Amorphous precursor calcination synthesis of aluminum phosphate-based molecular sieve and preparation method and application thereof

Abstract

The application discloses an amorphous precursor calcination synthesis aluminum phosphate-based molecular sieve and a preparation method and application thereof, and belongs to the technical field of solid-phase synthesis molecular sieves. The preparation method comprises the following steps: S1, preparing an aluminum phosphate amorphous precursor; and S2, preparing an aluminum phosphate-based molecular sieve. The application successfully introduces heteroatoms (Si, Co, Cu, Fe, Mg, Mn, Ni, V, Zn and the like) and transition metal elements with oxidation activity into the molecular sieve framework to obtain MeAPO-11 with a wide active center distribution range and mutual separation. The AEL type specific pore channel configuration is used to effectively combine the shape selective and metal oxidation activity, so that the performance of the molecular sieve can be significantly improved in a catalytic reaction. The synthesis method is simple, efficient, economical, and environmentally friendly.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid phase synthesis of molecular sieve, in particular to a method for synthesizing aluminum phosphate-based molecular sieve by calcining amorphous precursor and application thereof. BACKGROUND

[0002] Aluminum phosphate-based molecular sieve (AlPO4-n) is a very important member of the molecular sieve family. Its framework atoms are easily replaced by specific heteroatoms, giving the molecular sieve specific acidity and catalytic activity. Its advent greatly enriches the structure, classification and application of important porous crystalline materials such as molecular sieves, and has a milestone significance in the history of porous materials. The aluminum phosphate-based molecular sieve with AEL topology (AlPO4-11, SAPO-11, MeAPO-11) is one of the most important ones. In recent years, this type of molecular sieve has performed extremely outstandingly in the industrial catalysis fields such as hydroisomerization, alkylation, Beckmann rearrangement, etc., thus having very important research value.

[0003] Hydrothermal synthesis is the most basic and commonly used method for preparing AEL-type aluminum phosphate molecular sieve. First, the reaction raw materials are mixed in a certain proportion, and then the mixed gel is poured into a special high-pressure reactor for crystallization in a closed environment using the self-generated pressure of water. The crystallization time generally needs to be maintained for tens of hours, several days or even dozens of days. The solvent (water) has good dispersion effect, which promotes the dissolution of the reaction raw materials and is beneficial to the growth of crystals, improving the integrity of the crystal morphology and the crystallinity of the product. However, the hydrothermal synthesis method has obvious disadvantages. First, the reaction time is long and the product yield is low. Second, the reaction usually requires a high pressure environment, which brings certain safety hazards. Third, the crystallization process produces waste, and after the crystallization process is completed, a large amount of wastewater is generated during the separation of solid products, which pollutes the environment and cannot meet the development requirements of green chemistry.

[0004] In recent years, researchers have been committed to developing resource-saving, simple and efficient, and environmentally friendly green synthesis methods from the perspective of environmental protection and rational allocation of resources. Solid phase synthesis is an effective method for preparing thermodynamically stable solid crystalline products by directly calcining solid phase raw materials or precursors. This method is simple to operate, avoids the use of a large amount of solvent, and its crystallization process does not produce high pressure, so it is a convenient, efficient and environmentally friendly synthesis method.

[0005] Chinese patent CN112456513B discloses a method for successfully preparing AEL type molecular sieve by simply calcining a highly uniform amorphous precursor containing fluorine, but in the preparation of this amorphous precursor, the gelation process involves the use of propylene oxide (PO), which on the one hand increases the economic cost and is not conducive to practical application; on the other hand, propylene oxide is flammable, has low boiling point and is toxic, and strict requirements are required for storage and use. SUMMARY

[0006] The purpose of the present application is to provide an amorphous precursor calcination synthesis of aluminum phosphate-based molecular sieve and its preparation method and application, successfully introducing heteroatoms (Si, Co, Cu, Fe, Mg, Mn, Ni, V, Zn, etc.) and transition metal elements with oxidation activity into the molecular sieve framework, obtaining MeAPO-11 with a wide range of active center distribution and mutual separation, effectively combining the shape selective and metal oxidation activity of the specific channel configuration of AEL type, which can significantly improve its performance in catalytic reaction, and the synthesis method is simple, efficient, economic, and environmentally friendly.

