Titanium-silicon complex catalyst, preparation method thereof and method for depolymerizing polyethylene terephthalate

Abstract

The application relates to the technical field of chemical degradation of waste polyesters, and discloses a titanium-silicon compound catalyst, a preparation method thereof and a method for depolymerizing polyethylene terephthalate. The preparation method of the titanium-silicon compound catalyst comprises the following steps: (1) preparing a solution by reacting a titanium compound, an orthosilicate compound and a solvent with an organic acid solution; and (2) obtaining the titanium-silicon compound catalyst by post-treating the solution. The catalyst has the characteristics of high PET depolymerization rate, low polymerization degree of depolymerization products, high purity of bis(2-hydroxyethyl) terephthalate (BHET) in the depolymerization products and low titanium residual amount in the target product in the PET degradation reaction. The BHET obtained by the method can be directly used for preparing PET polyester products or other high-value-added products, so that the closed-loop recycling of PET is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical degradation of waste polyester and relates to a titanium-silicon composite catalyst and a preparation method thereof and a method for depolymerizing polyethylene terephthalate. Background Art

[0002] Polyethylene terephthalate (PET, also known as polyester) is a semi-crystalline thermoplastic polymer material with excellent performance and low cost. It is widely used in fibers, films, bottles, and other fields. Currently, domestic PET production reaches approximately 60 million tons per year. This huge polyester market has led to a growing amount of waste polyester. Polyester has stable chemical properties and does not degrade effectively naturally for 16 to 48 years. This not only damages the environment but also wastes petroleum resources. Therefore, effectively utilizing waste resources and recycling and reusing waste polyester products is one of the key issues for achieving sustainable development in the polyester industry.

[0003] There are two main methods for recycling waste polyester: physical and chemical. Physical recycling involves recycling discarded polyester products, removing impurities, cleaning, crushing, drying, and then melt-pelletizing them for reshaping. This method is simple, requires minimal investment, and is low-cost. However, physical recycling can only be used for downgraded recycling. Furthermore, the recycled polyester contains a large amount of impurities, making quality improvement difficult. Furthermore, the number of recycling cycles is limited, leading to secondary pollution. Chemical recycling, on the other hand, achieves a closed-loop "polymer-monomer-polymer" recovery process, yielding a variety of high-value recycled products with excellent economic and social benefits.

[0004] Chemically recycled polyester is based on the reversibility of polycondensation reactions and the nucleophilic reaction mechanism of ester exchange. By depolymerizing waste polyester into monomers or polymerization intermediates, separating and purifying them, high-purity monomers are obtained, and then polymerized into high-quality recycled polyester, thus realizing the closed-loop recycling of waste polyester. Compared with other chemical regeneration methods, alcoholysis technology is more mature, and the ethylene glycol alcoholysis method has a simple reaction route, mild reaction conditions, low requirements for temperature and pressure, a high safety factor, and can be used in conjunction with industrial PET polymerization equipment. It is suitable for industrial mass production, greatly improving economic benefits and reducing equipment maintenance costs. However, due to the reversible nature of the polycondensation reaction, the depolymerization and polymerization of PET is an equilibrium reaction, and it is difficult to achieve an ideal depolymerization yield. A certain amount of oligomer products will exist in the depolymerization product, and the separation and purification process of the product is difficult, and the purity and yield of the target product are not high. Currently, the depolymerization catalysts commonly used in industry are metal salts represented by zinc acetate. After depolymerization, they will remain in the target product and are difficult to remove. High levels of catalyst residues will lead to serious thermal degradation side reactions in the recycled product, affecting the quality of the recycled polyester.

