Process for purifying 2,5-furandicarboxylic acid

Abstract

The present application relates to the purification technical field of 2,5-furan dicarboxylic acid, and discloses a purification method of 2,5-furan dicarboxylic acid, which 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 catalyst are contacted to perform a hydrogenation reaction; (2) the product obtained in step (1) is subjected to solid-liquid separation and washing; wherein the catalyst is a carbon-coated nickel nanocomposite, the carbon-coated nickel nanocomposite has a core-shell structure with a shell layer and a core, the shell layer is a graphitized carbon layer, the core is a nickel nanoparticle, and the nickel nanoparticle comprises a face-centered cubic lattice structure and / or a hexagonal close-packed lattice structure. The method can efficiently remove 5-formyl-furan-2-carboxylic acid impurities, and significantly improve the product purity of 2,5-furan dicarboxylic acid.

Description

Technical Field

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

[0002] With societal development, resources and the environment have become key factors restricting sustainable human development. The development of biosynthesis and resource utilization technologies is crucial for solving this problem. Developing green and renewable biomass resources to replace traditional petroleum resources is a focus of current social development and research. Among these, 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, and it can adversely affect the polymerization reaction of 2,5-furandicarboxylic acid.

[0004] CN104334537A discloses a method for purifying crude furan-2,5-dicarboxylic acid by hydrogenation. The method involves purifying the crude furan-2,5-dicarboxylic acid composition (cFDCA) by hydrogenation of an FDCA composition dissolved in a hydrogenation solvent such as water. Hydrogenation is performed by contacting the solvated FDCA composition with hydrogen gas in the presence of a hydrogenation catalyst at a hydrogen partial pressure of 10 psi to 900 psi within a temperature range of 130°C to 225°C. However, this method requires relatively harsh hydrogenation conditions and necessitates the use of noble metal catalysts such as carbon-supported palladium, resulting in high purification costs. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of high purification cost of 2,5-furandicarboxylic acid and difficulty in removing 5-formyl-furan-2-carboxylic acid impurities in the existing technology, and to provide a purification method for 2,5-furandicarboxylic acid that does not require the use of precious metal catalysts, has good purification effect and low processing cost.

[0006] To achieve the above objectives, the present invention provides a method for purifying 2,5-furandicarboxylic acid, the method comprising:

[0007] (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 catalyst are brought into contact to carry out hydrogenation reaction;

[0008] (2) The product obtained in step (1) is subjected to solid-liquid separation and washing;

[0009] The catalyst is a carbon-coated nickel nanocomposite material with a core-shell structure, wherein the shell is a graphitized carbon layer and the core is nickel nanoparticles, and the nickel nanoparticles include a face-centered cubic lattice structure and / or a hexagonal close-packed lattice structure.

[0010] The inventors of this invention discovered in their research 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. However, in existing technologies, the hydrogenation catalysts used are generally noble metal catalysts, and the conditions for the hydrogenation reaction are still quite stringent to ensure highly selective hydrogenation of 5-formyl-furan-2-carboxylic acid.

[0011] This invention utilizes a carbon-coated nickel nanocomposite material as a catalyst in the highly selective hydrogenation reaction of 5-formyl-furan-2-carboxylic acid. This nanocomposite material forms a core-shell structure by coating nickel nanoparticles with a graphitized carbon layer. Through the synergistic effect of the graphitized carbon shell and the nickel core, it exhibits highly efficient catalytic activity and selectivity, and effectively improves the stability of non-precious metal nickel under acidic conditions. It can achieve selective hydrogenation of small amounts of 5-formyl-furan-2-carboxylic acid impurities in crude 2,5-furandicarboxylic acid without the need for precious metals, thereby significantly reducing processing costs.

[0012] The purification method provided by this invention uses a stable and highly selective carbon-coated nickel nanocomposite material as a catalyst under relatively mild conditions to efficiently convert 5-formyl-furan-2-carboxylic acid impurities that are difficult to remove by other methods into easily removable 5-hydroxymethyl-furan-2-carboxylic acid. This allows for the removal of impurities through simple water washing, significantly improving the purity of 2,5-furandicarboxylic acid products. Attached Figure Description

[0013] Figure 1 The image shows the XRD pattern of the carbon-coated nickel nanocomposite material prepared in Example 1.

[0014] Figure 2AThis is the N2 adsorption-desorption isotherm curve of the carbon-coated nickel nanocomposite material prepared in Example 1;

[0015] Figure 2B This is a pore size distribution curve of the carbon-coated nickel nanocomposite material prepared in Example 1;

[0016] Figure 3 This is a TEM image of the carbon-coated nickel nanocomposite material prepared in Example 2;

[0017] Figure 4A This is the N2 adsorption-desorption isotherm curve of the carbon-coated nickel nanocomposite material prepared in Example 2;

[0018] Figure 4B This is a pore size distribution diagram of the carbon-coated nickel nanocomposite material prepared in Preparation Example 2. Detailed Implementation

[0019] 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.

[0020] In this invention, the term "core-shell structure" refers to a core composed of nickel nanoparticles and a shell composed of graphitized carbon layers. The term "graphitized carbon layer" refers to a carbon structure with a clearly observable layered structure under a high-resolution transmission electron microscope, rather than an amorphous structure, with an interlayer spacing of approximately 0.34 nm. The composite material formed by coating nickel nanoparticles with this graphitized carbon layer is spherical or near-spherical.

