Palladium catalyst for selective hydrogenation of acetylene as well as preparation method and application of palladium catalyst

Abstract

The invention provides a preparation method of a palladium catalyst for acetylene selective hydrogenation, which comprises the following steps: S1, dropwise adding an amine compound into a palladium salt solution until the pH value of a mixed solution is 6-14, and then stirring and dispersing the mixed solution to form a palladium complex solution; s2, the gamma-Al2O3 pellets are impregnated in a palladium complex solution, impregnation liquid is removed after sufficient adsorption, drying, roasting and reduction are conducted, and the palladium catalyst is obtained. According to the preparation method of the palladium catalyst for acetylene selective hydrogenation, an amine compound is used as an alkali source, a coordination agent and a stabilizer at the same time, through coordination of N atoms and Pd, large steric hindrance is formed, different Pd active centers are effectively isolated, and the prepared Pd catalyst has the advantages that the dispersion is high, ethylene and Pd are easily adsorbed in a pi bond mode, and the catalytic activity of the catalyst is improved. Therefore, the catalyst is more easily desorbed from an active center, excessive hydrogenation is avoided, and the catalyst shows high activity and ethylene selectivity in acetylene selective hydrogenation reaction.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a palladium catalyst for the selective hydrogenation of acetylene, its preparation method, and its application. Background Technology

[0002] Ethylene is an important raw material for the production of various chemicals. It is derived from petroleum cracking. This process route produces acetylene along with ethylene, accounting for about 0.5-3%. The presence of this acetylene can not only poison the Ziegler-Natta catalyst in the ethylene polymerization reaction, but may also generate explosive metal acetylides, posing certain safety hazards. Therefore, before the ethylene polymerization reaction, the concentration of acetylene impurities in ethylene needs to be reduced to below 5 ppm.

[0003] Selective hydrogenation of acetylene can convert acetylene into the target product ethylene, and Pd catalysts are widely used in this reaction. However, Pd has high hydrogenation activity, which easily leads to over-hydrogenation of acetylene to ethane and the formation of green oil, which covers active sites and causes catalyst deactivation. Geometric effects are one of the main factors affecting the selectivity of selective hydrogenation of acetylene, mainly because the spatial arrangement of active metal atoms affects the adsorption configuration of ethylene. As shown in the figure, ethylene molecules have three adsorption modes, with adsorption strength π-bond mode < di-σ mode < methinedine mode. When ethylene is adsorbed with a single Pd atom in π-bond mode, the desorption energy of ethylene is lower than the energy required for over-hydrogenation, making over-hydrogenation less likely and resulting in high selectivity for ethylene. Therefore, by reducing the number of continuous Pd sites, the adsorption configuration of ethylene can be transformed into a weak π-bond adsorption mode, which can improve the selectivity of ethylene. In addition, electronic effects can also significantly affect the hydrogenation activity and selectivity of acetylene. Electron-rich Pd can weaken the adsorption strength of acetylene and ethylene, improve the selectivity of the reaction, and provide more Pd sites for hydrogen adsorption activation, thereby improving hydrogenation activity. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a palladium catalyst for selective hydrogenation of acetylene, its preparation method and its application, which solves the problem of poor selectivity in acetylene hydrogenation. The prepared palladium catalyst has high activity and can significantly improve the selectivity of acetylene hydrogenation.

[0005] The technical solution adopted in this invention is: A method for preparing a palladium catalyst for selective hydrogenation of acetylene, wherein the palladium catalyst includes a support and palladium disposed on the support, wherein the support is γ-Al2O3 microspheres, and the palladium catalyst is prepared by impregnation, drying, calcination and reduction using palladium salt as a precursor and amine compound as a base source, ligand and stabilizer. The preparation method specifically includes the following steps: Step S1. At 25~80℃, add amine compounds dropwise to the palladium salt solution until the pH of the mixture is 6~14, then stir and disperse the mixture to form a palladium complex solution; Step S2. Immerse γ-Al2O3 microspheres in a palladium complex solution. After sufficient adsorption, remove the impregnation solution, dry the microspheres, calcine them, and finally reduce them under a reducing atmosphere to obtain the palladium catalyst.

[0006] Preferably, in the method for preparing the palladium catalyst for selective hydrogenation of acetylene, the palladium salt in step S1 is selected from one or more of palladium nitrate, palladium chloroacetic acid, and palladium acetate; the dispersion time is 1-24 h.

