Method for preparing dimethyl terephthalate through one-step catalysis of waste polyester and dimethyl terephthalate

Abstract

The invention relates to a method for preparing dimethyl terephthalate by catalyzing waste polyester in one step and dimethyl terephthalate. The invention relates to a method for preparing dimethyl terephthalate by catalyzing waste polyester in one step, which comprises the following steps: mixing a waste polyester material, a catalyst and a depolymerization solution for depolymerization reaction to obtain dimethyl terephthalate, the catalyst is selected from aromatic acid, aromatic acid alkali metal salt, a composition of aromatic acid and carbonate, a composition of aromatic acid and phosphate, a composition of aromatic acid and acetate, a composition of aromatic acid alkali metal salt and carbonate and a composition of aromatic acid alkali metal salt and phosphate; and a composition of aromatic acid alkali metal salt and acetate. The invention also provides the dimethyl terephthalate prepared by the method. The method provided by the invention solves the problems of low product purity and yield in the existing polyester waste chemical recovery method, and also solves the problems of high catalyst cost, harsh reaction conditions and easy secondary pollution to the environment in the existing recovery method.

Description

Technical Field

[0001] The present invention relates to the technical field of waste polyester resource recovery, and particularly relates to a method for catalytically preparing dimethyl terephthalate from waste polyester in one step and dimethyl terephthalate. Background Art

[0002] With the continuous increase in global plastic consumption, the recycling and high-value conversion of polyester waste (such as PET) have become key issues in solving "white pollution" and resource recycling. Chemical recycling methods have attracted much attention because they can efficiently convert waste polyester into monomer raw materials (such as dimethyl terephthalate, DMT). However, there are still many problems in existing chemical recycling methods, and urgent improvements are needed to achieve industrial application.

[0003] For example, in the acid-base synergistic catalysis method, phenolic substances are used as auxiliaries to cooperate with alkaline catalysts to achieve polyester depolymerization at a temperature of 60°C to 200°C. Although this method can improve the depolymerization efficiency to a certain extent, phenolic auxiliaries have potential environmental risks and are difficult to meet the requirements of high-end materials. In the composite metal catalysis method, composite metal catalysts such as zinc chloride and zinc acetate are used, and the reaction needs to be carried out at a high temperature of 220°C to 300°C for 8 to 24 hours. Although the yield of this method is relatively high, the high temperature leads to a sharp increase in energy consumption, and the pretreatment steps are cumbersome. It is necessary to separate oligomers, and there is easily metal residue, so the process economy is poor and it is difficult to be applied to actual industrial production. In the organic base synergistic catalysis method, urea / guanidine organic bases and inorganic bases are used for synergistic catalysis to achieve rapid depolymerization at a temperature of 25°C to 80°C. However, this method relies on toxic solvents such as DMAC (N,N-dimethylacetamide) and DMF (N,N-dimethylformamide) for pretreatment, and the catalyst cost is high, which limits its large-scale application. In the glycol-methanol two-step method, high-temperature and high-pressure (150°C to 260°C, 10 to 70 atm) depolymerization is combined with alcoholysis process. However, multiple-step reactions and complex separation processes significantly increase the equipment investment and operation cost, and the high-temperature conditions exacerbate side reactions, affecting the purity of DMT. In the continuous alcoholysis process, a series of multi-stage alcoholysis reactors are used to achieve continuous production. However, the DMT yield is 92%, and this process needs to carry out alcoholysis and subsequent transesterification reactions at a high temperature of 180°C to 200°C. The process is long, easily generates by-products and heavy metal residues, and the equipment is complex (multi-stage reaction kettle, distillation system), with high investment and maintenance costs. In the ethylene glycol salt catalysis method, ethylene glycol monosodium is used as a catalyst to achieve PET depolymerization in methanol. However, the catalyst preparation requires multiple steps (heating, drying, suspension aging), the process is complex and time-consuming (the aging period reaches 7 days), the reaction needs to premix the solvent and control the temperature strictly (60°C), the industrial continuity is poor, and there is strong alkaline wastewater pollution, and there is a risk of catalyst residue in the product.

[0004] In summary, the existing chemical recycling methods for polyester waste generally have problems such as harsh reaction conditions, high catalyst cost, insufficient product purity, and complex processes, which severely restrict their industrial applications. Therefore, it is of great practical significance to develop a polyester waste recycling method that is efficient, environmentally friendly, economical, and can obtain high-purity products. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for catalytically preparing dimethyl terephthalate from waste polyester in one step and dimethyl terephthalate, so as to solve the problems of low product purity and yield in the existing chemical recycling methods for polyester waste, and can also solve the problems of high catalyst cost, harsh reaction conditions, many side reactions, and easy secondary environmental pollution in the existing chemical recycling methods for polyester waste.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present invention is as follows: A method for catalytically preparing dimethyl terephthalate from waste polyester in one step, comprising the following steps: Mixing the waste polyester material, catalyst, and depolymerization liquid for depolymerization reaction to obtain dimethyl terephthalate; The catalyst is selected from at least one of aromatic acids, aromatic acid alkali metal salts, compositions of aromatic acids and carbonates, compositions of aromatic acids and phosphates, compositions of aromatic acids and acetates, compositions of aromatic acid alkali metal salts and carbonates, compositions of aromatic acid alkali metal salts and phosphates, and compositions of aromatic acid alkali metal salts and acetates.

