Method and product for preparing regenerated cationic dyeable polyester chips from waste polyester materials

Abstract

The invention discloses a method for preparing regenerated cationic dyeable polyester chips from waste polyester materials and provides products thereof, the method comprising: S1, pretreatment: drying and removing water from the waste polyester materials; S2, heating and melting: the dried waste polyester materials enter a twin-screw system, melt-extrude the raw materials, and devolatilize and remove impurities from the molten waste polyester materials to obtain a polyester melt; S3, depolymerization: the filtered polyester melt enters a depolymerization kettle for depolymerization reaction with ethylene glycol, and after depolymerization, a depolymerization liquid mixed with ethylene terephthalate BHET and ethylene glycol EG is obtained, and the yield of ethylene terephthalate BHET in the depolymerization liquid is more than 98%; S4, polymerization reaction: after the depolymerization liquid is evaporated at normal pressure in a pre-polycondensation kettle to remove excess ethylene glycol, a SIPE solution is added for copolymerization reaction, and then the depolymerization liquid is sent to a polycondensation kettle for polycondensation reaction to obtain a regenerated cationic dyeable polyester chips. The invention has a short process flow, a high product yield, low energy consumption cost, and high product quality.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a method for preparing regenerated cationic dyeable polyester chips from waste polyester materials and a product thereof. Background Art

[0002] The sources of recycled PET in my country are mainly divided into the following three categories: waste polyester beverage bottles, waste polyester packaging films, waste polyester yarns and waste textiles. Among them, waste polyester beverage bottles still account for more than 60%.

[0003] At present, the recycling of waste polyester materials is mainly divided into two categories: chemical method and physical method. The physical method is the main method used in China at this stage. Traditional physical methods include direct opening method and granulation spinning method. The direct opening method is to open polyester textiles into short fibers, and then spin them to produce mops or low-grade blankets, which belongs to the lowest value utilization; the granulation spinning method is to process polyester textiles into cloth foam, and then melt-spin to produce ordinary cotton-type short fibers. It is the most commonly used method. However, the physical method is due to the inevitable thermal degradation of polyester during the recycling process, which leads to a decrease in viscosity, and it cannot effectively remove impurities. The performance of recycled polyester fibers is significantly lower than that of virgin fibers.

[0004] The chemical method is to depolymerize waste polyester into small molecules, such as terephthalic acid (TPA), dimethyl terephthalate (DMT), ethylene glycol terephthalate (BHET), and ethylene glycol (EG). These small molecules can be repolymerized as polyester raw materials after purification to obtain recycled polyester comparable to virgin polyester. However, in the current process, due to the complexity of the raw materials such as waste polyester materials, there are many by-products of depolymerization; and the depolymerization process is not in place, and it cannot be completely depolymerized, which affects the subsequent polymerization, resulting in substandard product quality, and it is currently impossible to achieve commercialization.

[0005] Therefore, those skilled in the art urgently need to develop a method for preparing raw cationic dyeable polyester chips using waste polyester materials as raw materials, which method requires short process flow, high product yield, low energy consumption cost, and high quality of the prepared products. Summary of the invention

[0006] In view of the above-mentioned problems in the prior art, the purpose of the present invention is to provide a method and product for preparing regenerated cationic dyeable polyester chips from waste polyester materials with a short process flow, high product yield and low energy consumption cost. The product obtained by this method has high quality and fully meets the filament-grade quality of the corresponding national standard FZ_T 51003-2011 cationic dyeable polyester chips (CDP).

[0007] In order to achieve the above-mentioned purpose, the present invention provides a method for preparing regenerated cationic dyeable polyester chips from waste polyester materials, which adopts the following technical scheme:

[0008] A method for preparing regenerated cationic dyeable polyester chips from waste polyester materials comprises the following steps:

[0009] S1. Preprocessing:

[0010] Drying and removing water from waste polyester materials;

[0011] S2, heating and melting:

[0012] The dried waste polyester material enters the twin-screw system to melt and extrude the raw material. A vacuum system is installed at the front end of the twin-screw to devolatilize and remove impurities from the molten waste polyester material to obtain a polyester melt.

[0013] S3, depolymerization:

[0014] After precise filtration, the polyester PET melt enters the depolymerization reactor to undergo a full depolymerization reaction with ethylene glycol. After depolymerization, a depolymerization liquid of ethylene terephthalate BHET and ethylene glycol EG is obtained, and the BHET yield in the depolymerization liquid is more than 98%;

[0015] S4. Polymerization reaction:

[0016] After the depolymerization liquid is evaporated at normal pressure in a pre-polycondensation kettle to remove excess ethylene glycol, the SIPE solution is added to carry out copolymerization reaction, and then the depolymerization liquid is sent to a polycondensation kettle for polycondensation reaction to obtain regenerated cationic dyeable polyester chips.

