Preparation method of 2, 5-furandicarboxylic acid

Abstract

The invention belongs to the crossing field of chemistry and chemical engineering and energy, and particularly relates to a preparation method of 2, 5-furandicarboxylic acid (FDCA), which comprises the following steps: 1) oxidizing furfural by using a nitrogen-doped carbon supported metal cobalt-based catalyst, molecular oxygen as an oxidant and cesium carbonate as an alkali additive to obtain furoic acid; and 2) reacting the mixture obtained by drying the filtrate with CO2 at high temperature, and acidifying with dilute acid to obtain FDCA. A mixture obtained after the filtrate is dried contains cesium furoate and cesium carbonate, wherein cesium carbonate is used for promoting carboxylation of a C-H bond on the C5 site of cesium furoate. The conversion rate of furfural is 99.5%, the selectivity of furoic acid is 99.7%, the yield of FDCA is 81%, and the purity is 99%. The non-precious metal cobalt single atom is adopted as the catalyst, the catalytic efficiency is far higher than that of nanoparticles, and the catalyst can be repeatedly utilized; the reaction process is green and friendly, and the process is simple and easy to amplify; the cheap furfural is used for replacing expensive 5-hydroxymethylfurfural (5-HMF), and a route for preparing FDCA from C5 is developed; greenhouse gas CO2 is fixed and reduced in emission, resource utilization is achieved, and comprehensive benefits are remarkable.

Description

Technical Field

[0001] The present invention belongs to the cross - field of chemical engineering and energy, and particularly relates to a preparation method of 2,5 - furandicarboxylic acid. Background Art

[0002] 2,5 - Furandicarboxylic acid (FDCA) is mainly obtained by the oxidation of 5 - hydroxymethylfurfural (5 - HMF) which is produced by the dehydration reaction of hexose (C6) in biomass. It is an important dicarboxylic acid. In recent years, as a substitute for traditional petroleum - based chemical terephthalic acid (PTA), the application of FDCA in polyester, polyamide polymers and metal - organic frameworks has been widely studied. The polyethylene furanoate (PEF) polyester plastic synthesized with FDCA as a monomer exhibits excellent gas barrier properties, high modulus and low melting point and other characteristics, and has been favored by international giants such as Coca - Cola, BASF, DuPont, Dow, Procter & Gamble, etc.

[0003] There are many challenges in both technology and economy in preparing FDCA from 5-HMF, which are mainly manifested in the following aspects: on the one hand, in the process of dehydrating biomass hexose to prepare 5-HMF, the selectivity of 5-HMF is low, the product separation is difficult, and the yield is low; on the other hand, the structure of 5-HMF itself is extremely unstable and it is easy to age and form humin. The literature (K.I.Galkin et al., Angewandte Chemie, 2016, 55, 8338-8342.) shows that 5-HMF is easy to age and deteriorate in the solution state, and the yield of the target product is low. Therefore, the market price of 5-HMF is extremely high, about 4500-6000 yuan / kg. There is also the problem of catalyst cost. The oxidation of 5-HMF to prepare FDCA mainly uses homogeneous catalysts (such as KMnO4, HNO3, Co / Mn / Br, Ni / Mn / Br, etc.) and supported noble metal catalysts (commonly such as Pt, Ru, Au, Pd and their alloys). Patent CN105688988A discloses a method for oxidizing 5-HMF to prepare FDCA using a Ni / Mn / Br catalyst. Using nickel acetate / manganese acetate / hydrogen bromide as the catalyst and acetic acid as the solvent, the maximum yield of FDCA is 89% at 180°C. Patent CN103724303A discloses a method for oxidizing 5-HMF to prepare FDCA using a basic carrier supported by two noble metals Au and Pt as the catalyst. The catalyst AuPt / MgO reacts with 10 times of NaOH for 8 hours at 60°C and 0.3 MPa of oxygen, and the yield of FDCA is 99%. It can be seen that homogeneous catalysts have deficiencies such as difficult recycling and environmental pollution; supported noble metal catalysts have high costs, require a large amount of alkali to be added during the reaction, are easy to corrode equipment, and increase the hidden danger of wastewater discharge. To sum up, using expensive 5-HMF raw materials and high-cost noble metal catalysts directly leads to a high preparation cost of FDCA and does not have the market competitiveness of the product. Therefore, finding substitutes for 5-HMF raw materials and low-cost catalysts are the two key technologies for large-scale preparation of FDCA.