[0007] To achieve the above purpose, the present application provides a preparation method for amorphous precursor calcination synthesis of aluminum phosphate-based molecular sieve, comprising the following steps:

[0008] S1, preparing an aluminum phosphate amorphous precursor: adding an aluminum source, a phosphorus source, a heteroatom, hydrofluoric acid and a structure directing agent into deionized water, stirring uniformly at room temperature, drying and grinding to obtain an amorphous precursor powder;

[0009] S2, preparing an aluminum phosphate-based molecular sieve: transferring the amorphous precursor powder obtained in S1 to an open container and heating for crystallization, and after crystallization, performing ultrasonic water washing, centrifugation, drying and calcination to obtain an AEL type aluminum phosphate-based molecular sieve.

[0010] Preferably, in S1, the molar ratio of the aluminum source, the phosphorus source, the heteroatom, the structure directing agent, the hydrofluoric acid and the deionized water is 1:(0.1-5.0):(0.01-5.0):(0.01-1.0):(0.1-5.0):(2.0-150).

[0011] Preferably, in S1, the heteroatom is one or more of a silicon source, a cobalt source, an iron source, a magnesium source, a manganese source and a zinc source.

[0012] The silicon source is one of white carbon black, tetraethyl orthosilicate and silica sol; the cobalt source is one of cobalt acetate, cobalt sulfate, cobalt nitrate and cobalt chloride; the iron source is one of iron acetate, iron nitrate, iron sulfate and iron chloride; the magnesium source is one of magnesium ethoxide, magnesium acetate, magnesium nitrate, magnesium sulfate and magnesium chloride; the manganese source is one of manganese acetate, manganese nitrate, manganese chloride and manganese sulfate; and the zinc source is one of zinc acetate, zinc nitrate, zinc sulfate and zinc chloride.

[0013] Preferably, the aluminum source is one of aluminum isopropoxide, pseudo-boehmite, and crystalline aluminum chloride.

[0014] Preferably, in S1, the phosphorus source is one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0015] Preferably, in S1, the structure-directing agent is one or more of 1-ethyl-3-methylimidazolium bromide ([Emim]Br), 1-ethyl-3-methylimidazolium hydroxide ([Emim]OH), diethylamine (DEA), di-n-propylamine (DPA), di-n-propylamine hydrochloride (DPA·HCl), di-n-propylamine phosphate (DPA·H3PO4), diisopropylamine (DIPA), di-n-butylamine (DBA), and di-n-butylamine hydrochloride (DBA·HCl).

[0016] Preferably, in S1, the drying temperature is 50-120℃, and the drying time is 1-24h.

[0017] Preferably, in S2, the temperature for heating and crystallization is 100-450℃, and the time for heating and crystallization is 0.1-12h.

[0018] The drying temperature is 20-120℃, and the drying time is 1-24h.

[0019] The calcination temperature is 300-600℃, and the calcination time is 2-12h.

[0020] The application also provides an amorphous precursor calcined to synthesize an aluminum phosphate-based molecular sieve, which is prepared by the above-described method for preparing an amorphous precursor calcined to synthesize an aluminum phosphate-based molecular sieve.

[0021] The application also provides an application of an amorphous precursor calcined to synthesize an aluminum phosphate-based molecular sieve, which is applied to a normal alkane isomerization reaction.

[0022] Therefore, the application of the above-described amorphous precursor calcined to synthesize an aluminum phosphate-based molecular sieve, the preparation method and the application thereof have the following beneficial effects:

[0023] (1) The heteroatoms (Si, Co, Cu, Fe, Mg, Mn, Ni, V, Zn, etc.) and transition metal elements with oxidation activity are introduced into the molecular sieve framework to obtain MeAPO-11 with a wide distribution range of active centers and mutual separation, and the shape-selectivity and metal oxidation activity of the AEL type specific pore channel configuration are effectively combined, which can significantly improve the performance in the catalytic reaction.

