Preparation method of small crystal grain saPO-34 molecular sieve, molecular sieve prepared by the method and application thereof

Abstract

The application discloses a preparation method of small-grain SAPO-34 molecular sieve, the molecular sieve prepared by the method and application of the molecular sieve. The preparation method of the small-grain SAPO-34 molecular sieve comprises the following steps: mixing an aluminum source, a phosphorus source, a template agent R, water and an optional silicon source to prepare a crystallization solution; adding high-silicon SAPO-18 molecular sieve into the crystallization solution, and performing crystallization and calcination to obtain the small-grain SAPO-34 molecular sieve, wherein the SiO2 / Al2O3 molar ratio of the high-silicon SAPO-18 molecular sieve is 1.0-10.0. The small-grain SAPO-34 molecular sieve prepared by the method is used as a catalyst for a methanol-to-olefin reaction, and the reaction activity is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of molecular sieve materials, and particularly relates to a preparation method of small-grain SAPO-34 molecular sieve, a molecular sieve prepared by the method and application thereof. BACKGROUND

[0002] In 1982, UCC first introduced AlPO4 molecular sieve. The framework of this type of molecular sieve is neutral, has no exchangeable cation, lacks the proton acid required for catalytic activity of positive carbon ions, and has weak acid catalytic performance. In 1984, Lok et al. introduced Si into the AlPO4 series of molecular sieves, and synthesized a series of silicoaluminophosphate (SAPO) molecular sieves. This type of molecular sieve includes 13 three-dimensional microporous framework structures composed of tetrahedrons, some of which are new structures, and some of which are similar to conventional zeolites, have pore structures from six-membered rings to twelve-membered rings, and have pore diameters of 0.3-0.8 nm, thus being able to adapt to the requirements of adsorption and diffusion of molecules of different sizes. The framework is electronegative, has exchangeable cations, and has proton acidity.

[0003] Ethylene and propylene are important organic chemical raw materials in modern chemical industry. The production methods of low-carbon olefins can be generally divided into two categories: a petroleum route and a non-petroleum route. The catalytic preparation of low-carbon olefins (MTO or DTO) from methanol or dimethyl ether as raw materials is a new type of process most likely to replace the petroleum route. At present, the synthesis process of methanol or dimethyl ether is very mature, and the raw materials are abundant, such as coal, natural gas and solid waste, which can be directly synthesized by synthesis gas. The technology of using natural gas as raw material to synthesize methanol from synthesis gas and then converting the methanol into low-carbon olefins (MTO) has realized large-scale industrial production and is in the process of accelerating commercialization.

[0004] The catalytic materials used in MTO reactions are concentrated on small-pore and medium-pore acid molecular sieves, and the most widely used is SAPO molecular sieve, such as SAPO-18 and SAPO-34. The arrangement modes of double six-membered rings of SAPO-18 and SAPO-34 molecular sieves are completely different: the double six-membered rings of two adjacent layers of SAPO-34 molecular sieve are distributed in parallel in the same direction, and this arrangement causes the whole structure to expand in a certain direction; and the double six-membered rings of two adjacent layers of SAPO-18 molecular sieve are cross-distributed, and such a structure causes the pore size to be strictly controlled, and the structure is more compact. Due to the limitation of small pores, SAPO-18 and SAPO-34 molecular sieves can only adsorb primary alcohols and straight-chain hydrocarbons, and branched isomeric hydrocarbons, naphthenes and aromatic hydrocarbons cannot be adsorbed, so that methanol on the small-pore zeolite is mainly converted into C2-C4 straight-chain olefins, and compounds with more than 6 carbons are extremely few, and the low-carbon olefins have good selectivity to the MTO process.

[0005] CN200810043287.0 discloses a catalyst for converting oxygen-containing compounds into low-carbon olefins, the main component of which is SAPO-34 molecular sieve, which is a flaky crystal, and the length-width ratio of one crystal face is less than 4.0, and the length-width ratio of the other two crystal faces is greater than 4.0.

[0006] CN201910774542.7 discloses a low-silicon SAPO-34 molecular sieve, a preparation method and application thereof. By adding different proportions of silicon sol and ethyl silicate to control the interaction of silicon source, aluminum source and template, a slow heating method is adopted, and the crystal grain size is reduced by adding SAPO-34 crystal seeds, which can be used for methanol or dimethyl ether to prepare low-carbon olefins.

