A modified thin-layer hydrotalcite catalyst, its preparation and use in the synthesis of a biomass fuel precursor

Abstract

The application belongs to the field of biomass fuel precursor synthesis, and particularly relates to a modified thin-layer hydrotalcite catalyst, preparation thereof and application thereof in biomass fuel precursor synthesis. Metal salt solutions A of Mg, Al and Hf are dissolved in deionized water to obtain the metal salt solutions A; an alkaline solution B is prepared; the solutions A and B are added into deionized water, and the pH value of the system is kept at 8-10 during the mixing process; after the mixing is completed, high-temperature aging is performed, the precipitate is washed and dried to obtain the modified thin-layer hydrotalcite catalyst. The application is obtained through reasonable design of the composition and proportion of the thin-layer hydrotalcite, and is obtained through a simple and easy preparation method, and has low industrialization cost and is more easy to scale up. The modification of hafnium makes the hydrotalcite have a thinner layered structure and more defect sites, and exhibits more excellent catalytic performance, and exhibits excellent catalytic effect on various types of ketones and furfural under mild conditions.

Description

TECHNICAL FIELD

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

[0002] The reduction of fossil fuels and the environmental defects brought by 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 plays an important role in the entire energy system. Biomass has great advantages of wide source, green and pollution-free, and renewable, and is considered as one of the ideal fossil energy substitutes. According to the use requirements of bio-jet fuel, C8-C15 chain length alkanes become the main target product. At present, 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 attracted great interest in the relevant field, and furfural and ketones are used to prepare biomass fuel precursors through aldol condensation, and further hydrogenation to prepare high-performance aviation fuel, which is functionally equivalent to petroleum fuel. This greatly stimulates the research interest in the high-value conversion of biomass furfural, but the aldol condensation reaction to produce fuel precursors with suitable carbon chain length has not been fully solved.

[0004] 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 class of bio-liquid fuel precursors from furfural and methyl isobutyl ketone. Although the final conversion rate and selectivity reached 95% and 98%, respectively, the MOF-based catalyst in the process needs to be finely controlled in structure, which is not conducive to large-scale preparation, and the reaction temperature is high.

[0005] Document (Synthesis of jet-fuel precursors from renewable biomass through aldol condensation of cyclopentanone and furfural on base catalysts, Catalysis Today, 443, 2025, 114962) reports a method for preparing jet fuel precursors by reacting furfural and cyclopentanone, although CaO with low cost is used as a catalyst in the process, but the final yield is only 57%. The low product yield does not meet the requirements of efficient catalysis, and does not have the significance of in-depth study. SUMMARY

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

[0007] To solve the above technical problems, the technical solutions adopted by the present application are 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 keeping the pH value of the system at 8-10 during the mixing process; after the mixing is completed, high-temperature aging is carried out, the precipitate is washed and dried to obtain the modified thin-layer hydrotalcite catalyst.

[0009] The metal salt of hafnium can be selected from hafnium oxychloride octahydrate, hafnium tetrachloride, hafnium sulfate, etc.

[0010] The metal salt of magnesium can be selected from magnesium nitrate, magnesium sulfate, magnesium acetate, magnesium chloride, etc.; the metal salt of aluminum can be selected from aluminum nitrate, aluminum chloride, aluminum sulfate, etc.

[0011] The alkaline solution B can be prepared by using one or two of NaOH, NaCO3, KOH, 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] Further, the molar ratio of Hf ions to trivalent metal ions in the metal salt solution A is 1:10.

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

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

[0017] The precipitate is washed to neutral and vacuum dried at 80 DEG C for 12 h.

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

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

[0020] The temperature of the precursor synthesis reaction is 70-150 DEG C, and the reaction time is 2-10 h, and compared with a MOF-based catalyst, the catalyst can start the reaction under milder conditions.

[0021] Further, the temperature of the reaction is 90-140 DEG C, and the reaction time is 3-8 h.

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

[0023] The synthesis of the biomass fuel precursor is carried out in a high-pressure reaction kettle.

