Device and method for preparing PBT (polybutylene terephthalate) or elastomer thereof by utilizing regenerated DMT (dimethyl terephthalate)

Abstract

The invention discloses a device and a method for preparing PBT (polybutylene terephthalate) or an elastomer thereof by utilizing regenerated DMT (dimethyl terephthalate), a four-kettle type polymerization device is composed of a pretreatment part, an ester exchange part and a polycondensation part which are arranged in a communicated manner, a continuous polymerization production method is combined, DMT, BDO (butanediol) and an ester exchange catalyst are mixed and pulped, an ester exchange product with high diester content is obtained through two times of ester exchange, and then the PBT or the elastomer thereof is prepared. Carrying out pre-polycondensation and final polycondensation reaction to prepare rPBT; wherein after a transesterification product is obtained, PTMEG is mixed for pre-polycondensation, and then final polycondensation is performed to prepare rTPEE. According to the scheme, continuous polymerization of two products can be realized on the same device, the energy consumption of reaction temperature control can be reduced, the effects of energy consumption saving, quality control and cost reduction are achieved, the production efficiency is improved while the stable product quality is ensured, and high-value reutilization of recycled polyester is realized.

Description

Technical Field

[0001] The invention relates to a device and a method for preparing rPBT or rTPEE by utilizing recycled polyester regenerated DMT, belonging to the technical field of waste polyester recycling. Background Art

[0002] In the fiber market, compared to PET fiber, also a thermoplastic polyester, PBT fiber boasts a high degree of commercialization and lower costs. Its comprehensive processability and heat resistance give it an advantage in the engineering plastics sector. On the one hand, PBT fiber possesses excellent strength and toughness, capable of withstanding significant bending forces. Its tensile and compressive properties are also excellent, and its wrinkle resistance is outstanding. This gives fabrics made from PBT fiber excellent resilience and wrinkle resistance (for example, in the production of undergarments, such fabrics are not only comfortable to wear and wrinkle-resistant, but also have a soft feel). The apparel value of PBT fiber is continuously increasing. On the other hand, TPEE, a polyester elastomer derived from PBT, is widely used due to its unique properties (for example, TPEE elastomers are used in automotive parts and shoe applications involving midsoles and their supporting components, shoelaces, tongues, artificial leather, yarn, and other shoe components, with the potential for creating 100% TPEE sports shoes. Its controllable strength and flexibility also have potential application value in medical devices and instruments). The demand and market value of TPEE are also rising.

[0003] However, the current production capacity for synthesizing PBT from recycled DMT is relatively limited, and the batch polymerization method has significant disadvantages, including low product quality stability, large indicator variations due to process fluctuations, and high costs. Therefore, it is necessary to develop a continuous polymerization method for preparing rPBT and rTPEE from recycled DMT. This would not only expand the high-value utilization of waste polyester but also enable the continuous production of both products on the same unit. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems and provide a device and method for preparing PBT or its elastomer using recycled DMT, thereby improving production flexibility and enabling factories to quickly switch to producing different products according to market orders and demand changes, thereby further enhancing the company's market adaptability and competitiveness.

[0005] The technical solution of the present invention is: a device for preparing PBT or its elastomer using recycled DMT, which is characterized by: comprising a pretreatment part, an ester exchange part and a condensation part which are connected to each other, the pretreatment part comprising a pulping kettle and a melting kettle; the ester exchange part comprising a first ester exchange kettle and a second ester exchange kettle; the condensation part comprising a pre-condensation kettle and a final condensation kettle, the discharge end of the pulping kettle is connected to the feed end of the first ester exchange kettle through a first pipe, the discharge end of the first ester exchange kettle is connected to the feed end of the second ester exchange kettle through a second pipe, a first melt pump is provided on the second pipe, a third pipe is provided between the second ester exchange kettle and the pre-condensation kettle, a second melt pump is provided on the third pipe, the first end of the third pipe is connected to the discharge end of the second ester exchange kettle, the second end of the third pipe is connected to the feed end of the pre-condensation kettle, the third end of the third pipe is connected to the melting kettle through a fourth pipe, and a fifth pipe is provided between the pre-condensation kettle and the final condensation kettle.

[0006] The above-mentioned device for preparing PBT or its elastomer using regenerated DMT, wherein: the fourth pipeline is also provided with a syringe for online quantitative addition of slurry.

