Catalyst for catalyzing propane dehydrogenation to prepare propylene as well as preparation method and application of catalyst

Abstract

The invention belongs to the field of catalysts, and particularly relates to a catalyst for catalyzing propane dehydrogenation to prepare propylene as well as a preparation method and application thereof. The catalyst comprises a carrier, an active component and an auxiliary agent, the active component and the auxiliary agent are loaded on the carrier, the carrier is a hydro-thermally synthesized MEL structure all-silicon molecular sieve containing Sn heteroatoms, and the molecular sieve can present a two-dimensional spherical flower-shaped morphology assembled by nano sheet-shaped microcrystals, has rich hierarchical porous structures and a relatively large outer surface area, and can be used for preparing the catalyst. The advantages of micropores and mesopores of the molecular sieve are combined, the reaction mass transfer diffusion process can be effectively enhanced, the contact area between the active component and the reaction gas propane is increased, and the catalytic activity is improved. The prepared catalyst is novel in morphology and structure, shows excellent propylene selectivity and high propane conversion rate in the propane dehydrogenation catalysis process, reduces the carbon deposition regeneration frequency and has good industrial application prospects.

Description

Technical Field

[0001] The invention relates to the field of propane dehydrogenation catalysis, and in particular to a catalyst for catalyzing propane dehydrogenation to produce propylene, and a preparation method and application thereof. Background Art

[0002] As the second largest petrochemical raw material intermediate after ethylene, propylene is widely used in the synthesis of important bulk chemicals such as polypropylene, acrylonitrile, acrylic acid, propylene oxide and acetone. In recent years, with the increasing demand for downstream derivatives, the traditional propylene production process can no longer meet the needs of the chemical industry. The use of low-cost propane direct dehydrogenation to propylene (PDH) technology is the main development direction for the future expansion of propylene production capacity due to its advantages such as short process flow, high propylene yield, low investment cost and high economy.

[0003] The key core technology of propane dehydrogenation technology lies in the development of catalysts with high activity, high selectivity and high stability. At present, the industrialized propane dehydrogenation catalysts mainly include two categories: Pt series and Cr series. Among them, due to the pollution of Cr series catalysts to the environment and other problems, its use is greatly restricted; while the PtSn / Al2O3 supported catalyst represented by the Oleflex process has high activity and good propylene selectivity (84-88%), but it is easy to sinter and deactivate at high temperature, and the acidity of the Al2O3 carrier itself is also easy to cause catalyst coking and deactivation and reduce the selectivity of the target product propylene, requiring frequent regeneration. Therefore, further improving and perfecting the catalyst performance and developing a propane dehydrogenation catalyst with excellent performance, high propylene selectivity and good stability is the key to solving the technical problems of propane dehydrogenation.

[0004] Molecular sieves have special pore structures, shape selection effects and good hydrothermal stability, making them excellent carriers for preparing dehydrogenation catalysts. In recent years, the use of molecular sieve carriers to replace traditional γ Al2O3 carriers for propane dehydrogenation to propylene has become a hot topic and a difficult point in research. CN115870012A discloses a spherical composite carrier in which aluminum oxide and titanium silicon molecular sieve are mixed in a weight ratio of 1: (0.2-1). After loading the active component Pt, the auxiliary agent Sn and the alkali metal Na, the catalyst exhibits good dehydrogenation activity and propylene selectivity of 92%-95%. CN107303497A uses extruded multi-level pore ZSM-5 molecular sieve and aluminum oxide as carriers, and the catalyst prepared after loading the active component Pt, the auxiliary agent Sn and Na exhibits good catalytic activity, and the selectivity of propylene is 90%-96%. CN104307555A discloses a MFI type molecular sieve catalyst for propane dehydrogenation to propylene, which uses a multi-component heteroatom ZSM-5 molecular sieve as a carrier and is impregnated with a Pt active component. The catalyst has a propylene selectivity of up to 95% when the catalyst is used as a diluent gas containing hydrogen at high temperature, which still needs to be further improved. CN109746026A discloses a nano-multi-level porous all-silicon molecular sieve with an MFI structure, which has a particle size of 50-500nm and a specific surface area of ​​300m 2 / g or more, corresponding to a pore volume of 0.25cm 3 / g or more, at least one of the active components of Group VIII metals and at least one of Group IIB metals, rare earth metals, alkali metals and alkaline earth metals are introduced into the above molecular sieve as auxiliary agents for catalytic dehydrogenation of propane to propylene. The prepared catalyst has excellent catalytic activity and stability, and the propylene selectivity is 90.1%-95.8%.

[0005] Compared with traditional Al2O3 carriers and molecular sieve carriers, all-silicon molecular sieves can inhibit the occurrence of carbon deposition side reactions such as propane cracking and deep dehydrogenation during high-temperature catalysis to a certain extent due to their weak acidity, which is beneficial to improving the selectivity of the target product propylene and extending the single-pass service life of the catalyst, but it is still difficult to avoid sintering deactivation at high temperatures. At the same time, the pure microporous structure of the molecular sieve is also prone to adversely affect the diffusion of reactants and products, resulting in the generation of carbon deposition and reduced catalyst stability. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems in the above-mentioned prior art and provide a catalyst for catalytic dehydrogenation of propane to produce propylene, and its preparation method and application. The present invention synthesizes a MEL structure all-silicon molecular sieve containing Sn heteroatoms with a multi-level pore structure, a high surface area and a pore volume, and uses it as a carrier to prepare a supported propane dehydrogenation catalyst. The catalyst combines the advantages of microporous molecular sieves and mesoporous structures, the active components are more evenly dispersed, the reaction mass transfer and diffusion process is faster, and it exhibits excellent propylene selectivity, high propane conversion rate and good stability in the process of catalytic propane dehydrogenation.

[0007] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0008] The first aspect of the present invention is to provide a catalyst, comprising a carrier and an active component and an optional auxiliary component loaded on the carrier, wherein the active component is selected from at least one of the noble metal elements of Group VIII; the auxiliary component is selected from one or more of the metal elements of Group IVA, the alkali metal elements of Group IA, and the alkaline earth metal elements of Group IIA; wherein the carrier is a molecular sieve of MEL structure containing Sn heteroatom.