[0004] Furfural is mainly formed by the dehydration reaction of pentose (C5) in biomass waste, such as agricultural straws, corncobs, camellia husks, etc., and has achieved industrial production. Compared with 5-HMF, furfural has a higher yield, more stable properties, and a cheaper price. The domestic price of furfural is <60 yuan / kg. At present, there are literature and patent reports on preparing FDCA using furfural and its derivatives as raw materials, such as attached Figure 1As shown, furfural is oxidized by HNO3 to obtain furoic acid, and then methyl furoate is obtained through an esterification reaction using a base as a catalyst. After chloromethylation at the C5 position of the methyl ester, it is oxidized and hydrolyzed to obtain FDCA (Gonis, G.; Amstutz, E. D. J Org Chem, 1962, 27, 2946 - 2947). This production method has many deficiencies such as the need to use a large amount of acids and bases, serious equipment corrosion and environmental pollution, complex reaction steps, low FDCA yield, and is not suitable for large-scale production. The literature (Banerjee A., et al. Nature, 2016, 531: 215 - 219) reported the preparation of FDCA from furoic acid and CO2 under the action of carbonate at high temperature and high pressure, and the highest product yield reached 71%. This method has main problems such as the safety of high-pressure operation and unstable product quality. Patent (CN202010039036.6) discloses a continuous production method of FDCA from furfural, using an organic solvent as the solvent and a metal nanoparticle supported on a molecular sieve as the catalyst. However, this method has main problems such as the recovery of organic solvents and low catalyst efficiency. Patent (CN202110895449.9) discloses a method for preparing FDCA from furfural through three steps including catalytic hydrogenation, hydroxymethylation reaction, and oxidation reaction. This method has deficiencies such as high-pressure hydrogen, solvent addition, and many reaction steps.

[0005] Supported heterogeneous catalysts are of great significance for improving the recyclability and stability of catalysts, reducing catalyst costs, and reducing environmental pollution, and are widely used in fields such as energy storage and conversion, organic synthesis, drug preparation, and environmental governance. Research shows that the active components of supported metal catalysts are mainly metals, and the active sites are concentrated on the atoms on the particle surface. Therefore, synthesizing smaller-sized particles is an effective method to improve the activity and selectivity of metal catalysts. Metal single-atom catalysts achieve the maximum utilization efficiency of atoms. The raw materials of the metal cobalt single-atom catalyst disclosed in Patent CN201810029041.1 are inexpensive and renewable, meeting the concepts of sustainable development and green manufacturing.

[0006] In summary, there are many problems in the reported numerous FDCA production routes, such as long reaction routes, harsh conditions, operation safety, and unstable product quality. To achieve the efficient and green production of FDCA, not only the selection of the process route but also the development of an efficient catalytic system needs to be considered. Summary of the Invention

[0007] The present invention uses biomass furfural as a raw material, adopts a transition metal cobalt single-atom catalyst, and prepares furoic acid through oxidation, and further prepares 2,5-furandicarboxylic acid (FDCA) through a carboxylation reaction. The process has the advantages of simplicity, stable product quality, easy scale-up production, and environmental friendliness, and thus the present invention is completed.

[0008] In a first aspect, the present invention provides a method for preparing 2,5-furandicarboxylic acid, wherein the 2,5-furandicarboxylic acid is obtained through an oxidation reaction and a carboxylation reaction. Among them, the catalyst used in the oxidation reaction is a cobalt-based catalyst, and the preparation steps are as follows:

[0009] S1. Oxidation reaction: Mix the raw material, catalyst, oxidant, and base additive and add them to a solvent, react under a certain pressure and temperature. After the oxidation reaction is completed, filter to recover the catalyst, and dry the filtrate to obtain a reaction product;

[0010] S2. Carboxylation reaction: Put the reaction product obtained in step S1 into a tubular furnace, react for a period of time under a reaction atmosphere and reaction temperature, and cool after the carboxylation reaction to obtain FDCA.

[0011]

[0012] Further, the raw material is furfural, and the furfural includes a non-hydroxy furfural compound and a hydroxy furfural compound.

[0013] Further, the cobalt-based catalyst is selected from one or more of nitrogen-doped carbon-supported metal cobalt single atoms, doped carbon-supported metal cobalt nanoclusters, and / or nitrogen-doped carbon-supported metal cobalt nanoparticles, and preferably a nitrogen-doped carbon-supported transition metal cobalt single-atom catalyst.

[0014] Further, the molar ratio of the raw material to the cobalt-based catalyst is: 0.25 - 30:0.005 - 1.5 mmol; preferably 1 - 10:0.03 - 0.3 mmol.

[0015] Further, the oxidant is selected from one or more of molecular oxygen, H2O2, N2, air, and / or a mixed gas containing oxygen, and preferably molecular oxygen.

[0016] Further, in step S1, cesium carbonate can also be replaced by one or more of potassium carbonate, sodium carbonate, and their mixtures.

[0017] Further, the solvent in step S1 is water.

