Method for preparing DOTP from waste PET
By employing a two-step alcoholysis method involving heating and pressurizing a mixed solvent of butanol and ethylene glycol, followed by ester exchange with isooctanol and solvent separation by distillation, the problems of high temperature, high energy consumption, and low purity in the PET alcoholysis method have been solved, achieving efficient and low-cost preparation of DOTP.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- QINGDAO INST OF BIOENERGY & BIOPROCESS TECH CHINESE ACADEMY OF SCI
- Filing Date
- 2026-01-27
- Publication Date
- 2026-05-12
AI Technical Summary
Existing PET alcoholysis methods suffer from problems such as high reaction temperature, high energy consumption, low product purity, and difficult separation. In particular, the close boiling points of isooctanol and ethylene glycol lead to low separation efficiency, increasing energy consumption and cost.
A two-step alcoholysis method was adopted. First, the reaction was carried out under heat and pressure in a mixed solvent of butanol and ethylene glycol. After post-treatment, DBTP was obtained. Then, it underwent transesterification with isooctanol under negative pressure. Finally, the solvent was separated by distillation to achieve efficient preparation of DOTP.
High yield and high purity of DOTP were achieved under mild reaction conditions, reducing energy consumption and simplifying the solvent separation process. The product purity reached ≥99%, meeting national standards.
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Figure CN122010725A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing DOTP from waste PET, belonging to the field of polyester plastic polymer depolymerization technology. Background Technology
[0002] Polyethylene terephthalate (PET) is a highly crystalline thermoplastic polyester widely used in packaging, textiles, electronics, and the automotive industry due to its excellent mechanical properties, chemical stability, and lightweight nature. Statistics show that global annual PET production exceeds 70 million tons, but the recycling rate is less than 15%. A large amount of waste PET is disposed of through landfills or incineration, leading to serious microplastic pollution and resource waste. Therefore, the efficient recycling and reuse of PET has become an important issue for sustainable development.
[0003] Among chemical recycling methods, alcoholysis has attracted much attention due to its mild reaction conditions and the direct use of the products in the synthesis of recycled polyester. Traditional alcoholysis technology uses ethylene glycol (EG) as a solvent to depolymerize PET into monomers such as diethyl terephthalate (BHET) or dimethyl terephthalate (DMT), but it suffers from problems such as low purity of the depolymerized products and complex process flows. In recent years, isooctyl alcoholysis has become a research hotspot because it can produce high-value-added products such as the plasticizer diisooctyl terephthalate (DOTP). For example, Chinese patent CN118439951A. However, its industrial application faces two major challenges: First, the reaction temperature is too high: traditional isooctyl alcoholysis requires temperatures above 200℃, resulting in high energy consumption and a high risk of side reactions (such as EG oxidation and PET thermal degradation), leading to increased impurities in the product. Second, separation is difficult: EG and isooctyl alcohol have similar boiling points, making distillation separation energy-intensive and inefficient. Furthermore, residual EG affects the purity of DOTP, requiring multi-stage distillation or adsorption treatment, significantly increasing costs. On the other hand, some reports describe the preparation of DOTP using DMT-isooctanol transesterification, such as the transesterification reaction of DMT and isooctanol at 160℃ disclosed in Chinese patent CN119954645A. However, the preparation and purification of the intermediate DMT are complex, and the post-processing of DOTP is cumbersome. Liu Bifang et al. (Hubei Chemical Industry, 1990, 1, 27-29) reported a method for preparing DOTP by transesterification at 140-165℃, but the post-processing involved steam vacuum distillation, which introduced new impurity solvents, and the isooctanol solvent separated after the reaction could not be effectively recovered. Therefore, it is crucial to reduce energy consumption and achieve the preparation of high-purity DOTP under simple process conditions.
[0004] Therefore, it is of great significance to develop a PET alcoholysis method with mild reaction conditions, high yield, high purity, and easy separation of EG and isooctyl alcohol. Summary of the Invention
[0005] In order to solve the above-mentioned problems of existing PET alcoholysis, the present invention provides a method for preparing DOTP from waste PET.