[0009] In a preferred embodiment of the present invention, the molecular sieve has a crystal size of 250-500 nm and a specific surface area of ​​500 m 2 / g or more, pore volume is 0.70cm 3 / g or more, and the mesopore / micropore volume ratio is 1-8, and the molecular sieve contains Sn metal element.

[0010] In a more preferred embodiment of the present invention, the molecular sieve has at least one of the following characteristics:

[0011] The crystal size of the molecular sieve is 250-500 nm; and / or,

[0012] The specific surface area of ​​the molecular sieve is 500-800m 2 / g; and / or,

[0013] The pore volume of the molecular sieve is 0.7-1.0 cm 3 / g; and / or,

[0014] The mesopore / micropore volume ratio is 1.5-5; and / or,

[0015] The intracrystalline micropores are distributed in the range of 0.4-2nm, preferably 0.5-1.5nm, and the intercrystalline mesopores are distributed in the range of 2-10nm;

[0016] External surface area is 150-400m 2 / g.

[0017] In a preferred embodiment of the present invention, the molecular sieve is an all-silicon molecular sieve of MEL structure containing Sn heteroatom; and / or,

[0018] The molecular sieve can present a two-dimensional spherical flower morphology of nano-thin sheet microcrystals assembled under low temperature conditions of 120° C. (preferably under hydrothermal conditions).

[0019] As described above, the molecular sieve is a two-dimensional all-silicon molecular sieve with a MEL structure and containing Sn heteroatoms and having a multi-level pore structure, a relatively high surface area and a relatively high pore volume.

[0020] The content of Sn in the molecular sieve of the present invention is preferably adjusted according to the content of Sn in the target catalyst. For example, as a propane dehydrogenation catalyst, the content of Sn in the molecular sieve is preferably such that the total mass of the catalyst is 100wt%, and the mass percentage of Sn metal in the molecular sieve is 0.1wt%-5.0wt%, preferably 0.2wt%-4.0wt%, and more preferably 0.2wt%-2.0wt%.

[0021] According to the present invention, preferably, the molecular sieve is prepared by the following method: the preparation method of the molecular sieve comprises subjecting a mixture containing a silicon source, an organic template, a synthesis aid, a Sn source and water to a hydrothermal reaction, followed by solid-liquid separation, optional washing, optional drying, and calcination to obtain the molecular sieve;

[0022] The organic template is a small molecule quaternary ammonium salt, and the synthesis auxiliary is a long-chain quaternary ammonium salt with more than 10 carbon atoms.

[0023] In a preferred embodiment of the present invention, the preparation method comprises the following steps:

[0024] (1) mixing a silicon source, an organic template, a synthesis aid, a Sn source and water to form a mixed gel;

[0025] (2) subjecting the mixed gel to a hydrothermal reaction to obtain a reaction mixture;

[0026] (3) After the reaction mixture is cooled, solid-liquid separation, optional washing, optional drying, and calcination are performed to obtain the molecular sieve.

[0027] According to the present invention, the silicon source can be selected in a wide range. In a preferred embodiment of the present invention, the silicon source is at least one of tetraethyl orthosilicate, tetraethyl orthosilicate, tetraethyl silicate-28, tetraethyl silicate-40, silica gel, and silica sol, and is preferably at least one of tetraethyl orthosilicate, tetraethyl orthosilicate, tetraethyl silicate-28, and tetraethyl silicate-40.

[0028] According to the present invention, the organic template can be selected in a wide range. In a preferred embodiment of the present invention, the organic template is selected from one or more of tetrabutylammonium hydroxide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium fluoride and cyclohexylamine.

[0029] According to the present invention, the synthesis auxiliary agent can be selected from a wide range. In a preferred embodiment of the present invention, the synthesis auxiliary agent is selected from at least one of dodecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide.

[0030] According to the present invention, the Sn source can be selected from a wide range. In a preferred embodiment of the present invention, the Sn source is at least one of the salts containing the Sn element, including but not limited to SnCl4.

[0031] According to the present invention, the molar ratio of the silicon source to the organic template, the synthesis auxiliary agent, the Sn source and the water can be selected within a wide range. In a preferred embodiment of the present invention, the molar ratio of the silicon source to the organic template, the synthesis auxiliary agent, the Sn source and the water calculated as SiO2 is 1:(0.10.8):(0.005-0.4):(0.0005-0.025):(5-50), preferably 1:(0.10.5):(0.005-0.2):(0.001-0.02):(10-40); more preferably 1:(0.15-0.45):(0.01-0.1):(0.001-0.01):(10-30).

[0032] According to the present invention, the mixing conditions in step (1) can be selected within a wide range. In a preferred embodiment of the present invention, the mixing conditions in step (1) include: a temperature of 20-30°C and a time of 3-12h; preferably, the stirring speed is 400-600rpm relative to 10g of the mixture system.

[0033] According to the present invention, the conditions for the hydrothermal reaction treatment can be selected within a wide range. In a preferred embodiment of the present invention, the conditions for the hydrothermal reaction treatment include: a temperature of 120-190°C, preferably 120-180°C, and / or a time of 36-150h.

[0034] According to the present invention, the calcination conditions can be selected within a wide range. In a preferred embodiment of the present invention, the calcination conditions include: a temperature of 500-600° C., preferably 550-580° C.; and / or a time of 4-6 hours.

