Bis(2-hydroxyethyl) terephthalate and polybutylene terephthalate, and preparation method and application thereof

Abstract

The application relates to the technical field of chemical recycling of waste polyesters, and discloses bis(2-hydroxyethyl) terephthalate and polybutylene terephthalate as well as a preparation method and application thereof. The method comprises the following steps: in the presence of a first catalyst, carrying out a depolymerization reaction on polyesters containing polyethylene terephthalate and alcohol, and then sequentially carrying out solid-liquid separation, decolorization and crystallization on a reaction system obtained through the reaction. The polybutylene terephthalate product prepared by the method has the characteristics of good color and low metal ion content. The product does not need to be converted into terephthalic acid monomers, and can be directly used for preparing regenerated PBT polyesters. The polyesters also have the characteristics of good color, and also have high viscosity.

Description

Technical Field

[0001] This invention relates to the field of chemical recycling technology for waste polyester, specifically to a bis(2-hydroxyethyl) terephthalate and polybutylene terephthalate, their preparation methods, and applications. Background Technology

[0002] Polyethylene terephthalate (PET) possesses excellent mechanical and processing properties. In 2023, my country's PET production capacity reached 7,442 tons, primarily used in fibers, plastic bottles, and films. However, due to its difficulty in natural degradation, the amount of waste generated after its lifespan is enormous, with a recycling rate of less than 10%. High-quality bottle flakes are mainly recycled physically, while other aged bottles, flakes containing large amounts of additives or colored materials, and fibers are discarded in large quantities, leading to environmental pollution. As global awareness of the pollution problems caused by waste polymer materials deepens, the polymer recycling industry has demonstrated significant economic value and environmental benefits.

[0003] Polybutylene terephthalate (PBT) is one of the five major engineering plastics, possessing excellent mechanical properties, processing performance, and electrical insulation. It is widely used in automobiles, machinery, precision instrument components, electronics, and textiles. Utilizing waste PET polyester materials to prepare recycled PBT polyester can transform waste polyester into high-value-added products, not only reducing environmental pollution but also creating significant economic value, aligning with the concept of green development. CN113549200B directly uses 1,4-butanediol to chemically depolymerize PBT polyester under high-temperature conditions to prepare recycled PBT polyester. However, this method has two drawbacks: first, the production and consumption of PBT polyester are far less than that of PET polyester, making it difficult to obtain waste PBT polyester raw materials for stable plant operation; second, under the reaction conditions of this method, 1,4-butanediol easily dehydrates and cyclizes to generate large amounts of tetrahydrofuran, which is flammable and explosive. This would cause a rapid increase in pressure within the depolymerization reactor, requiring an upgrade in the explosion-proof rating of the production equipment and rapidly increasing investment, which is detrimental to industrial production.

[0004] Therefore, in order to solve the above-mentioned problems, there is a need for bis(2-hydroxyethyl) terephthalate and polybutylene terephthalate, as well as their preparation methods and applications. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of insufficient waste polyester recovery rate, high risk of PET material preparation process by direct alcoholysis with 1,4-butanediol, low viscosity of PBT material, unsatisfactory L and b values, and high purification difficulty in the existing technology, and to provide a method for preparing bis(2-hydroxyethyl) terephthalate and polybutylene terephthalate, and their application.

[0006] To achieve the above objectives, the present invention provides a method for reducing the metal content in bis(2-hydroxyethyl) terephthalate products, characterized in that the method comprises: in the presence of a first catalyst, mixing a polyester containing polyethylene terephthalate with an alcohol to carry out a depolymerization reaction, and then sequentially performing solid-liquid separation, decolorization and crystallization on the reaction system obtained from the reaction.

[0007] The second aspect of the present invention provides a bis(2-hydroxyethyl) terephthalate product prepared by the method described in one aspect of the present invention.

[0008] The third aspect of the present invention provides a bis(2-hydroxyethyl) terephthalate product, characterized in that the purity of the bis(2-hydroxyethyl) terephthalate product is not less than 97 wt%, and the metal ion weight content is not greater than 50 ppm.

[0009] A fourth aspect of the present invention provides a method for preparing polybutylene terephthalate, characterized in that the method comprises:

[0010] (1) In the presence of a second catalyst, the bis(2-hydroxyethyl) terephthalate sample was contacted with 1,4-butanediol and subjected to transesterification.

[0011] (2) In the presence of a third catalyst, the product obtained from the transesterification reaction in step (1) is subjected to a polymerization reaction;

[0012] The purity of the bis(2-hydroxyethyl) terephthalate sample is not less than 97 wt%, and the metal ion weight content is not greater than 50 ppm.

[0013] The fifth aspect of the present invention provides a polybutylene terephthalate product prepared by the method described in the fourth aspect of the present invention.

[0014] The sixth aspect of this invention provides a polybutylene terephthalate product, characterized in that the intrinsic viscosity of the product is not less than 0.6 dL / g under the solvent conditions of phenol: 1,1,2,2-tetrachloroethane = 1:1, the L value is not less than 70, and the b value is not greater than 5.