[0007] At present, it is very important to develop a more simple and efficient, low-cost preparation method which can greatly reduce the crystal grain size of SAPO-34 molecular sieve and improve the catalytic activity of methanol to olefins. SUMMARY

[0008] In view of the problems of low relative crystallinity and large molecular sieve crystal grain size of SAPO-34 molecular sieve in the prior art, the present application provides a preparation method of small-grain SAPO-34 molecular sieve, and the molecular sieve prepared by the method and its application. The SAPO-34 molecular sieve prepared by the method has small crystal grain size, and when used as a catalyst for methanol to low-carbon olefins reaction, it has high catalytic activity and good reaction stability.

[0009] The first aspect of the present application provides a preparation method of small-grain SAPO-34 molecular sieve, comprising the following steps:

[0010] (1) mixing an aluminum source, a phosphorus source, a template R, water and an optional silicon source to prepare a crystallization solution;

[0011] (2) adding high-silicon SAPO-18 molecular sieve to the crystallization solution prepared in step (1), and crystallizing and calcining to obtain the small-grain SAPO-34 molecular sieve.

[0012] Further, in step (1), the molar ratio of each component in the crystallization solution is as follows: SiO2: Al2O3: P2O5: R: H2O = 0-0.16: 1: 0.5-2.0: 1.0-7.0: 5-70, calculated based on SiO2 for the silicon source, Al2O3 for the aluminum source and P2O5 for the phosphorus source.

[0013] Further, in step (1), the aluminum source is selected from at least one of pseudo-boehmite, aluminum oxide, high-purity aluminum oxide (purity ≥ 99.99%), and aluminum isopropoxide, the silicon source is selected from at least one of silicon sol and tetraethyl orthosilicate, and the phosphorus source is selected from at least one of phosphoric acid and phosphorous acid.

[0014] Further, in step (1), the template agent R is selected from at least one of N,N-diisopropylethylamine, tetraethylammonium hydroxide, triethylamine or tetraethylammonium bromide.

[0015] Further, in step (1), the template agent R is preferably a mixed template agent, selected from at least two of N,N-diisopropylethylamine, tetraethylammonium hydroxide, triethylamine or tetraethylammonium bromide.

[0016] Further, in step (2), the high-silicon SAPO-18 molecular sieve has a SiO2 / Al2O3 molar ratio of 1.0-10.0, preferably 1.1-3.5, and further preferably 1.5-3.5.

[0017] Further, preferably, in step (2), the high-silicon SAPO-18 molecular sieve has a morphology of a sheet shape, a length of 200-800 nm, a width of 200-800 nm, and a thickness of 5-50 nm.

[0018] Further, in step (2), the high-silicon SAPO-18 molecular sieve has a solid-liquid mass ratio with the crystallization liquid (based on the total mass of the phosphorus source, the aluminum source and the silicon source) of 0.05-50, preferably 0.08-40, and further preferably 0.35-15.

[0019] Further, in step (2), the crystallization conditions are as follows: a crystallization temperature of 130-200℃ and a crystallization time of 2-96 hours.

[0020] Further, the crystallization is preferably a temperature-variable crystallization, which is divided into a low-temperature T1 stage crystallization for X hours and a high-temperature T2 stage crystallization for Y hours, and 0

[0021] Further, after the crystallization, the intermediate crystalline material product can be separated from the obtained mixture by any separation mode known in the art, such as filtration, washing and drying. Herein, the filtration, washing and drying can be performed in any manner known in the art. The drying temperature can be 80-200℃, and preferably 100-150℃. The drying time can be 6-48 hours, and preferably 12-30 hours. The drying can be performed under normal pressure or under reduced pressure, and is usually performed under normal pressure for energy saving.

[0022] Further, in step (2), the calcination conditions are as follows: a calcination temperature of 500-600℃ and a calcination time of 4-24 hours.

[0023] Further, in step (2), the preparation method of the high-silicon SAPO-18 molecular sieve comprises the following steps: mixing an aluminum source, a phosphorus source, a silicon source, a template T and water, crystallizing, drying and calcining to obtain the high-silicon SAPO-18 molecular sieve; and the molar ratio of raw materials in the reaction system is as follows: 1.0 Al2O3: 0.5-1.5 P2O5: 1.0-10.0 SiO2: 0.5-3.0 R: 20-100 H2O.