[0021] The term "mesopore" is defined as a pore with a diameter in the range of 2–50 nm. Pores with a diameter less than 2 nm are defined as micropores, and pores with a diameter greater than 50 nm are defined as macropores.

[0022] The term "mesopore distribution peak" refers to the mesopore distribution peak on the pore distribution curve obtained by calculating the desorption curve according to the Barrett-Joyner-Halenda (BJH) method.

[0023] This invention provides a method for purifying 2,5-furandicarboxylic acid, the method comprising:

[0024] (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 catalyst are brought into contact to carry out hydrogenation reaction;

[0025] (2) The product obtained in step (1) is subjected to solid-liquid separation and washing;

[0026] The catalyst is a carbon-coated nickel nanocomposite material with a core-shell structure, wherein the shell is a graphitized carbon layer and the core is nickel nanoparticles, and the nickel nanoparticles include a face-centered cubic lattice structure and / or a hexagonal close-packed lattice structure.

[0027] According to the present invention, 5-formyl-furan-2-carboxylic acid can be hydrogenated to 5-hydroxymethyl-furan-2-carboxylic acid with high selectivity through the hydrogenation reaction in step (1), and then 5-hydroxymethyl-furan-2-carboxylic acid can be removed by solid-liquid separation and washing, thereby obtaining purified 2,5-furandicarboxylic acid product.

[0028] In the highly selective hydrogenation reaction of 5-formyl-furan-2-carboxylic acid, a carbon-coated nickel nanocomposite material is used as a catalyst. This nanocomposite material forms a core-shell structure by coating nickel nanoparticles with a graphitized carbon layer. Through the synergistic effect of the graphitized carbon shell and the nickel core, it has highly efficient catalytic activity and selectivity, enabling the selective hydrogenation of a small amount of 5-formyl-furan-2-carboxylic acid impurities in crude 2,5-furandicarboxylic acid without the need for precious metals, thus significantly reducing processing costs.

[0029] In this invention, the crystal structure of nickel nanoparticles is characterized by XRD testing.

[0030] The present invention does not have any particular limitation on the source of the 2,5-furandicarboxylic acid raw material in step (1). This method can be applied to any 2,5-furandicarboxylic acid raw material containing 5-formyl-furan-2-carboxylic acid impurities obtained by conventional methods.

[0031] The present invention has a wide range of options for the content of the 5-formyl-furan-2-carboxylic acid impurity. Preferably, the content of the 5-formyl-furan-2-carboxylic acid impurity in the 2,5-furandicarboxylic acid raw material is 0.1-30%, more preferably 0.2-20%, and more preferably 0.5-10%.

[0032] In this invention, the content of each component in the 2,5-furandicarboxylic acid raw material is determined by high performance liquid chromatography (HPLC).

[0033] 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.

[0034] According to the present invention, preferably, in step (1), the mass ratio of 2,5-furandicarboxylic acid raw material to catalyst, based on the content of 5-formyl-furan-2-carboxylic acid impurities, is 0.05-100:1, more preferably 0.5-50:1, and more preferably 0.5-5:1. Using the above-mentioned preferred catalyst dosage can achieve the selective hydrogenation reaction of 5-formyl-furan-2-carboxylic acid while avoiding the occurrence of side reactions.

[0035] The inventors of this invention discovered in their research that using a carbon-coated nickel nanocomposite material as a catalyst, through the synergistic effect of the graphitized carbon shell and the nickel core, results in highly efficient catalytic activity and selectivity, enabling the efficient selective hydrogenation of 5-formyl-furan-2-carboxylic acid impurities under mild conditions. Preferably, the temperature of the hydrogenation reaction in step (1) is 50-200℃, more preferably 60-160℃, and even more preferably 80-125℃, for example, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, etc., or a temperature range between two points. Within the above-mentioned preferred temperature range, it is beneficial for the reactants to fully dissolve in the solvent described in this invention, allowing the hydrogenation reaction to proceed fully, while avoiding side reactions such as hydrogenation of carbon-carbon double bonds and carboxyl groups in 2,5-furandicarboxylic acid caused by excessively high reaction temperatures, effectively improving the recovery rate of 2,5-furandicarboxylic acid in this invention.

[0036] According to the present invention, preferably, the pressure of the hydrogen gas in step (1) is 0.5-4 MPa, more preferably 1-3 MPa.

[0037] In this invention, the total amount of organic solvent and water used in step (1) is within a wide range, as long as it is sufficient to fully dissolve the 2,5-furandicarboxylic acid raw material containing the 5-formyl-furan-2-carboxylic acid impurity. Preferably, in step (1), the amount of organic solvent and water used is such that the concentration of the 2,5-furandicarboxylic acid raw material containing the 5-formyl-furan-2-carboxylic acid impurity is 20-100 g / L, preferably 25-50 g / L.

[0038] In this invention, preferably, the organic solvent is selected from at least one of tetrahydrofuran, 1,4-dioxane, and dimethyl sulfoxide. 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 allowing 5-formyl-furan-2-carboxylic acid to dissolve uniformly in the solvent and to fully contact with the catalyst and hydrogen, thereby being reduced to 5-hydroxymethyl-furan-2-carboxylic acid, which has better water solubility, and further improving the purification effect.

