Process for purifying 2,5-furandicarboxylic acid

Abstract

The application relates to the chemical technology field and discloses a 2,5-furan dicarboxylic acid purification method. The method comprises the following steps: (1) in the presence of an organic solvent and water, 2,5-furan dicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurities, hydrogen and a selective hydrogenation catalyst are contacted to carry out a hydrogenation reaction; and (2) the product obtained in the step (1) is subjected to solid-liquid separation and washing. The catalyst comprises a carrier and an active metal component Pd supported on the carrier, the content of the Pd is 0.1-2% by mass, and the carrier is a nitrogen-doped nanometer carbon cage. The method has good purification effect, low processing cost and can obtain a high 2,5-furan dicarboxylic acid recovery rate.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, specifically to a method for purifying 2,5-furandicarboxylic acid. Background Technology

[0002] Generally, 2,5-furandicarboxylic acid (FDCA), synthesized from biomass resources, has a structure similar to terephthalic acid and is readily degradable in nature. It is mainly used to synthesize high-performance biodegradable polymers such as polyesters, nylons, and epoxy resins. In particular, polyethylene 2,5-furandicarboxylate (PEF), obtained by polymerizing 2,5-furandicarboxylic acid with ethylene glycol, exhibits superior mechanical and thermal properties and better gas barrier properties compared to polyethylene terephthalate (PET).

[0003] Currently, the main byproducts in the production of 2,5-furandicarboxylic acid include 2,5-dicarboxyfuran (DFF), 5-hydroxymethyl-furan-2-carboxylic acid (HFCA), and 5-formyl-furan-2-carboxylic acid (FFCA). Among these, 5-formyl-furan-2-carboxylic acid is a difficult impurity to remove from crude 2,5-furandicarboxylic acid because its solubility in various solvents is very close to that of 2,5-furandicarboxylic acid. This results in low purity of 2,5-furandicarboxylic acid and adversely affects its polymerization reaction.

[0004] Chinese patent application CN103965146A discloses a purification method for furanyl dicarboxylic acid. This method involves a salt-forming reaction, in which an aqueous solution of furanyl dicarboxylic acid is filtered, acidified, and a solid is precipitated. The solid is then washed and dried to obtain the final product. A pre-purification process is added to address the low purity of the furanyl dicarboxylic acid raw material. However, due to the salt-forming reaction, this method generates a large amount of acidic wastewater containing salt during the acidification step, posing a significant environmental burden. Furthermore, the furanyl dicarboxylic acid product obtained by this method cannot completely remove acyl groups, causing the product to turn yellow and potentially affecting subsequent polymerization reactions.

[0005] Chinese patent application CN113121480A provides a method for purifying and refining 2,5-furandicarboxylic acid using a melt crystallization method. This method requires heating the material to above 290°C, resulting in high energy consumption and demanding equipment requirements. Chinese patent application CN110713474A provides a method for refining furan dicarboxylic acid using a dissolution crystallization method, which involves the use and removal of large amounts of high-boiling-point solvents, similarly increasing energy consumption and method complexity. Therefore, improving the purity of 2,5-furandicarboxylic acid remains a challenge that requires further investigation by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of high purification cost of 2,5-furandicarboxylic acid, difficulty in removing 5-formyl-furan-2-carboxylic acid impurities, and low recovery rate of 2,5-furandicarboxylic acid in the existing technology, and to provide a purification method for 2,5-furandicarboxylic acid. This method has good purification effect, low processing cost, and can obtain a high recovery rate of 2,5-furandicarboxylic acid.

[0007] To achieve the above objectives, the present invention provides a method for purifying 2,5-furandicarboxylic acid, wherein the method includes the following steps:

[0008] (1) In the presence of organic solvent and water, 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity, hydrogen and selective hydrogenation catalyst are contacted to carry out hydrogenation reaction;

[0009] (2) The product obtained in step (1) is subjected to solid-liquid separation and washing;

[0010] The catalyst comprises a support and an active metal component Pd supported on the support, wherein the Pd content is 0.1-2% by mass; the support is a nitrogen-doped carbon nanocage; the nitrogen-doped carbon nanocage has a hollow cage-like structure, and the BET specific surface area of ​​the nitrogen-doped carbon nanocage is 400-1000 m². 2 / g; the pore size of the nitrogen-doped carbon nanocage is 2-50nm; based on the total molar amount of nitrogen, the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 85% as determined by X-ray photoelectron spectroscopy.

[0011] The inventors of this invention discovered that 5-hydroxymethyl-furan-2-carboxylic acid has a significantly higher solubility in water than 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid. By selectively hydrogenating 5-formyl-furan-2-carboxylic acid to 5-hydroxymethyl-furan-2-carboxylic acid, this impurity can be removed by water washing. Therefore, efficiently achieving selective hydrogenation of small amounts of 5-formyl-furan-2-carboxylic acid impurities in crude 2,5-furandicarboxylic acid is of great significance.

[0012] In the hydrogenation reaction of 5-formyl-furan-2-carboxylic acid, this invention unexpectedly discovered that using nitrogen-doped nano-carbon cages with a hollow cage-like structure and a high specific surface area as a support for Pd selective hydrogenation catalysts, in conjunction with the method and reaction conditions described in this invention, can achieve the hydrogenation of a small amount of 5-formyl-furan-2-carboxylic acid to 5-hydroxymethyl-furan-2-carboxylic acid while limiting the hydrogenation conversion of 2,5-furandicarboxylic acid. This provides a foundation for the subsequent removal of impurities and the purification of the 2,5-furandicarboxylic acid product.

[0013] The purification method provided by this invention can efficiently convert 5-formyl-furan-2-carboxylic acid impurities, which are difficult to remove by other methods, into easily removable 5-hydroxymethyl-furan-2-carboxylic acid under relatively mild conditions. This allows for the removal of impurities through simple water washing, significantly improving the purity of the 2,5-furandicarboxylic acid product. For example, in the embodiments, the recovery rate of 2,5-furandicarboxylic acid is greater than 90%; and the content of 2,5-furandicarboxylic acid in the purified product is greater than 99%. Attached Figure Description

[0014] Figure 1 This is a TEM image of the nitrogen-doped carbon nanocage prepared in Example 1;

[0015] Figure 2 This is the XPS image of the nitrogen-doped carbon nanocage prepared in Example 1;

[0016] Figure 3 The XPS N1s peak spectrum of the nitrogen-doped carbon nanocage prepared in Example 1 is shown.

[0017] Figure 4 The BJH pore size distribution curve of the nitrogen-doped carbon nanocage prepared in Example 1 is shown.

[0018] Figure 5 This is the N1s peak spectrum of XPS for the nitrogen-doped carbon nanocage prepared in Example 2.

[0019] Figure 6 This is the N1s peak spectrum of XPS for the nitrogen-doped carbon nanocage prepared in Example 3. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] In this invention, the Pd content in the catalyst is calculated by the amount of feed.

[0022] In this invention, the "hollow cage-like structure" of the nitrogen-doped nano-carbon cage refers to a hollow sphere or quasi-sphere formed by a graphitized carbon layer surrounding it.

[0023] In this invention, the surface morphology of the material is characterized by high-resolution transmission electron microscopy (HRTEM). The HRTEM used is a JEM-2100 (Japan Electronics Corporation), and the HRTEM testing conditions are: accelerating voltage of 200 kV. The diameter of the nitrogen-doped carbon nanocage can be measured from the HRTEM images.

[0024] In this invention, the term "nitrogen-doped carbon nanocage" refers to the element nitrogen. Specifically, this term refers to the nitrogen element that exists in various forms within the nitrogen-doped carbon nanocage during the preparation process of the nitrogen-doped carbon nanocage.

