Monolithic catalyst and method for its preparation and use

Abstract

This invention provides a monolithic catalyst, its preparation method, and its application. The monolithic catalyst comprises a substrate and a coating; the substrate has a thermal conductivity ≥50 W / (m·K) and a regular microchannel structure; the coating comprises a three-dimensional porous metal framework and is metallurgically bonded to the inner wall of the substrate. The monolithic catalyst provided by this invention can improve the conversion rate of the feedstock and the selectivity of the product in the hydrogenation reaction of 2-methylglutaronitrile.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, and particularly relates to an integral catalyst, its preparation method, and its application. Background Technology

[0002] Dianitrile compounds (such as 2-methylglutaronitrile) are important intermediates in the synthesis of polymers (such as polyamides and polyesters), and their hydrogenation reactions can generate corresponding diamine products (such as 2-methylpentanediamine). This process is widely used in chemical, pharmaceutical, and materials synthesis fields and is a key step in the production of high-performance polymers. In industrial practice, such reactions are usually carried out in fixed-bed reactors, requiring catalysts to promote efficient reaction.

[0003] However, existing catalysts result in low feed conversion rates and low product selectivity. Therefore, developing a catalyst that achieves both high feed conversion rates and high product selectivity is a pressing technical problem that needs to be solved at this stage. Summary of the Invention

[0004] The main objective of this invention is to provide a monolithic catalyst that can improve the conversion rate of feedstock and the selectivity of products in the hydrogenation reaction of 2-methylglutaronitrile.

[0005] The present invention also provides a method for preparing a monolithic catalyst, which can prepare the above-mentioned monolithic catalyst and is simple and low in cost.

[0006] The present invention also provides a method for preparing 2-methylpentanediamine, which is obtained by hydrogenating 2-methylglutaronitrile using the above-mentioned monolithic catalyst, thereby improving the conversion rate of raw materials and the selectivity of products.

[0007] In a first aspect, the present invention provides an integral catalyst comprising a substrate and a coating;

[0008] The thermal conductivity of the substrate is ≥50W / (m·K), and the substrate has a regular microchannel structure;

[0009] The coating comprises a three-dimensional porous metal framework, which is metallurgically bonded to the inner wall of the substrate.

[0010] In the monolithic catalyst described above, the hydraulic diameter of the microchannels is 1~3 mm, and the wall thickness is 0.2~1.0 mm;

[0011] And / or, the substrate includes at least one of silicon carbide, aluminum nitride, and metal.

[0012] The monolithic catalyst described above, wherein the coating comprises a first metal and a second metal;

[0013] The first metal includes at least one of Group 8, Group 9, and Group 10 metals;

[0014] The second metal includes at least one of Group 6, Group 7, and Group 11 metals.

[0015] In the monolithic catalyst described above, the first metal includes at least one of iron, cobalt, nickel, ruthenium, rhodium, and palladium;

[0016] And / or, the second metal includes at least one of chromium, molybdenum, tungsten, rhenium, copper, and silver;

[0017] And / or, the second metal accounts for 0.5 to 15% of the mass percentage of the first metal.

[0018] For the monolithic catalyst described above, the specific surface area of ​​the coating is ≥30m². 2 / g.

[0019] Secondly, the present invention provides a method for preparing the monolithic catalyst as described above, comprising the following steps:

[0020] 1) Form a pre-alloyed powder from a first system comprising a first metal, a second metal, and a pore-forming metal;

[0021] 2) The second system, comprising the pre-alloyed powder, binder, and dispersant, is ball-milled to obtain a pre-alloyed slurry;

[0022] 3) The pre-alloyed slurry is coated onto the surface of the substrate to obtain an intermediate;

[0023] 4) The intermediate is heat-treated to obtain an integral catalyst precursor;

[0024] 5) The monolithic catalyst precursor is subjected to alkaline etching activation treatment to obtain the monolithic catalyst.

[0025] The preparation method described above, wherein forming a pre-alloyed powder from a first system comprising a first metal, a second metal, and a pore-forming metal comprises: preparing the pre-alloyed powder from the first system comprising a first metal, a second metal, and a pore-forming metal by means of a melting-crushing method and / or a mechanical alloying method;

[0026] And / or, the mass ratio of the pore-forming metal to the first metal is (0.4~1.5):1;

[0027] And / or, the D50 of the pre-alloyed powder is <20 μm.

[0028] In the preparation method described above, the adhesive includes at least one of polyethylene glycol, polyvinyl alcohol, and methylcellulose;

[0029] And / or, the binder accounts for 0.5% to 8% of the mass of the pre-alloyed powder;

[0030] And / or, the dispersant includes polyacrylates and / or citrates;

[0031] And / or, the dispersant accounts for 0.05~3% of the mass percentage of the pre-alloyed powder;

[0032] And / or, the ball milling treatment time is 8~48h, and the ball-to-material ratio is (3~20):1;

[0033] And / or, the solid content of the pre-alloyed slurry is 30-60%, and the viscosity is 300-1000 mPa·s.

[0034] As described above, the step of coating the pre-alloy slurry onto the substrate surface includes: immersing the substrate in the pre-alloy slurry and subjecting it to a pulling process and a blowing process to obtain the intermediate.

