A method for directly preparing 2,5-dimethylfuran by catalyzing 5-hydroxymethylfurfural in one step with high efficiency

Abstract

The invention discloses a method for directly preparing 2,5-dimethylfurans from a one-step process of 5-hydroxymethylfurfural with high efficiency, the method being to catalyze 5-hydroxymethylfurfural with supported ZrO2-Co / Al2O3 catalyst, and preparing 2,5-dimethylfurans in high yield in a step. The catalyst used in the present invention is a non-precious metal catalyst derived from hydrotalcite, which is first prepared by coprecipitation to prepare a layered hydroxide precursor, which is pyrolyzed in static air to obtain a mixed metal oxide, and then ZrO2-doped Co / Al2O3 is obtained after the mixed metal oxide is reduced in a hydrogen / argon mixed gas. The catalyst cost of the present invention is low, and the preparation method is simple, and it is possible to achieve the high yield preparation of 2,5-dimethylfurans from a one-step process of 5-hydroxymethylfurfural, with a maximum yield of 97.3%, and the catalyst remains stable after 5 cycles, while the lower boiling point of the solvent makes it easy to separate the product, simple to operate, safe, and has good industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of clean and green catalytic synthesis of high-value-added chemicals using biomass resources, and specifically relates to a method for directly preparing 2,5-dimethylfuran by catalyzing 5-hydroxymethylfurfural. Background Art

[0002] To achieve carbon neutrality sooner rather than later and address the fluctuating supply of expensive fossil fuels and the resulting environmental pollution from their consumption, scientists are searching for sustainable renewable energy sources, such as hydropower, wind power, biomass, and solar energy. Biomass is a key raw material for the production of next-generation liquid fuels and renewable chemicals. In recent years, the development of economically viable technologies for producing commodities and specialty chemicals from sustainable biomass has garnered significant attention due to its abundant reserves, low cost, and renewable nature.

[0003] Compared with traditional biomass fuels, 2,5-dimethylfuran has many obvious advantages, such as energy density far exceeding ethanol, easy solubility in gasoline, high octane number, strong explosion resistance, high boiling point, low volatility, insolubility in water and easy storage. Therefore, adding it to gasoline can greatly improve the combustion performance of gasoline. It is a renewable liquid fuel with broad application prospects.

[0004] In recent years, there have been several reports on the preparation of 2,5-dimethylfuran (2,5-DMF). The production of 2,5-DMF from biomass involves the following steps: First, the biomass undergoes a simple pretreatment to produce cellulose, hemicellulose, and lignin. The macromolecular lignin is then decomposed into monosaccharides, which are then subjected to an acid-catalyzed dehydration reaction to produce the biomass-based platform compound 5-hydroxymethylfurfural. 5-hydroxymethylfurfural is then selectively hydrodeoxygenated over a hydrogenation catalyst to yield 2,5-DMF. Dumesic et al. (Nature, 2007, 447(7147):982-985) first employed a Cu-Ru / C catalyst to hydrogenate the CO bond in 5-hydroxymethylfurfural to produce 2,5-DMF. The reaction was performed at 220°C and a hydrogen pressure of 0.68 MPa for 10 hours, achieving a 2,5-DMF yield exceeding 70%. Vlachos et al. (ChemCatChem, 2014, 6(3):848-856) used isopropanol as a solvent and a Ru / C catalyst with a 35:1 molecular ratio of 5-hydroxymethylfurfural to Ru. The reaction was carried out at 190°C and a nitrogen atmosphere of 2.04 MPa for 6 h, achieving a 72% yield of 2,5-dimethylfuran. Hou et al. (Fuel, 2016, 163:74-79) used graphene-supported Pt as a catalyst and reacted at 120°C and a hydrogen pressure of 3 MPa for 2 h, achieving complete conversion of 5-hydroxymethylfurfural and a 73.2% yield of 2,5-dimethylfuran. The catalysts used in these methods all exhibit low product yields and high reaction temperatures, which are not conducive to energy conservation, emission reduction, and large-scale application.

