Propane dehydrogenation catalyst as well as preparation method and application thereof

Abstract

The invention relates to a propane dehydrogenation catalyst. The catalyst comprises a molded alumina-silicon carbide composite carrier, a platinum component and a rare earth component, wherein the platinum component and the rare earth component are loaded on the composite carrier; the composite carrier is prepared from the following components in percentage by mass: 60 to 90 weight percent of aluminum oxide and 10 to 40 weight percent of silicon carbide; based on the total mass of the catalyst, in terms of elements, the mass fraction of platinum is 0.05-0.30 wt%, and the mass fraction of the rare earth element oxide is 0.20-3.0 wt%. Meanwhile, the invention also discloses a preparation method and application of the catalyst. The catalyst disclosed by the invention can give consideration to high propane conversion rate, high propylene selectivity and long-period stability under the condition that components such as tin and halogen are not introduced, and is suitable for production of low-carbon olefins mainly containing propylene in industrial devices such as a fixed bed and a moving bed.

Description

Technical Field

[0001] This invention relates to the field of petrochemical catalytic materials technology, and in particular to a propane dehydrogenation catalyst, its preparation method, and its application. Background Technology

[0002] Low-carbon olefins, represented by propylene, are important basic raw materials for modern petrochemicals. They can be used to prepare a variety of bulk and fine chemical products such as polypropylene, propylene oxide, acetone, acrolein, acrylic acid and its esters, acrylonitrile, and cumene. They are characterized by large output, wide application, and a long industrial chain. With the continuous growth in demand for polyolefin materials, high-performance propylene-based monomers, and their downstream products, propylene consumption has been rising year by year. The traditional model of obtaining propylene by means of steam cracking and refinery dry gas is no longer able to meet the needs of new and expanded plants in terms of resource utilization and cost control. There is an urgent need to develop propylene production routes that are dedicated to propylene production, have relatively simple processes, and are more energy efficient.

[0003] Propane dehydrogenation (PDH) is a process that uses propane as a feedstock to directly produce low-carbon olefins, primarily propylene. It offers advantages such as a short process flow, high selectivity, and ease of large-scale plant development. Considering factors such as plant investment, energy consumption, environmental friendliness, and feedstock adaptability, it is considered one of the most competitive new propylene production processes. Thermodynamically, propane dehydrogenation is a reversible reaction involving an increase in molecular number and strong endothermic activity. To drive the reaction towards dehydrogenation, it typically requires operation at higher temperatures and lower pressures. However, at high temperatures, the C-C bonds are more prone to breakage, easily inducing side reactions such as cracking and aromatization, generating a large amount of byproducts and coking. Simultaneously, the uneven exothermic and endothermic reaction can cause large local temperature gradients in the bed, leading to active metal sintering and rapid catalyst deactivation. Therefore, developing propane dehydrogenation catalysts with high activity, high propylene selectivity, good anti-coking properties, and excellent heat transfer characteristics is crucial for achieving stable and efficient operation of the PDH process.

[0004] Currently, industrial catalysts used for propane dehydrogenation mainly include chromium-based catalysts and platinum-based catalysts. Chromium-based catalysts have problems such as high toxicity of hexavalent chromium and high environmental risks, and their application is subject to increasingly strict restrictions. Platinum-based catalysts have become the focus of research and application because they are non-toxic and can be operated under milder conditions. Among the existing published literature, patent CN101898130B reports a propane dehydrogenation catalyst with platinum group metals as the main active component, tin as an auxiliary agent, and supported on an alumina support. The activity and stability of the catalyst are improved by regulating the Pt / Sn interaction. Patent CN106588545A discloses a method for preparing a platinum-tin based propane dehydrogenation catalyst, which improves the reaction performance by introducing auxiliary agents such as carbon into the Pt-Sn system. Patent CN109876808A discloses a propane dehydrogenation catalyst with platinum as the main active component and indium and fourth-period metal elements as auxiliary agents, which aims to improve propane conversion and propylene selectivity. In addition, there are various platinum-based propane dehydrogenation catalyst formulations based on a single alumina support and combined with Sn, Ga, In, Zn, and auxiliary agents such as halogens and alkali metals. However, the above-mentioned technical solutions mostly use pure alumina carriers, which have limited thermal conductivity and are prone to generating large temperature gradients in the bed. At the same time, they generally rely on second metals such as Sn and halogen additives, which still have problems such as rapid carbon deposition, rapid activity decay, equipment corrosion and high environmental pressure under high temperature conditions. There is still a lack of effective solutions for platinum-based propane dehydrogenation catalysts that can achieve both high efficiency in heat transfer and high stability under halogen-free conditions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a propane dehydrogenation catalyst with high conversion rate, high selectivity and long-term stability.