[0007] By mixing the waste polyester material, catalyst, and depolymerization liquid for depolymerization reaction, the waste polyester can be directly and efficiently converted into high-value-added dimethyl terephthalate, realizing the high-value recycling of waste polyester, improving the resource recycling rate, and the obtained dimethyl terephthalate has the advantages of high yield and purity, effectively solving the problems of low product purity and yield in the existing chemical recycling methods for polyester waste.

[0008] Using aromatic acids, aromatic acid alkali metal salts, and their compositions with carbonates, phosphates, acetates, etc. as catalysts, these catalysts are widely sourced, low-cost, and exhibit good catalytic activity and stability during the reaction, effectively reducing the production cost and solving the problem of high catalyst cost in the existing chemical recycling methods for polyester waste.

[0009] The present invention has strong adaptability to colored or impurity-containing polyester (such as colored PET) and excellent anti-interference ability. Even in the case of complex components such as pigments and impurities in the waste polyester, the depolymerization reaction can still be efficiently carried out without complex pretreatment of the waste polyester, further reducing the production cost and improving the practicality and economy of the process.

[0010] Among them, during the polyester depolymerization process, the catalytic system achieves efficient depolymerization through the synergistic action of multiple mechanisms: alkaline catalysts (such as Na2CO3, K3PO4) increase the pH value of the system, promoting the deprotonation of methanol / ethylene glycol hydroxyl groups to generate highly active methoxy / ethylene glycol oxyanions, and breaking the PET ester bond through nucleophilic attack; Lewis acid catalysts (such as potassium acetate, magnesium acetate) coordinate with the carbonyl oxygen atoms through metal ions, polarize the ester bond and enhance its reactivity, accelerating the depolymerization kinetics; buffers (NaHCO3, sodium benzoate) maintain a weakly alkaline environment (pH 7-9), inhibiting side reactions while maintaining the activity of nucleophiles; catalysts containing aromatic rings (such as sodium p-hydroxybenzoate) adsorb on the PET surface directionally through π-π stacking and hydrogen bonding, stabilizing the transition state to improve regioselectivity; phase transfer catalysts (such as potassium p-sulfobenzoate) strengthen the solid-liquid mass transfer by reducing the interfacial tension, and thermally stable catalysts (such as Cs3PO4) maintain structural stability at high temperatures, combined with recyclable design (such as the selective precipitation of calcium acetate) to achieve green recycling. This multi-mechanism synergistic system reduces the reaction activation energy by 30-50%, realizes the selective production of more than 99.9% DMT under mild conditions of 120°C - 180°C, effectively avoiding side reactions such as hydrolysis and oxidation, and providing a technical solution with both high efficiency and sustainability for the chemical recycling of waste PET.

[0011] Preferably, the aromatic acid is selected from at least one of benzoic acid, o-toluic acid, m-toluic acid, p-toluic acid, o-aminobenzoic acid, m-aminobenzoic acid, p-aminobenzoic acid, o-hydroxybenzoic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, o-methoxybenzoic acid, m-methoxybenzoic acid, p-methoxybenzoic acid, ascorbic acid, 2,4-dihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, and 4-hydroxy-3-methoxybenzoic acid.

[0012] Preferably, the alkali metal salts of aromatic acids are selected from at least one of sodium benzoate, potassium benzoate, sodium o-toluate, potassium o-toluate, sodium m-toluate, potassium m-toluate, sodium p-toluate, potassium p-toluate, sodium o-hydroxybenzoate, potassium o-hydroxybenzoate, sodium m-hydroxybenzoate, potassium m-hydroxybenzoate, sodium p-hydroxybenzoate, potassium p-hydroxybenzoate, sodium o-methoxybenzoate, potassium o-methoxybenzoate, sodium m-methoxybenzoate, potassium m-methoxybenzoate, sodium p-methoxybenzoate, potassium p-methoxybenzoate, sodium 2,4-dihydroxybenzoate, potassium 2,4-dihydroxybenzoate, sodium 3,4,5-trihydroxybenzoate, potassium 3,4,5-trihydroxybenzoate, sodium 4-hydroxy-3-methoxybenzoate, potassium 4-hydroxy-3-methoxybenzoate, and potassium p-sulfobenzoate.

[0013] Preferably, the carbonate is selected from at least one of sodium bicarbonate, potassium bicarbonate, sodium carbonate, and potassium carbonate.

[0014] Preferably, the phosphate is selected from at least one of trisodium phosphate, tripotassium phosphate, and cesium phosphate.

[0015] Preferably, the acetate is selected from at least one of sodium acetate, potassium acetate, calcium acetate, and magnesium acetate.