[0006] The technical solution of this invention: One objective of this invention is to provide a method for preparing DOTP from waste PET, the method comprising the following steps: (1) PET waste is dissolved in a mixed reaction solvent of butanol and ethylene glycol, and reacted under heat and pressure in the presence of a catalyst. After post-treatment, the depolymerization product DBTP containing the catalyst is obtained. (2) Add isooctyl alcohol to the depolymerization product DBTP containing the catalyst, carry out transesterification under negative pressure, and simultaneously distill off butanol. After post-treatment, DOTP is obtained.
[0007] Further specifying, the catalyst in (1) is one or more alkaline compounds with zinc, potassium, sodium, titanium, etc. as the metal center.
[0008] Furthermore, the catalyst is one or more of the following: a silicon azide-based metal compound, potassium alkoxide, sodium alkoxide, and organotitanium compound.
[0009] Furthermore, the catalyst is selected from one or more of the following: Zn(HMDS)2, Mg(HMDS)2, potassium methoxide, potassium ethoxide, potassium tert-butoxide, potassium methylsilanolate, potassium trimethylsilanolate, potassium triethylsilanolate, potassium phenyldimethylsilanolate, potassium phthalimide, potassium fluorotitanate, potassium titanium oxalate, sodium methoxide, sodium ethoxide, sodium tert-butoxide, sodium methylsilanolate, sodium trimethylsilanolate, tetrapropyl titanate, tetrabutyl titanate, n-butyl titanate, n-propyl titanate, and isopropyl titanate.
[0010] Further specifying, the mass ratio of catalyst to PET is 1:10000 to 1:20.
[0011] Furthermore, the mass ratio of catalyst to PET is specified as 4:100.
[0012] Further, the reaction temperature in (1) is 50~150℃ and the pressure is 0.1~0.5 MPa.
[0013] Further specifying, (1) the reaction temperature is 50~100℃ and the pressure is 0.1~0.25 MPa.
[0014] Further specifying, (1) the reaction temperature is 100℃ and the pressure is 0.13 MPa.
[0015] Further specifying, in (1), the post-treatment is a two-stage vacuum distillation to remove butanol and ethylene glycol, with the butanol distillation temperature being 20~60℃ and the ethylene glycol distillation temperature being 80~120℃.
[0016] Further specifying, in (1), the post-treatment is a two-stage vacuum distillation to remove butanol and ethylene glycol, with the butanol distillation temperature at 40°C and the ethylene glycol distillation temperature at 100°C.
[0017] Further restrictions are imposed, in (2) the transesterification reaction temperature is 50~150℃ and the pressure is 0.01~0.15 MPa.
[0018] Further specifying, (2) the transesterification reaction temperature is 50~100℃ and the pressure is 0.05~0.1 MPa.
[0019] Further specifying, (2) the transesterification reaction temperature is 90℃ and the pressure is 0.08 MPa.
[0020] Further specifying, in (2), the post-treatment is a two-stage distillation to remove butanol and isooctyl alcohol, with the butanol distillation temperature being 20~60℃ and the isooctyl alcohol distillation temperature being 80~120℃.
[0021] Further specifying, in (2), the post-treatment is a two-stage distillation to remove butanol and isooctyl alcohol, with the butanol distillation temperature at 40°C and the isooctyl alcohol distillation temperature at 80°C.
[0022] Further specifying, PET waste refers to polyester blended clothing.
[0023] The second objective of this invention is to provide a DOTP prepared by the above method with a purity ≥99%, an acid value ≤0.03, and a platinum-cobalt color ≤20, which can be directly used as a plasticizer.
[0024] Furthermore, the prepared DOTP can be used as a plasticizer in the production of polyvinyl chloride (PVC) products, such as cables, shoe soles, and toys; it can also be used in building materials, automotive products, and other fields.
