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

Abstract

The invention relates to the technical field of molecular sieve preparation, and provides a ZSM-5 molecular sieve as well as a preparation method and application thereof. The preparation method of the ZSM-5 molecular sieve comprises the following steps: obtaining a mixed solution containing an aluminum source, an additive, a silicon source, an alkali source, an organic template agent, a ZSM-5 seed crystal and a solvent; performing crystallization treatment and roasting treatment on the mixed solution in sequence to prepare a ZSM-5 molecular sieve; the additive comprises amino acid and / or alcohol; the alkali source comprises a first alkali source containing Na and a second alkali source containing M, and M is selected from at least one of Li, K and Cs. According to the preparation method of the ZSM-5 molecular sieve provided by the invention, the amino acid and / or alcohol component is added as an additive, and more than two different alkali sources are matched for use, so that the ZSM-5 molecular sieve which is low in silica-alumina ratio, high in crystallinity and low in non-framework aluminum content and has nanoscale crystal grains can be prepared.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve preparation technology, and more specifically, to a ZSM-5 molecular sieve, its preparation method, and its application. Background Technology

[0002] ZSM-5 molecular sieves are commonly used molecular sieve catalysts in petrochemical and industrial catalysis. ZSM-5 molecular sieves synthesized via conventional hydrothermal methods typically have a silica-to-alumina ratio in the range of 30 to ∞. Further reducing the silica-to-alumina ratio in the synthesis system often results in problems such as the presence of impurities, amorphous substances, and low crystallinity. Furthermore, increasing the aluminum content in the synthesis system leads to the formation of negatively charged [AlO4]. - A significant amount of positive charge compensation is required, but adding excessive inorganic cations to the synthesis system can affect the phase selectivity of the product and prolong the crystallization induction period. Furthermore, there is a significant difference in crystallization rates between silicon and aluminum sources during the crystallization of ZSM-5 molecular sieves. Typically, organic template agents preferentially interact with silicon sources to form silicon-rich MFI structures. In aluminum-rich crystallization systems, the preferential crystallization of silicon sources leads to a large amount of aluminum source remaining in the solution, which not only fails to obtain the target aluminum-rich ZSM-5 molecular sieve but also wastes the aluminum source.

[0003] Therefore, it is of great significance to develop a method for preparing ZSM-5 molecular sieves with low silicon-to-aluminum ratio and high crystallinity. Summary of the Invention

[0004] The purpose of this invention is to provide a ZSM-5 molecular sieve and its preparation method, so as to solve the technical problem that it is difficult to synthesize ZSM-5 molecular sieves with low silicon-to-aluminum ratio, high crystallinity and low non-framework aluminum content in the prior art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing ZSM-5 molecular sieve, comprising: obtaining a mixed solution comprising an aluminum source, an additive, a silicon source, an alkali source, an organic template agent, ZSM-5 seed crystals and a solvent; and sequentially subjecting the mixed solution to crystallization treatment and calcination treatment to obtain ZSM-5 molecular sieve;

[0007] The additives include amino acids and / or alcohols;

[0008] The alkali source includes a first alkali source containing Na and a second alkali source containing M, wherein M is selected from at least one of Li, K, and Cs.

[0009] The method for preparing ZSM-5 molecular sieve provided by this invention can play a role in complexing and activating aluminum sources by adding additives and using two or more different alkali sources in combination, thereby assisting the aluminum sources to enter the molecular sieve framework and synthesizing ZSM-5 molecular sieves with low silicon-to-aluminum ratio and low non-framework aluminum content.

[0010] Furthermore, different alkali metals have varying effects on crystal growth during molecular sieve synthesis. Na alone readily yields large-particle crystals aggregated from nanocrystals, while using Li, K, or Cs alone delays sieve crystallization, leading to reduced product crystallinity. By employing two or more different alkali sources in combination, not only can the prepared molecular sieve exhibit high crystallinity, but nanocrystals can also be formed. The nanoparticle ZSM-5 molecular sieve effectively reduces diffusion resistance, facilitating the diffusion of reactant and product molecules, thereby enhancing catalytic activity.

[0011] According to some embodiments of the present invention, the amino acid includes at least one selected from glutamic acid, glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, lysine, arginine, and histidine.