[0039] According to a particularly preferred embodiment of the present invention, the organic solvent is 1,4-dioxane. In this preferred embodiment, it is advantageous to improve the solubility of 2,5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid in the solvent, further improving the purification effect of 2,5-furandicarboxylic acid.

[0040] According to the present invention, in order to ensure high solubility of 5-furandicarboxylic acid and 5-formyl-furan-2-carboxylic acid in the solvent, the volume ratio of the organic solvent to water is preferably 0.5-5:1, more preferably 1-3:1; for example, it can be typical but not limiting ratios such as 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, and 3:1. Adopting the above preferred embodiments is beneficial to further improve the purification effect of 2,5-furandicarboxylic acid.

[0041] In this invention, the composition of the carbon-coated nickel nanocomposite material can be selected from a wide range, as long as it has a shell of graphitized carbon layer and a core of nickel nanoparticles. Depending on the preparation method, the carbon layer may also contain doping elements, for example, it may be doped with only oxygen without nitrogen, or it may contain both nitrogen and oxygen. Preferably, the carbon-coated nickel nanocomposite material includes nickel, carbon, oxygen, hydrogen, and optionally nitrogen.

[0042] This invention allows for a wide range of selection for the content of each element in the carbon-coated nickel nanocomposite material. Preferably, based on the total mass of the carbon-coated nickel nanocomposite material, the content of nickel is 30-70 wt%, the content of carbon is 30-70 wt%, the content of oxygen is 0.3-6 wt%, the content of nitrogen is 0-6 wt%, and the content of hydrogen is 0.1-2.5 wt%. More preferably, based on the total mass of the carbon-coated nickel nanocomposite material, the content of nickel is 50-70 wt%, the content of carbon is 30-50 wt%, the content of oxygen is 0.3-3 wt%, the content of nitrogen is 0-3 wt%, and the content of hydrogen is 0.1-1.5 wt%.

[0043] The analysis of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) in this invention was performed on an Elementar Micro Cube elemental analyzer. The specific operating methods and conditions are as follows: 1-2 mg of sample was weighed in a tin cup, placed in the autosampler tray, and introduced into the combustion tube through a ball valve for combustion at 1000°C (helium purging was used to remove atmospheric interference during sample introduction). The combusted gas was then reduced with copper to form nitrogen, carbon dioxide, and water. The mixed gas was separated by three desorption columns and sequentially detected by a TCD detector. Oxygen analysis utilized high-temperature decomposition; under the action of a carbon catalyst, oxygen in the sample was converted to CO, which was then detected by a TCD detector.

[0044] The metal element content is the normalized result after deducting the carbon, hydrogen, oxygen, and nitrogen content of the material.

[0045] According to the present invention, preferably, the carbon-coated nickel nanocomposite material in step (1) is a mesoporous material having at least one mesoporous distribution peak; in some embodiments, the carbon-coated nickel nanocomposite material manufactured in a single batch has at least two mesoporous distribution peaks; it is understood that if multiple batches of carbon-coated nickel nanocomposite materials are mixed, more mesoporous distribution peaks can be present in the mesoporous range. When the nanocomposite material has a hierarchical mesoporous structure with different pore size ranges, it can exhibit more unique properties, and the hierarchical mesoporous structure has a wider range of applicable applications, resulting in higher mass transfer efficiency of the nanocomposite material and thus better catalytic performance.

[0046] According to the present invention, preferably, the carbon-coated nickel nanocomposite material has a mesoporous distribution peak in the pore size range of 2nm-5nm and 5nm-20nm, respectively. In the above-mentioned preferred embodiment, this facilitates the diffusion of reactant molecules within the catalyst channels, improves the hydrogenation reaction effect, and further enhances the purification effect.

[0047] According to the present invention, preferably, the proportion of mesopore volume to total pore volume in the carbon-coated nickel nanocomposite material is greater than 90%, more preferably greater than 95%.

[0048] According to the present invention, preferably, the specific surface area of ​​the carbon-coated nickel nanocomposite material is greater than 140 m². 2 / g, preferably greater than 200m 2 / g.

[0049] This invention utilizes the BET test method to detect the pore structure properties of materials. Specifically, a Quantachrome AS-6B analyzer is used for measurement. The specific surface area of ​​the catalyst is obtained using the Brunauer-Emmett-Taller (BET) method, and the pore distribution curve is calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0050] The present invention does not impose any particular limitation on the preparation method of the carbon-coated nickel nanocomposite material, and it can be prepared by methods known in the art.

[0051] According to a preferred embodiment of the present invention, the method for preparing the carbon-coated nickel nanocomposite material includes:

[0052] S1. Mix a nickel-containing compound, a polycarboxylic acid, and a solvent to form a homogeneous solution;

[0053] S2. Remove the solvent from the homogeneous solution to obtain the precursor;

[0054] S3. The precursor is pyrolyzed at high temperature in an inert or reducing atmosphere.

[0055] According to the present invention, the precursor is a water-soluble mixture, which refers to a water-soluble mixture containing nickel obtained by dissolving a nickel-containing compound and a polycarboxylic acid in a solvent to form a homogeneous solution, and then directly removing the solvent.

[0056] This invention does not particularly limit the method for solvent removal; for example, direct evaporation can be used. Any feasible existing technology can be used for the temperature and process of the direct evaporation, such as spray drying at 80°C-120°C or drying in an oven.

