Method for purifying colored regenerated dmt

Abstract

This invention discloses a method for purifying colored recycled DMT, belonging to the field of polyester recycling monomer purification technology. The method includes the following steps: dissolving colored recycled dimethyl terephthalate in an organic solvent to obtain a solution; adding a decolorizing adsorbent to the solution for adsorption and decolorization treatment, followed by filtration with the aid of a filter material to obtain a filtrate; removing the organic solvent from the filtrate, followed by washing with methanol to obtain a washed material; dissolving the washed material in methanol, performing heating dissolution, cooling crystallization, and washing to obtain a primary product; repeating the heating dissolution, cooling crystallization, and washing steps to obtain a crystalline product; and then performing vacuum distillation to obtain purified DMT. This invention not only achieves efficient decolorization and purification of colored recycled DMT but also avoids the high-energy-consumption and high-risk traditional distillation route.

Description

Technical Field

[0001] This invention relates to the field of polyester recycling and regeneration monomer purification technology, and in particular to a purification method for colored recycled DMT. Background Technology

[0002] Existing chemical recycling processes for polyethylene terephthalate (PET), such as methanol hydrolysis, can convert waste PET into basic chemicals like dimethyl terephthalate (DMT) and ethylene glycol. However, when the raw materials are complex wastes containing dyes, plasticizers, and other processing aids, such as colored fibers, colored bottle flakes, or fishing nets, the resulting crude DMT usually has a colored or dark appearance. If these coloring impurities are not effectively removed, they will affect the color and mechanical properties of the polyester product during subsequent repolymerization or refining, limiting its application in high-value fields. Traditional decolorization and purification methods, such as multi-step solvent washing, activated carbon adsorption, or high-temperature distillation, while effective to some extent, generally suffer from limitations such as high energy consumption, complex processes, and insufficient system adaptability. Although some publicly available technologies propose using activated carbon treatment combined with methanol washing to improve DMT purity, the overall process lacks systematic optimization. Especially for depolymerization products from complex waste PET sources containing various dyes and auxiliary agent residues, existing methods still struggle to achieve deep and stable decolorization while ensuring product yield. Furthermore, the significant differences in impurity composition and content among recycled DMT from different sources (such as textiles, fishing nets, and bottle flakes) further increase the difficulty of developing universal purification technologies. Therefore, efficient and economical decolorization processes for colored recycled DMT from complex sources still require further research and improvement. Summary of the Invention

[0003] The purpose of this invention is to provide a purification method for colored recycled DMT to solve the aforementioned problems in the background art. Specifically, this invention addresses the common problem in recycled DMT obtained from the depolymerization of colored waste PET: high content and complex composition of dyes, auxiliaries, and their degradation products. These products have strong binding forces with DMT molecules, are easily co-soluble and co-crystallized, and are difficult to completely remove through simple adsorption, washing, or conventional crystallization methods. Therefore, this invention proposes a staged synergistic purification method that achieves deep decolorization and high purification while ensuring yield.

[0004] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is to provide a method for purifying colored regenerated DMT, comprising the following steps: Colored recycled dimethyl terephthalate (DMT) was dissolved in an organic solvent to obtain a solution; A decolorizing adsorbent is added to the solution for adsorption and decolorization treatment, and then filtered with the aid of a filter material to obtain the filtrate. Remove the organic solvent from the filtrate, and then wash with methanol to obtain the washed material; The washed material is dissolved in methanol, and then subjected to heating to dissolve, cooling to crystallize, and washing to obtain a primary product. The heating to dissolve, cooling to crystallize, and washing steps are then repeated to obtain a crystalline product, which is then subjected to vacuum distillation to obtain refined DMT.

