A catalyst for propane dehydrogenation to propylene, its preparation and application

Abstract

This invention discloses a catalyst for propane dehydrogenation to propylene, its preparation, and its application. The catalyst comprises active metal Pt, auxiliary metal Sn, and an alumina support. Based on the mass of the catalyst, the total Pt content is 0.26%–1.40%, the Sn content is 0.02%–0.90%, and the alumina content is 97.70%–99.72% by mass fraction. The Pt content on the catalyst surface is 0.40%–0.85%. When applied to the propane dehydrogenation reaction, this catalyst can significantly improve propane conversion and propylene selectivity.

Description

Technical Field

[0001] This invention relates to a catalyst for propane dehydrogenation to propylene, its preparation and application, and particularly to a catalyst suitable for fluidized bed propane dehydrogenation to propylene, its preparation and application. Background Technology

[0002] The shape and size of catalyst particles are generally determined according to the requirements of the reactor used in industrial production. Currently, there are four types of reactors commonly used in industry: fixed bed, fluidized bed (boiling bed), suspended bed, and moving bed. Fixed bed reactors commonly use spherical, cylindrical, cloverleaf, four-leaf, and sheet-like catalysts. Moving bed reactors often use large spherical catalyst particles. Fluidized bed reactors generally use smaller spherical or strip-shaped catalyst particles.

[0003] Spherical catalysts have advantages such as good flow properties, high filling coefficient, uniform fluid distribution, low resistance, and small pressure drop, and are widely used in the technology of dehydrogenation of low-carbon alkanes to produce olefins.

[0004] Currently, catalysts for the dehydrogenation of low-carbon alkanes to olefins are mainly prepared by supporting the active component Pt on a γ-Al₂O₃ support and other auxiliary agents, such as EP100222A and CN1185994A. However, since the dehydrogenation reaction is carried out at a high temperature of around 600℃, the high reaction temperature often leads to a large amount of coking on the catalyst. As the catalyst is used for a longer period of time, it is necessary to perform multiple high-temperature carbonization regeneration treatments. This causes the γ-Al₂O₃ support to easily undergo sintering and α-phase transformation, resulting in a significant decrease in the specific surface area of ​​the support, destruction of the pore structure, and consequently, aggregation of the active component, leading to a severe decrease in catalyst activity. Therefore, it is necessary to further modify the γ-Al₂O₃ support to give the catalyst higher thermal stability.

[0005] CN112973771A discloses a spherical catalyst support containing molecular sieves and alumina, its preparation, and its application. This catalyst support is prepared by precipitating inorganic aluminum salts with ammonia and acidifying them to obtain a sol. A mixed solution of ball-milled boehmite and molecular sieves, along with a sol-modifying agent, is added to the sol. The mixture is then drop-formed and aged in an oil-ammonia column, and finally washed, dried, and calcined to obtain high-strength, high-specific-surface-area composite microspheres. This method involves mixing a suspension slurry obtained by ball-milling boehmite and molecular sieves with a dilute sol and then re-gelling it, which results in uneven dispersion of the molecular sieves. Furthermore, the doping of solid molecular sieves also leads to a decrease in the support strength.

[0006] CN105478100A discloses a method for preparing silicon-containing γ-Al₂O₃ microspheres. The method involves stirring and slurrying pseudoboehmite dry adhesive powder and deionized water, acidifying with dilute nitric acid, adding urea and a predetermined amount of sodium silicate solution, stirring for 5 hours, adding kerosene and fatty alcohol polyoxyethylene ether, stirring for another 5 hours, forming microspheres by drop in an oil-ammonia column, curing the wet microspheres in ammonia water for 2 hours, filtering, washing with deionized water, drying, and calcining to obtain silicon-containing γ-Al₂O₃ microspheres. This method results in long curing times, difficult washing, and low production efficiency for the γ-Al₂O₃ microspheres.

[0007] CN104289220A discloses a method for preparing and using a high thermal stability low-carbon alkane dehydrogenation catalyst. The method for preparing the carrier involves adding an aluminum source to an alkaline aqueous solution, stirring, and continuing to add alkaline aqueous solution dropwise to adjust the pH of the mixed solution to 7–14. After filtration and washing with deionized water, dilute nitric acid is added to form a sol. A silicon source is then added, stirred, filtered, and aged for 10–48 hours. The mixture is then drop-formed, dried, and calcined to obtain γ-Al₂O₃ microspheres containing Si. Alternatively, the method involves adding an aluminum source to an alkaline aqueous solution, stirring, and continuing to add alkaline aqueous solution dropwise to adjust the pH of the mixed solution to 7–14. After filtration and washing with deionized water, dilute nitric acid is added to form a sol. This process is stirred, filtered, and aged for 10–48 hours. The mixture is then drop-formed, dried, and calcined to obtain γ-Al₂O₃ microspheres. These microspheres are then immersed in an aqueous or ethanolic solution of the silicon source at 60–120°C for 2–6 hours, followed by drying and calcination to obtain γ-Al₂O₃ microspheres containing Si. The disadvantages of this method are its long preparation cycle, complex process, requirement for pH control, and inability to guarantee product consistency. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a catalyst for propane dehydrogenation to propylene, its preparation, and its application. This catalyst features good sphericity, high crushing strength, large pore volume and size, high Pt loading, and an environmentally friendly, odorless product. When applied to the propane dehydrogenation reaction, it can significantly improve propane conversion and propylene selectivity.

