SAPO-5 molecular sieve as well as preparation method and application thereof

Abstract

The invention provides an SAPO-5 molecular sieve as well as a preparation method and application thereof. The SAPO-5 molecular sieve comprises spherical particles composed of nanocrystals, and the nanocrystals comprise a plurality of strip-shaped nanocrystals. The SAPO-5 molecular sieve provided by the invention is suitable for heterogeneous catalysis, adsorption, separation and ion exchange, is especially suitable for an isomerization reaction of m-toluene, and has relatively high conversion rate and target product selectivity.

Description

Technical Field

[0001] The invention belongs to the field of catalysts and relates to the field of silicoaluminophosphate molecular sieves, and specifically relates to a SAPO-5 molecular sieve and a preparation method and application thereof. Background Art

[0002] Silicoaluminophosphates (SAPO molecular sieves) were first invented by Union Carbide Corporation (UCC) in the United States (Lok, BM; Messina, CA; Patton, RL; Gajek, RT; Cannan, TR; Flanigen, EMJAm. Chem. Soc. 1984, 106, 6092). SAPO molecular sieves are a three-dimensional crystal structure composed of AlO4, SiO4 and PO4 tetrahedrons through shared oxygen atoms. In the pores of the crystal, SiO4 is a 4+ Partially replace P 5+ or Al 3+ Produce acidity. SAPO-5 molecular sieve has an AFI type structure, and its skeleton is a one-dimensional pore structure of twelve-membered rings composed of four-membered rings and six-membered rings, with a pore size of 0.8 nanometers, and has good thermal stability and hydrothermal stability (Xu Qinhua, SAPO molecular sieve. Petrochemicals, 1988, 3, 186-192). SAPO-5 molecular sieve is widely used in the fields of shape-selective catalysis, catalyst carriers, cracking reactions and aromatic compound reactions.

[0003] In the synthesis of SAPO-5 molecular sieve, the most commonly used method is hydrothermal synthesis. Zhang Guohong (Zhang Guohong, Synthesis phase diagram and performance study of SAPO-5 molecular sieve. Petrochemicals, 1989, 9, 600-605) synthesized SAPO-5 molecular sieve by hydrothermal synthesis, using tetraethyl orthosilicate as silicon source, phosphoric acid as phosphorus source, aluminum hydroxide powder as aluminum source, triethylamine as template, and two-stage crystallization at 150℃ and 180℃. Yu Xiaobo et al. (Preparation and characterization of SAPO-5 molecular sieve. Journal of Jilin Institute of Chemical Technology, 2011, 28, 4-7.) prepared SAPO-5 molecular sieve by hydrothermal synthesis, using aluminum isopropoxide as aluminum source, phosphoric acid as phosphorus source, silicon dioxide as silicon source, and triethylamine as template, and investigated the effect of different hydrothermal synthesis conditions on the crystal morphology of SAPO-5 molecular sieve. Scanning electron microscopy shows that when the crystallization temperature is 140°C, the SAPO-5 molecular sieve crystals obtained are hexagonal flakes with more cubic impurities. When the crystallization temperature is 180°C, the SAPO-5 molecular sieve crystals obtained are hexagonal prisms, and when the temperature rises to 200°C, the SAPO-5 molecular sieve obtained is spherical. Li Hongyuan et al. (Li Hongyuan, Liang Juan, Liu Baoxiang, et al. Synthesis of silicon aluminum phosphate molecular sieve SAPO-5. Journal of Catalysis, 1987, 1, 103-107) prepared SAPO-5 molecular sieve by hydrothermal synthesis, using pseudo-boehmite as aluminum source, phosphoric acid as phosphorus source, silica sol as silicon source, tetraethylammonium hydroxide as template, and crystallization temperature of 200°C. Liu Zhongmin et al. (Beibei Gao, Peng Tian, ​​Mingrun Li, Miao Yang, Yuan Qiao, Linying Wang, Shutao Xu and Zhongmin Liu, J. Mater. Chem. A, 2015, 3, 7741–7749) used triethylamine as a structure-directing agent to synthesize a columnar SAPO-5 molecular sieve formed by hexagonal sheet stacking.