[0012] In this invention, the nitrogen (N) inherent in the amino acid additives interacts with the molecular sieve framework during hydrothermal synthesis, promoting the entry of the aluminum source into the molecular sieve framework. Compared to alcohol additives, amino acid additives, which contain both hydroxyl and nitrogen, are more effective in promoting the entry of the aluminum source into the molecular sieve framework.

[0013] Among them, the differences in acidity and alkalinity of different types of amino acids after dissolving in water are reflected in the complexed activated aluminum source. Non-alkaline amino acids (such as glutamic acid, leucine, etc.) provide more favorable conditions for the aluminum source to enter the molecular sieve framework.

[0014] According to some embodiments of the present invention, the alcohol includes at least one selected from methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, and glycerol.

[0015] According to some embodiments of the present invention, the first alkali source includes at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0016] According to some embodiments of the present invention, the second alkali source includes at least one of lithium hydroxide, potassium hydroxide, cesium hydroxide, lithium carbonate, potassium carbonate, and cesium carbonate.

[0017] According to some embodiments of the present invention, the molar ratio of the first alkali source (calculated as Na2O) to the second alkali source (calculated as M2O) is 0.5 to 3.

[0018] Preferably, the molar ratio of the first alkali source (calculated as Na2O) to the second alkali source (calculated as M2O) is 1 to 2.5.

[0019] According to some embodiments of the present invention, the ZSM-5 seed crystals are selected from non-Na-type ZSM-5 molecular sieves. For example, NH4 can be selected. + ZSM-5 molecular sieve and H + Type ZSM-5 molecular sieve. The Na contained in Na-type molecular sieves can affect the control of the metal ratio in the mixed solution, which can lead to the appearance of impurities in the prepared molecular sieve.

[0020] According to some embodiments of the present invention, a method for obtaining a mixed solution includes: adding an aluminum source and an additive to a solvent and stirring for 2 to 12 hours, preferably 2 to 5 hours; then adding a silicon source, an alkali source, an organic template agent and ZSM-5 seed crystals, stirring and mixing to obtain a mixed solution.

[0021] According to some embodiments of the present invention, the aluminum source includes at least one of aluminum sol, boehmite, aluminum hydroxide, aluminum isopropoxide, aluminum sec-butoxide, sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, and aluminum oxide.

[0022] According to some embodiments of the present invention, the silicon source includes at least one of silica sol, tetraethyl orthosilicate, methyl orthosilicate, silica, and water glass.

[0023] According to some embodiments of the present invention, the organic template agent includes at least one selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrabutylammonium hydroxide, n-butylamine, ethylenediamine, and ethanolamine.

[0024] According to some embodiments of the present invention, the solvent includes at least one of water and diglycerides.

[0025] According to some embodiments of the present invention, the silicon source is SiO2, the aluminum source is Al2O3, the alkali source is Na2O and M2O, the organic template agent is OSDA, the additive is ADD, the solvent is I, and the molar ratio of each component in the mixed solution is: SiO2 / Al2O3 = 10~30, (Na2O+M2O) / SiO2 = 0.025~0.25, OSDA / SiO2 = 0.01~0.8, ADD / SiO2 = 0.0005~0.2, I / SiO2 = 3~300.

[0026] According to some embodiments of the present invention, SiO2 / Al2O3 = 10 to 20.

[0027] According to some embodiments of the present invention, (Na2O+M2O) / SiO2 = 0.05~0.15.

[0028] According to some embodiments of the present invention, OSDA / SiO2 = 0.05 to 0.2.

[0029] According to some embodiments of the present invention, ADD / SiO2 = 0.001 to 0.1, for example, it can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.012, 0.015, 0.018, 0.020, 0.025, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, etc.

[0030] Preferably, ADD / SiO2 = 0.001 to 0.01.

[0031] More preferably, ADD / SiO2 = 0.003 to 0.008.

[0032] According to some embodiments of the present invention, I / SiO2 = 20 to 50.

[0033] According to some embodiments of the present invention, the mass of the ZSM-5 seed crystal accounts for 0.05 to 10% of the mass of the silicon source in the mixed solution, calculated as SiO2, preferably 0.5 to 8%, and more preferably 2 to 6%.

