Surface aluminum-rich zsm-5 molecular sieve, its preparation method and application

Abstract

The application relates to a surface aluminum-rich ZSM-5 molecular sieve and a preparation method and application thereof, the ZSM-5 molecular sieve is a kind of flat cylinder, the average crystal grain size of the ZSM-5 molecular sieve is 0.2-3.0 mu m, the molar ratio of the molar ratio of the bulk phase silicon aluminum and the surface silicon aluminum ratio is 1.2-5.0, and the relative crystallinity is 80-110%. The ZSM-5 molecular sieve of the application is rich in aluminum on the outer surface, and has relatively optimal catalytic activity.

Description

TECHNICAL FIELD

[0001] The present application relates to a surface aluminum-rich ZSM-5 molecular sieve and a preparation method and application thereof. BACKGROUND

[0002] The crystal structure of ZSM-5 molecular sieve belongs to an orthorhombic system, and is formed by connecting silicon (aluminum) oxygen tetrahedrons through oxygen bridge bonds, and has two-dimensional ten-membered ring channels, and the basic structural unit is composed of eight five-membered rings. The channel structure is composed of intersecting straight cylinder channels with an elliptical cross section (channel size is 0.54 nm x 0.56 nm) and Z-shaped channels with a nearly circular cross section (channel size is 0.52 nm x 0.58 nm). The channel, i.e., its cavity, does not have a cage similar to the A-type, X-type and Y-type zeolites. ZSM-5 molecular sieve has a stable framework structure, a tunable pore size, a high specific surface area, good shape selectivity and good water and thermal stability, and therefore has wide application value in the fields of adsorption, separation, shape-selective catalysis and the like. In the synthesis process, the Al distribution, morphology and channel structure regulation can effectively improve the catalytic performance of the molecular sieve, and the Al distribution is an important factor affecting the catalytic activity of the molecular sieve. The pore structure of ZSM-5 molecular sieve belongs to microporous structure, and for larger reactant molecules, there is a diffusion limitation, which can reduce the accessibility of the active center. SUMMARY

[0003] The purpose of the present application is to provide a surface aluminum-rich ZSM-5 molecular sieve and a preparation method and application thereof. The ZSM-5 molecular sieve of the present application is surface aluminum-rich, and when used in a hydrocarbon catalytic cracking reaction, the conversion rate and the target product yield can be improved.

[0004] In order to achieve the above purpose, the present application provides a surface aluminum-rich ZSM-5 molecular sieve in a first aspect. The ZSM-5 molecular sieve is a prolate cylindrical body, the average crystal grain size of the ZSM-5 molecular sieve is 0.2-3.0 μm, the ratio of the molar ratio of the bulk phase silicon aluminum molar ratio to the molar ratio of the surface silicon aluminum ratio is 1.2-5.0, and the relative crystallinity is 80-110%.

[0005] Optionally, the ratio of the molar ratio of the bulk phase silicon aluminum molar ratio to the molar ratio of the surface silicon aluminum ratio of the ZSM-5 molecular sieve is 1.2-4.0.

[0006] Optionally, the relative crystallinity of the ZSM-5 molecular sieve is 85-100%, and the average crystal grain size is 0.4-2 μm.

[0007] Optionally, the average height of the ZSM-5 molecular sieve is 0.2-1.0 μm, and the average height-diameter ratio is 1:(2-10).

[0008] The second aspect of the present application provides a method for preparing the surface aluminum-rich ZSM-5 molecular sieve provided by the first aspect of the present application, the method comprising:

[0009] (1) mixing a first template agent, a first silicon source and a first solvent at 30-50°C for 0.5-3.0 hours to obtain a first mixed product;

[0010] (2) mixing a first alkali metal hydroxide, a first aluminum source and a second solvent at 20-80°C for 0.5-2.0 hours to obtain a second mixed product;

[0011] (3) mixing the first mixed product with the second mixed product and then performing dynamic crystallization, taking out the obtained solid and performing a first calcination; or,

[0012] The method comprises:

[0013] S1, mixing a second template agent, a second silicon source and a third solvent at 30-50°C for 0.5-3.0 hours, and then sequentially performing a first hydrothermal treatment and a second hydrothermal treatment on the obtained third mixed product to obtain a fourth mixed product; wherein the conditions of the first hydrothermal treatment include a temperature of 80-120°C and a time of 1-6 hours; the conditions of the second hydrothermal treatment include a temperature of 160-180°C and a time of 12-60 hours;

[0014] S2, mixing a second alkali metal hydroxide, a second aluminum source and a fourth solvent at 20-80°C for 0.5-2.0 hours to obtain a fifth mixed product;

[0015] S3, mixing the fourth mixed product with the fifth mixed product, performing a third hydrothermal treatment on the obtained mixture, taking out the obtained solid and performing a second calcination.

[0016] Optionally, the first silicon source is selected from one or more of tetramethyl orthosilicate and tetraethyl orthosilicate;

[0017] The second silicon source is selected from one or more of silica sol, water glass and solid silica gel;

[0018] The first template agent and the second template agent are each independently selected from one or more of tetrapropylammonium bromide, tetrapropylammonium hydroxide, n-butylamine and hexanediamine;

[0019] The first aluminum source and the second aluminum source are each independently selected from one or more of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum isopropyl alcohol and aluminum sol;

[0020] The first alkali metal hydroxide and the second alkali metal hydroxide are each independently selected from one or more of lithium hydroxide, sodium hydroxide and potassium hydroxide.

[0021] Optionally, a molar ratio of a total amount of the first template agent, the first solvent and the second solvent, an amount of the first alkali metal hydroxide and the first silicon source is (0.06-0.55):(10-110):(0.02-1.5):1; a molar ratio of an amount of the first silicon source and the first aluminum source is (20-500):1; wherein the first silicon source is calculated as SiO2, the first alkali metal hydroxide is calculated as alkali metal oxide, and the first aluminum source is calculated as Al2O3.

[0022] A molar ratio of a total amount of the second template agent, the third solvent and the fourth solvent, an amount of the second alkali metal hydroxide and the second silicon source is (0.06-0.55):(10-100):(0.02-1.5):1; a molar ratio of an amount of the second silicon source and the second aluminum source is (20-500):1; wherein the second silicon source is calculated as SiO2, the second alkali metal hydroxide is calculated as alkali metal oxide, and the second aluminum source is calculated as Al2O3.

[0023] Optionally, in step (2), a molar ratio of an amount of the first alkali metal hydroxide, the second solvent and the first aluminum source is (1.5-5):(60-500):1.

[0024] In step S2, a molar ratio of an amount of the second alkali metal hydroxide, the fourth solvent and the second aluminum source is (1.5-5):(60-500):1.

[0025] Optionally, the conditions of the dynamic crystallization include: a temperature of 160-180℃, and a time of 12-60 hours.

[0026] The conditions of the third hydrothermal treatment include: a temperature of 160-180℃, and a time of 12-60 hours.

[0027] The conditions of the first calcination and the second calcination each independently include: a temperature of 400-600℃, and a time of 2-6 hours.

[0028] The third aspect of the present application provides an application of the surface aluminum-rich ZSM-5 molecular sieve provided by the first aspect of the present application in petroleum chemical industry and / or fine chemical industry.

[0029] The ZSM-5 molecular sieve of the present application has the feature of aluminum-rich external surface, and aluminum is mainly distributed on the external surface of the molecular sieve, which can improve the accessibility of the active sites of the molecular sieve, promote the catalytic conversion of macromolecular reactants, improve the conversion rate and the yield of target products, and is also beneficial to improving the modification efficiency of subsequent metal or non-metal modification process of the molecular sieve, and can be applied in the fields of petroleum chemical industry and fine chemical industry, and has good industrial application value, especially for the catalytic cracking reaction of hydrocarbons.

[0030] Other features and advantages of the present application will be illustrated in the following detailed description of the embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0032] Figure 1 is a SEM photo of ZSM-5 molecular sieve prepared in Example 1 of the present application;

[0033] Figure 2 is a SEM photo of ZSM-5 molecular sieve prepared in Example 2 of the present application;

[0034] Figure 3 is a SEM photo of ZSM-5 molecular sieve prepared in Example 3 of the present application;

[0035] Figure 4 is a SEM photo of ZSM-5 molecular sieve prepared in Example 4 of the present application. DETAILED DESCRIPTION

[0036] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application.