[0016] Preferably, the catalyst is selected from potassium p-sulfobenzoate, a composition of potassium carbonate and benzoic acid, a composition of potassium bicarbonate and sodium benzoate, a composition of sodium acetate and p-hydroxybenzoic acid, a composition of tripotassium phosphate and o-hydroxybenzoic acid, a composition of potassium acetate and p-methoxybenzoic acid, a composition of potassium carbonate and ascorbic acid, a composition of potassium bicarbonate and p-methylbenzoic acid, a composition of sodium carbonate and 2,4-dihydroxybenzoic acid, a composition of trisodium phosphate and sodium 2,4-dihydroxybenzoate, a composition of potassium bicarbonate and 3,4,5-trihydroxybenzoic acid, or a composition of potassium bicarbonate and 4-hydroxy-3-methoxybenzoic acid.

[0017] Preferably, the depolymerization solution is selected from a mixture of methanol and ethylene glycol.

[0018] Among them, through experimental research, it is found that the addition of ethylene glycol significantly reduces the viscosity of the reaction system, improves the mass transfer efficiency. At the same time, the interaction between its hydroxyl group and the polyester molecular chain helps to generate DMT directionally. Experiments show that when the volume ratio of methanol to ethylene glycol is 4:1, the reaction rate and product purity reach the optimal balance.

[0019] By selecting a methanol-ethylene glycol dual-solvent system as the depolymerization solution, the reaction activity and the convenience of product separation are taken into account. Methanol helps to improve the reaction rate, while ethylene glycol is beneficial to the separation and purification of the product. The two act synergistically to improve the purity and yield of the product and simplify the subsequent separation and purification process.

[0020] Preferably, the volume ratio of the methanol to the ethylene glycol is 4:1 to 8:1.

[0021] Preferably, the waste polyester material is selected from at least one of waste polyethylene terephthalate (PET), waste polybutylene terephthalate (PBT), waste polytrimethylene terephthalate (PTT), and waste poly(cyclohexylene dimethylene terephthalate) (PCT).

[0022] Among them, polyethylene terephthalate (PET) is the key treatment object of the present invention due to its wide application scenarios and recycling requirements. The waste polyester material needs to be pre-crushed into centimeter-sized fragments or pieces to increase the reaction contact area and improve the depolymerization efficiency.

[0023] Preferably, the temperature of the depolymerization reaction is 120°C to 180°C.

[0024] Preferably, the time of the depolymerization reaction is 1 h to 8 h.

[0025] Preferably, the time of the depolymerization reaction is 2 h to 6 h.

[0026] Preferably, the temperature of the depolymerization reaction is 140 °C to 160 °C.

[0027] Through experiments, it is found that under these temperature and time conditions, the polyester molecular chains are fully depolymerized, while avoiding the decomposition or carbonization of DMT caused by high temperature. For example, using potassium p-sulfobenzoate as a catalyst and reacting at 140 °C for 4 hours, the PET conversion rate can reach 99.8%, and the DMT yield is as high as 99.5%.

[0028] The reaction conditions adopted in the present invention are mild. Compared with the harsh conditions such as high temperature and high pressure commonly used in the prior art, the equipment corrosion is significantly reduced, the energy consumption is reduced, and at the same time, the safety of the production process is improved, making it more suitable for industrial continuous production.

[0029] Preferably, the dosage of the catalyst is 1 wt% to 20 wt% of the waste polyester material.

[0030] By optimizing the catalyst dosage and solvent ratio, the reaction energy consumption and subsequent purification cost can be significantly reduced. For example, using potassium p-sulfobenzoate as a catalyst, the catalyst dosage is 20% of the polyester mass, and the amount of the depolymerization solution used is 4 mL / g. After the reaction, DMT can be directly separated by crystallization, and the purity reaches more than 99.9%.

[0031] Preferably, the mass ratio of the catalyst to the polyester waste plastic is (0.005 - 0.2):1; the addition amount of the depolymerization solution per gram of the polyester waste plastic is 1 to 6 mL.

[0032] Preferably, the ratio of the depolymerization solution to the waste polyester material is 2:1 to 6:1 in mL:g.

[0033] Preferably, after the depolymerization reaction is completed, a mixed solution and a solid are obtained, and the solid is dimethyl terephthalate; The obtained mixed solution is distilled, and the distillate is ethylene glycol.

[0034] Preferably, the yield of the dimethyl terephthalate can reach 99.9%, the purity of the dimethyl terephthalate can reach 99.9%, the yield of the ethylene glycol can reach 98.9%, and the purity of the ethylene glycol can reach 99.3%.

[0035] The present invention also provides a dimethyl terephthalate prepared by the method as described in the present invention.