[0007] The present invention also provides a method for preparing PBT or an elastomer thereof using recycled DMT, comprising the following steps:

[0008] Step S1——

[0009] The regenerated DMT, BDO and transesterification catalyst are added to a beating kettle and stirred evenly, and then the mixed slurry enters the first transesterification kettle for transesterification reaction at a temperature between 170 and 200°C, and the transesterification rate is controlled to be 80-90%. The mixed slurry then enters the second transesterification kettle for transesterification reaction at a temperature between 200 and 220°C, and the transesterification rate is controlled to be 95-99%, thereby obtaining a mixed melt of DBT and its oligomers.

[0010] Preferably, the regenerated DMT is purified from recycled polyester, with a purity of ≥98%. After recycling the polyester, the waste PBT is crushed and cleaned to remove impurities such as fillers and flame retardants. After drying and dehydration (moisture content <0.01%), the PBT undergoes an ester exchange reaction with methanol using an environmentally friendly tetrabutyl titanate catalyst (which is heavy metal-free, can be recovered through acid precipitation (e.g., with dilute sulfuric acid), and can be recycled for at least five times). This depolymerization reaction produces DMT and BDO at a temperature of 200-220°C and a pressure of 2-3 MPa. The mass ratio of methanol to PBT is 4:1.

[0011] More preferably, after the reaction solution is cooled, DMT crystallizes and precipitates (its solubility decreases significantly with decreasing temperature), and crude DMT is obtained by filtration. The regenerated DMT can completely replace the original product, achieving closed-loop recovery of PBT. The BDO-methanol mixture is recovered by distillation to meet the boiling point of BDO of 230°C and the boiling point of methanol of 65°C, thereby obtaining BDO.

[0012] More preferably, crude DMT can be dissolved in an organic solvent and stirred uniformly at 60°C. The resulting 5-10% w / v solution is then sprayed through a 50-100 μm diameter capillary nozzle into an autoclave filled with scCO₂ at a pressure of 10-15 MPa and a temperature of 35-40°C. Nanosized DMT particles precipitate in the scCO₂ and are collected through a filter at the bottom of the autoclave. The resulting nanosized regenerated DMT has a significantly increased specific surface area and a higher transesterification reaction rate, making it suitable for efficient catalytic polymerization.

[0013] More preferably, a third monomer (such as dimethyl isophthalate (DMI), dimethyl adipate (DMA), or dimethyl 2,6-naphthalenedicarboxylate (NDC)) is introduced into the crude DMT to improve the flexibility, low-temperature resistance, or rigidity of the recycled polyester. The crude DMT and the third monomer are dissolved in methanol at a ratio of 5-20 mol%. Under the catalysis of tetrabutyl titanate, an ester exchange reaction is carried out at a controlled temperature of 180-210°C for 2-3 hours. The temperature is then raised to 250-270°C under vacuum conditions for polycondensation to produce the corresponding modified recycled DMT. The resulting modified recycled DMT can be functionalized and applied to various product applications, such as automotive interior materials and flexible packaging films.

[0014] Furthermore, in step S1: the molar ratio of the regenerated DMT to the BDO is 1:1.5-3.0.

[0015] Furthermore, in step S1: the ester exchange catalyst is one or more of acetic acid compounds such as manganese acetate and zinc acetate or titanate compounds, the structural formula of titanate is preferably Ti(OR)4, the R is preferably a C1~10 alkyl group, the titanate compound is more preferably tetrabutyl titanate, and the mass ratio of the metal element content in the ester exchange catalyst to the theoretical synthesis amount is 0.003%~0.013%:1.

[0016] Step S2——

[0017] PTMEG is added to a melting kettle for melting at a temperature of 40 to 80° C., and then an antioxidant is added to obtain a mixed slurry. The mixed slurry is added online through a quantitative syringe to a third pipe set between the second transesterification kettle and the pre-condensation kettle to obtain a reaction melt.

[0018] Furthermore, in step S2: the molecular weight of the PTMEG is 800 to 3000, and the amount added is 3 to 65% of the polymer. The molecular weight and amount of the PTMEG can be controlled according to the required strength of the final product.