[0037] The present application provides a surface aluminum-rich ZSM-5 molecular sieve, which is a kind of oblate cylinder, the average crystal size of the ZSM-5 molecular sieve is 0.2-3.0 μm, the ratio of the molar ratio of the bulk phase silicon-aluminum to the molar ratio of the surface silicon-aluminum is 1.2-5.0, and the relative crystallinity is 80-110%.

[0038] The ZSM-5 molecular sieve of the present application contains aluminum mainly distributed on the outer surface of the molecular sieve, which improves the accessibility of the active sites of the molecular sieve, increases the collision probability of the reactant molecules with the active centers of the molecular sieve catalyst, and thus effectively improves the catalytic performance thereof, is also beneficial to improving the modification efficiency of the subsequent metal or non-metal modification process of the molecular sieve, and can be applied in the fields of petroleum and chemical industry, fine chemical industry, etc., and has good industrial application value. In the present application, the kind of oblate cylinder refers to a kind of cylinder with small height-diameter ratio, which is similar to a moon cake, and the radial cross section of the oblate cylinder can be circular, elliptical, etc.

[0039] In one embodiment of the present application, the ratio of the bulk Si / Al molar ratio to the surface Si / Al ratio of the ZSM-5 molecular sieve can vary in a wide range, preferably 1.2-4, more preferably 1.2-2. The bulk Si / Al ratio is determined by XRF method, and the surface Si / Al ratio is determined by XPS method, which are well known to those skilled in the art and will not be described here.

[0040] In one embodiment of the present application, the relative crystallinity of the ZSM-5 molecular sieve is 85-100%, and the average crystal size is 0.4-2 μm, preferably 0.6-2.0 μm. In the present application, the crystallinity of the molecular sieve sample is determined by X-ray diffraction method. The relative crystallinity of the molecular sieve is based on the ZSM-5 molecular sieve standard sample of XRD standard sample of Petrochemical Science Research Institute of China, and the crystallinity of the standard sample is considered as 100%. The crystal size refers to the size of the widest part of the crystal, which can be obtained by measuring the size of the widest part of the crystal projection plane in the SEM or TEM image of the sample, and the average crystal size is obtained by selecting any 10 molecular sieve crystals in the SEM or TEM image and calculating the average value.

[0041] In one embodiment of the present application, the average height of the ZSM-5 molecular sieve can be 0.2-1.0 μm, or 0.1-1 μm, preferably 0.2-0.8 μm, and the average height-diameter ratio can vary in a wide range, for example, it can be 1:(2-10), preferably 1:(4-8). In the present application, the height-diameter ratio refers to the ratio of the height of the molecular sieve to the maximum diameter of its top or bottom surface, and the average height-diameter ratio can be obtained by selecting any 10 molecular sieves in the SEM or TEM image, calculating the height-diameter ratio of each, and then taking the average value.

[0042] The second aspect of the present application provides a method for preparing the surface aluminum-rich ZSM-5 molecular sieve provided in the first aspect of the present application.

[0043] In one embodiment, the method for preparing the surface aluminum-rich ZSM-5 molecular sieve provided in the first aspect of the present application comprises: (1) mixing a first template agent, a first silicon source and a first solvent at 30-50°C for 0.5-3.0 hours to obtain a first mixed product; (2) mixing a first alkali metal hydroxide, a first aluminum source and a second solvent at 20-80°C for 0.5-2.0 hours to obtain a second mixed product; (3) mixing the first mixed product with the second mixed product and then performing dynamic crystallization, and taking out the obtained solid and performing a first calcination.