[0025] Beneficial effects: This invention first obtains DBTP intermediate by butanol depolymerization under slightly positive pressure conditions. After centrifugation, filtration, and distillation, DOTP is then prepared by isooctanol transesterification under negative pressure conditions. The entire reaction process is carried out in a relatively mild temperature environment, ultimately achieving the efficient preparation of DOTP and the fine chemical ethylene glycol. Compared with existing technologies, it has at least the following advantages: (1) The two-step alcoholysis method adopted in this invention effectively solves the problem that the traditional one-step method for preparing DOTP from PET alcoholysis often faces the challenges of high reaction temperature and difficulty in completely separating isooctanol and ethylene glycol from the system due to their similar boiling points. In the butanol hydrolysis process, the solvents are butanol and ethylene glycol, and in the isooctanol transesterification process, the solvents are butanol and isooctanol. The boiling point difference between the solvents is large throughout the process, making separation simple and efficient. It can be carried out under relatively mild reaction conditions, resulting in a high reaction yield. The DOTP obtained after distillation and purification has a purity of ≥99%, an acid value of ≤0.03, and a platinum-cobalt color of ≤20, meeting the national standard for superior grade DOTP and effectively reducing energy consumption.
[0026] (2) The two-step alcoholysis method used in this invention solves the problems of existing DMT transesterification for DOTP preparation, which involves harsh preparation conditions for intermediate DMT, uncontrollable byproducts, complex purification, and poor connection between the two steps, thus affecting the transesterification activity and DOTP purity (<99%). This invention starts from waste PET, first performing butanol hydrolysis, which is milder and safer than methanol hydrolysis. Moreover, the obtained product does not need to be sublimated / distilled, but is directly connected to the subsequent transesterification after solvent removal. The process is simple and highly applicable. Attached Figure Description
[0027] Figure 1 Here is a photograph of the DOTP prepared in Example 1; Figure 2 The DOTP prepared in Example 1 1 1H NMR (CDCl3, 273 K, 400 MHz) spectrum; Figure 3 The butanol recovered in Example 1 1 1H NMR (CDCl3, 273 K, 400 MHz) spectrum; Figure 4 The isooctyl alcohol recovered in Example 1 1 1H NMR (CDCl3, 273 K, 400 MHz) spectrum; Figure 5 The ethylene glycol recovered in Example 1 1 1H NMR (CDCl3, 273 K, 400 MHz) spectrum. Detailed Implementation
[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.
[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art may make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0030] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.
[0031] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.
[0032] Example 1: A method and purification process for the efficient preparation of DOTP from polyester blended clothing is described below:
[0033] Includes the following steps: (1) Butanol hydrolysis: 1 kg of PET polyester clothing was weighed into a reactor, then n-butanol solvent and potassium tert-butoxide catalyst were added. The reaction was carried out at 100℃ under slight positive pressure for 4 h. The amount of catalyst added was 4 wt% of PET, the mass ratio of n-butanol solvent to PET was 1 / 5, and the pressure was 0.13 MPa. After the reaction was completed, a milky white depolymerization solution was obtained.
[0034] (2) Separation: The depolymerized emulsion was subjected to two-stage vacuum distillation to separate butanol and ethylene glycol, which were collected in a collection vessel at vacuum temperatures of 40°C and 100°C, respectively; DBTP was finally obtained from the reaction vessel.
[0035] (3) Isooctyl alcohol transesterification: Isooctyl alcohol solvent was added to the above-treated product DBTP, and the reaction was carried out at 90℃ under slight negative pressure for 8 h. Butanol was continuously distilled off during the reaction. The mass ratio of DBTP to isooctyl alcohol solvent was 1 / 9, and the pressure was 0.08 MPa. After the reaction was completed, a white homogeneous solution was obtained.
[0036] (4) Secondary distillation: The above reaction solution is first distilled at 40°C to separate n-butanol, and then distilled a second time at 80°C to separate isooctanol, to obtain the final DOTP product, such as... Figure 1 As shown.
[0037] Characterization showed that the yield of DBTP was 96% and the yield of DOTP was 98%. The purity of DOTP was characterized as 99.8%, acid value 0.03%, and color 18. The recovery yield of butanol was 98.6% with a purity >99%, isooctanol was 97.1% with a purity of 99.1%, and ethylene glycol was 96.4% with a purity of 98.2%.
[0038] The DOTP, butanol, isooctyl alcohol, and ethylene glycol prepared in this embodiment 1 1H NMR (CDCl3, 273 K, 400 MHz) spectrum, as shown Figures 2-5 As shown.