[0057] According to the present invention, in step S1, other organic compounds besides the aforementioned nickel-containing compound, polycarboxylic acid, and solvent may also be added to form a homogeneous solution. These other organic compounds can be any organic compound that can supplement the carbon source required in the product and does not contain other doped atoms, preferably non-volatile organic compounds such as organic polyols and lactic acid. Furthermore, nitrogen-containing compounds may be added to adjust the nitrogen content in the nanocomposite material according to actual application needs. These nitrogen-containing compounds include, but are not limited to, hexamethylenetetramine.

[0058] The nickel-containing compound mentioned in step S1 may be selected from at least one of nickel hydroxide, nickel oxide and nickel salts, wherein the nickel salts include, but are not limited to, one or more of organic acid salts, carbonates and basic carbonates, wherein the organic acid salt of nickel is preferably an organic carboxylate of nickel without heteroatoms, more preferably an acetate of nickel without heteroatoms, wherein the heteroatoms refer to metal atoms other than nickel.

[0059] The aforementioned polycarboxylic acids can be nitrogen-containing polycarboxylic acids, such as ethylenediaminetetraacetic acid, iminodiacetic acid, diethylenetriaminepentaacetic acid, 1,3-propanediaminetetraacetic acid, etc.; or they can be nitrogen-free polycarboxylic acids, such as citric acid, maleic acid, trimesic acid, terephthalic acid, malic acid, etc. It is understood that when the polycarboxylic acid is a nitrogen-free polycarboxylic acid, and other organic compounds are also nitrogen-free, the graphitized carbon layer of the resulting composite material will be nitrogen-free, only doped with oxygen. In this case, the mass ratio of the nickel-containing compound, the polycarboxylic acid, and other organic compounds is 1:(0.1-10):(0-10), preferably 1:(0.5-5):(0-5), more preferably 1:(0.8-3):(0-3), meaning that no other organic compounds may be added.

[0060] When the polycarboxylic acid is a nitrogen-free polycarboxylic acid but a nitrogen-containing compound is added; or when the polycarboxylic acid is a nitrogen-containing polycarboxylic acid, the graphitized carbon layer of the resulting composite material contains nitrogen and oxygen. It should be noted that when the polycarboxylic acid is a nitrogen-containing polycarboxylic acid, a nitrogen-containing compound may not be added; it is sufficient that the mass ratio of the nitrogen element to the nickel-containing compound and the polycarboxylic acid is within a certain range. In some embodiments, the mass ratio of the nickel-containing compound, the polycarboxylic acid, and the nitrogen-containing compound is 1:(0.1-100):(0-100), preferably 1:(0.5-5):(0.5-5), and more preferably 1:(0.8-2):(1-2).

[0061] In this invention, the solvent used in step S1 is preferably water and / or ethanol. This invention does not have a particular limitation on the amount of solvent used, as long as it is sufficient to form the homogeneous solution. Those skilled in the art can select the appropriate solvent based on actual needs.

[0062] In some specific embodiments of the present invention, the high-temperature pyrolysis includes: heating the precursor to a constant temperature range under an inert or reducing atmosphere, and maintaining the constant temperature range.

[0063] The heating rate is 0.5-30℃ / min, preferably 1-10℃ / min; the isothermal temperature is 400-800℃, preferably 500-800℃; the isothermal time is 20-600min, preferably 60-480min; the inert atmosphere is nitrogen or argon; the reducing atmosphere is hydrogen or a mixture of hydrogen and an inert gas; and the volume content of hydrogen in the reducing atmosphere is not less than 5%.

[0064] According to another embodiment of the present invention, the present invention further includes acid treatment of the product of the above-mentioned high-temperature pyrolysis.

[0065] Specifically, the acid treatment includes contacting the product of the high-temperature pyrolysis with an acid; the acid is preferably provided by an aqueous solution of the acid.

[0066] Preferably, the concentration of the aqueous solution of the acid is 0.1-5 mol / L, and more preferably 0.5-2 mol / L.

[0067] Preferably, the acid is an inorganic protic acid, which includes, but is not limited to, at least one of hydrofluoric acid, hydrochloric acid, nitric acid and sulfuric acid, and is preferably hydrochloric acid and / or sulfuric acid.

[0068] In some specific embodiments of the present invention, the acid treatment conditions are: treatment at 30-100°C for more than 1 hour, preferably treatment at 60-100°C for 1-20 hours, and more preferably treatment at 70-90°C for 1-10 hours.

[0069] This invention prepares carbon-coated nickel nanocomposites using the method described above, instead of employing the pyrolysis method using metal-organic framework (MOF) compounds as precursors. This latter method requires the preparation of crystalline solid materials (i.e., MOFs) with periodic structures in a solvent under high temperature and pressure. Typically, the conditions for preparing MOFs are quite stringent, the required ligands are expensive, and mass production is difficult. In contrast, the precursor of this invention is directly produced by the reaction of a nickel-containing compound with a polycarboxylic acid, achieving 100% atomic utilization of the Ni precursor. The preparation process eliminates the need for commonly used ligands such as dicyandiamine and melamine, which are prone to sublimation or decomposition and easily generate carbon nanotubes. Furthermore, it overcomes the drawbacks of existing technologies that require high-temperature, high-pressure reactors for self-assembly of metal-organic framework precursors, resulting in significant waste of organic solvents and cumbersome purification steps. Furthermore, when nitrogen-containing polycarboxylic acids are used as the carbon and nitrogen sources for nanomaterials, they simultaneously act as carbon reducing agents during high-temperature carbonization. Therefore, there is no need to introduce flammable reducing gases such as hydrogen, or flammable gases such as CH4 and C2H4, during the preparation process. This method enables the selective hydrogenation of small amounts of 5-formyl-furan-2-carboxylic acid impurities in crude 2,5-furandicarboxylic acid without the need for precious metals, thus significantly reducing processing costs.