[0017] The raw materials of this technical solution are waste polyester materials (including waste polyester bottle flakes, polyester waste silk, polyester waste textiles, etc.). After pretreatment to remove water and impurities, they are completely depolymerized into BHET monomers, and SIPE solution is added to repolymerize into high-quality cationic dyeable polyester chips. Not only is the overall process route short, but the quality of the prepared products is completely up to the filament grade, the energy cost is low, there are almost no by-products, and the consumption of raw materials and fresh ethylene glycol is small. Among them, SIPE (sodium diethylene glycol sulfonate isophthalate) solution is prepared by the reaction of the third monomer SIPM (sodium dimethyl phthalate-5-sulfonate) and EG (ethylene glycol).

[0018] Preferably, in step S1: the moisture content of the waste polyester material is controlled to be below 100 ppm or between 100-200 ppm through a pre-crystallization drying system, wherein the drying temperature of the pre-crystallization drying system is 140° C.-175° C., and the drying time is 4-8 hours.

[0019] Preferably, in step S2: the heating temperature of the screw is controlled at 255-285° C.; ensuring that the waste polyester material fully forms a PET melt.

[0020] Preferably, in step S2: after the waste polyester material is melted, ethylene glycol is injected into the twin-screw system, and the amount of ethylene glycol added is controlled to account for 0.2-1.5wt% of the melt, so that the melt is reduced in viscosity and homogenized in the twin-screw cavity; a low-viscosity polyester melt is formed, which is convenient for subsequent filtration and impurity removal. For example, a melt filter with a filtration accuracy of 100um can be used for filtration to preliminarily remove a large amount of various impurities in the melt, thereby promoting the reaction efficiency and reliability of subsequent process preparation.

[0021] Preferably, in step S3: the reaction temperature in the depolymerization reactor is controlled at 180-235° C., the reaction time is 30-120 min, and the pressure is controlled at 0.05-0.15 MPa; and / or; the weight ratio of ethylene glycol to the PET melt after impurities are removed is controlled between 1.4:1 and 0.8:1.

[0022] In this embodiment, the ester bond of the polyester chain is more easily broken under the action of ethylene glycol, and more 1, 2, and 3 monomers of BHET can be obtained during the depolymerization process. The 1, 2, and 3 monomers of BHET account for more than 96% of the total amount, which can more effectively promote the alcoholysis reaction of PET and ethylene glycol, so that PET is completely degraded, and the vast majority of the product components are BHET and its oligomers.

[0023] Preferably, in step S4: the normal pressure evaporation temperature is controlled to be 240° C.-265° C., and the time is 20-50 minutes.

[0024] Furthermore, in step S4: the excess evaporated ethylene glycol from the depolymerization reaction and the small molecules in the polymerization reaction are condensed and recovered by the condenser of the pre-condensation reactor, and then enter the ethylene glycol distillation recovery system for distillation. The absolute pressure in the ethylene glycol distillation recovery system is controlled between 8kpa-16kpa, and the distillation temperature is controlled at 140℃-170℃. The high-purity ethylene glycol enters the depolymerization reactor for recycling. The residue is regularly discharged from the bottom of the distillation reactor for export as a raw material for polyester paint, etc. This condensation and distillation step can remove diethylene glycol and some impurities in the process, and the purified ethylene glycol is sent to the depolymerization reactor for recycling.

[0025] Preferably, in step S4: after removing excess ethylene glycol from the pre-condensation reactor, ethylene glycol is first added to cool the BHET, and after cooling, the SIPE solution is added to carry out copolymerization reaction to obtain a prepolymer.

[0026] Further, in step S4: ethylene glycol is added to cool BHET to 220°C-235°C, and then a 40wt% ethylene glycol solution of SIPE is added to carry out copolymerization reaction, the copolymerization reaction time is controlled to be 30-60 minutes, and the amount of SIPE added is 1.5wt%-3.0wt% of the BHET melt.

