Purification method of BHET

Abstract

The present invention provides a BHET purification method, which comprises: mixing a BHET-containing mixture with a solvent to obtain a BHET solution to be purified, and carrying out filtration treatment to obtain a filtrate; the filtrate passes through a resin bed layer at the flow speed of 2-10 BV / h for purification treatment, and BHET purified liquid is obtained; the resin bed layer comprises H-type gel cation exchange resin, OH-type gel anion exchange resin and a solvent, at least part of the surface of the H-type gel cation exchange resin contains sulfonic acid groups and H < + >, and at least part of the surface of the OH-type gel anion exchange resin contains quaternary ammonium groups and OH <->; the volume ratio of the H-type gel cation exchange resin to the OH-type gel anion exchange resin is 1: (1-5). The method can be used for removing metal ion impurities and inorganic impurities.

Description

Technical Field

[0001] This invention relates to the field of waste textile recycling technology, and in particular to a purification method for BHET. Background Technology

[0002] Waste textile raw materials have complex origins, and various metal ion impurities and inorganic salts are introduced during their production, processing and use. These metal ion impurities include iron ions, calcium ions, sodium ions, antimony ions, etc. However, after alcoholysis, these metal ion impurities and inorganic salts remain in diethyl terephthalate (BHET). When BHET is used as a polymer monomer for repolymerization under high temperature and high pressure, it will have an adverse effect on the polymerization reaction process and the quality of the final product.

[0003] Therefore, developing efficient purification technologies capable of deeply removing various metal ion impurities and inorganic impurities from BHET has become a core bottleneck in promoting the industrialization of chemical recycling technology for waste textiles and ensuring the safety and high quality of downstream products. Summary of the Invention

[0004] Based on this, the present invention provides a purification method for BHET, which can reduce the ineffective retention of BHET, efficiently remove metal ion impurities from the feed solution, achieve deep removal of various metal ion impurities and inorganic impurities, and ensure the color and performance of subsequent products.

[0005] In a first aspect, the present invention provides a method for purifying BHET, comprising the following steps:

[0006] The mixture containing BHET is mixed with a solvent to obtain a BHET solution to be purified, which is then filtered to obtain a filtrate.

[0007] The filtrate is purified by passing it through a resin bed at a flow rate of 2 BV / h to 10 BV / h to obtain BHET purified solution.

[0008] The resin bed comprises an H-type gel cation exchange resin, an OH-type gel anion exchange resin, and a solvent. The H-type gel cation exchange resin has at least a portion of its surface containing sulfonic acid groups and H+. + The OH-type gel anion exchange resin has at least a portion of its surface containing quaternary ammonium groups and OH groups. - The volume ratio of the H-type gel cation exchange resin to the OH-type gel anion exchange resin is 1:(1~5); BV is the total packing volume of the H-type gel cation exchange resin and the OH-type gel anion exchange resin in the resin bed.

[0009] Furthermore, the BHET-containing mixture is further treated with an adsorbent before filtration when the mixture meets at least one of the following conditions:

[0010] a. The color intensity of the BHET-containing mixture is >50 Hazen;

[0011] b. The BHET-containing mixture contains organic matter with a molecular weight >1000 g / mol.

[0012] Furthermore, the filtration process includes using a filter membrane with an average pore size of 0.3 μm to 0.5 μm.

[0013] Furthermore, the diameter of the resin bed is D, the filling height of the resin bed is H, and the diameter-to-height ratio of the resin bed, D / H, is 1:(2~8).

[0014] Furthermore, the H-type gel cation exchange resin satisfies at least one of the following conditions:

[0015] c. Crosslinking degree is 8%~12%;

[0016] d. Total volumetric exchange capacity ≥ 2.0 mmol / mL.

[0017] Furthermore, the OH-type gel anion exchange resin satisfies at least one of the following conditions:

[0018] e. Crosslinking degree is 8%~12%;

[0019] f. Total volumetric exchange capacity ≥ 1.0 mmol / mL.

[0020] Furthermore, the method includes crystallizing the BHET purification solution to obtain purified BHET crystals; the purification process is stopped when at least one of the following conditions is met:

[0021] g. The color of the BHET purification solution is >10;

[0022] h. The metal ion impurity content of the purified BHET crystal is >5 mg / kg;

[0023] i. The inorganic impurity content of the purified BHET crystal is >10ppm;

[0024] j. The color value L of the purified BHET crystal is <95;

[0025] k. The color value b of the purified BHET crystal is >2;

[0026] l. The purified BHET crystal has a color value a > 0.5 or < -0.5.

[0027] Furthermore, after the purification process is stopped, a regeneration process is also included.

[0028] Furthermore, before the purification process, the resin bed is heated to 65°C to 75°C and kept at that temperature for 10 to 20 minutes.

[0029] Furthermore, the BHET-containing mixture comprises BHET, metal ion impurities, and inorganic impurities, and based on the total mass of the BHET-containing mixture, the BHET-containing mixture satisfies at least one of the following conditions:

[0030] m. The mass percentage of the BHET is >70%;

[0031] n. The concentration of the metal ion impurity is 5 mg / kg to 50 mg / kg;

[0032] o. The concentration of the inorganic impurities is 10 mg / kg to 150 mg / kg.