[0044] According to the present application, the total amount of the first template agent, the first solvent and the second solvent, the molar ratio of the amount of the first alkali metal hydroxide and the first silicon source can be in a large range, for example, can be (0.06-0.55) : (10-110) : (0.02-1.5) : 1, preferably (0.10-0.50) : (15-85) : (0.03-1.2) : 1; the molar ratio of the amount of the first silicon source and the first aluminum source can also be in a large range, for example, can be (20-500) : 1, preferably (25-200) : 1; wherein the first silicon source is calculated as SiO2, the first alkali metal hydroxide is calculated as alkali metal oxide (for example, when the first alkali metal hydroxide is NaOH, the first alkali metal hydroxide is calculated as Na2O), and the first aluminum source is calculated as Al2O3. In an embodiment, the total molar amount of OH contained in the first template agent and the first alkali metal hydroxide and the molar amount of the first silicon source calculated as SiO2 (denoted as OH / SiO2 for short) is (0.01-1.5) : 1, preferably (0.02-1.2) : 1. -

[0045] According to the present application, in step (2), the molar ratio of the amount of the first alkali metal hydroxide, the second solvent and the first aluminum source is (1.5-5) : (60-500) : 1, preferably (2.0-4.5) : (80-450) : 1.

[0046] According to the present application, in step (3), the dynamic crystallization is well known to those skilled in the art, and the conditions of the dynamic crystallization can include a temperature of 80-200°C and a time of 4-80 hours, preferably a temperature of 160-180°C and a time of 12-60 hours.

[0047] According to the present application, step (3) further comprises, after the obtained solid is taken out, sequentially performing first washing and first drying, and then performing first calcination. The solution used for washing is not specifically limited in the present application, for example, can be deionized water, and drying is a technical means commonly used by those skilled in the art, which can be performed in a constant temperature drying oven or can be natural air drying, and the conditions of the first drying can include a temperature of 90-120°C and a time of 2-24 hours.

[0048] ​In another embodiment, the method for preparing the surface-aluminum-rich ZSM-5 molecular sieve provided in the first aspect of the present application comprises: S1, mixing a second template agent, a second silicon source and a third solvent at 30-50°C for 0.5-3.0 hours, and subjecting the obtained third mixture to a first hydrothermal treatment and a second hydrothermal treatment in sequence to obtain a fourth mixture; wherein the first hydrothermal treatment is carried out at a temperature of 80-150°C for 1-6 hours; and the second hydrothermal treatment is carried out at a temperature of 160-180°C for 2-24 hours; S2, mixing a second alkali metal hydroxide, a second aluminum source and a fourth solvent at 20-80°C for 0.5-2.0 hours to obtain a fifth mixture; S3, mixing the fourth mixture and the fifth mixture, and subjecting the obtained mixture to a third hydrothermal treatment, and taking out the obtained solid and subjecting it to a second calcination. According to the present application, the total amount of the second template agent, the third solvent and the fourth solvent, and the molar ratio of the amount of the second alkali metal hydroxide to the amount of the second silicon source can vary in a relatively large range, for example, can be (0.06-0.55):(10-110):(0.02-1.5):1, preferably (0.10-0.50):(15-85):(0.03-1.2):1; and the molar ratio of the amount of the second silicon source to the amount of the second aluminum source can also vary in a relatively large range, for example, can be (20-500):1, preferably (25-200):1; wherein the second silicon source is calculated as SiO2, the second alkali metal hydroxide is calculated as alkali metal oxide, and the second aluminum source is calculated as Al2O3. In one embodiment, the total molar amount of OH contained in the second template agent and the second alkali metal hydroxide to the molar amount of the second silicon source calculated as SiO2 (denoted as OH / SiO2) is (0.01-1.5):1, preferably (0.02-1.2):1. -

[0049] According to the present application, in step S1, the first hydrothermal treatment is carried out at a temperature of 80-150°C for 1-6 hours; and the second hydrothermal treatment is carried out at a temperature of 160-180°C for 12-60 hours.

[0050] According to the present application, in step S2, the molar ratio of the amount of the second alkali metal hydroxide to the amount of the fourth solvent to the amount of the second aluminum source is (1.5-5):(60-500):1, preferably (2-4.5):(80-450):1.

[0051] ​According to the present application, the hydrothermal treatment is well known to those skilled in the art, for example, it can be carried out in a heat-resistant closed container. In one embodiment, the third hydrothermal treatment in step S3 is carried out under the conditions of 160-180℃ for 12-60 hours. The present application does not limit the conditions of the hydrothermal treatment, which can be carried out under the autogenous pressure of the reaction system or under an external pressure, preferably under the autogenous pressure.

