A process and system for recovering dmt and dmc from polyester-containing blended fabrics

Abstract

The application provides a process and system for recovering DMT and DMC from polyester-containing blended fabric, comprising: under the action of an ionic catalyst, a depolymerization reaction of polyester-containing blended fabric and DMC; after the reaction, the material is subjected to solid-liquid separation and first crystallization to obtain a crystallization mother liquor and a DMT crude product, the DMT crude product is subjected to dissolution, removal of solid impurities and recrystallization to obtain a DMT pure product; the crystallization mother liquor is subjected to light removal, reaction rectification and extractive rectification to obtain a second DMC fraction, which is recycled to the depolymerization reaction; a methanol fraction, which is recycled to the reaction rectification; and an extractant fraction, which is recycled to the extractive rectification. The operation conditions are mild, the material and energy are closely coupled between units, a multiple circulation network of DMC, methanol, extractant and catalyst is formed, the overall resource utilization rate is high, the degree of greenness is high, and an economic and feasible technical scheme which is easy to industrialize is provided for chemical recycling of waste polyester textiles.

Description

Technical Field

[0001] This invention relates to the field of DMT recycling technology, and specifically to a process and system for recovering DMT and DMC from polyester blended fabrics. Background Technology

[0002] With the rapid development of the textile industry, the large-scale generation of waste textiles, especially synthetic fiber blended fabrics (such as polyester-cotton and polyester blends), has brought severe environmental pressure and resource waste problems. Chemical depolymerization technology has attracted widespread attention because it can convert waste polyester into high-value monomers (such as dimethyl terephthalate, DMT) and is an important way to realize the resource recycling of textiles.

[0003] However, the efficient separation of depolymerization products from synthetic fibers is a key bottleneck restricting the industrial application of this technology. The depolymerization process forms a complex multi-component system containing the target monomer (DMT), unreacted residues, catalysts, solvents (such as dimethyl carbonate, DMC), byproducts, dye molecules, and trace impurities. Due to the similar physicochemical properties and strong interactions among the components, residual oligomers, dyes, metal ions, and other impurities can interfere with the molecular assembly, nucleation, and crystal growth of DMT crystals, making it difficult to obtain high-purity monomers using conventional crystallization processes. Furthermore, the efficient recovery and recycling of DMC, which serves as both a reaction medium and a raw material, lacks effective process design, resulting in significant solvent losses and high operating costs.

[0004] In existing technologies, synergistic approaches combining membrane separation, distillation, crystallization, and extraction have been developed for the separation of complex depolymerization systems, but significant shortcomings remain. For example, in monomer purification, high-melting-point monomers such as DMT are often separated through crystallization, but this process is easily affected by soluble impurities. Although some studies have attempted to use membrane separation and adsorption for pretreatment, existing methods are either too costly or insufficient in removing high-boiling-point impurities, residual catalysts, and dye molecules from depolymerization systems. For instance, in the pretreatment stage of blended fabrics, although some studies have used eutectic solvents, ionic liquids, or low-boiling-point bio-based solvents (such as HFIP) for component separation, solvent recovery costs and separation efficiency still need improvement. Through exploratory experiments, our research team discovered that DMC can not only serve as a raw material for depolymerization reactions, but its low boiling point (90°C) and ease of separation from dyes and catalysts make it an ideal green solvent. However, a systematic integrated process solution is still lacking for efficiently recovering DMC from complex systems after depolymerization and simultaneously obtaining high-purity DMT. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention discloses a process and system for recovering DMT and DMC from polyester-blended fabrics, which can simultaneously achieve efficient purification of DMT and recycling of DMC from complex depolymerization systems.

[0006] To achieve the above technical objectives, on the one hand, this invention proposes a process for recovering DMT and DMC from polyester-blended fabrics, the method comprising: (1) Under the action of an ionic catalyst, polyester blended fabrics undergo depolymerization reaction with DMC; (2) Perform solid-liquid separation on the reacted material and take the liquid phase material; (3) The liquid phase material is subjected to a first crystallization to obtain crystallization mother liquor and crude DMT; The crude DMT is dissolved, solid impurities are removed, and it is recrystallized to obtain pure DMT. The mother liquor for crystallization is subjected to the following treatments in sequence: S1: Input the light-light-removal tower for separation, collect the first DMC fraction from the top of the tower and recycle it to step (1). S2: The bottom product of the light-light removal tower is subjected to transesterification with methanol in a reactive distillation column; S3: The product collected from the top of the reactive distillation column is subjected to extractive distillation to separate the following: The second DMC fraction is recycled to step (1). The methanol fraction is recycled to step S2; The extractant fraction is recycled for further extractive distillation.

[0007] To address the issue of impurities interfering with DMT crystallization in the DMC depolymerization system, the aforementioned technical solution achieves high-purity DMT through a two-stage crystallization coupling process. Specifically: the first crystallization separates crude DMT from the mother liquor in the liquid phase, achieving initial enrichment of DMT; after dissolving, the crude DMT is filtered to remove insoluble solid impurities (such as residual fibers, carbonized particles, etc.), followed by recrystallization. Utilizing the amplification effect of the difference in solubility between impurities and DMT in the solvent, soluble impurities (such as oligomers, dye molecules, etc.) are thoroughly removed. This two-stage crystallization coupling ensures both the DMT yield through the first crystallization and the product purity through recrystallization, ultimately yielding a high-purity DMT product that meets the quality requirements of repolymerization or high-end applications.

[0008] Furthermore, the aforementioned technical solution constructs a three-stage coupled DMC recovery process of "light weight removal-reactive distillation-extractive distillation," forming two DMC circulating streams. Specifically: the first stream originates from the top of the light weight removal column, directly recovering most of the DMC from the crystallization mother liquor. Utilizing the significant boiling point difference between DMC and components such as DMT, EC, and DD, rapid separation is achieved through preliminary distillation (light weight removal), and the resulting first DMC fraction is directly reused in the depolymerization reaction. The second stream originates from the extractive distillation operation, where the DMC-methanol mixture collected from the top of the reactive distillation column is deeply purified through extractive distillation, and the resulting second DMC fraction is also reused in the depolymerization reaction. Through the synergistic replenishment of the two DMC fractions, a high DMC recovery rate is ensured, while the energy load of a single distillation is reduced through staged recovery, achieving closed-loop recycling of DMC in the depolymerization system.