[0009] The first aspect of this invention provides a catalyst for the dehydrogenation of propane to propylene, the catalyst comprising an active metal Pt, a promoter metal Sn, and an alumina support; wherein, based on the mass of the catalyst, the total Pt content is 0.26%–1.40%, the Sn content is 0.02%–0.90%, and the alumina content is 97.70%–99.72% by mass fraction; and the Pt content on the catalyst surface is 0.40%–0.85%.

[0010] Furthermore, the specific surface area of ​​the catalyst is 85–110 m². 2 / g, with a pore volume of 0.62~0.83mL / g.

[0011] Furthermore, the catalyst is in the form of spherical particles with an average diameter of 1.7–1.9 mm.

[0012] Furthermore, the catalyst has the following pore size distribution: pores with a pore size of less than 2 nm account for 1.3% to 3.5% of the total pore volume, and pores with a pore size of 2-50 nm account for 96.5% to 98.7% of the total pore volume, preferably 97.0% to 98.0%.

[0013] Furthermore, the catalyst has an average pore size of 14.5–18.5 nm.

[0014] Furthermore, the crushing strength of the catalyst is 65-85 N / particle.

[0015] Furthermore, the sphericity of the catalyst is 97.6% to 99.9%.

[0016] A second aspect of the present invention provides a method for preparing a catalyst for propane dehydrogenation to propylene, comprising:

[0017] (1) Aluminum hydroxide sol was mixed with organic Pt salt solution, and the resulting mixture was dropped into a four-layer oil-ammonia-oil-water mixed column to form a catalyst precursor. The mixture was dried and calcined.

[0018] (2) The catalyst precursor obtained in step (1) is impregnated with loaded Pt, dried and calcined to obtain the catalyst;

[0019] The mixing column has four layers arranged from top to bottom: the first layer is the first oil layer, the second layer is the ammonia water layer, the third layer is the second oil layer, and the fourth layer is the water layer. The second oil layer is selected from modified transformer oil.

[0020] Furthermore, the aluminum hydroxide sol contains 15 wt% to 26 wt% aluminum oxide.

[0021] Further, the preparation method of the aluminum hydroxide sol includes: mixing aluminum hydroxide with water to obtain a slurry, adding a gelling agent, and stirring evenly to obtain aluminum hydroxide sol. Further, the gelling agent is selected from one or more inorganic acids (such as nitric acid) and organic acids (such as acetic acid and citric acid), preferably nitric acid. When the gelling agent contains an inorganic acid, the mass concentration of the inorganic acid is 30% to 50%. When the gelling agent contains an organic acid, the mass concentration of the organic acid is 30% to 50%. Further, the amount of gelling agent added is 1 wt% to 10 wt% of the aluminum hydroxide by mass of alumina, preferably 2 wt% to 8 wt%. Further, the aluminum hydroxide is preferably aqueous aluminum hydroxide, such as wet aluminum hydroxide material. Preferably, the water content in the aluminum hydroxide is 17 wt% to 25 wt%. Preferably, the properties of the aluminum hydroxide after calcination are as follows: specific surface area of ​​110 to 201 m². 2 The aluminum hydroxide has a pore volume of 0.8–2.0 mL / g and an average pore size of 15–17 nm. The calcination conditions are as follows: temperature 600–850℃, time 2–12 h, and an oxygen-containing atmosphere such as air. The aluminum hydroxide can be commercially available or prepared using conventional methods. Preferably, the aluminum hydroxide is a hydrated macroporous pseudoboehmite with a water content of 19 wt%–23 wt%.

[0022] Further, the organic Pt salt in the organic Pt salt solution is one or more of platinum acetylacetonate or tetra(triphenylphosphine)platinum, preferably platinum acetylacetonate, and the solvent used is preferably acetone. Further, the concentration of the organic Pt salt in the organic Pt salt solution is 1.0 wt% to 1.9 wt%. The amount of the organic Pt salt solution added is 9% to 11% of the aluminum hydroxide sol by mass of aluminum oxide.