[0033] This invention provides a method for purifying BHET. After filtration, the BHET solution to be purified removes insoluble impurities, preventing these impurities from clogging resin channels or affecting the contact efficiency between the resin and the feed solution, thus laying the foundation for subsequent deep impurity removal. During the purification stage, the H-type gel cation exchange resin in the resin bed, through H-type cation exchange resin bound to its surface sulfonic acid groups… + The resin undergoes an ion exchange reaction with metal ion impurities (metal cations) in the filtrate to form a resin-metal ion complex, thereby immobilizing the metal cations. Simultaneously, the OH-type gel anion exchange resin binds OH groups to its surface via quaternary ammonium groups. - The resin undergoes an ion exchange reaction with anionic impurities in the filtrate to form a resin-anion complex, thereby fixing the acid radical ions. The H-type gel cation exchange resin releases H+ through exchange. + OH groups released by the exchange with OH-type gel anion exchange resin - In-situ neutralization to generate water within the reaction column completely eliminates the reverse reaction driving force of the ion exchange reaction, promoting the continuous and in-depth removal of both ion exchange reactions. This achieves synergistic and in-depth removal of various metal ion impurities and inorganic salts, significantly reducing the inorganic impurities in BHET. Controlling the filtrate flow rate within the range of 2~10 BV / h ensures sufficient contact between the feed solution and the resin, guaranteeing thorough impurity exchange while reducing ineffective retention of BHET in the resin bed and minimizing product loss. Maintaining a volume ratio of H-type gel cation exchange resin to OH-type gel anion exchange resin of 1:(1~5) allows for the release of H+ from both resins. + With OH -By matching the adsorption capacity to the anions and cations, the efficiency of in-situ neutralization is maximized, while ensuring a matching adsorption capacity for these impurities. This further enhances the deep impurity removal effect, ultimately achieving continuous and stable operation exceeding 500 BV per cycle, thus ensuring the color and performance of subsequent products. This invention achieves deep and continuous removal of various metal ion impurities and inorganic impurities from complex-sourced BHET, significantly reducing ignition residue. The process is stable and reliable, providing key technology and material support for the production of BHET and its high-value-added downstream products. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] In a first aspect, the present invention provides a method for purifying BHET, comprising the following steps:

[0036] The BHET solution to be purified was filtered to obtain the filtrate.

[0037] The filtrate was purified by passing it through a resin bed at a flow rate of 2-10 BV / h to obtain the BHET purified solution.

[0038] The resin bed comprises an H-type gel cation exchange resin, an OH-type gel anion exchange resin, and a solvent. The H-type gel cation exchange resin has at least a portion of its surface containing sulfonic acid groups and H+. + OH-type gel anion exchange resins have at least a portion of their surface containing quaternary ammonium groups and OH groups. - The volume ratio of H-type gel cation exchange resin to OH-type gel anion exchange resin is 1:(1~5); BV is the total packing volume of H-type gel cation exchange resin and OH-type gel anion exchange resin in the resin bed.

[0039] For example, the flow rate of the filtrate through the resin bed is any value or a range of any two of the following: 2 BV / h, 3 BV / h, 4 BV / h, 5 BV / h, 6 BV / h, 7 BV / h, 8 BV / h, 9 BV / h, 10 BV / h.

[0040] For example, the volume ratio of H-type gel cation exchange resin to OH-type gel anion exchange resin is any value or a range of any two of the following: 1:1, 1:2, 1:3, 1:4, 1:5.

[0041] The packing volume of the resin bed in this invention refers to the total packing volume of H-type gel cation exchange resin and OH-type gel anion exchange resin in the resin column, i.e., the bed volume (BV). Specifically, the flow rate of the filtrate through the resin bed at a rate of 2-10 BV / h refers to the volume of filtrate flowing through the resin bed per unit time, which is 2 to 10 times the total packing volume of H-type gel cation exchange resin and OH-type gel anion exchange resin in the resin bed.

[0042] The H-type gel cation exchange resin of this invention is a gel-type strong acid cation exchange resin; the OH-type gel anion exchange resin is a gel-type strong base anion exchange resin.

[0043] Performing a filtration process on the BHET solution to be purified can effectively remove insoluble solid impurities. This filtration process is a pretreatment step that can reduce the risk of resin bed clogging and ensure that the feed solution is evenly distributed in the resin column and in full contact with the resin, thereby creating favorable conditions for subsequent deep ion exchange purification. For example, the filtration process includes vacuum filtration of the BHET solution to be purified.

[0044] The purification method provided by this invention works by constructing a dynamic synergistic purification system. During the purification stage, when the filtrate flows through the resin bed, the following core reactions occur:

[0045] 1) Cation exchange: Metal ion impurities in the solution (such as Zn) 2+ Ca 2+ Na + (e.g., metal cations) and H on H-type gel cation exchange resin + An exchange occurs, where metal cations are adsorbed by the resin and form a resin-metal ion complex. The reaction is: R-SO3 - H + +Mn + →R-SO3 - Mn + +H + This fixes metal ion impurities.

[0046] 2) Anion exchange: Anionic impurities in the solution (such as Cl-) - SO4 2- CH3COO - (etc.) and OH groups on OH-type gel anion exchange resin - An exchange occurs, where anionic impurities are captured by the resin and form a resin-anionic complex, the reaction being: R-NR'3 + OH - +Xn - →R-NR'3+Xn - +OH- This fixes the acid radical ions.

[0047] 3) In-situ neutralization: During the above ion exchange process, the H-type gel cation exchange resin exchanges H+... + OH groups exchanged with OH-type gel anion exchange resin - A rapid in-situ neutralization reaction occurs within the resin column to generate water (H₂O). + + OH - →H2O). This neutralization reaction can completely consume the free H+ in the reaction system. + and OH - This completely eliminates the reverse reaction driving force of ion exchange, prompting the cation exchange and anion exchange reactions to continue in the forward direction, thereby achieving synergistic and deep removal of various metal ion impurities and inorganic salt impurities in the feed solution.

[0048] By controlling the feed flow rate of the filtrate within the range of 2~10 BV / h, the residence time of the filtrate in the resin bed can be precisely controlled. This ensures that the filtrate is in full contact with the functional groups of the cation and anion exchange resins, ensuring that the ion exchange reaction between metal cations and anion impurities is more thorough. It also avoids prolonged ineffective retention of BHET in the resin column due to excessively slow flow rates, thereby effectively controlling the loss rate of the target product and ultimately significantly reducing the ignition residue of the BHET product.

[0049] By controlling the volume ratio of cation exchange resin to anion exchange resin at 1:(1~5), the amount of H released by both resins can be increased. + With OH - The appropriate amount of material is used to maximize the in-situ neutralization efficiency while ensuring the matching of adsorption capacity for anions and cations, further enhancing the deep impurity removal effect, and ultimately achieving continuous and stable operation of more than 500 BV per cycle, thus ensuring the color and performance of subsequent products.

[0050] The BHET purification method provided by this invention achieves deep purification through the above mechanism, covering most sources of inorganic impurities, without introducing new inorganic salts, thereby significantly reducing the ignition residue of BHET products.

