An integrated chromium-based catalyst in a propane dehydrogenation device and a preparation method thereof

Abstract

The application discloses a monolithic chromium catalyst in a propane dehydrogenation device and a preparation method thereof, and belongs to the technical field of propane dehydrogenation catalysts. The catalyst comprises a honeycomb ceramic base and an active coating. The material of the honeycomb ceramic base is cordierite. The active coating is loaded with active components in a molar ratio of 0.8-1.2:1.6-2.4:1 of zirconium, chromium and lanthanum. The active coating is uniformly coated on the surface of the honeycomb ceramic base. The comprehensive performance of the chromium catalyst is remarkably improved through comprehensive optimization of the introduction of an auxiliary agent, surface modification, a synthesis process and a structural design.

Description

Technical Field

[0001] This application relates to the field of propane dehydrogenation catalyst technology, and in particular to an integral chromium-based catalyst for a propane dehydrogenation unit and its preparation method. Background Technology

[0002] With the rapid development of propane dehydrogenation to propylene technology, chromium-based catalysts have become a research hotspot in this field due to their high activity, selectivity, and stability. However, existing chromium-based catalysts still have some shortcomings in terms of preparation processes and performance optimization, affecting their efficiency and economy in industrial applications.

[0003] Patent CN118874456B discloses a chromium-based propane dehydrogenation catalyst and its preparation method. This patent utilizes the synergistic effect of specific surfactants (such as N-dihydroxyethylalkylamide and hexadecyltrimethylammonium bromide) to improve the propane conversion, propylene selectivity, and propylene yield of the catalyst. However, this technical solution places high demands on the selection and dosage of surfactants in the catalyst preparation process, leading to increased process complexity and cost. Furthermore, although the propane conversion and propylene selectivity are improved, the catalyst's resistance to carbon buildup and its stability during long-term operation still require further verification.

[0004] Patent CN110841709B discloses a method for preparing a chromium-based catalyst for propane dehydrogenation to propylene. This patent utilizes a composite of titanium silicate molecular sieve TS-1 and alumina gel to adjust the acidity and acid strength of the support surface and construct a hierarchical porous structure, thereby improving the loading and dispersion of the active components and the catalyst's resistance to carbon deposition. However, in this technical solution, the preparation process of the composite support involves complex pore-expanding agent usage and multiple calcination steps, resulting in high energy consumption and operational difficulty. Furthermore, although the catalyst's resistance to carbon deposition is improved, its thermal stability and activity maintenance under high-temperature reaction conditions still have room for improvement.

[0005] The above problems indicate that existing chromium-based propane dehydrogenation catalysts still have certain shortcomings in terms of the simplification of the preparation process, the stability of long-term operation, and the performance under high-temperature conditions. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide an integral chromium-based catalyst for propane dehydrogenation unit that is easy to prepare, has strong anti-carbon deposition ability and good high-temperature stability, and its preparation method.

[0007] The technical solution adopted by the present invention to solve its technical problem is: an integral chromium-based catalyst in a propane dehydrogenation device, characterized in that: it includes a honeycomb ceramic substrate and an active coating, wherein the honeycomb ceramic substrate is made of cordierite, and the active coating is loaded with an active component composed of zirconium, chromium and lanthanum in a molar ratio of 0.8~1.2:1.6~2.4:1, and the active coating is uniformly covered on the surface of the honeycomb ceramic substrate.

[0008] This invention utilizes zirconium (Zr) and lanthanum (La) doping to form a composite support on an active coating. These additives, along with active chromium, interact with the alumina lattice, altering its surface acidity distribution. The introduction of Zr and La regulates the acid strength and quantity distribution on the support surface, making propane reactant molecules more readily adsorbed and activated, while simultaneously suppressing side reactions. The honeycomb ceramic matrix, made of cordierite, possesses a low coefficient of thermal expansion and a high melting point, maintaining structural integrity under high-temperature (>600℃) reaction conditions and resisting thermal stress cracking. The integral design further enhances mechanical strength, reduces active coating detachment due to airflow erosion, and extends service life. The regular channels of the honeycomb structure significantly reduce pressure drop during gas passage, improving device efficiency. The uniform channel distribution also promotes sufficient contact between reactants and active sites, improving mass transfer efficiency and preventing localized carbon buildup or concentrated side reactions. The introduction of lanthanum (La) not only modulates acidity but also inhibits carbon deposition through its redox properties. The synergistic effect of La³⁺ and active chromium promotes the oxidative removal of carbon precursors, reduces coking on the catalyst surface, and maintains long-term activity. The active coating adopts a one-step impregnation-calcination loading method, eliminating the need for complex surfactants or multiple calcination steps. The honeycomb matrix directly serves as the support, eliminating the molding process of traditional powder catalysts and reducing energy consumption and raw material costs. The addition of zirconium (Zr) forms Zr-O-Al bonds with the alumina support, anchoring chromium species and inhibiting their migration and aggregation at high temperatures, ensuring high dispersion of active sites, thereby improving propylene selectivity and yield stability. The monolithic structure is adaptable to frequent start-stop and variable operating conditions. The cordierite matrix has strong corrosion resistance and can maintain stable performance even in feed gases containing trace impurities (such as sulfur and water), reducing the risks of industrial applications.

[0009] Specifically, in the above-mentioned monolithic chromium-based catalyst, the active coating contains composite support particles, the active components are loaded on the composite support particles, and the composite support particles are coated with a hydrophobic coating and a carbon barrier layer.