[0027] Since the temperature of the mixed solution of BHET and EG entering the precondensation reactor in step S3 is lower than 240°C, the mixed solution needs to be heated to about 240°C-265°C in order to evaporate the excess EG in a certain period of time under normal pressure. The copolymerization reaction of SIPE and BHET needs to be controlled at 220-235°C, and adding a small amount of cold EG can achieve the cooling effect. At the same time, the BHET monomer will not undergo a depolymerization side reaction with EG. Therefore, it is more conducive to obtaining high-quality polyester chips.

[0028] Preferably, in step S4: the prepolymer after the copolymerization reaction is completed is fed into a polycondensation kettle, the polycondensation kettle is turned on in a low vacuum mode through a vacuum system, the temperature is controlled to be 270° C.-275° C., the vacuum pressure is an absolute pressure of 1 kpa-1.5 kpa, and the reaction time in the polycondensation kettle is controlled to be 30 minutes-60 minutes to obtain a polycondensate;

[0029] Then, the high vacuum mode is turned on for the polycondensate, and the cooling point is controlled between 270-280°C according to the final reaction temperature. When the viscosity in the polycondensation reactor reaches 0.56dl / g and the reaction temperature finally reaches 295°C-300°C, the polycondensation reaction obtains regenerated cationic dyeable polyester chips.

[0030] Among them, the role of low vacuum mode is to prevent too much polymer from being entrained into the vacuum pipeline in the early stage of the reaction and affecting the operation of the vacuum system. In high vacuum mode, the cooling point is the temperature of the polycondensation kettle when the heat medium heating valve of the polycondensation kettle is closed, that is, the temperature inside the polycondensation kettle when the temperature starts to drop. The higher the vacuum degree in the high vacuum state, the better.

[0031] In this embodiment, the prepolymer is continuously polycondensed to obtain a regenerated cationic dyeable polyester melt with higher purity.

[0032] The present invention also provides a regenerated cationic dyeable polyester chip prepared by the above method, wherein:

[0033] The intrinsic viscosity is 0.56-0.60dl / g (measured by the phenol-tetrachloroethane method with a phenol:tetrachloroethane ratio of 3:2);

[0034] Melting point ≥ 249℃;

[0035] Terminal carboxyl content ≤ 35 mol / t;

[0036] L value ≥ 70;

[0037] b value 2 to 4;

[0038] Ash content ≤ 0.4%.

[0039] It shows that the polyester chips prepared by the chemical method of the present invention are of high quality and the product performance is reliably guaranteed.

[0040] In addition, in the preparation method provided by the present invention, adding a flame retardant in step S4 can also be used to produce flame retardant slices; it can also be used to produce low-viscosity slices; adding a third monomer SIPM and a fourth monomer polyethylene glycol (PEG) in step S4 can also be used to produce low-temperature cationic slices (ECDP).

[0041] The present invention can bring the following beneficial effects:

[0042] 1) The present invention maintains production continuity and simplicity through the sequential coordination of pretreatment, melting, viscosity reduction, filtration, depolymerization and polymerization steps; due to the use of the ethylene glycol depolymerization process, the depolymerization is more complete and thorough, and most of the products are BHET and its oligomers, which improves the quality of the products prepared by subsequent polymerization reactions, is suitable for large-scale commercial industrial production, and has obvious economic value.

[0043] 2) The process of the present invention can also realize repeated recycling of the raw material ethylene glycol, thereby improving the recycling rate of resources and being more energy-saving and environmentally friendly.

[0044] 3) The slices produced by the present invention are not only of excellent quality but also of lower cost, further reducing the manufacturing cost of the chemical production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the process of the preparation method of the present invention.

[0046] The meanings of the symbols in the figure are as follows:

[0047] 1- Pre-crystallization and drying system; 2- Twin screw system; 3- Vacuum system; 4- Depolymerization kettle; 5- Pre-polycondensation kettle; 6- Polycondensation kettle. DETAILED DESCRIPTION

[0048] The following will be combined with specific embodiments to clearly and completely describe the technical solutions in the present invention. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and cannot be used to limit the protection scope of the present invention.

[0049] The present invention provides a method for preparing regenerated cationic dyeable polyester chips from waste polyester materials, comprising the following steps:

[0050] S1. Preprocessing:

[0051] Drying and removing water from waste polyester materials;

[0052] S2, heating and melting:

[0053] The dried waste polyester material enters the twin-screw system to melt and extrude the raw material. A vacuum system (the vacuum degree can be optimally set to -0.98MPa) is installed at the front end of the twin-screw to devolatilize and remove impurities from the molten waste polyester material to obtain a polyester melt.