[0006] Another technical problem to be solved by the present invention is to provide a method for preparing the propane dehydrogenation catalyst.

[0007] The third technical problem to be solved by the present invention is to provide the application of the propane dehydrogenation catalyst.

[0008] To address the aforementioned problems, the present invention provides a propane dehydrogenation catalyst, characterized in that: the catalyst comprises a shaped alumina-silicon carbide composite support and platinum and rare earth components supported on the composite support; the composite support is composed of 60-90 wt% alumina and 10-40 wt% silicon carbide; based on the total mass of the catalyst, the platinum content is 0.05-0.30 wt%, and the rare earth oxide content is 0.20-3.0 wt%.

[0009] The rare earth element is one or a combination of yttrium and lanthanum. As an oxide, the sum of the mass fractions of yttrium oxide and lanthanum oxide is 0.30 to 2.0 wt%. The average content of the rare earth element in the outer layer region (0.20 to 0.50 mm from the outer surface inward) is 1.5 to 5.0 times the average content in the inner region of the catalyst particles. The platinum component is dispersed in the outer layer region of the catalyst particles in a metallic or metal oxide state, and the average particle size of platinum is 1 to 5 nm.

[0010] The alumina is γ-Al2O3.

[0011] The specific surface area of ​​the composite carrier is 80–180 m². 2 / g, with a total pore volume of 0.40–0.90 mL / g.

[0012] The composite carrier is an extruded body, and the molding shape is one or more combinations of cylinder, clover, or hollow cylinder, with an extrusion diameter of 1.0 to 2.5 mm.

[0013] The preparation method of the propane dehydrogenation catalyst as described above includes the following steps: S1 Preparation of Composite Support: Pseudo-Bayer stone powder, silicon carbide powder, binder and pore-forming agent are mixed in a mass ratio of 60-90:40-10:3:1, and 1-4 wt% dilute nitric acid aqueous solution is added to knead into a plastic slurry with a water content of 45%-50%; the plastic slurry is extruded into strips, dried, and calcined in air at 700-900℃ for 2-6 h to obtain an alumina-silicon carbide composite carrier; S2 rare earth modification: The composite support is impregnated with an aqueous solution containing rare earth salts at 15–80°C, with the volume of the impregnation solution controlled to be 60–90% of the total pore volume of the composite support. After impregnation for 0.5–10 h, it is dried at 80–140°C for 2–12 h and then calcined in air at 500–800°C for 1–5 h to obtain a rare earth modified composite support, wherein the rare earth loading is 0.20–3.0 wt% based on oxides. S3 platinum loading: At 15–80°C, the rare earth modified composite support is impregnated with a platinum-containing aqueous solution, and the volume of the impregnation solution is controlled to be 60–90% of the total pore volume of the rare earth modified composite support. After impregnation for 0.5–10 h, it is dried at 80–140°C for 2–12 h, and then calcined or reduced at 300–600°C for 1–5 h in an inert gas or a hydrogen-containing inert gas mixture to obtain a platinum-rare earth propane dehydrogenation catalyst with an alumina-silicon carbide composite support.

[0014] In step S1, the binder is one or two of silica sol, clay, and kaolin, and the pore-forming agent is selected from one or more of cellulose, methylcellulose, starch, and organic polymers.

[0015] In step S2, the rare earth salt in the aqueous solution containing rare earth salts is yttrium nitrate, lanthanum nitrate, or a mixture thereof, and the rare earth loading is 0.20 to 3.0 wt% based on oxides.

[0016] In step S3, the platinum-containing aqueous solution is chloroplatinic acid or platinum nitrate aqueous solution, with a platinum element loading of 0.05 to 0.30 wt%; the reducing atmosphere is a hydrogen / inert gas mixture with a volume fraction of 1 to 20%.