[0051] It should be noted that polyethylene terephthalate (PET) is the world's most produced synthetic polyester material. Due to its excellent mechanical properties, chemical stability, and processability, it is widely used in fibers, bottle flakes, and films. With the continuous growth in PET fiber consumption, the resulting waste textiles pose a significant pressure on the environment. Chemical recycling of waste textiles has become a key pathway for pollution control and resource recycling. Among these technologies, ethylene glycol (EG) alcoholysis can depolymerize waste PET into diethyl terephthalate (BHET) monomers, which can then be repolymerized to generate recycled PET (r-PET), aligning with green chemistry and sustainable development principles.

[0052] In some implementations, the subsequent products include, but are not limited to, recycled polyethylene terephthalate (r-PET).

[0053] In some embodiments, the mixture containing BHET is further treated with an adsorbent before filtration when the mixture meets at least one of the following conditions:

[0054] a. The chromaticity of mixtures containing BHET is >50 Hazen;

[0055] b. Mixtures containing BHET contain organic matter with a molecular weight >1000 g / mol.

[0056] The method for measuring colorimetry in this invention is as follows: referring to the GB / T 3143-1982 standard, the colorimetry of the BHET solution to be purified is determined to be >50 Hazen using the platinum-cobalt colorimetric method.

[0057] For BHET mixtures with deep color or containing large organic molecules, an adsorption pretreatment step is performed before filtration. This adsorption pretreatment step specifically removes colored impurities and organic impurities with a molecular weight >1000 g / mol, effectively preventing subsequent resin bed contamination and clogging. The adsorbent fixes colored substances through adsorption, reducing the color of the mixture and preventing these substances from affecting the color of subsequent r-PET products. Simultaneously, it adsorbs organic impurities within this molecular weight range, reducing their contamination of the resin bed, maintaining its ion exchange activity, and extending the resin column's lifespan. This step, together with subsequent filtration and mixed-bed purification, forms a synergistic treatment system, further optimizing the purity of the BHET raw material and providing more comprehensive assurance for subsequent processes and product quality.

[0058] For example, the adsorbent includes, but is not limited to, at least one of activated carbon, molecular sieve or silica gel.

[0059] In some embodiments, the mixture containing BHET is mixed with a solvent under an inert gas atmosphere to obtain a BHET solution to be purified.

[0060] In some preferred embodiments, the BHET solution to be purified is further heated to 50°C to 80°C.

[0061] Heating the BHET solution to be purified to 50℃~80℃ can accelerate the diffusion rate of metal cations and inorganic anions in the feed solution, improve their contact efficiency with the functional groups of the resin, and thus accelerate the ion exchange reaction process, ensuring deep deimpurification at a flow rate of 2-10 BV / h. On the other hand, it can increase the solubility of BHET in the solvent, reduce the probability of its crystallization and adsorption on the resin surface or inside the column, and reduce the ineffective retention and loss of the target product.

[0062] In some preferred embodiments, the BHET solution to be purified includes a solvent and a mixture containing BHET, wherein the solvent accounts for 85-95% of the total mass of the BHET solution to be treated, and the mixture containing BHET accounts for 5-15%.

[0063] In some specific embodiments, the BHET-containing mixture and solvent are mixed and heated to 50°C~80°C under stirring to dissolve, thereby obtaining the BHET solution to be purified. Subsequently, the BHET solution to be purified is kept warm and filtered, and the filtrate is kept warm in a water bath for later use. Based on the total mass of the BHET solution to be treated, the mixing ratio of the BHET-containing mixture and the solvent is: the solvent accounts for 85%~95%, and the BHET-containing mixture accounts for 5%~15%.

[0064] The above steps promote the dissolution of BHET and remove insoluble particles, preventing blockage of subsequent resin beds.

[0065] In some implementations, the filtration process uses a sand core funnel and a microporous membrane. This effectively removes insoluble particulate matter from BHET-containing mixtures.

[0066] In some preferred embodiments, the filtration process includes using a filter membrane with a pore size of 0.3 μm to 0.5 μm.

[0067] For example, the pore size of the filter membrane is any value or a range of any two of the following: 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm.

[0068] Using a filter membrane with a pore size of 0.3μm to 0.5μm for filtration, fine insoluble impurities in BHET-containing mixtures, including mechanical debris and trace amounts of undissolved solid particles, can be precisely retained. This pore size range can efficiently remove impurities, achieving precise retention of fine insoluble impurities in the feed solution while maintaining an appropriate filtration flux to ensure feed solution treatment efficiency and guarantee that the filtrate entering subsequent purification stages meets the cleanliness requirements. Filtrate filtered through this membrane reduces the risk of resin channel blockage in subsequent resin columns, maintains the ion exchange activity of the resin, ensures the continuous and stable operation of the purification process, and avoids interference from fine impurities on the ion exchange reaction, improving the uniformity and thoroughness of impurity removal.

[0069] In some embodiments, the resin column is prepared by the following process: H-type gel cation exchange resin and anion exchange resin are mixed at a volume ratio of 1:(1~5) to obtain a mixed resin; the mixed resin is wet-filled into the reaction column while deionized water is present inside the column to obtain a resin bed; the resin bed is always submerged below the surface of the deionized water; before feeding, the liquid level in the reaction column is adjusted to be flush with the upper surface of the resin bed.

[0070] Mixing two resins at a volume ratio of 1:(1~5) and wet packing them can construct a synergistic and efficient ion exchange system, while simultaneously removing air from the resin gaps to ensure sufficient contact between the feed solution and the functional groups of the resin. Maintaining the resin bed in an submerged state and adjusting the liquid level to be flush with the top surface of the resin can keep the resin bed moist and free of air bubbles, maintain its ion exchange activity, and ensure stable flow of subsequent feed solutions through the resin bed, thereby improving the consistency of purification results.

[0071] In some specific embodiments, after obtaining the mixed resin, before wet filling the mixed resin, the reaction column is preheated to 70~80°C and kept at that temperature for 10~20 minutes.

[0072] The aforementioned ion exchange resin packing process—wet packing—refers to a packing method in which a liquid medium (deionized water in this scheme) is pre-added into the reaction column, and the resin is kept submerged in the liquid throughout the process, thereby avoiding contact between the resin and air. Preheating the reaction column to 70~80℃ and maintaining this temperature creates a stable temperature environment for the subsequent ion exchange reaction, ensuring the reaction rate and efficiency. This preheating operation avoids temperature fluctuations caused by contact between the cold column and the feed liquid, maintains the activity of the resin's functional groups, and reduces the precipitation and retention losses of BHET due to temperature changes.

