A small-grain pt / SAPO-11 catalyst, a preparation method and application thereof in catalyzing long-chain alkane hydrogen isomerization

Abstract

The application relates to a small-grain Pt / SAPO-11 catalyst, a preparation method and application of the catalyst in catalyzing long-chain alkane hydrogen isomerization. An initial gel is prepared by mixing an aluminum source, a phosphorus source, a silicon source, a template agent and a mineralizer in an ethylene glycol solvent system; the initial gel is subjected to hydrothermal crystallization, washing, drying and calcination to obtain an SAPO-11 molecular sieve primary product; the SAPO-11 molecular sieve primary product is subjected to mild acid treatment to obtain an SAPO-11 molecular sieve; finally, the SAPO-11 molecular sieve is subjected to an equal-volume impregnation method to load platinum, and is subjected to drying and calcination to obtain a final catalyst. Through the synergistic effect of ethylene glycol solvothermal treatment, ammonium fluoride mineralization and acid treatment, the SAPO-11 carrier with small grain size, large specific surface area and micropore-mesopore multi-level structure is prepared. The obtained Pt / SAPO-11 catalyst is used for long-chain alkane hydrogen isomerization reaction, and exhibits extremely high conversion rate and excellent isomerization selectivity in n-dodecane conversion, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of catalytic chemical technology, and particularly relates to a small-crystal Pt / SAPO-11 catalyst, its preparation method, and its application in the catalytic hydroisomerization of long-chain alkanes. Background Technology

[0002] Hydroisomerization of alkanes is a key reaction in petroleum refining and biofuel upgrading. Converting straight-chain alkanes into branched isomers can significantly lower the pour point of lubricating oils, improve the low-temperature fluidity of diesel fuel, and increase the octane number of gasoline. It is also a core step in the preparation of aviation kerosene from oil-based feedstocks. In this reaction, the design of a bifunctional catalyst is crucial: the metal center is responsible for the dehydrogenation and hydrogenation of alkanes, while the acidic support is responsible for the skeletal isomerization of intermediate olefins. The synergistic matching of these two catalysts in terms of space and activity directly determines the efficiency and selectivity of the reaction.

[0003] SAPO-11 molecular sieves are considered one of the ideal acidic supports for the hydroisomerization of long-chain alkanes due to their unique AEL topology (ten-membered elliptical ring straight channels with pore sizes of 0.39 nm × 0.63 nm) and moderate acid strength. Compared with molecular sieves such as ZSM-5 and ZSM-22, SAPO-11 has moderate acid strength, which can effectively catalyze isomerization reactions without inducing excessive cracking side reactions. Pt / SAPO-11 bifunctional catalysts formed by supporting noble metals such as platinum have been widely used in the field of n-alkane hydroisomerization, and their catalytic performance is closely related to the crystallite size, pore structure, and acidity distribution of the molecular sieve.

[0004] Synthesized SAPO-11 crystals are typically on the micrometer scale, with micropores as the main pore structure and a limited external surface area. When processing long-chain n-alkanes, the diffusion resistance of macromolecules within the micropores increases significantly, making it difficult for reactants to fully reach acidic sites and for products to be extracted in a timely manner. This results in limited isomerization and intensified secondary cracking. Reducing the crystal size is an effective way to solve this problem—smaller crystals mean a larger external surface area and more acidic sites at the pore openings, which can significantly shorten the diffusion path and improve the accessibility of active sites.

[0005] Existing fine-graining strategies, such as introducing special template agents or surfactants, using segmented crystallization, adding seed crystals or growth inhibitors, are either complex and costly, or they adversely affect the acidity of the molecular sieve while reducing the grain size, making it difficult to achieve good synergistic control between grain size and acidity characteristics. Summary of the Invention

[0006] The technical problem solved by this invention is as follows: In the preparation of SAPO-11 molecular sieves, the conventional hydrothermal synthesis method yields large crystal sizes (micrometer scale), which significantly restricts the diffusion of long-chain alkane molecules through the micropores and limits the acidic sites accessible to reactants, resulting in low conversion and selectivity in the hydroisomerization reaction. Existing strategies for refining crystals (such as using special templates, additives, or complex processes) are costly, complex, or may damage the acidic properties of the molecular sieve, making it difficult to balance crystal refinement with acidity retention.

[0007] To address the technical problems existing in the prior art, this invention designs a small-crystal Pt / SAPO-11 catalyst, its preparation method, and its application in the catalytic hydroisomerization of long-chain alkanes. The core idea is to achieve effective refinement of SAPO-11 crystallites while maintaining their acidic characteristics through systematic optimization of synthesis conditions, without relying on expensive template agents and complex post-treatment. Based on this, a Pt / SAPO-11 catalyst with both high activity and high selectivity in the hydroisomerization reaction of long-chain alkanes is prepared.

