Method for synthesizing 2, 5-hexanedione by catalyzing 5-methylfurfural through low-temperature low-pressure water phase hydrogenation

Abstract

The invention discloses a method for synthesizing 2, 5-hexanedione by catalyzing 5-methylfurfural through low-temperature low-pressure water-phase hydrogenation, and belongs to the technical field of biomass fine chemical engineering. The method for synthesizing 2, 5-hexanedione by catalyzing 5-methylfurfural through low-temperature and low-pressure aqueous phase hydrogenation comprises the following steps: putting a 5-methylfurfural aqueous solution and a Pd / CePO4 catalyst into a closed container, and reacting in a hydrogen atmosphere to prepare 2, 5-hexanedione. Compared with the prior art, the method for converting 5-methylfurfural into 2, 5-hexanedione has the advantages that the raw materials and the catalyst are low in cost, green and environment-friendly, the operation process conditions are easy to realize, the yield of the target product 2, 5-hexanedione is high, and the process system is expected to replace the existing 2, 5-hexanedione production process, has huge potential of large-scale application, and is suitable for industrial production. The vigorous popularization is worthy.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass fine chemistry, and more specifically relates to a method for synthesizing 2,5 - hexanedione by catalytic hydrogenation of 5 - methylfurfural in low - temperature and low - pressure aqueous phase. Background Art

[0002] As an important chemical raw material, 2,5 - hexanedione has a very wide range of uses. It can be used as a polymerization monomer, high - boiling - point solvent, leather tanning agent, rubber vulcanization accelerator, etc., and can be processed into a variety of high - value - added downstream products. Among its downstream products, 3 - methylcyclopent - 2 - en - 1 - one can be used to produce methylcyclopentadiene and polycycloalkanes as high - density fuels and their additives; 2,5 - hexanediol is a widely used chiral molecule synthesis intermediate, polymerization monomer, and cross - linker; 3 - methylcyclopentanone and 3 - methylcyclopentanol can be used in the synthesis of spices, dyes, and pesticides; reacting with nitro - containing compounds to synthesize pyrrole - type compounds as pharmaceuticals, pesticides, antibacterial agents, dyes or their important intermediates; through a series of conversions with nitrous acid, etc. to isocarboxazid.

[0003] At present, the industrial production route of 2,5 - hexanedione is mainly as follows: It is prepared by hydrogenation and ring - opening of 2,5 - dimethylfuran in water, but the raw material price is relatively high. Sodium acetoacetic ester is prepared from ethyl acetoacetate and sodium, which reacts with pure iodine to form diethyl diacetyl succinate, and then it is hydrolyzed with 10wt% aqueous sodium hydroxide solution. The reaction is carried out in an ether solvent and under strong alkaline conditions. Cellulose raw materials are directly hydrolyzed with inorganic acids under strong acidic conditions at high temperature and high pressure, and the yield is about 50%, which is relatively low. Regarding other preparation routes of 2,5 - hexanedione, some researchers have prepared it by dehydration and oxidation of glycerol starting from glycerol. Although the raw materials are cheap and easily available, the reaction steps are complex, the yield is about 67%, and organic solvents and homogeneous catalysts are used, so the separation process is relatively difficult. There are also researchers who use 5 - chloromethylfurfural to prepare it by hydrogenation and ring - opening in the aqueous phase, but the raw material price is expensive.

[0004] In recent years, in view of the above problems, some researchers have begun to explore the preparation of 2,5 - hexanedione with 5 - methylfurfural as the raw material in the aqueous phase, but there is currently a lack of practical preparation systems and methods to achieve this process. The main bottleneck restricting the practical application of this biomass green conversion process lies in: the complex catalyst preparation process and high cost. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for synthesizing 2,5-hexanedione from 5-methylfurfural by catalytic hydrogenation at low temperature and low pressure in aqueous phase, so as to solve the problems existing in the above-mentioned prior art. By using inexpensive and stable low-loaded Pd / CePO4 as a catalyst and green solvent water as a reaction phase, 5-methylfurfural is directly converted into 2,5-hexanedione with a yield of more than 95% under relatively mild conditions, especially low temperature and low pressure hydrogen.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a method for synthesizing 2,5-hexanedione by catalytic hydrogenation of 5-methylfurfural at low temperature and low pressure in aqueous phase, comprising the following steps:

[0008] 5-Methylfurfural solution is reacted with Pd / CePO4 catalyst in a hydrogen atmosphere to produce 2,5-hexanedione.