[0015] The seventh aspect of the present invention provides the use of the polybutylene terephthalate product described in the sixth aspect of the present invention in at least one of the fields of automobiles, machinery, precision instrument components, electronic appliances and textiles.

[0016] The eighth aspect of the present invention provides the application of the method described in the first aspect of the present invention in at least one of improving the purity of bis(2-hydroxyethyl) terephthalate, reducing the metal ion content of bis(2-hydroxyethyl) terephthalate, and improving the color of polybutylene terephthalate.

[0017] The ninth aspect of the present invention provides the application of the product described in the second aspect of the present invention in improving the color of polybutylene terephthalate.

[0018] The tenth aspect of the present invention provides the application of the method described in the fourth aspect of the present invention in improving the color of at least one of polybutylene terephthalate.

[0019] Through the above technical solution, the present invention has the following beneficial effects:

[0020] (1) The bis(2-hydroxyethyl) terephthalate (BHET) sample prepared by this invention has a purity ≥97%, a melting point of 109℃, a color value L≥90, b≤5, and a metal ion content ≤30ppm. BHET with high purity, low metal ion residue and ideal color value is less likely to cause an increase in the yellow index of PBT polyester and an increase in side reactions in subsequent regeneration polymerization, thus preparing regenerated PBT polyester with the required color and intrinsic viscosity.

[0021] (2) This invention uses BHET to directly prepare recycled PBT polyester without first converting the BHET into terephthalic acid monomer. The recycled PBT polyester prepared has a PBT intrinsic viscosity ≥0.6dL / g, L value ≥70, and b value ≤5 under the solvent conditions of phenol:tetrachloroethane = 1:1, and has a good color. It realizes the chemical recycling and reuse of waste PET polyester to prepare high-performance PBT polyester, which has good economic benefits. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] As mentioned above, the present invention provides a method for reducing the metal content in bis(2-hydroxyethyl) terephthalate products, characterized in that the method includes: in the presence of a first catalyst, mixing a polyester containing polyethylene terephthalate with an alcohol to carry out a depolymerization reaction, and then sequentially performing solid-liquid separation, decolorization and crystallization on the reaction system obtained from the reaction.

[0024] According to a preferred embodiment of the present invention, the first catalyst and the components and their mass ratios described herein correspond to the definitions in patent applications 202310836415.1 and / or 202310841232.9, which are hereby incorporated in their entirety by reference.

[0025] In some embodiments of the present invention, preferably, the first catalyst is selected from titanium-containing compounds and / or titanium-containing compositions, more preferably from at least one of organotitanium compounds, inorganic titanium compounds, titanium-silicon composite catalysts and titanium-rare earth composite catalysts, and more preferably from at least one of tetraethyl titanate, tetrabutyl titanate, tetraisopropyl titanate, tetraisobutyl titanate, titanium acetylacetone oxide, di(acetylacetone)diisopropyl titanate, titanium glycol, titanium phosphate, silicate-modified alkyl titanate and diol-modified alkyl titanate titanium.

[0026] In some embodiments of the present invention, preferably, the silicate-modified alkyl titanate is selected from at least one of n-butyl silicate-modified alkyl titanate, n-ethyl silicate-modified alkyl titanate, and n-propyl silicate-modified alkyl titanate.

[0027] In some embodiments of the present invention, preferably, the polyester is selected from polyesters with a polyethylene terephthalate (PET) content of greater than 70 wt% (more preferably 80-100 wt%).

[0028] In this invention, the content of polyethylene terephthalate (PET) can be determined by nuclear magnetic resonance hydrogen spectroscopy.

[0029] In some embodiments of the present invention, preferably, the depolymerization reaction is carried out in the presence of a protective gas. The protective gas can be a common gas that provides an inert atmosphere.

[0030] In some embodiments of the present invention, preferably, the protective gas is selected from nitrogen and / or argon.

[0031] In some embodiments of the present invention, preferably, the polyester containing polyethylene terephthalate is pulverized into particles with a diameter of 0.1-3 cm.

[0032] In some embodiments of the present invention, preferably, the particles are dried until their moisture content is no more than 1 wt%.

[0033] In this invention, the moisture content is calculated by drying the PET in an oven, weighing it, and then drying until the PET weight is no longer lost.

[0034] In some embodiments of the present invention, preferably, the amount of the first catalyst is 0.01-0.5 wt%, more preferably 0.02-0.3 wt%, and more preferably 0.05-0.2 wt%, based on the total weight of the polyester.

[0035] In some embodiments of the present invention, preferably, the mass ratio of the polyester to the alcohol is 1:2-10, more preferably 1:2-6.

[0036] Preferably, the alcohol is selected from diols, and more preferably from at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol.

[0037] In some embodiments of the present invention, preferably, the temperature of the depolymerization reaction is 200-240°C, more preferably 200-220°C.

[0038] In some embodiments of the present invention, preferably, the pressure of the depolymerization reaction is 0.2-0.6 mPa, more preferably 0.25-0.4 mPa.

[0039] In some embodiments of the present invention, preferably, the depolymerization reaction takes 2-5 hours, more preferably 2.5-4 hours.