[0005] The mechanism of action of titanium-based catalysts is similar to that of common metal catalysts. During the alcoholysis of polyester, the titanium ions on the titanium-based catalyst, due to their low potential, first attack the carbonyl carbon on the polyester. This complex is then redistributed through coordination bonds, reducing the charge on the carbonyl carbon and making it more susceptible to attack by the hydroxyl oxygen on the ethylene glycol, thereby cleaving the ester bond in the PET molecule and forming the alcoholysis product. Compared to other catalysts, titanium-based catalysts offer higher selectivity and catalytic activity, while their residual content poses no significant environmental or human hazards, making them highly efficient and environmentally friendly. However, as they are commonly used polyester polymerization catalysts, excessive residual titanium catalyst levels can lead to severe side reactions, reduced product performance, and poor color. By introducing a certain amount of silicon atoms into the titanium active center, not only can the catalytic activity of titanium be effectively modulated, reducing the amount of titanium required in the reaction system, but it can also significantly reduce the residual titanium content in the target monomer, thereby preventing any impact on its regeneration.

[0006] Therefore, in order to solve the above problems, the present invention provides a catalyst and an alcoholysis method for efficiently alcoholyzing waste polyester. Summary of the Invention

[0007] The present invention aims to solve the problems existing in the prior art, such as the presence of heavy metal components in the depolymerization catalyst, low depolymerization efficiency, high catalyst residue in the depolymerization product, and low quality of the recycled polyester. The present invention provides a titanium-silicon composite catalyst that can be used for the alcoholysis of polyethylene terephthalate (PET) and a preparation method thereof, and provides a method for depolymerizing polyethylene terephthalate using the catalyst.

[0008] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a titanium-silicon composite catalyst, the method comprising:

[0009] (1) preparing a titanium compound, an orthosilicate compound, and a solvent and reacting them with an organic acid solution to obtain a solution;

[0010] (2) The solution is post-treated to obtain a titanium-silicon composite catalyst.

[0011] The second aspect of the present invention provides a titanium-silicon composite catalyst prepared by the first aspect of the present invention.

[0012] A third aspect of the present invention provides a method for depolymerizing polyethylene terephthalate (PET),

[0013] The method includes:

[0014] In the presence of a catalyst and a protective atmosphere, the treated polyethylene terephthalate-containing material and alcohol are subjected to a depolymerization reaction to obtain an alcoholysis product containing bis(2-hydroxyethyl) terephthalate (BHET);

[0015] Wherein, the catalyst is the titanium-silicon composite catalyst prepared according to the first aspect of the present invention.

[0016] Through the above technical solution, the present invention achieves the following beneficial effects:

[0017] (1) The titanium-silicon composite catalyst developed by the present invention for alcoholysis of PET has high efficiency and high selectivity, low addition amount, and PET depolymerization rate>99.5%. After depolymerization is completed, the degree of polymerization in the depolymerization product is only 1-3, and the total content of BHET monomer, BHET dimer, and BHET trimer is>99wt%, of which the BHET monomer content is>93wt%.

[0018] (2) The high-efficiency titanium-silicon composite catalyst developed by the present invention does not contain heavy metals and is harmless to the environment and human body. The target product BHET has a low titanium residue content and has little effect on PET regeneration.

[0019] (3) The BHET obtained by the method of the present invention can be directly used to prepare PET or other high value-added products, thereby realizing the closed-loop recycling of PET.

[0020] (4) The titanium-silicon composite catalyst developed by the present invention uses titanium as the main catalyst body, with a content of 10-50wt%; the pH value of the titanium-silicon composite catalyst is 2-5, and the infrared spectrum of the catalyst is at 1022cm -1 An absorption peak is observed at . To facilitate catalyst removal from the depolymerization system, the titanium-silicon composite catalyst is a heterogeneous system. Even after boiling in ethylene glycol at high temperature for four hours, the catalyst's activity remains unchanged, and no alcoholysis occurs during the high-temperature alcoholysis of polyester. Furthermore, the introduction of silicon atoms into the titanium active center effectively modulates the titanium's catalytic activity. Hydroxycarboxylic acids, such as citric acid and lactic acid, form a relatively stable structure with titanate esters, enabling the depolymerization of most waste plastics containing ≥75% PET, with stable catalyst activity. DETAILED DESCRIPTION

[0021] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0022] The first aspect of the present invention provides a method for preparing a titanium-silicon composite catalyst, the method comprising:

[0023] (1) preparing a titanium compound, an orthosilicate compound, and a solvent and reacting them with an organic acid solution to obtain a solution;

[0024] (2) The solution is post-treated to obtain a titanium-silicon composite catalyst.