[0024] Further, the crystallization, drying and calcining can adopt conventional technical methods in the art.

[0025] Further, the aluminum source is at least one selected from the group consisting of pseudo-boehmite, aluminum oxide, high-purity aluminum oxide (purity ≥ 99.99%), and aluminum isopropyl alcohol, the silicon source is at least one selected from the group consisting of silica sol and tetraethyl orthosilicate, and the phosphorus source is at least one selected from the group consisting of phosphoric acid and phosphorous acid.

[0026] Further, the template T is at least one selected from the group consisting of N,N-diisopropyl ethylamine, tetraethyl ammonium hydroxide, triethylamine and tetraethyl ammonium bromide.

[0027] Further, when the template T is at least two selected from the group consisting of N,N-diisopropyl ethylamine, tetraethyl ammonium hydroxide, triethylamine and tetraethyl ammonium bromide, the prepared high-silicon SAPO-18 molecular sieve has a flaky morphology.

[0028] The second aspect of the present application provides a small-grain SAPO-34 molecular sieve prepared by the above preparation method, wherein the SAPO-34 molecular sieve has a grain size of 50-800 nm, preferably 100-600 nm.

[0029] Further, the small-grain SAPO-34 molecular sieve has a cubic morphology and has abundant intracrystalline pores.

[0030] The third aspect of the present application provides an application of the above small-grain SAPO-34 molecular sieve in a process for converting methanol into low-carbon olefins, which comprises: contacting the small-grain SAPO-34 molecular sieve as a catalyst with a methanol raw material to obtain low-carbon olefins.

[0031] Further, the methanol raw material can be pure methanol, crude methanol containing water (water content 60-85%), or methanol containing inert gas (inert gas volume fraction 10%-20%).

[0032] Further, the reactor can adopt a fixed bed or a fluidized bed reactor. The reaction conditions are preferably as follows: reaction temperature 350-500 ℃, reaction pressure 0-1 MPa, weight hourly space velocity 1-6 h-1, and reaction time 0.5-5 h. 1 .

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] The present application adopts adding high-silicon SAPO-18 molecular sieve into the crystallization solution of silicon-free or ultra-low-silicon SAPO-34 molecular sieve, and then performing transformation to obtain small-grained SAPO-34 molecular sieve. In the preparation process, by controlling the silicon-aluminum ratio and the adding amount of the added SAPO-18 molecular sieve, and preferably adopting temperature-variable crystallization, intercrystalline pores and intracrystalline pores are formed, which is beneficial to diffusion. The small-grained SAPO-34 molecular sieve prepared by the method of the present application is applied to the methanol-to-olefin reaction as a catalyst, which can more greatly improve the product diffusion, reduce the mass transfer resistance, and delay the generation of reaction carbon deposition, thereby improving the catalytic reaction activity of the methanol-to-olefin reaction.

[0035] The small-grained SAPO-34 molecular sieve provided by the present application has a cubic shape with a certain hollow structure, and the size is 50-800 nm. The molecular sieve is used as a catalyst for the methanol-to-olefin reaction, and the reaction activity is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a scanning electron microscope image of the high-silicon SAPO-18 molecular sieve synthesized in Comparative Example 3;

[0037] Figure 2 is an XRD pattern of the high-silicon SAPO-18 molecular sieve synthesized in Comparative Example 3;

[0038] Figure 3 is an XRD pattern of the SAPO-34 / SAPO-18 composite molecular sieve synthesized in Comparative Example 5;

[0039] Figure 4 is a scanning electron microscope image of the SAPO-34 molecular sieve synthesized in Comparative Example 6;

[0040] Figure 5 is an XRD pattern of the SAPO-34 molecular sieve synthesized in Example 1;

[0041] Figure 6 is a scanning electron microscope image of the SAPO-34 molecular sieve synthesized in Example 6;

[0042] Figure 7 is an XRD pattern of the SAPO-34 synthesized in Example 6. DETAILED DESCRIPTION

[0043] The present application will be further described by the following examples, but the protection scope of the present application is not limited to the examples.

