A method for preparing dioctyl terephthalate from polyethylene terephthalate

Abstract

This invention discloses a method for preparing dioctyl terephthalate (DOTP) from polyethylene terephthalate (PET), comprising: crushing, washing, and drying waste PET to obtain PET particles; depolymerizing the obtained PET particles in the presence of ethylene glycol and a composite depolymerization catalyst to obtain a depolymerization product; adding the obtained depolymerization product to octanol and a transesterification catalyst for transesterification reaction; after the reaction is completed, post-treatment yields dioctyl terephthalate; wherein the composite depolymerization catalyst is a mixture of zinc oxide and germanium dioxide; and the transesterification catalyst is a supported solid acid catalyst. This invention features high raw material utilization and good environmental performance, using waste PET as raw material to prepare DOTP via transesterification reaction, thus solving the pollution problem of waste PET; simultaneously, ethylene glycol, octanol, and the catalyst can be recycled during the reaction, reducing raw material consumption and wastewater.

Description

Technical Field

[0001] This invention belongs to the field of plasticizer preparation technology, specifically relating to a method for preparing dioctyl terephthalate from polyethylene terephthalate. Background Technology

[0002] Dioctyl terephthalate (DOTP) is an important general-purpose plasticizer widely used in the processing of polyvinyl chloride (PVC) products. It boasts advantages such as good compatibility, high plasticizing efficiency, and low volatility, resulting in significant demand in the plastics, rubber, and coatings industries. Traditional DOTP preparation methods use terephthalic acid (PTA) or dimethyl terephthalate (DMT) as raw materials, reacting with octanol via esterification or transesterification under a catalyst. However, this process relies on petroleum-based feedstocks, is significantly affected by fluctuations in crude oil prices, and suffers from problems such as long reaction cycles, high energy consumption, and large wastewater discharge.

[0003] Meanwhile, polyethylene terephthalate (PET), as the world's largest-produced polyester material, is widely used in beverage bottles, packaging films, textile fibers, and other fields, resulting in a surge in the amount of waste PET (such as waste beverage bottles and industrial PET waste). Currently, the main recycling methods for waste PET include physical recycling (melting and regranulation) and chemical recycling (depolymerization into monomers for reuse). However, the performance of physically recycled products deteriorates significantly, making them difficult to use in high-value-added fields. Although chemical recycling can achieve monomer recycling, existing depolymerization processes (such as ethylene glycol depolymerization and methanol depolymerization) require high-temperature and high-pressure conditions, resulting in high energy consumption and difficulty in product separation, which limits its industrial application.

[0004] In existing technologies, although some studies have attempted to prepare DOTP by reacting PET depolymerization products with octanol, the following key problems exist: (1) Incomplete PET depolymerization results in residual oligomers, leading to low efficiency in subsequent transesterification reactions and insufficient DOTP purity; (2) Strong acids (such as sulfuric acid) or heavy metal salts (such as tetrabutyl titanate) are required as catalysts. Strong acids are prone to corroding equipment and generating acidic wastewater, while heavy metal catalysts pose a risk of residue and do not meet environmental protection requirements; (3) Multiple separation and purification processes are required during the reaction, making the process complex and production costs high. Therefore, developing an efficient, environmentally friendly, and low-cost method for preparing DOTP from PET is of great significance for achieving high-value recycling of waste PET and green production of DOTP. Summary of the Invention

[0005] The purpose of this invention is to provide a method for efficiently preparing high-purity DOTP from waste PET through a stepwise catalytic reaction.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing dioctyl terephthalate from polyethylene terephthalate includes: crushing, washing, and drying waste PET to obtain PET particles; subjecting the obtained PET particles to a depolymerization reaction in the presence of ethylene glycol and a composite depolymerization catalyst to obtain a depolymerization product; adding the obtained depolymerization product to octanol and a transesterification catalyst to undergo a transesterification reaction; after the reaction is completed, post-treatment yields dioctyl terephthalate; wherein the composite depolymerization catalyst is a mixture of zinc oxide and germanium dioxide; and the transesterification catalyst is a supported solid acid catalyst.

[0008] Preferably, the temperature of the depolymerization reaction is 160-230℃ and the pressure range is 3-10MPa; the temperature of the transesterification reaction is 140-220℃ and the pressure is 50-100Pa.