[0054] S3, depolymerization:

[0055] Reaction formula: PET+(n-1)EG→n BHET

[0056] After precise filtration, the polyester melt enters the depolymerization reactor and undergoes a full depolymerization reaction with ethylene glycol. After depolymerization, a depolymerization liquid containing ethylene terephthalate BHET and ethylene glycol EG is obtained, and the yield of BHET in the depolymerization liquid is more than 98%;

[0057] S4. Polymerization reaction:

[0058] Reaction formula: SIPE+BHET→CDP

[0059] After the depolymerization liquid is evaporated at normal pressure in a pre-polycondensation kettle to remove excess ethylene glycol, the SIPE solution is added to carry out copolymerization reaction, and then the depolymerization liquid is sent to a polycondensation kettle for polycondensation reaction to obtain regenerated cationic dyeable polyester chips.

[0060] As a preferred embodiment, in step S1, the moisture content of the waste polyester material is controlled to be below 100 ppm or between 100-200 ppm through a pre-crystallization drying system, wherein the drying temperature of the pre-crystallization drying system is 140°C-175°C and the drying time is 4-8 hours.

[0061] As another preferred embodiment, in step S2: the heating temperature of the screw is controlled to be 255-285°C.

[0062] As another preferred embodiment, in step S2: after the waste polyester material is melted, ethylene glycol is injected into the twin-screw system, and the amount of ethylene glycol added is controlled to be 0.2-1.5wt% of the melt, so that the melt is reduced in viscosity and homogenized in the twin-screw cavity.

[0063] As another preferred embodiment, in step S3: the reaction temperature in the depolymerization reactor is controlled at 180-235°C, the reaction time is about 30-120 min min, and the pressure is controlled at 0.05-0.15 MPa. In addition, the weight ratio of ethylene glycol to the PET melt after impurities are removed is controlled between 1.4:1 and 0.8:1.

[0064] In addition, in step S3, the atmospheric evaporation temperature is controlled to be 240°C-265°C, and the time is 20-50 minutes, so as to facilitate the evaporation and recycling of excess ethylene glycol. More preferably, the excess evaporated ethylene glycol from the depolymerization reaction and the small molecules formed by the polymerization reaction are condensed and recovered by the condenser of the pre-condensation reactor, and then enter the ethylene glycol distillation recovery system for distillation, and the absolute pressure is controlled between 8kpa-16kpa, and the distillation temperature is controlled at 140°C-170°C, so that high-purity ethylene glycol enters the depolymerization reactor for recycling. The residue is regularly discharged from the bottom of the distillation reactor for export as raw materials for polyester paint, etc. This condensation and distillation step can remove diethylene glycol and some impurities in the process, and the purified ethylene glycol is used to be sent to the depolymerization reactor for recycling.

[0065] As another preferred embodiment, in step S4, 250 ml to 450 ml of ethylene glycol is first added to the pre-condensation reactor to cool it down, and then the SIPE solution is added after cooling to carry out copolymerization reaction to obtain a prepolymer.

[0066] More preferably, in step S4: the temperature in the pre-condensation reactor is lowered to 220°C-235°C and then 40wt% of ethylene glycol solution of SIPE is added for copolymerization reaction, the copolymerization reaction time is controlled to be 30-60 minutes, and the amount of SIPE added is 1.5%-3.0% of the BHET melt.

[0067] As another preferred embodiment, the prepolymer after the copolymerization reaction is completed is fed into a polycondensation kettle, a low vacuum mode is turned on by a vacuum system, the temperature is controlled to be 270° C.-275° C., the vacuum pressure is 1 kpa-1.5 kpa absolute pressure, and the reaction time in the polycondensation kettle is controlled to be 30 minutes-60 minutes to obtain a polycondensate;

[0068] The high vacuum mode is turned on for the polycondensate, and the cooling point is controlled between 270-280°C according to the final reaction temperature. When the viscosity in the polycondensation reactor reaches 0.58dl / g and the reaction temperature finally reaches 295°C-300°C, the polycondensation reaction obtains regenerated cationic dyeable polyester chips.