[0010] The carbon barrier layer of this invention utilizes its dense inorganic network structure to form a physical barrier on the surface of the composite support particles, effectively preventing the secondary polymerization of olefins generated in the propane dehydrogenation reaction to form coke precursors, thereby inhibiting carbon deposition at the source. Simultaneously, the hydrophobic coating forms a hydrophobic barrier on the support surface through chemical bonding, preventing trace water molecules in the feed gas from eroding the active components, reducing the binding of water molecules to acidic sites on the alumina support surface, maintaining the stability of the support's acidic distribution, and preventing catalyst deactivation due to hydrothermal environment. Furthermore, the "core-shell confined space" structure of the composite support particles optimizes the reaction path through the size selectivity of the shell pores, extending the residence time of reactants to fully activate CH bonds, while suppressing the deep dehydrogenation side reaction of propylene, improving the directional exposure and utilization efficiency of active sites. The high thermal stability of the carbon barrier layer can also anchor Cr species at high temperatures, reducing their migration and aggregation, and maintaining a highly dispersed state of active sites. The low surface energy of the hydrophobic coating and the alkaline sites in the carbon barrier layer effectively reduce the chemical adsorption of sulfur- or chlorine-containing impurities, preventing the active sites from being poisoned and enhancing the catalyst's resistance to impurity poisoning. In terms of preparation, the hydrophobic coating and carbon barrier layer can be formed in one step using a sol-gel method, significantly reducing energy consumption compared to traditional processes. The coating structure also ensures that carbon deposits are mainly concentrated on the surface of the carbon barrier layer, allowing for rapid activity recovery through gentle oxidation during regeneration, significantly increasing the number of regeneration cycles and reducing industrial replacement costs.

[0011] A method for preparing an integral chromium-based catalyst for the above-mentioned propane dehydrogenation unit includes the following steps: (1) Select a cordierite honeycomb ceramic substrate as the support structure; immerse the honeycomb ceramic substrate in a dilute nitric acid solution with a mass fraction of 4.5%~5.5% for 100min~150min, then rinse it with deionized water until neutral, and dry it at 110℃~130℃ for 3.5h~4.5h. (2) Immerse the dried honeycomb ceramic substrate in a silica sol solution with a mass concentration of 8%~12% for 25min~35min; (3) The active coating powder is mixed with a polyvinyl alcohol solution with a mass fraction of 4.5%~5.5% to prepare a slurry with a solid content of 25%~35%. The slurry is applied to the honeycomb ceramic substrate with a coating thickness of 60μm~100μm. After coating, it is dried and calcined to obtain the final product.

[0012] In this preparation method, the cordierite matrix is ​​first etched with dilute nitric acid. This selective etching of the surface glass phase exposes more active sites and forms a micron-level rough surface, significantly enhancing the chemical bonding between the subsequent silica sol layer and the matrix, increasing the mechanical bonding strength by 40%–50%. Next, a transition layer is formed on the matrix surface by silica sol impregnation. This transition layer, with a thermal expansion coefficient between that of the matrix and the active coating, effectively alleviates interfacial stress caused by thermal expansion differences at high temperatures. Simultaneously, its mesoporous structure provides high specific surface area loading sites for the active components, reducing reactant diffusion resistance. Regarding the slurry formulation and coating process, polyvinyl alcohol solution is used as a binder, optimizing the slurry's rheological properties and achieving uniform dispersion of the active coating powder and precise control of the coating thickness. Low-temperature drying and segmented calcination processes ensure the stability of the coating and the formation of a porous structure. Replacing the traditional multi-loading process with a one-step impregnation method reduces the process time by more than 50%, while the use of low-concentration reagents reduces acid consumption and silica sol usage.

[0013] Preferably, the honeycomb ceramic substrate has a diameter of 80mm~120mm, a length of 180mm~220mm, and a pore density of 350 holes / in. 2 ~450 holes / in 2 The hole wall thickness is 0.1mm~0.5mm.

[0014] The selected diameter is compatible with the tube diameter of industrial-grade fixed-bed reactors, with a single module length of 180~220mm, allowing for multi-section stacking to adapt to different production capacity requirements and avoid edge effects or airflow short-circuiting caused by size mismatch. Furthermore, the synergistic design of diameter and pore density ensures uniform radial airflow diffusion, controlling the Reynolds number within the laminar flow range, reducing pressure drop by 60%~70% compared to traditional granular beds, and decreasing energy consumption by 15%~20%. The turbulent micro-vortices formed within the pores at the selected pore density reduce boundary layer thickness, thereby increasing the mass transfer rate of propane molecules diffusing to active sites.

[0015] Preferably, the preparation method of the active coating powder in step (3) of the above-mentioned method for preparing the monolithic chromium catalyst includes the following steps: (a) An alumina precursor is mixed with a solution of zirconium, chromium and lanthanum nitrates in a certain proportion to form a suspension, wherein the alumina precursor is aluminum isopropoxide, the molar ratio of zirconium, chromium and lanthanum is 0.8~1.2:1.6~2.4:1, and the total mass of zirconium, chromium and lanthanum nitrates is 4.5%~5.5% of the mass of the alumina precursor; (b) The suspension was prepared into composite carrier particles by spray drying, with the inlet air temperature being 190℃~210℃ during spray drying; (c) The obtained composite carrier particles were subjected to surface modification treatments of hydrophobic coating and carbon barrier layer in succession; (d) Then, the composite carrier particles were mixed with chromium acetylacetone solution and microwave-assisted loading was performed.

[0016] This invention utilizes aluminum isopropoxide (instead of traditional aluminum salts) hydrolyzed to generate alumina, avoiding residual impurities such as Cl⁻ and forming a high-purity γ-Al₂O₃ support. Its mesoporous structure (pore size 3-5 nm) provides well-organized loading sites for the active components. Zirconium (Zr), chromium (Cr), and lanthanum (La) nitrates are simultaneously hydrolyzed and co-precipitated with the alumina precursor. Metal ions are embedded into the support lattice through Al-O-Zr / Cr / La bonds, forming atomically dispersed composite oxides. The density of active sites can be increased to 2-3 times that of traditional impregnation methods. Then, spray drying at 190℃-210℃ instantly dehydrates the suspension droplets, forming spherical particles with a diameter of 20μm-50μm, retaining the interconnected mesopores (2-10 nm) and macropores (100-500 nm) formed by solvent evaporation. The instantaneous curing characteristic of spray drying prevents localized enrichment caused by metal ion migration, resulting in significantly better Zr / Cr / La distribution uniformity than traditional calcination methods. A 1-2 nm thick hydrophobic layer is formed on the surface of the composite carrier particles by fluorosilane vapor deposition, which prevents water molecules from contacting the acidic sites of the carrier. Chromium acetylacetone generates local hot spots (instantaneous temperature of about 300℃) due to the high-frequency vibration of polar molecules in a microwave field, which promotes the rapid embedding of Cr³⁺ into oxygen vacancies on the carrier surface. The loading time is shortened from the traditional 6-8 hours to 12-18 minutes, and the energy consumption is greatly reduced.

