Acid-base bifunctional hybrid catalyst for synthesizing crotonaldehyde and preparation method of acid-base bifunctional hybrid catalyst

Abstract

The invention discloses an acid-base bifunctional hybrid catalyst for synthesizing crotonaldehyde and a preparation method of the acid-base bifunctional hybrid catalyst. According to the catalyst, mesoporous silica is used as a carrier, and aluminum species serving as Lewis acid sites and organic amido serving as alkaline sites are modified on the surface and in pore channels of the carrier through chemical bonds in a contemporaneous manner. The surface of a pore channel of the carrier is modified with Lewis acid sites and organic amine alkaline sites in time through chemical bonds, the alkaline sites efficiently catalyze condensation of acetaldehyde to generate 3-hydroxybutyraldehyde, and adjacent Lewis acid sites immediately promote dehydration of acetaldehyde to generate crotonaldehyde, so that efficient proceeding of cascade reaction is realized. Meanwhile, the catalyst is prepared through stable chemical bonding, active components are not prone to loss, and the catalyst has excellent stability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde and its preparation method. Background Technology

[0002] Crotonaldehyde, also known as 2-butenal, is a high-value-added chemical intermediate widely used in food, pharmaceuticals, pesticides, and synthetic rubber. Its most important downstream product is sorbic acid and its potassium salt, which, as a highly efficient and non-toxic food preservative, is experiencing continuously growing market demand. In addition, crotonaldehyde can also be used to synthesize fragrances, 3-methoxybutyraldehyde, and the pesticide thiamethoxam, among other important fine chemicals.

[0003] The main production routes for crotonaldehyde are the propionaldehyde method and the acetaldehyde method. The propionaldehyde method is difficult to scale up due to high raw material costs and expensive catalysts. The mainstream process for crotonaldehyde production is the acetaldehyde method, where two molecules of acetaldehyde undergo a condensation reaction to produce 3-hydroxybutyraldehyde, which is then further dehydrated to produce crotonaldehyde. Industrially, crotonaldehyde is mainly produced through the aldol condensation of acetaldehyde and subsequent dehydration. Industrially, the two-step reaction is usually carried out separately. This process typically uses a homogeneous base catalyst (such as sodium hydroxide), which, although highly active, presents environmental problems such as difficulty in catalyst separation, severe equipment corrosion, and the generation of large amounts of alkaline and saline wastewater.

[0004] To address the aforementioned issues, heterogeneous catalysts capable of simultaneously catalyzing acetaldehyde condensation and dehydration have become a research hotspot. CN115947349A discloses a heteroatom β-zeolite that can be used for the aldol condensation reaction of low-carbon aldehydes, such as the synthesis of crotonaldehyde from acetaldehyde, but the conversion rate is limited. CN101462044A discloses a composite catalyst of alkaline earth metal oxides and zeolites or alumina, which solves the problems of wastewater and high energy consumption in crotonaldehyde production, but the reaction conditions are relatively harsh.

[0005] Therefore, developing a heterogeneous catalyst with mild reaction conditions and high conversion and selectivity for the efficient synthesis of crotonaldehyde by acetaldehyde condensation and dehydration has important industrial application value. Summary of the Invention

[0006] To address the aforementioned problems, one objective of this invention is to provide an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde, which exhibits mild catalytic conditions, high product yield, and is suitable for industrial application.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A bifunctional acid-base hybrid catalyst for the synthesis of crotonaldehyde, wherein the catalyst is supported on mesoporous silica, and the surface and pores of the support are simultaneously modified by chemical bonds with aluminum species as Lewis acid sites and organic amine groups as basic sites.

[0009] In this invention, the pore surface of the support is simultaneously modified with Lewis acid sites and organic amine basic sites through chemical bonding. The basic sites efficiently catalyze the condensation of acetaldehyde to 3-hydroxybutyraldehyde, while the adjacent Lewis acid sites subsequently promote its dehydration to crotonaldehyde, achieving a highly efficient tandem reaction. Simultaneously, the catalyst is prepared through stable chemical bonding, preventing the loss of active components and exhibiting excellent stability.

[0010] In one embodiment of the present invention, the mesoporous silica carrier has an ordered mesoporous structure, preferably comprising one or more of SBA-15, MCM-41, and KIT-6.

[0011] In one embodiment of the present invention, the aluminum species is an organoaluminum compound, preferably one or more of aluminum alkoxides, alkyl aluminum, and aluminum chelates, more preferably aluminum trisec-butoxide and / or aluminum triisopropoxide.