[0034] According to some embodiments of the present invention, the temperature of the crystallization treatment is 110-200°C, preferably 140-180°C, for example, 140°C, 150°C, 160°C, 170°C, 180°C, etc.; the time of the crystallization treatment is 2-200 hours, preferably 24-150 hours, for example, 24 hours, 30 hours, 40 hours, 48 ​​hours, 50 hours, 60 hours, 72 hours, 80 hours, 90 hours, 100 hours, 105 hours, 110 hours, 120 hours, 125 hours, 130 hours, 135 hours, 144 hours, 150 hours, etc.

[0035] According to some embodiments of the present invention, the calcination temperature is 400–700°C, preferably 500–600°C; the calcination time is 0.5–8 h, preferably 4–6 h.

[0036] According to some embodiments of the present invention, the calcination process is carried out in air.

[0037] According to some embodiments of the present invention, the crystallized product is subjected to cooling, filtration, washing, and drying, followed by calcination.

[0038] According to some embodiments of the present invention, the drying temperature is 50-150°C, preferably 80-120°C; the drying time is 0.5-48h, preferably 4-24h.

[0039] Secondly, the present invention provides a ZSM-5 molecular sieve, which is prepared by the preparation method described in the first aspect.

[0040] According to some embodiments of the present invention, the SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve is <25.

[0041] Preferably, the SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve is <20, for example, it can be 19.5, 19, 18.5, 18, 17, 16, 15, 14, 13, 12, 10, 8, 6, etc.

[0042] According to some embodiments of the present invention, the crystallinity of the ZSM-5 molecular sieve is >70%.

[0043] Preferably, the crystallinity of the ZSM-5 molecular sieve is >75%, for example, it can be 75.1%, 75.5%, 76%, 77%, 78%, 79%, 80%, 82%, 85%, 88%, 89%, 90%, 92%, 95%, etc.

[0044] According to some embodiments of the present invention, the non-framework aluminum content of the ZSM-5 molecular sieve is ≤25%.

[0045] Preferably, the non-framework aluminum content of the ZSM-5 molecular sieve is <15%, for example, it can be 0%, 1%, 3%, 5%, 6%, 8%, 10%, 11%, 13%, 14%, etc.

[0046] According to some embodiments of the present invention, the crystal particle size of the ZSM-5 molecular sieve is <500nm, preferably ≤300nm, and more preferably ≤100nm.

[0047] Thirdly, the present invention provides the application of the ZSM-5 molecular sieve described in the second aspect in the field of catalysts.

[0048] The beneficial effects of this invention are at least as follows:

[0049] The method for preparing ZSM-5 molecular sieve provided by the present invention involves adding amino acids and / or alcohol components as additives and using two or more different alkali sources in combination to prepare ZSM-5 molecular sieves with low silicon-to-aluminum ratio, high crystallinity, low non-framework aluminum content, and nanoscale crystals. Attached Figure Description

[0050] Figure 1 The XRD diffraction pattern of the product obtained in Example 1 is shown.

[0051] Figure 2 The product obtained in Example 1 27 Al MAS NMR image.

[0052] Figure 3 This is an SEM image of the product obtained in Example 1.

[0053] Figure 4 This is an SEM image of the product obtained in Comparative Example 2. Detailed Implementation

[0054] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely for illustrating this patent and do not limit the scope of protection of this invention in any way.

[0055] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the reagents used in the following embodiments are conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or by existing methods; unless otherwise specified, the reagent dosages are those used in routine experimental operations; unless otherwise specified, the experimental methods are conventional methods.

[0056] In the various embodiments and comparative examples of the present invention, the performance data were tested according to the following test methods:

[0057] (1) XRD phase analysis: The phases were determined using a Bruker D8 Focus diffractometer with a graphite monochromator, a Cu target Kα light source, a wavelength λ of 0.154 nm, a tube voltage of 40 kV, and a tube current of 40 mA. The diffraction signal was recorded in the 2θ range of 3-90° (scanning speed of 2° / min). The relative crystallinity of the molecular sieve can be calculated based on the XRD test results.

[0058] (2) Element content of molecular sieve: obtained by energy dispersive spectroscopy surface scan test.

[0059] (3) Non-framework aluminum content: through 27 The Al MAS NMR test results were obtained using a Bruker AvanceⅢ / WB-400 spectrometer, with a resonance frequency of 79.50 MHz, a rotation speed of 12 kHz, and a relaxation time of 4 s.

