A method for preparing primary-color biodegradable poly(butylene terephthalate)-co-poly(butylene carbonate)

Abstract

The present invention provides a method for preparing virgin biodegradable poly(butylene terephthalate)-co-(butylene carbonate), which relates to the circular regeneration of fiber textile materials and the synthesis of biodegradable polymer materials. The present invention uses colored waste polyester textiles as raw materials, first alcoholyzes them with ethylene glycol to bis(2-hydroxyethyl) terephthalate (BHET) in the presence of a catalyst, then transesterifies the above alcoholysis product to obtain crude colored dimethyl terephthalate (DMT), then purifies and decolorizes the crude colored DMT to obtain colorless refined DMT, and then transesterifies the colorless refined DMT with 1,4-butanediol (BDO) to obtain virgin bis(2-hydroxybutyl) terephthalate (BHBT). The virgin BHBT is then polycondensed with butylene methylene carbonate (BMBC) obtained by transesterifying dimethyl carbonate (DMC) with 1,4-butanediol (BDO) to obtain a method for virgin biodegradable PBCT. The virgin PBCT obtained by the present invention has a quality comparable to that of virgin PBCT because the dyes and impurities in the raw materials are removed to the greatest extent in the intermediate links; at the same time, it is beneficial to the conservation of fossil resources, can reduce environmental pollution, and reduce carbon emissions.

Description

Technical Field

[0001] The present invention relates to the technical field of circular regeneration of fiber textile materials and synthesis of biodegradable polymer materials, and particularly to a method for preparing primary-color biodegradable poly(butylene terephthalate)-co-poly(butylene carbonate) from colored waste polyester textiles. Background Art

[0002] With the doubling of the global production of polyester textiles, the annual output of waste polyester textiles has reached 40 million tons. Due to restrictions such as technology, most waste polyester textiles are landfilled or incinerated as garbage; since polyester (PET) is difficult to degrade in the soil under natural conditions, landfill treatment not only pollutes underground water resources but also causes soil compaction; while incineration produces environmentally unfriendly VOCs, etc., and at the same time this low-end treatment method is also a great waste of fossil resources.

[0003] Regarding the treatment technology of colored waste polyester textiles, it is usually to decompose them into small molecules by chemical methods and then re-polymerize the small molecules to manufacture new fiber-forming polymers or prepare other chemical raw materials, that is, chemical recycling. However, because colored waste polyester textiles contain dyes, inorganic pigments, and other dyeing and chemical auxiliaries, etc., their existence will affect chemical recycling, resulting in the continuous reduction of the quality of the recycled products after each chemical recycling, so multiple recycling cannot be achieved; at the same time, there are also the following problems in the chemical recycling and utilization of colored waste polyester textiles: if colored waste polyester textiles are directly chemically recycled without sorting by color before treatment, only recycled polyester with a black color can be obtained, which greatly restricts its application fields and the grade of the final products; if sorted by color before treatment, there will also be problems such as a large color difference between the product color and the raw material due to chemical reactions and other factors during the recycling process, and secondary dyeing, color compensation, color matching, etc. need to be carried out during later use, which not only easily causes environmental pollution, but also has problems such as poor processing performance due to impurities such as inorganic pigments, dyeing chemicals, and gel agglomerated particles not being removed. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing primary-color biodegradable poly(butylene terephthalate)-co-poly(butylene carbonate) from colored waste polyester textiles. This method realizes the resource utilization of colored waste polyester textiles, and the color, performance, and other quality indicators of the prepared poly(butylene terephthalate)-co-poly(butylene carbonate) material can be comparable to those of the original PBCT, thus greatly enhancing the added value.

[0005] The present invention is implemented by adopting the following technical solutions:

[0006] A method for preparing primary-color biodegradable poly(butylene terephthalate)-co-poly(butylene carbonate) from colored waste polyester textiles, comprising the following steps:

[0007] (1) Compact the colored waste polyester textiles into pellet materials or friction materials; then transport the materials to an alcoholysis kettle and carry out alcoholysis using ethylene glycol;

[0008] (2) Transport the alcoholyzed materials to a flash evaporation device or a vacuum distillation device, distill out the unreacted ethylene glycol (EG) and recycle it, and obtain an alcoholysis product;

[0009] (3) Carry out a transesterification reaction on the alcoholysis product and methanol in an ester exchange reactor I under the action of a catalyst;

[0010] (4) Transport the materials after the transesterification reaction to a flash evaporation device or a vacuum distillation device, distill out the unreacted methanol and the gaseous by-product EG, recycle methanol and EG, and collect the transesterification product, namely colored crude dimethyl terephthalate (DMT);

[0011] (5) Feed the colored crude DMT into a vacuum distillation kettle, carry out vacuum distillation at 210 °C to 240 °C and a pressure of 8 to 10 KPa for 15 min to 35 min, sublime and then condense into a multi-set of parallel collection tanks with switchable operation, release the condensed colorless refined DMT after treatment with a rotary scraper, and then transport it to a refined DMT storage tank through a screw conveyor; multiple collection tanks are switched for treatment to achieve continuous production of continuous refined DMT; the impurities left after vacuum distillation continuously enter the impurity collection tank;

[0012] (6) Carry out a transesterification reaction on the colorless refined DMT, 1,4-butanediol (BDO) and a catalyst in an ester exchange reactor II;

[0013] (7) Feed the materials after the transesterification in step (6) into a flash evaporation device or a vacuum distillation device, distill out the unreacted BDO and the gaseous by-product methanol, recycle BDO and methanol; collect the transesterification product, namely primary-color BHBT;

[0014] (8) Carry out a transesterification reaction on dimethyl carbonate (DMC), BDO and a transesterification catalyst in an ester exchange reactor III, and distill out the reaction by-products methanol and DMC that form an azeotrope with it through a fractionating column, and send them to an extractive distillation tower for separation and recovery;

[0015] (9) Feed the materials after the transesterification in step (8) into a flash evaporation device or a vacuum distillation device, distill out the unreacted DMC, and collect BMBC;

[0016] (10) Transport BMBC and primary-color BHBT to a pre-condensation reactor and carry out a pre-condensation reaction in the presence of a catalyst;

[0017] (11) The material after the pre-condensation reaction is transported to the final condensation reactor for the final condensation reaction to obtain virgin poly(butylene terephthalate)-co-poly(butylene carbonate) (PBCT).

[0018] (12) The virgin poly(butylene terephthalate)-co-poly(butylene carbonate) (PBCT) produced after the final condensation reaction is discharged, and after water-cooled casting and pelletizing, virgin PBCT chips are obtained; the quality indexes of the virgin PBCT chips are as follows: intrinsic viscosity 1.10 dl / g to 1.21 dl / g, whiteness L value ≥ 83.