[0035] And / or, the heat treatment temperature is 500~800℃, and the time is 0.5~8h;

[0036] And / or, the alkaline etching activation treatment is performed at a temperature of 50~100℃ for a time of 0.5~8h.

[0037] Thirdly, the present invention provides a method for preparing 2-methylpentanediamine, which is obtained by hydrogenating 2-methylpentanedionitrile using the monolithic catalyst as described above or the monolithic catalyst prepared by the method described above.

[0038] The monolithic catalyst provided by this invention includes a coating of a three-dimensional porous metal framework that is metallurgically bonded to the inner wall of a substrate and the thermal conductivity of the substrate is limited. This enables high heat transfer efficiency, low bed pressure drop, no wear and pulverization, and easy separation and recovery, thereby improving the conversion rate of raw materials and the selectivity of products. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0040] Dianitrile compounds (such as 2-methylglutaronitrile, MGN) are key intermediates in the synthesis of high-performance polymers (such as polyamides and polyesters). The conversion of these compounds to their corresponding diamines (such as 2-methylpentanediamine) via catalytic hydrogenation is a crucial production step in the chemical, pharmaceutical, and materials synthesis fields. In industrial practice, this reaction is typically carried out in a fixed-bed reactor, and its core lies in using highly efficient catalysts to promote efficient and highly selective reaction processes.

[0041] Currently, the most commonly used process in industry is the fixed-bed granular catalyst technology. The catalysts used in this technology typically use metals such as nickel, cobalt, and iron, or their alloys, as the active component. These are prepared into millimeter-sized particles through loading or impregnation methods and randomly stacked in a reactor to form a catalyst bed. During the reaction, the gas-liquid two-phase feed mixture passes through this granular bed and undergoes a hydrogenation reaction on the catalyst surface. However, this traditional technology has several inherent defects that have long remained unresolved, severely restricting the process's economy, safety, and production efficiency. These defects are as follows:

[0042] 1) Low heat transfer efficiency and localized hot spots: The randomly stacked particulate catalyst bed has only point contact within it, resulting in extremely poor overall thermal conductivity. For highly exothermic reactions such as dionitrile hydrogenation, the large amount of heat released during the reaction is difficult to dissipate quickly and uniformly, easily forming localized high-temperature zones within the bed, especially in the axial region. These localized high temperatures not only trigger a series of side reactions such as deamination, cyclization, and polymerization, significantly reducing the selectivity of the target diamine product, but also accelerate the sintering, agglomeration, and carbon deposition deactivation of the catalyst's active components, drastically shortening the catalyst's lifespan.

[0043] 2) Excessive bed pressure drop limits production capacity: The tortuous and narrow pore channels formed by the random accumulation of particles result in significant flow resistance for the reaction fluid, leading to a high bed pressure drop. This not only significantly increases the energy consumption of the circulating hydrogen compressor, but more importantly, it severely limits the usable liquid hourly space velocity, thus restricting the processing capacity and production capacity per unit reactor volume. With prolonged operation, catalyst pulverization or carbon buildup further exacerbates the pressure drop, forcing frequent adjustments to process parameters to maintain operation and impacting production stability.

[0044] 3) Insufficient mechanical strength and pulverization of catalysts: Particulate catalysts are prone to mechanical wear and pulverization during loading, operation (affected by fluid erosion and thermal stress), and unloading. The resulting fine catalyst powder migrates with the products, clogging downstream pipelines, heat exchangers, and filters, increasing system maintenance costs and operational risks. Simultaneously, powder accumulation within the bed exacerbates pressure drop issues, and the loss of precious metal active components directly increases catalyst consumption and production costs.

[0045] 4) Difficulty in catalyst separation and recovery (for slurry bed processes): Although slurry bed reactors can improve heat transfer, the catalyst is suspended in the reaction liquid in powder form. After the reaction, a complex and expensive solid-liquid separation system (such as cross-flow filtration) is required to separate the product from the catalyst. This process involves large equipment investment, cumbersome operation, and the risk of catalyst loss, leading to continuous loss of active components and potential secondary pollution.

[0046] The inventors of this application have discovered through research that if a coating including a three-dimensional porous metal skeleton is metallurgically bonded to the inner wall of a substrate, and the thermal conductivity of the substrate is limited, the problem of local hot spots can be solved, the bed pressure drop can be reduced, the catalyst can be free from wear and pulverization, long-term stable operation can be achieved, and the catalyst can be separated and recovered more easily, thereby improving the conversion rate of raw materials and the selectivity of products.

[0047] In a first aspect, the present invention provides an integral catalyst comprising a substrate and a coating; the substrate has a thermal conductivity ≥50W / (m·K) and a regular microchannel structure; the coating comprises a three-dimensional porous metal framework and is metallurgically bonded to the inner wall of the substrate.