[0024] (2) The preparation method has the advantages of low cost, easy operation, fast crystallization, high yield and no wastewater generation, which opens up new ideas for the green synthesis of aluminum phosphate-based molecular sieves and lays a good foundation for the synthesis of other porous crystal materials.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 The XRD pattern of MgAlPO-11-1 prepared by the amorphous precursor calcination synthesis of aluminum phosphate-based molecular sieves, its preparation method, and application example 1 of this invention is shown.

[0027] Figure 2 This is the Ar-physical adsorption-desorption isotherm of MgAlPO-11-1 prepared by the amorphous precursor calcination synthesis of aluminum phosphate-based molecular sieves, its preparation method, and application example 1 of this invention.

[0028] Figure 3 This is a SEM image of MgAlPO-11-1 prepared by calcining amorphous precursors to synthesize aluminum phosphate-based molecular sieves, the preparation method thereof, and application example 1 of this invention.

[0029] Figure 4 This is a graph showing the relationship between temperature and hexadecane conversion rate under the action of catalysts obtained from the molecular sieves prepared by calcination of amorphous precursors of the present invention, the preparation method thereof, and the application of the catalysts obtained by the molecular sieves in Examples 1-3 and Comparative Example 1.

[0030] Figure 5 This is a graph showing the relationship between temperature and hexadecane selectivity under the action of catalysts prepared by calcining amorphous precursors to synthesize aluminum phosphate-based molecular sieves, their preparation method, and their application in Examples 1-3 and Comparative Example 1.

[0031] Figure 6 This is a graph showing the relationship between the conversion rate and the yield of n-hexadecane isomers when the amorphous precursor of the present invention is calcined to synthesize aluminum phosphate-based molecular sieves, the preparation method thereof, and the catalysts obtained by applying the molecular sieves in Examples 1-3 and Comparative Example 1. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0034] Example 1

[0035] An amorphous precursor calcination synthesis of magnesium-substituted heteroatom aluminophosphate-based molecular sieve, a preparation method thereof comprises the following steps:

[0036] S1, preparing an aluminophosphate amorphous precursor: sequentially adding 2.0 g of aluminum isopropoxide, 1.05 g of phosphoric acid (85 wt%), and 0.02 g of magnesium chloride hexahydrate into 18 g of deionized water at room temperature, fully stirring, then adding 0.1 g of hydrofluoric acid (10 wt%) and 2.0 g of 1-ethyl 3-methylimidazole hydroxide ([Emim]OH) for continuous stirring, after fully mixing, transferring the mixture to a culture dish for drying at 100℃ for 6 h, and grinding to obtain an amorphous precursor powder;

[0037] S2, preparing an aluminophosphate-based molecular sieve: transferring the amorphous precursor powder obtained in S1 to an open container for heating at 180℃ for 4 h for crystallization, after the crystal is cooled to room temperature, performing ultrasonic water washing, centrifugation, and drying, and then calcining at 550℃ in an air atmosphere for 12 h to obtain a magnesium-substituted heteroatom AEL-type aluminophosphate-based molecular sieve, which is recorded as MgAlPO-11-1.

[0038] Example 2

[0039] An amorphous precursor calcination synthesis of magnesium-substituted heteroatom aluminophosphate-based molecular sieve, a preparation method thereof comprises the following steps:

[0040] S1, preparing an aluminophosphate amorphous precursor: sequentially adding 2.0 g of aluminum isopropoxide, 1.05 g of phosphoric acid (85 wt%), and 0.02 g of magnesium chloride hexahydrate into 18 g of deionized water at room temperature, fully stirring, then adding 0.1 g of hydrofluoric acid (10 wt%) and 2.0 g of 1-ethyl 3-methylimidazole hydroxide ([Emim]OH) for continuous stirring, after fully mixing, transferring the mixture to a culture dish for drying at 100℃ for 6 h, and grinding to obtain an amorphous precursor powder;

[0041] S2, preparing an aluminophosphate-based molecular sieve: transferring the amorphous precursor powder obtained in S1 to an open container for heating at 180℃ for 4 h for crystallization, after the crystal is cooled to room temperature, performing ultrasonic water washing, centrifugation, and drying, and then calcining at 550℃ in an air atmosphere for 12 h to obtain a magnesium-substituted heteroatom AEL-type aluminophosphate-based molecular sieve, which is recorded as MgAlPO-11-1.