[0008] It should be noted that, in this invention, unless otherwise specified, the specific meaning of "comprising" in relation to composition definition and description includes both open-ended meanings such as "comprising," "including," etc., and closed-ended meanings such as "composed of," etc., and similar meanings.

[0009] To solve the aforementioned technical problems, the present invention adopts the following solution:

[0010] [First technical solution]

[0011] A small-crystal Pt / SAPO-11 catalyst, comprising a support and an active metal, wherein the active metal is supported on the surface and in the pore structure of the support, the support being a SAPO-11 molecular sieve, and the active metal being Pt.

[0012] Furthermore, the preparation method of the aforementioned SAPO-11 molecular sieve includes the following steps:

[0013] S1: Mix and stir the aluminum source, phosphorus source, silicon source, template agent, and alcohol to obtain a mixture;

[0014] S2: Add the mineralizer to the above mixture to obtain the initial gel;

[0015] S3: The initial gel obtained in S2 is subjected to a crystallization reaction to obtain the crystallized product;

[0016] S4: The crystallized product is washed, separated, dried, and calcined to obtain the initial product of SAPO-11 molecular sieve;

[0017] S5: Disperse the SAPO-11 molecular sieve primary product uniformly in an acid solution;

[0018] S6: The acid solution containing the initial product of SAPO-11 molecular sieve was placed in a constant temperature water bath and heated while being stirred continuously to obtain acid-treated SAPO-11 molecular sieve.

[0019] S7: Wash, dry, and calcine the acid-treated SAPO-11 molecular sieve to obtain the SAPO-11 molecular sieve.

[0020] Further, in step S1, the molar ratio of aluminum source, phosphorus source, silicon source, template agent, alcohol, and mineralizer is 1:(1-1.8):(0.2-0.4):(1.8-5):(50-60):(0.1-0.3), wherein the aluminum source is calculated as alumina, the phosphorus source as phosphorus oxide, and the silicon source as silicon dioxide;

[0021] Furthermore, in step S1, the aluminum source is selected from at least one of boehmite, aluminum isopropoxide, aluminum sulfate, and boehmite.

[0022] The phosphorus source is selected from at least one of phosphoric acid, phosphorous acid, and hypophosphoric acid;

[0023] The silicon source is selected from at least one of tetraethyl orthosilicate, silicon dioxide, and acidic silica sol;

[0024] The template agent is selected from at least two of di-n-propylamine, diisopropylamine, dimethylamine, and diethylamine;

[0025] Ethylene glycol is selected as the alcohol.

[0026] In step S2, ammonium fluoride is selected as the mineralizing agent.

[0027] Furthermore, in step S3, the initial gel crystallization temperature is 190-200℃, and the crystallization time is 72-120h;

[0028] In step S4, the crystallized product is washed until pH=7, calcined at 550-650℃ for 4-10 hours.

[0029] Furthermore, in step S5, the concentration of the acid solution in the acid treatment is 0.1-0.5 mol / L, and the volume of the acid solution is 20 times the mass of the SAPO-11 molecular sieve.

[0030] In step S6, the constant temperature water bath temperature is 40-70℃, and the heating time is 1-4 hours.

[0031] Furthermore, in step S7, the acid-treated SAPO-11 molecular sieve is washed to pH=7 and then subjected to subsequent drying treatment.

[0032] The roasting temperature is 550-650℃ and the roasting time is 4-6 hours.

[0033] In this invention, ethylene glycol is selected as the alcohol substance to replace water in the traditional molecular sieve crystallization reaction and serve as the solvent for the mixture in step S1. By changing the dielectric constant, viscosity and dissolution / transport behavior of the solvent on silicon and aluminum species, the crystallization kinetics are controlled, thereby obtaining a product with higher silicon content, larger specific surface area and smaller grains.

[0034] In this invention, ammonium fluoride is selected as the mineralizing agent to accelerate the entire crystallization reaction, reduce the crystallization time, and directly obtain H-type SAPO-11 molecular sieve after calcination.

[0035] In step S4 of this invention, there are no specific limitations on the drying temperature and time of the crystallized product obtained after washing and separation; the drying effect on the product is the determining factor. In specific embodiments, a drying temperature of 60–120°C and a drying time of 12–24 hours can generally be selected.

[0036] In step S7 of this invention, there are no special limitations on the subsequent drying temperature and time; the treatment effect on the product is the primary consideration. In specific embodiments, a temperature of 60-120°C and a drying time of 6-12 hours are generally selected.

[0037] In this invention, the acid solution mentioned in step S5 is generally an organic acid solution, such as oxalic acid or citric acid.