[0012] In one embodiment of the invention, the aluminum species is introduced via chemical grafting.

[0013] In one embodiment of the present invention, the organic amine group is introduced by chemical grafting of an aminosilane coupling agent of the general formula (R”O)3Si-R'-N(R)2, wherein R” is a C1-C2 alkyl group, R' is a C1-C6 alkylene group, and R is H or a C1-C4 alkyl group; preferably, the aminosilane coupling agent is 3-aminopropyltriethoxysilane and / or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

[0014] Another object of the present invention is to provide a method for preparing a catalyst.

[0015] A method for preparing the above-mentioned catalyst, the method comprising the following steps:

[0016] S1: Mesoporous silica carrier undergoes dehydration pretreatment;

[0017] S2: The first reaction is carried out by contacting the first solution containing an aluminum source to obtain an aluminum-containing intermediate;

[0018] S3: A second reaction is carried out by contacting a second solution containing aminosilane to obtain the catalyst;

[0019] S2 and S3 can be performed in interchangeably or simultaneously.

[0020] In one embodiment of the present invention, the solvent of the solutions in S2 and S3 is a C6-C10 aromatic hydrocarbon and / or a C6-C10 alkane, preferably one or more of toluene, benzene, xylene, and n-hexane.

[0021] In one embodiment of the present invention, the reaction temperature in S2 and S3 is 50-120°C, and the reaction time is 2-24 hours.

[0022] Another object of the present invention is to provide an application of an acid-base bifunctional hybrid catalyst.

[0023] Application of an acid-base bifunctional hybrid catalyst, wherein the catalyst is the catalyst described above or a catalyst prepared by the method described above, and the catalyst is used to synthesize crotonaldehyde.

[0024] Another object of the present invention is to provide a method for synthesizing crotonaldehyde.

[0025] A method for synthesizing crotonaldehyde, wherein the method employs the catalyst described above, or the catalyst prepared by the method described above, wherein the method uses an acid-base bifunctional hybrid catalyst to catalyze the condensation-dehydration reaction of acetaldehyde.

[0026] In one embodiment of the present invention, the reaction is carried out in a batch reactor or a continuous flow fixed-bed reactor at a temperature of 0-150°C. The preferred reaction temperature for the batch reactor is 50-80°C, and the preferred temperature for the fixed-bed reactor is 100-140°C.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The catalyst provided by the present invention can achieve efficient acetaldehyde condensation and dehydration tandem reaction, and significantly improve the selectivity and yield of crotonaldehyde.

[0029] (2) The catalyst is prepared through stable chemical bonding, the active components are not easily lost, and it has good thermal stability and reusability.

[0030] (3) The catalyst is a solid, which is easy to separate from the reaction system and can realize continuous production. It avoids the equipment corrosion and wastewater pollution problems of homogeneous catalysis process, which is in line with the development direction of green chemistry. Detailed Implementation

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the specific embodiments will be briefly introduced below. Obviously, the embodiments described below are some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these embodiments without creative effort.

[0032] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. All raw materials or instruments used are commercially available conventional products, including but not limited to those used in the embodiments of this application.

[0033] The materials involved in this invention are: P123 template agent (polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, molecular weight 5800), 2M hydrochloric acid, tetraethyl orthosilicate (99%), aluminum tri-sec-butoxide (97%), toluene (99.85%, ultra-dry), ethanol (99.7%, anhydrous), 3A molecular sieve, graphite powder, 3-aminopropyltriethoxysilane (99%), N-methyl-3-aminopropyltrimethoxysilane, aluminum nitrate nonahydrate (98%), etc., provided by Beijing Innocare; acetaldehyde (99.5%) is a product of Wanhua Chemical.

[0034] The analytical characterization instruments involved in this invention include: a gas chromatograph (Agilent 7890A), where the material is diluted with acetonitrile by a certain factor before testing to obtain the content of substances such as acetaldehyde for calculating conversion and selectivity; and a fully automated temperature-programmed chemisorption analyzer (MICROMERITICS, AutoChem II 2920) for temperature-programmed desorption (TPD) to detect the loading of acidic and basic sites. Acidic and basic sites are tested using ammonia and carbon dioxide, respectively, with helium as the carrier gas, and the temperature is increased to 600°C at a constant rate of 10°C / min and held for 5 min.