[0004] However, the market has diverse demands for SAPO-5 molecular sieves, especially for the catalytic isomerization reaction of meta-xylene to produce para-xylene. Since para-xylene is economically important compared to meta-xylene and o-xylene, how to improve the conversion rate and selectivity of the target product is one of the areas that researchers are focusing on. Summary of the invention

[0005] In order to overcome the problems existing in the prior art, the present invention provides a SAPO-5 molecular sieve and a preparation method and application thereof. The SAPO-5 molecular sieve has a special morphology and is used for the isomerization reaction of meta-xylene, and has a high conversion rate and target product (para-xylene) selectivity.

[0006] In one aspect, the present invention provides a SAPO-5 molecular sieve, wherein the SAPO-5 molecular sieve comprises spherical particles composed of nanocrystals, and the nanocrystals comprise a plurality of elongated nanocrystals.

[0007] The SAPO-5 molecular sieve provided by the present invention is composed of nanocrystals of smaller size, is more suitable for the isomerization reaction of meta-xylene to prepare para-xylene, and has higher reactant conversion rate and product selectivity.

[0008] On the other hand, the present invention also provides a method for preparing the SAPO-5 molecular sieve of the present invention, comprising subjecting a mixture containing an aluminum source, a phosphorus source, a silicon source, water and a structure directing agent to a crystallization treatment, wherein the structure directing agent comprises R is a C1-C6 straight chain or branched chain alkyl group, or a C3-C6 cycloalkyl group, preferably R is a C4-C6 straight chain or branched chain alkyl group.

[0009] The preparation method of SAPO-5 molecular sieve of the present invention is simple in process. The compounds used as structure-directing agents have high product efficiency, low cost, low equipment requirements, and good industrial application prospects, especially 4-butylmorpholine.

[0010] On the other hand, the present invention also provides the use of the SAPO-5 molecular sieve or the SAPO-5 molecular sieve prepared by the preparation method of the present invention in heterogeneous catalysis, adsorption separation or ion exchange, especially the use as a catalyst in the isomerization reaction of meta-xylene.

[0011] On the other hand, the present invention also provides a method for preparing p-xylene, wherein the SAPO-5 molecular sieve described in the present invention or the SAPO-5 molecular sieve prepared by the preparation method of the present invention is used as a catalyst to contact with m-xylene for an isomerization reaction.

[0012] By using the SAPO-5 molecular sieve of the present invention or the SAPO-5 molecular sieve prepared by the preparation method of the present invention as a catalyst for the isomerization reaction of meta-xylene to prepare para-xylene, a higher reactant conversion rate and product selectivity are achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings are used to provide further understanding of the present application and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present application, but do not constitute a limitation to the present application.

[0014] Figure 1 This is the XRD spectrum of the SAPO-5 molecular sieve prepared in Example 1.

[0015] Figure 2This is a scanning electron microscope image of the SAPO-5 molecular sieve prepared in Example 1, wherein the right image is an enlarged image.

[0016] Figure 3 This is the XRD spectrum of the SAPO-5 molecular sieve prepared in Example 2.

[0017] Figure 4 This is a scanning electron microscope image of the SAPO-5 molecular sieve prepared in Example 2, wherein the right image is an enlarged image.

[0018] Figure 5 This is the XRD spectrum of the SAPO-5 molecular sieve prepared in Example 3.

[0019] Figure 6 This is a scanning electron microscope image of the SAPO-5 molecular sieve prepared in Example 3, wherein the right image is an enlarged image.

[0020] Figure 7 This is the XRD spectrum of the SAPO-5 molecular sieve prepared in Example 4.

[0021] Figure 8 This is a scanning electron microscope image of the SAPO-5 molecular sieve prepared in Example 4, wherein the right image is an enlarged image.

[0022] Fig. 9 It is the XRD spectrum of the product obtained in Comparative Example 1.

[0023] Fig.10 It is a scanning electron microscope image of the product obtained in Comparative Example 1.

[0024] Fig.11 It is the XRD spectrum of the product obtained in Comparative Example 2.

[0025] Fig.12 It is a scanning electron microscope image of the product obtained in Comparative Example 2. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments and drawings. The specific embodiments described herein are only used to explain the present invention and are not intended to constitute any limitation to the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concepts of the present disclosure. Such structures and technologies are also described in many publications.