[0039] Example 2: The difference between this embodiment and Example 1 is that the catalyst is tetrabutyl titanate, while the remaining process steps and parameter settings are the same as in Example 1. Specifically, the steps include: (1) Butanol hydrolysis: 1 kg of polyester clothing was weighed into a reaction vessel, n-butanol solvent was added, and then tetrabutyl titanate catalyst was added. The reaction was carried out at 100℃ under slight positive pressure for 4 h. The amount of catalyst added was 4 wt% of PET, the mass ratio of n-butanol solvent to PET was 1 / 5, and the pressure was 0.13 MPa. After the reaction was completed, a milky white depolymerization solution was obtained.
[0040] (2) Separation: The depolymerized emulsion was subjected to two-stage vacuum distillation to separate butanol and ethylene glycol, which were collected in a collection vessel at vacuum temperatures of 40°C and 100°C, respectively; DBTP was finally obtained from the reaction vessel.
[0041] (3) Isooctyl alcohol transesterification: Isooctyl alcohol solvent was added to the above-treated product DBTP, and the reaction was carried out at 90℃ under slight negative pressure for 8 h. Butanol was continuously distilled off during the reaction. The mass ratio of DBTP to isooctyl alcohol solvent was 1 / 9, and the pressure was 0.08 MPa. After the reaction was completed, a white homogeneous solution was obtained.
[0042] (4) Secondary distillation: The above reaction solution is first distilled at 40°C to separate n-butanol, and then distilled at 80°C to separate isooctyl alcohol to obtain the final DOTP product.
[0043] Characterization showed that the yield of DBTP was 93% and the yield of DOTP was 95%. The purity of DOTP was characterized as 99.5%, acid value 0.02, and color 12. The recovery yield of butanol was 98.3% with a purity of 98%, the recovery yield of isooctanol was 96.8% with a purity of 98.8%, and the recovery yield of ethylene glycol solvent was 99.4% with a purity of 97.2%.
[0044] Example 3: The difference between this embodiment and Embodiment 1 is that: (1) the reaction temperature is 80℃, while the remaining process steps and parameter settings are the same as in Embodiment 1. Specifically, it includes the following steps: (1) Butanol hydrolysis: 1 kg of polyester clothing was weighed into a reaction vessel, n-butanol solvent was added, followed by potassium tert-butoxide catalyst, and the reaction was carried out at 80℃ under slight positive pressure for 4 h. The amount of catalyst added was 4 wt% of PET, the mass ratio of n-butanol solvent to PET was 1 / 5, and the pressure was 0.13 MPa. After the reaction was completed, a milky white depolymerization solution was obtained.
[0045] (2) Separation: The depolymerized emulsion was subjected to two-stage vacuum distillation to separate butanol and ethylene glycol, which were collected in a collection vessel at vacuum temperatures of 40°C and 100°C, respectively; DBTP was finally obtained from the reaction vessel.
[0046] (3) Isooctyl alcohol transesterification: Isooctyl alcohol solvent was added to the above-treated product DBTP, and the reaction was carried out at 90℃ under slight negative pressure for 8 h. Butanol was continuously distilled off during the reaction. The mass ratio of DBTP to isooctyl alcohol solvent was 1 / 9, and the pressure was 0.08 MPa. After the reaction was completed, a white homogeneous solution was obtained.
[0047] (4) Secondary distillation: The above reaction solution is first distilled at 40°C to separate n-butanol, and then distilled at 80°C to separate isooctyl alcohol to obtain the final DOTP product.
[0048] Characterization showed that the yield of DBTP was 90% and the yield of DOTP was 91%. The purity of DOTP was characterized as 99.2%, acid value 0.03, and color 19. The recovery yield of butanol was 97.3% with a purity of 99.2%, the recovery yield of isooctanol was 98.8% with a purity of 99.8%, and the recovery yield of ethylene glycol solvent was 98.4% with a purity of 99.2%.
[0049] Example 4: The difference between this embodiment and Embodiment 1 is that: (1) the reaction temperature is 120℃, while the remaining process steps and parameter settings are the same as in Embodiment 1. Specifically, the steps are as follows: (1) Butanol hydrolysis: 1 kg of polyester clothing was weighed into a reaction vessel, n-butanol solvent was added, and then potassium tert-butoxide catalyst was added. The reaction was carried out at 120℃ under slight positive pressure for 4 h. The amount of catalyst added was 4 wt% of PET, the mass ratio of n-butanol solvent to PET was 1 / 5, and the pressure was 0.13 MPa. After the reaction was completed, a milky white depolymerization solution was obtained.
