Preparation of Co / NC catalyst and method for catalytically oxidizing furan aldehyde alcohol compound by using Co / NC catalyst

Abstract

The invention relates to the technical field of catalysts, and particularly discloses preparation of a Co / NC catalyst and a method for catalytically oxidizing a furan aldehyde alcohol compound by using the Co / NC catalyst. The preparation method comprises the following steps: mixing a nitrogen source compound, cobalt nitrate, a carbon source compound and water, heating, stirring, drying, calcining at a certain temperature under a nitrogen condition to obtain the double-atom dispersed Co / NC catalyst, and continuously introducing oxygen at normal pressure in combination with a water solvent and alkali to obtain the double-atom dispersed Co / NC catalyst. According to the method, the effect of efficiently catalyzing and oxidizing the high-concentration biomass-based furan aldehyde alcohol compound is achieved. By means of the catalyst, a simpler and milder oxidation reaction system for catalyzing the biomass-based furan aldehyde alcohol compound can be constructed, efficient oxidation of a high-concentration substrate, especially efficient catalytic oxidation under a complex mixed substrate, can be realized in a water solvent environment under the condition that oxygen is continuously introduced under pressurization or normal pressure, and the catalyst has a wide application prospect. The catalyst and the catalytic reaction system have good industrial application prospects.

Description

Technical Field

[0001] The invention belongs to the field of catalysts, and in particular relates to a Co / NC catalyst, a preparation method and a method for catalytically oxidizing furan aldehyde alcohol compounds. Background Art

[0002] The development of biomass-based chemicals and materials meets the country's major needs for building a green, sustainable, low-carbon chemical industry and a circular economy system. Carboxylic acids, the products of biomass-based aldol oxidation, are an important class of biomass-based chemicals. In particular, biomass-based 2,5-furandicarboxylic acid (FDCA) has a chemical structure and properties similar to petroleum-based terephthalic acid (TPA). Polyethylene 2,5-furandicarboxylate (PEF) synthesized from FDCA and ethylene glycol has better gas barrier properties and biodegradability than PET, making PEF an even more ideal material than PET in packaging and other fields. Based on this, FDCA is considered to be one of the most ideal biomass-based alternatives to TPA, and has received great attention from academia and industry at home and abroad in recent years.

[0003] Although HMF can obtain high yield (95-99%) of FDCA in both precious metal (such as gold, platinum, palladium and ruthenium) and non-precious metal (such as manganese, cobalt and cerium) based catalytic systems (ACS Catal. 2015, 5, 6529 –6544; J. Ind. Eng. Chem. 2019, 77, 209 – 214; Ind. Eng. Chem. Res. 2020, 59, 4895–4904), most studies in the prior art can only oxidize HMF in organic solvents, and under organic solvent conditions, it is difficult to separate and purify the oxidized FDCA.

[0004] Patent CN 113198512 A mixes and dissolves dicyandiamide, cobalt nitrate hexahydrate and water, and then drops formaldehyde, mixes and stirs at 105°C to remove moisture, grinds the solid obtained after drying into powder, and then calcines under nitrogen conditions to obtain a Co-NC catalyst. Similarly, this catalyst needs to oxidize 5-hydroxymethylfurfural under oxygen pressure and organic solvent conditions to obtain FDCA, and the yield is only 29.1%. However, the use of organic solvents makes the reaction system environmentally unfriendly and brings difficulties to the separation / purification of subsequent products. The current catalyst can only catalyze the efficient oxidation of refined and purified 5-hydroxymethylfurfural to synthesize FDCA. Unreacted byproducts such as sugars, humus and levulinic acid will cause significant deactivation of the catalyst. For example, Au / ZrO 2The yield of FDCA from the catalytic oxidation of impure crude 5-hydroxymethylfurfural (with a concentration of only 0.06 mol / L, or 0.76 wt%) is only 74% (125 °C, 30 bar air, 5 h) (ACS Sustainable Chem. Eng. 2020, 8, 11512−11521). And because 5-hydroxymethylfurfural has a high boiling point and active chemical properties, its separation and purification requires high energy consumption and large losses, which ultimately results in very high costs for the separation and purification of 5-hydroxymethylfurfural. Therefore, there is an urgent need to develop and design an efficient oxidation catalyst that can tolerate high concentrations of crude 5-hydroxymethylfurfural in an aqueous system, which will greatly help reduce the cost of synthesizing FDCA and promote the industrial production of FDCA. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention proposes a method for efficiently catalytically oxidizing a furan aldehyde alcohol compound reaction substrate containing impurities such as humus and levulinic acid in an aqueous phase and an alkali. First, the first aspect of the present invention provides a method for preparing a Co / NC catalyst, comprising: S1: Dissolve dicyandiamide, water and cobalt salt, add formaldehyde and mix well; S2: remove water, dry and grind into powder, and calcine under inert gas atmosphere; In some specific embodiments of the first aspect of the present invention, the input volume ratio of formaldehyde and water in step S1 is (1-4):15, preferably 2.2:15.