[0044] In this invention, the crystal form of the molecular sieve product is determined by X-ray diffraction (XRD). A Bruker D8 Advance diffractometer is used, with a Cu-Kα ray source, operating voltage of 40 kV, current of 200 mA, scanning range of 5-50°, scanning step size of 0.02°, and scanning speed of 4° / min.

[0045] In this invention, the morphology of the molecular sieve product is determined by scanning electron microscopy (SEM). The SEM images of the molecular sieve are obtained using a Nova NanoSEM 450 scanning electron microscope. Before testing, the sample is ground into a 200-400 mesh powder, fixed with double-sided conductive adhesive, and tested under high vacuum conditions with a microscope emission voltage of 200 kV. During the test, a random field of view is selected, and the average sum of the particle sizes of all crystals in that field of view is calculated. This operation is repeated 10 times, and the average sum of the 10 averages is taken as the crystal particle size.

[0046] In the embodiments and comparative examples of this invention, during the methanol-to-olefins reaction: a small fixed-bed device is used, the methanol feed pump is turned on, the methanol flow rate is set, the feed valve is opened, and methanol enters the reactor to start the reaction. The reaction product is taken after a certain reaction time, and samples are taken once at regular intervals. The samples are analyzed using an Agilent 7890 gas chromatograph.

[0047] The distribution of hydrocarbon products (wt%) was quantitatively detected by the FID detector of the chromatography and calculated using the correction normalization method.

[0048]

Comparative Example 1

[0049] Preparation of low-silica SAPO-18 molecular sieves

[0050] Using boehmite, phosphoric acid, silica sol, and N,N-diisopropylethylamine as the aluminum source, phosphorus source, silicon source, and template agent (T) respectively, the ingredients were weighed and mixed in a molar ratio of Al2O3:P2O5:SiO2:T:H2O = 1.0:1.0:0.2:2.0:45. The mixture was then placed in a crystallization vessel lined with polytetrafluoroethylene and crystallized at 195°C under autogenous pressure for 24 hours. The crystallized product was washed with deionized water until neutral. The separated solid was dried in an oven at 100°C and calcined in a muffle furnace at 550°C for 6 hours to obtain a low-silica SAPO-18 molecular sieve, denoted as A1. The SiO2 / Al2O3 molar ratio of A1 was 0.18.

[0051] [Comparative Example 2]

[0052] Preparation of high-silica SAPO-18 molecular sieves

[0053] Alumina, phosphoric acid, silica sol, and N,N-diisopropylethylamine were weighed and mixed in a molar ratio of Al₂O₃:P₂O₅:SiO₂:T:H₂O = 1.0:1.0:2.0:2.0:45. The mixture was then placed in a crystallization vessel lined with polytetrafluoroethylene (PTFE) and crystallized at 195°C under autogenous pressure for 24 hours. The crystallized product was washed with deionized water until neutral. The separated solid was dried in an oven at 100°C and calcined in a muffle furnace at 550°C for 6 hours to obtain a high-silica SAPO-18 molecular sieve, denoted as A₂. The SiO₂ / Al₂O₃ molar ratio of A₂ was 1.8.

[0054] [Comparative Example 3]

[0055] Preparation of sheet-like high-silica SAPO-18 molecular sieves

[0056] Alumina, phosphoric acid, silica sol, N,N-diisopropylethylamine, and tetraethylammonium hydroxide were weighed and mixed as aluminum source, phosphorus source, silicon source, and mixed template agent (T1+T2) respectively, in a molar ratio of Al2O3:P2O5:SiO2:T1:T2:H2O = 1.0:1.0:2.0:1.51:0.59:45. The mixture was then placed in a crystallization vessel lined with polytetrafluoroethylene and crystallized at 195°C under autogenous pressure for 24 hours. The crystallized product was washed with deionized water until neutral. The separated solid was dried in an oven at 100°C and calcined in a muffle furnace at 550°C for 6 hours to obtain a sheet-like high-silica SAPO-18 molecular sieve, denoted as A3. The scanning electron microscope image of A3 is shown below. Figure 1 As shown, the length is 200–400 nm, the width is 200–400 nm, and the height is 20–30 nm. The XRD pattern for A3 is shown below. Figure 2 As shown, the SiO2 / Al2O3 molar ratio of A3 is 1.9.

