Monolithic hierarchical porous reticular nickel catalyst as well as preparation method and application thereof

Abstract

The invention discloses an integral hierarchical porous reticular nickel catalyst as well as a preparation method and application thereof, and belongs to the technical field of chemical catalytic materials. According to the catalyst, a commercial nickel net is used as a supporting framework, and a porous nickel active layer with micron-level thickness is constructed on the surface of a nickel net wire, so that an integral structure with macro-mesoporous-micro hierarchical pore channels is formed. The preparation method comprises the following steps: burying the nickel net in mixed powder containing aluminum powder and an activating agent (aluminum chloride or ammonium chloride), and carrying out high-temperature roasting in an inert atmosphere to form a nickel-aluminum alloy layer on the surface of the nickel net; and then aluminum is removed through alkali liquor corrosion, and the monolithic catalyst with the raney nickel type porous structure on the surface is obtained. The catalyst has the advantages of excellent mass and heat transfer performance, high specific surface area, abundant active sites, simple preparation process and low cost. When the catalyst is applied to an adiponitrile hydrogenation reaction, high activity and high selectivity are shown. Assistants such as Fe, Cr, Mo, Co, Zn and the like can be introduced through post-modification, so that the performance is further improved.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalytic materials technology, specifically relating to a structured monolithic catalyst, particularly a monolithic fixed-bed nickel catalyst with a nickel mesh as the framework and a porous nickel active layer on the surface, its preparation method, and its application in the hydrogenation of adiponitrile to synthesize hexamethylenediamine. Background Technology

[0002] Fixed-bed reactors are widely used reaction devices in chemical production, and their core component is the catalyst. Traditional fixed-bed catalysts typically consist of an active component (such as nickel) supported on alumina, silica, or other carriers, which are then pressed into tablets or extruded. These catalysts suffer from problems such as high internal mass transfer resistance and poor thermal conductivity, which can easily lead to hot spots within the reactor, affecting reaction selectivity and catalyst lifetime.

[0003] To improve mass and heat transfer performance, monolithic catalysts (such as honeycomb ceramics and foamed metal catalysts) have emerged. Among them, nickel foam, with its three-dimensional interconnected porous structure, has become an ideal monolithic catalyst framework. However, nickel foam itself has a high production cost, and it usually requires secondary loading of active components on its surface (such as loading nickel salts through impregnation and then reducing them), which is a complex process and further increases the production cost of the catalyst. In addition, the bonding force between the secondary loaded active layer and the nickel foam matrix may be insufficient, posing a risk of detachment during use.

[0004] Raney nickel is a traditional highly active hydrogenation catalyst, produced by leaching aluminum from a nickel-aluminum alloy with an alkaline solution. It possesses a large specific surface area and abundant pore structure. However, it is usually present in powder form and cannot be used directly in fixed-bed reactors. It needs to be mixed with a binder to form a catalyst. The presence of the binder can block some of its pores, leading to a decrease in activity.

[0005] In addition, traditional powder encapsulation aluminizing methods often use ammonium chloride as an activator, and the process has the problem of matching the ammonium chloride decomposition temperature window with the aluminizing temperature.

[0006] Therefore, developing an integral fixed-bed nickel catalyst that combines excellent mass and heat transfer performance, high specific surface area, high activity, and simple preparation process with low cost is of great significance for promoting the development of important chemical processes such as adiponitrile hydrogenation. Summary of the Invention

[0007] One objective of this invention is to overcome the shortcomings of the prior art and provide an integral multi-level porous network nickel catalyst with a unique structure, excellent performance, and low cost.

[0008] Another objective of this invention is to provide a method for preparing the above-mentioned catalyst, which is simple in process and easy to scale up for production.

[0009] Another object of the present invention is to provide the application of the above-mentioned catalyst in the hydrogenation of adiponitrile to synthesize hexamethylenediamine, which can significantly improve the reaction activity and selectivity.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an integral multi-level porous network nickel catalyst, which uses a commercial nickel mesh as an integral support framework, and grows a porous nickel active layer with a thickness of micrometers in situ on the surface of the wires of the nickel mesh, thereby forming an integral catalyst with a macroscopic network channel of the nickel mesh itself and a microscopic porous structure of the grown porous nickel active layer; wherein, the mesh of the nickel mesh is 20-200 mesh and the wire diameter is 0.05-0.5 mm.