[0017] Preferably, in the preparation method of the above-mentioned active coating powder, the hydrophobic coating surface modification treatment in step (c) includes the following steps: immersing the composite carrier particles in an ethanol solution of 3-aminopropyltriethoxysilane with a concentration of 0.8wt%~1.3wt% for 10h~12h, and then heat-treating them at 115℃~125℃ for 100min~150min.

[0018] The composite carrier particles were immersed in a 0.8–1.3 wt% APTES ethanol solution for 10–12 hours, causing the ethoxy groups of the silane coupling agent to undergo hydrolytic condensation with the hydroxyl groups on the carrier surface, forming a covalently bonded Si-O-Al / Zr network. The amino groups (-NH2) align outwards, forming a superhydrophobic surface with a contact angle >130°, significantly enhancing the barrier to water molecules. Subsequently, heat treatment at 115–125°C for 100–150 minutes promotes further cross-linking of unreacted silane molecules, forming a dense and flexible organic-inorganic hybrid layer. The amino groups of APTES interact with strong Lewis acid sites (such as Al) on the carrier surface. 3+The coordination of the Cr active site neutralizes the acid strength, reducing coking and methane byproducts caused by excessive propane cracking, thus improving reaction selectivity. Simultaneously, the moderately retained weakly Brønsted acid sites (such as Si-OH, acid content 0.1 mmol / g) synergistically promote the breaking of the CH bond in propane dehydrogenation, increasing conversion rate. The hydrophobic surface also reduces the adsorption affinity of coking precursors (such as propylene and aromatics), increasing adsorption free energy and inhibiting their retention and polymerization, thus lowering the initial coking rate. The hydrophobic layer and the subsequent carbon barrier layer form a "hydrophobic-oxidation" composite barrier, allowing coking to preferentially form on the surface of the carbon barrier layer and be oxidized and removed, protecting the active sites inside the support from contamination.

[0019] Preferably, in the preparation method of the above-mentioned active coating powder, the surface modification treatment of the carbon barrier layer in step (c) includes the following steps: placing the composite carrier particles in a chemical vapor deposition device, introducing methane as a carbon source gas, controlling the reaction temperature to be 670℃~730℃, the deposition time to be 7min~9min, and obtaining a carbon barrier layer with a thickness of 1nm~5nm.

[0020] Under high-temperature conditions (670℃~730℃), methane cracks to generate sp² hybridized graphene-like carbon layers (1~5nm thick). The six-membered ring lattice spacing (0.34nm) is smaller than that of carbon deposition precursors (such as polycyclic aromatic hydrocarbons, >1nm), creating a molecular sieve effect that prevents the diffusion of large carbon species into the support. By controlling the reaction temperature and time, appropriate amounts of five-membered / seven-membered ring topological defects are also introduced into the carbon layer. The electronic coupling between these defect sites and active Cr centers inhibits the nucleation and growth of carbon deposits. At high temperatures (>600℃), the ultrathin carbon film can activate O2 to generate reactive oxygen species (such as ·O⁻), which then bind the adsorbed carbon deposits (C₂, C₂, and C₂). x Hᵧ) is oxidized to CO2. During the CVD process, methane reacts with metals (such as Cr and Zr) on the support surface to form a carbide transition layer (such as Cr3C2 and ZrC), which enables the carbon film to form a chemical bond with the support, thereby improving its peel strength.

[0021] Preferably, in the preparation method of the above-mentioned active coating powder, the specific operation of microwave-assisted loading in step (d) is as follows: the composite carrier particles are mixed with a chromium acetylacetone solution with a concentration of 0.07 mol / L to 0.13 mol / L and then placed in a microwave reactor. The microwave power is set to 380 W to 420 W, and the irradiation time is 12 min to 18 min. In this invention, the microwave-assisted loading process uses microwave electric field polarization to cause the polar ligands of chromium acetylacetone to vibrate and dissociate at high frequency. The released Cr³⁺ is captured by oxygen vacancies on the carrier surface, forming a stable Cr-O-Al / Zr bond structure. The non-thermal effect of microwaves promotes the dispersion of Cr in single-atom form, with an atomic dispersion of over 90%, significantly increasing the density of active sites for propane dehydrogenation. Microwave irradiation directly excites the local thermal effect on the carrier surface, enabling the decomposition and loading of Cr(acac)₃ to be completed in one step, greatly shortening the loading time. Furthermore, microwave selective heating of the active sites avoids overall high-temperature treatment, thereby controlling the Cr grain size to 1-2 nm. Even after 1000 hours of operation at high temperature (650℃), the grain growth rate remains less than 10%. Microwave irradiation also excites the generation of oxygen vacancies on the support surface. These oxygen vacancies, acting as electronic defect sites, synergistically work with the Cr active centers to lower the energy barrier for propane CH bond breaking, thus improving the conversion rate. Trace amounts of undecomposed acac⁻ ligands, acting as weak acid sites, effectively inhibit excessive propylene dehydrogenation to generate byproducts, achieving a propylene selectivity of 95%-96%.

[0022] Preferably, in the above-mentioned method for preparing the monolithic chromium catalyst, the drying temperature in step (3) is 110℃~130℃ and the time is 100min~150min. This drying condition can slowly remove free water from the coating, avoid coating cracking caused by rapid water loss, and ensure the integrity and stability of the coating.

[0023] Preferably, in the above-mentioned method for preparing the monolithic chromium-based catalyst, the calcination temperature in step (3) is 450℃~550℃, and the time is 3.5h~4.5h. These calcination conditions can fully decompose the precursor, transforming it into a highly active oxide phase, while effectively controlling the grain growth of the active component and maintaining a high specific surface area, thereby improving the activity and selectivity of the catalyst. Furthermore, these conditions can enhance the interaction between the active component and the support, improving the mechanical strength and thermal stability of the catalyst, enabling it to maintain good performance during long-term operation.

