Modified thin-layer hydrotalcite catalyst, preparation thereof and application of modified thin-layer hydrotalcite catalyst in synthesis of biomass fuel precursor

Abstract

The invention belongs to the field of biomass fuel precursor synthesis, and particularly relates to a modified thin-layer hydrotalcite catalyst, preparation thereof and application of the modified thin-layer hydrotalcite catalyst in biomass fuel precursor synthesis. The preparation method comprises the following steps: dissolving metal salts of Mg, Al and Hf in deionized water to obtain a metal salt solution A; preparing an alkaline solution B; adding the solution A and the solution B into deionized water, and keeping the pH value of the system at 8-10 in the mixing process; and after mixing, carrying out high-temperature aging, washing the precipitate, and drying to obtain the modified thin-layer hydrotalcite catalyst. Through reasonable design of the components and the proportion of the thin-layer hydrotalcite, the composite material is obtained through a simple and feasible preparation method, the industrial cost is low, and large-scale production is easier. Due to modification of hafnium, hydrotalcite has a thinner layered structure and more defect sites, shows more excellent catalytic performance and shows an excellent catalytic effect on various ketones and furfural under mild conditions.

Description

Technical Field

[0001] The invention belongs to the field of biomass fuel precursor synthesis, and particularly relates to a modified thin-layer hydrotalcite catalyst and its preparation and application in biomass fuel precursor synthesis. Background Art

[0002] The reduction of fossil fuels and the environmental drawbacks of their use are encouraging the exploration of new energy sources for the chemical industry. Biomass is the fourth largest energy source after coal, oil and natural gas, and occupies an important position in the entire energy system. Biomass is considered to be one of the ideal fossil energy substitutes due to its wide range of sources, green and pollution-free, and renewable advantages. According to the requirements for the use of bio-jet fuel, alkanes with a chain length of C8-C15 have become the main target products. Currently, many research strategies focus on using biomass-derived raw materials as platform chemicals to synthesize fuels.

[0003] More specifically, the high-value conversion of biomass furfural as a platform molecule has aroused great interest in related fields. Furfural and ketones are condensed to prepare biomass fuel precursors through aldol condensation, and further hydrogenated to prepare high-performance aviation fuels. This biofuel is functionally equivalent to petroleum fuels. This has greatly stimulated the research interest in the high-value conversion of biomass furfural, but the production of fuel precursors with suitable carbon chain lengths by aldol condensation reaction has not been fully solved.

[0004] The literature (Defective UiO-66(Zr) as an efficient catalyst for the synthesis of bio jet-fuel precursors via aldol condensation of furfural and MIBK, Journal of Catalysis, 401, 2021, 27-39) reported a method for preparing C11 bioliquid fuel precursors by reacting furfural with methyl isobutyl ketone. Although the final conversion rate and selectivity reached 95% and 98% respectively, the process required fine structural control of the MOF-based catalyst, which was not conducive to large-scale preparation, and the reaction temperature was high.

[0005] The literature (Synthesis of jet-fuel precursors from renewable biomass through aldol condensation of cyclopentanone and furfural on base catalysts, Catalysis Today, 443, 2025, 114962) reported a method for preparing jet fuel precursors by reacting furfural with cyclic ketones. Although low-cost CaO was used as a catalyst in the process, the final yield was only 57%. The low product yield does not meet the requirements of efficient catalysis and is not meaningful for in-depth research. Summary of the invention

[0006] The purpose of the present invention is to provide a modified thin-layer hydrotalcite catalyst and its preparation, and further provide the application of the catalyst in the synthesis of biomass fuel precursors.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A modified thin-layer hydrotalcite catalyst is prepared by the following method: dissolving metal salts of Mg, Al and Hf in deionized water to obtain a metal salt solution A; preparing an alkaline solution B; adding solution A and solution B into deionized water, and maintaining the pH value of the system at 8-10 during the mixing process; performing high-temperature aging after the mixing, washing the precipitate and drying to obtain the modified thin-layer hydrotalcite catalyst.

[0009] The metal salt of hafnium may be hafnium dichloride octahydrate, hafnium tetrachloride, hafnium sulfate or the like.

[0010] The metal salt of Mg may be magnesium nitrate, magnesium sulfate, magnesium acetate, magnesium chloride, etc.; the metal salt of Al may be aluminum nitrate, aluminum chloride, aluminum sulfate, etc.

[0011] The alkaline solution B can be prepared using one or two of NaOH, NaCO3, KOH, and K2CO3.