[0027] In a first aspect, the present invention provides a SAPO-5 molecular sieve, wherein the SAPO-5 molecular sieve comprises spherical particles composed of nanocrystals, and the nanocrystals comprise elongated nanocrystals.

[0028] In some embodiments of the first aspect, the size of the spherical particles is 0.5 micrometers to 20 micrometers, and the size of the nanocrystals is 20 nanometers to 3000 nanometers.

[0029] In some embodiments of the first aspect, the size of the spherical particles is 0.8 micrometers to 20 micrometers, and the size of the nanocrystals is 20 nanometers to 3000 nanometers.

[0030] In other embodiments of the first aspect, the size of the spherical particles is 1 micrometer to 15 micrometers, and the size of the nanocrystals is 50 nanometers to 2000 nanometers.

[0031] In the present application, the long strip shape refers to a structure in three-dimensional space, in which one dimension is larger than the other two dimensions, such as a rod, stick, or bar.

[0032] In other embodiments of the first aspect, the elongated nanocrystals are oriented and arranged in the same direction.

[0033] In some embodiments of the first aspect, the SAPO-5 molecular sieve comprises one or more of first spherical particles and second spherical particles.

[0034] The first spherical particles are spherical particles with a size of 1 micron to 5 microns, preferably 1.2 microns to 3 microns, composed of elongated nanocrystals with a size of 20 nanometers to 2000 nanometers, preferably 50 nanometers to 1200 nanometers;

[0035] The second spherical particles are spherical particles with a size of 5 to 20 microns, preferably 5 to 15 microns, composed of elongated nanocrystals with a size of 200 nanometers to 3000 nanometers, preferably 500 nanometers to 2000 nanometers.

[0036] In other embodiments of the first aspect, the SAPO-5 molecular sieve is a spherical particle with a size of 1 micron to 5 microns composed of 20 nanometers to 2000 nanometers of elongated nanocrystals. In some embodiments, the SAPO-5 molecular sieve is a spherical particle with a size of 1 micron to 5 microns composed of 50 nanometers to 1200 nanometers of elongated nanocrystals.

[0037] In other embodiments of the first aspect, the SAPO-5 molecular sieve is a spherical particle with a size of 1.2 microns to 3 microns, which is composed of 50 nanometers to 1200 nanometers long strip-shaped nanocrystals.

[0038] In other embodiments of the first aspect, the SAPO-5 molecular sieve is a spherical particle with a size of 5 microns to 20 microns composed of 200 nanometers to 3000 nanometers of elongated nanocrystals. In some embodiments, the SAPO-5 molecular sieve is a spherical particle with a size of 5 microns to 20 microns composed of 500 nanometers to 2000 nanometers of elongated nanocrystals.

[0039] In other embodiments of the first aspect, the SAPO-5 molecular sieve is a spherical particle with a size of 5 micrometers to 15 micrometers, which is composed of 500 nanometers to 2000 nanometers long strip-shaped nanocrystals.

[0040] In some embodiments of the first aspect, the SAPO-5 molecular sieve is synthesized by a hydrothermal method, and the synthesis raw materials include an aluminum source, a phosphorus source, a structure directing agent, a silicon source and water; the structure directing agent includes R is a C1-C6 straight chain or branched chain alkyl group, or a C3-C6 cycloalkyl group, preferably R is a C4-C6 straight chain or branched chain alkyl group, and preferably the structure directing agent includes tetrabutylmorpholine.

[0041] Using 4-butylmorpholine as a structure directing agent is beneficial to the synthesis of the spherical SAPO-5 molecular sieve described in the present invention.

[0042] In some embodiments of the first aspect, the molar ratio of the aluminum source, the phosphorus source, the silicon source, the structure directing agent and water is (0.2-2.5):(0.5-5.0):(0.05-1.5):(1-4):(30-200), wherein the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, and the phosphorus source is calculated as H3PO4.

[0043] The present invention has a wide selection range for the aluminum source, as long as it can provide aluminum. Specifically, the aluminum source is selected from at least one of pseudo-boehmite and aluminum isopropoxide.