[0052] According to the present application, the calcination is a conventional technique for those skilled in the art, which can be carried out in a muffle furnace, a tube furnace, etc. In one embodiment, the conditions of the first calcination and the second calcination are each independently selected from the group consisting of 400-600℃ for 2-6 hours, preferably 450-600℃ for 3-6 hours.

[0053] According to the present application, step S3 further comprises sequentially carrying out the second washing and the second drying after the obtained solid is taken out, and then carrying out the second calcination. The present application does not limit the solution used in the washing, which can be deionized water for example. The drying is a conventional technique for those skilled in the art, which can be carried out in a constant temperature drying oven or by natural air drying. The conditions of the second drying can comprise 90-120℃ for 2-24 hours.

[0054] According to the present application, the first silicon source is selected from one or more of tetramethyl orthosilicate and tetraethyl orthosilicate; the second silicon source is selected from one or more of silica sol, water glass and solid silica gel; the first template agent and the second template agent are each independently selected from one or more of tetrapropyl ammonium bromide, tetrapropyl ammonium hydroxide, n-butylamine and hexanediamine; the first aluminum source and the second aluminum source are each independently selected from one or more of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum isopropoxide and aluminum sol; the first alkali metal hydroxide and the second alkali metal hydroxide are each independently selected from one or more of lithium hydroxide, sodium hydroxide and potassium hydroxide.

[0055] According to the present application, the present application does not limit the method for taking out the solid, which can be carried out by filtration, centrifugal separation, etc.

[0056] The third aspect of the present application provides the use of the surface aluminum-rich ZSM-5 molecular sieve provided by the first aspect of the present application in petroleum chemical industry and / or fine chemical industry.

[0057] In one preferred embodiment of the present application, the present application provides the use of the surface aluminum-rich ZSM-5 molecular sieve in a hydrocarbon catalytic cracking reaction.

[0058] The present application will be further described in the following examples, but the present application is not limited in any way by the examples.

[0059] The raw materials used in the following examples and comparative examples are commercially available unless otherwise specified.

[0060] In the following examples and comparative examples, the morphology of the molecular sieve sample is observed by taking SEM photos of the sample. The average height of the molecular sieve is calculated by averaging the heights of 10 randomly selected particles in the SEM photos. The average aspect ratio is calculated by averaging the aspect ratios of 10 randomly selected particles.

[0061] The crystallite size of the molecular sieve is measured by SEM. The average crystallite size of the molecular sieve sample is obtained by averaging the crystallite sizes of 10 randomly selected particles.

[0062] The crystallinity of the sample is detected by X-ray diffraction method. The instrument is Empyrean. The test conditions are: tube voltage 40 kV, tube current 40 mA, Cu target Kα radiation, 2θ scanning range 5°-35°, scanning rate 2(°) / min.

[0063] The bulk silicon-aluminum ratio of the sample is determined by XRF method. The instrument is a ZSX Primus II(Rigaku) X-ray fluorescence spectrometer. The test conditions are: excitation voltage 50 kV, excitation current 50 mA, rhodium palladium. The intensity of each element spectrum peak is determined by a scintillation counter and a proportional counter for molecular sieve element composition analysis.

[0064] The surface silicon-aluminum ratio of the sample is determined by XPS method. The instrument is an ESCALab250 X-ray photoelectron spectrometer from ThermoFisher. The test conditions are: excitation source is monochromatic Al Kα X-ray, excitation energy 1496.6 eV, power 150 W. The electron binding energy is corrected using the C1s peak of contaminant carbon(284.8 eV).

[0065] Example 1

[0066] (1) 111.65 grams of tetrapropylammonium hydroxide aqueous solution(mass fraction 25.0%) was weighed, 623.14 grams of deionized water was added, stirred at room temperature for 10 min, then 91.2 grams of tetraethyl orthosilicate was added, and stirred at 40°C water bath for 2.0 h to obtain a first mixed product;

[0067] (2) 3.44 grams of sodium hydroxide particles was weighed, 76.80 grams of deionized water was added, and the sodium hydroxide was completely dissolved, then 8.16 grams of aluminum nitrate was added, and stirred at room temperature(25°C, same below) for 1.0 h to obtain a second mixed product(aluminum source solution);

[0068] (3) slowly added the second mixture product into the first mixture product, mixed uniformly, stirred at room temperature for 4.0 h; the obtained precursor solution was moved into a synthesis kettle, dynamically crystallized at 170°C for 48 h; after the crystallization was completed, centrifugal filtration, washing, drying, and calcination at 550°C for 4 h were performed to obtain ZSM-5 molecular sieve A, the SEM photograph of which is shown in Figure 1 .