[0009] Preferably, the post-treatment after the transesterification reaction includes:

[0010] (1) Ethylene glycol is recovered by distillation;

[0011] (2) Cool the remaining mixture to 50-150℃ and filter to separate the catalyst;

[0012] (3) Add 0.5-5% activated clay by mass to the obtained filtrate and stir and adsorb at 80-90℃ for 0.5-2h;

[0013] (4) The liquid phase obtained in step (3) is subjected to vacuum distillation. Unreacted octanol is collected at 100-170℃ and dioctyl terephthalate is collected at 190-260℃ to obtain dioctyl terephthalate.

[0014] Furthermore, the pressure for recovering unreacted octanol is 50-80 Pa; the pressure for distilling dioctyl terephthalate is 20-50 Pa. More specifically, the pressure for recovering unreacted octanol is 55-80 Pa; the pressure for distilling dioctyl terephthalate is 20-45 Pa.

[0015] Furthermore, the waste PET used in this invention is one or more of the following: waste PET bottles, waste PET film waste, waste PET textiles, etc.

[0016] Furthermore, the particle size of the crushed waste PET is 1-10mm.

[0017] More specifically, the present invention provides a method for preparing dioctyl terephthalate from polyethylene terephthalate, comprising the following steps:

[0018] Step 1: After removing impurities from the waste PET, crush it into particles with a diameter of 1-8mm.

[0019] Step 2: Soak the PET particles obtained in Step 1 in a 3-12% (w / w) NaOH solution at 50-95℃ for 1-5 hours; wash with deionized water until neutral. Dry at 80-120℃ for 3-8 hours to obtain PET particles.

[0020] Step 3: Add the PET particles obtained in Step 2, ethylene glycol, and composite depolymerization catalyst to a high-pressure reactor at a certain mass ratio, purge the air in the reactor with nitrogen, raise the temperature to 180-220℃, stir at 300-500 r / min, and pressurize at 3-10 MPa. The depolymerization reaction is carried out for 2-4 hours to obtain the depolymerization product.

[0021] Step 4: Add the depolymerization product obtained in Step 3 to octanol and transesterification catalyst for transesterification reaction. The reaction temperature is 140-220℃, the pressure is 50-100Pa, and the reaction is mechanically stirred for 3-5 hours. At the same time, the ethylene glycol generated in the reaction is separated by distillation column.

[0022] Step 5: Cool the reaction mixture obtained in Step 4 to 80-100℃, filter to separate the catalyst; add 0.5-5% by mass of activated clay to the filtrate, and stir at 80-90℃ for 0.5-2 hours for adsorption.

[0023] Step Six: Perform vacuum distillation on the sample obtained in Step Five. Collect the unreacted octanol at 100-170℃ and collect dioctyl terephthalate at 190-260℃ to obtain the high-purity DOTP product.

[0024] Furthermore, in step one, the particle size of the PET crushed particles is 2-5mm.

[0025] Furthermore, the composite depolymerization catalyst is a mixture of zinc oxide (ZnO) and germanium dioxide (GeO2) in a mass ratio of (2-6):1. ZnO can lower the activation energy of PET ester bond cleavage and promote the initiation of the depolymerization reaction, while GeO2 can inhibit the formation of oligomers during the depolymerization process and increase the content of diethyl terephthalate (BHET) in the depolymerization product.

[0026] Furthermore, the transesterification catalyst is a supported solid acid catalyst;

[0027] Furthermore, the solid acids are zirconium sulfate (Zr(SO4)2), zirconium chloride (ZrCl4), and zirconium nitrate (Zr(NO3)4), and the support is mesoporous silica (SBA-15); the loading is 5-15%. In this technical solution, the high specific surface area of ​​the mesoporous SBA-15 support is utilized to further improve the dispersibility of zirconium sulfate and zirconium chloride, thereby further enhancing the catalytic efficiency.

[0028] Furthermore, in step two, the NaOH solution has a mass fraction of 5-10%, the soaking temperature is 65-85℃, the soaking time is 2-6h, the drying temperature is 90-110℃, and the drying time is 4-6h.

[0029] Furthermore, the mass ratio of PET particles to ethylene glycol and composite depolymerization catalyst is 1:(2-4):(0.02-0.05).