[0009] Preferably, the 5-methylfurfural solution is added in the form of an aqueous solution; the concentration of furfural in the 5-methylfurfural solution is 0.08 mol / L.

[0010] Preferably, the usage ratio of the 5-methylfurfural solution to the Pd / CePO4 catalyst is 1 mL:4 mg.

[0011] Preferably, the Pd / CePO4 catalyst is a complex composed of cerium phosphate and palladium.

[0012] Preferably, the mass fraction of palladium in the Pd / CePO4 catalyst is 0.5%.

[0013] Preferably, the reaction temperature is 90° C., the reaction time is 6 h, and the pressure is 1 MPa.

[0014] Furthermore, the preparation steps of the Pd / CePO4 catalyst include:

[0015] A 0.1-0.2 mol / L aqueous solution of cerium nitrate was prepared and placed in a stirrer. A 0.1-0.2 mol / L aqueous solution of ammonium monohydrogen phosphate was added dropwise thereto until no more precipitation occurred. After continuous stirring for 1 hour, the mixture was transferred to a polytetrafluoroethylene hydrothermal reactor and reacted at 180-200°C for 12-24 hours. After the reaction was completed, the solid was centrifuged and filtered, washed, and then dried at 70°C overnight. The CePO4 sample was calcined in air at a temperature of 600°C for 4 hours.

[0016] The above CePO4 sample is weighed and mixed with a Pd source and dispersed in water, wherein the Pd source is palladium chloride, palladium acetate, sodium chloropalladate or potassium chloropalladate. Pd is loaded on CePO4 by impregnation to obtain a Pd / CePO4 catalyst.

[0017] The technical principle of the present invention is as follows:

[0018] Before, the inventors of the present invention developed a Ni2P / REPO4 catalyst with a simple preparation method and low cost. By using this catalyst, they explored the preparation of 2,5 - hexanedione from 5 - methylfurfural in the aqueous phase. Under the conditions of 130 °C, 2 MPa, H2, and 4 h, the yield of 2,5 - hexanedione can reach over 90%. On this basis, we tried to further reduce the reaction conditions to seek a preparation process with lower temperature, lower pressure, higher yield, and more conducive to industrial production. Thus, the method for catalytic hydrogenation of 5 - methylfurfural to synthesize 2,5 - hexanedione in the aqueous phase under low temperature and low pressure as described in this application was provided.

[0019] In the Pd / CePO4 catalyst, the main function of Pd is to activate 5 - methylfurfural and also has the function of activating hydrogen, but it has fewer acid - base sites. While rare - earth phosphate (REPO4) has the ability to activate hydrogen, and combining with Pd can significantly improve the catalytic efficiency. In this regard, the present invention uses CePO4 as a carrier and loads Pd in it to obtain Pd / CePO4. The results show that Pd / CePO4 has excellent reaction performance for the aqueous - phase hydrogenation of 5 - methylfurfural to 2,5 - hexanedione. This is because the process of aqueous - phase hydrogenation of 5 - methylfurfural to 2,5 - hexanedione involves hydrogenation and dehydration processes. CePO4 activates hydrogen at low temperature, promoting the hydrogenation process, and the appropriate acid - base sites on the surface of CePO4 promote the dehydration process.

[0020] The present invention discloses the following technical effects:

[0021] The present invention uses a low - loading Pd / CePO4 as a catalyst and green solvent water as the reaction phase, and directly converts 5 - methylfurfural into 2,5 - hexanedione with a yield of over 95% under relatively mild conditions. Compared with the prior art, the method for converting 5 - methylfurfural into 2,5 - hexanedione provided by the present invention has low raw material and catalyst costs, green and mild reaction conditions, easy - to - achieve operating process conditions, and a high yield of the target product 2,5 - hexanedione. This process system is expected to innovate and replace the existing production process of 2,5 - hexanedione, has great potential for scale application, and is worthy of strong promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the XRD pattern of Pd / CePO4 catalyst, Pd / CeO2 catalyst and Pd / SiO2 catalyst;

[0023] Figure 2 is the cycle diagram of Pd / CePO4 catalyst under the conditions of 90 °C, 1 MPa, H2, and 6 h;

[0024] Figure 3Transmission electron microscope images of Pd / CePO4 catalyst (a), Pd / CeO2 catalyst (b) and Pd / SiO2 catalyst (c). Detailed implementation manners

[0025] The various exemplary implementation manners of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0026] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0028] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are also obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0029] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0030] It should be noted that the aspects not described in detail in the present invention are all conventional operation means in the art and are not the focus of the present invention.

