A purification method for 2,5-furandicarboxylic acid

Abstract

This invention discloses a purification method for 2,5-furandicarboxylic acid, comprising the following steps: 1) Pre-treating the crude FDCA to be purified to obtain a pre-treated FDCA salt solution for later use; 2) Adjusting the pH of the pre-treated FDCA salt solution obtained in step 1) with dilute acid until the pH value is 4-5, then adding activated carbon to a beaker for decolorization and impurity removal, and filtering the solution in the beaker after treatment to obtain the FDCA salt solution; 3) Slowly adding strong acid to the FDCA salt solution obtained in step 2) while stirring until the pH value of the solution is <1, then filtering the reacted material to obtain a solid precipitate, washing the solid precipitate with deionized water, and drying it to obtain purified FDCA. The process of this invention is simple, carried out under normal temperature and pressure conditions, has high purification efficiency, and is suitable for large-scale scale-up and production.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a purification method for 2,5-furandicarboxylic acid. Background Technology

[0002] 2,5-Furfurandicarboxylic acid (FDCA) is an important chemical monomer. Its structure consists of a furan ring and two carboxyl groups. Compared with the petroleum-based monomer terephthalic acid (PTA), FDCA is mainly obtained by oxidation of various biomass platform compounds and has a wide range of applications in food packaging, surfactants, pharmaceuticals and many other fields.

[0003] Because FDCA has a very similar chemical structure to PTA, it has been widely studied and applied as a substitute for PTA in the preparation of polyester materials. Since the upstream raw materials of FDCA are all derived from biomass energy in nature, the development and application of FDCA can help reduce global carbon emissions and mitigate environmental pollution, making it a new type of green and environmentally friendly material.

[0004] According to surveys, the global annual demand for FDCA will exceed 1 million tons in the next decade. Internationally, research and industrialization of FDCA started earlier in some developed countries in Europe and America. Domestically, FDCA-related research and reports have emerged frequently in recent years, but industrialization has been slow, core technologies are poorly mastered, and the quality of FDCA products is relatively poor. Not only is the purity low, but the color is also yellowish, far from meeting the needs of downstream polyester. The quality issues of the products urgently need to be addressed. The most common problem is the yellowing of FDCA, mainly due to the generation of many monoacid impurities during FDCA synthesis, such as furoic acid and 5-formylfuran-2-carboxylic acid. During polyester synthesis, these monoacid impurities affect the polymerization effect, leading to yellowing of the polyester during polymerization.

[0005] Currently, most FDCA purification techniques are based on PTA purification methods, which use H2 hydrogenation reduction to remove pigments and other impurities from the product. However, this method requires significant investment in equipment and raw materials, carries high safety risks, and has high requirements for the materials to be purified. It is less effective for FDCA with low purity and high b-value, often requiring multiple purification processes, resulting in complex procedures and low yields. Secondly, based on the acidity and solubility characteristics of FDCA, since FDCA is insoluble in water, an alkaline solution is used to dissolve FDCA into a salt solution, forming a homogeneous system. The solution is then decolorized and impurities removed, followed by the addition of a strong acid to neutralize the alkali, causing FDCA to precipitate. For example, CN103965146A discloses an FDCA purification method in which the authors achieved good purification results by dissolving FDCA in an alkali solution and then treating it with activated carbon. However, this method requires FDCA with a purity greater than 95%. According to the inventors, FDCA with a purity of about 90% only achieves a purity of 96% after purification using this method. Multiple purification cycles are required to obtain a higher purity, but the loss rate in this process is relatively large, resulting in a low overall yield.

[0006] This invention addresses the issues of FDCA color and purity by developing a purification method for FDCA. This method can significantly improve the purity of crude FDCA of different purities, greatly reduce the color b value, and significantly alleviate yellowing during subsequent polyester polymerization. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of this invention is to provide a simple purification method for 2,5-furandicarboxylic acid, which can significantly improve the purity of FDCA and greatly reduce the color b value, thereby reducing the risk of yellowing during subsequent polyester polymerization.

[0008] A method for purifying 2,5-furandicarboxylic acid includes the following steps:

[0009] 1) Pre-treat the crude FDCA to be purified to obtain a pre-treated FDCA salt solution for later use;

[0010] 2) Adjust the pH of the pretreated FDCA salt solution obtained in step 1) with dilute acid until the pH value is 4-5. Then add activated carbon to the beaker to decolorize and remove impurities. After the treatment, filter the solution in the beaker to obtain the FDCA salt solution.