[0005] Preferably, the purification method includes the following steps: S1. Dissolve colored recycled dimethyl terephthalate (DMT) in an organic solvent and form a homogeneous solution under heating conditions; S2. Add a decolorizing adsorbent to the solution described in step S1 for adsorption and decolorization treatment, and then use a filter aid to filter the solution to remove the decolorizing adsorbent and insoluble impurities, thereby obtaining a clear filtrate. S3. Remove the organic solvent from the filtrate obtained in step S2 under reduced pressure to obtain the decolorized solid material. S4. The solid material after decolorization in step S3 is washed with methanol at low temperature to further remove residual impurities and obtain the washed material. By controlling the methanol washing process at low temperature, the loss of DMT dissolution can be reduced while the easily soluble impurities are preferentially dissolved, thereby improving the decolorization effect while ensuring the yield. S5. Dissolve the washed material described in step S4 in methanol, and perform heating dissolution, cooling crystallization and washing to obtain a primary product. Then, repeat the heating dissolution, cooling crystallization and washing steps to obtain a crystalline product. S6. The crystallized product obtained in step S5 is subjected to vacuum distillation to obtain purified DMT.

[0006] In this invention, the decolorizing adsorbent refers to a solid material capable of adsorbing polar or weakly polar impurities such as dyes, auxiliaries, and their degradation products contained in colored regenerated DMT in an organic solvent system. In the organic solvent system involved in this invention, activated clay, compared to conventional activated carbon adsorbents, exhibits higher selective adsorption capacity for dyes and byproducts, while showing weaker non-selective adsorption of DMT and is relatively less prone to forming a dense filter cake, thus making it more suitable for the decolorization process of this invention. The filter aid material refers to a porous material capable of improving filtration performance, promoting solid-liquid separation, and preventing filter clogging, including but not limited to diatomaceous earth. In the organic solvent system involved in this invention, a large number of fine adsorbent particles exist in the system after decolorization adsorption treatment. Without the addition of filter aid material, a dense filter cake is easily formed, leading to a significant increase in filtration resistance or even filter clogging, affecting the stable implementation of the process. Therefore, this invention, by limiting the addition of specific types and amounts of filter aid material, improves the filter cake structure, increases the porosity of the filter layer, and prevents fine powder compaction and clogging, thereby significantly improving filtration efficiency and process stability.

[0007] Preferably, the colored recycled dimethyl terephthalate is obtained by depolymerization of waste polyethylene terephthalate (PET); the waste polyethylene terephthalate is derived from one or more of dyed polyester fiber cloth, colored fishing nets, and colored bottle flakes.

[0008] The method provided by this invention is particularly suitable for the purification of depolymerization products of waste PET with high dye loading, such as dyed polyester fiber cloth, colored fishing nets, and colored bottle flakes. It provides a systematic and industrially implementable solution for the high-quality recycling of recycled DMT from complex sources.

[0009] Preferably, the organic solvent is one or more selected from acetonitrile, dimethyl carbonate, and dichloromethane.

[0010] Preferably, the decolorizing adsorbent is activated clay, and the amount added is 50% to 150% of the mass of the colored regenerated dimethyl terephthalate.

[0011] Preferably, the adsorption decolorization treatment time is 30-120 minutes.

[0012] Preferably, the filter aid material is diatomaceous earth, and the amount added is 50% to 150% of the mass of the colored regenerated dimethyl terephthalate.

[0013] Preferably, the amount of methanol used in the methanol washing process is 100% to 300% of the mass of the colored regenerated dimethyl terephthalate, and the methanol temperature is 0 to 5°C.

[0014] Preferably, the cycle of heating to dissolve, cooling to crystallize, and washing is performed twice.

[0015] Preferably, the temperature of the vacuum distillation is 150~220℃. Below 150℃, the distillation rate of DMT decreases significantly, which is detrimental to industrial efficiency; above 220℃, DMT is prone to thermal discoloration or side reactions, affecting the color and stability of the product. Therefore, it is preferable to control the vacuum distillation at 150~220℃. More preferably, the temperature of the vacuum distillation is 180℃.

[0016] Preferably, during the dissolution process in methanol, the amount of methanol used is 500% to 1000% of the mass of the colored regenerated dimethyl terephthalate.

[0017] The beneficial technical effects of the present invention are as follows: The purpose of this invention is to address the common problems in recycled DMT obtained from the depolymerization of colored waste PET, such as high content and complex composition of dyes, auxiliaries and their degradation products, strong binding force with DMT molecules, easy co-solubility and co-crystallization, which make it difficult to completely remove them by simple adsorption, washing or conventional crystallization methods. The invention proposes a staged synergistic purification method to achieve deep decolorization and high purification while ensuring yield.