[0018] Further, the molar ratio of the raw material to the alkali additive in step S1 is: 0.25 to 30: 1.0 to 45 mmol; preferably 1 to 10: 1.5 to 30 mmol.

[0019] Further, the oxygen pressure in step S1 is 0.1 to 80 bar, preferably 1 to 40 bar.

[0020] Further, the temperature of the furfural oxidation reaction in step S1 is 30 to 150 °C, preferably 50 to 100 °C.

[0021] Further, the furfural oxidation reaction time in step S1 is 1 to 6 h, preferably 2 to 4 h.

[0022] Further, the reaction atmosphere in step S2 is CO2.

[0023] Further, the temperature of the carboxylation reaction in step S2 is 150 to 350 °C, preferably 180 to 320 °C, more preferably 200 to 290 °C.

[0024] Further, the carboxylation reaction time in step S2 is 6 to 48 h, preferably 11 to 18 h, more preferably 12 to 15 h.

[0025] In a second aspect, the present invention provides an application of a cobalt-based catalyst in the preparation of furoic acid. The method for preparing furoic acid is an oxidation reaction, and the specific steps are as follows: The raw material, catalyst, oxidant and alkali additive are mixed and added to a solvent, and the reaction is carried out under a certain pressure and temperature. After the oxidation reaction is completed, the catalyst is recovered by filtration, and the filtrate is dried to obtain the reaction product, which is furoic acid.

[0026]

[0027] Further, the raw material is furfural, and the furfural includes a non-hydroxy furfural compound and a hydroxy furfural compound.

[0028] Further, the cobalt-based catalyst is selected from one or more of nitrogen-doped carbon-supported metal cobalt single atoms, doped carbon-supported metal cobalt nanoclusters, and / or nitrogen-doped carbon-supported metal cobalt nanoparticles, preferably a nitrogen-doped carbon-supported transition metal cobalt single atom catalyst.

[0029] Further, the molar ratio of the raw material to the cobalt-based catalyst is: 0.25 to 30: 0.005 to 1.5 mmol; preferably 1 to 10: 0.03 to 0.3 mmol.

[0030] Further, the oxidant is selected from one or more of molecular oxygen, H2O2, N2, air, and / or a mixed gas containing oxygen, preferably molecular oxygen.

[0031] Further, in step S1, cesium carbonate can also be replaced by one or more of potassium carbonate, sodium carbonate, and their mixtures.

[0032] Further, in step S1, the solvent is water.

[0033] Further, the molar ratio of the raw material to the alkali additive in step S1 is: 0.25 - 30: 1.0 - 45 mmol; preferably 1 - 10: 1.5 - 30 mmol.

[0034] Further, the oxygen pressure in step S1 is 0.1 - 80 bar, preferably 1 - 40 bar.

[0035] Further, the temperature of the furfural oxidation reaction in step S1 is 30 - 150 °C, preferably 50 - 100 °C.

[0036] Further, the reaction time of the furfural oxidation reaction in step S1 is 1 - 6 h, preferably 2 - 4 h.

[0037] In a third aspect, the present invention provides an application of a cobalt-based catalyst in the preparation of 2,5-furandicarboxylic acid, wherein the 2,5-furandicarboxylic acid is obtained by an oxidation reaction and a carboxylation reaction. Among them, the catalyst used in the oxidation reaction is a cobalt-based catalyst, and the preparation steps are as follows:

[0038] S1. Oxidation reaction: Mix the raw material, catalyst, oxidant, and alkali additive and add them to a solvent, and react under a certain pressure and temperature. After the oxidation reaction is completed, filter and recover the catalyst, and dry the filtrate to obtain the reaction product;

[0039] S2. Carboxylation reaction: Put the reaction product obtained in step S1 into a tubular furnace and react for a period of time under a reaction atmosphere and reaction temperature. After the carboxylation reaction, cool to obtain FDCA.

[0040]

[0041] Further, the raw material is furfural, and the furfural includes a non-hydroxy furfural compound and a hydroxy furfural compound.

[0042] Further, the cobalt-based catalyst is selected from one or more of nitrogen-doped carbon-supported metal cobalt single atoms, doped carbon-supported metal cobalt nanoclusters, and / or nitrogen-doped carbon-supported metal cobalt nanoparticles, preferably a nitrogen-doped carbon-supported transition metal cobalt single atom catalyst.

[0043] Further, the molar ratio of the raw material to the cobalt-based catalyst is: 0.25 - 30: 0.005 - 1.5 mmol; preferably 1 - 10: 0.03 - 0.3 mmol.

[0044] Further, the oxidant is selected from one or more of molecular oxygen, H2O2, N2, air, and / or a mixed gas containing oxygen, preferably molecular oxygen.