[0025] In one embodiment of the present invention, preferably, the titanium compound is selected from one or more of tetrabutyl titanate, isopropyl titanate, tetraethyl titanate, titanium ethylene glycol, titanium acetylacetonate, and diisopropyl di(acetylacetonate) titanate.

[0026] In one embodiment of the present invention, preferably, the orthosilicate is selected from tetrabutyl orthosilicate, tetraethyl orthosilicate, and tetramethyl orthosilicate.

[0027] In one embodiment of the present invention, preferably, the organic acid in the organic acid solution is selected from one or more of citric acid, malic acid, salicylic acid, tartaric acid, and lactic acid.

[0028] In one embodiment of the present invention, preferably, the solvent is selected from one or more of ethanol, isopropanol, and water.

[0029] In one embodiment of the present invention, preferably, the molar ratio of the titanium compound to the orthosilicate compound is 95:5-70:30.

[0030] In one embodiment of the present invention, preferably, the molar ratio of the titanium compound to the organic acid in the organic acid solution is 1:8-1:0.5.

[0031] In one embodiment of the present invention, preferably, the molar ratio of the titanium compound to the solvent is 1:1-1:50.

[0032] In one embodiment of the present invention, preferably, the preparation temperature is 20-40°C.

[0033] In one embodiment of the present invention, preferably, during the preparation process in step (1), the stirring time is 2-3 hours.

[0034] In one embodiment of the present invention, preferably, the mass ratio of the organic acid to the dissolving solvent contained in the organic acid solution in step (1) is 1:3-10; at a temperature of 30-70°C and a stirring speed of 10-30 r / min, the organic acid is completely dissolved in the dissolving solvent and then transferred into a burette.

[0035] In an embodiment of the present application, preferably, the process of the reaction comprises: dropping the organic acid solution in the burette into the mixture of the titanium compound, the orthosilicate compound and the solvent at a dropping speed of 1 mL / min, and after the dropping is completed, reacting at 20-40℃ for 2-3h.

[0036] In an embodiment of the present application, preferably, the process of the post-treatment in step (2) comprises:

[0037] (i) heating the solution to distill off small molecules.

[0038] (ii) after the small molecules are not distilled off, cooling the product to obtain the titanium-silicon complex catalyst.

[0039] In an embodiment of the present application, preferably, in the process of the post-treatment in step (i), the solution is heated to 100-150℃.

[0040] In an embodiment of the present application, preferably, the temperature after the cooling in step (ii) is room temperature, and the product after the cooling is dried in a vacuum drying box for 1-3h.

[0041] The second aspect of the present application provides a titanium-silicon complex catalyst prepared by the first aspect of the present application.

[0042] In an embodiment of the present application, preferably, in the titanium-silicon complex catalyst, the content of titanium element is 10-50wt%, and the content of silicon element is 0.3-9.5wt%.

[0043] In an embodiment of the present application, preferably, the pH value of the titanium-silicon complex catalyst is 2-5.

[0044] In an embodiment of the present application, preferably, the titanium-silicon complex catalyst has an absorption peak at 1022cm -1 In the titanium-silicon complex catalyst prepared by the present application, the substance formed by the preparation method of the first aspect of the present application may exist, thereby being reflected in the infrared spectrum. The titanium-silicon complex catalyst of the present application can have a better effect of depolymerizing polyethylene terephthalate.

[0045] The third aspect of the present application provides a method for depolymerizing polyethylene terephthalate (PET), which comprises:

[0046] under the presence of the catalyst and the protective atmosphere, depolymerizing the treated polyethylene terephthalate (PET) containing material and alcohol to obtain an alcoholysis product containing bis(2-hydroxyethyl) terephthalate;

[0047] The catalyst is selected from the titanium-silicon complex catalyst prepared in the first aspect of the application.

[0048] In an embodiment of the application, preferably, the alcohol is a dihydric alcohol, preferably selected from at least one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol.

[0049] In an embodiment of the application, preferably, the mass ratio of the polyethylene terephthalate to the alcohol is 1:2-1:8, preferably 1:3-1:5. If the amount of the alcohol is too small or exceeds the above range, the depolymerization reaction is insufficient, the oligomer increases, and the yield of the final product BHET is affected.