[0019] Preferably, the alcoholysis process parameters in step (1) are as follows: temperature 197 °C to 256 °C, reaction time 40 min to 260 min, mass ratio of the colored waste polyester textiles to ethylene glycol 1:2 to 8, the catalyst is one or a combination of zinc acetate, manganese acetate, cobalt acetate, calcium acetate, sodium carbonate, and the addition amount of the catalyst is 0.05 wt% to 0.5 wt% based on the mass of the colored waste polyester textiles.

[0020] Preferably, the process parameters of the transesterification reaction in step (3) are: temperature 55 °C to 135 °C, reaction time 30 min to 240 min, mass ratio of BHET to methanol 1:2 to 5, the catalyst is one or a combination of zinc acetate, manganese acetate, potassium carbonate, cobalt acetate, sodium carbonate, calcium acetate, sodium hydroxide, and the addition amount of the catalyst is 0.05 wt% to 0.3 wt% based on the mass of BHET.

[0021] Preferably, in step (4), the colored crude DMT is fed into a vacuum distillation kettle, and the gas-phase pipeline of the vacuum distillation kettle is connected to multiple sets of collection tanks arranged in parallel and capable of being switched for operation. The collection tanks are designed with rotary scraper devices.

[0022] Preferably, the refined DMT storage tank has a heating function and can heat the refined DMT into a liquid state.

[0023] Preferably, multiple sets of recrystallization tanks arranged in parallel and capable of being switched for operation can be provided in front of the refined DMT storage tank. The DMT after vacuum distillation sublimation-condensation treatment is dissolved in hot methanol, the dissolution temperature is 55 °C to 135 °C, and then it enters the cooling recrystallization tank for recrystallization. The high-purity DMT virgin solid is transported to the refined DMT storage tank after being treated by a scraper and heated into a liquid.

[0024] Preferably, the process parameters of the transesterification reaction in step (6) are as follows: temperature is 155°C to 225°C, reaction time is 120 min to 300 min, the molar ratio of DMT to BDO is 1:3 to 15, and the catalyst is one or a combination of titanium phthalate, tetra-isopropyl titanate, tetramethyl titanate, tetra-butyl titanate, tetra-octyl titanate, titanium fluorosalt, alkoxytin, zinc acetate, and the addition amount of the catalyst is 0.01 wt% to 0.20 wt% based on the mass of DMT.

[0025] Preferably, the process parameters of the transesterification reaction in step (8) are as follows: temperature is 92°C to 160°C, the molar ratio of DMC to BDO is 2.5 to 8:1, and the catalyst is one or a combination of zinc acetate, manganese acetate, cobalt acetate, calcium acetate, sodium carbonate, sodium hydroxide, tetra-butyl titanate, and the addition amount of the catalyst is 0.01 wt% to 0.5 wt% based on the theoretical mass of BMBC generated.

[0026] Preferably, the process parameters of the pre-condensation reaction in step (10) are as follows: temperature is 185°C to 235°C, the residual vacuum pressure is 1 to 15 KPa; reaction time is 55 min to 130 min, and the catalyst is one or a combination of tin octoate, tetra-butyl titanate, antimony trioxide, and the addition amount of the catalyst is 0.03 wt% to 0.10 wt% based on the theoretical mass of PBCT generated.

[0027] Preferably, the process parameters of the final condensation reaction in step (11) are as follows: temperature is 200°C to 245°C, the residual vacuum pressure is 25 to 130 Pa, and reaction time is 60 min to 360 min.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention uses colored waste polyester (PET) textiles as raw materials to prepare biodegradable primary polybutylene terephthalate - co - butylene carbonate (PBCT), and the whole process is a continuous operation. General equipment can be used in the process, and it has excellent universality and integration for industrial promotion; at the same time, it overcomes the inherent unsolvable disadvantages of batch quality differences and high operating costs brought by batch operation.

[0030] 2. Through separation processes such as continuous flash evaporation, continuous vacuum distillation, and optional recrystallization, the present invention can remove dyes, pigments, dyeing chemicals, and impurities such as gel agglomeration particles generated during polymerization and production processing in textile raw materials to the greatest extent, obtaining highly pure recycled raw materials, thereby enabling the recycling of colored waste polyester textiles multiple times or even infinitely; and the quality of the obtained primary PBCT can be comparable to that of virgin PBCT; at the same time, it is beneficial to the conservation of fossil resources, reduction of environmental pollution, and reduction of carbon emissions.

[0031] 3. Compared with the poly(butylene terephthalate)-co-poly(butylene adipate) (PBAT) that has been industrialized in the market, the primary color PBCT prepared by the present invention does not produce acidic substances during the degradation process and will not cause soil hardening and acidification when applied to agricultural mulch films; moreover, it has good melt spinning spinnability and is more widely applicable. Detailed implementation manners

[0032] The present invention will be further described below in conjunction with embodiments.

[0033] Example 1

[0034] A method for preparing primary color biodegradable poly(butylene terephthalate)-co-poly(butylene carbonate) from colored waste polyester textiles, the specific steps are as follows:

[0035] (1) Compact the colored waste polyester textiles into agglomerated materials; then convey the materials to an alcoholysis kettle, and add ethylene glycol (EG) and a catalyst according to the ratio for alcoholysis; wherein the specifications of the agglomerated materials are irregular spherical shapes with a maximum diameter not exceeding 3 cm. The temperature of the alcoholysis reaction is 256 °C, the reaction time is 40 min, the mass ratio of the colored waste polyester textiles to ethylene glycol is 1:8, the catalyst is sodium carbonate, and the addition amount of the catalyst is 0.05 wt%, based on the mass of the colored waste polyester textiles.

[0036] (2) Convey the alcoholyzed materials to a flash evaporation device or a vacuum distillation device, distill out the unreacted ethylene glycol and recycle it, and obtain an alcoholysis product;

[0037] (3) Carry out a transesterification reaction on the alcoholysis product and methanol under the action of a catalyst; the process parameters of the transesterification reaction are: the temperature is 135 °C, the reaction time is 60 min, the mass ratio of BHET to methanol is 1:5, the catalyst is sodium hydroxide, and the addition amount of the catalyst is 0.3 wt%, based on the mass of BHET.

[0038] (4) Convey the materials after the transesterification reaction to a flash evaporation device or a vacuum distillation device, distill out the unreacted methanol and gaseous by-products, wherein methanol and ethylene glycol are recycled, and collect the transesterification product, namely colored crude DMT; the gas-phase pipeline of the vacuum distillation kettle is connected to multiple sets of collection tanks arranged in parallel and operable in a switchable manner, and the collection tanks are designed with rotary scraper devices.

[0039] (5) Feed the colored crude DMT into a vacuum distillation kettle, and carry out vacuum distillation at 235°C and a pressure of 10 KPa for 35 minutes. The sublimated colorless refined DMT condenses into multiple sets of parallel collection tanks with switchable operation, and after condensation, it is discharged after being processed by a rotary scraper, and then transported to the refined DMT storage tank through a screw conveyor; multiple collection tanks are switched for processing to achieve continuous production of refined DMT; the impurities left after vacuum distillation continuously enter the impurity collection tank; among them, the colorless refined DMT storage tank has a heating function and can heat the colorless refined DMT into a liquid state.

