A method for purifying high purity furanic acid

Abstract

The present application belongs to the technical field of fine chemical product purification, and particularly relates to a high-purity furfuryl acid purification method. The method is directed to a crude furfuryl acid obtained after pretreatment of a furfuryl alcohol oxidation reaction liquid, and a combined purification process of "double-agent synergistic decolorization-vacuum concentration-double-solvent gradient recrystallization" is innovatively adopted. First, the crude furfuryl acid is deeply decolorized with a composite system of activated carbon and diatomite, and organic pigments, small particles and metal ions are simultaneously removed. Then, the crude furfuryl acid is sequentially subjected to step-by-step recrystallization with deionized water and an ethanol-water mixed solvent, and trace by-products are accurately separated. Finally, vacuum drying is performed, and a high-purity furfuryl acid product with a purity of greater than or equal to 99.9% is finally obtained. Compared with the existing single decolorization or single solvent recrystallization process, the present application has high efficiency and strong compatibility, and can be realized by small-scale modification on the basis of the existing furfuryl acid production equipment, is suitable for large-scale production, and fills the gap of high-purity furfuryl acid purification and large-scale production in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical product purification technology, specifically relating to a method for purifying high-purity furoic acid. It is particularly suitable for fields such as the preparation of pharmaceutical intermediates and high-end electronic packaging materials, where the purity requirement of furoic acid is ≥99.9%. It can achieve efficient purification of crude furoic acid and solve the bottleneck problem of raw material purity in high-end application scenarios. Background Technology

[0002] Furoic acid, as an important fine chemical intermediate, requires a purity of ≥99.9% in high-end applications (pharmaceuticals, high-end electronics), with strict limits on impurities such as furfuryl alcohol, furfural, and metal ions (total impurities ≤0.1%). Current furoic acid production mainly relies on furfural oxidation. The crude furoic acid obtained after preliminary filtration of the oxidation reaction solution typically has a purity of only 98%~99.5%, containing pigments, minor impurities, byproducts (furfuryl alcohol, furfural dicarboxylic acid), and residual metal catalysts, requiring further purification.

[0003] Existing methods for purifying furoic acid have significant drawbacks. For example, Chinese patent CN202111069255X discloses a method for preparing furoic acid using a single activated carbon decolorization process combined with water recrystallization, which can only increase the purity of furoic acid to about 99.5%, failing to effectively remove tiny particles and metal ions. Another example is Chinese patent CN2022101138028, which discloses a method for recovering furfuryl alcohol using an ethanol-water mixed solvent for recrystallization, but suffers from difficulties and high costs in solvent recovery. Other related processes also generally suffer from cumbersome purification steps, poor industrial compatibility, and unstable product purity, all of which fail to meet the large-scale demand for high-purity furoic acid in high-end fields.

[0004] Therefore, developing a highly targeted, efficient, and compatible method for purifying high-purity furoic acid has become an urgent need in the industry. Summary of the Invention

[0005] To address the problems of existing purification technologies, such as difficulty in achieving a purity of 99.9%, incomplete impurity removal, and poor industrial compatibility, this invention provides a combined purification method of "dual-agent synergistic decolorization + dual-solvent gradient recrystallization," which can achieve efficient purification of crude furoic acid and stably obtain products with a purity of ≥99.9%, meeting the needs of high-end applications.

[0006] The core innovation of this invention is the combined process of "dual-agent synergistic decolorization + dual-solvent gradient recrystallization", which targets the removal of different types of impurities, and the synergistic effect of each step ensures the purification effect.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for purifying high-purity furoic acid. The crude product system after pretreatment and filtration of furfural oxidation reaction solution is processed through four core steps: dual-agent synergistic decolorization, vacuum concentration, dual-solvent gradient recrystallization, and vacuum drying.

