An in-situ preparation of a high mechanical strength and five-coordinated Al 3+ Alumina spherical carrier method and application thereof

Abstract

The present invention discloses a method for in-situ preparing an alumina spherical carrier with high mechanical strength and containing pentacoordinate Al<supgt;3+< / supgt; and its application, belonging to the technical field of catalyst carrier preparation. The preparation method of the alumina spherical carrier includes: first, subjecting the alumina spheres to high-temperature activation and heat preservation, then uniformly mixing the highly active alumina spheres with the modifier powder, adding water to submerge the mixture of the alumina spheres and the modifier powder, sealing the system in a reaction kettle for aging treatment, drying and calcining to obtain the alumina spherical carrier. The preparation method of the present invention can change the morphology of the alumina spherical carrier, provide its mechanical strength, in-situ construct a special structure of pentacoordinate Al<supgt;3+< / supgt; in the alumina spherical carrier, and this structure can be used to anchor and disperse active metal components, inhibit the sintering of active metals and the separation of active phases, reduce coke deposition, improve the stability of the catalyst, and extend the service life of the catalyst.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst carrier preparation, and particularly relates to an in-situ preparation method of a catalyst carrier having high mechanical strength and containing five-coordinated Al 3+ A method for preparing an alumina spherical carrier, a prepared alumina spherical carrier, a spherical dehydrogenation catalyst and their application in propane dehydrogenation reaction. Background Art

[0002] Propane dehydrogenation is a propylene production process with high atomic utilization, simple process and high olefin yield. It has the advantages of single feed and rich hydrogen production. At present, the domestic propane dehydrogenation unit mainly adopts ABB Lummus's Catofin process (Cr-based catalyst) and UOP's Oleflex process (Pt-based catalyst). Cr-based catalysts are toxic and have multiple steps such as cyclic reaction, charring, steam purging, exhaust and catalyst reduction. Under such harsh cyclic process, Cr-based catalysts used for a long time will cause alumina crystallization and sintering, resulting in irreversible deactivation. Pt-based catalysts (containing Sn) have the advantages of high product selectivity, long catalyst life and environmental friendliness. At present, the recycling and reuse technology of precious metal catalysts is mature, which makes the application of precious metal catalysts more extensive. Precious metal catalysts usually use activated alumina with large specific surface area and high mechanical strength as carriers, but under harsh reaction conditions such as high temperature, they will face the problem of phase separation and sintering of active component metal Pt-Sn. Pt-Sn phase separation weakens the interaction between metals, making it difficult to exert the synergistic effect of the two metals, and the catalytic activity is reduced; Pt-Sn phase sintering (particle aggregation) will lead to reduced product selectivity, reduced anti-coking performance, and rapid catalyst deactivation. Therefore, it is urgent to develop alumina molded carriers with specific structures to solve the problems of Pt-Sn phase separation and particle sintering in propane dehydrogenation catalysts.

[0003] Alumina carriers can be modified to increase specific surface area and obtain a more developed pore structure. For example, Chinese patent publication number CN117225400A discloses a method for preparing a modified alumina carrier. Disodium hydrogen phosphate and tungstate are added as modifiers during the synthesis of alumina, and a mixture of sorbitol, glycerol, ethanol and water is added to the synthetic solution system. The specific surface area of ​​the prepared alumina can reach 300-400m 2 / g, pore volume 0.5-1.2cm 3 / g, pore size is 8-10nm, by adjusting the roasting parameters, roasting in steps, and reasonably controlling the temperature and time, the formation of mesopores can be promoted to obtain a mesoporous carrier. Further introducing active ingredients into the prepared modified alumina carrier can prepare a catalyst with high catalytic efficiency, accelerate the adsorption and desorption process, effectively inhibit carbon deposition, and thus increase the service life of the catalyst. The Chinese patent with publication number CN107837798A introduces a method for preparing an alumina pellet carrier, in which the alumina pellet and the modifier solution are sealed in a reactor for aging treatment, the modifier is selected from at least one of ammonium bicarbonate, ammonium carbonate and ammonium acetate, and the aging treatment temperature is 120-200 o C, the pores with a diameter greater than 200Å in the obtained alumina spheres account for 5.0-40% of the total pore volume. The carrier is used for catalytic reforming reactions, which not only improves the activity and selectivity of the catalyst, but also improves the catalyst's ability to resist carbon deposition. The modifier replaces the pore expander to form pores in the alumina spheres, thereby improving the pore structure of the alumina spheres. The Chinese patent with publication number CN117463309A provides a method for simultaneously improving the crushing strength and specific surface area of ​​alumina spherical carriers. Alumina sol is mixed with a pore expander and an organic amine salt template agent and then dropped into a ball shape. After drying and calcining, a specific surface area of ​​more than 200 m 2 / g, crushing strength higher than 45 N / particle, low bulk density alumina spherical carrier, its propane dehydrogenation reaction alkane conversion rate, olefin selectivity and platinum dispersion are significantly higher than the unmodified alumina carrier. It can be seen that effective macropore distribution is conducive to reducing catalyst carbon deposition, improving the dispersion of active components and extending the service life of the catalyst, but there is no special structure on its surface to anchor the metal active components, which makes the active metal components in the catalyst prone to migration and aggregation during the high-temperature reaction, forming irreversible catalyst deactivation, resulting in a significant decrease in catalyst activity and selectivity. The propane dehydrogenation reaction conditions are harsh (550-600℃), and the properties of the catalyst carrier are required to be high. Not only does it require a high specific surface area and a large pore volume to promote the dispersion of active metals, but it also requires the construction of a special structure to anchor the active components, inhibit the sintering of active metals and the separation of active phases, improve the stability of the active components of the catalyst, and extend the service life of the catalyst.