[0070] According to the present invention, the product obtained in step (1) is a mixture containing the catalyst, and the catalyst is separated by solid-liquid separation in step (2). The solid-liquid separation can be performed using conventional methods in the art, such as filtering the product. Preferably, the temperature for solid-liquid separation in step (2) is 30-140°C, more preferably 35-100°C, and even more preferably 60-80°C. Using the above-mentioned preferred solid-liquid separation temperature 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 solid catalyst.

[0071] Preferably, 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. The present invention does not particularly limit the method for removing the solvent; for example, evaporation can be used.

[0072] 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.

[0073] The present invention does not have any particular limitation on the specific operation method and number of times of washing in step (2). Preferably, the number of times of washing is 1-10 times, and more preferably 2-5 times.

[0074] According to the present invention, 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%.

[0075] The recovery rate (%) is calculated as follows: (mass of 2,5-furandicarboxylic acid product / mass of 2,5-furandicarboxylic acid in raw materials) × 100%.

[0076] The present invention will be described in detail below through embodiments.

[0077] Unless otherwise specified, all reagents used in the following examples are commercially available and of analytical grade.

[0078] This invention utilizes the BET test method to detect the pore structure properties of materials. Specifically, a Quantachrome AS-6B analyzer is used for measurement. The specific surface area of ​​the catalyst is obtained using the Brunauer-Emmett-Taller (BET) method, and the pore distribution curve is calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0079] The analysis of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) in this invention was performed on an Elementar Micro Cube elemental analyzer. The specific operating methods and conditions are as follows: 1-2 mg of sample was weighed in a tin cup, placed in the autosampler tray, and introduced into the combustion tube through a ball valve for combustion at 1000°C (helium purging was used to remove atmospheric interference during sample introduction). The combusted gas was then reduced with copper to form nitrogen, carbon dioxide, and water. The mixed gas was separated by three desorption columns and sequentially detected by a TCD detector. Oxygen analysis utilized high-temperature decomposition; under the action of a carbon catalyst, oxygen in the sample was converted to CO, which was then detected by a TCD detector.

[0080] The metal element content is the normalized result after deducting the carbon, hydrogen, oxygen, and nitrogen content of the material.

[0081] The following preparation examples illustrate the preparation of carbon-coated nickel nanocomposites.

[0082] Preparation Example 1

[0083] 1) Weigh 4.38 g (15 mmol) of ethylenediaminetetraacetic acid and 1.85 g (20 mmol) of nickel hydroxide and add them to 150 mL of deionized water. Stir at 75 °C to obtain a homogeneous solution and continue heating to evaporate to dryness. Grind the solid to obtain the precursor.

[0084] 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 at a flow rate of 80 mL / min, and heat it to 600℃ at a rate of 3℃ / min. After holding the temperature for 3 hours, stop heating and cool it to room temperature under a nitrogen atmosphere to obtain the composite material.

[0085] 3) Add the composite material obtained in step 2) to 60 mL of 0.5 mol / L H2SO4 solution, stir and reflux at 80 °C for 6 h, filter the solution, wash with deionized water until neutral, and then dry the powder in an oven at 100 °C for 2 h to obtain carbon-coated nickel nanocomposite material.

[0086] like Figure 1 The figure shown is the XRD pattern of the carbon-coated nickel nanocomposite material. Figure 1 It shows that only diffraction peaks of carbon materials, as well as diffraction peaks of hcp-Ni and fcc-Ni, exist. Figure 2A This is the N2 adsorption-desorption isotherm curve of the carbon-coated nickel nanocomposite material prepared in Example 1; Figure 2B This is a pore size distribution curve of the carbon-coated nickel nanocomposite material prepared in Example 1. It shows that the pore size distribution of this material exhibits two peaks at diameters of 3.7 nm and 10.0 nm. The specific surface area of ​​this nanocomposite material is 224 m². 2 / g, pore volume is 0.457cm³ 3 / g, of which mesoporous volume accounts for 99.7% of the total pore volume. Elemental analysis determined that the nanomaterial contained 37.42wt% C, 0.54wt% H, 1.45wt% N, 1.86wt% O, and 58.73wt% Ni after normalization.

[0087] Preparation Example 2

[0088] 1) Weigh 10 mmol of nickel hydroxide and 10 mmol of citric acid and add them to 150 mL of deionized water. Stir at 80 °C to obtain a homogeneous solution and continue heating to evaporate to dryness. Grind the solid to obtain the precursor.

[0089] 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 at a flow rate of 150 mL / min, and heat it to 575℃ at a rate of 2.5℃ / min. After holding the temperature for 2 hours, stop heating and cool it to room temperature under a nitrogen atmosphere to obtain the composite material.

