Preparation method and use of a porous, low-silicon SAPO-34 molecular sieve

Abstract

The present invention provides a method for preparing a porous, low-silica SAPO-34 molecular sieve. The present invention also provides the porous, low-silica SAPO-34 molecular sieve prepared by the said preparation method and its uses. The preparation method provided by the present invention uses a homologous microporous SAPO-34 molecular sieve as a silicon source, and at the same time adds a preliminary hydrothermal treatment before the addition of the template agent. The prepared molecular sieve product has a low silicon-aluminum ratio and is easy to regulate, and has a porous structure and a honeycomb-like microscopic morphology. The specific surface area and pore volume have been greatly improved. The SAPO-34 molecular sieve product provided by the present invention has excellent catalytic performance and can be used to catalyze various reaction types, especially can be used to catalyze the reaction of converting organic oxygenates into light olefins, can significantly improve the selectivity of diolefins, and the service life of the catalyst is also extended.

Description

Technical Field

[0001] The present invention relates to the field of catalyst preparation, and in particular to a preparation method of a porous, low-silicon SAPO-34 molecular sieve, the porous, low-silicon SAPO-34 molecular sieve prepared thereby and its uses, and also relates to a method for producing olefins from oxygen-containing organic compounds. Background Art

[0002] The MTO process for producing olefins from methanol is one of the important chemical technologies. Using methanol synthesized from coal or natural gas as a raw material to produce light olefins is the core technology for developing the production of ethylene, propylene and other chemical products from non-petroleum resources.

[0003] The SAPO-34 molecular sieve is one of the common catalysts for the reaction of producing olefins from methanol. It has high activity and good selectivity for ethylene and propylene, but the selectivity for butene is not high, and its small-pore microporous structure easily leads to catalyst deactivation. The SAPO-34 molecular sieve can be divided into medium-high-silicon SAPO-34 molecular sieves and low-silicon SAPO-34 molecular sieves. The low-silicon SAPO-34 molecular sieve has more excellent MTO catalytic performance, but its preparation process is more demanding than that of the medium-high-silicon SAPO-34 molecular sieve, and it is usually difficult to prepare a pure-phase product.

[0004] To further improve the performance of the SAPO-34 molecular sieve, a large number of related studies have been carried out in the industry, including:

[0005] The non-patent literature "Key parameters in hydrothermal synthesis and characterization of low silicon content SAPO-34 molecular sieve" (Microporous and Mesoporous Materials, 2009, 126, 1-7) mentions several common methods for synthesizing low-silicon SAPO-34 molecular sieves: the first is to add fluoride to promote the depolymerization of silicon species to synthesize low-silicon SAPO-34 molecular sieves; the second is to add mineralizer hydrochloric acid to synthesize low-silicon SAPO-34 molecular sieves; the third is to first synthesize a high-silicon molecular sieve and then desilicate it to synthesize low-silicon SAPO-34 molecular sieves. However, these methods often have problems such as difficulty in synthesizing high-crystallinity pure-phase SAPO-34 molecular sieves, poor repeatability and many steps.

[0006] In the non-patent literature "An effective route to improve the catalytic performance of SAPO-34 in the methanol-to-olefin reaction" (Journal of Natural Gas Chemistry, 2012, 21, 431-434), oxalic acid was used as a treatment solution to post-treat the synthesized SAPO-34 molecular sieve, and finally a hierarchical pore SAPO-34 molecular sieve was prepared. This molecular sieve has a low silicon content and improved MTO catalytic performance. However, the post-treatment method is complex and produces more pollution, which limits its application in industrial production.

[0007] Chinese Patent CN 104556142A discloses a preparation method of a low-silicon SAPO-34 molecular sieve. In this method, a silicon phosphoaluminate dry gel is first synthesized to fully mix silicon, phosphorus and aluminum species, and then a special segmented crystallization method is used to synthesize a high-crystallinity low-silicon SAPO-34 molecular sieve. However, this method is relatively complex, the crystallization conditions are not easy to control, and it is not easy to realize industrial application.

[0008] Chinese Patent CN 110467201B discloses a preparation method of a hierarchical pore SAPO-34 molecular sieve. This method uses SBA-15, MCM-41, MCM-48 or kaolin as a silicon source, and after aging and segmented isothermal crystallization, a SAPO-34 molecular sieve with a honeycomb-like surface is obtained. However, the silicon sources used in this method are all mesoporous molecular sieves, the synthesis process is complex and the cost is high. At the same time, the addition of these mesoporous molecular sieves only serves as a silicon source, and the silica on their skeletons is mostly amorphous, so it is necessary to dissolve and activate them through a segmented crystallization process.

[0009] It can be seen from this that a large number of studies have been carried out on SAPO-34 molecular sieves in the prior art, and the product performance has also been improved to a certain extent. However, compared with medium-high silicon molecular sieves with mature processes, the preparation of low-silicon molecular sieves is more difficult, and their catalytic performance is more excellent. Therefore, it is necessary to develop a preparation method of low-silicon SAPO-34 molecular sieves with simple process and good repeatability, which is more suitable for industrial production and can obtain molecular sieve products with excellent performance. Summary of the Invention

[0010] To make up for the deficiencies in the prior art, an object of the present invention is to provide a preparation method of a porous, low-silicon SAPO-34 molecular sieve. This preparation method has a simple process and good repeatability. The prepared molecular sieve product has a porous structure of "micropores + mesopores" and a low silicon-aluminum ratio, so it can be used as a catalyst for various reactions, has excellent catalytic performance and a long service life.