[0017] The propane dehydrogenation catalyst described above is applied in the propane dehydrogenation to propylene reaction, characterized in that: the catalyst is tableted, crushed, and sieved before being loaded into a fixed-bed or moving-bed reactor; propane or a propane / hydrogen mixture is introduced at 550–630°C and atmospheric pressure to 0.25 MPa to carry out the propane dehydrogenation reaction; and the propane volume hourly space velocity is 800–4000 h⁻¹. -1 The single-cycle reaction time is 10–30 h to obtain low-carbon olefin products mainly composed of propylene. When the catalyst activity decreases, the feed gas is stopped, and air or an air / water vapor mixture is introduced for regeneration by calcination at 520–580 °C for 0.5–3 h. After regeneration, the atmosphere is switched to a hydrogen-containing atmosphere for reduction activation, the propane feed is restored, and the above reaction and regeneration steps are repeated to achieve continuous propane to propylene production.

[0018] Compared with the prior art, the present invention has the following advantages: 1. This invention utilizes silicon carbide as a high thermal conductivity framework and alumina as a high specific surface area active carrier to significantly reduce the axial and radial temperature difference of the bed, suppress local overheating and platinum sintering, which is beneficial to the stable operation of industrial equipment under high load.

[0019] 2. This invention improves the dispersion and thermal stability of platinum species by gradient enrichment of rare earth elements on the outer layer of particles, weakens strong acid centers, reduces deep cracking and aromatization side reactions, and balances propane conversion rate and propylene selectivity.

[0020] 3. The catalyst formulation of this invention does not contain tin, halogens, or other volatile corrosive components, thus avoiding equipment corrosion and halogen emissions at high temperatures and reducing environmental and safety risks.

[0021] 4. The preparation process of this invention adopts a mature extrusion-calcination-impregnation route, which is simple and easy to scale up, making it suitable for the process modification and industrial application of existing platinum-based propane dehydrogenation catalyst production lines.

[0022] 5. When the catalyst of this invention is used for propane dehydrogenation to propylene, the high thermal conductivity of the silicon carbide framework and the stabilizing effect of rare earth elements on platinum can significantly reduce the bed temperature difference and coking rate. Furthermore, it can achieve high propane conversion, high propylene selectivity, and long-term stability without introducing components such as tin and halogens. It is also suitable for the production of low-carbon olefins, mainly propylene, in industrial plants such as fixed-bed and moving-bed plants. Detailed Implementation

[0023] Unless otherwise stated, all percentages in this invention are mass percentages, with mass units in g, temperature units in ℃, pressure units in MPa, and volume units in mL.

[0024] A propane dehydrogenation catalyst comprises a shaped alumina-silicon carbide composite support and platinum and rare earth components supported on the composite support. The composite support consists of 60–90 wt% alumina and 10–40 wt% silicon carbide, preferably with a silicon carbide mass fraction of 15–35 wt% and an alumina mass fraction of 65–85 wt%. Based on the total mass of the catalyst, the platinum mass fraction is 0.05–0.30 wt%, and the rare earth element oxide mass fraction is 0.20–3.0 wt%. The catalyst does not contain metallic elements such as Sn, Ga, In, Zn, Cu, Ni, and Co, nor halogen elements such as Cl, Br, and I.

[0025] Wherein: the rare earth element is one or a combination of two of yttrium and lanthanum, and the sum of the mass fractions of yttrium oxide and lanthanum oxide is 0.30 to 2.0 wt% based on oxides. The average content of the rare earth element in the outer layer region of 0.20 to 0.50 mm from the outer surface inward is 1.5 to 5.0 times, preferably 2.0 to 4.0 times, the average content in the inner region of the catalyst particles. The platinum component is dispersed in the outer layer region of the catalyst particles in a metallic state or in a metal oxide state. The average particle size of platinum is 1 to 5 nm, preferably 1.5 to 3.0 nm.

[0026] Aluminum oxide is γ-Al2O3.

[0027] The specific surface area of ​​the composite carrier is 80–180 m². 2 / g, with a total pore volume of 0.40–0.90 mL / g.

[0028] The composite carrier is an extruded material, with one or more combinations of cylindrical, clover-shaped, or hollow cylindrical shapes. The extrusion diameter is 1.0–2.5 mm. It has high mechanical strength and wear resistance, and is suitable for long-term operation of industrial fixed-bed and moving-bed reactors.