[0011] 3) While stirring, slowly add strong acid to the FDCA salt solution obtained in step 2) until the pH value of the solution is <1. Then filter the reaction material to obtain a solid precipitate. Wash the solid precipitate with deionized water and dry it to obtain purified FDCA.

[0012] Furthermore, when the purity of the crude FDCA to be purified is greater than 80%, the pretreatment process of the crude FDCA to be purified in step 1) is as follows:

[0013] Add the crude FDCA to be purified to a beaker containing alkaline solution and stir thoroughly until completely dissolved.

[0014] Furthermore, when the purity of the crude FDCA to be purified is greater than or equal to 60% and less than or equal to 80%, the crude FDCA to be purified is added to a beaker containing alkaline solution and stirred thoroughly to dissolve it completely. Then, sodium hypochlorite solution is added and stirred, followed by the addition of activated carbon and stirring to remove impurities and decolorize, thus obtaining a pretreated FDCA salt solution.

[0015] Furthermore, the mass ratio of the crude FDCA to be purified to the alkaline solution is 1:2~5; wherein the alkaline solution is a sodium hydroxide solution with a pH value greater than 10.

[0016] Further, the mass ratio of the crude FDCA to be purified in step 1) to the activated carbon in step 2) is 1:0.01~0.5.

[0017] Furthermore, in step 2), the dilute acid is 5% dilute hydrochloric acid or 30% dilute phosphoric acid; in step 3), the strong acid is concentrated hydrochloric acid.

[0018] Furthermore, the mass fraction of sodium hypochlorite is 10%; the mass ratio of sodium hypochlorite to crude FDCA to be purified is 0.01~0.2.

[0019] Furthermore, when the purity of the crude FDCA to be purified is not less than 80%, the color value b of the purified FDCA is less than 0; when the purity of the crude FDCA to be purified is 60%~80%, the color value b of the purified FDCA is less than 1.

[0020] Furthermore, the activated carbon is at least one of the following: fruit shell activated carbon, coal-derived activated carbon, and petroleum-based activated carbon.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1) This invention dissolves crude 2,5-furandicarboxylic acid of different purities into a salt solution with alkali, and then purifies it through decolorization, impurity removal and other processes to obtain higher quality 2,5-furandicarboxylic acid, which can be directly applied to the synthesis of PEF polyester and can greatly reduce the risk of yellowing of downstream polyester products.

[0023] 2) When the purity of the crude product is greater than 80%, it is only necessary to adjust the pH of the 2,5-furandicarboxylate solution with dilute hydrochloric acid and add activated carbon treatment to increase the purity to greater than 99.99% and decrease the b value to less than 0; when the purity of the crude product is 60%~80%, it is possible to increase the purity to greater than 99.9% and decrease the b value to less than 1 by using sodium hypochlorite and dilute phosphoric acid.

[0024] 3) The process of this invention is simple, carried out under normal temperature and pressure conditions, requires simple equipment, has high purification efficiency, and is suitable for large-scale scale-up and production;

[0025] 4) The FDCA raw material required in this invention has low requirements. Only crude FDCA with a purity greater than 60% is needed to achieve purification. After purification, FDCA can reach a purity of more than 99.9% and a b value of less than 1. It can be directly used to synthesize polyester without any other treatment. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited to the scope described.

[0027] It should be noted that the crude FDCA used in the example was synthesized by the inventor through an oxidation reaction using HMF as raw material, sodium hypochlorite as oxidant, and non-precious metal oxide as catalyst. This is existing technology, and the specific synthesis method will not be described in detail here. Example 1

[0028] 1) Add 29g of alkaline solution and 10g of crude FDCA to be purified (purity 93.52%, impurity 1 accounts for 3.35%, impurity 2 accounts for 3.13%, b value 4.21) to 50g of water and stir until completely dissolved to obtain FDCA salt solution;

[0029] 2) Slowly add dilute hydrochloric acid dropwise to the salt solution containing FDCA to adjust the pH value to around 5. Then add 1g of activated carbon to the salt solution, adjust the stirring speed to 400rpm, stir for 1h, and then filter to obtain a clear decolorized solution.