[0024] Hydrotalcite is a kind of material developed rapidly in recent years, also known as layered double hydroxide. Hydrotalcite is applied as a basic catalyst in various basic catalytic reactions, but the basicity of hydrotalcite itself is weak, although the doping of a third metal has been proved to be a simple and effective method for improving the catalytic performance of hydrotalcite; however, for different catalytic systems and different catalytic performance requirements, and for specific application catalysts, how to design the modified thin-layer hydrotalcite becomes the research focus. The present application is obtained through reasonable design of the composition and proportion of the thin-layer hydrotalcite by a simple and easy preparation method, and has low industrialization cost and is more easy to scale up. The modification of hafnium makes the hydrotalcite have a thinner layered structure and more defect sites, and exhibits more excellent catalytic performance, and shows excellent catalytic effect 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 DRAWINGS

[0025] Figure 1 Transmission electron microscopy image of the modified thin-layer hydrotalcite catalyst prepared in Example 1. DETAILED DESCRIPTION

[0026] The technical solutions of the present application are described below with specific examples, but the scope of protection of the present application is not limited thereto: Example 1

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

[0028] A solution A was prepared by adding 2.9 g of magnesium nitrate hexahydrate, 1.4 g of aluminum nitrate nonahydrate and 0.15 g of hafnium oxychloride octahydrate into 100 mL of deionized water and stirring until completely dissolved. A solution B was prepared by adding 2 g of NaOH into 100 mL of deionized water and stirring until completely dissolved. Solutions A and B were simultaneously added dropwise into 100 mL of deionized water, and the system was stirred vigorously and maintained at a pH of 10; after the dropwise addition was completed, the system was aged at 80°C for 12 h. After the aging was completed, the solid material was washed to neutral, and then vacuum dried to obtain the modified thin-layer hydrotalcite catalyst.

[0029] Biomass fuel precursor synthesis:

[0030] In a high-pressure reaction kettle, 5 g of methyl isobutyl ketone, 1.1 g of biomass furfural and 0.11 g of catalyst were added, and after the temperature was raised to 120°C under an inert atmosphere, the reaction was timed for 4 h. 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 precursors was 98%.

[0031] Example 2

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

[0033] A solution A was prepared by adding 2.9 g of magnesium nitrate hexahydrate, 1.4 g of aluminum nitrate nonahydrate and 0.15 g of hafnium oxychloride octahydrate into 100 mL of deionized water and stirring until completely dissolved. A solution B was prepared by adding 2.5 g of NaOH into 100 mL of deionized water and stirring until completely dissolved. Solutions A and B were simultaneously added dropwise into 100 mL of deionized water, and the system was stirred vigorously and maintained at a pH of 10; after the dropwise addition was completed, the system was aged at 80°C for 12 h. After the aging was completed, the solid material was washed to neutral, and then vacuum dried to obtain the modified thin-layer hydrotalcite catalyst.

[0034] Biomass fuel precursor synthesis:

[0035] In a high-pressure reaction kettle, 5 g of methyl isobutyl ketone, 1.1 g of biomass furfural and 0.11 g of catalyst were added, and after the temperature was raised to 120°C under an inert atmosphere, the reaction was timed for 4 h. 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 precursors was 98%.

[0036] Example 3

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

[0038] Solution A was prepared by adding 2.9 g of magnesium nitrate hexahydrate, 1.4 g of aluminum nitrate nonahydrate and 0.14 g of hafnium sulfate into 100 mL of deionized water and stirring until completely dissolved. Solution B was prepared by adding 2.5 g of NaOH into 100 mL of deionized water and stirring until completely dissolved. Solutions A and B were simultaneously added dropwise into 100 mL of deionized water, and the system was stirred vigorously while maintaining a pH of 10. After the dropwise addition was completed, the system was aged at 90°C for 15 h while stirring. After the aging was completed, the solid material was washed until it was neutral, and then it was vacuum dried to obtain the hafnium-modified thin-layer hydrotalcite catalyst.

[0039] Biomass fuel precursor synthesis:

[0040] In a high-pressure reactor, 7.7 g of cyclohexanone, 1.5 g of biomass furfural and 0.18 g of catalyst were sequentially added, and after the temperature was raised to 150°C under an inert atmosphere, the reaction was timed for 6 h. After the reaction was completed, gas chromatography was used for analysis, and the conversion rate of furfural reached 95%, and the selectivity of the C11 fuel precursor was 98%.

Claims

1. A method for preparing 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; after the mixing is completed, perform high-temperature aging, wash the precipitate and dry it to obtain a modified thin-layer hydrotalcite catalyst.

2. The method for preparing the modified thin-layer hydrotalcite catalyst according to claim 1, wherein: 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 method for preparing the modified thin-layer hydrotalcite catalyst according to claim 1, wherein: The high temperature aging temperature is 50-90℃, and the aging time is 8-24 h.

4. The method for preparing the modified thin-layer hydrotalcite catalyst according to claim 3, wherein: The molar ratio of Hf ions to trivalent metal ions in the metal salt solution A is 1:10; when solution A and 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 method for preparing the modified thin-layer hydrotalcite catalyst according to claim 1, wherein: Solution A and solution B were added dropwise to deionized water under stirring at not less than 700 r / min.

6. The method for preparing the modified thin-layer hydrotalcite catalyst according to claim 1, wherein: 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: 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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