[0057] [Comparative Example 4]

[0058] (1) Using boehmite, phosphoric acid, N,N-diisopropylethylamine and tetraethylammonium hydroxide as aluminum source, phosphorus source and mixed template agent (R1+R2) respectively, the ingredients were weighed in a molar ratio of Al2O3:P2O5:R1:R2:H2O=1.0:1.0:1.5:1.0:40, and mixed evenly to obtain a crystallization solution;

[0059] (2) Add Al obtained from Comparative Example 1 to the above crystallization solution. The solid-liquid mass ratio of Al to the crystallization solution (based on the total mass of Al2O3 and P2O5) is 0.1:1.0. The above reaction mixture is loaded into a crystallization vessel with a polytetrafluoroethylene liner and crystallized at 130°C under autogenous pressure for 12 hours, and then crystallized at 180°C under autogenous pressure for 24 hours. The crystallization product is washed with deionized water until neutral. The separated solid is dried in an oven at 100°C and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-18 molecular sieve, denoted as A4.

[0060] [Comparative Example 5]

[0061] (1) High-purity alumina, phosphoric acid, triethylamine and tetraethylammonium bromide were weighed as aluminum source, phosphorus source and mixed template agent (R1+R2) respectively, and mixed evenly to obtain crystallization solution.

[0062] (2) Add Al obtained in Comparative Example 1 to the above crystallization solution. The solid-liquid mass ratio of Al to the crystallization solution is 0.5:1.0. The reaction mixture is placed in a crystallization vessel with a polytetrafluoroethylene liner and crystallized at 150°C under autogenous pressure for 16 hours, followed by crystallization at 190°C for 18 hours. The crystallized product is washed with deionized water until neutral. The solid is separated, dried in an oven at 100°C, and calcined in a muffle furnace at 550°C for 6 hours to obtain a SAPO-34 / SAPO-18 composite molecular sieve, denoted as A5. The XRD pattern of A5 is shown below. Figure 3 As shown.

[0063] [Comparative Example 6]

[0064] Using boehmite, phosphoric acid, silica sol, triethylamine, and tetraethylammonium hydroxide as the aluminum source, phosphorus source, silicon source, and mixed template agent (R1+R2) respectively, the ingredients were weighed and mixed in a molar ratio of Al2O3:P2O5:SiO2:R1:R2:H2O = 1.0:1.0:0.2:1.6:0.4:40. After thorough mixing, the reaction mixture was placed in a crystallization vessel lined with polytetrafluoroethylene and crystallized at 150°C under autogenous pressure for 16 hours, followed by crystallization at 195°C under autogenous pressure for 24 hours. The crystallized product was washed with deionized water until neutral. The separated solid was dried in an oven at 100°C and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-34 molecular sieve, denoted as A6. The grain size of A6 is 1–3 μm. The scanning electron microscope image of A6 is shown below. Figure 4 As shown.

[0065]

Example 1

[0066] Compared to Comparative Example 4, the difference lies in that the SAPO-18 molecular sieve A2 obtained in Comparative Example 2 was added to the crystallization solution for crystallization, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 hours, and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-34 molecular sieve, denoted as S1. The crystallite size of S1 is 500–700 nm. The XRD pattern of S1 is shown below. Figure 5 As shown.

[0067]

Example 2

[0068] High-purity alumina, phosphoric acid, silica sol, tetraethylammonium hydroxide, and triethylamine were weighed and mixed as aluminum source, phosphorus source, silicon source, and mixed template agent (R1+R2) respectively, with a molar ratio of Al2O3:P2O5:SiO2:R1:R2:H2O = 1.0:1.0:0.02:1.5:1.5:30. The mixture was then added to A2 obtained in Comparative Example 2. The solid-liquid mass ratio of A2 to the crystallization solution was 0.3:1.0. The above reaction mixture was placed in a crystallization vessel with a polytetrafluoroethylene liner and crystallized at 120°C under autogenous pressure for 24 hours, followed by crystallization at 195°C under autogenous pressure for 24 hours. The crystallization product was washed with deionized water until neutral, and the solid was separated and dried in an oven at 100°C and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-34 molecular sieve, denoted as S2. The S2 grain size is 400–600 nm. The XRD pattern of S2 is similar. Figure 5 .