[0019] Furthermore, in step S2: the antioxidant includes but is not limited to one or more of antioxidant 1010, antioxidant 168 or antioxidant BHT, and the added amount is 0.01% to 0.5%:1 by mass ratio to the theoretical polyester yield.

[0020] More preferably, the antioxidant is a compound of antioxidant 1010 and antioxidant 168, preferably in a mass ratio of 3:1.

[0021] Step S3——

[0022] The reaction melt is transported to a pre-polycondensation kettle through a melting kettle, and a polycondensation catalyst and a side reaction suppression aid are directly added to the pre-polycondensation kettle, or the polycondensation catalyst and the side reaction suppression aid are added to a third pipeline provided between the second transesterification kettle and the pre-polycondensation kettle to carry out a pre-polycondensation reaction, wherein the reaction pressure is 1000-3000 Pa, the reaction temperature is 220-250° C., and the reaction time is 50-90 min to obtain a pre-polycondensation product with a high degree of polymerization.

[0023] Furthermore, in step S3: the polycondensation catalyst is one or more of a titanate compound or a hydroxycarboxylic acid-titanate chelate, the hydroxycarboxylic acid in the hydroxycarboxylic acid-titanate chelate is preferably an organic acid containing one or more hydroxyl groups, and the hydroxycarboxylic acid-titanate chelate is more preferably a citric acid-tetrabutyl titanate chelate, and the mass ratio of the metal element content in the polycondensation catalyst to the theoretical synthesis amount is 0.003% to 0.013%:1.

[0024] Furthermore, in step S3, the side reaction suppression agent is one or more of trimethyl phosphite, triphenyl phosphate, trimethyl phosphate, triethyl phosphite, triethyl phosphate, and tributyl phosphate, and the mass ratio of the side reaction suppression agent added to the theoretical synthesis amount is 0.0002% to 0.0012%:1. The side reaction suppression agent forms a stable complex with the titanate compound, protecting the titanium compound catalyst, ensuring its catalytic effect and reducing the catalytic effect on side reactions.

[0025] Step S4——

[0026] The pre-polycondensation product is conveyed to a final polycondensation kettle through a filter and a delivery pump for a final polycondensation reaction, wherein the reaction pressure is 10-200 Pa, the reaction temperature is 235-260° C., and the reaction time is 0.5-1.5 h, to obtain rPBT with a viscosity of 0.90-1.20 dL / g and a melting point of 215-225° C., or rTPEE with a viscosity of 0.8-1.5 dL / g and a melting point of 205-220° C. The rPBT or rTPEE can be pelletized to obtain slices of a certain shape and size.

[0027] The preparation process of rPBT using the technical solution of the present invention is as follows: DMT, BDO, and an ester exchange catalyst are mixed and slurried, and the slurry is sequentially fed into the first and second ester exchange kettles for continuous ester exchange to obtain an ester exchange product with a high diester content. The ester exchange product is then fed into a prepolymerization kettle via a melt pump, where a polycondensation catalyst combination is simultaneously added. The prepolymer passes through a coarse filter and enters the final polycondensation kettle for the final polycondensation reaction to synthesize rPBT. The preparation process of rTPEE is as follows: After the ester exchange product is obtained in the rPBT synthesis process, PTMEG is treated in a melt kettle and then injected into the pipe melt between the second ester exchange kettle and the precondensation kettle, or directly injected into the prepolymerization kettle melt, for polycondensation to produce rTPEE.

[0028] The present invention utilizes recycled DMT to prepare rPBT or rTPEE. Compared with the existing DMT method or PTA method, the preparation method requires a lower reaction temperature and reduces degradation, thereby achieving energy conservation, consumption reduction, and cost reduction. Moreover, the present invention achieves continuous polymerization production of two products in the same device, further improving production efficiency while ensuring stable product quality, facilitating the high-value reuse of recovered polyester, and effectively realizing a closed-loop polyester circular economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the device flow of the present invention.

[0030] The meanings of the reference numerals in the figure are: 1-pulping kettle, 2-first transesterification kettle, 3-second transesterification kettle, 4-melting kettle, 5-injector, 6-pre-polycondensation kettle, 7-final polycondensation kettle, 8-first pipeline, 9-second pipeline, 10-third pipeline, 11-fourth pipeline, 12-fifth pipeline, 13-first melt pump, 14-second melt pump. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below with reference to the accompanying drawings to make it easier to understand and grasp. The components involved, such as the pipes and melt pumps, are commonly used by those skilled in the art and are not specifically required in this application.