[0029] A method for preparing a propane dehydrogenation catalyst includes the following steps: S1 Preparation of Composite Support: Pseudo-Bayer stone powder, silicon carbide powder, binder, and pore-forming agent are mixed at a mass ratio of 60–90:40–10:3:1. The binder is one or two of silica sol, clay, and kaolin, and the pore-forming agent is one or more of cellulose, methylcellulose, starch, and organic polymers. A 1–4 wt% dilute nitric acid aqueous solution is added and kneaded to form a plastic slurry with a water content of 45%–50%. The plastic slurry is extruded into strips, dried, and calcined in air at 700–900℃ for 2–6 h to obtain an alumina-silicon carbide composite carrier.

[0030] S2 rare earth modification: At 15–80 °C, the composite support is impregnated with an aqueous solution containing rare earth salts, with the impregnation solution volume controlled to be 60–90% of the total pore volume of the composite support. The rare earth salts in the aqueous solution are yttrium nitrate, lanthanum nitrate, or mixtures thereof, with a rare earth loading of 0.20–3.0 wt% based on oxides. After impregnation for 0.5–10 h, the mixture is dried at 80–140 °C for 2–12 h and calcined in air at 500–800 °C for 1–5 h to obtain a rare earth modified composite support, wherein the rare earth loading is 0.20–3.0 wt% based on oxides. By controlling the volume of the rare earth impregnation solution and the impregnation method, rare earth elements are enriched in the catalyst shell region, forming a content gradient that decreases from the outside to the inside, thereby stabilizing platinum species during subsequent platinum loading and use.

[0031] S3 platinum loading: At 15–80 °C, a rare earth-modified composite support is impregnated with a platinum-containing aqueous solution, with the impregnation solution volume controlled to be 60–90% of the total pore volume of the rare earth-modified composite support. The platinum-containing aqueous solution is chloroplatinic acid or platinum nitrate aqueous solution, with a platinum loading of 0.05–0.30 wt%. After impregnation for 0.5–10 h, it is dried at 80–140 °C for 2–12 h, and then calcined or reduced at 300–600 °C for 1–5 h in an inert gas or a hydrogen-containing inert gas mixture to obtain a platinum-rare earth propane dehydrogenation catalyst with an alumina-silicon carbide composite support. The reducing atmosphere is a hydrogen / inert gas mixture with a volume fraction of 1–20%.

[0032] A propane dehydrogenation catalyst is applied in the propane dehydrogenation to propylene reaction. The specific process is as follows: The catalyst is tableted, crushed, and sieved before being packed into a fixed-bed or moving-bed reactor. Propane or a propane / hydrogen mixture is introduced at 550–630 °C and atmospheric pressure to 0.25 MPa to carry out propane dehydrogenation reaction, with a propane volume hourly space velocity of 800–4000 h⁻¹. -1The single-cycle reaction time is 10–30 h to obtain low-carbon olefin products, mainly propylene. When the catalyst activity decreases, the feed gas is stopped, and air or an air / water vapor mixture is introduced for regeneration at 520–580 °C for 0.5–3 h (the regeneration time can be adjusted according to the degree of catalyst coking, bed temperature difference, and composition of the regeneration tail gas). After regeneration, the atmosphere is switched to hydrogen-containing atmosphere for reduction activation, propane feed is restored, and the above reaction and regeneration steps are repeated to achieve continuous propane to propylene production.

[0033] Example 1 Preparation of composite carrier A Take 700 g of pseudo-Bayer stone powder, 300 g of α-silicon carbide powder (average particle size 3-10 μm, volume fraction approximately 30%), 30 g of kaolin as an inorganic binder, and 10 g of methylcellulose as a pore-forming agent. Add 2 wt% dilute nitric acid aqueous solution, controlling the amount added to ensure the water content of the mixture is 45%-50%. Knead in a kneader for 40 min to obtain a uniform and plastic extrudate. Extrude the extrudate into clover-shaped extrusion strips using a screw extruder, with an extrusion diameter of 1.6 mm and a strip length of 3-5 mm. Allow to age at room temperature for 4 h.