[0042] Example 3

[0043] An amorphous precursor calcination synthesis of magnesium-substituted heteroatom aluminophosphate-based molecular sieve, a preparation method thereof comprises the following steps:

[0044] S1, preparing aluminum phosphate amorphous precursor: 2.0 g aluminum isopropoxide, 1.05 g phosphoric acid (85 wt%), 0.06 g magnesium chloride were sequentially added into 18 g deionized water at room temperature, fully stirred, then 0.1 g hydrofluoric acid (10 wt%) and 2.0 g 1-ethyl 3-methylimidazole hydroxide ([Emim]OH) were added and continuously stirred, after fully mixed, the mixture was transferred to a culture dish and dried at 100℃ for 6 h, after grinding, the amorphous precursor powder was obtained;

[0045] S2, preparing aluminum phosphate-based molecular sieve: the amorphous precursor powder obtained in S1 was transferred to an open container and heated at 180℃ for 4 h for crystallization, after the crystal was cooled to room temperature, ultrasonic water washing, centrifugation and drying were carried out, and then the magnesium-substituted heteroatom AEL-type aluminum phosphate-based molecular sieve was obtained by calcining at 550℃ in air atmosphere for 12 h, which was recorded as MgAlPO-11-3.

[0046] Example 4

[0047] A method for preparing a cobalt-substituted heteroatom aluminum phosphate-based molecular sieve by calcining an amorphous precursor, comprising the following steps:

[0048] S1, preparing aluminum phosphate amorphous precursor: 2.0 g aluminum isopropoxide, 1.05 g phosphoric acid (85 wt%), 0.06 g magnesium chloride were sequentially added into 18 g deionized water at room temperature, fully stirred, then 0.1 g hydrofluoric acid (10 wt%) and 2.0 g 1-ethyl 3-methylimidazole hydroxide ([Emim]OH) were added and continuously stirred, after fully mixed, the mixture was transferred to a culture dish and dried at 100℃ for 6 h, after grinding, the amorphous precursor powder was obtained;

[0049] S2, preparing aluminum phosphate-based molecular sieve: the amorphous precursor powder obtained in S1 was transferred to an open container and heated at 180℃ for 4 h for crystallization, after the crystal was cooled to room temperature, ultrasonic water washing, centrifugation and drying were carried out, and then the magnesium-substituted heteroatom AEL-type aluminum phosphate-based molecular sieve was obtained by calcining at 550℃ in air atmosphere for 12 h, which was recorded as MgAlPO-11-3.

[0050] Example 5

[0051] A method for preparing a cobalt-substituted heteroatom aluminum phosphate-based molecular sieve by calcining an amorphous precursor, comprising the following steps:

[0052] S1, preparing aluminum phosphate amorphous precursor: 3.2 g aluminum isopropoxide, 1.62 g phosphoric acid (85 wt%), 0.12 g iron chloride were sequentially added into 18 g deionized water at room temperature, fully stirred, then 0.15 g hydrofluoric acid (10 wt%) and 2.5 g 1-ethyl 3-methylimidazole hydroxide ([Emim]OH) were added and continuously stirred, after fully mixed, the mixture was transferred into a culture dish and dried at 100℃ for 6 h, after grinding, the amorphous precursor powder was obtained;

[0053] S2, preparing aluminum phosphate-based molecular sieve: the amorphous precursor powder obtained in S1 was transferred into an open container and heated at 230℃ for 3 h for crystallization, after the crystal was cooled to room temperature, ultrasonic water washing, centrifugation and drying were carried out, and then the iron-substituted heteroatom AEL-type aluminum phosphate-based molecular sieve FeAlPO-11 was obtained by calcining at 600℃ in air atmosphere for 6 h.