[0050] In an embodiment of the application, preferably, the amount of the catalyst is 0.05-0.5 wt% of the polyethylene terephthalate, preferably 0.1-0.4 wt%. If the amount of the rare earth complex catalyst is too large, the residual amount of the catalyst in the final product BHET is large, and the production of the catalyst is affected.

[0051] In the application, the amount of the polyethylene terephthalate is measured based on the polyethylene terephthalate contained in the polyethylene terephthalate (PET) containing material.

[0052] In the application, the "treatment" of the "treated polyethylene terephthalate (PET) containing material" is to clean the polyethylene terephthalate (PET) containing material to remove oil stains, dust, non-PET impurities, etc. In addition, the polyethylene terephthalate containing material can be waste PET bottle pieces, waste PET long fibers, waste PET short fibers, waste polyester bubble material, waste PET film, or a material with a PET content of ≥75 wt%.

[0053] In an embodiment of the application, preferably, the reaction temperature of the depolymerization reaction is 190-250°C, preferably 200-230°C. If the reaction temperature is too low, the depolymerization reaction is insufficient, the oligomer increases, and the yield of the final product BHET is affected.

[0054] In an embodiment of the application, preferably, the reaction pressure of the depolymerization reaction is 0.2-0.6 MPa, preferably 0.35-0.5 MPa. If the reaction pressure is too low, the depolymerization reaction is insufficient, the oligomer increases, and the yield of the final product BHET is affected.

[0055] In one embodiment of the present invention, the depolymerization reaction preferably takes place for 1-5 hours, preferably 2-4 hours. If the reaction time is too short, the depolymerization reaction may be incomplete, resulting in an increase in oligomers and a reduction in the yield of the final product, BHET.

[0056] The present invention will be described in detail below through examples.

[0057] In the following examples, the depolymerization rate of polyethylene terephthalate is shown in (Formula 1), and the yield of the product BHET is shown in (Formula 2), wherein the molecular weight of BHET is 254 g / mol and the molecular weight of the repeating unit in PET is 192 g / mol.

[0058]

[0059]

[0060] Example 1

[0061] Isopropyl titanate (37.5 g) and butyl orthosilicate (9.2 g) were added into a reactor, and 80 mL of isopropanol was added. After stirring at 30°C for 1 hour, citric acid (16 g) was dissolved in 80 mL of isopropanol and slowly added dropwise to the reactant. The temperature was raised to 50°C and the reaction was carried out for 2 hours. The reactant was rotary evaporated at 70°C until the evaporation rate of small molecules slowed down significantly, and then dried in a vacuum drying oven at 70°C for 2 hours to obtain a titanium-silicon composite catalyst A.

[0062] Example 2

[0063] n-Butyl titanate (22.4 g) and ethyl orthosilicate (10.3 g) were added into a reactor, and 60 mL of ethanol was added. After stirring at 25°C for 1 hour, tartaric acid (23 g) was dissolved in 70 mL of ethanol and slowly added dropwise to the reactant. The temperature was raised to 40°C and the reaction was carried out for 3 hours. The reactant was rotary evaporated at 60°C until the evaporation rate of small molecules slowed down significantly, and then dried in a vacuum drying oven at 65°C for 4 hours to obtain a titanium-silicon composite catalyst B.

[0064] Example 3

[0065] Diisopropyl di(acetylacetonate)titanate (53.9 g) and ethyl orthosilicate (3.1 g) were added into a reactor, and then 50 mL of ethanol and 30 mL of isopropanol were added. After stirring at 35°C for 1.5 hours, salicylic acid (27.6 g) was dissolved in 80 mL of ethanol and slowly added dropwise to the reactant. The temperature was raised to 55°C and the reaction was carried out for 5 hours. The reactant was rotary evaporated at 70°C until the evaporation rate of small molecules slowed down significantly, and then dried in a vacuum drying oven at 70°C for 2 hours to obtain a titanium-silicon composite catalyst C.

[0066] Example 4

[0067] This example is used to illustrate the depolymerization of PET.

