A metal hybrid ionic liquid catalyst based on an electron density modulation strategy and its application

Abstract

This invention discloses a metal hybrid ionic liquid catalyst based on an electron density modulation strategy and its applications. The main components include the preparation of the metal hybrid ionic liquid catalyst and its use in the aldol condensation reaction of formaldehyde and propionaldehyde to produce methacrolein. The hybridization of metal ions can modulate the electron density of the ionic liquid, thereby improving catalytic activity and stability. This catalyst can increase the generation frequency of methacrolein per unit active site by 2%–52% and reduce catalyst consumption by 15%–57%. It features mild reaction conditions, ease of preparation, and suitability for large-scale industrial applications.

Description

Technical Field

[0001] This invention relates to a metal-hybrid ionic liquid catalyst based on an electron density modulation strategy, applied to the aldol condensation reaction of formaldehyde and propionaldehyde to produce methacrolein. The hybridization of metal ions significantly modulates the electron density of the ionic liquid, thereby effectively improving catalytic activity and stability. Its advantages include good catalytic activity, high catalyst stability, mild reaction conditions, and a simple catalyst preparation process, belonging to the field of fine chemicals. Background Technology

[0002] Methacrolein (MAL) is an important chemical with reactive properties and conjugated double bonds, exhibiting characteristics of both olefins and aldehydes. Therefore, it is widely used in the synthesis of key materials in aerospace, decorative, and construction industries. For example, polymethacrylamide, required for rocket shells, is typically synthesized from two raw materials: methacrylonitrile and methacrylic acid, which are prepared by the cyanation and oxidation reactions of MAL, respectively. MAL can also be synthesized into methyl methacrylate through oxidation and esterification reactions, or via a one-step oxidative esterification method, and is widely used in the manufacture of plexiglass. Furthermore, the reduction product of MAL, methyl allyl alcohol, is increasingly attracting attention in the production of next-generation water-reducing agents. Therefore, the production of methacrolein has a significant impact on downstream chemicals and industrial chains. Currently, the main methods for producing MAL include the aldol condensation of formaldehyde and propionaldehyde and the C4 oxidation method of isobutylene / tert-butanol. In comparison, the aldol condensation of formaldehyde and propionaldehyde effectively overcomes the safety hazards and selectivity control difficulties associated with the high-temperature gas-solid reaction in the C4 oxidation method, thus attracting increasing attention. CN101316809 discloses a method for producing unsaturated aldehydes, in which amines and protic acids with 4-20 carbon atoms or their salts are used as catalysts to carry out a condensation reaction between two aldehydes. CN101074192A uses diethylamine hydrochloride as a catalyst for the aldol condensation reaction of formaldehyde and propionaldehyde to synthesize MAL. However, the high volatility of diethylamine may pose a potential hazard to the environment and a threat to the safety of operators. Furthermore, the highly acidic hydrochloric acid can easily corrode equipment. CN102659542A discloses a method for preparing MAL by catalyzing the condensation of formaldehyde and propionaldehyde using imidazole or pyridine ionic liquids. US2518416 and US2639295 describe methods using organic amines and inorganic acids as catalysts, while US6552232B2 explores a method for synthesizing MAL using inorganic alkaline solutions or alkaline ionic liquids. However, the above methods generally require high temperatures (100–200 °C) and pressures (0.1–5.0 MPa), and involve long reaction times and significant catalyst loss. Therefore, developing a highly efficient and stable catalyst that can carry out catalytic reactions under mild conditions to improve product formation rates and reduce catalyst loss is of paramount importance. Summary of the Invention

[0003] To address the shortcomings of the existing technologies, this invention proposes a novel metal hybrid ionic liquid catalyst based on an electron density modulation strategy, which can significantly improve the catalytic activity and stability of the aldol condensation of formaldehyde and propionaldehyde to prepare methacrolein under mild conditions.

[0004] A metal hybrid ionic liquid catalyst based on an electron density modulation strategy and its application, wherein the catalyst preparation method includes the following steps:

[0005] a) Preparation of ionic liquid aqueous solution. Weigh a certain mass of deionized water and place it in a three-necked flask. Add a certain mass of diethanolamine and place the three-necked flask in a low-temperature constant-temperature reaction bath and stir thoroughly. Add a certain mass of organic acid to a constant-pressure dropping funnel and slowly add it dropwise to the three-necked flask while stirring vigorously. After the addition is complete, continue the reaction for 2-4 hours.