[0054] Example 6

[0055] A method for preparing a manganese-substituted heteroatom aluminum phosphate-based molecular sieve by calcining an amorphous precursor, comprising the following steps:

[0056] S1, preparing aluminum phosphate amorphous precursor: 3.2 g aluminum isopropoxide, 1.62 g phosphoric acid (85 wt%), 0.12 g iron chloride were sequentially added into 18 g deionized water at room temperature, fully stirred, then 0.15 g hydrofluoric acid (10 wt%) and 2.5 g 1-ethyl 3-methylimidazole hydroxide ([Emim]OH) were added and continuously stirred, after fully mixed, the mixture was transferred into a culture dish and dried at 100℃ for 6 h, after grinding, the amorphous precursor powder was obtained;

[0057] S2, preparing aluminum phosphate-based molecular sieve: the amorphous precursor powder obtained in S1 was transferred into an open container and heated at 230℃ for 3 h for crystallization, after the crystal was cooled to room temperature, ultrasonic water washing, centrifugation and drying were carried out, and then the iron-substituted heteroatom AEL-type aluminum phosphate-based molecular sieve FeAlPO-11 was obtained by calcining at 600℃ in air atmosphere for 6 h.

[0058] Example 7

[0059] A method for preparing a zinc-substituted heteroatom aluminum phosphate-based molecular sieve by calcining an amorphous precursor, comprising the following steps:

[0060] S1, Preparation of aluminum phosphate amorphous precursor: 2.6 g aluminum isopropoxide, 1.35 g phosphoric acid (85 wt%), 0.18 g zinc chloride were added into 18 g deionized water at room temperature, stirred well, then 0.15 g hydrofluoric acid (10 wt%) and 3.2 g diisopropylamine (DIPA) were added and stirred, after mixing well, the mixture was transferred to a culture dish and dried at 100℃ for 6 h, after grinding, the amorphous precursor powder was obtained;

[0061] S2, Preparation of aluminum phosphate-based molecular sieve: the amorphous precursor powder obtained in S1 was transferred to an open container and heated at 250℃ for 1.5 h for crystallization, after the crystal was cooled to room temperature, ultrasonic water washing, centrifugation and drying were carried out, and then the zinc-substituted heteroatom AEL-type aluminum phosphate-based molecular sieve ZnAlPO-11 was obtained by calcining at 600℃ in air atmosphere for 6 h.

[0062] Comparative Example 1

[0063] A magnesium-substituted heteroatom aluminum phosphate-based molecular sieve prepared by a propylene oxide-involved solid-phase synthesis method, the preparation method comprising the following steps:

[0064] S1, 2.0 g aluminum isopropoxide, 1.05 g phosphoric acid (85 wt%), 0.1 g hydrofluoric acid (10 wt%) and 0.02 g magnesium chloride were added into 18 g deionized water at room temperature, stirred well in an ice bath, then 8.0 mL propylene oxide (PO) was added, after removing the bubbles by ultrasonic, a hydrogel was prepared, the hydrogel was dried at 100℃ for 2 h to obtain a monolithic phosphosilicate aluminogel;

[0065] S2, 3.0 g 1-ethyl 3-methylimidazolium hydroxide ([Emim]OH) and 18 g deionized water were added into the dry gel, stirred at room temperature for 2 h, and dried at 100℃ for 6 h to obtain a molecular sieve precursor;

[0066] S2, the precursor was placed in a crucible and heated at 180℃ for 4 h for crystallization, after the crystal was cooled to room temperature, ultrasonic water washing, centrifugation and drying were carried out, and then a magnesium-substituted heteroatom AEL-type aluminum phosphate-based molecular sieve was obtained by calcining at 550℃ in air atmosphere for 12 h, which was recorded as MgAlPO-11-4.