[0048] The monolithic catalyst provided by this invention has a substrate with a thermal conductivity ≥50 W / (m·K). The coating comprises a three-dimensional porous metal framework and is metallurgically bonded to the inner wall of the substrate. This achieves high heat transfer efficiency, low bed pressure drop, no wear or pulverization, and easy separation and recovery, thereby improving the conversion rate of raw materials and the selectivity of products. This is because the high thermal conductivity of the substrate, acting as the structural framework and efficient heat transfer channel of the catalyst, provides an efficient path for the removal of reaction heat, enabling rapid removal of reaction heat and avoiding the impact of local high temperatures on reaction selectivity and catalyst stability, thus eliminating local hot spots. Furthermore, the regular microchannel structure of the substrate provides a low-resistance flow path for the reaction fluid, significantly reducing the system pressure drop. Reaction products can flow out directly without complex separation, and the catalyst is free from wear and pulverization, enabling long-term stable operation. The coating forms a strong interface with the inner wall of the substrate through metallurgical bonding, ensuring excellent adhesion. Its three-dimensional porous metal framework provides high catalytic active sites, significantly suppressing side reactions, thereby improving the conversion rate of raw materials and the selectivity of products.

[0049] Therefore, the monolithic catalyst provided by the present invention includes a coating of a three-dimensional porous metal framework that is metallurgically bonded to the inner wall of the substrate and the thermal conductivity of the substrate is limited, which can achieve high heat transfer efficiency, low bed pressure drop, no wear and pulverization, and easy separation and recovery, thereby improving the conversion rate of raw materials and the selectivity of products.

[0050] In some embodiments of the present invention, the hydraulic diameter of the microchannel is 1 to 3 mm, for example, it can be a range of 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm or any two of these; the wall thickness is 0.2 to 1.0 mm, for example, it can be a range of 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm or any two of these.

[0051] In this invention, the hydraulic diameter and wall thickness of the microchannels are within the above range, which can balance the structural strength and heat transfer efficiency of the monolithic catalyst and avoid insufficient mechanical strength due to excessively thin walls or thermal conductivity due to excessively thick walls.

[0052] In some embodiments, the substrate includes at least one of silicon carbide, aluminum nitride, and metal.

[0053] The aforementioned substrate can provide high thermal conductivity, thereby enabling rapid removal of reaction heat, avoiding the impact of local high temperatures on reaction selectivity and catalyst stability, and eliminating local hot spots.

[0054] In some embodiments of the present invention, the coating comprises a first metal and a second metal; the first metal comprises at least one of Group 8, Group 9, and Group 10 metals; and the second metal comprises at least one of Group 6, Group 7, and Group 11 metals.

[0055] In this invention, the first metal serves as the catalytic active framework, providing high intrinsic activity, while the second metal serves as a performance-improving agent, adjusting the catalytic performance of the first metal through electronic or geometric effects. The synergistic effect of the two metals can improve the conversion rate of raw materials and the selectivity of products.

[0056] In some embodiments of the present invention, the first metal includes at least one selected from iron, cobalt, nickel, ruthenium, rhodium, and palladium.

[0057] In some embodiments, the second metal includes at least one selected from chromium, molybdenum, tungsten, rhenium, copper, and silver.

[0058] The aforementioned first and second metals can further enhance the conversion rate of raw materials and the selectivity of products through synergistic effects.

[0059] In some embodiments, the second metal comprises 0.5% to 15% of the first metal by mass, for example, it can be a range of 0.5%, 1%, 3%, 5%, 7%, 10%, 12%, 15%, or any two of these. Preferably, it is 1% to 10%, more preferably 2% to 8%.

[0060] In this invention, the mass percentage of the second metal relative to the first metal is within the above-mentioned range, which enables the active component (first metal) and the auxiliary agent (second metal) to work synergistically, suppressing side reactions and avoiding the masking of active sites or electronic structure imbalance caused by excessive auxiliary agent.

[0061] In some embodiments of the present invention, the specific surface area of ​​the coating is ≥30m². 2 / g, for example, can be 30m 2 / g、40m 2 / g, 50m 2 / g、60m 2 / g、70m 2 / g、80m 2 / g、90m 2 / g, 100m 2 / g、200m 2 / g、300m 2 / g、500m 2 / g, 1000m 2 The range of / g or any two thereof is preferably 50~150m. 2 / g.

[0062] The high specific surface area of ​​the coating provides ample active sites, which can significantly improve the conversion rate of raw materials and the selectivity of products.

[0063] Secondly, the present invention provides a method for preparing the monolithic catalyst as described above, comprising the following steps:

[0064] 1) Form a pre-alloyed powder from a first system comprising a first metal, a second metal, and a pore-forming metal;

[0065] 2) The second system, comprising pre-alloyed powder, binder, and dispersant, is ball-milled to obtain a pre-alloyed slurry;

[0066] 3) The pre-alloyed slurry is coated onto the surface of the substrate to obtain the intermediate;

[0067] 4) The intermediate is heat-treated to obtain an integral catalyst precursor;

[0068] 5) The monolithic catalyst precursor is subjected to alkaline etching activation treatment to obtain the monolithic catalyst.

[0069] Specifically, in step 1), the present invention does not limit the method of forming the pre-alloyed powder, as long as the first system including the first metal, the second metal, and the pore-forming metal forms a pre-alloyed powder with uniform composition.