[0006] b) Preparation of metal hybrid ionic liquid catalyst. A certain mass of the ionic liquid aqueous solution is weighed and placed in a three-necked flask, and a certain mass of the metal salt is weighed into the powder feeding funnel. The metal salt is slowly added to the ionic liquid aqueous solution under ultrasonic and mechanical stirring, and the reaction continues for 2 to 8 hours.

[0007] The organic acid mentioned is one or a combination of acetic acid, propionic acid, hydrochloric acid, and sulfuric acid.

[0008] The cations in the metal salt include Li + 、Na + K + Cs + 、Ba 2+ Mn 2+ Zn 2+ and Y 3+ One or more of the following; the anion in the metal salt includes Cl... - NO3 - CH3COO - SO4 2- PO3 - SO3CF3 - and BF4 - One or more of them.

[0009] The molar ratio of the metal salt to the ionic liquid is (0.1 to 1):1.

[0010] Compared with existing catalyst preparation techniques, the advantages of this invention are: the addition of metal ions significantly modulates the electron density of the ionic liquid, improves catalytic activity and stability, provides mild reaction conditions, and simplifies the catalyst preparation process. Detailed Implementation

[0011] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0012] Comparative Example 1

[0013] Weigh 25.5g of deionized water into a three-necked flask, add 8.5g of diethanolamine, and place the flask in a low-temperature constant-temperature reaction bath with thorough stirring. Add 6.0g of propionic acid to a constant-pressure dropping funnel, and slowly add it dropwise to the three-necked flask while stirring vigorously. After the addition is complete, continue the reaction for 2–4 hours to obtain an ionic liquid catalyst. Accurately weigh 1.60g of the ionic liquid catalyst obtained above, and add a mixed solution of 0.52g of formaldehyde aqueous solution and 0.38g of propionaldehyde dropwise to the catalyst. Catalytic reaction is carried out at 15°C to obtain methacrolein.

[0014] Example 1

[0015] 10g of the ionic liquid diethanolamine propionate aqueous solution was placed in a three-necked flask, and 0.66g of lithium acetate was placed in a powder feeding funnel. The metal salt was slowly added to the ionic liquid aqueous solution under ultrasonic and mechanical stirring. After the addition was complete, the reaction continued for 4 hours to obtain a metal hybrid ionic liquid catalyst. 1.64g of the obtained metal hybrid ionic liquid catalyst was accurately weighed, and a mixed solution of 0.50g of formaldehyde aqueous solution and 0.37g of propionaldehyde was added dropwise to the catalyst. The catalytic reaction was carried out at 15°C to obtain methacrolein.

[0016] Example 2

[0017] 10 g of the ionic liquid diethanolamine propionate aqueous solution was weighed and placed in a three-necked flask. 0.82 g of sodium acetate was weighed and placed in a powder feeding funnel. The metal salt was slowly added to the ionic liquid aqueous solution under ultrasonic and mechanical stirring. After the addition was complete, the reaction continued for 4 hours to obtain a metal hybrid ionic liquid catalyst. 1.65 g of the metal hybrid ionic liquid catalyst obtained above was accurately weighed, and a mixed solution of 0.50 g of formaldehyde aqueous solution and 0.37 g of propionaldehyde was added dropwise to the catalyst. The catalytic reaction was carried out at 15 °C to obtain methacrolein.

[0018] Example 3

[0019] 10g of the ionic liquid diethanolamine propionate aqueous solution was placed in a three-necked flask, and 0.99g of potassium acetate was placed in a powder feeding funnel. The metal salt was slowly added to the ionic liquid aqueous solution under ultrasonic and mechanical stirring. After the addition was complete, the reaction continued for 4 hours to obtain a metal hybrid ionic liquid catalyst. 1.66g of the obtained metal hybrid ionic liquid catalyst was accurately weighed, and a mixed solution of 0.49g of formaldehyde aqueous solution and 0.36g of propionaldehyde was added dropwise to the catalyst. The catalytic reaction was carried out at 15°C to obtain methacrolein.

[0020] Example 4

[0021] 10 g of the ionic liquid diethanolamine propionate aqueous solution was placed in a three-necked flask, and 1.92 g of cesium acetate was placed in a powder feeding funnel. The metal salt was slowly added to the ionic liquid aqueous solution under ultrasonic and mechanical stirring. After the addition was complete, the reaction continued for 4 hours to obtain a metal hybrid ionic liquid catalyst. 1.70 g of the metal hybrid ionic liquid catalyst obtained above was accurately weighed, and a mixed solution of 0.46 g of formaldehyde aqueous solution and 0.34 g of propionaldehyde was added dropwise to the catalyst. The catalytic reaction was carried out at 15 °C to obtain methacrolein.