[0044] The present invention has a wide range of choices for the silicon source, and can be various silicon sources commonly used in the art. Specifically, the silicon source is an organic silicon source and / or an inorganic silicon source. In some embodiments, the silicon source is selected from at least one of silica sol, white carbon black and tetraethyl orthosilicate.

[0045] In other embodiments of the first aspect, the molar ratio of the aluminum source, phosphorus source, silicon source, structure directing agent and water is (0.5-1.5):(1.0-3.0):(0.1-0.8):(2-4):(50-110).

[0046] In some embodiments of the first aspect, the SAPO-5 molecular sieve is prepared by crystallizing a mixture containing an aluminum source, a phosphorus source, a silicon source, water, and a structure directing agent.

[0047] In some embodiments, the crystallization temperature is 150-220° C., such as 150° C., 160° C., 180° C., 190° C., 200° C., or 210° C. In some embodiments, the crystallization temperature is 180-200° C.

[0048] In some embodiments, the crystallization time is 20 to 100 hours; preferably 48 to 72 hours, for example 48 hours, 55 hours, 60 hours or 65 hours.

[0049] In some embodiments of the first aspect, the SAPO-5 molecular sieve is prepared by subjecting a mixture containing an aluminum source, a phosphorus source, a silicon source, water and a structure directing agent to crystallization and drying treatments.

[0050] In some embodiments, the drying temperature is 40 to 150° C.; the drying time is 8 to 30 hours.

[0051] In some embodiments, the drying temperature is 60 to 100° C. In some embodiments, the drying time is 10 to 20 hours.

[0052] In a second aspect, the present invention also provides a method for preparing the SAPO-5 molecular sieve of the present invention, comprising subjecting a mixture containing an aluminum source, a phosphorus source, a silicon source, water and a structure directing agent to a crystallization treatment, wherein the structure directing agent comprises R is a C1-C6 straight chain or branched chain alkyl group, or a C3-C6 cycloalkyl group, preferably R is a C4-C6 straight chain or branched chain alkyl group.

[0053] In some embodiments, the structure directing agent comprises 4-butylmorpholine;

[0054] In some embodiments, the crystallization temperature is 150-220° C., such as 150° C., 160° C., 180° C., 190° C., 200° C., or 210° C. In some embodiments, the crystallization temperature is 180-200° C.

[0055] In some embodiments, the crystallization time is 20 to 100 hours; preferably 48 to 72 hours, for example 48 hours, 55 hours, 60 hours or 65 hours.

[0056] In some embodiments, the crystallization is performed under stirring, and the stirring speed is 5 to 50 rpm.

[0057] In the present invention, there is no particular limitation on the order of adding the materials during the mixing of the aluminum source, phosphorus source, silicon source, water and structure directing agent, and the materials may be added together or separately. In order to enhance the mixing uniformity, preferably, the aluminum source, phosphorus source and water may be mixed first, and then the structure directing agent and silicon source may be added.

[0058] In some embodiments of the second aspect, the molar ratio of the aluminum source, the phosphorus source, the silicon source, the structure directing agent and water is (0.2-2.5):(0.5-5.0):(0.05-1.5):(1-4):(30-200), wherein the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, and the phosphorus source is calculated as H3PO4.

[0059] In other embodiments of the second aspect, the molar ratio of the aluminum source, phosphorus source, silicon source, structure directing agent and water is (0.5-1.5):(1.0-3.0):(0.1-0.8):(2-4):(50-110).

[0060] In some embodiments of the second aspect, the preparation method further comprises drying the crystallized product;

[0061] Preferably, the drying temperature is 40 to 150° C.; and the drying time is 8 to 30 hours.

[0062] In some embodiments of the second aspect, the drying temperature is 40-150°C; preferably 60-100°C; preferably 100°C.

[0063] In some embodiments of the second aspect, the drying time is 8 to 30 hours; preferably 10 to 20 hours; preferably 10 hours.

[0064] In some embodiments, the method further comprises: performing solid-liquid separation and washing before drying the crystallized product.

[0065] The present invention has no particular limitation on the solid-liquid separation and washing, which can be carried out according to conventional technical means in the art, and the present invention will not elaborate on them here.

[0066] In a third aspect, the present invention further provides the use of the SAPO-5 molecular sieve described in the present invention or the SAPO-5 molecular sieve prepared by the preparation method described in the present invention in heterogeneous catalysis, adsorption separation or ion exchange, especially the use as a catalyst in the isomerization reaction of meta-xylene.