[0073] The resin bed packing amount of this invention refers to the total packing volume of H-type gel cation exchange resin and OH-type gel anion exchange resin in the resin column, i.e., the bed volume (BV). The resin bed packing amount is determined based on the size of the reaction column.

[0074] In some embodiments, the inner diameter of the resin bed is D, the filling height of the resin bed is H, and the diameter-to-height ratio of the resin bed, D / H, is 1:(2~8).

[0075] For example, the diameter-to-height ratio of the resin bed is any value or a range of any two of the following: 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8.

[0076] Maintaining a resin bed diameter-to-height ratio of 1:(2~8) optimizes the flow path and residence time of the feed solution within the resin column. This ratio range allows the filtrate to flow through the resin bed in a stable manner, ensuring sufficient contact between the feed solution and the anion and cation exchange resins, and avoiding incomplete impurity exchange caused by excessively high local flow rates. Simultaneously, a suitable diameter-to-height ratio maintains appropriate column pressure, ensuring a stable feed flow rate of 2-10 BV / h, improving the operational stability of the resin column, further supporting long-term continuous operation in a single cycle, and enhancing the consistency of deep impurity removal.

[0077] In some embodiments, the H-type gel cation exchange resin satisfies at least one of the following conditions:

[0078] c. Crosslinking degree is 8%~12%;

[0079] d. Total volumetric exchange capacity ≥ 2.0 mmol / mL.

[0080] For example, the degree of crosslinking of the H-type cation exchange tree is any value or a range of any combination of 8%, 9%, 10%, 11%, 12%, etc.

[0081] For example, the volumetric total exchange capacity of H-type cation exchange trees is ≥2.0 mmol / mL, ≥3.0 mmol / mL, ≥4.0 mmol / mL, ≥5.0 mmol / mL, etc.

[0082] The crosslinking degree of H-type gel cation exchange resin is controlled at 8%~12%. This range can balance mechanical strength, exchange capacity and inorganic ion selectivity, meet the requirements of long-term operation, adapt to feed solution temperature of 50~80℃ and subsequent acid and alkali cleaning treatment (regeneration treatment), and endow the resin with suitable mechanical strength and swelling properties. It can withstand the fluid pressure when the feed solution passes through, avoid resin breakage, and ensure that the internal pore structure of the resin is suitable, which facilitates the contact and exchange reaction between metal cations and sulfonic acid groups, and maintains the long-term stable operation and ion exchange activity of the resin.

[0083] The measurement of the total volumetric exchange capacity of the H-type gel cation exchange resin of this invention is performed in accordance with the current national standard GB / T8144-2008.

[0084] H-type gel cation exchange resin with a total volume exchange capacity ≥2.0 mmol / mL has a sufficient number of sulfonic acid groups, which can improve the adsorption capacity for metal cations, extend the single-cycle operation time of the resin, reduce the regeneration frequency, further ensure the continuous stability of the process, and at the same time improve the removal depth of metal ion impurities, helping to reduce BHET inorganic impurities.

[0085] In some preferred embodiments, the H-type gel cation exchange resin includes, but is not limited to, at least one of sulfonic acid-modified cross-linked polystyrene, sulfonic acid-modified phenolic resin, sulfonic acid-modified acrylic resin, and sulfonic acid-modified polyethersulfone resin.

[0086] In some embodiments, the OH-type gel anion exchange resin satisfies at least one of the following conditions:

[0087] e. Crosslinking degree is 8%~12%;

[0088] f. Total volumetric exchange capacity ≥ 1.0 mmol / mL.

[0089] For example, the degree of crosslinking of the OH-type gel anion exchange resin is any value of 8%, 9%, 10%, 11%, 12%, or any combination of both.

[0090] For example, the total volumetric exchange capacity of OH-type gel anion exchange resins is ≥1.0 mmol / mL, ≥2.0 mmol / mL, ≥3.0 mmol / mL, ≥4.0 mmol / mL, ≥5.0 mmol / mL, etc.

[0091] OH-type gel anion exchange resins have a crosslinking degree of 8%~12%, which balances mechanical strength, exchange capacity, and inorganic ion selectivity, meeting the requirements for long-term operation. This ensures the resin possesses good mechanical strength and chemical stability, is adaptable to feed solution temperatures of 50~80℃ and subsequent acid-base cleaning (regeneration) treatments, avoids resin structure damage, and maintains a suitable pore structure to facilitate contact and exchange between anionic impurities and quaternary ammonium groups.

[0092] The measurement of the total volumetric exchange capacity of the OH-type gel cation exchange resin of this invention is performed in accordance with the current national standard GB / T5760-2000.

[0093] OH-type gel anion exchange resin with a total volume exchange capacity ≥1.0 mmol / mL has a sufficient number of quaternary ammonium groups, which can efficiently adsorb anionic impurities in the filtrate. It forms a synergistic impurity removal effect with H-type gel cation exchange resin, ensuring that inorganic salt impurities are completely removed, while extending the single-cycle operating life of the resin and supporting continuous and stable process.

[0094] In some preferred embodiments, the OH-type gel anion exchange resin includes, but is not limited to, at least one of quaternary ammonium modified cross-linked polystyrene, quaternary ammonium modified phenolic resin, quaternary ammonium modified acrylic resin, and quaternary ammonium modified epoxy resin.

[0095] The present invention does not limit the shape of the H-type gel cation exchange resin; for example, the H-type gel cation exchange resin is spherical.

[0096] The present invention does not limit the shape of the OH-type gel anion exchange resin; for example, the OH-type gel anion exchange resin is spherical.

[0097] In some preferred embodiments, the particle size D of the H-type gel cation exchange resin 50 The particle size D of the OH-type gel anion exchange resin is 0.60 mm to 0.70 mm; and / or the particle size D of the OH-type gel anion exchange resin is... 50 The diameter is 0.54 mm to 0.64 mm.

[0098] For example, the particle size D of H-type gel cation exchange resin 50 It is any value or a range of any two of the following: 0.60 mm, 0.62 mm, 0.64 mm, 0.66 mm, 0.68 mm, 0.70 mm.

[0099] For example, the OH-type gel anion exchange resin is any value or a range of any two of 0.54 mm, 0.56 mm, 0.58 mm, 0.60 mm, 0.62 mm, 0.64 mm, etc.