[0004] Studies have shown that the unsaturated five-coordinated Al on the (100) plane of γ-alumina surface 3+ (Al V ) The center is the anchoring position of the metal precursor. This special structure can promote the formation of a strong interaction between the metal and the carrier and inhibit the high-temperature sintering of the active metal. CN118767904A provides a kind of Al-containing V A method for preparing a moving bed spherical alumina carrier, wherein the method modifies high-purity pseudo-boehmite to obtain an Al-containing VAlumina powder was used as raw material to prepare a moving bed spherical alumina carrier by composite hydrogel molding. V The content can be adjusted, which is used to solve the problem that Pt particles are prone to sintering and PtSn phase separation in commercial PtSn catalysts. This method is suitable for preparing Al-containing catalysts from alumina powder as raw materials. V The moving bed alumina carrier prepared by this method relies on adding acid, gelatin, gum arabic, etc. to control the slurry state, so that the Al-containing V The powder is bonded to obtain a spherical alumina carrier with mechanical strength that meets the application standards of the moving bed. However, this method is to construct Al V When the powder is balled, adding acid and glue will affect some Al V The accessibility of the site does not involve in situ construction of the spherical support itself. V There is no mature method for in-situ construction of such special sites on alumina molded bodies. If this special structure can stably exist in the alumina molded body and in-situ change the morphology of alumina to obtain the crushing strength required by industrial catalysts, it will enhance the activity and stability of industrial catalysts and have broad application prospects. Summary of the invention

[0005] In view of the problems of easy separation of active metal phases and sintering of particles in current propane dehydrogenation catalysts, the present invention invents a modified preparation method for an alumina spherical carrier, which transforms the morphology of alumina in situ, enhances the interaction between crystal particles, improves the crushing strength of the alumina spherical carrier, and simultaneously constructs a special microscopic chemical environment in situ on its surface to anchor active components, inhibits sintering of active metals and separation of active phases, and prolongs the service life of the catalyst.

[0006] One of the purposes of the present invention is to provide an in-situ prepared high mechanical strength and penta-coordinated Al 3+ A method for preparing an alumina spherical carrier.

[0007] The second purpose of the present invention is to provide an alumina spherical carrier prepared by this method.

[0008] The third object of the present invention is to provide a spherical dehydrogenation catalyst prepared by the alumina spherical carrier.

[0009] A fourth object of the present invention is to provide an application of the spherical dehydrogenation catalyst in propane dehydrogenation reaction.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0011] In the first aspect, the present invention provides an in-situ preparation method of a high mechanical strength and a penta-coordinated Al 3+The method of preparing an alumina spherical carrier comprises the following steps:

[0012] S1. Activate the alumina pellets at a temperature of 350-650°C and keep them warm at a temperature of 150-180°C to keep the alumina pellets in a highly active state;

[0013] S2, evenly mixing high-activity alumina beads and modifier powder, making the outer surface of the alumina beads fully contact with the modifier powder, adding water to immerse the mixture of the alumina beads and the modifier powder, sealing the system in a reactor for aging treatment, so that the microscopic morphology of the alumina changes from a fine short needle-like morphology to an interlaced fiber-like morphology, washing, drying, and calcining to obtain an alumina spherical carrier;

[0014] The modifier is selected from at least one of urea, ammonium carbonate, ammonium bicarbonate, ammonium acetate, ammonium citrate and ammonium oxalate.

[0015] Step S1:

[0016] High temperature activation is carried out at 350-650℃ to remove impurities such as oil layer, curing agent, adsorbed water and CO2 on the surface of alumina balls, remove part of interlayer water, and remove part of hydroxyl groups. The Al atoms after dehydroxylation are in a highly active state, which is the CO3 formed after the modifier is dissolved. 2- , NH4 + Combined with Al atoms, it provides space and reaction sites, so that the alumina pellets can undergo phase transformation and morphology transformation during the aging process. The activated alumina pellets are kept at 150-180°C to prevent them from contacting with water in the air to destroy the reaction sites. This active site removes CO3 after modification. 2- NH4 + Able to form Al V , which is to construct Al in alumina spherical support V The activation temperature is too low, the crystal phase is not transformed, the mechanical strength of the product is low, and the Al V If the activation temperature is too high, the crystal morphology changes too quickly, which easily forms large alumina aggregates. The interaction between the aggregates is poor, the mechanical strength of the product is low, and the alumina carrier is easy to break.