[0007] Preferably, in the method for preparing the palladium catalyst for selective hydrogenation of acetylene, the amine compound in step S1 is selected from one or more of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0008] Preferably, in the method for preparing the palladium catalyst for selective hydrogenation of acetylene, the general structural formula of the palladium complex solution in step S1 is: [Pd(L)]X m+ Where L is NH2-(CH2)2-[NH-(CH2)2] p -NH2, P=1-3, X is the anion, and m is the charge of the complex cation.

[0009] Preferably, in the method for preparing the palladium catalyst for selective hydrogenation of acetylene, the adsorption time in step S2 is 6-24 h.

[0010] Preferably, in the method for preparing the palladium catalyst for selective hydrogenation of acetylene, the drying temperature in step S2 is 100-120℃, the drying time is 1-4h, the calcination temperature is 300-600℃, and the calcination time is 1-6h.

[0011] Preferably, in the method for preparing the palladium catalyst for selective hydrogenation of acetylene, the reduction temperature in step S2 is 200-400℃ and the reduction time is 2-5 h.

[0012] Preferably, in the method for preparing the palladium catalyst for selective hydrogenation of acetylene, the palladium loading in the palladium catalyst is 0.05-1.00 wt.%.

[0013] A palladium catalyst for selective hydrogenation of acetylene, the palladium catalyst being prepared according to a method for preparing palladium catalysts for selective hydrogenation of acetylene.

[0014] An application of a palladium catalyst for the selective hydrogenation of acetylene, wherein the palladium catalyst is used in the selective hydrogenation reaction of acetylene.

[0015] Advantages of this invention: (1) The method for preparing the palladium catalyst for selective hydrogenation of acetylene of the present invention uses an amine compound as a base source, a coordinating agent and a stabilizer simultaneously, avoiding the addition of additional traditional inorganic bases, and can react with Pd 2+ It forms a stable complex and can also interact with the hydroxyl groups on the support surface through hydrogen bonds, firmly anchoring itself on the support and preventing Pd migration. Its large steric hindrance prevents Pd aggregation, and the final catalyst has high dispersion and high stability.

[0016] (2) The method for preparing palladium catalyst for selective hydrogenation of acetylene of the present invention forms a large steric hindrance by coordinating the N atom of the amine compound with Pd, which effectively isolates different Pd active centers, facilitates the adsorption of ethylene molecules in π bond mode, and makes it easier to desorb from the active center, avoids over-hydrogenation, and significantly improves the selectivity of ethylene.

[0017] (3) The method for preparing palladium catalyst for selective hydrogenation of acetylene of the present invention, wherein N coordinates with Pd, making the Pd surface rich in electrons, weakening the adsorption strength of acetylene and ethylene, and providing more Pd sites for H2 adsorption activation, thereby improving hydrogenation activity. The catalyst exhibits high activity and ethylene selectivity in the selective hydrogenation reaction of acetylene. Attached Figure Description

[0018] Figure 1 The graph shows the acetylene conversion rate as a function of temperature for the Pd / Al2O3-catalyzed selective hydrogenation reaction of acetylene prepared in Examples 1-3 and Comparative Examples 1-2 of this invention.

[0019] Figure 2 The graphs show the ethylene selectivity as a function of temperature for the Pd / Al2O3-catalyzed selective hydrogenation of acetylene prepared in Examples 1-3 and Comparative Examples 1-2 of this invention. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments.

[0021] Example 1 A method for preparing a palladium catalyst for selective hydrogenation of acetylene, the palladium catalyst comprising a support and palladium disposed on the support, wherein the support is γ-Al2O3 microspheres, the palladium catalyst uses palladium salt as a precursor and amine compounds as a base source, ligand and stabilizer simultaneously, and is prepared by impregnation, drying, calcination and reduction. The preparation method specifically includes the following steps: Step S1. At 50°C, tetraethylenepentamine was added dropwise to a palladium nitrate solution containing 0.05 g Pd until the pH of the mixture reached 9. The mixture was then stirred and dispersed for 8 hours to form a palladium complex solution with the following structural formula: [Pd(NH2-(CH2)2-NH-(CH2)2-NH-(CH2)2-NH-(CH2)2-NH2] 2+ ; Step S2. 50g of γ-Al2O3 microspheres were immersed in a palladium complex solution and fully adsorbed for 12h. The impregnation solution in the precursor solution was removed, and the microspheres were dried at 110℃ for 2h, calcined at 500℃ for 2h, and finally reduced at 300℃ for 2h in a mixed atmosphere of 95%Ar and 5%H2 to obtain a 0.10wt.%Pd / Al2O3 catalyst.