[0034] The obtained wet extruded strip was placed in a forced-air drying oven and dried at 120℃ for 6 h. Then, under air atmosphere, the temperature was increased to 800℃ at a rate of 3℃ / min and held for 4 h. It was then naturally cooled to room temperature to obtain alumina-silicon carbide composite carrier A. The BET specific surface area is approximately 120 m². 2 The total pore volume is approximately 0.63 mL / g, and the average pore size is approximately 18 nm. The wear rate, measured by roller abrasion tests, is less than 0.5%, and the single-particle compressive strength is greater than 60 N, meeting the mechanical strength and wear resistance requirements of industrial fixed-bed and moving-bed devices. Due to the introduction of silicon carbide, the thermal conductivity of carrier A is significantly higher than that of pure alumina carrier prepared under the same conditions (as described in Comparative Example 1), providing a basis for subsequently reducing the bed temperature difference.

[0035] Example 2 Preparation of composite carriers B and C in different proportions Composite Carrier B: Following the method in Example 1, the mass ratio of pseudo-Bayer stone powder to α-silicon carbide powder was adjusted to 80:20. The remaining components and steps were the same. The calcination temperature was 780℃, and the temperature was maintained for 3 hours to obtain Composite Carrier B, with a specific surface area of ​​approximately 135 m². 2 / g, with a total pore volume of approximately 0.68 mL / g.

[0036] Composite carrier C: Following the method in Example 1, the mass ratio of pseudo-Bayer stone powder to α-silicon carbide powder was adjusted to 60:40, and the remaining steps were the same. The calcination temperature was 820℃, and the temperature was maintained for 4 h to obtain composite carrier C, with a specific surface area of ​​approximately 105 m². 2 / g, with a total pore volume of approximately 0.58 mL / g.

[0037] Measured using radially arranged thermocouples under simulated reaction conditions: When carriers A, B, and C were respectively filled into a fixed-bed tubular reactor with a diameter of 30 mm, and simulated heating was performed under the same flow rate of thermal inert gas (nitrogen), the maximum axial temperature differences of the bed after stable operation were approximately 12℃, 10℃, and 9℃, respectively, significantly lower than the temperature difference of over 20℃ when using pure alumina carriers (see Comparative Example 1). This indicates that the alumina-silicon carbide composite structure significantly improves the thermal conductivity of the bed, which is beneficial for suppressing local overheating.

[0038] Example 3 Preparation of rare earth modified carrier AY Take 1000 g of the composite carrier A obtained in Example 1 and place it in a rotary drum impregnation machine. Prepare an aqueous solution containing yttrium nitrate: the concentration is 0.15 g / mL based on Y2O3, and the total volume is 500 mL, which is about 80% of the pore volume of the carrier (about 630 mL). Slowly spray the impregnation solution while rotating the drum at room temperature for 1 hour, and continue to roll and age for 3 hours to allow the solution to uniformly enter the outer pores of the particles.

[0039] The impregnated support was dried at 120℃ for 6 h and then calcined in air at 650℃ for 3 h to obtain the rare earth modified support AY. The Y₂O₃ loading was approximately 0.8 wt% based on oxides. Analysis showed that the average Y content within a 0.3 mm range from the outer surface inward was approximately 2.5 times that of the inner core region, forming a gradient distribution that gradually decreases from the outside inward, providing conditions for subsequent stabilization of platinum species and regulation of acidic centers.

[0040] Example 4: Preparation of rare earth composite modified support B-LaY 1000 g of the composite carrier B obtained in Example 2 was used to prepare a mixed aqueous solution containing lanthanum nitrate and yttrium nitrate. The total concentration, based on oxides, was 0.20 g / mL, with a La₂O₃:Y₂O₃ mass ratio of 2:1. The total volume was 550 mL, approximately 80% of the carrier's pore volume. The impregnation, aging, drying, and calcination conditions were the same as in Example 3. In the obtained carrier B-LaY, the total rare earth loading was approximately 1.2 wt%. Both La and Y were enriched in the 0.25–0.35 mm region outside the particles, with an average content ratio of the outer layer to the inner layer of approximately 3.0.

