Method for recycling waste PET through efficient alcoholysis

Abstract

The invention belongs to the field of high polymer material recovery, and particularly relates to a method for recovering waste PET (Polyethylene Terephthalate) through efficient alcoholysis. The method for recovering the waste PET through efficient alcoholysis comprises the following steps: mixing the waste PET, a titanium-silicon oxide catalyst and an alcohol compound, and then carrying out high-temperature and high-pressure reaction; the preparation method of the titanium-silicon oxide catalyst comprises the following steps: adding a mixed solution of an organic titanium precursor and an organic silicon precursor into stirred water through a peristaltic pump, then carrying out a constant-temperature stirring reaction, and finally carrying out vacuum drying on a solid obtained by suction filtration. The titanium-silicon oxide which is prepared by using a template-free method and has high reaction activity is used as a catalyst to catalyze the alcoholysis reaction of the waste PET, and high-yield DMT can be recovered.

Description

Technical Field

[0001] The present invention belongs to the field of polymer material recycling, and particularly relates to a method for efficiently recovering waste PET by alcoholysis. Background Art

[0002] Polyethylene terephthalate (PET) is widely used in the food packaging, textile and clothing, and construction industries due to its high strength, wear resistance, and stable chemical properties. However, the extensive use of PET plastics has also caused environmental problems that cannot be ignored: after being discarded, PET degrades extremely slowly in the natural environment, resulting in a large amount of waste PET accumulating in the environment and posing a serious threat to the ecological environment. Therefore, effectively recycling waste PET is not only beneficial to environmental protection but also promotes the recycling of resources, which is of great significance for the sustainable development of the plastics industry.

[0003] Currently, the recycling of PET mainly includes physical methods, chemical methods, and biological methods. Physical methods mainly involve a series of physical operations such as crushing, cleaning, and separating waste PET to achieve the reprocessing and utilization of PET. Chemical methods use chemical reactions to depolymerize PET into monomers and then resynthesize specific high-value-added products. For example, through ethylene glycol alcoholysis and methanol alcoholysis reactions, PET can be respectively converted into raw materials such as bis(2-hydroxyethyl) terephthalate (BHET) and dimethyl terephthalate (DMT), which can be used to produce new PET. Biological methods rely on the catalytic action of enzymes to decompose PET into monomer compounds, but the current enzyme catalytic efficiency and applicable range still need to be further improved and expanded.

[0004] The patent application with the publication number CN115286775A discloses a method for preparing recycled DMT and its copolyesters. After washing, removing impurities, crushing, cutting, and mixing the waste PET for batching, it is alcoholyzed with ethylene glycol to obtain BHET, and then BHET is transesterified with methanol to obtain crude DMT. Finally, the recycled DMT is obtained through steps such as filtration, centrifugation, and distillation. However, this preparation method has too many steps and high energy consumption, and can only be used to recycle single waste polyester textiles.

[0005] The patent application with the publication number CN117181208A discloses the preparation method of a TiO 2 -SiO 2 solid acid catalyst for the alcoholysis of waste polyester. First, tetra(isopropyl) titanate and tetraethyl orthosilicate are mixed in a certain proportion, and then the mixed solution is added to an aqueous solution containing sodium carbonate and cetyltrimethylammonium bromide for hydrolysis reaction. Then, the solid precipitate is centrifuged, collected, and dried, and finally, it is calcined at high temperature to obtain a recyclable TiO 2 -SiO 2Solid acid catalysts. However, the preparation process of this catalyst is relatively long and a large amount of templating agent is used, which leads to problems such as the release of a large amount of toxic gases during the calcination process and high preparation costs. Therefore, there is an urgent need to study a catalyst with simple synthesis, low cost, environmental friendliness and high activity, which is of great significance for the chemical recycling of DMT from waste PET. Summary of the Invention

[0006] The object of the present invention is to provide a method for efficiently alcoholyzing and recycling waste PET in view of the above technical problems. By using highly reactive titanium silicate oxides as catalysts to catalyze the alcoholysis reaction of waste PET, DMT with high yield can be recovered.

[0007] In the technical solution of the present invention, the method for efficiently alcoholyzing and recycling waste PET is to mix waste PET, a titanium silicate oxide catalyst and an alcohol compound and then carry out a high-temperature and high-pressure reaction.