[0023] Furthermore, the organic Pt salt solution contains stannous chloride, and the concentration of stannous chloride in the organic Pt salt solution is 0.4 wt% to 11 wt%.

[0024] Furthermore, the four-layer oil-ammonia-oil-water mixture column is a straight column, preferably a cylindrical column.

[0025] Furthermore, in the four-layer oil-ammonia-oil-water mixture column, the first layer is a first oil layer, selected from one or more of white oil or diesel oil, preferably white oil, wherein the kinematic viscosity of the white oil at 40°C is 20-40 mmHg. 2 / s, preferably 25-35mm 2 / s. The height of the first layer is 30% to 50% of the height of the second layer.

[0026] Furthermore, in the four-layer oil-ammonia-oil-water mixture column, the second layer is an ammonia layer, and the concentration of the ammonia is 20wt% to 28wt%, preferably 22wt% to 26wt%.

[0027] Furthermore, in the four-layer oil-ammonia-oil-water mixture column, the third layer is the second oil layer, i.e., the liquid seal oil layer. The modified transformer oil used in the second oil layer has a density between that of ammonia and water. Preferably, the density of the modified transformer oil at 20°C is above 0.90 g / mL, more preferably 0.93–0.96 g / mL, and even more preferably 0.94–0.96 g / mL. The height of the third layer is 30%–50% of the height of the second layer, preferably 35%–45%.

[0028] Furthermore, the modified transformer oil comprises transformer oil and a water-soluble surfactant.

[0029] Furthermore, the water-soluble surfactant comprises 6% to 25% of the transformer oil mass, preferably 10% to 18%.

[0030] Furthermore, the water-soluble surfactant is one or more of lauroyl diethanolamine, nonylphenol polyoxyethylene ether (preferably with a degree of polymerization of 9, i.e., n=9) or octylphenol polyoxyethylene ether (preferably with a degree of polymerization of 7, i.e., n=7).

[0031] Furthermore, the transformer oil has a density (20°C) of 0.86–0.89 g / mL and a kinematic viscosity (40°C) of 9–15 mm. 2 / s.

[0032] Furthermore, the preparation process of the modified transformer oil is as follows:

[0033] A water-soluble surfactant is mixed with transformer oil, and the resulting mixture is subjected to heat treatment, namely, sealed heat treatment and open heat treatment, and the above heat treatment is repeated 3 to 6 times to obtain the modified transformer oil.

[0034] Furthermore, the conditions for the sealed heat treatment are as follows: heating temperature of 80–120°C and heating time of 6–20 hours. Furthermore, the conditions for the open heat treatment are as follows: heating temperature of 80–120°C and heating time of 6–20 hours.

[0035] Furthermore, in the four-layer oil-ammonia-oil-water mixture column, the fourth layer is an aqueous layer, preferably deionized water or a dilute acid solution. The height of the fourth layer is 1.0 to 2.0 times the height of the second layer, preferably 1.2 to 1.5 times.

[0036] Furthermore, the fourth layer is preferably a dilute acid solution. The acid in the dilute acid solution is selected from at least one of acetic acid and citric acid. The mass concentration of the dilute acid solution is 3% to 8%.

[0037] Furthermore, the preparation method of the oil-ammonia-oil-water four-layer mixed column includes:

[0038] (1) Pour the material required for the fourth layer into a columnar container (preferably an acrylic container) and ensure that the solution is uniform;

[0039] (2) Slowly add the material required for the third layer onto the material of the fourth layer in step (1) and stabilize for 20-35 minutes;

[0040] (3) Slowly add the required material for the second layer onto the material for the third layer in step (2);

[0041] (4) Slowly add the required material for the first layer onto the material for the second layer in step (3) to obtain a four-layer mixed column of oil-ammonia-oil-water. Preferably, during the addition of the required material for the first layer, a peristaltic pump is used to slowly circulate the material up and down above the interface between the first and second layers to reduce the surface tension at the interface between the first and second layers. Then, let it stand for 30 to 60 minutes to stabilize. This ensures that the aluminum hydroxide sol can quickly pass through the contact interface between the first and second layers, preventing stagnation and tailing, which would affect the roundness.

[0042] Furthermore, the catalyst precursor is formed in a four-layer mixed column of oil-ammonia-oil-water, whereby a mixture of aluminum hydroxide sol and organic Pt salt solution is dripped into the four-layer mixed column of oil-ammonia-oil-water, wherein the inner diameter of the dripper used is 1.0 mm to 1.6 mm.