[0067] Test Test One

[0068] MgAlPO-11-1 obtained in Example 1 was tested by XRD, Ar-physical adsorption, SEM and other characterization techniques. Figure 1The XRD spectrum of the MgAlPO-11-1 obtained in Example 1 shows that the characteristic peaks of the crystallization product obtained by solid phase synthesis are located at 2θ = 8.09°, 9.43°, 20.44°, 21.08°, 22.12°, 22.53°, 22.70°, 23.16°, which are consistent with the standard AEL simulation spectrum, confirming that the product is indeed of AEL configuration, and no other impurity peaks and amorphous phase exist, further proving that the product has good phase purity.

[0069] The Ar-physical adsorption desorption isotherm of the MgAlPO-11-1 obtained in Example 1 is shown in Figure 2 The isotherm shows a mixed feature of type I and type IV isotherms, accompanied by a H3 type hysteresis loop, which reveals its unique pore structure characteristics: the type I isotherm feature is the rapid rise of adsorption amount in the low pressure region (P / P0<0.01), indicating that Ar molecules fill the micropores rapidly; the type IV isotherm feature is the gradual rise of adsorption amount in the P / P0>0.4 region, showing that the material contains mesoporous structure; the H3 type hysteresis loop in the medium-high pressure region (P / P0=0.45-0.90) confirms the existence of slit-shaped mesopores.

[0070] The SEM characterization results of the MgAlPO-11-1 obtained in Example 1 are shown in Figure 3 The morphology of the product is consistent with the morphology characteristics of AEL type molecular sieve, which is a typical rod-like structure, and the surface is smooth, the crystal length is in the range of 0.5-2 μm, and the diameter is small, about 0.1-0.5 μm.

[0071] Test two

[0072] Alkyne isomerization is an important catalytic process in petroleum refining and chemical production, the core goal of which is to convert linear alkanes (n-alkanes) into branched alkanes (isoalkanes), which plays an important role in improving fuel quality, optimizing lubricating oil performance, and promoting efficient use of chemical raw materials. MgAlPO-11 (AEL type molecular sieve) has one-dimensional elliptical 10-membered ring straight pores with a pore size of 0.39 nm x 0.63 nm, has a mild acidic property and a suitable medium-sized pore structure, effectively inhibits the occurrence of cracking reaction, and improves the isomerization selectivity of long-chain alkanes in the hydrogenation isomerization reaction, is a very effective catalyst, which follows a bifunctional catalytic mechanism in the n-alkane hydrogenation isomerization reaction, the core of which is the synergistic effect of metal sites and molecular sieve acid sites. The specific reaction mechanism involves three key steps of dehydrogenation-protonation and isomerization-hydrogenation saturation: n-alkane (such as n-hexadecane) is first dehydrogenated on the metal site (such as Pt) to generate the corresponding n-alkene, the n-alkene migrates to the Brønsted acid site (B acid) of the molecular sieve to be protonated to form a carbenium ion intermediate, the carbenium ion undergoes skeletal rearrangement through a cyclopropane carbenium ion mechanism, and the isomerized alkene intermediate returns to the metal site to be hydrogenated to generate the final isoalkane product.

[0073] The molar ratio of Mg / Al in the magnesium-substituted heteroatom AEL type aluminum phosphate-based molecular sieves prepared in Examples 1-3 was 0.01, 0.02, and 0.03, respectively, and the molar ratio of Mg / Al in the magnesium-substituted heteroatom AEL type aluminum phosphate-based molecular sieve prepared in Comparative Example 1 was 0.01. The molecular sieves prepared in Examples 1-3 and Comparative Example 1 were used to catalyze the n-hexadecane hydrogenation isomerization reaction: 1.0 g of the molecular sieve was taken as the catalyst carrier, 0.5 wt% of H2PtCl6 was impregnated by the equal-volume impregnation method, dried at 120°C for 4 h, calcined in a muffle furnace at 500°C for 4 h, and then reduced in a hydrogen atmosphere at 400°C for 4 h to obtain the isomerization catalyst, wherein the catalyst prepared from the molecular sieve of Example 1-3 was denoted as Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, and Pt / S-MgAlPO-11-3, respectively, and the catalyst prepared from the molecular sieve of Comparative Example 1 was denoted as Pt / H-MgAlPO-11. In a fixed-bed reactor, n-hexadecane was used as the model compound, H2 / C 12 =20, the pressure was 2.0 MPa, and the catalytic performance of Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, Pt / S-MgAlPO-11-3, and Pt / H-MgAlPO-11 was evaluated at 240-360°C.