[0008] Specifically, it includes the following aspects: (1) Two-agent synergistic decolorization process A composite decolorization system using activated carbon and diatomaceous earth is employed, with both working synergistically to achieve comprehensive removal of impurities. Activated carbon: Selected with a specific surface area of ​​800~1200 m² 2 / g of granular activated carbon has a pore size distribution concentrated in 2~5nm. It mainly adsorbs organic pigments, polar impurities and resinous polymers and other organic impurities. The appropriate pore size structure can improve the adsorption efficiency of trace organic impurities and reduce the amount of adsorbent used. Diatomaceous earth: Food-grade diatomaceous earth of 300-500 mesh is selected and activated by calcination at 600-800℃ before use. It mainly adsorbs tiny suspended particles, colloidal impurities, and metal ions (such as residual Co from oxidation reactions). 2+ Mn 2+ (etc.), utilizing its porous structure to enhance the retention of inorganic impurities, and calcination activation can improve its adsorption capacity; Process parameter optimization: The mass ratio of activated carbon to diatomaceous earth is controlled at 1:0.4~0.6, the decolorization temperature is 80~90℃, the stirring rate is 50~100r / min, and 0.1μm precision filtration is used to ensure the clarity of the filtrate. Under these parameters, the clarity of the filtrate can be ≥99.5%, and the residual metal ions are initially reduced to below 0.005%, laying the foundation for subsequent recrystallization.

[0009] (2) Reduced pressure concentration process The ultra-clear filtrate after decolorization is concentrated under reduced pressure to increase the concentration of furoic acid, reduce the amount of solvent used in subsequent recrystallization, and improve crystallization efficiency.

[0010] (3) Dual solvent gradient recrystallization process A stepwise recrystallization strategy was adopted, taking advantage of the difference in solubility of furoic acid and impurities in different solvents to remove residual impurities in a gradient manner. The first water recrystallization can initially improve the purity of furoic acid to over 99.7%, and the second ethanol-water mixed solvent recrystallization further improves the purity to over 99.9%.

[0011] (4) Vacuum drying process Secondary crystallization involves vacuum drying to remove residual solvents, ensuring product quality stability.

[0012] As a preferred technical solution, the purification method for high-purity furoic acid according to the present invention includes the following steps: (1) Pretreatment filtration: The crude furoic acid reaction solution (i.e. furfural oxidation reaction solution) is first filtered through a ceramic membrane to remove solid impurities with a particle size ≥0.22μm and catalyst residue to obtain the pretreated filtrate; (2) Synergistic decolorization with two agents: Add 0.2%~0.5% activated carbon (specific surface area 800~1200m²) by mass of crude furoic acid reaction solution to the pretreated filtrate. 2 The reaction solution of crude furoic acid (g) and 0.1%~0.3% diatomaceous earth (300~500 mesh) was decolorized at 80~90℃ under stirring for 30~50 min, and then filtered through 0.1μm precision to obtain an ultra-clear filtrate. (3) Vacuum concentration: The ultra-clear filtrate from step (2) is concentrated under vacuum conditions of -0.07 to -0.09 MPa, 65 to 75°C, and 80 to 120 r / min until the mass concentration of furoic acid in the filtrate reaches 45% to 55%. Low-boiling substances are continuously removed during the concentration process. (4) Gradient recrystallization with dual solvents: The concentrate from step (3) is recrystallized twice, first with water and then with an ethanol-water mixture. (5) Vacuum drying: The secondary refined crystals after step (4) are dried at a temperature of 70~80℃ and a vacuum degree of -0.08~-0.095MPa for 4~8h to obtain high-purity furoic acid product.

[0013] Specifically, in step (2), the mass ratio of activated carbon to diatomaceous earth is 1:0.4~0.6, the decolorization temperature is preferably 85~90℃, the decolorization time is preferably 35~45min, and the precision filtration uses a 0.1μm polyethersulfone filter membrane.

[0014] Specifically, the two recrystallization steps in step (4) are as follows: a. First recrystallization: Mix the concentrated solution with deionized water (conductivity ≤10μS / cm) at a mass ratio of 1:2.0~3.0, heat to 70~80℃, stir to dissolve, then cool to 25~35℃ at a cooling rate of 5~8℃ / h, and crystallize at a constant temperature for 3~5h. After filtration, obtain the first crystal, and rinse the surface of the crystal with a small amount of deionized water 2~3 times. b. Secondary recrystallization: Mix the primary crystal with an ethanol-water mixed solvent (ethanol purity ≥ 99.5%, ethanol to water volume ratio 1:3~5) at a mass ratio of 1:2.5~4.0, heat to 60~70℃, stir to dissolve, then cool to 20~30℃ at a cooling rate of 3~5℃ / h, and crystallize at a constant temperature for 3~5h. After filtration, obtain the secondary crystal, and rinse the crystal surface 2~3 times with a small amount of ethanol-water mixed solvent (volume ratio 1:4).