[0043] Furthermore, the residence time of the mixture of aluminum hydroxide sol and organic Pt salt solution in the four-layer oil-ammonia-oil-water mixed column is 5-18s, preferably 7-11s.

[0044] Furthermore, the drying temperature is 100℃~150℃, and the drying time is 6~10 hours; the calcination temperature is 750℃~950℃, and the calcination time is 1~4 hours.

[0045] Furthermore, in the catalyst precursor obtained in step (1), Pt exists in the form of single atoms.

[0046] Furthermore, the impregnation is preferably performed using a saturated impregnation method. The Pt precursor used in the impregnation solution is preferably at least one of PtCl4 and H2PtCl6. The drying conditions after impregnation are as follows: drying temperature 80–120°C, drying time 8–12 h. The calcination conditions after impregnation are as follows: calcination temperature 500–700°C, calcination time 2–6 h.

[0047] Furthermore, in the catalyst, based on the mass of the catalyst, the total Pt content is 0.26% to 1.40% by mass fraction, the Sn content is 0.02% to 0.90%, and the alumina content is 97.70% to 99.72%; in the catalyst, the Pt content on the catalyst surface is 0.40% to 0.85%.

[0048] Furthermore, the specific surface area of ​​the catalyst is 85–110 m². 2 / g, with a pore volume of 0.62~0.83mL / g.

[0049] Furthermore, the catalyst is in the form of spherical particles with an average diameter of 1.7–1.9 mm.

[0050] Furthermore, the catalyst has the following pore size distribution: pores with a pore size of less than 2 nm account for 1.3% to 3.5% of the total pore volume, and pores with a pore size of 2-50 nm account for 96.5% to 98.7% of the total pore volume, preferably 97.0% to 98.0%.

[0051] Furthermore, the catalyst has an average pore size of 14.5–18.5 nm.

[0052] Furthermore, the crushing strength of the catalyst is 65-85 N / particle.

[0053] Furthermore, the sphericity of the catalyst is 97.6% to 99.9%.

[0054] A third aspect of the present invention provides the application of the above-mentioned catalyst in the propane dehydrogenation reaction.

[0055] Furthermore, the application includes: a propane feedstock being contacted with the catalyst to undergo a dehydrogenation reaction to obtain the product propylene.

[0056] Furthermore, the propane dehydrogenation catalyst needs to be reduced before use. The catalyst precursor is reduced under a reducing atmosphere. The preferred reducing atmosphere is H2, the reduction temperature is 450–600°C, and the reduction time is 1–3 hours.

[0057] Furthermore, the preferred conditions for the propane dehydrogenation reaction are as follows: reaction temperature of 500–600 °C, reaction pressure of 0–1 MPa, and volume hourly space velocity of 50–200 h⁻¹. -1.

[0058] Compared with the prior art, the advantages of the present invention are as follows:

[0059] (1) In the catalyst preparation process of this invention, an organic Pt salt solution is added to the aluminum hydroxide sol. Due to the low solubility and large molecular weight of organic Pt, the organic molecules bonded to Pt atoms occupy a large steric hindrance, making it easy to form a single-atom Pt catalyst during the synthesis process. The metallic Pt is uniformly dispersed in the alumina support, which also plays a role in expanding the pores. During the molding process, the four-layer oil-ammonia-oil-water mixed column is different from the two-layer oil-ammonia column or hot oil column. It adds a third oil layer as a liquid-sealing oil layer and a fourth water layer, which allows the sol to quickly enter the third and fourth water layers after passing through the second ammonia layer. The pH value drops rapidly to neutral, making the spheres less likely to break or shrink during the drying process due to the volatilization of surface ammonia. This significantly increases the alumina particle size and mechanical strength, while also ensuring sufficient contact between the metal and the support, resulting in a more uniform load. Furthermore, the rapid decrease in pH value on the surface of the sol-gel microspheres simultaneously leads to a rapid decrease in the hydrophobicity of the particle surface, a significant increase in the interaction forces between particles, a shortening of the distance between particles, and partial collapse of the original structure. This results in an increase in the mesoporous structure of the support within the 2–50 nm range. Adding an appropriate amount of acidic solution to the fourth aqueous layer can further optimize the pore structure. Subsequent impregnation of the precursor with chloroplatinic acid solution increases the metal loading and the number of Pt sites on the outer nanoparticles. After calcination, the presence of both single-atom Pt and nanoparticle Pt in the catalyst provides a synergistic effect. The increase in Pt salt from the inside out facilitates the exposure of more active sites, accelerating the reaction and reducing carbon deposition.