[0011] Another object of the present invention is to provide a porous, low-silica SAPO-34 molecular sieve and its use.

[0012] Still another object of the present invention is to provide a method for producing olefins from organic oxygenates.

[0013] The preparation method of the porous, low-silica SAPO-34 molecular sieve provided by the present invention comprises the following steps:

[0014] S1: Mix an aluminum source, a phosphorus source, a silicon source and a first portion of water, and perform hydrothermal treatment at 60-120 °C for 2-8 hours to obtain a crystallization precursor solution;

[0015] S2: Mix the crystallization precursor solution with a template T and a second portion of water to obtain a mixed solution, wherein the molar ratio of the substances is Al2O3:P2O5:H2O:T = 1:0.8-3:10-300:0.5-5; and

[0016] S3: Perform hydrothermal crystallization on the mixed solution, and the obtained solid is dried and calcined to obtain the porous, low-silica SAPO-34 molecular sieve, wherein the Si / Al molar ratio is 0.05-0.12;

[0017] Wherein, the silicon source is a medium-high-silica SAPO-34 molecular sieve, the Si / Al molar ratio is 0.2-0.4, and based on Al2O3 in the aluminum source, the addition amount of the silicon source is 1-50 wt% of Al2O3.

[0018] The preparation method provided by the present invention uses a homologous microporous SAPO-34 molecular sieve as the silicon source. First, it is hydrothermally pretreated with a phosphorus source and an aluminum source, and the obtained crystallization precursor solution is subjected to one-step hydrothermal crystallization under the action of a template to obtain a low-silica SAPO-34 molecular sieve with a special morphology. The homologous SAPO-34 molecular sieve can not only be used as the silicon source but also act as a seed crystal, which can not only change the silicon-aluminum ratio to obtain a low-silica SAPO-34 molecular sieve, but also promote the crystallization process, reduce the molecular sieve crystallization time, improve the process stability, and greatly improve the molecular sieve synthesis yield. Moreover, the preparation process of the medium-high-silica SAPO-34 molecular sieve is mature and simple, and using it as the silicon source will not significantly increase the cost.

[0019] In the preparation method provided by the present invention, the Si / Al molar ratio of the prepared porous, low-silica SAPO-34 molecular sieve can be conveniently adjusted within the range of 0.05-0.12, for example, it can be about 0.05, about 0.06, about 0.07, about 0.08, about 0.09, about 0.10, about 0.11, about 0.12 or can be any combination of molar ratio ranges.

[0020] In the preparation method provided by the present invention, the medium-high silicon SAPO-34 molecular sieve used as the silicon source can be of common types in the art. It has a regular cubic structure and only contains microporous channels. It can be a commercially available product or can be prepared according to the conventional methods in the art, for example, prepared according to the preparation process described in Comparative Example 1 of the present invention. The prepared molecular sieve is detected by XRF and its silicon-aluminum ratio is calculated.

[0021] In the preparation method provided by the present invention, the dosage of the SAPO-34 molecular sieve used as the silicon source can be 1-50 wt% of the mass of Al2O3 (converted according to the mass of the aluminum source). For example, it can be about 1 wt%, about 5 wt%, about 10 wt%, about 15 wt%, about 20 wt%, about 25 wt%, about 30 wt%, about 35 wt%, about 40 wt%, about 45 wt%, about 50 wt% or can be any combination of weight percentage ranges. In some preferred embodiments, the dosage of the SAPO-34 molecular sieve used as the silicon source can be 15-30 wt% of the mass of Al2O3.

[0022] In the preparation method provided by the present invention, the aluminum source can be common types used in the art for preparing SAPO-34 molecular sieves. In some preferred embodiments, the aluminum source can be selected from one or more of pseudoboehmite, aluminum sol, and aluminum isopropoxide.

[0023] In the preparation method provided by the present invention, the phosphorus source can be common types used in the art for preparing SAPO-34 molecular sieves. In some preferred embodiments, the phosphorus source can be selected from one or both of phosphoric acid and phosphorous acid.

[0024] In the preparation method provided by the present invention, the first part of water is mainly used to make the aluminum source, phosphorus source, and silicon source mix evenly, and its dosage can be 70-85 wt% of the total amount of water.

[0025] In the preparation method provided by the present invention, in step S1, the aluminum source, phosphorus source, silicon source, and the first part of water can be in any mixing order, and the materials can also be made to mix evenly by means such as stirring. In some preferred embodiments, the aluminum source, silicon source, and the first part of water (such as deionized water) can be mixed first, stirred for 0.5-3 hours until uniform, and then the phosphorus source is added and stirred for 1-5 hours until uniform.

[0026] In the preparation method provided by the present invention, in step S1, the temperature of the hydrothermal treatment can further be 90-120 °C, and the time of the hydrothermal treatment can further be 2-6 hours.

[0027] In the preparation method provided by the present invention, the template T can be a common type used in the field for preparing SAPO-34 molecular sieve. In some preferred embodiments, the template T can be selected from one or more of triethylamine, diethylamine, diisopropylamine, tetraethylammonium hydroxide, N,N-diisopropylethylamine, cyclohexylamine, n-butylamine, and morpholine.

[0028] In the preparation method provided by the present invention, in step S2, the molar ratio of substances in the mixed solution can further be Al2O3:P2O5:H2O:T = 1:0.8 - 2:20 - 100:2 - 5. In some preferred embodiments, in step S2, the molar ratio of substances in the mixed solution can further be Al2O3:P2O5:H2O:T = 1:0.9 - 1.2:40 - 70:3 - 4.