[0069]

Example 3

[0070] Compared to Comparative Example 5, the difference lies in that the SAPO-18 molecular sieve A2 obtained in Comparative Example 2 was added to the crystallization solution for crystallization, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 hours, and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-34 molecular sieve, denoted as S3. The crystallite size of S3 is 550–750 nm. The XRD pattern of S3 is similar. Figure 5 .

[0071]

Example 4

[0072] Aluminum isopropoxide, phosphorous acid, tetraethylammonium hydroxide, and tetraethylammonium bromide were weighed out as aluminum source, phosphorus source, and mixed template agent (R1+R2) respectively, with a molar ratio of Al2O3:P2O5:R1:R2:H2O = 1.0:0.9:1.3:1.0:25. After thorough mixing, A2 obtained in Comparative Example 2 was added. The solid-liquid mass ratio of A2 to the crystallization solution was 0.06:1.0. The reaction mixture was placed in a crystallization vessel lined with polytetrafluoroethylene and crystallized at 195°C under autogenous pressure for 36 hours. The crystallized product was washed with deionized water until neutral, and the solid was separated, dried in an oven at 100°C, and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-34 molecular sieve, denoted as S4. The crystallite size of S4 was 500–800 nm. The XRD pattern of S4 was similar to... Figure 5 .

[0073]

Example 5

[0074] High-purity alumina, phosphorous acid, tetraethyl orthosilicate, triethylamine, and tetraethylammonium hydroxide were used as the aluminum source, phosphorus source, silicon source, and mixed template agent (R1+R2) respectively, with a molar ratio of Al2O3:P2O5:SiO2:R1:R2:H2O = 1.0:1.0:0.015:1.6:0.55:55. The mixture was weighed and thoroughly combined, and then A2 obtained from Comparative Example 2 was added. The solid-liquid mass ratio of A2 to the crystallization solution was 45:1.0. The above reaction mixture was placed in a crystallization vessel with a polytetrafluoroethylene liner and crystallized at 200°C under autogenous pressure for 48 hours. The crystallized product was washed with deionized water until neutral, and the solid was separated, dried in an oven at 100°C, and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-34 molecular sieve, denoted as S5. The grain size of S5 was 500–800 nm. The XRD pattern of S5 was similar to... Figure 5 .

[0075]

Example 6

[0076] High-purity alumina, phosphoric acid, triethylamine, and tetraethylammonium bromide were used as the aluminum source, phosphorus source, and mixed template agent (R1+R2), respectively, in a molar ratio of Al2O3:P2O5:R1:R2:H2O = 1.0:1.0:1.5:1.5:20. The mixture was thoroughly prepared and then A3 obtained in Comparative Example 3 was added. The solid-liquid mass ratio of A3 to the crystallization solution was 0.5:1.0. The reaction mixture was placed in a crystallization vessel lined with polytetrafluoroethylene and crystallized at 150°C under autogenous pressure for 16 hours, followed by crystallization at 190°C under autogenous pressure for 18 hours. The crystallized product was washed with deionized water until neutral, and the solid was separated and dried in an oven at 110°C. It was then calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-34 molecular sieve, denoted as S6. The crystallite size of S6 was 100–300 nm. A scanning electron microscope image of S6 is shown below. Figure 6 As shown, the XRD pattern of S6 is as follows: Figure 7As shown.

[0077]

Example 7

[0078] High-purity alumina, phosphorous acid, tetraethyl orthosilicate, triethylamine, and tetraethylammonium bromide were weighed and mixed as aluminum source, phosphorus source, silicon source, and mixed template agent (R1+R2) respectively, in a molar ratio of Al2O3:P2O5:SiO2:R1:R2:H2O = 1.0:1.0:0.015:1.6:0.55:55. After thorough mixing, A3 obtained in Comparative Example 3 was added. The solid-liquid mass ratio of A3 to the crystallization solution was 12:1.0. Crystallization was carried out at 160℃ under autogenous pressure for 12 hours, followed by crystallization at 195℃ under autogenous pressure for 30 hours. The mixture was centrifuged, washed with deionized water until neutral, dried in an oven at 110℃ for 12 hours, and calcined in a muffle furnace at 550℃ for 6 hours to obtain SAPO-34 molecular sieve, denoted as S7. The crystallite size of S7 was 200–450 nm. The XRD pattern of S7 was similar to... Figure 7 .