[0006] In some specific embodiments of the first aspect of the present invention, the input mass ratio of dicyandiamide to water in step S1 is (2-4):15, preferably 2.5:15.

[0007] In some specific embodiments of the first aspect of the present invention, the mass ratio of cobalt nitrate hexahydrate to water in step S1 is (0.014-0.015):15.

[0008] In some specific embodiments of the first aspect of the present invention, the stirring temperature of step S1 is 100-110°C, preferably 105°C.

[0009] In some specific embodiments of the first aspect of the present invention, in the step S2, the inert gas atmosphere is a nitrogen atmosphere, an argon atmosphere, or a mixture thereof.

[0010] In some specific embodiments of the first aspect of the present invention, the calcination temperature in the step S2 is 500-1000°C, preferably 900°C.

[0011] The second aspect of the present invention provides a Co / NC catalyst prepared by the method described in the first aspect.

[0012] In some specific embodiments of the second aspect of the present invention, the content of Co in the catalyst is 1.0-1.1 wt%, the content of N is 7-8 wt%, and the content of C is 86-89 wt%.

[0013] A third aspect of the present invention provides a method for catalytic oxidation of furanaldol compounds, characterized in that it comprises: Step 1: mixing the furan aldehyde alcohol compound with the Co / NC catalyst described in the second aspect, water, and a base to obtain a reaction system; Step 2: Under atmospheric pressure, continuously introduce 8-12 mL / min of oxygen flow into the reaction system to oxidize the furanaldol compounds at 30-60° C. to obtain oxidation products. In some specific embodiments of the third aspect of the present invention, the feed mass ratio of the furan aldehyde alcohol compound to the Co / NC catalyst in step 1 is (2-4):9, preferably 1:3.

[0014] In some specific embodiments of the third aspect of the present invention, the feed mass ratio of the base to the Co / NC catalyst is (2-3):9, preferably 5.0:18.

[0015] In some specific embodiments of the third aspect of the present invention, the mass ratio of water to alkali is (4-6):0.05.

[0016] In some specific embodiments of the third aspect of the present invention, the furan aldehyde compound in step 1 is selected from furfural, and the oxidation product in step 2 is furoic acid. or, The furan aldehyde alcohol compound in step 1 is selected from furfuryl alcohol, and the oxidation product in step 2 is furoic acid. or, The furan aldehyde alcohol compound in step 1 is selected from 5-methylfurfural, and the oxidation product in step 2 is 5-methylfuronic acid. or, The furan aldehyde alcohol compound in step 1 is selected from 5-methylfurfuryl alcohol, and the oxidation product in step 2 is 5-methylfurfuric acid. or, The furan aldehyde compound in step 1 is selected from 2,5-furan dimethanol, and the oxidation product in step 2 is 2,5-furandicarboxylic acid. or, The furan aldehyde alcohol compound in step 1 is selected from 5-hydroxymethyl furoic acid, and the oxidation product in step 2 is 2,5-furandicarboxylic acid. or, In step 1, the furan aldehyde alcohol compound is selected from 5-formyl furoic acid, and the oxidation product in step 2 is 2,5-furandicarboxylic acid.

[0017] The fourth aspect of the present invention provides a method for obtaining 2,5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural by batch feeding, characterized in that it comprises: Step a: 5-hydroxymethylfurfural, water, Co / NC catalyst and alkali are mixed to obtain a mixed system, and an oxygen flow is introduced under normal pressure; Step b: adding an equal amount of the furan aldehyde alcohol compound and the base in step a to the mixed system again and continuing the reaction for 1 to 3 hours while maintaining the oxygen flow; Step c: Repeat step b 8 to 12 times; Step d: After step c, the reaction is continued for 10 to 14 hours, and the oxygen flow is kept to obtain the oxidation product 2,5-furandicarboxylic acid.

[0018] In some specific embodiments of the fourth aspect of the present invention, the base in step a is sodium hydroxide.

[0019] In some specific embodiments of the fourth aspect of the present invention, the mass ratio of the furan aldehyde compound to water in step a is (0.05-0.07):5, preferably 0.06:5.

[0020] In some specific embodiments of the fourth aspect of the present invention, the molar ratio of the Co / NC catalyst to the base in step a is (1.6-2.0):0.5, preferably 0.18:0.05.

[0021] In some specific embodiments of the fourth aspect of the present invention, the reaction temperature of the step is 50-70° C., preferably 60° C. In some specific embodiments of the fourth aspect of the present invention, the oxygen flow rate in steps a-d is 8-12 mL / min, preferably 10 mL / min.