[0022] Example 5

[0023] 10g of the ionic liquid diethanolamine propionate aqueous solution was placed in a three-necked flask, and 2.55g of barium acetate was placed in a powder feeding funnel. The metal salt was slowly added to the ionic liquid aqueous solution under ultrasonic and mechanical stirring. After the addition was complete, the reaction continued for 4 hours to obtain a metal hybrid ionic liquid catalyst. 1.73g of the obtained metal hybrid ionic liquid catalyst was accurately weighed, and a mixed solution of 0.45g of formaldehyde aqueous solution and 0.33g of propionaldehyde was added dropwise to the catalyst. The catalytic reaction was carried out at 15°C to obtain methacrolein.

[0024] Example 6

[0025] 10g of the ionic liquid diethanolamine propionate aqueous solution was placed in a three-necked flask, and 2.48g of manganese acetate was placed in a powder feeding funnel. The metal salt was slowly added to the ionic liquid aqueous solution under ultrasonic and mechanical stirring. After the addition was complete, the reaction continued for 4 hours to obtain a metal hybrid ionic liquid catalyst. 1.73g of the obtained metal hybrid ionic liquid catalyst was accurately weighed, and a mixed solution of 0.45g of formaldehyde aqueous solution and 0.33g of propionaldehyde was added dropwise to the catalyst. The catalytic reaction was carried out at 15°C to obtain methacrolein.

[0026] Example 7

[0027] 10g of the ionic liquid diethanolamine propionate aqueous solution was placed in a three-necked flask, and 1.84g of zinc acetate was placed in a powder feeding funnel. The metal salt was slowly added to the ionic liquid aqueous solution under ultrasonic and mechanical stirring. After the addition was complete, the reaction continued for 4 hours to obtain a metal hybrid ionic liquid catalyst. 1.7g of the obtained metal hybrid ionic liquid catalyst was accurately weighed, and a mixed solution of 0.47g of formaldehyde aqueous solution and 0.34g of propionaldehyde was added dropwise to the catalyst. The catalytic reaction was carried out at 15°C to obtain methacrolein.

[0028] Example 8

[0029] 10 g of the ionic liquid diethanolamine propionate aqueous solution was placed in a three-necked flask. 2.66 g of yttrium acetate was placed in a powder feeding funnel. The metal salt was slowly added to the ionic liquid aqueous solution under ultrasonic and mechanical stirring. After the addition was complete, the reaction continued for 4 hours to obtain a metal hybrid ionic liquid catalyst. 1.67 g of the obtained metal hybrid ionic liquid catalyst was accurately weighed, and a mixed solution of 0.43 g of formaldehyde aqueous solution and 0.32 g of propionaldehyde was added dropwise to the catalyst. The catalytic reaction was carried out at 15 °C to obtain methacrolein.

[0030] Table 1. Results of catalyst activity and stability evaluation

[0031]

[0032] *Based on the initial generation rate of methacrolein per unit active site.

[0033] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An application of a metal hybrid ionic liquid catalyst based on an electron density modulation strategy, characterized by: A metal-hybrid ionic liquid catalyst is generated in situ from a metal salt and an aqueous ionic liquid, and then used in the aldol condensation of formaldehyde and propionaldehyde to prepare methacrolein. The cation in the metal salt includes Li. + 、Na + K + Cs + 、Ba 2+ and Mn 2+ One or more of the following; the anion in the metal salt includes Cl... − NO3 − CH3COO − SO4 2− PO3 − SO3CF3 − and BF4 − One or more of them.

2. The application of the metal hybrid ionic liquid catalyst according to claim 1, characterized in that: The molar ratio of the metal salt to the ionic liquid is (0.1~1):

1.

3. The application of the metal hybrid ionic liquid catalyst according to claim 1, characterized in that: The ionic liquid is one or a combination of several of diethanolamine acetate, diethanolamine propionate, diethanolamine hydrochloride, and diethanolamine sulfate.

4. The application of the metal hybrid ionic liquid catalyst according to claim 1, characterized in that: The preparation steps of the metal hybrid ionic liquid catalyst are as follows: metal salt is continuously added to the ionic liquid aqueous solution under ultrasonic and mechanical stirring, and the reaction continues for 2 to 8 hours.

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