[0009] Furthermore, the above technical solution constructs an internal circulation network for methanol and extractant through an integrated design of reactive distillation and extractive distillation. Specifically: in the reactive distillation column, methanol undergoes transesterification with the EC and DD-containing feedstock collected from the bottom of the light-duty removal column, converting the byproduct into reusable DMC; excess methanol and the product DMC form a mixture at the top of the column, which is then separated in the extractive distillation column; the methanol fraction collected from the top of the extractive distillation column is directly returned to the reactive distillation column as a reaction feedstock, forming an internal methanol circulation; the extractant stream collected from the bottom of the column is recycled for extractive distillation operations, achieving zero loss of extractant. This dual-circulation mechanism avoids external replenishment and emissions of methanol and extractant, significantly reducing feedstock consumption and waste generation, and improving the greenness of the process.

[0010] In a further example of the present invention, the temperature of the depolymerization reaction is 70~150°C, the reaction pressure is 0.5~4MPa, and the reaction time is 0.5~3h.

[0011] In a further example of the present invention, the ionic catalyst is selected from at least one of tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylphosphorus chloride, zinc chloride, sodium chloride, and potassium chloride.

[0012] In a further example of the present invention, the amount of the ionic catalyst is 8% to 20% of the weight of the polyester-blended fabric. In an optional example of the present invention, the amount of the ionic catalyst is 10% to 17% of the weight of the polyester-blended fabric.

[0013] In a further example of the present invention, the mass ratio of DMC to the polyester-containing blended fabric is (5~15):1. In an optional example of the present invention, the mass ratio of DMC to the polyester-containing blended fabric is (8~10):1.

[0014] In a further example of the present invention, the first crystallization is cooling crystallization, which includes: cooling the liquid phase material to 0-25°C at a rate of 0.1-2K / min to perform crystallization.

[0015] In a further example of the present invention, in step (3), at least one of acetonitrile, ethylene glycol, and methanol is used to dissolve the crude DMT, preferably methanol.

[0016] In a further example of the present invention, the mass ratio of the crude DMT to the solvent for dissolution is 1:(5~30) to improve the recrystallization efficiency.

[0017] In a further example of the invention, the recrystallized mother liquor is distilled, the solvent is collected from the top of the distillation column and used to dissolve the crude DMT, the DMT is enriched in the bottom of the column and recycled to the first crystallization.

[0018] In a further example of the present invention, the process further includes purifying the DMT product by vacuum distillation to obtain pure DMT.

[0019] In a further example of the present invention, the top temperature of the light-weight removal tower is 60~260℃, the bottom temperature is 160~460℃, the absolute pressure is 0.05~0.25MPa, the theoretical number of trays is 10~40, and the reflux ratio is 0.5~5.

[0020] In a further example of the present invention, the reactive distillation column has a top temperature of 50~250°C, a bottom temperature of 150~450°C, an absolute pressure of 0.05~0.25MPa, a theoretical plate number of 10~40, and a reflux ratio of 0.5~5.

[0021] In a further example of the present invention, the mass ratio of the bottom feed of the light-light-removal column to methanol in the reactive distillation column is 1:(0.5~1.4). In an optional example of the present invention, the mass ratio of the bottom feed of the light-light-removal column to methanol is 1:(0.5~1).

[0022] In a further example of the present invention, the extractive distillation is carried out in a partition column of the extractive distillation column, wherein the top temperature of the partition column is 50~250°C, the bottom temperature is 150~450°C, the absolute pressure is 0.05~0.25MPa, the number of theoretical plates is 20~100, and the reflux ratio is 2~10.

[0023] In a further example of the invention, the extractant used for the extractive distillation is selected from at least one of cyclohexane, o-xylene, and ethylene glycol, preferably cyclohexane or ethylene glycol.

[0024] In a further example of the present invention, the mass ratio of the extractant to the overhead product of the reactive distillation column is (0.2~2.5):1. In an optional example of the present invention, the mass ratio of the extractant to the overhead product of the reactive distillation column is (0.2~2):1.

[0025] In a further example of the present invention, the process further includes: evaporating and concentrating the bottom product of the reactive distillation column, leaching it with water, separating the solid and liquid components, flocculating it, and evaporating and crystallizing it to obtain the recovered ionic catalyst.

[0026] In a further example of the invention, the recovered ionic catalyst is recycled to step (1).

[0027] In a further example of the present invention, the solid phase material obtained from solid-liquid separation is combined and dissolved with the crude DMT product to prepare the DMT product.

[0028] In a further example of the invention, the condensate obtained from evaporation and crystallization is used in the water leaching operation.

[0029] In a further example of the present invention, the flocculant is selected from at least one of polyferric sulfate, polyferric chloride, polyaluminum chloride, polyaluminum sulfate, polyferric aluminum sulfate, polyferric aluminum chloride, polyacrylamide, polyquaternary ammonium salt, and polyether; preferably polyferric chloride and / or polyacrylamide.

[0030] On the other hand, the present invention proposes a system for recovering DMT and DMC from polyester-blended fabrics, the system comprising: A reaction vessel used for depolymerization reaction of polyester blended fabrics with DMC; The first solid-liquid separation device is used to separate the solid and liquid phases of the material after the depolymerization reaction and take the liquid phase material. A primary crystallizer is used for the crystallization operation of the liquid phase material; The second solid-liquid separation unit is used to separate the crystallized material to obtain crystallization mother liquor and crude DMT. Also includes: The DMT refining unit is used for refining crude DMT; it includes a first dissolving vessel, a third solid-liquid separation device, a secondary crystallizer and a fourth solid-liquid separation device connected in sequence, and DMT products are obtained from the solid phase outlet of the fourth solid-liquid separation device. A DMC refining and recovery unit is used to recover DMC from the crystallization mother liquor; it includes a light-weight removal column, a reactive distillation column, and an extractive distillation partition wall column connected in sequence; wherein... The feed inlet of the light component removal column receives the crystallization mother liquor, the top outlet of the column outputs the first DMC fraction and connects to the DMC inlet of the reactor, and the bottom outlet of the column is connected to the feed inlet of the reactive distillation column. The top outlet of the reactive distillation column is connected to the feed inlet of the extractive distillation column; The methanol fraction is output from the top of the extractive distillation partition wall column and recycled to the reactive distillation column. The second DMC fraction is output from the side stream outlet and connected to the DMC inlet of the reactor. The extractant fraction is output from the bottom outlet and recycled.