[0040] In some embodiments of the present invention, preferably, the method of mixing the polyester containing polyethylene terephthalate with the alcohol includes stirring.

[0041] In some embodiments of the present invention, preferably, the stirring speed is 50-400 rpm, more preferably 100-300 rpm.

[0042] In some embodiments of the present invention, preferably, the temperature for solid-liquid separation is 60-80℃, more preferably 68-80℃; and the time is 3-15 min, more preferably 5-10 min.

[0043] In some embodiments of the present invention, preferably, the decolorization method includes mixing the filtrate obtained after solid-liquid separation with activated carbon.

[0044] In some embodiments of the present invention, preferably, the mixing temperature is 60-80°C, more preferably 68-75°C; the mixing time is 0.5-4h, more preferably 0.5-2h; and the amount of activated carbon used is 2-40g relative to 1L of filtrate.

[0045] In this invention, the crystallization method can be cooling crystallization, and the crystallization conditions can include: a temperature of 0-4℃ and a time of 1-8h.

[0046] The second aspect of the present invention provides a bis(2-hydroxyethyl) terephthalate product prepared by the method described in one aspect of the present invention.

[0047] The third aspect of the present invention provides a bis(2-hydroxyethyl) terephthalate product, characterized in that the purity of the bis(2-hydroxyethyl) terephthalate product is not less than 97 wt%, and the metal ion weight content is not greater than 50 ppm.

[0048] In this invention, the purity of the bis(2-hydroxyethyl) terephthalate can be determined by testing with 1H NMR spectroscopy and high performance liquid chromatography.

[0049] In this invention, the metal ions refer to Zn, Sb, and Ti, and the metal ions can be detected by inductively coupled plasma mass spectrometry.

[0050] In some embodiments of the present invention, preferably, the purity of the bis(2-hydroxyethyl) terephthalate product is not less than 98 wt%.

[0051] In some embodiments of the present invention, preferably, the metal ion weight content of the bis(2-hydroxyethyl) terephthalate product is not greater than 20 ppm.

[0052] A fourth aspect of the present invention provides a method for preparing polybutylene terephthalate, characterized in that the method comprises:

[0053] (1) In the presence of a second catalyst, the bis(2-hydroxyethyl) terephthalate sample was contacted with 1,4-butanediol and subjected to transesterification.

[0054] (2) In the presence of a third catalyst, the product obtained from the transesterification reaction in step (1) is subjected to a polymerization reaction;

[0055] The purity of the bis(2-hydroxyethyl) terephthalate sample is not less than 97 wt%, and the metal ion weight content is not greater than 50 ppm.

[0056] In some embodiments of the present invention, preferably, the second catalyst is selected from a metal salt, more preferably from at least one of sodium acetate, magnesium acetate, zinc acetate and zinc acetate dihydrate, and more preferably zinc acetate.

[0057] In some embodiments of the present invention, preferably, the third catalyst is selected from at least one of titanium-containing compounds, germanium-containing compounds, and tin-containing compounds, more preferably from at least one of tetrabutyl titanate, isopropyl titanate, tetraethyl titanate, titanium glycolate, dibutyltin oxide, butylstanonic acid, tributyltin oxide, diethyldibutyltin, dioctyltin oxide, monobutyldiisooctanoate, and germanium dioxide, and more preferably from tetrabutyl titanate and / or isopropyl titanate.

[0058] In some embodiments of the present invention, preferably, the transesterification reaction is carried out in the presence of a protective gas.

[0059] In some embodiments of the present invention, preferably, the protective gas is selected from nitrogen and / or argon.

[0060] In some embodiments of the present invention, preferably, the polymerization reaction is carried out in the presence of a stabilizer.

[0061] In some embodiments of the present invention, preferably, the stabilizer is selected from phosphate esters and / or phosphites, more preferably from at least one of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, triphenyl phosphate and triphenyl phosphite, and more preferably from at least one of triethyl phosphate, triphenyl phosphate and triphenyl phosphite.

[0062] In some embodiments of the present invention, preferably, the amount of the second catalyst is 0.005-0.5 wt%, more preferably 0.05-0.4 wt%, based on the total weight of the bis(2-hydroxyethyl) terephthalate sample.

[0063] In some embodiments of the present invention, preferably, the amount of the third catalyst is 0.001-0.3 wt%, more preferably 0.05-0.2 wt%, based on the total weight of the bis(2-hydroxyethyl) terephthalate sample.

[0064] In some embodiments of the present invention, preferably, the amount of stabilizer used is 0.02-0.1 wt%, more preferably 0.04-0.08 wt%, based on the total weight of the bis(2-hydroxyethyl) terephthalate sample.

[0065] In some embodiments of the present invention, preferably, the molar ratio of the bis(2-hydroxyethyl) terephthalate sample to 1,4-butanediol is 1:1-5, more preferably 1:1-3.

[0066] In some embodiments of the present invention, preferably, the method further includes: preparing the bis(2-hydroxyethyl) terephthalate sample according to the method described in the first aspect of the present invention.

[0067] In some embodiments of the present invention, preferably, the temperature of the transesterification reaction is 120-180℃, more preferably 140-180℃; the pressure is 1000Pa-20000MPa, more preferably 1000Pa-10000mPa; and the time is 2-8h, more preferably 4-6h.