[0067] In a fourth aspect, the present invention further provides a method for preparing p-xylene, wherein the SAPO-5 molecular sieve described in the present invention or the SAPO-5 molecular sieve prepared by the preparation method of the present invention is used as a catalyst to contact with m-xylene for an isomerization reaction.

[0068] In some embodiments of the fourth aspect, the SAPO-5 molecular sieve is first inertly activated before use, and the conditions of the inert activation are: treatment at 300-500°C for 1-5 hours under an inert atmosphere; the conditions for the preparation of p-xylene are: reaction temperature of 300-400°C, volume space velocity of 1-4h -1 , carried out at 0.9-1.2atm.

[0069] The SAPO-5 molecular sieve provided by the present invention has a wide range of applications and can be applied to heterogeneous catalysis, adsorption, separation and ion exchange, etc.

[0070] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0071] The term "conversion" refers to the degree to which reactants are converted to products in a particular reaction. Thus, 100% conversion means that the reactants are completely consumed, while 0% conversion means that there is no reaction.

[0072] The term "para-xylene selectivity" means that the amount of para-xylene produced is greater than the amount present in the xylene isomer mixture at thermodynamic equilibrium. In the prior art, it is about 24 mol% at conventional production temperatures.

[0073] Examples and drawings are provided below to help understand the present invention. However, it should be understood that these examples and drawings are only used to illustrate the present invention, but do not constitute any limitation. The actual protection scope of the present invention is set forth in the claims. It should be understood that any modifications and changes can be made without departing from the spirit of the present invention.

[0074] The present invention will be described in detail below through examples.

[0075] In the method of the present invention, XRD data were measured using a German Bruker AXS D8 Advance X-ray diffractometer, and the test conditions were as follows: voltage 40 kV, current 80 mA, CuKα target, scanning speed 15° min -1 , the scanning range 2θ is 5-50°.

[0076] In the method of the present invention, the scanning electron microscope (SEM) image is obtained by a Japanese HITACHI S4800 field emission scanning electron microscope, and the test conditions are as follows: voltage 3kV, current 50mA.

[0077] The reagents used in the following examples are commercially available and of analytical grade.

[0078] The evaluation indicators are as follows:

[0079] Conversion rate of m-xylene:

[0080] Selectivity for para-xylene:

[0081] Yield of p-xylene: Y = conversion × selectivity × 100% = C × S × 100% (2-3)

[0082] Where: C is the conversion rate of meta-xylene; S is the catalyst selectivity for para-xylene; Y is the para-xylene yield;

[0083] ∑Ai is the content of all benzene ring-containing compounds in the product, and Ai is the content of meta-xylene in the product.

[0084] Example 1

[0085] Pseudo-boehmite (containing 70% by mass of Al2O3) and 85% by mass of phosphoric acid are added to water and stirred evenly; then the structure directing agent 4-butylmorpholine is added to the above mixture and stirred for 1.5 hours; then silica sol (containing 40% by weight of SiO2) is added dropwise to the above mixture and stirred for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the phosphorus source is calculated as H3PO4, and the molar ratio of Al2O3:H3PO4:structure directing agent:SiO2:H2O is 1.0:2.0:3.0:0.38:70.

[0086] The gel mixture finally obtained above was subjected to dynamic crystallization treatment at a stirring speed of 20 rpm. The obtained sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 200°C and the crystallization time was 60 hours. Thus, a spherical SAPO-5 molecular sieve was obtained.

[0087] The XRD spectrum of SAPO-5 molecular sieve is as follows Figure 1 As shown, from Figure 1 It can be seen that the synthesized silicoaluminophosphate molecular sieve has the peak shape of SAPO-5 molecular sieve, and the diffraction peak is relatively sharp and the intensity is obvious.

[0088] Figure 2 This is a scanning electron microscope image of the product. Figure 2 It can be seen that the material has a spherical morphology, the particle size of the spherical particles is 5-15μm, the spherical particles are composed of long strip nanocrystals, the size of the long strip nanocrystals is 500-2000 nanometers, and the aspect ratio of the long strip nanocrystals is 1.5-2.