[0008] In the prior art, the titanium silicate molecular sieve used as a catalyst has its active sites located inside the pores of the molecular sieve and can be used to catalyze the esterification reaction of small molecules, but it cannot act on the polymer chain of PET and shows poor catalytic activity. In the present invention, the obtained amorphous titanium silicate oxide catalyst has surface-exposed Si-O-Ti acidic sites that can effectively adsorb and activate the ester bonds on the PET polymer chain, thereby promoting the occurrence of the PET depolymerization reaction, achieving a high yield of DMT, and can also react with alcohol compounds to obtain monomer compounds without ionic residues, which is environmentally friendly.

[0009] Further, the waste PET includes, but is not limited to, one or more of waste PET staple fiber, waste PET filament, waste PET bottle chips, and waste PET film.

[0010] Further, the alcohol compound includes, but is not limited to, one or more of methanol, ethanol, propanol, butanol, and ethylene glycol.

[0011] Further, the mass ratio of waste PET, the titanium silicate oxide catalyst and the alcohol compound is 10-100:0.05-5.0:40-400.

[0012] Further, the mass of the titanium silicate oxide catalyst is 0.1-5.0% of the mass of the waste PET.

[0013] In the technical solution of the present invention, the preparation method of the titanium silicate oxide catalyst includes the following steps: first, a mixed solution of an organic titanium precursor and an organic silicon precursor is added to stirred water through a peristaltic pump, then a constant-temperature stirring reaction is carried out, and finally the solid obtained by suction filtration is vacuum dried.

[0014] In the preparation method of the above-mentioned titanium-silicon oxide catalyst, organic titanium and organic silicon are used as precursors, and the catalyst is prepared through co-hydrolysis and polycondensation reactions without the use of a template agent. By dropping the mixture with a peristaltic pump, the co-hydrolysis of the organic titanium precursor and the organic silicon precursor mixture can be achieved and dispersed in water. The subsequent constant-temperature stirring reaction further promotes the co-polycondensation reaction of the hydrolyzed precursors, thereby obtaining a uniform and amorphous titanium-silicon composite oxide.

[0015] Furthermore, the molar ratio of titanium element to silicon element in the organic titanium precursor and the organic silicon precursor is 1.0:0.1 - 10.0, preferably 1.0:0.2 - 4.0.

[0016] Preferably, the organic titanium precursor includes, but is not limited to, one or more of tetrabutoxytitanium, tetraisobutoxytitanium, tetra-tert-butyl titanate, and tetraethyl titanate.

[0017] Preferably, the organic silicon precursor includes, but is not limited to, one or more of tetraethoxysilane, methyltripropoxysilane, and propyltrimethoxysilane.

[0018] Furthermore, the mass ratio of the mixture to water is 10 - 50 g / 100 g.

[0019] Furthermore, the flow rate set by the peristaltic pump is 1.0 - 5.0 mL / min, and the rotation speed of the peristaltic pump is 10 - 50 rpm.

[0020] Furthermore, the temperature of the constant-temperature stirring reaction is 20 - 100 °C, preferably 25 - 80 °C, and the time is 1 - 10 h, preferably 1 - 5 h.

[0021] Furthermore, the vacuum drying temperature is 80 - 150 °C, and the drying time is 6 - 12 h.

[0022] Preferably, the reaction of waste PET, titanium-silicon oxide catalyst, and alcohol compounds is carried out in a sealed high-pressure reactor.

[0023] Furthermore, the temperature of the high-temperature and high-pressure reaction is 140 - 180 °C, the pressure is 1.0 - 5.0 MPa, and the time is 0.5 - 4.0 h.

[0024] Preferably, the temperature of the high-temperature and high-pressure reaction is 160 - 180 °C, and the pressure is 1.7 - 2.7 MPa.

[0025] Preferably, the reaction of waste PET, titanium-silicon oxide catalyst, and alcohol compounds is carried out in a sealed high-pressure reactor.