[0036] The beneficial effects of the present invention: The method for catalytically preparing dimethyl terephthalate from waste polyester of the present invention can directly and efficiently convert waste polyester into high - value - added dimethyl terephthalate by mixing waste polyester materials, catalysts and depolymerization liquids for depolymerization reaction. It realizes the high - value recycling of waste polyester, improves the recycling rate of resources, and the obtained dimethyl terephthalate has the advantages of high yield and purity. The catalysts selected in the present invention are rich in variety, including aromatic acids, aromatic acid alkali metal salts and their compositions with carbonates, phosphates, acetates, etc. These catalysts are widely sourced, low - cost, and show good catalytic activity and stability during the reaction, effectively reducing production costs. It solves the problems existing in the existing chemical recycling methods of polyester waste, such as high catalyst cost, harsh reaction conditions, many side reactions and easy secondary pollution to the environment. The entire production process of the present invention is more environmentally friendly, reduces the negative impact on the environment, and meets the requirements of sustainable development. The present invention not only improves the recycling rate of waste polyester, reduces production costs, but also reduces waste emissions and environmental pollution, with significant economic and environmental benefits. It provides an efficient and environmentally friendly solution for the high - value recycling of waste polyester, has broad application prospects, and has the value of popularization and application in the field of waste polyester resource recycling technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 1H NMR spectrum of DMT prepared in Example 1; 1 1H NMR spectrum; Figure 2 It is the test result diagram of DMT prepared in Example 52 by a third - party institution. DETAILED DESCRIPTION OF THE INVENTION

[0038] The following will illustrate the implementation manners of the present invention with reference to preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, rather than for limiting the protection scope of the present invention.

[0039] Example 1 A method for catalytically preparing dimethyl terephthalate from waste polyester in one step, comprising the following steps: Put 2000 g of waste polyethylene terephthalate (PET) bottle chips, 200 g of potassium p - sulfobenzoate and 8000 mL of depolymerization liquid (according to V (甲醇) :V (乙二醇)(prepared in a ratio of 4:1) were mixed and added into a titanium alloy reactor, placed on a heating plate, stirred and heated to 140 °C for 8 h of depolymerization reaction. After the reaction was completed, the temperature was lowered to room temperature to obtain a mixed solution and a precipitated solid. The precipitated solid was dimethyl terephthalate (DMT); The mixed solution was recovered by distillation to obtain a distillate, which was ethylene glycol.

[0040] Example 2 In this example, except for the depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 6:1), the other conditions were the same as those in Example 1.

[0041] Example 3 In this example, except for the depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 8:1), the other conditions were the same as those in Example 1.

[0042] Comparative Example 1 A method for preparing dimethyl terephthalate from waste polyester includes the following steps: 2000 g of waste polyethylene terephthalate (PET) bottle chips, 200 g of potassium p-sulfobenzoate and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 0.5:1) were mixed and added into a titanium alloy reactor, placed on a heating plate, stirred and heated to 140 °C for 8 h of depolymerization reaction. After the reaction was completed, the temperature was lowered to room temperature to obtain a mixed solution and a precipitated solid. The precipitated solid was dimethyl terephthalate (DMT); The mixed solution was recovered by distillation to obtain a distillate, which was ethylene glycol.

[0043] Comparative Example 2 In this comparative example, except for the depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 2:1), the other conditions were the same as those in Comparative Example 1.

[0044] Example 4 In this example, except that the depolymerization reaction time was 4 h, the other conditions were the same as those in Example 1.

[0045] Example 5 In this example, except that the depolymerization reaction time was 6 h, the other conditions were the same as those in Example 1.

[0046] Comparative Example 3 A method for preparing dimethyl terephthalate from waste polyester includes the following steps: Mix 2000 g of waste polyethylene terephthalate (PET) bottle chips, 200 g of potassium p-sulfobenzoate, and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) and add them to a titanium alloy reactor. Place it on a heating plate, turn on the stirrer and heat up to 140 °C, and carry out the depolymerization reaction for 0.5 h. After the reaction is completed, cool down to room temperature to obtain a mixed solution and precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed solution by distillation to obtain a distillate, which is ethylene glycol.

[0047] Control Example 4 In this control example, except that the depolymerization reaction time is 2 h, the other conditions are the same as those in Control Example 3.

[0048] Example 6 A method for catalytically preparing dimethyl terephthalate from waste polyester in one step, comprising the following steps: Mix 2000 g of waste polyethylene terephthalate (PET) bottle chips, 200 g of potassium p-sulfobenzoate, and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) and add them to a titanium alloy reactor. Place it on a heating plate, turn on the stirrer and heat up to 140 °C, and carry out the depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed solution and precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed solution by distillation to obtain a distillate, which is ethylene glycol.

[0049] Control Example 5 A method for preparing dimethyl terephthalate from waste polyester, comprising the following steps: Mix 2000 g of waste polyethylene terephthalate (PET) bottle chips, 200 g of potassium p-sulfobenzoate, and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) and add them to a titanium alloy reactor. Place it on a heating plate, turn on the stirrer and heat up to 100 °C, and carry out the depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed solution and precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed solution by distillation to obtain a distillate, which is ethylene glycol.

[0050] Control Example 6 In this comparative example, except that the temperature of the depolymerization reaction is 120 °C, the other conditions are the same as those in Comparative Example 5.

[0051] Comparative Example 7 In this comparative example, except that the temperature of the depolymerization reaction is 160 °C, the other conditions are the same as those in Comparative Example 5.

[0052] Comparative Example 8 In this comparative example, except that the temperature of the depolymerization reaction is 180 °C, the other conditions are the same as those in Comparative Example 5.