[0089] Example 2

[0090] Pseudo-boehmite (containing 70% by mass of Al2O3) and 85% by mass phosphoric acid are added to water and stirred evenly; then the structure directing agent 4-butylmorpholine is added to the above mixture and stirred for 1.5 hours; then silica sol (containing 40% by weight of SiO2) is added dropwise to the above mixture and stirred for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the phosphorus source is calculated as H3PO4, and the molar ratio of Al2O3:H3PO4:structure directing agent:SiO2:H2O is 1.0:2.0:3.0:0.38:110.

[0091] The gel mixture finally obtained above was subjected to dynamic crystallization treatment at a stirring speed of 20 rpm. The obtained sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 200°C and the crystallization time was 60 hours. Thus, a spherical SAPO-5 molecular sieve was obtained.

[0092] The XRD spectrum of SAPO-5 molecular sieve is as follows Figure 3 As shown, from Figure 3 It can be seen that the synthesized silicoaluminophosphate molecular sieve has the peak shape of SAPO-5 molecular sieve, and the diffraction peak is relatively sharp and the intensity is obvious.

[0093] Figure 4 This is a scanning electron microscope image of the product. Figure 4 It can be seen that the material has a spherical morphology, the particle size of the spherical particles is 1.2-3μm, the spherical particles are composed of elongated nanocrystals, the size of the elongated nanocrystals is 50-1200 nanometers, and the aspect ratio of the elongated nanocrystals is 2-5.

[0094] Example 3

[0095] Pseudo-boehmite (containing 70% by mass of Al2O3) and 85% by mass of phosphoric acid are added to water and stirred evenly; then the structure directing agent 4-butylmorpholine is added to the above mixture and stirred for 1.5 hours; then silica sol (containing 40% by weight of SiO2) is added dropwise to the above mixture and stirred for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the phosphorus source is calculated as H3PO4, and the molar ratio of Al2O3:H3PO4:structure directing agent:SiO2:H2O is 0.6:1.4:2.20:0.18:50.

[0096] The gel mixture finally obtained above was subjected to dynamic crystallization treatment at a stirring speed of 20 rpm. The obtained sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 200°C and the crystallization time was 60 hours. Thus, a spherical SAPO-5 molecular sieve was obtained.

[0097] The XRD spectrum of SAPO-5 molecular sieve is as follows Figure 5 As shown, from Figure 5 It can be seen that the synthesized silicoaluminophosphate molecular sieve has the peak shape of SAPO-5 molecular sieve, and the diffraction peak is relatively sharp and the intensity is obvious.

[0098] Figure 6 This is a scanning electron microscope image of the product. Figure 6 It can be seen that the material has a spherical morphology, the particle size of the spherical particles is 1.2-3μm, the spherical particles are composed of elongated nanocrystals, the size of the elongated nanocrystals is 50-1200 nanometers, and the aspect ratio of the elongated nanocrystals is 2-5.

[0099] Example 4

[0100] Pseudo-boehmite (containing 70% by mass of Al2O3) and 85% by mass phosphoric acid are added to water and stirred evenly; then the structure directing agent 4-butylmorpholine is added to the above mixture and stirred for 1.5 hours; then silica sol (containing 40% by weight of SiO2) is added dropwise to the above mixture and stirred for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the phosphorus source is calculated as H3PO4, and the molar ratio of Al2O3:H3PO4:structure directing agent:SiO2:H2O is 2.0:3.0:3.5:0.6:50.

[0101] The gel mixture finally obtained above was subjected to dynamic crystallization treatment at a stirring speed of 20 rpm. The obtained sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 200°C and the crystallization time was 60 hours. Thus, a spherical SAPO-5 molecular sieve was obtained.

[0102] The XRD spectrum of SAPO-5 molecular sieve is as follows Figure 7 As shown, from Figure 7 It can be seen that the synthesized silicoaluminophosphate molecular sieve has the peak shape of SAPO-5 molecular sieve, and the diffraction peak is relatively sharp and the intensity is obvious.

[0103] Figure 8 This is a scanning electron microscope image of the product. Figure 8It can be seen that the material has a spherical morphology, the particle size of the spherical particles is 5-20μm, the spherical particles are composed of long strip nanocrystals, the size of the long strip nanocrystals is 300-3000 nanometers, and the aspect ratio of the long strip nanocrystals is 1.5-2.