[0018] To address the significant differences in impurity distribution and migration behavior of colored regenerated DMT under different physical states, this invention introduces targeted purification methods with different mechanisms of action during the dissolved, undissolved, and phase transition phases of DMT. This allows each step to complement and enhance the others, thus constructing a staged synergistic purification method. Through this staged treatment, each step targets different spatial locations and types of coloring impurities. The effective reduction of impurity load in the previous stage creates more favorable initial conditions for the subsequent purification stage, significantly improving the overall decolorization depth and purification efficiency. Experimental results show that while decolorization adsorption or single purification methods such as washing and crystallization can reduce product color to some extent, they cannot simultaneously achieve both decolorization depth and DMT recovery rate. However, when processed according to the staged purification sequence described in this invention, product color is further reduced, and DMT loss is significantly minimized. Therefore, without relying on high-temperature distillation or strong adsorption materials, staged removal of multiple types of coloring impurities from colored regenerated DMT is achieved, significantly improving decolorization depth and purification efficiency.

[0019] Specifically, under the dissolved state of DMT, the synergistic treatment of decolorization adsorption and filter aid material achieves efficient removal of readily soluble or co-soluble dyes and auxiliaries dissolved in organic solvents. The filter aid material, by constructing a loose and porous filter cake structure, effectively disperses the fine powder of the decolorizing adsorbent, preventing it from compacting and entraining the mother liquor during filtration. This reduces the re-migration of adsorbed impurities, ensuring stable retention of the decolorization effect. This effect cannot be achieved by simple solid-liquid separation. For example, if centrifugal separation is used, relying solely on density difference for phase separation makes it difficult to control the spatial structure of the adsorbent powder and easily weakens the stability of the decolorization adsorption effect. Subsequently, under solid-state and low-solidity conditions, low-temperature methanol washing preferentially removes residual soluble impurities adsorbed or entrained on the surface and pores of the DMT solid, further reducing impurity load while minimizing DMT dissolution loss. During the subsequent dissolution-crystallization process, the concentration of coloring impurities in the mother liquor is significantly reduced, decreasing the probability of them participating in lattice construction and being embedded at the crystal growth interface. This thermodynamically and kinetically weakens the co-crystallization behavior of impurities and DMT. Finally, trace amounts of volatile impurities and residual solvents were removed by vacuum distillation, ensuring that the obtained DMT met the requirements for high-purity applications.

[0020] This invention not only achieves efficient decolorization and purification of colored regenerated DMT, but also avoids the high energy consumption and high risk of traditional distillation routes. The process conditions are mild, and the solvent can be recycled, making it highly applicable to industrial applications and of great potential for wider application.

[0021] Experimental results show that the purification method for colored recycled DMT defined in this invention can obtain refined DMT with a significantly reduced color intensity below APHA 10 and a purity of up to 99.8%. Furthermore, the process is simple, the solvent is recyclable, and it is applicable to the purification of depolymerization products from colored waste PET from various sources. Comparative experiments further demonstrate that omitting any key purification step leads to a decrease in DMT purity or a significant increase in color intensity, indicating that each step in the method of this invention has a synergistic effect and is indispensable. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a purification process effect diagram of the colored regenerated DMT purification method in Embodiment 1 of the present invention.

[0024] Figure 2 This is a liquid chromatogram of the purified DMT in Example 1 of the present invention. Detailed Implementation