[0045] Further, in step S1, cesium carbonate can also be replaced by one or more of potassium carbonate, sodium carbonate, and their mixtures.

[0046] Further, the solvent in step S1 is water.

[0047] Further, the molar ratio of the raw material to the base additive in step S1 is: 0.25 - 30: 1.0 - 45 mmol; preferably 1 - 10: 1.5 - 30 mmol.

[0048] Further, the oxygen pressure in step S1 is 0.1 - 80 bar, preferably 1 - 40 bar.

[0049] Further, the temperature of the furfural oxidation reaction in step S1 is 30 - 150 °C, preferably 50 - 100 °C.

[0050] Further, the reaction time of the furfural oxidation reaction in step S1 is 1 - 6 h, preferably 2 - 4 h.

[0051] Further, the reaction atmosphere in step S2 is CO2.

[0052] Further, the temperature of the carboxylation reaction in step S2 is 150 - 350 °C, preferably 180 - 320 °C, and further preferably 200 - 290 °C.

[0053] Further, the reaction time of the carboxylation reaction in step S2 is 6 - 48 h, preferably 11 - 18 h, and further preferably 12 - 15 h.

[0054] Beneficial Effects

[0055] Compared with the existing published patents and reported literatures, the patent of this application has the following positive effects:

[0056] 1. In the present invention, 2,5-furandicarboxylic acid (FDCA) is prepared through oxidation and carboxylation reactions. Among them, a cobalt-based catalyst is selected to participate in the oxidation reaction. Under this method, the conversion rate of furfural is 90.5%, the selectivity of furoic acid is 99.7%, the yield of FDCA is 77.3%, and the purity is 99%;

[0057] 2. Using non-precious metal cobalt single atoms as the catalyst, the catalytic efficiency is much higher than that of nanoparticles, and the used catalyst can be recycled with unchanged activity;

[0058] 3. The reaction process is green and friendly, and the process flow is simple and easy to scale up; inexpensive furfural is used to replace expensive 5-hydroxymethylfurfural (5-HMF) to develop a route for preparing FDCA from C5, reducing raw material costs; greenhouse gas CO2 is fixed, reduced and resourcefully utilized to enhance comprehensive benefits. Description of the Drawings

[0059] Figure 1 Comparison between the traditional process route for preparing FDCA and the process route of this application

[0060] (a) Traditional process route for preparing FDCA with furfural as the raw material;

[0061] (b) Compared with the process route of the application

[0062] Figure 2 Structural analysis of the single-atom cobalt catalyst

[0063] a) TEM image of the single-atom cobalt catalyst;

[0064] b) HAADF-STEM image of the single-atom cobalt catalyst;

[0065] c) TEM image of the cobalt nanoparticles;

[0066] d) XRD patterns of the single-atom cobalt catalyst and cobalt nanoparticles

[0067] Figure 3 Comparison of the catalytic performance of the single-atom cobalt catalyst (Co SAs@C) and the nanoparticle catalyst (Co NPs@C) a) Turnover frequency (TOF);

[0068] b) Activation energy (Ea)

[0069] Figure 4 NMR, FTIR, and HPLC detection result diagrams of FDCA

[0070] (a) Carbon nuclear magnetic spectrum ( 13 C-NMR spectrum);

[0071] (b) Hydrogen nuclear magnetic spectrum ( 1 H-NMR spectrum);

[0072] (c) Infrared spectrum (FTIR spectrum);

[0073] (d) Liquid phase detection diagram (HPLC diagram)

[0074] Figure 5 FDCA sample Detailed implementation manners

[0075] The specific embodiments of the present invention will be further described below. It should be noted here that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the following described embodiments can be combined with each other as long as they do not conflict with each other.

[0076] In the following experimental methods of the embodiments, unless otherwise specified, they are all conventional methods. Unless otherwise specified, the test materials used in the following embodiments can all be obtained through conventional commercial channels.

[0077] Term

[0078] Heterogeneous catalytic reaction: It is a catalytic process in which the reactants and the catalyst are not completely in the same phase. Usually, it involves a solid catalyst catalyzing in a liquid or gaseous reactant.

[0079] Cesium carbonate: Cesium carbonate is an inorganic compound, which is a white solid under normal temperature and pressure, extremely soluble in water, and rapidly absorbs moisture when placed in the air. The aqueous solution of cesium carbonate is strongly alkaline, can react with acids, produce corresponding cesium salts and water, and release carbon dioxide. Cesium carbonate is easy to transform and can be used as a precursor for other cesium salts, and is widely used in the variety of cesium salts.

[0080] Carboxylation reaction: (Carboxylation, or carboxylation reaction, carboxylation) is a large class of chemical reactions in organic chemistry, which refers to adding a carboxyl functional group to a substrate, and its reverse reaction is decarboxylation reaction.