[0015] Specifically, in step a, the preferred mass ratio of deionized water to concentrate is 1:2.5~2.8, the conductivity of deionized water is ≤5μS / cm, the preferred constant temperature crystallization temperature is 28~32℃, the preferred crystallization time is 3.5~4.5h, and the amount of deionized water used for rinsing is 5%~8% of the mass of the first refined crystal.

[0016] Specifically, in step b, the volume ratio of the ethanol-water mixed solvent is preferably 1:4~4.5, the ethanol purity is ≥99.7%, the mass ratio of the mixed solvent to the primary crystal is preferably 1:3.0~3.5, the isothermal crystallization temperature is preferably 22~28℃, the crystallization time is preferably 3.5~4.5h, and the amount of mixed solvent used for rinsing is 3%~5% of the mass of the secondary crystal.

[0017] Specifically, in step (5), the vacuum drying temperature is preferably 75~80℃ and the drying time is preferably 6~7h to avoid the decomposition of furoic acid by heat.

[0018] Specifically, the high-purity furoic acid finally obtained in step (5) has a purity of ≥99.9%, a furfuryl alcohol content of ≤0.05%, a furanaldehyde residue of ≤0.03%, a metal ion residue of ≤0.001%, and a total impurity content of ≤0.1%.

[0019] The method described in this invention targets crude furoic acid obtained after pretreatment of furfural oxidation reaction solution. It innovatively employs a combined purification process of "dual-agent synergistic decolorization-reduced pressure concentration-dual-solvent gradient recrystallization." First, a composite system of activated carbon and diatomaceous earth is used for deep decolorization, simultaneously removing organic pigments, microparticles, and metal ions. Then, the product undergoes stepwise recrystallization with deionized water and an ethanol-water mixed solvent to precisely separate trace byproducts. Finally, vacuum drying yields a high-purity furoic acid product with a purity ≥99.9%. Compared to existing single decolorization or single-solvent recrystallization processes, this invention offers highly targeted and efficient purification, can be implemented with minor modifications to existing furoic acid production equipment, has strong compatibility, and is suitable for large-scale mass production, filling a gap in the existing technology for high-purity furoic acid purification and mass production.

[0020] Compared with the prior art, the advantages of the present invention are: 1. Excellent purification effect: It can produce high-purity furoic acid with a purity of ≥99.9%, total impurities ≤0.1%, furfuryl alcohol ≤0.05%, metal ions ≤0.001%, furanaldehyde residue ≤0.03%, and solvent residue ≤0.15%, meeting the stringent requirements of high-end fields.

[0021] 2. Highly targeted to impurities: The dual-agent decolorization process thoroughly removes both organic and inorganic impurities, while gradient recrystallization precisely separates trace byproducts. Combined with multi-stage rinsing operations, it addresses the pain point of incomplete impurity removal in existing processes.

[0022] 3. Good industrial compatibility: The process steps are simple, requiring only the addition of a 0.1μm precision filtration device and a solvent distillation recovery device to the existing furoic acid production filtration and crystallization units, without the need to build a new production line; the new equipment are all conventional chemical equipment, with low procurement and modification costs, suitable for existing enterprises to upgrade quickly.

[0023] 4. Economic and environmentally friendly: The solvents used (water, ethanol) are easy to recycle, making them suitable for large-scale production. Detailed Implementation

[0024] To make the technical objectives, technical solutions, and beneficial effects of the present invention clearer, the technical solutions of the present invention will be further described below in conjunction with specific embodiments. However, the embodiments are intended to explain the present invention and should not be construed as limiting the present invention. Where no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in the field or the product manual shall apply.

[0025] Unless otherwise specified, the instruments and equipment used in the following examples are all commercially available conventional instruments and equipment; unless otherwise specified, the reagents, raw materials, etc. used in the following examples are all conventional commercially available products and can be obtained through commercial channels.

[0026] In the following examples, room temperature or normal temperature refers to 25±5℃.