[0025] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0026] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0028] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0029] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0030] Example 1 A method for purifying colored regenerated DMT, comprising the following steps: S1. The dyed polyester fiber fabric (source: lining fabric, purchased from Taobao) was depolymerized with methanol. The specific method was as follows: at 130℃, methanol (3 times the mass of the fabric) was catalyzed by 5% of the fabric mass of DES catalyst DBN-4MI in a 100 mL reactor to degrade the fabric. The reaction was carried out for 1.5 hours. After the reaction, the product was dissolved in acetonitrile. The solution was rotary evaporated and the solid was washed with cold methanol solution to obtain crude colored recycled DMT (purity 96.80%, color 75). It was added to acetonitrile, heated to 60℃ and stirred to completely dissolve it and form a homogeneous solution. S2. Add activated clay (from Maclean's reagent, CAS No. 70131-50-9) to the solution obtained in step S1. The amount of activated clay is 100% of the original colored regenerated DMT mass. Stir and decolorize at 60℃ for 45 min. Then add diatomaceous earth (from Maclean's reagent, CAS No. 68855-54-9). The amount of diatomaceous earth is 100% of the colored regenerated DMT mass. Perform diatomaceous earth-assisted filtration to remove adsorbent and insoluble impurities, and obtain a clear filtrate. S3. The filtrate obtained in step S2 is subjected to rotary evaporation to recover acetonitrile under reduced pressure, and a decolorized solid material is obtained (yield 97.00%, purity 98.56%, color 22). S4. The decolorized solid material obtained in step S3 is washed and filtered with cold methanol at 0~5℃. The amount of cold methanol used is 150% of the mass of the colored regenerated DMT. The washed material is obtained (yield 95.54%, purity 99.15%, color 12). S5. Add the washed material obtained in step S4 to methanol, with the amount of methanol being 800% of the mass of the colored regenerated DMT. Heat to 70°C to completely dissolve it, then cool to 5°C for crystallization. Wash with cold methanol at 0-5°C to obtain the initial product. Continue to cycle the initial product according to the above dissolution-cooling-washing steps. After two cycles, obtain the crystalline product (yield 92.33%, purity 99.70%, color 6). S6. The crystalline product obtained in step S5 is subjected to vacuum distillation at 180°C to collect the solid product, and purified DMT (yield 90.81%, purity 99.82%, color 4).

[0031] Example 2 Compared with Example 1, the only difference is that the solvent in S1 is replaced by dimethyl carbonate (DMC) instead of acetonitrile; the rest of the steps are the same.

[0032] Example 3 Compared with Example 1, the only difference is that the solvent in S1 is replaced by dichloromethane (DCM) instead of acetonitrile; the rest of the steps are the same.

[0033] Example 4 Compared with Example 1, the only difference is that the amount of activated clay in S2 is changed to 50% of the mass of colored recycled DMT.

[0034] Example 5 The only difference from Example 1 is that the amount of activated clay in S2 is changed to 150% of the mass of colored recycled DMT.

[0035] Example 6 The only difference from Example 1 is that the amount of diatomaceous earth used in S2 is 50% of the mass of the colored regenerated DMT.

[0036] Example 7 The only difference from Example 1 is that the amount of diatomaceous earth used in S2 is 150% of the mass of the colored regenerated DMT.

[0037] Example 8 The only difference from Example 1 is that the amount of methanol used in S4 is 100% of the mass of the colored regenerated DMT.

[0038] Example 9 The only difference from Example 1 is that the amount of methanol used in S4 is 300% of the mass of the colored regenerated DMT.

[0039] Example 10 The only difference from Example 1 is that the amount of methanol used in S5 is 500% of the mass of the colored regenerated DMT.

[0040] Example 11 The only difference from Example 1 is that the amount of methanol used in S5 is 1000% of the mass of the colored regenerated DMT.

[0041] Example 12 The only difference from Example 1 is that the number of cycles in S5 is 1.

[0042] Example 13 The only difference from Example 1 is that the number of cycles in S5 is 3.

[0043] Example 14 Compared with Example 1, the only difference is that the dyed polyester fiber cloth is replaced with PET fishing net of the same weight (source: 10-mesh thickened fishing net cloth, purchased from Taobao), and the other steps are the same.

[0044] Example 15 Compared with Example 1, the only difference is that the dyed polyester fiber cloth is replaced with an equal mass of colored PET bottle flakes (sourced from Pulse beverage bottles), and the other steps are the same.

[0045] Example 16 The only difference from Example 1 is that the amount of activated clay in S2 is changed to 80% of the mass of colored recycled DMT.

[0046] Example 17 The only difference from Example 1 is that the amount of activated clay in S2 is changed to 120% of the mass of colored regenerated DMT.

[0047] Comparative Example 1 Compared with Example 1, the only difference is that the addition of activated clay in step S2 is omitted, while the other steps are the same.

[0048] Comparative Example 2 Compared with Example 1, the only difference is that the addition of diatomaceous earth in step S2 is omitted, and the decolorized system is directly filtered; the other steps are the same.