[0031] Unless otherwise specified, the raw materials used in the following examples and comparative examples of the present invention are all commercially available products, and the sources of the commercially available products do not affect the technical effects of the present invention.

[0032] Unless otherwise specified, the room temperature involved in the present invention is calculated as 2[5±5]°C.

[0033] Example 1

[0034] Preparation of Pd / CePO4 catalyst:

[0035] Prepare 30 mL of 0.1 mol / L Ce(NO3)3·6H2O solution, place it in a stirrer, and slowly drip 30 mL of the prepared 0.1 mol / L (NH4)2HPO4 solution into it until no more precipitation occurs. After continuous stirring for 1 h, transfer the mixture into a polytetrafluoroethylene hydrothermal reaction kettle and react at 180 °C for 12 h. After the reaction, centrifuge to filter out the solid matter for washing, then dry it overnight at 70 °C and calcine it at a high temperature in an air atmosphere at 600 °C for 4 h to obtain the CePO4 sample.

[0036] Weigh 0.3 g of the above CePO4 sample and disperse it in 15 mL of water. Disperse 2.5 mg of palladium chloride in 5 mL of water. Mix the two and use the method of impregnation and evaporation to load Pd on CePO4. The impregnation and evaporation time is 2 h, and then reduce it in a hydrogen atmosphere at 150 °C for 2 h to obtain the Pd / CePO4 catalyst (where the mass fraction of palladium is 0.5%).

[0037] Preparation of 2,5 - hexanedione: Take 25 mL of 0.08 mol / L 5 - methylfurfural aqueous solution and place it in a pressure reaction vessel with a volume of 50 mL. Add 100 mg of the prepared Pd / CePO4 catalyst and stir and mix evenly at 350 r / min. Then close the reactor, purge it with hydrogen 5 times, and then fill it with hydrogen to adjust and maintain the internal pressure of the reactor at 1 MPa. After closing the gas circuit, raise the reaction temperature to 90 °C, maintain the stirring speed of 350 r / min, and end the reaction after 6 h. Cool it to room temperature and conduct GC quantitative analysis on the product. The yield of 2,5 - hexanedione is 98%.

[0038] Comparative Example 1

[0039] Preparation of Pd / CeO2 catalyst:

[0040] Prepare 30 mL of 0.1 mol / L Ce(NO3)3·6H2O solution, place it in a stirrer, and slowly drip 30 mL of the prepared 0.5 mol / L ammonia water solution into it until no more precipitation occurs. After continuous stirring for 1 h, transfer the mixture into a polytetrafluoroethylene hydrothermal reaction kettle and react at 180 °C for 12 h. After the reaction, centrifuge to filter out the solid matter for washing, then dry it overnight at 70 °C and calcine it at a high temperature in an air atmosphere at 600 °C for 4 h to obtain the CeO2 sample.

[0041] Weigh 0.3 g of the above CeO2 sample and disperse it in 15 mL of water. Disperse 2.5 mg of palladium chloride in 5 mL of water. Mix the two and use the impregnation and evaporation method to load Pd on CeO2. The impregnation and evaporation time is 2 h, and the Pd / CeO2 catalyst is obtained (where the mass fraction of palladium is 0.5%).

[0042] Preparation of 2,5 - hexanedione: Take 25 mL of 0.08 mol / L 5 - methylfurfural aqueous solution and place it in a 50 mL pressure reaction vessel. Add 100 mg of Pd / CeO2 catalyst and stir and mix evenly at 350 r / min. Then seal the reactor, purge it with hydrogen 5 times, and then fill it with hydrogen to adjust and maintain the internal pressure of the reactor at 1 MPa. After sealing the gas path, raise the reaction temperature to 90 °C, maintain the stirring speed of 350 r / min, end the reaction after 6 h, cool to room temperature, and conduct GC quantitative analysis on the product. The yield of 2,5 - hexanedione is 0%.

[0043] Comparative Example 2

[0044] Preparation of Pd / SiO2:

[0045] Weigh 0.3 g of commercial SiO2 and disperse it in 15 mL of water. Disperse 2.5 mg of palladium chloride in 5 mL of water. Mix the two and use the impregnation and evaporation method to load Pd on SiO2. The impregnation and evaporation time is 2 h, and the Pd / SiO2 catalyst is obtained (where the mass fraction of palladium is 0.5%).