[0060] (2) In the four-layer mixed column of oil-ammonia-oil-water of the present invention, on the one hand, since the density difference between ammonia and pure water is small, the density of the selected liquid sealing oil must be greater than that of ammonia and less than that of pure water, and the viscosity cannot be too high, otherwise it will affect the sphericity of the sol. By adding surfactants to transformer oil, the density can be increased without changing its viscosity, so that it meets the requirements. Water-soluble surfactants slowly penetrate into the oil under heating conditions, and the intermolecular interaction force is enhanced. During the evaporation of water, the intermolecular distance is shortened. After repeated cycles, the stability of the modified oil can be guaranteed. On the other hand, by using modified transformer oil liquid seal, the surface tension at the oil-water interface is significantly reduced due to the addition of surfactants. The pause when the sol balls pass through the oil-water interface is reduced, and they can pass through the interface quickly, reducing pulling and effectively improving the sphericity of the spherical carrier.

[0061] (3) The preparation process of the present invention is environmentally friendly. In the traditional oil-ammonia column pelletizing process, the volatilization of ammonia water causes serious environmental pollution problems and subsequent pollutant emissions. The present invention separates the second ammonia water layer and the fourth water layer with the second oil layer, so that the ammonia water layer is sealed on the fourth water layer, which can extend the service life and avoid the product from carrying out ammonia water and causing environmental pollution. After long-term use, deionized water can be replaced to ensure the liquid sealing effect. It is simple to operate in industry and saves costs.

[0062] (4) The catalyst prepared by the method of the present invention has a high propane conversion rate and propylene selectivity in the propane-to-propylene reaction, makes full use of the inner space of the catalyst, reduces carbon deposition, and has better catalytic activity. Detailed Implementation

[0063] The following examples further illustrate the catalyst for propane dehydrogenation to propylene, its preparation method, and its application effects according to the present invention. The examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0064] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0065] In this invention, the nitrogen adsorption-desorption curves of the samples were tested at -196℃ using a Micromeritics ASAP2020 fully automated physical adsorption instrument to determine the specific surface area, pore volume, and pore size distribution.

[0066] In this invention, the crushing strength is tested using a ZQJ-Ⅲ intelligent particle strength tester manufactured by Dalian Zhiqu Testing Machine Factory, and the average value of crushing ten spherical carriers is measured.

[0067] In this invention, the roundness is tested using an electron microscope from Olympus Corporation, and the average value is calculated after testing 20 samples.

[0068] In this invention, the Pt content on the catalyst surface was measured using XPS (the instrument was a Kratos Axis Ultra DLD).

[0069] Example 1

[0070] Take 250g of macroporous pseudoboehmite filter cake with a moisture content of 22wt% (calcined at 600℃ for 3h in air atmosphere, with the following properties: pore volume 0.87ml / g, specific surface area 175m²). 2 / g (average pore size 16nm), add deionized water and stir to make a homogeneous slurry, then add 26g of 45% nitric acid solution for gelation, finally preparing a pseudoboehmite sol with an alumina content of 20% by mass; take 300g of the above sol (alumina content 20wt%), add 6g of 1.2% acetylacetonate platinum solution, which also contains 2.4% stannous chloride, stir to homogeneity, and obtain a sol mixture;

[0071] Add 7g each of lauroyl diethanolamine and nonylphenol polyoxyethylene ether (n=9) to 100g of transformer oil (density 0.89g / mL at 20℃, kinematic viscosity 12mm at 40℃). 2 After mixing thoroughly, seal the container and heat in a 100℃ oven for 8 hours. Remove the seal and continue heating for 4 hours. Repeat this process three times to obtain modified transformer oil (density 0.94 g / mL at 20℃). Use a dropper with an inner diameter of 1.2 mm to apply the oil to the container (kinematic viscosity 32 mm at 40℃). 2 The above sol was added dropwise to a four-layer mixed column (cylinder) consisting of white oil, 25wt% ammonia, modified transformer oil, and deionized water, and the residence time in the four-layer mixed column was 8 seconds. The amount of white oil added was 35% of the volume of ammonia, the amount of modified transformer oil added was 38% of the volume of ammonia, and the amount of deionized water added was 1.3 times the volume of ammonia. The mixture was then dried at 130°C for 8 hours and calcined at 800°C for 3 hours.

[0072] Take 100g of the catalyst precursor prepared above, saturate it in an aqueous solution containing 2.0g of chloroplatinic acid, impregnate for 30min, dry in a drying oven at 90℃ for 10h, and calcine in a muffle furnace at 600℃ for 4h to obtain catalyst A of the present invention. The analytical results are shown in Table 1.

[0073] Example 2

[0074] Compared with Example 1, the difference is that the deionized water in the fourth layer of the four-layer mixed column was replaced with a 5wt% dilute acetic acid solution to obtain the catalyst B of the present invention. The analytical results are shown in Table 1.