[0100] In the BHET purification process of this invention, an ion exchange resin with an appropriate particle size is selected. The large specific surface area and short ion diffusion path brought about by the small particle size can effectively improve the mass transfer efficiency of impurity ions and ensure the efficient conduct of the ion exchange reaction; wherein D 50 The H-type gel cation exchange resin has a uniform particle size distribution of 0.60 mm to 0.70 mm. After packing, the resin bed porosity is stable, allowing the feed solution to flow evenly through the bed and avoiding channeling. This ensures sufficient contact between the feed solution and the resin to improve the metal cation exchange efficiency, while maintaining a suitable column pressure and a flow rate of 2-10 BV / h. 50The OH-type gel anion exchange resin has a particle size of 0.54 mm to 0.64 mm, which is compatible with the H-type gel cation exchange resin. After the two are mixed and packed, the bed structure is uniform, which can optimize the flow state of the feed solution, improve the synchronicity of the anion and cation exchange reaction, enhance the in-situ neutralization effect, and further promote the depth of ion exchange reaction to improve the purification accuracy. At the same time, the compatible particle size can also maintain the appropriate porosity of the resin bed, ensure the stability of the feed solution flow rate, and take into account the ion exchange efficiency, bed operation smoothness and the process requirements of industrial continuous production.

[0101] In some embodiments of the present invention, the H-type gel cation exchange resin includes sulfonic acid-modified cross-linked polystyrene; the sulfonic acid-modified cross-linked polystyrene is specifically prepared by the following process: cross-linked polystyrene is subjected to a sulfonation reaction with sulfuric acid of a concentration greater than or equal to 90% at 100-120°C for 2-6 hours to introduce sulfonic acid groups, thereby obtaining the H-type gel cation exchange resin.

[0102] The resulting H-type gel cation exchange resin is strongly acidic, enabling it to undergo efficient ion exchange reactions with metal cations (metal ion impurities) in the feed solution, achieving deep retention of metal ion impurities. Simultaneously, the sulfonic acid groups are stably bonded to the resin matrix, maintaining ion exchange activity at purification process temperatures of 50-80℃, ensuring stable impurity removal capabilities even after multiple cycles of use.

[0103] In some embodiments of the present invention, the OH-type gel anion exchange resin includes quaternary ammonium-modified cross-linked polystyrene; the quaternary ammonium-modified cross-linked polystyrene is specifically prepared by the following process: cross-linked polystyrene is reacted with chloromethyl ether at 20-40°C for 4-10 hours under zinc chloride catalysis, and the resulting intermediate is then amination with trimethylamine aqueous solution at 30-60°C for 2-5 hours to introduce quaternary ammonium groups, thereby obtaining the OH-type gel anion exchange resin.

[0104] The obtained OH-type gel anion exchange resin is strongly alkaline and can undergo a highly efficient ion exchange reaction with inorganic anion impurities in the feed solution, thereby achieving deep fixation of acid radical ions.

[0105] Meanwhile, the quaternary ammonium group exhibits excellent structural stability and can maintain high exchange activity within the purification temperature range of 50-80℃. It forms a synergistic deimpurification system with H-type gel cation exchange resin, helping to achieve comprehensive removal of inorganic salt impurities.

[0106] The aforementioned cross-linked polystyrene is prepared through the following process: styrene, divinylbenzene, and an initiator are mixed to obtain an oil phase; the prepared oil phase is dispersed in an aqueous phase containing gelatin or polyvinyl alcohol dispersant under stirring conditions to form a stable suspension system; the suspension system is subjected to a stepwise temperature-increasing reaction using a programmed temperature rise method, and finally, cross-linked polystyrene is obtained through polymerization. This cross-linked polystyrene serves as the matrix framework for H-type gel cation exchange resins and OH-type gel anion exchange resins. Strongly acidic H-type gel cation exchange resins can be prepared by introducing sulfonic acid groups through sulfonation, and strongly basic OH-type gel anion exchange resins can be prepared by introducing quaternary ammonium groups through chloromethylation and quaternization reactions. Its stable cross-linked structure is fundamental to ensuring the uniformity of resin column packing, ion exchange efficiency, and resin lifespan.

[0107] In some preferred embodiments, the mass percentage of divinylbenzene is 2%-12% based on the total mass of styrene monomers.

[0108] For example, the mass percentage of divinylbenzene is any value or a range of any two of 2%, 4%, 6%, 8%, 10%, 12%, etc., preferably 4 to 8%.

[0109] In some preferred embodiments, the stepwise heating reaction includes: first reacting at 70-80°C for 2-5 hours, and then heating to 85-95°C for 4-8 hours.

[0110] In some preferred embodiments, after the polymerization reaction is completed, the product is separated, washed and dried to obtain spherical cross-linked polystyrene white spheres.

[0111] The resulting spherical cross-linked polystyrene white spheres serve as the matrix for ion exchange resins. Their regular spherical structure ensures a uniform porosity during resin packing within the column, facilitating smooth flow of the feed solution and full contact with subsequently introduced functional groups. Simultaneously, the cross-linked structure endows the matrix with excellent chemical stability and mechanical strength, enabling it to withstand functionalization modifications such as sulfonation and quaternization, as well as temperature and flow rate shocks during the purification process, thus ensuring the resin's service life.

[0112] In some embodiments, before purification, the resin bed is heated to 50-80°C and held at that temperature for 10-20 minutes.

[0113] For example, the heating temperature is any value or a range of any two of 50°C, 60°C, 70°C, 80°C, etc.

[0114] For example, the heat preservation time is any value or a range of any two of 10 min, 15 min, 20 min, etc.

[0115] In this invention, heating the resin column to 50-80°C and holding it at that temperature for 10-20 minutes allows the filtrate to pass through a resin bed initially at 50-80°C for purification. This increases the ion exchange reaction rate, shortens the contact reaction time between the feed and the resin, and, while ensuring effective impurity removal, adapts to the filtrate flow rate requirement of 2-10 BV / h, thus improving process efficiency. Simultaneously, this temperature range optimizes the solubility of BHET in the feed, reduces BHET precipitation and adsorption / retention on the resin surface, further minimizing product loss, and maintains the ion exchange activity and structural stability of the resin, ensuring deep impurity removal.