[0017] Alumina pellets can be purchased commercially or prepared by yourself using methods such as oil-ammonia column molding. Generally, it refers to γ-Al2O3.

[0018] In some embodiments, the alumina spheres in step S1 are prepared by the following method:

[0019] S11, mixing the aluminum source uniformly, adding acid solution to peptize, and dispersing it in water, heating and adjusting the pH to alkaline, adding gelatin and gum arabic, and uniformly mixing to form a slurry;

[0020] S12, dropping the slurry into a liquid column consisting of an upper oil phase and a lower curing agent aqueous solution phase, the slurry droplets are gelled in the curing agent aqueous solution to form gel balls, and continue to be immersed in the curing agent aqueous solution to complete full curing, and obtain alumina balls after drying.

[0021] Preferably, the aluminum source in step S11 is at least one of pseudo-boehmite, boehmite, metallic aluminum, aluminum salt, aluminum alcohol, hydrated aluminum oxide, aluminum oxide, and aluminum-containing composite oxide;

[0022] Preferably, the slurry in step S11 is controlled to have the following mass contents:

[0023] The total mass content of the aluminum source is 5-20wt% calculated as alumina;

[0024] The mass content of the gelatin is 0.5-8wt%;

[0025] The mass content of the gum arabic is 0.5-8wt%.

[0026] Preferably, the thickness of the upper oil phase in step S12 is greater than 2 mm; and the thickness of the lower curing agent aqueous solution phase is greater than 5 cm.

[0027] Preferably, the curing agent aqueous solution phase in step S12 comprises water, formaldehyde, a surfactant and an acidic substance, and the acidic substance comprises at least one of nitric acid, hydrochloric acid, acetic acid or an aluminum salt, which is used to adjust the pH value of the curing agent aqueous solution phase to 2-4.

[0028] Step S2:

[0029] In some embodiments, the mass ratio of the high-activity alumina beads, the modifier powder and the water in step S2 is 1:1.5-4:3-6. The alumina beads are first mixed with the modifier powder so that the outer surface of the alumina beads is in full contact with the modifier powder, a certain amount of water is added to immerse the beads, and the beads are sealed in a reactor as soon as possible and transferred to a certain temperature for aging. If the modifier powder is not completely dissolved, the amount of water added is adjusted to control the crystal conversion rate.

[0030] In some embodiments, the aging treatment temperature in step S2 is 80-150° C. and the aging time is 3-60 h. The aging treatment temperature causes the modifier to decompose and generate pressure, which promotes the conversion of the alumina spherical carrier into decomposition energy to generate Al V sites, and morphology transformation is the key to improving the mechanical strength of alumina spherical supports.

[0031] In some embodiments, the drying temperature in step S2 is 60-90°C; the calcination temperature is 500-800°C, and the heating rate is less than 3°C / min, which slows down the calcination decomposition rate of the precursor and generates Al V Location.

[0032] The preparation method of the present invention directly modifies the alumina spheres, on the one hand, changes the microscopic morphology of the alumina to form an interwoven fibrous structure, thereby in situ improving the mechanical strength of the alumina spherical carrier; on the other hand, in situ constructs a special structure Al in the alumina spherical carrier. V , Al formed in situ V The distribution in the spherical carrier is more uniform, and the accessibility is not affected by impurities such as binders, and Al V It can anchor active components, inhibit active metal sintering and active phase separation, and is used to prepare propane dehydrogenation catalysts. It not only has high activity and selectivity, but also has strong catalyst stability.

[0033] In a second aspect, the present invention provides an alumina spherical carrier prepared by the above method.

[0034] The method of the present invention can produce high mechanical strength, containing Al V A catalyst support capable of anchoring active metals.

[0035] Preferably, the specific surface area of ​​the alumina spherical carrier is 150-240m 2 / g, pore volume is 0.36-0.70cm 3 / g,Al V (Five-coordinated Al 3+ ) accounts for 4.0wt%-21.5wt%, and the mechanical strength is 35-65N / particle.

[0036] In a third aspect, the present invention provides a spherical dehydrogenation catalyst prepared from the above-mentioned alumina spherical carrier.

[0037] The spherical dehydrogenation catalyst is prepared by the following method: the above-mentioned alumina spherical carrier is impregnated in a metal salt solution containing dehydrogenation activity, and the obtained impregnation product is dried and calcined at low temperature to obtain the dehydrogenation catalyst.

[0038] In some embodiments, the metal in the dehydrogenation active metal salt solution is selected from at least one of platinum, chromium, vanadium, nickel, gallium, tin, cobalt, and molybdenum.

[0039] In some embodiments, the low-temperature drying temperature is lower than 80° C., the drying time is 12-30 h, the roasting temperature is 500-800° C., and the roasting time is 4-24 h.

[0040] The selection, composition and preparation of the active metal of the dehydrogenation catalyst can be carried out according to conventional methods in the art. The preparation method can adopt an equal volume impregnation method, an excess impregnation method, etc., and the finished dehydrogenation catalyst is obtained after calcination.

[0041] In a fourth aspect, the present invention provides an application of a spherical dehydrogenation catalyst in a propane dehydrogenation reaction.