[0068] In some embodiments of the present invention, preferably, the temperature of the polymerization reaction is 190-280℃, more preferably 200-270℃; the pressure is 20-20000Pa, more preferably 50-20000Pa; and the time is 0.5-6h, more preferably 0.8-4h.

[0069] The fifth aspect of the present invention provides a polybutylene terephthalate product prepared by the method described in the fourth aspect of the present invention.

[0070] The sixth aspect of this invention provides a polybutylene terephthalate product, characterized in that the intrinsic viscosity of the product is not less than 0.6 dL / g under the solvent condition of phenol:tetrachloroethane = 1:1, the L value is not less than 70, and the b value is not greater than 5.

[0071] In some embodiments of the present invention, preferably, the intrinsic viscosity of the product is 0.6-1 dL / g under the solvent condition of phenol:tetrachloroethane = 1:1, with an L value of 70-100 and a b value of 2-5.

[0072] In some embodiments of the present invention, preferably, the molar content of the ethylene terephthalate structural unit on the main chain of the polybutylene terephthalate product is 0.05-0.5%.

[0073] In this invention, the intrinsic viscosity of the polybutylene terephthalate product is obtained by capillary viscometer method.

[0074] In this invention, the L value and b value can be obtained by spectrophotometer method.

[0075] The seventh aspect of the present invention provides the use of the polybutylene terephthalate product described in the sixth aspect of the present invention in at least one of the fields of automobiles, machinery, precision instrument components, electronic appliances and textiles.

[0076] The eighth aspect of the present invention provides the application of the method described in the first aspect of the present invention in at least one of improving the purity of bis(2-hydroxyethyl) terephthalate, reducing the metal ion content of bis(2-hydroxyethyl) terephthalate, and improving the color of polybutylene terephthalate.

[0077] The ninth aspect of the present invention provides the application of the product described in the second aspect of the present invention in improving the color of polybutylene terephthalate.

[0078] The tenth aspect of the present invention provides the application of the method described in the fourth aspect of the present invention in improving the color of at least one of polybutylene terephthalate.

[0079] The present invention will be described in detail below through examples. Unless otherwise specified, all raw materials used in the following examples are commercially available products. The depolymerization rate is >99%, calculated by weighing the undepolymerized PET particles relative to the weight of the PET feed. The content or purity of BHET was determined by 1H NMR spectroscopy and high-performance liquid chromatography. The content of ethylene terephthalate structural units was determined by 1H NMR spectroscopy.

[0080] Example 1

[0081] PET polyester bottle material (0.6 cm in diameter) was washed and dried (moisture content 0.2 wt%), and then added to a reactor at a mass ratio of 1:4 with ethylene glycol. 0.1 wt% (based on PET mass) of titanium glycolate was added. The air inside the reactor was replaced with nitrogen to ensure airtightness. Nitrogen gas was then introduced to bring the pressure inside the reactor to 0.35 MPa. Stirring was started (83 rpm), and the reactor temperature was set to 210°C. The reaction time was 3 hours after the reactor temperature reached the set temperature, yielding depolymerization products. The depolymerization rate of waste polyester was 100%. The total amount of oligomers with a degree of polymerization of 1–3 in the alcoholysis products was 99.5%, and BHET accounted for 89.3% of the depolymerization products.

[0082] The alcoholysis reaction solution was cooled to 100℃, and then the insoluble matter was filtered off while hot to obtain a filtrate. Deionized water was added to the filtrate, with the filtrate and deionized water mixed at a volume ratio of 1:3. The mixture was stirred with 5g of activated carbon (1L of depolymerization solution) at 71℃ for 2 hours, and then filtered to obtain a filtrate. The filtrate was placed in an environment of 0-4℃ for 8 hours to precipitate crystals. After filtration and drying, bis(dihydroxyethyl) terephthalate (BHET) was obtained with a purity of 98.0%, a melting point of 109℃, a color value of L=95.1, b=0.9, and a metal ion content of 17ppm.

[0083] The above-mentioned BHET, sodium acetate, and 1,4-butanediol (BDO) were added to a reactor with a BHET:BDO molar ratio of 1:1.5 and sodium acetate added at 0.3 wt% of BHET weight. The mixture was first heated to 180°C under inert gas protection and reacted for 1 hour. Then the system pressure was gradually reduced to 5000 Pa and the reaction was continued for 4 hours to form a hydroxybutyl terephthalate mixture. The mixture consisted of bis(dihydroxybutyl) terephthalate (BHBT), bis(dihydroxybutyl) terephthalate dimer (BHET dimer), and monosubstituted dihydroxybutyl terephthalate. The total molar content of BHBT and BHBT dimer was 97%.

[0084] The above-mentioned butylene terephthalate mixture was mixed with 0.2 wt% isopropyl titanate and 0.08 wt% triphenyl phosphite (based on BHET weight), and reacted at 260°C with the system pressure reduced to an absolute pressure of 1000 Pa for 1 hour. After the system pressure was further reduced to 200 Pa, regenerated polybutylene terephthalate (r-PBT) was obtained. The intrinsic viscosity of PBT (under the condition of phenol:tetrachloroethane = 1:1 solvent) was 0.72 dL / g, the L value was 72, and the b value was 4.2, wherein the molar content of ethylene terephthalate structural units on the main chain was 0.2%.