[0081] Conversion rate: In a chemical reaction system, it refers to the percentage of the amount of a certain raw material participating in the chemical reaction in the total amount of this raw material introduced into the reaction system. The value of the conversion rate indicates the degree of conversion of this raw material in the reaction process. The larger the conversion rate, the more raw material participates in the reaction. Generally, the raw materials entering the reaction system cannot all participate in the chemical reaction, so the value of the conversion rate is always less than 100%. The conversion rate is for the reaction raw materials, so whether the raw material is converted into the target product or by-products is counted in the conversion rate.

[0082] Selectivity: In a chemical reaction process, it refers to the percentage of the amount of raw material consumed by the target product generated in the total amount of this raw material participating in the reaction. It expresses the relative magnitude of the progress of the main and side reactions, and can accurately reflect whether the utilization of the raw material is reasonable. The higher the selectivity, the higher the utilization rate of the raw material, indicating that the reaction is more effective. On the contrary, the lower the selectivity, the lower the utilization rate of the raw material. For reactions involving catalysts, the level of selectivity also reflects the performance of the catalyst. A high selectivity of the reaction indicates good catalytic performance of the catalyst.

[0083] Example

[0084] Example 1 Preparation of Metal Cobalt Single-Atom Catalyst

[0085] The method for preparing the metal cobalt single-atom catalyst comprises the following steps:

[0086] 1) Dissolve 10 g of lignin in 1 L of deionized water to form solution A;

[0087] 2) Dissolve zinc acetate dihydrate (4.39 g, 20 mmol Zn 2+ ) and cobalt nitrate hexahydrate (5.82 g, 20 mmol Co 2+ ) in 0.1 L of deionized water to form solution B;

[0088] 3) Add solution B to solution A, quickly mix well with mechanical stirring, stir for 1 h, and then let it stand overnight at room temperature;

[0089] 4) Discard the supernatant, centrifuge the precipitate at 5000×g for 10 min, and then dry it overnight at 80 °C;

[0090] 5) Mix the dried precipitate with 10 times its weight of dicyandiamide by thoroughly grinding. Put the ground powder into a porcelain boat, place it in a tube furnace, introduce argon with a flow rate of 75 mL / min, and the heating program is as follows: heat from room temperature to 550

[0091] °C at a rate of 5 °C / min, hold for 2 h, then heat to 900 °C at a rate of 5 °C / min, keep warm for 4 h, and then cool naturally to room temperature to obtain a nitrogen-doped carbon-supported metal cobalt single-atom catalyst.

[0092] Example 2 Preparation of Metal Cobalt Nanoparticle Catalyst

[0093] 2.1 Preparation Method

[0094] (1) Dissolve 8 g of lignin in 1 L of deionized water to form solution A;

[0095] (2) Dissolve cobalt nitrate hexahydrate (5.82 g, 20 mmol Co 2+ ) in 0.1 L of deionized water to form solution B;

[0096] (3) Add solution B to solution A, quickly mix well with mechanical stirring, and adjust the pH of the mixture to

[0097] 6.8 with 10 wt.% ammonia water. Continue to stir the mixture for 1 h, and then let it stand overnight at room temperature;

[0098] (4) Discard the supernatant, centrifuge the precipitate at 5000×g for 10 min, and then dry it overnight at 80 °C;

[0099] (5) The dried precipitate is thoroughly ground and mixed with 10 times its weight of dicyandiamide. The ground powder is placed in a porcelain boat and put into a tube furnace. Argon is introduced with a flow rate of 75 mL / min. The heating program is as follows: from room temperature, it is heated to 550

[0100] °C at a rate of 5 °C / min, held for 2 h, then heated to 900 °C at a rate of 5 °C / min, and after holding for 4 h, it is naturally cooled to room temperature to obtain a nitrogen-doped carbon-supported cobalt metal nanoparticle catalyst.

[0101] 2.2 Results

[0102] As shown in the figure, the overall morphology of the cobalt metal single-atom catalyst is wrinkled graphite carbon flakes, and Co nanoparticles cannot be observed under TEM ( Figure 2 a). From Figure 2 b high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), it can be seen that individual cobalt metal atoms are evenly dispersed on the support (the bright spots in the figure are cobalt single atoms). For the cobalt metal nanoparticle catalyst, obvious Co nanoparticles can be observed by TEM ( Figure 2 c). XRD pattern analysis shows that ( Figure 2 d), no crystal diffraction peak of cobalt metal is observed for the cobalt metal single-atom catalyst, indicating that the dispersion of cobalt on the support is very good; while obvious crystal diffraction peaks appear for the cobalt metal nanoparticles, which is consistent with the TEM results.