[0069] The regenerated cationic dyeable polyester chips prepared by the method of the above embodiment have the following quality indicators: intrinsic viscosity of 0.58 dl / g;

[0070] Melting point ≥ 249℃;

[0071] Terminal carboxyl content ≤ 35 mol / t;

[0072] L value ≥ 70;

[0073] b value 2 to 4;

[0074] Ash content ≤ 0.4. Example 1

[0075] Combination Figure 1 This embodiment is a method for preparing regenerated cationic dyeable polyester chips from waste polyester materials, comprising the following steps:

[0076] S1. Preprocessing:

[0077] The waste polyester material is dried and dehydrated by the pre-crystallization drying system 1, and the drying temperature in the pre-crystallization drying system is 160° C. and the drying time is 6 hours to control the moisture content of the waste polyester material to be below 100 ppm;

[0078] S2, heating and melting:

[0079] The dried waste polyester material enters the twin-screw system 2, and the heating temperature of the screw is controlled to be 265°C. The raw material is melted and extruded. A vacuum system 3 (the vacuum degree can be optimally set to -0.98MPa) is installed at the front end of the twin screw to devolatilize and remove impurities from the molten waste polyester material. After the waste polyester material is melted, ethylene glycol (EG) is forcibly injected, and the amount of ethylene glycol added is controlled to account for 0.7wt% of the melt, so that the melt is forced to reduce viscosity (from 0.75 to about 0.35) and homogenize in the twin-screw cavity to obtain a low-viscosity polyester melt, which is convenient for more efficient filtering and impurity removal after exiting the screw.

[0080] S3, depolymerization:

[0081] After precise filtration, the low-viscosity polyester melt enters the depolymerization reactor 4 to fully depolymerize with ethylene glycol, and the reaction temperature in the depolymerization reactor is controlled at 210°C, the reaction time is about 60 minutes, and the pressure is controlled at 0.1 MPa; and the weight ratio of ethylene glycol to the PET melt after impurities are removed is controlled at 1.1:1; after depolymerization, a depolymerization liquid of ethylene terephthalate BHET and ethylene glycol EG is obtained, and the yield of ethylene terephthalate BHET in the depolymerization liquid reaches 100%, of which the mono-, di-, and tri-monomers of BHET account for 96% of the total, and the tetra-, penta-, and hexa-monomers account for 4% of the total;

[0082] S4. Polymerization reaction:

[0083] The depolymerization liquid is evaporated at normal pressure in the precondensation kettle, and the normal pressure evaporation temperature is controlled to be 260°C for 30 minutes. After removing the excess ethylene glycol, the BHET melt after evaporating the ethylene glycol is further filtered and impurities are removed through a monomer filter and enter the precondensation kettle 5. 350 ml of ethylene glycol is first added to the precondensation kettle to cool it down. After cooling to 228°C, 60wt% of SIPE / ethylene glycol solution is added for copolymerization. The copolymerization time is controlled to be 45 minutes. The amount of SIPE added is 2% of the BHET melt, and the prepolymer is obtained by reaction. In step S3, since the temperature of the mixed solution of BHET and EG entering the precondensation kettle is about 210°C, the excess EG in it needs to be evaporated out within a certain period of time under normal pressure, and the mixed solution needs to be heated to about 260°C. The copolymerization reaction of SIPE and BHET needs to be controlled at 228°C, and a small amount of cold EG can achieve a cooling effect. At the same time, the BHET monomer will not undergo a depolymerization side reaction with EG. Thus, it is more conducive to obtaining high-quality polyester chips; the prepolymer after the copolymerization reaction is completed is sent to the polycondensation reactor 6, and the low vacuum mode is turned on by the vacuum system, the temperature is controlled to be 272°C, the vacuum pressure is 1.2kpa absolute pressure, and the reaction time in the polycondensation reactor is controlled to be 45 minutes to obtain a polycondensate;

[0084] The high vacuum mode was turned on for the polycondensate, and the cooling point was controlled at 275°C according to the final reaction temperature. When the viscosity in the polycondensation reactor reached 0.58 dl / g and the reaction temperature finally reached 298°C, the polycondensation reaction obtained regenerated cationic dyeable polyester chips.

[0085] Among them, after depolymerization in step S3, ethylene glycol is evaporated, and the excess evaporated ethylene glycol and small molecules formed by the polymerization reaction are condensed and recovered by the condenser of the pre-condensation reactor 5, and then enter the ethylene glycol distillation recovery system (not shown in the figure) for distillation. The absolute pressure is controlled between 8kpa-16kpa, and the distillation temperature is controlled between 140°C-170°C to obtain high-purity ethylene glycol, which is sent to the depolymerization reactor for recycling.

[0086] The performance parameters of the obtained regenerated cationic dyeable polyester chips are:

[0087] The intrinsic viscosity is 0.58 dl / g; the melting point is 249°C; the terminal carboxyl content is 31 mol / t; the L value is 75; the b value is 2.5; and the ash content is 0.1%.