[0060] (4) Test of acid sites of molecular sieve samples: Pyridine infrared spectroscopy was used with a Nexus 670 Fourier transform infrared spectrometer manufactured by Nicolet. Before the test, the molecular sieve powder sample was pressed into a circular thin film with a diameter of 1.5 cm and a mass of about 12 mg for py-IR test. Before the test, the system and sample cell were evacuated at room temperature for 40 min. Then the system temperature was programmed to rise. After the test system temperature stabilized, the air background and sample bulk spectra were measured. Then pyridine was adsorbed at 200℃. After adsorption for 10 min, it was equilibrated for 5 min. Then it was desorbed at 200℃ for 40 min. Then infrared data were collected at 300℃.

[0061] (5) Crystal size: obtained from SEM images, taken using a FEI Nova Nano SEM 450 microscope.

[0062] Example 1

[0063] Aluminum sol and glutamic acid were added to water and stirred for 2 hours; then, an alkaline source (sodium hydroxide and potassium hydroxide), tetrapropylammonium hydroxide, silica sol, and NH4 were added. + -ZSM-5 seed crystals were mixed to obtain a mixed solution; NH4 + - The mass of ZSM-5 seed crystals is 5 wt% of the mass of the silica sol based on SiO2, and the components in the mixed solution (excluding NH4) + The molar ratio of the ZSM-5 seed crystals was SiO2:0.066Al2O3:0.1OSDA:0.005ADD:0.12(Na2O+K2O):35H2O, with a molar ratio of Na2O to K2O of 2. The mixed solution was placed in a polytetrafluoroethylene-lined pressure vessel and crystallized at 150℃ for 5 days. After crystallization, it was naturally cooled to room temperature. The crystallized product was filtered, washed, dried at 120℃ for 12 hours, and finally calcined in air at 550℃ for 5 hours to remove the template agent. The resulting product was designated Al, a ZSM-5 molecular sieve with SiO2 / Al2O3 = 16.5 and a crystallinity of 79.5%. The product contained no non-framework aluminum.

[0064] The XRD pattern of A1 is as follows: Figure 1 As shown, A1 is ZSM-5 molecular sieve.

[0065] A1 27 Al MAS NMR image as follows Figure 2 As shown, it can be seen that only tetracoordinated aluminum exists around 55 ppm in A1, and there is no non-skeletal aluminum at 0 ppm.

[0066] SEM image of A1 as follows Figure 3 As shown, A1 consists of small particles with a particle size of 20–40 nm.

[0067] Example 2

[0068] The preparation method is the same as in Example 1, except that: the components in the mixed solution (excluding NH4) + The molar ratio of the ZSM-5 seed crystal is SiO2:0.066Al2O3:0.1OSDA:0.03ADD:0.12(Na2O+K2O):35H2O, and the molar ratio of Na2O to K2O is 2.

[0069] The obtained product is designated A2, which is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 18.2, a crystallinity of 72.6%, and a non-framework aluminum content of 10%.

[0070] Example 3

[0071] The preparation method is the same as in Example 1, except that: the components in the mixed solution (excluding NH4) + The molar ratio of the ZSM-5 seed crystal is SiO2:0.066Al2O3:0.1OSDA:0.05ADD:0.12(Na2O+K2O):35H2O, and the molar ratio of Na2O to K2O is 2.

[0072] The obtained product is designated A3, which is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 17.9, a crystallinity of 50.4%, and a non-framework aluminum content of 30%.

[0073] Example 4

[0074] The preparation method is the same as in Example 1, except that: the components in the mixed solution (excluding NH4) + The molar ratio of the ZSM-5 seed crystal is SiO2:0.066Al2O3:0.1OSDA:0.001ADD:0.12(Na2O+K2O):35H2O, and the molar ratio of Na2O to K2O is 2.

[0075] The obtained product is designated A4, which is a ZSM-5 molecular sieve with SiO2 / Al2O3 = 17.5, crystallinity of 76.0%, and non-framework aluminum content of 5%.

[0076] Example 5

[0077] The preparation method is the same as in Example 1, except that: the components in the mixed solution (excluding NH4) + The molar ratio of the ZSM-5 seed crystal is SiO2:0.066Al2O3:0.1OSDA:0.008ADD:0.12(Na2O+K2O):35H2O, and the molar ratio of Na2O to K2O is 2.