[0030] 3) While stirring, slowly add concentrated hydrochloric acid with a mass fraction of 31% to the clear decolorized solution to adjust the pH value to less than 1. Filter the reacted material to obtain a white solid precipitate. Wash the white solid precipitate with sufficient deionized water and dry it. After drying, high-purity FDCA is obtained.

[0031] 4) Its purity was determined to be 99.99% by HPLC, with impurity 1 accounting for 0.01%; its b value was determined to be -0.33 by colorimeter. Example 2

[0032] The steps in the previous examples were repeated, except that the purity of the raw material used was 85.10%, with impurity 1 accounting for 12.42%, impurity 2 accounting for 2.48%, and a b-value of 5.05. HPLC analysis after purification showed that the purity of the obtained FDCA was 99.99%, with impurity 1 accounting for 0.01%. The b-value measured by a colorimeter was -0.22. Example 3

[0033] The steps of Example 1 were repeated, except that the purity of the raw material used was 80.56%, with impurity 1 accounting for 14.42%, impurity 2 accounting for 5.02%, and a b-value of 6.13. HPLC analysis after purification showed that the purity of the obtained FDCA was 99.99%, with impurity 1 accounting for 0.01%. The b-value measured by a colorimeter was -0.12. Example 4

[0034] 1) Add 29g of alkaline solution and 10g of crude FDCA to be purified (purity 75.24%, impurity 1 16.57%, impurity 2 4.85%, impurity 3 3.34%, b value 4.83) to 50g of water and stir until completely dissolved to obtain FDCA salt solution. Then add 0.5g of 10% sodium hypochlorite solution to the obtained FDCA salt solution, followed by 0.5g of activated carbon, and stir at 300rpm for 30min.

[0035] 2) Slowly add dilute phosphoric acid dropwise to the salt solution containing FDCA to adjust its pH value to around 4. Then add 1g of activated carbon to the solution, adjust the stirring speed to 400rpm, stir for 1h, and then filter to obtain a clear decolorized solution.

[0036] 3) While stirring, slowly add concentrated hydrochloric acid with a mass fraction of 31% to the clear decolorized solution to adjust the pH value to less than 1. Filter the reacted material to obtain a white solid precipitate. Wash the white solid precipitate with sufficient deionized water and dry it. After drying, high-purity FDCA is obtained.

[0037] 4) Its purity was determined to be 99.98% by HPLC, with impurity 1 accounting for 0.02%; its b value was determined to be 0.32 by colorimeter. Example 5

[0038] The steps of Example 4 were repeated, except that the purity of the raw material used was 68.16%, with impurity 1 accounting for 16.32%, impurity 2 accounting for 10.71%, impurity 3 accounting for 4.81%, and a b-value of 5.79. After purification, HPLC analysis showed that the purity of the obtained FDCA was 99.95%, with impurity 1 accounting for 0.04% and impurity 3 accounting for 0.01%. The b-value, measured by a colorimeter, was 0.54. Example 6

[0039] The steps of Example 4 were repeated, except that the purity of the raw material used was 62.93%, with impurity 1 accounting for 19.22%, impurity 2 accounting for 14.81%, and impurity 3 accounting for 3.04%, and a b-value of 8.54. After purification, HPLC analysis showed that the purity of the obtained FDCA was 99.91%, with impurity 1 accounting for 0.06% and impurity 3 accounting for 0.03%. The b-value, measured by a colorimeter, was 0.87.

[0040] The purification results of Examples 1-6 are shown in Table 1 below:

[0041]

[0042] Examples 1-3, with Example 1 as an example, show that when the purity of crude FDCA is greater than 80%, a brownish-red pigment appears in the solution during the alkali dissolution process as the crude solid dissolves. This indicates that some impurities in the crude product may react with the alkali and generate pigment during the dissolution process. After adding dilute hydrochloric acid to adjust the pH, the solution color gradually lightens, and some brown precipitate forms. Upon testing, most of this precipitate is identified as impurity 1.

[0043] Because FDCA has high solubility under strongly alkaline and weakly acidic conditions (pH 4-6), adjusting the pH to around 5 ensures sufficient dissolution of FDCA while allowing some impurities that are insoluble under acidic conditions to precipitate out, thus achieving purification. Furthermore, the lightening of the solution color after adding dilute hydrochloric acid indicates that hydrochloric acid can decompose some colored impurities. During the decolorization and impurity removal process, activated carbon fully adsorbs the aforementioned pigments and impurities, turning the solution colorless and transparent. After acidification, washing, and drying, pure white FDCA is finally obtained. Under these conditions, the purified FDCA generally has a purity greater than 99.99% and a b-value less than 0.