[0088] Example 2

[0089] The steps of this embodiment are basically the same as those of embodiment 1, except that:

[0090] S1. Pretreatment: The drying temperature in the pre-crystallization drying system is 140°C and the drying time is 8 hours to control the moisture content of the waste polyester material to be below 100ppm;

[0091] S2. During heating and melting: the heating temperature of the screw is controlled to be 255°C; the amount of ethylene glycol added is controlled to account for 0.2wt% of the melt, so that the melt is forced to reduce viscosity (from 0.75 to about 0.45) and homogenize in the twin-screw cavity to obtain a low-viscosity polyester melt, which is convenient for more efficient filtering and impurity removal after exiting the screw;

[0092] S3, during depolymerization: the reaction temperature in the depolymerization reactor is controlled at 180°C, the reaction time is about 120min, and the pressure is controlled at 0.08Mpa; and the weight ratio of ethylene glycol to the PET melt after impurities are removed is controlled at 1.4:1; after depolymerization, a depolymerization liquid of ethylene terephthalate BHET and ethylene glycol EG is obtained, and the yield of ethylene terephthalate BHET in the depolymerization liquid reaches 100%, wherein the mono-, di- and tri-monomers of BHET account for 95% of the total, and the tetra-, penta- and hexa-monomers account for 5% of the total;

[0093] S4, during the polymerization reaction: the depolymerization liquid is controlled to have a normal pressure evaporation temperature of 240°C for 50 minutes, and then enters the precondensation reactor 5 after removing excess ethylene glycol, and 250 ml of ethylene glycol is first added to the precondensation reactor to cool it down, and after cooling it down to 220°C, 60 wt% of SIPE / ethylene glycol solution is added to carry out copolymerization reaction, and the copolymerization reaction time is controlled to be 60 minutes, and the amount of SIPE added is 1.5 wt% of the BHET melt, and the reaction obtains a prepolymer;

[0094] The prepolymer after the copolymerization reaction is completed is sent to the polycondensation reactor 6, and the low vacuum mode is turned on by the vacuum system, the temperature is controlled to be 270° C., the vacuum pressure is an absolute pressure of 1 kPa, and the reaction time in the polycondensation reactor is controlled to be 30 minutes to obtain a polycondensate;

[0095] The high vacuum mode was turned on for the polycondensate, and the cooling point was controlled at 270°C according to the final reaction temperature. When the viscosity in the polycondensation reactor reached 0.56 dl / g and the reaction temperature finally reached 295°C, the polycondensation reaction obtained regenerated cationic dyeable polyester chips.

[0096] The performance parameters of the obtained regenerated cationic dyeable polyester chips are:

[0097] The intrinsic viscosity is 0.56 dl / g; the melting point is 248°C; the terminal carboxyl content is 29 mol / t; the L value is 74; the b value is 4; and the ash content is 0.1%.

[0098] Example 3

[0099] The steps of this embodiment are basically the same as those of embodiment 1, except that:

[0100] S1. Pretreatment: The drying temperature in the pre-crystallization drying system is 175°C and the drying time is 4 hours to control the moisture content of the waste polyester material to be below 100ppm;

[0101] S2, during heating and melting: the heating temperature of the screw is controlled to be 285°C; the amount of ethylene glycol added is controlled to account for 1.5wt% of the melt, so that the melt is forced to reduce viscosity (from 0.75 to about 0.3) and homogenize in the twin-screw cavity to obtain a low-viscosity polyester melt, which is convenient for more efficient filtering and impurity removal after exiting the screw;

[0102] S3, during depolymerization: the reaction temperature in the depolymerization reactor is controlled at 235°C, the reaction time is about 30 minutes, and the pressure is controlled at 0.15 MPa; and the weight ratio of ethylene glycol to the PET melt after impurities are removed is controlled at 0.8:1; after depolymerization, a depolymerization liquid of ethylene terephthalate BHET and ethylene glycol EG is obtained, and the yield of ethylene terephthalate BHET in the depolymerization liquid reaches 100%, wherein the mono-, di- and tri-monomers of BHET account for 97% of the total, and the tetra-, penta- and hexa-monomers account for 3% of the total;

[0103] S4, during the polymerization reaction: the depolymerization liquid is controlled to evaporate at 265°C at normal pressure for 20 minutes, and then enters the pre-condensation reactor 5 after removing excess ethylene glycol, 450 ml of ethylene glycol is first added to the pre-condensation reactor to cool it down, and after cooling to 235°C, 60 wt% of SIPE / ethylene glycol solution is added to carry out copolymerization reaction, and the copolymerization reaction time is controlled to be 60 minutes, and the amount of SIPE added is 3 wt% of the BHET melt, and the prepolymer is obtained by reaction;