[0075] Example 3

[0076] Compared with Example 1, the difference is that 5.4g of a 1.8% platinum acetylacetonate solution was added, which also contained 0.8% stannous chloride, to obtain the catalyst C of the present invention. The analytical results are shown in Table 1.

[0077] Example 4

[0078] Compared with Example 1, the difference is that in the preparation of modified transformer oil, the surfactant used was changed to lauroyl diethanolamine, the amount added was changed to 12g, the number of repetitions was changed to 4, and the density of the modified transformer oil at 20℃ was 0.95g / mL, thus obtaining the catalyst D of the present invention. The analysis results are shown in Table 1.

[0079] Example 5

[0080] The difference compared to Example 1 is that the white oil in the four-layer mixing column is changed to have a kinematic viscosity of 23 mmHg at 40°C. 2 / s of white oil, while changing the ammonia concentration to 21wt%, yielded the catalyst E of this invention, and the analytical results are shown in Table 1.

[0081] Example 6

[0082] Compared with Example 1, the difference is that the ammonia concentration is changed to 28wt%; in the preparation of modified transformer oil, the amount of lauroyl diethanolamine and nonylphenol polyoxyethylene ether added is changed to 4g each, and the density of the modified transformer oil at 20℃ is 0.93g / mL), thus obtaining the catalyst F of the present invention, and its analysis results are shown in Table 1.

[0083] Example 7

[0084] Compared with Example 1, the difference is that the amount of white oil added is 42% of the volume of ammonia water, the amount of modified transformer oil added is 32% of the volume of ammonia water, and the amount of deionized water added is 1.6 times the volume of ammonia water, thus obtaining the catalyst G of the present invention. The analysis results are shown in Table 1.

[0085] Comparative Example 1

[0086] The synthesis steps of the sol mixture are the same as in Example 1.

[0087] Compared with Example 1, the difference is that the four-layer oil-ammonia-oil-water mixed column is replaced with a two-layer oil-ammonia column, and the upper layer has a kinematic viscosity of 32 mmHg at 40°C. 2 / s of white oil, the lower layer of which is 25wt% ammonia water, the amount of white oil added is 25% of the volume of ammonia water, and the remaining molding steps remain unchanged, to obtain the comparative catalyst H of the present invention, and its analysis results are shown in Table 2.

[0088] Comparative Example 2

[0089] The synthesis steps of the sol mixture are the same as in Example 1.

[0090] Compared with Example 1, the difference is that only the first white oil column in the four-layer mixing column was removed, and a three-layer column was used to form a ball to obtain the comparative catalyst I of the present invention. The analysis results are shown in Table 2.

[0091] Comparative Example 3

[0092] The synthesis steps of the sol mixture are the same as in Example 1.

[0093] Compared with Example 1, the difference is that: 1. Only the fourth water column was removed to obtain the comparative catalyst J of the present invention, and its analysis results are shown in Table 2.

[0094] Comparative Example 4

[0095] The synthesis steps of the sol mixture are the same as in Example 1.

[0096] Compared with Example 1, the difference is that only the modified transformer oil layer in the four-layer mixed substrate was removed to obtain the comparative catalyst K of the present invention, and the analysis results are shown in Table 2.

[0097] Comparative Example 5

[0098] The synthesis steps of the sol mixture are the same as in Example 1.

[0099] Compared with Example 1, the difference is that the modified transformer oil in the second oil layer is replaced with transformer oil, while the other molding steps remain unchanged, resulting in the comparative catalyst L of the present invention. The analysis results are shown in Table 2.

[0100] Comparative Example 6

[0101] The method for synthesizing the sol mixture is the same as in Example 1.

[0102] Compared with Example 1, the difference is that the amount of white oil added is 16% of the volume of ammonia water, the amount of modified transformer oil added is 20% of the volume of ammonia water, and the amount of deionized water added is 0.4 times the volume of ammonia water, thus obtaining the comparative catalyst M of the present invention. The analysis results are shown in Table 2.

[0103] Table 1. Physicochemical properties of the catalysts obtained in each example.

[0104]

[0105] Table 2. Physicochemical properties of the catalysts obtained in each comparative example.