[0022] The fifth aspect of the present invention provides a method for catalytic oxidation of furan aldehyde alcohol compounds which is different from the fourth and third aspects, characterized in that it comprises: Fructose undergoes a dehydration reaction in a reaction system of a mixed phase of an inorganic salt, water, an inorganic acid and an organic solvent to obtain a product 5-hydroxymethylfurfural dispersed in an organic solvent; Separating water and organic solvent, evaporating the organic solvent to obtain crude product 5-hydroxymethylfurfural; The purity of the crude product 5-hydroxymethylfurfural is 50-90.wt%, and the crude product 5-hydroxymethylfurfural is directly used as the substrate 5-hydroxymethylfurfural in the reaction of step (I); Step (I): mixing the substrate 5-hydroxymethylfurfural with the catalyst according to claim 4, water and a base to obtain a reaction system; Step (II): Under oxygen atmosphere, pressurize to obtain 2,5-furandicarboxylic acid.

[0023] In some specific embodiments of the fifth aspect of the present invention, the pressure of the oxygen pressurization is 2.5~3.0MPa.

[0024] In some specific embodiments of the fifth aspect of the present invention, the mass fraction of 5-hydroxymethylfurfural in the reaction system is 1-10wt%.

[0025] In some specific embodiments of the fifth aspect of the present invention, the mass ratio of the Co / NC catalyst to water is 0.4:(2-3).

[0026] In some specific embodiments of the fifth aspect of the present invention, the mass ratio of the sodium hydroxide to the Co / NC catalyst is (2-4):4.

[0027] In some specific embodiments of the fifth aspect of the present invention, the oxidation in step (II) is carried out at 120-140°C, preferably at 130°C.

[0028] Beneficial Effects 1. Example 3 of the present invention provides a method for oxidizing pure 5-hydroxymethylfurfural to obtain 2,5-furandicarboxylic acid in an aqueous solvent and alkaline environment by continuously introducing oxygen at normal pressure (atmospheric pressure) with a specific cobalt loading amount and cobalt loading form. Compared with the prior art, this method can obtain a higher yield without pressurization.

[0029] 2. Example 8 of the present invention proposes a method for catalyzing a 5-hydroxymethylfurfural mixture of a complex mixed substrate (including by-product humus, levulinic acid and a small amount of residual solvent). The catalytic ability of the Co / NC catalyst in a complex substrate environment is significantly increased by changing the solvent from alcohol to water, the cobalt loading amount is 1%, and the input of alkali is increased, pressurized oxygen, etc., and the front-stage refining step of 5-hydroxymethylfurfural can be omitted, and the front-stage reaction mixture is directly catalyzed. This method overcomes the interference of impurities in the front-stage step and obtains a higher 2,5-furandicarboxylic acid, which can significantly save costs in production, reduce safety costs, and reduce safety hazards.

[0030] 3. Example 4 of the present invention also improves the intermittent feeding process of the process for preparing 2,5-furandicarboxylic acid from 5-hydroxymethylfurfural. By multiple feedings, the yield of 2,5-furandicarboxylic acid per unit time is significantly increased. Specifically, under the catalytic action of the catalyst, by intermittent feeding, efficient oxidation of refined and purified HMF with a reaction substrate mass concentration higher than 10% can be achieved, and the FDCA yield can still reach more than 95%.

[0031] 3. In the method of the present invention, when the mass concentration of the reaction substrate is 1%, the product generation rate of the prepared Co / NC catalyst for catalytic oxidation of HMF to synthesize FDCA is as high as 208 molFDCA mol Co -1 h -1 (5 bar O 2 , 120 ℃, NaOH), which is 1-2 orders of magnitude higher than other cobalt-based catalysts. It is particularly noteworthy that the Co / NC catalyst still exhibits excellent catalytic activity in a high-concentration HMF system. For example, when the reaction substrate mass concentration is 10% refined HMF, the FDCA yield can reach more than 86% in just 30 minutes (5 bar O 2 , 120 ℃, NaOH); Under the same reaction conditions, when the reaction substrate mass concentration is about 10% of the unrefined HMF crude product, it only takes 1 hour to react, and the FDCA yield can still reach more than 86%. It can be seen that the catalyst of the present invention can realize the preparation of FDCA by efficient conversion without purification of HMF crude product and in the case of high impurity content, which is currently impossible to achieve with other catalysts. The efficient oxidation of high-concentration HMF crude product will greatly improve the FDCA synthesis efficiency, and realize another green synthesis route of FDCA, that is, FDCA can be efficiently prepared by continuous two-step simple chemical reactions of raw material fructose, which reduces production costs and has broad industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The pathway for preparing FDCA by oxidation of HMF is shown; Figure 2 High-resolution transmission electron microscopy images of (a) Co / NC-900-10 and (b) Co / NC-900-11 catalysts are shown; Figure 3 Transmission electron microscopy image (a), elemental mapping (b), large-angle annular dark-field scanning transmission electron microscopy image (c), distance between diatomic sites (d), and synchrotron radiation fitting results (ef) of Co(1) / NC-900-1. Figure 4 The following is a comparison of the photographs before and after the oxidation of the crude unrefined HMF product catalyzed by Co(1) / NC-900-1 in Example 8. DETAILED DESCRIPTION

[0033] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0034] In the examples and comparative examples (Co / NC-yz catalyst, z represents the catalyst classification number; y represents the calcination temperature, y=500~1000°C).