[0040] Multiple sets of parallel recrystallization tanks with switchable operation can be set in front of the refined DMT storage tank. Dissolve the DMT after vacuum distillation sublimation-condensation treatment in hot methanol at a dissolution temperature of 130°C, and then enter the cooling recrystallization tank for recrystallization. The high-purity DMT primary color solid is transported to the refined DMT storage tank after being processed by a scraper and heated into a liquid.

[0041] (6) Carry out transesterification reaction on refined DMT, 1,4-butanediol (BDO) and a catalyst; the process parameters of the transesterification reaction are: temperature 225°C, reaction time 120 minutes, the molar ratio of DMT and BDO is 1:8, the catalyst is tetrabutyl titanate and zinc acetate, and the addition amount of the catalyst is 0.2 wt%, based on the mass of DMT.

[0042] (7) Feed the material after the transesterification in step (6) into a flash evaporation device or a vacuum distillation device to distill out the unreacted BDO and gaseous by-products, and among them, BDO and methanol are recycled; collect the transesterification product, namely the primary color BHBT.

[0043] (8) Carry out transesterification reaction on dimethyl carbonate (DMC), BDO and a transesterification catalyst. The reaction by-products methanol and DMC forming an azeotrope with it are taken out through a fractionating column and sent to an extractive distillation tower for separation and recovery; the process parameters of the transesterification reaction are: temperature 160°C, the molar ratio of DMC and BDO is 8:1, the catalyst is tetrabutyl titanate and cobalt acetate, and the addition amount of the catalyst is 0.5 wt%, based on the theoretical mass of BMBC generated.

[0044] (9) Feed the material after the transesterification in step (8) into a flash evaporation device or a vacuum distillation device to distill out DMC and collect BMBC.

[0045] (10) Transport BMBC and BHBT to a pre-condensation reactor and carry out pre-condensation reaction in the presence of a catalyst; the process parameters of the pre-condensation reaction are: temperature 235°C, vacuum residual pressure 2 KPa; reaction time 55 minutes, the catalyst is tin octoate and tetrabutyl titanate (tin octoate:tetrabutyl titanate is 1:3), and the addition amount of the catalyst is 0.1 wt%, based on the theoretical mass of PBCT generated.

[0046] (11) The material after pre - condensation reaction is transported to the final condensation reactor for final condensation reaction to obtain virgin poly(butylene terephthalate - co - butylene carbonate) (PBCT); the process parameters of the final condensation reaction are: temperature is 245 °C, residual vacuum pressure is 25 Pa, and reaction time is 60 min.

[0047] (12) The virgin poly(butylene terephthalate - co - butylene carbonate) (PBCT) generated after the final condensation reaction is discharged, and after water - cooled casting and pelletizing, virgin PBCT chips are obtained;

[0048] After detection, the quality indexes of the virgin PBCT chips are: intrinsic viscosity is 1.21 dl / g, and whiteness L value is 83.

[0049] Example 2

[0050] A method for preparing virgin biodegradable poly(butylene terephthalate - co - butylene carbonate), the specific steps are as follows:

[0051] (1) The colored waste polyester textiles are densified into friction materials; then the materials are transported to an alcoholysis kettle, and ethylene glycol (EG) and a catalyst are added in a certain proportion for alcoholysis; the temperature of the alcoholysis reaction is 200 °C, the reaction time is 260 min, the mass ratio of the colored waste polyester textiles to ethylene glycol is 1:6, the catalyst is calcium acetate and sodium carbonate, and the addition amount of the catalyst is 0.5 wt% based on the mass of the colored waste polyester textiles.

[0052] (2) The material after alcoholysis is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted EG and recycle it to obtain an alcoholysis product;

[0053] (3) The alcoholysis product and methanol are subjected to a transesterification reaction under the action of a catalyst; the process parameters of the transesterification reaction are: temperature is 85 °C, reaction time is 210 min, the mass ratio of BHET to methanol is 1:2, the catalyst is sodium hydroxide, and the addition amount of the catalyst is 0.1 wt% based on the mass of BHET.

[0054] (4) The material after the transesterification reaction is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted methanol and gaseous by - products, where methanol and ethylene glycol are recycled, and the transesterification product, namely colored crude DMT, is collected; the gas pipeline of the vacuum distillation kettle is connected to multiple sets of collection tanks arranged in parallel and operable in a switchable manner, and the collection tanks are designed with rotary scraper devices.

[0055] (5) Feed the colored crude DMT into a vacuum distillation kettle, and conduct vacuum distillation at 240 °C and a pressure of 8 KPa for 20 min. The sublimated primary DMT enters multiple sets of parallel collecting tanks that can be switched for operation, and is discharged after being treated by a rotary scraper, and is transported to the refined DMT storage tank through a screw conveyor; multiple collecting tanks are switched for treatment to achieve continuous production of continuous refined DMT; the impurities left after vacuum distillation continuously enter the impurity collection tank; among them, the refined DMT storage tank has a heating function and can heat the refined DMT into a liquid state.

[0056] Multiple sets of parallel recrystallization tanks that can be switched for operation can be arranged in front of the refined DMT storage tank. Dissolve the DMT after vacuum distillation sublimation-condensation treatment in hot methanol at a dissolution temperature of 120 °C, and then enter the cooling recrystallization tank for recrystallization. The high-purity DMT primary color solid is transported to the refined DMT storage tank after being treated by a scraper and heated into a liquid.

[0057] (6) Conduct a transesterification reaction on refined DMT, 1,4-butanediol (BDO), and a catalyst; among them, the process parameters of the transesterification reaction are: temperature 185 °C, reaction time 300 min, molar ratio of DMT to BDO 1:10, catalyst is tetramethyl titanate, and the addition amount of the catalyst is 0.08 wt%, based on the mass of DMT.

[0058] (7) Feed the material after the transesterification in step (6) into a flash evaporation device or a vacuum distillation device to distill out the unreacted BDO and gaseous by-products, and recycle BDO and methanol; collect the transesterification product, namely primary color BHBT;

[0059] (8) Conduct a transesterification reaction on dimethyl carbonate (DMC), BDO, and a transesterification catalyst. The reaction by-products methanol and DMC that form an azeotrope with it are taken out through a fractionating column and sent to an extractive distillation tower for separation and recovery; among them, the process parameters of the transesterification reaction are: temperature 92 °C, molar ratio of DMC to BDO 3:1, catalyst is zinc acetate, and the addition amount of the catalyst is 0.3 wt%, based on the theoretical mass of BMBC formed.