[0011] Furthermore, the thickness of the porous nickel active layer of the present invention is 1-50 μm, and it has the porous structure characteristics of Raney nickel.

[0012] Furthermore, the porous nickel active layer of the present invention is also modified with one or more co-catalytic metal elements selected from Fe, Cr, Mo, Co, and Zn.

[0013] Based on the above technical solutions, the catalyst structure of this invention creates a unique multi-level pore system: the large pore size (macroscale) of the nickel mesh itself ensures smooth transport of reactants and products, greatly reducing pressure drop; the micron-scale porous nickel layer (mesoscale and microscale) on the surface of the filaments provides a huge specific surface area and abundant active sites. This structure perfectly combines the excellent hydrodynamic properties of monolithic catalysts with the high specific surface activity of Raney nickel.

[0014] Secondly, the present invention provides a method for preparing the monolithic multi-level porous network nickel catalyst, comprising the following steps: 1. Pretreatment: Use an organic solvent (such as acetone or ethanol) to ultrasonically clean a commercial nickel mesh of a specific mesh size to remove surface oil and then dry it.

[0015] 2. Embedding and Aluminizing: The cleaned nickel mesh is completely embedded in a mixture of aluminum powder and activator; an inert gas (such as nitrogen or argon) is introduced into a tube furnace, and the temperature is programmed to rise to 400-700 ℃ and held for 1-10 hours. During this process, the gaseous components generated by the activator react with the surface of the nickel mesh, forming a uniform nickel-aluminum alloy layer on the surface of the nickel wire through a gas-solid phase mass transfer process.

[0016] In this step, the activator is preferably aluminum chloride (AlCl3) because it can directly sublimate to provide AlCl3 vapor, making the process more direct; ammonium chloride (NH4Cl) can also be used, which decomposes to produce HCl and then reacts with Al to generate AlCl3 vapor.

[0017] Furthermore, the mass ratio of aluminum powder to activator in the mixed powder is 5:1 to 20:1; the mass ratio of nickel mesh to mixed powder is 1:10-100.

[0018] More preferably, when the activator is ammonium chloride, the mass ratio of aluminum powder to ammonium chloride is 5:1 to 10:1; when the activator is aluminum chloride, the mass ratio of aluminum powder to aluminum chloride is 10:1 to 20:1.

[0019] 3. Alkali Etching Activation: After calcination, the sample is allowed to cool naturally and then directly immersed in a hot alkaline solution (sodium hydroxide or potassium hydroxide solution) of a certain concentration for 0.5-5 hours at 50-100 °C. Aluminum is selectively dissolved, leaving a porous nickel layer with a nanoporous structure, i.e., the Raney nickel structure. Finally, the sample is washed with deionized water until neutral, followed by alcohol washing and drying to obtain the final catalyst.

[0020] Optionally, a precursor solution of one or more metals, such as Fe, Cr, Mo, Co, and Zn, can be loaded onto the porous nickel catalyst prepared above by a post-modification method (such as equal-volume impregnation). After drying, calcination, and reduction, a modified catalyst is obtained to regulate its hydrogenation selectivity and stability.

[0021] Thirdly, the present invention provides the application of the monolithic multi-level porous network nickel catalyst in the catalytic hydrogenation reaction of adiponitrile to synthesize hexamethylenediamine. The catalyst of the present invention is filled into a fixed bed reactor for the reaction of adiponitrile to synthesize hexamethylenediamine. Under suitable reaction conditions (such as temperature 80-150 ℃, pressure 2.0-5.0 MPa, hydrogen flow rate), it exhibits a conversion rate and hexamethylenediamine selectivity that are much higher than those of traditional shaped nickel catalysts.

[0022] The beneficial effects of this invention are: 1. Structural Innovation: It pioneered an integral structure of "nickel mesh macro framework + surface Raney nickel microporous layer", realizing multi-level channel design and perfectly solving the contradiction between the poor mass and heat transfer of traditional powder-formed catalysts and the high cost and complex process of foamed nickel carriers.

[0023] 2. Excellent performance: It has the characteristics of low pressure drop, high thermal conductivity and high specific surface area, and has abundant and highly accessible active sites, exhibiting high activity and high selectivity in hydrogenation reactions.

[0024] 3. Low cost: The raw material is inexpensive commercial nickel mesh, which eliminates the need for expensive foamed nickel and complex secondary loading processes. The preparation method is simple, energy consumption is low, and it is very suitable for industrial production.