[0078] The obtained product is designated A5, which is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 16.8, a crystallinity of 79.4%, and a non-framework aluminum content of 3%.

[0079] Example 6

[0080] The preparation method is the same as in Example 1, except that: the components in the mixed solution (excluding NH4) + The molar ratio of the ZSM-5 seed crystal is SiO2:0.066Al2O3:0.1OSDA:0.01ADD:0.12(Na2O+K2O):35H2O, and the molar ratio of Na2O to K2O is 2.

[0081] The obtained product is designated A6, which is a ZSM-5 molecular sieve with SiO2 / Al2O3 = 19.2, crystallinity of 74.5%, and non-framework aluminum content of 8%.

[0082] Example 7

[0083] The preparation method is the same as in Example 1, except that the crystallization temperature is 170°C.

[0084] The obtained product is designated as A7, which is a ZSM-5 molecular sieve with SiO2 / Al2O3 = 20.5 and a crystallinity of 85.8%. The product contains no non-framework aluminum.

[0085] Example 8

[0086] The preparation method is the same as in Example 1, except that the crystallization temperature is 130°C.

[0087] The obtained product is designated A8, which is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 14.4, a crystallinity of 38.5%, and a non-framework aluminum content of 32%.

[0088] Example 9

[0089] The preparation method is the same as in Example 1, except that the crystallization temperature is 100°C.

[0090] The resulting product is denoted as A9. A9 is amorphous.

[0091] Example 10

[0092] The preparation method is the same as in Example 1, except that glutamic acid is replaced with lysine.

[0093] The obtained product is designated A10, which is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 19.8, a crystallinity of 77.8%, and a non-framework aluminum content of 12%.

[0094] Example 11

[0095] The preparation method is the same as in Example 3, except that glutamic acid is replaced with lysine.

[0096] The resulting product is denoted as A11. A11 is amorphous.

[0097] Example 12

[0098] The preparation method is the same as in Example 1, except that glutamic acid is replaced with ethanol.

[0099] The obtained product is designated A12, which is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 21.5, a crystallinity of 87.2%, and a non-framework aluminum content of 20%.

[0100] Example 13

[0101] The preparation method is the same as in Example 1, except that glutamic acid is replaced with ethylene glycol.

[0102] The obtained product is designated A13, which is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 21.7, a crystallinity of 88.6%, and a non-framework aluminum content of 18%.

[0103] Example 14

[0104] The preparation method is the same as in Example 1, except that glutamic acid is replaced with leucine.

[0105] The obtained product is designated A14, which is a ZSM-5 molecular sieve with SiO2 / Al2O3 = 17.0, crystallinity of 78.5%, and non-framework aluminum content of 3%.

[0106] Example 15

[0107] The preparation method is the same as in Example 1, except that aluminum sol, glutamic acid, alkaline sources (sodium hydroxide and potassium hydroxide), tetrapropylammonium hydroxide, silica sol and NH4 are added. + -ZSM-5 seed crystals are added to water and mixed to obtain a mixed solution.

[0108] The obtained product is designated A15, which is a ZSM-5 molecular sieve with SiO2 / Al2O3 = 22.0, crystallinity of 88.9%, and non-framework aluminum content of 23.0%.

[0109] Example 16

[0110] The preparation method is the same as in Example 1, except that: aluminum sol, glutamic acid, and alkaline sources (sodium hydroxide and potassium hydroxide) are added to water and stirred for 2 hours; then tetrapropylammonium hydroxide, silica sol, and NH4 are added. + -ZSM-5 seed crystals were mixed to obtain a mixed solution.

[0111] The obtained product is designated A16, which is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 22.3, a crystallinity of 78.9%, and a non-framework aluminum content of 25%.

[0112] Example 17

[0113] The preparation method is the same as in Example 1, except that: aluminum sol is replaced with sodium aluminate, silica sol is replaced with tetraethyl orthosilicate, tetrapropylammonium hydroxide is replaced with tetrapropylammonium bromide, and NH4 is used. + The mass of ZSM-5 seed crystals is 3 wt% of the mass of tetraethyl orthosilicate based on SiO2, and the components in the mixed solution (excluding NH4) + The molar ratio of the ZSM-5 seed crystal is SiO2:0.071Al2O3:0.15OSDA:0.005ADD:0.08(Na2O+K2O):20H2O, and the molar ratio of Na2O to K2O is 1.