[0035] The inventor of the present invention cleverly discovered during the research process that by adopting a method of a small molecule quaternary ammonium salt template and a long-chain quaternary ammonium salt synthesis aid, the axial growth of the crystal can be suppressed, so that the crystal structure of the molecular sieve during the synthesis process tends to grow in a two-dimensional structure. According to the present invention, more preferably, the steps of the molecular sieve include the following:

[0036] (1) mixing a silicon source, an organic template, a synthesis aid, a Sn source dissolved in deionized water, and deionized water in a certain proportion, stirring evenly, to form a mixed gel;

[0037] (2) transferring the mixed gel into a high pressure hydrothermal autoclave for hydrothermal reaction at 120-180° C.;

[0038] (3) After the hydrothermal reaction kettle is cooled to room temperature, solid-liquid separation, washing, drying and calcination are sequentially performed to prepare a MEL structure all-silicon molecular sieve containing Sn heteroatoms;

[0039] The silicon source in step (1) is one of tetraethyl orthosilicate, tetraethyl orthosilicate, tetraethyl silicate-28, tetraethyl silicate-40, silica gel, and silica sol, preferably tetraethyl orthosilicate, tetraethyl orthosilicate, tetraethyl silicate-28, and tetraethyl silicate-40; more preferably tetraethyl orthosilicate.

[0040] The template agent in step (1) is a small molecule quaternary ammonium salt; and the synthesis auxiliary agent is a long-chain quaternary ammonium salt.

[0041] Preferably, the organic template in step (1) is a small molecule quaternary ammonium salt, including one or more of tetrabutylammonium hydroxide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium fluoride, and cyclohexylamine, more preferably tetrabutylammonium hydroxide (TBAOH).

[0042] Preferably, the synthesis aid (OSDA) in step (1) is a long-chain quaternary ammonium salt having more than 10 carbon atoms, preferably at least one of decanyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide.

[0043] Preferably, the silicon source in step (1) is calculated as silicon dioxide (SiO2), and the corresponding molar ratio of each component SiO2:TBAOH:OSDA:Sn:H2O in the mixed gel is 1.0:(0.10.8):(0.005-0.4):(0.0005-0.025):(5-50); more preferably 1.0:(0.10.5):(0.005-0.2):(0.001-0.02):(10-40); further preferably 1.0:(0.15-0.45):(0.01-0.1):(0.001-0.01):(10-30).

[0044] Preferably, in step (1), the amount of Sn source used is such that the mass percentage of the Sn source metal element in the molecular sieve is 0.1wt%-5.0wt%, preferably 0.3wt%-4.0wt%, and more preferably 0.3wt%-2.0wt%, based on the total mass of the catalyst.

[0045] Preferably, the Sn source is a salt containing Sn element.

[0046] The mixing and stirring conditions in step (1) include: a temperature of 20-30° C., a stirring time of 3-12 h, and a stirring speed of 400-600 rpm relative to 10 g of the mixture system.

[0047] Wherein, the hydrothermal treatment conditions in step (2) include: the hydrothermal reaction temperature is 120-180°C and the time is 36-150h.

[0048] Preferably, the hydrothermal treatment temperature is 120-160°C and the time is 72-120h.

[0049] In the step (3), the hydrothermal crystallization product is naturally cooled to room temperature (eg, 25° C.); the solid-liquid separation is performed by centrifugation.

[0050] Preferably, the centrifugal conditions include: a rotation speed of 3000-5000 rpm and a time of 0.5-2 h.

[0051] The washing in step (3) is performed with deionized water. The method of the present invention has no particular limitation on the amount of water and the number of times of the washing. It is only necessary to clean the free ions and the precursor solution, and the final pH value can be 7.0-7.5.

[0052] The drying conditions in step (3) include: temperature of 80-120° C. and time of 6-10 h.

[0053] The calcination conditions in step (3) include: a temperature of 500-600° C., preferably 550-580° C.; a heating rate of 1-2° C. / min, and a time of 4-6 hours.

[0054] According to the preparation method of the present invention, the obtained molecular sieve has the following characteristics:

[0055] Preferably, the MEL structured all-silicon molecular sieve containing Sn heteroatoms prepared by the method can present a two-dimensional spherical flower morphology of nanocrystal assembly, with a grain size of 250-500nm; more preferably 250-400nm; and / or,

[0056] Preferably, the molecular sieve has a specific surface area of ​​up to 500 m2 / g or more, more preferably a specific surface area of ​​500-700m 2 / g; and / or,

[0057] Preferably, the pore volume of the molecular sieve is 0.7 cm 3 / g or more, and the mesopore / micropore volume ratio is 1-8, and more preferably the pore volume is 0.7-1.0cm 3 / g, and the mesopore / micropore volume ratio is 1.5-5; and / or,

[0058] Preferably, the multi-level pore sizes of the molecular sieve are distributed in the range of 0.4-2 nm and 2-10 nm, more preferably 0.5-1.5 nm and 2-8 nm.

[0059] According to the present invention, the active component is selected from at least one of the noble metal elements of Group VIII. In a preferred embodiment of the present invention, the active component is selected from at least one of Pt, Ir, Au, Pd, and Rh. Preferably, the active component is Pt.

[0060] In a preferred embodiment of the present invention, based on the total mass of the catalyst being 100 wt%, the loading amount of the active component calculated as metal element is 0.1 wt%-1.0 wt%, more preferably 0.1 wt%-0.5 wt%.

[0061] In a preferred embodiment of the present invention, taking the total mass of the catalyst as 100wt%, the mass percentage of Sn metal element in the molecular sieve is 0.1wt%-5.0wt%, preferably 0.2wt%-4.0wt%, more preferably 0.2wt%-2.0wt%.

[0062] According to the present invention, the auxiliary agent component is selected from one or more of metal elements in Group IVA, metal elements in Group IA, and metal elements in Group IIA; in a preferred embodiment of the present invention, the auxiliary agent component is selected from at least one of alkali metal elements in Group IA and alkaline earth metal elements in Group IIA; preferably at least one of Li, Na, K, Rb, Cs, Mg, Ca, and Sr; and / or,

[0063] Taking the total mass of the catalyst as 100wt%, the loading amount of the auxiliary component is 0wt%-2.0wt%, preferably 0.1wt%-1.0wt%.

[0064] More preferably: taking the total mass of the catalyst as 100wt%, the mass percentage of Sn heteroatom metal elements in the molecular sieve is 0.1wt%-5.0wt%, preferably 0.2wt%-4.0wt%, more preferably 0.2wt%-2.0wt%, and further more preferably 0.3wt%-2.0wt%.