[0042] Beneficial effects:

[0043] (1) In the preparation method of the alumina spherical carrier provided by the present invention, steps S1 and S2 are the process of activating and modifying the formed alumina gel beads. Compared with the unmodified alumina spherical carrier directly calcined, the mechanical strength of the alumina spherical carrier prepared by steps S1 and S2 is significantly improved, the pore structure and specific surface area thereof are slightly improved, the bulk density of the spherical carrier is reduced, and a pentacoordinated Al can be constructed in the alumina spherical carrier. 3+ Special structure.

[0044] (2) Pentacoordinated Al 3+ The special structure can anchor the active components, promote the dispersion of active metals, inhibit the sintering of active metals and the separation of active phases, inhibit coke deposition, and improve the activity and stability of the dehydrogenation catalyst.

[0045] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The SEM images of the surface and cross section of the alumina spherical carrier of the present invention;

[0047] Figure 2 The nitrogen adsorption and desorption isotherms (a) and pore size distribution diagram (b) of the alumina spherical carrier and dehydrogenation catalyst of the present invention are shown;

[0048] Figure 3 The alumina spherical carrier of the present invention is 27 Al NMR spectrum;

[0049] Figure 4 The performance diagram of the spherical catalyst for propane dehydrogenation reaction of the present invention, wherein (a) propane conversion rate; (b) propylene selectivity; (c) propylene yield;

[0050] Figure 5 This is a weight loss curve diagram of the spherical catalyst of the present invention after being used in propane dehydrogenation reaction;

[0051] Figure 6This is the CO-DRIFT diagram of the spherical catalyst of the present invention. DETAILED DESCRIPTION

[0052] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0053] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0054] Example 1

[0055] A method for preparing an alumina spherical carrier and a spherical dehydrogenation catalyst comprises the following steps:

[0056] (1) Take 150g of SB powder produced by Sasol Company of Germany and mix it with 100g of pseudo-boehmite, add 500g of 1% nitric acid solution to dissolve it, disperse the above aluminum sol in 1200g of deionized water, stir it evenly and heat it to 60 o C, adding ammonia water to adjust the solution system pH to 8.0, then adding 40g gelatin and 40g gum arabic, stirring and dissolving them fully to prepare a uniformly dispersed slurry;

[0057] (2) Prepare a curing agent aqueous solution, that is, add formaldehyde and surfactant to water, where the formaldehyde content is 1wt% and the surfactant (AEO-6) content is 0.4wt%, and then add nitric acid to adjust the pH to 4.0. Drop the slurry prepared in (1) into the liquid column of the upper white oil layer and the lower curing agent aqueous solution layer, where the thickness of the upper white oil layer is 5mm and the thickness of the lower curing agent aqueous solution layer is 30cm. Control the temperature in the liquid column to 5-10 o C. The slurry droplets shrink into balls in the white oil phase, and after passing through the oil-water interface and entering the curing agent aqueous solution phase, a gelation reaction occurs to form composite gel balls. The composite gel balls are immersed in the curing agent aqueous solution for 10-60 minutes to be completely cured.

[0058] (3) Take out the formed gel balls and place them at 100 o C and then dried at 350 o C for 2 h to obtain an activated alumina spherical carrier.

[0059] (4) Take 10 g of the activated and dried highly active alumina spherical carrier and mix it thoroughly with 25 g of urea, so that the urea powder fills the gaps in the spherical carrier and covers the alumina spherical carrier. Add 30 g of deionized water to the Teflon liner, seal the Teflon liner in the reactor, and transfer it to 120 oC oven for aging for 48 h. After aging, cool to room temperature and wash and separate the alumina spherical carrier. o C and then heated at 600 o C for 3 h to obtain a penta-coordinated Al 3+ The alumina spherical carrier is denoted as Al2O3-1.

[0060] (5) Take the five-coordinated Al after calcination 3+ 4.5 g of Al2O3-1 alumina spherical carrier was impregnated in 5 g of a solution containing 8 wt% Ga(NO3)3 and 2 wt% H2PtCl6 and placed in a rotary evaporator for 50 o C water bath with rotary heating for 6 h, then raise the temperature to 80 o C and slowly evaporated until the mass of the mixture was less than 1.25 times the mass of the alumina spherical support, and then transferred to 50 o Continue drying in oven at 500 o C for 3 h to obtain a spherical dehydrogenation catalyst, which was recorded as PtGa-Al2O3-1.