[0031] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention utilizes a dual-stream DMC recovery mechanism combining preliminary distillation in a light-light-removal tower with deep purification through extractive distillation. Combined with reactive distillation, byproducts EC and DD are converted into reusable DMC and DMT, achieving efficient separation and recovery of DMC. The design incorporating internal methanol and extractant circulation reduces raw material replenishment and solvent emissions, significantly lowering raw material costs and environmental pressure. Furthermore, the two-stage purification process, coupled with first crystallization and recrystallization, effectively removes multi-component impurities from the depolymerization system, obtaining high-purity DMT products, thus achieving efficient synergistic recovery of DMT and DMC.

[0032] The process and system for recovering DMT and DMC from polyester blended fabrics of this invention adopts conventional chemical equipment, operates under mild conditions, and has close material and energy coupling between units, forming a multi-cycle network of DMC, methanol, and extractant. The overall resource utilization rate is high and the degree of greening is high, providing an economical, feasible, and easily industrialized technical solution for the chemical recycling of waste polyester textiles. Attached Figure Description

[0033] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This diagram illustrates a structural representation of a system for recovering DMT and DMC from polyester-blended fabrics according to the present invention.

[0034] Figure 2 This diagram shows another structural diagram of the system for recovering DMT and DMC from polyester-blended fabrics according to the present invention.

[0035] The above figures include the following reference numerals: 1-Reaction vessel; 21-First solid-liquid separation device; 22-Second solid-liquid separation device; 23-Third solid-liquid separation device; 24-Fourth solid-liquid separation device; 25-Fifth solid-liquid separation device; 31-First-stage crystallizer; 32-Second-stage crystallizer; 33-Evaporation crystallizer; 41-First dissolving vessel; 42-Second dissolving vessel; 51-Light weight removal tower; 52-Reactive distillation tower; 53-Extractive distillation partition wall tower; 54-Ambient pressure distillation tower; 55-Vacuum pressure distillation tower; 6-Evaporation concentrator; 7-Flocculation device; 81-DMT refining unit; 82-DMC refining and recovery unit; 83-Catalyst recycling and recovery unit; 84-Pretreatment unit. Detailed Implementation

[0036] To facilitate understanding of the present invention, a more comprehensive description will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the invention in any way, i.e., not intended to limit the scope of protection of the invention.

[0037] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0038] Furthermore, it should be noted that although the various steps of the preparation method of the present invention are described in a specific order in the description of the present invention, these orders are not restrictive. Without departing from the basic principles of the present invention, those skilled in the art can perform the steps in different orders.

[0039] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "multiple" or "at least one" means two or more.

[0040] All numerical designations, such as pH, temperature, length, flow rate, and range, are approximate values. It should be understood that, while not always explicitly stated, all numerical designations are preceded by the term "approximately." It should also be understood that, while not always explicitly stated, the reagents described herein are merely examples, and their equivalents are known in the art.

[0041] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0042] In a first aspect, the present invention proposes a process for recovering DMT and DMC from polyester-blended fabrics, the method comprising: (1) Under the action of an ionic catalyst, polyester blended fabrics undergo depolymerization reaction with DMC; (2) Perform solid-liquid separation on the reacted material and take the liquid phase material; (3) The liquid phase material is subjected to a first crystallization to obtain crystallization mother liquor and crude DMT; The crude DMT is dissolved, solid impurities are removed, and it is recrystallized to obtain pure DMT. The crystallization mother liquor is subjected to the following treatments in sequence: S1: Input light-light-removal tower 51 for separation, collect the first DMC fraction from the top of the tower and recycle it to step (1). S2: The bottom product of the light-light removal tower 51 is subjected to transesterification with methanol in the reactive distillation tower 52; S3: The product collected from the top of the reactive distillation column 52 is subjected to extractive distillation to separate the following: The second DMC fraction is recycled to step (1). The methanol fraction is recycled to step S2; The extractant fraction is recycled for further extractive distillation.

[0043] In step (1), the polyester blended fabric and DMC (dimethyl carbonate) are fed into reactor 1 together for depolymerization reaction. In this reaction process, DMC plays the role of depolymerizing agent and solvent.

[0044] Optionally, the depolymerization reaction is carried out at a temperature of 70~150℃, a reaction pressure of 0.5~4MPa, and a reaction time of 0.5~3h.

[0045] Optionally, the ionic catalyst is at least one of tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylphosphine chloride, zinc chloride, sodium chloride, and potassium chloride.

[0046] Optionally, the amount of the ionic catalyst is 8% to 20% of the weight of the polyester-blended fabric. A suitable amount of ionic catalyst can improve the depolymerization reaction efficiency. In an optional example of the present invention, the amount of the ionic catalyst is 10% to 17% of the weight of the polyester-blended fabric.

[0047] Optionally, the mass ratio of DMC to the polyester-containing blended fabric is (5~15):1. In an optional example of the present invention, the mass ratio of DMC to the polyester-containing blended fabric is (8~10):1.

[0048] It should be noted that the present invention does not limit the equipment used for the reaction in step (1), and can be a container that can solve the reaction, such as a reaction vessel, preferably a reaction vessel with a stirring device.

[0049] It should be noted that the specific composition of polyester-containing blended fabrics is not limited in this invention. Fabrics containing polyester polymers (polymers linked by ester bonds) and blends with other components, such as polyester-cotton, polyester filament, polyester linen, and polyester wool, are all suitable for the process of this invention. Optionally, in the process described in this invention, the polyester-containing blended fabrics are preferably pretreated before use; the pretreatment includes washing, drying, and / or mechanically crushing waste fabrics to remove impurities and obtain a material form suitable for the reaction.

[0050] It should be noted that the process of the present invention can be used for the depolymerization and recycling of waste textiles. The polyester-blended textiles often contain metal ions, auxiliaries, dye molecules, etc., so after the depolymerization reaction, these impurities will exist in the material after the reaction in step (1).