[0065] Based on the total mass of the catalyst, the sum of the mass percentages of the above-mentioned carrier, all active components and metal additive components is 100%.

[0066] In a preferred embodiment of the present invention, the morphology of the catalyst can present a two-dimensional spherical flower morphology of nanocrystal assembly under low temperature conditions of 120° C. (preferably hydrothermal conditions).

[0067] The second aspect of the present invention is to provide a method for preparing the catalyst described in the first aspect, comprising loading the active component source and the optional auxiliary component source on the carrier, and then obtaining the catalyst by calcination.

[0068] According to the present invention, the calcination conditions can be selected within a wide range. In a preferred embodiment of the present invention, the calcination conditions include: a temperature of 550-600° C., and / or a time of 4-6 hours.

[0069] In a preferred embodiment of the present invention, the loading method is to immerse the carrier in a solution containing the active component source and the auxiliary component source, and then remove the solvent; preferably,

[0070] The solution containing the active component source and the auxiliary component source is an aqueous solution; further preferably,

[0071] The active ingredient source is water-soluble; and / or,

[0072] The auxiliary component source is water-soluble.

[0073] Preferably, the amount of the active component source, the auxiliary agent group and the carrier is such that: based on the total mass of the catalyst as 100wt%, the loading amount of the active component in terms of metal element is 0.1wt%-1.0wt%, more preferably 0.1wt%-0.5wt%; the mass percentage of the Sn metal element in the molecular sieve is 0.1wt%-5.0wt%, preferably 0.2wt%-4.0wt%, more preferably 0.2wt%-2.0wt%; the loading amount of the auxiliary agent component is 0wt%2.0wt%, preferably 0.1wt%-1.0wt%.

[0074] As an example, more preferably, a more specific preparation method of one of the catalysts of the present invention comprises the following:

[0075] (a) the method for preparing the molecular sieve described above, to obtain the molecular sieve;

[0076] (b) Loading active components and additives: The active component noble metal Pt source and / or alkali metal additive K source are uniformly mixed by an excess impregnation method and loaded on the above molecular sieve carrier to prepare a catalyst.

[0077] According to the present invention, the step of preparing a propane dehydrogenation catalyst by loading the active component and the auxiliary metal component onto the MEL structure all-silicon molecular sieve containing Sn heteroatoms by an excess impregnation method in step (b) comprises the following steps:

[0078] (1) Taking the total mass of the catalyst as 100wt%, weigh the corresponding mass of the active component noble metal component Pt source and / or the alkali metal additive K source according to their respective mass percentage ratios, dissolve them in deionized water, stir and mix them evenly, add them to the above molecular sieve, and fully immerse them for a certain period of time so that the active metal components are fully dispersed on the surface of the molecular sieve;

[0079] (2) The impregnated molecular sieve sample is subjected to rotary evaporation to remove the solvent, drying and calcination in sequence to obtain the corresponding catalyst.

[0080] In a specific embodiment of the present invention, the active component precious metal Pt source in step (1) can be selected from platinum nitrate, platinum chloride, diammine platinum tetrachloride, tetraammine platinum nitrate, chloroplatinic acid, preferably chloroplatinic acid H2PtCl6·6H2O;

[0081] The alkali metal auxiliary agent K source in step (1) includes one of its nitrate, sulfate and chloride, preferably potassium chloride (KCl).

[0082] Further preferably, the amount of each raw material is used so that, based on the total weight percentage of the catalyst, the loading amount of the precious metal active component Pt is 0.1wt%-0.5wt% of the total mass of the catalyst; the loading amount of the alkali metal K additive is 0.1wt%-0.5wt% of the total mass of the catalyst; the mass percentage of the Sn metal element in the molecular sieve is 0.1wt%-5.0wt%, preferably 0.2wt%-4.0wt%, and more preferably 0.2wt%-2.0wt%.

[0083] The stirring conditions in step (1) include: a temperature of 20-30° C., a time of 10 to 30 min; and a stirring speed of 400-600 rpm relative to 10 g of the mixture system.

[0084] Preferably, during the immersion process, the temperature is 20-30° C. and the time is 4-6 hours.

[0085] The conditions for rotary evaporation in step (2) include: a water bath temperature of 70-80° C., a rotary speed of 120-150 rpm, and a vacuum degree of 75-65 mbar.

[0086] The drying conditions in step (2) include: a temperature of 80-120° C. and a drying time of 6 to 10 hours.

[0087] Preferably, the calcination conditions in step (2) include: temperature of 550-600°C, time of 4-6h, and heating rate of 1-2°C / min.

[0088] As mentioned above, preferably, the carrier is a MEL structure all-silicon molecular sieve containing Sn heteroatoms prepared by hydrothermal synthesis using an organic template and a synthetic auxiliary agent; the carrier presents a two-dimensional spherical flower morphology assembled by nanocrystals, with a grain size of 250-500nm and a specific surface area of ​​500m 2 / g or more, pore volume is 0.7cm 3 / g or above, and the pore volume ratio of mesopores to micropores is 2-5, and the pore sizes of intracrystalline micropores and intercrystalline mesopores are distributed in the range of 0.5-1.5nm and 2-8nm, respectively.

[0089] As mentioned above, preferably, in order to improve the dispersion of the active components of the catalyst, the particle size of the MEL structure all-silicon molecular sieve containing Sn heteroatoms is 250-500nm, more preferably 250-400nm.

[0090] As mentioned above, preferably, the specific surface area of ​​the MEL structure two-dimensional all-silicon molecular sieve is 500m 2 / g or more, more preferably a specific surface area of ​​500-700m 2 / g.

[0091] As mentioned above, preferably, the pore volume of the MEL structure two-dimensional all-silicon molecular sieve is 0.7 cm 3 / g or more, and the mesopore / micropore volume ratio is 1-8, and more preferably the pore volume is 0.7-1.0cm 3 / g, and the mesopore / micropore volume ratio is 1.5-5.