[0022] Example 2 A method for preparing a palladium catalyst for selective hydrogenation of acetylene, the palladium catalyst comprising a support and palladium disposed on the support, wherein the support is γ-Al2O3 microspheres, the palladium catalyst uses palladium salt as a precursor and amine compounds as a base source, ligand and stabilizer simultaneously, and is prepared by impregnation, drying, calcination and reduction. The preparation method specifically includes the following steps: Step S1. At 40°C, triethylenetetramine is added dropwise to a palladium nitrate solution containing 0.075 g Pd until the pH of the mixture reaches 12. The mixture is then stirred and dispersed for 14 h to form a palladium complex solution with the following structural formula: [Pd(NH2-(CH2)2-NH-(CH2)2-NH-(CH2)2-NH2] 2+ ; Step S2. Immerse 50g of γ-Al2O3 microspheres in a palladium complex solution. After sufficient adsorption for 18h, remove the impregnation solution, dry the microspheres at 110℃ for 3h, calcine them at 400℃ for 3h, and finally reduce them at 350℃ for 2h in a mixed atmosphere of 95%Ar and 5%H2 to obtain a 0.15wt.%Pd / Al2O3 catalyst.

[0023] Example 3 A method for preparing a palladium catalyst for selective hydrogenation of acetylene, the palladium catalyst comprising a support and palladium disposed on the support, wherein the support is γ-Al2O3 microspheres, the palladium catalyst uses palladium salt as a precursor and amine compounds as a base source, ligand and stabilizer simultaneously, and is prepared by impregnation, drying, calcination and reduction. The preparation method specifically includes the following steps: Step S1. At 60°C, diethylenetriamine was added dropwise to a chloropalladium acid solution containing 0.1 g Pd until the pH of the mixture reached 7. The mixture was then stirred and dispersed for 20 h to form a palladium complex solution with the structural formula: [Pd(NH2-CH2-CH2-NH2)Cl]. + ; Step S2. 50g of γ-Al2O3 microspheres were immersed in a palladium complex solution and fully adsorbed for 24h. The impregnation solution was then removed, and the microspheres were dried at 110℃ for 4h, calcined at 250℃ for 3h, and finally reduced at 350℃ for 2h in a mixed atmosphere of 95%Ar and 5%H2 to obtain a 0.20wt.%Pd / Al2O3 catalyst.

[0024] Comparative Example 1 A method for preparing a palladium catalyst for selective hydrogenation of acetylene, the palladium catalyst comprising a support and palladium disposed on the support, wherein the support is γ-Al2O3 microspheres; The preparation method specifically includes the following steps: Step S1. At 50°C, add 5% NaOH solution dropwise to a palladium nitrate solution containing 0.05g Pd until the pH of the mixture is 9. Then stir and disperse the mixture for 8 hours to form a palladium solution. Step S2. Immerse 50g of γ-Al2O3 microspheres in palladium solution. After sufficient adsorption for 12h, remove the impregnation solution, dry the microspheres at 110℃ for 2h, calcine at 500℃ for 2h, and finally reduce them at 300℃ for 2h in a mixed atmosphere of 95%Ar and 5%H2 to obtain 0.10wt.%Pd / Al2O3 catalyst.

[0025] Comparative Example 2 A method for preparing a palladium catalyst for selective hydrogenation of acetylene, the palladium catalyst comprising a support and palladium disposed on the support, wherein the support is γ-Al2O3 microspheres; The preparation method specifically includes the following steps: Step S1. At 50°C, ammonia water is added dropwise to a palladium nitrate solution containing 0.05g Pd until the pH of the mixture is 9. The mixture is then stirred and dispersed for 8 hours to form a palladium solution. Step S2. Immerse 50g of γ-Al2O3 microspheres in palladium solution. After sufficient adsorption for 12h, remove the impregnation solution, dry the microspheres at 110℃ for 2h, calcine at 500℃ for 2h, and finally reduce them at 300℃ for 2h in a mixed atmosphere of 95%Ar and 5%H2 to obtain 0.10wt.%Pd / Al2O3 catalyst.