[0025] In this invention, the terms "pyrrole nitrogen," "pyridine nitrogen," "graphite nitrogen," and "oxidized nitrogen" have their conventional meanings in the art, specifically referring to: pyridine nitrogen as a nitrogen species identified by characteristic spectral peaks corresponding to binding energies of 398.7-399.1 eV in X-ray photoelectron spectroscopy; pyrrole nitrogen as a nitrogen species identified by characteristic spectral peaks corresponding to binding energies of 398.8-400.2 eV in X-ray photoelectron spectroscopy; graphite nitrogen as a nitrogen species identified by characteristic spectral peaks corresponding to binding energies of 401.2-409.8 eV in X-ray photoelectron spectroscopy; and oxidized nitrogen as a nitrogen species identified by characteristic spectral peaks corresponding to binding energies of 402.8-403.6 eV in X-ray photoelectron spectroscopy.

[0026] In this invention, X-ray photoelectron spectroscopy analysis was performed on an ESCALab250 X-ray photoelectron spectrometer from Thermo Scientific equipped with ThermoAvantage V5.926 software. The excitation source was monochromatic AlKα X-rays with an energy of 1486.6 eV and a power of 150 W. The transmission energy used for narrow scanning was 30 eV, and the baseline vacuum during analysis was 6.53 × 10⁻⁶. -9 mbar, electron binding energy was corrected using the C1s peak (284.6 eV) of elemental carbon, data processing was performed on Thermo Avantage software, and quantitative analysis was performed using the sensitivity factor method in the analysis module.

[0027] In this invention, the graphitization degree of nitrogen-doped carbon nanocages is characterized by Raman spectroscopy. The peak at 1355 cm⁻¹ (D peak) is attributed to structural defects, indicating amorphous carbon. The peak at 1585 cm⁻¹... -1 The peak (G peak) is attributed to carbon in a planar structure. I0 is typically used. D / I G The degree of graphitization of a material is characterized by the intensity ratio of the D peak to the G peak. D / I GThe higher the value, the more defects and the lower the degree of graphitization. The Raman spectrum of the material was obtained using an RM2000 microconfocal Raman spectrometer (Reinshaw product). Technical specifications: The excitation source was a He-Ne laser with a wavelength of 525 nm.

[0028] This invention provides a method for purifying 2,5-furandicarboxylic acid, wherein the method includes the following steps:

[0029] (1) In the presence of organic solvent and water, 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity, hydrogen and selective hydrogenation catalyst are contacted to carry out hydrogenation reaction;

[0030] (2) The product obtained in step (1) is subjected to solid-liquid separation and washing;

[0031] The selective hydrogenation catalyst comprises a support and an active metal component Pd supported on the support, wherein the Pd content is 0.1-2% by mass; the support is a nitrogen-doped carbon nanocage; the nitrogen-doped carbon nanocage has a hollow cage-like structure, and the BET specific surface area of ​​the nitrogen-doped carbon nanocage is 400-1000 m². 2 / g; the pore size of the nitrogen-doped carbon nanocage is 2-50nm; based on the total molar amount of nitrogen, the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 85% as determined by X-ray photoelectron spectroscopy.

[0032] The purification method provided by the present invention can selectively hydrogenate 5-formyl-furan-2-carboxylic acid to 5-hydroxymethyl-furan-2-carboxylic acid through the hydrogenation reaction in step (1), and then remove 5-hydroxymethyl-furan-2-carboxylic acid through solid-liquid separation and washing, thereby obtaining purified 2,5-furandicarboxylic acid product.

[0033] The purification method provided by this invention, in the hydrogenation reaction of 5-formyl-furan-2-carboxylic acid, uses an organic solvent and water as a mixed solvent, which can improve the solubility of 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid in the solvent, thereby making 5-formyl-furan-2-carboxylic acid uniformly dissolved in the solvent and able to fully contact with the selective hydrogenation catalyst and hydrogen gas, thus being reduced to 5-hydroxymethyl-furan-2-carboxylic acid, which has better water solubility.

[0034] In this invention, the source of the 2,5-furandicarboxylic acid raw material is not particularly limited, and the method can be applied to any 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurities obtained by conventional methods. Preferably, the 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurities is selected from the crude product obtained during the oxidation of 5-hydroxymethylfurfural to produce 2,5-furandicarboxylic acid. In this invention, to better illustrate the excellent purification effect of the purification method of this invention, a 2,5-furandicarboxylic acid raw material containing impurities can be prepared in-house as a simulated crude product. Preferably, 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid are mixed (preferably mechanically mixed) to obtain a 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurities.

[0035] In this invention, the selection range for the content of 5-formyl-furan-2-carboxylic acid impurity is relatively wide. Preferably, in step (1), based on the total amount of 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity, the content of the 5-formyl-furan-2-carboxylic acid impurity is 0.1-20% by mass, more preferably 0.2-15% by mass, and even more preferably 0.5-10% by mass.

[0036] In this invention, the content of each component in the 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity was determined by high performance liquid chromatography (HPLC).

[0037] Those skilled in the art will know that, in addition to 5-formyl-furan-2-carboxylic acid (FFCA), the main byproducts of the 2,5-furan-2-carboxylic acid raw material obtained by conventional 2,5-furan-2-carboxylic acid production methods may also include 2,5-diformylfuran (DFF), 5-hydroxymethyl-furan-2-carboxylic acid (HFCA), etc. The 2,5-furan-2-carboxylic acid raw material used in this invention may contain the above-mentioned other byproducts. When the above-mentioned byproducts are contained, each byproduct can be further removed by means known in the prior art.

[0038] In this invention, preferably, in step (1), the organic solvent is selected from at least one of tetrahydrofuran, 1,4-dioxane, and ethylene glycol dimethyl ether, more preferably 1,4-dioxane. Using a mixture of the above-mentioned organic solvent and water as a solvent helps to improve the solubility of 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid in the solvent, thereby ensuring that 5-formyl-furan-2-carboxylic acid is uniformly dissolved in the mixed solvent, allowing it to fully contact the catalyst and hydrogen, and thus be reduced to 5-hydroxymethyl-furan-2-carboxylic acid, which has better water solubility, further improving the purification effect. In this invention, the range of suitable amounts of the organic solvent and water in step (1) is wide, as long as the 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurities is fully dissolved. Preferably, in step (1), the volume ratio of the organic solvent to water is 0.5-5:1, more preferably 1-3.5:1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, or any value between two groups. The advantage of this preferred embodiment is that within this range, the solvent has high solubility for 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid, thereby improving the purification effect.

[0039] In this invention, preferably, in step (1), the amount of organic solvent and water used is such that the concentration of 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity is 20-150 g / L, preferably 25-50 g / L.

[0040] In this invention, preferably, in step (1), the mass ratio of the selective hydrogenation catalyst to the 5-formyl-furan-2-carboxylic acid impurity is 1:0.1-20, more preferably 1:0.2-10, and even more preferably 1:0.5-5. For example, it can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, or any value between any two groups. The advantage of this preferred embodiment is that, under the condition of avoiding side reactions, the selective hydrogenation reaction of 5-formyl-furan-2-carboxylic acid can be achieved using an appropriate amount of catalyst.

[0041] In this invention, preferably, in step (1), the temperature of the hydrogenation reaction is 80-160℃, more preferably 80-120℃, for example, it can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, or any value between two groups. Using the above-mentioned preferred temperature range is beneficial for the reactants to fully dissolve in the aforementioned preferred organic solvent, which is conducive to the full progress of the hydrogenation reaction and effectively improves the recovery rate of 2,5-furandicarboxylic acid in this invention. At the same time, it avoids side reactions such as hydrogenation of carbon-carbon double bonds and carboxyl groups in 2,5-furandicarboxylic acid due to excessively high reaction temperatures, and avoids the reactants being unable to dissolve and hindering the reaction process due to excessively low temperatures.