[0051] In step (2), the material after the depolymerization reaction is separated by solid-liquid separation to obtain a liquid material containing impurities such as DMT, EC (ethylene carbonate), DD (dimethyl 2,5-dioxadipic acid), DMC, dyes, metal ions and auxiliaries, as well as a solid material containing cotton fibers; optionally, the solid material can be washed and dried to obtain cotton fibers.

[0052] It should be noted that the specific operation of solid-liquid separation in step (2) of the present invention is not limited. It can be selected as any operation that can separate the liquid phase material from the solid phase material, such as filtration, centrifugation, etc. Those skilled in the art can make the selection according to the actual working conditions.

[0053] Through experiments, the research and development team of this invention discovered that the solubility of DMT in DMC varies greatly with temperature. If the liquid phase material is cooled before entering the subsequent separation process, it may cause DMT to precipitate, affecting the stability of the process or the purity of the product. Based on this discovery, in step (3) of the process of this invention, after the liquid phase material is crystallized for the first time, DMT and DMC are then purified and recovered separately.

[0054] In step (3), the first crystallization includes cooling the liquid phase material to 0-25°C at a rate of 0.1-2K / min, and performing crystallization under this temperature condition.

[0055] It should be noted that the present invention does not limit the equipment settings for the first crystallization. A crystallization vessel with controllable temperature, or a crystallization vessel resistant to organic solvents and high and low temperatures, can be selected according to the needs of those skilled in the art.

[0056] The present invention provides a DMT refining unit 81 with two crystallization couplings.

[0057] Based on the first crystallization, by dissolving and removing solid impurities, insoluble impurities (mainly including additives doped during polymer polymerization) in crude DMT can be removed, which is beneficial to improving the quality of pure DMT obtained by subsequent recrystallization.

[0058] Optionally, at least one of acetonitrile, ethylene glycol, and methanol is used to dissolve the crude DMT. Since the mother liquor after subsequent recrystallization requires solvent recovery, selecting a specific solvent with a significantly different boiling point from DMT facilitates obtaining a solvent of the required purity at the top of the distillation column using atmospheric distillation (distillation column), which can then be recycled to the crude DMT dissolution process, reducing operational complexity and cost. In an optional embodiment of the invention, methanol is used to dissolve the crude DMT.

[0059] It should be noted that the DMT-enriched stream obtained from the bottom of atmospheric distillation column 54 will be returned to the crystallizer for further recrystallization to ensure the DMT yield. Furthermore, since the bottom of atmospheric distillation column 54 may accumulate some high-boiling-point impurities, its bottom material can be periodically discharged as solid waste.

[0060] Optionally, the atmospheric distillation operation is carried out in an atmospheric distillation column 54, wherein the top temperature of the column is 40~90℃, the bottom temperature is 80~280℃, the absolute pressure is 0.05~0.25MPa, the number of theoretical plates is 10~80, and the reflux ratio is 0.5~8.

[0061] It should be noted that the present invention does not limit the specific operation for removing solid impurities. The operation can be any operation that can achieve solid-liquid separation, such as filtration, centrifugation, etc. Those skilled in the art can choose according to the actual working conditions.

[0062] In the actual process, the purity of the DMT product can be detected by XRD and high-performance liquid chromatography. Examples demonstrate that the process of this invention can obtain DMT products with a purity of over 99%, and the DMT recovery rate can reach 92%. In the actual process, when further product purification is required, the pure DMT product can be subjected to vacuum distillation to collect a higher purity DMT product (pure DMT product) from the top of the column, and the bottom material can be periodically discharged.

[0063] The present invention provides a three-stage coupled DMC refining and recovery unit 82 consisting of "light weight removal-reactive distillation-extractive distillation".

[0064] In this process, because the DMC content in the crystallization mother liquor is high and its boiling point differs significantly from that of other components, most of the DMC in the mother liquor is first separated from the top of the light-light ...

[0065] Optionally, the top temperature of the light-light-removal column 51 is 60~260℃, the bottom temperature is 160~460℃, the absolute pressure is 0.05~0.25MPa, the theoretical plate number is 10~40, and the reflux ratio is 0.5~5. By controlling a moderate vacuum to lower the boiling point of DMC, high-temperature energy consumption is avoided. The bottom temperature is controlled below the boiling point of DMT to prevent product loss and to facilitate the full enrichment of EC and DD in the bottom material. The bottom material enters the reactive distillation column directly in a hot state at a suitable temperature, which not only recovers sensible heat but also provides a high-concentration substrate for the transesterification reaction, achieving dual optimization of energy and materials.

[0066] Optionally, this invention achieves synergistic optimization of energy consumption and separation efficiency by controlling the recovery ratio of DMC in the light distillation column to 30%–70%, avoiding both complete distillation (avoiding high energy consumption and DMT loss) and insufficient distillation (avoiding excessive load on the reactive distillation column). On the one hand, it avoids increased energy consumption and equipment investment caused by over-distillation; on the other hand, it retains an appropriate amount of DMC for the subsequent reactive distillation stage, ensuring sufficient enrichment of EC and DD in the bottoms material, which is beneficial for the smooth progress of the subsequent transesterification reaction; at the same time, this ratio range allows most of the DMC to be recovered at low cost and directly recycled to the depolymerization reaction, significantly reducing the amount of fresh solvent added and improving the economic and environmental friendliness of the process.

[0067] After most of the DMC in the mother liquor is separated by the light liquor removal column 51, the content of EC and DD in the bottom product is relatively high. Through transesterification with methanol in the reactive distillation column 52, both EC and DD can be converted into DMC and ethylene glycol (EG). The specific reaction formulas are shown in Formula 1 and Formula 2, respectively. Formula 1; Formula 2.

[0068] The reactive distillation column 52 has a top temperature of 50~250℃, a bottom temperature of 150~450℃, an absolute pressure of 0.05~0.25MPa, a theoretical plate number of 10~40, and a reflux ratio of 0.5~5. Optionally, the reactive distillation column 52 is filled with a catalyst for catalytic transesterification, which may be a supported solid base, such as at least one of KF / γ-Al2O3 or KF / Mg-Fe oxide.