[0114] The obtained product is designated A17, a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 16.8, a crystallinity of 78.8%, and a non-framework aluminum content of 0%. The particle size of A17 is 50–90 nm.

[0115] Example 18

[0116] The preparation method is the same as in Example 1, except that potassium hydroxide in the alkali source is replaced with an equimolar amount of lithium hydroxide.

[0117] The product obtained was designated A18, a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 17.2, a crystallinity of 70.8%, and a non-framework aluminum content of 0%. The particle size of A18 was 30–60 nm.

[0118] Example 19

[0119] The preparation method is the same as in Example 1, except that potassium hydroxide in the alkali source is replaced with an equimolar amount of cesium hydroxide.

[0120] The product obtained was designated A19, a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 16.4, a crystallinity of 65.2%, and a non-framework aluminum content of 0%. The particle size of A19 was 40–50 nm.

[0121] Example 20

[0122] The preparation method is the same as in Example 1, except that the molar ratio of Na2O and K2O is 0.5.

[0123] The product obtained was designated A20, a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 15.2, a crystallinity of 51.5%, and a non-framework aluminum content of 2%. A20 consists of crystal clusters (low crystallinity causes the molecular sieve to agglomerate, making it difficult to determine the crystal size).

[0124] Example 21

[0125] The preparation method is the same as in Example 1, except that the molar ratio of Na2O to K2O is 3.

[0126] The product obtained was designated A21, a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 17.0, a crystallinity of 80.8%, and a non-framework aluminum content of 3%. The particle size of A21 was 200–300 nm.

[0127] Comparative Example 1

[0128] The preparation method is the same as in Example 1, except that glutamic acid is not added.

[0129] The obtained product is designated as B1, which is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 22.8, a crystallinity of 89.0%, and a non-framework aluminum content of 40%.

[0130] Comparative Example 2

[0131] The preparation method is the same as in Example 1, except that the alkali source is sodium hydroxide.

[0132] The resulting product, designated B2, is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 17.9, a crystallinity of 82.5%, and a non-framework aluminum content of 18%. Figure 4 As shown, B2 consists of large particles with a particle size of 1–3 μm.

[0133] Comparative Example 3

[0134] The preparation method is the same as in Example 1, except that the alkali source is potassium hydroxide.

[0135] The obtained product, designated B3, is a ZSM-5 molecular sieve with a SiO2 / Al2O3 ratio of 15.7, a crystallinity of 50.3%, and a non-framework aluminum content of 14%. B3 consists of crystal clusters (low crystallinity causes the molecular sieve to agglomerate, making it difficult to determine the crystal size).

[0136] Molecular sieve performance evaluation

[0137] (1) The SiO2 / Al2O3, crystallinity, and non-framework aluminum content of the products of each embodiment and comparative example are shown in Table 1.

[0138] Table 1

[0139]

[0140]

[0141] (2) Evaluation of molecular sieve acidity

[0142] The molecular sieves prepared in Example 1 and Comparative Example 1 were subjected to acid exchange treatment, and the resulting catalyst samples were labeled as AC1 and BC1, respectively. The acid characterization results are shown in Table 2.

[0143] The acid exchange treatment includes: calcining the molecular sieve in air at 550°C for 4 hours to obtain molecular sieve powder, then exchanging the molecular sieve powder with a 10% ammonium nitrate aqueous solution at 90°C at a liquid-to-solid weight ratio of 4 for 9 hours, and filtering, washing and drying the resulting solid to obtain the catalyst sample.

[0144] Table 2

[0145] sample <![CDATA[B acid content (μmolL -1 )]]> <![CDATA[L acid content (μmolL -1 )]]> B / L AC1 221.5 156.2 1.4 BC1 145.3 155.2 0.9

[0146] Wherein, B / L represents the ratio of Brønsted acid content to Lewis acid content; the contents of Brønsted acid and Lewis acid are obtained by pyridine infrared spectroscopy.