[0041] Example 5 Preparation of Catalyst Cat-1 (Pt-Y / Al2O3-SiC) 1000 g of the support AY obtained in Example 3 was placed in a rotary drum impregnation machine. A hexachloroplatinic acid aqueous solution was prepared with a concentration of 0.04 g / mL (based on Pt) and a total volume of 500 mL, approximately 80% of the support's pore volume. The sample was sprayed and impregnated at room temperature for 1 h, followed by rolling aging for 4 h. The impregnated sample was dried at 110 °C for 8 h, then calcined at 500 °C for 2 h in a nitrogen atmosphere, and subsequently reduced at 550 °C for 3 h in a 5% H2 / 95% N2 mixture to obtain catalyst Cat-1. Based on the total mass of the catalyst, the Pt content was approximately 0.20 wt%, and the Y2O3 content was approximately 0.80 wt%.

[0042] Example 6 Preparation of Catalyst Cat-2 (Pt-LaY / Al2O3-SiC) 1000 g of the support B-LaY obtained in Example 4 was impregnated with an aqueous solution of hexachloroplatinic acid, with the impregnation liquid volume being approximately 85% of the pore volume of the support. The impregnation, aging, drying, and calcination reduction conditions were the same as in Example 5, except that the target Pt content was adjusted to 0.15 wt%. Catalyst Cat-2 was obtained, with a Pt content of approximately 0.15 wt%, a La2O3 content of approximately 0.80 wt%, and a Y2O3 content of approximately 0.40 wt% based on the total mass of the catalyst.

[0043] Example 7 Catalyst Cat-3 (low Pt content) Referring to Example 5, only the concentration of the hexachloroplatinic acid solution was adjusted to 0.02 g / mL, while all other conditions remained unchanged, to obtain catalyst Cat-3 with a Pt content of approximately 0.10 wt% and a Y₂O₃ content of approximately 0.80 wt%. This example illustrates that reasonable propylene selectivity and stability can still be obtained with relatively low noble metal loadings.

[0044] Comparative Example 1: Pure alumina supported Pt-Y catalyst Comp-1 Using pseudo-Bayer stone powder as raw material, without adding silicon carbide, pure alumina carrier Al-A was obtained by extrusion, drying, and calcination at 800℃ for 4 hours according to the method in Example 1, with a specific surface area of ​​approximately 130 m². 2 / g, with a total pore volume of approximately 0.70 mL / g. Subsequently, the comparative catalyst Comp-1 was prepared under the same rare earth impregnation and platinum impregnation conditions as in Examples 3 and 5. Its Pt and Y2O3 contents were basically the same as those of Cat-1, but the support did not contain silicon carbide.

[0045] Comparative Example 2: Pt catalyst Comp-2 supported by an unmodified rare earth element The composite support A obtained in Example 1 was directly impregnated, dried, and calcined and reduced according to the platinum impregnation steps in Example 5 to obtain catalyst Comp-2. This catalyst contains approximately 0.20 wt% Pt and does not contain rare earth components, and was used to evaluate the effect of rare earth gradient modification on catalytic performance.

[0046] Comparative Example 3: Conventional Pt-Sn / Al2O3 catalyst Comp-3 Using a commercially available low-surface-area active alumina extrusion support as the carrier, a Pt-Sn / Al2O3 catalyst Comp-3 was obtained by sequentially impregnating hexachloroplatinic acid and tin chloride solutions via a conventional stepwise impregnation method, followed by drying, calcination, and reduction. The catalyst contained approximately 0.40 wt% Pt and 0.80 wt% Sn. This catalyst formulation and preparation route represent existing industrial Pt-Sn / Al2O3 propane dehydrogenation catalysts and are used to compare the performance and environmental advantages of the tin-free and halogen-free formulations of this invention.

[0047] Evaluation method for propane dehydrogenation: The catalysts were tableted, crushed, and sieved to obtain particles of 0.25–0.40 mm, which were then packed into a stainless steel tubular fixed-bed reactor with an inner diameter of 8 mm, at a loading rate of 0.5 g. The propane volume hourly space velocity (GHSV) was 1200 h⁻¹. -1 The hydrogen / propane volume ratio is 1:1, with the balance being nitrogen, and the reaction pressure is 0.10 MPa.

[0048] Before the reaction, the mixture of 5% H2 / 95% N2 was reduced at 550℃ for 2 h. Then, the reaction gas was switched to a mixture of propane, hydrogen and nitrogen, with a hydrogen / propane volume ratio of 1:1 and the remainder being nitrogen. The reaction temperature was adjusted to 590℃ for propane dehydrogenation reaction, and the reaction was run continuously for 20 h.