[0024] Compared with existing technologies, the beneficial effects of the monolithic chromium-based catalyst and its preparation method in a propane dehydrogenation device of the present invention are as follows: In the present invention, a honeycomb ceramic substrate serves as a supporting structure, and its surface is firmly bonded to the active coating through a silicon-oxygen network structure. The reaction performance is optimized through additive regulation and surface modification techniques within the active coating, while the uniform dispersion of the active components is achieved through the synthesis process. The present invention abandons the traditional use of chromium nitrate as the chromium source, employing organic chromium complexes (such as chromium acetylacetone) as the precursor of the active components, significantly reducing pollution emissions during the calcination process. During the loading process, microwave radiation technology is used to achieve uniform dispersion of chromium species. The present invention significantly improves the overall performance of the chromium-based catalyst through comprehensive optimization of additive introduction, surface modification, synthesis process, and structural design. The introduction of rare earth additives improves the acidity distribution on the support surface, promoting the activation of reactants; the combination of a hydrophobic coating and a carbon barrier layer effectively extends the catalyst's lifespan; the synthesis process simplifies the preparation process and reduces environmental pollution; and the monolithic catalyst design greatly improves the economic efficiency and operational convenience of industrial applications. Detailed Implementation

[0025] In the monolithic catalyst structure of this invention, the honeycomb ceramic substrate serves as a supporting structure for the active coating. Its internal structure features regularly arranged pores, which effectively reduce bed pressure drop and improve mass transfer efficiency. The active coating is uniformly coated on the surface of the honeycomb ceramic substrate and firmly adheres through a calcination process, forming a stable catalytic layer.

[0026] In the preparation process, a cordierite honeycomb ceramic matrix was first selected as the basic structure of the monolithic catalyst. The preferred dimensions of the honeycomb ceramic matrix were a diameter of 100 mm, a length of 200 mm, and a pore density of 400 holes / in. 2 The pore wall thickness is 0.3 mm. This design meets the requirements of industrial-scale propane dehydrogenation units while ensuring low flow resistance of the reactant gas within the pores. The honeycomb ceramic substrate requires pretreatment before use to remove surface impurities and enhance coating adhesion. A preferred procedure is to immerse the honeycomb ceramic substrate in a 5% (w / w) dilute nitric acid solution for 2 hours, followed by repeated rinsing with deionized water until neutral, and finally drying at 120°C for 4 hours. After drying, the honeycomb ceramic substrate is then immersed in a 10% (w / w) silica sol solution for surface activation treatment for 30 minutes. This step forms a silicon-oxygen network structure on the surface of the honeycomb ceramic substrate, thereby enhancing the adhesion of the subsequent active coating.

[0027] The preparation process of the active coating includes four main steps: preparation of the composite carrier, introduction of additives, surface modification, and loading of active components.

[0028] The composite carrier was prepared using a sol-gel method. A preferred procedure involved mixing an alumina precursor with a nitrate solution of zirconium, chromium, and lanthanum in a specific ratio. The alumina precursor was aluminum isopropoxide, and the molar ratio of the three active ingredients (zirconium, chromium, and lanthanum) was 1:2:1, with the total active ingredient content accounting for 5% of the composite carrier's mass. The mixture was stirred and evaporated at 80°C to form a sol, followed by spray drying to produce composite carrier particles with uniform particle size. The spray drying conditions were an inlet air temperature of 200°C, an outlet air temperature of 100°C, and a spray pressure of 0.2 MPa. The resulting composite carrier particles had an average particle size of approximately 50 μm, exhibiting a high specific surface area and uniform additive distribution.

[0029] After the composite carrier particles were prepared, they underwent surface modification to improve their resistance to poisoning and mass transfer efficiency. Surface modification consisted of two parts: a hydrophobic coating and a carbon barrier layer. The hydrophobic coating was constructed using a silane coupling agent. A preferred method involved immersing the composite carrier particles in an ethanol solution containing 3-aminopropyltriethoxysilane. The concentration of the silane coupling agent was 1%, and the immersion time was 12 hours. After immersion, the composite carrier particles were removed and heat-treated at 120°C for 2 hours to induce a condensation reaction between the silane groups and the hydroxyl groups on the carrier surface, generating stable Si-O-Al bonds. The carbon barrier layer was constructed using chemical vapor deposition (CVD). Specifically, the composite carrier particles were placed in a CVD apparatus, methane was introduced as the carbon source gas, the reaction temperature was controlled at 700°C, and the deposition time was 8 minutes. The resulting carbon layer was approximately 3 nm thick, effectively shielding against carbon buildup while allowing reactant molecules to diffuse smoothly to the active sites.

[0030] The loading of the active component employs a green synthesis process. Specifically, the composite carrier particles are mixed with a chromium acetylacetone solution and then subjected to microwave-assisted loading. During microwave-assisted loading, it is preferable to mix the composite carrier particles with a 0.1 mol / L chromium acetylacetone solution and place the mixture in a microwave reactor, setting the power to 400 W and the irradiation time to 15 min. The localized hotspot effect generated by microwave radiation accelerates solvent evaporation and chromium species fixation, avoiding chromium agglomeration caused by slow solvent evaporation in traditional impregnation methods.

[0031] After the active coating is prepared, it is applied to the surface of a honeycomb ceramic substrate. A preferred method involves mixing the active coating powder with a suitable amount of binder to form a slurry. The binder is a 5% (w / w) polyvinyl alcohol solution, and the slurry has a solid content of 30%. The slurry is then uniformly coated onto the surface of the honeycomb ceramic substrate, with the coating thickness controlled to be within 100 μm. After coating, the honeycomb ceramic substrate is dried at 120°C for 2 hours, followed by calcination at 500°C for 4 hours to ensure the active coating adheres firmly to the surface of the honeycomb ceramic substrate. The resulting monolithic catalyst exhibits good mechanical strength and low bed pressure drop, making it suitable for application in large-scale propane dehydrogenation units.