[0027] The following examples all use the same crude furoic acid (purity 99.2%, furfuryl alcohol content 0.21%, metal ion residue 0.008%, total impurities 0.8%) as the treatment object. Example 1

[0028] Example 1 provides a method for purifying high-purity furoic acid, the specific steps of which are as follows: 1) Pretreatment filtration: Take 100 kg of crude furoic acid reaction solution, filter it through a 0.22 μm ceramic membrane to remove solid impurities and catalyst residue, and obtain pretreated filtrate; 2) Synergistic decolorization with two agents: Add 0.3 kg of activated carbon (specific surface area 1000 m²) to the pretreated filtrate. 2 The mixture was prepared by stirring and decolorizing at 85°C for 40 minutes with 0.15 kg of diatomaceous earth (400 mesh, activated by calcination at 700°C before use) and 0.15 kg of diatomaceous earth (400 mesh, activated by calcination at 700°C before use). The mixture was then filtered through a 0.1 μm polyethersulfone membrane to obtain an ultra-clear filtrate. 3) Vacuum concentration: The ultra-clear filtrate from step 2) is concentrated under vacuum conditions of -0.08 MPa, 70°C, and 100 r / min. About 10 kg of low-boiling matter is collected and concentrated to a furoic acid mass concentration of 50% (about 190 kg of concentrate). 4) Recrystallization using a dual solvent gradient: a. First recrystallization: Mix the concentrated solution from step 3) with 475 kg of deionized water (conductivity 3 μS / cm), heat to 75°C, stir at 100 r / min to dissolve, cool to 30°C at 6°C / h, and crystallize at a constant temperature for 4 h. Filter using a Buchner funnel to obtain first-stage crystals (88.6 kg, purity 99.75%), and rinse the crystal surface twice with 4.5 kg of deionized water. b. Secondary recrystallization: The primary crystals were mixed with 310 kg of ethanol-water mixed solvent (ethanol purity 99.7%, ethanol / water volume ratio 1:4), heated to 65°C, stirred at 100 r / min to dissolve, cooled to 25°C at 4°C / h, and crystallized at a constant temperature for 4 h. The secondary crystals were obtained by filtration and the crystal surface was rinsed twice with 2.6 kg of ethanol-water mixed solvent (ethanol purity 99.7%, ethanol / water volume ratio 1:4). 5) Vacuum drying: The secondary refined crystals were dried for 6 hours at a temperature of 75℃, a vacuum degree of -0.09MPa, and a stirring rate of 40r / min to obtain 85.2kg of high-purity furoic acid product, with a yield of 89.5%.

[0029] Product test results: purity 99.93%, furfural content 0.03%, furfural residue 0.02%, metal ion residue 0.0008%, total impurity content 0.07%. Example 2

[0030] Example 2 provides a method for purifying high-purity furoic acid, the specific steps of which are as follows: 1) Pretreatment filtration: Take 100 kg of crude furoic acid reaction solution, filter it through a 0.22 μm ceramic membrane to remove solid impurities and catalyst residue, and obtain pretreated filtrate; 2) Synergistic decolorization with two agents: Add 0.4 kg of activated carbon (specific surface area 1200 m²) to the pretreated filtrate. 2 The mixture was prepared by stirring and decolorizing 0.2 kg of diatomaceous earth (500 mesh, activated by calcination at 800℃ before use) at 90℃ and 80 r / min for 35 min, and then filtered through a 0.1 μm polyethersulfone membrane to obtain an ultra-clear filtrate. 3) Vacuum concentration: The ultra-clear filtrate from step 2) is concentrated under vacuum conditions of -0.09 MPa, 75°C, and 120 r / min. About 8 kg of low-boiling matter is collected and concentrated to a furoic acid mass concentration of 55% (about 175 kg of concentrate). 4) Recrystallization using a dual solvent gradient: a. First recrystallization: Mix the concentrated solution from step 3) with 490 kg of deionized water (conductivity 4 μS / cm), heat to 80 °C, stir at 120 r / min to dissolve, cool to 32 °C at 7 °C / h, and crystallize at a constant temperature for 3.5 h. Filter using a Buchner funnel to obtain first-stage crystals (90.3 kg, purity 99.78%), and rinse the crystal surface twice with 5.4 kg of deionized water. b. Secondary recrystallization: The primary crystals were mixed with 316 kg of ethanol-water mixed solvent (ethanol purity 99.7%, ethanol / water volume ratio 1:4.5), heated to 70°C, stirred at 120 r / min to dissolve, cooled to 28°C at 5°C / h, and crystallized at a constant temperature for 3.5 h. The secondary crystals were obtained by filtration, and the crystal surface was rinsed twice with 2.7 kg of ethanol-water mixed solvent (ethanol purity 99.7%, ethanol / water volume ratio 1:4.5). 5) Vacuum drying: The secondary refined crystals were dried for 6.5 hours at a temperature of 80℃, a vacuum degree of -0.095MPa, and a stirring rate of 50r / min to obtain 86.8kg of high-purity furoic acid product, with a yield of 90.3%.

