CN109999896B - High-efficiency catalyst applied to preparation of cyclohexanone by selective hydrogenation of phenol and preparation method thereof - Google Patents

Abstract

An efficient catalyst applied to the selective hydrogenation of phenol to produce cyclohexanone and a preparation method thereof belong to the field of novel catalytic materials. The invention takes basic KL molecular sieve as a carrier, adopts a simple impregnation method to introduce active nano-palladium, obtains a supported Pd/KL catalyst through reduction, and applies the catalyst to the selective hydrogenation of phenol to produce cyclohexanone products. Due to the special pore structure and basic site of the catalyst support, under mild reaction conditions, the product cyclohexanone can be directly obtained by selective hydrogenation of phenol, and the phenol conversion rate and cyclohexanone selectivity are both over 95%. The advantages of the method are: the preparation process of the catalyst involved in the present invention is simple and efficient, and the problem of increased preparation cost caused by the addition of other additives is avoided, the energy consumption of the reaction is low, the separation of the reaction product is simple, and it has a good application in the industry. development prospects.

Description

A kind of high-efficiency catalyst used in selective hydrogenation of phenol to produce cyclohexanone and its preparation method

technical field

The invention belongs to the field of catalytic materials, and in particular relates to a catalyst used in the selective hydrogenation of phenol to produce cyclohexanone and a catalytic technology thereof. The catalyst supports nano-palladium on a KL molecular sieve carrier to form a Pd/KL solid catalyst.

Background technique

As a widely used petrochemical product, cyclohexanone is an important intermediate in the production of nylon 6, nylon 66 and caprolactam, and is also an excellent solvent in the industry, especially in polymers such as fibers and polyurethanes.

At present, the industrial production methods of cyclohexanone mainly include cyclohexane oxidation method, phenol hydrogenation method and the like. Among them, the phenol hydrogenation method has high product selectivity and few side reactions, and at the same time, the efficient conversion of phenolic substances can significantly reduce the oxygen content of biofuels, which is of great significance to the improvement of biofuel quality. The most widely used phenol hydrogenation method is the liquid-phase hydrogenation of phenol to produce cyclohexanone. Hydrogenation generates cyclohexanol, which is further dehydrogenated at high temperature to generate cyclohexanone. This method has a complicated process flow and high energy consumption; Cyclohexanone, compared with the two-step method, has the advantages of simple operation and high reaction efficiency, and has gradually become a research hotspot. However, the design and preparation of high-efficiency catalysts is the key to this reaction, especially using a single catalyst under mild conditions to simultaneously achieve high conversion and high selectivity is still a challenge. In recent years, many researchers have devoted themselves to developing efficient catalysts for the selective hydrogenation of phenol.

A large number of studies have shown that using Pd as the active center to catalyze the hydrogenation of phenol shows high reaction efficiency and cyclohexanone selectivity. At present, supported palladium catalysts are mainly divided into the following categories:

(1) The oxide-supported palladium catalyst is a widely used phenol hydrogenation catalyst in industry at present. The reported supports mainly include MgO, γ-Al ₂ O ₃ , TiO ₂ , SiO ₂ and the like. For example, Chinese patent CN 106946668A discloses a method for producing cyclohexanone by hydrogenation of phenol. The method adds a water-soluble alkali metal-containing compound in the preparation process of the TiO ₂ supported palladium catalyst to promote the one-step production of phenol by catalytic hydrogenation. To obtain cyclohexanone, the addition of alkali metal greatly improves the conversion rate of phenol and the selectivity of cyclohexanone. South China University of Technology Du Li et al [Zhang J, Huang G, Zhang C, et al. Immobilization of highly active Pd nano-catalysts on functionalized mesoporous silica supports using mercapto groups as anchoring sites and their catalytic performance for phenol hydrogenation[J]. Chinese Journal of Catalysis , 2013, 34(8): 1519-1526.] The thiol-modified Pd-SH-MCM-41 and thiol-modified Pd-SH-MCM-41 and Pd-SH-SBA-15 catalyst, the strong interaction between surface-SH groups and Pd nanoparticles makes Pd nanoparticles highly dispersed on the surface of the carrier, thus showing high reactivity and cyclohexanone selectivity. However, in the above methods, it is necessary to add additives to change the properties of the carrier or improve the dispersion of active centers, thereby improving the catalytic performance, which not only makes the operation process complicated and tedious, but also increases the production cost of the preparation process.