[0074] The conversion rate, selectivity, and isomer yield of n-hexadecane are shown in Table 1. Figures 4-6 Figure 4 ​It can be seen that under the catalysis of Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, Pt / S-MgAlPO-11-3 and Pt / H-MgAlPO-11, the conversion of n-hexadecane first increases with the increase of temperature, and when the temperature increases to 320℃, the conversion tends to be flat with the increase of temperature. In particular, under the same temperature, the activity of Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, Pt / S-MgAlPO-11-3 catalysts increases with the increase of Mg content, because in the bifunctional catalytic system, when the dehydrogenation / hydrogenation function of the metal site (Pt) reaches a sufficient level, the control step of the reaction rate will be transferred to the conversion process of the carbenium ion on the acid site, and with the increase of the acid, the activity of the catalyst is further improved, but the selectivity of isomers decreases slightly with the increase of Mg content in the catalyst. From Figure 5 It can be found that the isomer selectivity of Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, Pt / S-MgAlPO-11-3 and Pt / H-MgAlPO-11 all show a rapid downward trend after 320℃, which is closely related to the competition mechanism between the pore structure of the molecular sieve, the diffusion limitation and the reaction kinetics. From Figure 6 It can be seen that with the increase of n-hexadecane conversion, the isomer yield of Pt / S-MgAlPO-11-1 catalyst first increases and then decreases, and when the conversion is 96%, the isomer yield reaches the maximum of 90%, and then rapidly decreases to about 45%. The specific analysis of this phenomenon is as follows: in the initial stage, the concentration of reactant (n-C 16 ) is high, and the olefins generated by the dehydrogenation of the metal site (Pt) rapidly undergo single-branched isomerization on the adjacent B acid site, at this time the main reaction (isomerization) rate is greater than the side reaction (cracking) rate; when the conversion reaches 60-80%, the single-branched product accumulates to the maximum; when the conversion continues to increase (>80%), the product retention in the pore causes the secondary reaction to intensify, and the single-branched isomer further converts into multi-branched products with greater steric hindrance, which are difficult to diffuse and prone to cracking, ultimately causing the total isomer yield to decrease. This phenomenon essentially reflects the inherent characteristics of microporous molecular sieves in balancing reaction selectivity and mass transfer efficiency.

[0075] The catalytic performance of Pt / S-MgAlPO-11-1, Pt / S-MgAlPO-11-2, Pt / S-MgAlPO-11-3 and Pt / H-MgAlPO-11 on the catalytic performance of n-alkane hydroisomerization is compared, and the results are shown in Table 1. It can be seen that Pt / S-MgAlPO-11-1 and Pt / H-MgAlPO-11 with the same Mg / Al molar ratio have different catalytic performances: the former has a maximum isomer yield of 90.2%, while the latter only has a maximum isomer yield of 86.7%. This comparison shows that the present application improves the catalytic performance while realizing a more green and environmentally friendly synthesis process, which fully proves the effectiveness and advancement of the present application.

[0076] Table 1 Comparison of the catalytic performance of bifunctional catalysts on n-alkane hydroisomerization

[0077]

[0078] Therefore, the present application uses the above amorphous precursor to synthesize aluminum phosphate-based molecular sieves, and the preparation method and application thereof, successfully introduces heteroatoms (Si, Co, Cu, Fe, Mg, Mn, Ni, V, Zn, etc.) and transition metal elements with oxidation activity into the molecular sieve framework, obtains MeAPO-11 with a wide range of active center distribution and mutual separation, effectively combines the shape selective selectivity and metal oxidation activity of the AEL type specific pore channel configuration, and can significantly improve the performance in the catalytic reaction, and the synthesis method is simple, efficient, economical and environmentally friendly.