[0050] (2) Separation: The depolymerized emulsion was subjected to two-stage vacuum distillation to separate butanol and ethylene glycol, which were collected in a collection vessel at vacuum temperatures of 40°C and 100°C, respectively; DBTP was finally obtained from the reaction vessel.
[0051] (3) Isooctyl alcohol transesterification: Isooctyl alcohol solvent was added to the above-treated product DBTP, and the reaction was carried out at 90℃ under slight negative pressure for 8 h. Butanol was continuously distilled off during the reaction. The mass ratio of DBTP to isooctyl alcohol solvent was 1 / 9, and the pressure was 0.08 MPa. After the reaction was completed, a white homogeneous solution was obtained.
[0052] (4) Secondary distillation: The above reaction solution is first distilled at 40°C to separate n-butanol, and then distilled at 80°C to separate isooctyl alcohol to obtain the final DOTP product.
[0053] Characterization showed that the yield of DBTP was 99% and the yield of DOTP was 97%. The purity of DOTP was characterized as 99.4%, acid value 0.03, and color 15. The recovery yield of butanol was 98.4% with a purity of 98.2%, the recovery yield of isooctanol was 97.8% with a purity of 99.2%, and the recovery yield of ethylene glycol solvent was 99.4% with a purity of 98.2%.
[0054] Example 5: The difference between this embodiment and Example 1 is that the catalyst dosage is 2 wt% of PET, while the remaining process steps and parameter settings are the same as in Example 1. Specifically, the steps include the following: (1) Butanol hydrolysis: 1 kg of polyester clothing was weighed into a reaction vessel, n-butanol solvent was added, and then potassium tert-butoxide catalyst was added. The reaction was carried out at 100℃ under slight positive pressure for 4 h. The amount of catalyst added was 2 wt% of PET, the mass ratio of n-butanol solvent to PET was 1 / 5, and the pressure was 0.13 MPa. After the reaction was completed, a milky white depolymerization solution was obtained.
[0055] (2) Separation: The depolymerized emulsion was subjected to two-stage vacuum distillation to separate butanol and ethylene glycol, which were collected in a collection vessel at vacuum temperatures of 40°C and 100°C, respectively; DBTP was finally obtained from the reaction vessel.
[0056] (3) Isooctyl alcohol transesterification: Isooctyl alcohol solvent was added to the above-treated product DBTP, and the reaction was carried out at 90℃ under slight negative pressure for 8 h. Butanol was continuously distilled off during the reaction. The mass ratio of DBTP to isooctyl alcohol solvent was 1 / 9, and the pressure was 0.08 MPa. After the reaction was completed, a white homogeneous solution was obtained.
[0057] (4) Secondary distillation: The above reaction solution is first distilled at 40°C to separate n-butanol, and then distilled at 80°C to separate isooctyl alcohol to obtain the final DOTP product.
[0058] Characterization showed that the yield of DBTP was 93% and the yield of DOTP was 95%. The purity of DOTP was characterized as 99.5%, acid value 0.02, and color 14. The recovery yield of butanol was 99.4% with a purity of 97.2%, the recovery yield of isooctanol was 97.6% with a purity of 97.2%, and the recovery yield of ethylene glycol solvent was 98.4% with a purity of 99.2%.
[0059] Example 6: The difference between this embodiment and Example 1 is that the catalyst dosage is 1 wt% of PET, while the remaining process steps and parameter settings are the same as in Example 1. Specifically, the steps include the following: (1) Butanol hydrolysis: 1 kg of polyester clothing was weighed into a reaction vessel, then n-butanol solvent was added, followed by potassium tert-butoxide catalyst. The reaction was carried out at 100℃ under slight positive pressure for 4 h. The catalyst was added at 1 wt% of PET, the mass ratio of n-butanol solvent to PET was 1 / 5, and the pressure was 0.13 MPa. After the reaction was completed, a milky white depolymerization solution was obtained.
[0060] (2) Separation: The depolymerized emulsion was subjected to two-stage vacuum distillation to separate butanol and ethylene glycol, which were collected in a collection vessel at vacuum temperatures of 40°C and 100°C, respectively; DBTP was finally obtained from the reaction vessel.