[0049] Comparative Example 3 Compared with Example 1, the only difference is that the low-temperature methanol washing in step S4 is omitted, and the decolorized solid material obtained in step S3 is directly used in S5, while the other steps are the same.

[0050] Comparative Example 4 Compared with Example 1, the only difference is that the methanol recrystallization in step S5 is omitted, and the washed material obtained in step S4 is directly subjected to vacuum distillation in step S6, while the other steps are the same.

[0051] Comparative Example 5 Compared with Example 1, the only difference is that the recycling step in step S5 is omitted, and the initial product of S5 is directly subjected to vacuum distillation according to the conditions of step S6, while the other steps are the same.

[0052] Comparative Example 6 Compared with Example 1, the only difference is that step S6, which involves vacuum distillation, is omitted; the other steps are the same.

[0053] Comparative Example 7 The only difference from Example 1 is that the clarified filtrate obtained in step S2 is used as the product for characterization and analysis.

[0054] Comparative Example 8 Compared with Example 1, the only difference is that steps S2 and S3 are omitted, and the solution obtained in step S1 is processed according to the conditions of step S4 and then used as the product for characterization and analysis.

[0055] Comparative Example 9 Compared with Example 1, the only difference is that steps S2, S3, and S4 are omitted, and the solution obtained in step S1 is processed according to the conditions in step S5 and then used as the product for characterization and analysis.

[0056] Comparative Example 10 Compared with Example 1, the only difference is that steps S2, S3, S4, and S5 are omitted, and the solution obtained in step S6 is processed according to the conditions of step S6 and then used as the product for characterization and analysis.

[0057] Comparative Example 11 Compared to Example 1, the only difference is that the cold methanol at 0-5°C in step S4 is replaced with methanol at room temperature (20-25°C). After washing, only the DMT recovery rate and color change of the material in this step are measured.

[0058] Comparative Example 12 Compared with Example 1, the only difference is that the decolorizing adsorbent in step S2 is replaced by an equal mass of activated carbon instead of activated clay, while the other steps are the same.

[0059] Test case The purity and color of the purified DMT obtained in Examples 1-17 and Comparative Examples 1-12 were characterized and analyzed, and the results are shown in Tables 1-8.

[0060] Wherein, DMT purity (%) = DMT peak area / peak area of ​​all detectable components; DMT chromaticity = equivalent APHA chromaticity value.

[0061] Table 1. Comparison of DMT color and purity under different purification conditions. Table 2. Effect of white clay dosage on DMT purification effect Table 3 Omits the impact of individual process steps on DMT purification efficiency. Table 4 shows the impact of completing only a single process step on the DMT purification effect. Table 5. Effects of different solvent systems on DMT purification efficiency Table 6. Effect of methanol washing temperature on DMT recovery and decolorization effect Table 7. Effect of Adsorbent on Purification Efficiency Table 8 shows the main targets and performance impacts of each key step. As can be seen from the data in the table, the purified DMT obtained by the methods of Examples 1 to 17 all have high purity and low color value, indicating that the method of the present invention can effectively remove impurities and coloring substances from colored regenerated DMT. In contrast, the purity and color of the DMT obtained by Comparative Examples 1 to 3 are significantly worse than those of the examples, indicating that omitting key steps will affect the purification effect.

[0062] As shown in Table 2, the decolorization of the colored regenerated DMT can be achieved within the range of 50% to 150% of the mass of the activated clay relative to the colored regenerated DMT. Among them, the purity and color of DMT are more stable within the preferred dosage range, indicating that this dosage range has good applicability.

[0063] As can be seen from Table 3, the steps of activated clay decolorization, diatomaceous earth-assisted filtration, low-temperature methanol washing, methanol recrystallization, repeated dissolution and crystallization, and vacuum distillation all play an important role in improving the purity of DMT and reducing its color. The absence of any step will lead to a decrease in the purity of DMT or an increase in its color, indicating that the above steps are irreplaceable in the method of the present invention.