[0032] In practical applications, the monolithic catalyst is installed in the fixed-bed reactor of the propane dehydrogenation unit. A preferred operating condition in the fixed-bed reactor is a reaction temperature of 600°C, a reaction pressure of 0.1 MPa, and a propane volume hourly space velocity (WHSV) of 1000 h⁻¹. -1 The reaction gas consists of propane and water vapor, with a molar ratio of water vapor to propane of 1.5:1. During the reaction, propane molecules enter the surface of the active coating through the pores of the honeycomb ceramic matrix and undergo a dehydrogenation reaction at the active sites to generate propylene. Due to the presence of rare earth additives in the active coating, the acidity distribution on the support surface is optimized, promoting the adsorption and activation of propane molecules. Simultaneously, the hydrophobic coating effectively reduces the poisoning effect of water vapor on the active sites, while the carbon barrier layer prevents carbon deposits from directly contacting the active sites, thereby extending the catalyst's lifespan. Furthermore, the monolithic catalyst design significantly reduces bed pressure drop, improving the economics and operational convenience of industrial applications.

[0033] In this embodiment, the connection and positional relationships between the various components are clearly defined. The honeycomb ceramic substrate serves as the supporting structure, and its surface is firmly bonded to the active coating through a silicon-oxygen network structure. The reaction performance is optimized within the active coating through additive regulation and surface modification techniques, while the uniform dispersion of the active components is achieved through a green synthesis process. This monolithic catalyst design not only solves the problems existing in the prior art but also provides new technical support for the efficient preparation and industrial application of propane dehydrogenation catalysts.

[0034] To enable those skilled in the art to fully understand and implement this invention, the specific implementation principle of this invention is further explained below in conjunction with a specific application scenario.

[0035] Firstly, in the preparation of the monolithic catalyst, the honeycomb ceramic substrate serves as the core supporting structure for the active coating. Its regularly arranged pores significantly reduce the flow resistance of the reactant gases within the bed. The honeycomb ceramic substrate is made of cordierite and undergoes immersion in dilute nitric acid solution and activation with silica sol, resulting in a silicon-oxygen network structure on its surface. This structure not only enhances the adhesion between the honeycomb ceramic substrate and the active coating but also provides a uniform and stable interfacial environment for the subsequent loading of composite carrier particles.

[0036] The preparation of the active coating begins with the fabrication of the composite carrier. An alumina precursor is mixed with a nitrate solution of zirconium, chromium, and lanthanum using a sol-gel method, followed by spray drying to obtain composite carrier particles with uniform particle size. The composite carrier particles have a high specific surface area and uniform additive distribution, laying the foundation for subsequent loading of the active components. In the surface modification stage of the composite carrier particles, the hydrophobic coating generates Si-O-Al bonds through the condensation reaction of a silane coupling agent, effectively reducing the poisoning effect of water vapor on the active sites. Simultaneously, an ultrathin carbon film is deposited using chemical vapor deposition, with a thickness controlled at approximately 3 nm. This not only shields the active sites from direct contact by carbon deposits but also allows propane molecules to diffuse smoothly to the active sites, thereby maintaining high reaction efficiency.

[0037] The loading of the active component employs a green synthesis process combining microwave-assisted and ultrasonic dispersion. In the microwave-assisted loading process, the composite carrier particles are mixed with an acetylacetone chromium solution and placed in a microwave reactor. The local hot spot effect generated by microwave radiation accelerates solvent evaporation and chromium species fixation, avoiding chromium agglomeration caused by slow solvent evaporation in the traditional impregnation method.

[0038] After the active coating is prepared, it is mixed with a binder to form a slurry, which is then uniformly coated onto the surface of the honeycomb ceramic substrate. The coating thickness is strictly controlled within 100 μm to ensure the mechanical strength and mass transfer efficiency of the catalyst. The coated honeycomb ceramic substrate is then dried and calcined to ensure that the active coating adheres firmly to the surface of the substrate. The resulting monolithic catalyst exhibits good mechanical strength and low bed pressure drop, making it suitable for application in large-scale propane dehydrogenation units.

[0039] In practical applications, the monolithic catalyst is installed in the fixed-bed reactor of the propane dehydrogenation unit. A preferred operating condition for the fixed-bed reactor is a reaction temperature of 600°C, a reaction pressure of 0.1 MPa, and a propane volume hourly space velocity of 1000 h⁻¹. -1The reaction gas consists of propane and water vapor, with a molar ratio of water vapor to propane of 1.5:1. During the reaction, propane molecules enter the surface of the active coating through the pores of the honeycomb ceramic matrix and undergo a dehydrogenation reaction at the active sites to generate propylene. Due to the presence of rare earth additives in the active coating, the acidity distribution on the support surface is optimized, promoting the adsorption and activation of propane molecules. Simultaneously, the hydrophobic coating effectively reduces the poisoning effect of water vapor on the active sites, while the carbon barrier layer prevents carbon deposits from directly contacting the active sites, thereby extending the catalyst's lifespan. The monolithic catalyst structure design significantly reduces bed pressure drop, improving the economics and operational convenience of industrial applications.

[0040] The present invention will be further described below with reference to specific embodiments, wherein Embodiment 1 is the preferred embodiment.

[0041] Example 1: Preparation of active coating powder: (a) The alumina precursor is mixed with a solution of zirconium, chromium and lanthanum nitrates in a certain proportion to form a suspension, wherein the alumina precursor is aluminum isopropoxide, the molar ratio of zirconium, chromium and lanthanum is 1:2:1, and the total mass of zirconium, chromium and lanthanum nitrates is 5% of the mass of the alumina precursor.

[0042] (b) The suspension was prepared into composite carrier particles by spray drying. The inlet air temperature was 200°C, the outlet air temperature was 100°C, and the spray pressure was 0.2 MPa.

[0043] (c) The obtained composite carrier particles were subjected to surface modification treatments of hydrophobic coating and carbon barrier layer. The composite carrier particles were immersed in an ethanol solution of 1% 3-aminopropyltriethoxysilane for 10 h, followed by heat treatment at 120 °C for 120 min. Then the composite carrier particles were placed in a chemical vapor deposition apparatus, and methane was introduced as the carbon source gas. The reaction temperature was controlled at 700 °C and the deposition time was 8 min.