[0104] Comparative Example 1

[0105] Pseudo-boehmite (containing 70% by mass of Al2O3) and 85% by mass phosphoric acid are added to water and stirred evenly; then the structure directing agent morpholine is added to the above mixture and stirred for 1.5 hours; then silica sol (containing 40% by weight of SiO2) is added dropwise to the above mixture and stirred for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the phosphorus source is calculated as H3PO4, and the molar ratio of Al2O3:H3PO4:structure directing agent:SiO2:H2O is 1.0:2.0:3.0:0.38:70.

[0106] The gel mixture finally obtained above was subjected to dynamic crystallization treatment, with a stirring speed of 20 rpm. The obtained sample was centrifuged, washed, and dried at 100°C for 10 hours. Among them, the crystallization temperature was 200°C and the crystallization time was 60 hours. Thus, a silicoaluminophosphate molecular sieve was obtained.

[0107] The XRD spectrum of silicoaluminophosphate molecular sieve is as follows: Fig. 9 As shown, from Fig. 9 It can be seen that the synthesized silicoaluminophosphate molecular sieve has the peak shape of SAPO-34 molecular sieve, and the diffraction peak is relatively sharp and the intensity is obvious.

[0108] Scanning electron microscope image of silicoaluminophosphate molecular sieve Fig.10 As shown. Fig.10 It can be seen that the material morphology is cubic and the cubic particle size is 4 to 10 μm.

[0109] It can be seen from this that the SAPO-34 molecular sieve is obtained by using the structure directing agent morpholine, rather than the SAPO-5 molecular sieve of the present invention.

[0110] Comparative Example 2

[0111] Pseudo-boehmite (containing 70% by mass of Al2O3) and 85% by mass phosphoric acid are added into water and stirred evenly; then, silica sol (containing 40% by weight of SiO2) is added dropwise into the mixture obtained above and stirred for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the phosphorus source is calculated as H3PO4, and the molar ratio of Al2O3:H3PO4:structure directing agent:SiO2:H2O is 1.0:2.0:0:0.38:70.

[0112] The gel mixture finally obtained above was subjected to dynamic crystallization treatment at a stirring speed of 20 rpm. The obtained sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 200°C and the crystallization time was 60 hours. Thus, an amorphous product was obtained.

[0113] The XRD spectrum of the product of Comparative Example 2 is as follows Fig.11 As shown, from Fig.11 It can be seen that the synthesized product is an amorphous product without a crystal structure.

[0114] Fig.12 This is a scanning electron microscope image of the product. Fig.12 It can be seen that the material is in irregular granular form.

[0115] Test Example 1

[0116] The molecular sieves obtained in Examples 1-4 and the comparative example were used as catalysts for the isomerization reaction of meta-xylene, wherein the test conditions were as follows: the initial activity and selectivity of the meta-xylene isomerization reaction (main target product, para-xylene) of the sample were evaluated by pulse micro-chromatography, the reaction tube was a stainless steel tube with a diameter of 20 mm and a length of 800 mm, each containing 0.2 g of the molecular sieves calcined (550°C, 6 hours) in each example, first activated by high-purity nitrogen at 723K for 2 hours, then the reaction temperature was controlled to 360°C, and the raw materials were injected at normal pressure for isomerization reaction. The catalytic effect of the reaction in the example test is shown in Table 1. The raw material of the reaction is meta-xylene, and the volume space velocity of meta-xylene is 2h -1 The microreactor was coupled with a S-2305 gas chromatograph, and the product composition was detected by a hydrogen flame detector and quantitatively analyzed by the modified area normalization method.

[0117] Table 1

[0118]

[0119]

[0120] It can be seen from the results in Table 1 that the application of the SAPO-5 molecular sieve of the present invention in the isomerization reaction of meta-xylene has significantly higher meta-xylene conversion rate and para-xylene selectivity than the comparative example; especially the molecular sieves prepared in Examples 2 and 3.

[0121] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A SAPO-5 molecular sieve, comprising spherical particles composed of nanocrystals, wherein the nanocrystals include a plurality of elongated nanocrystals.