[0030] Furthermore, the depolymerization reaction pressure is 3-10 MPa.

[0031] Furthermore, in step four, the mass ratio of octanol to PET is (3-6):1, and the amount of transesterification catalyst used is 1-5% of the mass of PET.

[0032] Furthermore, the activated clay used in step five has a mass fraction of 1-3%.

[0033] Furthermore, the vacuum pump used in step six is ​​a vacuum oil pump, and the pressure is recorded using a digital vacuum display gauge, with a pressure of 20-50 Pa.

[0034] Compared with the prior art, the present invention has the following innovations and technical advantages:

[0035] (1) The present invention has high raw material utilization rate and good environmental protection. It uses waste PET as raw material to prepare DOTP through transesterification reaction, which solves the pollution problem of waste PET. At the same time, ethylene glycol, octanol and catalyst can be recycled during the reaction process, reducing raw material consumption and wastewater.

[0036] (2) The reaction temperature of this invention is milder than that of the traditional high temperature and high pressure depolymerization process, and the energy consumption is low; and it does not require strong acid or heavy metal catalysts, thus avoiding equipment corrosion and product contamination.

[0037] (3) The product of this invention has high purity and simple process. The PET is completely depolymerized through composite depolymerization catalyst, and the BHET content is more than 95%. The supported solid acid catalyst has high selectivity and the transesterification reaction conversion rate is more than 98%. The final DOTP product has a purity of ≥99%, which meets the industrial grade plasticizer standard. The whole process does not require complicated separation steps, is easy to operate, and is easy to scale up industrially.

[0038] (4) The present invention uses low-cost waste PET, and the recycling of ethylene glycol, octanol and catalyst further reduces production costs. Compared with the traditional PTA method for preparing DOTP, the production cost can be reduced by 15-20%, which has good market competitiveness. Attached Figure Description

[0039] Figure 1 Flowchart for preparing DOTP from waste PET.

[0040] Figure 2 This is the result of DOTP purity (ester content) test. Detailed Implementation

[0041] See Figure 1 The present invention will be further described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0042] Example 1

[0043] A method for preparing dioctyl terephthalate from polyethylene terephthalate includes the following steps:

[0044] (1) PET pretreatment: Take waste PET beverage bottles, remove the labels and caps, crush them to a particle size of 3 mm, soak them in 8% NaOH solution at 70°C for 1.5 h, wash them with deionized water until neutral, and dry them at 90°C for 5 h to obtain pretreated PET particles;

[0045] (2) Catalytic depolymerization of PET: 100g of pretreated PET particles, 300g of ethylene glycol, and 3g of composite depolymerization catalyst (ZnO:GeO2=4:1) were added to a high-pressure reactor, purged with nitrogen 4 times, heated to 200℃, pressure was 5MPa, stirring speed was 400r / min, and reaction was carried out for 3h to obtain the depolymerization product (BHET content 96.2%).

[0046] (3) Transesterification reaction: 400g octanol and 2g supported solid acid catalyst (Zr(SO4)2 / SBA-15, loading 12wt%) were added to the depolymerization product, the temperature was raised to 160℃, the pressure was 70Pa, and the reaction was stirred for 4h. The reactants were collected and recovered by distillation in a distillation column (recovery rate 92%).

[0047] (4) Product separation and purification: Cool to 90℃, filter to recover the catalyst; add 2g of activated clay to the filtrate, adsorb at 85℃ for 0.8h; vacuum distillation: remove and recover excess octanol at 70Pa and 130℃ (recovery rate 88%), then distill at 250℃ and vacuum pressure 40Pa to collect the DOTP fraction, obtaining 190.1g of DOTP product with a purity of 99.41% (see test results). Figure 2 The yield was 97.3%.

[0048] Example 2

[0049] A method for preparing dioctyl terephthalate from polyethylene terephthalate includes the following steps:

[0050] (1) PET pretreatment: Same as in Example 1;

[0051] (2) Catalytic depolymerization of PET: The operation steps are the same as in Example 1, and the depolymerized product has a BHET content of 95.8%;

[0052] (3) Transesterification reaction: Add 400g octanol and 2g supported solid acid catalyst (ZrCl4 / SBA-15, loading 12wt%) to the depolymerization product, heat to 160℃, pressure 70Pa, stir for 4h, and collect ethylene glycol by distillation (recovery rate 93%).