[0116] In some embodiments, the filtrate passes through a resin bed to first obtain waste liquid, and then obtains BHET purified solution. The volume of the waste liquid is n times the total packing volume BV, where 0.5 ≤ n < 1.

[0117] For example, n is any value of 0.5, 0.6, 0.7, 0.8, 0.9, etc., or a range of any combination of both.

[0118] BV refers to the total packing volume of H-type gel cation exchange resin and OH-type gel anion exchange resin in the resin bed. In the purification method provided by this invention, the initial n·BV volume of liquid flowing out after the initial feed contains a significant amount of impurities (such as deionized water), resulting in low BHET purity. By controlling the waste liquid volume to 0.5BV~1BV, the residual solvent in the resin column and loosely adsorbed impurities on the resin bed surface can be fully replaced, allowing the resin bed and feed liquid to reach dynamic adsorption equilibrium. After the discharge of this volume of waste liquid, the subsequently collected BHET purified solution can be ensured to be in a stable high-purity state, guaranteeing that the impurity removal effect meets the requirements, while maximizing the recovery rate of the effective purified solution and reducing BHET product loss.

[0119] In some preferred embodiments, the first 0.5 BV of effluent is discarded during the initial feeding stage to balance the column bed and remove unstable components.

[0120] In some implementations, after discarding the waste liquid, continuous purification is performed, and the BHET purified liquid flowing out of the reactor outlet is collected.

[0121] In some specific implementations, the flow rate of the BHET purified solution flowing out of the outlet is controlled by adjusting the stopcock of the reaction column.

[0122] In some specific embodiments, the flow rate of the BHET purified solution flowing out of the outlet is 2-10 BV / h.

[0123] In some specific implementations, the flow rate of continuous purification is constant; that is, the flow rate of the BHET purified solution flowing out of the outlet is constant at 2~10 BV / h.

[0124] The filtrate flows through the resin bed and is purified before exiting the reaction column outlet to obtain BHET purified solution. The flow rate of the filtrate through the resin column can be controlled by adjusting the outflow rate of the purified solution at the reaction column outlet. This flow rate is controlled to be 2~10 BV / h.

[0125] This invention involves real-time sampling and detection of the BHET purified solution obtained from the outlet of the reaction column. The detection indicators include, but are not limited to, at least one of the following: liquid phase composition, metal ion impurity content, inorganic impurities, pH value, conductivity, or color purity analysis. This serves as a rapid indicator for judging the purification effect, ensuring response efficiency. In some embodiments, the BHET purified solution is further subjected to crystallization treatment to obtain purified BHET crystals; the purification process is stopped when at least one of the following conditions is met:

[0126] g. BHET purified solution color > 10;

[0127] h. The content of metal ion impurities in the purified BHET crystals is >5 mg / kg;

[0128] i. The inorganic impurity content of the purified BHET crystals is >10ppm;

[0129] j. The color value L of the purified BHET crystal is <95;

[0130] k. The color value b of the purified BHET crystal is >2;

[0131] l. The color value a of the purified BHET crystal is >0.5 or <-0.5.

[0132] This invention refers to the GB / T 30921.7-2016 standard and uses a colorimeter method to detect the color value of BHET crystals.

[0133] In some embodiments, the crystallization process includes: cooling and crystallizing the prepared BHET purified solution from the outlet, filtering, and drying to obtain purified BHET crystals. The content of inorganic impurities and metal ion impurities in the obtained purified BHET crystals is then detected.

[0134] In some implementations, a regeneration process is included after the purification process is stopped.

[0135] In some preferred embodiments, the regeneration process includes the following steps: rinsing the resin bed with acid solution and alkaline solution respectively, followed by washing with deionized water until the pH is 6.5-7.5.

[0136] For example, the pH is any value of 6.5, 7, 7.5, etc., or a range of any combination of both.

[0137] In this invention, when the BHET purified solution meets at least one of the above conditions, it indicates that the resin processing capacity has reached saturation (i.e., one purification cycle is completed, denoted as reaching saturation within a single cycle). The feeding of the filtrate and the collection of the BHET purified solution should be stopped; and the resin column should be replaced. The resin column can be replaced with a regenerated resin column or a resin column that has not undergone purification treatment.

[0138] The old resin column that has reached saturation in a single cycle will be regenerated, including the following process: the resin bed can be rinsed with acid solution and alkaline solution respectively, and then washed with deionized water until the pH is 6.5~7.5.

[0139] By monitoring the color, metal ion impurity content, inorganic impurity content, color value (L value), a value, and b value of the BHET purification solution, the purification process is stopped and the collection of BHET purification solution is halted when at least one of the above conditions is met. This allows for precise control of the purification endpoint, ensuring that all collected purification solutions meet quality requirements and guaranteeing batch stability of the product.

[0140] After regeneration (by rinsing the resin column with acid and alkali solutions respectively), the adsorbed metal cations and anions on the resin can be efficiently desorbed, restoring the resin's ion exchange activity and enabling resin recycling.

[0141] Washing with water to pH 6.5-7.5 can thoroughly remove residual acid and alkali solutions from the resin column, preventing residual acids and alkalis from contaminating subsequent purification solutions, ensuring that the purification effect of the regenerated resin is consistent with that of the fresh resin, and reducing the raw material cost for industrial production.

[0142] In some preferred embodiments, when the purification effect indicates that the resin treatment capacity is saturated, the old resin column to be replaced is rinsed with 3%~5% hydrochloric acid solution and 3%~5% sodium hydroxide solution, respectively, and then washed with deionized water until the pH is 6.5~7.5, and then set aside for use.

[0143] In some preferred embodiments, all purification operations must ensure that the resin bed is always submerged below the liquid surface. Keeping the resin bed moist prevents channeling and ensures effective purification.

[0144] In some embodiments, the BHET-containing mixture comprises BHET, metal ion impurities, and inorganic impurities, and satisfies at least one of the following conditions based on the total mass of the BHET-containing mixture:

[0145] m.BHET's mass percentage > 70%;

[0146] n. The concentration of metal ion impurities is 5-50 mg / kg;

[0147] o. The concentration of inorganic impurities is 10-150 mg / kg.

[0148] For example, the mass percentage of BHET is any value or a range of any two of 70%, 75%, 80%, 85%, 90%, etc.