[0005] Hu et al. (Industrial & Engineering Chemistry Research, 2014, 53(8):3056-3064) used tetrahydrofuran as solvent, 5-hydroxymethylfurfural as reaction substrate, and Ru / C as catalyst. The reaction was carried out at 200°C and 2 MPa of hydrogen pressure for 2 h. The yield of 2,5-dimethylfuran reached 94.7%. Ru / C showed good stability and catalytic activity. After a simple regeneration process, Ru / C could be recycled at least 6 times. Peng et al. (Angewandte Chemie International Edition, 2021, 60(12):6807-6815) used nitrogen-doped mesoporous carbon (NC) supported on Pd as catalyst and formic acid as hydrogen donor solvent. Through the dual action of hydrogenation and hydrogen transfer reaction, a 97.1% yield of 2,5-dimethylfuran was obtained at 160°C and 0.5 MPa of hydrogen pressure. Although the catalysts used in these methods achieve extremely high 2,5-dimethylfuran yields, the complex catalyst preparation methods and the rarity of precious metals greatly limit their large-scale production and are not conducive to their industrial application. Summary of the Invention

[0006] The present invention aims to provide a method for directly preparing 2,5-dimethylfuran in one step by catalyzing 5-hydroxymethylfurfural with high efficiency. The method has a simple catalyst preparation method, low cost, high 5-hydroxymethylfurfural conversion rate and high 2,5-dimethylfuran yield.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a supported ZrO2-Co / Al2O3 catalyst, 5-hydroxymethylfurfural, tetrahydrofuran or 1,4-dioxane are placed in a stainless steel reactor, and the reaction is carried out at a constant temperature of 120-180°C and sealed with stirring for 4-6 hours under a 1.0-3.0 MPa hydrogen atmosphere to obtain 2,5-dimethylfuran.

[0008] The supported ZrO2-Co / Al2O3 catalyst is ZrO2 doped in mesoporous Al2O3 loaded with Co clusters, wherein the molar ratio of ZrO2 in the catalyst to the Al element in the mesoporous Al2O3 is 0.01 to 0.08, and the molar ratio of the Co clusters to the Al element in the mesoporous Al2O3 is 2 to 5. The catalyst is prepared by the following method:

[0009] Co(NO3)2 and Al(NO3)3 were dissolved in deionized water to obtain solution A; Zr(NO3)4 was dissolved in deionized water to obtain solution B; solution A and solution B were mixed to obtain solution C, and the mixture was uniformly dispersed under ultrasound; NaOH and Na2CO3 were dissolved in deionized water to obtain solution E and solution F respectively; solution C and solution E were simultaneously added dropwise to solution F. During the addition process, a constant temperature water bath of 40 to 50°C and strong magnetic stirring were maintained, and a constant flow pump was used to maintain the pH of the mixed solution at 10±0.5. After the addition of solution C was completed, the mixed solution was heated to 60 to 70°C and stirred for 30 to 40 minutes to complete the precipitation; the mixture was then added to a vacuum evaporator. The mixture was aged at 60-70°C for 20-24 hours, and the precipitate was collected by filtration and washed with deionized water until the filtrate was close to neutral. The precipitate was dried at 60-80°C for 10-12 hours, and the obtained solid was recorded as ZrO2-Co / Al2O3-HT. The ZrO2-Co / Al2O3-HT was then calcined at 300-700°C in static air for 2-6 hours, and the obtained solid was recorded as ZrO2-Co / Al2O3-MMO. Subsequently, the ZrO2-Co / Al2O3-MMO was reduced at 500-900°C in a mixed atmosphere of H2 and Ar for 1-3 hours, and naturally cooled to obtain a supported ZrO2-Co / Al2O3 catalyst.

[0010] In the above-mentioned supported ZrO2-Co / Al2O3 catalyst, the molar ratio of ZrO2 to the Al element in mesoporous Al2O3 is preferably 0.02-0.04, and the molar ratio of Co clusters to the Al element in mesoporous Al2O3 is 3.

[0011] In the preparation method of the above-mentioned supported ZrO2-Co / Al2O3 catalyst, ZrO2-Co / Al2O3-HT is preferably calcined at 600°C in static air for 4 hours.

[0012] In the preparation method of the above-mentioned supported ZrO2-Co / Al2O3 catalyst, ZrO2-Co / Al2O3-MMO is preferably reduced at 700°C for 2h in a mixed atmosphere of H2 and Ar with a volume ratio of 1:9.