[0044] (d) Then, the composite carrier particles were mixed with chromium acetylacetone solution and microwave-assisted loading was performed to obtain the active coating powder: the composite carrier particles were mixed with chromium acetylacetone solution with a concentration of 0.1 mol / L and placed in a microwave reactor. The microwave power was set to 400 W and the irradiation time was 15 min.

[0045] Preparation of monolithic chromium-based catalysts: (1) A cordierite-based honeycomb ceramic substrate was selected as the supporting structure. The dimensions of the honeycomb ceramic substrate were 100 mm in diameter and 200 mm in length, with a pore density of 400 holes / in. 2The pore wall thickness is 0.3 mm; the honeycomb ceramic substrate is immersed in 5% dilute nitric acid for 120 min, then rinsed with deionized water until neutral, and dried at 120℃ for 4 h.

[0046] (2) Immerse the dried honeycomb ceramic substrate in a silica sol solution with a mass concentration of 10% for 30 min.

[0047] (3) The active coating powder is mixed with a 5% polyvinyl alcohol solution to prepare a slurry with a solid content of 30%. The slurry is applied to the honeycomb ceramic substrate with a coating thickness of 800 μm. After coating, it is dried at 120℃ for 120 min and calcined at 500℃ for 4 h to obtain the final product.

[0048] Example 2: Preparation of active coating powder: (a) The alumina precursor is mixed with a solution of zirconium, chromium and lanthanum nitrates in a certain proportion to form a suspension, wherein the alumina precursor is aluminum isopropoxide, the molar ratio of zirconium, chromium and lanthanum is 0.9:2.2:1, and the total mass of zirconium, chromium and lanthanum nitrates is 4.8% of the mass of the alumina precursor.

[0049] (b) The suspension was prepared into composite carrier particles by spray drying. The inlet air temperature was 195°C, the outlet air temperature was 95°C, and the spray pressure was 0.2 MPa.

[0050] (c) The obtained composite carrier particles were subjected to surface modification treatments of hydrophobic coating and carbon barrier layer. The composite carrier particles were immersed in an ethanol solution of 3-aminopropyltriethoxysilane with a concentration of 0.9wt% for 11.5h, followed by heat treatment at 118℃ for 130min. Then the composite carrier particles were placed in a chemical vapor deposition apparatus, and methane was introduced as the carbon source gas. The reaction temperature was controlled at 690℃ and the deposition time was 8.5min.

[0051] (d) Then, the composite carrier particles were mixed with chromium acetylacetone solution and microwave-assisted loading was performed to obtain the active coating powder: the composite carrier particles were mixed with chromium acetylacetone solution with a concentration of 0.09 mol / L and placed in a microwave reactor. The microwave power was set to 390 W and the irradiation time was 16 min.

[0052] The preparation of the monolithic chromium-based catalyst is the same as in Example 1.

[0053] Example 3: Preparation of active coating powder: (a) The alumina precursor is mixed with a solution of zirconium, chromium and lanthanum nitrates in a certain proportion to form a suspension, wherein the alumina precursor is aluminum isopropoxide, the molar ratio of zirconium, chromium and lanthanum is 1.1:1.8:1, and the total mass of zirconium, chromium and lanthanum nitrates is 5.2% of the mass of the alumina precursor.

[0054] (b) The suspension was prepared into composite carrier particles by spray drying. The inlet air temperature was 205°C, the outlet air temperature was 105°C, and the spray pressure was 0.2 MPa.

[0055] (c) The obtained composite carrier particles were subjected to surface modification treatments of hydrophobic coating and carbon barrier layer. The composite carrier particles were immersed in an ethanol solution of 3-aminopropyltriethoxysilane with a concentration of 1.1 wt% for 10.5 h, followed by heat treatment at 122 °C for 110 min. Then the composite carrier particles were placed in a chemical vapor deposition apparatus, and methane was introduced as the carbon source gas. The reaction temperature was controlled at 710 °C and the deposition time was 7.5 min.

[0056] (d) Then, the composite carrier particles were mixed with the chromium acetylacetone solution and microwave-assisted loading was performed to obtain the active coating powder: the composite carrier particles were mixed with the chromium acetylacetone solution with a concentration of 0.11 mol / L and placed in a microwave reactor. The microwave power was set to 410 W and the irradiation time was 14 min.

[0057] The preparation of the monolithic chromium-based catalyst is the same as in Example 1.

[0058] Example 4: Preparation of active coating powder: (a) The alumina precursor is mixed with a solution of zirconium, chromium and lanthanum nitrates in a certain proportion to form a suspension, wherein the alumina precursor is aluminum isopropoxide, the molar ratio of zirconium, chromium and lanthanum is 0.8:1.6:1, and the total mass of zirconium, chromium and lanthanum nitrates is 5.5% of the mass of the alumina precursor.

[0059] (b) The suspension was prepared into composite carrier particles by spray drying. The inlet air temperature was 190°C, the outlet air temperature was 90°C, and the spray pressure was 0.18 MPa.

[0060] (c) The obtained composite carrier particles were subjected to surface modification treatments of hydrophobic coating and carbon barrier layer. The composite carrier particles were immersed in an ethanol solution of 3-aminopropyltriethoxysilane with a concentration of 0.8 wt% for 12 h, followed by heat treatment at 115 °C for 150 min. Then the composite carrier particles were placed in a chemical vapor deposition apparatus, and methane was introduced as the carbon source gas. The reaction temperature was controlled at 670 °C and the deposition time was 9 min.

[0061] (d) Then, the composite carrier particles were mixed with the chromium acetylacetone solution and microwave-assisted loading was performed to obtain the active coating powder: the composite carrier particles were mixed with the chromium acetylacetone solution with a concentration of 0.07 mol / L and placed in a microwave reactor. The microwave power was set to 380 W and the irradiation time was 18 min.

[0062] Preparation of monolithic chromium-based catalysts: (1) A cordierite-based honeycomb ceramic substrate was selected as the supporting structure. The dimensions of the honeycomb ceramic substrate were 80 mm in diameter and 180 mm in length, with a pore density of 450 holes / in. 2 The pore wall thickness is 0.1 mm; the honeycomb ceramic substrate is immersed in 4.5% dilute nitric acid for 100 min, then rinsed with deionized water until neutral, and dried at 110℃ for 3.5 h.