[0042] In this invention, preferably, in step (1), the hydrogenation reaction time is 1-20h, more preferably 1-15h, and even more preferably 1-10h. For example, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, or any value between any two groups.

[0043] In this invention, preferably, in step (1), the pressure of the hydrogen gas is 0.5-4 MPa, more preferably 1-3 MPa. By selecting hydrogenation conditions within the above-preferred range, it has the advantage of suppressing side reactions and improving the recovery rate and purity of 2,5-furandicarboxylic acid.

[0044] In this invention, preferably, based on the total amount of selective hydrogenation catalyst, the Pd content is 0.1-1% by mass, more preferably 0.1-0.5% by mass.

[0045] In this invention, preferably, the nitrogen-doped carbon nanocage has a pore size of 2-20 nm.

[0046] In this invention, preferably, based on the total molar amount of nitrogen, the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 90% as determined by X-ray photoelectron spectroscopy.

[0047] In this invention, preferably, the molar ratio of pyrrolidine nitrogen to pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage, as determined by X-ray photoelectron spectroscopy, is greater than 5. The nitrogen species on the surface of the nitrogen-doped carbon nanocage provided by this invention are both pyridine nitrogen and pyrrolidine nitrogen, which is beneficial for improving the activity of the selective hydrogenation catalyst in the selective hydrogenation of 5-formyl-furan-2-carboxylic acid impurities to 5-hydroxymethyl-furan-2-carboxylic acid.

[0048] In this invention, preferably, based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy is used to determine that the molar content of pyrrole nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is 85.8-100%, and the molar content of pyridine nitrogen is 0-14.2%.

[0049] In this invention, preferably, the nitrogen-doped carbon nanocage may also contain oxygen, which may be formed in various forms within the nitrogen-doped carbon nanocage during its preparation. Preferably, X-ray photoelectron spectroscopy indicates that the molar content of carbon on the surface of the nitrogen-doped carbon nanocage is 89-92%, the molar content of nitrogen is 1-3%, and the molar content of oxygen is 5-10%.

[0050] In this invention, preferably, the nitrogen-doped carbon nanocage may contain doping elements known to those skilled in the art that can be applied to carbon materials. Preferably, the nitrogen-doped carbon nanocage does not contain elements such as nickel, sulfur, boron, phosphorus, fluorine, chlorine, bromine, or iodine.

[0051] In this invention, preferably, the nitrogen-doped carbon nanocage has a BET specific surface area of ​​400-800 m². 2 / g. The advantage of this preferred embodiment is that it can better disperse the metal components, promote mass transfer in the reaction process, and effectively improve catalyst activity and target product selectivity.

[0052] In this invention, preferably, the total pore volume of the nitrogen-doped carbon nanocage is 0.9-1.5 cm³. 3 / g.

[0053] In this invention, preferably, the nitrogen-doped carbon nanocage has a dual mesoporous distribution peak, and the dual mesoporous distribution peaks correspond to a first most probable pore size and a second most probable pore size, respectively. The first most probable pore size is 3.5-4 nm, and the second most probable pore size is 6-9.5 nm. In this preferred embodiment, the small pore size further provides a large specific surface area for the material, increasing the number of active sites, while the large pore size provides diffusion channels for molecules or ions, accelerating mass transfer and providing higher stability.

[0054] In this invention, preferably, in the Raman curve of the nitrogen-doped carbon nanocage, I D / I G The range is 0.2-1, more preferably 0.3-0.8. The nitrogen-doped carbon nanocage of the present invention has obvious D peaks and G peaks, and has a certain degree of graphitization.

[0055] In a preferred embodiment, the nitrogen-doped carbon nanocage is prepared by the following method:

[0056] (1) A solution containing a transition metal salt, a nitrogen-containing organic carboxylic acid and a solvent is provided, and then dried to obtain a precursor, wherein the nitrogen-containing organic carboxylic acid is ethylenediaminetetraacetic acid; the molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid, calculated based on the transition metal element, is 1:0.6-1;

[0057] (2) Under an inert or reducing atmosphere, the precursor obtained in step (1) is subjected to high-temperature pyrolysis to obtain pyrolysis products;

[0058] (3) The pyrolysis product is acid washed, then solid-liquid separation, washing and drying are performed.

[0059] In a preferred embodiment, the nitrogen-doped carbon nanocage is prepared by using a specific nitrogen-containing organic carboxylic acid and by controlling a specific ratio of transition metal salt to the specific nitrogen-containing organic carboxylic acid. The nitrogen-doped carbon nanocage has a hollow cage-like structure with a diameter of 2-200 nm. Based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 85%. The preparation method uses simple equipment and is easy to operate. In some embodiments, the nitrogen-doped carbon nanocage can be obtained under pure aqueous phase and atmospheric pressure conditions through simple mixing, pyrolysis, and acid washing.

[0060] In this invention, there is no particular limitation on the amount of each substance used in step (1) during the preparation of nitrogen-doped carbon nanocages. Preferably, in step (1), the molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid, calculated as a transition metal element, is 1:0.6-1, more preferably 1:0.6-0.9. A molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid within the above-mentioned range is beneficial for controlling the nitrogen content and the types of nitrogen species, so that the nitrogen on the surface of the prepared nitrogen-doped carbon nanocage exists in the form of pyrrole nitrogen and / or pyridine nitrogen.

[0061] In this invention, preferably, the amount of the transition metal salt and the nitrogen-containing organic carboxylic acid is such that the molar content of carbon on the surface of the nitrogen-doped nano carbon cage is 89-92%, the molar content of nitrogen is 1-3%, and the molar content of oxygen is 5-10%.

[0062] In this invention, preferably, the amount of transition metal salt and nitrogen-containing organic carboxylic acid used is such that the nitrogen on the surface of the nitrogen-doped carbon nanocage is mainly in the form of pyrrole nitrogen and / or pyridine nitrogen. Based on the total molar amount of nitrogen, the molar content of pyrrole nitrogen and / or pyridine nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 85%, preferably greater than 90%, as determined by X-ray photoelectron spectroscopy.

[0063] In this invention, the preparation process of nitrogen-doped carbon nanocages does not particularly limit the type of transition metal salt in step (1), and all transition metal salts conventionally defined in the art are applicable to this invention. Preferably, in step (1), the transition metal salt is selected from at least one of organic acid salts of transition metals, carbonates of transition metals, and basic carbonates of transition metals, and more preferably carbonates of transition metals and / or basic carbonates of transition metals.

[0064] In this invention, the nitrogen-doped carbon nanocage preparation process allows for a wide range of choices for the transition metal in step (1). Preferably, the transition metal is a Group VIII metal element, more preferably at least one of iron, cobalt, nickel, and copper, and even more preferably nickel.

[0065] In this invention, preferably, the transition metal salt is selected from basic nickel carbonate and / or nickel acetate.

[0066] In this invention, during the preparation process of nitrogen-doped carbon nanocages, step (1) does not particularly limit the method of forming the solution. For example, it can be formed by heating, and more preferably by heating and stirring. This invention also does not particularly limit the heating temperature or the stirring rate, as long as the solution can be formed.