[0070] In step 2), the pre-alloyed powder is mixed with additives, such as binders and dispersants, to form a pre-alloyed slurry whose rheological properties, stability, and coating performance all meet the process requirements. Specifically, the pre-alloyed powder, binder, dispersant, and solvent can be mixed and ball-milled to form a uniform and stable pre-alloyed slurry.

[0071] The solvent, as a liquid phase carrier, can be selected from one or more combinations of deionized water, ethanol, and mixtures thereof.

[0072] In step 3), the pre-alloyed slurry is coated onto the surface of the substrate in a uniform and thickness-controllable manner to obtain an intermediate.

[0073] In step 4), the intermediate is heat-treated to decompose and remove organic components (such as binders and dispersants) in the pre-alloyed slurry, so that sintering occurs between the pre-alloyed powder particles and between them and the substrate surface, thereby forming a dense cured alloy coating with excellent adhesion, and obtaining an integral catalyst precursor.

[0074] Heat treatment can be carried out in an inert atmosphere or a weakly reducing atmosphere, wherein the inert atmosphere can be selected from one or more combinations of nitrogen, argon and their mixtures.

[0075] Before heat treatment, the substrate (intermediate) with the wet coating can be pre-dried at a temperature of 80~150°C. The heating rate can be 1~20°C / min, preferably 2~10°C / min.

[0076] After heat treatment, the monolithic catalyst precursor can be cooled to room temperature under an inert or weakly reducing atmosphere.

[0077] In step 5), this step selectively removes the pore-forming metal from the cured alloy coating, thereby forming a final three-dimensional porous metal framework structure with a high specific surface area inside the coating, resulting in an integral catalyst.

[0078] Specifically, the monolithic catalyst precursor can be contacted with an alkaline aqueous solution under preset process conditions.

[0079] The alkaline aqueous solution contains a base, which may be selected from alkali metal hydroxides and / or alkaline earth metal hydroxides. In a preferred embodiment, the base is an alkali metal hydroxide. In a more preferred embodiment, the alkali metal hydroxide is sodium hydroxide (NaOH) and / or potassium hydroxide (KOH).

[0080] The concentration of alkali in the alkaline aqueous solution is generally 5~40wt%, preferably 10~30wt%, and more preferably 15~25wt%.

[0081] Through alkaline etching activation treatment, an alkaline aqueous solution selectively reacts with and dissolves the pore-forming metal (e.g., aluminum) in the cured alloy coating, thereby forming a three-dimensional, interconnected porous metal framework structure in situ inside the coating, resulting in an integral catalyst.

[0082] Following the in-situ alkaline etching activation treatment, a post-treatment step is further included. This step aims to remove residual alkaline solution and soluble byproducts from the monolithic catalyst and to dry the catalyst to obtain the final monolithic catalyst that is ready for use or storage.

[0083] Post-processing steps may include:

[0084] 1) Washing Treatment: This step aims to wash the monolithic catalyst, after alkaline etching and activation, until it reaches neutral. The washing step includes repeatedly rinsing or soaking the monolithic catalyst with deionized water. The washing step continues until the pH or conductivity of the washing effluent reaches a preset endpoint.

[0085] The endpoint of washing is defined as the conductivity of the washing effluent being <50µS / cm, preferably <20µS / cm.

[0086] 2) Drying: This step aims to remove moisture from the washed monolithic catalyst. The drying step can be carried out under an inert atmosphere, which can be nitrogen and / or argon.

[0087] The drying temperature range is generally 60~150℃, preferably 80~120℃, and more preferably 100~110℃.

[0088] The drying step typically lasts for 2 to 24 hours, preferably 4 to 12 hours, and more preferably 6 to 8 hours.

[0089] Preferably, to improve the stability of the final monolithic catalyst in air for ease of handling and storage, a passivation treatment may be further included after the drying process. The passivation treatment involves contacting the dried monolithic catalyst with an inert gas mixture containing a low concentration of oxidant at near-room temperature.

[0090] In one embodiment, the oxidant is oxygen, and its volume fraction in the inert gas (e.g., nitrogen) is generally 0.1 to 2.0%, preferably 0.5 to 1.0%.

[0091] The method for preparing the monolithic catalyst provided by this invention can directly form a coating with a three-dimensional porous metal skeleton on the inner wall of the substrate through in-situ activation. The coating is metallurgically bonded to the inner wall of the substrate, which can achieve high heat transfer efficiency, low bed pressure drop, no wear and pulverization, and easy separation and recovery, thereby improving the conversion rate of raw materials and the selectivity of products.

[0092] In some embodiments of the present invention, forming a pre-alloyed powder from a first system comprising a first metal, a second metal, and a pore-forming metal comprises: preparing the pre-alloyed powder from the first system comprising the first metal, the second metal, and the pore-forming metal by a melting-crushing method and / or a mechanical alloying method.

[0093] In one specific embodiment, the smelting-crushing method includes: heating raw materials of a predetermined ratio of a first metal, a pore-forming metal, and a second metal to complete melting by electric arc melting or high-frequency induction melting under an inert atmosphere (e.g., argon) or vacuum conditions, holding at that temperature for a period of time, and then rapidly cooling (e.g., by strip casting or copper mold casting) to form an alloy ingot. Subsequently, the alloy ingot is crushed by a crushing process (e.g., hydrogen-induced crushing, jaw crushing, or ball milling) and sieved to obtain a pre-alloyed powder with a specific particle size distribution.

