A method for purifying high-purity 3,4-ethylenedioxythiophene and its application

Abstract

The present invention relates to a method for purifying high-purity 3,4-ethylenedioxythiophene and its application, and belongs to the technical field of compound preparation. The method for purifying high-purity 3,4-ethylenedioxythiophene provided by the present invention comprises the following steps: (1) after the crude distillation feed liquid of 3,4-ethylenedioxythiophene after decarboxylation reaction is stirred and mixed with water, it is added into a melt crystallizer, cooled to 1°C to 6°C, kept cold until the feed liquid is completely crystallized, and the uncrystallized waste liquid is discharged; (2) the temperature is raised to 11°C to 14°C, and kept warm until the purity of the effluent is ≥99.99%; (3) the temperature is raised to 20°C to 30°C again, kept warm, and the effluent is collected to obtain high-purity 3,4-ethylenedioxythiophene. The purification method of the present invention can greatly improve the purity of EDOT, and compared with the existing distillation process, it can effectively reduce the problem of EDOT polymerization degradation caused by high temperature during multiple distillation processes, and the overall yield is higher.

Description

Technical Field

[0001] The present invention belongs to the technical field of compound preparation, and particularly relates to a method for purifying high-purity 3,4-ethylenedioxythiophene and application thereof. Background Art

[0002] Conductive polymers such as polypyrrole, polyaniline, and polythiophene have been discovered one after another. The most widely used monomer, 3,4-ethylenedioxythiophene (EDOT), was developed by Bayer in Germany in the 1980s and 1990s. It serves as the raw material for the conductive polymer PEDOT. Due to its high conductivity, transparent films, and ease of preparation, PEDOT is widely used in solid-state capacitors, antistatic coatings, and light-emitting diodes. In recent years, the synthesis and purification techniques of EDOT have been further refined, and the purity of EDOT directly affects the quality of the resulting polymer PEDOT.

[0003] Existing EDOT preparation processes primarily include a five-step process starting with chloroacetate and a three-step process using thiophene as a raw material. Patent CN201110453249.4 discloses a method for synthesizing EDOT from thiophene, achieving a purity of 99% after distillation and purification. Patent CN201210234948.4 discloses a five-step process for preparing EDOT from chloroacetate. After substitution, cyclization, etherification, alkalization and acidification, decarboxylation, and distillation, the purity of EDOT reaches 99.88%.

[0004] However, due to the inevitable introduction of impurities with properties very similar to EDOT during the synthesis process, the purity of EDOT after distillation is generally between 99.7% and 99.9%. Due to the similar boiling points, further distillation is difficult to remove trace impurities. During the polymer preparation process, trace impurities can lead to impure PEDOT polymers and affect their performance. Therefore, the high purity requirement for EDOT in high-purity polymers is urgently needed. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem in the prior art that the purity of EDOT in the production process is low, resulting in insufficient performance of the prepared PEDOT, and to provide a method for purifying high-purity 3,4-ethylenedioxythiophene and its application.

[0006] The present invention is achieved through the following technical solutions:

[0007] The present invention provides a method for purifying high-purity 3,4-ethylenedioxythiophene, comprising the following steps:

[0008] (1) After the decarboxylation reaction, the crude distilled 3,4-ethylenedioxythiophene liquid is stirred and mixed with water, and then added to a melt crystallizer, cooled to 1°C to 6°C, kept cold until the liquid is completely crystallized, and the uncrystallized liquid is discharged;

[0009] (2) Raise the temperature to 11°C to 14°C and keep warm until the purity of the effluent is ≥99.99%;

[0010] (3) Raise the temperature to 20°C to 30°C again, keep warm, and collect the effluent to obtain high-purity 3,4-ethylenedioxythiophene.

[0011] The present invention adopts EDOT decarboxylation crude distillation liquid, which does not undergo high-temperature and high-vacuum distillation in a distillation tower, but enters a low-temperature melt crystallizer for melt crystallization. The crystallization equipment of the present invention adopts a static spiral melt crystallizer. After a certain amount of water and the EDOT crude distillation liquid are fully stirred and mixed, the liquid enters the melt crystallizer. By gradually lowering the temperature of the heat medium layer, the material statically placed in the material layer is gradually cooled and melt-crystallized. The high-purity liquid crystallizes out first. After the crystallization is completed, the uncrystallized residual liquid is first discharged. Then, the temperature of the crystals in the material layer is slowly increased by the heat medium. The low-purity product is discharged first, and the high-purity product is discharged later. The purification method of the present invention effectively avoids the polymerization of EDOT during the high-temperature distillation process and improves the overall yield of EDOT. The purification method of the present invention can greatly improve the purity of EDOT, and the purity of the final product can reach 99.99% or above, which is unattainable by conventional EDOT distillation methods.