[0060] (9) Feed the material after the transesterification in step (8) into a flash evaporation device or a vacuum distillation device to distill out DMC and collect BMBC;

[0061] (10) Transport BMBC and BHBT to a pre-condensation reactor and conduct a pre-condensation reaction in the presence of a catalyst; among them, the process parameters of the pre-condensation reaction are: temperature 185 °C, vacuum residual pressure 10 KPa; reaction time 130 min, catalyst is tetrabutyl titanate, and the addition amount of the catalyst is 0.03 wt%, based on the theoretical mass of PBCT formed

[0062] (11) The material after pre - condensation reaction is transported to the final condensation reactor for final condensation reaction to obtain virgin poly(butylene terephthalate - co - butylene carbonate) (PBCT); the process parameters for the final condensation reaction are: temperature is 215 °C, residual vacuum pressure is 130 Pa, and reaction time is 340 min.

[0063] (12) The virgin poly(butylene terephthalate - co - butylene carbonate) (PBCT) produced after the final condensation reaction is discharged, and after water - cooled casting and pelletizing, virgin PBCT chips are obtained;

[0064] After testing, the quality indexes of the virgin PBCT chips are: intrinsic viscosity is 1.15 dl / g, and whiteness L value is 88.

[0065] Example 3

[0066] A method for preparing virgin biodegradable poly(butylene terephthalate - co - butylene carbonate) from colored waste polyester textiles, the specific steps are as follows:

[0067] (1) The colored waste polyester textiles are densified into agglomerated materials; then the materials are transported to an alcoholysis kettle, and ethylene glycol (EG) and a catalyst are added according to the ratio for alcoholysis; the agglomerated materials are in the form of irregular spheres with a maximum diameter not exceeding 3 cm. The temperature of the alcoholysis reaction is 200 °C, the reaction time is 240 min, the mass ratio of the colored waste polyester textiles to ethylene glycol is 1:6, the catalyst is sodium carbonate and manganese acetate, and the addition amount of the catalyst is 0.5 wt% based on the mass of the colored waste polyester textiles.

[0068] (2) The material after alcoholysis is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted ethylene glycol for recycling, and an alcoholysis product is obtained;

[0069] (3) The alcoholysis product and methanol are subjected to a transesterification reaction under the action of a catalyst; the process parameters for the transesterification reaction are: temperature is 85 °C, reaction time is 210 min, the mass ratio of BHET to methanol is 1:2, the catalyst is sodium carbonate and sodium hydroxide, and the addition amount of the catalyst is 0.1 wt% based on the mass of BHET.

[0070] (4) The material after transesterification reaction is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted methanol and gaseous by - products, where methanol and ethylene glycol are recycled, and the transesterification product, namely colored crude DMT, is collected; the gas pipeline of the vacuum distillation kettle is connected to multiple sets of collection tanks arranged in parallel and operable in a switchable manner, and the collection tanks are designed with rotary scraper devices.

[0071] (5) Feed the colored crude DMT into a vacuum distillation kettle, and conduct vacuum distillation at 240 °C and a pressure of 10 KPa for 15 minutes. The sublimated colorless refined DMT condenses in multiple sets of parallel collection tanks with switchable operation, and after condensation, it is discharged after being treated by a rotary scraper, and then conveyed to a refined DMT storage tank by a screw conveyor; multiple collection tanks are switched for treatment to achieve continuous production of refined DMT; the impurities remaining after vacuum distillation continuously enter an impurity collection tank; among them, the colorless refined DMT storage tank has a heating function and can heat the colorless refined DMT into a liquid state.

[0072] Multiple sets of parallel recrystallization tanks with switchable operation can be arranged in front of the refined DMT storage tank. Dissolve the DMT after vacuum distillation sublimation-condensation treatment in hot methanol at a dissolution temperature of 100 °C, and then enter a cooling recrystallization tank for recrystallization. The high-purity DMT primary color solid is conveyed to the refined DMT storage tank after being treated by a scraper and heated into a liquid.

[0073] (6) Conduct a transesterification reaction on refined DMT, 1,4-butanediol (BDO) and a catalyst; among them, the process parameters of the transesterification reaction are: temperature 185 °C, reaction time 300 minutes, the molar ratio of DMT to BDO is 1:10, the catalyst is tetraoctyl titanate, and the addition amount of the catalyst is 0.12 wt%, based on the mass of DMT.

[0074] (7) Feed the material after the transesterification in step (6) into a flash evaporation device or a vacuum distillation device to distill out the unreacted BDO and gaseous by-products, and among them, BDO and methanol are recycled; collect the transesterification product, namely the primary color BHBT;

[0075] (8) Conduct a transesterification reaction on dimethyl carbonate (DMC), BDO and a transesterification catalyst. The reaction by-products methanol and DMC that form an azeotrope with it are taken out through a fractionating column and sent to an extractive distillation tower for separation and recovery; among them, the process parameters of the transesterification reaction are: temperature 110 °C, the molar ratio of DMC to BDO is 3:1, the catalyst is tetrabutyl titanate and zinc acetate, and the addition amount of the catalyst is 0.05 wt%, based on the theoretical mass of BMBC generated.

[0076] (9) Feed the material after the transesterification in step (8) into a flash evaporation device or a vacuum distillation device to distill out DMC and collect BMBC;

[0077] (10) Convey BMBC and BHBT to a pre-condensation reactor and conduct a pre-condensation reaction in the presence of a catalyst; among them, the process parameters of the pre-condensation reaction are: temperature 185 °C, vacuum residual pressure 10 KPa; reaction time 130 minutes, the catalyst is tetrabutyl titanate, and the addition amount of the catalyst is 0.03 wt%, based on the theoretical mass of PBCT generated;

[0078] (11) The material after pre - condensation reaction is transported to the final condensation reactor for final condensation reaction to obtain virgin poly(butylene terephthalate - co - butylene carbonate) (PBCT); the process parameters of the final condensation reaction are: temperature is 215 °C, residual vacuum pressure is 130 Pa, and reaction time is 340 min.

[0079] (12) The virgin poly(butylene terephthalate - co - butylene carbonate) (PBCT) produced after the final condensation reaction is discharged, and after water - cooled casting and pelletizing, virgin PBCT chips are obtained;

[0080] After testing, the quality indexes of the virgin PBCT chips are: intrinsic viscosity is 1.13 dl / g, and whiteness L value is 89.

[0081] Example 4

[0082] A method for preparing virgin biodegradable poly(butylene terephthalate - co - butylene carbonate) from colored waste polyester textiles, the specific steps are as follows:

[0083] (1) The colored waste polyester textiles are densified into agglomerated materials; then the materials are transported to an alcoholysis kettle, and ethylene glycol (EG) and a catalyst are added according to the ratio for alcoholysis; the specification of the agglomerated materials is irregular spherical with a maximum diameter not exceeding 3 cm. The temperature of the alcoholysis reaction is 220 °C, the reaction time is 130 min, the mass ratio of the colored waste polyester textiles to ethylene glycol is 1:4, the catalyst is sodium carbonate and zinc acetate, and the addition amount of the catalyst is 0.1 wt% based on the mass of the colored waste polyester textiles.