[0094] In another specific embodiment, the mechanical alloying method includes: placing elemental powders of a first metal, a pore-forming metal, and a second metal in a predetermined ratio into a high-energy ball mill (e.g., a planetary ball mill), and performing long-term, high-intensity ball milling under an inert atmosphere until a uniform alloy phase powder is formed.

[0095] In some embodiments, the mass ratio of the pore-forming metal to the first metal is (0.4~1.5):1, for example, it can be a range of 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, or any combination thereof. Preferably, it is (0.8~1.2):1. This allows the coating to have a three-dimensional porous structure and a suitable specific surface area.

[0096] In some embodiments, the D50 of the pre-alloyed powder is <20 μm, for example, it can be a range of 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 15 μm, 19 μm or any combination thereof. Preferably, D50 is <10 μm, more preferably 1 μm to 8 μm. This ensures slurry stability and coating uniformity, and avoids large particles clogging microchannels.

[0097] In some embodiments of the present invention, the binder includes at least one of polyethylene glycol (PEG), polyvinyl alcohol (PVA), and methylcellulose (MC).

[0098] In some embodiments, the binder comprises 0.5% to 8% by mass of the pre-alloyed powder, for example, in the range of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any combination thereof. Preferably, it is 1% to 5%, more preferably 2% to 4%.

[0099] In some embodiments, the dispersant includes polyacrylates and / or citrates.

[0100] In some embodiments, the dispersant accounts for 0.05 to 3% of the mass percentage of the pre-alloyed powder, for example, it can be a range of 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any two of these. Preferably, it is 0.1 to 2%.

[0101] In this invention, a binder is used to provide the viscosity of the slurry and the initial strength of the coating, ensuring uniform wet film thickness after coating. A dispersant prevents powder agglomeration. By limiting the content of the binder and dispersant, the rheological properties of the pre-alloyed slurry and the coating adhesion can be balanced.

[0102] In some embodiments, the ball milling time is 8 to 48 hours, for example, it can be a range of 8 hours, 10 hours, 20 hours, 30 hours, 40 hours, 48 ​​hours, or any combination thereof; preferably 12 to 36 hours, more preferably 24 hours. The ball-to-material ratio is (3 to 20):1, for example, it can be a range of 3:1, 5:1, 7:1, 10:1, 12:1, 15:1, 20:1, or any combination thereof. Preferably, it is (5 to 15):1.

[0103] The ball milling time and ball-to-material ratio can form a uniform pre-alloyed slurry, which is beneficial to the uniformity of the subsequent coating process.

[0104] In some embodiments, the solid content of the pre-alloyed slurry is 30-60%, for example, it can be a range of 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any two of these; preferably 40-50%. The viscosity is 300-1000 mPa·s, for example, it can be a range of 300 mPa·s, 400 mPa·s, 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, 1000 mPa·s, or any two of these.

[0105] The solid content of the pre-alloyed slurry is beneficial for the subsequent coating process, which can effectively form a coating including a three-dimensional porous metal skeleton.

[0106] The viscosity of the pre-alloyed slurry is beneficial for the smooth progress of the subsequent coating process, avoiding excessive viscosity that could lead to uneven coating thickness.

[0107] In some embodiments of the present invention, coating the substrate surface with the pre-alloyed slurry includes: immersing the substrate in the pre-alloyed slurry and subjecting it to a pull-up process and a blow-out process to obtain an intermediate.

[0108] In one specific embodiment, the coating is performed by a slurry dip coating method, including the following steps:

[0109] 1) Immerse the substrate completely in the pre-alloyed slurry and maintain it for a preset immersion time. The immersion time is generally 1 to 10 minutes, preferably 2 to 5 minutes.

[0110] 2) Pull-out step: The substrate is vertically pulled out of the pre-alloyed slurry at a certain pull-out rate. The pull-out rate is one of the key parameters for controlling the initial wet film thickness of the coating. The pull-out rate is generally 0.5~10mm / s, preferably 1~5mm / s.

[0111] 3) Cleaning step: After lifting, the microchannels of the substrate are purged with a gas stream to remove excess pre-alloyed paste and ensure the patency of the microchannels. In one embodiment, the gas stream is compressed air, with an applied pressure of 0.1~0.5MPa, preferably 0.15~0.3MPa, and a duration of 10~60s.

[0112] The above coating steps can be repeated once or multiple times until the preset coating load is reached.

[0113] In some embodiments, the temperature of the heat treatment is 500~800°C, for example, it can be a range of 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C or any two of these; the time is 0.5~8h, for example, it can be a range of 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h or any two of these.

[0114] The temperature and time of heat treatment allow the binder to decompose fully, enabling the pre-alloyed particles to form a metallurgical bond with the substrate and improving adhesion.

[0115] In some embodiments, the temperature of the alkaline etching activation treatment is 50~100°C, for example, it can be a range of 50°C, 60°C, 70°C, 80°C, 90°C, 100°C or any two of these; preferably 60~90°C, more preferably 70~85°C. The time is 0.5~8h, for example, it can be a range of 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h or any two of these; preferably 1~4h, more preferably 2~3h.