[0067] In this invention, preferably, in step (1), the precursor is obtained by dissolving a transition metal salt and a nitrogen-containing organic carboxylic acid in a solvent to form a homogeneous solution, and then removing the solvent from the homogeneous solution. This invention does not particularly limit the type of solvent, as long as it can form a homogeneous solution. Preferably, the solvent is water and / or ethanol, more preferably water; this invention also does not particularly limit the amount of solvent used, again as long as it can form a homogeneous solution. The solvent in the homogeneous solution can be removed by direct evaporation. The evaporation temperature and process can adopt existing techniques known to those skilled in the art, for example, the solvent in the homogeneous solution can be removed by heating to dryness.

[0068] In this invention, the nitrogen-doped carbon nanocage preparation process allows for a wide range of selection for the high-temperature pyrolysis conditions in step (2). Preferably, the high-temperature pyrolysis conditions are: a heating rate of 0.5-30℃ / min, a high-temperature pyrolysis temperature of 850-1000℃, and a holding time of 20-600min; more preferably, the high-temperature pyrolysis conditions are: a heating rate of 1-20℃ / min, a high-temperature pyrolysis temperature of 850-950℃, and a holding time of 60-480min. Using the above-mentioned high-temperature pyrolysis conditions can adjust the types of nitrogen species and the removal rate of transition metals. For example, if the temperature is too low, it is not conducive to the removal of transition metals from the material, while if the temperature is too high, nitrogen-doped carbon nanocages containing other nitrogen species are easily generated.

[0069] According to a preferred embodiment of the present invention, in the nitrogen-doped carbon nanocage preparation process, step (2) involves a two-stage heating method to reach the high-temperature pyrolysis temperature. Specifically, the temperature is first increased to 400-800℃, preferably 500-700℃, at a rate of 1-20℃ / min, preferably 5-10℃ / min, and held at this temperature for 20-600min, preferably 60-480min. Then, the temperature is further increased to the high-temperature pyrolysis temperature at a rate of 1-20℃ / min, preferably 5-10℃ / min, and held at this temperature for 20-600min, preferably 60-480min. In this invention, the two-stage heating method is beneficial for forming nitrogen-doped carbon nanocages containing only pyrrole nitrogen or only pyrrole nitrogen and pyridine nitrogen in the nitrogen species.

[0070] In this invention, the type of inert atmosphere in step (2) of the nitrogen-doped carbon nanocage preparation process is not particularly limited, and any inert atmosphere conventionally defined in the art is applicable to this invention. Preferably, in step (2), the inert atmosphere is selected from at least one of nitrogen, argon, neon, and helium.

[0071] In this invention, the type of reducing atmosphere in step (2) of the nitrogen-doped carbon nanocage preparation process is not particularly limited, and any reducing atmosphere conventionally defined in the art is applicable to this invention. Preferably, the reducing atmosphere is provided by hydrogen and optionally an inert gas, wherein the inert gas is selected from at least one of nitrogen, argon, neon and helium.

[0072] In this invention, during the preparation process of nitrogen-doped carbon nanocages, step (3) involves acid washing the pyrolysis product using an acid washing agent. Specifically, this can be achieved by mixing the pyrolysis product with the acid washing agent. This invention does not impose any particular limitation on the mixing method; ultrasonic or stirring methods can be used. The acid washing agent can be any acid commonly used in the art, as long as it can remove the transition metals from the pyrolysis product. Preferably, the acid washing agent is an aqueous solution of an inorganic acid and / or an aqueous solution of an organic acid, more preferably at least one of an aqueous solution of hydrochloric acid, an aqueous solution of sulfuric acid, an aqueous solution of nitric acid, and an aqueous solution of citric acid, and even more preferably an aqueous solution of hydrochloric acid.

[0073] In this invention, during the preparation process of nitrogen-doped carbon nanocages, the concentration of the pickling agent in step (3) is not particularly limited. Preferably, the concentration of the inorganic acid aqueous solution and / or organic acid aqueous solution is 0.1-10 mol / L.

[0074] In this invention, during the preparation process of nitrogen-doped carbon nanocages, the pH of the pickling agent in step (3) is not particularly limited. Preferably, the pH of the inorganic acid aqueous solution and / or organic acid aqueous solution is less than 7. This invention does not have specific requirements on the amount of the pickling agent used, as long as it is sufficient to remove transition metals from the pyrolysis products.

[0075] In this invention, preferably, in the nitrogen-doped carbon nanocage preparation process, in step (3), the acid washing temperature is 20-120℃ and the time is 0.1-48h; more preferably, the temperature is 60-100℃ and the time is 4-12h.

[0076] In the nitrogen-doped carbon nanocage preparation process, step (3) does not have any particular limitation on the solid-liquid separation method. It can be carried out by solid-liquid separation methods known in the art, such as filtration.

[0077] In this invention, preferably, in the nitrogen-doped carbon nanocage preparation process, in step (3), the washing is used to remove the acid and metal ions remaining on the nitrogen-doped carbon nanocage during the acid washing process. Therefore, various water washing methods that can wash the nitrogen-doped carbon nanocage to neutrality are applicable to this invention.

[0078] In this invention, preferably, in the nitrogen-doped carbon nanocage preparation process, step (3) involves drying to remove water from the nitrogen-doped carbon nanocage. For example, atmospheric pressure drying or reduced pressure drying can be used. Preferably, the drying conditions may include a temperature of 80-140°C and a time of 6-10 hours.

[0079] In this art, conventionally defined preparation methods for selective hydrogenation catalysts are applicable to this invention. Preparation can be achieved through impregnation methods, such as isochoric impregnation, initial wet impregnation, ion exchange, deposition-precipitation, or vacuum impregnation. According to a specific embodiment of this invention, the selective hydrogenation catalyst can be prepared by an initial wet impregnation method: a solution containing a Pd precursor is introduced into a nitrogen-doped carbon nanocage support, impregnated at room temperature for 1-12 h, and then dried in an oven at 100-140°C for 6-24 h. The resulting catalyst precursor is then reduced in a reducing atmosphere (e.g., a mixture of hydrogen and nitrogen) at 200-600°C for 1-5 h to obtain the selective hydrogenation catalyst. In this invention, the type of Pd precursor is not particularly limited; the Pd is provided by a solution containing the Pd precursor, which is selected from soluble salts containing Pd, preferably chlorides and / or nitrates, such as palladium chloride and / or palladium nitrate. In this invention, the drying conditions are not particularly limited. Preferably, the drying conditions include a temperature of 80-120°C and a time of 8-20 hours. In this invention, the type of reducing atmosphere is not particularly limited; any reducing atmosphere conventionally defined in the art is applicable. Preferably, the reducing atmosphere is hydrogen and optionally an inert gas, wherein the inert gas is selected from at least one of nitrogen, argon, neon, and helium, and more preferably hydrogen and nitrogen. According to a preferred embodiment of the invention, the hydrogen content in the reducing atmosphere is 5-30% by volume, and the nitrogen content is 70-95% by volume. In this invention, the range of reducing conditions is relatively wide. Preferably, in step S2, the reducing conditions include a temperature of 200-600°C, a time of 1-5 hours, and a reducing atmosphere volume hourly space velocity (VHSV) of 1-100 h⁻¹. -1 More preferably, the reduction conditions include: a temperature of 300-500℃, a time of 2-4 hours, and a volume hourly space velocity (VHSV) of 5-50 h⁻¹. -1 .

[0080] In this invention, the product obtained in step (1) is a mixture containing a selective hydrogenation catalyst, which is separated by solid-liquid separation in step (2). The solid-liquid separation can be performed using conventional methods in the art, and this invention does not impose specific limitations on this; for example, the product can be filtered. Preferably, in step (2), the solid-liquid separation temperature is 20-100°C, more preferably 50-100°C. Using a solid-liquid separation temperature within the above-mentioned preferred range helps to ensure that 2,5-furandicarboxylic acid and 5-hydroxymethyl-furan-2-carboxylic acid are completely dissolved during the separation process, thereby ensuring sufficient separation from the selective hydrogenation catalyst.