[0084] (2) The material after alcoholysis is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted ethylene glycol and recycle it, and an alcoholysis product is obtained;

[0085] (3) The alcoholysis product and methanol are subjected to transesterification reaction under the action of a catalyst; the process parameters of the transesterification reaction are: temperature is 70 °C, reaction time is 210 min, the mass ratio of BHET to methanol is 1:3, the catalyst is sodium carbonate and cobalt acetate, and the addition amount of the catalyst is 0.15 wt% based on the mass of BHET.

[0086] (4) The material after transesterification reaction is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted methanol and gaseous by - products, and the methanol and ethylene glycol are recycled, and the transesterification product, namely colored crude DMT, is collected; the gas pipeline of the vacuum distillation kettle is connected to multiple sets of collecting tanks arranged in parallel and operable in a switchable manner, and the collecting tanks are designed with rotary scraper devices.

[0087] (5) Feed the colored crude DMT into a vacuum distillation kettle, and perform vacuum distillation at 230 °C and a pressure of 8 KPa for 25 min. The sublimated colorless refined DMT condenses into multiple sets of parallel collection tanks with switchable operation, and after condensation, it is discharged after being treated by a rotary scraper, and then transported to the refined DMT storage tank through a screw conveyor; multiple collection tanks are switched for treatment to achieve continuous production of continuous refined DMT; the impurities left after vacuum distillation continuously enter the impurity collection tank; among them, the colorless refined DMT storage tank has a heating function and can heat the colorless refined DMT into a liquid state.

[0088] Multiple sets of parallel recrystallization tanks with switchable operation can be set in front of the refined DMT storage tank. Dissolve the DMT after vacuum distillation sublimation-condensation treatment in hot methanol at a dissolution temperature of 100 °C, and then enter the cooling recrystallization tank for recrystallization. The high-purity DMT primary color solid is transported to the refined DMT storage tank after being treated by a scraper and heated into a liquid.

[0089] (6) Carry out a transesterification reaction on refined DMT, 1,4-butanediol (BDO) and a catalyst; among them, the process parameters of the transesterification reaction are: temperature 175 °C, reaction time 250 min, the molar ratio of DMT and BDO is 1:8, the catalyst is tetraoctyl titanate and zinc acetate, and the addition amount of the catalyst is 0.15 wt%, based on the mass of DMT.

[0090] (7) Feed the material after the transesterification in step (6) into a flash evaporation device or a vacuum distillation device to distill out the unreacted BDO and gaseous by-products, and among them, BDO and methanol are recycled; collect the transesterification product, that is, the primary color BHBT.

[0091] (8) Carry out a transesterification reaction on dimethyl carbonate (DMC), BDO and a transesterification catalyst. The reaction by-products methanol and DMC that form an azeotrope with it are taken out through a fractionating column and sent to an extractive distillation tower for separation and recovery; among them, the process parameters of the transesterification reaction are: temperature 110 °C, the molar ratio of DMC and BDO is 5:1, the catalyst is tetrabutyl titanate and calcium acetate, and the addition amount of the catalyst is 0.2 wt%, based on the theoretical mass of BMBC generated.

[0092] (9) Feed the material after the transesterification in step (8) into a flash evaporation device or a vacuum distillation device to distill out DMC and collect BMBC.

[0093] (10) Transport BMBC and BHBT to a pre-condensation reactor and carry out a pre-condensation reaction in the presence of a catalyst; among them, the process parameters of the pre-condensation reaction are: temperature 195 °C, vacuum residual pressure 10 KPa; reaction time 100 min, the catalyst is tetrabutyl titanate and antimony trioxide, and the addition amount of the catalyst is 0.06 wt%, based on the theoretical mass of PBCT generated.

[0094] (11) The material after pre - condensation reaction is transported to a final condensation reactor for final condensation reaction to obtain virgin poly(butylene terephthalate - co - butylene carbonate) (PBCT); the process parameters of the final condensation reaction are: temperature is 220 °C, residual vacuum pressure is 130 Pa, and reaction time is 310 min.

[0095] (12) The virgin poly(butylene terephthalate - co - butylene carbonate) (PBCT) generated after the final condensation reaction is discharged, and after water - cooled casting and pelletizing, virgin PBCT chips are obtained;

[0096] After testing, the quality indexes of the virgin PBCT chips are: intrinsic viscosity 1.17 dl / g, whiteness L value is 88.

[0097] Example 5

[0098] A method for preparing virgin biodegradable poly(butylene terephthalate - co - butylene carbonate) from colored waste polyester textiles, the specific steps are as follows:

[0099] (1) The colored waste polyester textiles are densified into agglomerated materials; then the materials are transported to an alcoholysis kettle, and ethylene glycol (EG) and a catalyst are added according to the ratio for alcoholysis; the agglomerated materials are in the form of irregular spheres with a maximum diameter not exceeding 3 cm. The temperature of the alcoholysis reaction is 220 °C, the reaction time is 180 min, the mass ratio of the colored waste polyester textiles to ethylene glycol is 1:4, the catalyst is sodium carbonate and cobalt acetate, and the addition amount of the catalyst is 0.1 wt% based on the mass of the colored waste polyester textiles.

[0100] (2) The material after alcoholysis is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted ethylene glycol and recycle it to obtain an alcoholysis product;

[0101] (3) The alcoholysis product and methanol are subjected to a transesterification reaction under the action of a catalyst; the process parameters of the transesterification reaction are: temperature is 70 °C, reaction time is 210 min, the mass ratio of BHET to methanol is 1:3, the catalyst is sodium carbonate and zinc acetate, and the addition amount of the catalyst is 0.15 wt% based on the mass of BHET.

[0102] (4) The material after the transesterification reaction is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted methanol and gaseous by - products, where methanol and ethylene glycol are recycled, and the transesterification product, i.e., colored crude DMT, is collected; the gas pipeline of the vacuum distillation kettle is connected to multiple parallel - arranged and switch - operable collection tanks, and the collection tanks are designed with rotary scraper devices.

[0103] (5) Feed the colored crude DMT into a vacuum distillation kettle, and perform vacuum distillation at 220 °C and a pressure of 10 KPa for 25 minutes. The sublimated colorless refined DMT condenses into multiple sets of parallel collection tanks with switchable operation, and after condensation, it is discharged after being treated by a rotary scraper, and then conveyed to a refined DMT storage tank through a screw conveyor; multiple collection tanks are switched for treatment to achieve continuous production of refined DMT; the impurities left after vacuum distillation continuously enter the impurity collection tank; among them, the colorless refined DMT storage tank has a heating function and can heat the colorless refined DMT into a liquid state.