[0053] (4) Product separation and purification: The experimental steps were the same as in Example 1, and 187.8g of DOTP product was obtained with a purity of 99.42% and a yield of 96.5%.

[0054] Example 3

[0055] A method for preparing dioctyl terephthalate from polyethylene terephthalate includes the following steps:

[0056] (1) PET pretreatment: Same as in Example 1;

[0057] (2) Catalytic depolymerization of PET: The operation steps are the same as in Example 1, and the depolymerized product has a BHET content of 96.3%;

[0058] (3) Transesterification reaction: 400g octanol and 2g supported solid acid catalyst (Zr(NO3)4 / SBA-15, loading 12wt%) were added to the depolymerization product, the temperature was raised to 160℃, the pressure was 70Pa, the reaction was stirred for 4h, and the ethylene glycol was collected by distillation (recovery rate 93%).

[0059] (4) Product separation and purification: The experimental steps were the same as in Example 1, and 192.73g of DOTP product was obtained with a purity of 99.7% and a yield of 97.5%.

[0060] Example 4

[0061] A method for preparing dioctyl terephthalate from polyethylene terephthalate includes the following steps:

[0062] (1) PET pretreatment: Take waste PET film, crush it to a particle size of 2 mm, soak it in 5% NaOH solution at 60°C for 2 h, wash it with deionized water until neutral, and dry it at 80°C for 6 h to obtain pretreated PET particles;

[0063] (2) Catalytic depolymerization of PET: 100g of pretreated PET particles, 200g of ethylene glycol, and 2g of composite depolymerization catalyst (ZnO:GeO2=3:1) were added to a high-pressure reactor, purged with nitrogen three times, heated to 180℃, pressure was 5MPa, stirring speed was 300r / min, and reaction was carried out for 4h to obtain the depolymerization product (BHET content 95.1%).

[0064] (3) Transesterification reaction: Add 300g octanol and 1g supported solid acid catalyst (Zr(SO4)2 / SBA-15, loading 10wt%) to the depolymerization product, heat to 150℃, maintain vacuum pressure 80Pa, stir for 5h, and collect ethylene glycol by distillation (recovery rate 90%).

[0065] (4) Product separation and purification: Cool to 80°C, filter to recover the catalyst; add 1g of activated clay to the filtrate and adsorb at 80°C for 1h; vacuum distillation: remove excess octanol at 60Pa and 120°C (recovery rate 85%), then distill at 250°C and 30Pa to collect the DOTP fraction, and obtain 187.1g of DOTP product with a purity of 99.34% and a yield of 95.8%.

[0066] Example 5

[0067] A method for preparing dioctyl terephthalate from polyethylene terephthalate includes the following steps:

[0068] (1) PET pretreatment: Take waste PET textile waste, crush it to a particle size of 5 mm, soak it in 10% NaOH solution at 80℃ for 1 h, wash it with deionized water until neutral, and dry it at 100℃ for 4 h to obtain pretreated PET particles.

[0069] (2) Catalytic depolymerization of PET: 100g of pretreated PET particles, 400g of ethylene glycol, and 5g of composite depolymerization catalyst (ZnO:GeO2=5:1) were added to a high-pressure reactor at a pressure of 5 MPa. The reactor was purged with nitrogen 5 times, heated to 220°C, stirred at 500 r / min, and reacted for 2 h to obtain the depolymerization product (BHET content 97.5%).

[0070] (3) Transesterification reaction: Add 600g octanol and 3g supported solid acid catalyst (Zr(SO4)2 / SBA-15, loading 15wt%) to the depolymerization product, heat to 180℃, maintain vacuum pressure 70Pa, stir for 3h, and collect ethylene glycol by distillation (recovery rate 94%).

[0071] (4) Product separation and purification: Cool to 90℃, filter to recover the catalyst; add 3g of activated clay to the filtrate and adsorb at 90℃ for 0.5h; vacuum distillation: remove excess octanol at 60Pa and 150℃ (recovery rate 90%), then distill at 240℃ and 30Pa to collect the DOTP fraction, and obtain 187.2g of DOTP product with a purity of 99.39% and a yield of 98.1%.