[0044] Examples 4-6, with Example 4 as a representative, show that when the purity of crude FDCA is between 60% and 80%, during the alkali dissolution process, as the crude solid dissolves, more brownish-red pigment appears in the solution, eventually darkening the solution color, indicating a higher level of impurities in the crude FDCA. After adding sodium hypochlorite and stirring, the pigment begins to slowly decrease, and the solution color changes from dark reddish-brown to yellow. Furthermore, as the purity of the crude FDCA decreases in these examples, the color deepens further. For instance, after treatment with sodium hypochlorite, the solution in Example 4 is pale yellow, while in Example 5 it is deep yellow. The change in solution color from reddish-brown to yellow is due to the strong oxidizing and bleaching properties of sodium hypochlorite, which promotes the decomposition of pigment impurities, and this process is irreversible. After adjusting the pH with dilute phosphoric acid, the solution color becomes even lighter, and a brown precipitate appears. This is because the phosphate ions in the phosphoric acid molecule can react with carbonyl groups and other groups in the chromogenic impurities; simultaneously, under acidic conditions, phosphate ions can also reduce some chromogenic oxide impurities to colorless forms, thus achieving a decolorization effect. Furthermore, the provided acidic environment causes some impurities that are insoluble under acidic conditions to precipitate out, thus achieving purification. Activated carbon then fully adsorbs the pigments and impurities, turning the solution colorless and transparent. After acidification, washing, and drying, pure white FDCA is finally obtained. Under these conditions, the purified FDCA generally has a purity greater than 99.9% and a b-value less than 1.

Claims

1. A method for purifying 2,5-furandicarboxylic acid, characterized in that... Includes the following steps: 1) Pre-treat the crude FDCA to be purified to obtain a pre-treated FDCA salt solution for later use; 2) Adjust the pH of the pretreated FDCA salt solution obtained in step 1) with dilute acid until the pH value is 4-5. Then add activated carbon to the beaker to decolorize and remove impurities. After the treatment, filter the solution in the beaker to obtain the FDCA salt solution. The activated carbon is at least one of fruit shell activated carbon, coal-derived activated carbon, and petroleum-derived activated carbon. 3) While stirring, slowly add strong acid to the FDCA salt solution obtained in step 2) until the pH value of the solution is <1. Then filter the reaction material to obtain a solid precipitate. Wash the solid precipitate with deionized water and dry it to obtain purified FDCA. When the purity of the crude FDCA to be purified is greater than 80%, the pretreatment process of the crude FDCA to be purified in step 1) is as follows: Add the crude FDCA to be purified to a beaker containing alkaline solution and stir thoroughly until completely dissolved. When the purity of the crude FDCA to be purified is greater than or equal to 60% and less than or equal to 80%, the crude FDCA to be purified is added to a beaker containing alkaline solution and stirred thoroughly to dissolve it completely. Then, sodium hypochlorite solution is added and stirred, followed by the addition of activated carbon and stirring to remove impurities and decolorize, thus obtaining a pretreated FDCA salt solution.

2. The purification method for 2,5-furandicarboxylic acid according to claim 1, characterized in that... The mass ratio of the crude FDCA to be purified to the alkaline solution is 1:2~5; the alkaline solution is a sodium hydroxide solution with a pH value greater than 10. The mass ratio of the crude FDCA to be purified in step 1) to the activated carbon in step 2) is 1:0.01~0.

5.

3. The purification method for 2,5-furandicarboxylic acid according to claim 1, characterized in that... 2) The dilute acid in the step is 5% dilute hydrochloric acid or 30% dilute phosphoric acid; 3) The strong acid in the step is concentrated hydrochloric acid.

4. The purification method for 2,5-furandicarboxylic acid according to claim 1, characterized in that... The sodium hypochlorite has a mass fraction of 10%; the mass ratio of sodium hypochlorite to crude FDCA to be purified is 0.01~0.

2.

5. The purification method for 2,5-furandicarboxylic acid according to claim 1, characterized in that... When the purity of the crude FDCA to be purified is not less than 80%, the color value b of the purified FDCA is less than 0; when the purity of the crude FDCA to be purified is 60%~80%, the color value b of the purified FDCA is less than 1.

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