[0106] Catalyst number H I J K L M Average particle diameter, mm 1.73 1.79 1.70 1.72 1.73 1.72 <![CDATA[Specific surface area, m 2 / g]]> 100 109 101 104 102 101 Pore ​​volume, mL / g 0.471 0.428 0.409 0.443 0.417 0.425 Aperture distribution, % <2nm 4.0 4.3 4.5 4.2 5.1 4.4 2-50nm 95.6 95.7 95.4 95.6 94.7 95.3 >50nm 0.4 - 0.1 0.2 0.2 0.3 Average pore size, nm 12.7 11.4 13.0 12.5 12.1 12.4 Crushing strength, N / particle 29 31 37 34 40 42 Roundness, % 95.6 95.9 93.4 93.7 92.4 93.6

[0107] Table 3 Composition of catalysts in each embodiment

[0108] Catalyst number A B C D E F G Alumina (wt%) 98.9 98.9 99.0 98.9 98.9 98.9 98.9 Total Pt (wt%) 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Sn(wt%) 0.2 0.2 0.1 0.2 0.2 0.2 0.2 Surface Pt (wt%) 0.72 0.70 0.71 0.71 0.70 0.72 0.72

[0109] Table 4. Composition of catalysts in each comparative example

[0110] Catalyst number H I J K L M Alumina (wt%) 99.0 99.0 99.0 98.9 98.9 98.9 Total Pt (wt%) 0.8 0.9 0.8 0.9 0.9 0.9 Sn(wt%) 0.2 0.1 0.2 0.2 0.2 0.2 Surface Pt (wt%) 0.79 0.77 0.72 0.73 0.70 0.74

[0111] Catalyst evaluation

[0112] Take 5g of the above catalyst and reduce it at 520℃ for 1.5h under a hydrogen atmosphere. Then, load it into a fixed-bed reactor for propane dehydrogenation activity evaluation: reaction temperature 500℃, pressure 1MPa, volume hourly space velocity 150h⁻¹. -1 The results of propane dehydrogenation are listed in Table 5-6.

[0113] Table 5 Evaluation results of the catalysts in each example for propane dehydrogenation

[0114]

[0115] Table 6 Evaluation results of the comparative catalysts for propane dehydrogenation

[0116]

[0117]

[0118] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A catalyst for dehydrogenation of propane to propylene, the catalyst comprising an active metal Pt, an auxiliary metal Sn and an alumina carrier; the content of total Pt in the catalyst is 0.26%-1.40% by mass fraction, the content of Sn is 0.02%-0.90% by mass fraction, and the content of alumina is 97.70%-99.72% by mass fraction, based on the mass of the catalyst; the content of Pt on the surface of the catalyst is 0.40%-0.85%; the preparation method of the catalyst for dehydrogenation of propane to propylene comprises: (1)mixing an alumina hydroxide sol with an organic Pt salt solution, dropping the obtained mixture into an oil-ammonia water-oil-water four-layer mixing column for shaping, drying and calcining to obtain a catalyst precursor; (2)immersing the precursor obtained in step (1) in an impregnation solution containing Pt, drying and calcining to obtain the catalyst; in the mixing column, four layers are arranged from top to bottom, the first layer is a first oil layer, the second layer is an ammonia water layer, the third layer is a second oil layer, and the fourth layer is a water layer, and the second oil layer is selected from modified transformer oil; the first oil layer is selected from one or more of white oil or diesel oil, the modified transformer oil used in the second oil layer has a density between that of ammonia water and water, the modified transformer oil comprises transformer oil and water-soluble surfactant, the water-soluble surfactant is one or more of lauryl diethanolamine, nonylphenol polyoxyethylene ether or octylphenol polyoxyethylene ether; the fourth layer of water layer is deionized water or a dilute acid solution; the height of the first layer is 30%-50% of the height of the second layer; the height of the third layer is 30%-50% of the height of the second layer; the height of the fourth layer is 1.0-2.0 times the height of the second layer.

2. The catalyst of claim 1, wherein: The specific surface area of the catalyst is 85-110 m 2 / g, and the pore volume is 0.62-0.83 mL / g; and / or, the catalyst is in the form of spherical particles, and the average diameter of the particles is 1.7-1.9 mm; and / or, the pore size distribution of the catalyst is that the pore volume of pores with a pore size less than 2 nm accounts for 1.3%-3.5% of the total pore volume, and the pore volume of pores with a pore size of 2-50 nm accounts for 96.5%-98.7% of the total pore volume; and / or, the average pore size of the catalyst is 14.5-18.5 nm; and / or, the crushing strength of the catalyst is 65-85 N / particle; and / or, the roundness of the catalyst is 97.6%-99.9%.