[0103] Example 3 Preparation of furoic acid by oxidizing furfural with a cobalt metal single-atom catalyst

[0104] 3.1 Preparation method

[0105] 1) Add 1 mmol of furfural, 1.5 mmol of cesium carbonate, and 0.05 g of the cobalt single-atom catalyst to 10 mL of water;

[0106] 2) The reaction conditions are: oxygen at 1 atmosphere, reaction temperature 65 °C, and reaction time 11 h.

[0107] 3.2 Results

[0108] After the reaction, the conversion rate of furfural is measured to be 90.5% and the selectivity for furoic acid is 99.7% by HPLC.

[0109] Example 4 Preparation of furoic acid by catalyzing the oxidation of furfural with cobalt metal nanoparticles

[0110] 4.1 Preparation method

[0111] (1) Add 10 mL of water, 1 mmol of furfural, 1.5 mmol of cesium carbonate, and 0.05 g of the cobalt single-atom catalyst to a 100 mL round-bottom flask;

[0112] (2) The reaction conditions are as follows: oxygen at 1 atm, reaction temperature of 65 °C, and reaction time of 15 h.

[0113] 4.2 Results

[0114] After the reaction, the conversion rate of furfural was measured to be 53.7% and the selectivity for furoic acid was 44.5% by HPLC.

[0115] Example 5: Preparation of furoic acid by oxidation of furfural with a single-atom cobalt catalyst under alkali-free conditions

[0116] 5.1 Preparation method

[0117] 1) Add 10 mL of water, 1 mmol of furfural, and 0.05 g of the single-atom cobalt catalyst into a 100 mL round-bottom flask.

[0118] 2) The reaction conditions are as follows: oxygen at 1 atm, reaction temperature of 65 °C, and reaction time of 15 h.

[0119] 5.2 Results

[0120] After the reaction, the conversion rate of furfural was measured to be 7.0% and the selectivity for furoic acid was 44.4% by HPLC.

[0121] Example 6: Influence of temperature on the oxidation of furfural to furoic acid catalyzed by a single-atom cobalt catalyst

[0122] 6.1 Preparation method

[0123] (1) Add 10 mL of water, 1 mmol of furfural, 1.5 mmol of cesium carbonate, and 0.05 g of the single-atom cobalt catalyst into a 100 mL round-bottom flask.

[0124] (2) The reaction conditions are as follows: oxygen at 1 atm, reaction temperature and time are shown in Table 1.

[0125] 6.2 Results

[0126] After the reaction, the conversion rate of furfural and the selectivity for furoic acid were measured by HPLC, and the results are shown in Table 1.

[0127] Table 1 Influence of temperature on the oxidation of furfural to furoic acid catalyzed by a single-atom cobalt catalyst

[0128]

[0129]

[0130] Example 7: Influence of oxidant on the oxidation of furfural to furoic acid catalyzed by a single-atom cobalt catalyst

[0131] 7.1 Preparation method

[0132] 1) Add 0.25 mmol of furfural, 50 mol% of the catalyst, 0.25 mmol of Na2CO3, and 5 mL of deionized water into a 50 mL round-bottom flask;

[0133] 2) The reaction conditions are as follows: the reaction temperature is 80 °C, the reaction time is 2 h, and the oxidant is shown in Table 2.

[0134] 7.2 Results

[0135] After the reaction, the contents of furfural and furoic acid were determined by HPLC, and the effects of different oxidants (H2O2, O2, air, N2) on the conversion rate of furfural and the selectivity of furoic acid were compared. The results are shown in Table 2.

[0136] Table 2 Effects of oxidants on the oxidation of furfural to furoic acid over cobalt single-atom catalyst

[0137] oxidant Furfural conversion rate (%) Furoic acid selectivity (%) <![CDATA[H2O2]]> 99.0 78.0 <![CDATA[O2]]> 99.5 93.6 air 99.0 82.3 <![CDATA[N2]]> 32.0 12.4

[0138] For the preparation of furoic acid by the oxidation reaction of furfural, the participation of an oxidant is necessary, and pure oxygen has the best effect.

[0139] Example 8 Preparation of FDCA using furoic acid as the raw material

[0140] 8.1 Preparation without drying

[0141] Dissolve 1 mmol of furoic acid and 1.5 mmol of cesium carbonate in 5 mL of water. After drying the mixed solution, grind it into powder. Load the powder into a quartz boat, place it in a tubular furnace, and introduce CO2 at a flow rate of 50 mL / min. React at 260 °C for 18 h. The conversion rate of furoic acid measured by HPLC is 95.1%, and the yield of FDCA is 77.3%.