[0147] Generally, when the silica-alumina ratio of ZSM-5 molecular sieve decreases, the amounts of both Brønsted (B) acid and Lewis (L) acid increase. However, the increase in Lewis acid is greater than the increase in Brønsted (B) acid in ZSM-5 molecular sieve, which has a higher non-framework aluminum content, resulting in a smaller B / L ratio. Table 2 also shows that AC1 has a lower non-framework aluminum content than BC1.

[0148] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing ZSM-5 molecular sieve, characterized in that, include: A mixed solution comprising an aluminum source, additives, a silicon source, an alkali source, an organic template agent, ZSM-5 seed crystals, and a solvent was obtained; the mixed solution was then subjected to crystallization and calcination treatments in sequence to obtain ZSM-5 molecular sieves. The additives include amino acids and / or alcohols; The alkali source includes a first alkali source containing Na and a second alkali source containing M, wherein M is selected from at least one of Li, K, and Cs.

2. The preparation method according to claim 1, characterized in that, The amino acids include at least one of the following: glutamic acid, glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, lysine, arginine, and histidine. And / or, the alcohol includes at least one of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, and glycerol; And / or, the first alkali source includes at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate; And / or, the second alkali source includes at least one of lithium hydroxide, potassium hydroxide, cesium hydroxide, lithium carbonate, potassium carbonate, and cesium carbonate; And / or, the molar ratio of the first alkali source (calculated as Na2O) to the second alkali source (calculated as M2O) is 0.5 to 3, preferably 1 to 2.5; And / or, the ZSM-5 seed crystals are selected from non-Na-type ZSM-5 molecular sieves.

3. The preparation method according to claim 1 or 2, characterized in that, The method for obtaining the mixed solution includes: adding aluminum source and additives to solvent, stirring for 2 to 12 hours, then adding silicon source, alkali source, organic template agent and ZSM-5 seed crystals, stirring and mixing to obtain the mixed solution.

4. The preparation method according to any one of claims 1-3, characterized in that, The aluminum source includes at least one of aluminum sol, boehmite, aluminum hydroxide, aluminum isopropoxide, aluminum sec-butoxide, sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, and aluminum oxide. And / or, the silicon source includes at least one of silica sol, tetraethyl orthosilicate, methyl orthosilicate, silica, and water glass; And / or, the organic template agent comprises at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrabutylammonium hydroxide, n-butylamine, ethylenediamine, and ethanolamine; And / or, the solvent includes at least one of water and diglycerides.

5. The preparation method according to any one of claims 1-4, characterized in that, The silicon source is calculated as SiO2, the aluminum source as Al2O3, the alkali source as Na2O and M2O, the organic template agent as OSDA, the additive as ADD, and the solvent as I. The molar ratios of each component in the mixed solution are: SiO2 / Al2O3 = 10~30, (Na2O+M2O) / SiO2 = 0.025~0.25, OSDA / SiO2 = 0.01~0.8, ADD / SiO2 = 0.0005~0.2, and I / SiO2 = 3~300. Preferably, ADD / SiO2 = 0.001 to 0.1; more preferably, ADD / SiO2 = 0.001 to 0.01; even more preferably, ADD / SiO2 = 0.003 to 0.

008.

6. The preparation method according to any one of claims 1-5, characterized in that, The ZSM-5 seed crystal accounts for 0.05 to 10% of the mass of the silicon source in the mixed solution, calculated as SiO2.

7. The preparation method according to any one of claims 1-6, characterized in that, The crystallization treatment temperature is 110–200℃, preferably 140–180℃; the crystallization treatment time is 2–200h, preferably 24–150h. And / or, the calcination temperature is 400–700°C, and the calcination time is 0.5–8 h; And / or, the calcination process is carried out in air.

8. The preparation method according to any one of claims 1-7, characterized in that, The crystallized product is cooled, filtered, washed, and dried before being calcined.

9. A ZSM-5 molecular sieve, prepared by the preparation method according to any one of claims 1-8; Preferred, The SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve is <25, preferably <20; And / or, the crystallinity of the ZSM-5 molecular sieve is >70%, preferably >75%; And / or, the non-framework aluminum content of the ZSM-5 molecular sieve is ≤25%, preferably <15%; And / or, the crystal particle size of the ZSM-5 molecular sieve is <500nm, preferably ≤300nm, more preferably ≤100nm.

10. The application of the ZSM-5 molecular sieve according to claim 9 in the field of catalysts.

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