(2) A supported palladium catalyst with a carbon material as a carrier. [WangY, Yao J, Li HR, etal.Highly selective hydrogenation of phenol and derivatives over a Pd@carbonnitride catalyst in aqueous media[J].J.Am.Chem.Soc.,2011,133, 2362-2365.] Preparation of a mesoporous graphitic carbon nitride (mpg-C ₃ N ₄ ) carrier supported by palladium for the hydrogenation of phenol to cyclohexanone, because the nitrogen doped in the carrier provides abundant The basic sites simultaneously increase the electron density of palladium, thus exhibiting excellent catalytic performance. However, this mesoporous graphitic carbon nitride suffers from problems such as low yield and low stability of the finished product, making it difficult to mass-produce it in industry.

(3) Supported palladium catalysts supported by metal-organic frameworks (MOFs). Wang Bin et al. [Guan QQ, WangB, Chai XS, et al.Comparison of Pd-UiO-66 and Pd-UiO-66-NH ₂ catalysts performance for phenol hydrogenation in aqueous medium[J]. Fuel, 2017, 205, 130-141. ] Comparing the catalytic effect of Pd-UiO-66 and Pd-UiO-66- _NH2 catalysts in the hydrogenation of phenol, the Pd-UiO-66 catalyst has higher phenol conversion than the Pd-UiO-66- _NH2 catalyst However, most of the products produced were cyclohexanol, and the Pd-UiO-66- _NH2 catalyst exhibited higher cyclohexanone selectivity due to its amino basicity. This shows that it is difficult for this catalyst to ensure high conversion and high cyclohexanone selectivity at the same time.

Therefore, it is of great significance to develop a catalyst and a catalytic method for efficiently catalyzing the hydrogenation of phenol to cyclohexanone.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention provides a catalyst and a catalytic method for efficiently catalyzing the selective hydrogenation of phenol to produce cyclohexanone.

The invention is characterized in that: using alkaline KL molecular sieve as a carrier to support nano-palladium, a supported Pd/KL catalyst is prepared, and by utilizing the special pore structure and basic site of KL molecular sieve, phenol can be selectively hydrogenated to directly prepare cyclohexane ketone, while achieving high selectivity and high yield of the target product. The preparation process of the catalyst is simple, and no other treatment methods and the addition of additives such as alkali metals are required. At the same time, the catalytic method involved in the present invention has mild reaction conditions, and after the reaction, the catalyst and the reaction can be mixed only by conventional simple separation. The separation of the liquid greatly saves the production cost.

The technical scheme of the present invention is as follows:

The preparation of the catalyst in the present invention uses KL molecular sieve as a carrier, that is, KL molecular sieve is synthesized and prepared first, and then palladium nanoparticles are supported on the catalyst carrier by an impregnation method to prepare a Pd/KL supported catalyst.

The Pd/KL catalyst in the present invention is used in the selective hydrogenation of phenol to produce cyclohexanone: take a certain mass of phenol and the Pd/KL catalyst and add it into a dichloromethane solvent, and fill the system with H ₂ at a certain pressure, At a certain reaction temperature and after a certain time of reaction, the catalyst and the reaction mixture are separated by centrifugation, and the liquid mixture is taken for analysis to obtain cyclohexanone with high selectivity.