[0025] 4. High modifiability: The porous nickel layer on the surface is easy to modify with additives, and the catalyst performance can be flexibly adjusted according to different reaction requirements.

[0026] 5. High process flexibility: It offers two activators, aluminum chloride and ammonium chloride, to adapt to different process conditions and cost considerations. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention. Example 1

[0028] 1. Take a piece of pure nickel mesh (5cm × 5cm) with a mesh size of 40 (wire diameter of about 0.2 mm), ultrasonically clean it with acetone for 15 minutes, then clean it with anhydrous ethanol, and dry it in an oven at 80 ℃.

[0029] 2. Quickly and thoroughly mix 90g of aluminum powder (200 mesh) and 10g of anhydrous aluminum trichloride (AlCl3) powder in a dry environment. Completely embed the dried nickel mesh into the above mixed powder, place it in an alumina crucible, and seal it.

[0030] 3. Place the crucible in a tube furnace, introduce high-purity nitrogen gas (flow rate 50 mL / min), and heat to 500℃ at a rate of 5℃ / min, then maintain the temperature for 3 hours.

[0031] 4. After the process is complete, allow the furnace to cool to room temperature and remove the nickel mesh. A nickel-aluminum alloy layer will be visible on the surface. Immerse it in a 5 mol / L NaOH solution and etch it in an 80 ℃ water bath for 2 hours.

[0032] 5. After removal, the catalyst was repeatedly washed with deionized water until the pH was neutral, then washed with anhydrous ethanol, and dried in a vacuum drying oven at 60℃ for 4 hours to obtain the monolithic multi-level porous network nickel catalyst C-1. SEM observation showed that an active layer with a thickness of about 5-10 μm and rich nanopores was formed on the surface of the nickel wire. Example 2

[0033] The nickel mesh was 100 mesh (wire diameter approximately 0.1 mm), the mass ratio of aluminum powder to aluminum chloride was changed to 85:15, the calcination temperature was changed to 450℃, and the holding time was 4 hours. The remaining steps were the same as in Example 1. Catalyst C-2 was obtained. Example 3

[0034] Ammonium chloride was used as the activator. The nickel mesh was 60 mesh. The mixed powder was aluminum powder:ammonium chloride = 80g:10g (mass ratio 8:1). The calcination temperature was 600 ℃, and the holding time was 2 hours. The alkali concentration was 8 mol / L, the corrosion temperature was 90 ℃, and the time was 1.5 hours. Catalyst C-3 was obtained. Example 4

[0035] A 20-mesh nickel mesh (approximately 0.4 mm wire diameter) was used. The mass ratio of aluminum powder to aluminum chloride was 80:20. The calcination temperature was increased to 650 °C, and the holding time was extended to 6 hours to promote the growth of a thicker alloy layer. After alkaline etching, a catalyst C-4 with a porous layer thickness of approximately 30-40 μm was obtained. Example 5

[0036] Two g of catalyst C-1 prepared in Example 1 was impregnated in 5 mL of an aqueous solution containing 0.5 g of ferric nitrate nonahydrate (Fe(NO3)3·9H2O) using an equal-volume impregnation method. The mixture was allowed to stand for 12 hours, dried at 100 °C for 2 hours, calcined at 350 °C for 3 hours under a nitrogen atmosphere, and then reduced at 400 °C for 2 hours under a hydrogen atmosphere to obtain Fe-modified catalyst C-5. Example 6

[0037] Take 2g of catalyst C-1 prepared in Example 1 and impregnate it in a solution containing 0.3g of chromic anhydride (CrO3) and 0.2g of ammonium heptamolybdate ((NH4)6Mo7O). 24 The catalyst C-6, co-modified with Cr-Mo, was obtained by further processing in 5 mL of an aqueous solution of 4H2O (·4H2O) as in Example 5.

[0038] Comparative Example 1 Commercially extruded alumina-supported nickel catalyst (Ni content approximately 50 wt%), labeled Cat-Ref.