[0029] In the preparation method provided by the present invention, in step S2, the crystallization precursor solution can first be cooled to room temperature, and after adding the template T and the second portion of water, it can be stirred at room temperature for 1 - 6 hours until uniform to obtain the mixed solution.

[0030] In the preparation method provided by the present invention, since homologous SAPO-34 molecular sieve is used as the silicon source, the time of the hydrothermal crystallization step can be greatly shortened, and the process is also simplified. In step S3, the hydrothermal crystallization can be carried out under the condition of 160 - 220 °C for 2 - 12 hours. In some preferred embodiments, the crystallization can be carried out under the condition of 180 - 210 °C for 6 - 12 hours.

[0031] In the preparation method provided by the present invention, in step S3, the drying can be a common drying step in the field. In some preferred embodiments, the drying can be carried out under the condition of 80 - 150 °C for 6 - 24 hours. In some more preferred embodiments, the drying can be carried out under the condition of 100 - 130 °C for 10 - 15 hours.

[0032] In the preparation method provided by the present invention, in step S3, the calcination can be a common calcination step in the field. In some preferred embodiments, the calcination can be carried out under the condition of 400 - 700 °C for 2 - 10 hours. In some more preferred embodiments, the calcination can be carried out under the condition of 500 - 600 °C for 6 - 10 hours.

[0033] In the preparation method provided by the present invention, the mixing of materials can be promoted through the stirring step, and the stirring method can be a common method in the field, including but not limited to mechanical stirring, magnetic stirring, etc.

[0034] In the preparation method provided by the present invention, the required materials can be obtained through a separation step. For example, a solid substance is obtained by separation after crystallization. The separation method can be a common method in the art, including but not limited to (atmospheric or vacuum) filtration, centrifugation, etc.

[0035] The present invention also provides a porous, low-silica SAPO-34 molecular sieve prepared by the preparation method according to any one of the above technical solutions.

[0036] The total specific surface area of the porous, low-silica SAPO-34 molecular sieve provided by the present invention can be 650-720 m 2 / g. For example, it can be about 650 m 2 / g, about 660 m 2 / g, about 670 m 2 / g, about 680 m 2 / g, about 690 m 2 / g, about 700 m 2 / g, about 710 m 2 / g, about 720 m 2 / g or can be an interval of any combination. In some preferred embodiments, the total specific surface area can be 650-700 m 2 / g. In some more preferred embodiments, the total specific surface area can be 660-680 m 2 / g.

[0037] The total pore volume of the porous, low-silica SAPO-34 molecular sieve provided by the present invention can be 0.35-0.41 cm 3 / g. For example, it can be about 0.35 cm 3 / g, about 0.36 cm 3 / g, about 0.37 cm 3 / g, about 0.38 cm 3 / g, about 0.39 cm 3 / g, about 0.40 cm 3 / g, about 0.41 cm 3 / g, about 0.42 cm 3 / g or can be an interval of any combination. In some preferred embodiments, the total pore volume can be 0.36-0.40 cm 3 / g. In some more preferred embodiments, the total pore volume can be 0.36-0.38 cm 3 / g.

[0038] The porous, low-silica SAPO-3 molecular sieve provided by the present invention has a cubic morphology with honeycombs on the surface, as Figure 2-5 shown. Compared with the conventional cubic structure (such as Figure 6As shown in the figure, on the basis of retaining the basic cubic structure, the porous, low-silica SAPO-34 molecular sieve provided by the present invention presents a honeycomb shape.

[0039] The porous, low-silica SAPO-34 molecular sieve provided by the present invention includes both micropores and mesopores.

[0040] In the porous, low-silica SAPO-34 molecular sieve provided by the present invention, the total specific surface area of the micropores can account for 85-96% of the total specific surface area, for example, it can be about 85%, about 88%, about 90%, about 91%, about 92%, about 93%, about 94%, about 96% or any combination of intervals. The total specific surface area of the micropores can be 600-650 m 2 / g, for example, it can be about 600 m 2 / g, about 610 m 2 / g, about 620 m 2 / g, about 630 m 2 / g, about 640 m 2 / g, about 650 m 2 / g or any combination of intervals. In some preferred embodiments, the total specific surface area of the micropores can be 610-630 m 2 / g.

[0041] In the porous, low-silica SAPO-34 molecular sieve provided by the present invention, the total pore volume of the micropores can be 0.20-0.25 cm 3 / g, for example, it can be about 0.20 cm 3 / g, about 0.21 cm 3 / g, about 0.22 cm 3 / g, about 0.23 cm 3 / g, about 0.24 cm 3 / g, about 0.25 cm 3 / g or any combination of intervals. In some preferred embodiments, the total pore volume of the micropores can be 0.22-0.24 cm 3 / g.

[0042] Compared with the conventional microporous SAPO-34 molecular sieve, the SAPO-34 molecular sieve provided by the present invention has a "micropore + mesopore" porous structure, and has a low silicon-aluminum ratio (0.05-0.12). The specific surface area and pore volume have also been greatly improved. Therefore, it is particularly suitable for the reaction of producing (lower carbon) olefins from oxygenated organic compounds. For example, in the reaction of producing olefins from methanol, it can effectively reduce the carbon deposition rate, improve the diffusion rate of reaction raw materials and reaction products in the catalyst, thereby significantly extending the service life of the catalyst, and at the same time improving the selectivity of lower carbon olefins.