[0092] The third aspect of the present invention is to provide an application of the catalyst described in the first aspect or the catalyst obtained by the preparation method described in the second aspect in propane dehydrogenation catalysis.

[0093] Preferably, the application is a propane dehydrogenation method, comprising contacting propane with the catalyst, and carrying out a propane dehydrogenation reaction in a hydrogen atmosphere to obtain propylene.

[0094] As an example, preferably, the application includes: loading the catalyst into a reactor, diluting the reaction gas with H2, and performing a dehydrogenation reaction to obtain propylene; more preferably,

[0095] Propane gas mass space velocity is 1-50h -1, and / or, the feed pressure ratio of H2 to propane is 1:1-1:8, and / or, the dehydrogenation reaction temperature is 550-620°C.

[0096] Compared with the prior art, the present invention has the following beneficial effects:

[0097] (1) The catalyst provided by the present invention uses a MEL-structured all-silicon molecular sieve containing Sn heteroatoms as a carrier, and the Sn element is directly introduced into the molecular sieve framework. After the active components are loaded, the alloy formed by Pt and Sn can be better confined in the molecular sieve pores, effectively avoiding high-temperature migration and sintering, and enhancing the high-temperature stability of the catalyst.

[0098] (2) The molecular sieve carrier provided by the present invention is not only weakly acidic, but also can slow down the carbon deposition rate. At the same time, the addition of synthetic additives can effectively regulate the multi-level pore structure of the molecular sieve, shorten the gas diffusion path, increase the diffusion rate of propane and product propylene, solve the problem of rapid coking of microporous molecular sieves due to diffusion limitation, enhance catalytic activity, and improve the selectivity of the target product propylene.

[0099] (3) The catalyst provided by the present invention can present a unique two-dimensional spherical flower morphology structure under the action of a synthesis aid, thereby increasing the surface area and pore volume of the active components, improving the dispersion of the loaded active components, and increasing the contact area between the reaction gas and the active components, thereby improving the catalytic performance of propane dehydrogenation.

[0100] (4) When the catalyst provided by the present invention is used for the dehydrogenation of propane to produce propylene, it has excellent catalytic performance, high propylene selectivity, good stability, can effectively reduce the frequency of catalyst regeneration, improve production efficiency, and shows good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Figure 1 The XRD spectrum of the MEL structure all-silicon molecular sieve containing Sn heteroatom prepared in Example 1;

[0102] Figure 2 This is a graph showing the N2 physical adsorption-desorption curve of the molecular sieve prepared in Example 1;

[0103] Figure 3 This is a SEM image of the catalyst A1 prepared in Example 1;

[0104] Figure 4 This is a SEM image of the catalyst A4 prepared in Example 4;

[0105] Figure 5 This is the propane dehydrogenation performance diagram of catalyst A2 prepared in Example 2. DETAILED DESCRIPTION

[0106] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0107] The specific implementation modes of the present invention will be explained and described below. It should be understood that the description of the specific implementation modes below is only used to explain and describe the present invention, but not to limit the present invention.

[0108] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0109] Embodiment 1:

[0110] Synthesis of MEL structure all-silicon molecular sieve containing Sn atoms by hydrothermal method:

[0111] Weigh 44.84g of 25wt% TBAOH solution, 0.65g of hexadecyltrimethylammonium bromide, 0.17g of crystalline tin tetrachloride SnCl4·5H2O and 6.06g of deionized water respectively, mix them, stir evenly, then slowly add 37.54g of tetraethyl orthosilicate into the mixed solution, and continue stirring at room temperature for 12h to completely hydrolyze the tetraethyl silicate to form a uniform mixed gel in which the corresponding molar ratios of the substances are SiO2:TBAOH:CTAB:SnCl4:H2O=1:0.24:0.02:0.0025:12. The above gel solution was transferred into a 200 mL hydrothermal autoclave and crystallized at 160°C for 120 h. After cooling to room temperature, the crystallized product was centrifuged at 5000 rpm, washed with deionized water to pH = 7.5, and then dried at 120°C for 8 h. Finally, it was calcined at 580°C for 6 hours. After crushing and grinding, a MEL structure all-silicon molecular sieve containing Sn heteroatoms was obtained, which was recorded as Sn-MEL-1.

[0112] The phase structure and N2 physical adsorption-desorption curves of the molecular sieve samples are shown in Figure 1 and Figure 2 .from Figure 1 It can be seen that the synthesized molecular sieve has a typical MEL structure and good crystallinity; Figure 2It is a typical IV type adsorption isotherm, and the hysteresis loop in the range of P / P0=0.4-0.9 proves the distribution characteristics of multi-level pores in the molecular sieve crystal. According to the DFT model calculation, the micropore size distribution is 0.5-1.0nm, and the multi-level mesopores between crystals are distributed in 2-10nm.

[0113] Impregnation of active components and additives: Accurately measure 5.7 mL of a 0.019 M aqueous solution of chloroplatinic acid prepared in advance, add it to the above 7.0 g Sn-MEL-1 molecular sieve, stir at room temperature and 500 rpm to fully impregnate it, and keep the impregnation time for 4 hours. The impregnated sample is evacuated (vacuum degree 72 mbar) on a rotary evaporator at a water bath temperature of 70°C and a speed of 120 rpm to remove the solvent, placed in a drying oven at 100°C for 8 hours, and moved into a muffle furnace at 580°C for calcination for 6 hours to obtain a catalyst Pt / Sn-MEL-1 containing a two-dimensional all-silicon molecular sieve with a Sn heteroatom structure loaded with Pt, which is recorded as catalyst A1. Based on the total mass of the catalyst, the mass percentage of each metal component is Pt: 0.3wt%, Sn: 0.5wt%.

[0114] The SEM image of catalyst A1 is shown in Figure 3 As can be seen from the figure, the morphology of the catalyst presents an ellipsoidal morphology assembled by nanorod-like microcrystals, and the statistical grain size is between 250-300nm.