[0026] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0027] (1) The present invention uses a template-free method to prepare a highly reactive titanium-silicon oxide as a catalyst for catalyzing the alcoholysis reaction of waste PET, and high-yield DMT can be recovered;

[0028] (2) The co-hydrolysis of a mixed organic titanium precursor and an organic silicon precursor is carried out by dropping through a peristaltic pump, and further constant-temperature stirring is carried out to promote the co-condensation reaction of the precursors, and finally an amorphous titanium-silicon composite oxide is obtained;

[0029] (3) The preparation method of the titanium-silicon oxide catalyst does not require the use of a templating agent and a high-temperature calcination process, avoids the release of toxic gases during the catalyst synthesis process, and significantly reduces energy consumption, meets the requirements of green chemistry, and has the potential for industrial production;

[0030] (4) The obtained titanium-silicon oxide catalyst exhibits excellent catalytic activity. The Si-O-Ti acidic sites exposed on the surface can effectively adsorb and activate the ester bonds on the PET polymer chain, thereby promoting the occurrence of the PET depolymerization reaction, achieving a high yield of DMT, and can also react with alcohol compounds to obtain monomer compounds, without ionic residues, and is green and environmentally friendly. Specific Embodiments

[0031] The technical solutions of the present invention will be further described and illustrated below through specific examples. It should be understood that the specific examples described herein are only used to help understand the present invention and are not used for the specific limitation of the present invention. If there is no special description, the raw materials used in the embodiments of the present invention are all common raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0032] The conversion rate of waste PET and the yield of the product DMT are calculated according to the following formulas (1) and (2) respectively:

[0033] Conversion rate of PET = (m 0 -m 1 ) / m 0 ×100% (1);

[0034] Yield of DMT = (mass of DMT in the reaction solution) / (theoretical mass of DMT) × 100% (2);

[0035] Wherein, m 0 is the initial mass of waste PET, and m 1 is the mass of un-depolymerized PET after the reaction ends.

[0036] Example 1

[0037] The method for efficiently alcoholyzing and recovering waste PET in this example includes the following steps:

[0038] (1) Mix 10.21 g of tetrabutoxytitanium and 12.50 g of tetraethoxysilane evenly to obtain a mixed solution. The molar ratio of titanium element to silicon element is 1.0:2.0. Then add the mixed solution to 100 g of water through a peristaltic pump. The flow rate set for the peristaltic pump is 1.5 mL / min, and the rotation speed of the peristaltic pump is 20 rpm. Stir and react at 100 °C for 5 h. After suction filtration, vacuum-dry the solid product at 100 °C for 6 h to obtain a titanium-silicon oxide catalyst;

[0039] (2) Weigh 10 g of waste PET staple fiber and 0.25 g of titanium-silicon oxide catalyst and add them to a high-pressure reactor. After adding 48 g of methanol, seal it, and then heat it up to 160 °C. The pressure in the high-pressure reactor is 1.7 MPa, and stir and react for 2 h.

[0040] Example 2

[0041] The method for efficiently alcoholyzing and recycling waste PET in this example includes the following steps:

[0042] (1) Mix 10.21 g of tetra-tert-butyl titanate and 6.25 g of tetraethoxysilane evenly to obtain a mixed solution. The molar ratio of titanium element to silicon element is 1.0:1.0. Then add the mixed solution to 100 g of water through a peristaltic pump. The flow rate set for the peristaltic pump is 1.8 mL / min, and the rotation speed of the peristaltic pump is 24 rpm. Stir and react at 75 °C for 5 h. After suction filtration, vacuum-dry the solid product at 90 °C for 6 h to obtain a titanium-silicon oxide catalyst;

[0043] (2) Weigh 10 g of waste PET staple fiber and 0.25 g of titanium-silicon oxide catalyst and add them to a high-pressure reactor. After adding 48 g of methanol, seal it, and then heat it up to 160 °C. The pressure in the high-pressure reactor is 1.7 MPa, and stir and react for 2 h.

[0044] Example 3

[0045] The method for efficiently alcoholyzing and recycling waste PET in this example includes the following steps:

[0046] (1) Mix 10.21 g of tetrabutoxytitanium and 2.46 g of propyltrimethoxysilane evenly to obtain a mixed solution. The molar ratio of titanium element to silicon element is 1.0:0.5. Then add the mixed solution to 100 g of water through a peristaltic pump. The flow rate set for the peristaltic pump is 2.1 mL / min, and the rotation speed of the peristaltic pump is 28 rpm. Stir and react at 70 °C for 5 h. After suction filtration, vacuum-dry the solid product at 80 °C for 6 h to obtain a titanium-silicon oxide catalyst;

[0047] (2) The recycling method of PET is as follows: Weigh 10 g of waste PET staple fibers and 0.25 g of titanium silicate catalyst and add them into a high-pressure reactor. Then add 48 g of ethanol, seal the reactor, and heat it up to 160 °C. The pressure in the high-pressure reactor is 2.0 MPa, and stir and react for 2 h.