[0116] The temperature and time of alkaline etching activation treatment can selectively dissolve the pore-forming metal, forming a porous structure inside the coating, which can ensure the stability of the coating structure and performance.

[0117] Thirdly, the present invention provides a method for preparing 2-methylpentanediamine, which is obtained by hydrogenating 2-methylpentanedionitrile using the monolithic catalyst as described above or the monolithic catalyst prepared by the method described above.

[0118] The method for preparing 2-methylpentanediamine provided by the present invention uses the above-mentioned monolithic catalyst to hydrogenate 2-methylpentanedione, which can improve the conversion rate of the raw material 2-methylpentanedione and the selectivity of the product 2-methylpentanediamine.

[0119] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0120] Example 1

[0121] The preparation method of the monolithic catalyst in this embodiment includes the following steps:

[0122] 1) Pretreatment of substrate

[0123] Reaction-bonded silicon carbide (SiC) honeycomb ceramic with an outer diameter of 25 mm and a length of 200 mm was selected as the substrate. Its thermal conductivity is 120 W / (m·K), and it has a regular microchannel structure with a hydraulic diameter of 2.0 mm and a wall thickness of 0.5 mm.

[0124] First, the SiC substrate was placed in acetone and ultrasonically cleaned at 40 kHz for 30 min to remove surface organic contaminants. After removal, the substrate was immersed in an 8 wt% dilute nitric acid aqueous solution and treated in a constant temperature water bath at 60℃ for 1 h to activate the surface and form a micro-rough structure. After treatment, it was repeatedly rinsed with plenty of deionized water until the pH of the effluent was 7.0, and finally dried in a 120℃ forced-air oven for 4 h for later use.

[0125] 2) Preparation of pre-alloyed powder

[0126] Pre-alloyed powder was prepared using a smelting-crushing method. Metal raw materials with a purity higher than 99.9% were accurately weighed, with the following mass ratio: 65 parts cobalt (Co), 30 parts aluminum (Al), 3 parts iron (Fe), and 2 parts chromium (Cr).

[0127] After the weighed raw materials are mixed evenly, they are placed in a vacuum arc melting furnace and melted under an argon atmosphere to ensure the formation of a homogeneous alloy melt. The molten alloy melt is then poured into a water-cooled copper mold for rapid cooling to obtain an alloy ingot. Subsequently, the alloy ingot is subjected to staged crushing using a jaw crusher and a disc mill, and finally further refined by high-energy ball milling. After sieving, pre-alloyed powder with a D50 particle size of 5μm is collected.

[0128] 3) Preparation of pre-alloyed slurry

[0129] Pre-alloyed powder, binder polyvinyl alcohol (PVA, type 1788), dispersant sodium polyacrylate, and an appropriate amount of deionized water were added to a planetary ball mill jar. The ball-to-powder mass ratio was set to 10:1, and wet ball milling was performed at room temperature for 24 hours to obtain a pre-alloyed slurry. The binder comprised 3% of the pre-alloyed powder by mass, and the dispersant comprised 0.5% of the pre-alloyed powder by mass.

[0130] After ball milling, a uniform gray slurry with no obvious sedimentation was obtained. Its solid content was determined to be 45 wt%, and its viscosity at 25°C and a specific shear rate was 450 mPa·s.

[0131] 4) Slurry coating and heat treatment

[0132] The coating was performed using a slurry dip-coating method. The pretreated SiC substrate from step 1) was completely immersed vertically into the pre-alloyed slurry and the immersion time was maintained for 3 minutes. Subsequently, the substrate was vertically pulled out of the pre-alloyed slurry at a constant speed of 3 mm / s. Immediately afterward, the microchannels of the substrate were purged with compressed air at a pressure of 0.2 MPa for 30 seconds to remove excess pre-alloyed slurry.

[0133] The substrate with the wet coating was dried at 120°C for 2 hours and then placed in a tube furnace. Under a flowing argon atmosphere (flow rate 200 mL / min), it was heated to 700°C at a programmed heating rate of 5°C / min and held at this peak temperature for 3 hours. After the holding period, the substrate was allowed to cool naturally to room temperature with the furnace to obtain the monolithic catalyst precursor.

[0134] 5) In-situ alkaline etching activation and post-treatment

[0135] The monolithic catalyst precursor was completely immersed in a 20wt% sodium hydroxide (NaOH) aqueous solution and stirred at 80℃ for 3 hours to selectively dissolve aluminum from the coating.

[0136] After activation, the catalyst was removed and repeatedly rinsed with flowing deionized water, and the conductivity of the rinsing effluent was continuously monitored until it was below 20 µS / cm.

[0137] Finally, the cleaned catalyst was placed in a vacuum drying oven and dried at 110°C for 8 hours under a flowing nitrogen atmosphere. For ease of operation, after cooling to room temperature, a passivation treatment was performed for 2 hours using a mixture of oxygen and nitrogen (oxygen volume percentage of 0.5%). The resulting monolithic catalyst was then obtained.