[0090] 3) Add the composite material obtained in step 2) to 50 mL of 1 mol / L H2SO4 solution, stir and reflux at 90 °C for 4 h, filter the solution, wash with deionized water until neutral, and then dry the powder in an oven at 100 °C for 2 h to obtain carbon-coated nickel nanocomposite material.

[0091] Figure 3 This is a TEM image of the carbon-coated nickel nanocomposite material prepared in Example 2. From... Figure 3 Figure a) shows that the nanoparticles are uniform in size and well dispersed. From... Figure 3 Figure b) shows that the nickel nanoparticles are coated with a carbon layer with a certain degree of graphitization, forming a complete core-shell structure. Furthermore, according to the Scherrer equation, the average particle size of the Ni nanoparticles is 8.4 nm. Figure 4A This is the N2 adsorption-desorption isotherm curve of the carbon-coated nickel nanocomposite material prepared in Example 2. Figure 4B This is a pore size distribution diagram of the carbon-coated nickel nanocomposite material prepared in Example 2. From... Figure 4A It can be seen that this material exhibits a significant hysteresis loop between p / p0 = 0.4 and 1.0. From... Figure 4B It can be seen that the pore size distribution of this material exhibits two peaks at diameters of 3.3 nm and 6.3 nm. The specific surface area of ​​this nanocomposite material is 168 m². 2 / g, pore volume is 0.246cm³ 3 / g, of which mesoporous volume accounts for 100% of the total pore volume. Elemental analysis determined that the nanomaterial contained 28.60wt% C, 0.40wt% H, 1.94wt% O, and 69.06wt% Ni after normalization.

[0092] Preparation Example 3

[0093] The method is the same as in Preparation Example 1, except that the acid treatment in step 3) is not used.

[0094] The XRD diffraction peaks of the prepared carbon-coated nickel nanocomposite material are similar to those of the prepared material. Figure 1 Similarly, only diffraction peaks of carbon materials, as well as diffraction peaks of hcp-Ni and fcc-Ni, are present.

[0095] Preparation Example 4

[0096] Following the method in Preparation Example 1, except that the amount of nickel hydroxide added in step 1) was 0.93 g (10 mmol), the XRD diffraction peaks of the carbon-coated nickel nanocomposite material were similar to those in Example 1. Figure 1Similarly, only diffraction peaks for carbon materials, as well as diffraction peaks for hcp-Ni and fcc-Ni, are present. Correspondingly, the obtained nanomaterials contain 67.17 wt% C, 0.66 wt% H, 1.83 wt% N, 1.70 wt% O, and 28.64 wt% Ni.

[0097] The following examples illustrate the purification method for 2,5-furandicarboxylic acid.

[0098] Example 1

[0099] This example illustrates the use of the nanocomposite material prepared in Example 1 as a catalyst in step (1) for the purification of 2,5-furandicarboxylic acid.

[0100] (1) 50 mg of the nanocomposite material obtained in Preparation Example 1, 500 mg of 2,5-furandicarboxylic acid with an impurity content of 10 wt% (i.e. containing 450 mg of 2,5-furandicarboxylic acid and 50 mg of 5-formyl-furan-2-carboxylic acid), 10 mL of 1,4-dioxane, and 10 mL of water were added to the reactor. After H2 was introduced to replace the reactor four times, the reactor was stirred and heated under low pressure until the predetermined reaction temperature of 80°C was reached. H2 was introduced again to make the pressure inside the reactor 3.0 MPa. After the reaction was continued for 4 hours, the heating was stopped and the reactor was opened when the temperature dropped to 60°C.

[0101] (2) Filter the reaction solution obtained in step (1) at 60°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.

[0102] (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 500 mL. Perform quantitative analysis using high performance liquid chromatography.

[0103] The remaining solid mass was determined to be 431 mg, of which 2,5-furandicarboxylic acid contained 99.5 wt% and 5-formyl-furan-2-carboxylic acid contained 0.5 wt%. Therefore, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (431 mg / 450 mg × 100%) 95.8%, and the purity was 99.5%.

[0104] Example 2

[0105] This example illustrates the use of the nanocomposite material prepared in Example 2 as a catalyst in step (1) for the purification of 2,5-furandicarboxylic acid.

[0106] (1) 50 mg of the nanocomposite material obtained in Preparation Example 2, 1000 mg of 2,5-furandicarboxylic acid with an impurity content of 5% (i.e. containing 950 mg of 2,5-furandicarboxylic acid and 50 mg of 5-formyl-furan-2-carboxylic acid), 10 mL of 1,4-dioxane, and 10 mL of water were added to the reactor. After H2 was introduced to replace the reactor four times, the reactor was stirred and heated under low pressure until the predetermined reaction temperature of 100°C was reached. H2 was introduced again to make the pressure inside the reactor 2.0 MPa. After the reaction was continued for 4 hours, the heating was stopped and the reactor was opened when the temperature dropped to 80°C.

[0107] (2) The reaction solution obtained in step (1) was filtered at 80°C. After separating the catalyst, the reaction solution was removed by a rotary evaporator to obtain solid 2,5-furandicarboxylic acid containing 5-hydroxymethyl-furan-2-carboxylic acid impurities.

