinc salt, ammonium salt, and iron salt. D. Filter the reaction product to remove impurities, and then spray dry it to obtain BHET powder.

2. The method for chemically preparing BHET powder from polyester bottle flakes according to claim 1, characterized in that, In step A, the high-temperature embrittlement includes: causing the embrittlement agent to form high-temperature steam at a high temperature, and spraying the waste polyester bottle flakes with the high-temperature steam to cause them to become embrittled.

3. The method for chemically preparing BHET powder from polyester bottle flakes according to claim 2, characterized in that, In step A, the waste polyester bottle flakes are placed in a pipe, and high-temperature steam is continuously injected into the pipe to impact the waste polyester bottle flakes, causing them to become brittle.

4. The method for chemically preparing BHET powder from polyester bottle flakes according to claim 3, characterized in that, The pipe is 40cm high and has a pipe opening diameter of 15cm.

5. The method for chemically preparing BHET powder from polyester bottle flakes according to claim 1, characterized in that, In step B, the sieve used for sieving is 20-100 mesh; in step C, the amount of initiator added is 0.1-1.5% of the mass of the bottle flake powder; in step D, the filter used for filtration and impurity removal includes a 0.5μm filter.

6. The method for chemically preparing BHET powder from polyester bottle flakes according to claim 1, characterized in that, In step B, the sieve used for sieving is 40-60 mesh; in step C, the amount of ethylene glycol added is 0.5 times the mass of the bottle flake powder, and the amount of initiator added is 0.3% of the mass of the bottle flake powder.

7. The method for chemically preparing BHET powder from polyester bottle flakes according to claim 1, characterized in that, In step B, the crushing includes grinding.

8. The method for chemically preparing BHET powder from polyester bottle flakes according to claim 1, characterized in that, In step B, the sieving includes a vibrating screen; in step C, the temperature of the high-temperature reaction is 190~200℃.