[0069] Optionally, the mass ratio of the bottom product of the reactive distillation column 52, the light-light product removal column 51, and methanol is input as 1:(0.5~1.4). In an optional example of the present invention, the mass ratio of the bottom product of the light-light product removal column 51 to methanol is 1:(0.5~1).

[0070] The top of the reactive distillation column 52 yields a mixture containing low-boiling-point DMC and methanol. Further, the top product of the reactive distillation column 52 is input into the extractive distillation process. Through extractive distillation separation, a second DMC fraction is obtained and recycled to step (1); the methanol fraction is recycled to step S2, achieving methanol recycling within the process; the extractant fraction is recycled for the extractive distillation, achieving extractant recycling within the process; and DMC recycling within the process is achieved through steps S1 and S3.

[0071] It should be noted that the present invention does not limit the specific operation and equipment used in extractive distillation. Those skilled in the art can use appropriate quantities and connection methods of extractant and distillation column as needed to extract and separate the extractant from the top of the reactive distillation column 52 and recover the extractant.

[0072] Optionally, the extractive distillation is carried out in a partition column of the extractive distillation column, enabling the separation of azeotropic substances and the recovery of solvent in a single column. The top temperature of the partition column is 50~250℃, the bottom temperature is 150~450℃, the absolute pressure is 0.05~0.25MPa, the number of theoretical plates is 20~100, and the reflux ratio is 2~10. It should be noted that the specific structure of the partition column of the extractive distillation column is not limited in this invention; any partition column of the extractive distillation column that can achieve the separation of DMC, methanol, and extractant in one column can be used in this invention.

[0073] Optionally, the extractant used in the extractive distillation is selected from at least one of cyclohexane, o-xylene, and ethylene glycol. In an optional example of the invention, the extractant is selected from cyclohexane or ethylene glycol.

[0074] Optionally, the mass ratio of the extractant to the top product of the reactive distillation column 52 is (0.2~2.5):1, which is beneficial to improving extraction efficiency. In an optional example of the present invention, the mass ratio of the extractant to the top product of the reactive distillation column 52 is (0.2~2):1.

[0075] It is worth noting that catalyst recovery is also a key challenge in the separation of depolymerization systems. For homogeneous catalysts such as ionic liquids, their volatility is extremely low, and they readily form near-boiling or azeotropic systems with depolymerized monomers, making separation by traditional distillation difficult. Furthermore, impurities such as residual dyes and textile auxiliaries in the depolymerization system may form hydrogen bonds or undergo physical adsorption with the ionic liquid, further reducing the catalyst's recovery purity and recycling activity.

[0076] To address this issue, existing technologies mainly improve the degradation properties of catalysts and extend their cycle life through structural design; or use a combination of processes such as distillation and liquid-liquid extraction coupling, ultrafiltration membrane separation, or vacuum rotary evaporation to recover ionic liquids, which can increase the recovery rate to over 90%. However, the above separation processes suffer from high equipment investment and high operating costs, which limit their industrial application.

[0077] Optionally, the present invention also constructs a catalyst recycling unit 83 consisting of "evaporation concentration - water leaching - solid-liquid separation - flocculation - evaporation crystallization".

[0078] Specifically, the bottom product of the reactive distillation column 52 comprises a mixture containing EG, residual DMT, catalyst, and other impurities. Optionally, the process further includes: evaporating and concentrating the bottom product of the reactive distillation column 52, water leaching, solid-liquid separation, flocculation, and evaporation crystallization to obtain recovered ionic catalyst. By utilizing the characteristic that the ionic catalyst has significantly higher solubility in the aqueous phase than DMT, selective separation of the two is achieved through water leaching. Further, the charge neutralization and bridging effect of the flocculant on metal ions and water-soluble impurities is utilized to selectively remove impurities while retaining the catalyst in the aqueous phase. Finally, solid catalyst is obtained through evaporation crystallization, which is then dried or simply regenerated for reuse. It should be noted that a pathway for adding fresh ionic catalyst is also provided in the depolymerization reaction. This invention achieves a catalyst recovery rate of 80%, significantly reducing the amount of fresh catalyst required and improving process economy.

[0079] Optionally, EG can be separated by evaporation and concentration, and this fraction of EG can be used for the production of upstream polymers.

[0080] Optionally, the recovered ionic catalyst is recycled to step (1), thereby forming a catalyst cycle within the process, which reduces raw material costs and simultaneously reduces waste liquid treatment costs, thereby improving the economic benefits of the process.

[0081] The material after EG separation is a mixture containing catalyst, a small amount of DMT, dye, metal ions, and auxiliary impurities. This material is dissolved / leached in water. The water-soluble ionic catalyst, metal ions, and auxiliary agents enter the aqueous phase. The metal ions and other water-soluble impurities in the aqueous phase are further removed by flocculation. The combination of water leaching and flocculation improves the purity and activity retention of the catalyst. After solid-liquid separation, DMT and water-insoluble polymeric dyes are combined and dissolved with the crude DMT in solid form and enter the DMT refining and recovery unit.

[0082] Optionally, the flocculant is selected from at least one of polyferric sulfate, polyferric chloride, polyaluminum chloride, polyaluminum sulfate, polyferric aluminum sulfate, polyferric aluminum chloride, polyacrylamide, polyquaternary ammonium salt, and polyether, preferably polyferric chloride and / or polyacrylamide. It should be noted that this invention does not limit the amount of flocculant added; appropriate amounts of flocculant can be added during the specific process to remove metal ions and other water-soluble impurities from the aqueous phase. By replacing high-cost membrane separation or extraction processes with a water leaching-flocculation combination, the equipment investment is low and the operation is simple.

[0083] Optionally, the water leaching operation also includes a pathway for inputting fresh water; the present invention can optionally use the condensate obtained from evaporation and crystallization for the water leaching operation, using water as the leaching medium, combined with the reuse of evaporation condensate, to achieve a closed-loop circulation of process water, reduce fresh water consumption, eliminate organic extractant pollution, and meet the requirements of green chemical industry.