[0061] Example 2

[0062] A method for preparing an alumina spherical carrier and a spherical dehydrogenation catalyst comprises the following steps:

[0063] (1) Take 150g of SB powder produced by Sasol Company of Germany and mix it with 100g of pseudo-boehmite, add 500g of 1% nitric acid solution to dissolve it, disperse the above aluminum sol in 1200g of deionized water, stir it evenly and heat it to 60 o C, adding ammonia water to adjust the solution system pH to 8.0, then adding 40g gelatin and 40g gum arabic, stirring and dissolving them fully to prepare a uniformly dispersed slurry;

[0064] (2) Prepare a curing agent aqueous solution, in which the formaldehyde content is 1wt%, the surfactant (AEO-6) content is 0.4wt%, and nitric acid is added to adjust the pH to 4.0. Drop the slurry prepared in (1) into the liquid column of the upper white oil layer and the lower curing agent aqueous solution layer, in which the thickness of the upper white oil layer is 5mm and the thickness of the lower curing agent aqueous solution layer is 30cm. Control the temperature in the liquid column to 5-10 o C. The slurry droplets shrink into balls in the white oil phase, and after passing through the oil-water interface and entering the curing agent aqueous solution phase, a gelation reaction occurs to form composite gel balls. The composite gel balls are immersed in the curing agent aqueous solution for 10-60 minutes to be completely cured.

[0065] (3) Take out the formed gel balls and place them at 100 o C and then dried at 400 oC for 2 h to obtain an activated alumina spherical carrier.

[0066] (4) Take 10 g of the activated high-activity alumina spherical carrier dried at 170°C and mix it thoroughly with 25 g of urea so that the urea powder fills the gaps in the spherical carrier and covers the alumina spherical carrier. Add 30 g of deionized water to the Teflon liner, seal the Teflon liner in the reactor, and transfer it to 140 o C oven for aging for 18 h. After aging, cool to room temperature and wash and separate the alumina spherical carrier. o C and then heated at 600 o C for 3 h to obtain a penta-coordinated Al 3+ The alumina spherical carrier is denoted as Al2O3-2.

[0067] (5) Take 4.5 g of Al2O3-2 alumina spherical carrier, soak it in 5 g of solution containing 8 wt% Ga(NO3)3 and 2 wt% H2PtCl6, and place it in a rotary evaporator for 50 min. o C water bath with rotary heating for 6 h, then raise the temperature to 80 o C and slowly evaporated until the mass of the mixture was less than 1.25 times the mass of the alumina spherical support, and then transferred to 50 o Continue drying in oven at 500 o C for 3 h to obtain a spherical dehydrogenation catalyst, which was recorded as PtGa-Al2O3-2.

[0068] Comparative Example 1

[0069] A method for preparing an alumina spherical carrier and a dehydrogenation catalyst, which differs from Example 2 in that steps S1 and S2 described in the present invention are not performed.

[0070] (1) Take 150g of SB powder produced by Sasol Company of Germany and mix it with 100g of pseudo-boehmite, add 500g of 1% nitric acid solution to dissolve it, disperse the above aluminum sol in 1200g of deionized water, stir it evenly and heat it to 60 o C, adding ammonia water to adjust the solution system pH to 8.0, then adding 40g gelatin and 40g gum arabic, stirring and dissolving them fully to prepare a uniformly dispersed slurry;

[0071] (2) Prepare a curing agent aqueous solution, in which the formaldehyde content is 1wt%, the surfactant (AEO-6) content is 0.4wt%, and nitric acid is added to adjust the pH to 4.0. Drop the slurry prepared in (1) into the liquid column of the upper white oil layer and the lower curing agent aqueous solution layer, in which the thickness of the upper white oil layer is 5mm and the thickness of the lower curing agent aqueous solution layer is 30cm. Control the temperature in the liquid column to 5-10 oC. The slurry droplets shrink into balls in the white oil phase, and after passing through the oil-water interface and entering the curing agent aqueous solution phase, a gelation reaction occurs to form composite gel balls. The composite gel balls are immersed in the curing agent aqueous solution for 10-60 minutes to be completely cured.

[0072] (3) Take out the formed gel balls and place them at 100 o C and then dried at 600 o C for 3 h to obtain an alumina spherical carrier, which is recorded as Al2O3-3.

[0073] (4) Take 4.5 g of Al2O3-3 alumina spherical carrier, soak it in 5 g of solution containing 8 wt% Ga(NO3)3 and 2 wt% H2PtCl6, and place it in a rotary evaporator for 50 min. o C water bath with rotary heating for 6 h, then raise the temperature to 80 o C and slowly evaporated until the mass of the mixture was less than 1.25 times the mass of the alumina spherical support, and then transferred to 50 o Continue drying in oven at 500 o C for 3 h to obtain a spherical dehydrogenation catalyst, which was recorded as PtGa-Al2O3-3.

[0074] Comparative Example 2

[0075] A method for preparing an alumina spherical carrier and a dehydrogenation catalyst, which is different from Example 2 in that when performing step S1, 300 o C for activation.

[0076] (1) Take 150g of SB powder produced by Sasol Company of Germany and mix it with 100g of pseudo-boehmite, add 500g of 1% nitric acid solution to dissolve it, disperse the above aluminum sol in 1200g of deionized water, stir it evenly and heat it to 60 o C, adding ammonia water to adjust the solution system pH to 8.0, then adding 40g gelatin and 40g gum arabic, stirring and dissolving them fully to prepare a uniformly dispersed slurry;

[0077] (2) Prepare a curing agent aqueous solution, in which the formaldehyde content is 1wt%, the surfactant (AEO-6) content is 0.4wt%, and nitric acid is added to adjust the pH to 4.0. Drop the slurry prepared in (1) into the liquid column of the upper white oil layer and the lower curing agent aqueous solution layer, in which the thickness of the upper white oil layer is 5mm and the thickness of the lower curing agent aqueous solution layer is 30cm. Control the temperature in the liquid column to 5-10 o C. The slurry droplets shrink into balls in the white oil phase, and after passing through the oil-water interface and entering the curing agent aqueous solution phase, a gelation reaction occurs to form composite gel balls. The composite gel balls are immersed in the curing agent aqueous solution for 10-60 minutes to be completely cured.