[0053] Example 7 A method for catalytically preparing dimethyl terephthalate from waste polyester in one step includes the following steps: Mix 2000 g of waste polyethylene terephthalate (PET) bottle chips, 400 g of potassium p-sulfobenzoate and 1000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) and add them into a titanium alloy reaction kettle. Place it on a heating plate, turn on the stirrer and heat up to 140 °C for a depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed solution and precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed solution by distillation to obtain a distillate, which is ethylene glycol.

[0054] Example 8 In this comparative example, except that the dosage of potassium p-sulfobenzoate is 100 g, the other conditions are the same as those in Example 7.

[0055] Example 9 In this comparative example, except that the dosage of potassium p-sulfobenzoate is 200 g, the other conditions are the same as those in Example 7.

[0056] Comparative Example 9 A method for preparing dimethyl terephthalate from waste polyester includes the following steps: Mix 2000 g of waste polyethylene terephthalate (PET) bottle chips, 50 g of potassium p-sulfobenzoate and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) and add them into a titanium alloy reaction kettle. Place it on a heating plate, turn on the stirrer and heat up to 140 °C for a depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed solution and precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed solution by distillation to obtain a distillate, which is ethylene glycol.

[0057] Example 10 A method for preparing dimethyl terephthalate by one-step catalytic conversion of waste polyester, comprising the following steps: Mix 2000 g of waste polyethylene terephthalate (PET) bottle chips, 200 g of potassium p-sulfobenzoate and 9000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) in a titanium alloy reactor, place it on a heating plate, start stirring and heat up to 140 °C, carry out depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed solution and a precipitated solid, and the precipitated solid is dimethyl terephthalate (DMT); Recover the mixed solution by distillation to obtain a distillate, which is ethylene glycol.

[0058] Example 11 In this example, except that the amount of the depolymerization solution is 12000 mL, the other conditions are the same as those in Example 10.

[0059] Comparative Example 10 A method for preparing dimethyl terephthalate from waste polyester, comprising the following steps: Mix 2000 g of waste polyethylene terephthalate (PET) bottle chips, 200 g of potassium p-sulfobenzoate and 3000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) in a titanium alloy reactor, place it on a heating plate, start stirring and heat up to 140 °C, carry out depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed solution and a precipitated solid, and the precipitated solid is dimethyl terephthalate (DMT); Recover the mixed solution by distillation to obtain a distillate, which is ethylene glycol.

[0060] Comparative Example 11 In this comparative example, except that the amount of the depolymerization solution is 6000 mL, the other conditions are the same as those in Comparative Example 10.

[0061] Example 12 A method for preparing dimethyl terephthalate by one-step catalytic conversion of waste polyester, comprising the following steps: Mix 2000 g of waste polyethylene terephthalate (PET) bottle chips, 200 g of benzoic acid and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇)= Prepared by mixing in a ratio of 4:1) and adding it into a titanium alloy reactor. Place it on a heating plate, turn on the stirring and heat up to 140 °C, and carry out the depolymerization reaction for 4 h. After the reaction is completed, cool it down to room temperature to obtain a mixed liquid and a precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); The mixed liquid is recovered by distillation to obtain a distillate, which is ethylene glycol.

[0062] Example 13 In this example, except that sodium benzoate is used as the catalyst, the other conditions are the same as those in Example 12.

[0063] Example 14 In this example, except that p-toluic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0064] Example 15 In this example, except that p-hydroxybenzoic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0065] Example 16 In this example, except that potassium p-toluate is used as the catalyst, the other conditions are the same as those in Example 12.

[0066] Example 17 In this example, except that m-aminobenzoic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0067] Example 18 In this example, except that sodium p-hydroxybenzoate is used as the catalyst, the other conditions are the same as those in Example 12.

[0068] Example 19 In this example, except that p-methoxybenzoic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0069] Example 20 In this example, except that sodium p-methoxybenzoate is used as the catalyst, the other conditions are the same as those in Example 12.

[0070] Example 21 In this example, except that 2,4-dihydroxybenzoic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0071] Example 22 In this example, except that sodium 2,4-dihydroxybenzoate is used as the catalyst, the other conditions are the same as those in Example 12.

[0072] Example 23 In this example, except that 3,4,5-trihydroxybenzoic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0073] Example 24 In this example, except that 4-hydroxy-3-methoxybenzoic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0074] Example 25 In this example, except that o-toluic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0075] Example 26 In this example, except that m-toluic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0076] Example 27 In this example, except that o-aminobenzoic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0077] Example 28 In this example, except that p-aminobenzoic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0078] Example 29 In this example, except that m-methoxybenzoic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0079] Example 30 In this example, except that ascorbic acid is used as the catalyst, the other conditions are the same as those in Example 12.

[0080] Control Example 12 A method for preparing dimethyl terephthalate from waste polyester includes the following steps: Mix 2000 g of waste polyethylene terephthalate (PET) bottle chips, 200 g of potassium carbonate and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) and add them into a titanium alloy reaction kettle, place it on a heating plate, start stirring and heat up to 140 °C, carry out depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed solution and a precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed solution by distillation to obtain a distillate, which is ethylene glycol.