[0049] Catalyst composition and evaluation results: Table 1 lists the main components of catalysts Cat-1 to Cat-3 prepared in Examples 5 to 7 and catalysts Comp-1 to Comp-3 prepared in Comparative Examples 1 to 3; Table 2 shows the propane conversion and propylene selectivity of the above catalysts after 10 h and 20 h of reaction operation; Table 3 lists the axial temperature difference and coking of the corresponding catalysts in the industrial simulation bed.

[0050] Table 1 Main components of the catalyst Table 2. Evaluation results of propane dehydrogenation (590℃, 0.10 MPa, GHSV=1200 h) -1 ) Table 3. Bed temperature difference and carbon buildup (after 20 h) As shown in Table 2, under similar initial conversion conditions, the propane conversion of the catalyst Cat-1 prepared in Example 5 decreased by only 3 percentage points after 20 h of operation, while the conversion of Comp-1 in Comparative Example 1 decreased by about 10 percentage points. This indicates that under the same Pt ​​and rare earth loading, the introduction of the alumina-silicon carbide composite support significantly slowed down the catalyst deactivation, which is consistent with the smaller bed temperature difference in Table 3, reflecting the role of the high thermal conductivity framework in suppressing local overheating.

[0051] Compared with Comp-2, Cat-1 and Cat-2 showed an increase of about 2 to 4 percentage points in propylene selectivity at 10 h and 20 h, while the amount of coke deposited was significantly reduced. This indicates that the gradient enrichment of rare earth elements in the shell region effectively modulates the surface acidity and metal-support interaction, reduces deep cracking and aromatization side reactions, and balances propane conversion and propylene selectivity.

[0052] Compared with the traditional Pt-Sn / Al2O3 catalyst Comp-3, Cat-1 and Cat-2 do not contain Sn or halogen components at similar conversion and selectivity levels, avoiding halogen volatilization and potential equipment corrosion problems under high temperature conditions. Furthermore, the amount of precious metals used is significantly reduced (0.15-0.20 wt% vs. 0.40 wt%), which helps to reduce the overall cost of the catalyst and environmental risks.

[0053] From the perspective of the preparation process, the composite support preparation, rare earth modification and platinum loading steps involved in Examples 1 to 7 of this invention all adopt the industrially mature pseudo-Bayerstone-silicon carbide extrusion molding, conventional air calcination and conventional pore volume impregnation-drying-calcination / reduction route. There is no need to use organic template agents, high pressure equipment or complex organic ligand coordination steps. The process is simple, the equipment is universal, and it is easy to scale up or modify on existing platinum-based propane dehydrogenation catalyst production lines.

[0054] In summary, a comparison of Examples 5-7 with Comparative Examples 1-3 shows that the platinum-rare earth propane dehydrogenation catalyst with an alumina-silicon carbide composite support of the present invention exhibits superior comprehensive advantages in terms of thermal conductivity, anti-sintering and anti-coking properties, tin-free and halogen-free formulation, and process scalability. It maintained good stability in a 20-hour single-cycle evaluation, making it suitable for further scale-up research in various types of propane dehydrogenation industrial units, such as fixed-bed and moving-bed systems. It also demonstrates application potential as a replacement for traditional platinum-tin-aluminum catalysts in tin-free and halogen-free systems. Those skilled in the art can optimize and adjust the rare earth type, loading, composite support ratio, and molding shape within the scope of the spirit of this invention to obtain catalyst systems with similar performance.

Claims

1. A propane dehydrogenation catalyst, characterized in that: The catalyst comprises a shaped alumina-silicon carbide composite support and platinum and rare earth components supported on the composite support; the composite support consists of 60-90 wt% alumina and 10-40 wt% silicon carbide; based on the total mass of the catalyst, the platinum has a mass fraction of 0.05-0.30 wt% and the rare earth oxides have a mass fraction of 0.20-3.0 wt%.

2. The propane dehydrogenation catalyst according to claim 1, characterized in that: The rare earth element is one or a combination of yttrium and lanthanum. As an oxide, the sum of the mass fractions of yttrium oxide and lanthanum oxide is 0.30 to 2.0 wt%. The average content of the rare earth element in the outer layer region (0.20 to 0.50 mm from the outer surface inward) is 1.5 to 5.0 times the average content in the inner region of the catalyst particles. The platinum component is dispersed in the outer layer region of the catalyst particles in a metallic or metal oxide state, and the average particle size of platinum is 1 to 5 nm.