[0069] Example 2

[0070] (1) 34.5 g of a tetrapropylammonium bromide aqueous solution (25.0% by mass) was weighed, 425.0 g of deionized water was added, stirred at room temperature for 10 min, and then 60.0 g of methyl orthosilicate was added, stirred at a 30°C water bath for 5.0 h to obtain a first mixture product;

[0071] (2) 1.30 g of sodium hydroxide particles was weighed, added to 31.0 g of deionized water, and the sodium hydroxide was completely dissolved, and then 0.85 g of sodium aluminate was added, stirred at room temperature for 2.0 h to obtain a second mixture product (i.e., an aluminum source solution);

[0072] (3) The second mixture product was slowly added to the first mixture product, mixed uniformly, and stirred at room temperature for 4.0 h; the obtained precursor solution was moved into a synthesis kettle, dynamically crystallized at 180°C for 24 h; after the crystallization was completed, centrifugal filtration, washing, drying, and calcination at 500°C for 6 h were performed to obtain ZSM-5 molecular sieve B, the SEM photograph of which is shown in Figure 2 .

[0073] Example 3

[0074] (1) 65.13 g of a tetrapropylammonium hydroxide aqueous solution (25.0% by mass) was weighed, 462.62 g of deionized water was added, stirred at room temperature for 10 min, and then 165.20 g of a silica sol (SiO2 content 25%) was added, stirred at a 50°C water bath for 1.0 h; the obtained third mixture product was moved into a reaction kettle, hydrothermally treated at 80°C for 2 hours, and then the temperature was increased to 170°C to hydrothermally treat for 12 hours to obtain a fourth mixture product;

[0075] (2) 1.39 g of sodium hydroxide particles was weighed, added to 39.7 g of deionized water, and the sodium hydroxide was completely dissolved, and then 4.76 g of aluminum nitrate nonahydrate was added, stirred at room temperature for 1.0 h to obtain a fifth mixture product (i.e., an aluminum source solution);

[0076] (3) The fifth mixture product was added to the fourth mixture product, stirred uniformly, and the obtained precursor solution was continuously hydrothermally treated at 170°C for 36 h; after the hydrothermal treatment was completed, centrifugal filtration, washing, drying, and calcination at 550°C for 4 h were performed to obtain ZSM-5 molecular sieve C, the SEM photograph of which is shown inFigure 3 as shown.

[0077] Example 4

[0078] (1) 65.13 grams of tetrapropylammonium hydroxide aqueous solution (25.0% by mass) was weighed, 823.60 grams of deionized water was added, stirred at room temperature for 10 min, then 134.4 grams of tetraethyl orthosilicate was added, stirred at 50°C water bath for 1.0 h, to obtain a first mixed product;

[0079] (2) 2.0 grams of sodium hydroxide particles was weighed, 36.0 grams of deionized water was added, and the sodium hydroxide was completely dissolved, then 4.76 grams of aluminum nitrate nonahydrate was added, stirred at room temperature for 1.0 h, to obtain a second mixed product (i.e. aluminum source solution);

[0080] (3) The second mixed product was slowly added to the first mixed product, and stirred uniformly at room temperature for 4.0 h; the precursor solution was moved into a synthesis kettle, and dynamically crystallized at 160°C for 60 h; (5) after the crystallization was completed, centrifugal filtration, washing, drying, and calcination at 550°C for 4 h were performed, to obtain ZSM-5 molecular sieve D, the SEM photograph of which is shown in Figure 4 .

[0081] Example 5

[0082] ZSM-5 molecular sieve E was prepared by the same method as in Example 3, except that the amount of water in the second step solution was lower.