[0068] The treated waste PET bottle flakes and ethylene glycol were added to a reactor in a mass ratio of 1:4.5, and 0.3 wt% (based on the mass of PET) of a homemade titanium-silicon composite catalyst A was added. The air in the reactor was replaced with nitrogen. After confirming the airtightness of the reactor, a certain amount of nitrogen was introduced to make the pressure in the reactor reach 0.4 MPa. Stirring was started, and the temperature in the reactor was set to 200°C. The reaction time was set after the reactor temperature rose to the set temperature. The reaction time was 3 hours, and a depolymerization product was obtained. The PET depolymerization rate was 100%.

[0069] The depolymerized product was filtered while hot at 120°C to obtain a filtrate, and deionized water was added at a ratio of filtrate:water = 1:3. After stirring in an 80°C water bath for 2 hours, the filtrate was filtered to obtain a filtrate. The filtrate was crystallized at room temperature for 8 hours, and then cooled and crystallized at 0-5°C for 2 hours. Crystallized BHET was obtained by suction filtration, and dried in a drying oven at 70°C for 8 hours and then weighed to obtain the target monomer BHET with a purity of 97.1%.

[0070] Based on this example, it can be seen that the titanium-silicon composite catalyst of the present invention has high efficiency and high selectivity in the alcoholysis reaction of PET. The total content of products with a degree of polymerization of oligomers of 1-3 in the alcoholysis product is 99.2%, and BHET accounts for 93.7% of the depolymerization product. After separation and purification, the residual titanium content in the target monomer is 81 mg / kg.

[0071] Example 5

[0072] The method of Example 4 is followed, except that the catalyst is titanium-silicon composite catalyst B.

[0073] In Example 5, the PET depolymerization rate was 100%, the total content of oligomers with a degree of polymerization of 1-3 in the alcoholysis products was 99.1%, BHET accounted for 93.5% of the depolymerization products, and after separation and purification, the BHET purity was 97.0%, and the residual titanium content in the target monomer was 58 mg / kg.

[0074] Example 6

[0075] The method of Example 4 was followed, except that PET and ethylene glycol were added to the reactor at a mass ratio of 1:4.5, the catalyst was titanium-silicon composite catalyst C, and the depolymerization time was 2 hours.

[0076] In Example 6, the PET depolymerization rate was 100%, the total content of oligomers with a degree of polymerization of 1-3 in the alcoholysis product was 99.2 wt%, BHET accounted for 93.6 wt% of the depolymerization product, and after separation and purification, the purity of BHET was 97.8 wt%, and the residual titanium content in the target monomer was 47 mg / kg.

[0077] Example 7

[0078] According to the method of Example 5, the difference is that the catalyst dosage is 0.2wt%, and the depolymerization temperature is 210°C.

[0079] In Example 7, the PET depolymerization rate is 100%, the total content of products with a degree of polymerization of 1-3 in the alcoholysis product is 99.0%, the proportion of BHET in the depolymerization product is 93.0%, and after separation and purification, the purity of BHET is 97.2%, and the titanium residual amount in the target monomer is 34mg / kg.

[0080] Example 8

[0081] According to the method of Example 6, the difference is that the catalyst dosage is 0.1wt%, and the depolymerization pressure is 0.3MPa.

[0082] In Example 8, the PET depolymerization rate is 100%, the total content of products with a degree of polymerization of 1-3 in the alcoholysis product is 98.2%, the proportion of BHET in the depolymerization product is 90.5%, and after separation and purification, the purity of BHET is 96.9%, and the titanium residual amount in the target monomer is 25mg / kg.

[0083] Example 9

[0084] According to the method of Example 4, the difference is that PET and ethylene glycol are added into the reaction kettle at a mass ratio of 1:5, the catalyst dosage is 0.4wt%, and the depolymerization reaction temperature is 190°C.

[0085] In Example 9, the PET depolymerization rate is 100%, the total content of products with a degree of polymerization of 1-3 in the alcoholysis product is 99.0%, the proportion of BHET in the depolymerization product is 94.5%, and after separation and purification, the purity of BHET is 97.3%, and the titanium residual amount in the target monomer is 93mg / kg.