[0048] Example 4

[0049] The difference between this example and Example 1 is only that in step (1), 10.21 g of tetrabutoxytitanium and 1.25 g of tetraethoxysilane are mixed evenly to obtain a mixed solution. The molar ratio of titanium element to silicon element is 1.0:0.2. Then the mixed solution is added into 100 g of water through a peristaltic pump. The flow rate set for the peristaltic pump is 1.5 mL / min, and the rotation speed of the peristaltic pump is 20 rpm. Stir and react at 100 °C for 5 h. After suction filtration, the solid product is vacuum dried at 100 °C for 6 h to obtain the titanium silicate catalyst.

[0050] Example 5

[0051] The difference between this example and Example 1 is only that in step (1), 10.21 g of tetrabutoxytitanium and 25.0 g of tetraethoxysilane are mixed evenly to obtain a mixed solution. The molar ratio of titanium element to silicon element is 1.0:4.0. Then the mixed solution is added into 100 g of water through a peristaltic pump. The flow rate set for the peristaltic pump is 1.5 mL / min, and the rotation speed of the peristaltic pump is 20 rpm. Stir and react at 100 °C for 5 h. After suction filtration, the solid product is vacuum dried at 100 °C for 6 h to obtain the titanium silicate catalyst.

[0052] After the reactions in the above examples are completed, the yield of DMT in the reaction solution is quantitatively analyzed by GC-MS. The residual PET is separated from the reaction solution by centrifugation, dried, and weighed to calculate the conversion rate of PET. The yields of DMT obtained by recycling PET in Examples 1 - 5 are shown in Table 1:

[0053] Table 1 Activity of different titanium silicate catalysts in recycling PET

[0054] Ti / Si (mol) PET conversion rate (%) DMT yield (%) Example 1 1.0:2.0 100 98 Example 2 1.0:1.0 95 90 Example 3 1.0:0.5 88 78 Example 4 1.0:0.2 73 43 Example 5 1.0:4.0 92 87

[0055] In Examples 1 - 5, as the content of titanium element increases, the yield of DMT first increases and then decreases. When the titanium to silicon ratio is 1.0:2.0, the catalytic activity of the titanium silicate is the best, and the PET conversion rate and DMT yield reach 100% and 98% respectively.

[0056] Example 6

[0057] The difference between this example and Example 1 is only that in step (2), 10 g of waste PET short fibers and 0.25 g of titanium silicate oxide catalyst (titanium to silicon ratio is 1.0:2.0) are added to a high-pressure reactor, 48 g of methanol is added and then sealed, and then the temperature is raised to 140 °C, the pressure of the high-pressure reactor is 1.1 MPa, and the reaction is stirred for 2 h.

[0058] Example 7

[0059] The difference between this example and Example 1 is only that in step (2), 10 g of waste PET short fibers and 0.25 g of titanium silicate oxide catalyst (titanium to silicon ratio is 1.0:2.0) are added to a high-pressure reactor, 48 g of methanol is added and then sealed, and then the temperature is raised to 150 °C, the pressure of the high-pressure reactor is 1.4 MPa, and the reaction is stirred for 2 h.

[0060] Example 8

[0061] The difference between this example and Example 1 is only that in step (2), 10 g of waste PET short fibers and 0.25 g of titanium silicate oxide catalyst (titanium to silicon ratio is 1.0:2.0) are added to a high-pressure reactor, 48 g of methanol is added and then sealed, and then the temperature is raised to 170 °C, the pressure of the high-pressure reactor is 2.2 MPa, and the reaction is stirred for 2 h.

[0062] Example 9

[0063] The difference between this example and Example 1 is only that in step (2), 10 g of waste PET short fibers and 0.25 g of titanium silicate oxide catalyst (titanium to silicon ratio is 1.0:2.0) are added to a high-pressure reactor, 48 g of methanol is added and then sealed, and then the temperature is raised to 180 °C, the pressure of the high-pressure reactor is 2.7 MPa, and the reaction is stirred for 2 h.

[0064] After the reactions of the above examples are completed, the yield of DMT in the reaction solution is quantitatively analyzed by GC-MS, and the residual PET is separated from the reaction solution by centrifugation and weighed after drying to calculate the conversion rate of PET. The effects of different temperatures on the PET recovery reaction in Examples 6 - 9 are shown in Table 2.