[0038] [Second Technical Solution]

[0039] A method for preparing the above-mentioned small-crystal Pt / SAPO-11 catalyst includes the following steps:

[0040] Step 1: Prepare an aqueous solution containing active metal according to the content of active metal in small-crystal Pt / SAPO-11 catalyst;

[0041] Step 2: The support is uniformly impregnated in the aqueous solution containing the active metal described in Step 1 using the equal volume impregnation method to obtain the initial catalyst supported on the active metal.

[0042] Step 3: Aging the initial catalyst obtained in Step 2 at room temperature;

[0043] Step 4: Dry and calcine the catalyst aged in Step 3 to obtain the small-crystal Pt / SAPO-11 catalyst.

[0044] Furthermore, in step 1, the active metal is Pt, and the content of the active metal in the catalyst is 0.1wt%-1wt%.

[0045] In step 3, the aging time of the initial catalyst is 6-12 hours.

[0046] In step 4, the calcination temperature of the aged catalyst is 450-550℃, and the calcination time is 4-6h.

[0047] In this invention, there are no particular limitations on the drying temperature and time of the aged catalyst in step 4. The drying effect on the product shall prevail. In specific embodiments, 80-120℃ and 8-12h are generally selected.

[0048] The mechanism by which this invention successfully prepares small-crystal SAPO-11 catalysts is as follows:

[0049] The core mechanism by which this invention achieves successful preparation of small-crystal SAPO-11 lies in the synergistic effect of "solvent effect" and "mineralization promotion".

[0050] First, ethylene glycol, as a solvent, alters the dissolution, polymerization, and transport behavior of silicon and aluminum species in traditional hydrothermal systems due to its high viscosity and different dielectric constant. This increases the nucleation density in the system and inhibits further growth of crystal nuclei, thereby fundamentally controlling the grain size.

[0051] Secondly, the introduction of ammonium fluoride, which decomposes to produce F... - It can not only accelerate the mineralization of silicon and aluminum species and shorten the crystallization induction period, but also competitively participate in the construction of molecular sieve framework, improve the uniformity of silicon distribution in the framework, and thus ensure the integrity of the framework structure and high crystallinity while rapidly crystallizing.

[0052] The unique and excellent mechanism of the small-crystal SAPO-11 catalyst of this invention lies in:

[0053] The mechanism by which the catalyst of this invention exhibits excellent performance in hydroisomerization reactions can be attributed to a high degree of matching between diffusion and reaction.

[0054] The hierarchical porous structure constructed by small crystallites and acid treatment greatly shortens the diffusion path of long-chain alkane molecules in the micropores and provides mesopores as "fast channels", enabling reactant molecules to quickly reach the acidic sites near the pore opening and surface for skeletal isomerization. At the same time, the larger isomers generated can also be desorbed quickly, avoiding secondary cracking caused by prolonged retention in the micropores.

[0055] This improved diffusion performance, coupled with the moderate acid strength of the SAPO-11 molecular sieve itself, maximizes the enhancement of the isomerization reaction pathway, thereby maintaining extremely high selectivity for isoalkanes even at high conversion rates.

[0056] Meanwhile, by selectively removing non-framework aluminum and impurities from the surface and pores of SAPO-11 molecular sieve crystals using dilute acid, not only are the blocked micropores cleared, but slight etching is also formed on the crystal surface and near-surface region, constructing a mesoporous structure. This exposes more previously covered acidic sites and significantly improves the diffusion and mass transfer efficiency of molecules in the microporous system by eliminating barriers.

[0057] [Third technical solution]

[0058] A third aspect of the invention provides the use of the aforementioned small-crystal Pt / SAPO-11 catalyst in the hydroisomerization of long-chain alkanes to prepare isoalkanes:

[0059] Generally, in the hydrogenation isomerization of long-chain alkanes to prepare isoalkanes, the reaction temperature is 280-360℃, the reaction pressure is 2-4 MPa, and the mass hourly space velocity (WHSV) is 1.5-6 h⁻¹. -1 The volume ratio of hydrogen to raw materials is (600-1000):1.

[0060] When the catalyst of this invention is applied, the hydrogenation isomerization reaction of long-chain alkanes exhibits high conversion rate and high selectivity for isomeric alkanes.

[0061] This invention provides a small-crystal Pt / SAPO-11 catalyst, its preparation method, and its application in the catalytic hydroisomerization of long-chain alkanes, which has the following beneficial effects:

[0062] 1. This invention uses ethylene glycol instead of traditional water for solvothermal synthesis of SAPO-11 molecular sieves. By changing the dielectric constant, viscosity, and dissolution and transport behavior of silicon and aluminum species of the solvent, crystallization kinetics are controlled, thereby obtaining products with higher silicon content, larger specific surface area, and smaller crystallites.