The specific operation process of the present invention is as follows:

(1) Preparation of KL molecular sieve

According to the molar composition of potassium source: aluminum source: silicon source: water = (8-10): 1: (15-25): (350-600), the KL molecular sieve synthesis solution was prepared, and a certain amount of potassium hydroxide and aluminum was weighed. The source and deionized water were stirred until completely dissolved, then, 30% silica sol solution was added, and after aging at room temperature for 1 h, the synthesis solution was transferred to a polytetrafluoro-lined crystallization kettle, and crystallized at 120-170 ° C for 6 After -24h, the solid was washed and separated, dried at 80°C for 12h, and calcined at 500°C for 5h to obtain the KL molecular sieve carrier. The aluminum source used in the preparation process is any one of aluminum hydroxide, sodium metaaluminate, and aluminum sulfate octadecahydrate.

In the present invention, potassium hydroxide is used as potassium source to provide cations for L-type molecular sieves. The KL molecular sieve with special pore structure and basic site is obtained by the above method.

(2) Preparation of palladium supported catalyst

The KL molecular sieve carrier obtained in step (1) was dispersed in Na ₂ PdCl ₄ aqueous solution, stirred at room temperature for 12 h, washed, dried, and calcined at 350-500 ° C for 5 h; finally, added to NaBH ₄ solution for reduction, and dried at 80 ° C overnight , and finally the Pd/KL supported catalyst was obtained. The mass ratio of palladium to KL molecular sieve in the catalyst is (1-3):200.

Wherein, the concentration of the Na ₂ PdCl ₄ aqueous solution is 1.5mol/L-2mol/L, preferably 1.7mol/L.

The roasting condition in the step (2) is preferably roasting at 350° C. for 5h.

Another object of the present invention is to claim the application of the above-mentioned Pd/KL supported catalyst in the selective hydrogenation of phenol to produce cyclohexanone. The specific operation process is as follows:

Take by weighing a certain amount of phenol and Pd/KL catalyst, in the catalyst, the mol ratio of metal palladium and reactant is 1: (30-200), and in the reaction mixture, the mass concentration of phenol in solvent dichloromethane is 4.2-16.7g/mL , the reaction hydrogen pressure is 0.5-2.5MPa, and the reaction is carried out at 40-100 ℃ for 2-12h, and the stirring speed is 500-800rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation to obtain the product.

Compared with the prior art, the beneficial effect of the present invention is that the preparation process of the catalyst provided by the present invention is simple, efficient and low in cost. The catalyst prepared by applying the method of the invention can selectively hydrogenate phenol to directly obtain the target product cyclohexanone under mild conditions, the operation is simple, the energy consumption is low, and the excellent reaction catalytic activity can be achieved without adding any auxiliary agent. and the selectivity of cyclohexanone, the production cost for preparing cyclohexanone is greatly saved, the reaction product is single, and the conversion rate of phenol and the yield of cyclohexanone both exceed 95%. At the same time, the catalyst involved in the invention can separate the catalyst and the reaction mixture by centrifugation after the phenol hydrogenation reaction, and has a good application and development prospect in the industry.

Description of drawings

Fig. 1 is the scanning electron microscope picture (SEM) of Pd/KL catalyst;

Fig. 2 is the scanning transmission electron microscope picture (STEM) of Pd/KL catalyst;

Figure 3 is a powder X-ray diffraction pattern (XRD) of the Pd/KL catalyst.

Detailed ways

The present invention is described in detail below through the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial sources.

Example 1

(1) Preparation of KL molecular sieve

According to the molar composition of potassium source: aluminum source: silicon source: water=10:1:20:400, the KL molecular sieve synthesis solution was prepared. The potassium source, aluminum source and silicon source in the preparation process were potassium hydroxide, aluminum hydroxide, Silica sol. The metered potassium hydroxide, aluminum hydroxide and deionized water were refluxed and stirred in a boiling water bath for 1 hour until completely dissolved. After cooling to room temperature, a metered 30% silica sol solution was slowly added. After aging at room temperature for 1 hour, the synthesis solution was transferred to In a polytetrafluoro-lined crystallization kettle, hydrothermally crystallized at 170°C for 24h, the solid was washed and separated, dried at 80°C for 12h, and calcined at 500°C for 5h to obtain KL molecular sieve carrier.