[0104] Before the refined DMT storage tank, multiple sets of parallel recrystallization tanks with switchable operation can be set. Dissolve the DMT after vacuum distillation sublimation-condensation treatment in hot methanol at a dissolution temperature of 80 °C, and then enter the cooling recrystallization tank for recrystallization. The high-purity DMT primary color solid is conveyed to the refined DMT storage tank after being treated by a scraper and heated into a liquid.

[0105] (6) Carry out a transesterification reaction on refined DMT, 1,4-butanediol (BDO) and a catalyst; among them, the process parameters of the transesterification reaction are: temperature 175 °C, reaction time 250 minutes, the molar ratio of DMT to BDO is 1:8, the catalyst is tetrabutyl titanate and alkoxytin, and the addition amount of the catalyst is 0.13 wt%, based on the mass of DMT.

[0106] (7) Feed the material after the transesterification in step (6) into a flash evaporation device or a vacuum distillation device to distill out the unreacted BDO and gaseous by-products, and among them, BDO and methanol are recycled; collect the transesterification product, namely the primary color BHBT;

[0107] (8) Carry out a transesterification reaction on dimethyl carbonate (DMC), BDO and a transesterification catalyst. The reaction by-products methanol and DMC that form an azeotrope with it are taken out through a fractionating column and sent to an extractive distillation tower for separation and recovery; among them, the process parameters of the transesterification reaction are: temperature 125 °C, the molar ratio of DMC to BDO is 5:1, the catalyst is tetrabutyl titanate and manganese acetate, and the addition amount of the catalyst is 0.25 wt%, based on the theoretical mass of BMBC generated.

[0108] (9) Feed the material after the transesterification in step (8) into a flash evaporation device or a vacuum distillation device to distill out DMC and collect BMBC;

[0109] (10) Convey BMBC and BHBT to a pre-condensation reactor and carry out a pre-condensation reaction in the presence of a catalyst; among them, the process parameters of the pre-condensation reaction are: temperature 195 °C, vacuum residual pressure 5 KPa; reaction time 100 minutes, the catalyst is tetrabutyl titanate, tin octoate and antimony trioxide, and the addition amount of the catalyst is 0.06 wt%, based on the theoretical mass of PBCT generated;

[0110] (11) The material after pre - condensation reaction is transported to a final condensation reactor for final condensation reaction to obtain virgin poly(butylene terephthalate - co - butylene carbonate) (PBCT); the process parameters for the final condensation reaction are as follows: the temperature is 220 °C, the residual vacuum pressure is 120 Pa, and the reaction time is 310 min.

[0111] (12) The virgin poly(butylene terephthalate - co - butylene carbonate) (PBCT) generated after the final condensation reaction is discharged, and after water - cooling, pelletizing, virgin PBCT chips are obtained.

[0112] After testing, the quality indexes of the virgin PBCT chips are as follows: the intrinsic viscosity is 1.19 dl / g, and the whiteness L value is 89.

[0113] Example 6

[0114] A method for preparing virgin biodegradable poly(butylene terephthalate - co - butylene carbonate) from colored waste polyester textiles, the specific steps are as follows:

[0115] (1) The colored waste polyester textiles are densified into agglomerates; then the material is transported to an alcoholysis kettle, and ethylene glycol (EG) and a catalyst are added according to the ratio for alcoholysis; the agglomerates are irregular spherical shapes with a maximum diameter not exceeding 3 cm. The temperature of the alcoholysis reaction is 240 °C, the reaction time is 170 min, the mass ratio of the colored waste polyester textiles to ethylene glycol is 1:3, the catalyst is sodium carbonate and calcium acetate, and the addition amount of the catalyst is 0.3 wt% based on the mass of the colored waste polyester textiles.

[0116] (2) The material after alcoholysis is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted ethylene glycol for recycling, and an alcoholysis product is obtained.

[0117] (3) The alcoholysis product and methanol are subjected to a transesterification reaction under the action of a catalyst; the process parameters for the transesterification reaction are as follows: the temperature is 65 °C, the reaction time is 210 min, the mass ratio of BHET to methanol is 1:4, the catalyst is potassium carbonate and sodium hydroxide, and the addition amount of the catalyst is 0.2 wt% based on the mass of BHET.

[0118] (4) The material after the transesterification reaction is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted methanol and gaseous by - products, where methanol and ethylene glycol are recycled, and the transesterification product, namely colored crude DMT, is collected; the gas pipeline of the vacuum distillation kettle is connected to multiple sets of collection tanks arranged in parallel and operable in a switchable manner, and the collection tanks are designed with a rotary scraper device.

[0119] (5) Feed the colored crude DMT into a vacuum distillation kettle, and conduct vacuum distillation at 215°C and a pressure of 8 KPa for 30 minutes. The sublimated colorless refined DMT condenses into multiple sets of parallel collection tanks with switchable operation, and after condensation, it is discharged after being treated by a rotary scraper, and then conveyed to a refined DMT storage tank through a screw conveyor; multiple collection tanks are switched for treatment to achieve continuous production of refined DMT; the impurities left after vacuum distillation continuously enter the impurity collection tank; among them, the colorless refined DMT storage tank has a heating function and can heat the colorless refined DMT into a liquid state.

[0120] Multiple sets of parallel recrystallization tanks with switchable operation can be set in front of the refined DMT storage tank. Dissolve the DMT after vacuum distillation sublimation-condensation treatment in hot methanol at a dissolution temperature of 70°C, and then enter the cooling recrystallization tank for recrystallization. The high-purity DMT primary color solid is conveyed to the refined DMT storage tank after being treated by a scraper and heated into a liquid.

[0121] (6) Conduct a transesterification reaction on refined DMT with 1,4-butanediol (BDO) and a catalyst; among them, the process parameters of the transesterification reaction are: temperature 160°C, reaction time 200 minutes, the molar ratio of DMT to BDO is 1:6, the catalyst is tetraoctyl titanate and titanium fluorosalt, and the addition amount of the catalyst is 0.1 wt%, based on the mass of DMT.

[0122] (7) Feed the material after the transesterification in step (6) into a flash evaporation device or a vacuum distillation device to distill out the unreacted BDO and gaseous by-products, and among them, BDO and methanol are recycled; collect the transesterification product, namely the primary color BHBT;

[0123] (8) Conduct a transesterification reaction on dimethyl carbonate (DMC), BDO and a transesterification catalyst. The reaction by-products methanol and DMC that form an azeotrope with it are taken out through a fractionating column and sent to an extractive distillation tower for separation and recovery; among them, the process parameters of the transesterification reaction are: temperature 140°C, the molar ratio of DMC to BDO is 6:1, the catalyst is tetrabutyl titanate and sodium hydroxide, and the addition amount of the catalyst is 0.1 wt%, based on the theoretical mass of BMBC generated.