[0063] 2. This invention introduces ammonium fluoride, a mineralizing agent, into the solvothermal synthesis process of SAPO-11, which significantly accelerates the crystallization time, improves the degree of crystallization, and reduces the prolonged crystallization time caused by ethylene glycol replacing water as the solvent. Furthermore, F... - It can improve the distribution of silicon in the molecular sieve framework and enhance the hydrothermal stability of the molecular sieve.

[0064] 3. This invention modifies the solvothermal synthesized SAPO-11 molecular sieve by acid treatment, dissolving the aluminum and amorphous substances outside the framework that block the micropores, exposing more pores to participate in isomerization reactions, modulating Brønsted acidity, and gently etching to form a microporous-mesoporous multi-level structure, which significantly improves the diffusion and mass transfer of long-chain alkanes.

[0065] 4. The Pt / SAPO-11 catalyst prepared by this invention has excellent catalytic performance. After being loaded with Pt, it exhibits high conversion and high selectivity for isoalkanes in the hydrogenation isomerization reaction of n-dodecane. The isomerization yield is significantly better than that of the comparative example, demonstrating the dual advantages of high activity and high selectivity.

[0066] In summary, through systematic optimization of synthesis conditions, this invention achieves effective refinement of SAPO-11 crystals and preservation of acidic characteristics without relying on expensive template agents and complex post-processing. Based on this, a Pt / SAPO-11 catalyst with both high activity and high selectivity in the hydroisomerization reaction of long-chain alkanes is prepared. Attached Figure Description

[0067] Figure 1 : XRD patterns of SAPO-11 molecular sieves in Examples 1-2 and Comparative Examples 1-2 of the present invention;

[0068] Figure 2 : XRD patterns of SAPO-11 molecular sieves from Examples 7-8 of this invention. Detailed Implementation

[0069] The present invention will be further described below with reference to specific embodiments and accompanying drawings:

[0070] Example 1

[0071] The preparation method of small-crystal Pt / SAPO-11 catalyst and its application in catalyzing the hydroisomerization of long-chain alkanes specifically includes the following steps:

[0072] (1) Preparation of SAPO-11 molecular sieve:

[0073] Taking the initial gel with a molar ratio of aluminum source, phosphorus source, silicon source, template agent, alcohol, and mineralizer of 1:1.8:0.4:5:55:0.1 as an example, the aluminum source, phosphorus source, and silicon source are aluminum isopropoxide, phosphoric acid, and tetraethyl orthosilicate, respectively. The template agent is di-n-propylamine and diisopropylamine (the molar ratio of the two is 1:1). The alcohol is ethylene glycol, and the mineralizer is ammonium fluoride. According to the synthesis steps, each raw material is added to the gel in sequence, and after thorough stirring, it is crystallized at 200℃ for 96 hours.

[0074] The crystallized product was filtered and washed with deionized water until pH=7, and then dried in an oven at 120℃ for 12h. The dried solid was ground into a fine powder and calcined in a muffle furnace under air atmosphere at 550℃ for 6h at a heating rate of 5℃ / min.

[0075] The calcined SAPO-11 molecular sieve was poured into a 0.3 mol / L oxalic acid solution (the volume of the acid solution was 20 times the mass of the SAPO-11 molecular sieve), sonicated for 0.5 h, and then heated in a 60℃ constant temperature water bath for 1 h. During the heating process, magnetic stirring was used at a speed of 600 r / min.

[0076] The acid-treated SAPO-11 molecular sieve was filtered and washed with deionized water until pH=7, and then dried in an oven at 100℃ for 8 hours. The dried solid was ground into a fine powder and calcined in a muffle furnace under air atmosphere at 550℃ for 4 hours at a heating rate of 5℃ / min.

[0077] (2) Preparation of Pt / SAPO-11 catalyst:

[0078] The prepared chloroplatinic acid aqueous solution was uniformly added to the SAPO-11 molecular sieve using the equal volume impregnation method, and the impregnation was ensured to be uniform by ultrasonication and grinding. The loading of Pt was 0.5 wt%.

[0079] After impregnation, the catalyst was aged at room temperature for 8 hours, then dried in an oven at 100°C for 12 hours. The dried solid was then ground into fine powder and calcined in a muffle furnace under air atmosphere at 450°C for 4 hours at a heating rate of 2°C / min.