[0081] Preferably, in this invention, the method further includes: removing the solvent from the product obtained by the solid-liquid separation to obtain a solid of 2,5-furandicarboxylic acid containing 5-hydroxymethyl-furan-2-carboxylic acid impurities. This invention does not particularly limit the method for removing the solvent; for example, evaporation can be used.

[0082] In this invention, since the solubility of 5-hydroxymethyl-furan-2-carboxylic acid in water is significantly higher than that of 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid, 5-formyl-furan-2-carboxylic acid is hydrogenated to 5-hydroxymethyl-furan-2-carboxylic acid with high selectivity, and then the 5-hydroxymethyl-furan-2-carboxylic acid impurities are dissolved in water by washing. The remaining solid is the purified 2,5-furandicarboxylic acid product.

[0083] In this invention, there are no particular limitations on the specific operation method and number of times the washing is performed in step (2). Preferably, the number of washing cycles is 1-10 times, and more preferably 2-6 times.

[0084] In this invention, preferably, the recovery rate of the 2,5-furandicarboxylic acid product obtained by this purification method is greater than 90%, and the content of 2,5-furandicarboxylic acid in the 2,5-furandicarboxylic acid product is greater than 99%.

[0085] The recovery rate (%) is calculated as follows: (mass of 2,5-furandicarboxylic acid product / mass of 2,5-furandicarboxylic acid in raw materials) × 100%.

[0086] The present invention will be described in detail below through embodiments.

[0087] Unless otherwise specified, all reagents used in this invention are of analytical grade and are commercially available.

[0088] The surface morphology of the material was characterized by high-resolution transmission electron microscopy (HRTEM). The HRTEM used was a JEM-2100 (Nippon Electron Ltd.), and the testing conditions were: accelerating voltage of 200 kV. The diameter of the nitrogen-doped carbon nanocages was measured from the HRTEM images.

[0089] The pore structure properties of the material were detected using the BET test method. Specifically, a Quantachrome AS-6B analyzer was used for measurement. The specific surface area and pore volume of the material were obtained by the Brunauer-Emmett-Taller (BET) method, and the mesopore distribution curve was calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0090] The elemental composition of the material surface was determined by X-ray photoelectron spectroscopy (XPS). X-ray photoelectron spectroscopy analysis was performed on an ESCALab250 X-ray photoelectron spectrometer from Thermo Scientific equipped with Thermo Avantage V5.926 software. The excitation source was monochromatic Al Kα X-rays with an energy of 1486.6 eV and a power of 150 W. The narrow scan passthrough energy was 30 eV, and the baseline vacuum during analysis was 6.53 × 10⁻⁶. -9 mbar, electron binding energy was corrected using the C1s peak (284.6 eV) of elemental carbon, data processing was performed on Thermo Avantage software, and quantitative analysis was performed using the sensitivity factor method in the analysis module.

[0091] The degree of graphitization of the material was characterized by Raman spectroscopy at 1355 cm⁻¹. -1 The peak (D peak) is attributed to structural defects, consisting of amorphous carbon, at 1585 cm⁻¹. -1 The peak (G peak) is attributed to carbon in a planar structure. I0 is typically used. D / I G The degree of graphitization of a material is characterized by the intensity ratio of the D peak to the G peak. D / I G The higher the value, the more defects and the lower the degree of graphitization. The Raman spectrum of the material was obtained using an RM2000 microconfocal Raman spectrometer (Reinshaw product). Technical specifications: The excitation source was a He-Ne laser with a wavelength of 525 nm.

[0092] In this invention, high performance liquid chromatography (HPLC) is used to analyze the purified product of 2,5-furandicarboxylic acid. The HPLC conditions include using an Alltech OA-1000 organic acid column, a UV detector, a mobile phase of 0.005 mol / L H2SO4 aqueous solution, a flow rate of 0.6 mL / min, and a column temperature of 70 °C.

[0093] Preparation Examples 1-3 are used to illustrate the preparation of nitrogen-doped carbon nanocages.

[0094] Preparation Example 1

[0095] (1) Weigh 15g of basic nickel carbonate and 20.9g of ethylenediaminetetraacetic acid (molar ratio 1:0.7), add them to a beaker containing 40mL of deionized water, stir and mix evenly at 80℃, and continue to heat and evaporate to dryness to obtain a solid precursor.

[0096] (2) Place the precursor obtained in step (1) into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas with a flow rate of 80 mL / min, and heat it to 600℃ at a rate of 10℃ / min. After holding the temperature for 1 hour, continue to heat it to 900℃ at a rate of 10℃ / min and hold the temperature for 2 hours. Stop heating and cool it to room temperature under a nitrogen atmosphere to obtain the pyrolysis product.

[0097] (3) Add the pyrolysis product obtained in step (2) to an aqueous solution containing 2M hydrochloric acid and stir at 90°C for 8 hours. Then filter, collect the filtrate, wash with deionized water until the filtrate is neutral, and then dry the filter cake in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nano carbon cage Z1.

[0098] Figure 1 The image shows a TEM image of the nitrogen-doped carbon nanocage. As can be seen from the image, the nitrogen-doped carbon nanocage is a hollow cage-shaped carbon nanomaterial with a diameter of 5-20 nm.

[0099] Figure 2 The XPS spectrum of the nitrogen-doped carbon nanocage shows that, in addition to carbon, oxygen and nitrogen are present on the surface of the nitrogen-doped carbon nanocage. The atomic molar percentage of each element can be calculated from the peak area, where carbon is 90.06%, oxygen is 8.4%, and nitrogen is 1.54%.

[0100] Figure 3 The figure shows the N1s peak spectrum of the XPS of the nitrogen-doped carbon nanocage. It can be seen from the figure that the nitrogen on the surface of the nitrogen-doped carbon nanocage exists in the form of pyrrole nitrogen, and there are no other forms of nitrogen species. Based on the total molar amount of nitrogen, the content of pyrrole nitrogen is 100%.

[0101] BET testing showed that the nitrogen-doped carbon nanocage had a BET specific surface area of ​​466.24 m². 2 / g, pore volume is 0.978cm³ 3 / g. Figure 4 The figure shows the BJH pore size distribution curve of the nitrogen-doped carbon nanocage. As can be seen from the figure, there are two mesoporous distribution peaks at 3.68 nm and 6.15 nm.

[0102] Raman spectroscopy analysis revealed that the nitrogen-doped carbon nanocage exhibited distinct D and G peaks, I... D / I G The value is 0.5266, indicating that the nitrogen-doped carbon nanocage has a certain degree of graphitization.

[0103] Preparation Example 2

[0104] (1) Weigh 15g of basic nickel carbonate and 20.9g of ethylenediaminetetraacetic acid (molar ratio 1:0.7), add them to a beaker containing 40mL of deionized water, stir and mix evenly at 80℃, and continue to heat and evaporate to dryness to obtain a solid precursor.

[0105] (2) Place the precursor obtained in step (1) into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas with a flow rate of 80 mL / min, and heat it to 600℃ at a rate of 10℃ / min. After holding the temperature for 1 h, continue to heat it to 850℃ at a rate of 10℃ / min and hold the temperature for 2 h. Stop heating and cool it to room temperature under a nitrogen atmosphere to obtain the pyrolysis product.

[0106] (3) Add the pyrolysis product obtained in step (2) to an aqueous solution containing 2M hydrochloric acid and stir at 100°C for 8 hours. Then filter, collect the filtrate, wash with deionized water until the filtrate is neutral, and then dry the filter cake in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nano carbon cage Z2.