[0035] Embodiment 1: Dicyandiamide, cobalt nitrate hexahydrate, and 15.0 ml of water were mixed and dissolved in a 50 ml beaker, and then 2.2 ml of formaldehyde was added dropwise, mixed evenly at 105 °C and the water was removed. The solid obtained after drying was ground into powder, and then calcined at 500-1000 °C for 2 h under nitrogen to obtain catalysts of groups 1-11. The amounts of dicyandiamide, cobalt nitrate hexahydrate, and formaldehyde were referred to Table 1. The contents of the three elements Co / N / C in the catalyst were determined by inductively coupled plasma-mass spectrometry, and the results of the Co / N / C content (wt%) (based on the total amount of catalyst) are shown in Table 1.

[0036] Table 1 Embodiment 2: 1.78-2.5 g nitrogen source, 0.0140-0.0150 g cobalt nitrate hexahydrate, and 15.0 ml water were mixed and dissolved in a 50 ml beaker, and then 2.2 ml aldehyde was added dropwise, mixed evenly at 105 °C and the water was removed. The solid obtained after drying was ground into powder, and then calcined at 900 °C for 2 h under nitrogen to obtain group 12-14 catalysts. The contents of the three elements Co / N / C in the catalysts were determined by inductively coupled plasma-mass spectrometry. The relative contents of Co / N / C (based on the total amount of catalyst) are shown in Table 2: Table 2 Example 3 (catalytic oxidation using atmospheric pressure oxygen flow): 0.06 g of 5-hydroxymethylfurfural and 5.0 g of deionized water were added to a double-necked flask (25 ml) equipped with a condenser, and then 0.18 g of the catalysts in Table 1 and Table 2 and 0.05 g of sodium hydroxide were added respectively. The mixture was placed in a 30°C oil bath and a 10 mL / min oxygen flow was introduced and maintained for 4 h before the reaction was terminated. Samples were taken to detect the yield of 2,5-furandicarboxylic acid, and the results were shown in Table 3: Table 3 Test results of groups 1 to 14 Groups 3 to 7 evaluated the effect of carbonization temperature on the catalytic activity of Co / NC catalysts. When the carbonization temperature was increased from 500 °C to 800 °C, the obtained catalysts were used in the catalytic experiment of HMF, and the HMF conversion rate increased from 13.4% at 500 °C to 96.8% at 800 °C (Table 3, Groups 3 to 6). When the carbonization temperature was further increased to 900 °C and 1000 °C, the HMF conversion rate remained almost unchanged (Table 3, Groups 3 and 7). It is worth noting that the FDCA yield and carbonization temperature in the catalytic experiment of Co / NC catalyst show a "volcano-type" relationship, especially when the carbonization temperature is 900 °C, the FDCA yield reaches the maximum value (99.4%, Table 3, Group 1), indicating that at 900 °C, the carbon in the organic raw material has been fully carbonized to form a carbon carrier, Co mainly exists in the form of diatoms, N is doped into the graphite structure and coordinates with Co to anchor Co, which is beneficial to the dispersion of Co metal and its catalytic effect. When the temperature is further increased to 1000 °C, the N element content is relatively reduced, which will cause Co metal agglomeration and affect its efficiency in catalyzing the conversion of HMF to FDCA.

[0037] In addition, the effect of metal Co loading on the catalytic activity of Co / NC catalysts was further evaluated in groups 8 to 11. The Co loading was calculated as follows: after calcination, the mass fraction of metal Co in the catalyst was measured by inductively coupled plasma emission spectrometry (IPC-OES). The metal Co loading of group 8 was 0.5 wt%. When catalyzing HMF, the HMF conversion rate was 95.5%, while FFCA and FDCA were only 35.6% and 53.4%, respectively (Table 3, group 8).

[0038] When the metal Co loading was further increased to 1.0 and 1.1 wt%, HMF was almost completely converted to FDCA, as shown in Table 3, Groups 1 and 2. It is worth noting that when the metal Co loading was further increased (Groups 9-11, 5.0-15.0 wt%), the HMF conversion rate and FDCA yield decreased, and the intermediate product FFCA was mainly generated (Table 3, Groups 9-11).

[0039] In contrast, smaller metallic cobalt particles with a size of 16–20 nm were obtained on the Co / NC-900-10 (Co loading 10 wt%) catalyst. Figure 2 a), while the metal cobalt particles obtained on Co / NC-900-11 (Co loading 15%) catalyst have a size of 20-30 nm ( Figure 2 b). In addition, high-resolution transmission electron microscopy images of the Co / NC-900-10 and Co / NC-900-11 catalysts both showed lattice spacings of 0.34 nm and 0.205 nm, which were attributed to the (002) crystal plane of graphite and the (111) crystal plane of metallic cobalt, respectively ( Figure 2The above results indicate that the agglomeration occurs under high Co loading conditions to form nanoparticles.