[0046] Preparation of 2,5 - hexanedione: Take 25 mL of 0.08 mol / L 5 - methylfurfural aqueous solution and place it in a 50 mL pressure reaction vessel, add 100 mg of Pd / SiO2 catalyst, and stir and mix evenly at 350 r / min. Then seal the reactor, purge it with hydrogen at atmospheric pressure 5 times, and then fill it with hydrogen to adjust and maintain the internal pressure of the reactor at 1 MPa. After sealing the gas path, raise the reaction temperature to 90 °C, maintain the stirring speed of 350 r / min, end the reaction after 6 h, cool to room temperature, and conduct GC quantitative analysis on the product. The yield of 2,5 - hexanedione is 33%.

[0047] Comparative Example 3

[0048] Preparation of CePO4 catalyst:

[0049] Prepare 30 mL of 0.1 mol / L Ce(NO3)3·6H2O solution, place it in a stirrer, and drop 30 mL of the prepared 0.1 mol / L (NH4)2HPO4 solution into it until no more precipitation occurs. After continuously stirring for 1 h, transfer the mixture into a polytetrafluoroethylene hydrothermal reaction kettle and react at 180 °C for 12 h. After the reaction, centrifuge and filter out the solid matter for washing, then dry it overnight at 70 °C and perform high-temperature calcination in an air atmosphere at a temperature of 600 °C for 4 h to obtain the CePO4 catalyst.

[0050] Preparation of 2,5 - hexanedione: Take 25 mL of 0.08 mol / L 5 - methylfurfural aqueous solution, place it in a pressure reaction vessel with a volume of 50 mL, add 100 mg of the prepared CePO4 catalyst, and stir and mix evenly at 350 r / min. Then seal the reactor, purge it with hydrogen 5 times, and then fill it with hydrogen to adjust and maintain the internal pressure of the reactor at 1 MPa. After closing the gas circuit, raise the reaction temperature to 90 °C, maintain the stirring speed of 350 r / min, end the reaction after 6 h, cool it to room temperature, and perform GC quantitative analysis on the product. The yield of 2,5 - hexanedione is 0.

[0051] The reaction equation for the conversion of 5 - methylfurfural to prepare 2,5 - hexanedione is as follows:

[0052]

[0053] The yields of each product and the conversion rates of the reactants under the conditions of Example 1 and Comparative Examples 1 - 3 are shown in Table 1.

[0054] Table 1 Yields of each product and conversion rates of reactants under the conditions of Example 1 and Comparative Examples 1 - 3

[0055]

[0056]

[0057] As can be seen from Table 1, according to the synthesis process of the present invention, 5 - methylfurfural can be hydrogenated and converted into 2,5 - hexanedione under relatively mild conditions in an aqueous solution, and the yield is high. The yield under the conditions of the example > 95%, which has great potential for industrial application.

[0058] Figure 1 XRD patterns of Pd / CePO4 catalyst, Pd / CeO2 catalyst and Pd / SiO2 catalyst; Figure 2 Cycling diagram of Pd / CePO4 catalyst under the conditions of 90 °C, 1 MPa, H2, 6 h; Figure 3 Transmission electron microscope images of Pd / CePO4 catalyst (a), Pd / CeO2 catalyst (b) and Pd / SiO2 catalyst (c).

[0059] It can be seen from Figure 1 that the characteristic diffraction peak of the Pd(111) crystal plane can be observed at 40.5°, indicating that Pd is successfully loaded on the three carriers. It can be seen from Figure 2 that the Pd / CePO4 catalyst has excellent cyclic stability. It can be seen from Figure 3 that Pd is uniformly dispersed on the three carriers in the form of small spherical particles.

[0060] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other.

[0061] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for synthesizing 2,5-hexanedione from 5-methylfurfural by catalytic hydrogenation at low temperature and low pressure in aqueous phase, characterized in that: The steps include: 5-Methylfurfural solution is reacted with Pd / CePO4 catalyst in a hydrogen atmosphere to produce 2,5-hexanedione.

2. The method according to claim 1, characterized in that The 5-methylfurfural solution is added in the form of an aqueous solution; the concentration of furfural in the 5-methylfurfural solution is 0.08 mol / L.

3. The method according to claim 1, characterized in that The usage ratio of the 5-methylfurfural solution to the Pd / CePO4 catalyst is 1 mL:4 mg.

4. The method according to claim 1, wherein The Pd / CePO4 catalyst is a composite composed of cerium phosphate and palladium.

5. The method according to claim 4, characterized in that The mass fraction of palladium in the Pd / CePO4 catalyst is 0.5%.

6. The method according to claim 1, characterized in that The reaction temperature is 90° C., the reaction time is 6 h, and the pressure is 1 MPa.

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