[0085] Example 2

[0086] PET polyester bottle material (0.7 cm in diameter) was washed and dried (moisture content 0.5 wt%), and then added to a reactor at a mass ratio of 1:4 with ethylene glycol. 0.1 wt% (based on PET mass) of silicate-modified alkyl titanate was added. The air inside the reactor was replaced with nitrogen to ensure airtightness. Nitrogen was then introduced to bring the pressure inside the reactor to 0.4 MPa. Stirring was started (100 rpm), and the reactor temperature was set to 200℃. The reaction time was 3 hours after the reactor temperature reached the set temperature, yielding depolymerization products. The depolymerization rate of waste polyester was 100%. The total amount of oligomers with a degree of polymerization of 1–3 in the alcoholysis products was 99.5%, and BHET accounted for 88.9% of the depolymerization products.

[0087] The alcoholysis reaction solution was cooled to 100℃, and then the insoluble matter was filtered off while hot to obtain a filtrate. Deionized water was then added to the filtrate, with the filtrate and deionized water mixed at a volume ratio of 1:1.5. The mixture was stirred with 10g of activated carbon at 70℃ for 2 hours, and then filtered to obtain a filtrate. The filtrate was placed in an environment of 0-4℃ for 8 hours to precipitate crystals. After filtration and drying, bis(dihydroxyethyl) terephthalate (BHET) was obtained with a purity of 97.5%, a melting point of 109℃, a color value of L=93.5, b=3.4, and a metal ion content of 16ppm.

[0088] The above-mentioned BHET, magnesium acetate, and 1,4-butanediol (BDO) were added to a reactor with a BHET:BDO molar ratio of 1:3 and magnesium acetate added at 0.2 wt% of BHET weight. The mixture was first heated to 180°C under inert gas protection and reacted for 1 hour. Then, the system pressure was gradually reduced to 5000 Pa and the reaction was continued for 3 hours to form a modified hydroxybutyl terephthalate mixture. The mixture consisted of bis(dihydroxybutyl) terephthalate (BHBT), bis(dihydroxybutyl) terephthalate dimer (BHET dimer), and monosubstituted hydroxybutyl terephthalate. The total molar content of BHBT and BHBT dimer was 97.3%.

[0089] The modified butyl terephthalate mixture was mixed with 0.2% n-butyl titanate and 0.07% trimethyl phosphate (based on BHET weight), and reacted at 255°C with the system pressure slowly reduced to an absolute pressure of 1000 Pa for 1 hour. The system pressure was then reduced to 150 Pa to obtain regenerated polybutylene terephthalate (r-PBT). The intrinsic viscosity of PBT (under the condition of phenol:tetrachloroethane = 1:1 solvent) was 0.71 dL / g, the L value was 75, and the b value was 1.2. The molar content of ethylene terephthalate structural units in the main chain was 0.28%.

[0090] Example 3

[0091] After washing and drying the treated PET polyester bottle material (1 cm in diameter) (moisture content 0.7 wt%), it was added to a reactor at a mass ratio of 1:5 with ethylene glycol, along with 0.3 wt% (based on PET mass) of tetrabutyl titanate. The air inside the reactor was replaced with nitrogen to ensure airtightness. A certain amount of nitrogen was then introduced to bring the pressure inside the reactor to 0.3 MPa. Stirring was started (200 rpm), and the reactor temperature was set to 210°C. The reaction time was 3 hours after the reactor temperature reached the set temperature to obtain the depolymerization product. The depolymerization rate of waste polyester was 100%. The total amount of oligomers with a degree of polymerization of 1-3 in the alcoholysis product was 99.3%, and BHET accounted for 90.3% of the depolymerization product.

[0092] The alcoholysis reaction solution was cooled to 100℃, and then the insoluble matter was filtered off while hot to obtain a filtrate. Deionized water was then added to the filtrate, with the filtrate and deionized water mixed at a volume ratio of 1:2. The mixture was stirred with 3g of activated carbon at 75℃ for 1 hour, and then filtered to obtain a filtrate. The filtrate was placed in an environment of 0-4℃ for 24 hours to precipitate crystals. After filtration and drying, bis(dihydroxyethyl) terephthalate (BHET) was obtained with a purity of 97.6%, a melting point of 109℃, a color value of L=96.1, b=2.3, and a metal ion content of 21ppm.

[0093] The above-mentioned BHET, zinc acetate, and 1,4-butanediol (BDO) were added to a reactor with a BHET:BDO molar ratio of 1:2 and zinc acetate added at 0.2% of BHET. The mixture was first heated to 170°C under inert gas protection and reacted for 1.5 hours. Then, the system pressure was gradually reduced to 10000 Pa and the reaction was continued for 4 hours to form a modified hydroxybutyl terephthalate mixture. The mixture consisted of bis(dihydroxybutyl) terephthalate (BHBT), bis(dihydroxybutyl) terephthalate dimer (BHET dimer), and monosubstituted hydroxybutyl terephthalate. The total molar content of BHBT and BHBT dimer was 97.1%.