[0061] (3) Isooctyl alcohol transesterification: Isooctyl alcohol solvent was added to the above-treated product DBTP, and the reaction was carried out at 90℃ under slight negative pressure for 8 h. Butanol was continuously distilled off during the reaction. The mass ratio of DBTP to isooctyl alcohol solvent was 1 / 9, and the pressure was 0.08 MPa. After the reaction was completed, a white homogeneous solution was obtained.
[0062] (4) Secondary distillation: The above reaction solution is first distilled at 40°C to separate n-butanol, and then distilled at 80°C to separate isooctyl alcohol to obtain the final DOTP product.
[0063] Characterization showed that the yield of DBTP was 93% and the yield of DOTP was 91%. The purity of DOTP was characterized as 99.7%, acid value 0.01, and color 18. The recovery yield of butanol was 98.4% with a purity of 98.5%, the recovery yield of isooctanol was 97.8% with a purity of 99.7%, and the recovery yield of ethylene glycol solvent was 99.4% with a purity of 98.3%.
[0064] Example 7: The difference between this embodiment and Embodiment 1 is that the reaction temperature in (3) is 70°C, while the remaining process steps and parameter settings are the same as in Embodiment 1. Specifically, the steps are as follows: (1) Butanol hydrolysis: 1 kg of polyester clothing was weighed into a reaction vessel, n-butanol solvent was added, and then potassium tert-butoxide catalyst was added. The reaction was carried out at 100℃ under slight positive pressure for 4 h. The amount of catalyst added was 4 wt% of PET, the mass ratio of n-butanol solvent to PET was 1 / 5, and the pressure was 0.13 MPa. After the reaction was completed, a milky white depolymerization solution was obtained.
[0065] (2) Separation: The depolymerized emulsion was subjected to two-stage vacuum distillation to separate butanol and ethylene glycol, which were collected in a collection vessel at vacuum temperatures of 40°C and 100°C, respectively; DBTP was finally obtained from the reaction vessel.
[0066] (3) Isooctyl alcohol transesterification: Isooctyl alcohol solvent was added to the above-treated product DBTP, and the reaction was carried out at 70℃ under slight negative pressure for 8 h. Butanol was continuously distilled off during the reaction. The mass ratio of DBTP to isooctyl alcohol solvent was 1 / 9, and the pressure was 0.08 MPa. After the reaction was completed, a white homogeneous solution was obtained.
[0067] (4) Secondary distillation: The above reaction solution is first distilled at 40°C to separate n-butanol, and then distilled at 80°C to separate isooctyl alcohol to obtain the final DOTP product.
[0068] Characterization showed that the yield of DBTP was 97% and the yield of DOTP was 91%. The purity of DOTP was characterized as 99.2%, acid value 0.03, and color 15. The recovery yield of butanol was 98.4% and the purity was 98.2%, the recovery yield of isooctanol was 97.8% and the purity was 99.2%, and the recovery yield of ethylene glycol solvent was 99.4% and the purity was 98.2%.
[0069] Example 8: The difference between this embodiment and Embodiment 1 is that the reaction temperature in (3) is 120°C, while the remaining process steps and parameter settings are the same as in Embodiment 1. Specifically, the steps are as follows: (1) Butanol hydrolysis: 1 kg of polyester clothing was weighed into a reaction vessel, n-butanol solvent was added, and then potassium tert-butoxide catalyst was added. The reaction was carried out at 100℃ under slight positive pressure for 4 h. The amount of catalyst added was 4 wt% of PET, the mass ratio of n-butanol solvent to PET was 1 / 5, and the pressure was 0.13 MPa. After the reaction was completed, a milky white depolymerization solution was obtained.
[0070] (2) Separation: The depolymerized emulsion was subjected to two-stage vacuum distillation to separate butanol and ethylene glycol, which were collected in a collection vessel at vacuum temperatures of 40°C and 100°C, respectively; DBTP was finally obtained from the reaction vessel.
[0071] (3) Isooctyl alcohol transesterification: Isooctyl alcohol solvent was added to the above-treated product DBTP, and the reaction was carried out at 120℃ under slight negative pressure for 8 h. Butanol was continuously distilled off during the reaction. The mass ratio of DBTP to isooctyl alcohol solvent was 1 / 9, and the pressure was 0.08 MPa. After the reaction was completed, a white homogeneous solution was obtained.