[0079]

Example 8

[0080] Boehmite, phosphoric acid, silica sol, triethylamine, and N,N-diisopropylethylamine were used as the aluminum source, phosphorus source, silicon source, and mixed template agent (R1+R2) respectively, with a molar ratio of Al2O3:P2O5:SiO2:R1:R2:H2O = 0.9:1.0:0.01:2.0:0.2:60. The ingredients were weighed and mixed evenly, and then A3 obtained from Comparative Example 3 was added. The solid-liquid mass ratio of A3 to the crystallization solution was 7.0:1.0. The above reaction mixture was placed in a crystallization vessel with a polytetrafluoroethylene liner and crystallized at 140°C under autogenous pressure for 16 hours, and then crystallized at 200°C under autogenous pressure for 24 hours. The crystallized product was washed with deionized water until neutral, and the solid was separated and dried in an oven at 100°C and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-34 molecular sieve, denoted as S8. The S8 grain size is 300–500 nm. The XRD pattern of S8 is similar. Figure 7 .

[0081]

Example 9

[0082] Catalyst evaluation experiment

[0083] Comparative Examples 1-6 and Examples 1-8, samples A1-A6 and S1-S8, were respectively tableted, crushed, and sieved to obtain particles of 20-40 mesh size. Catalyst evaluation experiments were conducted using a fixed-bed catalytic reactor. The experimental conditions were: catalyst loading of 2.0 g, reaction temperature of 465 °C, reaction pressure of 0.1 MPa, reactant of 75% methanol, and weight hourly space velocity of 4 h⁻¹. -1 .

[0084] Table 1

[0085]

[0086]

[0087] The embodiments described above are merely detailed descriptions of the technical solutions of the present invention, but the present invention is not limited to the above embodiments, that is, the present invention does not depend on the steps described in the above embodiments to be implemented. In summary, any improvements made to the present invention by those skilled in the art, including the substitution of the raw materials and additives described in the present invention, the selection of specific implementation methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A preparation method of small crystal SAPO-34 molecular sieve, comprising the following steps: (1) Mix an aluminum source, a phosphorus source, a template R, water and an optional silicon source to obtain a crystallization solution; (2) Add high-silicon SAPO-18 molecular sieve to the crystallization solution prepared in step (1), crystallize and calcine to obtain the small crystal SAPO-34 molecular sieve; In step (1), the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the phosphorus source is calculated as P2O5. The molar ratios of the components in the crystallization solution are as follows: SiO2:Al2O3:P2O5:R:H2O = 0~0.02:1:0.5~2.0:1.0~7.0:5~70; In step (2), the SiO2 / Al2O3 molar ratio of the high-silicon SAPO-18 molecular sieve is 1.0~10.0; The small crystal SAPO-34 molecular sieve has a cubic shape with a certain hollow structure.

2. The preparation method according to claim 1, characterized in that, In step (1), the template R is selected from at least one of N,N-diisopropylethylamine, tetraethylammonium hydroxide, triethylamine or tetraethylammonium bromide.

3. The preparation method according to claim 2, characterized in that, In step (1), the template R is selected from at least two of N,N-diisopropylethylamine, tetraethylammonium hydroxide, triethylamine or tetraethylammonium bromide.

4. The preparation method according to claim 1, characterized in that, In step (2), the SiO2 / Al2O3 molar ratio of the high-silicon SAPO- 5. The preparation method according to claim 1, characterized in that, ​ 6. The preparation method according to claim 1, characterized in that, ​ 7. The preparation method according to claim 6, characterized in that, ​ 8. The preparation method according to claim 7, characterized in that, ​ 9. The preparation method according to claim 1, characterized in that, ​ 10. The preparation method according to claim 1, characterized in that, ​ ​ 12. The small-grained SAPO-34 molecular sieve according to claim 11, characterized in that, ​ ​ 14. The application according to claim 13, characterized in that, The reaction conditions are as follows: reaction temperature 350~500℃, reaction pressure 0~1MPa, weight hourly space velocity 1~6h. -1 .

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