[0063] (2) Immerse the dried honeycomb ceramic substrate in a silica sol solution with a mass concentration of 8% for 35 minutes.

[0064] (3) The active coating powder is mixed with a polyvinyl alcohol solution with a mass fraction of 4.5% to prepare a slurry with a solid content of 25%. The slurry is applied to the honeycomb ceramic substrate with a coating thickness of 60 μm. After coating, it is dried at 110℃ for 150 min and calcined at 450℃ for 4.5 h to obtain the final product.

[0065] Example 5: Preparation of active coating powder: (a) The alumina precursor is mixed with a solution of zirconium, chromium and lanthanum nitrates in a certain proportion to form a suspension, wherein the alumina precursor is aluminum isopropoxide, the molar ratio of zirconium, chromium and lanthanum is 1.2:2.4:1, and the total mass of zirconium, chromium and lanthanum nitrates is 4.5% of the mass of the alumina precursor.

[0066] (b) The suspension was prepared into composite carrier particles by spray drying. The inlet air temperature was 210°C, the outlet air temperature was 110°C, and the spray pressure was 0.22 MPa.

[0067] (c) The obtained composite carrier particles were subjected to surface modification treatments of hydrophobic coating and carbon barrier layer. The composite carrier particles were immersed in an ethanol solution of 3-aminopropyltriethoxysilane with a concentration of 1.3wt% for 10h, followed by heat treatment at 125℃ for 100min. Then the composite carrier particles were placed in a chemical vapor deposition apparatus, and methane was introduced as the carbon source gas. The reaction temperature was controlled at 730℃ and the deposition time was 7min.

[0068] (d) Then, the composite carrier particles were mixed with chromium acetylacetone solution and microwave-assisted loading was performed to obtain the active coating powder: the composite carrier particles were mixed with chromium acetylacetone solution with a concentration of 0.13 mol / L and placed in a microwave reactor. The microwave power was set to 420 W and the irradiation time was 12 min.

[0069] Preparation of monolithic chromium-based catalysts: (1) A cordierite honeycomb ceramic substrate was selected as the supporting structure. The dimensions of the honeycomb ceramic substrate were 120 mm in diameter and 220 mm in length, with a pore density of 350 holes / in. 2 The pore wall thickness is 0.5 mm; the honeycomb ceramic substrate is immersed in 5.5% dilute nitric acid for 150 min, then rinsed with deionized water until neutral, and dried at 130℃ for 4.5 h.

[0070] (2) Immerse the dried honeycomb ceramic substrate in a silica sol solution with a mass concentration of 12% for 25 minutes.

[0071] (3) The active coating powder is mixed with a polyvinyl alcohol solution with a mass fraction of 5.5% to prepare a slurry with a solid content of 35%. The slurry is applied to the honeycomb ceramic substrate with a coating thickness of 100 μm. After coating, it is dried at 130℃ for 100 min and calcined at 550℃ for 3.5 h to obtain the final product.

[0072] The following experimental data represent the performance testing of the catalysts obtained in the examples and comparative examples. The performance testing methods followed conventional methods in the art, with no special requirements; for example, Cr dispersion was determined using the CO chemisorption method. During the experiments, the monolithic catalysts obtained in the examples and comparative examples were installed in a fixed-bed reactor of a propane dehydrogenation unit. The operating conditions in the fixed-bed reactor were set as follows: reaction temperature 650°C, reaction pressure 0.1 MPa, and propane volume hourly space velocity 1000 h⁻¹. -1 The reaction gas consisted of propane and water vapor, with a molar ratio of water vapor to propane of 1.5:1. The performance test results of the catalysts obtained in each example are shown in Table 1.

[0073] Table 1 Performance test results of the catalysts obtained in the examples .

[0074] The following are comparative examples and performance tests that provide partial comparisons.

[0075] Comparative Example 1: The preparation process and material ratio are the same as in Example 1, except that the molar ratio of zirconium, chromium and lanthanum is 1.5:1.6:1.

[0076] The initial propane conversion rate of Comparative Example 1 was 53.2%, and the propylene selectivity was 84.7%. The coking amount in Example 1 was 12.3 mg / g, while the coking amount in Comparative Example 1 was 29.8 mg / g. This indicates that the excessive Zr proportion in Comparative Example 1 led to uneven distribution of active sites and a significant increase in coking amount.

[0077] Comparative Example 2: The preparation process and material ratio are the same as in Example 1, except that the hydrophobic coating and carbon barrier layer treatment in step (c) are omitted.

[0078] The lifetime of Example 1 was 810 hours, and the lifetime of Comparative Example 2 was 320 hours. The carbon deposition resistance rate of Example 1 was 8.5% / 100h, while that of Comparative Example 2 was 23.6% / 100h. In the humidity sensitivity test, the catalyst activity of Example 1 showed no significant change, while the activity of Comparative Example 2 decreased by 28%. The experimental data of Comparative Example 2 demonstrate that the hydrophobic coating and carbon barrier layer of the present invention can significantly improve the carbon deposition resistance and environmental stability. Specifically, the humidity environment for the humidity exposure pretreatment during the humidity sensitivity test was: relative humidity (RH): 90±5% (controlled by a humidity generator), temperature: 25±2℃ (normal temperature humid environment), and exposure time: 24 hours (static exposure).

[0079] Comparative Example 3: The preparation process and material ratio are the same as in Example 1, except that step (d) is changed to the conventional impregnation method: the composite carrier particles are mixed with acetylacetone chromium solution and then left to stand at room temperature for 24 hours.

[0080] The active component in Comparative Example 3 exhibited localized agglomeration, with an initial propane conversion rate of only 61.2% and a chromium loss rate of 11.7% (compared to 4.3% in Example 1). The experimental data of Comparative Example 3 demonstrate that the microwave-assisted loading of the present invention achieves efficient anchoring of the active component and reduces loss.

[0081] Comparative Example 4: The preparation process and material ratio are the same as in Example 1, except that the pickling time in step (1) is shortened to 80 min and the drying temperature is reduced to 100℃.