[0032] like Figure 1As shown, the present invention provides an apparatus for preparing PBT or its elastomer using recycled DMT, comprising a pretreatment section, an ester exchange section and a polycondensation section which are connected to each other, wherein the pretreatment section comprises a pulping kettle 1 and a melting kettle 4; the ester exchange section comprises a first ester exchange kettle 2 and a second ester exchange kettle 3; and the polycondensation section comprises a pre-polycondensation kettle 6 and a final polycondensation kettle 7.

[0033] According to the technical solution of the present invention, the discharge end of the beating kettle 1 is connected to the feed end of the first ester exchange kettle 2 through a first pipe 8, the discharge end of the first ester exchange kettle 2 is connected to the feed end of the second ester exchange kettle 3 through a second pipe 9, a first melt pump 13 is provided on the second pipe 9, a third pipe 10 is provided between the second ester exchange kettle 3 and the pre-condensation kettle 6, a second melt pump 14 is provided on the third pipe 10, a first end of the third pipe 10 is connected to the discharge end of the second ester exchange kettle 3, a second end of the third pipe 10 is connected to the feed end of the pre-condensation kettle 6, a third end of the third pipe 10 is connected to the melting kettle 4 through a fourth pipe 11, and a fifth pipe 12 is provided between the pre-condensation kettle 6 and the final condensation kettle 7.

[0034] Specifically, in the structure of the above-mentioned device for recovering polyester regenerated DMT to prepare rPBT and rTPEE, the fourth pipe 11 is further provided with an injector 5, through which the slurry is quantitatively added online.

[0035] After recycling polyester, the waste PBT is crushed and cleaned to remove impurities such as fillers and flame retardants. After drying and dehydration, PBT undergoes an ester exchange reaction with methanol under the action of the environmentally friendly tetrabutyl titanate catalyst, depolymerizing to produce DMT and BDO. The temperature is 200°C, the pressure is 2MPa, and the mass ratio of methanol to PBT is 4:1. After the reaction liquid is cooled, DMT crystallizes and is filtered to obtain crude DMT. The regenerated DMT can completely replace the original product, realizing closed-loop recovery of PBT; the BDO-methanol mixture is recovered by distillation to meet the boiling point of BDO at 230°C and the boiling point of methanol at 65°C, obtaining BDO that meets various physical performance indicators.

[0036] Example 1

[0037] A method for preparing rPBT using recycled polyester regenerated DMT, the steps are as follows:

[0038] (1) DMT and BDO were added to the nitrogen-substituted beating kettle 1 for beating. After mixing, manganese acetate was added and then the mixture entered the first transesterification kettle 2 for transesterification reaction. The molar ratio of DMT to BDO was 1:1.8; the mass ratio of the catalyst titanium content to the theoretical synthesis amount was 500 μg:1 g; the melt flow rate was controlled to pass through the first transesterification kettle 2. The transesterification temperature of the first transesterification kettle 2 was 200°C, the reaction time was 150 min, and the transesterification rate was 85%. The mixture then entered the second transesterification kettle 3. The transesterification temperature was 220°C, the reaction time was 50 min, and the transesterification rate was 98%.

[0039] (2) The melt obtained in step (1) is fed into a pre-condensation reactor 6, and the melt is uniformly mixed with the titanium compound and triphenyl phosphate, and then pre-condensed at 240°C for 60 minutes to obtain a pre-condensation product. The titanium compound is a mixture of tetrabutyl titanate and citric acid-tetrabutyl titanate chelate; the molar ratio of tetrabutyl titanate to citric acid-tetrabutyl titanate chelate is 2:1, and the mass ratio of the catalyst titanium content to the theoretical synthesis amount is 120 μg:1g.

[0040] (3) The melt is controlled to enter the final polycondensation reactor 7 for polycondensation reaction. The reaction time is 50 min, the melt temperature is controlled to be 250-255°C, and the material is discharged and pelletized to obtain rPBT. The intrinsic viscosity of rPBT is 0.98 dL / g and the melting point is 221°C.