[0065] Table 2 Effects of different recovery temperatures on the yield of DMT

[0066] Reaction temperature (°C) PET conversion rate (%) DMT yield (%) Example 1 160 100 98 Example 6 140 79 53 Example 7 150 91 83 Example 8 170 100 99 Example 9 180 100 99

[0067] As the reaction temperature increases, the activity of the titanium silicate oxide catalyst for the reaction of waste PET increases. At 160 °C, the PET conversion rate and DMT yield reach 100% and 99% respectively.

[0068] Example 10

[0069] The difference between this example and Example 1 is only that in step (2), 10 g of waste PET short fibers and 0.25 g of titanium silicate oxide catalyst are weighed and added to a high-pressure reactor. After adding 48 g of methanol, it is sealed, and then the temperature is raised to 160 °C. The pressure in the high-pressure reactor is 1.7 MPa, and the stirring reaction is carried out for 2 h. After the reaction, the catalyst is recovered and used for the next cycle reaction. After being used 5 times, the catalyst is calcined at 500 °C for 2 h for regeneration and then continues to be used. The activity of the catalyst during repeated use is shown in Table 3.

[0070] Table 3 Activity of titanium silicate oxide catalyst in recycling

[0071] Number of cycles 1 2 3 4 5 6 7 8 9 10 PET conversion rate (%) 100 100 100 100 100 100 100 100 100 100 DMT yield (%) 98 98 98 96 95 98 98 97 97 96

[0072] As can be seen from Table 3, after the titanium silicate oxide catalyst is recycled 5 times, the yield of DMT is still above 95%. After regeneration and reuse, the yield of DMT can still reach above 98%, showing good catalytic activity and stability.

[0073] Example 11

[0074] The difference between this example and Example 1 is that in step (2), 20 g of waste PET short fibers and 0.25 g of titanium silicate oxide catalyst are weighed and added to a high-pressure reactor. After adding 48 g of methanol, it is sealed, and then the temperature is raised to 160 °C. The pressure in the high-pressure reactor is 1.7 MPa, and the stirring reaction is carried out for 2 h.

[0075] Example 12

[0076] The difference between this example and Example 1 is that in step (2), 10 g of waste PET short fibers and 0.50 g of titanium silicate oxide catalyst are weighed and added to a high-pressure reactor. After adding 48 g of methanol, it is sealed, and then the temperature is raised to 160 °C. The pressure in the high-pressure reactor is 1.7 MPa, and the stirring reaction is carried out for 2 h.

[0077] Example 13

[0078] The difference between this example and Example 1 is that in step (2), 10 g and 0.8 g of catalyst are weighed and added to [the reactor]. After adding methanol, it is sealed, and then the temperature is raised to 160 °C. The pressure in the high-pressure reactor is 1.7 MPa, and the stirring reaction is carried out for 2 h.

[0079] Example 14

[0080] The difference between this example and Example 1 is that in step (2), 10 g of waste PET long fibers and 0.25 g of titanium silicate oxide catalyst are weighed and added to a high-pressure reactor. After adding 48 g of methanol, it is sealed, and then the temperature is raised to 160 °C. The pressure in the high-pressure reactor is 1.7 MPa, and the stirring reaction is carried out for 2 h.

[0081] Example 15

[0082] The difference between this example and Example 1 lies in that in step (2), 10 g of waste PET bottle chips and 0.25 g of titanium silicate oxide catalyst are weighed and added into a high-pressure reactor. After adding 48 g of methanol, it is sealed, then heated to 160 °C, the pressure of the high-pressure reactor is 1.7 MPa, and stirred for 2 h.

[0083] Example 16

[0084] The difference between this example and Example 1 lies in that in step (2), 10 g of waste PET film and 0.25 g of titanium silicate oxide catalyst are weighed and added into a high-pressure reactor. After adding 48 g of methanol, it is sealed, then heated to 160 °C, the pressure of the high-pressure reactor is 1.7 MPa, and stirred for 2 h.

[0085] Comparative Example 1

[0086] The difference between this comparative example and Example 1 lies in that in step (2), 10 g of waste PET staple fiber and 0.25 g of ZnO catalyst are weighed and added into a high-pressure reactor. After adding 48 g of methanol, it is sealed, then heated to 160 °C, the pressure of the high-pressure reactor is 1.7 MPa, and stirred for 2 h.