[0115] Embodiment 2:

[0116] The preparation method and conditions of the MEL structure all-silicon molecular sieve containing Sn atoms are the same as those in Example 1. The difference is that the amount of raw materials is adjusted so that SiO2:TBAOH:CTAB:SnCl4:H2O=1:0.24:0.02:0.005:12, and the Sn-MEL-2 molecular sieve is prepared.

[0117] Impregnation of active components and additives: Accurately measure 5.7 mL of a 0.019 M chloroplatinic acid aqueous solution prepared in advance, and weigh 0.068 g of potassium chloride, dissolve in 10 mL of deionized water, and stir thoroughly to mix evenly; add the mixed solution to the molecular sieve, stir thoroughly at room temperature and 500 rpm, impregnate evenly, and keep the impregnation time for 4 hours. The impregnated sample was vacuumed (vacuum degree 72 mbar) on a rotary evaporator at a water bath temperature of 70 ° C and a speed of 120 rpm to remove the solvent, placed in a drying oven at 100 ° C for 8 hours, and moved into a muffle furnace at 580 ° C for calcination for 6 hours to obtain the catalyst PtK / Sn-MEL-2 corresponding to the molecular sieve loaded with Pt and K metals, recorded as catalyst A2. Based on the total mass of the catalyst, the mass percentage of each metal component is Pt: 0.5wt%, Sn: 1.0wt%, K: 0.5wt%.

[0118] Embodiment 3:

[0119] The preparation method and conditions of the MEL structure all-silicon molecular sieve containing Sn atoms are the same as those in Example 1. The difference is that the amount of raw materials is adjusted so that SiO2:TBAOH:CTAB:SnCl4:H2O=1:0.24:0.05:0.005:20, and the Sn-MEL-3 molecular sieve is prepared.

[0120] Impregnation of active components and additives: The preparation method and conditions are the same as those in Example 2, except that, based on the total mass of the catalyst, the mass percentage of each metal component is Pt: 0.5wt%, Sn: 1.0wt%, K: 0.5wt%; the catalyst PtK / Sn-MEL-3 is obtained, which is recorded as catalyst A3.

[0121] Embodiment 4:

[0122] The preparation method and conditions of the MEL structure all-silicon molecular sieve containing Sn atoms are the same as those in Example 1. The difference is that the hydrothermal treatment temperature is 120°C, and the amount of raw materials is adjusted so that the molar ratio of each component is SiO2:TBAOH:CTAB:SnCl4:H2O=1:0.24:0.02:0.005:12, and the Sn-MEL-4 molecular sieve is prepared.

[0123] Impregnation of active components and additives: The preparation method and conditions are the same as those in Example 2, except that, based on the total mass of the catalyst, the mass percentage of each metal component is Pt: 0.5wt%, Sn: 1.0wt%, K: 0.5wt%; the corresponding molecular sieve loaded Pt catalyst Pt / Sn-MEL-4 is obtained, recorded as catalyst A4.

[0124] The SEM image of catalyst A4 is shown in Figure 4 As can be seen from the figure, the catalyst presents a unique two-dimensional spherical flower morphology assembled by nano-sheet microcrystals, and the statistical grain size is 250-300nm.

[0125] Embodiment 5:

[0126] The preparation method and conditions of the MEL structure all-silicon molecular sieve containing Sn atoms are the same as those in Example 2.

[0127] Impregnation of active components and additives: The preparation method and conditions are the same as those in Example 2, except that 0.0408 g of potassium chloride is added, and the mass percentage of each metal component, based on the total mass of the catalyst, is Pt: 0.3wt%, Sn: 1.0wt%, K: 0.3wt%; the catalyst PtK / Sn-MEL-2 with corresponding molecular sieve loaded with Pt and K is obtained, recorded as catalyst A5.

[0128] Comparative Example 1:

[0129] The MEL structure all-silicon molecular sieve without Sn atoms was prepared by hydrothermal method. Referring to the preparation method of the embodiment, the silicon source, organic template, synthesis auxiliary agent and water were stirred evenly to form a mixed gel with the corresponding molar ratio of each substance being SiO2:TBAOH:CTAB:H2O=1:0.24:0.05:12. The above gel solution was transferred into a 200mL hydrothermal kettle and crystallized at 120°C for 120h; the crystallized product was centrifuged at 5000rpm, washed with deionized water to pH=7.5, and then dried at 120°C for 8h, and finally roasted at 580°C for 6 hours, and the corresponding molecular sieve was obtained after crushing and grinding, which was recorded as MEL-5.

[0130] Impregnation of active components and additives: Accurately measure 8.5 mL of a 0.019 M aqueous solution of chloroplatinic acid prepared in advance, and dissolve 0.34 g of crystalline tin tetrachloride and 0.068 g of potassium chloride in deionized water, mix and stir evenly; then add the solution to the above-mentioned MEL-5 molecular sieve and fully impregnate for 4 hours. Then, the impregnated sample is vacuumed (vacuum degree 72 mbar) on a rotary evaporator with a water bath temperature of 70°C and a rotation speed of 120 rpm to remove the solvent, placed in a drying oven at 100°C for 8 hours, and moved into a muffle furnace at 580°C for calcination for 6 hours to obtain the corresponding molecular sieve loaded with Pt catalyst PtSnK / MEL-5, recorded as catalyst D1. Based on the total mass of the catalyst, the mass percentage of each metal component is Pt: 0.5wt%, Sn: 1.0wt%, K: 0.5wt%.

[0131] Comparative Example 2:

[0132] By using the over-impregnation method, referring to the preparation method in comparative example 1, the mixed solution of the active component Pt, the auxiliary agent Sn, and the auxiliary agent K component was co-impregnated on a commercially purchased high-silicon ZSM-11 molecular sieve (structure silicon-aluminum ratio of 44), stirred at room temperature and 500rpm to fully impregnate, and the impregnation time was maintained for 4h. The impregnated sample was evacuated (vacuum degree 72mbar) on a rotary evaporator at a water bath temperature of 70°C and a rotation speed of 120rpm to remove the solvent, placed in a drying oven at 100°C for 8h, and moved into a muffle furnace at 580°C for calcination for 6h to obtain a commercially available ZSM-11 molecular sieve-loaded PtSnK / ZSM-11 catalyst, recorded as catalyst D2. Based on the total mass of the catalyst, the mass percentage of each metal component is Pt: 0.5wt%, Sn: 1.0wt%, K: 0.5wt%.