[0108] (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 500 mL. Perform quantitative analysis using high performance liquid chromatography.

[0109] The remaining solid mass was determined to be 913 mg, of which 2,5-furandicarboxylic acid content was 99.8 wt% and 5-formyl-furan-2-carboxylic acid content was 0.2 wt%. Therefore, after treatment using this method, the recovery rate of 2,5-furandicarboxylic acid was (913 mg / 950 mg × 100%) 96.1%, and the purity was 99.8%.

[0110] Example 3

[0111] The reaction was carried out according to the method of Example 2, except that the reaction temperature in step (1) was 120°C and the reaction time was 3 hours.

[0112] The remaining solid mass was determined to be 906 mg, of which 2,5-furandicarboxylic acid content was 99.6 wt% and 5-formyl-furan-2-carboxylic acid content was 0.4 wt%. Therefore, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (906 mg / 950 mg × 100%) 95.4%, and the purity was 99.6%.

[0113] Example 4

[0114] This example illustrates the use of the nanocomposite material prepared in Example 3 as a catalyst in step (1) for the purification of 2,5-furandicarboxylic acid.

[0115] (1) 10 mg of the nanocomposite material obtained in Preparation Example 3, 1000 mg of 2,5-furandicarboxylic acid with an impurity content of 1% (i.e. containing 990 mg of 2,5-furandicarboxylic acid and 10 mg of 5-formyl-furan-2-carboxylic acid), 10 mL of 1,4-dioxane, and 10 mL of water were added to the reactor. After H2 was introduced to replace the reactor four times, the reactor was stirred and heated under low pressure until the predetermined reaction temperature of 100°C was reached. H2 was introduced again to make the pressure inside the reactor 1.0 MPa. After the reaction was continued for 4 hours, the heating was stopped and the reactor was opened when the temperature dropped to 80°C.

[0116] (2) The reaction solution obtained in step (1) was filtered at 80°C. After separating the catalyst, the reaction solution was removed by a rotary evaporator to obtain solid 2,5-furandicarboxylic acid containing 5-hydroxymethyl-furan-2-carboxylic acid impurities.

[0117] (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 500 mL. Perform quantitative analysis using high performance liquid chromatography.

[0118] The remaining solid mass was determined to be 976 mg, of which 2,5-furandicarboxylic acid content was 99.9 wt% and 5-formyl-furan-2-carboxylic acid content was less than 0.1 wt%. That is, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (976 mg / 990 mg × 100%) 98.6%, and the purity was 99.9%.

[0119] Example 5

[0120] The method is the same as in Example 1, except that 50 mg of the nanocomposite material obtained in Example 4 is used as the catalyst in step (1).

[0121] The remaining solid mass was determined to be 410 mg, of which 2,5-furandicarboxylic acid contained 99.1 wt% and 5-formyl-furan-2-carboxylic acid contained 0.9 wt%. Therefore, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (410 mg / 450 mg × 100%) 91.1%, and the purity was 99.1%.

[0122] Example 6

[0123] The method is the same as in Example 1, except that the amount of 1,4-dioxane added in step (1) is 15 mL and the amount of water added is 5 mL.

[0124] The remaining solid mass was determined to be 428 mg, of which 2,5-furandicarboxylic acid content was 99.0 wt% and 5-formyl-furan-2-carboxylic acid content was less than 1.0 wt%. That is, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (428 mg / 450 mg × 100%) 95.1%, and the purity was 99.0%.

[0125] Example 7

[0126] The method is the same as in Example 1, except that an equal volume of dimethyl sulfoxide is used instead of 1,4-dioxane.

[0127] The remaining solid mass was determined to be 405 mg, of which 2,5-furandicarboxylic acid content was 99.3 wt% and 5-formyl-furan-2-carboxylic acid content was less than 0.7 wt%. That is, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (405 mg / 450 mg × 100%) 90.0%, and the purity was 99.3%.

[0128] Example 8

[0129] The reaction was carried out according to the method of Test Example 1, except that the reaction temperature used in step (1) was 160°C and the reaction pressure was 4 MPa.

[0130] The remaining solid mass was determined to be 407 mg, of which 2,5-furandicarboxylic acid content was 99.2 wt% and 5-formyl-furan-2-carboxylic acid content was 0.8 wt%. Therefore, after treatment by this method, the recovery rate of 2,5-furandicarboxylic acid was (407 mg / 450 mg × 100%) 90.4%, and the purity was 99.2%.

[0131] Comparative Example 1

[0132] This example illustrates the purification of 2,5-furandicarboxylic acid using only water as the solvent in step (1).

[0133] (1) 50 mg of the nanocomposite material obtained in Preparation Example 1, 500 mg of 2,5-furandicarboxylic acid with an impurity content of 10 wt% (i.e. containing 450 mg of 2,5-furandicarboxylic acid and 50 mg of 5-formyl-furan-2-carboxylic acid), and 20 mL of water were added to the reactor. After H2 was introduced to replace the reactor 4 times, the reactor was stirred and heated under low pressure until the predetermined reaction temperature of 80°C was reached. H2 was introduced again to make the pressure inside the reactor 3.0 MPa. After the reaction was continued for 4 hours, the heating was stopped and the reactor was opened when the temperature dropped to 60°C.