[0040] However, transmission electron microscopy analysis revealed that no cobalt nanoparticles were observed in the Co / NC-900-1 (Co loading 1%) sample. Figure 3 a), while the elemental distribution map confirms the uniform distribution of cobalt (Co), nitrogen (N) and carbon (C) elements ( Figure 3 b). Using spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy, dispersed single cobalt atoms (red circles) and diatomic cobalt pairs (yellow boxes) were observed, among which diatomic pairs were the main component of cobalt ( Figure 3 cd) dispersed on carbon. By measuring the distance between the diatomic cobalt pairs, it was found that the atomic distance between the two atoms was between 3.02-3.10 Å ( Figure 3 d).

[0041] The chemical state and coordination environment of cobalt (Co) in Co / NC-900-1 were studied by X-ray absorption near-edge structure spectroscopy. Figure 3 e). Standard cobalt materials (Co foil, CoPc (cobalt phthalocyanine), CoO, Co 2 O 3 ) as a reference, the near-edge absorption energy of the cobalt site in Co / NC-900-1 is between CoO and CoPc, indicating that the electronic state of cobalt in Co / NC-900-3 is closer to Co 2+ , indicating that Co 2+ It exists in the form of divalent cobalt. In addition, the Fourier transform k of Co 3 The peak at 1.3 Å in the weighted extended X-ray absorption fine structure spectrum is attributed to the first coordination shell of Co-N / O ( Figure 3 f). It is worth noting that the Co-Co scattering peak at 2.2 Å was not detected in the EXAFS spectrum of Co / NC-900-3 ( Figure 3 f), further proving the atomic-level dispersion characteristics of cobalt, it can be seen that the preparation method of nitrogen-carbon doped cobalt catalyst involved in the present invention is very advanced.

[0042] By comparing Groups 1 and 12-14 in Tables 2 and 3, it can be seen that among the combinations of nitrogen sources and carbon sources, dicyandiamide, as a compound with an extremely high nitrogen content, can retain more nitrogen after high-temperature calcination, which is beneficial for the coordination and anchoring of metal atoms on N atoms to form highly dispersed metal atoms. Compared with other aldehydes, formaldehyde is used as a carbon source in combination with dicyandiamide to form a complex with Co, which is more conducive to the preparation of an efficient Co catalyst.

[0043] Comparative Example 1: 0.06 g of 5-hydroxymethylfurfural and solvent were added to a double-necked flask (25 ml) equipped with a condenser, and then 0.18 g of Co / NC-900-1 catalyst and base were added respectively. The above mixture was placed in an oil bath and a 10 mL / min oxygen flow was introduced and maintained for 4 h to terminate the reaction. Samples were taken to detect the yield of 2,5-furandicarboxylic acid, as shown in Table 4: Table 4 Test results of groups 3, 15-18 Example 4 (batch feeding to increase unit time yield): Step 1 (initial charge): 0.06 g of 5-hydroxymethylfurfural and 5.0 g of deionized water were added to a two-necked flask (25 ml) equipped with a condenser, and then 0.18 g of Co / NC-900-1 catalyst and 0.05 g of sodium hydroxide were added. The mixture was placed in an oil bath at 60 °C and an oxygen flow of 10 mL / min was introduced and maintained for 2 h.

[0044] Step 2 (interval addition): add 0.06 g of 5-hydroxymethylfurfural and 0.05 g of sodium hydroxide to the double-necked flask and continue to react for 2 h, add 0.06 g of 5-hydroxymethylfurfural once every 2 h, add 10 times in succession, and then continue to react for 12 h before ending the reaction, i.e., the total reaction time is 32 h. During this period, an oxygen flow of 10 mL / min is maintained. The yield of 2,5-furandicarboxylic acid is 95.2% after sampling and detection.

[0045] In continuous production, the amount of 2,5-furandicarboxylic acid obtained by the feeding method of Example 4 is significantly better than that of the feeding method of Group 18 of Comparative Example 1.

[0046] The feeding method of Group 18 in Comparative Example 1 has a higher yield when catalyzing 1% concentration of 5-hydroxymethylfurfural. However, when the single feeding method of Group 18 is adopted and the concentration of the substrate 5-hydroxymethylfurfural is increased to 10%, the yield of the target product 2,5-furandicarboxylic acid will be significantly reduced.

[0047] In Example 4, by means of intermittent feeding, efficient oxidation of refined and purified 5-hydroxymethylfurfural with a reaction substrate mass concentration higher than 10% can be achieved, and the yield of 2,5-furandicarboxylic acid can reach more than 95%.