[0041] Example 2

[0042] A method for preparing rTPEE using regenerated DMT, comprising the following steps:

[0043] (1) DMT and BDO were added to a nitrogen-purged beating kettle 1 for beating. After uniform mixing, tetraethyl titanate was added and then the mixture was introduced into the first transesterification kettle 2 for transesterification. The molar ratio of DMT to BDO was 1:1.8, and the mass ratio of the catalyst titanium content to the theoretical synthesis amount was 20 μg:1 g. The melt flow rate was controlled to pass through the first transesterification kettle 2. The transesterification temperature of the first transesterification kettle 2 was 200°C and the transesterification rate was 88%. The mixture then entered the second transesterification kettle 3. The transesterification temperature was 210°C and the transesterification rate was 98%.

[0044] (2) PTMEG was melted in a melting kettle 4 at a temperature of 60°C, and antioxidant 1010 and antioxidant 168 were added in a mass ratio of 3:1. The mixture was stirred for 30 minutes and then added online into the third pipe 10 using a syringe 5. The amount of PTMEG added was 10% of the theoretical output, and the ratio of the amount of antioxidant to the theoretical output was 0.1 mg:1 g.

[0045] (3) The obtained melt is fed into a precondensation reactor 6, and the melt is uniformly mixed with the titanium compound and trimethyl phosphate, and then precondensed for 60 minutes at a temperature of 240°C to obtain a precondensation product; the titanium compound is a mixture of tetrabutyl titanate and citric acid-tetrabutyl titanate chelate; the molar ratio of tetrabutyl titanate and citric acid-tetrabutyl titanate chelate is 2:1, the mass ratio of the catalyst titanium content to the theoretical synthesis amount is 80μg:1g; the mass ratio of the added amount of trimethyl phosphate to the theoretical synthesis amount is 5μg:1g.

[0046] (4) The melt is controlled to enter the final polycondensation reactor 7 for polycondensation reaction. The reaction time is 40 min, the melt temperature is controlled to be 240-245 °C, and the material is discharged and pelletized to obtain rTPEE. The intrinsic viscosity of rTPEE is 0.62 dL / g and the melting point is 209 °C.

[0047] Example 3

[0048] A method for preparing rTPEE using regenerated DMT, comprising the following steps:

[0049] (1) DMT and BDO were added to a nitrogen-purged beating kettle 1 for beating. After uniform mixing, tetrabutyl titanate was added and then the mixture was introduced into the first transesterification kettle 2 for transesterification. The molar ratio of DMT to BDO was 1:1.8, and the mass ratio of the catalyst titanium content to the theoretical synthesis amount was 15 μg:1 g. The melt flow rate was controlled to pass through the first transesterification kettle 2. The transesterification temperature of the first transesterification kettle 2 was 200°C and the transesterification rate was 85%. The mixture then entered the second transesterification kettle 3. The transesterification temperature was 210°C and the transesterification rate was 98%.

[0050] (2) PTMEG was melted in a melting kettle 4 at a temperature of 60°C, and antioxidant 1010 and antioxidant 168 were added in a mass ratio of 3:1. The mixture was stirred for 30 minutes and then added online into the third pipe 10 using a syringe 5. The amount of PTMEG added was 5% of the theoretical yield, and the ratio of the amount of antioxidant to the theoretical yield was 0.1 mg:1 g.

[0051] (3) The obtained melt is fed into a precondensation reactor 6, and the melt is uniformly mixed with the titanium compound and trimethyl phosphate, and then precondensed at 240°C for 60 minutes to obtain a precondensation product. The titanium compound is a mixture of tetrabutyl titanate and citric acid-tetrabutyl titanate chelate; the molar ratio of tetrabutyl titanate and citric acid-tetrabutyl titanate chelate is 2:1, the mass ratio of the catalyst titanium content to the theoretical synthesis amount is 80 μg:1g, and the mass ratio of the added amount of trimethyl phosphate to the theoretical synthesis amount is 5 μg:1g.

[0052] (4) The melt is controlled to enter the final polycondensation reactor 7 for polycondensation reaction. The reaction time is 50 min, the melt temperature is controlled to be 240-245°C, and the material is discharged and pelletized to obtain rTPEE. The intrinsic viscosity of rTPEE is 0.71 dL / g and the melting point is 215°C.