(2) Preparation of Pd/KL catalyst

The KL molecular sieve carrier obtained in step (1) was dispersed in an aqueous Na ₂ PdCl ₄ solution, stirred at room temperature for 12 h, washed, dried, and calcined at 350° C. for 5 h; finally, a NaBH ₄ solution with a mass fraction of 2% was prepared for reduction, and 80 After drying at ℃ overnight, the Pd/KL supported catalyst was finally obtained. The mass ratio of palladium to KL molecular sieve in the catalyst was 3:200. The morphology of the catalyst is shown in Figure 1; the palladium nanoparticles in the catalyst are shown in Figure 2; the crystallinity of the catalyst is shown in Figure 3.

(3) Application of Pd/KL catalyst in selective hydrogenation of phenol

Weigh 0.05g Pd/KL catalyst and 0.5mmol reactant phenol, the molar ratio of metal palladium and reactant in the catalyst is 1:100, disperse in 5mL of dichloromethane solvent, replace with hydrogen three times, fill with 1MPa hydrogen pressure, The reaction was carried out at 60° C. for 6 hours, and the stirring speed was 800 rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation, and the liquid mixture was taken and analyzed. The conversion rate of phenol was 96.5%, and the selectivity of cyclohexanone was 94%.

Example 2

(1) Preparation of KL molecular sieve

According to the molar composition of potassium source: aluminum source: silicon source: water = 10:1:20:400, the KL molecular sieve synthesis solution was prepared. The potassium source, aluminum source and silicon source in the preparation process were potassium hydroxide, octadecahydrate sulfuric acid, respectively. Aluminum, silica sol. Stir the metered potassium hydroxide, aluminum sulfate and deionized water until they are completely dissolved, slowly add a metered 30% silica sol solution, and after aging at room temperature for 1 hour, transfer the synthesis solution to a polytetrafluoro-lined crystallization kettle, and at 170 After hydrothermal crystallization at ℃ for 24h, the solid was washed and separated, dried at 80℃ for 12h, and calcined at 500℃ for 5h to obtain KL molecular sieve carrier.

(2) The preparation of palladium-supported catalyst was the same as in Example 1.

(3) Application of Pd/KL catalyst in selective hydrogenation of phenol

Weigh 0.05g Pd/KL catalyst and 0.5mmol reactant phenol, the molar ratio of metal palladium and reactant in the catalyst is 1:100, disperse in 5mL of dichloromethane solvent, replace with hydrogen three times, fill with 1MPa hydrogen pressure, The reaction was carried out at 60° C. for 6 hours, and the stirring speed was 800 rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation, and the liquid mixture was taken and analyzed. The conversion rate of phenol was 85%, and the selectivity of cyclohexanone was 95%.

Example 3

(1) Preparation of KL molecular sieve

According to the molar composition of potassium source: aluminum source: silicon source: water=9:1:20:400, the KL molecular sieve synthetic solution was prepared. The potassium source, aluminum source and silicon source in the preparation process were potassium hydroxide, aluminum hydroxide, Silica sol. The metered potassium hydroxide, aluminum hydroxide and deionized water were refluxed and stirred in a boiling water bath for 1 hour until completely dissolved. After cooling to room temperature, a metered 30% silica sol solution was slowly added. After aging at room temperature for 1 hour, the synthesis solution was transferred to In a polytetrafluoro-lined crystallization kettle, hydrothermally crystallized at 170°C for 24h, the solid was washed and separated, dried at 80°C for 12h, and calcined at 500°C for 5h to obtain KL molecular sieve carrier.

(2) The preparation of palladium-supported catalyst was the same as in Example 1.