[0124] (9) Feed the material after the transesterification in step (8) into a flash evaporation device or a vacuum distillation device to distill out DMC and collect BMBC;

[0125] (10) Convey BMBC and BHBT to a pre-condensation reactor and conduct a pre-condensation reaction in the presence of a catalyst; among them, the process parameters of the pre-condensation reaction are: temperature 205°C, vacuum residual pressure 5 KPa; reaction time 70 minutes, the catalyst is tetrabutyl titanate, stannous octoate and antimony trioxide, and the addition amount of the catalyst is 0.08 wt%, based on the theoretical mass of PBCT generated;

[0126] (11) The material after the pre - condensation reaction is transported to the final condensation reactor for the final condensation reaction to obtain the original - color poly(butylene terephthalate - co - butylene carbonate) (PBCT); the process parameters of the final condensation reaction are as follows: the temperature is 230 °C, the residual vacuum pressure is 120 Pa, and the reaction time is 320 min.

[0127] (12) The original - color poly(butylene terephthalate - co - butylene carbonate) (PBCT) generated after the final condensation reaction is discharged, and after water - cooled casting and pelletizing, the original - color PBCT slices are obtained;

[0128] After detection, the quality indexes of the original - color PBCT slices are as follows: the intrinsic viscosity is 1.16 dl / g, and the L value of whiteness is 86.

[0129] Example 7

[0130] A method for preparing the original - color biodegradable poly(butylene terephthalate - co - butylene carbonate) from colored waste polyester textiles, the specific steps are as follows:

[0131] (1) The colored waste polyester textiles are densified into agglomerated materials; then the materials are transported to an alcoholysis kettle, and ethylene glycol (EG) and a catalyst are added according to the ratio for alcoholysis; the specification of the agglomerated materials is irregular spherical with a maximum diameter not exceeding 3 cm. The temperature of the alcoholysis reaction is 240 °C, the reaction time is 200 min, the mass ratio of the colored waste polyester textiles to ethylene glycol is 1:3, the catalysts are sodium carbonate and cobalt acetate, and the addition amount of the catalyst is 0.3 wt% based on the mass of the colored waste polyester textiles.

[0132] (2) The material after alcoholysis is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted ethylene glycol and recycle it to obtain the alcoholysis product;

[0133] (3) The alcoholysis product and methanol are subjected to a trans - esterification reaction under the action of a catalyst; the process parameters of the trans - esterification reaction are as follows: the temperature is 55 °C, the reaction time is 210 min, the mass ratio of BHET to methanol is 1:4, the catalysts are calcium acetate and sodium hydroxide, and the addition amount of the catalyst is 0.2 wt% based on the mass of BHET.

[0134] (4) The material after the trans - esterification reaction is transported to a flash evaporation device or a vacuum distillation device to distill out the unreacted methanol and gaseous by - products, where methanol and ethylene glycol are recycled, and the trans - esterification product, namely the colored crude DMT, is collected; the gas - phase pipeline of the vacuum distillation kettle is connected to multiple sets of collection tanks arranged in parallel and capable of switching operations, and the collection tanks are designed with rotary scraper devices.

[0135] (5) Feed the colored crude DMT into a vacuum distillation kettle, and perform vacuum distillation at 210 °C and a pressure of 10 KPa for 30 minutes. The sublimated colorless refined DMT condenses into multiple sets of parallel collection tanks with switchable operation, and after condensation, it is discharged after being treated by a rotary scraper, and then conveyed to a refined DMT storage tank through a screw conveyor; multiple collection tanks are switched for treatment to achieve continuous production of refined DMT; the impurities left after vacuum distillation continuously enter the impurity collection tank; among them, the colorless refined DMT storage tank has a heating function and can heat the colorless refined DMT into a liquid state.

[0136] Before the refined DMT storage tank, multiple sets of parallel recrystallization tanks with switchable operation can be set. Dissolve the DMT after vacuum distillation sublimation-condensation treatment in hot methanol at a dissolution temperature of 55 °C, and then enter the cooling recrystallization tank for recrystallization. The high-purity DMT primary color solid is conveyed to the refined DMT storage tank after being treated by a scraper and heated into a liquid.

[0137] (6) Perform a transesterification reaction on refined DMT with 1,4-butanediol (BDO) and a catalyst; the process parameters of the transesterification reaction are: temperature 155 °C, reaction time 200 min, molar ratio of DMT to BDO 1:6, the catalyst is titanium phthalate and tetra-isopropyl titanate, and the addition amount of the catalyst is 0.1 wt%, based on the mass of DMT.

[0138] (7) Feed the material after the transesterification in step (6) into a flash evaporation device or a vacuum distillation device to distill out the unreacted BDO and gaseous by-products, and BDO and methanol are recycled; collect the transesterification product, namely the primary color BHBT;

[0139] (8) Perform a transesterification reaction on dimethyl carbonate (DMC), BDO and a transesterification catalyst. The reaction by-products methanol and DMC that form an azeotrope with it are taken out through a fractionating column and sent to an extractive distillation tower for separation and recovery; the process parameters of the transesterification reaction are: temperature 155 °C, molar ratio of DMC to BDO 6:1, the catalyst is tetrabutyl titanate, and the addition amount of the catalyst is 0.4 wt%, based on the theoretical mass of BMBC generated.

[0140] (9) Feed the material after the transesterification in step (8) into a flash evaporation device or a vacuum distillation device to distill out DMC and collect BMBC;

[0141] (10) Convey BMBC and BHBT to a pre-condensation reactor and perform a pre-condensation reaction in the presence of a catalyst; the process parameters of the pre-condensation reaction are: temperature 205 °C, vacuum residual pressure 10 KPa; reaction time 70 min, the catalyst is tetrabutyl titanate and tin isooctanoate, and the addition amount of the catalyst is 0.08 wt%, based on the theoretical mass of PBCT generated;

[0142] (11) The material after the pre - condensation reaction is transported to the final condensation reactor for the final condensation reaction to obtain the original - color poly(butylene terephthalate - co - butylene carbonate) (PBCT); the process parameters for the final condensation reaction are as follows: the temperature is 230 °C, the residual vacuum pressure is 110 Pa, and the reaction time is 300 min.

[0143] (12) The original - color poly(butylene terephthalate - co - butylene carbonate) (PBCT) produced after the final condensation reaction is discharged, and after water - cooled casting and pelletizing, the original - color PBCT slices are obtained;

[0144] After testing, the quality indexes of the original - color PBCT slices are as follows: the intrinsic viscosity is 1.21 dl / g, and the L value of whiteness is 87.