[0079] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: it can still modify or equivalently replace the technical solutions of the present application, and these modifications or equivalent replacements also cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for preparing aluminum phosphate-based molecular sieves by calcination of amorphous precursors, characterized in that, Includes the following steps: S1. Preparation of amorphous aluminum phosphate precursor: Add aluminum source, phosphorus source, heteroatom, hydrofluoric acid and structure directing agent to deionized water, stir evenly at room temperature, dry and grind to obtain amorphous precursor powder. S2. Preparation of aluminum phosphate-based molecular sieve: The amorphous precursor powder obtained in S1 is transferred to an open container and heated to crystallize. After crystallization, it is ultrasonically washed, centrifuged, dried and calcined to obtain AEL type aluminum phosphate-based molecular sieve. In S1, the mass ratio of aluminum source, phosphorus source, heteroatom, structure directing agent, hydrofluoric acid, and deionized water is 1:(0.1~5.0):(0.01~5.0):(0.01~1.0):(0.1~5.0):(2.0~150); The AEL-type aluminum phosphate-based molecular sieve includes both microporous and mesoporous structures. The mesoporous structure is a slit-shaped mesoporous structure; The AEL-type aluminum phosphate-based molecular sieve has a rod-shaped structure with a smooth surface, a crystal length of 0.5-2 μm, and a diameter of 0.1-0.5 μm.

2. The preparation method according to claim 1, characterized in that, In S1, the heteroatoms are one or more of the following sources: silicon, cobalt, iron, magnesium, manganese, and zinc. The silicon source is one of silica, tetraethyl orthosilicate, or silica sol; the cobalt source is one of cobalt acetate, cobalt sulfate, cobalt nitrate, or cobalt chloride; the iron source is one of ferric acetate, ferric nitrate, ferric sulfate, or ferric chloride; the magnesium source is one of magnesium ethoxide, magnesium acetate, magnesium nitrate, magnesium sulfate, or magnesium chloride; the manganese source is one of manganese acetate, manganese nitrate, manganese chloride, or manganese sulfate; and the zinc source is one of zinc acetate, zinc nitrate, zinc sulfate, or zinc chloride.

3. The preparation method according to claim 1, characterized in that, In S1, the aluminum source is one of aluminum isopropoxide, boehmite, or crystalline aluminum chloride.

4. The preparation method according to claim 1, characterized in that, In S1, the phosphorus source is one of phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate.

5. The preparation method according to claim 1, characterized in that, In S1, the structure directing agent is one or more of the following: 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium hydroxide, diethylamine, di-n-propylamine, di-n-propylamine hydrochloride, di-n-propylamine phosphate, diisopropylamine, di-n-butylamine, and di-n-butylamine hydrochloride.

6. The preparation method according to claim 1, characterized in that, In S1, the drying temperature is 50-120℃ and the drying time is 1-24h.

7. The preparation method according to claim 1, characterized in that, In S2, the temperature for heating and crystallization is 100-450℃, and the time for heating and crystallization is 0.1-12h; The drying temperature is 20-120℃, and the drying time is 1-24h; The roasting temperature is 300-600℃, and the roasting time is 2-12h.

8. Aluminum phosphate-based molecular sieve synthesized by calcination of amorphous precursors, characterized in that, The amorphous precursor was prepared by calcination synthesis of aluminum phosphate-based molecular sieves according to any one of claims 1-7.

9. The application of calcination synthesis of aluminum phosphate-based molecular sieves from amorphous precursors, characterized in that... The amorphous precursor described in claim 8, synthesized into aluminum phosphate-based molecular sieves by calcination, is applied to the isomerization reaction of n-alkane.

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