[0080] (3) Preparation of isoalkanes by hydrogenation isomerization of long-chain alkanes:

[0081] The calcined Pt / SAPO-11 catalyst was pressed into tablets in a mold and sieved into 20-40 mesh particles. 0.5 g of the tablets were weighed and loaded into the reaction tube of a fixed-bed reactor. Hydrogen was introduced into the reaction tube for catalyst reduction at a temperature of 400℃ for 4 hours, a hydrogen flow rate of 100 ml / min, a hydrogen pressure of 0.1 MPa, and a heating rate of 5℃ / min for the fixed-bed reactor.

[0082] Then, using n-dodecane as a starting material, a hydroisomerization reaction was carried out at a reaction temperature of 280-360℃, a reaction pressure of 2 MPa, and a mass hourly space velocity of 3 h⁻¹. -1 The hydrogen-to-feed volume ratio is 800:1; the heating rate of the fixed-bed reactor is 5℃ / min.

[0083] Example 2

[0084] This embodiment is basically the same as embodiment 1, except that:

[0085] (1) Preparation of SAPO-11 molecular sieve

[0086] The initial gel contained aluminum source, phosphorus source, silicon source, template agent, alcohol, and mineralizer in a molar ratio of 1:1.8:0.4:5:55:0.3. The aluminum source, phosphorus source, and silicon source were boehmite, phosphoric acid, and tetraethyl orthosilicate, respectively. The template agents were di-n-propylamine and diethylamine (in a molar ratio of 1:1). The alcohol was ethylene glycol, and the mineralizer was ammonium fluoride. The raw materials were added to the gel sequentially according to the synthesis steps, and after thorough stirring, the gel was crystallized at 200°C for 72 hours.

[0087] Example 3

[0088] This embodiment is basically the same as embodiment 1, except that:

[0089] (1) Preparation of SAPO-11 molecular sieve

[0090] The aluminum source, phosphorus source, and silicon source in the initial gel were aluminum isopropoxide, phosphorous acid, and tetraethyl orthosilicate, respectively. The template agents were di-n-propylamine and diisopropylamine (molar ratio of 1:1), the alcohol was ethylene glycol, and the mineralizing agent was ammonium fluoride. The raw materials were added to the gel in sequence according to the synthesis steps, and after thorough stirring, the gel was crystallized at 200℃ for 96 hours.

[0091] The crystallized product was filtered and washed with deionized water until pH=7, and then dried in an oven at 120℃ for 12h. The dried solid was ground into a fine powder and calcined in a muffle furnace under air atmosphere at 550℃ for 6h at a heating rate of 5℃ / min.

[0092] The calcined SAPO-11 molecular sieve was poured into a 0.1 mol / L citric acid solution (the volume of the acid solution was 20 times the mass of the SAPO-11 molecular sieve), sonicated for 0.5 h, and then heated in a 40℃ constant temperature water bath for 1 h. During the heating process, magnetic stirring was used at a speed of 600 r / min.

[0093] The acid-treated SAPO-11 molecular sieve was filtered and washed with deionized water until pH=7, and then dried in an oven at 120℃ for 6 hours. The dried solid was ground into a fine powder and calcined in a muffle furnace under air atmosphere at 650℃ for 6 hours at a heating rate of 5℃ / min.

[0094] Example 4

[0095] This embodiment is basically the same as embodiment 1, except that:

[0096] (1) Preparation of SAPO-11 molecular sieve

[0097] The aluminum source, phosphorus source, and silicon source in the initial gel are aluminum isopropoxide, hypophosphoric acid, and acidic silica sol, respectively. The template agents are di-n-propylamine and diisopropylamine (molar ratio of 1:1), the alcohol is ethylene glycol, and the mineralizing agent is ammonium fluoride. The raw materials are added to the gel in sequence according to the synthesis steps, and after thorough stirring, the gel is crystallized at 200℃ for 96 hours.

[0098] The crystallized product was filtered and washed with deionized water until pH=7, and then dried in an oven at 120℃ for 12h. The dried solid was ground into a fine powder and calcined in a muffle furnace under air atmosphere at 550℃ for 6h at a heating rate of 5℃ / min.

[0099] The calcined SAPO-11 molecular sieve was poured into a 0.5 mol / L oxalic acid solution (the volume of the acid solution was 20 times the mass of the SAPO-11 molecular sieve), sonicated for 0.5 h, and then heated in a 70℃ constant temperature water bath for 4 h. During the heating process, magnetic stirring was used at a speed of 600 r / min.

[0100] The acid-treated SAPO-11 molecular sieve was filtered and washed with deionized water until pH=7, and then dried in an oven at 60℃ for 12h. The dried solid was ground into a fine powder and calcined in a muffle furnace under air atmosphere at 600℃ for 4h at a heating rate of 5℃ / min.