[0133] Comparative Example 3:

[0134] By using the over-impregnation method, referring to the preparation method in comparative example 1, the active component Pt, the auxiliary agent Sn, and the auxiliary agent K component are co-impregnated on the traditional γ-Al2O3 carrier, stirred at room temperature and 500rpm to fully impregnate, and the impregnation time is maintained for 4h. The impregnated sample is evacuated (vacuum degree 72mbar) on a rotary evaporator at a water bath temperature of 70°C and a rotation speed of 120rpm to remove the solvent, placed in a drying oven at 100°C for 8h, and moved into a muffle furnace at 580°C for calcination for 6h to obtain a γ-Al2O3-loaded PtSnK catalyst, recorded as catalyst D3. Based on the total mass of the catalyst, the mass percentage of each metal component is Pt: 0.5wt%, Sn: 1.0wt%, K: 0.5wt%.

[0135] Test Example 1:

[0136] The physical structure of the MEL structure all-silicon molecular sieve containing Sn heteroatom in the above Examples 1-5 was analyzed by using an X-ray diffractometer model D8Advance of Bruker AXS Company of Germany. For details, see Figure 1 The N2 physical adsorption-desorption curves of the molecular sieve samples in Examples 1-5 were measured on a fully automatic adsorption instrument of model AutosorbiQ produced by Quantachrome Corporation of the United States. The calculation results of the specific surface area, pore volume and average pore diameter of the molecular sieve carrier samples in each catalyst in Examples 1-5 and Comparative Examples 1-3 are shown in Table 1.

[0137] Table 1:

[0138]

[0139] In Table 1, S Micro Refers to the micropore specific surface area of ​​the molecular sieve carrier used in the synthesis of each catalyst; S Ext Refers to the external specific surface area of ​​the synthetic molecular sieve; S BET Refers to the total specific surface area of ​​the synthetic molecular sieve; V Micro Refers to the micropore volume of synthetic molecular sieve; V meso Refers to the mesopore volume of the synthetic molecular sieve; V Total Refers to the total pore volume.

[0140] Test Example 2:

[0141] The catalysts in Examples 1-5 were analyzed by scanning electron microscopy using a Hitachi S-4800 cold field emission scanning electron microscope. Figure 3 ; Transmission electron microscopy analysis of each catalyst was carried out on a Tecnai20 model from FEI of the Netherlands, for example, see Figure 4The percentage of metal elements in each catalyst was determined by using a ThermoFiSheriCAPTQ ICP-MS inductively coupled plasma mass spectrometer.

[0142] Test Example 3:

[0143] The catalyst of the present invention was tested and evaluated in a constant temperature micro fixed bed reactor. The evaluation conditions were as follows: about 0.5 g of the catalyst was mixed with 10 g of quartz sand in sections and loaded into a quartz tube reactor with an inner diameter of Ф=10 mm. The reaction pressure was normal pressure, the reaction gas was diluted with H2, and the propane gas mass space velocity was 3 h -1 The feed pressure ratio of H2 to propane is 1:4, and the reaction temperature is 550°C-600°C; the product distribution is analyzed by Agilent 7890A gas chromatography.

[0144]

[0145]

[0146] The propane dehydrogenation performance evaluation results of each catalyst in the above Examples 1-5 and Comparative Examples 1-3 are shown in Table 2. Table 2 shows the propane conversion rate and propylene selectivity after 10 hours of catalytic reaction. Combining the reaction performance in Table 1 and Table 2, it can be obtained that after adding CTAB, the catalyst has good propane dehydrogenation activity and high propylene selectivity in the range of mesopore / micropore ratio of 2.0-5.0. The propane dehydrogenation performance of catalyst A2 in Example 2 is shown in the figure Figure 5 ,It can be seen from the figure that the catalyst still maintains good stability after 20 hours of continuous reaction.

[0147] After testing, the catalysts obtained in Example 1 and Examples 3-5 also have similar catalytic stability as that of Example 2.

[0148] Table 2:

[0149] catalyst Reaction time (h) Propane conversion rate / (%) Propylene selectivity / (%) A1 10 31.2 98.1 A2 10 29.5 97.4 A3 10 30.5 97.6 A4 10 26.8 97.2 A5 10 28.7 97.4 D1 10 20.2 97.3 D2 10 42.5 19.0 D3 10 36.3 90.2

[0150] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

[0151] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

[0152] All publications, patent applications, patents and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings conventionally understood by those skilled in the art. In the event of a conflict, the definition in this specification shall prevail.

[0153] When this specification uses the prefix "well-known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, etc., the objects introduced by the prefix cover those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as being suitable for similar purposes.

[0154] The endpoints and any values ​​of the scope disclosed in the present application document are not limited to the precise scope or value, and these scopes or values ​​should be understood to include values ​​close to these scopes or values. For numerical ranges, between the endpoint values ​​of each scope, between the endpoint values ​​of each scope and a separate point value, and between separate point values, one or more new numerical ranges can be combined with each other, and these numerical ranges should be considered as specifically disclosed in this article. Hereinafter, in principle, each technical solution can be combined with each other to obtain a new technical solution, which should also be considered as specifically disclosed in this article.

[0155] In the context of the present specification, any matters or items not mentioned are directly applicable to those known in the art without any changes except those explicitly stated.

[0156] Moreover, any embodiment described in this document may be freely combined with one or more other embodiments described in this document, and the technical solutions or technical ideas formed thereby are deemed to be part of the original disclosure or original record of the present invention, and should not be regarded as new content that has not been disclosed or anticipated in this document, unless a person skilled in the art considers that the combination is obviously unreasonable.