[0134] (2) The reaction solution obtained in step (1) was filtered at 60°C. After one filtration, the filter cake was a mixture of a black solid (catalyst) and a white solid (2,5-furandicarboxylic acid and some unreacted 5-formyl-furan-2-carboxylic acid). The filter cake was repeatedly washed with Na2CO3 aqueous solution to allow 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. Then, solid-liquid separation was performed to remove the catalyst. That is, when only water is used as a solvent, under the reaction conditions described in this invention, the hydrogenation reaction of 5-formyl-furan-2-carboxylic acid is less effective, and the catalyst is difficult to separate, making it difficult to achieve the effect of purifying 2,5-furandicarboxylic acid.

[0135] 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%.

[0136] 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, characterized in that, The method includes: (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 catalyst are brought into contact to carry out hydrogenation reaction; (2) The product obtained in step (1) is subjected to solid-liquid separation and washing; The catalyst is a carbon-coated nickel nanocomposite material, which has a core-shell structure with a shell and a core. The shell is a graphitized carbon layer, and the core is nickel nanoparticles. The nickel nanoparticles include a face-centered cubic lattice structure and / or a hexagonal close-packed lattice structure. The carbon-coated nickel nanocomposite material includes nickel, carbon, oxygen, hydrogen, and optionally nitrogen. Based on the total mass of the carbon-coated nickel nanocomposite material, the content of nickel is 30-70 wt%, the content of carbon is 30-70 wt%, the content of oxygen is 0.3-6 wt%, the content of nitrogen is 0-6 wt%, and the content of hydrogen is 0.1-2.5 wt%.

2. The method according to claim 1, wherein, The content of 5-formyl-furan-2-carboxylic acid impurity in the 2,5-furandicarboxylic acid raw material is 0.1-30 wt%.

3. The method according to claim 2, wherein, The content of 5-formyl-furan-2-carboxylic acid impurity in the 2,5-furandicarboxylic acid raw material is 0.2-20 wt%.

4. The method according to claim 3, wherein, The content of 5-formyl-furan-2-carboxylic acid impurity in the 2,5-furandicarboxylic acid raw material is 0.5-10 wt%.

5. The method according to any one of claims 1-4, wherein, In step (1), the mass ratio of 2,5-furandicarboxylic acid raw material to catalyst, based on the content of 5-formyl-furan-2-carboxylic acid impurities, is 0.05-100:

1.

6. The method according to claim 5, wherein, In step (1), the mass ratio of 2,5-furandicarboxylic acid raw material to catalyst, based on the content of 5-formyl-furan-2-carboxylic acid impurities, is 0.5-50:

1.

7. The method according to claim 6, wherein, In step (1), the mass ratio of 2,5-furandicarboxylic acid raw material to catalyst, based on the content of 5-formyl-furan-2-carboxylic acid impurities, is 0.5-5:

1.

8. The method according to any one of claims 1-4, wherein, The temperature of the hydrogenation reaction in step (1) is 50-200℃; And / or, the pressure of the hydrogen gas in step (1) is 0.5-4 MPa.

9. The method according to claim 8, wherein, The temperature of the hydrogenation reaction in step (1) is 60-160℃; And / or, the pressure of the hydrogen gas in step (1) is 1-3 MPa.

10. The method according to claim 9, wherein, The temperature of the hydrogenation reaction in step (1) is 80-125℃.

11. The method according to any one of claims 1-4, 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 20-100 g / L.

12. The method according to claim 11, 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 25-50 g / L.

13. The method according to any one of claims 1-4, wherein, The volume ratio of the organic solvent to water is 0.5-5:

1.

14. The method according to claim 13, wherein, The volume ratio of the organic solvent to water is 1-3:

1.

15. The method according to any one of claims 1-4, wherein, The organic solvent is selected from at least one of tetrahydrofuran, 1,4-dioxane, and dimethyl sulfoxide.

16. The method according to claim 15, wherein, The organic solvent is 1,4-dioxane.

17. The method according to any one of claims 1-4, wherein, Based on the total mass of the carbon-coated nickel nanocomposite material, the content of nickel is 50-70 wt%, the content of carbon is 30-50 wt%, the content of oxygen is 0.3-3 wt%, the content of nitrogen is 0-3 wt%, and the content of hydrogen is 0.1-1.5 wt%.

18. The method according to any one of claims 1-4, wherein, The carbon-coated nickel nanocomposite material mentioned in step (1) is a mesoporous material with at least one mesoporous distribution peak.

19. The method according to claim 18, wherein, The carbon-coated nickel nanocomposite material has at least two mesoporous distribution peaks.

20. The method according to claim 19, wherein, The carbon-coated nickel nanocomposite material has a mesoporous distribution peak in the pore size range of 2nm-5nm and 5nm-20nm, respectively.

21. The method according to claim 18, wherein, The proportion of mesopore volume to total pore volume in the carbon-coated nickel nanocomposite material is greater than 90%.

22. The method according to claim 21, wherein, The proportion of mesopore volume to total pore volume in the carbon-coated nickel nanocomposite material is greater than 95%.

23. The method according to any one of claims 1-4, wherein, The solid-liquid separation temperature in step (2) is 30-140℃.

24. The method according to claim 23, wherein, The temperature for solid-liquid separation in step (2) is 35-100℃.

25. The method according to claim 24, wherein, The solid-liquid separation temperature in step (2) is 60-80℃.

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