[0104] The prepolymer after the copolymerization reaction is completed is sent to the polycondensation reactor 6, and the low vacuum mode is turned on by the vacuum system, the temperature is controlled to be 275° C., the vacuum pressure is controlled to be an absolute pressure of 1.5 kPa, and the reaction time in the polycondensation reactor is controlled to be 60 minutes to obtain a polycondensate;

[0105] The high vacuum mode was turned on for the polycondensate, and the cooling point was controlled at 270°C according to the final reaction temperature. When the viscosity in the polycondensation reactor reached 0.60 dl / g and the reaction temperature finally reached 300°C, the polycondensation reaction obtained regenerated cationic dyeable polyester chips.

[0106] The performance parameters of the obtained regenerated cationic dyeable polyester chips are:

[0107] The intrinsic viscosity is 0.60dl / g; the melting point is 252°C; the terminal carboxyl content is 28mol / t; the L value is 78; the b value is 2.0; and the ash content is 0.1%.

[0108] Comparative Example 1

[0109] The steps of this embodiment are basically the same as those of embodiment 1, except that:

[0110] S2. During heating and melting: the heating temperature of the screw is controlled to be 250°C; the amount of ethylene glycol added is controlled to account for 0.7wt% of the melt, so that the melt is forced to reduce viscosity (from 0.75 to about 0.5) and homogenize in the twin-screw cavity to obtain a low-viscosity polyester melt, which is convenient for more efficient filtering and impurity removal after exiting the screw;

[0111] S3, during depolymerization: the low-viscosity polyester melt after precise filtration enters the depolymerization reactor 4 for sufficient depolymerization reaction with ethylene glycol, the reaction temperature in the depolymerization reactor is controlled at 210°C, the reaction time is about 60min, and the pressure is controlled at 0.1Mpa; and the weight ratio of ethylene glycol to the PET melt after impurities are removed is controlled at 1.1:1; after depolymerization, a depolymerization liquid of a mixture of ethylene terephthalate BHET and ethylene glycol EG is obtained, and the yield of ethylene terephthalate BHET in the depolymerization liquid reaches 100%, of which the mono-, di- and tri-monomers of BHET account for 92% of the total, and the tetra-, penta- and hexa-monomers account for 8% of the total.

[0112] The performance parameters of the obtained regenerated cationic dyeable polyester chips are:

[0113] The intrinsic viscosity is 0.53 dl / g; the melting point is 249°C; the terminal carboxyl content is 30 mol / t; the L value is 70; the b value is 3.5; and the ash content is 0.1%.

[0114] Comparative Example 2

[0115] The steps of this embodiment are basically the same as those of embodiment 2, except that:

[0116] S3, during depolymerization: the reaction temperature in the depolymerization reactor is controlled at 180°C, the reaction time is about 120min, and the pressure is controlled at 0.08Mpa; and the weight ratio of ethylene glycol to the PET melt after impurities are removed is controlled at 1.5:1; after depolymerization, a depolymerization liquid of ethylene terephthalate BHET and ethylene glycol EG is obtained, and the yield of ethylene terephthalate BHET in the depolymerization liquid reaches 100%, wherein the mono-, di- and tri-monomers of BHET account for 95% of the total, and the tetra-, penta- and hexa-monomers account for 5% of the total.

[0117] The performance parameters of the obtained regenerated cationic dyeable polyester chips are:

[0118] The intrinsic viscosity is 0.56 dl / g; the melting point is 249 ℃; the terminal carboxyl content is 31 mol / t; the L value is 71; the b value is 4.0; and the ash content is 0.1%.

[0119] Comparative Example 3

[0120] The steps of this embodiment are basically the same as those of embodiment 3, except that:

[0121] In step S3, depolymerization: the reaction temperature in the depolymerization kettle is controlled at 235° C., the reaction time is about 90 min, and the pressure is controlled at 0.15 MPa; and the weight ratio of ethylene glycol to the PET melt after impurities are removed is controlled at 0.7:1; after depolymerization, a depolymerization liquid of ethylene terephthalate BHET and ethylene glycol EG is obtained, and the yield of ethylene terephthalate BHET in the depolymerization liquid reaches 100%, wherein the mono-, di-, and tri-monomers of BHET account for 90% of the total amount, and the tetra-, penta-, and hexa-monomers account for 10% of the total amount.