[0012] A preferred embodiment of the method for purifying high-purity 3,4-ethylenedioxythiophene of the present invention further includes step (4): dehydrating the obtained high-purity 3,4-ethylenedioxythiophene with a desiccant and filtering to obtain a high-purity 3,4-ethylenedioxythiophene finished product. The obtained high-purity 3,4-ethylenedioxythiophene can be sold as a high-purity EDOT finished product after dehydration and filtration.

[0013] As a preferred embodiment of the method for purifying high-purity 3,4-ethylenedioxythiophene of the present invention, in the step (1), the temperature of the feed solution when it is completely crystallized is 1°C to 6°C.

[0014] Preferably, in step (1), the purity of the crude distillate liquid is not less than 99.0%.

[0015] At present, the purity of the crude distillation liquid of 3,4-ethylenedioxythiophene after decarboxylation reaction synthesized by the existing process is generally greater than 99.0%. The purification method of the present invention can purify the crude distillation liquid after decarboxylation prepared by the existing process to obtain high-purity 3,4-ethylenedioxythiophene with a purity of more than 99.99%.

[0016] As a preferred embodiment of the method for purifying high-purity 3,4-ethylenedioxythiophene of the present invention, in step (1), the preferred amount of water added is 30% to 40% of the weight of the feed liquid.

[0017] The purification method of the present invention mixes the initially distilled liquid with water. Since EDOT has low solubility in water, the uncrystallized liquid is discharged after crystallization, thereby removing water and impurities, effectively removing water-soluble impurities from the EDOT product while minimizing the impact on yield. However, too little water can result in poor impurity removal, while too much water can occupy equipment space and reduce its efficiency. Preferably, the amount of water added is 30% to 40% of the weight of the liquid.

[0018] As a preferred embodiment of the method for purifying high-purity 3,4-ethylenedioxythiophene of the present invention, in step (1), the cooling rate can be 0.5°C / h to 5°C / h, preferably 1°C / h to 2°C / h.

[0019] Preferably, in step (1), the uncrystallized liquid discharged mainly contains water and other impurities and can be treated as waste liquid.

[0020] As a preferred embodiment of the method for purifying high-purity 3,4-ethylenedioxythiophene of the present invention, in step (2), the heating rate is 1° C. / h to 2° C. / h.

[0021] As a preferred embodiment of the method for purifying high-purity 3,4-ethylenedioxythiophene of the present invention, in step (2), the effluent with a purity of <99.7% can be used as the starting material liquid in step (1) for further purification, and the effluent with a purity of 99.70% to 99.99% can be used as a general standard product.

[0022] Preferably, in step (3), the rate of heating again is not limited, and preferably heating at full speed.

[0023] Preferably, in step (4), the desiccant may be alumina, silica gel, anhydrous salt, or molecular sieve, and preferably the desiccant is a molecular sieve; and the filtration is preferably performed by a tetrafluoroethylene membrane filtration.

[0024] Another object of the present invention is to provide high-purity 3,4-ethylenedioxythiophene obtained by the method for purifying high-purity 3,4-ethylenedioxythiophene as described above.

[0025] Another object of the present invention is to provide the use of the high-purity 3,4-ethylenedioxythiophene in conductive materials.

[0026] The purity of 3,4-ethylenedioxythiophene obtained by the purification method of the present invention can reach above 99.99%. Using the high-purity 3,4-ethylenedioxythiophene of the present invention as a raw material for high-purity polymers can effectively improve the performance of downstream conductive polymers.

[0027] Another object of the present invention is to provide a conductive polymer dispersion, wherein the raw materials for preparing the conductive polymer dispersion include the high-purity 3,4-ethylenedioxythiophene.

[0028] The conductive polymer dispersion using 3,4-ethylenedioxythiophene obtained by the purification method of the present invention as a raw material can effectively improve material properties, and has significantly improved properties compared to 3,4-ethylenedioxythiophene monomer obtained by conventional distillation purification.