[0078] (3) Take out the formed gel balls and place them at 100 o C and then dried at 300 o C for 2 h to obtain an activated alumina spherical carrier.

[0079] (4) Take 10 g of the activated high-activity alumina spherical carrier dried at 170°C and mix it thoroughly with 25 g of urea so that the urea powder fills the gaps in the spherical carrier and covers the alumina spherical carrier. Add 30 g of deionized water to the Teflon liner, seal the Teflon liner in the reactor, and transfer it to 140 o C oven for aging for 18 h. After aging, cool to room temperature and wash and separate the alumina spherical carrier. o C and then heated at 600 o C for 3 h to obtain a penta-coordinated Al 3+ The alumina spherical carrier is denoted as Al2O3-4.

[0080] Comparative Example 3

[0081] A method for preparing an alumina spherical carrier and a dehydrogenation catalyst, which differs from Example 2 in that when performing step S2, the solid mixture of the modifier powder and the alumina spherical carrier is aged, and no water is added as a solvent in the Teflon lining. It can be foreseen that the reaction proceeds very quickly under this condition, thereby reducing the aging time to 6 hours.

[0082] (1) Take 150g of SB powder produced by Sasol Company of Germany and mix it with 100g of pseudo-boehmite, add 500g of 1% nitric acid solution to dissolve it, disperse the above aluminum sol in 1200g of deionized water, stir it evenly and heat it to 60 o C, adding ammonia water to adjust the solution system pH to 8.0, then adding 40g gelatin and 40g gum arabic, stirring and dissolving them fully to prepare a uniformly dispersed slurry;

[0083] (2) Prepare a curing agent aqueous solution, in which the formaldehyde content is 1wt%, the surfactant (AEO-6) content is 0.4wt%, and nitric acid is added to adjust the pH to 4.0. Drop the slurry prepared in (1) into the liquid column of the upper white oil layer and the lower curing agent aqueous solution layer, in which the thickness of the upper white oil layer is 5mm and the thickness of the lower curing agent aqueous solution layer is 30cm. Control the temperature in the liquid column to 5-10 o C, the slurry droplets shrink into balls in the white oil phase, and after passing through the oil-water interface and entering the curing agent aqueous solution phase, a gelation reaction occurs to form composite gel balls, which are immersed in the curing agent aqueous solution for 10-60 minutes to be completely cured;

[0084] (3) Take out the formed gel balls and place them at 100o C and then dried at 400 o C for 2 h to obtain an activated alumina spherical carrier;

[0085] (4) Take 10 g of the activated and dried highly active alumina spherical carrier at 170 °C and mix it thoroughly with 25 g of urea so that the urea powder fills the gaps in the spherical carrier and covers the alumina spherical carrier. Seal the Teflon liner in the reactor and transfer it to 140 °C. o After aging, the alumina spherical carrier was washed and separated at 80 o C and then heated at 600 o C for 3 h to obtain a penta-coordinated Al 3+ The alumina spherical carrier is marked as Al2O3-5.

[0086] 1. Analysis of the physical and chemical properties of the alumina spherical carrier and dehydrogenation catalyst in the present invention

[0087] The surface and cross-sectional morphologies of the alumina spherical carriers obtained in the examples and comparative examples were photographed using a JSM-7900F thermal field emission scanning electron microscope produced by JEOL Ltd. (JEOL) to observe changes in their microscopic morphologies ( Figure 1 ). Among them, the Al2O3-3 alumina spherical carrier prepared in comparative example 1 has short needle-like particles on the surface and inside, the Al2O3-1 prepared in example 1 has a rod-like structure on the surface, and the interior is still dominated by needle-like particles stacked in a morphology, and the Al2O3-2 prepared in example 2 has a surface transformed into a fiber flower-like structure, and the internal needle-like particles are transformed into an interwoven fiber mesh structure, which enhances the interaction between particles, which is the key to improving the mechanical strength of the alumina spherical carrier. Example 2 has a high activation temperature, strong activity, and a high conversion temperature. The internal crystal phase and morphology are transformed, and the content of penta-coordinated aluminum is also improved. The activation temperature and conversion temperature of Example 1 are both lower. Although it contains Al V , but the improvement in mechanical strength is small.

[0088] The specific surface area and pore size distribution of the alumina spherical carrier and the dehydrogenation catalyst obtained in the above examples and comparative examples were detected by a physical adsorption instrument ( Figure 2 , Table 1).