(3) Application of Pd/KL catalyst in selective hydrogenation of phenol

Weigh 0.05g Pd/KL catalyst and 0.5mmol reactant phenol, the molar ratio of metal palladium and reactant in the catalyst is 1:100, disperse in 5mL of dichloromethane solvent, replace with hydrogen three times, fill with 1MPa hydrogen pressure, The reaction was carried out at 60° C. for 6 hours, and the stirring speed was 800 rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation, and the liquid mixture was taken and analyzed. The conversion rate of phenol was 98.5%, and the selectivity of cyclohexanone was 97%.

Example 4

(1) The preparation of KL molecular sieve was the same as in Example 3.

(2) The preparation of palladium-supported catalyst was the same as in Example 1.

(3) Application of Pd/KL catalyst in selective hydrogenation of phenol

Weigh 0.05g Pd/KL catalyst and 0.5mmol reactant phenol, the molar ratio of metal palladium and reactant in the catalyst is 1:100, disperse in 5mL of dichloromethane solvent, replace with hydrogen three times, fill with 2MPa hydrogen pressure, The reaction was carried out at 60° C. for 6 hours, and the stirring speed was 800 rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation, and the liquid mixture was taken and analyzed. The conversion rate of phenol was 99.9%, and the selectivity of cyclohexanone was 90%.

Example 5

(1) The preparation of KL molecular sieve was the same as in Example 3.

(2) The preparation of palladium-supported catalyst was the same as in Example 1.

(3) Application of Pd/KL catalyst in selective hydrogenation of phenol

Weigh 0.05g Pd/KL catalyst and 0.5mmol reactant phenol, the molar ratio of metal palladium and reactant in the catalyst is 1:100, disperse in 5mL of dichloromethane solvent, replace three times with hydrogen, and fill with 0.5MPa hydrogen pressure , reacted at 60°C for 6h, stirring at 800rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation, and the liquid mixture was taken and analyzed. The conversion rate of phenol was 65%, and the selectivity of cyclohexanone was 96%.

Example 6

(1) The preparation of KL molecular sieve was the same as in Example 3.

(2) The preparation of palladium-supported catalyst was the same as in Example 1.

(3) Application of Pd/KL catalyst in selective hydrogenation of phenol

Weigh 0.05g Pd/KL catalyst and 0.5mmol reactant phenol, the molar ratio of metal palladium and reactant in the catalyst is 1:100, disperse in 5mL of dichloromethane solvent, replace with hydrogen three times, fill with 1MPa hydrogen pressure, The reaction was carried out at 80° C. for 3 hours, and the stirring speed was 800 rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation, and the liquid mixture was taken and analyzed. The conversion rate of phenol was 99%, and the selectivity of cyclohexanone was 93%.

Example 7

(1) The preparation of KL molecular sieve was the same as in Example 3.

(2) The preparation of palladium-supported catalyst was the same as in Example 1.

(3) Application of Pd/KL catalyst in selective hydrogenation of phenol

Weigh 0.05g Pd/KL catalyst and 0.5mmol reactant phenol, the molar ratio of metal palladium and reactant in the catalyst is 1:100, disperse in 5mL of dichloromethane solvent, replace with hydrogen three times, fill with 1MPa hydrogen pressure, The reaction was carried out at 100° C. for 2 h, and the stirring speed was 800 rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation, and the liquid mixture was taken and analyzed. The conversion rate of phenol was 99.2%, and the selectivity of cyclohexanone was 90%.

Example 8

(1) The preparation of KL molecular sieve was the same as in Example 3.

(2) The preparation of palladium-supported catalyst was the same as in Example 1.

(3) Application of Pd/KL catalyst in selective hydrogenation of phenol

Weigh 0.05g Pd/KL catalyst and 0.5mmol reactant phenol, the molar ratio of metal palladium and reactant in the catalyst is 1:100, disperse in 3mL of dichloromethane solvent, replace three times with hydrogen, and fill with 1MPa hydrogen pressure, The reaction was carried out at 60° C. for 6 hours, and the stirring speed was 800 rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation, and the liquid mixture was taken and analyzed. The conversion rate of phenol was 98.5%, and the selectivity of cyclohexanone was 97%.