[0035] Example 1

[0036] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde and its performance testing, including the following steps:

[0037] (1) Preparation of SBA-15 support: 4.0 g of P123 template agent was dissolved in 125 mL of 2 M hydrochloric acid and 30 g of water, and stirred at 40 °C until clear. 8.5 g of tetraethyl orthosilicate was added, and stirred at 40 °C for 24 hours. The mixture was transferred to a reaction vessel and hydrothermally heated at 100 °C for 24 hours. After filtration, washing, and drying, it was calcined in a muffle furnace at 550 °C for 6 hours to obtain the SBA-15 support.

[0038] (2) Preparation of Al-SBA-15 intermediate: 1.0 g of SBA-15 was dehydrated under vacuum at 300 °C for 3 hours. In a glove box, it was mixed with 20 mL of anhydrous toluene solution containing 0.5 mmol of aluminum trisec-butoxide. The mixture was refluxed at 110 °C for 8 hours under N2 protection. After hot filtration, it was washed with toluene and ethanol and dried under vacuum at 60 °C.

[0039] (3) Preparation of Al-NH2-SBA-15 catalyst: The Al-SBA-15 obtained above was vacuum-treated at 150℃ for 1 hour. It was mixed with 20 mL of anhydrous toluene solution containing 2.0 mmol of 3-aminopropyltriethoxysilane and refluxed at 80℃ for 12 hours under N2 protection. After the reaction was completed, it was filtered and purified by Soxhlet extraction with ethanol for 24 hours. Finally, it was vacuum-dried at 60℃ for 12 hours to obtain the final catalyst. Temperature-programmed desorption (TPD) analysis showed that both acidic and basic sites were successfully loaded on the support.

[0040] (4) Catalyst performance test: The above catalyst was used for the condensation and dehydration of acetaldehyde to produce crotonaldehyde. 50 mg of catalyst, 5 mmol of acetaldehyde, 5 mL of toluene, and a small amount of 3A molecular sieve were added to a high-pressure flask. The reaction system was placed in a 70℃ oil bath and stirred for 2 h. After the reaction, the high-pressure flask was placed in an ice-water bath to cool, and the product was taken out and its composition was analyzed by gas chromatography. The results showed that the acetaldehyde conversion rate was 95.1%, the crotonaldehyde selectivity was 88.3%, and the catalyst performance did not show significant decline after 20 cycles of recycling.

[0041] Example 2

[0042] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde and its performance test. The only difference from Example 1 is that the amount of aluminum trisec-butoxide used is 0.1 mmol.

[0043] Gas chromatography results showed that the acetaldehyde conversion rate was 90.7% and the crotonaldehyde selectivity was 71.5%.

[0044] Example 3

[0045] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde and its performance test. The only difference from Example 1 is that the amount of aluminum trisec-butoxide used is 2.0 mmol.

[0046] Gas chromatography results showed that the acetaldehyde conversion rate was 92.6% and the crotonaldehyde selectivity was 81.6%.

[0047] Example 4

[0048] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde and its performance test. The only difference from Example 1 is that the amount of 3-aminopropyltriethoxysilane used is 0.5 mmol.

[0049] Gas chromatography results showed that the acetaldehyde conversion rate was 86.0% and the crotonaldehyde selectivity was 67.0%.

[0050] Example 5

[0051] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde and its performance testing. The only difference from Example 1 is that the amount of 3-aminopropyltriethoxysilane used is 4.0 mmol.

[0052] Gas chromatography results showed that the acetaldehyde conversion rate was 93.8% and the crotonaldehyde selectivity was 84.1%.

[0053] Example 6

[0054] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde and its performance testing. The only difference from Example 1 is that the aluminum source is replaced with aluminum triisopropoxide.

[0055] Gas chromatography results showed that the acetaldehyde conversion rate was 94.4% and the crotonaldehyde selectivity was 86.9%.

[0056] Example 7

[0057] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde and its performance testing. The only difference from Example 1 is that the amine source is replaced with N-methyl-3-aminopropyltrimethoxysilane.

[0058] Gas chromatography results showed that the acetaldehyde conversion rate was 92.1% and the crotonaldehyde selectivity was 85.0%.

[0059] Example 8

[0060] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde and its performance testing. The only difference from Example 1 is that the solvent is replaced with anhydrous n-hexane.

[0061] Gas chromatography results showed that the acetaldehyde conversion rate was 88.9% and the crotonaldehyde selectivity was 85.8%.

[0062] Example 9

[0063] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde and its performance testing. The only difference from Example 1 is that the reaction temperature for the synthesis of crotonaldehyde is 50°C.

[0064] Gas chromatography results showed that the acetaldehyde conversion rate was 78.3% and the crotonaldehyde selectivity was 87.1%.