[0013] In the preparation method of the above-mentioned supported ZrO2-Co / Al2O3 catalyst, the heating rate of calcination and reduction is preferably 3-6°C·min -1 .

[0014] In the above-mentioned method for directly preparing 2,5-dimethylfuran from 5-hydroxymethylfurfural in one step with high efficiency, the added amount of the supported ZrO2-Co / Al2O3 catalyst is preferably 10% to 40% of the mass of 5-hydroxymethylfurfural.

[0015] In the above-mentioned method for directly preparing 2,5-dimethylfuran from 5-hydroxymethylfurfural in one step with high efficiency, the reaction is preferably carried out at a constant temperature of 150° C. with closed stirring under a 2 MPa hydrogen atmosphere for 6 hours.

[0016] The beneficial effects of the present invention are as follows:

[0017] The present invention first uses a coprecipitation method to prepare a ZrO2-doped Al2O3-loaded Co-type layered hydroxide precursor, which is then calcined at high temperature to form a mixed metal oxide. The resulting mixed metal oxide is then reduced with hydrogen to form a supported ZrO2-Co / Al2O3 catalyst. This catalyst, primarily composed of non-precious metals, is inexpensive and readily available, resulting in a low catalyst cost. It can produce 2,5-dimethylfuran from 5-hydroxymethylfurfural in a single step with a high yield. The reaction process is a one-step process, with a maximum yield of 97.3% for 2,5-dimethylfuran. The catalyst remains stable after five cycles. Using tetrahydrofuran or 1,4-dioxane, a solvent with a low boiling point, facilitates product separation, significantly reducing energy consumption during the separation process. The process is simple, safe, and has promising industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the XRD pattern of catalyst 2ZrO2-Co / Al2O3.

[0019] Figure 2 These are the transmission electron microscopy images (ab), high-resolution transmission electron microscopy images (c) and corresponding EDS mapping images (d) of the catalyst 2ZrO2-Co / Al2O3.

[0020] Figure 3 These are the stability test results of catalyst 2ZrO2-Co / Al2O3 in 5 cycles. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and examples, but the protection scope of the present invention is not limited to these examples.

[0022] Example 1

[0023] Mix 50mL of 0.75mol / L Co(NO3)2 aqueous solution and 50mL of 0.25mol / L Al(NO3)3 aqueous solution to obtain solution A; mix solution A with 50mL of 0.0025mol / L Zr(NO3)4 aqueous solution to obtain solution C; drop solution C into 100mL of 0.125mol / L Na2CO3 aqueous solution, and at the same time add 4mol / L NaOH aqueous solution, and use a constant flow pump to maintain the pH of the mixed solution at 10±0.5. During the addition process, maintain a constant temperature water bath at 40℃ and strong magnetic stirring. After the addition of solution C is completed, heat the mixed solution to 65℃, stir for 0.5h, and precipitation is completed; then let the mixture stand and age at 65℃ for 24h, then filter and collect the precipitate, and wash it with deionized water several times until the filtrate is close to neutral. The obtained precipitate was dried at 80 ° C for 12 h, and the obtained solid was recorded as ZrO2-Co / Al2O3-HT; then it was calcined at 600 ° C in static air for 4 h, and the obtained solid was recorded as ZrO2-Co / Al2O3-MMO. -1 The temperature was raised to 700°C at a heating rate and maintained for 2 hours. After natural cooling, a supported ZrO2-Co / Al2O3 catalyst was obtained. The molar ratio of ZrO2 in the catalyst to the Al element in mesoporous Al2O3 was 0.01, and the molar ratio of Co clusters to the Al element in mesoporous Al2O3 was 3. Therefore, the catalyst was recorded as 1ZrO2-Co / Al2O3.

[0024] A 100-mL stainless steel reactor was charged with 0.02 g of the 1ZrO₂-Co / Al₂O₃ catalyst, 0.1 g of 5-hydroxymethylfurfural, and 20 mL of tetrahydrofuran. The reactor atmosphere was replaced with nitrogen three times, then filled with 2 MPa of hydrogen. The temperature was raised to 150°C, and stirring was increased to 500 rpm. The reaction was continued in a sealed, constant-temperature, stirring chamber for 6 h. After the reaction, the reactor was cooled in an ice-water bath, and the reaction liquid was filtered and analyzed by gas chromatography, using n-butanol as the internal standard. The reaction results are shown in Table 1.