Claims

1. A catalyst comprising a carrier and an active component supported on the carrier and an optional auxiliary component, wherein the active component is selected from at least one of the noble metal elements of Group VIII; and the auxiliary component is selected from one or more of the metal elements of Group IVA, the alkali metal elements of Group IA, and the alkaline earth metal elements of Group IIA; in, The carrier is a molecular sieve with a MEL structure containing Sn heteroatoms.

2. The catalyst according to claim 1, characterized in that: The molecular sieve has a crystal size of 250-500 nm and a specific surface area of ​​500 m 2 / g or more, pore volume is 0.70cm 3 / g or more, and the mesopore / micropore volume ratio is 1-8, and the molecular sieve contains Sn metal element; preferably, the molecular sieve has at least one of the following characteristics: The specific surface area of ​​the molecular sieve is 500-800m 2 / g; and / or, The pore volume of the molecular sieve is 0.7-1.0 cm 3 / g; and / or, The mesopore / micropore volume ratio is 1.5-5; and / or, The intracrystalline micropores are distributed in the range of 0.4-2nm, preferably 0.5-1.5nm, and the intercrystalline mesopores are distributed in the range of 2-10nm; External surface area is 150-400m 2 / g.

3. The catalyst according to claim 1, characterized in that: The molecular sieve is an all-silicon molecular sieve of MEL structure containing Sn heteroatom; and / or, The molecular sieve can present a two-dimensional spherical flower morphology of nano-thin sheet microcrystal assembly under the condition of 120°C.

4. The catalyst according to claim 1, characterized in that The molecular sieve is prepared by the following method: the molecular sieve preparation method comprises subjecting a mixture containing a silicon source, an organic template, a synthesis auxiliary agent, a Sn source and water to a hydrothermal reaction, followed by solid-liquid separation, optional washing, optional drying, and calcination to obtain the molecular sieve; Wherein, the organic template is a small molecule quaternary ammonium salt, and the synthesis auxiliary agent is a long-chain quaternary ammonium salt with more than 10 carbon atoms.

5. The catalyst according to claim 4, characterized in that The preparation method of the molecular sieve comprises the following steps: (1) mixing a silicon source, an organic template, a synthesis aid, a Sn source and water to form a mixed gel; (2) subjecting the mixed gel to a hydrothermal reaction to obtain a reaction mixture; (3) After the reaction mixture is cooled, solid-liquid separation, optional washing, optional drying, and calcination are performed to obtain the molecular sieve.

6. The catalyst according to claim 4, characterized in that: The silicon source is at least one of tetraethyl orthosilicate, tetraethyl orthosilicate, tetraethyl silicate-28, tetraethyl silicate-40, silica gel, and silica sol, preferably at least one of tetraethyl orthosilicate, tetraethyl orthosilicate, tetraethyl silicate-28, and tetraethyl silicate-40; and / or, The organic template is selected from one or more of tetrabutylammonium hydroxide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium fluoride and cyclohexylamine; and / or, The synthesis auxiliary agent is selected from at least one of dodecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide; and / or, The Sn source is at least one of the salts containing Sn element.

7. The catalyst according to claim 4, characterized in that: The molar ratio of the silicon source calculated as SiO2 to the organic template, the synthesis auxiliary agent, the Sn source and water is 1:(0.10.8):(0.005-0.4):(0.0005-0.025):(5-50), preferably 1:(0.10.5):(0.005-0.2):(0.001-0.02):(10-40); more preferably 1:(0.15-0.45):(0.01-0.1):(0.001-0.01):(10-30).

8. The catalyst according to claim 5, characterized in that: In the preparation method of the molecular sieve: The mixing conditions in step (1) include: a temperature of 20-30° C. and a time of 3-12 h; preferably, a stirring speed of 400-600 rpm relative to 10 g of the mixture system; and / or, The conditions of the hydrothermal reaction treatment include: a temperature of 120-190° C., preferably 120-180° C., and / or a time of 36-150 h; and / or, The calcination conditions include: a temperature of 500-600° C., preferably 550-580° C.; and / or a calcination time of 4-6 hours.

9. The catalyst according to any one of claims 1 to 8, characterized in that: The active component is selected from at least one of Pt, Ir, Au, Pd and Rh. Preferably, the active component is Pt; and / or, Based on the total mass of the catalyst as 100wt%, the loading amount of the active component calculated as the metal element is 0.1wt%-1.0wt%, more preferably 0.1wt%-0.5wt%; and / or, Taking the total mass of the catalyst as 100wt%, the mass percentage of Sn metal element in the molecular sieve is 0.1wt%-5.0wt%, preferably 0.2wt%-4.0wt%, more preferably 0.2wt%-2.0wt%; and / or, The auxiliary agent component is selected from at least one of the alkali metal elements of Group IA and the alkaline earth metal elements of Group IIA; preferably at least one of Li, Na, K, Rb, Cs, Mg, Ca, and Sr; and / or, Taking the total mass of the catalyst as 100wt%, the loading amount of the auxiliary component is 0wt%-2.0wt%, preferably 0.1wt%-1.0wt%; and / or, The morphology of the catalyst can present a two-dimensional spherical flower morphology of nano-crystal assembly under the condition of 120°C.

10. A method for preparing the catalyst according to any one of claims 1 to 9, comprising loading the active component source and the optional auxiliary component source on the carrier, and then calcining to obtain the catalyst.

11. The preparation method according to claim 10, characterized in that: The calcination conditions include: a temperature of 550-600°C, and / or a time of 4-6 hours; and / or, The loading method is to immerse the carrier in a solution containing the active component source and the auxiliary component source, and then remove the solvent; preferably, The solution containing the active component source and the auxiliary component source is an aqueous solution; further preferably, The active ingredient source is water-soluble; and / or, The auxiliary component source is water-soluble.

12. Use of the catalyst according to any one of claims 1 to 9 or the catalyst obtained by the preparation method according to any one of claims 10 to 11 in propane dehydrogenation catalysis.

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