[0107] High-resolution transmission electron microscopy (HRTEM) observation and measurement revealed that the nitrogen-doped carbon nanocage has a hollow cage-like structure with a diameter of 5-20 nm.

[0108] XPS measurements revealed that the surface of this nitrogen-doped carbon nanocage contained not only carbon but also oxygen and nitrogen. The atomic percentage of each element could be calculated from the peak areas: carbon 91.05%, oxygen 7.48%, and nitrogen 1.47%. Nitrogen peaks in this nitrogen-doped carbon nanocage were further analyzed. Figure 5 As shown in the figure, the nitrogen on the surface of the nitrogen-doped carbon nanocage exists in two forms: pyrrole nitrogen and pyridine nitrogen. Based on the total molar amount of nitrogen, the content of pyrrole nitrogen is 92.01%, and the content of pyridine nitrogen is 7.99%.

[0109] BET testing showed that the nitrogen-doped carbon nanocage had a BET specific surface area of ​​713.17 m². 2 / g, pore volume is 1.482cm³ 3 / g. In the BJH pore size distribution curve of this nitrogen-doped carbon nanocage, two mesopore distribution peaks exist at 3.71 nm and 6.25 nm.

[0110] Raman spectroscopy analysis revealed that the nitrogen-doped carbon nanocage exhibited distinct D and G peaks, I... D / I G The value is 0.703, indicating that the nitrogen-doped carbon nanocage has a certain degree of graphitization.

[0111] Preparation Example 3

[0112] (1) Weigh 15g of nickel acetate and 22.3g of ethylenediaminetetraacetic acid (molar ratio of 1:0.9), add them to a beaker containing 40mL of deionized water, stir and mix evenly at 80℃, and continue to heat and evaporate to dryness to obtain a solid precursor.

[0113] (2) Place the precursor obtained in step (1) into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas with a flow rate of 150 mL / min, and heat it to 950 °C at a rate of 20 °C / min. After holding the temperature for 2 hours, stop heating and cool it to room temperature under a nitrogen atmosphere to obtain the pyrolysis product.

[0114] (3) Add the pyrolysis product obtained in step (2) to an aqueous solution containing 2M nitric acid and stir at 100°C for 8 hours. Then filter, collect the filtrate, wash with deionized water until the filtrate is neutral, and then dry the filter cake in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nano carbon cage Z3.

[0115] High-resolution transmission electron microscopy (HRTEM) observation and measurement revealed that the nitrogen-doped carbon nanocage has a hollow cage-like structure with a diameter of 5-20 nm.

[0116] XPS measurements revealed that the surface of this nitrogen-doped carbon nanocage contained not only carbon but also oxygen and nitrogen. The atomic percentage of each element could be calculated from the peak areas: carbon 89.96%, oxygen 7.97%, and nitrogen 2.07%. Nitrogen peaks in this nitrogen-doped carbon nanocage were further analyzed. Figure 6 As shown in the figure, the nitrogen on the surface of the nitrogen-doped carbon nanocage exists in two forms: pyrrole nitrogen and pyridine nitrogen. Based on the total molar amount of nitrogen, the content of pyrrole nitrogen is 85.80% and the content of pyridine nitrogen is 14.20%.

[0117] BET testing showed that the nitrogen-doped carbon nanocage had a BET specific surface area of ​​512.17 m². 2 / g, pore volume is 1.123cm³ 3 / g. In the BJH pore size distribution curve of this nitrogen-doped carbon nanocage, two mesopore distribution peaks exist at 3.59 nm and 9.25 nm.

[0118] Raman spectroscopy analysis revealed that the nitrogen-doped carbon nanocage exhibited distinct D and G peaks, I... D / I G The value of 0.324 indicates that the nitrogen-doped carbon nanocage has a certain degree of graphitization.

[0119] Preparation Examples 4-8 illustrate the preparation of selective hydrogenation catalysts.

[0120] Preparation Example 4

[0121] Nitrogen-doped Pd-based catalysts supported on nano-carbon cages were prepared by the initial wet impregnation method.

[0122] 0.5 mL of a 0.1 mol / L PdCl2 solution and 3.0 mL of deionized water were mixed and stirred until homogeneous. Then, 1.00 g of the nitrogen-doped carbon nanocage (Z1) obtained in Preparation Example 1 was added to the mixture. After stirring and impregnation at room temperature for 10 hours, the water was evaporated, and then the mixture was dried in an oven at 110 °C for 12 hours to obtain the catalyst precursor. The Pd loading was approximately 0.5% (mass percentage). The precursor prepared in the above steps was placed in a quartz tube and reduced in 20% H2 + N2 at 500 °C for 3 hours with a volume hourly space velocity (VHSV) of 20 h⁻¹. -1 A selective hydrogenation catalyst A1 with a Pd loading of 0.5% by mass was obtained (wherein the loading is based on the total amount of catalyst).

[0123] Preparation Example 5

[0124] Following the method of Preparation Example 4, except that the nitrogen-doped nano-carbon cage (Z2) obtained in Preparation Example 2 was used as a support to prepare a selective hydrogenation catalyst A2 with a Pd loading of 0.5% by mass (wherein the loading is based on the total amount of catalyst).

[0125] Preparation Example 6

[0126] Following the method of Preparation Example 4, except that the nitrogen-doped nano-carbon cage (Z3) obtained in Preparation Example 3 was used as a support to prepare a selective hydrogenation catalyst A3 with a Pd loading of 0.5% by mass (wherein the loading is based on the total amount of catalyst).

[0127] Preparation Example 7

[0128] Following the method of Preparation Example 4, except that the amount of 0.1 mol / L PdCl2 solution added was 0.2 mL, a selective hydrogenation catalyst A4 with a Pd loading of 0.2% by mass was prepared (wherein the loading is based on the total amount of catalyst).

[0129] Preparation Example 8

[0130] Following the method of Preparation Example 4, except that the amount of 0.1 mol / L PdCl2 solution added was 1 mL, a selective hydrogenation catalyst A5 with a Pd loading of 1% by mass was prepared (wherein the loading is based on the total amount of catalyst).

[0131] Examples 1-8 and Comparative Example 1 are used to illustrate the purification of 2,5-furandicarboxylic acid containing 5-formyl-furan-2-carboxylic acid impurities.

[0132] To better quantitatively investigate the reaction between 5-formyl-furan-2-carboxylic acid and 2,5-furandicarboxylic acid in this method, commercially available 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid reagents were mechanically mixed to prepare a 2,5-furandicarboxylic acid feedstock containing 5-formyl-furan-2-carboxylic acid impurities. Specifically:

[0133] Taking 2,5-furandicarboxylic acid with an impurity content of 10% by mass as an example, 900 mg of 2,5-furandicarboxylic acid solid powder and 100 mg of 5-formyl-furan-2-carboxylic acid solid powder were weighed separately and then ground and mixed in a mortar to obtain 2,5-furandicarboxylic acid raw material with an impurity content of 10% by mass.

[0134] Using this method, 2,5-furandicarboxylic acid raw materials with impurity contents of 1% and 5% by mass of 5-formyl-furan-2-carboxylic acid were prepared respectively.

[0135] Example 1

[0136] Example 1 illustrates the purification of 2,5-furandicarboxylic acid containing 5-formyl-furan-2-carboxylic acid impurities using selective hydrogenation catalyst A1 obtained in Preparation Example 4 as the catalyst in step (1).