[0084] Secondly, this invention proposes a system for recovering DMT and DMC from polyester-blended fabrics, such as... Figure 1 As shown, the system includes: Reactor 1 is used for the depolymerization reaction of polyester blended fabrics with DMC. The first solid-liquid separation device 21 is used to separate the solid and liquid phases of the material after the depolymerization reaction and take the liquid phase material. A primary crystallizer 31 is used for the crystallization operation of the liquid phase material; The second solid-liquid separation device 22 is used to separate the crystallized material to obtain crystallization mother liquor and crude DMT. Also includes: DMT refining unit 81 is used for refining crude DMT; it includes a first dissolving vessel 41, a third solid-liquid separation device 23, a secondary crystallizer 32 and a fourth solid-liquid separation device 24 connected in sequence, and DMT products are obtained from the solid phase outlet of the fourth solid-liquid separation device 24. DMC refining and recovery unit 82 is used to recover DMC from the crystallization mother liquor; it includes a light-weight removal column 51, a reactive distillation column 52, and an extractive distillation partition wall column 53 connected in sequence; wherein... The feed inlet of the light-light removal tower 51 receives the crystallization mother liquor, the top outlet of the tower outputs the first DMC fraction and connects to the DMC inlet of the reactor 1, and the bottom outlet of the tower is connected to the feed inlet of the reactive distillation tower 52. The top outlet of the reactive distillation column 52 is connected to the feed inlet of the extractive distillation column; The methanol fraction is output from the top outlet of the extractive distillation partition column 53 and recycled to the reactive distillation column 52. The second DMC fraction is output from the side outlet and connected to the DMC inlet of the reactor 1. The extractant fraction is output from the bottom outlet and recycled.

[0085] Furthermore, such as Figure 2 As shown, the device also includes a pretreatment unit 84 for cleaning, drying and / or mechanically crushing the polyester-blend fabric to be treated; the outlet of the pretreatment unit 84 is connected to the feed inlet of the reactor 1, thereby improving the efficiency of subsequent reaction extraction.

[0086] Furthermore, the apparatus also includes an atmospheric distillation column 54 for solvent recovery, the liquid phase outlet of the fourth solid-liquid separation device 24 is connected to the atmospheric distillation column 54, and the top outlet of the atmospheric distillation column 54 is connected to the solvent inlet of the first dissolving vessel 41.

[0087] Furthermore, such as Figure 2 As shown, the apparatus also includes a vacuum distillation column 55 for further purification of the DMT product. The solid phase outlet of the fourth solid-liquid separation device 24 is connected to the feed inlet of the vacuum distillation column 55, and pure DMT is collected from the top of the vacuum distillation column 55.

[0088] Furthermore, the system also includes a catalyst recycling unit 83: used to recover the ionic catalyst from the bottom product of the reactive distillation column 52, comprising an evaporator 6, a second dissolving vessel 42, a fifth solid-liquid separation device 25, a flocculation device 7, and an evaporator crystallizer 33 connected in sequence; wherein, the feed inlet of the evaporator 6 receives the bottom product of the reactive distillation column 52, and obtains a concentrated liquid after distilling off volatile components; the second dissolving vessel 42 is connected to the evaporator 6 and is used to dissolve the concentrated liquid; the fifth solid-liquid separation device 25 is connected to the second dissolving vessel 42 and is used to separate insoluble impurities; the flocculation device 7 is connected to the fifth solid-liquid separation device 25 and is used for flocculation and impurity removal; the evaporator crystallizer 33 is connected to the flocculation device 7, and the recovered ionic catalyst is collected from its solid phase outlet.

[0089] Furthermore, the outlet of the evaporator crystallizer 33 is connected to the catalyst inlet of the reactor 1 to form a complete catalyst cycle.

[0090] Furthermore, the solid phase outlet of the fifth solid-liquid separation device 25 is connected to the feed inlet of the first dissolving vessel 41 to improve the DMT yield.

[0091] Furthermore, the gas phase outlet of the evaporator crystallizer 33 is connected to the water inlet of the second dissolving vessel 42 via a condenser, thereby forming a complete internal water circulation.

[0092] Example

[0093] This embodiment demonstrates a process for recovering DMT and DMC from polyester-blended fabrics under specific operating conditions. It should be noted that this process is only a preferred embodiment and does not limit the scope of protection of this invention.

[0094] Taking the recycling process for 12,000 tons / year of polyester-cotton blended fabrics as an example. Specifically: In pretreatment unit 84, the recovered polyester-cotton blended fabric is pretreated by washing, drying, and crushing to obtain a polyester-containing blended fabric with a moisture content ≤5% and a particle size of 1~50mm. The polyester-containing blended fabric to be treated, an ionic catalyst (tetrabutylammonium chloride or tetrabutylammonium bromide), and DMC are fed into reactor 1 at a mass ratio of 1:0.13:10 for depolymerization reaction; the temperature of the reactor is controlled at 80~82℃, and the reaction time is 0.5h.

[0095] The first solid-liquid separation unit 21 separates the solid phase (cotton fiber) and the liquid phase material. The liquid phase material contains impurities such as DMT, EC, DD, DMC, dyes, metal ions, and auxiliaries. After washing the solid phase material, approximately 450 kg / h of cotton fiber is obtained; the liquid phase material is fed into the subsequent separation and recovery unit at a flow rate of 16,500 kg / h.

[0096] In the primary crystallizer 31, the liquid material is cooled to 5°C at a rate of 0.5 K / min to induce crystallization. Then, it is centrifuged by the second solid-liquid separation device 22 to obtain the primary crystallization mother liquor and crude DMT.

[0097] In DMT Refinement Unit 81: First, crude DMT is dissolved in methanol in the first dissolving vessel 41, with a mass ratio of crude DMT to solvent of 1:10. Then, impurities insoluble in the solvent are removed by filtration through the third solid-liquid separation device 23. Further, in the secondary crystallizer 32, the liquid phase material output from the third solid-liquid separation device 23 is cooled to 0-20°C at a rate of 0.1-2 K / min for crystallization.

[0098] After crystallization, the product was centrifuged using the fourth solid-liquid separation device 24 to obtain a solid DMT product with a flow rate of approximately 900 kg / h and a purity of 99%, yielding a yield of 92% (the mass of PET in the blended fabric was converted to the mass of dimethyl terephthalate by molar ratio as a reference for yield calculation). Furthermore, to improve the purity of the DMT product, it was purified by vacuum distillation column 55 to obtain pure DMT with a purity of 99.9%. The vacuum distillation column 55 had a top temperature of 120°C, a bottom temperature of 150°C, an absolute pressure of 1000 Pa, 40 theoretical plates, and a reflux ratio of 2.1.