[0029] The present invention has the following beneficial effects: the present invention adopts EDOT decarboxylation crude distillation liquid, which does not undergo high-temperature and high-vacuum distillation in a distillation tower, but enters a low-temperature crystallizer for crystallization. On the one hand, the polymerization of EDOT can be effectively avoided during the high-temperature distillation process. The residue in the conventional distillation kettle accounts for about 5% of the total distillation volume, which cannot be used due to excessive impurities and EDOT polymers. The use of low-temperature crystallization can effectively avoid this partial loss and improve the yield by 5%. On the other hand, the purity of the finished product obtained by the purification method of the present invention can reach>99.99%, which is unattainable by conventional EDOT distillation methods. Using the raw material purified by the present invention as the raw material for high-purity polymers can effectively improve the performance of downstream conductive polymers. At the same time, the energy consumption of the purification method of the present invention is about 20% of that of conventional distillation purification methods, which can greatly reduce costs. DETAILED DESCRIPTION

[0030] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0032] The crystallizer used in the following examples and comparative examples was a static melt crystallizer. The effluent after crystallization was quantitatively collected and analyzed in multiple stages and then mixed in stages based on purity. The primary crystallization yield referred to below is the ratio of qualified effluent to the original crude product. The qualified product includes standard products with a purity of 99.7% to 99.99%, and high-standard products with a purity greater than 99.99%.

[0033] Example 1

[0034] A method for purifying high-purity 3,4-ethylenedioxythiophene is:

[0035] (1) 1000 g of crude distilled 3,4-ethylenedioxythiophene liquid with a purity of 99.50% after decarboxylation reaction was added to 300 g of water, stirred for 30 minutes, and added to a melt crystallizer. The cooling water was started and cooled from room temperature to 1°C at a rate of 1°C / h. The cooling was stopped and kept cold until the temperature in the crystallizer reached 3°C, and the liquid was in a completely melted and crystallized state; and the uncrystallized waste liquid was discharged;

[0036] (2) Turn on the cooling water and heat it to 11°C at a rate of 1°C / h, keep it warm, collect effluent 1, and switch to collecting effluent 2 when the effluent purity is greater than 99.7%. Continue to keep it warm until the effluent purity is greater than 99.99%, and then collect effluent 3;

[0037] (3) Turn on the cooling water and raise the temperature to 27°C again, keep the temperature, and continue to collect the effluent until all the materials in the crystallizer have flowed out. Dehydrate with molecular sieve and filter to obtain high-purity 3,4-ethylenedioxythiophene.

[0038] Among them, the uncrystallized waste liquid in step (1) can be directly discarded. The purity of effluent 1 is less than 99.7%, and it can be used for recrystallization in the next batch. The weight of effluent 2 is 301g, the purity is 99.89%, and it can be used as a standard finished product after dehydration and filtration. The weight of effluent 3 is 672g, the purity is 99.995%, and it can be used as a high-standard finished product after dehydration and filtration. The first crystallization yield of this embodiment is 97.3%.

[0039] Example 2

[0040] A method for purifying high-purity 3,4-ethylenedioxythiophene is:

[0041] (1) 1000 g of crude distilled 3,4-ethylenedioxythiophene (EDT) with a purity of 99.40% after decarboxylation was added to 300 g of water, stirred for 1 hour, and added to a melt crystallizer. The jacket cooling water was started and the cooling water was cooled from room temperature to 1°C at a rate of 1.5°C / h. The cooling was stopped and the temperature in the crystallizer was kept cool until the liquid was in a completely melted and crystallized state; and the uncrystallized waste liquid was discharged;

[0042] (2) Turn on the cooling water to heat up, raise the temperature to 12°C at a rate of 1.5°C / h, keep warm, collect effluent 1, switch to collecting effluent 2 when the effluent purity is greater than 99.7%, continue to keep warm until the effluent purity is ≥99.99%, and collect effluent 3;

[0043] (3) Turn on the cooling water and raise the temperature to 20°C again, keep it warm, and continue to collect the effluent until all the material in the crystallizer flows out, thereby obtaining high-purity 3,4-ethylenedioxythiophene.