[0043] The present invention also provides a porous, low-silica SAPO-34 molecular sieve prepared by the preparation method according to any one of the above technical solutions, or the use of the porous, low-silica SAPO-34 molecular sieve according to any one of the above technical solutions as a catalyst, for example, as a catalyst for catalyzing organic oxygenates to produce (lower-carbon) olefins.

[0044] Among them, the reaction of producing (lower-carbon) olefins from organic oxygenates is known to those skilled in the art and can be carried out in a fixed-bed reactor, a moving-bed reactor, or a fluidized-bed reactor. The organic oxygenates can be one or more of methanol, ethanol, dimethyl ether, diethyl ether, methyl ethyl ether, halogenated substitutes of methane (such as chloromethane, bromomethane, etc.), dimethyl carbonate, and methyl formate, and preferably methanol.

[0045] The present invention also provides the use of the porous, low-silica SAPO-34 molecular sieve prepared by the preparation method according to any one of the above technical solutions, or the porous, low-silica SAPO-34 molecular sieve according to any one of the above technical solutions as a catalyst for catalyzing methanol to olefins.

[0046] The present invention also provides a method for producing olefins from organic oxygenates, which uses the porous, low-silica SAPO-34 molecular sieve prepared by the preparation method according to any one of the above technical solutions, or the porous, low-silica SAPO-34 molecular sieve according to any one of the above technical solutions as a catalyst.

[0047] The present invention also provides a method for producing olefins from methanol, which uses the porous, low-silica SAPO-34 molecular sieve prepared by the preparation method according to any one of the above technical solutions, or the porous, low-silica SAPO-34 molecular sieve according to any one of the above technical solutions as a catalyst.

[0048] In the method for producing olefins provided by the present invention, except for the catalyst, other process conditions can refer to the common process conditions in the art and can be appropriately adjusted by those skilled in the art.

[0049] The technical solution provided by the present invention has the following advantages:

[0050] (1) The preparation method provided by the present invention uses a homologous microporous SAPO-34 molecular sieve as the silicon source, and at the same time adds a pre-hydrothermal treatment before adding the template agent, thereby preparing a low-silica SAPO-34 molecular sieve with a hierarchical pore structure. The process is simple, the conditions are mild, the operability is strong, the repeatability is good, the synthesis yield is high, there is no need for high costs and complex equipment, and it is suitable for large-scale industrial production.

[0051] (2) The SAPO-34 molecular sieve product provided by the present invention has a low silicon-aluminum ratio and is easy to regulate. Moreover, it has a porous structure of "micropores + mesopores" and a honeycomb-like microscopic morphology, and its specific surface area and pore volume have been greatly improved.

[0052] (3) The SAPO-34 molecular sieve product provided by the present invention has two characteristics: a low silicon-aluminum ratio and a hierarchical pore structure. Through their synergistic effect, the catalytic performance is particularly excellent, and it can be used to catalyze various reaction types. In particular, it can be used to catalyze the reaction of converting organic oxygen-containing compounds (such as methanol) into light olefins, which can significantly improve the selectivity of diolefins and extend the service life of the catalyst.

[0053] In summary, the preparation method provided by the present invention and the resulting porous, low-silicon SAPO-34 molecular sieve have low cost, simple manufacturing, are suitable for large-scale production, and have important economic and social values, so they have very good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is the X-ray diffraction (XRD) pattern of the molecular sieves synthesized in Examples 1-5 and Comparative Examples 1-2. Among them, characteristic diffraction peaks of SAPO-34 molecular sieve (2θ = 9.5 ± 0.1°, 15.9 ± 0.1°, 20.5 ± 0.1° and 25.1 ± 0.1°) appear in the patterns of Examples 1-5 and Comparative Example 1, indicating that the molecular sieves synthesized in Examples 1-5 and Comparative Example 1 are all SAPO-34 molecular sieves with CHA topological structure; characteristic diffraction peaks of SAPO-5 molecular sieve also appear at 2θ = 7.4 ± 0.1°, 19.6 ± 0.1°, etc. in the pattern of Comparative Example 2.

[0055] Figure 2 It is the scanning electron microscope (SEM) image of the molecular sieve synthesized in Example 1.

[0056] Figure 3 It is the SEM image of the molecular sieve synthesized in Example 2.

[0057] Figure 4 It is the SEM image of the molecular sieve synthesized in Example 3.

[0058] Figure 5 It is the SEM image of the molecular sieve synthesized in Example 4.

[0059] Figure 6 It is the SEM image of the molecular sieve synthesized in Comparative Example 1.

[0060] Figure 7 It is the SEM image of the molecular sieve synthesized in Comparative Example 2.

[0061] Figure 8 N2 adsorption - desorption curve of the molecular sieves synthesized in Example 1 and Comparative Example 1. Detailed implementation manners

[0062] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments.

[0063] The raw materials or reagents used in the examples and comparative examples of the present invention are all commercially available products unless otherwise specified.

[0064] The percentages used in the examples and comparative examples of the present invention are all mass percentages unless otherwise specified.