[0025] Example 2

[0026] In Example 1, solution A was mixed with 50 mL of 0.0050 mol / L Zr(NO3)4 aqueous solution. Other steps were the same as in Example 1 to obtain a supported ZrO2-Co / Al2O3 catalyst. The molar ratio of ZrO2 in the catalyst to the Al element in the mesoporous Al2O3 was 0.02, and the molar ratio of Co clusters to the Al element in the mesoporous Al2O3 was 3. Therefore, the catalyst was recorded as 2ZrO2-Co / Al2O3. Figure 1 It can be seen that there is an obvious Co characteristic diffraction peak in the catalyst, indicating that the Co element in the catalyst is almost completely reduced to elemental Co. The average size of the Co particles calculated using the Scherrer formula is 31.5 nm. Figure 2 It can be seen that the catalyst as a whole presents a broken lamellar structure. High-resolution transmission electron microscopy analysis of the catalyst revealed that there are two different lattice fringes of 0.205nm and 0.299nm in 2ZrO2-Co / Al2O3, which are respectively attributed to the (111) crystal plane of Co and the (101) crystal plane of tetragonal zirconium dioxide (t-ZrO2), and there is an obvious lattice interface between the two crystal phases. The catalyst was further analyzed by EDS mapping (such as Figure 2 d) It can be seen that elements such as Co, Zr, O, and Al exist in the catalyst, and the distribution of each element is very uniform. Figure 2 There is an obvious interface between Co and t-ZrO2 in c, and t-ZrO2 is coated by Co in the center. This may be because ZrO2 is less doped. Under the strong interaction between t-ZrO2 and Co, Co moves around t-ZrO2, thus forming a coating structure.

[0027] The catalyst 2ZrO2-Co / Al2O3 was used to catalyze the production of 2,5-dimethylfuran from 5-hydroxymethylfurfural according to the method of Example 1. The reaction results are shown in Table 1.

[0028] Example 3

[0029] In Example 1, solution A was mixed with 50 mL of 0.0100 mol / L Zr(NO3)4 aqueous solution, and the other steps were the same as in Example 1 to obtain a supported ZrO2-Co / Al2O3 catalyst. The molar ratio of ZrO2 in the catalyst to the Al element in mesoporous Al2O3 was 0.04, and the molar ratio of Co clusters to the Al element in mesoporous Al2O3 was 3. Therefore, the catalyst was recorded as 4ZrO2-Co / Al2O3.

[0030] The catalyst 4ZrO2-Co / Al2O3 was used to catalyze the production of 2,5-dimethylfuran from 5-hydroxymethylfurfural according to the method of Example 1. The reaction results are shown in Table 1.

[0031] Example 4

[0032] In Example 1, solution A was mixed with 50 mL of 0.0200 mol / L Zr(NO3)4 aqueous solution, and the other steps were the same as in Example 1 to obtain a supported ZrO2-Co / Al2O3 catalyst. The molar ratio of ZrO2 in the catalyst to the Al element in the mesoporous Al2O3 was 0.08, and the molar ratio of Co clusters to the Al element in the mesoporous Al2O3 was 3. Therefore, the catalyst was recorded as 8ZrO2-Co / Al2O3.

[0033] The catalyst 8ZrO2-Co / Al2O3 was used to catalyze the production of 2,5-dimethylfuran from 5-hydroxymethylfurfural according to the method of Example 1. The reaction results are shown in Table 1.

[0034] Table 1 Conversion rate of 5-hydroxymethylfurfural and yield of 2,5-dimethylfuran over different catalysts

[0035]

[0036] As shown in Table 1, the method of the present invention can catalyze 5-hydroxymethylfurfural to produce 2,5-dimethylfuran in high yield, and the maximum yield of 2,5-dimethylfuran is 97.3 mol%.

[0037] The solid obtained after filtration in Example 2 was used as a catalyst to repeatedly catalyze 5-hydroxymethylfurfural to prepare 2,5-dimethylfuran. Figure 3 .Depend on Figure 3 It can be seen that after 5 cycles, the conversion rate of 5-hydroxymethylfurfural did not change, and the yield of 2,5-dimethylfuran decreased slightly, but its yield was still higher than 50%, indicating that the catalyst has good stability.