[0099] The mother liquor separated by the fourth solid-liquid separation unit 24 can be fed into the atmospheric distillation column 54 for distillation. The stream containing solvent is collected from the top of the column and returned to the first dissolving vessel as a solvent. The product collected from the bottom of the column is returned to the secondary crystallizer 32 for further recrystallization, or a portion is periodically collected and sent to the solid waste discharge station. The atmospheric distillation column 54 has a top temperature of 64.5℃, a bottom temperature of 99.9℃, an absolute pressure of 0.1MPa, a theoretical plate number of 16, and a reflux ratio of 2.

[0100] In DMC Refined Recycling Unit 82: The mother liquor entering the light component removal column 51 contains 85.8% DMC, 7.1% EC, 1.5% DD, 3.6% DMT (calculated based on an 80% recovery rate from the first crystallization), and 2.3% catalyst (all by mass fraction, the same below). The top temperature of the light component removal column 51 is 90℃, the bottom temperature is 247℃, the absolute pressure is 0.1MPa, the theoretical plate number is 20, and the reflux ratio is 1.3. DMC with a purity of 99.9% is collected from the top of the light component removal column 51 and can be directly returned to reactor 1 for recycling. The bottom material of the light component removal column 51 is fed into the reactive distillation column.

[0101] The feedstock from the light component removal column of reactive distillation column 52 contains 0.03% DMC, 54.55% EC, 12.24% DD, 14.02% DMT, and 19.16% catalyst; the mass ratio of the feedstock from the light component removal column to methanol in reactive distillation column 52 is 1:0.66. The top temperature of reactive distillation column 52 is 70°C, the bottom temperature is 198°C, the absolute pressure is 0.1 MPa, the theoretical plate number is 20, and the reflux ratio is 2.5. A feedstock with a composition of 12.0% methanol and 87.9% DMC is collected from the top of reactive distillation column 52 and fed into extractive distillation partition column 53; the feedstock from the reactive distillation column is fed into catalyst recycling unit 83.

[0102] The mass ratio of the top product from the reactive distillation column to the extractant ethylene glycol in the extractive distillation partition wall column 53 is 1:0.22. The top temperature of the extractive distillation partition wall column 53 is 64℃, the bottom temperature is 197℃, the absolute pressure is 0.1MPa, the theoretical plate number is 60, and the reflux ratio is 4.5. A second DMC fraction with a purity of 99.9% is collected from the side stream of the extractive distillation partition wall column 53 and recycled to the reactor; a methanol fraction with a purity of 99.9% is collected from the top of the column and recycled to the reactive distillation column 52; and an extractant fraction with a purity of 99% is collected from the bottom of the column and fed as the extractant into the extractant inlet of the extractive distillation partition wall column 53. The overall DMC recovery rate of the DMC purification and recovery unit 82 is 95% (obtained by comparing the sum of the DMC outlet masses in the light component removal column 51 and the extractive distillation partition wall column 53 with the initial mass of DMC added to the reaction).

[0103] In catalyst recycling unit 83: The EG (electromagnetic catalyst) is first fed into the evaporator 6 from the bottom of the reactive distillation column 52 to distill off and collect at a flow rate of approximately 308 kg / h. The concentrated material is then fed into the second dissolving vessel 42 for leaching and dissolving with water, dissolving the ionic catalyst in the aqueous phase. Since components such as DMT have low solubility in water, they are separated by the fifth solid-liquid separation device 25. The liquid phase material is then flocculated by polyacrylamide to remove metal ions and other water-soluble impurities. Finally, it is crystallized in the distillation crystallizer 33 to obtain the recovered ionic catalyst with a yield of 80% (based on the initial catalyst mass). This catalyst can be returned to the reactor 1 for recycling. The solid material separated from the fifth solid-liquid separation device 25 can be fed into the first dissolving vessel 41 for dissolution to recover the contained DMT, thus improving the DMT recovery rate.

[0104] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple improvements can be made without departing from the concept of the present invention, and all such improvements should be considered to fall within the scope of protection of the present invention.

Claims

1. A process for recovering DMT and DMC from polyester-blended fabrics, characterized in that, include: (1) Under the action of an ionic catalyst, polyester blended fabrics undergo depolymerization reaction with DMC; (2) Perform solid-liquid separation on the reacted material and take the liquid phase material; (3) The liquid phase material is subjected to a first crystallization to obtain crystallization mother liquor and crude DMT; The crude DMT is dissolved, solid impurities are removed, and it is recrystallized to obtain the DMT product. The crystallization mother liquor is subjected to the following treatments in sequence: S1: Input the light-removal tower (51) for separation, collect the first DMC fraction from the top of the tower and recycle it to step (1); S2: The bottom product of the light removal tower (51) is subjected to transesterification with methanol in a reactive distillation tower (52); S3: The product collected from the top of the reactive distillation column (52) is subjected to extractive distillation to separate the following: The second DMC fraction is recycled to step (1). The methanol fraction is recycled to step S2; The extractant fraction is recycled for further extractive distillation.

2. The process for recovering DMT and DMC from polyester-blended fabrics according to claim 1, characterized in that, The first crystallization is a cooling crystallization, which includes cooling the liquid phase material to 0-25°C at a rate of 0.1-2K / min.

3. The process for recovering DMT and DMC from polyester-blended fabrics according to claim 1, characterized in that, In step (3), at least one of acetonitrile, ethylene glycol, and methanol is used to dissolve the crude DMT, preferably methanol. Preferably, the mass ratio of crude DMT to solvent for dissolution is 1:(5~30). And / or, the recrystallization is cooling crystallization, comprising: cooling the dissolved material to 0~20°C at a rate of 0.1~2K / min; And / or, the mother liquor after recrystallization is distilled, the solvent is collected from the top of the distillation column and used to dissolve the crude DMT, the DMT is enriched in the bottom of the column and recycled to the first crystallization; And / or, the process further includes purifying the DMT product by vacuum distillation to obtain pure DMT.