[0053] Comparative Example 1

[0054] The same method as in Example 1 was used except that a conventional batch polymerization method was employed. The resulting rPBT had an intrinsic viscosity of 0.91 dl / g and a melting point of 211°C.

[0055] Comparative Example 2

[0056] The same method as in Example 3 was used except that a conventional batch polymerization method was employed. The resulting rTPEE had an intrinsic viscosity of 0.65 dl / g and a melting point of 203°C.

[0057] It can be seen from Examples 1 to 3 and Comparative Examples 1 to 2 that the continuous polymerization method has obvious advantages. While ensuring the stability of product quality and avoiding excessive differences in indicators due to process fluctuations, it can increase the efficiency of pushing materials in the four-reactor body, thereby accelerating the reaction of the materials, and can improve the internal material uniformity of the reaction process, which is more conducive to the demand-based production of two different products.

[0058] Among the technical solutions of the present invention, the continuous preparation of rPBT or rTPEE by a four-reactor polymerization process is the key technology of this case. Figure 1 The focus of the demonstration is on the components and specific structure of a device for producing rPBT and rTPEE from recycled polyester DMT. This helps reduce production costs and improve the market competitiveness of recycled chips or fibers. Components such as pipes and melt pumps can be configured conventionally by those skilled in the art based on existing techniques. This application does not require specific requirements regarding their model selection or combination.

[0059] Thus, using the technical solution of the present invention, the preparation process of rPBT is as follows: after DMT, BDO and an ester exchange catalyst are mixed and slurried, the slurry is sequentially fed into the first and second ester exchange kettles for continuous ester exchange to obtain an ester exchange product with a high diester content, the ester exchange product is fed into the prepolymerization kettle via a melt pump, and a polycondensation catalyst combination is simultaneously added. The prepolymer passes through a coarse filter and reaches the final polycondensation kettle, where rPBT is synthesized through a final polycondensation reaction. The preparation process of rTPEE is as follows: after obtaining the ester exchange product in the rPBT synthesis process, PTMEG is treated in a melting kettle and then injected into the pipe melt between the second ester exchange kettle and the prepolycondensation kettle, or directly injected into the prepolymerization kettle melt, and then polycondensed to synthesize rTPEE.

[0060] As can be seen from the above description, compared with existing technologies, the present continuous polymerization method for producing rPBT or rTPEE from recycled DMT not only broadens the path to high-value utilization of waste polyester but also enables the continuous production of two products on the same set of equipment. This flexibility enables the factory to quickly adjust production direction based on changes in orders and market demand, thereby enhancing the company's market adaptability and competitiveness.

[0061] The above describes the technical solution, working process and implementation effect of the present invention in detail. It should be noted that what is described is only a typical example of the present invention. In addition, the present invention can also have many other specific implementation methods. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection required by the present invention.

Claims

1. A device for preparing PBT or its elastomer using recycled DMT, characterized in that: The invention comprises a pretreatment part, an ester exchange part and a polycondensation part which are connected to each other, wherein the pretreatment part comprises a pulping kettle (1) and a melting kettle (4); the ester exchange part comprises a first ester exchange kettle (2) and a second ester exchange kettle (3); the polycondensation part comprises a pre-polycondensation kettle (6) and a final polycondensation kettle (7); the discharge end of the pulping kettle (1) is connected to the feed end of the first ester exchange kettle (2) through a first pipe (8); the discharge end of the first ester exchange kettle (2) is connected to the feed end of the second ester exchange kettle (3) through a second pipe (9); the second pipe (9) is provided with a first melt pump (11) and a second melt pump (12) which is connected to the feed end of the first ester exchange kettle (2) through a second pipe (9); 3), a third pipe (10) is provided between the second transesterification kettle (3) and the pre-condensation kettle (6), a second melt pump (14) is provided on the third pipe (10), a first end of the third pipe (10) is connected to the discharge end of the second transesterification kettle (3), a second end of the third pipe (10) is connected to the feed end of the pre-condensation kettle (6), a third end of the third pipe (10) is connected to the melting kettle (4) through a fourth pipe (11), and a fifth pipe (12) is provided between the pre-condensation kettle (6) and the final condensation kettle (7).