[0094] The modified butylene terephthalate mixture was mixed with 0.1 wt% tetrabutyl titanate and 0.04 wt% triphenyl phosphate (based on BHET weight), and reacted at 260°C with the system pressure slowly reduced to an absolute pressure of 1000 Pa for 1 hour. The system pressure was then reduced to 100 Pa to obtain regenerated polybutylene terephthalate (r-PBT). The intrinsic viscosity of PBT (under the condition of phenol:tetrachloroethane = 1:1 solvent) was 0.7 dL / g, the L value was 70, and the b value was 2.2. The molar content of ethylene terephthalate structural units in the main chain was 0.3%.

[0095] Example 4

[0096] After washing and drying PET polyester bottle material (0.5 cm in diameter) (moisture content 1 wt%), it was added to a reactor at a mass ratio of 1:3.5 with ethylene glycol. 0.1 wt% (based on PET mass) of tetrabutyl titanate and 0.1 wt% of lanthanum acetylacetone were also added. The air inside the reactor was replaced with nitrogen to ensure airtightness. Nitrogen was then introduced to bring the pressure inside the reactor to 0.35 MPa. Stirring was started (150 rpm), and the reactor temperature was set to 215°C. The reaction time was 3 hours after the reactor temperature reached the set temperature, yielding depolymerization products. The depolymerization rate of the waste polyester was 100%. The total amount of oligomers with a degree of polymerization of 1–3 in the alcoholysis products was 99.3%, and BHET accounted for 90.1% of the depolymerization products.

[0097] The alcoholysis reaction solution was cooled to 100℃, and then the insoluble matter was filtered off while hot to obtain a filtrate. Deionized water was then added to the filtrate, with the filtrate and deionized water mixed at a volume ratio of 1:2. The mixture was stirred with 20g of activated carbon at 72℃ for 2 hours, and then filtered to obtain a filtrate. The filtrate was placed in an environment of 0-4℃ for 24 hours to precipitate crystals. After filtration and drying, bis(dihydroxyethyl) terephthalate (BHET) was obtained with a purity of 97.9%, a melting point of 109℃, a color value of L=95.0, b=0.7, and a metal ion content of 19ppm.

[0098] The above-mentioned BHET, zinc acetate dihydrate, and 1,4-butanediol (BDO) were added to a reactor with a BHET:BDO molar ratio of 1:1.2 and the amount of zinc acetate dihydrate added was 0.3 wt% of BHET. The mixture was first heated to 175°C under inert gas protection and reacted for 1 hour. Then the system pressure was gradually reduced to 8000 Pa and the reaction was continued for 4.5 hours to form a modified hydroxybutyl terephthalate mixture. The mixture consisted of bis(dihydroxybutyl) terephthalate (BHBT), bis(dihydroxybutyl) terephthalate dimer (BHET dimer), and monosubstituted hydroxybutyl terephthalate. The total molar content of BHBT and BHBT dimer was 97.5%.

[0099] The modified butylene terephthalate mixture was mixed with 0.08 wt% isopropyl titanate and 0.08 wt% triethyl phosphite (based on BHET weight). The mixture was reacted at 258°C with the system pressure slowly reduced to an absolute pressure of 1000 Pa for 1 hour. The system pressure was then reduced to 100 Pa to obtain regenerated polybutylene terephthalate (r-PBT). The intrinsic viscosity of PBT (under the condition of phenol:tetrachloroethane = 1:1 solvent) was 0.65 dL / g, the L value was 76, and the b value was 3.8. The molar content of ethylene terephthalate structural units in the main chain was 0.20%.

[0100] Example 5

[0101] The method was carried out according to Example 1, except that 1 wt% sodium carbonate was used to replace titanium glycol to obtain bis(dihydroxyethyl) terephthalate (BHET) with a purity of 96.5%, a melting point of 109°C, a color value of L=90, b=3, and a metal ion content of 30 ppm. The resulting recycled polybutylene terephthalate (r-PBT) had a PBT viscosity (under the condition of phenol:tetrachloroethane = 1:1 solvent) of 0.60 dL / g, an L value of 70, and a b value of 5.

[0102] Example 6

[0103] The method was carried out according to Example 1, except that potassium carbonate was used instead of sodium acetate to obtain regenerated polybutylene terephthalate (r-PBT). The intrinsic viscosity of PBT (under the condition of phenol:tetrachloroethane = 1:1 solvent) was 0.6 dL / g, the L value was 70.2, and the b value was 4.6.

[0104] Example 7

[0105] The method was carried out according to Example 1, except that titanium acetylacetone was used to replace isopropyl titanate and triphenyl phosphite to obtain regenerated polybutylene terephthalate (r-PBT). The intrinsic viscosity of PBT (under the condition of phenol:tetrachloroethane = 1:1 solvent) was 0.6 dL / g, the L value was 72, and the b value was 4.3.