[0101] Example 5

[0102] This embodiment is basically the same as embodiment 1, except that:

[0103] (2) Preparation of Pt / SAPO-11 catalyst:

[0104] The prepared chloroplatinic acid aqueous solution was uniformly added dropwise onto SAPO-11 molecular sieve using an equal-volume impregnation method. Uniform impregnation was ensured by ultrasonication and grinding. The Pt loading was 0.1 wt%. After impregnation, the catalyst was aged at room temperature for 6 hours.

[0105] Example 6

[0106] This embodiment is basically the same as embodiment 1, except that:

[0107] (2) Preparation of Pt / SAPO-11 catalyst:

[0108] The prepared chloroplatinic acid aqueous solution was uniformly added dropwise onto SAPO-11 molecular sieve using an equal-volume impregnation method. Uniform impregnation was ensured by ultrasonication and grinding. The Pt loading was 1 wt%. After impregnation, the catalyst was aged at room temperature for 12 h.

[0109] Example 7

[0110] This embodiment is basically the same as embodiment 1, except that:

[0111] (1) Preparation of SAPO-11 molecular sieve:

[0112] The initial gel contained aluminum source, phosphorus source, silicon source, template agent, alcohol, and mineralizer in a molar ratio of 1:1:0.2:1.8:50:0.2. The aluminum source, phosphorus source, and silicon source were boehmite, phosphoric acid, and silicon dioxide, respectively. The template agents were dimethylamine and diethylamine (in a molar ratio of 1:1), the alcohol was ethylene glycol, and the mineralizer was ammonium fluoride. The raw materials were added to the gel sequentially according to the synthesis steps, and after thorough stirring, the gel was crystallized at 190°C for 72 hours.

[0113] The crystallized product was filtered and washed with deionized water until pH=7, and then dried in an oven at 60℃ for 24h. The dried solid was ground into a fine powder and calcined in a muffle furnace under air atmosphere at 650℃ for 4h at a heating rate of 5℃ / min.

[0114] Example 8

[0115] This embodiment is basically the same as embodiment 1, except that:

[0116] (1) Preparation of SAPO-11 molecular sieve:

[0117] The initial gel contained aluminum source, phosphorus source, silicon source, template agent, alcohol, and mineralizer in a molar ratio of 1:1.8:0.4:5:60:0.2. The aluminum source, phosphorus source, and silicon source were aluminum sulfate, phosphoric acid, and acidic silica sol, respectively. The template agents were diisopropylamine and diethylamine (molar ratio of 1:1), the alcohol was ethylene glycol, and the mineralizer was ammonium fluoride. The raw materials were added to the gel sequentially according to the synthesis steps, and after thorough stirring, the gel was crystallized at 200°C for 120 hours.

[0118] The crystallized product was filtered and washed with deionized water until pH=7, and then dried in an oven at 120℃ for 12h. The dried solid was ground into a fine powder and calcined in a muffle furnace under air atmosphere at 600℃ for 10h at a heating rate of 5℃ / min.

[0119] Comparative Example 1

[0120] This embodiment is basically the same as embodiment 1, except that:

[0121] (1) Preparation of SAPO-11 molecular sieve

[0122] The ethylene glycol in the initial gel was replaced with an equimolar amount of deionized water. An initial gel was prepared with the following molar ratio of aluminum source, phosphorus source, silicon source, template agent, water, and mineralizer: 1:1.8:0.4:5:55:0.1: aluminum, phosphorus, and silicon sources, respectively: aluminum isopropoxide, phosphoric acid, and tetraethyl orthosilicate. The template agents were di-n-propylamine and diisopropylamine (molar ratio of 1:1), the water was deionized water, and the mineralizer was ammonium fluoride. The raw materials were added to the gel sequentially according to the synthesis steps, and after thorough stirring, the gel was crystallized at 200°C for 96 hours.

[0123] Comparative Example 2

[0124] This embodiment is basically the same as embodiment 1, except that:

[0125] (1) Preparation of SAPO-11 molecular sieve

[0126] The initial gel contained aluminum source, phosphorus source, silicon source, template agent, alcohol, and mineralizer in a molar ratio of 1:1.8:0.4:5:55:0, meaning no ammonium fluoride mineralizer was added. The raw materials were added to the gel sequentially according to the synthesis steps, and after thorough stirring, the gel was crystallized at 200°C for 96 hours.

[0127] Comparative Example 3

[0128] This embodiment is basically the same as embodiment 1, except that:

[0129] (1) Preparation of SAPO-11 molecular sieve

[0130] Taking an initial gel with a molar ratio of aluminum source, phosphorus source, silicon source, template agent, alcohol, and mineralizer of 1:1.8:0.4:5:55:0.1 as an example, the aluminum source, phosphorus source, and silicon source are aluminum isopropoxide, phosphoric acid, and tetraethyl orthosilicate, respectively. The template agent is di-n-propylamine and diisopropylamine (molar ratio of 1:1). The alcohol is ethylene glycol, and the mineralizer is ammonium fluoride. Following the synthesis steps, each raw material is added sequentially to the gel, thoroughly stirred, and then crystallized at 200℃ for 96 hours. The crystallized product is filtered and washed with deionized water until pH=7, and then dried in an oven at 120℃ for 12 hours. The dried solid is ground into a fine powder and calcined in a muffle furnace under air atmosphere at 550℃ for 6 hours at a heating rate of 5℃ / min.