[0086] Example 10

[0087] According to the method of Example 4, the difference is that PET and ethylene glycol are added into the reaction kettle at a mass ratio of 1:3, and the catalyst dosage is 0.2wt%.

[0088] In Example 10, the PET depolymerization rate is 100%, the total content of products with a degree of polymerization of 1-3 in the alcoholysis product is 98.8%, the proportion of BHET in the depolymerization product is 93.9%, and after separation and purification, the purity of BHET is 97.0%, and the titanium residual amount in the target monomer is 57mg / kg.

[0089] Example 11

[0090] The method of Example 8 is followed, except that PET and ethylene glycol are added to the reactor at a mass ratio of 1:2, the reaction pressure is 0.35 MPa, and the reaction time is 4 hours.

[0091] In Example 11, the PET depolymerization rate is 100%, the total content of products with a degree of polymerization of 1-3 in the alcoholysis product is 98.0%, the content of BHET in the depolymerization product is 90.0%, the purity of BHET after separation and purification is 96.2%, and the titanium residue in the target monomer is 89 mg / kg.

[0092] Example 12

[0093] The method of Example 8 is followed, except that the waste PET bottle pieces are replaced with waste polyester bubble material, and the PET content is 93 wt%.

[0094] In Example 12, the PET depolymerization rate is 99%, the total content of products with a degree of polymerization of 1-3 in the alcoholysis product is 99.5%, the content of BHET in the depolymerization product is 91.3%, the purity of BHET after separation and purification is 98.0%, and the titanium residue in the target monomer is 23 mg / kg.

[0095] Example 13

[0096] The method of Example 8 is followed, except that the waste PET bottle pieces are replaced with a waste plastic with a PET content of 78.5%.

[0097] In Example 13, the PET depolymerization rate is 99%, the total content of products with a degree of polymerization of 1-3 in the alcoholysis product is 98.0%, the content of BHET in the depolymerization product is 99.1%, the purity of BHET after separation and purification is 98.40%, and the titanium residue in the target monomer is 22 mg / kg.

[0098] Example 14

[0099] In a three-necked flask, 83 g of self-made BHET monomer and 0.52 g of tetrabutyl titanate are added, and the temperature is gradually increased to 190°C under a nitrogen atmosphere. After 1 hour of reaction, the reduced pressure distillation device is replaced, and the temperature is increased to 280°C. The vacuum degree of the system is gradually adjusted to less than 300 Pa, and after 2.5 hours of reaction, a PET product with a number average molecular weight of 19,000 g / mol is obtained.

[0100] Comparative Example 1

[0101] The treated waste PET bottle pieces and ethylene glycol are added into a reaction kettle at a mass ratio of 1:4.5, and 0.3 wt% (based on the mass of PET) of tetrabutyl titanate is added, the depolymerization pressure is 0.4 MPa, the depolymerization temperature is 200℃, and the depolymerization time is 3 hours, to obtain a depolymerization product, the PET depolymerization rate is 100%, the total content of the product with a polymerization degree of 1-3 in the alcoholysis product is 97.6%, the proportion of BHET in the depolymerization product is 91.7%, after separation and purification, the purity of BHET is 96.6%, and the titanium residual amount in the target monomer is 258 mg / kg.

[0102] The experimental results of examples 4-11 and comparative example 1 are shown in Table 1.

[0103] Table 1

[0104]

[0105] Table 1 (continued)

[0106]

[0107]

[0108] Table 1 (continued)

[0109]

[0110] As can be seen from the results in Table 1, the examples 4-11 using the technical solutions of the present application have obviously better effects in the titanium residual amount in the target monomer and the total amount of the product with a polymerization degree of 1-3, etc. compared with comparative example 1, example 4-10 has obviously better effect in the purity of BHET, examples 4-7, 9 and 10 have obviously better effect in the proportion of BHET in the depolymerization product. The results of examples 12 and 13 also prove that the method of the present application can be applied to the depolymerization process of other polyethylene terephthalate-containing materials except waste PET bottle pieces. The results of example 14 prove that the BHET obtained by the method of the present application can be directly used to prepare PET polyester products or other high value-added products, realizing the closed-loop recycling utilization of PET.