[0044] Among them, effluent 1 has a purity of less than 99.7% and can be used for recrystallization in the next batch. Effluent 2 weighs 298g and has a purity of 99.83%. After dehydration and filtration, it can be used as a standard finished product. Effluent 3 weighs 670g and has a purity of 99.994%. After dehydration and filtration, it can be used as a high-standard finished product. The first crystallization yield in this example is 96.8%.

[0045] Example 3

[0046] A method for purifying high-purity 3,4-ethylenedioxythiophene is:

[0047] (1) 1000 g of crude distilled 3,4-ethylenedioxythiophene with a purity of 99.50% after decarboxylation reaction was added to 400 g of water, stirred for 1 hour, and then added to a melt crystallizer. The jacket cooling water was started and the cooling water was cooled from room temperature to 3°C at a rate of 2°C / h. The cooling was stopped and kept cold until the temperature in the crystallizer reached 6°C, and the liquid was in a completely crystallized state; and the uncrystallized waste liquid was discharged;

[0048] (2) Turn on the cooling water to heat up, raise the temperature to 14°C at a rate of 2°C / h, keep warm, collect effluent 1, switch to collecting effluent 2 when the effluent purity is greater than 99.7%, continue to keep warm until the effluent purity is greater than 99.99%, and then collect effluent 3;

[0049] (3) Turn on the cooling water and raise the temperature to 25°C again, keep it warm, and continue to collect the effluent until all the materials in the crystallizer flow out, thereby obtaining high-purity 3,4-ethylenedioxythiophene.

[0050] Among them, effluent 1 has a purity of less than 99.7% and can be used for recrystallization in the next batch. Effluent 2 weighs 300g and has a purity of 99.75%. After dehydration and filtration, it can be used as a standard finished product. Effluent 3 weighs 672g and has a purity of 99.992%. After dehydration and filtration, it can be used as a high-standard finished product. The first crystallization yield in this example is 97.2%.

[0051] Comparative Example 1

[0052] 1000g of 99.5% pure decarboxylated crude distillate was placed in a distillation kettle and subjected to distillation at elevated temperature. A 20g front fraction with a purity of 99.55% was collected, followed by 927g of the main fraction with a purity of 99.84%. A 50g residual material in the kettle was found with a purity of 85.95%. The residual material was dark in color and viscous, indicating that some of the product had polymerized. The primary distillation yield was 92.7%, and no high-purity samples were found in the distilled fractions.

[0053] Comparative Example 2

[0054] The difference between the operation process of this comparative example and that of Example 1 is that the cooling water cooling rate in step (1) is changed to 3°C / h, and the heating rate in step (2) is changed to 3°C / h. The rest of the operation process is the same as that of Example 1.

[0055] The effluent 2 obtained in this comparative example weighed 360 g and had a purity of 99.80%. After dehydration and filtration, it could be used as a standard finished product. The effluent 3 weighed 512 g and had a purity of 99.995%. After dehydration and filtration, it could be used as a high-quality finished product. The crystallization yield in this comparative example was 87.2%.

[0056] Comparative Example 3

[0057] The difference between the operation process of this comparative example and that of Example 1 is that the cooling water cooling rate in step (1) is changed to 5°C / h, and the heating rate in step (2) is changed to 3°C / h. The rest of the operation process is the same as that of Example 1.

[0058] In this comparative example, the obtained effluent 2 weighed 420 g and had a purity of 99.80%. After dehydration and filtration, it could be used as a standard finished product. The effluent 3 weighed 161 g and had a purity of 99.993%. After dehydration and filtration, it could be used as a high-standard finished product. The crystallization yield in this comparative example was 58.1%, while the crystallization yield of the high-standard product was only 16.1%.

[0059] Comparative Example 4

[0060] The difference between the operation process of this comparative example and that of Example 1 is that the cooling water cooling rate in step (1) is changed to 0.5°C / h, and the heating rate in step (2) is changed to 0.5°C / h. The rest of the operation process is the same as that of Example 1.

[0061] The effluent 2 obtained in this comparative example weighed 300 g and had a purity of 99.91%. After dehydration and filtration, it could be used as a standard finished product. The effluent 3 weighed 675 g and had a purity of 99.995%. After dehydration and filtration, it could be used as a high-quality finished product. The crystallization yield in this comparative example was 97.5%.

[0062] The heating rate and cooling rate of this comparative example are too slow, which makes the entire purification cycle too long, but the yield and purity are not significantly improved.