[0142] 8.2 Preparation after drying with N2

[0143] Dissolve 10 mmol of furoic acid and 10 mmol of cesium carbonate in 5 mL of water. After drying the mixed solution, grind it into powder. Load the powder into a quartz boat, place it in a tubular furnace, first introduce N2 to dry for 2 h, and then introduce CO2 at a flow rate of 40 mL / min. React at 290 °C for 18 h. The conversion rate of furoic acid measured by HPLC is 84.1%, and the yield of FDCA is 53.4%.

[0144] Example 9 Preparation of FDCA using 1 mmol of furfural and 1 mmol of furoic acid as the raw materials

[0145] 9.1 Oxidation reaction: Preparation of furoic acid from furfural

[0146] (1) Add 1 mmol of furfural, 1.5 mmol of cesium carbonate, and 0.05 g of cobalt single-atom catalyst into 10 mL of water;

[0147] (2) The reaction conditions are: oxygen at 1 atm, reaction temperature of 65 °C, and reaction time of 11 h.

[0148] 9.2 Carboxylation reaction: Preparation of FDCA from furoic acid

[0149] 1) Dissolve 1 mmol of furoic acid and 1.5 mmol of cesium carbonate in 5 mL of water to obtain a mixed solution;

[0150] 2) Dry the above mixed solution and grind it into powder. Load the powder into a quartz boat, place it in a tube furnace, and introduce CO2 at a flow rate of 50 mL / min. React at 260 °C for 18 h.

[0151] 9.3 Results

[0152] Through oxidation and carboxylation reactions, 2,5-furandicarboxylic acid (FDCA) was prepared. Among them, the amount of furfural was 1 mmol and the amount of furoic acid was 1 mmol. Under this method, the conversion rate of furfural was 90.5%, the selectivity of furoic acid was 99.7%, the yield of FDCA was 77.3%, and the purity was 99%.

[0153] Example 10 Preparation of FDCA using 30 mmol of furfural and 30 mmol of furoic acid as raw materials

[0154] 10.1 Oxidation reaction: Preparation of furoic acid from furfural

[0155] (1) Add 30 mmol of furfural, 45 mmol of cesium carbonate, and 2.4 g of cobalt single-atom catalyst to 300 mL of water;

[0156] (2) The reaction conditions are: oxygen at 1 atm, reaction temperature of 65 °C, and reaction time of 11 h.

[0157] 10.2 Carboxylation reaction: Preparation of FDCA from furoic acid

[0158] 1) Dissolve 30 mmol of furoic acid and 45 mmol of cesium carbonate in 150 mL of water to obtain a mixed solution;

[0159] 2) Dry the above mixed solution and grind it into powder. Load the powder into a quartz boat, place it in a tube furnace, and introduce CO2 at a flow rate of 50 mL / min. React at 260 °C for 18 h.

[0160] 10.3 Results

[0161] Through oxidation and carboxylation reactions, 2,5-furandicarboxylic acid (FDCA) was prepared. Among them, the amount of furfural was 30 mmol and the amount of furoic acid was 30 mmol. Under this method, the conversion rate of furfural was 90.1%, the selectivity of furoic acid was 95.0%, the yield of FDCA was 76.5%, and the purity was 99%.

[0162] Detection of the final product FDCA in Example 11

[0163] The final product FDCA obtained from the reaction was detected by NMR, FTIR, and HPLC respectively (as Figure 4 shown).

[0164] In the 13 C-NMR spectrum (a), peaks at 166.29 ppm, 150.14 ppm, and 115.81 ppm corresponding to the carboxyl C, furan ring C2, and C3 of FDCA were observed respectively; in the 1 H-NMR spectrum (b), only one type of H peak at 6.87 ppm, corresponding to the H on the C3 and C4 positions of the furan ring of FDCA, was observed. From the FTIR spectrum (c), stretching vibration peaks and bending vibration peaks of the C-H bond on the furan ring in FDCA, stretching vibration absorption peaks of the carboxyl C-O bond, stretching vibration peaks of the C═C bond in the furan ring, absorption peaks of the carboxyl C═O bond, and absorption peaks of the carboxyl O-H bond were detected.

[0165] The above results prove that during the calcination process, Cs2CO3 catalyzed the carboxylation reaction of furoic acid with CO2, and only 2,5-FDCA was produced, without the formation of 2,4-FDCA or 2,3-FDCA by-products. The results of the HPLC chart (d) show that the purity of the FDCA product is very high, containing only a very small amount of unreacted furoic acid.

[0166] Example 12 Recycling of the metal cobalt single-atom catalyst

[0167] After furfural was oxidized to furoic acid, the catalyst was recovered by filtration, washed thoroughly with deionized water, and activated by drying at 500 °C for 1 h under argon protection. After the activated catalyst was recycled 5 times, it still maintained a high catalytic activity, and the results are shown in Table 3.