[0065] Example 1

[0066] 1) 10.00 g of pseudoboehmite (aluminum oxide content 67%), 2.00 g of SAPO - 34 molecular sieve (Si / Al (molar ratio) = 0.32) (based on Al2O3 in pseudoboehmite, the addition amount of SAPO - 34 molecular sieve is 30% of the mass of Al2O3) and 33.35 g of deionized water were mixed and stirred. After stirring for 1 hour, 14.88 g of phosphoric acid (85%) was added dropwise. After continuing to stir for 2 hours, the obtained solution was filled into a reaction kettle with a polytetrafluoroethylene liner and hydrothermally treated at 100 °C for 4 hours to obtain a crystallization precursor solution.

[0067] 2) The hydrothermally treated crystallization precursor solution was cooled to room temperature, 7.63 g of deionized water was added, and stirred for 1 hour. 19.65 g of triethylamine T was added to obtain a mixed solution, in which the molar ratio of each substance was Al2O3:P2O5:H2O:T = 1.0:1.0:40.0:3.0. After continuing to stir at room temperature for 2 hours, it was transferred into a reaction kettle with a polytetrafluoroethylene liner and hydrothermally crystallized at 200 °C for 6 hours.

[0068] 3) After the crystallization was completed, the solid product was separated by centrifugation, washed repeatedly with deionized water until neutral, and dried at 120 °C for 12 hours to obtain the SAPO - 34 molecular sieve raw powder. It was calcined in an air atmosphere at 550 °C for 8 hours to obtain the SAPO - 34 molecular sieve, and the synthesis yield was 80%.

[0069] The XRD pattern of the SAPO - 34 molecular sieve sample is as Figure 1 shown, and the microscopic morphology is as Figure 2 shown in the SEM image. The SAPO - 34 molecular sieve has a honeycomb - like hierarchical pore structure. The molar elemental composition of the XRF - detected sample is Al 0.531 Si 0.058 P 0.411 , and Si / Al (molar ratio) = 0.109.

[0070] Example 2

[0071] 1) Mix 10.00 g of pseudo-boehmite (aluminum oxide content 67%), 1.25 g of SAPO-34 molecular sieve (Si / Al (molar ratio) = 0.37) (based on Al2O3 in pseudo-boehmite, the addition amount of SAPO-34 molecular sieve is 19% of the mass of Al2O3) and 45.35 g of deionized water, stir for 1 hour, then dropwise add 14.20 g of phosphoric acid (85%). After continuing to stir for 2 hours, put the obtained solution into a reaction kettle with a polytetrafluoroethylene inner lining, and carry out hydrothermal treatment at 100 °C for 6 hours to obtain a crystallization precursor solution.

[0072] 2) Cool the crystallization precursor solution after hydrothermal treatment to room temperature, add 9.52 g of deionized water, stir for 1 hour, then add 19.65 g of triethylamine T to obtain a mixed solution, where the molar ratio of each substance is Al2O3:P2O5:H2O:T = 1.0:0.95:51.8:3.0. After continuing to stir at room temperature for 2 hours, transfer it to a reaction kettle with a polytetrafluoroethylene inner lining, and carry out hydrothermal crystallization at 200 °C for 8 hours.

[0073] 3) After the crystallization is completed, centrifuge to separate the solid product, wash it repeatedly with deionized water until neutral, and dry it at 120 °C for 12 hours to obtain the original powder of SAPO-34 molecular sieve. Calcinate it in an air atmosphere at 550 °C for 8 hours to obtain the SAPO-34 molecular sieve, and the synthesis yield is 78%.

[0074] The XRD pattern of the SAPO-34 molecular sieve sample is as Figure 1 shown, and the microscopic morphology is as Figure 3 shown in the SEM image. The SAPO-34 molecular sieve has a honeycomb-like hierarchical pore structure. The molar elemental composition of the sample detected by XRF is Al 0.535 Si 0.045 P 0.420 , and Si / Al (molar ratio) = 0.084.

[0075] Example 3

[0076] 1) Mix 10.00 g of pseudo-boehmite (aluminum oxide content 67%), 1.00 g of SAPO-34 molecular sieve (Si / Al (molar ratio) = 0.25) (based on Al2O3 in pseudo-boehmite, the addition amount of SAPO-34 molecular sieve is 15% of the mass of Al2O3) and 60.00 g of deionized water, stir for 1 hour, then dropwise add 14.20 g of phosphoric acid (85%). After continuing to stir for 2 hours, put the obtained solution into a reaction kettle with a polytetrafluoroethylene inner lining, and carry out hydrothermal treatment at 90 °C for 2 hours to obtain a crystallization precursor solution.

[0077] 2) Cool the crystallized precursor solution after hydrothermal treatment to room temperature, add 16.12 g of deionized water, stir for 1 hour, then add 20.26 g of diisopropylamine T to obtain a mixed solution, where the molar ratio of each substance is Al2O3:P2O5:H2O:T = 1.0:0.95:70.0:3.0. Continue to stir at room temperature for 2 hours, then transfer it to a reaction kettle with a polytetrafluoroethylene inner lining and carry out hydrothermal crystallization at 200 °C for 12 hours.

[0078] 3) After the crystallization is completed, centrifuge to separate the solid product, wash it repeatedly with deionized water until neutral, and dry it at 120 °C for 12 hours to obtain the raw powder of SAPO-34 molecular sieve. Calcinate it in an air atmosphere at 550 °C for 8 hours to obtain the SAPO-34 molecular sieve, and the synthesis yield is 75%.

[0079] The XRD pattern of the SAPO-34 molecular sieve sample is as Figure 1 shown, and the microscopic morphology is as Figure 4 shown in the SEM image. The SAPO-34 molecular sieve has a honeycomb-like hierarchical pore structure. The molar elemental composition of the sample detected by XRF is Al 0.547 Si 0.030 P 0.423 , and Si / Al (molar ratio) = 0.055.