[0031] Product test results: purity 99.95%, furfuryl alcohol content 0.02%, furfural residue 0.01%, metal ion residue 0.0005%, total impurity content 0.05%. Example 3

[0032] Example 3 provides a method for purifying high-purity furoic acid, the specific steps of which are as follows: 1) Pretreatment filtration: Take 100 kg of crude furoic acid reaction solution, filter it through a 0.22 μm ceramic membrane to remove solid impurities and catalyst residue, and obtain pretreated filtrate; 2) Synergistic decolorization with two agents: Add 0.25 kg of activated carbon (specific surface area 800 m²) to the pretreated filtrate. 2 The mixture was prepared by stirring and decolorizing 0.1 kg of diatomaceous earth (300 mesh, activated by calcination at 600℃ before use) at 80℃ and 60 r / min for 45 min, and then filtered through a 0.1 μm polyethersulfone membrane to obtain an ultra-clear filtrate. 3) Vacuum concentration: The ultra-clear filtrate from step 2) is concentrated under vacuum conditions of -0.07 MPa, 65°C, and 80 r / min. About 12 kg of low-boiling matter is collected and concentrated to a furoic acid mass concentration of 45% (about 209 kg of concentrate). 4) Recrystallization using a dual solvent gradient: a. First recrystallization: Mix the concentrated solution from step 3) with 418 kg of deionized water (conductivity 5 μS / cm), heat to 70°C, stir at 80 r / min to dissolve, cool to 28°C at 5°C / h, and crystallize at a constant temperature for 4.5 h. Filter using a Buchner funnel to obtain first-stage crystals (87.5 kg, purity 99.72%), and rinse the crystal surface twice with 4.4 kg of deionized water. b. Secondary recrystallization: The primary crystals were mixed with 298 kg of ethanol-water mixed solvent (ethanol purity 99.5%, ethanol / water volume ratio 1:3.5), heated to 60℃, stirred at 80 r / min to dissolve, cooled to 22℃ at 3℃ / h, and crystallized at a constant temperature for 4.5 h. The secondary crystals were obtained by filtration, and the crystal surface was rinsed twice with 2.6 kg of ethanol-water mixed solvent (ethanol purity 99.5%, ethanol / water volume ratio 1:3.5). 5) Vacuum drying: The secondary refined crystals were dried for 7 hours at a temperature of 70℃, a vacuum degree of -0.08MPa, and a stirring rate of 30r / min to obtain 83.6kg of high-purity furoic acid product, with a yield of 88.6%.

[0033] Product test results: purity 99.91%, furfuryl alcohol content 0.04%, furfural residue 0.03%, metal ion residue 0.001%, total impurity content 0.09%.

[0034] Comparative Example 1 Comparative Example 1 uses a single activated carbon decolorization + water recrystallization process, specifically as follows: The difference between Comparative Example 1 and Example 1 is that in step 2), only 0.5 kg of activated carbon (with a specific surface area of ​​1000 m²) was added. 2 / g), without adding diatomaceous earth, was stirred and decolorized at 85°C and a stirring rate of 70 r / min for 40 min. Then, the same vacuum concentration method as in Example 1 was used. After concentration, it was recrystallized once with water (the specific steps are the same as the first recrystallization in Example 1). Then, the same vacuum drying method as in Example 1 was used to obtain the final product. The test results showed that the purity was 99.68%, the furfuryl alcohol content was 0.13%, and the total impurity content was 0.32%, which did not meet the requirements.