3. The catalyst of claim 2, wherein: the pore volume of pores with a pore size of 2-50 nm accounts for 97.0%-98.0% of the total pore volume. 4.The preparation method of the catalyst for dehydrogenation of propane to propylene according to any one of claims 1-3, comprising: (1)mixing an alumina hydroxide sol with an organic Pt salt solution, dropping the obtained mixture into an oil-ammonia water-oil-water four-layer mixing column for shaping, drying and calcining to obtain a catalyst precursor; (2)immersing the precursor obtained in step (1) in an impregnation solution containing Pt, drying and calcining to obtain the catalyst; in the mixing column, four layers are arranged from top to bottom, the first layer is a first oil layer, the second layer is an ammonia water layer, the third layer is a second oil layer, and the fourth layer is a water layer, and the second oil layer is selected from modified transformer oil.

5. The method of claim 4, wherein: The organic Pt salt in the organic Pt salt solution is one or more of acetylacetone platinum or tetra(triphenylphosphine) platinum, and the solvent used is acetone. And / or, the concentration of the organic Pt salt in the organic Pt salt solution is 1.0wt%-1.9wt%. And / or, the amount of the organic Pt salt solution added is 9%-11% of the mass of the aluminum hydroxide sol calculated as aluminum oxide.

6. The method of claim 5, wherein: The organic Pt salt in the organic Pt salt solution is acetylacetone platinum.

7. The method of claim 4, wherein: The organic Pt salt solution contains stannous chloride.

8. The method of claim 7, wherein: The concentration of stannous chloride in the organic Pt salt solution is 0.4wt%-11wt%.

9. The method of claim 4, wherein: The oil-ammonia water-oil-water four-layer mixed column is a straight column.

10. The method of claim 9, wherein: The oil-ammonia water-oil-water four-layer mixed column is a cylindrical column.

11. The method of claim 4, wherein: In the oil-ammonia water-oil-water four-layer mixed column, the first oil layer is selected from one or more of white oil or diesel oil.

12. The method of claim 11, wherein: The first oil layer is white oil, and the white oil has a kinematic viscosity of 20-40 mm 2 / s at 40°C.

13. The method of claim 12, wherein: The white oil has a kinematic viscosity at 40°C of 25 to 35 mm 2 / s.

14. The method of claim 4, wherein: In the oil-ammonia water-oil-water four-layer mixed column, the concentration of ammonia water in the ammonia water layer is 20wt%-28wt%.

15. The method of claim 14, wherein: The concentration of ammonia water in the ammonia water layer is 22wt%-26wt%.

16. The method of claim 4, wherein: In the oil-ammonia water-oil-water four-layer mixed column, the second oil layer uses modified transformer oil with a density between that of ammonia water and water.

17. The method of claim 4, wherein: The 20℃ density of the modified transformer oil is 0.90 g / mL or more.

18. The method of claim 17, wherein: The 20℃ density of the modified transformer oil is 0.93-0.96 g / mL.

19. The method of claim 4, wherein: The mass of the water-soluble surfactant is 6%-25% of the mass of the transformer oil.

20. The method of claim 19, wherein: The mass of the water-soluble surfactant is 10%-18% of the mass of the transformer oil.

21. The method of claim 4, wherein: The transformer oil has a density of 0.86-0.89 g / mL at 20°C and a kinematic viscosity of 9-15 mm 2 / s at 40°C.

22. The method of claim 4, wherein: The preparation process of the modified transformer oil is as follows: The water-soluble surfactant and the transformer oil are mixed, and the obtained mixture is subjected to heat treatment, i.e. sealed heating treatment and open heating treatment in turn, and the above heat treatment is repeated 3-6 times to obtain the modified transformer oil.

23. The method of claim 22, wherein: The sealed heating treatment is carried out at a temperature of 80-120℃ for 6-20 h.

24. The method of claim 22, wherein: The open heating treatment is carried out at a temperature of 80-120℃ for 6-20 h.

25. The method of claim 4, wherein: In the oil-ammonia water-oil-water four-layer mixed column, the fourth water layer is deionized water or a dilute acid solution; in the dilute acid solution, the dilute acid is at least one selected from acetic acid and citric acid; and the mass concentration of the dilute acid solution is 3%-8%.

26. The method of claim 25, wherein: The fourth water layer is a dilute acid solution.

27. The preparation method of claim 4, characterized in that: And / or, the height of the third layer is 35%-45% of the height of the second layer; And / or, the height of the fourth layer is 1.2-1.5 times the height of the second layer.

28. The method of claim 4, wherein: In step (2), the impregnation is a saturation impregnation method; and / or, the Pt precursor used in the impregnating solution is at least one selected from PtCl4 and H2PtCl6.

29. Use of the catalyst of any one of claims 1-3 in a propane dehydrogenation reaction.

30. The use according to claim 29, characterized in that: The catalyst needs to be reduced before use.

31. The use according to claim 30, characterized in that: The reducing atmosphere is H2, the reduction temperature is 450-600℃, and the reduction time is 1-3 h.

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