2. The SAPO-5 molecular sieve according to claim 1, wherein The size of the spherical particles is 0.5 micrometer to 20 micrometers, and the size of the nanocrystals is 20 nanometers to 3000 nanometers; preferably, the size of the spherical particles is 1 micrometer to 15 micrometers, and the size of the nanocrystals is 50 nanometers to 2000 nanometers.

3. The SAPO-5 molecular sieve according to claim 1 or 2, wherein: The plurality of long strip-shaped nanocrystals are oriented and arranged in the same direction; Preferably, the length of the elongated nanocrystals is 50 to 2000 nanometers; The aspect ratio of the long strip-shaped nanocrystals is 1.5-5.

4. The SAPO-5 molecular sieve according to claim 2, wherein: The SAPO-5 molecular sieve includes one or more of first spherical particles and second spherical particles; The first spherical particles are spherical particles with a size of 1 micron to 5 microns, preferably 1.2 microns to 3 microns, composed of elongated nanocrystals with a size of 20 nanometers to 2000 nanometers, preferably 50 nanometers to 1200 nanometers; The second spherical particles are spherical particles with a size of 5 micrometers to 20 micrometers, preferably 5 micrometers to 15 micrometers, composed of elongated nanocrystals with a size of 200 nanometers to 3000 nanometers, preferably 500 nanometers to 2000 nanometers.

5. The SAPO-5 molecular sieve according to any one of claims 1 to 4, wherein: The SAPO-5 molecular sieve is synthesized by a hydrothermal method, and the synthesis raw materials include an aluminum source, a phosphorus source, a structure directing agent, a silicon source and water; the structure directing agent includes R is a C1-C6 straight chain or branched chain alkyl group, or a C3-C6 cycloalkyl group, preferably R is a C4-C6 straight chain or branched chain alkyl group, and preferably the structure directing agent includes tetrabutylmorpholine.

6. The SAPO-5 molecular sieve according to claim 5, wherein: The molar ratio of the aluminum source, the phosphorus source, the silicon source, the structure directing agent and water is (0.2-2.5):(0.5-5.0):(0.05-1.5):(1-4):(30-200), wherein the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, and the phosphorus source is calculated as H3PO4; preferably, the molar ratio of the aluminum source, the phosphorus source, the silicon source, the structure directing agent and water is (0.5-1.5):(1.0-3.0):(0.1-0.8):(2-4):(50-110).

7. A method for preparing a SAPO-5 molecular sieve, comprising subjecting a mixture containing an aluminum source, a phosphorus source, a silicon source, water and a structure directing agent to crystallization treatment, wherein the structure directing agent comprises R is a C1-C6 straight or branched alkyl group, or a C3-C6 cycloalkyl group, preferably R is a C4-C6 straight or branched alkyl group; Preferably, the structure directing agent comprises 4-butylmorpholine; Preferably, the crystallization temperature is 150-220°C; preferably 180-200°C; Preferably, the crystallization time is 20 to 100 hours; preferably 48 to 72 hours; Preferably, the crystallization is carried out under stirring, and the stirring speed is 5 to 50 rpm.

8. The preparation method according to claim 7, further comprising drying the crystallized product; Preferably, the drying temperature is 40 to 150°C; preferably 60 to 100°C; Preferably, the drying time is 8 to 30 hours; preferably 10 to 20 hours.

9. Use of the SAPO-5 molecular sieve according to any one of claims 1 to 6 or the SAPO-5 molecular sieve prepared by the preparation method according to any one of claims 7 to 8 in heterogeneous catalysis, adsorption separation or ion exchange, especially as a catalyst in the isomerization reaction of meta-xylene.

10. A method for preparing para-xylene, comprising using the SAPO-5 molecular sieve according to any one of claims 1 to 6 or the SAPO-5 molecular sieve prepared by the preparation method according to any one of claims 7 to 8 as a catalyst in contact with meta-xylene for an isomerization reaction; Preferably, the SAPO-5 molecular sieve is first inertly activated before use, and the conditions for the inert activation are: treatment at 300-500°C for 1-5 hours under an inert atmosphere; the conditions for the preparation of p-xylene are: reaction temperature of 300-400°C, volume space velocity of 1h -1 ~4h -1 , carried out at 0.9atm-1.2atm.

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