[0064] Table 4 shows that neither adsorption decolorization, low-temperature methanol washing, recrystallization, nor vacuum distillation alone could simultaneously yield DMT products with high purity and low color. However, after implementing the complete process of adsorption decolorization, low-temperature washing, recrystallization, and vacuum distillation sequentially, the DMT purity significantly increased to 99.82%, and the color decreased to 4 APHA, which was significantly better than the results of any single step. This indicates that the preceding steps, by progressively reducing the impurity concentration in the system, altered the phase equilibrium and selectivity in the subsequent separation process. The decolorization effect of the complete process was far greater than the linear additive trend of the effects of each single step, indicating that the separation selectivity of the subsequent separation steps was enhanced after the impurity load in the preceding steps was reduced, thus producing a synergistic purification effect, rather than a simple additive effect.

[0065] As can be seen from Table 5, the method of the present invention can obtain purified DMT with high purity and low color in different solvent systems, indicating that the purification method has good adaptability to solvent systems.

[0066] As shown in Table 6, under the same methanol dosage, low-temperature (0~5℃) methanol washing can effectively reduce DMT color while maintaining a high DMT recovery rate. In contrast, although room temperature conditions can further dissolve some impurities and reduce color, the dissolution loss of DMT increases significantly. Under low-temperature conditions, the mass ratio of colored impurities to DMT in the washing solution is significantly higher than that under room temperature conditions, indicating that by controlling the methanol washing process at low temperatures, impurities can be preferentially dissolved compared to DMT, thereby improving the decolorization effect while ensuring the yield.

[0067] As shown in Table 7, when conventional activated carbon was used instead of activated clay (Comparative Example 12), the color of the DMT product increased significantly, and the yield decreased markedly. This indicates that activated carbon has a strong non-selective adsorption effect on DMT. Furthermore, its fine powder easily forms a dense filter cake, causing some adsorbed impurities to be released again during filtration, thus reducing decolorization stability. In contrast, activated clay exhibits higher selective adsorption capacity for coloring impurities in the solvent system of this invention, while showing weaker adsorption of DMT bulk molecules. Therefore, it can achieve deeper decolorization while maintaining a high yield.

[0068] As can be seen from Table 8, the purification steps of this invention differ from each other in terms of their target and failure modes. No single step can replace the others, and their synergistic effect comes from functional complementarity rather than effect superposition.

[0069] Figure 1 This is a purification process effect diagram of the colored regenerated DMT purification method in Embodiment 1 of the present invention.

[0070] Figure 2 This is a liquid chromatogram of the purified DMT in Example 1 of the present invention.

[0071] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for purifying colored regenerated DMT, characterized in that, Includes the following steps: Colored recycled dimethyl terephthalate was dissolved in an organic solvent to obtain a solution; A decolorizing adsorbent is added to the solution for adsorption and decolorization treatment, and then filtered with the aid of a filter material to obtain the filtrate. Remove the organic solvent from the filtrate, and then wash with methanol to obtain the washed material; The washed material is dissolved in methanol, and then subjected to heating to dissolve, cooling to crystallize, and washing to obtain a primary product. The heating to dissolve, cooling to crystallize, and washing steps are then repeated to obtain a crystalline product, which is then subjected to vacuum distillation to obtain refined DMT.

2. The purification method according to claim 1, characterized in that, The colored recycled dimethyl terephthalate is obtained by depolymerization of waste polyethylene terephthalate.

3. The purification method according to claim 1, characterized in that, The organic solvent is one or more of acetonitrile, dimethyl carbonate, and dichloromethane.

4. The purification method according to claim 1, characterized in that, The decolorizing adsorbent is activated clay, and the amount added is 50% to 150% of the mass of the colored regenerated dimethyl terephthalate.

5. The purification method according to claim 1, characterized in that, The adsorption and decolorization treatment time is 30-120 minutes.

6. The purification method according to claim 1, characterized in that, The filter aid material is diatomaceous earth, and the amount added is 50% to 150% of the mass of the colored regenerated dimethyl terephthalate.

7. The purification method according to claim 1, characterized in that, The amount of methanol used in the methanol washing process is 100% to 300% of the mass of the colored regenerated dimethyl terephthalate, and the methanol temperature is 0 to 5°C.

8. The purification method according to claim 1, characterized in that, The temperature for vacuum distillation is 150~220℃.

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