[0137] (1) Add 50 mg of selective hydrogenation catalyst A1, 1000 mg of 2,5-furandicarboxylic acid with an impurity content of 10% (i.e., containing 900 mg of 2,5-furandicarboxylic acid and 100 mg of 5-formyl-furan-2-carboxylic acid), 15 mL of 1,4-dioxane, and 15 mL of water to the reactor. After purging the reactor with H2 three times, stir and heat under low pressure until the temperature reaches the predetermined reaction temperature of 80°C. Then, purge H2 again to make the pressure inside the reactor 1 MPa. Continue the reaction for 8 hours and then stop heating. Release the pressure and open the reactor at 80°C.

[0138] (2) Filter the reaction solution obtained in step (1) at 80°C. After separating the catalyst, remove the solvent from the reaction solution by rotary evaporator to obtain solid 2,5-furandicarboxylic acid containing 5-hydroxymethyl-furan-2-carboxylic acid impurity.

[0139] (3) Wash the solid obtained in step (2) five times in a beaker with deionized water. After each washing, separate the aqueous phase from the solid by centrifugation. After drying and weighing the remaining solid, add a small amount of Na2CO3 aqueous solution to dissolve it and make up to 250 mL. Perform quantitative analysis using high performance liquid chromatography.

[0140] The remaining solid mass was determined to be 857 mg, of which 2,5-furandicarboxylic acid content was 99.97 wt% and 5-formyl-furan-2-carboxylic acid content was 0.03 wt%. That is, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (857 mg / 900 mg × 100%) 95.2%, and the purity was 99.97%.

[0141] Example 2

[0142] This example illustrates the purification of 2,5-furandicarboxylic acid containing 5-formyl-furan-2-carboxylic acid impurities using selective hydrogenation catalyst A2 obtained in Preparation Example 5 as the catalyst in step (1).

[0143] (1) Add 50 mg of selective hydrogenation catalyst A2, 500 mg of 2,5-furandicarboxylic acid with an impurity content of 5% (i.e., containing 475 mg of 2,5-furandicarboxylic acid and 25 mg of 5-formyl-furan-2-carboxylic acid), 10 mL of dioxane, and 10 mL of water to the reactor. After purging the reactor with H2 three times, stir and heat under low pressure until the temperature reaches the predetermined reaction temperature of 95°C. Then, purge H2 again to make the pressure inside the reactor 2 MPa. Continue the reaction for 2 hours, then stop heating and release the pressure when the temperature drops to 80°C.

[0144] (2) Filter the reaction solution obtained in step (1) at 80°C. After separating the catalyst, remove the solvent from the reaction solution by rotary evaporator to obtain solid 2,5-furandicarboxylic acid containing 5-hydroxymethyl-furan-2-carboxylic acid impurity.

[0145] (3) Wash the solid obtained in step (2) five times in a beaker with deionized water. After each washing, separate the aqueous phase from the solid by centrifugation. After drying and weighing the remaining solid, add a small amount of Na2CO3 aqueous solution to dissolve it and make up to 250 mL. Perform quantitative analysis using high performance liquid chromatography.

[0146] The remaining solid mass was determined to be 451 mg, of which 2,5-furandicarboxylic acid contained 99.45 wt% and 5-formyl-furan-2-carboxylic acid contained 0.55 wt%. That is, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (451 mg / 475 mg × 100%) 94.9%, and the purity was 99.45%.

[0147] Example 3

[0148] This example illustrates the purification of 2,5-furandicarboxylic acid containing 5-formyl-furan-2-carboxylic acid impurities using selective hydrogenation catalyst A3 obtained in Preparation Example 6 as the catalyst in step (1).

[0149] (1) Add 10 mg of selective hydrogenation catalyst A3, 2000 mg of 2,5-furandicarboxylic acid with an impurity content of 1% (i.e., containing 1980 mg of 2,5-furandicarboxylic acid and 20 mg of 5-formyl-furan-2-carboxylic acid), 15 mL of dioxane, and 15 mL of water to the reactor. After purging the reactor with H2 three times, stir and heat under low pressure until the temperature reaches the predetermined reaction temperature of 120°C. Then, purge H2 again to make the pressure inside the reactor 1.5 MPa. Continue the reaction for 2 hours, then stop heating and release the pressure when the temperature drops to 80°C.

[0150] (2) Filter the reaction solution obtained in step (1) at 80°C. After separating the catalyst, remove the solvent from the reaction solution by rotary evaporator to obtain solid 2,5-furandicarboxylic acid containing 5-hydroxymethyl-furan-2-carboxylic acid impurity.

[0151] (3) Wash the solid obtained in step (2) five times in a beaker with deionized water. After each washing, separate the aqueous phase from the solid by centrifugation. After drying and weighing the remaining solid, add a small amount of Na2CO3 aqueous solution to dissolve it and make up to 250 mL. Perform quantitative analysis using high performance liquid chromatography.

[0152] The remaining solid mass was determined to be 1913 mg, of which 2,5-furandicarboxylic acid contained 99.91 wt% and 5-formyl-furan-2-carboxylic acid contained 0.09 wt%. Therefore, after treatment using this method, the recovery rate of 2,5-furandicarboxylic acid was (1913 mg / 1980 mg × 100%) 96.6%, and the purity was 99.91%.

[0153] Example 4

[0154] The reaction was carried out according to the method of Example 1, except that the catalyst used in step (1) was 50 mg of the selective hydrogenation catalyst A4 obtained in Preparation Example 7, and the reaction time was 12 hours.

[0155] The remaining solid mass was determined to be 882 mg, of which 2,5-furandicarboxylic acid contained 99.21 wt% and 5-formyl-furan-2-carboxylic acid contained 0.79 wt%. Therefore, after treatment using this method, the recovery rate of 2,5-furandicarboxylic acid was (882 mg / 900 mg × 100%) 98.0%, and the purity was 99.21%.

[0156] Example 5

[0157] The reaction was carried out according to the method of Example 1, except that the catalyst used in step (1) was 50 mg of the selective hydrogenation catalyst A5 obtained in Preparation Example 8, and the reaction time was 3 hours.

[0158] The remaining solid mass was determined to be 835 mg, of which 2,5-furandicarboxylic acid content was 99.96 wt% and 5-formyl-furan-2-carboxylic acid content was 0.04%. That is, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (835 mg / 900 mg × 100%) 92.8% and the purity was 99.96%.

[0159] Example 6

[0160] The reaction was carried out according to the method of Example 1, except that the solvent used in step (1) was 20 mL of ethylene glycol dimethyl ether and 10 mL of water.

[0161] The remaining solid mass was determined to be 815 mg, of which 2,5-furandicarboxylic acid contained 99.15 wt% and 5-formyl-furan-2-carboxylic acid contained 0.85 wt%. That is, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (815 mg / 900 mg × 100%) 90.6%, and the purity was 99.15%.

[0162] Example 7

[0163] The reaction was carried out according to the method of Example 1, except that the reaction temperature used in step (1) was 160°C.

[0164] The remaining solid mass was determined to be 810 mg, of which 2,5-furandicarboxylic acid content was 99.75 wt% and 5-formyl-furan-2-carboxylic acid content was 0.25 wt%. That is, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (810 mg / 900 mg × 100%) 90.0%, and the purity was 99.75%.

[0165] Example 8

[0166] The reaction was carried out according to the method of Example 1, except that the reaction pressure used in step (1) was 4 MPa.

[0167] The remaining solid mass was determined to be 821 mg, of which 2,5-furandicarboxylic acid content was 99.73 wt% and 5-formyl-furan-2-carboxylic acid content was 0.27%. That is, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (821 mg / 900 mg × 100%) 91.2%, and the purity was 99.73%.

[0168] Comparative Example 1

[0169] This example illustrates the purification of 2,5-furandicarboxylic acid using only water as the solvent in step (1).