[0106] Example 8

[0107] The method was carried out according to Example 1, except that the stirring speed in the depolymerization reaction was 350 rpm. The resulting bis(dihydroxyethyl) terephthalate (BHET) had a purity of 97.2%, a melting point of 109°C, a color value of L = 93.3, b = 2.0, and a metal ion content of 34 ppm. The resulting recycled polybutylene terephthalate (r-PBT) had an intrinsic viscosity (in phenol:tetrachloroethane = 1:1 solvent) of 0.63 dL / g, an L value of 70, and a b value of 2.8, wherein the molar content of ethylene terephthalate structural units on the main chain was 0.34%.

[0108] Example 9

[0109] The method was carried out according to Example 1, except that the depolymerization reaction was carried out at a temperature of 196°C. The resulting bis(dihydroxyethyl) terephthalate (BHET) had a purity of 97.0%, a melting point of 109°C, a color value of L = 93.0, b = 2.1, and a metal ion content of 37 ppm. The resulting recycled polybutylene terephthalate (r-PBT) had an intrinsic viscosity (in a phenol:tetrachloroethane = 1:1 solvent) of 0.64 dL / g, an L value of 71, and a b value of 2.0, wherein the molar content of the ethylene terephthalate structural unit on the main chain was 0.43%.

[0110] Comparative Example 1

[0111] Terephthalic acid (PTA) and 1,4-butanediol (BDO), along with 0.3 wt% tetrabutyl titanate (based on PTA weight), were added to a reactor. Under a nitrogen atmosphere, the temperature was gradually increased to 190°C. The reaction proceeded until 90% of the theoretical distillate water was produced. The pressure was then reduced, and the temperature was raised to 260°C. The vacuum level of the system was gradually adjusted to 300 Pa. After reacting for 2.5 hours, PBT product was obtained. The intrinsic viscosity of PBT (under the condition of phenol:tetrachloroethane = 1:1 solvent) was 0.70 dL / g, L value was 65, and b value was 6.9.

[0112] Comparative Example 2

[0113] The procedure was carried out according to Example 1, except that it was not mixed with activated carbon and was directly refrigerated. The obtained bis(dihydroxyethyl) terephthalate (BHET) had a purity of 94.3%, a melting point of 109°C, a color value of L = 90.0, b = 4.5, and a metal ion content of 86 ppm. The obtained recycled polybutylene terephthalate had an intrinsic viscosity (in a phenol:tetrachloroethane = 1:1 solvent) of 0.56 dL / g, an L value of 64, and a b value of 5.2, wherein the molar content of the ethylene terephthalate structural unit in the main chain was 3.1%.

[0114] As can be seen from the results in Table 1, compared with the comparative example, the BHET product prepared by the embodiment using the technical solution of the present invention has beneficial effects such as high purity, good color and low metal ion content. The polybutylene terephthalate product has high viscosity, good color and basically the same properties as the virgin monomer polymer, realizing the recycling of waste polyester materials.

[0115] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for reducing the metal content in bis(2-hydroxyethyl) terephthalate products, characterized in that, The method includes: in the presence of a first catalyst, mixing a polyester containing polyethylene terephthalate with an alcohol to carry out a depolymerization reaction, and then sequentially performing solid-liquid separation, decolorization and crystallization on the reaction system obtained from the reaction.

2. The method according to claim 1, wherein, The first catalyst is selected from titanium-containing compounds and / or titanium-containing compositions, preferably from at least one of organotitanium compounds, inorganic titanium compounds, titanium-silicon composite catalysts and titanium-rare earth composite catalysts, and more preferably from at least one of tetraethyl titanate, tetrabutyl titanate, tetraisopropyl titanate, tetraisobutyl titanate, titanium acetylacetone oxide, di(acetylacetone)diisopropyl titanate, titanium glycol, titanium phosphate, silicate-modified alkyl titanate and diol-modified alkyl titanate; Preferably, the silicate-modified alkyl titanate is selected from at least one of n-butyl silicate-modified alkyl titanate, n-ethyl silicate-modified alkyl titanate, and n-propyl silicate-modified alkyl titanate.

3. The method according to claim 1 or 2, wherein, The polyester is selected from polyesters with a polyethylene terephthalate (PET) content greater than 70 wt%; Preferably, the depolymerization reaction is carried out in the presence of a protective gas; Preferably, the protective gas is selected from nitrogen and / or argon.

4. The method according to any one of claims 1-3, wherein, Based on the total weight of the polyester, the amount of the first catalyst is 0.01-0.5 wt%, preferably 0.02-0.3 wt%, and more preferably 0.05-0.2 wt%. Preferably, the mass ratio of the polyester to the alcohol is 1:2-10, more preferably 1:2-6; Preferably, the alcohol is selected from diols, and more preferably from at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol; Preferably, the temperature of the depolymerization reaction is 200-240℃, more preferably 200-220℃; Preferably, the pressure of the depolymerization reaction is 0.2-0.6 mPa, more preferably 0.25-0.4 mPa; Preferably, the depolymerization reaction takes 2-5 hours, more preferably 2.5-4 hours.