[0131] The calcined SAPO-11 molecular sieve is not acid-treated and directly serves as a support in the preparation process of Pt / SAPO-11 catalyst.

[0132] Figure 1 The images show the XRD patterns of SAPO-11 molecular sieves from Examples 1-2 and Comparative Examples 1-2 of this invention.

[0133] pass Figure 1It can be seen that the samples prepared in Examples 1-2 and Comparative Examples 1-2 all exhibit characteristic diffraction peaks of the AEL topology. Compared with Examples 1-2, the crystallinity of the SAPO-11 molecular sieve obtained in Comparative Examples 1-2 is significantly reduced, indicating that ethylene glycol and the mineralizing agent ammonium fluoride synergistically control the crystal formation during the solvothermal synthesis of SAPO-11.

[0134] Figure 2 The XRD patterns are of the SAPO-11 molecular sieves in Examples 7-8 of this invention.

[0135] pass Figure 2 It can be seen that the samples prepared in Examples 7-8 also have characteristic diffraction peaks of AEL topology, indicating that SAPO-11 molecular sieves can be prepared as long as they meet the initial gel ratio range, crystallization temperature and time range given by the technical solution of this invention.

[0136] To further clarify the effects of the technical solution of the present invention, the supports and catalysts obtained in Examples 1-6 and Comparative Examples 1-4 were systematically characterized under the same reaction conditions (reaction temperature 280-360℃, reaction pressure 2MPa, mass hourly space velocity 3h). -1 The catalytic performance of n-dodecane hydroisomerization was evaluated at a hydrogen-to-feed volume ratio of 800:1, and the results are shown in Tables 1-2.

[0137] Table 1

[0138] As shown in Table 1, the SAPO-11 supports obtained in Examples 1-4 all have small grain size and large specific surface area. After acid treatment, the mesoporous pore volume increases significantly, and the total acid content is within a suitable range.

[0139] In Example 2, due to the increased amount of ammonium fluoride, the crystallinity was further improved and the grain size was reduced to about 3.4 μm.

[0140] In contrast, in Comparative Example 1, when water was used as the solvent, the grains grew to 7.5 μm, and the specific surface area was significantly reduced.

[0141] Comparative Example 2 showed decreased crystallinity and uneven silicon distribution without the addition of mineralizer; Comparative Example 3, without acid treatment, resulted in minimal mesopore volume and severe pore blockage.

[0142] Table 2

[0143] In Table 2, nC 12 Conversion rate, iC 12 Selectivity and iC 12The yield calculation formula is as follows:

[0144] nC 12 Conversion rate = (1- )×100%

[0145] iC 12 Selectivity = ×100%

[0146] iC 12 Yield = nC 12 Conversion rate × iC 12 Selectivity × 100%

[0147] As shown in Table 2, Example 1 was tested at 340℃, 2MPa, and a mass hourly space velocity of 3h. -1 Under the given conditions, the conversion rate of n-dodecane can reach 87.7%, the selectivity of isododecane is 90.4%, and the yield is 79.3%.

[0148] In Example 4, due to the increased acid treatment intensity and improved diffusion performance, the conversion rate was further increased to 90.4%, and the yield reached 69.2%.

[0149] Example 6 achieved a higher conversion rate of 94.0% than Example 1 at a higher Pt loading and 340°C, but with slightly lower selectivity and the highest yield of isomeric dodecane was 76.2%.

[0150] Compared with the examples, the conversion rates and selectivity of Comparative Examples 1-3 were significantly lower, which fully demonstrates that the synergistic effect of ethylene glycol, ammonium fluoride and acid treatment is crucial to improving the catalytic performance of SAPO-11.

[0151] In summary, this invention successfully obtained a SAPO-11 molecular sieve support with small crystals, high specific surface area, and tunable acidity by solvothermal synthesis using ethylene glycol as a solvent, introducing ammonium fluoride as a mineralizing agent to accelerate crystallization and regulate silicon distribution, followed by mild acid treatment to dissolve aluminum outside the framework and construct a microporous-mesoporous multi-level structure. The resulting catalyst, after being loaded with Pt, exhibits high activity and high selectivity for isoalkanes in the hydrogenation isomerization reaction of long-chain alkanes.