[0083] (1) 65.13 grams of tetrapropylammonium hydroxide aqueous solution (25.0% by mass) was weighed, 482.32 grams of deionized water was added, stirred at room temperature for 10 min, then 165.20 grams of silica sol (SiO2 content 25%) was added, stirred at 50°C water bath for 1.0 h, and the obtained third mixed product was moved into a reaction kettle, and hydrothermally treated at 80°C for 2 hours, and then hydrothermally treated at 170°C for 12 hours, to obtain a fourth mixed product;

[0084] (2) 1.39 grams of sodium hydroxide particles was weighed, 20.0 grams of deionized water was added, and the sodium hydroxide was completely dissolved, then 4.76 grams of aluminum nitrate nonahydrate was added, stirred at room temperature for 1.0 h, to obtain a fifth mixed product (i.e. aluminum source solution);

[0085] (3) The fifth mixed product was added to the fourth mixed product, and stirred uniformly, and the obtained precursor solution was continuously hydrothermally treated at 170°C for 36 h; after the hydrothermal treatment was completed, centrifugal filtration, washing, drying, and calcination at 550°C for 4 h were performed, to obtain ZSM-5 molecular sieve E.

[0086] Comparative Example 1

[0087] The same method as in Example 1 was used to prepare the molecular sieve a, except that the third mixture was subjected to one hydrothermal treatment in step (1), and the temperature of the hydrothermal treatment was 160℃, and the time was 8 hours.

[0088] Comparative Example 2

[0089] The ZSM-5 molecular sieve b of the conventional crystal grain was purchased from Sinopec Catalyst Company Qilu Branch, and the molar ratio of silicon and aluminum (SiO2 / Al2O3) was 50.

[0090] Table 1

[0091]

[0092]

[0093]

[0094] In Table 1, R represents a template agent, and the ratio of the molar ratio of the bulk phase silicon and aluminum to the molar ratio of the surface silicon and aluminum represents the ratio of the molar ratio of the bulk phase silicon and aluminum to the molar ratio of the surface silicon and aluminum.

[0095] Reaction evaluation

[0096] The molecular sieves prepared in the examples and the comparative examples were subjected to ammonium exchange, so that the content of sodium oxide was less than 0.1% by weight, to obtain H-type molecular sieves, and the ammonium exchange conditions were as follows: molecular sieve: ammonium chloride: H2O = 1:0.5:10, the ammonium exchange temperature was 85℃, and the ammonium exchange time was 1h. After the ammonium exchange, the molecular sieves were filtered, washed, and dried, and then were calcined at 550℃ for 2h. The H-type molecular sieve samples obtained above were evaluated on a fixed bed micro reactor FB, and the raw oil was a model compound decalin, and the evaluation conditions were as follows: the reaction temperature was 600℃, and the weight ratio of the catalyst to the oil was 0.15. The results are shown in Table 2.

[0097] Table 2

[0098]

[0099]

[0100] As can be seen from Table 2, the surface aluminum-rich ZSM-5 molecular sieve of the present application has better catalytic performance, and has higher conversion rate and low carbon olefin yield when used in catalytic cracking reactions.

[0101] The preferred embodiments of the present application are described in detail above with reference to the drawings, but the present application is not limited to the specific details in the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0102] It should be further noted that each of the various technical features described in the above embodiments can be combined with any other technical features in any suitable manner, and the present application shall be deemed to disclose all possible combinations thereof, without causing unnecessary repetition.

[0103] Furthermore, any combination of the various embodiments of the present application can be made, as long as it does not deviate from the spirit of the present application, and it shall be deemed to be disclosed by the present application.

Claims

1. A surface aluminum-rich ZSM-5 molecular sieve for catalytic cracking reaction, the ZSM-5 molecular sieve being a prolate cylinder, the ZSM-5 molecular sieve having an average crystal size of 0.2-3.0 μm, a ratio of a bulk phase molar ratio of silicon to aluminum to a molar ratio of surface silicon to aluminum of 1.2-5.0, and a relative crystallinity of 80-110%.

2. The ZSM-5 molecular sieve of claim 1, wherein, The ZSM-5 molecular sieve has a ratio of a bulk phase molar ratio of silicon to aluminum to a molar ratio of surface silicon to aluminum of 1.2-4.

0.