[0122] The performance parameters of the obtained regenerated cationic dyeable polyester chips are:

[0123] The intrinsic viscosity is 0.52dl / g; the melting point is 248°C; the terminal carboxyl content is 28mol / t; the L value is 73; the b value is 3.8; and the ash content is 0.1%.

[0124] It should be noted that the above embodiments can be freely combined as needed. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention.

Claims

1. A method for preparing regenerated cationic dyeable polyester chips from waste polyester materials, characterized in that: The steps include: S1. Preprocessing: Drying and removing water from waste polyester materials; The moisture content of the waste polyester material is controlled to be below 100 ppm or between 100-200 ppm by a pre-crystallization drying system, wherein the drying temperature of the pre-crystallization drying system is 140° C.-175° C. and the drying time is 4-8 hours; S2, heating and melting: The dried waste polyester material enters the twin-screw system to melt and extrude the raw material. A vacuum system is installed at the front end of the twin-screw to devolatilize and remove impurities from the molten waste polyester material to obtain a polyester melt. In step S2, the heating temperature of the screw is controlled at 255-285° C.; and / or; In step S2, the waste polyester material is melted and then ethylene glycol is injected into the twin-screw system, and the amount of ethylene glycol added is controlled to be 0.2-1.5wt% of the melt, so that the melt is reduced in viscosity and homogenized in the twin-screw cavity; S3, depolymerization: The filtered polyester PET melt enters the depolymerization reactor to undergo a full depolymerization reaction with ethylene glycol, and a depolymerization liquid of ethylene terephthalate BHET and ethylene glycol EG is obtained after depolymerization, and the BHET yield in the depolymerization liquid is more than 98%; In step S3, the reaction temperature in the depolymerization reactor is controlled at 180-235° C., the reaction time is 30-120 min, and the pressure is controlled at 0.05-0.15 MPa; and / or; In step S3, the weight ratio of ethylene glycol to the PET melt after impurities are removed is controlled to be between 1.4:1 and 0.8:1; S4. Polymerization reaction: After the depolymerization liquid is evaporated in a pre-polycondensation kettle at normal pressure to remove excess ethylene glycol, the SIPE solution is added to carry out copolymerization reaction, and then the depolymerization liquid is sent to a polycondensation kettle for polycondensation reaction to obtain regenerated cationic dyeable polyester chips; Control the atmospheric pressure evaporation temperature to 240℃-265℃ and the time to 20-50 minutes; The excess evaporated ethylene glycol from the depolymerization reaction and the small molecules in the polymerization reaction are condensed and recovered in the condenser of the pre-condensation reactor, and then enter the ethylene glycol distillation recovery system for rectification. The absolute pressure in the ethylene glycol distillation recovery system is controlled between 8kpa-16kpa, and the distillation temperature is controlled between 140℃-170℃. The high-purity ethylene glycol is obtained and enters the depolymerization reactor for recycling; After removing excess ethylene glycol from the precondensation reactor, ethylene glycol is first added to cool the BHET, and after cooling, SIPE solution is added to carry out copolymerization reaction to obtain a prepolymer; Add ethylene glycol to cool BHET to 220-235°C, then add ethylene glycol solution of SIPE with a concentration of 40wt% to carry out copolymerization reaction. The copolymerization reaction time is controlled to be 30-60 minutes, and the amount of SIPE added is 1.5wt%-3.0wt% of the BHET melt; The prepolymer after the copolymerization reaction is completed is sent to the polycondensation kettle, and the low vacuum mode of the polycondensation kettle is turned on through the vacuum system, the temperature is controlled to be 270°C-275°C, the vacuum pressure is 1kpa-1.5kpa absolute pressure, and the reaction time in the polycondensation kettle is controlled to be 30 minutes-60 minutes to obtain a polycondensate; The high vacuum mode is turned on for the polycondensate, and the cooling point is controlled between 270-280°C according to the final reaction temperature. When the viscosity in the polycondensation reactor reaches 0.56 dl / g and the reaction temperature finally reaches 295°C-300°C, the polycondensation reaction obtains the regenerated cationic dyeable polyester chips; Regenerated cationic dyeable polyester chips: The intrinsic viscosity is 0.56-0.60dl / g; Melting point ≥ 249℃; Terminal carboxyl content ≤35 mol / t; L value ≥ 70; b value 2 to 4; Ash content ≤ 0.4.

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