[0065] Example 10

[0066] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde. The difference from Example 1 is that basic sites are first loaded onto the support, followed by acidic sites. The method includes the following steps:

[0067] (1) Preparation of NH2-SBA-15 intermediate: 1.0 g of SBA-15 described in Example 1 was dehydrated under vacuum at 300 °C for 3 hours. It was then mixed with 20 mL of anhydrous toluene solution containing 2.0 mmol of 3-aminopropyltriethoxysilane and refluxed at 80 °C for 12 hours under N2 protection. After the reaction, the mixture was filtered, purified by Soxhlet extraction with ethanol for 24 hours, and dried under vacuum at 60 °C to obtain the NH2-SBA-15 intermediate.

[0068] (2) Preparation of NH2-Al-SBA-15 catalyst: The above NH2-SBA-15 intermediate was vacuum-treated at 150 °C for 1 hour, and then mixed with 20 mL of anhydrous toluene solution containing 0.5 mmol of aluminum trisec-butoxide. The mixture was refluxed at 110 °C for 8 hours under N2 protection. After the reaction, the mixture was hot-filtered, washed with toluene and ethanol, and vacuum-dried at 60 °C to obtain the final catalyst. TPD analysis showed that both acidic and basic sites were successfully loaded onto the support.

[0069] (3) Catalyst performance test: The above catalyst was used for the condensation and dehydration of acetaldehyde to produce crotonaldehyde. 50 mg of catalyst, 5 mmol of acetaldehyde, 5 mL of toluene, and a small amount of 3A molecular sieve were added to a high-pressure flask. The reaction system was placed in a 70℃ oil bath and stirred for 2 h. After the reaction, the high-pressure flask was placed in an ice-water bath to cool, and the product was taken out and its composition was analyzed by gas chromatography. The results showed that the acetaldehyde conversion rate was 93.%, the crotonaldehyde selectivity was 82.8%, and the catalyst performance did not show significant decline after 20 cycles of recycling.

[0070] Example 11

[0071] This embodiment provides a method for preparing an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde. The difference from Example 1 is that both acidic and basic sites are simultaneously supported on a support, and the method includes the following steps:

[0072] (1) Preparation of Al-NH2-SBA-15 catalyst: 1.0 g of SBA-15 prepared in Example 1 was dehydrated under vacuum at 300 °C for 3 hours. In a glove box, 20 mL of anhydrous toluene was measured, and 0.5 mmol of aluminum trisec-butoxide and 2.0 mmol of 3-aminopropyltriethoxysilane were added simultaneously, and the mixture was shaken to mix thoroughly. The SBA-15 support was transferred to a reaction flask, and the mixed solution was also transferred to the reaction flask using a syringe under N2 protection. The reaction system was heated to 85 °C and refluxed for 16 hours. During this process, aluminum species and aminosilane reacted simultaneously with the silanol groups on the surface of the support. After the reaction was completed, the mixture was cooled to room temperature and the solid product was collected by filtration. The solid product was purified by continuous extraction with ethanol in a Soxhlet extractor for 24 hours. The purified solid was dried under vacuum at 60 °C for 12 hours to obtain the final acid-base bifunctional catalyst. TPD analysis showed that both acidic and basic sites were successfully loaded on the support.

[0073] (2) Catalyst performance test: The above catalyst was used for the condensation and dehydration of acetaldehyde to produce crotonaldehyde. 50 mg of catalyst, 5 mmol of acetaldehyde, 5 mL of toluene, and a small amount of 3A molecular sieve were added to a high-pressure flask. The reaction system was placed in a 70℃ oil bath and stirred for 2 h. After the reaction, the high-pressure flask was placed in an ice-water bath to cool, and the product was removed and its composition was analyzed by gas chromatography. The results showed that the acetaldehyde conversion rate was 91.1%, the crotonaldehyde selectivity was 84.8%, and the catalyst performance did not show significant decline after 20 cycles of recycling.

[0074] Example 12

[0075] This embodiment provides a method for using an acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde, including the following steps:

[0076] (1) Preparation of Al-NH2-SBA-15 catalyst: Same as in Example 1

[0077] (2) Catalyst performance test: The Al-NH2-SBA-15 catalyst powder was uniformly mixed with 5 wt% graphite powder, pressed into shape on a tablet press, and crushed to obtain 20-40 mesh particles. 2.0 g of the above-mentioned shaped catalyst was packed into a stainless steel fixed-bed reactor with an inner diameter of 10 mm, and the two ends of the reactor were filled with inert quartz sand. High-purity nitrogen was introduced as the carrier gas and dilution gas, and the molar ratio of nitrogen to acetaldehyde was controlled at 10:1, and the mass hourly space velocity of acetaldehyde was 1.0 h⁻¹. The reaction was stably operated at 120 °C, and the reaction products were analyzed by gas chromatography after condensation. The results showed that the acetaldehyde conversion rate was 89.1%, the crotonaldehyde selectivity was 85.0%, and the catalytic performance did not show significant decline after 200 h of use.