[0048] Comparative Example 2: Comparative Example 2 is the same as step 1 of Example 4. The difference between Comparative Example 2 and Example 4 is that in the interval addition of step 2, only 0.06 g of 5-hydroxymethylfurfural is added each time without adding sodium hydroxide, and the yield of 2,5-furandicarboxylic acid is 31.2% by sampling and detection.

[0049] Comparative Example 3 The difference between Comparative Example 3 and Example 4 is that 5.0 ml of methanol is used instead of 5.0 g of deionized water in step 1. Step 1 is as follows: 0.06 g of 5-hydroxymethylfurfural and 5.0 ml of methanol are added to a double-necked flask (25 ml) equipped with a condenser, and then 0.18 g of Co / NC-900-1 catalyst and 0.05 g of sodium hydroxide are added, and the mixture is placed in an oil bath at 60° C. and an oxygen flow of 10 mL / min is introduced and maintained for 2 h.

[0050] Step 2 is the same as step 3. The yield of 2,5-furandicarboxylic acid detected by sampling is 18.7%. When adding in batches but using methanol as the input solvent, the yield of 2,5-furandicarboxylic acid is greatly reduced compared with the prior art and Example 4.

[0051] Example 5 (Oxidation Effects of Various Furan Aldehyde Substrates): Step 1: Into a two-necked flask (25 ml) equipped with a condenser, 0.06 g of the substrate described in Table 5 and 5.0 g of deionized water were added, and then 0.18 g of Co / NC-900-1 catalyst and 0.050 g of sodium hydroxide were added. The mixture was placed in an oil bath at 60 °C and an oxygen flow of 10 mL / min was introduced and maintained for 2 h.

[0052] Step 2: Add 0.06 g of the substrate described in Table 5 and 0.05 g of sodium hydroxide to the double-necked flask and continue the reaction for 2 h. Add material once every 2 h, add material continuously for 10 times, and then continue the reaction for 12 h. Then terminate the reaction and take samples to detect the selectivity of the product and the substrate conversion rate.

[0053] Table 5 Test results of groups 19 to 25 The results of groups 23 to 29 showed that when alcohols or aldehydes such as furfuryl alcohol, furfural, 5-methylfurfural and 5-methylfurfuryl alcohol were used as reaction substrates, product selectivities as high as 89%-99% could be obtained in the Co / NC catalytic reaction.

[0054] Example 6 (catalysis of pure HMF at a concentration of about 1 wt%): After mixing 0.03 g of 5-hydroxymethylfurfural, 3.0 g of deionized water, 0.05 g of Co / NC-900-1 catalyst and 0.03 g of sodium hydroxide, the resulting mixture was added into a 25 ml reactor. The reaction was terminated after stirring in an oil bath at 0.5 MPa oxygen and 120 °C for 8 min. Samples were taken to detect the substrate conversion rate and product yield. The test results are listed in Table 6 Group 26.

[0055] Example 7 (catalyzing pure HMF at a concentration of about 9.1 wt%): After mixing 0.30 g of 5-hydroxymethylfurfural, 2.7 g of deionized water, 0.20 g of Co / NC-900-1 catalyst and 0.30 g of sodium hydroxide, the resulting mixture was added into a 25 ml reactor and stirred in an oil bath at 2.0 MPa of oxygen and 120 °C for 0.5 h before the reaction was terminated. Samples were taken to detect the substrate conversion rate and product yield. The test results are listed in Table 6 Group 27.

[0056] Example 8 (Catalytic oxidation of mixed substrates): 30g fructose and 18g NaCl were dissolved in 90g water and poured into a 1L Hastelloy reactor, and then 0.3g sulfuric acid and 500g tetrahydrofuran were added. The reactor was sealed and heated to 150℃ for 1.5h and then cooled to terminate the reaction. The aqueous phase and the tetrahydrofuran organic phase were separated, and the organic phase contained 5-hydroxymethylfurfural, a fructose dehydration product. The tetrahydrofuran organic phase containing 5-hydroxymethylfurfural was concentrated and recovered by a rotary evaporator under vacuum conditions and 40℃ to recover the tetrahydrofuran solvent, and 19.7g of 5-hydroxymethylfurfural concentrated solution was obtained, of which the concentration of 5-hydroxymethylfurfural was 61 wt.%, and the rest was by-product humus, levulinic acid and a small amount of residual solvent.

[0057] 0.5 g of the above mixture (unpurified HMF crude product, the mixture is a crude product with a 5-hydroxymethylfurfural concentration of 61 wt.%) was mixed with 0.5 g of deionized water, 0.40 g of Co / NC-900-1 catalyst and 0.30 g of sodium hydroxide, and the resulting mixture was added into a 25 ml reactor. The reaction was terminated after stirring in an oil bath at 3.0 MPa oxygen and 130 °C for 1 h. Samples were taken to detect the substrate conversion rate and product yield. The test results are listed in Table 6 Group 28.