[0080] Example 4

[0081] 1) Mix and stir 27.24 g of aluminum isopropoxide, 1.23 g of SAPO-34 molecular sieve (Si / Al (molar ratio) = 0.28) (the addition amount of SAPO-34 molecular sieve is 18% of the mass of Al2O3 based on Al2O3 in aluminum isopropoxide) and 50.00 g of deionized water. After stirring for 1 hour, add 15.16 g of phosphoric acid (85%) dropwise. After continuing to stir for 2 hours, transfer the obtained solution to a reaction kettle with a polytetrafluoroethylene inner lining and carry out hydrothermal treatment at 100 °C for 4 hours to obtain a crystallized precursor solution.

[0082] 2) Cool the crystallized precursor solution after hydrothermal treatment to room temperature, add 17.74 g of deionized water, stir for 1 hour, then add 20.25 g of diisopropylamine T to obtain a mixed solution, where the molar ratio of each substance is Al2O3:P2O5:H2O:T = 1.0:0.99:50.0:3.0. Continue to stir at room temperature for 2 hours, then transfer it to a reaction kettle with a polytetrafluoroethylene inner lining and carry out hydrothermal crystallization at 200 °C for 6 hours.

[0083] 3) After the crystallization is completed, centrifuge to separate the solid product, wash it repeatedly with deionized water until neutral, and dry it at 120 °C for 12 hours to obtain the raw powder of SAPO-34 molecular sieve. Calcinate it in an air atmosphere at 550 °C for 8 hours to obtain the SAPO-34 molecular sieve, and the synthesis yield is 82%.

[0084] The XRD pattern of the SAPO-34 molecular sieve sample is as Figure 1 shown, and the microscopic morphology is as Figure 5 shown in the SEM image. The SAPO-34 molecular sieve has a honeycomb-like hierarchical pore structure. The molar elemental composition of the sample detected by XRF is Al 0.549 Si 0.053 P 0.398 , and Si / Al (molar ratio) = 0.096.

[0085] Example 5

[0086] 1) Mix 10.00 g of pseudoboehmite (aluminum oxide content 67%), 1.50 g of SAPO-34 molecular sieve (Si / Al (molar ratio) = 0.22) (based on Al2O3 in pseudoboehmite, the addition amount of SAPO-34 molecular sieve is 22% of the mass of Al2O3) and 50.00 g of deionized water and stir. After stirring for 1 hour, add 16.35 g of phosphoric acid (85%). After continuing to stir for 2 hours, put the obtained solution into a reaction kettle with a polytetrafluoroethylene lining and hydrothermally treat it at 120 °C for 3 hours to obtain a crystallization precursor solution.

[0087] 2) Cool the hydrothermally treated crystallization precursor solution to room temperature, add 16.00 g of deionized water, stir for 1 hour, then add 16.65 g of triethylamine T1 and 7.25 g of diethylamine T2. In the obtained mixed solution, the molar ratio of each substance is Al2O3:P2O5:H2O:T1:T2 = 1.0:1.1:61.7:2.5:1.5. After continuing to stir at room temperature for 2 hours, transfer it into a reaction kettle with a polytetrafluoroethylene lining and hydrothermally crystallize it at 200 °C for 10 hours.

[0088] 3) After the crystallization is completed, centrifuge to separate the solid product, wash it repeatedly with deionized water until neutral, and dry it at 120 °C for 10 hours to obtain the SAPO-34 molecular sieve raw powder. Calcinate it in an air atmosphere at 550 °C for 8 hours to obtain the SAPO-34 molecular sieve, and the synthesis yield is 77%.

[0089] The XRD pattern of the SAPO-34 molecular sieve sample is as Figure 1 shown, and the microscopic morphology is similar to that of the products in Examples 1-4, being a honeycomb-like hierarchical pore structure. The molar elemental composition of the sample detected by XRF is Al 0.595 Si 0.067 P 0.337 , and Si / Al (molar ratio) = 0.112.

[0090] Comparative Example 1

[0091] 10.00 g of pseudo-boehmite (aluminum oxide content 67%), 14.88 g of phosphoric acid (85%) and 47.23 g of deionized water were mixed and stirred. After stirring for 1 hour, 7.71 g of silica sol (30%) was added dropwise. After stirring evenly, 19.65 g of template triethylamine was added, and stirring continued for 1 hour. Aging was carried out at room temperature for 2 hours. The molar ratio of each substance in the obtained mixture was: 3.0 TEA: 0.6 SiO2: 1.0 Al2O3: 1.0 P2O5: 50 H2O. The above gel was loaded into a reaction kettle with a polytetrafluoroethylene inner lining and hydrothermally crystallized at 200 °C for 48 hours. The obtained product was centrifugally washed with deionized water, filtered, dried, and then calcined in an air atmosphere at 550 °C for 8 hours to obtain SAPO-34 molecular sieve, and the synthesis yield was 48%.

[0092] The XRD pattern of the SAPO-34 molecular sieve sample is as Figure 1 shown, and the microscopic morphology is as Figure 6 shown in the SEM image. The SAPO-34 molecular sieve has a typical cubic morphology. The molar elemental composition of the XRF-detected sample is Al 0.552 Si 0.114 P 0.334 , and Si / Al (molar ratio) = 0.206.