[0012] The total concentration of metal ions in the metal salt solution A is 0.005-0.5 mol / L; the concentration of metal cations in the alkaline solution B is 0.05-2 mol / L.

[0013] Preferably, the total concentration of metal ions in the metal salt solution A is 0.01-0.3 mol / L; the concentration of cations in the alkaline solution B is 0.2-1 mol / L.

[0014] Furthermore, the molar ratio of Hf ions to trivalent metal ions in the metal salt solution A is 1:10.

[0015] Preferably, solution A and solution B are added dropwise to deionized water under stirring at not less than 700 r / min. When solution A and solution B are mixed, the pH value of the mixed solution is preferably maintained at 9-10. Specifically, a constant flow pump can be selected to mix solution A and solution B.

[0016] The temperature of high temperature aging is 50-90°C, and the aging time is 8-24h; preferably, the temperature of high temperature aging is 60-90°C, and the aging time is 10-20h.

[0017] The precipitate was thoroughly washed until neutral and dried under vacuum at 80 °C for 12 h.

[0018] The catalyst is applied in the synthesis of biomass fuel precursors, furfural, ketone and the catalyst are reacted in an inert gas atmosphere, the molar ratio of furfural to ketone is 1:1-10, and the mass ratio of furfural to catalyst is 5-50:1.

[0019] Preferably, the molar ratio of furfural to ketone is 1:1-8, and the mass ratio of furfural to catalyst is 5-20:1.

[0020] The temperature of the precursor synthesis reaction is 70-150°C and the reaction time is 2-10h. Compared with MOF-based catalysts, the reaction can be started under milder conditions.

[0021] Furthermore, the reaction temperature is 90-140° C., and the reaction time is 3-8 h.

[0022] The ketone may be selected from one or more of acetone, butanone, pentanone, methyl isobutyl ketone, methyl isopropyl ketone, cyclopentanone, cyclohexanone and hexanedione.

[0023] The biomass fuel precursor synthesis is carried out in a high-pressure reactor.

[0024] Hydrotalcite is a material that has developed rapidly in recent years, also known as layered double metal hydroxide. Hydrotalcite is used as an alkaline catalyst in a variety of base-catalyzed reactions, but the alkalinity of hydrotalcite itself is relatively weak. Although the doping of a third metal has been proven to be a simple and effective method to improve the catalytic performance of hydrotalcite; however, for different catalytic systems and different requirements for catalytic performance, as well as catalysts for specific applications, how to design modified thin-layer hydrotalcite has become a research focus. The present invention is obtained by a simple and easy preparation method through a reasonable design of the composition and proportion of the thin-layer hydrotalcite, with low industrial cost and easier to scale up production. The modification of hafnium gives the hydrotalcite a thinner layered structure and more defect sites, showing more excellent catalytic performance. It shows excellent catalytic effects on various types of ketones and furfural under mild conditions, and has excellent catalytic performance and excellent universality in the field of fuel precursor synthesis based on biomass furfural. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a transmission electron microscopy image of the modified thin layer hydrotalcite catalyst prepared in Example 1. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is described below with specific embodiments, but the protection scope of the present invention is not limited thereto: Embodiment 1

[0027] The modified thin layer hydrotalcite catalyst is prepared by the following steps:

[0028] Add 2.9g magnesium nitrate hexahydrate, 1.4g aluminum nitrate nonahydrate and 0.15g hafnium dichloride octahydrate to 100mL deionized water, stir until completely dissolved to prepare solution A. Add 2g NaOH to 100mL deionized water, stir until completely dissolved to prepare solution B. Add solutions A and B dropwise to 100mL deionized water at the same time, stir vigorously and keep the pH of the system at 10; after the addition is completed, stir and age at 80°C for 12h. After aging, wash the solid material to neutrality and vacuum dry to obtain the modified thin-layer hydrotalcite catalyst.

[0029] Biomass fuel precursor synthesis:

[0030] 5g of methyl isobutyl ketone, 1.1g of biomass furfural and 0.11g of catalyst were added to the autoclave, and the temperature was raised to 120°C under an inert atmosphere, and the reaction was timed for 4 hours. After the reaction was completed, gas chromatography was used for analysis, and the conversion rate of furfural reached 99%, and the selectivity of C11 fuel precursor was 98%.