[0145] The above - mentioned is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing virgin biodegradable poly(butylene terephthalate)-co-poly(butylene carbonate) from colored waste polyester textiles, characterized in that, It includes the following steps: (1) Compact the colored waste polyester textiles into pellets or friction materials; then convey the materials to an alcoholysis kettle, and simultaneously add ethylene glycol as the alcoholysis agent and a catalyst for alcoholysis. The molar ratio of the colored waste polyester textiles to ethylene glycol is 1:2 - 8; (2) Convey the alcoholyzed materials to a flash evaporation device or a vacuum distillation device to distill out the unreacted ethylene glycol and recycle it, obtaining bis(2-hydroxyethyl) terephthalate as the alcoholysis product; (3) Convey the alcoholysis product, methanol, and the catalyst to an ester exchange reactor I in proportion and conduct an ester exchange reaction under the action of the catalyst; (4) Convey the materials after the ester exchange reaction to a flash evaporation device or a vacuum distillation device to distill out the unreacted methanol and the gaseous by-product ethylene glycol. Methanol and ethylene glycol are recycled, and collect the ester exchange product, i.e., the colored crude dimethyl terephthalate; (5) Feed the colored crude dimethyl terephthalate into a vacuum distillation kettle, and conduct vacuum distillation at 210°C - 240°C and a pressure of 8 - 10 KPa for 15 min - 35 min. After sublimation, it enters a set of switchable parallel collection tanks for sublimation. The sublimated colorless refined DMT is discharged after being treated by a rotary scraper, and then conveyed to a refined dimethyl terephthalate storage tank through a screw conveyor; Multiple collection tanks are switched for treatment to achieve continuous production of refined dimethyl terephthalate; The impurities left after vacuum distillation continuously enter the impurity collection tank; (6) Conduct an ester exchange reaction on the colorless refined dimethyl terephthalate, 1,4-butanediol, and the catalyst in an ester exchange reactor II according to a certain ratio; (7) Feed the materials after the ester exchange in step (6) into a flash evaporation device or a vacuum distillation device to distill out the unreacted 1,4-butanediol and the gaseous by-product methanol. 1,4-butanediol and methanol are recycled; Collect the ester exchange product, i.e., the original color bis(2-hydroxybutyl) terephthalate; (8) Conduct an ester exchange reaction on dimethyl carbonate, 1,4-butanediol, and an ester exchange catalyst in an ester exchange reactor III according to a certain ratio. The reaction by-products methanol and dimethyl carbonate that form an azeotrope with it are taken out through a fractionating column and sent to an extractive distillation tower for separation and recovery; (9) Feed the materials after the ester exchange in step (8) into a flash evaporation device or a vacuum distillation device to distill out dimethyl carbonate, and collect butanediol dimethyl carbonate, and the structural formula is as follows: ； (10) Convey butanediol dimethyl carbonate and the above-mentioned original color bis(2-hydroxybutyl) terephthalate to a pre-condensation reactor in proportion and conduct a pre-condensation reaction in the presence of a catalyst; (11) Convey the materials after the pre-condensation reaction to a final condensation reactor for a final condensation reaction to obtain the original color regenerated poly(butylene terephthalate)-co-poly(butylene carbonate); (12) Discharge the original color poly(butylene terephthalate)-co-poly(butylene carbonate) formed after the final condensation reaction, and obtain the original color poly(butylene terephthalate)-co-poly(butylene carbonate) chips after water cooling, casting, and granulation; The quality indexes of the original color poly(butylene terephthalate)-co-poly(butylene carbonate) chips: intrinsic viscosity 1.10 dl / g - 1.21 dl / g, whiteness L value ≥ 83; The process parameters of the transesterification reaction in step (3) are as follows: the temperature is 55°C to 135°C, the reaction time is 30 min to 240 min, the mass ratio of bis(2-hydroxyethyl) terephthalate to methanol is 1:2 to 5, the catalyst is one or a combination of zinc acetate, manganese acetate, potassium carbonate, cobalt acetate, sodium carbonate, calcium acetate, and sodium hydroxide, and the addition amount of the catalyst is 0.05 wt% to 0.3 wt% based on the mass of bis(2-hydroxyethyl) terephthalate; In step (4), the colored crude DMT is fed into a vacuum distillation kettle. The gas-phase pipeline of the vacuum distillation kettle is connected to multiple sets of collection tanks arranged in parallel and operable in a switchable manner, and the collection tanks are designed with rotary scraper devices; The process parameters of the transesterification reaction in step (6) are as follows: the temperature is 155°C to 225°C, the reaction time is 120 min to 300 min, the molar ratio of DMT to 1,4-butanediol is 1:3 to 15, the catalyst is one or a combination of titanium phthalate, tetraisopropyl titanate, tetramethyl titanate, tetrabutyl titanate, tetraoctyl titanate, titanium fluorosalt, alkoxytin, and zinc acetate, and the addition amount of the catalyst is 0.01 wt% to 0.20 wt% based on the mass of dimethyl terephthalate; The purified dimethyl terephthalate storage tank has a heating function and can heat the purified dimethyl terephthalate to a liquid state; Before the purified dimethyl terephthalate storage tank, multiple groups of recrystallization tanks arranged in parallel and operable in a switchable manner can be provided. The dimethyl terephthalate after sublimation-condensation treatment by vacuum distillation is dissolved in hot methanol at a dissolution temperature of 55°C to 135°C, and then enters a cooling recrystallization tank for recrystallization. The high-purity DMT primary color solid is transported to the purified dimethyl terephthalate storage tank after being treated by a scraper and heated to a liquid.

2. The method according to claim 1, wherein The alcoholysis process parameters in step (1) are as follows: the temperature is 197°C to 256°C, the reaction time is 40 min to 260 min, the mass ratio of colored waste polyester textiles to ethylene glycol is 1:2 to 8, the catalyst is one or a combination of zinc acetate, manganese acetate, cobalt acetate, calcium acetate, and sodium carbonate, and the addition amount of the catalyst is 0.05 wt% to 0.5 wt% based on the mass of colored waste polyester textiles; 3. The method according to claim 1, wherein The process parameters of the transesterification reaction in step (8) are as follows: the temperature is 92°C to 160°C, the molar ratio of dimethyl carbonate to 1,4-butanediol is 2.5 to 8:1, the catalyst is one or a combination of zinc acetate, manganese acetate, cobalt acetate, calcium acetate, sodium carbonate, sodium hydroxide, and tetrabutyl titanate, and the addition amount of the catalyst is 0.01 wt% to 0.5 wt% based on the theoretical mass of BMBC generated; 4. The method according to claim 1, wherein The process parameters of the pre-condensation reaction in step (10) are as follows: the temperature is 185°C to 235°C, the vacuum residual pressure is 1 to 15 KPa; the reaction time is 55 min to 130 min, the catalyst is one or a combination of tin 2-ethylhexanoate, tetrabutyl titanate, and antimony trioxide, and the addition amount of the catalyst is 0.03 wt% to 0.10 wt% based on the theoretical mass of poly(butylene terephthalate)-co-(butylene carbonate) generated.

5. The method according to claim 1, wherein The process parameters of the final condensation reaction in step (11) are as follows: the temperature is 200°C to 245°C, the residual vacuum pressure is 25 to 130 Pa, and the reaction time is 60 min to 360 min.

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