2. The device for preparing PBT or an elastomer thereof by utilizing recycled DMT according to claim 1, characterized in that: The fourth pipe (11) is also provided with a syringe (5) for online quantitative addition of slurry.

3. A method for preparing PBT or an elastomer thereof using recycled DMT, characterized in that: The method comprises: Step S1: adding regenerated DMT, BDO and transesterification catalyst into a beating kettle (1) and stirring them evenly, and then the mixed slurry enters a first transesterification kettle (2) to carry out transesterification reaction at a temperature between 170 and 200° C., controlling the transesterification rate to be 80 to 90%, and then enters a second transesterification kettle (3) to carry out transesterification reaction at a temperature between 200 and 220° C., controlling the transesterification rate to be 95 to 99%, thereby obtaining a mixed melt of DBT and its oligomers; Step S2: PTMEG is added to a melting kettle (4) for melting, wherein the temperature of the melting kettle (4) is 40 to 80° C., and then an antioxidant is added to obtain a mixed slurry, and the mixed slurry is added online to a third pipe (10) provided between the second transesterification kettle (3) and the pre-polycondensation kettle (6) through a quantitative syringe to obtain a reaction melt; Step S3: transporting the reaction melt to the pre-polycondensation kettle (6) through the melting kettle (4), adding the polycondensation catalyst and the side reaction suppressing agent directly to the pre-polycondensation kettle (6), or adding the polycondensation catalyst and the side reaction suppressing agent to the third pipe (10) provided between the second transesterification kettle (3) and the pre-polycondensation kettle (6), and performing a pre-polycondensation reaction, wherein the reaction pressure is 1000-3000 Pa, the reaction temperature is 220-250° C., and the reaction time is 50-90 min to obtain a pre-polycondensation product; Step S4: The pre-polycondensation product is transported to a final polycondensation reactor (7) for a final polycondensation reaction, wherein the reaction pressure is 10-200 Pa, the reaction temperature is 235-260°C, and the reaction time is 0.5-1.5 h, to obtain rPBT with a viscosity of 0.90-1.20 dL / g and a melting point of 215-225°C, or rTPEE with a viscosity of 0.8-1.5 dL / g and a melting point of 205-220°C.

4. The method for preparing PBT or an elastomer thereof using recycled DMT according to claim 3, characterized in that: The regenerated DMT is obtained by purifying recycled polyester with a purity of ≥98%.

5. The method for preparing PBT or an elastomer thereof using recycled DMT according to claim 3, characterized in that: In step S1, the molar ratio of the regenerated DMT to the BDO is 1:1.5-3.

0.

6. The method for preparing PBT or an elastomer thereof using recycled DMT according to claim 3, characterized in that: In step S1, the transesterification catalyst is one or more of acetic acid compounds such as manganese acetate and zinc acetate or titanate compounds, and the mass ratio of the metal element content in the transesterification catalyst to the theoretical synthesis amount is 0.003% to 0.013%:

1.

7. The method for preparing PBT or an elastomer thereof by utilizing recycled DMT according to claim 3, characterized in that: In step S2, the molecular weight of the PTMEG is 800 to 3000, and the amount added is 3 to 65% of the polymer.

8. The method for preparing PBT or an elastomer thereof using recycled DMT according to claim 3, characterized in that: In step S2, the antioxidant includes but is not limited to one or more of antioxidant 1010, antioxidant 168 or antioxidant BHT, and the added amount is 0.01% to 0.5% by mass ratio to the theoretical polyester yield:

1.

9. The method for preparing PBT or an elastomer thereof by utilizing recycled DMT according to claim 3, characterized in that: In step S3, the polycondensation catalyst is one or more of a titanate compound or a hydroxycarboxylic acid-titanate chelate, and the mass ratio of the metal element content in the polycondensation catalyst to the theoretical synthesis amount is 0.003% to 0.013%:

1.

10. The method for preparing PBT or an elastomer thereof by utilizing recycled DMT according to claim 3, characterized in that: In step S3, the side reaction suppression auxiliary agent is one or more of trimethyl phosphite, triphenyl phosphate, trimethyl phosphate, triethyl phosphite, triethyl phosphate, and tributyl phosphate, and the mass ratio of the added amount of the side reaction suppression auxiliary agent to the theoretical synthesis amount is 0.0002% to 0.0012%:1.

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