[0111] The above describes the preferred embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. A method for preparing a titanium-silicon composite catalyst, the method comprising: (1) preparing a titanium compound, an orthosilicate compound, and a solvent and reacting them with an organic acid solution to obtain a solution; wherein the organic acid in the organic acid solution is selected from one or more of citric acid, malic acid, salicylic acid, tartaric acid, and lactic acid; (2) post-treating the solution to obtain a titanium-silicon composite catalyst; The post-processing process includes: (i) heating the solution to distill out small molecules; (ii) after the small molecules are distilled out, cooling the material to obtain a titanium-silicon composite catalyst; Wherein, in the titanium-silicon composite catalyst, the content of titanium element is 10-50wt%, and the content of silicon element is 0.3-9.5wt%.

2. The preparation method according to claim 1, wherein The titanium compound is selected from one or more of tetrabutyl titanate, isopropyl titanate, tetraethyl titanate, titanium glycolate, titanium acetylacetonate, and diisopropyl di(acetylacetonate) titanate.

3. The preparation method according to claim 1, wherein The orthosilicate compound is selected from one or more of tetrabutyl orthosilicate, tetraethyl orthosilicate, and tetramethyl orthosilicate.

4. The preparation method according to claim 1, wherein The solvent is selected from one or more of ethanol, isopropanol and water.

5. The preparation method according to any one of claims 1 to 3, wherein The molar ratio of the titanium compound to the orthosilicate compound is 95:5-70:

30.

6. The preparation method according to claim 1 or 2, wherein The molar ratio of the titanium compound to the organic acid in the organic acid solution is 1:8-1:0.

5.

7. The preparation method according to claim 1 or 4, wherein The molar ratio of the titanium compound to the solvent is 1:1-1:

50.

8. The preparation method according to claim 1, wherein The reaction temperature in step (1) is 20-40°C.

9. The preparation method according to claim 1, wherein The reaction time in step (1) is 2-3 hours.

10. A titanium-silicon composite catalyst prepared by the preparation method according to any one of claims 1 to 9.

11. The titanium-silicon composite catalyst according to claim 10, wherein The pH value of the titanium-silicon composite catalyst is 2-5.

12. The titanium-silicon composite catalyst according to claim 10 or 11, wherein In the infrared spectrum of the titanium-silicon composite catalyst, the -1 There is an absorption peak at.

13. A method for depolymerizing polyethylene terephthalate, the method comprising: In the presence of a catalyst and a protective atmosphere, the treated polyethylene terephthalate-containing material and alcohol are subjected to a depolymerization reaction to obtain an alcoholysis product containing bis(2-hydroxyethyl) terephthalate; Wherein, the catalyst is the titanium-silicon composite catalyst according to any one of claims 10-12.

14. The method according to claim 13, wherein The alcohol is a diol.

15. The method according to claim 14, wherein The alcohol is selected from at least one or more of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, and 1,6-hexanediol.

16. The method according to claim 13, wherein: The mass ratio of the polyethylene terephthalate to the alcohol is 1:2-1:

8.

17. The method according to claim 16, wherein The mass ratio of the polyethylene terephthalate to the alcohol is 1:3-1:

5.

18. The method according to claim 13, wherein The amount of the catalyst used is 0.05-0.5 wt% of the polyethylene terephthalate.

19. The method according to claim 18, wherein The amount of the catalyst used is 0.1-0.4 wt % of the polyethylene terephthalate.

20. The method according to claim 13, wherein The reaction temperature of the depolymerization reaction is 190-250°C.

21. The method according to claim 20, wherein The reaction temperature of the depolymerization reaction is 200-230°C.

22. The method according to claim 13, wherein The reaction pressure of the depolymerization reaction is 0.2-0.6 MPa.

23. The method according to claim 22, wherein The reaction pressure of the depolymerization reaction is 0.35-0.5 MPa.

24. The method according to claim 13, wherein The reaction time of the depolymerization reaction is 1-5 hours.

25. The method according to claim 24, wherein The reaction time of the depolymerization reaction is 2-4 hours.

Images