5. The method according to any one of claims 1-4, wherein, The solid-liquid separation temperature is 60-80℃, preferably 68-80℃; the time is 3-15 min, preferably 5-10 min; Preferably, the decolorization method includes mixing the filtrate obtained after solid-liquid separation with activated carbon; Preferably, the mixing temperature is 60-80℃, more preferably 68-75℃; the mixing time is 0.5-4h, more preferably 0.5-2h; and the amount of activated carbon used is 2-40g relative to 1L of filtrate.

6. The bis(2-hydroxyethyl) terephthalate product prepared by the method according to any one of claims 1-5.

7. A bis(2-hydroxyethyl) terephthalate product, characterized in that, The purity of the bis(2-hydroxyethyl) terephthalate product is not less than 97 wt%, and the metal ion weight content is not greater than 50 ppm.

8. The bis(2-hydroxyethyl) terephthalate product according to claim 7, wherein, The purity of the bis(2-hydroxyethyl) terephthalate product is not less than 98 wt%; and / or, the metal ion weight content of the compound is not greater than 20 ppm.

9. A method for preparing polybutylene terephthalate, characterized in that, The method includes: (1) In the presence of a second catalyst, the bis(2-hydroxyethyl) terephthalate sample was contacted with 1,4-butanediol and subjected to transesterification. (2) In the presence of a third catalyst, the product obtained from the transesterification reaction in step (1) is subjected to a polymerization reaction; The purity of the bis(2-hydroxyethyl) terephthalate sample is not less than 97 wt%, and the metal ion weight content is not greater than 50 ppm.

10. The method according to claim 9, wherein, The second catalyst is selected from metal salts, preferably from at least one of sodium acetate, magnesium acetate, zinc acetate and zinc acetate dihydrate, and more preferably zinc acetate; Preferably, the third catalyst is selected from at least one of titanium-containing compounds, germanium-containing compounds, and tin-containing compounds, and more preferably from at least one of tetrabutyl titanate, isopropyl titanate, tetraethyl titanate, titanium glycolate, dibutyltin oxide, butylstannic acid, tributyltin oxide, diethyldibutyltin, dioctyltin oxide, monobutyldiisooctanoate, and germanium dioxide, and more preferably from tetrabutyl titanate and / or isopropyl titanate; Preferably, the transesterification reaction is carried out in the presence of a protective gas; More preferably, the protective gas is selected from nitrogen and / or argon; Preferably, the polymerization reaction is carried out in the presence of a stabilizer; More preferably, the stabilizer is selected from phosphate esters and / or phosphites, more preferably from at least one of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, triphenyl phosphate and triphenyl phosphite, and more preferably from at least one of triethyl phosphate, triphenyl phosphate and triphenyl phosphite.

11. The method according to claim 9 or 10, wherein, Based on the total weight of the bis(2-hydroxyethyl) terephthalate sample, the amount of the second catalyst is 0.005-0.5 wt%, preferably 0.05-0.4 wt%. Preferably, based on the total weight of the bis(2-hydroxyethyl) terephthalate sample, the amount of the third catalyst is 0.001-0.3 wt%, more preferably 0.05-0.2 wt%. Preferably, based on the total weight of the bis(2-hydroxyethyl) terephthalate sample, the amount of stabilizer is 0.02-0.1 wt%, more preferably 0.04-0.08 wt%. Preferably, the molar ratio of the bis(2-hydroxyethyl) terephthalate sample to 1,4-butanediol is 1:1-5, more preferably 1:1-3; Preferably, the method further includes: preparing the bis(2-hydroxyethyl) terephthalate sample according to the method of any one of claims 1-5.

12. The method according to any one of claims 9-11, wherein, The transesterification reaction is carried out at a temperature of 120-180℃, preferably 140-180℃; a pressure of 1000Pa-20000MPa, preferably 1000Pa-10000MPa; and a time of 2-8h, preferably 4-6h. Preferably, the polymerization reaction is carried out at a temperature of 190-280℃, more preferably 200-270℃; at a pressure of 20-20000Pa, more preferably 50-20000Pa; and for a time of 0.5-6h, more preferably 0.8-4h.

13. The polybutylene terephthalate product prepared by the method according to any one of claims 9-12.

14. A polybutylene terephthalate product, characterized in that, The intrinsic viscosity of this product in a mixed solvent of phenol and tetrachloroethane at a volume ratio of 1 is not less than 0.6 dL / g, the L value is not less than 70, and the b value is not greater than 5.

15. The use of the polybutylene terephthalate product of claim 13 or 14 in at least one of the fields of automobiles, machinery, precision instrument components, electronics and textiles.

16. The application of the method according to any one of claims 1-5 in improving the purity of bis(2-hydroxyethyl) terephthalate, reducing the metal ion content of bis(2-hydroxyethyl) terephthalate, and improving the color of polybutylene terephthalate.

17. The use of the bis(2-hydroxyethyl) terephthalate product according to claim 7 or 8 in improving the color of polybutylene terephthalate.

18. The use of the bis(2-hydroxyethyl) terephthalate product according to any one of claims 6-8, or the method according to any one of claims 9-12, in improving the color of polybutylene terephthalate.