[0035] Comparative Example 2 Comparative Example 2 employs a two-agent decolorization + single-ethanol recrystallization process, specifically as follows: The difference between Comparative Example 2 and Example 1 is that in step 4), the concentrated liquid after pretreatment and double-agent decolorization is recrystallized using only a single ethanol solvent (purity 99.7%) (the specific steps are the same as the secondary recrystallization in Example 1), and then the same vacuum drying method as in Example 1 is used to obtain the final product. The test results show that the purity is 99.82%, the furfuryl alcohol content is 0.08%, and the total impurity content is 0.18%, which does not meet the requirements.

[0036] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for purifying high-purity furoic acid, characterized in that, Includes the following steps: (1) Pretreatment filtration: The crude furoic acid reaction solution is first filtered through a ceramic membrane to remove solid impurities with a particle size ≥0.22μm and catalyst residue to obtain pretreatment filtrate; (2) Dual-agent synergistic decolorization: Add 0.2%~0.5% activated carbon and 0.1%~0.3% diatomaceous earth of crude furoic acid reaction solution to the pretreated filtrate, and decolorize for 30~50 min under stirring at 80~90℃. The ultra-clear filtrate is obtained by precision filtration. (3) Vacuum concentration: The ultra-clear filtrate from step (2) is concentrated under vacuum conditions of -0.07 to -0.09 MPa, 65 to 75°C, and 80 to 120 r / min until the mass concentration of furoic acid in the filtrate reaches 45% to 55%. Low-boiling substances are continuously removed during the concentration process. (4) Gradient recrystallization with dual solvents: The concentrate from step (3) is recrystallized twice, first with water and then with an ethanol-water mixture. (5) Vacuum drying: The secondary refined crystals after step (4) are dried at a temperature of 70~80℃ and a vacuum degree of -0.08~-0.095MPa for 4~8h to obtain high-purity furoic acid product.

2. The method according to claim 1, characterized in that, In step (2), the mass ratio of activated carbon to diatomaceous earth is 1:0.4~0.6, the decolorization temperature is 85~90℃, and the decolorization time is 35~45min.

3. The method according to claim 1, characterized in that, The specific steps for the two recrystallizations in step (4) are as follows: a. First recrystallization: Mix the concentrated solution with deionized water at a mass ratio of 1:2.0~3.0, heat to 70~80℃, stir to dissolve, then cool to 25~35℃ at a cooling rate of 5~8℃ / h, and crystallize at a constant temperature for 3~5h. After filtration, obtain the first crystal, and rinse the crystal surface with a small amount of deionized water 2~3 times. b. Secondary recrystallization: Mix the primary refined crystals with an ethanol-water mixed solvent at a mass ratio of 1:2.5~4.0, heat to 60~70℃, stir to dissolve, then cool to 20~30℃ at a cooling rate of 3~5℃ / h, and crystallize at a constant temperature for 3~5h. After filtration, obtain secondary refined crystals, and rinse the crystal surface 2~3 times with a small amount of ethanol-water mixed solvent.

4. The method according to claim 3, characterized in that, In step a, the mass ratio of deionized water to concentrate is 1:2.5~2.8, the conductivity of deionized water is ≤5μS / cm, the isothermal crystallization temperature is 28~32℃, the crystallization time is 3.5~4.5h, and the amount of deionized water used for rinsing is 5%~8% of the mass of the first refined crystal.

5. The method according to claim 3, characterized in that, In step b, the volume ratio of the ethanol-water mixed solvent is 1:4~4.5, the ethanol purity is ≥99.7%, the mass ratio of the mixed solvent to the primary crystal is 1:3.0~3.5, the isothermal crystallization temperature is 22~28℃, the crystallization time is 3.5~4.5h, and the amount of mixed solvent used for rinsing is 3%~5% of the mass of the secondary crystal.

6. The method according to any one of claims 1 to 3, characterized in that, In step (5), the vacuum drying temperature is 75~80℃ and the drying time is 6~7h.

7. The method according to any one of claims 1 to 3, characterized in that, Step (5) The final high-purity furoic acid has a purity of ≥99.9%, furfuryl alcohol content ≤0.05%, furanaldehyde residue ≤0.03%, metal ion residue ≤0.001%, and total impurity content ≤0.1%.