[0063] Comparative Example 5

[0064] The operating procedures of this comparative example are different from those of Example 1 in that the amount of water added to the crude steamed material in step (1) is changed to 200 g, and the rest of the operating procedures are the same as those of Example 1.

[0065] In this comparative example, effluent 2 weighed 330 g and had a purity of 99.80%. After dehydration and filtration, it could be used as a standard finished product. Effluent 3 weighed 573 g and had a purity of 99.993%. After dehydration and filtration, it could be used as a high-quality finished product. The primary crystallization yield in this comparative example was 90.3%. The reduced water content affected the separation of water-soluble impurities during the post-crystallization drainage operation.

[0066] Comparative Example 6

[0067] The difference between the operation process of this comparative example and that of Example 1 is that the temperature in step (2) is raised to 16° C. and then kept warm. The rest of the operation process is the same as that of Example 1.

[0068] The weight of effluent 2 obtained in this comparative example was 480 g, with a purity of 99.93%. After dehydration and filtration, it could be used as a standard finished product. The weight of effluent 3 was 462 g, with a purity of 99.994%. After dehydration and filtration, it could be used as a high-quality finished product. The crystallization yield in this comparative example was 94.2%.

[0069] Comparative Example 7

[0070] The difference between the operation process of this comparative example and that of Example 1 is that the cooling water is heated to 20° C. in step (2) and then kept warm. The rest of the operation process is the same as that of Example 1.

[0071] The resulting effluent 2 weighed 580 g and had a purity of 99.94%. After dehydration and filtration, it could be used as a standard finished product. The effluent 3 weighed 343 g and had a purity of 99.995%. After dehydration and filtration, it could be used as a high-quality finished product. The crystallization yield in this comparative example was 92.3%. The high-quality finished product yield was 34.3%.

[0072] According to the prior art CN110310832A dispersion preparation method, the purified monomer of the present invention was applied to a PEDOT dispersion for solid capacitors and an impregnation test was performed, resulting in the following application examples and comparative application examples.

[0073] Application Example 1

[0074] The preparation method of the conductive polymer dispersion is as follows:

[0075] (1) 8.8 g of a sulfonated modified polystyrene-polyisoprene diblock copolymer having a weight average molecular weight of 100,000 and 135.5 g of deionized water were added to a reaction vessel, heated and stirred to dissolve, and then 6.40 g of hydrogen peroxide and 0.006 g of ferric chloride were added. After stirring and dissolving, the mixture was cooled to room temperature to obtain a mixed solution;

[0076] (2) 3.0 g of high-purity 3,4-ethylenedioxythiophene (3) obtained in the collected solution of Example 1 was added to the mixed solution, and a polymerization reaction was carried out at room temperature;

[0077] (3) After the polymerization reaction stops, the pH value is adjusted, and the PEDOT / PSS dispersion is obtained after aging and removal of inorganic salts.

[0078] The dispersion of this embodiment was used as an impregnation liquid and impregnated onto the oxide layer. The dispersant was then removed by evaporation to form a PEDOT / PSS film to prepare a solid-state capacitor. The statistical average performance parameters of three groups of capacitors were prepared. The capacitor core package used for the preparation adopted a 16V910uF specification.

[0079] Application Example 2

[0080] The only difference between this application example and application example 1 is that the raw material added in step (2) of the method for preparing the conductive polymer dispersion is the high-purity 3,4-ethylenedioxythiophene collected in liquid 3 of Example 2, and the rest is the same as application example 1.

[0081] Application Example 3

[0082] The only difference between this application example and application example 1 is that the raw material added in step (2) of the method for preparing the conductive polymer dispersion is the high-purity 3,4-ethylenedioxythiophene collected in liquid 3 of Example 3, and the rest is the same as application example 1.

[0083] Comparative Application Example 1

[0084] The only difference between this comparative example and Application Example 1 is that the raw material added in step (2) of the preparation method of the conductive polymer dispersion is 3,4-ethylenedioxythiophene from the collected liquid 2 of Example 1, and the rest is the same as Application Example 1.

[0085] Application Comparative Example 2

[0086] The only difference between this comparative example and Application Example 1 is that the raw material added in step (2) of the preparation method of the conductive polymer dispersion is 3,4-ethylenedioxythiophene from the collected liquid 2 of Example 2, and the rest is the same as Application Example 1.