4. The process for recovering DMT and DMC from polyester-blended fabrics according to claim 1, characterized in that, The light-removal tower (51) has a top temperature of 60~260℃, a bottom temperature of 160~460℃, an absolute pressure of 0.05~0.25MPa, a theoretical number of trays of 10~40, and a reflux ratio of 0.5~5.

5. The process for recovering DMT and DMC from polyester-blended fabrics according to claim 1, characterized in that, The reactive distillation column (52) has a top temperature of 50~250℃, a bottom temperature of 150~450℃, an absolute pressure of 0.05~0.25MPa, a theoretical plate number of 10~40, and a reflux ratio of 0.5~5. And / or, the mass ratio of the bottom material of the light-removal tower to methanol is 1:(0.5~1.4), preferably 1:(0.5~1).

6. The process for recovering DMT and DMC from polyester-blended fabrics according to claim 1, characterized in that, The extractive distillation is carried out in a partition column of the extractive distillation column. The top temperature of the partition column is 50~250℃, the bottom temperature is 150~450℃, the absolute pressure is 0.05~0.25MPa, the theoretical plate number is 20~100, and the reflux ratio is 2~10. And / or, the extractant used for the extractive distillation is selected from at least one of cyclohexane, o-xylene, and ethylene glycol, preferably cyclohexane or ethylene glycol; And / or, the mass ratio of the extractant to the top product of the reactive distillation column (52) is (0.2~2.5):1, preferably (0.2~2):

1.

7. The process for recovering DMT and DMC from polyester-blended fabrics according to claim 1, characterized in that, The process further includes: evaporating and concentrating the bottom product of the reactive distillation column (52), extracting it with water, separating it from its solids and liquids, flocculating it, and evaporating it to crystallize it, so as to obtain the recovered ionic catalyst; Preferably, the recovered ionic catalyst is recycled to step (1); Preferably, the solid material obtained from solid-liquid separation is combined with the crude DMT product and dissolved to prepare the DMT product; Preferably, the condensate obtained from evaporation and crystallization is used in the water leaching operation; Preferably, the flocculant is selected from at least one of polyferric sulfate, polyferric chloride, polyaluminum chloride, polyaluminum sulfate, polyferric aluminum sulfate, polyferric aluminum chloride, polyacrylamide, polyquaternary ammonium salt, and polyether.

8. A system for recovering DMT and DMC from polyester-blended fabrics, characterized in that, include: The reactor (1) is used for the depolymerization reaction of polyester blended fabrics with DMC; The first solid-liquid separation device (21) is used to separate the solid and liquid phases of the material after the depolymerization reaction and take the liquid phase material. A primary crystallizer (31) is used for the crystallization operation of the liquid phase material; The second solid-liquid separation device (22) is used to separate the crystallized material to obtain crystallization mother liquor and crude DMT. Also includes: DMT refining unit (81) for refining crude DMT; includes a first dissolving vessel (41), a third solid-liquid separation device (23), a secondary crystallizer (32) and a fourth solid-liquid separation device (24) connected in sequence, from which DMT product is obtained; A DMC refining and recovery unit (82) is used to recover DMC from the crystallization mother liquor; it includes a light-light product removal column (51), a reactive distillation column (52), and an extractive distillation partition wall column (53) connected in sequence; wherein... The feed inlet of the light-light removal tower (51) receives the crystallization mother liquor, the top outlet of the tower outputs the first DMC fraction and connects to the DMC inlet of the reactor (1), and the bottom outlet of the tower connects to the feed inlet of the reactive distillation tower (52). The top outlet of the reactive distillation column (52) is connected to the feed inlet of the extractive distillation partition column (53); The top outlet of the extractive distillation partition column (53) outputs methanol fraction and is recycled to the reactive distillation column (52). The side outlet outputs the second DMC fraction and is connected to the DMC inlet of the reactor (1). The bottom outlet outputs extractant fraction and is recycled.

9. The system for recovering DMT and DMC from polyester-blended fabrics according to claim 8, characterized in that, It also includes a catalyst recycling unit (83): used to recover the ionic catalyst from the bottom product of the reactive distillation column (52), comprising, in sequence, an evaporator (6), a second dissolving vessel (42), a fifth solid-liquid separation device (25), a flocculation device (7), and an evaporator crystallizer (33); wherein, The feed inlet of the evaporator (6) receives the bottom product of the reactive distillation column (52), and after evaporating the volatile components, a concentrated liquid is obtained. The second dissolving vessel (42) is connected to the evaporator (6) and is used to dissolve the concentrate; The fifth solid-liquid separation device (25) is connected to the second dissolving vessel (42) and is used to separate insoluble impurities; The flocculation device (7) is connected to the fifth solid-liquid separation device (25) and is used for flocculation and impurity removal; The evaporator crystallizer (33) is connected to the flocculation device (7) and the recovered ionic catalyst is collected from its solid phase outlet; Preferably, the outlet of the evaporator crystallizer (33) is connected to the catalyst inlet of the reactor (1); Preferably, the solid phase outlet of the fifth solid-liquid separation device (25) is connected to the feed inlet of the first dissolving vessel (41); Preferably, the gas phase outlet of the evaporator crystallizer (33) is connected to the water inlet of the second dissolving vessel (42) via a condenser.

10. The system for recovering DMT and DMC from polyester-blended fabrics according to claim 8 or 9, characterized in that, The apparatus further includes a pretreatment unit (84) for cleaning, drying and / or mechanically crushing the polyester-blend fabric to be treated; the outlet of the pretreatment unit (84) is connected to the feed inlet of the reactor (1); And / or, the apparatus further includes an atmospheric distillation column (54) for recovering solvent, the liquid phase outlet of the fourth solid-liquid separation device (24) being connected to the atmospheric distillation column (54), and the top outlet of the atmospheric distillation column (54) being connected to the solvent inlet of the first dissolving vessel (41); And / or, the apparatus further includes a vacuum distillation column (55) for further purification of the DMT product, wherein the solid outlet of the fourth solid-liquid separation unit (24) is connected to the feed inlet of the vacuum distillation column (55) and pure DMT is drawn from the top of the vacuum distillation column (55).

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