[0081] Control Example 13 In this control example, except that tripotassium phosphate is used as the catalyst, the other conditions are the same as those in Control Example 12.

[0082] Comparative Example 14 In this comparative example, except that potassium acetate was used as the catalyst, the other conditions were the same as those in Comparative Example 12.

[0083] Example 31 A method for catalytically preparing dimethyl terephthalate from waste polyester in one step, comprising the following steps: Mix 2000 g of waste polyethylene terephthalate (PET) bottle chips, 200 g of catalyst (100 g of potassium carbonate + 300 g of benzoic acid) and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) and add them into a titanium alloy reaction kettle, place it on a heating plate, turn on the stirrer and heat up to 120 °C, carry out the depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed liquid and a precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed liquid by distillation to obtain a distillate, which is ethylene glycol.

[0084] Example 32 In this example, except that the catalyst used was 50 g of potassium bicarbonate + 150 g of sodium benzoate, the other conditions were the same as those in Example 31.

[0085] Example 33 In this example, except that the catalyst used was 50 g of sodium acetate + 150 g of p-hydroxybenzoic acid, the other conditions were the same as those in Example 31.

[0086] Example 34 In this example, except that the catalyst used was 50 g of tripotassium phosphate + 150 g of o-hydroxybenzoic acid, the other conditions were the same as those in Example 31.

[0087] Example 35 In this example, except that the catalyst used was 50 g of potassium acetate + 150 g of p-methoxybenzoic acid, the other conditions were the same as those in Example 31.

[0088] Example 36 In this example, except that the catalyst used was 50 g of potassium bicarbonate + 150 g of p-toluic acid, the other conditions were the same as those in Example 31.

[0089] Example 37 In this example, except that the catalyst used was 50 g of sodium carbonate + 150 g of 2,4-dihydroxybenzoic acid, the other conditions were the same as those in Example 31.

[0090] Example 38 In this example, except that the catalyst selected is 50 g of trisodium phosphate + 150 g of 2,4-dihydroxybenzoic acid, the other conditions are the same as those in Example 31.

[0091] Example 39 In this example, except that the catalyst selected is 50 g of potassium bicarbonate + 150 g of 3,4,5-trihydroxybenzoic acid, the other conditions are the same as those in Example 31.

[0092] Example 40 In this example, except that the catalyst selected is 50 g of potassium bicarbonate + 150 g of 4-hydroxy-3-methoxybenzoic acid, the other conditions are the same as those in Example 31.

[0093] Example 41 In this example, except that the catalyst selected is 50 g of potassium carbonate + 150 g of m-toluic acid, the other conditions are the same as those in Example 31.

[0094] Example 42 In this example, except that the catalyst selected is 50 g of tripotassium phosphate + 150 g of m-hydroxybenzoic acid, the other conditions are the same as those in Example 31.

[0095] Control Example 15 In this control example, except that the catalyst is 50 g of sodium acetate + 150 g of tripotassium phosphate, the other conditions are the same as those in Control Example 25.

[0096] Control Example 16 In this control example, except that the catalyst is 50 g of sodium carbonate + 150 g of calcium acetate, the other conditions are the same as those in Control Example 25.

[0097] Example 43 A method for catalytically preparing dimethyl terephthalate from waste polyester in one step, comprising the following steps: Mix 2000 g of waste polybutylene terephthalate (PBT) bottle chips, 200 g of potassium p-sulfobenzoate and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) and add them into a titanium alloy reaction kettle, place it on a heating plate, turn on the stirring and heat up to 140 °C, carry out the depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed liquid and precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed liquid by distillation to obtain a distillate, which is ethylene glycol.

[0098] Example 44 A method for catalytically preparing dimethyl terephthalate from waste polyester in one step, comprising the following steps: Add 2000 g of waste polytrimethylene terephthalate (PTT) bottle chips, 200 g of potassium p-sulfobenzoate, and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) into a titanium alloy reactor, place it on a heating plate, turn on the stirrer and heat up to 140 °C, carry out the depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed liquid and a precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed liquid by distillation to obtain a distillate, which is ethylene glycol.

[0099] Example 45 A method for catalytically preparing dimethyl terephthalate from waste polyester in one step, comprising the following steps: Add 2000 g of waste poly(cyclohexane dimethanol terephthalate) (PCT) bottle chips, 200 g of potassium p-sulfobenzoate, and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) into a titanium alloy reactor, place it on a heating plate, turn on the stirrer and heat up to 140 °C, carry out the depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed liquid and a precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed liquid by distillation to obtain a distillate, which is ethylene glycol.

[0100] Example 46 A method for catalytically preparing dimethyl terephthalate from waste polyester in one step, comprising the following steps: Add 2000 g of waste polyethylene terephthalate (PET) colored bottle chips, 200 g of potassium p-sulfobenzoate, and 8000 mL of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) into a titanium alloy reactor, place it on a heating plate, turn on the stirrer and heat up to 140 °C, carry out the depolymerization reaction for 4 h. After the reaction is completed, cool down to room temperature to obtain a mixed liquid and a precipitated solid. The precipitated solid is dimethyl terephthalate (DMT); Recover the mixed liquid by distillation to obtain a distillate, which is ethylene glycol.