Claims

1. A method for directly preparing 2,5-dimethylfuran by catalyzing 5-hydroxymethylfurfural in one step, characterized in that: The supported ZrO2-Co / Al2O3 catalyst, 5-hydroxymethylfurfural, tetrahydrofuran or 1,4-dioxane are placed in a stainless steel reactor, and reacted at a constant temperature of 120-180°C under a 1.0-3.0 MPa hydrogen atmosphere with stirring for 4-6 hours to obtain 2,5-dimethylfuran. The supported ZrO2-Co / Al2O3 catalyst is a ZrO2 doped in mesoporous Al2O3 loaded with Co clusters, wherein the molar ratio of ZrO2 in the catalyst to the Al element in the mesoporous Al2O3 is 0.01 to 0.08, and the molar ratio of the Co cluster to the Al element in the mesoporous Al2O3 is 2 to 5. The catalyst is prepared by the following method: Co(NO3)2 and Al(NO3)3 were dissolved in deionized water to obtain solution A; Zr(NO3)4 was dissolved in deionized water to obtain solution B; solution A and solution B were mixed to obtain solution C, and the mixture was uniformly dispersed under ultrasound; NaOH and Na2CO3 were dissolved in deionized water to obtain solution E and solution F respectively; solution C and solution E were simultaneously added dropwise to solution F. During the addition process, a constant temperature water bath of 40 to 50 °C and strong magnetic stirring were maintained, and a constant flow pump was used to maintain the pH of the mixed solution at 10±0.

5. After the addition of solution C was completed, the mixed solution was heated to 60 to 70 °C and stirred for 30 to 40 min to complete the precipitation; the mixture was then allowed to stand at 60 to 70 °C for aging for 20 to 24 h, and the precipitate was collected by filtration and washed with deionized water until the filtrate was close to neutral. The obtained precipitate was dried at 60 to 80 °C for 10 to 12 h, and the obtained solid is recorded as ZrO2-Co / Al2O3-HT; then ZrO2-Co / Al2O3-HT is calcined at 300-700 °C in static air for 2-6 h, and the obtained solid is recorded as ZrO2-Co / Al2O3-MMO. Subsequently, ZrO2-Co / Al2O3-MMO is reduced at 500-900 °C in a mixed atmosphere of H2 and Ar for 1-3 h, and naturally cooled to obtain a supported ZrO2-Co / Al2O3 catalyst.

2. The method for directly preparing 2,5-dimethylfuran from 5-hydroxymethylfurfural in one step according to claim 1, characterized in that: The added amount of the supported ZrO2-Co / Al2O3 catalyst is 10% to 40% of the mass of 5-hydroxymethylfurfural.

3. The method for directly preparing 2,5-dimethylfuran by catalyzing 5-hydroxymethylfurfural in one step according to claim 1 or 2, characterized in that: In the supported ZrO2-Co / Al2O3 catalyst, the molar ratio of ZrO2 to the Al element in the mesoporous Al2O3 is 0.02-0.04, and the molar ratio of the Co cluster to the Al element in the mesoporous Al2O3 is 3.

4. The method for directly preparing 2,5-dimethylfuran by catalyzing 5-hydroxymethylfurfural in one step according to claim 1, characterized in that: ZrO2-Co / Al2O3-HT was calcined at 600 °C in static air for 4 h.

5. The method for directly preparing 2,5-dimethylfuran by catalyzing 5-hydroxymethylfurfural in one step according to claim 1, characterized in that: ZrO2-Co / Al2O3-MMO was reduced at 700 °C for 2 h in a mixed atmosphere of H2 and Ar with a volume ratio of 1:

9.

6. The method for directly preparing 2,5-dimethylfuran by catalyzing 5-hydroxymethylfurfural in one step according to claim 1, characterized in that: The heating rate of the calcination and reduction is 3-6°C·min -1 .

7. The method for directly preparing 2,5-dimethylfuran by catalyzing 5-hydroxymethylfurfural in one step according to claim 1, characterized in that: The reaction was carried out at 150 °C in a sealed container with constant stirring under a 2 MPa hydrogen atmosphere for 6 h.

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