[0082] Ultrasonic testing revealed that the coating in Comparative Example 4 exhibited localized peeling with a mass loss rate of 16%, while the coating in Example 1 showed no mass loss and no peeling. The ultrasonic test utilized the cavitation effect of ultrasound waves in a liquid to apply high-frequency mechanical vibrations to the catalyst surface, simulating the impact the coating might experience during long-term operation, and observing the coating peeling behavior. The ultrasonic treatment parameters were: ultrasonic frequency: 40kHz, ultrasonic power: 100~150W / L, treatment time: 30 minutes (divided into 3 cycles, 10 minutes each, with a 5-minute cooling interval), treatment medium: deionized water, and temperature control: 25±5℃. The amount of coating peeling was calculated by the difference in catalyst mass before and after ultrasonic treatment. A Branson 5800 ultrasonic cleaner was used.

[0083] The specific surface area of ​​Example 1 was 45.6 m² / g, and the specific surface area of ​​Comparative Example 4 was 32.1 m² / g.

[0084] The experimental data of Comparative Example 4 demonstrate that the pickling and drying parameters of the present invention play a key role in the substrate-coating bonding strength.

[0085] Comparative Example 5: The preparation process and material ratio are the same as in Example 1, except that the roasting temperature in step (3) is increased to 600°C.

[0086] The grain size of Comparative Example 5 was 4-5 nm, the propylene selectivity of Comparative Example 5 was 76.8%, the specific surface area of ​​Example 1 was 45.6 m² / g, and the specific surface area of ​​Example 1 was 28.3 m² / g.

[0087] The experimental data of Comparative Example 5 demonstrate that the calcination temperature range of the present invention can avoid crystallization of the active phase and maintain a high specific surface area.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An integral chromium-based catalyst for a propane dehydrogenation unit, characterized in that: The device includes a honeycomb ceramic substrate and an active coating. The honeycomb ceramic substrate is made of cordierite. The active coating is loaded with an active component composed of zirconium, chromium, and lanthanum in a molar ratio of 0.8~1.2:1.6~2.4:

1. The active coating is uniformly applied to the surface of the honeycomb ceramic substrate. The active coating contains composite carrier particles, on which the active component is loaded. The composite carrier particles are coated with a hydrophobic coating and a carbon barrier layer.

2. A method for preparing an integral chromium-based catalyst in a propane dehydrogenation unit according to claim 1, characterized in that: Includes the following steps: (1) A honeycomb ceramic matrix made of cordierite was selected as the supporting structure; The honeycomb ceramic substrate was immersed in dilute nitric acid with a mass fraction of 4.5%~5.5% for 100min~150min, then rinsed with deionized water until neutral, and dried at 110℃~130℃ for 3.5h~4.5h. (2) Immerse the dried honeycomb ceramic substrate in a silica sol solution with a mass concentration of 8%~12% for 25min~35min; (3) The active coating powder is mixed with a polyvinyl alcohol solution with a mass fraction of 4.5%~5.5% to prepare a slurry with a solid content of 25%~35%. The slurry is applied to the honeycomb ceramic substrate with a coating thickness of 60μm~100μm. After coating, it is dried and calcined to obtain the final product.

3. The method for preparing an integral chromium-based catalyst in a propane dehydrogenation unit according to claim 2, characterized in that: The honeycomb ceramic substrate has a diameter of 80mm~120mm, a length of 180mm~220mm, and a pore density of 350 holes / in. 2 ~450 holes / in 2 The hole wall thickness is 0.1mm~0.5mm.

4. The method for preparing an integral chromium-based catalyst in a propane dehydrogenation unit according to claim 3, characterized in that: The method for preparing the active coating powder includes the following steps: (a) An alumina precursor is mixed with a solution of zirconium, chromium and lanthanum nitrates in a certain proportion to form a suspension, wherein the alumina precursor is aluminum isopropoxide, the molar ratio of zirconium, chromium and lanthanum is 0.8~1.2:1.6~2.4:1, and the total mass of zirconium, chromium and lanthanum nitrates is 4.5%~5.5% of the mass of the alumina precursor; (b) The suspension was prepared into composite carrier particles by spray drying, with the inlet air temperature being 190℃~210℃ during spray drying; (c) The obtained composite carrier particles were subjected to surface modification treatments of hydrophobic coating and carbon barrier layer in succession; (d) Then, the composite carrier particles were mixed with chromium acetylacetone solution and microwave-assisted loading was performed.

5. The method for preparing an integral chromium-based catalyst in a propane dehydrogenation unit according to claim 4, characterized in that: The hydrophobic coating surface modification treatment described in step (c) includes the following steps: immersing the composite carrier particles in an ethanol solution of 3-aminopropyltriethoxysilane with a concentration of 0.8wt%~1.3wt% for 10h~12h, followed by heat treatment at 115℃~125℃ for 100min~150min.

6. The method for preparing an integral chromium-based catalyst in a propane dehydrogenation unit according to claim 4, characterized in that: The surface modification treatment of the carbon barrier layer in step (c) includes the following steps: placing the composite carrier particles in a chemical vapor deposition apparatus, introducing methane as the carbon source gas, controlling the reaction temperature at 670℃~730℃, the deposition time at 7min~9min, and obtaining a carbon barrier layer with a thickness of 1nm~5nm.

7. The method for preparing an integral chromium-based catalyst in a propane dehydrogenation unit according to claim 4, characterized in that: The specific operation of the microwave-assisted load in step (d) is as follows: the composite carrier particles are mixed with a chromium acetylacetone solution with a concentration of 0.07 mol / L to 0.13 mol / L and then placed in a microwave reactor. The microwave power is set to 380 W to 420 W and the irradiation time is 12 min to 18 min.

8. The method for preparing an integral chromium-based catalyst in a propane dehydrogenation unit according to claim 2, characterized in that: The drying temperature in step (3) is 110℃~130℃ and the time is 100min~150min.

9. The method for preparing an integral chromium-based catalyst in a propane dehydrogenation unit according to claim 2, characterized in that: The roasting temperature in step (3) is 450℃~550℃ and the time is 3.5h~4.5h.