[0087] Application Comparative Example 3

[0088] The only difference between this comparative example and Application Example 1 is that the raw material added in step (2) of the preparation method of the conductive polymer dispersion is 3,4-ethylenedioxythiophene from the collected liquid 2 of Example 3, and the rest is the same as Application Example 1.

[0089] Comparative Application Example 4

[0090] The only difference between this comparative example and Application Example 1 is that the raw material added in step (2) of the preparation method of the conductive polymer dispersion is the main fraction 3,4-ethylenedioxythiophene obtained by distillation in Comparative Example 1, and the rest is the same as Application Example 1.

[0091] Application Comparative Example 5

[0092] The difference between this comparative example and Application Example 1 is that in the preparation method of the conductive polymer dispersion, the raw material added in step (2) is commercially available 3,4-ethylenedioxythiophene with a purity of 99.8%, and the rest is the same as Application Example 1.

[0093] The performance test results of the capacitors obtained from Application Examples 1-3 and Comparative Application Examples 1-5 are shown in Table 1.

[0094] Table 1 Performance test results of capacitors obtained from application examples 1-3 and comparative examples 1-5

[0095] serial number CAP(uF) DF (%) ESR(mΩ) Example 1 920 1.76 4.56 Example 2 924 1.88 4.63 Example 3 922 1.83 4.52 Comparative Application Example 1 906 2.23 5.29 Application Comparative Example 2 903 2.32 5.63 Application Comparative Example 3 905 2.29 5.78 Application Example 4 904 2.38 5.54 Application Comparative Example 5 900 2.42 5.82

[0096] The capacitors obtained from Examples 1-3 and Comparative Examples 1-5 were subjected to cyclic charge and discharge tests, and the capacity decay was measured after 5,000 cycles. The results are shown in Table 2 below.

[0097] Table 2 Cyclic performance test results of capacitors obtained from application examples 1-3 and comparative examples 1-5

[0098]

[0099]

[0100] As shown in Table 1, the high-purity 3,4-ethylenedioxythiophene monomer of the present invention exhibits significant advantages in solid-state capacitor capacitance and impedance compared to conventional monomers, enabling industrial applications in high-end capacitors. Table 2 demonstrates that the high-purity 3,4-ethylenedioxythiophene monomer of the present invention exhibits charge-discharge performance comparable to conventional monomers.

[0101] Compared with the conventional distillation purification method, the purification method of the present invention effectively avoids the problem of low yield caused by EDOT polymerization due to excessively high temperature due to the use of a lower working temperature. In the present invention, a portion of high-purity products can be collected in a single operation, and the effluent with relatively low purity can also be recycled and applied to prepare high-purity monomers. However, even if the configuration of the distillation tower is adjusted, the ordinary distillation method cannot separate impurities and the purity cannot be increased to more than 99.99%. Through comparison with the embodiments, it can be seen that the use of the EDOT of this patent in the dispersion liquid for solid-state capacitors can effectively improve the initial performance of the capacitor.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for purifying 3,4-ethylenedioxythiophene, characterized in that: The following steps are involved: (1) After the decarboxylation reaction, the crude distilled 3,4-ethylenedioxythiophene liquid was stirred and mixed with water, and then added to a melt crystallizer, cooled to 1°C to 6°C, kept cold until the liquid was completely crystallized, and the non-crystallized waste liquid was discharged; the cooling rate was 1°C / h to 2°C / h; (2) heating to 11°C to 14°C and maintaining the temperature until the purity of the effluent is ≥99.99%; the heating rate is 1°C / h to 2°C / h; (3) Raise the temperature to 20°C to 30°C again, keep warm, and collect the effluent to obtain 3,4-ethylenedioxythiophene.

2. The method for purifying 3,4-ethylenedioxythiophene according to claim 1, characterized in that: The method further comprises the step (4): dehydrating the obtained 3,4-ethylenedioxythiophene through a desiccant, filtering, and obtaining a finished 3,4-ethylenedioxythiophene product.

3. The method for purifying 3,4-ethylenedioxythiophene according to claim 1, wherein In the step (1), the amount of water added is 30% to 40% of the weight of the feed liquid.

4. The method for purifying 3,4-ethylenedioxythiophene according to claim 1, wherein In step (2), the effluent with a purity of less than 99.7% can be used as the starting material in step (1) for further purification, and the effluent with a purity of 99.70% to 99.99% can be used as a general standard product.

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