[0101] Example 47 In this example, except for using waste polyethylene terephthalate (PET) non-woven fabric, the other conditions are the same as those in Example 46.

[0102] Example 48 In this example, except for using waste polyethylene terephthalate (PET) blister sheets, the other conditions are the same as those in Example 46.

[0103] Example 49 In this example, except for using waste polyethylene terephthalate (PET) films, the other conditions are the same as those in Example 46.

[0104] Example 50 In this example, except for using waste polyethylene terephthalate (PET) foam materials, the other conditions are the same as those in Example 46.

[0105] Example 51 In this example, except for using waste polyethylene terephthalate (PET) waste clothes, the other conditions are the same as those in Example 46.

[0106] Example 52 A method for catalytically depolymerizing waste polyester to dimethyl terephthalate in one step. This example is a ton-scale amplification experiment on the optimal depolymerization conditions, including the following steps: Mix 500 kg of crushed waste polyethylene terephthalate (PET) bottle chips, 50 kg of potassium p-sulfobenzoate, and 2000 L of depolymerization solution (prepared according to V (甲醇) :V (乙二醇) = 4:1) and add them into a 316 stainless steel high-pressure reactor with a volume of 3.4 m 3 . Place it on a heating plate, start stirring and heat up to 140 °C for 4 h of depolymerization reaction. After the reaction is completed, through cooling crystallization, filtration, washing, and drying, 485 kg of DMT is obtained (the yield has an error of 4% during the filtration, washing, and drying processes), and the purity is 99.95%.

[0107] Detection and analysis 1) Nuclear magnetic resonance analysis Perform nuclear magnetic resonance analysis on the dimethyl terephthalate (DMT) prepared in Example 1, and the results are as Figure 1 shown.

[0108] From the Figure 1 analysis, it can be known that the purity of the obtained DMT ≥ 99.9%.

[0109] 2) Yield and purity analysis of dimethyl terephthalate (DMT) and ethylene glycol (EG) The precipitated solids obtained in Examples 1 to 52 and Comparative Examples 1 to 16, namely dimethyl terephthalate (DMT), were added to dichloromethane for dissolution. The dissolved solution was measured for DMT yield and purity by NMR, and ethylene glycol (EG) was recovered by distillation. The obtained distillate was measured for EG yield and purity by NMR. The results are shown in Tables 1 to 10.

[0110] Table 1 shows the comparison results of different volume ratios of methanol to ethylene glycol Table 2 shows the comparison results of different depolymerization reaction times Table 3 shows the comparison results of different depolymerization reaction temperatures Table 4 shows the comparison results of different dosages of potassium p-sulfobenzoate Table 5 shows the comparison results of different dosages of depolymerized solution Table 6 shows the comparison results of catalyst types Table 7 shows the catalyst types in Examples 31 to 42, and Comparative Examples 15 and 16 Table 8 shows the comparison results of different catalyst combinations Table 9 shows the comparison results of different waste polyester materials Table 10 shows the comparison results of different polyester products The DMT obtained in Example 52 was measured by a third-party agency, and the results are as Figure 2 shown.

[0111] From Figure 2 it can be seen that the DMT obtained in Example 52 was 485 kg (the yield had an error of 4% due to the filtration, washing, and drying processes), and the purity was 99.95%.

[0112] In summary, the method for preparing dimethyl terephthalate from waste polyester by one-step catalysis according to the present invention has the following advantages: 1) A green and efficient catalyst system, abandoning traditional toxic metals or complex organic catalysts, and adopting a composite catalyst system of carbonates, phosphates, acetates, aromatic acids and aromatic acid alkali metal salts. For example, the synergistic effect of potassium carbonate and benzoic acid not only has low cost and environmental friendliness, but also can accurately regulate the reaction path through the acid-base synergistic effect to inhibit the generation of side reactions. Compared with the existing phenolic auxiliaries, this system completely eliminates environmental risks; compared with metal catalysts, product pollution is avoided and the purity is significantly improved. 2) Mild reaction conditions and ultra-short time consumption. The optimized reaction temperature is 120°C to 160°C, and the time is shortened to 1 to 8 hours. Compared with the existing high temperature of 220°C to 300°C and the existing complex pretreatment, this method realizes low-temperature and high-efficiency conversion through the design of catalyst active sites and enhanced mass transfer, reduces energy consumption by more than 40%, significantly weakens the corrosion of equipment, and does not require the intervention of additional solvents. 3) A breakthrough improvement in product purity. Through the regulation of catalyst selectivity and reaction kinetics, the purity of DMT is stably ≥99.9%, far exceeding the existing technology (generally <99%). This technology can directly obtain electronic-grade DMT by inhibiting the residue of oligomers and the generation of by-products, eliminating the high-cost rectification step, and providing high-quality raw materials for downstream high-end polyester synthesis. 4) Process integration and industrialization advantages. Using a one-step continuous reaction device, waste polyester can be directly fed after simple crushing without a multi-step depolymerization-alcoholysis separation process. The catalyst can be recycled more than 5 times. Combined with an online purification module, efficient co-production of DMT and ethylene glycol is achieved. The overall process yield >99%, and the yield is increased by 15% to 20% compared with the traditional method. It has great promotion and application value in the field of waste polyester resource recovery technology.