[0072] (4) Secondary distillation: The above reaction solution is first distilled at 40°C to separate n-butanol, and then distilled at 80°C to separate isooctyl alcohol to obtain the final DOTP product.
[0073] Characterization showed that the yield of DBTP was 97% and the yield of DOTP was 98%. The purity of DOTP was characterized as 99.5%, acid value 0.02, and color 15. The recovery yield of butanol was 98.4% with a purity of 98.2%, the recovery yield of isooctanol was 97.8% with a purity of 99.2%, and the recovery yield of ethylene glycol solvent was 99.4% with a purity of 98.2%.
[0074] Comparative Example 1: This comparative example uses a one-step method to synthesize DOTP, which specifically includes the following steps: 1 kg of polyester clothing was weighed into a reaction vessel, and then isooctanol solvent and potassium tert-butoxide were added. The reaction was carried out at 150 °C under positive pressure for 4 h. The catalyst added was 4 wt% of PET, the isooctanol solvent to PET mass ratio was 1 / 5, and the pressure was 0.3 MPa. After the reaction was completed, a red depolymerization solution was obtained.
[0075] Characterization showed that the DOTP conversion rate was 65%, the yield was 40%, and the purity of DOTP was 80%; the purity of the isooctanol recovered solvent was 85%, and the purity of the ethylene glycol recovered solvent was 83%.
[0076] The above description is only a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.
Claims
1. A method for preparing DOTP from waste PET, characterized in that, include: (1) Dissolve PET waste in a mixed reaction solvent of butanol and ethylene glycol, and react under heat and pressure in the presence of a catalyst. After post-treatment, the depolymerization product DBTP containing the catalyst is obtained. (2) Add isooctyl alcohol to the depolymerization product DBTP containing the catalyst, carry out transesterification under negative pressure, and simultaneously distill off butanol. After post-treatment, DOTP is obtained.
2. The method according to claim 1, characterized in that, (1) The catalyst is one or more alkaline compounds with zinc, potassium, sodium, titanium, etc. as the metal center, and the mass ratio of the catalyst to PET is 1:10000~1:
20.
3. The method according to claim 2, characterized in that, The catalyst is one or more of the following: a silicon azide-based metal compound, potassium alkoxide, sodium alkoxide, and organotitanium compound.
4. The method according to claim 3, characterized in that, The catalyst is one or more of the following: Zn(HMDS)2, Mg(HMDS)2, potassium methoxide, potassium ethoxide, potassium tert-butoxide, potassium methylsilanolate, potassium trimethylsilanolate, potassium triethylsilanolate, potassium phenyldimethylsilanolate, potassium phthalimide, potassium fluorotitanate, potassium titanium oxalate, sodium methoxide, sodium ethoxide, sodium tert-butoxide, sodium methylsilanolate, sodium trimethylsilanolate, tetrapropyl titanate, tetrabutyl titanate, n-butyl titanate, n-propyl titanate, and isopropyl titanate.
5. The method according to claim 1, characterized in that, (1) The reaction temperature is 50~150℃ and the pressure is 0.1~0.5 MPa.
6. The method according to claim 1, characterized in that, (1) The post-treatment is a two-stage vacuum distillation to remove butanol and ethylene glycol. The distillation temperature of butanol is 20~60℃ and the distillation temperature of ethylene glycol is 80~120℃.
7. The method according to claim 1, characterized in that, (2) The transesterification reaction temperature is 50~150℃ and the pressure is 0.01~0.15 MPa.
8. The method according to claim 1, characterized in that, (2) The post-treatment is a two-stage distillation to remove butanol and isooctyl alcohol. The distillation temperature of butanol is 20~60℃ and the distillation temperature of isooctyl alcohol is 80~120℃.
9. The method according to claim 1, characterized in that, PET waste consists of polyester blended clothing.
10. A DOTP prepared by the method according to any one of claims 1 to 9, characterized in that, With a purity of ≥99%, acid value ≤0.03, and platinum-cobalt color ≤20, it can be used directly as a plasticizer.