[0078] Comparative Example 1

[0079] Compared with Example 1, the difference is that only aluminum (acidic site) is loaded on the support, and no amine (basic site) is loaded. That is, the Al-SBA-15 obtained in step (2) is used to directly catalyze the synthesis of crotonaldehyde from acetaldehyde. Gas chromatography analysis showed that the acetaldehyde conversion rate was 7.3% and the crotonaldehyde selectivity was 0.8%.

[0080] Comparative Example 2

[0081] Compared with Example 11, the difference is that only amines (basic sites) are loaded on the support, and aluminum (acidic sites) is not loaded. That is, the NH2-SBA-15 obtained in step (1) is used to directly catalyze the synthesis of crotonaldehyde from acetaldehyde. Gas chromatography analysis showed that the acetaldehyde conversion rate was 90.5% and the crotonaldehyde selectivity was 2.2%.

[0082] Comparative Example 3

[0083] 50 mg each of Al-SBA-15 from Example 1 and NH2-SBA-15 from Example 11 were physically mixed in a mortar for 10 min to obtain a physically mixed catalyst, which was used to catalyze the synthesis of crotonaldehyde from acetaldehyde. Gas chromatography analysis showed that the acetaldehyde conversion rate was 70.4% and the crotonaldehyde selectivity was 56.6%.

[0084] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An acid-base bifunctional hybrid catalyst for the synthesis of crotonaldehyde, characterized in that, The catalyst uses mesoporous silica as a support, and the surface and pores of the support are simultaneously modified by chemical bonds with aluminum species as Lewis acid sites and organic amine groups as basic sites.

2. The catalyst according to claim 1, characterized in that, The mesoporous silica carrier has an ordered mesoporous structure, preferably comprising one or more of SBA-15, MCM-41, and KIT-6.

3. The catalyst according to claim 1 or 2, characterized in that, The aluminum species is an organoaluminum compound, preferably one or more of aluminum alkoxides, alkyl aluminum, and aluminum chelates, more preferably aluminum trisec-butoxide and / or aluminum triisopropoxide. And / or, the aluminum species are introduced via chemical grafting.

4. The catalyst according to any one of claims 1-3, characterized in that, The organic amine group is introduced by chemical grafting of an aminosilane coupling agent with the general formula (R”O)3Si-R'-N(R)2, wherein R” is a C1-C2 alkyl group, R' is a C1-C6 alkylene group, and R is H or a C1-C4 alkyl group; preferably, the aminosilane coupling agent is 3-aminopropyltriethoxysilane and / or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

5. A method for preparing the catalyst according to any one of claims 1-4, characterized in that, The method includes the following steps: S1: Mesoporous silica carrier undergoes dehydration pretreatment; S2: The first reaction is carried out by contacting the first solution containing an aluminum source to obtain an aluminum-containing intermediate; S3: A second reaction is carried out by contacting a second solution containing aminosilane to obtain the catalyst; S2 and S3 can be performed in interchangeably or simultaneously.

6. The method according to claim 5, characterized in that, The solvents in solutions S2 and S3 are C6-C10 aromatic hydrocarbons and / or C6-C10 alkanes, preferably one or more of toluene, benzene, xylene, and n-hexane; And / or, the reaction temperature in S2 and S3 is 50-120℃, and the reaction time is 2-24 hours.

7. Application of an acid-base bifunctional hybrid catalyst, wherein the catalyst is the catalyst according to any one of claims 1-4, or the catalyst prepared by the method according to claim 5 or 6, and the catalyst is used to synthesize crotonaldehyde.

8. A method for synthesizing crotonaldehyde, said method using the catalyst according to any one of claims 1-4, or the catalyst prepared by the method according to claim 5 or 6, characterized in that, The method uses an acid-base bifunctional hybrid catalyst to catalyze the condensation-dehydration reaction of acetaldehyde.

9. The method according to claim 8, characterized in that, The reaction is carried out in a batch reactor or a continuous flow fixed-bed reactor at a temperature of 0-150°C. The preferred reaction temperature for a batch reactor is 50-80°C, and the preferred temperature for a fixed-bed reactor is 100-140°C.