[0093] Comparative Example 2

[0094] 1) 10.00 g of pseudo-boehmite (aluminum oxide content 67%), 7.71 g of silica sol (30%) and 37.23 g of deionized water were mixed and stirred. After stirring for 1 hour, 14.88 g of phosphoric acid (85%) was added dropwise. After continuing to stir for 2 hours, the obtained solution was loaded into a reaction kettle with a polytetrafluoroethylene inner lining and hydrothermally treated at 100 °C for 4 hours to obtain a crystallization precursor solution.

[0095] 2) The crystallization precursor solution after hydrothermal treatment was cooled to room temperature, 10.00 g of deionized water was added, and after stirring for 1 hour, 19.65 g of triethylamine was added. The molar ratio of each substance in the obtained mixed solution was 3.0 TEA: 0.6 SiO2: 1.0 Al2O3: 1.0 P2O5: 50 H2O. Stirring continued at room temperature for 2 hours, and then it was transferred into a reaction kettle with a polytetrafluoroethylene inner lining and hydrothermally crystallized at 200 °C for 48 hours.

[0096] 3) After crystallization, the solid product was separated by centrifugation, washed repeatedly with deionized water until neutral, dried at 120 °C for 12 hours to obtain the SAPO-34 molecular sieve raw powder. It was calcined in an air atmosphere at 550 °C for 8 hours to obtain the SAPO-34 molecular sieve, and the synthesis yield was 51%.

[0097] The XRD pattern of the SAPO-34 molecular sieve sample is as Figure 1As shown, the microscopic morphology is as Figure 7 shown in the SEM image of Figure 7 . The SAPO-34 molecular sieve has a typical cubic morphology, and a small amount of SAPO-5 prism structure appears.

[0098] Comparative Example 3

[0099] 10.00 g of pseudo-boehmite (aluminum oxide content 67%), 14.88 g of phosphoric acid (85%) and 47.23 g of deionized water were mixed and stirred. After stirring for 1 hour, 2.00 g of SAPO-34 molecular sieve (Si / Al (molar ratio) = 0.32) was added (calculated based on Al2O3 in pseudo-boehmite, the addition amount of SAPO-34 molecular sieve was 30% of the mass of Al2O3). After stirring evenly, 19.65 g of template triethylamine was added, and stirring was continued for 1 hour, followed by aging at room temperature for 2 hours. The molar ratio of each substance in the obtained gel was: 3.0 TEA: 1.0 Al2O3: 1.0 P2O5: 50 H2O. The above gel was loaded into a reaction kettle with a polytetrafluoroethylene lining and hydrothermally crystallized at 200 °C for 24 hours. No solid molecular sieve product was obtained after crystallization.

[0100] Comparative Example 4

[0101] The SAPO-34 molecular sieve was prepared according to Example 1 disclosed in Chinese Patent CN 110467201B.

[0102] Test Example 1

[0103] The N2 adsorption and desorption tests were carried out on 4 samples of Examples 1-3 and Comparative Example 1 using a Micrometitics ASAP 2020 adsorption instrument, and the results are shown in Table 1 and Figure 8 as shown.

[0104] As can be seen from Table 1, the honeycomb low-silicon SAPO-34 molecular sieve of the present invention has a relatively high specific surface area. From Figure 8 the N2 adsorption and desorption curve, it can also be seen that the SAPO-34 molecular sieve synthesized by the conventional method (Comparative Example 1, Curve A) shows a typical Type I isotherm, that is, only micropores exist, while the SAPO-34 molecular sieve synthesized in Example 1 (Curve B) shows an obvious hysteresis loop in the range of relative pressure > 0.7, presenting a typical Type IV isotherm, indicating that in addition to micropores, mesoporous channels also exist in this molecular sieve.

[0105] This shows that the SAPO-34 molecular sieve catalyst prepared by the method of the present invention has a hierarchical pore structure and a relatively high specific surface area.

[0106] Table 1 Pore structure parameters of the SAPO-34 molecular sieves synthesized in Examples 1-3 and Comparative Example 1

[0107]

[0108]

[0109] a: Calculated by the t-plot method.

[0110] Test Example 2

[0111] Using a fixed-bed catalytic reaction evaluation device, the molecular sieve catalysts prepared in Examples 1-5 and Comparative Examples 1 and 4 were evaluated for the methanol-to-olefins reaction.

[0112] The evaluation conditions were as follows: Weigh 0.8 g of each of the above molecular sieve catalyst samples and place them in the reactor. Activate with nitrogen at 500 °C for 0.5 h, then cool down to 450 °C. The raw material methanol solution passes through a flow metering pump and is mixed with the carrier gas - nitrogen and enters the preheating furnace, where it vaporizes into a gas and then enters the reactor for reaction. The nitrogen flow rate is 14 mL / min, and the methanol space velocity is 3.50 h -1 , and the reaction products were analyzed online by an Agilent 7890B chromatograph. In addition, the catalyst service life was calculated based on the time from the start of the reaction to when the methanol conversion reached 99.0%. The evaluation results are shown in Table 2.

[0113] Table 2 Catalyst Evaluation Results for Methanol-to-Olefins

[0114]

[0115] It can be seen from the results in Table 2 that compared with the SAPO-34 molecular sieve catalyst synthesized by the conventional method (Comparative Example 1), the honeycomb-shaped, porous, low-silicon SAPO-34 molecular sieve prepared in the present invention has excellent catalytic performance (the highest diolefin selectivity can reach over 83%) and an extended service life (the highest can reach 200 min) as a catalyst. The catalyst of Comparative Example 4 also has a honeycomb-shaped hierarchical pore structure, and compared with the catalyst of Comparative Example 1, its catalytic performance and service life have certain improvements, but it is still far inferior to the catalyst of the present invention.