[0138] Example 2

[0139] The preparation method of the monolithic catalyst in this embodiment is basically the same as that in Example 1, except that the substrate used in step 1) is SS316L stainless steel foam metal with a pore density of 40 PPI.

[0140] Example 3

[0141] The preparation method of the monolithic catalyst in this embodiment is basically the same as that in Example 1, except that the mass ratio of the pre-alloyed powder in step 2) is Ni:Al:Fe:Cr=65:30:3:2.

[0142] Example 4

[0143] The preparation method of the monolithic catalyst in this embodiment is basically the same as that in Example 1, except that the mass ratio of the pre-alloyed powder in step 2) is Co:Al:Cr=62:30:8.

[0144] Example 5

[0145] The preparation method of the monolithic catalyst in this embodiment is basically the same as that in Example 1, except that the peak isothermal temperature (temperature of heat treatment) in step 4) is 550°C.

[0146] Example 6

[0147] The preparation method of the monolithic catalyst in this embodiment is basically the same as that in Example 1, except that the substrate used in step 1) is copper foam with a pore density of 60 PPI.

[0148] Example 7

[0149] The preparation method of the monolithic catalyst in this embodiment is basically the same as that in Example 1, except that the mass ratio of the pre-alloyed powder in step 2) is Co:Al:Re=65:30:1.

[0150] Example 8

[0151] The preparation method of the monolithic catalyst in this embodiment is basically the same as that in Example 1, except that the mass ratio of the pre-alloyed powder in step 2) is Co:Al:Cu=65:30:4.

[0152] Example 9

[0153] The preparation method of the monolithic catalyst in this embodiment is basically the same as that in Example 1, except that the mass ratio of the pre-alloyed powder in step 2) is Co:Al:Fe:Cr=55:40:3:2.

[0154] Example 10

[0155] The preparation method of the monolithic catalyst in this embodiment is basically the same as that in Example 1, except that in step 5), the concentration of the alkaline solution is 15wt%, the activation temperature is 90℃, and the time is 4h.

[0156] Example 11

[0157] The preparation method of the monolithic catalyst in this embodiment is basically the same as that in Example 1, except that the mass ratio of the pre-alloyed powder in step 2) is Co:Al:Fe=60:30:20.

[0158] Comparative Example 1

[0159] The preparation method of the catalyst in this comparative example includes the following steps:

[0160] Preparation of powdered Raney cobalt catalyst:

[0161] Using the same smelting-crushing method as steps 1) and 2) in Example 1, a pre-alloyed powder with a composition (mass ratio) of Co:Al:Fe:Cr = 65:30:3:2 was prepared. The obtained alloy ingot was further processed by air jet milling until a pre-alloyed powder with a D50 particle size of 20 μm was obtained.

[0162] Subsequently, in a reactor equipped with mechanical stirring, the pre-alloyed powder was slowly added to a 20 wt% NaOH aqueous solution (solid-liquid ratio 1:5), and activated by stirring at 80°C for 3 h. After activation, the powder was repeatedly decanted and washed until neutral, and then dried at 110°C for 8 h under nitrogen protection to finally obtain powdered Raney cobalt catalyst.

[0163] Comparative Example 2

[0164] The preparation method of the monolithic catalyst in this comparative example is basically the same as that in Example 1, except that cordierite honeycomb ceramic is used as the substrate, which has a thermal conductivity of about 2 W / (m·K).

[0165] Comparative Example 3

[0166] The preparation method of the monolithic catalyst in this comparative example is basically the same as that in Example 1. The difference is that the heat treatment process in step 4) is omitted. During the alkaline etching activation process, large-area blistering and wrinkling of the coating were observed, and it peeled off from the substrate surface in sheets, making it impossible to obtain a complete monolithic catalyst.

[0167] Experimental example:

[0168] Catalyst activity and selectivity tests in Examples 1-11 and Comparative Examples 2-3:

[0169] Reaction apparatus: A shell-and-tube reactor with an inner diameter of 25 mm and a length of 500 mm is used. One or more monolithic catalysts to be tested are packed in the tube side. The shell side is circulated with heat transfer oil for temperature control.

[0170] Standard reaction conditions: reaction pressure 5.0 MPa, reaction temperature 110℃, liquid hourly space velocity (LHSV) of liquid-phase feedstock (containing MGN, ethanol, and NaOH) 1.2 h⁻¹. -1 The molar ratio of hydrogen to MGN is 150:1.

[0171] Product analysis: After the reaction has been running stably for 24 hours, the liquid product was collected and analyzed by gas chromatography (GC) to calculate the MGN conversion and MPMD (2-methylpentanediamine) selectivity.

[0172] MGN conversion rate (%) = [(raw material MGN concentration - product MGN concentration) / raw material MGN concentration] × 100%;

[0173] MPMD selectivity (%) = [Product MPMD concentration / (Raw material MGN concentration - Product MGN concentration)] × 100%.

[0174] Catalyst activity and selectivity tests in Comparative Example 1:

[0175] In a 2L slurry loop reactor system, 160g of the catalyst from Comparative Example 1 was mixed with 1600g of ethanol to form a catalyst slurry, which was then kept circulating at high speed within the reactor by a circulation pump.