[0149] For example, the concentration of metal ion impurities is any value or a range of any two of the following: 5 mg / kg, 10 mg / kg, 15 mg / kg, 20 mg / kg, 25 mg / kg, 30 mg / kg, 35 mg / kg, 40 mg / kg, 45 mg / kg, 50 mg / kg.

[0150] For example, the concentration of inorganic impurities is any value or a range of any two of the following: 10 mg / kg, 20 mg / kg, 30 mg / kg, 40 mg / kg, 50 mg / kg, 60 mg / kg, 70 mg / kg, 80 mg / kg, 90 mg / kg, 100 mg / kg, 110 mg / kg, 120 mg / kg, 130 mg / kg, 140 mg / kg, 150 mg / kg.

[0151] In some embodiments, the metal ion impurities include, but are not limited to, at least one metal cation selected from iron ions, calcium ions, sodium ions, and antimony ions.

[0152] The concentration of the aforementioned metal ion impurities is 5-50 mg / kg, meaning the total concentration of all metal cations contained in the metal ion impurities is 5-50 mg / kg.

[0153] In this invention, the mixture containing BHET is sintered to obtain ignition residue, and the concentration of the ignition residue of the mixture containing BHET is 10-150 mg / kg.

[0154] This invention relates to a mixed-bed purification system designed for mixtures containing BHET with a BHET mass percentage >70%, metal ion impurity concentration of 5-50 mg / kg, and inorganic impurity concentration of 10-150 mg / kg. This system exhibits excellent adaptability: the resin's high selectivity for impurities efficiently removes both metal ion and inorganic impurities while reducing ineffective BHET retention, achieving a high recovery rate; the resin's exchange capacity is precisely matched to the metal ion impurity concentration, allowing its content to be reduced to extremely low levels through single-cycle operation, eliminating the adverse effects of metal ion impurities on subsequent r-PET polymerization and ensuring product color and performance; and the synergistic effect and in-situ neutralization mechanism of the anion and cation exchange resins achieve comprehensive and deep removal of inorganic impurities, ultimately meeting the dual requirements of industrial production and high-quality r-PET preparation for both raw material purity and product yield.

[0155] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0156] In this invention, the colorimetric method is based on GB / T 3143-1982 standard, using the platinum-cobalt colorimetric method to determine the colorimetric value of the test solution. The color value method is based on GB / T 30921.7-2016 standard, using a colorimeter to detect the color value of BHET crystals. The mass percentage of BHET is determined by liquid chromatography. The sample crystals are dissolved in methanol and analyzed using high-performance liquid chromatography (HPLC), with qualitative analysis based on retention time and ultraviolet absorption spectroscopy, and quantitative analysis based on peak area. The content of BHET, MHET, and dimers is calculated using the external standard method.

[0157] The method for detecting inorganic impurities is in accordance with GB / T 7531-2008. The sample is sintered, and the content of the ignition residue is the inorganic impurity content.

[0158] The content of metal ion impurities shall be in accordance with the standard GB / T 30921.2-2016.

[0159] Unless otherwise specified, all reagents involved in the embodiments and comparative examples of this invention are commercially available products and can be obtained through commercial channels.

[0160] The experiments used products shown in Table 1 as H-type gel cation exchange resins and OH-type gel anion exchange resins, and crude BHET as shown in Table 2 as a mixture containing BHET. The metal ion impurities in Table 2 include: iron ions, calcium ions, sodium ions, antimony ions, etc.

[0161] Example 1

[0162] The mixture S-1 containing BHET was dissolved in a solvent under inert gas protection and heated to form a homogeneous phase (to obtain the BHET solution to be purified). While hot, it was filtered through a sintered sand funnel and a 0.45 μm filter membrane to remove insoluble particles, and the filtered filtrate was kept at 70 °C.

[0163] H-type gel cation exchange resin and OH-type gel anion exchange resin were mixed at a volume ratio of 1:2 to obtain a well-mixed resin.

[0164] With deionized water in the reaction column, the mixed resin was wet-charged to obtain a 100 mL resin bed (diameter-to-height ratio of 1:3). Simultaneously, the resin bed was heated to 75°C and held at that temperature for 20 minutes. It was ensured that the mixed resin remained submerged below the liquid surface to prevent drying and the introduction of air bubbles.

[0165] Before feeding, adjust the liquid level in the reaction column to be flush with the upper surface of the resin bed. Pour the filtrate into the feed end of the reaction column, allowing it to pass through the resin bed. BHET purified solution is obtained at the outlet of the reaction column. First, 50 ml of waste liquid is collected and discarded (the volume of the waste liquid is 0.5 times the total packing volume BV). Then, the flow rate of the BHET purified solution from the outlet is controlled at a constant flow rate of 4 BV / h (allowing the filtrate to pass through the resin bed at a flow rate of 4 BV / h) for continuous purification, yielding BHET purified solution L-1.

[0166] During the purification process described above, the BHET purified solution obtained from the outlet of the reaction column was sampled in real time, and the BHET purified solution was subjected to crystallization treatment: after cooling to room temperature for crystallization, it was dried in a vacuum oven at 50°C and pulverized into powder to obtain purified BHET crystals. The color of the BHET purified solution, as well as the BHET mass fraction, metal ion impurity content, inorganic impurity content, and color value of the purified BHET crystals, were measured.

[0167] BHET premium products meet at least one of the following conditions:

[0168] A. The color of the BHET purification solution is >10;

[0169] B. The metal ion impurity content of BHET crystals is >5 mg / kg;

[0170] C. The inorganic impurity content of BHET crystals is >10ppm;

[0171] D. The color value L of BHET crystal is <95;

[0172] E. The color value b of BHET crystal is >2;

[0173] The color value a of F.BHET crystals is >0.5 or <-0.5.

[0174] Once a purification cycle is completed, it is considered that saturation has been reached within a single cycle, at which point the collection of BHET purified solution is stopped (purification process is stopped). The old resin column that has reached saturation within a single cycle is then regenerated, including the following process: the resin bed is rinsed with acid solution and alkaline solution respectively, and then washed with deionized water until the pH reaches 7.0, to obtain the regenerated resin column.

[0175] Table 1:

[0176]

[0177] Table 2:

[0178]

[0179] Examples 2-9

[0180] Examples 2-9 are basically the same as Example 1, with the only difference being Table 3 below.