[0089] Table 1 Pore structure data of alumina spherical carrier and dehydrogenation catalyst

[0090]

[0091] The compressive strength of the alumina spherical carriers obtained in the above embodiments and comparative examples was tested using an intelligent particle strength tester. The specific test method is as follows: 20 samples were taken according to the quartering method, and their strengths were measured using a particle strength tester, which were recorded as P1, P2, ..., P20. The crushing strength of the alumina spherical carrier P A = (P1+P2+…P20) / 20 (Table 2), it can be noted that at the aging temperature of 140 o The mechanical strength of the samples prepared at 40 °C was significantly improved. The activation temperature of the sample synthesized in Comparative Example 2 was low, the crystal phase was not transformed, and the mechanical strength of the product was low. The sample synthesized in Comparative Example 3 had no water as a medium, although it contained Al V However, the mechanical strength is significantly reduced and it cannot be used as a spherical carrier for moving bed alumina.

[0092] Table 2 Mechanical strength test data of alumina spherical carrier and dehydrogenation catalyst (N / particle)

[0093]

[0094] Solid-state nuclear magnetic resonance (NMR) characterization was performed using a Bruker Advance III 400 spectrometer equipped with a Bruker 4.0 mm MAS probe at a resonance frequency of 104.0 MHz. The NMR spectra of the samples are shown in Figure 3 The NMR parameters of the samples are listed in Table 3. The test results show that the penta-coordinated Al 3+ The proportion is higher, which proves that this synthesis scheme can construct five-coordinated Al in alumina spherical carriers. 3+ The special structure.

[0095] Table 3 NMR parameters of samples

[0096]

[0097] 2. Analysis of propane dehydrogenation performance of the alumina spherical dehydrogenation catalyst in the present invention

[0098] The propane dehydrogenation reaction was carried out in a fixed bed tubular reactor with a feed gas ratio of propane to nitrogen of 1:9, a total flow rate of 30 mL / min, and a reaction temperature of 550 o C, the catalyst was first pretreated in 40mL / min hydrogen for 1h, and then propane-nitrogen mixed gas was introduced to test the dehydrogenation reaction performance. The corresponding relationship between propane conversion rate, propylene selectivity and propylene yield of propane dehydrogenation reaction and time is shown in Figure 4 Compared with the catalyst synthesized in Comparative Example 1, Examples 1 and 2 show higher propylene yields.

[0099] Catalyst carbon deposition analysis was carried out in a thermogravimetric-mass spectrometer according to 10 o C / min heating rate, from room temperature to 800 o C, the carbon deposit amount is counted in Table 4, and the weight loss curve of the catalyst after reaction is as follows Figure 5 shown.

[0100] Table 4 Carbon deposition of propane dehydrogenation on alumina spherical catalyst

[0101]

[0102] Compared with the comparative example PtGa-Al2O3-3, the conversion rate of propane dehydrogenation reaction of PtGa-Al2O3-1 and PtGa-Al2O3-2 is significantly improved, and the propylene selectivity of PtGa-Al2O3-2 is also significantly higher than that of PtGa-Al2O3-3, and the coke selectivity is low.

[0103] CO-DRITF was performed in the diffuse reflectance mode of a Bruker VERTEX 70V. The sample stage was filled with sample powder and the sample surface was leveled. A hydrogen-argon mixture (H2:Ar=1:9, 40 mL / min) was introduced at 400 o The sample was reduced at 30 °C for 30 min and then cooled to 30 o C, switch to nitrogen to collect sample background, use high-purity CO (> 99.99%) as the probe molecule, allow the sample to fully adsorb CO, then pass nitrogen to purge, and record the infrared spectrum after 30 minutes of purge ( Figure 6 ). Using CO molecules that are sensitive to electronic / geometric structures as probes is an important means of obtaining information about metal species and can be used to compare the size differences of Pt particles. The spectral band of bridge-adsorbed CO appears at 1750-1900 cm -1 , while the linear adsorption of CO appears between 1900-2100 cm -1 Between. Figure 6 As shown, both samples have no -1 The spectral bands attributable to the bridge-type adsorption of CO by Pt particles are obvious, indicating that there are no large Pt particles in the two samples. -1 The band at 2043 cm indicates that CO is adsorbed on the platform. -1 The bands at 1950-2010 cm -1 The bands at 1900-2100cm -1The results are shown in Table 5. It can be observed that compared with the PtGa / Al2O3-3 synthesized in Comparative Example 1, the peak intensity ratio of the PtGa / Al2O3-2 synthesized in Example 2 attributed to CO adsorption at the corners or steps of unsaturated coordination is significantly reduced, while the intensity ratio of the band attributed to the strong interaction between metals is increased, indicating that the penta-coordinated Al 3+ The spherical support pairs can enhance the interaction between metals, inhibit the phase separation of active metals, and improve the activity and stability of the catalyst.