[0176] Under the same standard reaction conditions as in Example 1 (reaction temperature 110°C, pressure 5.0 MPa, hydrogen to MGN molar ratio 150:1), an ethanol solution containing MGN and NaOH was continuously pumped into the circulating loop. The product was continuously separated by a cross-flow ceramic membrane filtration system installed in the loop to separate the liquid product from the catalyst slurry. During operation, the pressure differential of the filtration system was observed to gradually increase over time, and trace amounts of catalyst metal ions were detected in the product.

[0177] 2) Coating adhesion test:

[0178] According to ASTM D3359 standard, the cross-section of the prepared monolithic catalyst was tested for tape adhesion using the cross-cut method, and the grade was rated (0B to 5B). 5B is the highest grade, representing no peeling.

[0179] 3) Pressure drop test:

[0180] Under standard reaction conditions, the pressure difference (ΔP) between the inlet and outlet of the reactor is measured.

[0181] Table 1

[0182]

[0183] As shown in Table 1, compared with the comparative example, the monolithic catalyst provided by the present invention includes a coating of a three-dimensional porous metal skeleton that is metallurgically bonded to the inner wall of the substrate and the thermal conductivity of the substrate is limited. This can achieve high heat transfer efficiency, low bed pressure drop, no wear and pulverization, and easy separation and recovery, thereby improving the conversion rate of raw materials and the selectivity of products.

[0184] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to what has been described above. Various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A monolithic catalyst, characterized in that, Including substrate and coating; The thermal conductivity of the substrate is ≥50W / (m·K), and the substrate has a regular microchannel structure; The coating comprises a three-dimensional porous metal framework, which is metallurgically bonded to the inner wall of the substrate.

2. The monolithic catalyst according to claim 1, characterized in that, The microchannel has a hydraulic diameter of 1~3mm and a wall thickness of 0.2~1.0mm; And / or, the substrate includes at least one of silicon carbide, aluminum nitride, and metal.

3. The monolithic catalyst according to claim 1 or 2, characterized in that, The coating comprises a first metal and a second metal; The first metal includes at least one of Group 8, Group 9, and Group 10 metals; The second metal includes at least one of Group 6, Group 7, and Group 11 metals.

4. The monolithic catalyst according to claim 3, characterized in that, The first metal includes at least one of iron, cobalt, nickel, ruthenium, rhodium, and palladium; And / or, the second metal includes at least one of chromium, molybdenum, tungsten, rhenium, copper, and silver; And / or, the second metal accounts for 0.5 to 15% of the mass percentage of the first metal.

5. The monolithic catalyst according to any one of claims 1-4, characterized in that, The specific surface area of ​​the coating is ≥30m². 2 / g.

6. A method for preparing a monolithic catalyst as described in any one of claims 1-5, characterized in that, Includes the following steps: 1) Form a pre-alloyed powder from a first system comprising a first metal, a second metal, and a pore-forming metal; 2) The second system, comprising the pre-alloyed powder, binder, and dispersant, is ball-milled to obtain a pre-alloyed slurry; 3) The pre-alloyed slurry is coated onto the surface of the substrate to obtain an intermediate; 4) The intermediate is heat-treated to obtain an integral catalyst precursor; 5) The monolithic catalyst precursor is subjected to alkaline etching activation treatment to obtain the monolithic catalyst.

7. The preparation method according to claim 6, characterized in that, The process of forming a pre-alloyed powder from a first system comprising a first metal, a second metal, and a pore-forming metal comprises: preparing the pre-alloyed powder from the first system comprising the first metal, the second metal, and the pore-forming metal by means of a melting-crushing method and / or a mechanical alloying method; And / or, the mass ratio of the pore-forming metal to the first metal is (0.4~1.5):1; And / or, the D50 of the pre-alloyed powder is <20 μm.

8. The preparation method according to claim 6 or 7, characterized in that, The adhesive includes at least one of polyethylene glycol, polyvinyl alcohol, and methylcellulose; And / or, the binder accounts for 0.5% to 8% of the mass of the pre-alloyed powder; And / or, the dispersant includes polyacrylates and / or citrates; And / or, the dispersant accounts for 0.05~3% of the mass percentage of the pre-alloyed powder; And / or, the ball milling treatment time is 8~48h, and the ball-to-material ratio is (3~20):1; And / or, the solid content of the pre-alloyed slurry is 30-60%, and the viscosity is 300-1000 mPa·s.

9. The preparation method according to any one of claims 6-8, characterized in that, The step of coating the pre-alloy slurry onto the surface of the substrate includes: immersing the substrate in the pre-alloy slurry and subjecting it to a pulling process and a blowing process to obtain the intermediate; And / or, the heat treatment temperature is 500~800℃, and the time is 0.5~8h; And / or, the alkaline etching activation treatment is performed at a temperature of 50~100℃ for a time of 0.5~8h.

10. A method for preparing 2-methylpentanediamine, characterized in that, The 2-methylglutaronitrile is obtained by hydrogenation using the monolithic catalyst according to any one of claims 1-5 or the monolithic catalyst prepared by any one of claims 6-9.

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