[0087] Comparative Example 2

[0088] The difference between this comparative example and Example 1 lies in that in step (2), 10 g of PET staple fiber and 0.25 g of titanium silicalite (TS-1, titanium-silicon molar ratio is 30, specific surface area is 350 m 2 / g) was added to a high-pressure reactor. After adding 48 g of methanol, it was sealed, and then the temperature was raised to 160 °C. The pressure in the high-pressure reactor was 1.7 MPa, and the reaction was stirred for 2 h. After the reactions in the above examples and comparative examples were completed, the yield of DMT in the reaction solution was quantitatively analyzed by GC-MS. The residual PET was separated from the reaction solution by centrifugation, and the conversion rate of PET was calculated by weighing after drying. In Examples 11 and 12 of the PET recovery reaction, the conversion rate of PET was 100%, and the yields of DMT were 97% and 99% respectively; in Example 13, an excessive amount of titanium-silicon oxide catalyst was added, the conversion rate of PET was 100%, but part of DMT was adsorbed, resulting in the DMT yield being reduced to 93%; in Examples 14-16, in the recovery reactions of waste PET long fibers, waste PET bottle chips and waste PET films, the conversion rate of PET was 100%, and the DMT yields were 97%, 96% and 97% respectively; in Comparative Example 1, ZnO catalyst was used, the conversion rate of PET was 23%, and the DMT yield was 11%; in Comparative Example 2, titanium-silicate molecular sieve was used as the catalyst, the conversion rate of PET was 3%, and the DMT yield was 1%. Finally, it should be noted that the specific examples described herein are only illustrative of the spirit of the present invention and not a limitation on the embodiments of the present invention. Those skilled in the art of the present invention can make various modifications or supplements to the described specific examples or use similar methods for substitution. It is not necessary and impossible to list all the embodiments here. And these obvious changes or variations derived from the essence of the present invention still fall within the protection scope of the present invention. Interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A method for efficiently recovering waste PET by alcoholysis, characterized in that: The high-efficiency recycling method comprises mixing the waste PET, titanium silicon oxide catalyst and alcohol compound and then subjecting the mixture to high-temperature and high-pressure reaction.

2. The method for recovering waste PET by efficient alcoholysis according to claim 1, characterized in that: The mass ratio of waste PET, titanium silicon oxide catalyst and alcohol compound is 10-100:0.05-5.0:40-400.

3. The method for recovering waste PET by efficient alcoholysis according to claim 1 or 2, characterized in that: The alcohol compound includes one or more of methanol, ethanol, propanol, butanol, and ethylene glycol.

4. The method for recovering waste PET by efficient alcoholysis according to claim 1 or 2, characterized in that: The mass of the titanium silicon oxide catalyst is 0.1 to 5.0% of the mass of the waste PET.

5. The method for recovering waste PET by efficient alcoholysis according to claim 1, characterized in that: The preparation method of titanium silicon oxide catalyst comprises the following steps: firstly, adding the mixed liquid of organic titanium precursor and organic silicon precursor into the stirred water through a peristaltic pump, then carrying out constant temperature stirring reaction, and finally vacuum drying the solid obtained by filtration.

6. The method for recovering waste PET by efficient alcoholysis according to claim 5, characterized in that: The molar ratio of titanium element to silicon element in the organic titanium precursor and the organic silicon precursor is 1.0:0.1-10.

0.

7. The method for recovering waste PET by efficient alcoholysis according to claim 5 or 6, characterized in that: The organic titanium precursor includes one or more of tetrabutoxytitanium, tetraisobutoxytitanium, tetra-tert-butyl titanate, and tetraethyl titanate; And / or the organosilicon precursor includes one or more of tetraethoxysilane, methyltripropoxysilane, and propyltrimethoxysilane.

8. The method for recovering waste PET by efficient alcoholysis according to claim 5, characterized in that: The flow rate of the peristaltic pump is set to 1.0-5.0 mL / min, and the rotation speed of the peristaltic pump is set to 10-50 rpm.

9. The method for recovering waste PET by efficient alcoholysis according to claim 5, characterized in that: The temperature of the constant temperature stirring reaction is 20 to 100°C and the time is 1 to 10 hours; And / or the vacuum drying temperature is 80-150°C and the drying time is 6-12h.

10. The method for recovering waste PET by efficient alcoholysis according to claim 1, characterized in that: The temperature of the high temperature and high pressure reaction is 140-180°C, the pressure is 1.0-5.0MPa, and the time is 0.5-4.0h.