[0170] (1) Add 50 mg of selective hydrogenation catalyst A1, 1000 mg of 2,5-furandicarboxylic acid with an impurity content of 10% (i.e., containing 900 mg of 2,5-furandicarboxylic acid and 100 mg of 5-formyl-furan-2-carboxylic acid), and 30 mL of water to the reactor. After purging the reactor with H2 three times, stir and heat under low pressure until the temperature reaches the predetermined reaction temperature of 80°C. Then, purge H2 again to make the pressure inside the reactor 1 MPa. Continue the reaction for 8 hours and then stop heating. At 80°C, release the pressure and open the reactor.

[0171] (2) Filter the reaction solution obtained in step (1) at 80℃. Since the solubility of 2,5-furandicarboxylic acid is low at this temperature when water is used as the solvent, some 2,5-furandicarboxylic acid (including some unreacted 5-formyl-furan-2-carboxylic acid) does not dissolve in the reaction solution and is separated from the catalyst by filtration. Therefore, after one filtration, the filter cake is a mixture of black solid (catalyst) and white solid (undissolved reaction raw materials). To analyze the content of 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid in the entire reaction system, the filter cake needs to be repeatedly rinsed with Na2CO3 aqueous solution during filtration. This allows some undissolved 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid to react with Na2CO3 to form their corresponding easily soluble sodium salts, thereby achieving complete separation of 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid from the catalyst.

[0172] (3) Mix all the reaction solution and the washing liquid of the filter cake and bring the volume to 500 mL. Perform quantitative analysis using high performance liquid chromatography.

[0173] After measurement and conversion, the content of 2,5-furandicarboxylic acid in the reaction solution and the washing liquid of the filter cake was 883 mg, and the content of 5-formyl-furan-2-carboxylic acid was 89 mg. That is, when only water is used as a solvent, under the reaction conditions described in this invention, due to the low solubility of the reaction raw materials (2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid), the hydrogenation reaction of 5-formyl-furan-2-carboxylic acid is poor, and the purification of 2,5-furandicarboxylic acid cannot be achieved.

[0174] As can be seen from the above embodiments, the purification method of the present invention can successfully purify 2,5-furandicarboxylic acid containing 5-formyl-furan-2-carboxylic acid impurities, with a recovery rate of over 90% and a purity of over 99.9%.

[0175] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for purifying 2,5-furandicarboxylic acid, wherein, The method includes the following steps: (1) In the presence of organic solvent and water, 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity, hydrogen and selective hydrogenation catalyst are contacted to carry out hydrogenation reaction; (2) The product obtained in step (1) is subjected to solid-liquid separation and washing; The selective hydrogenation catalyst comprises a support and an active metal component Pd supported on the support, wherein the content of Pd is 0.1-2% by mass; the support is a nitrogen-doped carbon nanocage; the nitrogen-doped carbon nanocage has a hollow cage-like structure, and the BET specific surface area of ​​the nitrogen-doped carbon nanocage is 400-1000 m². 2 / g; the pore size of the nitrogen-doped carbon nanocage is 2-50nm; based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen and pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 90%; Among them, the molar ratio of pyrrole nitrogen to pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage, as measured by X-ray photoelectron spectroscopy, is greater than 5.

2. The method according to claim 1, wherein, In step (1), the 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity is selected from the crude product obtained when producing 2,5-furandicarboxylic acid by the oxidation of 5-hydroxymethylfurfural.

3. The method according to claim 1, wherein, In step (1), the total amount of 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity is used as the basis, and the content of the 5-formyl-furan-2-carboxylic acid impurity is 0.1-20% by mass.

4. The method according to claim 3, wherein, In step (1), the total amount of 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity is used as the basis, and the content of the 5-formyl-furan-2-carboxylic acid impurity is 0.2-15% by mass.

5. The method according to claim 4, wherein, In step (1), the total amount of 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity is used as a basis, and the content of the 5-formyl-furan-2-carboxylic acid impurity is 0.5-10% by mass.

6. The method according to claim 1, wherein, In step (1), the organic solvent is selected from at least one of tetrahydrofuran, 1,4-dioxane and ethylene glycol dimethyl ether; And / or, in step (1), the volume ratio of the organic solvent to water is 0.5-5:

1.

7. The method according to claim 6, wherein, In step (1), the organic solvent is 1,4-dioxane; And / or, in step (1), the volume ratio of the organic solvent to water is 1-3.5:

1.

8. The method according to any one of claims 1-7, wherein, In step (1), the amount of organic solvent and water used is such that the concentration of 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity is 20-150 g / L.

9. The method according to claim 8, wherein, In step (1), the amount of organic solvent and water used is such that the concentration of 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurity is 25-100 g / L.

10. The method according to claim 1, wherein, In step (1), the mass ratio of the selective hydrogenation catalyst to the 5-formyl-furan-2-carboxylic acid impurity is 1:0.1-20.

11. The method according to claim 10, wherein, In step (1), the mass ratio of the selective hydrogenation catalyst to the 5-formyl-furan-2-carboxylic acid impurity is 1:0.2-10.

12. The method according to claim 10, wherein, In step (1), the mass ratio of the selective hydrogenation catalyst to the 5-formyl-furan-2-carboxylic acid impurity is 1:0.5-5.

13. The method according to claim 1, wherein, In step (1), the temperature of the hydrogenation reaction is 80-160℃; And / or, in step (1), the hydrogenation reaction takes 1-20 hours; And / or, in step (1), the pressure of the hydrogen gas is 0.5-4 MPa.

14. The method according to claim 13, wherein, In step (1), the temperature of the hydrogenation reaction is 80-120℃; And / or, in step (1), the hydrogenation reaction takes 1-15 hours; And / or, in step (1), the pressure of the hydrogen gas is 1-3 MPa.

15. The method according to claim 13, wherein, In step (1), the hydrogenation reaction takes 1-10 hours.

16. The method according to claim 1, wherein, The Pd content is 0.1-1 by mass, based on the total amount of selective hydrogenation catalyst.

17. The method of claim 16, wherein, The Pd content is 0.1-0.5% by mass, based on the total amount of selective hydrogenation catalyst.

18. The method according to claim 1, wherein, The nitrogen-doped carbon nanocage has a pore size of 2-20 nm.

19. The method according to claim 1, wherein, Based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy determined that the molar content of pyrrole nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage was 85.8-100%, and the molar content of pyridine nitrogen was 0-14.2%.

20. The method according to claim 1, wherein, X-ray photoelectron spectroscopy revealed that the molar content of carbon on the surface of the nitrogen-doped carbon nanocage was 89-92%, the molar content of nitrogen was 1-3%, and the molar content of oxygen was 5-10%.

21. The method according to claim 1, wherein, The nitrogen-doped carbon nanocage has a BET specific surface area of ​​400-800 m². 2 / g.

22. The method according to claim 1, wherein, The total pore volume of the nitrogen-doped carbon nanocage is 0.9-1.5 cm³. 3 / g.

23. The method according to claim 1, wherein, The nitrogen-doped carbon nanocage has a dual mesoporous distribution peak, and the dual mesoporous distribution peaks correspond to a first most probable pore size and a second most probable pore size, respectively. The first most probable pore size is 3.5-4 nm, and the second most probable pore size is 6-9.5 nm.

24. The method according to claim 1, wherein, In the Raman curve of the nitrogen-doped carbon nanocage, I D / I G The range is 0.2-1.

25. The method according to claim 24, wherein, In the Raman curve of the nitrogen-doped carbon nanocage, I D / I G The range is 0.3-0.

8.

26. The method according to claim 1, wherein, In step (2), the temperature for solid-liquid separation is 20-100℃.

27. The method according to claim 26, wherein, In step (2), the temperature for solid-liquid separation is 50-100℃.

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