[0116] Thus, it can be seen that the SAPO-34 molecular sieve product provided by the present invention has both the characteristics of a low silicon-to-aluminum ratio and a hierarchical pore structure. Through the synergistic effect of the two, it can effectively reduce or eliminate the diffusion and mass transfer limitations in the methanol-to-olefins reaction, reduce the occurrence of secondary reactions, and thus significantly improve the selectivity of light olefins and the catalyst life, and therefore has great industrial practical value.

[0117] In addition, it can be seen from Examples 1-5 that the preparation method of the present invention also has good reproducibility, and the silicon-aluminum ratio is easy to adjust. The expected molecular sieve products can be obtained, and the synthesis yield is high. It can be seen from Comparative Example 2 and Comparative Example 3 that changing the silicon source or process conditions cannot obtain the expected pure-phase product, or even any molecular sieve product.

[0118] Unless otherwise specified, the terms used in the present invention have the meanings commonly understood by those skilled in the art.

[0119] The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the protection scope of the present invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above embodiments, but is only defined by the claims.

Claims

1. A preparation method of a porous, low-silica SAPO-34 molecular sieve, characterized in that, The following steps are involved: S1: Mix the aluminum source, phosphorus source, silicon source and the first portion of water, and perform hydrothermal treatment at 60-120° C. for 2-8 hours to obtain a crystallization precursor solution; S2: mixing the crystallization precursor solution, the template T and the second portion of water to obtain a mixed solution, wherein the molar ratio of the substances is Al2O3:P2O5:H2O:T=1:0.8-3:10-300:0.5-5; as well as S3: hydrothermally crystallizing the mixed solution at 160-220° C. for 2-12 hours, and drying and calcining the resulting solid to obtain the porous, low-silicon SAPO-34 molecular sieve, wherein the Si / Al molar ratio is 0.05-0.12; The silicon source is a medium-high silicon SAPO-34 molecular sieve, the Si / Al molar ratio is 0.2-0.4, and based on the Al2O3 in the aluminum source, the added amount of the silicon source is 15-30wt% of the Al2O3.

2. The preparation method according to claim 1, characterized in that, The aluminum source is selected from one or more of pseudo-boehmite, aluminum sol, and aluminum isopropoxide; and / or The phosphorus source is selected from one or both of phosphoric acid and phosphorous acid; and / or The first portion of water accounts for 70-85 wt % of the total amount of water.

3. The preparation method according to claim 1, characterized in that, The template agent T is selected from one or more of triethylamine, diethylamine, diisopropylamine, tetraethylammonium hydroxide, N,N-diisopropylethylamine, cyclohexylamine, n-butylamine, and morpholine.

4. The preparation method according to claim 1, characterized in that In step S2, the molar ratio of substances in the mixed solution is Al2O3:P2O5:H2O:T=1:0.8~2:20~100:2~5.

5. The preparation method according to claim 4, characterized in that, In step S2, the molar ratio of substances in the mixed solution is Al2O3:P2O5:H2O:T=1:0.9~1.2:40~70:3~4.

6. The preparation method according to claim 1, characterized in that, In the step S2, the crystallization precursor solution is first cooled to room temperature, the template T and the second portion of water are added, and then stirred at room temperature for 1 to 6 hours until the mixture is uniform, thereby obtaining the mixed solution.

7. The preparation method according to any one of claims 1-6, characterized in that, In step S3, the drying is performed at 80-150° C. for 6-24 hours; and / or The calcination is carried out at 400-700° C. for 2-10 hours.

8. A porous, low-silica SAPO-34 molecular sieve, characterized in that, It is prepared according to the preparation method according to any one of claims 1 to 7.

9. The porous, low-silica SAPO-34 molecular sieve according to claim 8, wherein, The total specific surface area of the porous, low-silica SAPO-34 molecular sieve is 650 to 720 m 2 / g, and the total pore volume is 0.35 to 0.41 cm 3 / g; and / or The porous, low-silicon SAPO-34 molecular sieve has a cubic morphology with a honeycomb surface.

10. The porous, low-silica SAPO-34 molecular sieve according to claim 8 or 9, characterized in that, The porous, low-silica SAPO-34 molecular sieve includes microporous channels and mesoporous channels, and the total specific surface area of the micropores is 600-650 m 2 / g, and the total pore volume of the micropores is 0.20-0.25 cm 3 / g.

11. Use of the porous, low-silicon SAPO-34 molecular sieve prepared by the preparation method according to any one of claims 1 to 7 or the porous, low-silicon SAPO-34 molecular sieve according to any one of claims 8 to 10 as a catalyst for catalyzing the production of olefins from organic oxygen compounds.

12. The use according to claim 11, characterized in that, The organic oxygen-containing compound is methanol.

13. A method for producing olefins from an organic oxygen-containing compound, characterized in that, The method uses the porous, low-silicon SAPO-34 molecular sieve prepared by the preparation method according to any one of claims 1 to 7 or the porous, low-silicon SAPO-34 molecular sieve according to any one of claims 8 to 10 as a catalyst.

14. The method according to claim 13, wherein The organic oxygen-containing compound is methanol.

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