[0058] Table 6 Test results of Examples 6-8 When sodium hydroxide was used as a reaction additive, the catalysis of pure HMF at a concentration of about 1 wt% took only 8 min (Table 6, group 26).

[0059] Even when catalyzing pure HMF with a concentration of about 9.1 wt% (Table 6, group 27) or crude unpurified HMF with a concentration of about 9.6 wt% (Table 6, group 28), the FDCA yields can reach 92% and 86%, respectively. On the other hand, the unpurified HMF solution is black and opaque, but after catalytic oxidation by Co / NC-900-1, the reaction solution becomes clear and transparent, which is conducive to the subsequent separation and purification of the final product FDCA ( Figure 4 ). It can be seen that the product generation rate of the prepared Co / NC catalyst for catalytic oxidation of HMF to synthesize FDCA is as high as 208 mol FDCA molCo -1 h -1 (5 bar O 2 , 120 ℃, NaOH, Table 6, Group 26), which is 1-2 orders of magnitude higher than other cobalt-based catalysts. It can also catalyze high-concentration pure HMF or high-concentration HMF crude products, and can eliminate black impurities in HMF crude products ( Figure 4 ). It can be seen that the catalyst synthesized in the present invention has an important promoting significance for the large-scale production of FDCA, and solves the problem that the current non-precious metal catalyst cannot catalyze the high-concentration HMF of more than 10 wt% to prepare FDCA by efficient selective oxidation. At the same time, it can also greatly improve the FDCA synthesis efficiency and reduce the production cost.

[0060] Comparative Example 4: The difference between Comparative Example 4 and Group 26 in Example 6 is that the solvent and base are charged differently.

[0061] Table 7 Test results of replacing group 26 In Table 7, “ / ” represents no investment; Comparative Example 5 (replacement experiment of catalytic oxidation of mixed substrate): The difference between Comparative Example 5 and Group 28 in Example 6 is that the solvent and base are charged differently.

[0062] Table 8 Test results of replacing group 28 In Table 8, “ / ” represents no investment; The catalytic conditions of Comparative Example 4 Group 31 are that sodium hydroxide is added but the solvent is methanol, the catalytic conditions of Comparative Example 4 Group 32 are that the solvent is water but no sodium hydroxide is added, and the catalytic conditions of Comparative Example 4 Group 33 are that the solvent is methanol but no sodium hydroxide is added.

[0063] Comparative Example 6: The present catalytic system is compared with the prior art catalytic system, and the results are shown in Table 9: Table 9 Comparison of this catalytic system with other catalytic systems Note: ① a Catalyst dosage refers to the molar ratio of precious metal to HMF; b The catalyst dosage represents the mass ratio of catalyst to HMF; c HMF concentration; d The generation rate refers to the molar amount of target product obtained per mole of metal per hour [mol FDCA molmetal -1 h -1 ]; e The generation rate refers to the amount of target product obtained per unit metal mass per hour [mmol FDCA g catalyst -1 h -1 ]; 5-hydroxymethylfurfural (HMF); 2,5-furandicarboxylic acid (FDCA).

[0064] ②The above other catalytic systems are from the following references: [1] ChemSusChem 2022, 15, e202201333. [2] Appl. Catal., B 244 (2019) 965-973. [3] Green Chem. 21 (2019) 2923-2927. [4] ACS Sustainable Chem. Eng. 8 (2020) 4801-4808. [5] Angew.Chem. Int.Ed. 2021, 60,18103-18110. [6] ACS Catal. 2021, 11, 13, 7828-7844. [7] ACS Catal. 2023, 13, 11104-11116. [8] China-Chem 60 (2017) 950-957. [9] Green Chem.20, 3530-3541 (2018).

[10] ChemSusChem 8, 1206-1217 (2015).

[11] Nature 603, 271-275 (2022). It should be noted that, although the above embodiments have been described in this article, the patent protection scope of the present invention is not limited thereby. Therefore, based on the innovative concept of the present invention, changes and modifications made to the embodiments described herein, or equivalent structures or equivalent process changes made using the contents of the present invention specification and drawings, directly or indirectly applying the above technical solutions to other related technical fields, are all included in the patent protection scope of the present invention.

Claims

1. A method for preparing a Co / NC catalyst, comprising: S1: Mix dicyandiamide, water and cobalt salt, add formaldehyde and mix well; S2: Remove water, dry and grind into powder, and calcine under inert gas atmosphere.

2. The method for preparing the Co / NC catalyst according to claim 1, characterized in that: In the step S1, the input volume ratio of formaldehyde and water is (1-4):15, preferably 2.2:15, and / or, the input mass ratio of dicyandiamide and water in the step S1 is (2-4):15, preferably 2.5:15, and / or, the cobalt salt is cobalt nitrate hexahydrate, and the mass ratio of cobalt nitrate hexahydrate to water in the step S1 is (0.014-0.015):15, and / or, the stirring temperature in the step S1 is 100-110°C, preferably 105°C, and / or, in the step S2, the inert gas atmosphere is one of nitrogen atmosphere and argon atmosphere or a mixture thereof, and / or, the calcination temperature in the step S2 is 500-1000°C, preferably 900°C.