[0113] The above embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention.

Claims

1. A method for preparing dimethyl terephthalate by catalytically treating waste polyester in one step, characterized in that, It includes the following steps: Mix waste polyester materials, a catalyst, and a depolymerization liquid for depolymerization reaction to obtain dimethyl terephthalate; The catalyst is selected from at least one of aromatic acids, alkali metal salts of aromatic acids, compositions of aromatic acids and carbonates, compositions of aromatic acids and phosphates, compositions of aromatic acids and acetates, compositions of alkali metal salts of aromatic acids and carbonates, compositions of alkali metal salts of aromatic acids and phosphates, and compositions of alkali metal salts of aromatic acids and acetates.

2. The method for preparing dimethyl terephthalate by one-step catalytic conversion of waste polyester according to claim 1, characterized in that, The aromatic acid is selected from at least one of benzoic acid, o-methylbenzoic acid, m-methylbenzoic acid, p-methylbenzoic acid, o-aminobenzoic acid, m-aminobenzoic acid, p-aminobenzoic acid, o-hydroxybenzoic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, o-methoxybenzoic acid, m-methoxybenzoic acid, p-methoxybenzoic acid, ascorbic acid, 2,4-dihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, and 4-hydroxy-3-methoxybenzoic acid. And / or, the alkali metal salt of the aromatic acid is selected from at least one of sodium benzoate, potassium benzoate, sodium o-methylbenzoate, potassium o-methylbenzoate, sodium m-methylbenzoate, potassium m-methylbenzoate, sodium p-methylbenzoate, potassium p-methylbenzoate, sodium o-hydroxybenzoate, potassium o-hydroxybenzoate, sodium m-hydroxybenzoate, potassium m-hydroxybenzoate, sodium p-hydroxybenzoate, potassium p-hydroxybenzoate, sodium o-methoxybenzoate, potassium o-methoxybenzoate, sodium m-methoxybenzoate, potassium m-methoxybenzoate, sodium p-methoxybenzoate, potassium p-methoxybenzoate, sodium 2,4-dihydroxybenzoate, potassium 2,4-dihydroxybenzoate, sodium 3,4,5-trihydroxybenzoate, potassium 3,4,5-trihydroxybenzoate, sodium 4-hydroxy-3-methoxybenzoate, potassium 4-hydroxy-3-methoxybenzoate, and potassium p-sulfobenzoate. And / or, the carbonate is selected from at least one of sodium bicarbonate, potassium bicarbonate, sodium carbonate, and potassium carbonate. And / or, the phosphate is selected from at least one of trisodium phosphate, tripotassium phosphate, and cesium phosphate. And / or, the acetate is selected from at least one of sodium acetate, potassium acetate, calcium acetate, and magnesium acetate.

3. The method for preparing dimethyl terephthalate by one-step catalytic conversion of waste polyester according to claim 1, wherein The depolymerization liquid is selected from a mixture of methanol and ethylene glycol.

4. The method for preparing dimethyl terephthalate by catalytically treating waste polyester in one step according to claim 3, characterized in that, The volume ratio of the methanol to the ethylene glycol is 4:1 to 8:

1.

5. The method for preparing dimethyl terephthalate by one-step catalytic conversion of waste polyester according to claim 1, wherein The waste polyester materials are selected from at least one of waste polyethylene terephthalate (PET), waste polybutylene terephthalate (PBT), waste polytrimethylene terephthalate (PTT), and waste poly(cyclohexylene dimethylene terephthalate) (PCT).

6. The method for preparing dimethyl terephthalate by catalytically treating waste polyester in one step according to claim 1, wherein The temperature of the depolymerization reaction is 120°C to 180°C; And / or, the time of the depolymerization reaction is 1 h to 8 h.

7. The method for preparing dimethyl terephthalate by catalytically treating waste polyester in one step according to claim 1, characterized in that, The dosage of the catalyst is 1 wt% to 20 wt% of the waste polyester materials; And / or, the volume ratio of the depolymerization liquid to the waste polyester materials is 2:1 to 6:1 in mL:g.

8. The method for preparing dimethyl terephthalate by one-step catalytic conversion of waste polyester according to claim 1, wherein After the depolymerization reaction is completed, a mixed solution and a solid are obtained, and the solid is dimethyl terephthalate; Distill the obtained mixed solution, and the distillate is ethylene glycol.

9. The method for preparing dimethyl terephthalate by catalytically treating waste polyester in one step according to claim 8, wherein, The yield of dimethyl terephthalate can reach 99.9%, the purity of dimethyl terephthalate can reach 99.9%, the yield of ethylene glycol can reach 98.9%, and the purity of ethylene glycol can reach 99.3%.

10. Dimethyl terephthalate prepared by the method according to any one of claims 1 to 9.

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