[0104] Table 5 CO-DRIFT graph of samples 1900-2100 cm -1 Band separation results of the position

[0105]

[0106] After comparative analysis with the samples synthesized in the examples and comparative examples, it was found that the alumina spherical carrier synthesized by the innovative preparation method of the present invention showed a significant microscopic morphology change. The originally independently stacked fine needle-shaped particles were transformed into an interwoven alumina fiber network. This transformation greatly improved the mechanical strength of the spherical alumina carrier and achieved Al V In situ construction of sites, these Al V The sites are conducive to the dispersion and fixation of active metal components, effectively improving the activity and stability of the catalyst. In contrast, the spherical alumina carrier in Comparative Example 1, because no modifier was added during the preparation process, its microscopic morphology is still a fine needle-like structure, which has low mechanical strength. At the same time, due to the lack of effective modification treatment, Al V The content of sites is also relatively low. When the carrier is used as a propane dehydrogenation catalyst carrier, its dehydrogenation activity is poor and the deactivation rate is fast. The activation temperature of Comparative Example 2 is lower than the limit temperature set by the present invention, resulting in the Al atoms in the alumina remaining in a stable state. Due to the influence of the mass transfer effect, the formed alumina spheres are difficult to react effectively with the modifier, and the Al atoms cannot be successfully constructed on the surface of the unactivated alumina spherical carrier. V In Comparative Example 3, water was not used as the synthesis medium, although a higher concentration of Al V However, due to the rapid conversion process and insufficient solid-phase contact, the mechanical strength of the spherical alumina carrier is not enhanced. This spherical alumina carrier with low mechanical strength is prone to wear and pulverization during use and cannot meet the use standards of the moving bed reactor. In summary, the performance of the sample synthesized by the technical solution proposed in the present invention is significantly better than that of the comparative example. The key technologies of the present invention lie in the pre-activation process, the selection of the modifier and the use of the reaction medium, which are all to improve the mechanical strength of the spherical alumina carrier and construct Al VThe modification scheme is based on the careful design of raw material properties and modification targets, aiming to synthesize Al2O3 with high mechanical strength. V The rich spherical alumina carrier is crucial and indispensable in every step.

[0107] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and essence of the claims of the present invention; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. An in-situ preparation of a high mechanical strength and penta-coordinated Al 3+ The method of producing an alumina spherical carrier is characterized in that The following steps are involved: S1. Activate the alumina balls at 400°C and keep them at 150-180°C to keep them in a highly active state. S2. Evenly mix the high-activity alumina beads and the modifier powder, so that the outer surface of the alumina beads is in full contact with the modifier powder, add water to immerse the mixture of the alumina beads and the modifier powder, seal the system in a reactor for aging treatment, the aging temperature is 140° C., the aging time is 18 hours, the microscopic morphology of the alumina is changed from a fine short needle-like morphology to an interlaced fiber-like morphology, wash, dry, and calcine to obtain an alumina spherical carrier; The modifier is selected from at least one of urea, ammonium carbonate, ammonium bicarbonate, ammonium acetate, ammonium citrate and ammonium oxalate.

2. The method according to claim 1, characterized in that The alumina spheres in step S1 are prepared by the following method: S11, adding an aluminum source to an acid solution for peptization, dispersing the aluminum source in water, heating and adjusting the pH to alkaline, adding gelatin and gum arabic, and mixing uniformly to form a slurry; S12, dropping the slurry into a liquid column consisting of an upper oil phase and a lower curing agent aqueous solution phase, the slurry droplets are gelled in the curing agent aqueous solution to form gel balls, and continue to be immersed in the curing agent aqueous solution to complete full curing, and obtain alumina balls after drying.

3. The method according to claim 2, characterized in that The aluminum source in step S11 is at least one of pseudo-boehmite, boehmite, metallic aluminum, aluminum salt, aluminum alcohol, hydrated aluminum oxide, aluminum oxide, and aluminum-containing composite oxide; The following mass contents are controlled in the slurry of step S11: The mass content of the aluminum source is 5-20wt% in terms of alumina; The mass content of the gelatin is 0.5-8wt%; The mass content of the gum arabic is 0.5-8wt%.

4. The method according to claim 2, characterized in that: The thickness of the upper oil phase in step S12 is greater than 2 mm; the thickness of the lower curing agent aqueous solution phase is greater than 5 cm; The curing agent aqueous solution phase in step S12 includes water, formaldehyde, a surfactant and an acidic substance, and the acidic substance includes at least one of nitric acid, hydrochloric acid, acetic acid or aluminum salt, which is used to adjust the pH value of the curing agent aqueous solution phase to 2-4.

5. The method according to claim 1, characterized in that The mass ratio of the high-activity alumina beads, the modifier powder and the water in step S2 is 1:1.5-4:3-6.

6. The method according to claim 1, characterized in that The drying temperature in step S2 is 60-90°C; the roasting temperature is 500-800°C, and the heating rate is less than 3°C / min.

7. An alumina spherical carrier, characterized in that: The method is prepared by any one of claims 1 to 6.

8. A spherical dehydrogenation catalyst, characterized in that: The catalyst is prepared by the following method: the alumina spherical carrier according to claim 7 is impregnated in a metal salt solution containing dehydrogenation activity, and the impregnated product is dried and calcined at low temperature to obtain a dehydrogenation catalyst.

9. Use of the spherical dehydrogenation catalyst according to claim 8 in propane dehydrogenation reaction.

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