[0031] Example 2

[0032] The modified thin layer hydrotalcite catalyst is prepared by the following steps:

[0033] Add 2.9g magnesium nitrate hexahydrate, 1.4g aluminum nitrate nonahydrate and 0.12g hafnium tetrachloride to 100mL deionized water and stir until completely dissolved to prepare solution A. Add 2.5g NaOH to 100mL deionized water and stir until completely dissolved to prepare solution B. Add solutions A and B dropwise to 100mL deionized water at the same time, stir vigorously and keep the pH of the system at 10; after the addition is complete, stir and age at 80°C for 12h. After aging, wash the solid material to neutrality and vacuum dry to obtain the hafnium-modified thin-layer hydrotalcite catalyst.

[0034] Biomass fuel precursor synthesis:

[0035] 4.5g butanone, 1.5g biomass furfural and 0.1g catalyst were added to the autoclave in sequence, and the temperature was raised to 100°C under an inert atmosphere, and the reaction was timed for 4 hours. After the reaction was completed, gas chromatography was used for analysis, and the conversion rate of furfural reached 98%, and the selectivity of C9 fuel precursor was 97%.

[0036] Example 3

[0037] The modified thin layer hydrotalcite catalyst is prepared by the following steps:

[0038] Add 2.9g magnesium nitrate hexahydrate, 1.4g aluminum nitrate nonahydrate and 0.14g hafnium sulfate to 100mL deionized water, stir until completely dissolved to prepare solution A. Add 2.5g NaOH to 100mL deionized water, stir until completely dissolved to prepare solution B. Add solutions A and B dropwise to 100mL deionized water at the same time, stir vigorously and keep the pH of the system at 10; after the addition is complete, stir and age at 90°C for 15h. After aging, wash the solid material to neutrality and vacuum dry to obtain the hafnium-modified thin-layer hydrotalcite catalyst.

[0039] Biomass fuel precursor synthesis:

[0040] 7.7 g of cyclohexanone, 1.5 g of biomass furfural and 0.18 g of catalyst were added to the autoclave in sequence, and the temperature was raised to 150°C under an inert atmosphere, and the reaction was timed for 6 hours. After the reaction was completed, gas chromatography was used for analysis, and the conversion rate of furfural reached 95%, and the selectivity of C11 fuel precursor was 98%.

Claims

1. A preparation method of a modified thin layer hydrotalcite catalyst, characterized in that: Dissolving metal salts of Mg, Al and Hf in deionized water to obtain a metal salt solution A; Prepare alkaline solution B; add solution A and solution B into deionized water, and keep the pH value of the system at 8-10 during the mixing process; perform high-temperature aging after the mixing, wash the precipitate and dry it to obtain a modified thin-layer hydrotalcite catalyst.

2. The preparation of the modified thin layer hydrotalcite catalyst according to claim 1, characterized in that: The total concentration of metal ions in the metal salt solution A is 0.005-0.5 mol / L; the concentration of metal cations in the alkaline solution B is 0.05-2 mol / L.

3. The preparation of the modified thin layer hydrotalcite catalyst according to claim 1, characterized in that: The high temperature aging temperature is 50-90℃, and the aging time is 8-24 h.

4. The preparation of the modified thin layer hydrotalcite catalyst according to claim 3, characterized in that: The molar ratio of Hf ions to trivalent metal ions in the metal salt solution A is 1:10; when the solution A and the solution B are mixed, the pH value of the mixed solution is maintained at 9-10; the high temperature aging temperature is 60-90°C, and the aging time is 10-20 h.

5. The preparation of the modified thin layer hydrotalcite catalyst according to claim 1, characterized in that: Solution A and solution B were added dropwise into deionized water under stirring at not less than 700 r / min.

6. The preparation of the modified thin layer hydrotalcite catalyst according to claim 1, characterized in that: The metal salts of hafnium are hafnium oxychloride hydrate, hafnium tetrachloride and hafnium sulfate.

7. The modified thin-layer hydrotalcite catalyst obtained by the preparation method according to any one of claims 1 to 6.

8. Use of the catalyst according to claim 7 in the synthesis of biomass fuel precursors, characterized in that: The furfural, ketone and catalyst are reacted in an inert gas atmosphere, the molar ratio of furfural to ketone is 1:1-10, and the mass ratio of furfural to catalyst is 5-50:

1.

9. Use of the catalyst according to claim 8 in the synthesis of biomass fuel precursors, characterized in that: The reaction temperature is 70-180°C and the reaction time is 2-10 h.

10. Use of the catalyst according to claim 9 in the synthesis of biomass fuel precursors, characterized in that: The molar ratio of furfural to ketone is 1:1-8, and the mass ratio of furfural to catalyst is 5-20:1; the temperature of the synthesis reaction is 90-160°C, and the reaction time is 3-8 h.

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