[0168] Table 3 Recycling of the cobalt single-atom catalyst

[0169] Number of cycles Furfural conversion rate (%) Furoic acid selectivity (%) 1 100 96.9 2 99.5 95.7 3 99.4 94.8 4 99.4 93.9 5 99.2 92.5

[0170] In summary, FDCA was prepared by oxidation and carboxylation reactions. Among them, both furfural and furoic acid were 1 mmol, and the molar ratio of furfural to cesium carbonate was 1:1.5. Under this method, the conversion rate of furfural was 90.5%, the selectivity of furoic acid was 99.7%, the yield of FDCA was 77.3%, and the purity was 99%. The catalyst was reused in 5 batches with unchanged activity, and the FDCA prepared in this application had a high purity.

Claims

1. A method for preparing 2,5-furandicarboxylic acid, wherein the 2,5-furandicarboxylic acid is prepared by oxidation reaction and carboxylation reaction, wherein: The catalyst used in the oxidation reaction is a cobalt-based catalyst, and the preparation steps are as follows: S1. Oxidation reaction: The raw materials, catalyst, oxidant and base additive are mixed and added to a solvent, and reacted under a certain pressure and temperature. After the oxidation reaction is completed, the catalyst is filtered and recovered, and the filtrate is dried to obtain a reaction product; S2. Carboxylation reaction: The reaction product prepared in step S1 is placed in a tubular furnace, reacted for a period of time under the reaction atmosphere and reaction temperature, and cooled after the carboxylation reaction to obtain FDCA.

2. An application of a cobalt-based catalyst in the preparation of furoic acid. The method for preparing furoic acid is an oxidation reaction, and the specific steps are as follows: raw materials, catalysts, oxidants and alkaline additives are mixed and added to a solvent, reacted under a certain pressure and temperature, after the oxidation reaction is completed, the catalyst is filtered and recovered, and the filtrate is dried to obtain a reaction product, which is furoic acid.

3. Use of a cobalt-based catalyst in the preparation of 2,5-furandicarboxylic acid, wherein the 2,5-furandicarboxylic acid is prepared by oxidation reaction and carboxylation reaction, wherein: The catalyst used in the oxidation reaction is a cobalt-based catalyst, and the preparation steps are as follows: S1. Oxidation reaction: The raw materials, catalyst, oxidant and base additive are mixed and added to a solvent, and reacted under a certain pressure and temperature. After the oxidation reaction is completed, the catalyst is filtered and recovered, and the filtrate is dried to obtain a reaction product; S2. Carboxylation reaction: The reaction product prepared in step S1 is placed in a tubular furnace, reacted for a period of time under the reaction atmosphere and reaction temperature, and cooled after the carboxylation reaction to obtain FDCA.

4. The raw material in step S1 according to any one of claims 1 to 3 is furfural, and the furfural includes hydroxyl-free furfural compounds and hydroxyl-containing furfural compounds.

5. The cobalt-based catalyst according to any one of claims 1 to 3, selected from one or more of nitrogen-doped carbon-supported metal cobalt single atoms, doped carbon-supported metal cobalt nanoclusters and / or nitrogen-doped carbon-supported metal cobalt nanoparticles, preferably a nitrogen-doped carbon-supported transition metal cobalt single atom catalyst.

6. The molar ratio of the raw material to the cobalt-based catalyst as claimed in any one of claims 1 to 3 is: 0.25-30: 0.005-1.5 mmol; preferably 1-10: 0.03-0.3 mmol.

7. The oxidant according to any one of claims 1 to 3 is selected from one or more of molecular oxygen, H2O2, N2, air and / or a mixed gas containing oxygen, preferably molecular oxygen.

8. The alkaline additive in step S1 of any one of claims 1 to 3 is selected from one or more of cesium carbonate, potassium carbonate, sodium carbonate and mixtures thereof, preferably cesium carbonate; the molar ratio of the raw material to the alkaline additive in step S1 is: 0.25-30:1.0-45 mmol; preferably 1-10:1.5-30 mmol.

9. In step S1 according to any one of claims 1 to 3, the oxygen pressure is 0.1 to 80 bar, preferably 1 to 40 bar; the furfural oxidation reaction temperature is 30 to 150° C., preferably 50 to 100° C.; the furfural oxidation reaction time is 1 to 6 hours, preferably 2 to 4 hours.

10. The carboxylation reaction temperature in step S2 according to any one of claims 1 to 3 is 150 to 350°C, preferably 180 to 320°C, and more preferably 200 to 290°C; the carboxylation reaction time is 6 to 48 hours, preferably 11 to 18 hours, and more preferably 12 to 15 hours.

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