3. The ZSM-5 molecular sieve of claim 1, wherein, The ZSM-5 molecular sieve has a relative crystallinity of 85-100% and an average crystal size of 0.4-2 μm.

4. The ZSM-5 molecular sieve of claim 1, wherein, The ZSM-5 molecular sieve has an average height of 0.2-1.0 μm and an average height-diameter ratio of 1:(2-10). 5.A method for preparing the surface aluminum-rich ZSM-5 molecular sieve for catalytic cracking reaction according to any one of claims 1-4, the method comprising: (1) mixing a first template agent, a first silicon source and a first solvent at 30-50 ℃ for 0.5-3.0 hours to obtain a first mixed product; (2) mixing a first alkali metal hydroxide, a first aluminum source and a second solvent at 20-80 ℃ for 0.5-2.0 hours to obtain a second mixed product; (3) mixing the first mixed product and the second mixed product and then performing dynamic crystallization, and taking out the obtained solid and performing a first calcination; Or, the method comprising: S1. mixing a second template agent, a second silicon source and a third solvent at 30-50 ℃ for 0.5-3.0 hours, and then sequentially performing a first hydrothermal treatment and a second hydrothermal treatment on the obtained third mixed product to obtain a fourth mixed product; wherein the first hydrothermal treatment has a temperature of 80-150 ℃ and a time of 1-6 hours; and the second hydrothermal treatment has a temperature of 160-180 ℃ and a time of 12-60 hours; S2. mixing a second alkali metal hydroxide, a second aluminum source and a fourth solvent at 20-80 ℃ for 0.5-2.0 hours to obtain a fifth mixed product; S3. mixing the fourth mixed product and the fifth mixed product, performing a third hydrothermal treatment on the obtained mixture, and then taking out the obtained solid and performing a second calcination.

6. The method of claim 5, wherein, The first silicon source is selected from one or more of tetramethyl orthosilicate and tetraethyl orthosilicate; The second silicon source is selected from one or more of silica sol, water glass and solid silica gel; The first template agent and the second template agent are each independently selected from one or more of tetrapropylammonium bromide, tetrapropylammonium hydroxide, n-butylamine and hexanediamine; The first aluminum source and the second aluminum source are each independently selected from one or more of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum isopropoxide and aluminum sol; The first alkali metal hydroxide and the second alkali metal hydroxide are each independently selected from one or more of lithium hydroxide, sodium hydroxide and potassium hydroxide.

7. The method of claim 5, wherein, a total amount of the first template agent, the first solvent and the second solvent, a molar ratio of an amount of the first alkali metal hydroxide and the first silicon source is (0.06-0.55):(10-110):(0.02-1.5):1; a molar ratio of an amount of the first silicon source and the first aluminum source is (20-500):1; wherein the first silicon source is calculated as SiO2, the first alkali metal hydroxide is calculated as alkali metal oxide, and the first aluminum source is calculated as Al2O3; a total amount of the second template agent, the third solvent and the fourth solvent, a molar ratio of an amount of the second alkali metal hydroxide and the second silicon source is (0.06-0.55):(10-100):(0.02-1.5):1; a molar ratio of an amount of the second silicon source and the second aluminum source is (20-500):1; wherein the second silicon source is calculated as SiO2, the second alkali metal hydroxide is calculated as alkali metal oxide, and the second aluminum source is calculated as Al2O3.

8. The method of claim 5, wherein, In step (2), a molar ratio of an amount of the first alkali metal hydroxide, the second solvent and the first aluminum source is (1.5-5):(60-500):1; In step S2, a molar ratio of an amount of the second alkali metal hydroxide, the fourth solvent and the second aluminum source is (1.5-5):(60-500):

1.

9. The method of claim 5, wherein, The conditions of the dynamic crystallization include: a temperature of 160-180℃, and a time of 12-60 hours; The conditions of the third hydrothermal treatment include: a temperature of 160-180℃, and a time of 12-60 hours; The conditions of the first calcination and the second calcination each independently include: a temperature of 400-600℃, and a time of 2-6 hours.

10. Use of the surface aluminum-rich ZSM-5 molecular sieve for catalytic cracking reaction according to any one of claims 1-4 in petrochemical and / or fine chemical industry.

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