3. The propane dehydrogenation catalyst according to claim 1, characterized in that: The alumina is γ-Al2O3.

4. The propane dehydrogenation catalyst according to claim 1, characterized in that: The specific surface area of ​​the composite carrier is 80–180 m². 2 / g, with a total pore volume of 0.40–0.90 mL / g.

5. The propane dehydrogenation catalyst according to claim 4, characterized in that: The composite carrier is an extruded body, and the molding shape is one or more combinations of cylinder, clover, or hollow cylinder, with an extrusion diameter of 1.0 to 2.5 mm.

6. A method for preparing a propane dehydrogenation catalyst according to any one of claims 1 to 5, comprising the following steps: S1 Preparation of Composite Support: Pseudo-Bayer stone powder, silicon carbide powder, binder and pore-forming agent are mixed in a mass ratio of 60-90:40-10:3:1, and 1-4 wt% dilute nitric acid aqueous solution is added to knead into a plastic slurry with a water content of 45%-50%; the plastic slurry is extruded into strips, dried, and calcined in air at 700-900℃ for 2-6 h to obtain an alumina-silicon carbide composite carrier; S2 rare earth modification: The composite support is impregnated with an aqueous solution containing rare earth salts at 15–80°C, with the volume of the impregnation solution controlled to be 60–90% of the total pore volume of the composite support. After impregnation for 0.5–10 h, it is dried at 80–140°C for 2–12 h and then calcined in air at 500–800°C for 1–5 h to obtain a rare earth modified composite support, wherein the rare earth loading is 0.20–3.0 wt% based on oxides. S3 platinum loading: At 15–80°C, the rare earth modified composite support is impregnated with a platinum-containing aqueous solution, and the volume of the impregnation solution is controlled to be 60–90% of the total pore volume of the rare earth modified composite support. After impregnation for 0.5–10 h, it is dried at 80–140°C for 2–12 h, and then calcined or reduced at 300–600°C for 1–5 h in an inert gas or a hydrogen-containing inert gas mixture to obtain a platinum-rare earth propane dehydrogenation catalyst with an alumina-silicon carbide composite support.

7. The method for preparing a propane dehydrogenation catalyst as described in claim 6, characterized in that: In step S1, the binder is one or two of silica sol, clay, and kaolin, and the pore-forming agent is selected from one or more of cellulose, methylcellulose, starch, and organic polymers.

8. The method for preparing a propane dehydrogenation catalyst as described in claim 6, characterized in that: In step S2, the rare earth salt in the aqueous solution containing rare earth salts is yttrium nitrate, lanthanum nitrate, or a mixture thereof, and the rare earth loading is 0.20 to 3.0 wt% based on oxides.

9. The method for preparing a propane dehydrogenation catalyst as described in claim 6, characterized in that: In step S3, the platinum-containing aqueous solution is chloroplatinic acid or platinum nitrate aqueous solution, with a platinum element loading of 0.05 to 0.30 wt%; the reducing atmosphere is a hydrogen / inert gas mixture with a volume fraction of 1 to 20%.

10. The propane dehydrogenation catalyst according to any one of claims 1 to 5 is applied in the propane dehydrogenation to propylene reaction, characterized in that: The catalyst is tableted, crushed, and sieved before being packed into a fixed-bed or moving-bed reactor. Propane or a propane / hydrogen mixture is introduced at 550–630 °C and atmospheric pressure to 0.25 MPa to carry out propane dehydrogenation reaction, with a propane volume hourly space velocity of 800–4000 h⁻¹. -1 The single-cycle reaction time is 10–30 h to obtain low-carbon olefin products mainly composed of propylene. When the catalyst activity decreases, the feed gas is stopped, and air or an air / water vapor mixture is introduced for regeneration by calcination at 520–580 °C for 0.5–3 h. After regeneration, the atmosphere is switched to a hydrogen-containing atmosphere for reduction activation, the propane feed is restored, and the above reaction and regeneration steps are repeated to achieve continuous propane to propylene production.

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