[0026] The Pd / Al2O3 catalysts prepared in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 were evaluated for selective hydrogenation of acetylene using a fixed-bed apparatus. The catalyst dosage was 20 mg, and the reaction gas composition was 1 vol% C2H2, 10 vol% H2, 20 vol% C2H4, with Ar as the equilibrium gas. The space velocity was 150,000 ml / (g•h), and the temperature was increased from room temperature. The content of the gas after the reaction was analyzed by gas chromatography. The metal dispersion of Pd / Al2O3 prepared in Examples 1-3 and Comparative Examples 1-2 is shown in Table 1.

[0027] Table 1 .

[0028] As shown in Table 1, the metal dispersion of Pd / Al2O3 prepared in Examples 1-3 is much higher than that in Comparative Examples 1-2, indicating that Pd in ​​Examples 1-3 is more dispersed and has fewer continuous Pd sites, which is conducive to the adsorption of ethylene with Pd in ​​a π-bond mode, making it less prone to excessive hydrogenation and resulting in high selectivity for ethylene.

[0029] Figure 1 The graph shows the acetylene conversion rate versus temperature for the Pd / Al₂O₃-catalyzed selective hydrogenation of acetylene prepared in Examples 1-3 and Comparative Examples 1-2. Figure 1 It can be concluded that the conversion rate gradually increases with increasing temperature. In Examples 1-3, acetylene was basically completely converted at a reaction temperature of 125°C, while the conversion rate of Comparative Examples 1-2 was significantly lower than that of Examples 1-3.

[0030] Figure 2 The graph shows the ethylene selectivity as a function of temperature for the Pd / Al₂O₃-catalyzed selective hydrogenation of acetylene prepared in Examples 1-3 and Comparative Examples 1-2. Figure 2 It can be concluded that Examples 1-3 all obtained high ethylene selectivity at different temperatures, which was much higher than that of Comparative Examples 1-2.

[0031] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a palladium catalyst for the selective hydrogenation of acetylene, characterized in that, The palladium catalyst includes a support and palladium disposed on the support, wherein the support is γ-Al2O3 microspheres, and the palladium catalyst is prepared by impregnation, drying, calcination and reduction of palladium salt as a precursor and amine compound as a base source, ligand and stabilizer. The preparation method specifically includes the following steps: Step S1. At 25~80℃, add amine compounds dropwise to the palladium salt solution until the pH of the mixture is 6~14, then stir and disperse the mixture to form a palladium complex solution; Step S2. Immerse γ-Al2O3 microspheres in a palladium complex solution. After sufficient adsorption, remove the impregnation solution, dry the microspheres, calcine them, and finally reduce them under a reducing atmosphere to obtain the palladium catalyst.

2. The method for preparing the palladium catalyst for selective hydrogenation of acetylene according to claim 1, characterized in that: In step S1, the palladium salt is selected from one or more of palladium nitrate, palladium chloroacetic acid, and palladium acetate; the dispersion time is 1-24h.

3. The method for preparing the palladium catalyst for selective hydrogenation of acetylene according to claim 1, characterized in that: In step S1, the amine compound is selected from one or more of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

4. The method for preparing the palladium catalyst for selective hydrogenation of acetylene according to claim 1, characterized in that: The general structural formula of the palladium complex solution in step S1 is: [Pd(L)]X m+ Where L is NH2-(CH2)2-[NH-(CH2)2] p -NH2, P=1-3, X is the anion, and m is the charge of the complex cation.

5. The method for preparing the palladium catalyst for selective hydrogenation of acetylene according to claim 1, characterized in that: The adsorption time in step S2 is 6-24 hours.

6. The method for preparing the palladium catalyst for selective hydrogenation of acetylene according to claim 1, characterized in that: In step S2, the drying temperature is 100-120℃ and the drying time is 1-4h, while the calcination temperature is 300-600℃ and the calcination time is 1-6h.

7. The method for preparing the palladium catalyst for selective hydrogenation of acetylene according to claim 1, characterized in that: In step S2, the reduction temperature is 200-400℃ and the reduction time is 2-5 h.

8. The method for preparing the palladium catalyst for selective hydrogenation of acetylene according to claim 1, characterized in that: The palladium loading in the palladium catalyst is 0.05-1.00 wt.%.

9. A palladium catalyst for the selective hydrogenation of acetylene, characterized in that: The palladium catalyst is prepared according to any one of claims 1 to 8.

10. The application of the palladium catalyst for selective hydrogenation of acetylene according to claim 9, characterized in that: Palladium catalysts are used in the selective hydrogenation of acetylene.

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