3. A Co / NC catalyst prepared by the method according to any one of claims 1 or 2.

4. The Co / NC catalyst according to claim 3, characterized in that The content of Co in the catalyst is 1.0-1.1 wt %, the content of N is 7-8 wt %, and the content of C is 86-89 wt %.

5. A method for catalytic oxidation of furan aldehyde alcohol compounds under normal pressure, characterized in that ,include: Step 1: mixing the furan aldehyde alcohol compound with the Co / NC catalyst according to any one of claims 3 or 4, water and a base to obtain a reaction system; Step 2: Under atmospheric pressure, continuously introducing an oxygen flow into the reaction system to oxidize the furan aldehyde alcohol compound at 30-60° C. to obtain an oxidation product; In step 1, the furan aldehyde alcohol compound is selected from furfural, and in step 2, the oxidation product is furoic acid. or, The furan aldehyde alcohol compound in step 1 is selected from furfuryl alcohol, and the oxidation product in step 2 is furoic acid. or, The furan aldehyde alcohol compound in step 1 is selected from 5-methylfurfural, and the oxidation product in step 2 is 5-methylfuronic acid. or, The furan aldehyde alcohol compound in step 1 is selected from 5-methylfurfuryl alcohol, and the oxidation product in step 2 is 5-methylfurfuric acid. or, The furan aldehyde compound in step 1 is selected from 2,5-furan dimethanol, and the oxidation product in step 2 is 2,5-furandicarboxylic acid. or, The furan aldehyde alcohol compound in step 1 is selected from 5-hydroxymethyl furoic acid, and the oxidation product in step 2 is 2,5-furandicarboxylic acid. or, In step 1, the furan aldehyde alcohol compound is selected from 5-formyl furoic acid, and the oxidation product in step 2 is 2,5-furandicarboxylic acid.

6. The method for catalytic oxidation of furanaldehyde compounds under normal pressure according to claim 5, characterized in that In step 1, the feeding mass ratio of the furan aldehyde alcohol compound to the Co / NC catalyst is (2-4):9, preferably 1:3, and / or, the feeding mass ratio of the base to the Co / NC catalyst is (2-3):9, preferably 5.0:18, and / or, the feeding mass ratio of the water to the base is (4-6): 0.05, and / or, the flow rate of the oxygen flow in step 2 is 8-12 mL / min.

7. A method for obtaining 2,5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural by batch feeding, characterized in that: include: Step a: mixing 5-hydroxymethylfurfural, water, alkali, and the Co / NC catalyst according to any one of claims 3 or 4 to obtain a mixed system, and introducing an oxygen flow under normal pressure; Step b: adding an equal amount of the furan aldehyde alcohol compound and the base in step a to the mixed system again and continuing the reaction for 1 to 3 hours while maintaining the oxygen flow; Step c: Repeat step b 8 to 12 times; Step d: After step c, the reaction is continued for 10 to 14 hours while maintaining the flow of oxygen to obtain an oxidation product, 2,5-furandicarboxylic acid.

8. The method for obtaining 2,5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural by batch feeding according to claim 7, characterized in that: The base in step a is sodium hydroxide, and / or the feed mass ratio of 5-hydroxymethylfurfural and water in step a is (0.05-0.07):5, preferably 0.06:5, and / or the feed molar ratio of Co / NC catalyst and base in step a is (1.6-2.0):0.5, preferably 0.18:0.05, and / or the reaction temperature in the step is 50-70°C, preferably 60°C, and / or the oxygen flow rate in steps a-d is 8-12 mL / min, preferably 10 mL / min.

9. A method for catalytic oxidation of furan aldehyde alcohol compounds, characterized in that: include: Step (Ⅰ): mixing the substrate 5-hydroxymethylfurfural with the catalyst according to any one of claims 3 or 4, water and a base to obtain a reaction system; Step (II): Oxidation under oxygen atmosphere and pressure to obtain 2,5-furandicarboxylic acid.

10. The method according to claim 9, characterized in that: The following steps are also included: Fructose undergoes a dehydration reaction in a reaction system of a mixed phase of an inorganic salt, water, an inorganic acid and an organic solvent to obtain a product 5-hydroxymethylfurfural dispersed in an organic solvent; Separating water and organic solvent, evaporating the organic solvent to obtain crude product 5-hydroxymethylfurfural; The purity of the crude product 5-hydroxymethylfurfural is 50-90.wt%, and the crude product 5-hydroxymethylfurfural is directly used as the substrate 5-hydroxymethylfurfural in the reaction of step (I).

Images