[0181] Example 10

[0182] The process is basically the same as in Example 1, except that the color of the BHET-containing mixture S-2 is 300, and the BHET-containing mixture contains organic matter with a molecular weight >1000 g / mol; the mixture is also pretreated with an adsorbent before filtration.

[0183] Comparative Example 1

[0184] It is basically the same as Example 1, except that it uses a mixture D-1 containing BHET and wet-filled macroporous strong acid cationic resin.

[0185] For every 100 BV of BHET purified solution obtained, the relevant indicators of the purified BHET crystals were tested, as shown in Table 4. Within a single cycle, the removal capacity for metal ion impurities essentially reached saturation after the exchange factor reached 300 BV, while the removal capacity for inorganic impurities was relatively poor.

[0186] Comparative Example 2

[0187] It is basically the same as Example 1, except that it uses a mixture D-2 containing BHET and wet-filled activated carbon (model NPYL-1).

[0188] For every 100 BV of purified BHET solution obtained, the relevant indicators of the purified BHET crystals were tested, as shown in Table 5.

[0189] Under the same bed volume and residence time, activated carbon has poor removal capabilities for both metal ion impurities and inorganic impurities.

[0190] Comparative Example 3

[0191] The process was essentially the same as in Example 1, except that it involved filtration only, without resin bed purification. The resulting BHET product contained 79.38 mg / kg of inorganic impurities and 7.5 mg / kg of metal ion impurities.

[0192] Comparative Example 4

[0193] The process is essentially the same as in Example 1, except that filtration is not performed; only resin bed purification is conducted. Starting from 300 BV, the inorganic impurity content is >10 mg / kg, and the metal ion impurity content is >5 mg / kg.

[0194] Table 3:

[0195]

[0196] Table 4:

[0197]

[0198] Table 5:

[0199]

[0200] Test case

[0201] In the purification process of Examples 1, 4, 6 and 10 above, 100 BV of BHET purified solution (1 BV = 100 mL) was collected from the outlet of the reaction column. The BHET purified solution obtained from the outlet of the reaction column was sampled in real time and crystallized: after cooling to room temperature for crystallization, it was dried in a vacuum oven at 50°C and pulverized into powder to obtain purified BHET crystals.

[0202] The color of the BHET purification solution, as well as the BHET mass fraction, metal ion impurity content, inorganic impurity content, and color value of the purified BHET crystals, were measured.

[0203] The test results for the BHET purified solution of Example 1 are shown in Table 6. The test results for the BHET purified solution of Example 4 are shown in Table 7. The test results for the BHET purified solution of Example 6 are shown in Table 8. The test results for the BHET purified solution of Example 10 are shown in Table 9.

[0204] Table 6: Detection results of BHET purified solution from Example 1

[0205]

[0206] Table 7: Detection results of BHET purified solution from Example 4

[0207]

[0208] Table 8: Detection results of BHET purified solution from Example 6

[0209]

[0210] Table 9: Detection results of BHET purified solution from Example 10

[0211]

[0212] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for purifying BHET, characterized in that, Includes the following steps: The mixture containing BHET is mixed with a solvent to obtain a BHET solution to be purified, which is then filtered to obtain a filtrate. The filtrate is purified by passing it through a resin bed at a flow rate of 2 BV / h to 10 BV / h to obtain BHET purified solution. The resin bed comprises an H-type gel cation exchange resin, an OH-type gel anion exchange resin, and a solvent. The H-type gel cation exchange resin has at least a portion of its surface containing sulfonic acid groups and H+. + The OH-type gel anion exchange resin has at least a portion of its surface containing quaternary ammonium groups and OH groups. - The volume ratio of the H-type gel cation exchange resin to the OH-type gel anion exchange resin is 1:(1~5); BV is the total packing volume of the H-type gel cation exchange resin and the OH-type gel anion exchange resin in the resin bed.

2. The purification method for BHET according to claim 1, characterized in that, The process prior to filtration further includes treating the BHET-containing mixture with an adsorbent when the BHET-containing mixture meets at least one of the following conditions: a. The color intensity of the BHET-containing mixture is >50 Hazen; b. The BHET-containing mixture contains organic matter with a molecular weight >1000 g / mol.

3. The purification method for BHET according to claim 1, characterized in that, The filtration process includes using a filter membrane with an average pore size of 0.3 μm to 0.5 μm.

4. The purification method for BHET according to claim 1, characterized in that, The diameter of the resin bed is D, the filling height of the resin bed is H, and the diameter-to-height ratio of the resin bed, D / H, is 1:(2~8).

5. The purification method for BHET according to claim 1, characterized in that, The H-type gel cation exchange resin satisfies at least one of the following conditions: c. Crosslinking degree is 8%~12%; d. Total volumetric exchange capacity ≥ 2.0 mmol / mL.

6. The purification method for BHET according to claim 1, characterized in that, The OH-type gel anion exchange resin satisfies at least one of the following conditions: e. Crosslinking degree is 8%~12%; f. Total volumetric exchange capacity ≥ 1.0 mmol / mL.

7. The purification method for BHET according to claim 1, characterized in that, The process also includes crystallizing the BHET purification solution to obtain purified BHET crystals; the purification process is stopped when at least one of the following conditions is met: g. The color of the BHET purification solution is >10; h. The metal ion impurity content of the purified BHET crystal is >5 mg / kg; i. The inorganic impurity content of the purified BHET crystal is >10ppm; j. The color value L of the purified BHET crystal is <95; k. The color value b of the purified BHET crystal is >2; l. The purified BHET crystal has a color value a > 0.5 or < -0.

5.

8. The purification method for BHET according to claim 1, characterized in that, After the purification process is stopped, a regeneration process is also included.

9. The purification method for BHET according to claim 1, characterized in that, Before the purification process, the resin bed is heated to 65°C to 75°C and kept at that temperature for 10 to 20 minutes.

10. The purification method for BHET according to any one of claims 1-9, characterized in that, The BHET-containing mixture comprises BHET, metal ion impurities, and inorganic impurities, and based on the total mass of the BHET-containing mixture, the BHET-containing mixture satisfies at least one of the following conditions: m. The mass percentage of the BHET is >70%; n. The concentration of the metal ion impurity is 5 mg / kg to 50 mg / kg; o. The concentration of the inorganic impurities is 10 mg / kg to 150 mg / kg.

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