Example 9

(1) The preparation of KL molecular sieve was the same as in Example 3.

(2) The preparation of palladium-supported catalyst was the same as in Example 1.

(3) Application of Pd/KL catalyst in selective hydrogenation of phenol

Weigh 0.05g Pd/KL catalyst and 0.5mmol reactant phenol, the molar ratio of metal palladium and reactant in the catalyst is 1:100, disperse in 8mL of dichloromethane solvent, replace with hydrogen three times, fill with 1MPa hydrogen pressure, The reaction was carried out at 60° C. for 6 hours, and the stirring speed was 800 rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation, and the liquid mixture was taken and analyzed. The conversion rate of phenol was 88%, and the selectivity of cyclohexanone was 99%.

Example 10

(1) The preparation of KL molecular sieve was the same as in Example 3.

(2) The preparation of palladium-supported catalyst was the same as in Example 1.

(3) Application of Pd/KL catalyst in selective hydrogenation of phenol

Weigh 0.05g Pd/KL catalyst and 0.5mmol reactant phenol, the molar ratio of metal palladium and reactant in the catalyst is 1:50, disperse in 5mL of dichloromethane solvent, replace three times with hydrogen, fill with 1MPa hydrogen pressure, The reaction was carried out at 60° C. for 6 hours, and the stirring speed was 800 rpm. After the reaction, the catalyst and the reaction mixture were separated by centrifugation, and the liquid mixture was taken and analyzed. The conversion rate of phenol was 98%, and the selectivity of cyclohexanone was 93%.

The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (1)

1. A method for preparing cyclohexanone by selective hydrogenation of phenol by Pd/KL catalysis is characterized in that a certain amount of phenol and a Pd/KL catalyst are weighed, and the molar ratio of metal palladium in the catalyst to a reactant is 1: (30-200), the mass concentration of phenol in a solvent dichloromethane in the reaction mixture is 4.2-16.7g/mL, the pressure of reaction hydrogen is 0.5-2.5MPa, the reaction is carried out for 2-12h at 40-100 ℃, the stirring speed is 500-800rpm, and after the reaction is finished, the catalyst and the reaction mixture are separated by centrifugation to obtain the high-selectivity cyclohexanone;

the Pd/KL catalyst is prepared by the following specific steps:

(1) preparation of KL molecular sieve

According to the potassium source: an aluminum source: silicon source: water ═ 8-10: 1: (15-25): (350-600) preparing KL molecular sieve synthetic liquid by using the molar composition, wherein an aluminum source is any one of aluminum hydroxide, sodium metaaluminate and aluminum sulfate octadecahydrate; weighing a certain amount of potassium hydroxide, an aluminum source and deionized water, stirring until the potassium hydroxide, the aluminum source and the deionized water are completely dissolved, then adding 30% of silica sol solution, aging at room temperature for 1h, transferring the synthetic liquid into a polytetrafluoroethylene lining crystallization kettle, crystallizing at 120-170 ℃ for 6-24h, washing and separating the solid, drying at 80 ℃ for 12h, and roasting at 500 ℃ for 5h to obtain a KL molecular sieve carrier;

(2) preparation of palladium supported catalyst

Dispersing the KL molecular sieve carrier obtained in the step (1) in a concentration of 1.7mmol/LNa₂PdCl₄Stirring in water solution at room temperature for 12h, washing, drying, and roasting at 350 deg.C for 5 h; finally, add NaBH₄Reducing the solution, and drying the solution at 80 ℃ overnight to finally obtain the Pd/KL supported catalyst; the mass ratio of palladium to the KL molecular sieve in the catalyst is (1-3): 200.

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