Claims

1. A method for preparing dioctyl terephthalate from polyethylene terephthalate, characterized in that, include: Waste PET is crushed, washed, and dried to obtain PET particles; the obtained PET particles are subjected to a depolymerization reaction in the presence of ethylene glycol and a composite depolymerization catalyst to obtain depolymerization products; the obtained depolymerization products are added to octanol and an ester exchange catalyst to carry out an ester exchange reaction. After the reaction is completed, the product is post-treated to obtain dioctyl terephthalate; the composite depolymerization catalyst is a mixture of zinc oxide and germanium dioxide; the ester exchange catalyst is a supported solid acid catalyst.

2. The method for preparing dioctyl terephthalate from polyethylene terephthalate according to claim 1, characterized in that, In the composite depolymerization catalyst, the mass ratio of zinc oxide to germanium dioxide is (2-6):

1.

3. The method for preparing dioctyl terephthalate from polyethylene terephthalate according to claim 1, characterized in that, The temperature for the depolymerization reaction is 160-230℃, and the pressure is 3-10MPa; the temperature for the transesterification reaction is 140-220℃, and the pressure is 50-100Pa.

4. The method for preparing dioctyl terephthalate from polyethylene terephthalate according to claim 1, characterized in that, In the supported solid acid catalyst, the solid acid is zirconium sulfate, zirconium chloride, or zirconium nitrate, and the support is mesoporous silica; the solid acid loading is 5-15%.

5. The method for preparing dioctyl terephthalate from polyethylene terephthalate according to claim 1, characterized in that, In the depolymerization reaction, the mass ratio of PET particles to ethylene glycol and composite depolymerization catalyst is 1: (2-4): (0.02-0.05); in the transesterification reaction, the mass ratio of octanol to PET particles is (3-6): 1, and the amount of transesterification catalyst is 1-5% of the mass of PET particles.

6. The method for preparing dioctyl terephthalate from polyethylene terephthalate according to claim 1, characterized in that, Post-transfer reaction processing includes: (1) Ethylene glycol is recovered by distillation; (2) Cool the remaining mixture to 50-150℃ and filter to separate the catalyst; (3) Add 0.5-5% activated clay by mass to the obtained filtrate and stir and adsorb at 80-90℃ for 0.5-2h; (4) The liquid phase obtained in step (3) is subjected to vacuum distillation. Unreacted octanol is collected at 100-170℃ and dioctyl terephthalate is collected at 190-260℃ to obtain dioctyl terephthalate.

7. The method for preparing dioctyl terephthalate from polyethylene terephthalate according to claim 6, characterized in that, The pressure for recovering unreacted octanol is 50-80 Pa; the pressure for distilling dioctyl terephthalate is 20-50 Pa.

8. The method for preparing dioctyl terephthalate from polyethylene terephthalate according to claim 7, characterized in that, Waste PET refers to one or more of the following: waste PET bottles, waste PET film waste, and waste PET textile waste; the particle size of waste PET after crushing is 1-10mm.

9. The method for preparing dioctyl terephthalate from polyethylene terephthalate according to any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: After removing impurities from the waste PET, crush it into 1~8mm particles; Step 2: Soak the granules obtained in Step 1 in NaOH aqueous solution at 50-95℃; wash with deionized water; dry; to obtain PET granules; Step 3: Add the PET particles obtained in Step 2, ethylene glycol, and composite depolymerization catalyst into a high-pressure reactor, heat to 180-220℃ in a nitrogen atmosphere, and maintain a pressure of 3-10 MPa until the reaction is complete to obtain the depolymerization product. Step 4: Add octanol and transesterification catalyst to the depolymerization product obtained in Step 3 to carry out transesterification reaction at a temperature of 140-220℃ and a pressure of 50-100Pa. At the same time, separate the ethylene glycol generated in the reaction by distillation column. Step 5: Cool the reaction mixture obtained in Step 4 to 80-100℃, filter to separate the catalyst; add 0.5-5% by mass of activated clay to the filtrate, and stir at 80-90℃ for 0.5-2 hours for adsorption. Step 6: Perform vacuum distillation on the sample obtained in Step 5. Collect the unreacted octanol at a pressure of 50-80 Pa and a temperature of 100-170 °C, and collect dioctyl terephthalate at a pressure of 20-50 Pa and a temperature of 190-260 °C to obtain the dioctyl terephthalate product.

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