[0039] Application and catalytic performance evaluation The catalysts obtained in all Examples 1-6 and the comparative examples were loaded into a fixed-bed reactor for evaluation of adiponitrile hydrogenation. Reaction conditions: catalyst loading 5 mL, reaction temperature 120 °C, pressure 3.0 MPa, hydrogen flow rate 100 mL / min, and liquid hourly space velocity (LHSV) of the adiponitrile methanol solution (10 wt%) feed at 2 h⁻¹. -1 After running for 100 hours, stable data was recorded. The results are shown in the table below: catalyst Adiponitrile conversion rate (%) Hexamethylenediamine selectivity (%) Remark C-1 (This invention) 99.5 98.2 Basic formula (aluminum chloride), excellent performance C-2 (This invention) 99.3 98.0 High-mesh nickel mesh, lower voltage drop C-3 (This invention) 98.8 97.5 Ammonium chloride works well. C-4 (This invention) 99.7 97.8 Thicker active layer, slightly increased activity C-5 (This invention) 99.2 99.0 Fe additives significantly improve selectivity C-6 (This invention) 99.0 99.5 Cr-Mo dual adjuvants offer optimal selectivity. Cat-Ref (Comparative Example) 95.1 92.3 Traditional catalysts Based on the above embodiments, the catalysts obtained by this invention are significantly superior to traditional catalysts in both activity and selectivity. In particular, the catalysts modified with additives (C-5, C-6) exhibit further advantages in selectivity, demonstrating the effectiveness and tunability of this invention.

[0040] It should be further noted that the above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A monolithic, multi-level, channelled, reticulated nickel catalyst, characterised in that, The application discloses a monolithic multi-level channel net-like nickel catalyst, which comprises a commercial nickel net as a monolithic support framework, and a micrometer-thick porous nickel active layer grown in situ on the wire surface of the nickel net, so as to form a monolithic catalyst with macroscopic network channels of the nickel net itself and a microscopic porous structure of the grown porous nickel active layer. The nickel net has a mesh number of 20-200 meshes and a wire diameter of 0.05-0.5 mm.

2. The monolithic, multi-level pore, reticulated nickel catalyst of claim 1, wherein, The thickness of the porous nickel active layer is 1-50 micrometers, and the porous nickel active layer has the porous structure characteristics of Raney nickel.

3. The monolithic, multi-level, net-like pore, nickel catalyst according to claim 1 or 2, characterized in that The surface of the porous nickel active layer is further modified with one or more than one catalytic metal element of Fe, Cr, Mo, Co and Zn.

4. Process for the preparation of the monolithic multi-level porous reticulated nickel catalyst according to any one of claims 1 to 3, characterized in that, The application further discloses a preparation method of the monolithic multi-level channel net-like nickel catalyst. (1) pretreatment: washing and drying the nickel net; (2) buried aluminum infiltration: burying the pretreated nickel net in a mixed powder containing aluminum powder and an activating agent, and calcining the nickel net at 400-700 DEG C for 1-10 hours in an inert atmosphere, so that a nickel-aluminum alloy layer is formed on the surface of the nickel net; (3) alkali etching activation: after the sample obtained in step (2) is cooled, it is placed in an alkali solution and etched at 50-100 DEG C for 0.5-5 hours, so that the aluminum component is removed and a porous nickel active layer is formed on the surface of the nickel net; after washing and drying, the monolithic multi-level channel net-like nickel catalyst is obtained.

5. The method of claim 4, wherein, In step (2), the mass ratio of the aluminum powder to the activating agent in the mixed powder is 5:1 to 20:1; and the mass ratio of the nickel net to the mixed powder is 1:10-100.

6. The method according to claim 4 or 5, characterized in that, The activating agent is aluminum chloride or ammonium chloride; when the activating agent is ammonium chloride, the mass ratio of the aluminum powder to the ammonium chloride is 5:1 to 10:1; and when the activating agent is aluminum chloride, the mass ratio of the aluminum powder to the aluminum chloride is 10:1 to 20:

1.

7. The method of claim 4, wherein, In step (2), the inert atmosphere is a nitrogen or argon atmosphere.

8. The method of claim 4, wherein, In step (3), the alkali solution is a sodium hydroxide or potassium hydroxide solution with a concentration of 1-10 mol / L.

9. The method of claim 4, wherein, After the alkali etching activation in step (3), an additive modification step is further included: a soluble salt solution containing one or more than one metal of Fe, Cr, Mo, Co and Zn is loaded onto the obtained catalyst by an equal-volume impregnation method or a preliminary wet impregnation method, and then the catalyst is dried, calcined and reduced.

10. The monolithic multi-level channel net-like nickel catalyst according to any one of claims 1-3 is applied to the synthesis of hexamethylenediamine by catalyzing the hydrogenation reaction of adiponitrile.