[0152] The present invention has been described above by way of example with reference to the embodiments and accompanying drawings. Obviously, the implementation of the present invention is not limited to the above-described manner. Any improvements made by adopting the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A small-grained Pt / SAPO-11 catalyst, characterized in that: The small-crystal Pt / SAPO-11 catalyst comprises a support and an active metal, wherein the active metal is supported on the surface and in the pore structure of the support, the support is a SAPO-11 molecular sieve, and the active metal is Pt.

2. The small-grained Pt / SAPO-11 catalyst according to claim 1, characterized in that: The preparation method of the aforementioned SAPO-11 molecular sieve includes the following steps: S1: Mix and stir the aluminum source, phosphorus source, silicon source, template agent, and alcohol to obtain a mixture; S2: Add the mineralizer to the above mixture to obtain the initial gel; S3: The initial gel obtained in S2 is subjected to a crystallization reaction to obtain the crystallized product; S4: The crystallized product is washed, separated, dried, and calcined to obtain the initial product of SAPO-11 molecular sieve; S5: Disperse the SAPO-11 molecular sieve primary product uniformly in an acid solution; S6: The acid solution containing the initial product of SAPO-11 molecular sieve was placed in a constant temperature water bath and heated while being stirred continuously to obtain acid-treated SAPO-11 molecular sieve. S7: Wash, dry, and calcine the acid-treated SAPO-11 molecular sieve to obtain the SAPO-11 molecular sieve.

3. The method for preparing the small-crystal Pt / SAPO-11 catalyst according to claim 2, characterized in that: In step S1, the molar ratio of aluminum source, phosphorus source, silicon source, template agent, alcohol, and mineralizer is 1:(1-1.8):(0.2-0.4):(1.8-5):(50-60):(0.1-0.3), wherein the aluminum source is calculated as alumina, the phosphorus source as phosphorus oxide, and the silicon source as silicon dioxide.

4. The method for preparing the small-crystal Pt / SAPO-11 catalyst according to claim 3, characterized in that: In step S1, the aluminum source is selected from at least one of boehmite, aluminum isopropoxide, aluminum sulfate, and boehmite. The phosphorus source is selected from at least one of phosphoric acid, phosphorous acid, and hypophosphoric acid; The silicon source is selected from at least one of tetraethyl orthosilicate, silicon dioxide, and acidic silica sol; The template agent is selected from at least two of di-n-propylamine, diisopropylamine, dimethylamine, and diethylamine; Ethylene glycol is selected as the alcohol. In step S2, ammonium fluoride is selected as the mineralizing agent.

5. The method for preparing the small-crystal Pt / SAPO-11 catalyst according to claim 2, characterized in that: In step S3, the initial gel crystallization temperature is 190-200℃, and the crystallization time is 72-120h. In step S4, the crystallized product is washed until pH=7, calcined at 550-650℃ for 4-10 hours.

6. The method for preparing the small-crystal Pt / SAPO-11 catalyst according to claim 2, characterized in that: In step S5, the concentration of the acid solution in the acid treatment is 0.1-0.5 mol / L, and the volume of the acid solution is 20 times the mass of the SAPO-11 molecular sieve. In step S6, the constant temperature water bath temperature is 40-70℃, and the heating time is 1-4 hours.

7. The method for preparing the small-grained Pt / SAPO-11 catalyst according to claim 2, characterized in that: In step S7, the acid-treated SAPO-11 molecular sieve is washed to pH=7 and then subjected to subsequent drying treatment; the calcination temperature is 550-650℃ and the calcination time is 4-6h.

8. A method for preparing the small-grained Pt / SAPO-11 catalyst according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Prepare an aqueous solution containing active metal according to the content of active metal in small-crystal Pt / SAPO-11 catalyst; Step 2: The support is uniformly impregnated in the aqueous solution containing the active metal described in Step 1 using the equal volume impregnation method to obtain the initial catalyst supported on the active metal. Step 3: Aging the initial catalyst obtained in Step 2 at room temperature; Step 4: Dry and calcine the catalyst aged in Step 3 to obtain the small-crystal Pt / SAPO-11 catalyst.

9. The method for preparing the small-grained Pt / SAPO-11 catalyst according to claim 8, characterized in that: In step 1, the active metal is Pt, and the content of the active metal in the catalyst is 0.1wt%-1wt%. In step 3, the aging time of the initial catalyst is 6-12 hours. In step 4, the calcination temperature of the aged catalyst is 450-550℃, and the calcination time is 4-6h.

10. Use of the small-crystal Pt / SAPO-11 catalyst according to any one of claims 1-7 in the preparation of isoalkanes by hydroisomerization of long-chain alkanes.

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